JP2005079249A - Alignment method, exposure method, exposure apparatus, and device manufacturing method - Google Patents

Abstract

【Task】
To provide an alignment method capable of achieving high-precision alignment accuracy while ensuring high-speed processing capability without increasing apparatus cost.
[Solution]
This alignment method includes a step of obtaining a plurality of measurement results obtained when a plurality of marks AM having different shapes are measured by the ellipsometer 54, and a step of measuring the alignment marks AM of the wafer W by the ellipsometer 54. , Comparing the measurement result with a plurality of measurement results to determine the shape of the alignment mark AM, and obtaining the position correction amount of the wafer W based on the determined shape of the alignment mark AM. .
[Selection] Figure 4

Description

  The present invention relates to an alignment method for aligning a substrate using an alignment mark formed on the substrate, and in particular, a fine IC, LSI, VLSI or the like formed on a reticle surface in an exposure apparatus for semiconductor manufacturing. The present invention relates to an alignment method for performing relative alignment (alignment) between an electronic circuit pattern and a wafer.

  2. Description of the Related Art A projection exposure apparatus for manufacturing a semiconductor is required to be able to project and expose a circuit pattern on a reticle surface as an exposure original with higher resolution on a wafer surface as the integrated circuit becomes finer and higher in density. This exposure apparatus includes, for example, what is called a stepper (one that exposes each shot in a batch by step and repeat) and one that is called a scanner (one that scans and exposes each shot by step and scan).

  Since the projection resolving power of the circuit pattern depends on the numerical aperture (NA) and exposure wavelength (λ) of the projection optical system, a method of increasing the numerical aperture NA of the projection optical system by fixing the exposure wavelength or a shorter exposure wavelength λ An exposure method for converting the wavelength into consideration has been studied. For example, to reduce the exposure wavelength λ, it has been studied to use g-line as i-line and excimer laser oscillation wavelength (λ = 248 nm, 193 nm, 157 nm, etc.) from i-line. It has already been commercialized.

  Along with the miniaturization of circuit patterns, it is required to align the reticle as the exposure original on which the circuit pattern is formed and the wafer as the exposure target with high accuracy. The applicant has already proposed a system using an offset analyzer as a method of reducing a process error called WIS (Wafer Induced Shift), which is one of several types of alignment errors ( Patent Document 1).

  One example of WIS is that the alignment mark shape itself or the resist shape applied on the substrate becomes asymmetric due to process errors. For example, in the planarization process in a metal CMP (Chemical Mechanical Polishing) process or the like, the structure of the alignment mark becomes asymmetric. As a result, the rotation error shown in FIG. 10 and the magnification error shown in FIG. 11 occur in the alignment by the global alignment method, which causes a decrease in accuracy.

  When WIS as shown in FIG. 10 occurs, the shape of the resist applied on the wafer W becomes uneven, and the alignment marks formed corresponding to each shot in the wafer are detected unevenly. End up. For example, the resist shape in the shot near the center of the wafer has the same uneven shape (the corrugated convex portion or concave portion corresponding to one period is symmetrical), but the resist shape in the left and right end shots near the wafer periphery. Is non-uniform (asymmetric), and the asymmetry is reversed between the leftmost shot and the rightmost shot.

  Therefore, in the alignment by the system using the offset analyzer, the alignment accuracy in the exposure apparatus is improved as follows. That is, before aligning the wafer in the exposure apparatus, the surface shape of the wafer before and after resist application (the uneven shape of the alignment mark before application and the resist shape immediately above the alignment mark after application) is measured with an atomic force microscope (Atomic). (Force Microscope). Based on the measured alignment mark shape and resist shape, various output signals of the alignment detection system (usually provided in the exposure apparatus) when their three-dimensional relative positional relationship is changed are simulated in advance. Calculate and prepare. Compare the output signal from the alignment detection system that detected the alignment mark when actually exposing the wafer with the output signal from the simulation prepared in advance, and from the comparison result, the alignment mark shape (resist shape on the alignment mark) and By grasping the three-dimensional relative positional relationship with the resist shape and the positional deviation (offset amount) between the detected alignment mark position and the actual alignment mark position, the offset amount is corrected to improve the alignment accuracy.

  FIG. 12 shows the wafer W and the information flow in the system using the offset analyzer OA. As shown in 1), the wafer W as a substrate is carried to the offset analyzer OA before resist application, and the three-dimensional shape of the alignment mark formed on the surface of the wafer W before application is measured by an atomic force microscope AFM. Is done. Subsequently, as shown in 2), the wafer W is transported to the coater (coating machine) CT, and a resist is applied to the surface thereof. As shown in 3), the wafer W is again transported to the offset analyzer OA, and after the resist coating. The three-dimensional shape of the resist at the position corresponding to the alignment mark is measured by the atomic force microscope AFM.

  As shown in 4), the wafer W is carried to a stepper ST as an exposure apparatus, and an alignment mark AS (output signal) is detected by an alignment scope AS as an alignment detection system, and subsequently, as shown in 5). Signal information of the alignment mark is sent from the stepper ST to the offset analyzer OA. As shown in 6), the alignment mark signal (output signal) obtained by the alignment scope AS is obtained from the three-dimensional relative positional relationship between the resist shape and the alignment mark shape before and after the resist application measured by the offset analyzer OA in advance. ) And the actual alignment mark position, the offset amount in the alignment detection is calculated, and the offset amount is sent to the stepper ST.

  In the stepper ST, the wafer W is aligned (positioned) based on the received offset amount, exposure is performed, and the wafer W is transported to the developer (developer) DV for development after the exposure of all shots is completed. . Thereafter, a circuit pattern is formed on the surface through a necessary treatment and a semiconductor device is finally obtained. However, the procedure is well known, and the description thereof is omitted.

  An offset amount generated by the WIS is calculated by an optical simulator configured in the offset analyzer OA. Since the calculation model of this optical simulator requires a mark having a size close to the wavelength or an accuracy less than the wavelength order, a vector diffraction model is used. As this vector diffraction model, for example, optical simulators called FDTD, RCWA, and FETD are sold.

  FDTD (Finite Difference Time Domain Method) is translated as “time domain difference method”, and TEMPESTpr (trade name) is commercially available software. In this calculation model, the Maxwell equation is differentiated with respect to time and space, and the difference equation is alternately calculated for the magnetic field and the electric field until the electromagnetic field in the region is stabilized. The electromagnetic field in the analysis space is calculated using a leapfrog algorithm. In this method, the time response of the output point is obtained. Therefore, a transient solution or frequency response can be directly obtained.

  In addition, the differential method and FETD (finite element method), which will be described later, handle second-order partial differentiation, but FDTD performs calculation by first-order partial differentiation. There are methods such as the moment method and the finite element method for antenna analysis, but FDTD has a simple algorithm, excellent accuracy, and is suitable for analysis of complex materials and materials with different material constants. It is known that Particularly in the analysis of the dielectric, it is only necessary to change constants such as the dielectric constant and the number of time steps, and the analysis can be performed relatively easily. Although this method has a drawback that analysis time is long, it is a method that has attracted considerable attention in recent years due to the speeding up of computers accompanying the miniaturization of semiconductors.

  RCWA (Rigorous Coupled-Wave Analysis) is a model that solves an eigenvalue equation by representing an electric field in a periodic structure by a Fourier series. FETD is translated as “time domain finite element method” and solves the Maxwell equation by the finite element method. This model uses the same time explicit method as the difference method for integration in the time direction, and commercially available software includes EMFlex (trade name).

Further, the applicant uses the principle of the ellipsometry method described later to make polarized light incident on a periodic pattern formed on the wafer and based on a change in the state of the luminous flux of reflected light from the periodic pattern. A method has been proposed in which the line width of a periodic pattern is measured to obtain the optimum focus position and optimum dose amount of the wafer in the exposure process by the exposure apparatus (for example, Patent Document 2 and Patent Document 3).
JP 2000-228356 A Japanese Patent Laid-Open No. 9-36037 Japanese Patent Laid-Open No. 10-22205

  According to the system using the offset analyzer, errors due to WIS can be effectively reduced. However, recent exposure apparatuses are required to have a high-speed processing capability of, for example, exposing 100 wafers having a diameter of 300 mm in one hour. In this case, if the alignment method by the system using the offset analyzer is used, it takes time and there is a problem that necessary processing capability cannot be exhibited.

  The processing capacity of the offset analyzer mainly depends on the shape measurement time by the atomic force microscope AFM. For example, the measurement time required for measuring the shape of a measurement length of 20 μm with the atomic force microscope AFM is several minutes or more. In order to achieve the above processing capability in such a case, one offset analyzer used for one exposure apparatus must be equipped with a plurality of atomic force microscopes, which increases the cost of the apparatus. There is a problem that it ends up.

  As another configuration, when a plurality of offset analyzers are used in one exposure apparatus, even when a plurality of cantilevers are configured in one atomic force microscope, there is still a problem of an increase in apparatus cost. End up.

  On the other hand, without measuring the shape by the offset analyzer for the total number of wafers, for example, by measuring the shape of only the first wafer in each manufacturing lot and not measuring the shape of other wafers in that lot. By adopting, high-speed processing capability (high throughput) can be achieved. However, when there is variation in WIS between wafers, it is not preferable from the viewpoint of alignment accuracy to use the measured value of the wafer whose shape has been measured as the measured value of another wafer that has not been subjected to the shape measurement.

  The present invention has been made in view of the above circumstances, and provides an alignment method capable of achieving high-precision alignment accuracy while ensuring high-speed processing capability without increasing apparatus cost. For illustrative purposes.

  In order to achieve the above exemplary object, an alignment method according to one aspect of the present invention is a method for aligning substrates, in which a plurality of marks having different shapes are measured with an ellipsometer, respectively. A step of obtaining a plurality of measurement results, a step of measuring an alignment mark on the substrate with an ellipsometer, a step of determining the shape of the alignment mark by comparing the measurement results with the plurality of measurement results, and Obtaining a substrate position correction amount based on the shape of the alignment mark.

  The alignment method according to another aspect of the present invention is characterized in that the plurality of marks and the alignment mark have a diffraction grating shape.

  The alignment method as another aspect of the present invention is characterized in that a plurality of measurement results are obtained by an optical simulator.

  In the alignment method according to another aspect of the present invention, in the step of obtaining the position correction amount, a detection result obtained when the alignment mark is detected by the position detection unit is calculated based on the determined shape of the alignment mark. The position correction amount is obtained based on the calculated detection result.

  The alignment method as another aspect of the present invention is characterized in that the detection result is calculated by an optical simulator.

  In the alignment method according to another aspect of the present invention, the position detecting unit illuminates the alignment mark with 0th-order light, and ± nth order (n = 1, 2, 3...) From the alignment mark. A detection result is obtained by selecting and using the reflected light.

  In the alignment method according to another aspect of the present invention, when a plurality of substrates are exposed, a position correction amount for the substrate to be exposed first is obtained, and the alignment of the plurality of substrates is executed based on the position correction amount. It is characterized by that.

  An exposure method according to another aspect of the present invention is characterized in that the substrate is aligned by the alignment method described in any one of the above, and the substrate is exposed.

  An exposure apparatus according to another aspect of the present invention is characterized in that the substrate is aligned by the alignment method described in any one of the above, and the substrate is exposed.

  A device manufacturing method according to another aspect of the present invention is characterized in that a substrate is exposed by the exposure apparatus and a predetermined process is performed on the exposed substrate.

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  As described above, according to the present invention, even when there is an asymmetry in alignment marks formed on a substrate such as a wafer, it is possible to achieve high-precision alignment accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a configuration of an offset analyzer OA for performing the alignment method according to the first embodiment of the present invention. The offset analyzer OA can measure the shape of the alignment mark of the wafer W as a substrate by using the ellipsometer 54. An ellipsometer is an apparatus that observes a change in a light flux state (polarization state) when light is reflected on the surface of a substance and obtains information about the substance from the observation result, which will be described later.

  A chuck 52 which is a suction member that sucks the wafer W is disposed on the XYZ stage 51, and the wafer W is sucked on the chuck 52. A pre-measurement system 53 and an ellipsometer 54 with a measurement accuracy of about 3 μm are configured to be able to observe and detect marks on the wafer W, and a vector in the computer 55 that controls the XYZ stage 51, the pre-measurement system 53, and the spectroscopic ellipsometer 54. A diffraction model optical simulator is configured. A storage device 56 that stores various databases as a library, which will be described later, is configured to be accessible from the computer 55.

[Ellipsometry]
First, the principle of ellipsometry as a method for measuring the cross-sectional shape of a periodic pattern such as an alignment mark will be described. In this ellipsometry method, linearly polarized light of P-polarized light and S-polarized light having a phase difference of 0 and an amplitude ratio of 1 is incident on a periodic pattern at a predetermined incident angle θ or while changing the incident angle, and the reflection This is a method of measuring the cross-sectional shape by measuring the phase difference (Δ) of light and the amplitude ratio (Ψ). The detection principle is described in Principle of Optics (Pergamon Press: M. Born and E. Wolf) or Japanese Patent Application Laid-Open No. 11-211421.

  FIG. 2 is a diagram schematically showing a cross section of an L & S (line & space) pattern as a periodic pattern. On the wafer W, the substances M1 and M2 having different refractive indexes are alternately arranged alternately. Such a periodic structure is known to have birefringence, and the property is referred to as structural birefringence.

For example, when the substance M1 is air and the substance M2 is a resist, the measurement light beam 2 having a predetermined wavelength and a predetermined polarization state is incident at a predetermined incident angle θ ₁ on a periodic pattern formed by the substances M1 and M2. A reflected light beam 3a that is transmitted through the substance M2 (resist), reflected from the surface of the wafer (substrate) W, and again transmitted through the substance M2 (resist); and a reflected light beam 3b that is directly reflected from the surface of the substance M2 (resist). Measure the state of the reflected light beam 3 formed by combining. Note that the substance M1 may be a resist, and the substance M2 may be a metal or the like constituting the alignment mark.

  Generally, it is known that reflected light has birefringence characteristics when the pitch of the periodic pattern is sufficiently smaller than the wavelength of the measurement light to be irradiated. Further, when the pitch of the periodic pattern is larger than the wavelength of the measurement light to be irradiated, diffracted light is generated, but the same measurement can be performed using this diffracted light.

  FIG. 3 shows an example of an optical system of an apparatus for measuring a cross-sectional shape of a periodic pattern using an ellipsometry method. The ellipsometry method includes a method in which incident light is used as broadband light and spectrally detects the wavelength of reflected light, and a method in which incident light is used as single wavelength light and the incident angle is variously changed. FIG. 3 illustrates the former method. In the present application, such a method of spectrally detecting the wavelength of the reflected light is referred to as a spectroscopic ellipsometry method.

  The incident light 4 a emitted from the light source 41 passes through a rotatable polarizer 42, so that the polarization plane (S-polarized light, P-polarized light) is adjusted and the phase is adjusted, and the light is irradiated toward the periodic pattern 43. . The reflected light 4 b reflected by the periodic pattern 43 is spatially wavelength-separated by the spectroscopic optical system 44 according to the wavelength. In the separated light 4 c, the intensity ratio and phase difference of S-polarized light and P-polarized light for each wavelength are detected by a photodetector 45 in which photoelectric detectors are arranged in an array, and the information is sent to a computer 46. The computer 46 compares information from the light detector 45 with library information described later to calculate the cross-sectional shape of the periodic pattern 43, and the calculation result is used as the cross-sectional shape of the periodic pattern 43 as the measurement object. Is output.

  In the spectroscopic ellipsometry method, even if the resist film thickness and the resist pattern shape are different, the same intensity ratio / phase difference state may occur depending on the incident conditions of incident light (incident angle, wavelength of incident light, etc.). Therefore, measurement accuracy is also improved by detecting changes in reflected light under a plurality of incident conditions (irradiation with a plurality of incident angles or irradiation with incident light with a plurality of wavelengths).

  The above-described cross-sectional shape measuring apparatus using the ellipsometry method is sold by the above-mentioned measuring instrument manufacturer as a CD (Critical Dimension, that is, line width of a periodic pattern) measuring apparatus using light. With these devices, it is possible to measure not only CD measurement but also the height of a periodic pattern and the side wall angle (Side wall angle).

  The cross-sectional shape of the periodic pattern 43 as the measurement object is measured according to the procedure shown in FIG.

  First, as a preparatory stage before measurement, a cross-sectional shape of the assumed periodic pattern 43 is defined on a computer 46 using a vector diffraction model optical simulator (for example, RCWA), and the state of reflected light from each cross-sectional shape is defined. The state value obtained by simulation calculation is stored as a library. That is, based on the optical constants (refractive index n, absorption coefficient k, thickness d of each substance) of the substance M2 constituting the periodic pattern 43 (step 1), incident light incident conditions (wavelength λ or incident angle θ) (Step 2), and information (change in intensity ratio or change in phase difference) obtained from the reflected light when incident light enters the assumed cross-sectional shape (step 3) is obtained by calculation (step 4). .

  Define different cross-sectional shapes and perform a series of calculations for each cross-sectional shape (step 3), save the library as a library by associating the obtained calculation results with the corresponding cross-sectional shapes. Save it on the device. Here, the library means that the light flux state obtained by the simulation calculation based on the optical constant and the periodic pattern having a different cross-sectional shape is the cross-sectional shape or optical constant of the periodic pattern corresponding to the light flux state. Data or database associated with

  The optical constant of the periodic pattern used in step 1 differs depending on whether the incident angle θ or the incident light wavelength λ is used as the incident condition parameter. When the incident angle θ is changed using a single wavelength and the reflected light obtained at each incident angle θ is measured, the optical constant for the single wavelength used for the measurement is input to the computer. On the other hand, when the incident angle is fixed and the wavelength λ of the incident light is changed and the reflected light obtained for each wavelength λ is measured, the optical constant for each wavelength used for the measurement is input to the calculator 46. There is a need.

  Next, the incident light 4a is actually incident on the periodic pattern 43 as the measurement object (step 5), and information (change in intensity ratio, change in phase difference) of the obtained reflected light 4b is detected by the photodetector 45. Detect (step 6). The light flux information of the library stored in the storage device is compared with the information of the actual reflected light 4b obtained from the detected value, and the light flux information that matches the information of the actual reflected light 4b is extracted from the library. (Step 7). Of the cross-sectional shapes defined on the computer 46, the cross-sectional shape of the periodic pattern associated with the luminous flux information is set as the actual cross-sectional shape of the periodic pattern 43 (step 8).

  In the foregoing, the principle of the ellipsometry method and the method for measuring the cross-sectional shape of the periodic pattern using the principle have been described. The present invention relates to an alignment method in which the method of cross-sectional shape of a periodic pattern using the ellipsometry method is used for detecting an alignment mark.

[Embodiment 1]
In the alignment method according to the first embodiment of the present invention, the alignment mark AM (see FIGS. 1 and 6) has a diffraction grating shape, and the alignment mark is used by using an ellipsometer with an offset analyzer separate from the exposure apparatus ST. Is measured. In the present embodiment, the stepper ST is described as an example of the exposure apparatus, but of course, the exposure apparatus may be a scanner that performs scanning exposure. The spectroscopic ellipsometer 54 measures the light flux state of the reflected light 4b from the diffraction grating-shaped alignment mark AM, that is, the phase and intensity.

  Prior to the measurement by the spectroscopic ellipsometer 54, process errors are previously determined by using optical constants of the alignment mark AM (the complex refractive index n, the absorption coefficient k, the film thickness d, etc. of each material of the vertical structure constituting the alignment mark AM). Assuming various cross-sectional shapes that can be asymmetrical due to WIS, calculation is performed by a vector diffraction model optical simulator (for example, RCWA), and the data is stored as a library corresponding to the luminous flux state of the reflected light 4b when measured by the spectroscopic ellipsometer 54. Stored in the device 56. Simulation calculation is performed using the cross-sectional shape of the alignment mark AM and the incident condition (incident angle θ and incident light wavelength λ) of the incident light 4a incident on the alignment mark AM as parameters, and the calculated result (the luminous flux of the reflected light 4b). (Data corresponding to the state) is associated with the cross-sectional shape as a parameter to be a library. A plurality of libraries are prepared in advance by changing the parameters of the incident condition and cross-sectional shape in various ways, and the libraries are stored in the storage device 56.

  The spectroscopic ellipsometer 54 is actually used to measure the light flux state (phase / intensity) of the reflected light 4b from the alignment mark AM, and the cross-sectional shape corresponding to the light flux state as the measurement result is stored in the storage device 56. Select from multiple libraries. That is, a library closest to the light flux state of the reflected light 4b from the alignment mark AM measured by the spectroscopic ellipsometer 54 is selected from a plurality of libraries prepared in advance, and a cross section associated with the selected library. Select a shape. The cross-sectional shape thus selected substantially corresponds to the cross-sectional shape of the actual alignment mark AM, and is substantially the same shape.

  When the cross-sectional shape of the alignment mark AM is selected, output signal data to be output from the alignment scope AS when the cross-sectional shape is detected by the alignment scope AS is calculated by calculation based on the selected cross-sectional shape. .

  Based on the calculated output signal data, a displacement amount, that is, a position correction amount between the detected position of the alignment mark AM and the original position of the alignment mark AM is calculated. This position correction amount may be calculated by inputting the cross-sectional shape of the alignment mark AM as input by a vector diffraction model optical simulator (for example, RCWA) used in the spectroscopic ellipsometer 54 at the time of creating the library, as in the conventional offset analyzer. . Further, an alignment signal is obtained under the condition of the alignment scope AS of the exposure apparatus ST by using an optical simulator (for example, FDTD method, FETD method, etc.) of a different vector diffraction model, and an alignment offset (= position correction amount) generated therefrom is obtained. Then, alignment and exposure of the reticle R and the wafer W may be performed using the correction amount.

  Next, the alignment method in the present invention will be specifically described.

  An exposure apparatus using an alignment method using a diffraction grating-shaped alignment mark AM has already been proposed by the applicant in Japanese Patent Application Laid-Open No. 5-343291, etc., and is actually applied to a product. An example of this exposure apparatus ST is shown in FIG. In FIG. 5, an exposure apparatus ST projects and exposes a pattern formed on a reticle R illuminated by exposure light onto the surface of a wafer W via a projection lens 1. In the exposure apparatus ST, the diffraction grating-shaped alignment mark AM provided on the wafer W surface is illuminated by the monochromatic light from the illumination means through the projection lens 1, and the reflected diffraction light from the diffraction grating-shaped alignment mark AM is reflected. After passing through the projection lens 1, the light is guided out of the exposure optical path by the mirror 8, and ± n-order light (n = 1, 2, 3...) Of the reflected diffracted light is selectively extracted by the stopper 12. An interference image is formed on the image pickup device 14 such as a CCD camera by the projection optical means by the extracted n-order light.

  In a two-dimensional window having a predetermined size provided for the video signal from the image sensor 14, the video signal is integrated in one direction of two-dimensional coordinates to obtain a one-dimensional projection integrated signal. Next, the one-dimensional projection integrated signal is converted into a spatial frequency domain by orthogonal transformation, and a spatial frequency component inherently appearing from the interference image based on the periodicity of the diffraction grating-shaped alignment mark AM from the one-dimensional projection integrated signal on the spatial frequency domain. The wafer W is aligned by detecting the position of the selected alignment mark AM having a diffraction grating shape.

  The exposure apparatus ST using the alignment method shown in FIG. 5 is a low-cost and stable non-exposure light (light that does not expose a resist), for example, a TTL-Offaxis method using a light source such as a He-Ne laser or a semiconductor laser. It has a feature that the baseline is stable. In this alignment method, the calculation time when the offset analyzer OA is calculated using a vector diffraction model optical simulator (for example, the FDTD method) is approximately one-tenth of the calculation time in the conventional bright field detection image processing method. Shortened.

  In the alignment method using this diffraction grating-shaped alignment mark AM, illumination light is used for imaging using only ± nth-order light (n = 1, 2, 3...) Of reflected diffraction light. Is only one light beam of 0th order light equal to the optical axis, and only this one has to be calculated.

  By adopting an alignment method using diffraction grating-shaped alignment marks AM, not only can the speed be increased by measuring the alignment mark shape using an ellipsometry method, but also a vector diffraction model optical simulator (for example, FDTD method) can be used. In this case, the calculation time can be reduced by one digit or more, and the speed of the offset analyzer OA can be increased.

  Furthermore, TIS (Tool Induced Shift) which is a performance error of the alignment optical system (alignment scope AS) of the exposure apparatus ST can be reduced, and as a result, the manufacturing cost can be reduced. For example, in conventional bright field illumination, it is necessary to remove coma, which is one of the TIS factors, within the numerical aperture range for detection of bright field image processing. On the other hand, according to this alignment method, since only the ± nth order light (n = 1, 2, 3,...) Of the reflected diffracted light is used, it is only necessary to remove the coma aberration of only this light beam portion. Therefore, it is a great advantage as in the case of shortening the calculation time.

  FIG. 6 is a conceptual diagram of calculation of an offset amount (position correction amount) in the offset analyzer OA in the alignment method using the diffraction grating-shaped alignment mark AM. In FIG. 6, a resist RS is applied to a diffraction grating-shaped alignment mark AM, and the cross-sectional shape of the alignment mark AM is measured by an optical CD measuring instrument using the principle of ellipsometry. With this cross-sectional shape information as an input, an alignment signal 57 is calculated by an optical simulator of a vector diffraction model. At this time, an asymmetrical WIS exists in the diffraction grating-shaped alignment mark AM as shown in FIG. Although depending on the semiconductor process, for example, the bottom (lower part) 58 of the alignment mark AM serves as a mask during etching. If it is assumed that the alignment with respect to the bottom 58 is correct, the offset amount 59 can be calculated based on the cross-sectional shape of the alignment mark AM and the alignment signal 57 corresponding thereto. This offset amount 59 is transmitted to the exposure apparatus ST, and alignment (alignment) and exposure of the wafer W are performed using the offset amount 59.

  Note that the creation of a library by the ellipsometry method requires a huge amount of calculation when it is created by changing the mark shape in various ways. For example, even if 10 CPUs each having a 2 GHz clock are used in parallel, calculation takes several hours. It takes time. However, since this calculation has only to be performed before measurement, it does not affect the actual measurement of the alignment mark AM on the wafer W and the calculation of the offset amount 59.

  As described above, according to the present embodiment, the alignment method using the diffraction grating-shaped alignment mark AM, measuring the cross-sectional shape of the alignment mark AM by the ellipsometry method, and illuminating only with the 0th-order light is provided. By adopting it, it is possible to ensure high-precision alignment accuracy even if the alignment mark shape asymmetry due to the above-described process occurs, and it is not necessary to mount a large number of atomic force microscopes AFM etc., and the alignment scope AS TIS (apparatus factor error) can be easily reduced, the overall cost of the exposure system can be reduced, and the speed of the offset analyzer can be increased.

[Embodiment 2]
FIG. 7 shows the wafer W and information flow in the offset analyzer OA using the alignment method according to the second embodiment of the present invention. In the offset analyzer previously proposed by the applicant, the shape of the alignment mark AM before and after the resist coating on the wafer W is measured by an atomic force microscope AFM or the like, as shown in FIG. ing. The reason why the shape of the alignment mark AM is measured before the resist coating is that it is difficult to measure the shape of the alignment mark AM via the resist RS by the atomic force microscope AFM after the resist coating.

  In the present invention, the same object can be achieved by measuring the shape of the alignment mark AM before and after the resist coating. Furthermore, since the ellipsometry method used in the present invention uses light, it is possible to measure the shape of the alignment mark AM after applying the resist without measuring the shape of the alignment mark AM before applying the resist. Of course, in order to create a library, calculation is performed in advance by an optical simulator assuming a state after resist coating.

  1 shows an example in which the offset analyzer OA is configured separately from the exposure apparatus ST. According to this configuration, after measuring the shape of the alignment mark AM, the wafer W is separated from the chuck 52 and transferred. At this stage, the alignment mark AM is detected by the exposure apparatus ST. Therefore, the shape of the alignment mark AM when the shape is measured by the offset analyzer OA and the shape of the alignment mark AM when detected by the exposure apparatus ST need to have a level of identity that can ignore the difference. Therefore, the offset analyzer OA and the exposure apparatus ST need to be substantially the same in environmental conditions (temperature, humidity, atmospheric pressure, etc.), chuck shape, chuck performance, and the like. The configuration in which the offset analyzer OA is separated from the exposure apparatus ST is not an essential condition. Even if the offset analyzer OA is configured in the exposure apparatus ST, the other objects of the present invention can be achieved although the throughput is somewhat reduced. it can.

  FIG. 8 shows an example in which the wafer W is transported to the exposure position ST together with the wafer W while being attracted, instead of transporting the wafer W away from the chuck 52 to the exposure apparatus ST as in the configuration of FIG. . In this configuration, chuck marks 131 and 132 are formed on the chuck 121 that attracts the wafer W. In the offset analyzer OA, the detection system has three functions. The first is a pre-detection function by the pre-detection system 53, and the second is a function (not shown) for detecting the alignment mark AM. In this alignment mark AM detection function, illumination is performed with the 0th order light shown in FIG. 5, and ± nth order light (n = 1, 2, 3,...) Of the reflected diffracted light is selectively detected. The third is a conventional bright field detection function (not shown) for detecting the chuck marks 131 and 132 on the chuck 121. In the offset analyzer OA shown in FIG. 8, unlike the offset analyzer OA shown in FIG. 1, a highly accurate XYZ stage 51 is used as in the exposure apparatus ST.

  In the offset analyzer OA of FIG. 1, after measuring the shape of the alignment mark AM, when the offset amount 59 is calculated by the optical simulator, the wafer W is transferred to the exposure apparatus ST. In the offset analyzer OA of FIG. 8, the offset amount 59 is calculated in the same manner. Thereafter, the position of the alignment mark AM of a predetermined limited shot in the wafer W is further detected by the detection function of the alignment mark AM in the offset analyzer OA. Detection is performed depending on the accuracy of the AYX stage 51 to perform global alignment, and the positions of the chuck marks 131 and 132 on the chuck 121 are detected by the bright field detection function. Thereby, since the position information of the wafer W can be detected by detecting the chuck marks 131 and 132, the wafer W is transferred together with the chuck 121 to the exposure apparatus ST shown in FIG. .

  Next, in the exposure apparatus ST shown in FIG. 9, only the chuck marks 131 and 132 are detected and exposure is performed. The chuck 121 transported while attracting the wafer W is attracted to the chuck 133 that attracts the chuck of the exposure apparatus ST. The focus detection system 129, 130 detects the focus of the chuck mark, and if necessary, drives in the focus direction, and then performs two-dimensional measurement on the chuck mark 131, 132 by the alignment scope AS based on the detection principle of bright field image processing. Measure possible mark positions. This measurement is performed on the plurality of chuck marks 131 and 132, and the XY stage with an interferometer is driven based on the measurement result and calculation result of the offset analyzer OA to move the wafer W to a position corresponding to each shot. Focus measurement is performed in each shot, and exposure is performed after driving in the focus direction as necessary. After all shot exposure, the chuck 121 is transported to the outside of the exposure apparatus ST while adsorbing the wafer W.

  In the exposure apparatus ST shown in FIG. 9, a TTL-Offaxis method of a bright field detection system using a cheap and stable non-exposure light (light that does not expose a resist), for example, a light source such as a He-Ne laser or a semiconductor laser. It is used for the alignment scope AS for detecting the positions of the chuck marks 131 and 132, and has a feature that the base line is stable. In this exposure apparatus ST, since the alignment scope AS is only used for detection of the chuck marks 131 and 132, the configuration can be simplified and the TIS removal is not necessary, so that the apparatus cost is greatly increased. Can be reduced.

  According to the configuration in which the wafer W is transported from the offset analyzer OA to the exposure apparatus ST in a state where the wafer W is attracted to the chuck 121 having the chuck marks 131 and 132 as in the above-described embodiment, depending on the process. Since deterioration in alignment accuracy due to the shape of the alignment mark AM becoming asymmetric is prevented, alignment with high accuracy and high throughput is possible without being affected by a semiconductor formation process such as CMP. Therefore, complicated optimization in the process becomes unnecessary, and CoO (Cost of Ownership) can be improved.

  Of course, the offset analyzer OA may also be configured separately from the exposure apparatus ST, or may be configured in the exposure apparatus ST. For example, the object of the present invention can be achieved even if the exposure system and the XY stage of the measurement system are configured adjacent to each other and the function of the offset analyzer OA is provided on the measurement stage side. In the present embodiment, an exposure apparatus that exposes a circuit pattern has been expressed as an exposure apparatus. However, as described above, it is an expression for convenience, and the exposure apparatus here includes a so-called stepper, scanner, and X-ray of the same magnification. The exposure machines include all exposure methods such as an exposure machine, an EB direct drawing machine, and an EUV exposure machine. The alignment method of the present invention is effective for these exposure machines.

  Next, an embodiment of a device manufacturing method using the above-described exposure apparatus will be described with reference to FIGS. FIG. 13 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, and the like). Here, the manufacture of a semiconductor chip will be described as an example. In step 101 (circuit design), a device circuit is designed. In step 102 (mask production), a mask on which the designed circuit pattern is formed is produced. In step 103 (wafer manufacture), a wafer (object to be processed) is manufactured using a material such as silicon. Step 104 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the mask and wafer. Step 105 (assembly) is called a post-process, and is a process of forming a semiconductor chip using the wafer created in step 104, and includes processes such as an assembly process (dicing and bonding), a packaging process (chip encapsulation), and the like. . In step 106 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device created in step 105 are performed. Through these steps, the semiconductor device is completed and shipped (step 107).

  FIG. 14 is a detailed flowchart of the wafer process in Step 104. In step 111 (oxidation), the wafer surface is oxidized. In step 112 (CVD), an insulating film is formed on the surface of the wafer. In step 113 (electrode formation), an electrode is formed on the wafer by vapor deposition or the like. In step 114 (ion implantation), ions are implanted into the wafer. In step 115 (resist process), a photosensitive agent is applied to the wafer. Step 116 (exposure) uses the exposure apparatus 1 to expose a circuit pattern on the mask onto the wafer. In step 117 (development), the exposed wafer is developed. In step 118 (etching), portions other than the developed resist image are removed. In step 119 (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. According to the manufacturing method of the present embodiment, it is possible to manufacture a higher-quality device than before.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these, A various deformation | transformation and change are possible within the range of the summary.

It is the figure which showed typically the structure of the offset analyzer for enforcing the alignment method which concerns on Embodiment 1 of this invention. It is the figure which showed typically the cross section of the L & S (line & space) pattern as a periodic pattern. It is a figure which shows an example of the optical system of the cross-sectional shape measuring apparatus of a periodic pattern using the ellipsometry method. It is a flowchart explaining the procedure which measures the cross-sectional shape of the periodic pattern as a measuring object. It is the schematic which showed the structural example of the exposure apparatus typically. It is a figure explaining the concept of calculation of offset amount (position correction amount) in an offset analyzer. It is a figure which shows the wafer and the flow of information in the offset analyzer using the alignment method which concerns on Embodiment 2 of this invention. The figure which shows typically the structure of the offset analyzer for enforcing the alignment method which concerns on Embodiment 2 of this invention, Comprising: The figure which shows the example conveyed with the chuck | zipper to an exposure position in the state which adsorb | sucked the wafer It is. It is a figure which shows typically the structural example of the exposure apparatus which exposes with respect to the wafer conveyed by the chuck | zipper from the offset analyzer shown in FIG. It is a figure which shows typically the rotation error which generate | occur | produces in the alignment by a global alignment system. It is a figure which shows typically the magnification error which generate | occur | produces in the alignment by a global alignment system. It is a figure which shows the wafer and the flow of information in the offset analyzer using the alignment method which concerns on Embodiment 1 of this invention. It is a flowchart for demonstrating the device manufacturing method which has an exposure process by the exposure apparatus shown in FIG. 14 is a detailed flowchart of Step 104 shown in FIG. 13.

Explanation of symbols

AM: Alignment mark AS: Alignment scope (alignment detection system)
G: reference mark IL: illumination device OA: offset analyzer R, 112: reticle RS: resist ST: stepper (exposure device)
SIL: Field stop W: Wafer (substrate)
3, 3a, 3b: reflected light beam 4a: incident light 4b: reflected light 4c: separated light 5: polarization beam splitter
6: λ / 4 plate
7: Lens
10: Beam splitter
11,13 Fourier transform lens
15: LED (light source)
16: Condenser lens 17: Reference mask 19: Sequential lens 22, 105: He-Ne laser (light source)
23: Acousto-optic element (AO element)
24: Lens 54: Spectroscopic ellipsometer 55, 151: Computer 56: Storage device 57: Alignment signal 59: Offset amount (position correction amount)
101, 116: Imaging device (CCD camera)
107: Fiber 108: Alignment illumination optical system 109: Beam splitter 110: Relay lens 111: Objective lens 113: Reduction projection optical system 114: Mirror 115: Elector 117: Image 118: XY stage with interferometer 120: Illumination for reticle pattern exposure Optical system 122: θ-Z stage 123: tilt stage 125: bar mirror 126: laser interferometer 129: focus measurement system (light projection system)
130: Focus measurement system (detection system)
152: Optical system
153: Detection optical system
154: Correction optical system

Claims (10)

A method for aligning substrates,
Obtaining a plurality of measurement results obtained when measuring a plurality of marks having different shapes with an ellipsometer, and
Measuring an alignment mark on the substrate with an ellipsometer;
Comparing the measurement results with the plurality of measurement results to determine the shape of the alignment mark;
Obtaining a position correction amount of the substrate based on the determined shape of the alignment mark. The alignment method according to claim 1, wherein the plurality of marks and alignment marks have a diffraction grating shape. The alignment method according to claim 1, wherein the plurality of measurement results are obtained by an optical simulator. In the step of obtaining the position correction amount, based on the determined shape of the alignment mark, a detection result obtained when the alignment mark is detected by a position detection unit is calculated,
The alignment method according to claim 1, wherein the position correction amount is obtained based on the calculated detection result. The alignment method according to claim 1, wherein the detection result is calculated by an optical simulator. The position detection means illuminates the alignment mark with zero-order light and selects and uses reflected light of ± n-order (n = 1, 2, 3,...) From the alignment mark. The alignment method according to claim 1, wherein the detection result is obtained. 2. The exposure apparatus according to claim 1, wherein when a plurality of substrates are exposed, the position correction amount with respect to a substrate to be exposed first is obtained, and alignment of the plurality of substrates is executed based on the position correction amount. Alignment method. An exposure method comprising: aligning the substrate by the alignment method according to claim 1 to expose the substrate. An exposure apparatus comprising: aligning the substrate by the alignment method according to claim 1 to expose the substrate. 10. A device manufacturing method, wherein a substrate is exposed by the exposure apparatus according to claim 9, and a predetermined process is performed on the exposed substrate.

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