JP2005189371A - Gray scale mask, method for manufacturing optical device, method for manufacturing substrate and method for manufacturing gray scale mask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high accuracy gray scale mask having transmittance approximate to a designed value. <P>SOLUTION: The gray scale mask is produced by forming a fine pattern on a reticle, reducing and transferring the pattern onto a wafer whose surface is coated with a resist by exposure by using an exposure transfer apparatus, developing the resist and etching the wafer by using the remaining resist as a mask. The distance S between the fine patterns is controlled to be ≥0.3 λ/NA, wherein NA is the numerical aperture of the exposure apparatus and λ is the wavelength of the light used for exposure. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a gray scale mask used for manufacturing an optical element using optical lithography, a method for manufacturing an optical element using the gray scale mask, and a photo of a substrate surface using the gray scale mask. The present invention relates to a method for manufacturing a resist in a predetermined shape and a method for manufacturing the gray scale mask described above.

  Optical elements such as microlenses have been put into practical use mainly in the fields of digital cameras, optical communications, and MEMS, and the range of use has been increasing. They are also used as light source integrators for exposure apparatuses that use excimer lasers as light sources. Yes. An example of a conventional method for manufacturing a microlens is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-107209 (Patent Document 1). This is because the resist formed on the surface of the optical substrate is exposed to light using a gray scale mask (a mask having a change in light transmittance that can be regarded as analog), and the resist is developed. Form a three-dimensional resist pattern in the shape and use it as a microlens, or, as described above, etch the lens-shaped resist together with the optical substrate to form a lens-shaped resist pattern. It transfers to an optical base material and forms the micro lens which consists of an optical base material.

  An example is shown in FIG. A resist 12 is applied on a substrate 11 made of quartz (a). In this case, a positive type resist is used. Then, the resist 12 is irradiated with light through the gray scale mask 13 (b). In the figure, the hatched portion is a gray scale, and the light transmittance decreases toward the center of the hatched portion. The part which is not hatched is a transparent part.

  When the resist 12 exposed in this way is developed, a lot of the portion that has been strongly irradiated with light is removed, and a portion that has been weakly irradiated with the light has a small amount of removal, as shown in FIG. A microlens array pattern is formed on the resist 12.

  When the resist 12 and the substrate 11 are simultaneously dry-etched in such a state, the microlens pattern formed on the resist 12 is transferred to the substrate 11, and the microlens array is formed on the surface of the substrate 11 without the resist 12. Is formed. Due to the difference in etching rate between the resist 12 and the substrate 11, the microlens pattern formed on the resist 12 and the microlens pattern formed on the surface of the substrate 11 have different unevenness, but the microlens having desired unevenness The shape of the microlens pattern formed on the resist 12 may be determined in advance so that the above pattern is formed on the surface of the substrate 11. In the case of an optical element that leaves the resist 12 and has desired optical characteristics depending on its shape, the final product may be obtained in the step (c).

  According to such a method, only a microlens, a cylindrical lens, and various optical elements such as an array, a diffraction grating, and a Fresnel lens, and other purposes other than the optical element are used. A substrate having a pattern can be manufactured.

  As a gray scale mask used for such a purpose, it has a fine light transmission portion, and by changing the ratio of the light transmission portion to the light non-transmission portion, the gray scale mask is substantially changed in gray scale (analog transmission amount change). ) Is generally a gray scale mask. Such a fine light transmission portion pattern is manufactured by a method such as EB drawing, laser plotter drawing, projection exposure, or contact exposure.

  That is, a resist is applied to the surface of the transparent substrate on which the light shielding film is formed, and is exposed to a predetermined pattern shape by EB drawing, laser plotter drawing, projection exposure, contact exposure, etc., and then the resist is developed, and the remaining resist is developed. The light shielding film is etched as a mask to form openings having a predetermined pattern. Among these, the method by projection exposure using a stepper has an advantage that a gray scale mask can be manufactured in an extremely short time as compared with, for example, EB drawing, and efficiency is high.

  Moreover, the shape of a pattern can use circular, a square, a regular hexagon etc., and there is no restriction | limiting in particular in a shape. In the case of a circle, the diameter is about 0.3 to 20 μm.

JP 2003-107209 A

  Recently, it has been desired to increase the shape accuracy of optical elements manufactured using a gray scale mask. One condition for increasing the shape accuracy of the optical element is to increase the accuracy of the gray scale mask, that is, the light transmittance in each part of the manufactured gray scale mask (hereinafter referred to as “grayness”). Is required to be as designed. Therefore, by reducing the size of each fine pattern formed on the gray scale mask and increasing the dimensional accuracy, the resolution of the gray level can be improved and the gray level can be changed in a minute portion. It became necessary to do.

  As described above, in order to change the gray level, it is general to change the ratio of the light transmitting part and the light non-transmitting part per unit area of the fine pattern in each part of the gray scale mask. That is, when the absorption of light in the mask itself is ignored, the gray level in the case of having a fine pattern that allows all incident light in a predetermined portion to be 1, and the maximum light amount that the resist is not sensitive to the incident light amount in the predetermined portion ( If the gray level in the case of having a fine pattern that transmits a resist threshold light amount) is 0, the gray level in each portion of the gray scale mask is the area ratio of the fine pattern in that portion {(the fine pattern in the predetermined portion ) − (Area of fine pattern with gray degree of 0)} / (area of fine pattern with gray degree of 1)}, according to the gray degree required for the part, The area ratio of the fine pattern is determined, and the distribution or shape of the fine pattern is changed accordingly.

  However, it has been found that when a gray scale mask is manufactured based on such a design concept, the gray level in each portion of the completed gray scale mask may differ from the design value. This problem is particularly likely to occur when the fine pattern density is high.

  The present invention has been made in view of such circumstances. A highly accurate gray scale mask having a gray level close to a design value, a method of manufacturing an optical element using the gray scale mask, and further, the gray scale. It is an object of the present invention to provide a method for manufacturing a substrate having a predetermined shape on the surface using a mask.

  A first means for solving the above problem is a gray scale mask manufactured by a lithography method using an exposure apparatus and changing the distribution state of light transmitting portions of a plurality of fine patterns depending on the degree of gray scale. The minimum distance S between the fine patterns is 0.3λ / NA or more, where NA is the numerical aperture of the exposure apparatus and λ is the wavelength of light used for exposure. It is a gray scale mask (Claim 1).

  The gray scale mask targeted by this means is manufactured on the substrate by lithography, and a fine pattern is manufactured on the substrate, and the distribution state of the light transmitting portions of the plurality of fine patterns is changed depending on the degree of gray scale. It is a grayscale mask.

  The inventor investigated the cause that the gray level of the actually produced gray scale mask differs from the design value, especially when the density distribution of the fine pattern is high. As shown in FIG. 11, as a result of overlapping the image of the fine pattern of the gray scale mask formed on the image with blur and the image of the adjacent fine pattern (or the blur of the adjacent drawing area) It was found that the same part as that irradiated with the exposure light was formed in the part corresponding to. In FIG. 11, A and B are patterns to be originally formed, but a pattern is formed like C in a region where a pattern should not be originally formed, and A and B are connected. Therefore, the design pattern density and the actual pattern density are different, and the gray level is also different from the design value and the actual value.

  In order to actually obtain a predetermined gray level, when a gray scale mask is manufactured by exposure transfer using a reticle formed by separating a large number of circular opening patterns, a microscope of the pattern formed on the gray scale mask is used. A photograph is shown in FIG. As can be seen from FIG. 12, circular patterns that should originally be independent are connected. This is because, as described above, a place that should not be exposed due to the blurring at the time of exposure is exposed from the adjacent exposure amount area, and as a result, the amount of accumulated energy in that portion is blocked during resist development. This is considered to cause a reduction in the resist film thickness.

  Therefore, as a result of experiments, as will be shown later in the examples, the closest edge interval S between the fine patterns of the gray scale mask to be manufactured, the numerical aperture of the exposure apparatus NA, and the light used for exposure It has been found that if the wavelength is set to λ, if it is 0.3λ / NA or more, there is no deformation or connection between fine patterns in the gray scale mask.

  The second means for solving the above-mentioned problems uses the gray scale mask which is the first means, and exposes and transfers the pattern of the gray scale mask onto a resist-coated substrate, and then the resist. And developing a resist pattern having a shape corresponding to the pattern of the gray-scale mask by developing the optical element (Claim 2).

  The gray scale mask as the first means has no connection between fine patterns, and therefore the intensity distribution on the exposure surface is close to the design value. Therefore, by using such a gray scale mask, an optical element having optical characteristics close to the design value can be manufactured.

  A third means for solving the above-mentioned problems uses the gray scale mask which is the first means, exposes and transfers the pattern of the gray scale mask onto a resist-coated substrate, and then the resist. Developing a resist pattern having a shape corresponding to the pattern of the gray scale mask, and further etching the resist and the substrate simultaneously to transfer the resist pattern to the substrate. A method for manufacturing a substrate to be performed (claim 3).

  The gray scale mask as the first means has no deformation between fine patterns, and therefore the gray level is close to the design value. Therefore, by using such a gray scale mask, a substrate having a shape close to a design value in consideration of the selection ratio can be manufactured. It goes without saying that such a substrate is used as an optical element.

  A fourth means for solving the above problem is a method of manufacturing a gray scale mask manufactured by a lithography method using an exposure apparatus, wherein the numerical aperture of the exposure apparatus is NA, and the light source used for the exposure apparatus is When the wavelength is λ, an original plate having a pattern in which the minimum interval S of the opening pattern on the projection surface of the exposure apparatus is 0.3λ / NA or more is prepared, and a resist is applied on the substrate on which the light shielding film is formed. And an image of the original plate is projected onto the substrate coated with the resist by the exposure apparatus to obtain a gray scale mask having openings formed from the substrate coated with the resist. A mask manufacturing method (claim 4).

  When a gray scale mask is formed by lithography using an original plate such as a reticle, the aperture pattern on the projection surface depends on the numerical aperture NA of the exposure apparatus used for manufacturing the gray scale mask and the light source wavelength λ used. By designing the original plate so that the minimum dark space of 0.3λ / NA or more can be formed, the light shielding part of the opening and the opening can be formed almost as designed value, and the gray having a gray level close to the designed value A scale mask can be manufactured.

  As described above, according to the present invention, a highly accurate gray scale mask having a gray level close to a design value, a method of manufacturing an optical element using the gray scale mask, and a surface using the gray scale mask. In addition, it is possible to provide a method for manufacturing a substrate having a predetermined shape and a method for manufacturing a highly accurate gray scale mask.

  The exposure light intensity distribution at the edge portion of the pattern was measured on the assumption that the fine pattern was exposed and transferred onto the wafer using an exposure transfer device (stepper), and this wafer was used as a gray scale mask. An L / S pattern (pitch 40 μm, line and space) in which the amount of transmitted light changes stepwise, assuming that the wavelength λ of light used for exposure is 436 nm (g line) and the numerical aperture NA of the projection optical system of the exposure transfer apparatus is 0.45. FIG. 1 shows the light intensity distribution on the wafer surface when a reticle having a width of 20 μm) is used and exposure is performed at a reduction ratio of 1/5.

  In FIG. 1, the horizontal axis represents the wafer surface position (μm), and the vertical axis represents the relative intensity of light. The position where the horizontal axis is 0 is the position of the boundary between the line and the space. Since the wafer pattern should also be created with this part as a boundary, the threshold value that the resist should have is about 0.25. Further, as can be seen from FIG. 1, it can be seen that light oozes out to a region where a pattern is not to be formed and is 0 at a position of about 290 nm.

  It should be noted here that the degree of change in the amount of light in the region where the pattern should not be formed decreases as the distance from the position 0 increases. Therefore, in this case, if the boundary of the region where a certain pattern is to be formed is separated from the boundary of the region where the adjacent pattern is to be formed by about 290 nm or more, the total amount of light from the patterns on both sides can be obtained. It can be said that the threshold value of the resist is not exceeded.

  This is shown in FIG. In FIG. 2, 1 is a light intensity distribution curve in a boundary region of a certain pattern, and 2 is a light intensity distribution curve in a pattern adjacent to the pattern. Reference numeral 3 denotes a position where the light intensity distribution curve 1 intersects the threshold, and this position is the position of the designed pattern boundary, that is, the position of the boundary when the fine pattern is present alone. Reference numeral 4 denotes a position where the light intensity distribution curve 2 intersects the threshold value. This position is the position of the designed pattern boundary, that is, the position of the boundary formed on the wafer when one pattern exists alone. .

In this example, the positions 3 and 4 are separated by a distance from the point where the light intensity distribution curves 1 and 2 intersect with the threshold to a point that can be regarded as substantially zero. Between the position 3 and the position 4, the exposure is performed with the light amount corresponding to the sum of the light intensity distribution curve 1 and the light intensity distribution curve 2, and the light intensity distribution curves 1 and 2 have the characteristics as described above. Therefore, the total amount of light does not exceed the threshold value. Therefore, the resist remains after development between the positions 3 and 4, and the pattern is not connected.
Therefore, it can be seen from the above-mentioned data that if the position 3 and the position 4 are separated from each other by about 290 nm or more, the pattern is not deformed and the pattern is formed at the designed interval.

Similarly, when the same L / S reticle is used with the same exposure wavelength λ = 436 nm (g line) and the NA is changed to 0.53, 0.60, and 0.63, the light quantity distribution on the wafer surface is examined. 4 and FIG. From these figures, it can be seen that the light intensity distribution is zero at a position of about 250 nm when the NA is 0.53, about 220 nm when the NA is 0.60, and about 210 nm when the NA is 0.63.
From these results, in the case of L / S pattern, from the boundary where a single pattern is formed
0.3λ / NA
It is estimated that the light intensity distribution becomes 0 at a position separated by a distance.

  In order to confirm this relationship, the same data was obtained for NAs of 0.53, 0.60, and 0.63, assuming that the wavelength used for exposure transfer was 365 nm (i-line). The results are shown in FIGS. 6, 7, and 8, respectively. From these figures, it can be seen that the light intensity distribution is 0 at a position of about 210 nm when the NA is 0.53, about 180 nm when the NA is 0.60, and about 175 nm when the NA is 0.63.

From these data, in the case of L / S pattern, from the boundary where a single pattern is formed
0.3λ / NA
It was confirmed that the light intensity distribution was 0 at a position far away from it. Therefore, if the boundary of the region where a certain pattern is to be formed is separated by 0.3λ / NA or more from the boundary of the region where an adjacent pattern is to be formed for the reason described in FIG. It can be seen that when forming, the fine patterns formed on the mask do not have a connected shape, but are formed at intervals as designed, and a gray level close to the intended gray level is obtained.

  FIG. 9 shows a photograph of an example in which a circular pattern is created by exposure transfer using an i-line stepper (exposure wavelength 365 nm) with a numerical aperture of the projection optical system of 0.63. The interval between the circular patterns is 200 nm, and the diameter of the circular pattern is 550 nm. As can be seen from FIG. 9, each circular pattern is independent, and as shown in FIG. 11, the part corresponding to the light-shielding part in the middle of the originally independent pattern is the same as the exposure light is irradiated. Such a part is avoided.

  In the embodiment of the present invention, when manufacturing a gray scale mask, a fine pattern is formed on a reticle, and the pattern is subjected to reduced exposure on a wafer coated with a resist by an exposure transfer device, and then the resist is applied. The gray scale mask is manufactured by developing and etching the light shielding film using the remaining resist as a mask.

  Alternatively, a resist is coated on a quartz substrate on which a chromium film is formed, and is placed in an exposure transfer device. On the other hand, a reticle having a fine opening pattern is prepared, and the reticle pattern is transferred to a quartz substrate on which a chromium film is formed. Then, by developing the resist and etching the chromium film, a gray scale mask having a predetermined opening is formed.

  Although these methods themselves are not different from the conventional gray scale mask manufacturing method, in the embodiment of the present invention, the design value of the interval between fine patterns formed on the gray scale mask is set as described above. Thus, it is set to 0.3λ / NA or more. Therefore, for the reasons described above, a mask is obtained in which the patterns are not deformed and an intensity distribution close to the design value is obtained. Therefore, a gray scale mask having a gray level close to the design value is obtained.

  Since the method of forming an optical element and a substrate having a pattern formed on the surface using this gray scale mask is the same as the method described in the background art section, the description thereof is omitted.

  Even when a gray scale mask is manufactured using a laser plotter or an EB drawing apparatus, a desired high-precision strength can be obtained by setting the minimum interval between patterns so that each pattern does not deform. A gray scale mask having a distribution is obtained. The same applies to the gray scale mask manufactured by the contact exposure method.

It is a figure which shows the light intensity distribution in the pattern boundary when exposure of the pattern of L / S is performed using the g-line stepper whose NA of a projection optical system is 0.45. It is a figure for demonstrating the reason why the connection of a pattern does not generate | occur | produce. It is a figure which shows the light intensity distribution in the pattern boundary when performing exposure of the pattern of L / S using the g-line stepper whose NA of a projection optical system is 0.53. It is a figure which shows the light intensity distribution in the pattern boundary when the exposure of the pattern of L / S is performed using the g-line stepper whose NA of the projection optical system is 0.60. It is a figure which shows the light intensity distribution in the pattern boundary when exposure of the pattern of L / S is performed using the g-line stepper whose NA of the projection optical system is 0.63. It is a figure which shows the light intensity distribution in the pattern boundary when exposure of the pattern of L / S is performed using i line | wire stepper whose NA of a projection optical system is 0.53. It is a figure which shows light intensity distribution in the pattern boundary when exposure of the pattern of L / S is performed using the i line | wire stepper whose NA of a projection optical system is 0.60. It is a figure which shows the light intensity distribution in the pattern boundary when exposing the pattern of L / S using the i line | wire stepper whose NA of a projection optical system is 0.63. It is a figure which shows the photograph of the example which created the circular pattern using exposure transfer by the method of this invention using the i line | wire stepper whose NA of a projection optical system is 0.63. It is a figure which shows the example of the process of manufacturing a microlens using a gray scale mask. It is a figure which shows generation | occurrence | production of the connection of a pattern. It is a figure which shows the example of the microscope picture of the pattern actually formed in the gray scale mask.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light intensity distribution curve, 2 ... Light intensity distribution curve, 3 ... Position, 4 ... Position, 11 ... Substrate, 12 ... Resist, 13 ... Gray scale mask

Claims (4)

A gray scale mask manufactured by a lithography method using an exposure apparatus and changing a distribution state of light transmission portions of a plurality of fine patterns according to the degree of gray scale, wherein the minimum interval S between the fine patterns is A gray scale mask, wherein NA is a numerical aperture of the exposure apparatus and λ is a wavelength of light used for exposure, and is 0.3λ / NA or more. The grayscale mask according to claim 1 is used, and the pattern of the grayscale mask is exposed and transferred onto a resist-coated substrate, and then the resist is developed, so that the pattern of the grayscale mask is developed. A method for producing an optical element comprising a step of forming a resist pattern having a different shape. A shape corresponding to the pattern of the gray scale mask by using the gray scale mask according to claim 1 and exposing and transferring the pattern of the gray scale mask onto a substrate coated with a resist, and then developing the resist. Forming a resist pattern, and further etching the resist and the substrate simultaneously to transfer the resist pattern to the substrate. A method of manufacturing a gray scale mask manufactured by a lithography method using an exposure apparatus, wherein NA is a numerical aperture of the exposure apparatus and λ is a wavelength of a light source used for the exposure apparatus. An original plate having a pattern in which the minimum interval S between the opening patterns is 0.3λ / NA or more is prepared, a resist is applied on a substrate on which a light-shielding film is formed, and the resist is applied to the substrate. A method of manufacturing a gray scale mask, wherein an image of an original plate is projected by the exposure apparatus, and a gray scale mask having an opening formed is obtained from a substrate coated with the resist.

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