JP2020042100A - Exposure method, exposure apparatus and method for manufacturing article - Google Patents

Abstract

To provide a technology for reducing exposure unevenness while maintaining productivity.SOLUTION: An exposure method is provided for an exposure apparatus that includes a projection optical system for projecting a mask pattern onto a substrate and scans and exposes the substrate, and the method includes: a step of obtaining information about variation in the optical characteristics of the projection optical system which occurs during scanning exposure; a step of determining a target exposure time as a target value of an exposure time per one spot on the substrate so as to reduce exposure unevenness caused by the variation; a step of adjusting exposure conditions so as to control an exposure time per one spot on the substrate to the determined target exposure time; and a step of scanning and exposing the substrate in accordance with the adjusted exposure conditions.SELECTED DRAWING: Figure 1

Description

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

  A display such as a liquid crystal panel or an organic EL panel is manufactured by patterning a transparent thin film electrode into a desired shape on a glass substrate using a photolithography technique. In the photolithography process, a mask (or reticle) on which a pattern is drawn in advance is irradiated with exposure light, and the pattern on the mask is projected onto a substrate such as a glass substrate coated with a photoresist via a projection optical system. An exposure apparatus is used. In the manufacture of displays, an exposure apparatus using a mirror projection system suitable for large-screen exposure is often used.

  In recent years, displays for smartphones and tablets have been required to have higher definition, and accordingly, exposure apparatuses have been required to have higher resolution performance and higher productivity (higher throughput) than before. In an exposure apparatus, a mask on which a circuit pattern to be exposed is drawn is placed on a mask stage, and the mask is irradiated with illumination light. In the case of a scanning exposure apparatus, exposure is performed while simultaneously scanning a mask stage and a substrate stage on which a substrate to be exposed is mounted. In order to ensure high productivity in a scanning exposure apparatus, it is necessary to perform exposure while operating a mask stage and a substrate stage at high speed. At this time, the drive of the mask stage or the substrate stage becomes a vibration source, and this vibration is transmitted to the structure of the exposure apparatus main body and optical components arranged in the projection optical system. Such vibrations periodically change the shape of the exposed resist pattern, causing exposure unevenness on the substrate. The exposure unevenness refers to unevenness in the intensity of light reflected or transmitted on the substrate, which is seen on the substrate after the exposure. Exposure unevenness is a phenomenon observed due to variations in the profile of the exposed resist pattern (resist width, taper angle, resist height after exposure, etc.) and variations in the position where the pattern is formed. Since a panel in which exposure unevenness is conspicuous is not preferable from the viewpoint of quality, it is necessary to take care to suppress vibration so as to minimize exposure unevenness during panel production.

  Japanese Patent Laying-Open No. 2015-87514 (Patent Document 1) discloses an exposure apparatus having a function of detecting whether or not exposure unevenness has occurred in an exposure result using past data accumulated in the apparatus. According to this, it is detected that the apparatus is in a state where exposure unevenness is likely to occur, and the operation of the apparatus is stopped when a diagnosis result of an item causing an exposure unevenness exceeds a threshold. This suppresses mass production of defective products.

JP 2015-87514 A

  However, as the definition of the panel becomes higher, the exposure pattern becomes finer, and the threshold value of the cause of the exposure unevenness has also become extremely severe. For this reason, even when relatively small vibrations occur in the apparatus, exposure unevenness is likely to occur, and the operation of the apparatus is frequently stopped, thereby reducing productivity.

  An object of the present invention is to provide, for example, a technique for reducing exposure unevenness while maintaining productivity.

  According to one aspect of the present invention, there is provided an exposure method in an exposure apparatus that includes a projection optical system that projects a pattern of a mask onto a substrate, and scans and exposes the substrate. A step of acquiring information on the characteristic variation, and a step of determining a target exposure time that is a target value of an exposure time per point on the substrate so as to reduce exposure unevenness caused by the variation; Adjusting the exposure conditions so that the exposure time per point becomes the determined target exposure time; and performing scanning exposure of the substrate according to the adjusted exposure conditions. A method is provided.

  According to the present invention, for example, a technique for reducing exposure unevenness while maintaining productivity is provided.

FIG. 1 is a diagram illustrating a configuration of an exposure apparatus according to an embodiment. FIG. 4 is a diagram illustrating an example of image vibration on a substrate surface. FIG. 3 is a diagram showing an influence of the vibration shown in FIG. 2 on a position deviation of an exposure pattern. FIG. 3 is a diagram showing an influence of the vibration shown in FIG. 2 on a line width of an exposure pattern. The figure which shows the example of the shape of the opening part of a slit. FIG. 4 is a diagram illustrating a relationship between an exposure time per point on a substrate and a variation in positional deviation of an exposure pattern. FIG. 9 is a diagram illustrating an example of an exposure result affected by vibration. 5 is a flowchart illustrating an exposure method according to the embodiment. 9 is a flowchart illustrating adjustment processing of the exposure apparatus according to the embodiment. 5 is a flowchart illustrating an exposure method according to the embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following embodiments merely show specific examples of implementation of the present invention, and the present invention is not limited to the following embodiments. In addition, not all combinations of features described in the following embodiments are necessarily essential for solving the problem of the present invention.

<First embodiment>
FIG. 1 is a diagram illustrating a configuration of an exposure apparatus according to the present embodiment. In this specification, directions are indicated in an XYZ coordinate system in which a horizontal plane is an XY plane. Generally, the substrate P is placed on the substrate stage 401 such that the surface thereof is parallel to a horizontal plane (XY plane). Therefore, hereinafter, directions orthogonal to each other in a plane along the surface of the substrate P are defined as an X axis and a Y axis, and a direction perpendicular to the X axis and the Y axis is defined as a Z axis.

  The illumination optical system 1 includes a light source 101, an ND filter 102, an optical integrator 103, a stop 104, a condenser lens 105, a slit 106, a lens 107, a mirror 108, and a lens 109. The light source 101 emits ultraviolet light such as a high-pressure mercury lamp. The ND filter 102 has a predetermined transmittance, and adjusts the intensity of light emitted from the light source 101. The optical integrator 103 is composed of, for example, a fly-eye lens. The fly-eye lens is composed of a group of a plurality of minute lenses, and a plurality of secondary light sources are formed near the light exit surface. The stop 104 is a stop for determining the overall shape of a set of secondary light sources formed by the optical integrator 103. The overall shape of the set of secondary light sources is called the illumination shape. The condenser lens 105 Koehler-illuminates the slit 106 with light from the optical integrator 103. The slit 106 shapes the light from the light source. The opening of the slit 106 is formed in a shape for irradiating the mask with a masking blade. The light passing through the slit 106 irradiates the mask M via the lens 107, the mirror 108, and the lens 109.

  The mask stage 201 holds the mask M and is movable in the Y-axis direction. The laser interferometer 202 measures the position of the mask stage 201.

  The projection optical system 3 projects the pattern drawn on the mask M onto a substrate P on which a photosensitive material has been applied. In one example, the projection optical system 3 can be an Offner type optical system. In the case of the Offner optical system, the mask M is irradiated with arc-shaped light to secure a good image area. Therefore, the shape of the light transmitting portion (opening) of the slit 106 and the irradiation shape of the exposure light reaching the substrate P are also arc shapes. The light transmitted through the mask M reaches the substrate P after being reflected by the trapezoidal mirror 301, the concave mirror 302, the convex mirror 303, the concave mirror 302, and the trapezoidal mirror 301 in this order. Thus, the pattern on the mask M is transferred onto the substrate P.

  In the present embodiment, an accelerometer 304 for measuring vibration is attached to the concave mirror 302. An accelerometer 305 for measuring vibration is also attached to the convex mirror 303. Accelerometers 304 and 305 measure the attitude change of concave mirror 302 and convex mirror 303, respectively. When the amount of change in attitude of the concave mirror 302 and the convex mirror 303 is measured by the accelerometers 304 and 305, the amount of displacement of the image of the mask pattern on the substrate surface can be calculated. By calculating the displacement information from the accelerometers 304 and 305, the amount of vibration of the image due to the vibration from the entire projection optical system 3 can be obtained. In the present embodiment, the accelerometers 304 and 305 are attached to the concave mirror 302 and the convex mirror 303, respectively, but the accelerometers may be installed on other optical components.

  The substrate stage 401 holds the substrate P and is movable at least in the X and Y directions. When the substrate stage 401 holds the substrate P and drives in the Y direction in synchronization with the mask stage 201, scanning exposure of the substrate P can be performed. When exposing a plurality of panels on the substrate P, the exposure is performed while shifting the substrate stage 401 in the X direction and the Y direction. The laser interferometer 402 measures the position of the substrate stage 401.

  The measurement results output from the laser interferometers 202 and 402 and the accelerometers 304 and 305 are sent to the control unit 5 that controls the operation of the entire exposure apparatus. The control unit 5 is configured by, for example, a computer including a CPU and a memory, and controls scanning exposure. The control unit 5 can calculate the time change of the deviation of the position of the image of the mask pattern on the substrate P using the measurement result of the relative position between the mask stage 201 and the substrate stage 401. The deviation of this position changes with time, and when viewed from one position on the substrate P, an optical image of a pattern exposed at that position is observed while vibrating during scanning exposure. The control unit 5 calculates the cycle of the vibration of the optical image. Further, the control unit 5 calculates the oscillation period of the concave mirror 302 and the convex mirror 303 using the measurement results of the accelerometers 304 and 305. The vibrations of the concave mirror 302 and the convex mirror 303 also contribute to the temporal vibration of the optical image at one point on the substrate P. The user can set various parameters of the exposure apparatus via the operation unit 6. The vibration of the exposure apparatus is measured in advance at the time of manufacture or the like, and can be input via the operation unit 6 after the apparatus is started. The input parameter values are transmitted to the control unit 5, and each unit in the exposure apparatus can be adjusted.

  The control unit 5 can obtain the period of the vibration of the optical image at the position of one point on the substrate P based on the input information. In addition, the control unit 5 sets the scanning speed of the mask stage 201 and the substrate stage 401, the light source 101, the ND filter 102, and the slit 106 in an appropriate state in order to perform exposure under conditions that are hardly affected by the vibration of the optical image. be able to.

  Next, the effect of the vibration of the optical image at one point on the substrate P on the exposure pattern will be described using a simple model. Hereinafter, image vibration on the substrate surface is referred to as image vibration.

  FIG. 2 is a diagram illustrating an example of an image vibration model. In FIG. 2, the horizontal axis represents time, and the vertical axis represents the deviation of the position of the image observed at a certain point on the substrate. This image vibration is obtained by measuring vibration of an optical component constituting the projection optical system 3 or vibration due to a synchronization control error between the mask stage 201 and the substrate stage 401, or both. In FIG. 2, the image vibration is a single vibration having a period T and an amplitude A. The influence of this image vibration on the exposure pattern was calculated by lithography simulation. The conditions at this time were a cycle T = 50 msec, an amplitude A = 0.3 μm, and the line width of the pattern to be exposed was set to 2.5 μm. Note that FIG. 2 shows data of five periods of the image vibration.

  FIG. 3 shows a result of calculating a deviation of a position where an exposure pattern is formed when the image vibration shown in FIG. 2 is input by using a lithography simulation. The horizontal axis indicates the time for five periods of image vibration. At the time of exposure, a certain finite time width is required to expose one point on the substrate. The width of the time is represented by (１ ／) × T (dotted line), (2/2) × T (dotted line), (3/2) × T (dotted line) with respect to the period T of the image vibration. (Point), (4/2) × T (solid line). The graph shows the positional deviation of the pattern exposed at that time. If the image vibration shown in FIG. 2 occurs at the time of scanning exposure, the deviation of the position of the exposure pattern changes along the profile of the image vibration. In the result of the exposure time per point of (1/2) × T and (3/2) × T, the position of the exposure pattern fluctuates at the same cycle as the cycle of the image vibration in FIG. On the other hand, the result of the exposure time per point (2/2) × T and (4/2) × T indicates that the position of the exposure pattern does not change (deviation 0) and that the exposure pattern The position has not changed. In FIG. 3, the results of (2/2) × T and (4/2) × T show that the deviation of the pattern position remains 0, so the graph is shown by a straight line with a deviation of 0. Does not appear as a rising or falling waveform.

  FIG. 4 shows the result of calculating the change in the line width of the exposure pattern when the image vibration shown in FIG. 2 is input using lithography simulation. Similar to FIG. 3, the horizontal axis represents the time for five periods of image oscillation, and the width of the exposure time per point is shifted by four levels. The result of the exposure time per point (1/2) × T and (3/2) × T indicates that the value of the line width of the exposure pattern fluctuates in half the period of the image vibration in FIG. In the results of the exposure time per point of (2/2) × T and (4/2) × T, the line width of the exposure pattern was unchanged. In the graph of FIG. 4, the results of (2/2) .times.T and (4/2) .times.T are unchanged while the pattern line width is kept at 2.5 .mu.m, and are exactly the same.

  From the results shown in FIGS. 3 and 4, even when the optical image of the mask pattern formed at the substrate position is vibrating, the length of time for exposing one point on the substrate is an integer of the period T of the image vibration. It was found that the exposure pattern position and line width did not change when the magnification was doubled. Even in a vibration in which a plurality of vibration modes are combined, if exposure is performed for an integral multiple of the period of the vibration, the profile of the exposure pattern does not fluctuate similarly to the result of the present embodiment. In addition, since these vibration sources each have a natural frequency, the frequency of the vibration that causes the exposure unevenness may be set to the value of the least common multiple of the cycle calculated from each of the natural frequencies.

  When the projection optical system is of the Offner type, the shape of the slit 106 is an arc as described above. This is because, when an image on the mask M is formed on the substrate P, a good image forming area becomes an arc shape, and exposure is performed using this good area. FIG. 5 shows an example of the opening (light irradiation area) of the slit 106. As shown in FIG. 5, the slit 106 has an arc-shaped opening in the scanning exposure direction. Here, assuming that the opening width of the slit 106 in the scanning exposure direction is W and the exposure time per point on the substrate is t, the scanning speed V of the substrate stage 401 is represented by the following equation.

V = W / t (Equation 1)
Note that the image of the slit 106 is formed at the position of the mask M at the same magnification as the slit 106. In the embodiment, the scanning speed V and / or the opening width W of the slit are adjusted so that the time t represented by the expression 1 is equal to an integral multiple of the period T of the image vibration.

  Also, from the results of FIGS. 3 and 4, it can be seen that as the exposure time per point on the substrate becomes longer, the variation in the deviation of the exposure pattern position and the variation in the line width deviation attenuate while oscillating. . FIG. 6 is a diagram showing this phenomenon, in which the horizontal axis shows the exposure time per point on the substrate, and the vertical axis shows the variation of the pattern position deviation. In the figure, an allowable value S indicated by a dashed line indicates a threshold value determined as an allowable value for the visibility of exposure unevenness. This allowable value may be obtained by an experiment or may be set based on another physical quantity. The target exposure time, which is the exposure time per one point on the substrate, is determined so that the variation falls below the allowable value, in other words, the variation falls within the allowable range. Here, for example, if the minimum time is determined as the target exposure time in the range of time in which the variation falls below the allowable value, the exposure apparatus can produce a device while maintaining the productivity.

  In FIG. 6, the vertical axis shows the variation of the pattern position deviation, and the allowable value of the exposure time per one point on the substrate is determined based on this. However, instead of the variation of the pattern position deviation, the variation of the line width deviation of the pattern may be used, or both of them may be used.

  The image fluctuation may be obtained by capturing an optical image transferred to the substrate that has been subjected to the scanning exposure, and processing an image obtained by the capturing. Hereinafter, description will be made with reference to FIG. FIG. 7 is a schematic view showing a result of exposing a region surrounded by a dashed line on the substrate P on which a photosensitive material such as a resist is applied by one scanning exposure. When the vibration that causes the periodic fluctuation of the optical image affects the exposure result, an exposure unevenness of an arc-shaped dark and light stripe pattern shown by a broken line is observed. For example, the control unit 5 processes the image of the exposure result obtained by the imaging, measures the pitch D of the striped pattern, and can determine the cycle T of the vibration based on the pitch D. Assuming that the scanning speed of the substrate stage is V, the cycle T of vibration is represented by the following equation.

T = D / V (Equation 2)
The cycle T of the vibration thus obtained may be displayed on a display unit or the like (not shown) of the operation unit 6.

  The exposure apparatus can adjust exposure conditions in accordance with, for example, a cycle T of vibration. The adjustment of the exposure condition can be performed, for example, by adjusting at least two of the illuminance of the exposure light, the scanning speed of the mask stage 201 and the substrate stage 401, and the width of the slit 106 in the scanning direction. Adjustment of the illuminance of the exposure light can be performed based on at least one of the output of the light source 101 and the transmittance of the ND filter 102.

  The exposure method according to the present embodiment will be described with reference to FIG. In S21, the control unit 5 acquires information on a change in the optical characteristics of the projection optical system that occurs during the scanning exposure. In the present embodiment, the control unit 5 acquires vibration information from each factor such as outputs from the laser interferometers 202 and 402 and the accelerometers 304 and 305. In S22, the control unit 5 calculates the period of the image vibration from each factor based on the acquired vibration information from each factor. In S23, the control unit 5 determines a cycle T resulting from combining the vibrations. In S24, the control unit 5 determines the exposure condition and adjusts it as necessary. In S24, the target exposure time, which is the target value of the exposure time per point on the substrate, is determined so as to reduce the exposure unevenness caused by the image vibration. Then, the exposure conditions are adjusted so that the exposure time per point on the substrate becomes the target exposure time. After this adjustment is completed, scanning exposure is performed in S25 according to the exposure conditions adjusted in S24, and the exposure process ends when exposure of a predetermined number of substrates is completed.

  FIG. 9 shows details of the exposure condition determination and adjustment processing in S24. In S11, the control unit 5 determines a target exposure time based on the image vibration period T determined in S23, and adjusts the exposure condition so that the exposure time per one point on the substrate becomes the target exposure time. I do. As a specific example, the control unit 5 determines the scanning speed of the mask stage 201 and the substrate stage 401 and the width of the slit 106 with respect to the scanning exposure direction. In S12, the control unit 5 determines whether the current illuminance is within an allowable range. If the illuminance is within the allowable range, the adjustment process ends. If the illuminance is out of the allowable range, the process proceeds to S13, and the control unit 5 determines whether the ND filter 102 needs to adjust the illuminance. If adjustment is necessary, the adjustment of the ND filter 102 is performed in S14. If the adjustment of the ND filter 102 is not necessary, the process proceeds to S16. After the adjustment of the ND filter 102 is completed in S14, in S15, the control unit 5 determines whether the current illuminance is within an allowable range. If the illuminance is within the allowable range, the adjustment ends. If the illuminance is not within the allowable range, the process proceeds to S16. In S16, the output of the light source is adjusted. Adjustment of the output of the light source can be performed, for example, by adjusting the voltage input to the light source. With this adjustment, the illuminance falls within the allowable range, and the adjustment of the exposure apparatus is completed.

  FIG. 10 is a flowchart showing a method for adjusting and exposing an exposure apparatus using an exposed substrate. In S31, as described with reference to FIG. 7, the control unit 5 measures the pitch D of the uneven exposure from the result of the exposure, and determines the cycle of the vibration based on the result. In step S32, the exposure condition is determined and adjusted, similarly to step S24 in FIG. After these adjustments are completed, exposure is started in S33, and the exposure processing ends when exposure of a predetermined number of substrates is completed.

<Embodiment of Article Manufacturing Method>
The article manufacturing method according to the embodiment of the present invention is suitable for manufacturing an article such as a micro device such as a semiconductor device or an element having a fine structure. In the article manufacturing method of the present embodiment, a step of forming a latent image pattern on the photosensitive agent applied to the substrate using the above-described exposure apparatus (a step of exposing the substrate) and a step of forming the latent image pattern in the step Developing the substrate. Further, such a manufacturing method includes other well-known steps (oxidation, film formation, vapor deposition, doping, planarization, etching, resist peeling, dicing, bonding, packaging, and the like). The article manufacturing method of the present embodiment is advantageous in at least one of the performance, quality, productivity, and production cost of the article as compared with the conventional method.

1: illumination optical system, 3: projection optical system, 5: control unit, 6: operation unit, 304, 305: accelerometer, 401: substrate stage, 402: laser interferometer, M: mask, P: substrate

Claims (11)

An exposure method in an exposure apparatus that includes a projection optical system that projects a pattern of a mask onto a substrate, and scans and exposes the substrate.
A step of acquiring information on fluctuations in the optical characteristics of the projection optical system that occur during scanning exposure,
Determining a target exposure time which is a target value of the exposure time per point on the substrate so as to reduce the exposure unevenness caused by the fluctuation;
Adjusting exposure conditions so that the exposure time per point on the substrate is the determined target exposure time;
Performing a scanning exposure of the substrate according to the adjusted exposure conditions,
An exposure method, comprising:   2. The exposure method according to claim 1, wherein the target exposure time is determined such that a variation in a deviation of a position of the pattern transferred onto the substrate is less than an allowable value. 3.   3. The exposure method according to claim 2, wherein the target exposure time is determined to be a minimum time in a time range in which the variation is less than the allowable value. 4.   2. The exposure method according to claim 1, wherein the target exposure time is determined such that a variation in a deviation of a line width of a pattern transferred onto the substrate is less than an allowable value. 3.   5. The exposure method according to claim 4, wherein the target exposure time is determined to be a minimum time in a time range in which the variation is less than the allowable value.   The exposure method according to claim 1, wherein the target exposure time is determined to be a value that is an integral multiple of a cycle of the fluctuation.   The fluctuation is obtained by measuring vibration of an optical component in the projection optical system, or vibration due to a synchronization control error between a mask stage holding the mask and a substrate stage holding the substrate, or both. The exposure method according to any one of claims 1 to 6, wherein the exposure method is performed.   The method according to claim 1, wherein the variation is obtained by capturing an optical image transferred to the substrate on which the scanning exposure has been performed, and processing an image obtained by the capturing. Exposure method according to item.   9. The method according to claim 1, wherein the adjustment of the exposure condition is performed by adjusting at least two of the illuminance of the exposure light, the scanning speed, and the width of the slit for shaping the light of the light source in the scanning direction. The exposure method according to claim 1. An exposure apparatus that performs scanning exposure of a substrate,
A projection optical system for projecting a pattern of a mask onto the substrate,
A control unit for controlling the scanning exposure,
The control unit includes:
Obtain information on the change in the optical characteristics of the projection optical system that occurs during scanning exposure,
Determine a target exposure time which is a target value of the exposure time per point on the substrate so as to reduce the exposure unevenness caused by the fluctuation,
An exposure apparatus wherein an exposure condition is adjusted such that an exposure time per one point on the substrate becomes the determined target exposure time. Exposing a substrate according to the exposure method according to any one of claims 1 to 9,
Developing the exposed substrate in the step,
And manufacturing an article from the developed substrate.

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