JP6532302B2 - Alignment method, exposure apparatus, and method of manufacturing article - Google Patents

Description

  The present invention relates to an alignment method, an exposure apparatus, and a method of manufacturing an article.

  An exposure apparatus used for manufacturing a semiconductor device transfers a pattern formed on an original (such as a reticle) onto a substrate (such as a wafer having a resist layer formed on the surface) via a projection optical system. In order to transfer a pattern with high accuracy, it is required to align the original with the substrate with high accuracy. As one of alignment methods, there is a method using an off-axis alignment detection system (OA detection system). The OA detection system has an optical axis different from the optical axis of the projection optical system, and detects the position of the substrate without the intervention of the projection optical system. Substrate alignment is performed based on the detection result.

  The position detection of the substrate by the OA detection system includes the step of determining the distance (baseline amount) between the pattern projection position and the reference mark using the reference plate on which the reference mark is formed. Here, the reference plate may be deformed (stretched) due to exposure heat or the like, and the baseline amount may change. In order not to impair the position detection accuracy, it is necessary to periodically measure the baseline amount, and when the change amount is large, it is necessary to update the baseline amount used for position detection. However, frequent baseline volume measurements reduce throughput. On the other hand, Patent Document 1 discloses a method of measuring the baseline amount at indefinite intervals in units of the number of processing substrates and time according to the tendency of the change of the baseline amount, and reducing the frequency thereof.

Japanese Patent Application Laid-Open No. 6-097032

  In Patent Document 1, the tendency of change in baseline amount is estimated based on the baseline amount measured at a predetermined timing. If the estimation accuracy is bad, there is a possibility that the baseline amount can not be measured at an appropriate timing, which is disadvantageous in terms of improving the alignment accuracy and throughput.

  An object of the present invention is, for example, to provide an exposure apparatus that is advantageous in terms of improving alignment accuracy and throughput.

In order to solve the above problems, the present invention is to sequentially perform exposure for a plurality of substrates, using the reference plate marks are formed, a sequentially performs alignment method for alignment of a plurality of substrates, the reference plate Measurement step for obtaining the actual measurement value of the deformation amount, an estimation step for obtaining the estimation value of the deformation amount of the reference plate with respect to the elapsed time of exposure, and determining whether the difference between the actual measurement value and the estimation value exceeds a predetermined threshold a determining step of, when the difference in the determining step is determined to exceed the predetermined threshold value, the second measured obtaining a second measured value by actually measuring the deformation amount of the reference plate, the measured value second having an updating step, the updating to the measured value.

  According to the present invention, it is possible to provide an exposure apparatus that is advantageous, for example, in terms of improving alignment accuracy and throughput.

It is a figure which shows the schematic of exposure apparatus. It is a figure showing the scope concerning the embodiment of the present invention. FIG. 5 is a view showing a reference mark on a reference plate according to an embodiment of the present invention. It is a figure which shows the time change of the deformation amount of the reference | standard plate which concerns on embodiment of this invention. It is a flowchart which shows the correction method of the estimated value which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like.

First Embodiment
FIG. 1 is a schematic view showing a configuration of an exposure apparatus to which the alignment method according to the present embodiment can be applied. Here, a step-and-scan type scanning projection exposure apparatus (scanner) was used. The scanning projection exposure apparatus 100 includes an illumination optical system 1, an alignment measurement unit 2, an original stage 3b, a projection optical system 4, a substrate stage 5b, an off-axis measurement unit (detection optical system) 9, and a control unit. 8 and a reference plate 10. In FIG. 1, a direction parallel to the optical axis of the illumination optical system is taken as a Z axis, and X and Y axes orthogonal to each other are taken in a plane perpendicular to the Z axis.

  The illumination optical system 1 has a light source (not shown), and irradiates the original (reticle) 3a with illumination light formed in a slit shape (for example, an arc shape). The original stage 3 b holds the original 3 a and is movable in the Y-axis direction. The projection optical system 4 adopts, for example, a mirror projection method constituted by a plurality of mirrors, and projects the image of the pattern formed on the original plate 3a onto the substrate 5a held on the substrate stage 5b, for example at equal magnification. Do. The substrate stage (substrate holding unit) 5b is disposed on the surface plate 6, holds the substrate 5a, and is movable in six directions, for example, X, Y, Z, ωx, ωy, and ωz. At the time of exposure, the original 3 a held by the original stage 3 b and the substrate 5 a held by the substrate stage 5 b have a conjugate positional relationship (the object plane and the image plane of the projection optical system 4) via the projection optical system 4. Placed in).

  The alignment measurement unit 2 is disposed between the illumination optical system 1 and the original 3a, and includes at least two alignment scopes (not shown). The scanning projection exposure apparatus 100 sequentially aligns a pattern with a shot when transferring the pattern of the original 3 a to a plurality of exposure areas (shots) on the substrate 5 a. At this time, the alignment measurement unit 2 simultaneously detects the mark (substrate side mark) formed on the substrate 5 a and the mark (original plate side mark) formed on the original plate 3 a through the projection optical system 4. (Observe.

  The off-axis measurement unit (measurement optical system) 9 is disposed at a position away from the optical axis of the projection optical system 4 and at a position between the projection optical system 4 and the substrate 5 a in the Z-axis direction. Then, it has an optical axis parallel to the optical axis of the projection optical system 4 and includes scopes 9a to 9e arranged in parallel in the X-axis direction as shown in FIG. At least two scopes need to be included. The off-axis measuring unit 9 detects (observes) a plurality of marks provided in the shot area on the substrate 5 a without the projection optical system 4. The scopes 9a to 9e can be moved individually, and can be positioned according to the substrate side marks.

  The reference plate 10 is disposed at a position detectable by the off-axis measurement unit 9, for example, a position facing the off-axis measurement unit 9, and a plurality of reference marks corresponding to the positions of the respective scopes 9a to 9e as shown in FIG. 10a to 10e are included. That is, each of the scopes 9a to 9e of the off-axis measurement unit 9 can individually detect each of the reference marks 10a to 10e at the corresponding positions. In the scanning projection exposure apparatus 100, a drive unit (not shown) may be provided to move the reference marks 10a to 10e at positions corresponding to the scopes 9a to 9e. Alternatively, the reference plate 10 may be moved together with the movement of the substrate stage 5b by, for example, integrally forming the reference plate 10 and the substrate stage 5b without installing the driving unit. Also, the reference plate 10 may be divided or may be a single connected reference plate.

  The control unit 8 is formed of, for example, a computer, etc., is connected to each component of the scanning projection exposure apparatus 100 through a line, and controls operation and adjustment of each component according to a program or the like. The control unit 8 may be configured integrally (within a common housing) with the other parts of the scanning projection exposure apparatus 100 or separately from the other parts of the scanning projection exposure apparatus 100 It may be configured in another housing). The control unit 8 determines the shape information of the shot (X, Y and Z directions based on the position of the mark of the shot measured by the alignment measurement unit 2 and the position of the mark of the shot measured by the off-axis measurement unit 9). Find the position etc.)

  The scanning projection exposure apparatus 100 having the above configuration obtains the position of the substrate 5a (the position of the mark of the shot) as follows. First, the control unit 8 measures the reference marks 10a to 10e of the reference plate 10 using the scopes 9a to 9e to obtain the distance between the scopes (first distance). Further, the control unit 8 measures the same substrate side mark by the alignment measurement unit 2 and the off-axis measurement unit 9 to acquire the distance between the measurement units (second distance). Then, the position of the substrate 5a (the position of the mark of the shot) is obtained based on the information of the first distance and the second distance.

  The control unit 8 determines the moving speed of the original stage 3b or the substrate stage 5b or the projection magnification of the projection optical system 4 based on the acquired shape information of the shot so that the mark on the original 3a and the mark of the shot overlap. . Then, while synchronizing the original plate stage 3 b and the substrate stage 5 b with each other, the control unit 8 scans at a speed ratio according to the projection magnification of the projection optical system 4 and performs exposure processing (scan exposure). Thereby, the pattern formed on the original plate 3a can be transferred to the shot of the substrate 5a. The scanning projection exposure apparatus 100 repeats scanning exposure for each of a plurality of shots of the substrate 5a, and sequentially performs scanning exposure on a plurality of substrates.

  In the present embodiment, the first distance obtained using the reference plate 10 may change as the number of processed substrates increases. Hereinafter, the amount of change of the first distance (the amount of deformation of the reference plate) will be described. FIGS. 4A to 4E are graphs showing temporal changes in reference plate deformation amount when the vertical axis represents the reference plate deformation amount and the horizontal axis represents the number of processing substrates (processing time). Curves H shown in FIGS. 4 (a) to 4 (e) are curves showing the measured values of the reference plate deformation amount with respect to the number of processed substrates. When the number of processed substrates increases, the reference plate 10 is deformed by exposure heat or the like, and the first distance also changes accordingly. Plots M1 to M6 are reference plate deformation amounts measured at the substrates P1 to P6 (uncertain time intervals). The first distance used to determine the position of the substrate 5a is determined based on the difference in the values on the vertical axis between the plots, that is, the difference in the amount of change in the first distance between the processing substrates.

  In measurement of the deformation amount of the reference plate 10, the reference marks 10a to 10e are sequentially measured using any one of the scopes 9a to 9e. When the reference plate 10 is deformed (stretched) by the exposure heat, the measured values of the drawn reference marks 10a to 10e change, so that the amount of deformation can be detected. If all the reference marks 10a to 10e can not be measured with one scope due to the restriction of the driving range of the substrate stage 5b, a plurality of scopes may be used and divided and measured. In that case, the same reference mark is measured with a plurality of scopes, the offset between the scopes is canceled, and the amount of deformation is calculated.

  At the time of processing the substrate P1, the value of the vertical axis of the plot M1, that is, the amount of deformation of the reference plate 10 from the start of the substrate processing to the substrate P1 is large. In this case, the first distance used for alignment is updated to the first distance measured by the substrate P1. At the stage where the number of processed substrates is small, the rate of increase in the amount of deformation of the reference plate 10 is high (the slope of the curve H is steep). In fact, the amount of deformation between plot M1 and plot M2 is large enough to require updating of the first distance used for alignment. After the substrate P3, the rate of increase in deformation amount is low (the slope of the curve H is gentle), and there may be a substrate in which the update of the first distance used for alignment is unnecessary. For example, the difference between the amounts of deformation of M5 and M4 is small. If this difference is a difference to the extent that the update of the first distance is unnecessary, the alignment of the substrate P5 can be performed using the first distance measured by the substrate P4.

  FIG. 4A shows a conventional method of measuring the amount of deformation of the reference plate 10 for each substrate processing. In the conventional method, the throughput is reduced because the first distance is measured on all the processing substrates. Therefore, in order to reduce the frequency of measurement, the amount of deformation of the reference plate 10 is estimated. Hereinafter, the estimation method will be described. A curve H0 shown in FIG. 4B indicates an estimated value of the amount of deformation of the reference plate 10. Plots Y1 to Y6 are estimated values of the amount of change of the first distance in the substrates P1 to P6 (uncertain time intervals).

A specific method of calculating the estimated value of the change amount of the first distance will be described. Assuming that the amount of change generated with the time constant K at the time (the number of processed substrates) n at which Δt time has elapsed since the previous calculation of the amount of change is Φ (n), the change Φ (n) is expressed by the following equation (1) Can.
Φ (n) = ICo- (ICo-Φ (n-1)) exp (-Δt / K) (1)
Here, ICo is represented by the following equation (2).
ICo = ICk × (W / W0) (2)
W0 is a reference exposure load and an arbitrary constant (for example, 50 watts). W is an integrated load amount, which is a value obtained by dividing the integrated path light amount Δe by Δt (Δe / Δt). K is a unique constant (time constant) derived from a function of physical properties (for example, thermal conductivity) of the material of the reference plate 10. Further, ICk is a saturation value of the amount of change determined by the transmittance of the original 3a, the exposure conditions (exposure speed, illuminance, shot size, etc.) and K. The IC k is calculated by least squares approximation or the like on the basis of the actual measurement value of the deformation amount of the reference plate 10 measured at an arbitrary interval after continuous exposure has been performed beforehand and time elapses to the extent that the deformation amount saturates. In actual exposure processing, exposure speed, illuminance, and shot size are changed by the process. Therefore, the integrated load amount W is calculated from the integrated exposure amount Δe during exposure and the elapsed time Δt, and the ratio to the reference exposure load W0 is multiplied by ICk to calculate the saturation value ICo under actual exposure conditions. Apply to 1). Using equation (1), an estimation unit (not shown) calculates an estimated value of the amount of change of the first distance.

  FIG. 5 is a flowchart showing a method of correcting the estimated value. In S101, the time constant K is determined from the physical properties of the material of the reference plate 10, and continuous exposure is performed in advance, and ICk is calculated based on the measured value of the amount of deformation of the reference plate 10. In S102, the estimated value of the deformation amount of the reference plate 10 is calculated by the parameter obtained in S101 and the equation (1).

  S103 to S106 will be described with reference to FIG. In S103, a determination unit (not shown) determines whether the difference between the estimated value obtained in S102 and the actually measured value measured last time exceeds a predetermined threshold. Let T be a predetermined threshold value, and Y1 to Y10 be estimated values of the deformation amount of the reference plate 10 when processing the substrates P1 to P10. At the start of the exposure process (when processing the substrate P1), since the measurement of the deformation amount has not been performed yet, the previous actual measurement value used for the determination of the threshold value is zero. The difference between the actual measured value 0 and the estimated value Y1 is compared with the threshold value T. As shown in FIG. 4C, since the threshold value T is not exceeded (S103 (No)), measurement of the deformation amount is not performed, and in the alignment correction (alignment of the substrate P1) in S106, the estimated value Y1 is Use the calculated first distance. The same processing as this is performed for the substrate P2 and thereafter.

  The threshold T is determined based on the amount of change permitted by the desired alignment accuracy. For example, the relationship between the amount of change and the alignment error is measured in advance, and the threshold is determined from the relationship. In addition, the difference between the estimated value and the actual value to be compared with the threshold includes not only the difference in a certain substrate but also an error obtained by accumulating the differences in a plurality of substrates.

  Since the change from the measured value 0 exceeds the threshold value T with the estimated value Y2 of the substrate P2 (S103 (YES)), the deformation of the reference plate 10 is measured (S104), and the deformation M1 is calculated (S105) . The first distance calculated from the deformation amount M1 is used for alignment correction (alignment of the substrate P2) in S106. From the substrate P3 onward, this M1 is the actual measurement value of the comparison object used in the determination in S103, and the variation from this M1 is compared with the threshold value T. In the figure, since the variation from the actual measurement value M1 exceeds the threshold T at the estimated value Y6 for the substrate P6 (S103 (YES)), the deformation is measured (S104), and the deformation M2 is It is calculated (S105). The first distance calculated from the deformation amount M2 is used for the alignment correction (alignment of the substrate P6) in S106. Since the rate of increase of the deformation of the reference plate 10 is low on and after the substrate P7, the change is stable within the threshold and there is no need to measure the deformation. As described above, in S106, alignment correction is performed using the estimated value or the measured value according to the determination result of S103. The processing from S103 to S106 is performed for each substrate, and it is determined in S107 whether it is the final processed substrate, and the processing is repeatedly performed until the final processed substrate.

  FIG. 4D is a diagram showing the time change of the reference plate deformation amount when the substrate processing flow is temporarily stopped. After the processing of the substrate P10, when the flow is temporarily stopped due to an error, a manual operation, or the like, the reference plate 10 cools and contracts, and the deformation amount returns to the state at the start of the exposure. When the exposure processing is restarted on the substrate P11 and the estimated value at that time is Y11, the amount of change from the previous actual measurement value M2 exceeds the threshold value T (S103 (YES)). Therefore, the measurement of the deformation amount is performed again (S104), the deformation amount M3 is calculated (S105), and the calculation result is used for the alignment correction (S106). In the subsequent substrate processing, comparison with the estimated value is performed based on this M3.

As described above, when the estimated value of the deformation amount is used to determine the necessity of updating the first distance used for alignment, the frequency of measuring the deformation amount of the reference plate 10 can be reduced.

  As described above, according to the present embodiment, it is possible to provide an exposure apparatus that is advantageous in terms of improving alignment accuracy and throughput.

Second Embodiment
Next, a method of calculating the saturation value ICk according to the second embodiment of the present invention will be described. In the first embodiment, in order to obtain the saturation value ICk, it is necessary to perform continuous exposure in advance before the substrate alignment and exposure processing steps, and to wait for the time for the deformation amount to saturate. In the present embodiment, the saturation value ICk is not calculated in advance before the exposure processing step, but is calculated while advancing the exposure processing step. The method will be described with reference to FIG. Since the saturation value ICk is not determined at the start of the exposure process, the deformation amount of the reference plate 10 is actually measured on the substrates P1 to P6. At the processing stage of the substrate P6, since the deformation of the reference plate 10 is saturated to some extent, the values of the deformations M1 to M6 actually measured are used to calculate the saturation value ICk by the least square approximation. In the process of the substrate P7, since the saturation value ICk is calculated, the estimated value of the deformation amount is calculated using the equation (1), and is used for the correction of the alignment. Similarly, in the substrate P8 and thereafter, the actual deformation is not measured, and the estimated value of the deformation is calculated and corrected. By calculating the saturation value ICk using the deformation amount of the reference plate 10 measured during the exposure processing step, the step of performing continuous exposure in advance can be omitted, and the productivity can be improved. As described above, the present embodiment can also provide an exposure apparatus that is advantageous in terms of improving alignment accuracy and throughput.

(Product manufacturing method)
The method of manufacturing an article according to the embodiment of the present invention is suitable, for example, for manufacturing an article such as a microdevice such as a semiconductor device or an element having a microstructure. In the method of manufacturing an article according to the present embodiment, a latent image pattern is formed in the step of forming a latent image pattern on the photosensitive agent applied to the substrate using the above-described exposure apparatus (the step of exposing the substrate) And developing the substrate. Furthermore, such a manufacturing method includes other known steps (oxidation, film formation, deposition, doping, planarization, etching, resist stripping, dicing, bonding, packaging, etc.). The method of manufacturing an article according to the present embodiment is advantageous in at least one of the performance, quality, productivity, and production cost of an article, as compared to the conventional method.

  Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the present invention.

1 illumination optical system 2 alignment measurement unit 3a original 3b original plate stage 4 projection optical system 5a substrate 5b substrate stage 6 surface plate 8 control unit 9 off-axis measurement unit (measurement optical system)
10 Reference plate

Claims (9)

An alignment method in which alignment of the plurality of substrates is sequentially performed using a reference plate on which marks are formed in order to sequentially perform exposure on the plurality of substrates,
A measurement step of obtaining an actual measurement value of the deformation amount of the reference plate;
An estimation step of determining an estimated value of the deformation amount of the reference plate with respect to the elapsed time of the exposure;
A determination step of determining whether a difference between the actual measurement value and the estimated value exceeds a predetermined threshold value;
A second measurement step of measuring a deformation amount of the reference plate to determine a second measured value when it is determined in the determination step that the difference exceeds the predetermined threshold value;
An updating step of updating the actual measurement value to the second actual measurement value. The alignment method according to claim 1, wherein the alignment is performed based on the second measured value.   When it is determined in the determination step that the difference does not exceed the predetermined threshold value, the second measurement step is not performed, and the alignment is performed based on the estimated value. Or the alignment method as described in 2.   The alignment method according to any one of claims 1 to 3, wherein the measured value is set to zero until it is determined for the first time that the difference exceeds the predetermined threshold.   The method according to any one of claims 1 to 4, wherein, in the estimation step, the estimation value is determined using a constant determined by the physical properties of the substrate and a saturation value of the deformation amount of the reference plate. Alignment method.   The alignment method according to claim 5, wherein the physical property includes thermal conductivity.   The alignment method according to claim 5 or 6, wherein the saturation value is determined using an actual measurement value of a deformation amount of a reference plate measured in advance. An exposure apparatus that sequentially aligns a plurality of substrates using a reference plate on which marks are formed, and sequentially exposes the plurality of substrates,
A measurement optical system that measures the position of the mark;
Calculation means for calculating the amount of deformation of the reference plate from the position of the mark measured by the measurement optical system;
Estimation means for estimating the amount of deformation with respect to the elapsed time of the exposure;
Judgment means for judging whether a difference between an actual measurement value obtained by the measurement optical system and the calculation means and an estimated value obtained by the estimation means exceeds a predetermined threshold value;
Updating means for updating the actual measurement value to a second actual measurement value obtained again by the measurement optical system and the calculation means when it is determined by the determination means that the difference exceeds a predetermined threshold value; An exposure apparatus characterized by having. A process of exposing a substrate using the alignment method according to any one of claims 1 to 7 or the exposure apparatus according to claim 8.
And b. Developing the substrate exposed in the step.

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