JP7587359B2 - Alignment apparatus, method for determining position of mark, program, lithography apparatus, and article manufacturing method - Google Patents

Description

The present invention relates to an alignment apparatus, a method for determining the position of a mark, a program, a lithography apparatus, and an article manufacturing method.

In lithography equipment, such as exposure devices used in semiconductor device manufacturing, precise alignment between the master and the substrate is required when exposing a circuit pattern drawn on the master onto the substrate.

Alignment is usually performed by observing the alignment marks and patterns formed on the substrate using a measurement optical system (hereafter referred to as an alignment scope) and processing the image signal of the captured pattern. Pattern matching is widely used in image signal processing for pattern position measurement. Pattern matching is a method of calculating the degree of correlation between the image signal of the measurement target and a template pattern to find the matching point with the highest degree of correlation.

On the other hand, depending on the thickness and coating unevenness of the photoresist applied to the substrate before exposure, and the semiconductor manufacturing process before exposure, it may be difficult to accurately observe the pattern to be measured using an alignment scope. One cause of the decrease in the observation accuracy of the alignment scope is a decrease in the contrast of the image signal of the captured pattern. Here, a state in which the contrast is decreased means that the brightness distribution of the image is biased toward a certain brightness within the range of gradations being used. In position measurement using a pattern image signal with low contrast, the amount of information on the edges of the image is small, and the position measurement accuracy of pattern matching may be significantly decreased compared to when a pattern image signal with good contrast is used. The decrease in position measurement accuracy by pattern matching may decrease the alignment accuracy between the substrate and the original.

In this case, the position measurement accuracy can be improved by improving the contrast of the pattern image signal through signal processing. Histogram expansion is a commonly known processing method for improving contrast (Patent Document 1). Histogram expansion is a method of stretching biased luminance distribution within the range of gradations being used, and is expected to improve the contrast of the signal. Patent Document 2 proposes a method of performing alignment without reducing the accuracy of calculations by performing histogram flattening, even when the image contrast is low. Furthermore, histogram expansion has the problem that the gradations of the image signal become coarse, but Patent Document 3 limits the range of histogram expansion to prevent the gradations from becoming coarse due to histogram expansion.

Japanese Unexamined Patent Publication No. 61-45667 Patent No. 3506200 Patent No. 4532640

In Patent Documents 1 and 2, when the histogram is expanded to improve the contrast of an image, the luminance is distributed intermittently within the range of gradations being used, which effectively reduces the gradations available for calculation. The above process is effective when you want to intentionally reduce the gradations while maintaining calculation accuracy, but is not effective for improving calculation accuracy.

In Patent Document 3, the upper and lower limits of the histogram expansion are set to suppress the decrease in gradation. However, because a limit is placed on the histogram expansion range, it cannot be said that the contrast of the image signal is improved to the maximum.

The present invention aims to provide an alignment device that is advantageous for improving the accuracy of mark position measurement, for example.

According to one aspect of the present invention, there is provided an alignment device that aligns a substrate by detecting a mark formed on the substrate, the alignment device comprising: a stage that holds and moves the substrate; an imaging unit that images the mark formed on the substrate held by the stage to obtain an image of the mark; and a processing unit that processes the image to determine a position of the mark, wherein the processing unit performs contrast enhancement processing on each of a plurality of first images obtained by imaging the mark with the imaging unit to obtain a second image having a coarser gradation than each of the plurality of first images, and determines the position of the mark based on a third image having a finer gradation than the second images, which is generated by accumulating a plurality of the second images.

The present invention can provide, for example, an alignment device that is advantageous in improving the accuracy of mark position measurement.

FIG. 1 is a diagram showing the configuration of an exposure apparatus. 13 is a flowchart of an alignment process. 13 is a flowchart of a contrast enhancement process. 5A to 5C are diagrams illustrating contrast enhancement processing. 6A to 6C are diagrams for explaining a histogram extension process. 13 is a flowchart of a contrast enhancement process.

The following embodiments are described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe multiple features, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicate explanations are omitted.

First Embodiment
One aspect of the present invention relates to an alignment apparatus that aligns a substrate by detecting a mark formed on the substrate. The alignment apparatus according to the present invention can be applied to alignment between an original and a substrate in a lithography apparatus such as an exposure apparatus or an imprint apparatus, but can also be applied to other apparatuses such as a processing apparatus, an inspection apparatus, and a microscope. An example in which the alignment apparatus according to the present invention is applied to an exposure apparatus will be described below.

FIG. 1 is a diagram showing the configuration of an exposure apparatus 100 in the first embodiment. The exposure apparatus 100 includes a substrate chuck WC that holds a substrate W, and a substrate stage WS that supports the substrate chuck WC and aligns the substrate W to a predetermined position. The exposure apparatus 100 further includes an illumination optical system IL that emits exposure light for transferring a pattern of an original R onto the substrate W, and a projection optical system PO that projects the exposure light onto the substrate W. A circuit pattern is drawn on the original R, and the original R is supported by an original stage (not shown). The exposure apparatus 100 further includes an alignment detection system A that measures the positions of the substrate W and the original R. The alignment detection system A may include an imaging unit that captures an image of a mark formed on the substrate W held by the substrate stage WS to obtain an image of the mark.

The alignment processing device AP functions as a processing unit that processes the image obtained by the alignment detection system A (imaging unit) to determine the position of the mark. The alignment processing device AP detects the position of the mark pattern P formed on the substrate W by executing a position detection process described below. The control device CP performs overall control of the exposure process. The alignment processing device AP and the control device CP can each be realized by a computer including a CPU and memory. Note that the alignment processing device AP and the control device CP do not need to be independent device configurations. For example, the functions of the alignment processing device AP may be performed by the control device CP.

In one example, the alignment processing device AP detects the relative positions of the original R and the substrate W using the alignment detection system A, and performs alignment by controlling the substrate stage WS based on the detection results. The control device CP then controls the illumination optical system IL to emit exposure light, and exposes the pattern drawn on the original R onto the substrate W placed on the substrate stage WS through the projection optical system PO.

Next, the alignment of the original R and the substrate W by the alignment detection system A will be described. Illumination light from the light source LS is reflected by the beam splitter BS and illuminates the pattern P of the mark formed on the substrate W. Diffracted light from the pattern P is magnified to a predetermined magnification by the imaging optical system LO, forming an image of the pattern P on the sensor S. The sensor S photoelectrically converts the formed image into an image signal and inputs it to the alignment processing device AP. The alignment processing device AP measures the position of the pattern P by a position detection process described below. The above pattern position measurement is performed for multiple points on the substrate W, and the position of the substrate stage WS is adjusted with respect to the original R based on the measured pattern position information.

Next, the position measurement process flow of this embodiment will be described. FIG. 2 is a flow chart of the alignment process in this embodiment. In S102, the control device CP controls the substrate transport device (not shown) to load the substrate W onto the substrate stage WS. In S103, the control device CP moves the substrate stage WS to the pre-alignment position of the pattern P (prestored in the memory of the control device CP). In S104, the alignment processing device AP controls the alignment detection system A with the substrate stage WS stopped to capture multiple images of the same position including the area of the pattern P of the mark on the substrate W. The multiple images obtained by capturing these multiple images are called "pattern image group 1". Pattern image group 1 is stored, for example, in the memory of the alignment processing device AP.

In S105, the alignment processing device AP determines whether or not to perform contrast enhancement processing on the pattern image group 1. For example, a setting value for whether or not to perform contrast enhancement processing is specified by default, and the setting value can be changed by a user operation. If contrast enhancement processing is to be performed, in S106, the alignment processing device AP performs contrast enhancement processing on the pattern image group 1. The image obtained by the contrast enhancement processing is called "pattern image 3." Pattern image 3 is stored, for example, in the memory of the alignment processing device AP. Note that, if contrast enhancement processing is not to be performed, the alignment processing device AP obtains pattern image 3 by selecting a specific image from the pattern image group 1, or by combining a specific number of images from the pattern image group 1.

In S107, the alignment processing device AP performs pattern matching (template matching) processing on the pattern image 3 using a template previously stored in the memory of the alignment processing device AP. The pattern matching processing is a process of searching for and determining the position of the pattern P in the pattern image 3 using a template in which the ideal shape of the pattern P of the mark on the substrate W is represented by a plurality of discrete feature points. Specifically, the position at which the degree of correlation (similarity) is maximum is searched for, and this position is determined as the pre-alignment position (measurement value). Information on the determined pre-alignment position of the pattern P is transferred to the control processing device CP.

In S108, the control processing device CP moves the substrate stage WS to a position where fine alignment measurement is performed based on the pre-alignment position information. Then, in S109, the alignment processing device AP performs fine alignment of the substrate W, and obtains position information of the substrate W from the calculated position information of the pattern P.

After the above alignment process is completed, the control device CP moves the substrate stage WS and performs exposure based on the position information of the substrate W calculated by fine alignment and the position information of the original R.

The contrast enhancement process and pattern matching process in the present invention are not necessarily performed only in the calculation process of the prealignment position as described above. The contrast enhancement process and pattern matching process may be performed in fine alignment. Also, prealignment does not necessarily have to be performed, and fine alignment may be performed without prealignment.

The position measurement calculation in this embodiment does not necessarily have to be a pattern matching process of an image, but may be any position measurement calculation that can measure the position of a pattern image. For example, a position measurement calculation may be performed by matching a one-dimensional signal pattern to a one-dimensional signal obtained by integrating an image that has been subjected to contrast enhancement processing in a non-measurement direction (e.g., a direction perpendicular to the position measurement direction).

Next, the contrast enhancement process in S106 will be described with reference to the flowchart in FIG. 3. In S202, the alignment processing device AP counts the number of pattern images in the pattern image group 1 obtained in S104 that have undergone the histogram expansion process described below. In S203, the alignment processing device AP determines, from the number of images counted in S202, whether or not the histogram expansion process has been performed on all of the pattern image group 1.

If there are pattern images for which the histogram expansion process has not been performed, in S204, the alignment processing device AP calculates the maximum pixel value and the minimum pixel value in one of the pattern images. In S205, the alignment processing device AP performs histogram expansion of the pattern image based on the calculated maximum pixel value and minimum pixel value.

Then, in S202, the alignment processing device AP again counts the number of pattern images that have been subjected to the histogram expansion process, and repeats the above process until the histogram expansion process has been performed on all of the pattern image group 1. This generates pattern image group 2, which is an image group in which the histogram expansion process has been performed on the pattern image group 1.

After it is determined in S203 that the histogram extension process has been performed on all of the pattern image group 1, in S206 the alignment processing device AP synthesizes the pattern image group 2 to generate a composite image. The composite image can be generated, for example, by accumulating the pixel values of each pixel of all the images in the pattern image group 2. Alternatively, the composite image can be generated by accumulating the pixel values of each pixel of a predetermined number of images in the pattern image group 2.

In the above example, the contrast enhancement process is a histogram expansion process that expands the luminance region in the histogram for each of the pattern image group 1. FIG. 4 shows the change in the image histogram in the process of generating a high-contrast pattern image 3 from the pattern image group 1 (or a plurality of images therein) by the histogram expansion process, which is the contrast enhancement process of this embodiment. Each of the plurality of pattern image groups 1 (N images in FIG. 4) before the histogram expansion is performed has a low contrast and a histogram biased toward a certain luminance distribution. For example, assume that N=5, the image gradation is 8-bit gradation from 0 to 255, the pixel values of pixel 1 of each image are 19, 19, 23, 18, 18, and the pixel values of pixel 2 of each image are 19, 22, 17, 22, 19, respectively. Also assume that the maximum pixel values of the five images are 43, 43, 44, 44, 45, and the minimum pixel values are 8, 9, 9, 9, 7, respectively. The pixel values vary for the same pixel in each image due to noise that occurs during imaging.

When the histogram expansion process is performed on each of the N pattern image groups 1, the histogram is stretched, and N pattern image groups 2 with improved contrast are generated. On the other hand, the histograms of the individual images have intermittent luminance distribution and coarse gradation. In the above specific example, when the histogram expansion is performed by linear conversion described below, the pixel values of pixel 1 of the five pattern image groups 2 are, for example, 80, 75, 102, 18, and 65, and the pixel values of pixel 2 are 80, 97, 58, 94, and 80, respectively. The pixel values of pixel 1 and pixel 2 of the first image are the same before and after the histogram expansion. Therefore, the luminance after the histogram expansion is distributed intermittently, and the gradation becomes coarse. On the other hand, due to the influence of noise, the second and subsequent images have different pixel values. Finally, by accumulating the N pattern image groups after the histogram expansion process, a pattern image 3 with high contrast and fine gradation is obtained.

In the above specific example, the average value of pixel 1 in pattern image group 2 is 79, and the average value of pixel 2 is 82, so that pixels that had the same pixel value in the first image now have different pixel values. The same can be said for all pixels in the above example of two pixels. The pixel value of each pixel after accumulation reflects the variation in pixel value of the same pixel after accumulation due to noise, and pixels that had the same pixel value before accumulation now have different pixel values after accumulation, resulting in an image with high contrast and fine gradation.

Note that in the above example, N, which represents the number of images, is set to 5, but this is merely an example to simplify the explanation.

Next, the histogram expansion process shown in S204 and S205 of FIG. 3 will be explained using an example of a method for directly linearly converting pixel values.

First, the maximum pixel value and minimum pixel value of the region of interest of the input image are calculated. Next, a luminance conversion equation is found that converts, for example, the calculated maximum pixel value into the maximum value of the gradation of the image, and the calculated minimum pixel value into the minimum value of the gradation of the image. The pixel values of each pixel of the image are then converted according to the calculated luminance conversion equation. However, the maximum pixel value and minimum pixel value after conversion do not necessarily have to be the maximum and minimum values of the gradation being used. It is sufficient to find a luminance conversion equation that converts the maximum pixel value into a value larger than that, and the minimum pixel value into a value smaller than that.

Figure 5 (A), (B), and (C) show how the luminance of an input image is converted by the luminance conversion formula. In Figure 5, (A) is a histogram of the input image, and (B) is a histogram of the output image after histogram expansion processing, with the horizontal axis representing luminance and the vertical axis representing the frequency with which a certain luminance appears in the image. (C) is a graph showing the characteristics of the luminance conversion formula that associates the luminance values of the input image and the output image, with the vertical axis corresponding to the luminance value of the input image and the horizontal axis corresponding to the luminance value of the output image.

The above-described histogram expansion process is an example of a contrast enhancement process, and the present invention is not limited to the above-described histogram expansion process. Instead of the above-described histogram expansion process, a histogram flattening process that flattens the histogram levels may be used.

Second Embodiment
In the first embodiment described above, it is assumed that a pattern matching process of a two-dimensional signal is performed, but in the second embodiment, it is assumed that a pattern matching process of a one-dimensional signal is performed. Therefore, in the second embodiment, instead of capturing a plurality of images of the pattern P of the mark on the substrate W in S104 of FIG. 2, a process of capturing a single image (hereinafter, "pattern image 4") is performed. In addition, as the contrast enhancement process in S106 of FIG. 2, the process shown in the flowchart of FIG. 6 is performed instead of the process shown in FIG. 3. In this embodiment, a one-dimensional signal in the measurement direction is generated from the single pattern image 4, and the XY position of the pattern P is measured, thereby performing alignment between the original R and the substrate W. Note that the histogram extension process in this embodiment is a process in which the processing target is replaced from a two-dimensional image signal to a one-dimensional signal in the histogram extension process described in the first embodiment.

The contrast enhancement process of S106 in this embodiment will be described with reference to the flowchart in FIG. 6. In this process, one-dimensional signals for position measurement are generated in each of the first direction of the pattern P and the second direction perpendicular thereto (e.g., the X direction and the Y direction), and histogram extension processing is performed on each one-dimensional signal. Hereinafter, the direction (X direction/Y direction) of the one-dimensional signal generated here will be referred to as the "signal generation direction."

In S302, the alignment processing device AP counts the number of pixel columns that have undergone histogram expansion processing within a predetermined pixel range in the signal generation direction (first direction, for example, X direction) of the pattern image 4 obtained in S104. In S303, the alignment processing device AP determines whether the number of pixel columns that have undergone histogram expansion processing counted in S302 has reached a specified number.

If the counted number of pixel columns that have undergone histogram expansion processing does not reach a specified number, histogram expansion processing is performed in S304 and S305. In S304, the alignment processing device AP calculates the maximum pixel value and minimum pixel value in one pixel column (a pixel column of interest) within a specified pixel range that has not undergone histogram expansion processing. In S305, the alignment processing device AP performs histogram expansion of the pixel column of interest based on the calculated maximum pixel value and minimum pixel value.

Then, in S302, the alignment processing device AP again counts the number of pixel columns that have been subjected to the histogram expansion process, and repeats the above process until the histogram expansion process has been performed on a prescribed number of pixel columns. This generates a pattern image signal group 5, which is an image signal group in which the histogram expansion process has been performed for each pixel column in the first direction (X direction) within a predetermined pixel range of the pattern image 4 obtained by imaging.

The contents of the histogram expansion process are the same as those in the first embodiment, and the maximum pixel value and the minimum pixel value are found in S304 for each of a plurality of pixel rows in the first direction (X direction) and a plurality of pixel rows in the second direction (Y direction). Next, a luminance conversion equation is found that converts the maximum pixel value to a value greater than the maximum pixel value and the minimum pixel value to a value less than the maximum pixel value. After that, the pixel value of each pixel is converted according to the luminance conversion equation. Also, instead of the above histogram expansion process, a histogram flattening process that flattens the histogram levels may be used.

After it is determined in S303 that the histogram extension process has been performed on a predetermined pixel range of the pattern image 4, S306 is executed. In S306, the alignment processing device AP accumulates the pattern image signal group 5 in the non-signal generation direction (second direction, for example, the Y direction) to generate a first image signal (referred to as "pattern image signal 6"), which is a one-dimensional image signal in the signal generation direction.

Then, in S307, the alignment processing device AP determines whether signal generation has been completed for all signal generation directions (X direction and Y direction). If signal generation has not been completed for all signal generation directions, in S308, the alignment processing device AP changes the signal generation direction and repeats the above process (S302 to S306) until signal generation has been completed for all signal generation directions. As a result, one-dimensional signals for position measurement in the X direction and Y direction are finally generated. This generates a second image signal, which is a one-dimensional image signal obtained by integrating the image signals of multiple pixel columns in the second direction (Y direction) for which histogram extension processing has been performed in the first direction (X direction).

Then, as described in the first embodiment, the process proceeds to S107. In S107, the process determines the position of the mark based on the first image signal and the second image signal.

The accumulation of the one-dimensional signal group in the non-signal generating direction performed in S306 does not necessarily have to be performed after it is determined in S303 that the number of pixel columns has reached the preset number. For example, the signal generated by sequentially accumulating the pixel columns whose histograms have been expanded in S305 may be used as the final measurement signal.

<Embodiment of an article manufacturing method>
The article manufacturing method according to the embodiment of the present invention is suitable for manufacturing articles such as microdevices such as semiconductor devices and elements having fine structures. The article manufacturing method according to the present embodiment includes a step of forming a latent image pattern on a photosensitive agent applied to a substrate using the above-mentioned exposure apparatus (a step of exposing the substrate) and a step of developing the substrate on which the latent image pattern has been formed in the step. Furthermore, the manufacturing method includes other well-known steps (oxidation, film formation, deposition, doping, planarization, etching, resist stripping, dicing, bonding, packaging, etc.). The article manufacturing method according to the present embodiment is advantageous in at least one of the performance, quality, productivity, and production cost of the article compared to conventional methods.

Other Embodiments
The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) for implementing one or more of the functions.

The invention is not limited to the above-described embodiment, and various modifications and variations are possible without departing from the spirit and scope of the invention. Therefore, the following claims are appended to disclose the scope of the invention.

100: exposure device, W: substrate, R: original, WC: substrate chuck, WS: substrate stage, A: alignment detection system, IL: illumination optical system, PO: projection optical system, BS: beam splitter, LS: light source, AP: alignment processing device, CP: control processing device

Claims (10)

1. An alignment apparatus for aligning a substrate by detecting a mark formed on the substrate, comprising:
a stage for holding and moving the substrate;
an imaging unit that captures an image of the mark formed on the substrate held by the stage to obtain an image of the mark;
a processing unit for processing the image to determine the position of the mark,
The processing unit includes:
performing contrast enhancement processing on each of a plurality of first images obtained by imaging the mark with the imaging unit, thereby obtaining a second image having a coarser gradation than each of the plurality of first images;
determining the position of the mark based on a third image which is generated by integrating a plurality of the second images and has finer gradations than the second images;
An alignment device comprising: 2 . The alignment apparatus according to claim 1 , wherein the contrast enhancement process is a histogram expansion process that expands a luminance region in a histogram for each of the plurality of first images. The histogram extension process includes, for each of the plurality of first images,
Find the maximum and minimum pixel values,
determining a luminance conversion formula for converting the maximum pixel value to a value greater than the maximum pixel value and converting the minimum pixel value to a value smaller than the minimum pixel value;
3. The alignment apparatus according to claim 2, further comprising a process for converting a pixel value of each pixel in accordance with the luminance conversion formula. 2. The alignment apparatus according to claim 1, wherein the contrast enhancement processing is a histogram equalization processing for equalizing a histogram level for each of the plurality of first images. The alignment device according to claim 1, characterized in that the first image is obtained by capturing an image with the imaging unit while the stage is stopped. 2. The alignment device according to claim 1, wherein the second images are obtained by performing contrast enhancement processing on each of the first images obtained by imaging the mark a plurality of times with the imaging unit. 1. A method for determining a position of a mark formed on a substrate, comprising the steps of:
performing contrast enhancement processing on each of a plurality of first images obtained by capturing images of the mark on the substrate, to obtain a second image having a coarser gradation than each of the plurality of first images;
obtaining a third image having finer gradations than the second images, the third image being generated by integrating a plurality of the second images;
determining a position of the mark based on the third image;
The method according to claim 1, further comprising: A program for causing a computer to execute each step of the method according to claim 7. An alignment device according to any one of claims 1 to 6,
A lithography apparatus configured to transfer a pattern of an original onto a substrate held by a stage of the alignment apparatus. forming a pattern on a substrate using a lithographic apparatus according to claim 9;
a step of processing the substrate on which the pattern is formed, wherein the method for manufacturing an article is characterized by manufacturing an article from the processed substrate.

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