JP2004079831A - Exposure method and apparatus, and device manufacturing method - Google Patents

Abstract

Provided is an exposure technique capable of maintaining high control of the exposure amount even when exposing conditions are switched during an exposing step as in the case of using a double exposure method.
When a first wafer is exposed by using a first reticle, dummy irradiation is performed (step 126), and a change rate of a transmittance of an optical system is obtained (step 128). After performing the exposure while performing the prediction control of the exposure amount while calculating the transmittance based on the calculated values (steps 130 to 132), the change rate of the transmittance is calculated and stored (step 135). Similarly, in the case of performing exposure with the second reticle, the rate of change of transmittance is calculated and stored, and thereafter, in the case of performing exposure using the first reticle R1, the change is finally stored for the same reticle R1. The change rate of the transmittance is called up and the transmittance is calculated (steps 129 and 130).
[Selection diagram] Fig. 4

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exposure method used for transferring a mask pattern onto a substrate via a projection optical system in a lithography process for manufacturing various devices such as a semiconductor element, a liquid crystal display element, or a thin film magnetic head. The present invention relates to an apparatus and a device manufacturing method using this exposure method, and more particularly to an exposure amount control technique when performing exposure through an optical system whose transmittance gradually changes by irradiation with an exposure beam.
[0002]
[Prior art]
In order to cope with the improvement of the integration and fineness of a semiconductor device, an exposure apparatus that performs a lithography process (typically, a resist coating process, an exposure process, and a resist development process) for manufacturing a semiconductor device includes: There is a demand for further improving imaging characteristics such as resolution and transfer fidelity. In order to improve the imaging characteristics in this way, it is necessary to first increase the exposure amount control accuracy and expose the resist applied on the wafer as a substrate with an appropriate exposure amount.
[0003]
In recent exposure apparatuses, an ultraviolet laser beam such as a KrF excimer laser (wavelength: 248 nm) or an ArF excimer laser (wavelength: 193 nm) is used as an exposure beam in order to obtain higher resolution. Wavelength F ₂ Use of a laser (wavelength: 157 nm) or the like is also being studied. However, when an excimer laser is used as an exposure beam, the transmittance of an optical element in an illumination optical system or a projection optical system that illuminates a reticle as a mask, or a coating material of the optical element (for example, a thin film such as an anti-reflection film) is reduced. New phenomena such as fluctuations in a short time have been discovered. Therefore, in an exposure apparatus that uses an ultraviolet laser beam as an exposure beam, it is necessary to correct the change in the transmittance of the optical system due to the irradiation of the exposure beam when controlling the exposure amount.
[0004]
The conventional exposure amount control method assumes that the transmittance change rate of the optical system takes a continuous value in a series of exposure sequences. This is a method of predicting the current transmittance based on the measured or calculated transmittance change speed. In this method, the light amount on the wafer surface is calculated from the calculation result and the incident light amount measured on the incident side of the optical system. Then, from the light amount on the wafer surface obtained in this way, an exposure time (in the case of a batch exposure type) or a scanning speed (a scanning exposure such as a step-and-scan method) so that a desired exposure amount is obtained. Type)).
[0005]
[Problems to be solved by the invention]
In the conventional exposure amount control technique as described above, control is performed on the assumption that the current transmittance change speed of the optical system is always substantially equal to the immediately preceding transmittance change speed.
In this regard, recently, with the miniaturization of the exposure pattern, a so-called double exposure method in which two or more exposures are performed to form a certain predetermined pattern is sometimes used. In this case, in a series of exposure sequences, exposure is performed by exchanging two or more types of reticles. Therefore, if the reticle pattern abundance greatly changes, the amount of light in an optical system (projection optical system or the like) subsequent to the reticle decreases. It changes greatly. Further, when the illumination optical system is switched to annular illumination or deformed illumination due to reticle exchange, the optical path of the exposure beam in the illumination optical system or the projection optical system changes greatly.
[0006]
For this reason, the change rate of the transmittance of the optical system may become discontinuous before and after the exposure condition switching such as the reticle exchange or the illumination optical system switching. In this case, if the exposure amount control is performed on the assumption that the transmittance change rate of the optical system is constant as in the related art, an error occurs in the exposure amount on the actual wafer surface due to the difference in the transmittance change rate, and the exposure There was a disadvantage that the quantity control accuracy was reduced.
[0007]
In view of the above, it is a first object of the present invention to provide an exposure technique that can maintain high control of the exposure amount even when the transmittance of the optical system fluctuates.
A second object of the present invention is to provide an exposure technique capable of maintaining high control of the exposure amount even when exposing conditions are changed during the exposing step as in the case of using the double exposure method.
[0008]
[Means for Solving the Problems]
The exposure method according to the present invention is different from the exposure method in which the pattern of the mask (R1) is projected onto the substrate (W) by an exposure beam using the optical system (8, 13 to 19, PL). The change information of the transmittance of the optical system is calculated for each exposure condition, and when the substrate is exposed by switching from the first exposure condition to the second exposure condition, the change in the first exposure condition is performed. The amount of exposure to the substrate is predicted and controlled based on the exposure history for the substrate and the calculated change information of the transmittance of the optical system with respect to the second exposure condition.
[0009]
According to the present invention, for example, before the start of the exposure by the multiple exposure method, the change information of the transmittance of the optical system for each of a plurality of exposure conditions (type of mask pattern, type of aperture stop of illumination system, etc.) ( For example, a change amount (change rate) of the transmittance per unit integrated energy or a function representing the change) is calculated. When exposing the substrate by switching from the first exposure condition to the second exposure condition, the exposure history under the first exposure condition (the integrated exposure energy, the exposure time, or the exposure time under the first exposure condition) A change in the transmittance of the optical system is predicted with high accuracy from the measured value of the transmittance after exposure, etc.) and the change information of the transmittance calculated for the second exposure condition. For example, by controlling the exposure time in the case of the batch exposure type, or by controlling the intensity (output) of the exposure beam in the case of the scanning exposure type, in accordance with the predicted change in transmittance. Exposure amount control accuracy can be kept high.
[0010]
In this case, as an example, before exposing the substrate under the first exposure condition, the change information of the transmittance of the optical system is calculated, and during the exposure of the substrate under the first exposure condition, the calculation is performed. Further, the amount of exposure to the substrate may be predicted and controlled based on the change information of the transmittance of the optical system. This means that, for example, before exposure of the substrate is started, dummy exposure is performed in the absence of the substrate to calculate transmittance change information. Thus, the exposure amount can be controlled with high accuracy immediately after the start of the actual exposure of the substrate.
[0011]
Further, the change information of the transmittance of the optical system under the second exposure condition may be calculated after the exposure of the substrate under the first exposure condition is completed.
Further, based on the change information of the transmittance of the optical system calculated after performing the exposure of the substrate under the first exposure condition, the exposure of the substrate at the time of starting the exposure under the second exposure condition is performed. It is desirable to predict the exposure.
[0012]
Further, an illumination optical system (1, 3, 6, 7, 7A, 7B, 8, 11 to 19) for illuminating the mask and a projection optical system (PL) for projecting the pattern of the mask onto the substrate are provided. In this case, an example of the optical system includes at least a part (8, 13 to 19) of the illumination optical system and the projection optical system.
Further, when exposing the substrate through the optical system under the first and second exposure conditions, the optical system measures the transmittance information of the optical system at the start and end of the exposure, respectively. The change rate of the transmittance with respect to the incident energy may be calculated, and the calculated change rate of the transmittance with respect to the incident energy may be used as the change information of the transmittance of the optical system. This means that, for example, in the case where the substrate is exposed alternately under the first and second exposure conditions, the change information of the transmittance calculated when the substrate was previously exposed under the same exposure condition is used. Thus, the exposure amount can be controlled with high accuracy using the latest transmittance change information. Furthermore, by using the change rate of the transmittance with respect to the incident energy (gradient of the first order approximation), the exposure amount can be controlled with high accuracy by a simple calculation.
[0013]
Next, the exposure apparatus according to the present invention uses an optical system (8, 13 to 19, PL) to project a mask pattern onto a substrate with an exposure beam using first and second exposure conditions different from each other. An exposure condition switching system (12, 20A) for switching to the first exposure condition and a calculation system (9, 32, 41 to 44) for calculating transmittance change information of the optical system for each of the first and second exposure conditions And when exposing the substrate by switching from the first exposure condition to the second exposure condition, the exposure history for the substrate under the first exposure condition and the calculated second exposure condition And a control system (45) for predicting and controlling the amount of exposure to the substrate based on the change information of the transmittance of the optical system.
[0014]
According to the present invention, when performing exposure by switching the first and second exposure conditions, the change in the transmittance of the optical system is predicted using the change information of the transmittance under the same exposure condition and the exposure history. Then, based on the result, the exposure amount for the substrate can be controlled with high accuracy.
In this case, as an example, before the substrate is exposed under the first exposure condition, the calculation system calculates the change information of the transmittance of the optical system, and the control system determines the change information of the first exposure condition. While the substrate is exposed, the amount of exposure to the substrate is predicted and controlled based on the calculated change information of the transmittance of the optical system. Thus, the exposure amount can be controlled with high accuracy immediately after the start of the exposure.
[0015]
Further, the control system starts exposing the substrate under the second exposure condition based on transmittance information of the optical system calculated after exposing the substrate under the first exposure condition. It is desirable to predict the amount of exposure at that time.
In the case where an illumination optical system that illuminates the mask and a projection optical system that projects the pattern of the mask onto the substrate are provided, an example of the optical system includes at least a part of the illumination optical system and And a projection optical system.
[0016]
Further, the device manufacturing method of the present invention includes a step of transferring the device pattern (R1, R2) onto the workpiece (W) using the exposure method of the present invention. According to the present invention, high exposure amount control accuracy can be obtained, and high-performance devices can be mass-produced with high accuracy.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. In this embodiment, the present invention is applied to the case where exposure is performed by a step-and-scan type projection exposure apparatus.
FIG. 1 shows a schematic configuration of a projection exposure apparatus of the present embodiment. In FIG. 1, an ArF excimer laser light source 1 having an oscillation wavelength of 193 nm and a narrow band is used as an exposure light source. In addition, as an exposure light source, a KrF excimer laser (wavelength 248 nm), F ₂ Laser (wavelength 157 nm), Kr ₂ Laser (wavelength 146 nm) or Ar ₂ In addition to a laser light source such as a laser (having a wavelength of 126 nm), a harmonic generation light source of a YAG laser or a harmonic generation device of a semiconductor laser can be used.
[0018]
Exposure light IL composed of ultraviolet pulse light as an exposure beam generated by the ArF excimer laser light source 1 passes through a beam matching unit (BMU) 3 including a movable mirror and the like for matching an optical path with an exposure apparatus main body. Through a light-shielding pipe 5 to a variable attenuator 6 as an optical attenuator. An exposure controller 30 for controlling the amount of exposure to a resist (photosensitive material) on the wafer controls the start and stop of light emission of the ArF excimer laser light source 1, the output determined by the oscillation frequency and pulse energy, and variable dimming. The extinction ratio for the exposure light in the device 6 is adjusted stepwise or continuously.
[0019]
The exposure light IL that has passed through the variable dimmer 6 passes through a beam shaping optical system including lens systems 7A and 7B arranged along a predetermined optical axis, and then fly-eye as an optical integrator (uniformizer or homogenizer). The light enters the lens 11. An aperture stop system 12 of an illumination system is arranged on the exit surface of the fly-eye lens 11. FIG. 2 shows an aperture stop system 12. In FIG. 2, a circularly arranged disk of the aperture stop system 12 has a plurality of circular aperture stops 12a, 12e to 12h having various sizes. The aperture stop 12b for deformed illumination comprising four eccentric small apertures, and the aperture stop 12c for annular illumination having two different values of the ratio between the outer and inner diameters of the orbicular zone (orbicular zone ratio). 12d are formed. In order to set a desired illumination system, the disk of the aperture stop system 12 is rotated by a rotation mechanism (not shown), and the corresponding aperture stop is set on the exit surface of the fly-eye lens 11 (pupil of the illumination optical system) of FIG. Plane). At the time of normal illumination, for example, an intermediate circular aperture stop 12g is used.
[0020]
Returning to FIG. 1, the exposure light IL emitted from the fly-eye lens 11 and having passed through a predetermined aperture stop in the aperture stop system 12 is incident on a beam splitter 8 having a high transmittance and a low reflectance. A part of the exposure light reflected by the beam splitter 8 enters an integrator sensor 9 composed of a photoelectric detector, and a detection signal of the integrator sensor 9 is supplied to an exposure controller 30. The transmittance and the reflectance of the beam splitter 8 are measured with high precision in advance and stored in a storage unit in the exposure controller 30, and the exposure controller 30 (details will be described later) indirectly receives a detection signal from the integrator sensor 9. It is configured such that the amount of incident light of the exposure light IL to the projection optical system PL and its integral value can be monitored. In order to monitor the amount of light incident on the projection optical system PL, for example, as shown by a dotted line in FIG. 1, a beam splitter 8A is arranged in front of the lens system 7A, and reflected light from the beam splitter 8A is photoelectrically converted. The light may be received by the detector 9A, and the detection signal of the photoelectric detector 9A may be supplied to the exposure controller 30.
[0021]
The exposure light IL transmitted through the beam splitter 8 enters a fixed illumination field stop (fixed blind) 15A in a reticle blind mechanism 16 via a mirror 13 and a condenser lens system 14. As disclosed in, for example, Japanese Patent Application Laid-Open No. 4-196513, the fixed blind 15A has a linear slit shape or a rectangular shape (hereinafter collectively referred to) in the direction perpendicular to the scanning direction at the center in the circular visual field of the projection optical system PL. (Referred to as “slit shape”). Further, in the reticle blind mechanism 16, a movable blind 15B for changing the width of the illumination visual field in the scanning direction is provided separately from the fixed blind 15A, and the movable blind 15B reduces the scanning movement stroke of the reticle stage. The width of the light-shielding band of the reticle R is reduced. The information on the aperture ratio of the movable blind 15B is also supplied to the exposure controller 30, and the value obtained by multiplying the incident light amount obtained from the detection signal of the integrator sensor 9 by the aperture ratio is the actual incident light amount on the projection optical system PL.
[0022]
The exposure light IL shaped like a slit by the fixed blind 15A of the reticle blind mechanism 16 passes through the imaging lens system 17, the optical path bending mirror 18, and the main condenser lens system 19, and the reticle R1 as a mask (or A slit-shaped illumination area is irradiated with a uniform intensity distribution on the circuit pattern area of R2). That is, the arrangement surface of the opening of the fixed blind 15A or the opening of the movable blind 15B is almost conjugate with the pattern surface of the reticle R1 by the combined system of the imaging lens system 17 and the main condenser lens system 19. In this example, an ArF excimer laser light source 1, a beam matching unit 3, a variable dimmer 6, a beam shaping optical system (7A, 7B), a fly-eye lens 11, an aperture stop system 12, a beam splitter 8, and a mirror 13 An illumination optical system is constituted by the condenser lens system 19.
[0023]
Under the exposure light IL, an image of a circuit pattern in the illumination area of the reticle R1 is projected at a predetermined projection magnification β (β is, for example, 1/4, 1/5, etc.) via a bi-telecentric projection optical system PL. The light is transferred to a slit-shaped exposure area of a resist layer on a wafer W serving as a substrate disposed on the image plane of the projection optical system PL. The exposure area is located on one of the plurality of shot areas on the wafer. The reticle R1 (R2) and the wafer W can be regarded as a first object and a second object, respectively, and the projection optical system PL can be regarded as a projection system. The wafer W as a substrate to be exposed is, for example, a disk-shaped substrate such as a semiconductor (silicon or the like) or an SOI (silicon on insulator) having a diameter of 200 mm or 300 mm. Although the projection optical system PL of this example is a dioptric system (refractive system), it goes without saying that a catadioptric system (catadioptric system) can also be used. Hereinafter, the Z axis is taken parallel to the optical axis AX of the projection optical system PL, the X axis is taken in the scanning direction (here, the direction parallel to the plane of FIG. 1) in a plane perpendicular to the Z axis, and is orthogonal to the scanning direction. The description will be made taking the Y axis in the non-scanning direction (in this case, the direction perpendicular to the plane of FIG. 1).
[0024]
First, the reticle R1 is sucked and held on the reticle stage 20A, and the reticle stage 20A is mounted on the reticle base 20B so as to be able to move at a constant speed in the X direction and to be finely movable in the X, Y, and rotation directions. ing. The two-dimensional position and rotation angle of reticle stage 20A (reticle R) are measured in real time by a laser interferometer in drive control unit 22. Based on this measurement result and control information from a main control system 27 composed of a computer that controls the operation of the entire apparatus, a drive motor (such as a linear motor or a voice coil motor) in the drive control unit 22 is driven by the reticle stage 20A. Control the scanning speed and position.
[0025]
A reticle loader system (not shown) for efficiently exchanging reticle R1 with another reticle R2 (or another reticle) is provided near reticle stage 20A, and a reticle loaded on reticle stage 20A. A reticle discriminating device (not shown) for reading bar code information indicating the type of the reticle is also provided, and a discrimination result from the reticle discriminating device is supplied to the main control system 27. The main control system 27 sets the illumination conditions via the aperture stop system 12 in accordance with the type of reticle determined (minimum line width, pattern abundance ratio, phase shift reticle, etc.). Thus, for example, when performing exposure by the double exposure method, the reticle on the reticle stage 20A can be quickly replaced, and the optimal illumination condition can be reliably set according to the type of the replaced reticle.
[0026]
Although the reticle stage 20A of this example is of a single holder type, the reticle stage 20A may be of a double holder type capable of adsorbing two reticles in parallel. Alternatively, a reticle stage 20A may be of a double stage type in which two stages are arranged in parallel. By employing such a double holder method or a double stage method, for example, exposure by a double exposure method can be performed more efficiently.
[0027]
On the other hand, the wafer W is held by suction on a Z tilt stage 24Z via a wafer holder WH, and the Z tilt stage 24Z moves on a XY stage 24XY that moves two-dimensionally along an XY plane parallel to the image plane of the projection optical system PL. , A wafer stage 24 is constituted by the Z tilt stage 24Z and the XY stage 24XY. The Z tilt stage 24 </ b> Z controls the focus position (position in the Z direction) and the tilt angle of the wafer W to adjust the surface of the wafer W to the image plane of the projection optical system PL by an autofocus method and an autoleveling method. The stage 24XY performs constant-speed scanning of the wafer W in the X direction and stepping in the X and Y directions. The two-dimensional position and rotation angle of the Z tilt stage 24Z (wafer W) are measured in real time by a laser interferometer in the drive control unit 25. Based on this measurement result and the control information from the main control system 27, the drive motor (such as a linear motor) in the drive control unit 25 controls the scanning speed and position of the XY stage 24XY. The rotation error of the wafer W is corrected, for example, by slightly rotating the reticle stage 20A via the main control system 27 and the drive control unit 22.
[0028]
The main control system 27 sends to the drive control units 22 and 25 various information such as the respective movement positions, movement speeds, movement accelerations, and position offsets of the reticle stage 20A and the XY stage 24XY. At the time of scanning exposure, the reticle R1 is scanned via the XY stage 24XY in synchronization with the reticle R1 being scanned in the + X direction (or -X direction) at the speed Vr via the reticle stage 20A with respect to the illumination area of the exposure light IL. Then, the wafer W is scanned with respect to the exposure area of the pattern image of the reticle R in the −X direction (or + X direction) at a speed β · Vr (β is a projection magnification from the reticle R1 to the wafer W).
[0029]
Further, the main control system 27 performs control for synchronizing the movement of each blade of the movable blind 16B provided in the reticle blind mechanism 16 with the movement of the reticle stage 20A during scanning exposure. Further, the main control system 27 sets various exposure conditions for scanning and exposing the resist in each shot area on the wafer W with an appropriate exposure amount, and executes an optimal exposure sequence in cooperation with the exposure controller 30. That is, when a command to start scanning exposure to one shot area on the wafer W is issued from the main control system 27 to the exposure controller 30, the exposure controller 30 starts the emission of the ArF excimer laser light source 1 and the integrator sensor 9 , The integral value of the amount of light incident on the projection optical system PL is calculated. The integrated value is reset to 0 at the start of the scanning exposure. Then, the exposure controller 30 sequentially predicts and calculates the transmittance of the optical system from the beam splitter 8 to the projection optical system PL based on the integral value of the incident light amount, as described later, and according to the transmittance thus predicted. Then, the output (oscillation frequency and pulse energy) of the ArF excimer laser light source 1 and the dimming rate of the variable dimmer 6 are controlled so that an appropriate exposure amount can be obtained at each point of the resist on the wafer W after the scanning exposure. I do. Then, at the end of the scanning exposure on the shot area, the emission of the ArF excimer laser light source 1 is stopped.
[0030]
In addition, an irradiation amount monitor 32 composed of a photoelectric detector is installed near the wafer holder WH on the Z tilt stage 24Z in this example, and a detection signal of the irradiation amount monitor 32 is also supplied to the exposure controller 30. The irradiation amount monitor 32 has a light receiving surface large enough to cover the entire exposure region of the projection optical system PL, and drives the XY stage 24XY to set the light reception surface at a position covering the exposure region of the projection optical system PL. Thus, the amount of exposure light IL that has passed through the projection optical system PL can be measured. In this example, the transmittance from the beam splitter 8 to the projection optical system PL is calculated using the detection signals of the integrator sensor 9 and the irradiation amount monitor 32. Note that, instead of the irradiation amount monitor 32, an uneven illuminance sensor having a pinhole-shaped light receiving unit for measuring the light amount distribution in the exposure area may be used.
[0031]
That is, in this example, the “optical system” for which the transmittance is calculated (measured) includes the beam splitter 8 and the optical members from the mirror 13 to the main condenser lens system 19 in the illumination optical system, and the projection optical system PL. Contains. When the optical system includes a reflective optical member such as a mirror or a concave mirror, the transmittance of the object to be calculated (measured) includes data due to the reflectance of the reflective optical member. Further, for example, when the variation of the transmittance of the optical member from the beam splitter 8 and the mirror 13 to the main condenser lens system 19 in the illumination optical system is considerably smaller than the variation of the transmittance of the projection optical system PL. In, the optical system whose transmittance is to be calculated (measured) can be regarded as only the projection optical system PL.
[0032]
Further, in this example, since the ArF excimer laser light source 1 substantially in the vacuum ultraviolet region is used, absorptive gases such as oxygen, carbon dioxide and water vapor are removed from the optical path of the exposure beam, and the gas in the optical path is removed. It is desirable to replace the gas with a nitrogen gas or a rare gas (helium, neon, argon, krypton, xenon, radon), which is a transparent gas substantially transmitting vacuum ultraviolet light. The gas used to actually replace the optical path of the exposure beam in such a permeable gas is hereinafter referred to as a “purge gas”, and in this example, a dry nitrogen gas having an extremely low oxygen content as the purge gas ( N ₂ ). As a result, a sub-chamber 35 is provided to block the exposure light paths from the inside of the pipe 5 to the variable dimmer 6, the lens systems 7A and 7B, and the fly-eye lens 11 to the main condenser lens system 19 from the outside air. The purge gas is supplied through a pipe 36 to the entire space 35 and the entire space inside the lens barrel of the projection optical system PL (space between a plurality of lens elements).
[0033]
It should be noted that a purge gas is provided in the first optical path space of the exposure light between the main condenser lens system 19 of the illumination optical system and the projection optical system PL and in the second optical path space of the exposure light between the projection optical system PL and the wafer W. May be supplied. In particular, as an exposure light source, F ₂ When a laser light source or the like is used, oxygen molecules, water molecules, and carbon dioxide molecules contained in air cause F ₂ Since the laser light is absorbed, it is necessary to replace the above-described first and second optical path spaces with nitrogen gas or a rare gas in addition to the space inside the sub-chamber 35 and the lens barrel of the projection optical system PL. When replacing the first optical path space with a purge gas, for example, when providing a reticle chamber as an airtight chamber covering a reticle stage 20A holding the reticle R1 (R2), and replacing the second optical path space with a purge gas, For example, a purge chamber may be provided as an airtight chamber that covers a wafer stage 24 that holds a wafer, and a purge gas may be supplied into the reticle chamber and the wafer chamber.
[0034]
Next, a transmittance measurement system of an optical system including the projection optical system PL in the projection exposure apparatus of the present embodiment will be described with reference to FIG.
FIG. 3 shows an arrangement for measuring the transmittance of the optical system by the projection exposure apparatus shown in FIG. 1. In FIG. 3, the light receiving surface of the irradiation amount monitor 32 is driven by driving the XY stage 24XY. It is set in the exposure area of the PL. In this state, the pulse light emission of the ArF excimer laser light source 1 is started, and a part of the exposure light IL incident on the beam splitter 8 is reflected and incident on the integrator sensor 9. At the same time, the exposure light IL that has passed through the projection optical system PL enters the irradiation amount monitor 32, and detects a signal (hereinafter, referred to as “incident energy Ei”) of the integrator sensor 9 and a detection signal (hereinafter, referred to as “incident energy Ei”). Hereinafter, referred to as “transmission energy Eo”) is taken into the exposure controller 30 in parallel.
[0035]
In the exposure controller 30 shown in FIG. 3, the incident energy Ei from the integrator sensor 9 is supplied to the input unit of the incident light amount integration unit 41 and the first input unit of the direct transmittance calculation unit 42. Since the exposure light IL of this example is a pulse light, a peak hold (P / H) circuit and an analog-to-digital converter (ADC) are provided in the data input units in the incident light amount integration unit 41 and the direct transmittance calculation unit 42, respectively. Is arranged.
[0036]
On the other hand, the transmitted energy Eo detected by the irradiation amount monitor 32 is supplied to the second input unit of the direct transmittance calculator 42. The direct transmittance calculator 42 calculates the transmittance T of the optical system by dividing the transmission energy Eo by the incident energy Ei as shown in the following equation, and supplies the calculated transmittance T to the transmittance history storage 43. I do.
T = Eo / Ei (1)
The transmittance history storage unit 43 sequentially stores the supplied transmittance T together with a number i indicating the order of sampling. The transmittance T in the sampling order i is defined as the transmittance Ti. The exposure controller 30 is provided with a control unit 45 for controlling the operation of each unit in the controller, and the control unit 45 exchanges various data and commands with the main control system 27 in FIG. ing. As an example, the control unit 45 is supplied with information on the target output (or pulse energy) and emission frequency of the exposure light IL, a command indicating the timing of transmittance measurement, and the like from the main control system 27. The timing information of the sampling of the detection signal from the external sensor is supplied to each unit in the exposure controller 30. Then, the transmittance history storage unit 43 reads out the i-th transmittance Ti in accordance with an instruction from the control unit 45 and supplies the i-th transmittance Ti to the first input unit of the predicted transmittance calculation unit 44.
[0037]
In addition, the incident light amount integration unit 41 integrates (integrates) the incident energy Ei for each incident pulse light to calculate the total incident energy e, and uses the calculated total incident energy e as the second value of the predicted transmittance calculation unit 44. Supply to input section. The total incident energy e is normally reset to 0 immediately before the start of pulse emission. Further, the total incident energy e at the timing when the i-th transmittance Ti is measured is stored as a total incident energy ei in the storage unit in the incident light amount integration unit 41, and the total incident energy ei is also determined as necessary. Is supplied to the second input unit of the predicted transmittance calculating unit 44.
[0038]
The predicted transmittance calculator 44 calculates a change rate of the supplied transmittance Ti with respect to the input total energy e as described later, and calculates the current transmittance T of the optical system from the change rate and the incident total energy e. (Now) is obtained, and the transmittance T (now) is supplied to the control unit 45. The control unit 45 uses the transmittance T (now) to output and vary the output of the ArF excimer laser light source 1 so that the integrated exposure amount of the exposure light IL at each point of the resist on the wafer W becomes an appropriate exposure amount. The dimming rate in the dimmer 6 is controlled.
[0039]
In this example, the incident light amount integration unit 41, the direct transmittance calculation unit 42, the predicted transmittance calculation unit 44, and the control unit 45 represent software functions executed by the microprocessor in this example. Needless to say, each of the functions may be realized by hardware.
Next, in this example, the change in the transmittance of the optical system from the beam splitter 8 to the projection optical system PL is measured, and the double exposure method is performed using the reticles R1 and R2 while controlling the exposure amount based on the measurement result. The operation when scanning exposure is performed will be described with reference to the flowcharts of FIGS. 4 and 5 and FIG.
[0040]
First, the exposure process by the projection exposure apparatus of FIG. 1 is started in step 121 of FIG. 4, and the reticle R1 is loaded on the reticle stage 20A in step 122 under the control of the main control system 27. In parallel with this, the main control system 27 sets the illumination conditions via the aperture stop system 12 of the illumination system. For example, when the minimum line width of the pattern of the reticle R1 is extremely small, the modified illumination or the annular illumination is selected. The use of the reticle R1 and the set illumination conditions corresponding thereto correspond to the “first exposure condition” of the present invention. In the next step 123, the first wafer W of one lot on which a resist is applied, for example, is loaded onto the wafer stage 24. In the next step 124, it is determined whether the loaded wafer is the first wafer. Since this is the first sheet, the operation proceeds to step 125, where the first transmittance measurement is performed.
[0041]
To this end, as shown in FIG. 3, the light receiving surface of the irradiation amount monitor 32 is moved to the exposure area of the projection optical system PL, and the ArF excimer laser light source 1 emits, for example, several pulses, and directly transmits light. The rate calculator 42 takes in the detection signal (incident energy Ei) from the integrator sensor 9 and the detection signal (transmission energy Eo) from the irradiation amount monitor 32, and calculates the transmittance T (= Ta1) from equation (1). I do. At this time, the average value of the measurement results of several pulses may be used as the transmittance Ta1.
[0042]
In the next step 126, after resetting the total incident energy e in the incident light amount integration section 41 to 0, the ArF excimer laser light source 1 emits the exposure light IL by dummy irradiation (by blank shot) for a predetermined time. The dummy irradiation time is preferably short in order to increase the throughput, but may be set to, for example, the exposure time of several shots to one wafer in order to increase the measurement accuracy. In this example, as an example, the dummy irradiation time is set to be the same as the exposure time for one wafer. In order to shorten the measurement time and increase the measurement accuracy, the output P of the ArF excimer laser light source 1 may be set to the maximum value and the oscillation frequency may be set to the maximum value to perform the dummy irradiation. At this time, the total incident energy e (= ΔE1) integrated by the incident light amount integration unit 41 is supplied to the predicted transmittance calculation unit 44.
[0043]
In the next step 127, a second transmittance measurement is performed. That is, the ArF excimer laser light source 1 emits, for example, several pulses, and the direct transmittance calculator 42 takes in the incident energy Ei from the integrator sensor 9 and the transmitted energy Eo from the irradiation amount monitor 32, and obtains the equation (1). , The transmittance T (= Ta2) is calculated. These transmittances Ta1 and Ta2 are stored in the transmittance history storage unit 43.
[0044]
In the next step 128, the predicted transmittance calculator 44 reads out the transmittances Ta1 and Ta2 from the transmittance history storage 43, and divides the difference between the two transmittances by the total incident energy ΔE1 therebetween as in the following equation. , The transmittance change rate TVa is calculated. The change rate TVa is stored in the storage unit in the predicted transmittance calculator 44 in association with the reticle R1.
[0045]
TVa = (Ta2-Ta1) / ΔE1 (2)
At this stage, the total incident energy e in the incident light amount integration unit 41 is reset. In the next step 130, the predicted transmittance calculator 44 calculates the current transmittance T (now) of the optical system using the calculated change rate TVa. That is, the latest (last) actually measured transmittance T of the optical system is defined as Tj, and the current total incident energy e integrated by the incident light amount integration unit 41 from the time when the transmittance Tj is measured is defined as ej. The predicted transmittance calculator 44 calculates the current transmittance T (now) of the above optical system by adding the transmittance change TVa · ej to the latest measured transmittance Tj as in the following equation. I do. The calculated or predicted transmittance T (now) is supplied to the control unit 45.
[0046]
T (now) = Tj + TVa.ej (3)
In the next step 131, the control unit 45 controls the output (= pulse energy × frequency) P of the ArF excimer laser light source 1 using the predicted current transmittance T (now). This output P is the output at the stage of entering the beam splitter 8 in FIG. 3, that is, the energy per unit time determined based on the detection signal of the integrator sensor 9. In this case, the initial value of the transmittance T of the optical system from the beam splitter 8 to the projection optical system PL (the value measured first in step 125 for the first wafer of one lot) is T. ₀ And This transmittance T ₀ The value of the output P corresponding to ₀ [W], the area of the slit-shaped exposure region on the wafer W is S [cm]. ² ], The length of the exposure region in the scanning direction is L [mm], and the resist sensitivity (appropriate exposure amount) is I [J / cm]. ² Assuming that the scanning speed of the wafer stage 24 at the time of scanning exposure is Vw [mm / sec], the following relationship exists between them.
[0047]
I · S = (L / Vw) P ₀ ・ T ₀ … (4)
From equation (4), the reference value P ₀ Is determined as follows.
P ₀ = (Vw / L) (IS) / T ₀ … (5)
In this example, the output P is controlled by setting the scanning speed Vw to a predetermined maximum value in order to increase the throughput. At present, the initial value T of the transmittance in the equation (5) ₀ Has been changed to the current value T (now), the following relationship is established.
[0048]
PT (now) = P ₀ ・ T ₀ … (6)
From this equation (6), the output P is as follows.
P = P ₀ (T ₀ / T (now)) ... (7)
The control unit 45 controls at least one of the output of the ArF excimer laser light source 1 itself and the dimming rate of the variable dimmer 6 so that the output P satisfies the expression (7). In this case, as an example, the output of the ArF excimer laser light source 1 itself is controlled in a range where the output of the laser light source itself falls within a predetermined standard. 6 may be controlled.
[0049]
In the next step 132, the pattern image of the reticle R1 is transferred to the first shot area of the wafer W by the scanning exposure method. In the next step 133, it is determined whether or not exposure of all shot areas has been completed. Here, since the operation has not been completed, the operation returns to step 130, and the predicted transmittance calculator 44 again calculates the current transmittance T (now) of the optical system for the current total incident energy ej from equation (3). Subsequently, the output P is calculated from the equation (7) by the control unit 45, and based on the result, at least one of the output of the ArF excimer laser light source 1 itself and the dimming rate of the variable dimmer 6 is controlled (step S1). 131) The pattern image of the reticle R1 is transferred to the second shot area by the scanning exposure method (step 132). The operations of steps 130 to 133 are repeatedly executed for all the shot areas on the wafer W, and when the exposure of all the shot areas is completed, the operation shifts from step 133 to step 134 to perform the optical operation similarly to step 125. The transmittance T (= Ta3) of the system is measured, and the total incident energy e in the incident light amount integration unit 41 is reset.
[0050]
In the next step 135, the estimated transmittance calculator 44 calculates the transmittances Ta2 and Ta3 measured in steps 128 and 134, and the total incident energy integrated by the incident light amount integrating unit 41 during the exposure of the wafer W. Using e (= ΔE2), the latest change rate TVa of the transmittance is calculated from the following equation, and the calculated change rate TVa is stored corresponding to the reticle R1.
[0051]
TVa = (Ta3-Ta2) / ΔE2 (8)
In the next step 136, it is determined whether or not to continue exposure with the same reticle R1. In the normal exposure method, the operation moves to step 123 because the same reticle R1 is used, and the second and subsequent wafers are exposed. In this example, since the exposure is performed by the double exposure method, the operation shifts from step 136 to step 141 in FIG. Here, the actual transmittance T of the optical system from the beam splitter 8 to the projection optical system PL, the calculated transmittance T (now), and the output at the stage of the beam splitter 8 of the ArF excimer laser light source 1 The mutual relationship of P will be described with reference to FIG.
[0052]
The vertical axis in FIG. 6A shows the change in the actual transmittance T (the transmittance calculated by the direct transmittance calculator 42) of the optical system, and the vertical axis in FIG. 6B shows the optical system. 6C shows the change in the current transmittance T (now) calculated by the predicted transmittance calculator 44, and the vertical axis in FIG. 6C shows the change in the output P, and FIGS. ) Indicates that the wafer to be exposed is the n-th wafer (n = 1, 2,...). Further, since the exposure energy to be irradiated is substantially proportional to the number n of wafers, the horizontal axes in FIGS. 6A to 6C can be regarded as the total incident energy e to the optical system. The total incident energy e is reset every time the actual transmittance T is measured. In the horizontal axes of FIGS. 6A and 6B, sections (d), (R1) and (R2) represent sections where dummy irradiation, exposure of reticle R1 and exposure of reticle R2 are performed, respectively. . Furthermore, the initial value of the actual transmittance T and the calculated transmittance T (now) is T ₀ And the initial value (reference value) of the output P is P ₀ It has been.
[0053]
Further, in FIG. 6A, the actual transmittance T of the optical system has a large variation as shown by a solid line 50A during exposure through the reticle R1, and is indicated by a dotted line 50B during exposure through the reticle R2, as an example. Thus, the amount of fluctuation is small. This corresponds to, for example, a case where the pattern existence rate of the reticle R1 is smaller than the pattern existence rate of the reticle R2. When the dummy irradiation and the step 128 are completed for the first wafer in this example, the actual transmittance T has changed to the value T5b, but the calculated transmittance T (now) (FIG. 6B) ) And output P (FIG. 6C) are T ₀ And P ₀ Remains. At the start of exposure to the first shot area, the calculated current transmittance T (now) value T6b is the actual transmittance T value T5b, and the output P is determined from equation (7). It is set to the value P2b. Thereafter, the exposure of all the shot areas of the first wafer is completed, and when step 135 is completed, the actual transmittance T changes in a curve to a value T5c, and the calculated current transmittance T is calculated. (Now) changes linearly to the value T6c according to the equation (3). Then, the output P changes to a value P2c in inverse proportion to the current transmittance T (now).
[0054]
In this state, in step 141 in FIG. 5, reticle R1 on reticle stage 20A in FIG. 1 is replaced with another reticle R2. In parallel with this, the main control system 27 sets the illumination conditions for the reticle R2 via the aperture stop system 12 of the illumination system. For example, when the minimum line width of the reticle R2 is several times the resolving power of the projection optical system PL, an illumination method (normal illumination) using a medium circular aperture stop is selected. The use of the reticle R2 and the set illumination conditions corresponding thereto correspond to the “second exposure condition” of the present invention. In the subsequent steps 142 to 155, the pattern image of the reticle R2 is transferred to each shot area of the wafer W as in steps 123 to 136 in FIG.
[0055]
That is, first, the first wafer W of one lot is loaded on the wafer stage 24 (step 142), and the wafer W is the wafer that has been mounted as it is after the pattern image of the reticle R1 has been transferred. Subsequently, it is determined whether or not the wafer W is the first wafer (step 143). Since the wafer is the first wafer, the operation proceeds to step 144, and the first operation for the reticle R2 in the arrangement of FIG. A transmittance measurement is performed. At this time, the transmittance T calculated from the equation (1) is Tb1. Subsequently, after the ArF excimer laser light source 1 performs dummy irradiation with the total incident energy ΔE1 for a predetermined time (step 145), the second transmittance measurement is performed (step 146). Assuming that the transmittance T measured at this time is Tb2, the predicted transmittance calculating unit 44 calculates the transmittance change rate TVb when the reticle R2 is used as follows (step 147). The change rate TVb is stored in the storage unit in the predicted transmittance calculator 44 in association with the reticle R2.
[0056]
TVb = (Tb2−Tb1) / ΔE1 (9)
In the next step 149, the predicted transmittance calculator 44 calculates the calculated change rate TVb, the latest (last) actually measured transmittance Tj of the optical system, and the time when the transmittance Tj is measured. The current transmittance T (now) of the optical system is calculated from the following equation using the current total incident energy ej accumulated by the incident light amount integration unit 41.
[0057]
T (now) = Tj + TVb · ej (10)
In the next step 150, similarly to step 131, the control unit 45 uses the predicted current transmittance T (now) so that the output P of the ArF excimer laser light source 1 becomes the value of the following equation. At least one of the output of the laser light source 1 itself and the dimming rate of the variable dimmer 6 is controlled. The reference value P ₀ Is set by equation (5), but a new value may be set for reticle R2.
[0058]
P = P ₀ (T ₀ / T (now)) ... (11)
In the next step 151, the pattern image of the reticle R2 is transferred to the first shot area of the wafer W by the scanning exposure method. In the next step 152, it is determined whether or not exposure of all shot areas has been completed. Since the operation has not been completed here, the operation returns to step 149, and the predicted transmittance calculator 44 again calculates the current transmittance T (now) of the optical system from equation (10). Subsequently, the output P is calculated from the equation (11) in the control unit 45, and after at least one of the output of the ArF excimer laser light source 1 itself and the dimming rate of the variable dimmer 6 is controlled based on the result (step 150) The pattern image of the reticle R2 is transferred to the second shot area by the scanning exposure method (Step 151). The operations of steps 149 to 152 are repeatedly executed for all shot areas on the wafer W. When the exposure for all shot areas is completed, the wafer W subjected to the double exposure undergoes a process such as development. From the wafer stage 24. Then, the operation proceeds from step 152 to step 153, where the transmittance T (= Tb3) of the optical system is measured as in step 146, and the total incident energy e in the incident light amount integration unit 41 is reset.
[0059]
In the next step 154, the predicted transmittance calculator 44 calculates the transmittances Tb2 and Tb3 measured in steps 146 and 153, and the total incident energy integrated by the incident light amount integration unit 41 during exposure of the wafer W. Using e (= ΔE3), the latest change rate TVb of the transmittance is calculated from the following equation, and the calculated change rate TVb is stored corresponding to the reticle R2.
[0060]
TVb = (Tb3−Tb2) / ΔE3 (12)
In the next step 155, it is determined whether or not to continue the exposure with the same reticle R2. When the operation is continued with the same reticle R2, the operation returns to step 142 to perform exposure on the next wafer. However, the operation of this example returns from step 155 to step 122 in FIG. Double exposure is performed on the wafer.
[0061]
In the exposure of the reticle R2 to the first wafer in this example, at the time when the dummy irradiation and the step 147 are completed, the actual transmittance T (FIG. 6A) has changed to the value T5d. The transmitted transmittance T (now) (FIG. 6B) and the output P (FIG. 6C) remain at T6c and P2c, respectively. At the start of exposure to the first shot area, the calculated current transmittance T (now) value T6d is the actual transmittance T value T5d, and the output P is set to the value P2d. Thereafter, the exposure of all the shot areas of the first wafer is completed, and when step 154 is completed, the actual transmittance T changes in a curve to the value T5e, and the calculated current transmittance T is calculated. (Now) changes linearly to the value T6e according to the equation (10). Then, the output P changes to a value P2e so as to be inversely proportional to the current transmittance T (now).
[0062]
Next, in order to expose the second wafer, in step 121 in FIG. 4, the reticle R2 on the reticle stage 20A in FIG. 1 is replaced with the reticle R1, and the illumination conditions corresponding to the reticle R1 are set. Thereafter (step 122), a second wafer is loaded on wafer stage 24 (step 123). In the next step 124, since the wafer is the second wafer, the operation shifts to step 129, where the predicted transmittance calculating unit 44 determines the change rate of the transmittance corresponding to the reticle R1 stored in the internal storage unit. After calling the TVa, the process proceeds to step 130, where the called change rate TVa, the transmittance Tj of the optical system actually measured last (here, the transmittance Tb3 measured in step 153), and the transmittance thereof The current transmittance T (now) of the optical system is calculated from Expression (3) using the current total incident energy ej accumulated by the incident light amount integration unit 41 after the measurement of the rate Tb3. The calculated or predicted transmittance T (now) is supplied to the control unit 45.
[0063]
In response to this, the control unit 45 controls the output P of the ArF excimer laser light source 1 using the predicted current transmittance T (now) (step 131). Then, as in the case of the first wafer, by repeating steps 130 to 133, while controlling the output P so as to offset the fluctuation amount of the transmittance of the optical system, all shot areas of the second wafer are controlled. The pattern image of the reticle R1 is transferred by the scanning exposure method. In the next step 134, the transmittance T (= Ta3) of the optical system is measured, and the total incident energy e is reset. In the subsequent step 135, the predicted transmittance calculator 44 calculates the transmittances Tb3, Ta3 measured last in steps 153 and 134, respectively, and the total incident light integrated by the incident light amount integrating unit 41 during exposure to this wafer. Using the energy e (= ΔE2), the latest change rate TVa of the transmittance is calculated from the following equation, and the calculated change rate TVa is stored in correspondence with the reticle R1.
[0064]
TVa = (Ta3-Tb3) / ΔE2 (13)
At the start of exposure when steps 129 and 130 are completed for the second wafer, the calculated value T6f of the transmittance T (now) (FIG. 6B) is the actual value T5e of the transmittance T. . Then, when the exposure of the reticle R1 to all the shot areas of the second wafer is completed and the step 135 is completed, the calculated current transmittance T (now) changes linearly to the value T6g. . On the other hand, the output P (FIG. 6C) changes so as to be inversely proportional to the current transmittance T (now).
[0065]
Next, the operation proceeds from step 136 to step 141 in FIG. 5, the reticle R1 on the reticle stage 20A in FIG. 1 is replaced with another reticle R2, and the illumination condition is set accordingly. In this case also, in the next step 142, the second wafer (on which the pattern image of the reticle R1 has been transferred) is placed on the wafer stage 24 as it is. In the next step 143, since the wafer is the second wafer, the operation proceeds to step 148, where the predicted transmittance calculator 44 determines the change rate of the transmittance corresponding to the reticle R2 stored in the internal storage unit. After calling the TVb, the process proceeds to step 149, where the called change rate TVb, the transmittance Tj of the optical system actually measured last (here, the transmittance Ta3 measured in step 134), and the transmittance thereof The current transmittance T (now) of the optical system is calculated from Expression (10) using the total incident energy ej accumulated by the incident light amount integration unit 41 after the measurement of the rate Ta3. The calculated or predicted transmittance T (now) is supplied to the control unit 45.
[0066]
In response to this, the control unit 45 controls the output P of the ArF excimer laser light source 1 using the predicted current transmittance T (now) (step 150). Then, similarly to the first wafer, steps 149 to 152 are repeated to control the output P so as to cancel out the variation in the transmittance of the optical system, thereby controlling the entire shot area of the second wafer. The pattern image of the reticle R2 is transferred by the scanning exposure method. The wafer subjected to the double exposure is carried out of the wafer stage 24 in order to go through a process such as development. In the next step 153, the transmittance T (= Tb3) of the optical system is measured, and the total incident energy e is reset. In the next step 154, the predicted transmittance calculator 44 calculates the transmittances Ta3 and Tb3 last measured in steps 134 and 153, respectively, and the total incident light integrated by the incident light amount integration unit 41 during exposure to this wafer. Using the energy e (= ΔE3), the latest change rate TVb of transmittance is calculated from the following equation, and the calculated change rate TVb is stored corresponding to the reticle R2.
[0067]
TVb = (Tb3-Ta3) / ΔE3 (14)
At the start of exposure when steps 148 and 149 are completed for the second wafer, the calculated value T6h of the transmittance T (now) (FIG. 6B) is a measured value of the actual transmittance T. . Then, when the exposure of the reticle R2 to all the shot areas of the second wafer is completed and the step 154 is completed, the calculated current transmittance T (now) changes linearly to the value T6i. . On the other hand, the output P (FIG. 6C) changes so as to be inversely proportional to the current transmittance T (now).
[0068]
Next, the operation returns from step 155 to step 122 in FIG. 4, for the third and subsequent wafers of the first lot, transmittance calculation, output control, Exposure to each shot area is repeated. That is, at the time of exposure of the reticle R1, the current transmission T is obtained from the equation (3) based on the latest measured value Tj of the transmittance T, the rate of change TVa of the transmittance finally calculated for the same reticle R1, and the total incident energy ej. The rate T (now) is calculated (predicted), and the amount of exposure is controlled based on the transmittance T (now). Similarly, at the time of exposure of the reticle R2, from the equation (10) based on the latest measured value Tj of the transmittance T, the transmittance change rate TVb finally calculated for the same reticle R2, and the current total incident energy ej. The current transmittance T (now) is calculated (predicted), and the exposure amount is controlled based on the transmittance T (now). When the exposure of all the wafers in one lot is completed, the operation moves from step 155 to step 156, and the exposure process ends. Further, although different from this example, for example, when the exposure of only the reticle R1 is performed and the exposure of all the wafers is completed, the operation proceeds from the step 136 to the step 137, and the exposure process is completed. .
[0069]
As described above, according to this example, when performing exposure while exchanging the reticles R1 and R2 by the double exposure method, the latest measured value Tj of the transmittance of the optical system, the transmittance calculated last for the same reticle. Of the optical system is predicted on the basis of the change rate TVa (or TVb) of the optical system and the total incident energy ej that has been incident so far from the measurement of the transmittance, and based on the prediction result, The exposure is controlled so that each wafer is exposed with an appropriate exposure. Therefore, despite the fact that exposure is performed alternately under two significantly different exposure conditions, it is possible to maintain high exposure amount control accuracy with simple control.
[0070]
When performing exposure on the first wafer of one lot, dummy irradiation is first performed on each of the reticles R1 and R2 to determine the transmittance change rate TVa (or TVb). Therefore, high exposure dose control accuracy can be obtained from the first wafer.
Next, another example of the embodiment of the present invention will be described with reference to FIGS. In this example, for example, when two reticles to be double-exposed are commonly used for a large number of wafers, the change rate of the transmittance of the optical system is calculated and stored in advance. In this embodiment, the projection exposure apparatus shown in FIGS. 1 to 3 is used.
[0071]
7 and 8 are flowcharts showing the operation of the present example. First, an exposure preparation process is started in step 201 of FIG. 7, and in step 202, the reticle R1 is loaded on the reticle stage 20A. In the next step 203, the transmittance of the optical system is measured. In the next step 204, dummy irradiation (total incident energy Δe) is performed in the same manner as in step 126, and in the next step 205, the transmittance of the optical system is again measured. Is measured, and in the next step 206, the transmittance change rate TVa is calculated by the predicted transmittance calculator 44 in the same manner as in step 128. The calculated change rate TVa is stored corresponding to the total incident energy Δe. In this example, the total incident energy Δe for one time is set equal to the total incident energy when actually exposing one wafer using the reticles R1 and R2.
[0072]
In the next step 207, it is determined whether or not the above operation has been repeated k times (k is a preset integer of 2 or more). If not, the operation returns to step 204, and the dummy irradiation, transmittance Measurement and calculation of the transmittance change rate TVa are performed. The calculated change rate TVa is stored corresponding to the total incident energy 2 · Δe,..., K · Δe. Thereafter, the operation shifts from step 207 to step 208, and waits until the transmittance of the optical system returns to the original state.
[0073]
After that, in steps 209 to 214, the rate of change TVb of the transmittance of the optical system corresponds to the total incident energy Δe,..., K · Δe with the reticle R2 loaded on the reticle stage 20A as in steps 202 to 207. Calculated and stored.
The vertical axis of FIG. 9A shows a change in the actual transmittance T (the transmittance calculated by the direct transmittance calculator 42) of the optical system, and the horizontal axis of 9A shows the total incident energy e. It is. In FIG. 9A, a solid curve 51 shows an example of a change in transmittance when the reticle R1 is used, and a dotted curve 52 shows an example of a change in transmittance when the reticle R2 is used. . The transmittance change rates TVa and TVb corresponding to the reticles R1 and R2 are respectively a series of measured values T ₀ , T1b, T1c,... And T ₀ , T2b, T2c,... Are obtained by dividing the difference of the total incident energy Δe.
[0074]
With the exposure preparation step completed in this way, the exposure step by the double exposure method in step 221 in FIG. 8 is started. Then, after loading the first wafer on the wafer stage 24 in FIG. 1 (step 222) and loading the reticle R1 on the reticle stage 20A (step 223), the transmittance of the optical system in the state of FIG. Is measured (step 224). In the next step 225, the predicted transmittance calculator 44 calculates the latest actually measured transmittance Tj of the optical system, the total incident energy e since the start of the exposure process (a value not reset at the time of transmittance measurement). ), The change rate TVa of the transmissivity stored corresponding to the total incident energy k ′ · Δe (k ′ = 1, 2,..., K) closest to the incident light and the transmissivity Tj from when the transmissivity Tj is measured. Using the total incident energy ej integrated by the light amount integration unit 41, the current transmittance T (now) of the above optical system is calculated from the equation (3). The transmittance change rate TVa may be, for example, a value obtained by interpolating two change rates having close incident total energies.
[0075]
In the next step 226, similarly to step 131, the control unit 45 uses the predicted current transmittance T (now) to output the output P of the ArF excimer laser light source 1 so that an appropriate exposure amount can be obtained on the wafer. (The value including the dimming rate of the variable dimmer 6) is controlled, and in the next step 227, the pattern image of the reticle R1 is transferred to one shot area on the wafer. Then, after Steps 225 to 227 are repeated for all shot areas on the wafer, the operation proceeds from Step 228 to Step 229, and reticle R1 on reticle stage 20A is replaced with reticle R2. In subsequent steps 230 to 234, the transmittance measurement and the incident total energy k ′ · Δe (k ′ = 1, 2,..., K) closest to the incident total energy e are performed in the same manner as steps 224 to 228. The current transmittance T (now) is calculated from the equation (10) using the transmittance change rate TVb stored in advance and stored, the exposure amount control according to the transmittance T (now), and each shot area The pattern image of the reticle R2 is transferred to the reticle R2. The wafer after the double exposure is carried out of the wafer stage 24.
[0076]
In the next step 235, it is determined whether or not exposure of all wafers in one lot has been completed. If not, the operation returns to step 202 and the next wafer is loaded on wafer stage 24. . For the second and subsequent wafers, similarly to the first wafer, the current transmittance T (now) is calculated using the transmittance change rates TVa and TVb stored for each of the reticles R1 and R2. Thus, the pattern image of the reticle is transferred while controlling the exposure amount. Then, when the exposure of all the wafers is completed, the exposure process is completed.
[0077]
The vertical axis of FIG. 9B indicates a change in the current transmittance T (now) calculated by the predicted transmittance calculator 44 of the optical system of the present example, and the vertical axis of FIG. 9C indicates the present example. 9B, the horizontal axis in FIGS. 9B and 9C indicates that the wafer to be exposed is the n-th wafer (n = 1, 2,...). . The horizontal axes in FIGS. 9B and 9C can be regarded as the total incident energy e (the value not reset at the time of measuring the transmittance) for the optical system. In the horizontal axis of FIG. 9B, sections (R1) and (R2) represent sections in which reticles R1 and R2 are exposed, respectively.
[0078]
As shown in FIG. 9B, at the start of the exposure of the pattern of the reticle R1 onto the first wafer, the calculated current transmittance T (now) is a measured value (here, the initial value T). ₀ ), And the output P of the ArF excimer laser light source 1 is equal to the reference value P, as shown in FIG. ₀ Is set to Thereafter, until the exposure of the pattern of the reticle R1 to all the shot areas of the first wafer is completed, the calculated current transmittance T (now) changes linearly to the value T3b according to the equation (3). I do. The change rate TVa used in the first wafer is the first two transmittances T in FIG. ₀ , T1b, the value T3b substantially matches the actual measured value of the transmittance. Then, the output P changes to a value P1b so as to be inversely proportional to the current transmittance T (now).
[0079]
In this state, in step 229 in FIG. 8, reticle R1 on reticle stage 20A in FIG. 1 is replaced with another reticle R2. When exposure of the pattern of the reticle R2 to the first wafer is started, the calculated current transmittance T (now) changes linearly from the value T3b to the value T3c according to the equation (10). However, the output P changes to a value P1c so as to be inversely proportional to the current transmittance T (now).
[0080]
Next, after the second wafer is loaded and the reticle R1 is loaded, when exposure of the pattern of the reticle R1 is started, the calculated current transmittance T (now) of FIG. 9B is calculated. Changes linearly from the measured value T3d to the value T3e, and the output P in FIG. 9C changes in inverse proportion from the value P1d to the value P1e. Thereafter, when the reticle R1 is replaced with the reticle R2 and exposure is started, the calculated current transmittance T (now) changes linearly from the measured value T3f, and the output P is inversely proportional to the value P1f. Change. For the third and subsequent wafers, the current transmittance T (now) of the optical system is calculated using the change rates TVa and TVb calculated and stored in advance in the same manner, and the exposure is performed based on the result. Volume control is performed.
[0081]
As described above, according to this example, the change rate TVa or TVb from which the current transmittance T (now) is calculated when performing exposure using the reticle R1 or R2 is the incident rate shown in FIG. A value measured in a section where the total energy e is almost the same is used. Therefore, when performing exposure by the double exposure method, a step of obtaining a change rate of transmittance by performing dummy irradiation can be omitted, so that high throughput can be obtained.
[0082]
In the above embodiment, the change rates TVa and TVb (first-order approximation) are calculated from the two measured values of the transmittance as the change information of the transmittance of the optical system. , Measurement of change information and subsequent control during exposure are simple. Alternatively, for example, the transmittance may be approximated by a function of second order or higher with respect to the total incident energy from three measured values of the transmittance, and the coefficient of the approximated function may be stored. Further, the change in the transmittance may be approximated by using, for example, an exponential function (exp (x)) other than the quadratic function. In these cases, when the current transmittance T (now) is calculated, a function of the second order or higher or an exponential function is used, so that the calculation accuracy of the current transmittance is improved, and the exposure amount is further reduced. Control accuracy is also improved.
[0083]
In the above embodiment, the present invention is applied to the case where double exposure is performed. However, it goes without saying that the present invention can be applied to the case where multiple exposure is performed by alternately using three or more reticles. No. Further, the present invention can be applied to a case where exposure is alternately performed while switching exposure conditions such as an aperture stop of an illumination system among a plurality of conditions using one reticle.
[0084]
In addition, since the total incident energy is substantially proportional to the number of shot areas exposed on one wafer, the change rate (or function) of the transmittance per shot area is used when calculating the change information of the transmittance. At the time of exposure, the current transmittance T (now) may be calculated using the number of shots exposed and the rate of change thereof. Further, when the total incident energy is substantially proportional to time, the change rate (or function) of the transmittance per unit time is obtained when obtaining the change information of the transmittance. The current transmittance T (now) may be calculated using the exposure time and the rate of change thereof.
[0085]
In the above embodiment, the output P (including the dimming rate of the variable dimmer 6) of the ArF excimer laser light source 1 is controlled in order to control the exposure so as to satisfy the expression (4). However, the scanning speed Vw of the wafer stage and the width L of the exposure region in the scanning direction may be controlled together with or instead of the above.
The present invention can be applied not only to a scanning exposure type exposure apparatus but also to a batch exposure type exposure apparatus (eg, a stepper). As described above, when the present invention is applied to the one-shot exposure type exposure apparatus, for example, in the exposure amount control step of step 131 in FIG. 4, appropriate exposure is performed on the wafer in accordance with the current transmittance T (now) of the optical system. The exposure time may be calculated so as to obtain the amount, and the exposure may be performed using the calculated exposure time.
[0086]
In the above embodiment, the present invention is applied to a projection exposure apparatus having a projection optical system PL. However, the present invention is directed to a proximity type or contact type exposure apparatus which does not use the projection optical system PL. Can also be applied. In this case, the optical system for which the transmittance is measured and calculated is the optical system from the beam splitter 8 to the main condenser lens system 19 in FIG.
[0087]
Further, the present invention can also be applied to a charged particle beam exposure apparatus using a charged particle beam such as an electron beam as an exposure beam. In this case, the optical system whose transmittance is to be measured and calculated is an electron optical system including an electronic lens and a deflector.
In addition, the illumination optical system and projection optical system composed of multiple lenses are incorporated into the exposure apparatus main body to perform optical adjustment, and a reticle stage and wafer stage consisting of many mechanical parts are attached to the exposure apparatus main body to perform wiring and piping. The exposure apparatus of the above-described embodiment can be manufactured by connecting and further performing overall adjustment (electrical adjustment, operation confirmation, and the like). It is desirable that the manufacture of the exposure apparatus be performed in a clean room in which the temperature, cleanliness, and the like are controlled.
[0088]
Further, when manufacturing a semiconductor device on a wafer using the projection exposure apparatus of the above embodiment, this semiconductor device is a step of designing the function and performance of the device, a step of manufacturing a reticle based on this step, A step of producing a wafer from a silicon material, a step of performing alignment by the projection exposure apparatus of the above-described embodiment to expose a reticle pattern to the wafer, a device assembling step (including a dicing step, a bonding step, and a package step); It is manufactured through an inspection step and the like.
[0089]
The application of the exposure apparatus is not limited to an exposure apparatus for manufacturing a semiconductor element. For example, an exposure apparatus for a display apparatus such as a liquid crystal display element or a plasma display formed on a square glass plate, and an imaging apparatus. The present invention can be widely applied to an exposure apparatus for manufacturing various devices such as an element (eg, a CCD), a micromachine, a thin-film magnetic head, and a DNA chip. Further, the present invention can be applied to an exposure step (exposure apparatus) when a reticle (photomask or the like) on which a reticle pattern of various devices is formed by using a photolithography step.
[0090]
It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention.
[0091]
【The invention's effect】
According to the present invention, when performing exposure while switching a plurality of different exposure conditions, even if the manner in which the transmittance of the optical system changes greatly depending on the exposure conditions, it is determined for each exposure condition so far. Since the exposure amount is controlled using the change information of the transmittance of the optical system, the control accuracy of the exposure amount can be kept high even if the transmittance of the optical system varies.
[0092]
Further, according to the present invention, for example, when double exposure is performed while alternately switching two exposure conditions, the transmittance change information calculated last under the same exposure condition and the latest transmittance measurement Since the current transmittance of the optical system can be predicted with high accuracy by using the value and the value, by controlling the exposure based on the predicted transmittance, the control accuracy of the exposure can be maintained high. .
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a projection exposure apparatus used in an embodiment of the present invention.
FIG. 2 is a diagram showing an aperture stop system 12 in FIG.
FIG. 3 is a configuration diagram including a partial functional block diagram showing a state in which a dose monitor 32 is moved to an exposure area of a projection optical system PL in order to measure the transmittance of the optical system in the embodiment of the present invention. It is.
FIG. 4 is a flowchart illustrating an exposure operation using a reticle R1 according to an example of an embodiment of the present invention.
FIG. 5 is a flowchart illustrating an exposure operation using a reticle R2 according to an example of an embodiment of the present invention.
FIG. 6 is a diagram showing changes in the transmittance T of the optical system, the calculated current transmittance T (now), and the output P of the exposure light corresponding to the exposure operations in FIGS. 4 and 5;
FIG. 7 is a flowchart showing an exposure preparation step in another example of the embodiment of the present invention.
FIG. 8 is a flowchart showing an exposure operation in another example of the embodiment of the present invention.
FIG. 9 is a diagram showing changes in the transmittance T of the optical system, the calculated current transmittance T (now), and the output P of exposure light corresponding to the exposure operations in FIGS. 7 and 8;
[Explanation of symbols]
Reference Signs List 1 ArF excimer laser light source, 11 fly-eye lens, 8 beam splitter, 9 integrator sensor, 16 reticle blind mechanism, R1, R2 reticle, PL projection optical system, W wafer, 20A reticle stage, Reference numeral 24: wafer stage, 27: main control system, 30: exposure controller, 32: irradiation amount monitor, 41: incident light amount integration unit, 42: direct transmittance calculation unit, 43: transmittance history storage unit, 44: predicted transmittance Calculation unit, 45 ... Control unit

Claims (14)

In an exposure method using an optical system, a pattern of a mask is projected onto a substrate with an exposure beam,
Calculating transmittance change information of the optical system for each of the first and second exposure conditions different from each other;
When exposing the substrate by switching from the first exposure condition to the second exposure condition, the exposure history for the substrate under the first exposure condition and the calculated second exposure condition with respect to the second exposure condition An exposure method, comprising: predicting and controlling an exposure amount for the substrate based on information on a change in transmittance of an optical system. Before exposing the substrate under the first exposure condition, calculating change information of the transmittance of the optical system,
2. The method according to claim 1, wherein, while exposing the substrate under the first exposure condition, an exposure amount of the substrate is predicted and controlled based on the calculated change information of the transmittance of the optical system. Exposure method. 3. The exposure method according to claim 2, wherein the change information of the transmittance of the optical system under the second exposure condition is calculated after the exposure of the substrate under the first exposure condition is completed. . The exposure history for the substrate is an exposure time for exposing the substrate under the first exposure condition, or a time while the first exposure condition is set for the substrate. Item 1. The exposure method according to Item 1. The exposure amount when starting exposure of the substrate under the second exposure condition, based on change information of transmittance of the optical system calculated after performing exposure of the substrate under the first exposure condition. The exposure method according to any one of claims 1 to 4, wherein An illumination optical system that illuminates the mask, and a projection optical system that projects the pattern of the mask onto the substrate,
The exposure method according to any one of claims 1 to 5, wherein the optical system includes at least a part of the illumination optical system and the projection optical system. When exposing the substrate via the optical system under the first and second exposure conditions, transmittance information of the optical system at the start and end of exposure is measured, and the transmittance of the optical system is measured. Calculate the rate of change of the rate with respect to the incident energy,
The exposure method according to any one of claims 1 to 6, wherein the calculated change rate of the transmittance with respect to incident energy is used as change information of the transmittance of the optical system. The exposure method according to any one of claims 1 to 7, wherein the first and second exposure conditions are conditions for performing exposure using different mask patterns. In an exposure apparatus that projects a mask pattern on a substrate with an exposure beam using an optical system,
An exposure condition switching system for switching exposure conditions to different first and second exposure conditions,
A calculation system for calculating change information of the transmittance of the optical system for each of the first and second exposure conditions;
When exposing the substrate by switching from the first exposure condition to the second exposure condition, the exposure history for the substrate under the first exposure condition and the calculated second exposure condition with respect to the second exposure condition An exposure apparatus comprising: a control system that predictively controls an exposure amount of the substrate based on information on a change in transmittance of an optical system. The calculating system calculates change information of the transmittance of the optical system before exposing the substrate under the first exposure condition,
The control system predicts and controls an exposure amount of the substrate based on the calculated change information of the transmittance of the optical system while exposing the substrate under the first exposure condition. An exposure apparatus according to claim 9. The exposure history for the substrate is an exposure time for exposing the substrate under the first exposure condition, or a time while the first exposure condition is set for the substrate. Item 10. An exposure apparatus according to Item 9. The control system includes:
The exposure amount when starting exposure of the substrate under the second exposure condition based on change information of transmittance of the optical system calculated after performing exposure of the substrate under the first exposure condition. The exposure apparatus according to any one of claims 9 to 11, which predicts the following. An illumination optical system that illuminates the mask, and a projection optical system that projects the pattern of the mask onto the substrate,
The exposure apparatus according to claim 9, wherein the optical system includes at least a part of the illumination optical system and the projection optical system. A device manufacturing method, comprising a step of transferring a device pattern onto a workpiece using the exposure method according to claim 1.

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