JP2006106597A - Mask for formation of three-dimensional optical element form - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve surface roughness caused by a domain boundary portion even under conditions that the domain boundary portion after quantization is resolved when fabricating a three-dimensional form into a photosensitive material by modulating transmittance. <P>SOLUTION: In a transmittance control type mask for formation of a three-dimensional optical element form to fabricate the three-dimensional optical element form of the photosensitive material by distribution of the film thickness according to the exposure light quantity in the photosensitive material after development, a plurality of mask patterns having shifted boundaries of domains on the mask quantized by the gradation levels of transmittance are prepared and are subjected to multiple exposure to form a three-dimensional form. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a process for producing a three-dimensional shape of a photosensitive material by changing the exposure amount using a substantially linear characteristic portion in which the remaining film thickness of the photosensitive material changes in accordance with the exposure amount.

  In general, a circuit pattern of a semiconductor element manufactured using a lithography technique is designed by a combination of an opening formed in a mask and a light shielding portion, and is transferred by irradiating a photosensitive material with exposure light transmitted through the mask. . Resist, which is a typical example of the photosensitive material, includes a positive type and a negative type, and is usually selected appropriately in view of the situation of each process. The circuit pattern generally does not consider the thickness direction.

  In recent years, a technique for forming a finer pattern by adjusting a partial exposure amount for the purpose of further miniaturization has been studied. A proposal has also been made to control the shape in the height direction by partially adjusting the exposure amount. For example, Patent Document 1 discloses a method of forming a three-dimensional shape in a photoresist. The method will be described below with reference to FIG.

  FIG. 6A shows a characteristic curve (photosensitive curve) of a positive photoresist. As shown in FIG. 6A, the relationship between the incident exposure energy and the residual resist ratio after development can be obtained by experimentally obtaining a characteristic curve of a positive photoresist in advance. As shown in FIG. 6 (b), a small area is considered as a minimum unit, and 9 pieces of 3 × 3 are considered as one lump. In FIG. 6B, 52 is a light shielding part and 51 is an opening. Among the nine, the ratio of the number of the light shielding portions 52 and the openings 51 is changed, and as shown in FIG. 6C, the region 53 including only the opening portions 51, the region 54 having one light shielding portion 52, and the light shielding portions 52. Are two regions 55, four light-shielding portions 52 are regions 56, five light-shielding portions 52 are regions 57, and regions 57 are formed of only the light-shielding portions 52. The opening density distribution, that is, the intensity distribution generated by the transmittance distribution is converted into a change in resist film thickness due to the sensitivity characteristics of the positive resist, as shown in FIG. Patent Document 1 proposes to form a three-dimensional shape in a positive resist using such a mask.

  In addition, the need for a three-dimensional shape to be formed is changing to a more difficult shape. For example, in a lens array having a partially bordered arc shape disclosed in Patent Document 2, there is a portion where the shape is discontinuous, and it is necessary to produce a shape that is opposite to the photosensitive material and exposure conditions such as a curved surface and a vertical sidewall. . For this reason, it has been found that there is a limit to the setting of exposure conditions for smoothing the curved surface, and the boundary of the quantized region on the mask is resolved even with a slight light amount difference. When the boundary of the quantization region of the mask is resolved, it becomes close to the shape on the quantized staircase, and considering the error from the design shape, it becomes a shape error that swings positively or negatively at the boundary of the quantization region . We call this quantization error. Although a finer gradation and a wider transmittance adjustment range are required for the mask, there is a limit to the mask manufacturing technique, and a solution by means other than the mask manufacturing technique is required.

  As an attempt to reduce the surface roughness of the curved surface, there is a method disclosed in Patent Document 3. In the first exposure, the mask is brought into close contact for exposure, and the edge of the pattern is transferred sharply. In the second exposure, the mask is removed from the photosensitive material and the exposure is performed with reduced resolution. Since the resolving power is reduced by the second exposure, a shape having a smooth curved surface can be transferred to the photosensitive material.

  In addition, there is a method disclosed in Patent Document 4 as a method for compensating for the lack of gradation of the mask. According to this method, exposure is performed a plurality of times by shifting the mask in the horizontal direction by an amount equal to or less than the width of the quantized region in total. As a result, the amount of exposure can be changed with the number of steps equal to or greater than the number of gradations of the mask.

  Another method is disclosed in Patent Document 5. According to this method, the light intensity distribution is generated in two stages by arranging two masks simultaneously on the optical path of the exposure light. In this method, a light amount pattern corresponding to the spherical lens shape is formed with the first mask, and a shape corresponding to the aspheric lens shape is formed by overlapping the light amount distribution corresponding to the aspheric amount with the second mask. ing.

Japanese Unexamined Patent Publication No. 63-289817 Japanese Patent Laid-Open No. 62-115718 JP 05-033164 A JP 2002-107942 A JP 2002-278079 A

  However, the following problems remain in the prior art.

  That is, in Patent Document 1, the change in transmittance is limited to nine groups, and there are too few steps to obtain a smooth curved surface. In addition, the area ratio is considered for 9 as a whole, but it is very difficult to change only the transmittance without resolving the aperture / shading part by the projection exposure method with the conventional mask design method. It is.

  In Patent Document 3, a smooth curved surface is obtained because the resolution is adjusted using defocus. However, a part of the boundary disclosed in Patent Document 2 is an arc-shaped lens array. If it has a sharp shape, it cannot be produced.

  In Patent Document 4, it is difficult to transfer and form a sharp shape because multiple exposure is performed while shifting the mask. In addition, since the lateral displacement pitch is basically the same between the skirt and the vicinity of the top, it is difficult to form a spherical lens surface in which the quantization region width changes. Furthermore, it is desirable to move the mask in one direction, and when the mask is moved two-dimensionally to form a spherical lens, a shape error that varies in the circumferential direction occurs. It is difficult.

  In Patent Document 5, two masks need to be simultaneously disposed on the optical path, and cannot be applied to an exposure apparatus using a general reduction optical system. Further, this method aims at a shape having a low spatial frequency and a small amplitude, and improvement of surface roughness having a high spatial frequency cannot be expected.

  Accordingly, the present invention solves the following problems that have been difficult in the prior art at the same time, and uses a reduction projection type exposure apparatus to form a three-dimensional shape without requiring a special modification, thereby achieving a sharp shape. The object is to improve the surface roughness on the curved surface due to the quantization error while simultaneously realizing the formation of.

  In order to achieve the above object, the invention described in claim 1 is a transmittance-controlled three-dimensional method for producing a three-dimensional optical element shape of a photosensitive material by a film thickness distribution after development of the photosensitive material according to the exposure amount. An optical element shape formation mask is characterized in that a plurality of mask patterns are prepared by shifting boundaries of regions on the mask quantized for each gradation of transmittance, and multiple exposure is performed to form a three-dimensional shape.

  According to a second aspect of the present invention, in the first aspect of the present invention, the shift amount of the region boundary on the quantized mask is a quantization point that is the midpoint of the sampling points when the prepared patterns are (2N-1) types. It is characterized by being shifted in both directions by 1 / (2-1) of the region width.

  According to a third aspect of the present invention, in the first aspect of the present invention, the shift amount of the region boundary on the quantized mask is the quantized region width which is the midpoint of the sampling points when the prepared patterns are (2N) types. It is characterized by being shifted by a width of 1 / (2N).

  According to a fourth aspect of the present invention, in the first aspect of the invention, the plurality of mask patterns in which the region boundaries on the quantized mask are shifted are formed on one mask.

  The invention described in claim 5 is characterized in that, in the invention described in claim 2 or 3, at least one kind of shifted new region boundary on the quantized mask is used in the element.

  According to the first aspect of the present invention, since the pattern in which the region boundary is shifted by the multiple exposure is exposed, the exposure amount step in each region boundary is reduced, and each position is shifted. The influence on the surface roughness is reduced even under exposure conditions with high capability.

  According to the invention described in claim 2, in addition to the invention described in claim 1, the number of divisions is an odd number, so that the position of the new region boundary can be easily placed on the basis of the mask formed by the conventional design procedure. Becomes easy.

  According to the invention described in claim 3, in addition to the invention described in claim 1, the number of times of multiple exposure becomes an even number, and when the shape and arrangement of the device to be produced are symmetrical, the consistency is obtained. Mask pattern can be provided.

  According to the invention described in claim 4, the invention described in claim 1 for performing exposure using a plurality of patterns can be implemented without increasing the number of masks, and a three-dimensional shape and an exposure method with reduced costs can be provided.

  According to the fifth aspect of the present invention, the effect of the present invention can be maximized by optimizing without unnecessarily increasing the mask data by changing the number by which the region boundary is shifted in partial portions. it can.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

<Embodiment 1>
1 and 2 are diagrams for explaining the results of the first embodiment of the present invention, and are the results of measurement with an interference type surface roughness meter.

  When experiments were repeated to achieve both a sharp shape and a smooth curved surface shape, the following findings were obtained. The experiment used an i-line stepper, and the resist used was AZ-P4000 series manufactured by Clariant Co., Ltd., whose main photosensitive wavelength is g-line.

  In the experiment, the focus was set near the resist surface from various experiments to form a sharp shape at the same time. FIG. 1 shows the result of exposure with a transmittance modulation mask quantized in this state using the conventional design method. The pattern is formed in a one-dimensional shape (cylindrical shape) to facilitate measurement. FIG. 1 is a result of measurement using an interference type surface roughness meter, and it can be seen that a number of vertical stripes, which are quantization errors, are running. Since the center of the measurement result is the center of the curved surface and has a concave shape, it can be seen that the interval of the quantization error boundary becomes narrower toward the periphery.

  Next, FIG. 2 shows a result obtained by sequentially superposing and exposing using three kinds of patterns. The pattern design shape, exposure, and other conditions are the same. Three masks are designed, and the exposure amount is 1/3 each. A total of three sheets, each of which is designed by shifting left and right around the quantization area boundary having the best approximation by the width of 1/3 of the quantization area width. As can be seen from FIG. 2, the unevenness (color change) running vertically due to the quantization error is reduced.

  The mask boundary used in this embodiment will be described with reference to FIGS.

  In both figures, only one half from the center of the cross section and the pattern of the one-dimensional shaped pattern is shown. In the present embodiment, in FIG. 3, the design shape 1 is sampled in order to design the mask pattern, and the midpoint of the sampling point 2 is defined as the region boundary 3. The transmittance of the mask is designed so that the region between the region boundaries 3 has the shape height of the sampling points.

  Further, as shown in FIG. 4, three types of patterns in which the region boundaries are shifted to the shift region a6 and the shift region b7 on both sides of the region boundary 3 were prepared. Here, the region boundary of the multiple exposure pattern is shifted on both sides around the region boundary. However, the procedure is not one, and the region boundary may be divided into 1/3 each on the side where the exposure amount is reduced in the created shape. good. Further, if each boundary position is designed more precisely in accordance with the production shape (more precisely, the required exposure amount), a result close to the target shape can be obtained.

  In the present embodiment, the three patterns in which the region boundaries are changed are arranged in the horizontal or vertical direction and the arrangement is repeated. Then, when exposing, one mask was shifted left and right at the element pitch, and three types of patterns were overlaid for exposure. By doing so, we succeeded in three types of exposure while limiting the number of masks to one. Further, there is a useless pattern that is not exposed as many times as necessary at the edge of the pattern, but only the width of the element pitch of the microlens array is wasted. The effective area of the mask could be used to the maximum.

  In addition, even if it is stored in one mask, the effective area is divided into, for example, four patterns, each having a pattern with different area boundaries, or divided into three by defining a dividing line in the horizontal direction, and one type is used during exposure. Only the exposure pattern may be extracted and sequentially exposed. Although the number of shots is increased as compared with the exposure procedure shown in this embodiment mode, a target shape can be manufactured.

<Embodiment 2>
Next, a second embodiment of the present invention will be described.

  In this embodiment, the number of divisions is an even number of four. Multiple exposure was performed on a pattern in which the region boundaries were evenly shifted on both sides around the originally designed region boundary, and a shape with reduced surface roughness was obtained. Further, in the present embodiment, the region boundaries are equally shifted on both sides, but may be finely divided into four on the side where the exposure amount is small. At that time, each region boundary position may be designed finely in accordance with the production shape instead of the equal division. This is because a shape close to a desired shape can be obtained by designing a stricter mask. It is important to note that if too detailed procedures are set, not only will mask design work be carried out, but the amount of data for mask production will become enormous, and processing may not be possible within a realistic range. It is. Therefore, as the processing, the amount of change in the height of the shape with respect to the change in the horizontal direction, that is, the design of a relatively coarse content where the inclination is steep, and the fine design in the portion where the inclination is loose, etc. You can use different design procedures.

  In the present embodiment, a lens array having a hexagonal outline is manufactured. The hexagonal lens has a honeycomb-shaped outline to increase the lens density. Similar to the first embodiment, patterning is possible even if patterns in which the boundaries of the regions are shifted in one direction are arranged and exposed by shifting in one direction. Here, since the size of the element was slightly larger, as shown in FIG. 5, four sets of four patterns were arranged as one set. In this case, all types of patterns can be exposed by shifting the exposure by one element in the horizontal direction and the vertical direction. The shift amount at this time is the element pitch shown as the shift amount in the figure. In addition, the effect of this method is that the number of elements that are wasted in the peripheral portion is reduced as compared with the case where they are simply arranged in one direction. With the lens array shape and pattern arrangement of the present embodiment, multiple exposure can be effectively performed by rotating the mask 180 degrees for exposure.

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

It is a figure for demonstrating Embodiment 1 of this invention, and is a figure which shows the surface roughness state at the time of producing by the conventional method. It is a figure for demonstrating Embodiment 1 of this invention, and is a figure which shows the state of the surface roughness at the time of producing by this invention. It is a figure explaining the procedure of the position setting of a region boundary. It is a figure explaining the procedure of the position setting of a region boundary. It is a figure for demonstrating pattern arrangement | positioning. It is a figure which shows the characteristic curve (photosensitive curve) of a positive type photoresist.

Explanation of symbols

1 Design Shape 2 Sampling Point 3 Area Boundary 4 Mask Pattern

Claims (5)

In the transmittance control type three-dimensional optical element shape forming mask for producing the three-dimensional optical element shape of the photosensitive material by the film thickness distribution after development of the photosensitive material according to the exposure amount,
A three-dimensional optical element shape forming mask characterized by preparing a plurality of mask patterns in which boundaries of regions on a mask quantized for each gradation of transmittance are shifted, and forming a three-dimensional shape by multiple exposure.   The shift amount of the region boundary on the quantized mask is shifted in both directions by 1 / (2-1) of the quantization region width which is the midpoint of the sampling point when the prepared patterns are (2N-1) types. The three-dimensional optical element shape forming mask according to claim 1.   The shift amount of the region boundary on the quantized mask is characterized in that when the prepared pattern is (2N) types, it is shifted by 1 / (2N) each of the quantization region width which is the midpoint of the sampling point. The three-dimensional optical element shape forming mask according to claim 1.   2. The three-dimensional optical element shape forming mask according to claim 1, wherein the plurality of mask patterns in which the region boundaries on the quantized mask are shifted are formed on one mask.   4. The three-dimensional optical element shape forming mask according to claim 2, wherein at least one type of shifted new region boundary on the quantized mask is used in the element.

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