JP2009038271A - Exposure apparatus and method, and device manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extend an exposure amount range without deteriorating exposure amount accuracy. Improve pattern line width accuracy in a shot.
When exposing a shot area of a photosensitive substrate through the mask while scanning the mask and the photosensitive substrate, a plurality of target exposure amount profiles are calculated from the target exposure amount distribution in the shot in the scanning direction. Then, for each target exposure profile, the shot area is exposed through the mask while controlling the exposure according to the target exposure profile.
[Selection] Figure 9

Description

  The present invention relates to an exposure apparatus and method for manufacturing a device such as a semiconductor element such as an IC or LSI, a liquid crystal substrate, a thin film magnetic head using a photolithography technique.

  Conventionally, in a manufacturing process of a semiconductor element formed from an ultrafine pattern such as LSI or VLSI, a reduction is performed by reducing and exposing a circuit pattern drawn on a mask onto a substrate (wafer) coated with a photosensitive agent. A projection exposure apparatus is used. As the mounting density of semiconductor elements has been improved, further miniaturization of circuit patterns has been demanded, and exposure methods and exposure apparatuses that can make the finished dimensions (pattern line width) uniform have been made.

In a conventional exposure apparatus or exposure method, the photosensitive agent is exposed with an exposure amount corresponding to the photosensitive agent applied on the substrate. In a step-and-scan type exposure apparatus, exposure is repeated with a constant exposure amount while moving an exposure shot area (position) on the substrate surface. However, even when the photosensitive agent is repeatedly exposed at a constant exposure amount in each exposure shot on the wafer surface, a difference (pattern line width error) occurs between the obtained pattern line width and the design pattern line width. . In order to maintain the uniformity of the pattern line width, various exposure methods for correcting the exposure amount according to the exposure shot are disclosed. For example, Patent Document 1 discloses a method for controlling an exposure amount according to an nth order polynomial function of a scanning distance from a reference position in a shot.
Japanese Patent Application Laid-Open No. 07-029810

However, in the method of expressing the exposure amount in the exposure shot as a position function in the shot and realizing the desired exposure amount by one scanning exposure, if the required exposure amount range is larger than the laser output range, the laser Accuracy cannot be secured. Therefore, a problem that the pattern line width accuracy in the shot cannot be ensured may occur.
An object of the present invention is to improve pattern line width accuracy in a shot in view of the above-described problems in the prior art.

  In order to solve the above-described problems, an exposure apparatus of the present invention is an exposure apparatus that exposes a shot area of a photosensitive substrate through the mask while scanning the mask and the photosensitive substrate, in the scanning direction. A plurality of target exposure profile is calculated from the target exposure distribution in the shot, and the shot area is exposed through the mask while controlling the exposure according to the target exposure profile for each target exposure profile. It is characterized by.

  The exposure method of the present invention is an exposure method in which a shot area of the photosensitive substrate is exposed through the mask while scanning the mask and the photosensitive substrate, and the target exposure amount distribution in the shot in the scanning direction Measuring a plurality of target exposure profiles from the target exposure distribution, and controlling the exposure amount in accordance with the target exposure profile for each target exposure profile, the shot region via the mask It is characterized by exposing.

  According to the present invention, for example, the pattern line width accuracy in a shot can be improved.

In a preferred embodiment of the present invention, when the shot area of the photosensitive substrate is scanned and exposed with a slit-shaped light beam (slit-shaped exposure light), the accuracy of the laser is ensured by placing one exposure control within the laser output range. In addition, the multiple exposure based on a plurality of target laser output profiles (target exposure profile) adjusts the final shot exposure dose distribution shape in the scanning direction of the photosensitive substrate, thereby ensuring the pattern line width accuracy. .
More specifically, when the shot area is scanned and exposed with the slit light beam, the shape of the exposure amount distribution in the scanning direction is precisely adjusted by controlling the output of the laser. When adjusting the shape of the exposure distribution, if the laser output range that can guarantee the laser output accuracy is exceeded, the exposure distribution is divided based on the divided target laser output profile group and multiple exposure is performed. Is realized accurately.

In addition, an exposure amount detector that moves along the scanning direction on the photosensitive substrate surface is provided, and an exposure amount detection unit that detects the relationship between the shape of the target laser output profile and the exposure amount distribution shape on the photosensitive substrate is used. Adjust the laser output.
The exposure amount distribution on the photosensitive substrate surface designates the exposure amount distribution as a function of the distance from a predetermined position on the substrate to the position of each exposure shot.
The present embodiment relates to a step-and-scan type exposure method that controls laser output based on a target laser output profile group of each exposure shot obtained in the following two steps. The first step is a step of calculating the exposure amount distribution of each exposure shot according to the exposure area and the target exposure amount of each exposure shot. The second step is a step of calculating a target laser output profile group according to the exposure dose distribution of each exposure shot obtained in the first step.

Embodiments of the present invention will be described below with reference to the drawings.
[First embodiment]
FIG. 1 shows a schematic configuration of a step-and-scan type exposure apparatus according to an embodiment of the present invention. In the figure, reference numeral 101 denotes a pulse laser light source in which a gas such as ArF is sealed to emit laser light. This light source emits light having a wavelength of 193 nm in the far ultraviolet region. Also, the laser light source is provided with a front mirror constituting a resonator, a narrowing module for narrowing the exposure wavelength, a monitor module for monitoring wavelength stability and spectral width, a shutter, and the like. ing. The narrowing module is composed of a diffraction grating, a prism and the like. The monitor module includes a spectroscope and a detector.

  The laser control device 102 controls gas exchange operation of the laser light source, control for stabilizing the wavelength, control of the discharge applied voltage, and the like. In this embodiment, independent control only by the laser control device 102 is not performed, but control can be performed by a command from the main control device 103 that controls the entire exposure apparatus connected by the interface cable.

  The beam emitted from the pulsed laser light source 101 is shaped into a predetermined beam shape via a beam shaping optical system (not shown) of the illumination optical system 104, and then enters the optical integrator lens 105 to form a secondary light source. Reference numeral 107 denotes a condenser lens having a function of changing the illuminance distribution of the mask (or reticle) 113. The condenser lens 107 directs the light beam from the secondary light source formed by the optical integrator lens 105 to the variable slit 110 that can change the aperture width, and the variable slit 110 is Koehler illuminated. The variable slit 110 is a mechanism that can change the opening width described later.

  The aperture of the aperture stop 106 of the illumination optical system 104 is substantially circular, and the illumination system controller 108 can set the diameter of the aperture and thus the numerical aperture (NA) of the illumination optical system to a desired value. Yes. In this case, the value of the ratio of the numerical aperture of the illumination optical system to the numerical aperture of the projection lens 114 described later is the coherence factor (σ value). Therefore, the illumination system controller 108 can set the σ value by controlling the aperture stop 106 of the illumination system.

  A half mirror 111 is disposed on the optical path of the illumination optical system 104, and a part of the exposure light that illuminates the mask 113 is reflected and extracted by the half mirror. A photo sensor 109 is disposed on the optical path of the reflected light of the half mirror 111, and generates an output corresponding to the intensity (exposure energy) of the exposure light. The output of the photo sensor 109 is converted into exposure energy per pulse by an integration circuit (not shown) that performs integration for each pulse emission of the pulse laser light source 101, and is input to the main controller 103 via the illumination system controller 108. Has been.

  On the pupil plane of the projection lens 114 (Fourier transform plane with respect to the mask), an aperture stop (not shown) of the projection lens having a substantially circular aperture is arranged, and the diameter of the aperture is controlled by a driving means such as a motor. Thus, it can be set to a desired value.

  A circuit pattern of a semiconductor element to be baked is formed on the mask 113 and irradiated from the illumination optical system 104. The variable blade 112 in the two-dimensional direction has a light shielding plate arranged on a surface orthogonal to the optical axis, so that the irradiation area of the circuit pattern surface of the mask 113 can be arbitrarily set. FIG. 2 shows a state in which the mask 113 is illuminated. A slit-shaped light beam 203 shielded by the variable blade 112 illuminates a part of the circuit pattern 202 of the mask indicated by hatching.

  A part of the circuit pattern 202 is reduced and projected at a reduction magnification β (β is, for example, 1/4) on the wafer 115 coated with a photoresist by the projection lens 114 of FIG. At this time, the multi-pulse exposure by pulsed light emission of the pulsed laser light source 101 is performed while the mask 113 and the wafer 115 are scanned (scanned) with respect to the slit light beam 203 at the same speed ratio as the reduction ratio β of the projection lens 114. repeat. The scanning direction is the short direction of the slit light beam 203. As a result, the circuit pattern 202 on the entire mask surface is transferred to one chip area or a plurality of chip areas on the wafer.

  The wafer stage 116 can move in a three-dimensional direction, and can move in the optical axis direction (Z direction) of the projection lens 114 and in a plane orthogonal to this direction (XY plane). By measuring the distance between the moving mirror 117 fixed to the wafer stage with the laser interferometer 118, the position of the XY plane of the wafer stage 116 is detected. The stage control device 120 under the control of the main control device 103 detects the position of the wafer stage 116 by the laser interferometer 118 and controls the driving means 119 such as a motor to thereby move the wafer stage to a predetermined XY plane. Move to position.

  Reference numerals 121 and 122 denote a projection optical system and a detection optical system which constitute a focus surface detection means in a single stage configuration. The light projecting optical system 121 projects a plurality of light beams composed of non-exposure light that does not expose the photoresist on the wafer. The plurality of light beams are respectively collected and reflected on the wafer 115. The light beam reflected by the wafer 115 enters the detection optical system 122. Although not shown, a plurality of position detecting light receiving elements are arranged in the detection optical system 122 so as to correspond to the respective reflected light beams. The light receiving surface of each position detecting light receiving element and the reflection point of each light beam on the wafer are configured to be substantially conjugate by the imaging optical system. The positional deviation of the wafer surface in the optical axis direction of the projection lens 114 is measured as the positional deviation of the incident light beam on the position detecting light receiving element in the detection optical system 122. The same focus plane information is used as the focus plane information without being re-measured in the multiple exposure process.

  Although not shown, in the case of a twin stage configuration, the focus plane detection means is configured in a measurement station different from the projection lens 114. The same focus plane information is used as the focus plane information measured at the measurement station without being re-measured in the multiple exposure process as in the case of the single stage configuration.

  In this embodiment, after the mask and the wafer are positioned so as to have a predetermined relationship, scan exposure is performed to transfer the circuit pattern on the entire mask surface to the chip area of the wafer. Scan exposure control is performed by the laser control device 102, the wafer stage control device 120, and the mask stage control device 126 based on a synchronization signal from the main control device 103. Thereafter, a so-called step-and-scan method is adopted in which the wafer is driven (stepped) in the XY plane by a predetermined amount by the wafer stage 116, and other areas of the wafer are sequentially projected and exposed in the same manner.

  FIG. 3A shows a state in which a plurality of chip regions in the wafer 115 are subjected to scanning exposure while being repeated in a step-and-scan manner in the order indicated by the dashed arrows. Reference numeral 302 denotes an exposure shot at a certain point in time (the range in which the mask circuit pattern is exposed by scanning), 303 denotes a slit-shaped light beam, Y indicates the scanning exposure direction, and X indicates the direction orthogonal to the scanning direction (non-scanning direction). ing. FIG. 3B shows an enlarged exposure shot. The slit-shaped light beam 303 is exposure light that forms an image by passing the slit-shaped light beam 203 that irradiates a part of the mask circuit pattern of FIG. 2 through the projection lens. By controlling the light intensity distribution in the X direction (non-scanning direction) of the slit light beam 303, the exposure amount distribution in the X direction (non-scanning direction) of the exposure shot 302 is adjusted. Further, by controlling the laser output according to the position of the exposure shot 302 in the Y direction (scanning direction), the exposure amount distribution in the Y direction (scanning direction) of the exposure shot 302 is adjusted.

Next, a method for adjusting the exposure amount in the exposure apparatus of FIG. 1 will be described. When the circuit pattern drawn on the mask is scanned and exposed (transferred) to the chip area of the wafer, one of the important conditions for determining the finished dimension of the circuit pattern is the exposure amount.
The exposure amount adjustment method of this embodiment is an adjustment method related to the exposure amount distribution in the scanning direction indicated by 304 in FIG. A target laser output profile group including a plurality of target laser output profiles is generated based on a required exposure amount distribution and a laser output range, and a desired exposure amount distribution is achieved by a plurality of exposures.

  A detailed procedure of the exposure amount adjustment method of this embodiment will be described with reference to FIGS. FIG. 4 is a diagram showing the exposure amount distribution in the slit by the variable slit 110, FIG. 5 is an exposure amount distribution calculation flowchart, FIG. 6 is a target laser output profile group calculation flowchart, and FIG. 7 is a scanning multiple exposure flowchart. FIG. 8A shows a target laser output profile, and FIG. 8B shows a target laser output profile group.

  First, a method for calculating the target laser output profile from the exposure dose distribution will be described. A target exposure distribution in each exposure shot is given as a function of the distance from the reference position of each exposure shot in the photosensitive substrate (step 502). A target laser output profile 804 for performing exposure in one scan is generated from the laser oscillation frequency, the scanning speed of the wafer stage 116, and the exposure amount distribution 401 in the slit (step 602). The target laser output profile 804 is given as a discrete laser output for each predetermined distance as a function of the distance from the reference position of each exposure shot. An exposure amount control method by adjusting laser output is disclosed in Japanese Patent Application Laid-Open No. 07-029810 (Patent Document 1).

  Next, a method for converting the target laser output profile into the target laser output profile group will be described. It is determined whether the laser output range (target laser output profile range 801) required in the target laser output profile 804 is within the range that can be achieved by the laser (laser output range 802) (step 603). When the target laser output profile range 801 is within the laser output range 802, exposure is performed by controlling the laser output based on the target laser output profile 804. If the target laser output profile range 801 is not within the laser output range 802, the process proceeds to the step of generating the target laser output profile group 807 (807a, 807b) (steps 604, 605).

In the step of generating the target laser output profile group 807, the number of times of exposure at the time of multiple exposure (number of times of multiple exposure) and the reference exposure amount at each reference exposure are calculated. The number of multiple exposures is determined by the ratio between the target laser output profile range 801 and the laser output range 802 (step 604). Here, first, a laser output range 802 in which the maximum laser output 805a in the target laser output profile 804 is the maximum value is set as the first reference. Then, the maximum laser output 805b in the profile 804 that does not fall within the laser output range 802 based on the first reference is selected as the maximum value of the laser output range based on the second reference. This process is repeated until the following (Equation 1) is satisfied.
Laser output range for each standard x number of multiple exposures ≥ target laser output profile range (Equation 1)
In this case, it is necessary to repeat exposure (perform multiple exposure) for the selected number of references.

In the above description, in the step of generating the target laser output profile group 807, the calculation is performed from the maximum laser output 805a side, but the calculation may be started from the minimum laser output side.
Further, the number of multiple exposures may be arbitrary as long as it satisfies (Equation 1). However, the target laser output profile range per scan needs to be smaller than the laser output range. In this embodiment, it is assumed that the exposure amount can be satisfied by two multiple scanning exposures with the target laser output profiles 807a and 807b.

  Next, a target laser output profile for each criterion is determined. Profiles in which the target laser output of the target laser output profile 804 that is outside the laser output range with respect to each reference 808a, 808b, 808c is zero output are set as target laser output profiles 807a, 807b for each reference. In the target laser output profiles 807a and 807b for each reference, a profile existing outside the laser output range with respect to the reference is treated as a target value zero.

A method of performing multiple exposure based on the generated target laser output profile group 807 will be described. As described above, the focus position information is measured and stored at the head of the multiple exposure, and the wafer stage 116 is appropriately controlled by the wafer stage controller 120. In the target laser output profile group 807, exposure is performed along the target laser output profile 807a. Of the target laser output profile 807a, the zero output portion 808a performs idle oscillation with a laser applied voltage of zero. Next, in the target laser output profile group 807, exposure is performed along the other target laser output profile 807b. Of the target laser output profile 807b, the zero output portions 808b and 808c oscillate at a laser applied voltage of zero. This process is repeated until the prescribed number of multiple exposures is satisfied to achieve a desired exposure amount distribution (steps 702 and 703).
The laser output range is switched by controlling the aperture stop 106, for example. However, the control may be performed by controlling the laser oscillation frequency, the scanning speed of the wafer stage 116, the exposure amount distribution 401 in the slit, and the like.

  Of the target laser output profile group, the exposure order of the target laser output profiles 807a and 807b is arbitrary. At this time, the exposure amount distribution exposed on the photosensitive substrate based on each target laser output profile is obtained by weighting the exposure amount distribution 401 in the slit to the laser output (901a, 901b). The exposure distribution 902 finally exposed to the photosensitive substrate (wafer) is a value obtained by integrating the laser outputs exposed to the photosensitive substrate based on each target laser output profile.

Referring to FIG. 1, a detector for measuring the exposure amount distribution on wafer 115 uses exposure amount detector 127 placed on wafer stage 116. The exposure amount detector 127 can measure the entire area irradiated with the slit light beam by moving the wafer stage 116. The exposure amount detector of this embodiment is a line type sensor or a pinhole type sensor in which photosensor cells are arranged uniformly in the scanning direction Y.
In each shot, the photosensitive substrate is exposed based on the target laser output profile group generated by the above-described method. At this time, multiple exposure is performed by repeatedly exposing a single shot for a specified number of multiple exposures and then multiple shots for different shots, or exposing the wafer surface once for each shot. It is arbitrary whether or not is realized.
According to this embodiment, the exposure range can be expanded without degrading the exposure accuracy by performing multiple exposure on each exposure shot in the wafer surface.

[Example of device manufacturing method]
Next, an embodiment of a device manufacturing method using the above-described exposure apparatus will be described with reference to FIGS. FIG. 10 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, and the like). Here, a semiconductor chip manufacturing method will be described as an example.
In step 1 (circuit design), a semiconductor device circuit is designed. In step 2 (mask production), a mask (also referred to as an original plate or a reticle) is produced based on the designed circuit pattern. In step 3 (wafer manufacture), a wafer (also referred to as a substrate) is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer using the mask and the wafer by the above exposure apparatus using the lithography technique. Step 5 (assembly) is referred to as a post-process, and is a process for forming a semiconductor chip using the wafer produced in step 4. including. In step 6 (inspection), the semiconductor device manufactured in step 5 undergoes inspections such as an operation confirmation test and a durability test. Through these steps, a semiconductor device is completed and shipped (step 7).

  FIG. 11 is a detailed flowchart of the wafer process in Step 4. In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition. In step 14 (ion implantation), ions are implanted into the wafer. In step 15 (resist process), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the exposure apparatus described above to expose the wafer through the circuit pattern of the mask. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed. By repeatedly performing these steps, multiple circuit patterns are formed on the wafer.

1 is a view showing a schematic configuration of an exposure apparatus according to a first embodiment of the present invention. It is explanatory drawing of the mask part in FIG. It is a figure which shows a mode that a wafer is scanned and exposed in the apparatus of FIG. It is a figure which shows the change of the exposure profile by the variable slit in the apparatus of FIG. It is a flowchart of exposure amount distribution calculation in the apparatus of FIG. It is a flowchart of target laser output profile group calculation in the apparatus of FIG. It is a flowchart of the scanning multiple exposure in the apparatus of FIG. It is a figure which shows the target laser output profile and target laser output profile group which are calculated in the apparatus of FIG. FIG. 9 is a diagram showing an exposure amount distribution exposed on the photosensitive substrate based on each target laser output profile in the target laser output profile group of FIG. 8 and an exposure amount distribution finally exposed on the photosensitive substrate. It is a flowchart for demonstrating manufacture of the device using an exposure apparatus. 11 is a detailed flowchart of the wafer process in Step 4 in the flowchart shown in FIG. 10.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Pulse laser light source 102 ... Laser controller 103 ... Main controller of exposure apparatus 104 ... Illumination optical system 105 ... Integrator lens 106 ... Illumination system aperture stop 107 ... Condenser lens 108 ... Illumination system controller 109 ... Photo sensor 110 ... Variable Slit 111 ... Half mirror 112 ... Variable blade 113 ... Mask (reticle)
DESCRIPTION OF SYMBOLS 114 ... Projection lens 115 ... Wafer 116 ... Wafer stage 117 ... Moving mirror 118 ... Laser interferometer 119 ... Wafer stage control means 120 ... Wafer stage control device 121, 122 ... Focus surface detection means 123 ... Mask stage 124 ... Moving mirror 125 ... Laser interferometer 126 ... Mask stage control device 127 ... Exposure amount detector 202 ... Circuit pattern 203 ... Slit beam

Claims (7)

An exposure apparatus that exposes a shot area of the photosensitive substrate through the mask while scanning the mask and the photosensitive substrate,
Calculating a plurality of target exposure profile from the target exposure distribution in the shot in the scanning direction;
For each target exposure profile, the shot area is exposed through the mask while controlling the exposure according to the target exposure profile.
An exposure apparatus characterized by that.   2. The exposure apparatus according to claim 1, wherein the plurality of target exposure amount profiles are calculated by dividing the target exposure amount distribution into a plurality of ranges.   The exposure apparatus according to claim 2, wherein the range is determined based on a light amount range of a pulse laser light source. An exposure method for exposing a shot area of the photosensitive substrate through the mask while scanning the mask and the photosensitive substrate,
Measure the target exposure distribution in the shot in the scanning direction,
Calculating a plurality of target exposure profiles from the target exposure distribution;
For each target exposure profile, the shot area is exposed through the mask while controlling the exposure according to the target exposure profile.
An exposure method characterized by the above.   5. The exposure method according to claim 4, wherein the plurality of target exposure amount profiles are calculated by dividing the target exposure amount distribution into a plurality of ranges.   6. The exposure method according to claim 5, wherein the range is determined based on a light amount range of a pulse laser light source. Exposing the substrate using the exposure apparatus according to any one of claims 1 to 3,
Developing the substrate exposed in said step;
A device manufacturing method comprising:

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