JP2002139824A - Distributed density mask and method for producing the same by multistage exposure method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively and easily produce a distributed density mask at a high production speed without requiring a special equipment. SOLUTION: A mask blank is divided into unit cells and light transmissive regions or light shielding regions of the respective unit cells are determined. The determined light transmissive regions or light shielding regions are disposed on each gird and necessary pattern forming frequency, focal depth and beam diameter are calculated by CAD(computer aided design) and converted into data. A sensitive material on the mask blank is multistage-patterned by prescribed frequency on the basis of the data under prescribed conditions (focal depth and beam diameter) and the mask blank is developed and rinsed to obtain a three-dimensional sensitive material pattern. The shape of the sensitive material pattern is transferred to a light shielding film by etching.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a density distribution mask (reticle) used when manufacturing an article having a three-dimensional surface shape, and a method of manufacturing such a density distribution mask. The density distribution mask manufactured by this method is particularly suitable for manufacturing an article having a fine three-dimensional structure surface shape, and applicable technical fields include, for example, an optical component manufacturing field, a micromachining field, and a wall-mounted TV. Examples include the display field, the liquid crystal display field, and the solar cell manufacturing field.

[0002]

2. Description of the Related Art A special surface shape represented by a spherical surface or an aspherical surface has been used for a refracting surface or a reflecting surface of an optical element. In recent years, in connection with liquid crystal display elements, liquid crystal projectors, and the like, special surface shapes have been required for microlenses and the like. Therefore, as a method of forming the refraction surface and the reflection surface without molding or polishing, a layer of a photoresist (a typical example of a photosensitive material) is formed on the surface of an optical substrate, and the photoresist layer is two-dimensionally formed. Exposure through a concentration distribution mask having a typical transmittance distribution, and developing the photoresist to obtain a convex or concave surface shape of the photoresist, followed by anisotropic etching of the photoresist and the optical substrate It is known that a desired three-dimensional refraction surface or reflection surface shape is obtained on the surface of the optical substrate by engraving and transferring the surface shape of the photoresist onto the optical substrate (Japanese Patent Application Laid-Open No. -23
No. 0159, and Japanese Patent Publication No. 8-504515).

[0003] There is a density distribution mask used to obtain a special surface shape of a three-dimensional structure such as a refraction surface or a reflection surface. A density distribution mask (gradation mask (GM)) having a rate distribution is used.

In the density distribution mask described in Japanese Patent Publication No. Hei 8-504515, in order to form a two-dimensional transmittance distribution pattern, the mask pattern is divided into unit cells called light transmission apertures. The opening dimension of each unit cell is
The light transmission amount or the light shielding amount is set according to the height of the corresponding position of the photoresist pattern to be formed. The light-shielding film pattern of the unit cell is composed of two types, a region where a light-shielding film is present and light transmittance is 0%, and a region where no light-shielding film is present and light transmittance is 100%. Are arranged in such a manner that a region where the light transmittance is 0% and a region where the light transmittance is 100% are brought together in one direction to form one lump. The minimum size of the light-shielding film pattern is an ultrafine pattern that is shorter than the wavelength of light used for exposure. In addition, a drawing method using electron beam (EB) irradiation is employed as a manufacturing method.

Japanese Patent Application Laid-Open No. Hei 7-230159 describes a method of manufacturing a density distribution mask by changing the amount of light transmitted through a unit cell by changing the amount of laser beam irradiation during writing in the unit cell. Have been.

[0006]

[Problems to be Solved by the Invention] JP-T 8-50451
The density distribution mask described in Japanese Patent Publication No. 5 has the following problem. A lot of time is required for EB drawing. That is, a great deal of labor and cost are required to manufacture the density distribution mask. Since ultra-fine drawing is required, a dedicated expensive drawing device is required. When the manufactured density distribution mask is used, a step is exposed on the photosensitive material between a region where the light-shielding film is present and a region where the light-shielding film is not present, so that a smooth shape is not obtained. Since the light-shielding film pattern is very fine, light at the time of reduced exposure is likely to cause diffraction, and an adjacent effect between unit cells is generated.
Therefore, much know-how accumulation is required.

The method of manufacturing a density distribution mask described in Japanese Patent Application Laid-Open No. Hei 7-230159 does not require a dedicated device, and is less expensive than the invention described in Japanese Patent Application Laid-Open No. 8-504515. It has advantages that it can be manufactured in a short time, a smooth shape can be manufactured, there is little adjacent effect, and no light diffraction occurs. However, this method requires a new program for modulating the laser power for each unit cell, and it is necessary to synchronize this program with the drawing shape program. Further, the drawing pattern shape is limited to a circular shape.

In order to solve the above-mentioned problems of the prior art, the present invention requires a density distribution mask having a density distribution in which the transmittance changes smoothly and a special device for providing such a density distribution mask. It is an object of the present invention to provide a manufacturing method that can be manufactured at low manufacturing cost at a low manufacturing cost and easily.

[0009]

The concentration distribution mask of the present invention is used in a process for forming a photosensitive material pattern having a three-dimensional structure on a substrate, and an area used for exposure is suitably used. It is divided without gaps by unit cells of various shapes and sizes, and at least some of the unit cells have a light transmission amount or a light shielding amount of a value corresponding to the height of the corresponding position of the photosensitive material pattern. Is provided with a light-shielding pattern. The light-shielding pattern may have a predetermined optical density by changing the light transmittance from the center of the unit cell to the periphery. A light-shielding pattern in which the light transmittance changes from the center of the unit cell toward the periphery can achieve an effect that it is easy to predict the effect of the adjacent effect of the adjacent unit cell and an effect that the light diffraction is small. it can.

It is preferable that the light-shielding pattern has a light-transmitting portion whose cross-sectional shape changes smoothly and the light transmittance changes continuously. When exposure is performed using a density distribution mask provided with such a light-shielding pattern, the photosensitive material has a smooth shape without steps. In addition, since the light-shielding film pattern does not need to be ultra-fine at about the exposure wavelength, light at the time of reduced exposure does not cause diffraction, and the adjacent effect between unit cells is small.

The light-shielding pattern may be such that the unit cell is divided into grids, and the light transmittance in the grid changes discontinuously, so that the entire unit cell has a predetermined light transmission amount. . At that time, the light transmittance is 0% and 100%
Arrange a grid with light transmittance located in the middle of
It is preferable that a halftone can be obtained by changing the light transmittance discontinuously and controlling the total light transmission amount of the unit cell.

A feature of the density distribution mask of the present invention resides in that the amount of transmitted light is entirely controlled in order to form a desired shape. Therefore, the light-shielding pattern may change continuously or may change discontinuously. Since the size of the grid can be reduced, it is possible to arrange a grid having an intermediate transmittance discontinuously (for example, randomly) as an arrangement method. Also, grids having the same transmittance can be arranged as a block. When this method is advanced, a continuous density distribution arrangement is obtained. The grid portion indicates a portion on a scanning line by a laser beam or an electron beam (EB). One unit of the grid is the product of the distances scanned within the minimum time for turning on / off the diameter of the laser or electron beam. For example, a beam diameter of 0.
When the scanning distance is 2 μm and the ON / OFF scanning distance is 0.2 μm, the unit grid is 0.2 μm × 0.2 μm.

The method of manufacturing the concentration distribution mask of the present invention is not limited to the concentration distribution mask described above, but may be any method used for forming a photosensitive material pattern having a three-dimensional structure on a substrate. set to target. In the present invention, a light-shielding film is formed on a transparent substrate, and a mask blank in which a photosensitive material film is further formed thereon is prepared, and drawing of the mask blank on the photosensitive material is performed in a plurality of drawing steps over the entire surface. Divided, according to the light transmission distribution and the sensitivity characteristics of the photosensitive material of the mask blanks, which were determined based on the three-dimensional structure design value of the photosensitive material pattern to be formed,
A density distribution mask is manufactured by a multi-stage exposure method in which the number of times of writing is set for each unit cell.

More specifically, a desired three-dimensional structure is separately designed. Based on this design, a density distribution mask is manufactured. Specifically, according to the sensitivity characteristics of the photosensitive material on the mask blank and the light transmission amount distribution of the unit cell according to the desired shape design, the number of times of writing with a laser or an electron beam directly irradiating the photosensitive material is multi-stepped. Set to.
The important thing here is "set the number of drawing times in multiple steps"
Means that "a laser or an electron beam that scans a unit cell of interest passes a plurality of times. In other words, even though setting the number of times of drawing, it means simply overwriting, so a special operation Does not require.

The number of times (frequency) of multiple writing varies depending on the type of photosensitive material. For example, in the case of a positive resist, since the resist in the drawing portion is removed by development, the grid portion where the light transmission amount is desired to be increased is increased. Exposure. In each writing, the entire surface is irradiated by scanning the mask blanks with a laser beam or an electron beam. As a matter of course, in the case of a negative resist, many light-shielded grid portions are exposed. This control is performed for each grid.
The control is performed by “drawing count” and “drawing ON / OFF”. Controlling with “drawing count” and “drawing ON / OFF” seems to require a lot of labor, but low power enables high-speed beam scanning.
N and OFF can be electrically controlled with a simple program and can be electrically controlled with high precision, the focal position can be easily set electrically (depth change), and the beam diameter at the time of irradiation can be changed electrically. This control is very simple because it can be easily changed, and drawing can be performed at high speed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, the method of manufacturing a concentration distribution mask according to the present invention includes the following steps. (A) Step of dividing mask blanks into unit cells (step S1). That is, from the desired three-dimensional shape,
The mask blanks are divided into grids, and the two-dimensional light intensity distribution pattern of the density distribution mask to be obtained is arranged and designed in a grid.

(B) A step of determining a light transmitting region or a light shielding region of each unit cell based on a "sensitivity curve" formulated from the processing process conditions and the sensitivity of the photosensitive material (step S2). (C) CAD (Computer Aided Design) by arranging the light transmission area or light shielding area determined above on “each grid”
Calculating the required number of times of writing, the depth of focus, and the beam diameter in step (step S3).

(D) Based on the data of step (C), the photosensitive material on the mask blank is drawn a large number (multi-steps) a predetermined number of times (multi-step) under predetermined conditions (depth of focus, beam diameter). (The number of times of drawing is changed by the method) (step S4). This step is shown in FIG.
(A) to (d) are drawn in multiple stages. Here, as an example, a case where drawing is performed in four times is shown, and by drawing a necessary number of times out of the four times, the light transmission amount of the unit cell is determined. The figure shown as (A) at the top is a drawing pattern when all four of these are drawn.

In each drawing, a plurality of light beams or electron beams are simultaneously or sequentially scanned along a scanning line indicated by an arrow in the upper right of FIG.
N, OFF ". The drawing area is set to be different each time.

The light transmittance change in the unit cell may “change from the center to the periphery” or “divide the unit cell into a grid, and the light transmittance changes discontinuously in the grid”. In some cases. Light transmittance is 0 on the grid
A “portion having an intermediate transmittance” indicating an intermediate value between% and 100% can be arranged. That is, 0% and 100%
Light transmittance showing an intermediate value of, for example, 30%, 50%, 7
A portion having an intermediate transmittance such as 0% can be arranged.

Since the size of the grid can be reduced, a grid having an intermediate transmittance can be arranged discontinuously (for example, randomly) as an arrangement method.
Also, grids having the same transmittance can be arranged as a block. When this method is advanced, a continuous density distribution arrangement is obtained. In this case, since the intermediate gradation can be made very fine, the unit cell size can be drastically reduced. Therefore, a gradation can be easily formed even in a shape in which a desired shape changes rapidly, that is, a shape having a steep gradient. The random arrangement has an advantage that the amount of light wrap around with adjacent cells can be averaged.

FIG. 5 shows an example in which a "portion having an intermediate transmittance" having a light transmittance between 0% and 100% is arranged on the grid. Here, a unit cell having a side of 1 μm is divided into 5 × 5 = 25 cells having a side of 0.2 μm. For example,
When five levels of light transmittance portions of white, black, 30%, 50%, and 70% are arranged, the gradation cannot be obtained when all white or all black are used. is there. Therefore, theoretically, 25 × 4 = 100 gradations. That is,
In an n-level density change, there are n-1 gradations. Further, the gradation varies depending on the division number (grid number) of the unit cell. In the above example, the number of grids × (n−1) = 25 × 4 = 100
It is. Table 1 below shows the relationship between grid light transmittance and gradation.
It was set as follows.

FIG. 5 shows a light transmittance arrangement of (A) a unit cell of 30/100 gradation and (B) a unit cell of 60/100 gradation. (C) is 0/100 gradation, 30/10
FIG. 5D shows an example in which the 0 gradation and the 60/100 gradation are combined, and the number of gradations of each grid is indicated by a numerical value. The example in FIG. 5 is a case where a random number is generated to form a light transmission density distribution at each grid address.

(E) A step of developing and rinsing the mask blanks drawn in step (D) to obtain a three-dimensional photosensitive material pattern (step S5). The cross-sectional shape of the photosensitive material pattern obtained in this step is conceptually as shown in FIG. 3A, but the cross-sectional shape of the photosensitive material pattern after the actual development is as shown in FIG. The film has a continuous film thickness distribution. In FIG. 3, reference numeral 12 denotes a mask blank material substrate, and reference numeral 14 denotes a light shielding film (for example, Cr
16a is a conceptual sectional view of a patterned photosensitive material, and 16 is a sectional view of a photosensitive material pattern after development.

(F) Thereafter, a step of transferring the photosensitive material pattern shape to the light shielding film 14 by dry etching or wet etching (step S6). The cross-sectional shape of the light-shielding film pattern 14 obtained in this step is shown in FIG.
It has a continuous film thickness distribution as shown in (3).

To manufacture an article having a three-dimensional structure using the obtained density distribution mask, the density distribution mask is used,
A step of reducing exposure on a substrate coated with a photosensitive material with a reduction optical exposure machine, a step of developing and rinsing the exposed photosensitive material to form a photosensitive material pattern of a three-dimensional structure, It comprises a step of transferring the pattern to the substrate by a dry etching method using the photosensitive material pattern as a mask. In the above-described reduction exposure step, it is effective to perform defocusing (focal defocusing) in a state where the focus deviates from the surface of the photosensitive material layer during exposure.

When the present invention is compared with the concept of the unit cell in the density distribution mask described in Japanese Patent Application Laid-Open No. 8-504515 (reference), the optical density (optical density: OD) of the exposure light passing through the unit cell is compared. Values), the number of writing times, irradiation power, photosensitive material layer thickness, light-shielding film (for example, Cr film) thickness, and dry etching selectivity are designed to be the same. That is, in the method of the reference, the amount of light transmission is digitally changed by a light-shielding film having a light transmittance of 0% and 100% as shown in the diagram on the left side of FIG.
In the present invention, the light transmission amount is continuous as shown in the diagram on the right side of FIG. 4 (in the figure, the light transmission amount is shown in a stepwise manner, but as shown in FIG. 3, the film thickness becomes continuous due to development). Is changing. This continuous change in the amount of light transmission is realized by changing the cross-sectional shape (thickness distribution of the photosensitive material) of the photosensitive material after drawing according to the number of times of drawing, irradiation energy, and sensitivity of the photosensitive material at the time of drawing. It was done.
In FIG. 4, the upper side is a plan view of the unit cell, and the lower side is a cross-sectional view.

The light transmittance change in the unit cell may “change from the center to the periphery” as in the example of FIG. 3, or “unit cell is divided into grids” as shown in FIG. However, the light transmittance changes discontinuously in the grid. "

The change in the thickness of the photosensitive material layer is transferred to a light-shielding film (for example, a Cr film) thereunder by dry etching. In this step, the change in the exposure condition appears as a change in the thickness difference of the light-shielding film, that is, a change in the light transmission amount.

The number of times of drawing and the irradiation energy are determined by a separately prepared simulation. That is, the relationship between the light-shielding film thickness and the amount of light transmission is graphed and expressed in advance by a mathematical formula. Then, the optical density of each unit cell is determined so that the set of the light transmission amounts (OD) of the unit cells represents a desired shape, and then the distribution of the light transmission amount from the center is set so as to have the optical density. Set. As described above, when the light transmission amount is set from the center of the unit cell, a light transmission amount distribution that continuously changes from the center can be manufactured. Further, a light transmission amount distribution that changes discontinuously can be manufactured.
In an arrangement of grids having intermediate light transmittances, a random arrangement can be used in a discontinuous light transmission amount distribution, or a grid can be arranged so as to form a block and a partially continuous arrangement. When it changes in one direction from the center or the periphery, it is a continuous change.

As described above, the biggest drawbacks of the reference method are that the production time is long, the cost is high, an adjacent effect (light wraparound) occurs, and the pattern arrangement direction (where the light transmitting portion is arranged even in the same pattern). : The right shape or the left shape is different even if the shape is the same), and the diffraction of light is large, and it is difficult to predict the amount of diffraction. According to the manufacturing method of the present invention, it is possible to manufacture a mask having a continuously changing density distribution at low cost, easily, at a high manufacturing speed without requiring a special device.

[0032]

(Example) (Shape and arrangement in unit cell, and shape and arrangement of "light transmission" and "light-shielding" grids) Shape and arrangement in unit cell
The shape and arrangement of the “light transmission” and “light shielding” grids will be described. The following example shows a typical example, and the dimensions of the unit cell, the dimensions of the grid, the position and the size of the base point, etc. should be designed in accordance with a desired shape. It is not limited to the example. That is, since the number of gradations is determined by the dimensions of each unit cell and the grid, these dimensions are determined by the target shape and the target gradation.

FIG. 6 shows an example in which a circular pattern that transmits light is formed at the center of a polygonal unit cell as a typical example of changing the unit cell shape. The polygonal shape is determined by “a method of covering a polygonal mesh from above when a desired shape is viewed from above”. The “most effective polygon” that expresses the density distribution mask characteristic according to a desired shape, that is, for example, when a gentle curved surface continues, or when a discontinuous surface is formed, depending on the amount of change in gradation. And the "combination", the optimal shape can be determined. Similarly, the size of the unit cell is also determined by how fine a necessary gradation for a desired shape is obtained. That is, when many gradations are required in a short distance, it is desirable to select a unit cell having a relatively small size and to reduce the grid size (which can be easily changed by changing the beam diameter) as much as possible.

FIG. 7 shows an example of a unit cell arrangement of a density distribution mask of MLA (microlens array). Here, an example of a combination pattern of unit cells arranged at the center is shown. (A) shows an example of a combination pattern of unit cells arranged in a central portion, and (A) shows an example of a combination pattern of unit cells arranged in a peripheral portion. In each case, the unit cell is indicated by a solid line, and the dashed arrow indicates that the unit cell is also arranged in that direction.

Since (a) is arranged near the center of the MLA, the desired shape is a gentle curved shape. Therefore, the number of gradations is not so required. Therefore, the unit cells are composed of relatively large unit cells, and the unit cells are arranged radially. Since (a) is arranged in the peripheral portion, the desired shape is a curved surface shape that changes rapidly. Therefore, the number of gradations needs to be large. Therefore, as the four corners of the MLA are approached, it is necessary to form a unit cell having a smaller size and reduce the dot size. Also, the shape of the unit cell is not limited to square,
Triangular ones are also arranged, and by changing the positions of the dots in the unit cell, it is easy to cope with the adjacent effect of the light transmission amount.

FIG. 8 shows the difference in the position of the initial pattern, which is the starting point of the increase or decrease of the light transmitting area or light blocking area in a typical unit cell, and the method of changing the light transmission or light blocking quantity. . In each case, the outermost square represents a unit cell, and the inner square represents a light transmitting area or a light shielding area, respectively. Here, an arrangement having a starting point at the center of the unit cell is shown. (A) shows that the starting point is located at the center of the unit cell, and (B) shows that the starting point is located at one of the four corners.

FIG. 9 shows an example in which the number of openings (portions without Cr) that transmit light is increased. Although not particularly described, the same applies to the case where the light transmission area is reduced. FIG. 9A shows an example of a method of increasing the area spirally from the center. In this example, a certain unit cell N
5 shows a representative example of a method of increasing dots from o. In addition, a method of increasing or decreasing one representative dot at a time is shown. Therefore, the dimensions and dot dimensions of the initial quadrangular shape arranged at the center of the dots shown here are model-like, and are not limited to squares in the present invention, and may be polygons such as rectangles and triangles. .
Also, it goes without saying that a circular shape including an elliptical shape may be used. FIG. 9A shows an example in which the unit cell is a regular hexagon. In this case, the dot indicated by the hatched portion is a circle, and the transmission amount or the light shielding amount changes by changing the size of the dot.

Although not shown in the figure, the laser beam diameter and the electron beam diameter at the time of writing may be various values, such as a value unique to the device or a changeable value. But it can be changed. In the case of laser, it can be changed by changing the applied current value or aperture, and in the case of electron beam drawing, it can be changed by changing the acceleration voltage. By utilizing this, the optimum beam diameter is determined from the desired shape dimensions, accuracy, number of gradations, and the like. Basically, the smaller the beam diameter, the better. However, the thinner the beam, the longer it takes to draw.

The focal depth at the time of writing has a deep relationship with the beam diameter and the sectional shape. Changing the focal depth is not so important when the beam diameter is large, but becomes important when the beam diameter is small. By changing the depth of focus, the cross-sectional shape can be made smooth. The change of the focal depth is input data at the time of input, such as a cross-sectional shape and a sensitivity curve, and is determined at the time of design.

(Design of Density Distribution Mask) An example of a minute pitch MLA in which the distance between adjacent microlenses is made as close as possible to zero is shown. In the MLA for liquid crystal projectors,
The pixel size for 9 ″ -XGA is 18 μm × 18 μm. In this MLA, 1 μm each on both sides of the lens.
17μm × 17μ
m microlens area, and M
The LA area is 17 × 17/18 × 18 = 289/324.
= 0.892, and even if all the light can be effectively collected by the MLA, the light collection efficiency is only 89%. That is, it is important to reduce the area of the non-formed portion of the MLA to improve the light use efficiency.

Specifically, when a 1/5 (reduced) stepper is used, the actually manufactured density distribution mask reticle pattern dimension is 90 μm × 90 μm. This one
MLA are divided into 3.0 μm unit cells, and the height × width = 3
It is divided into 0 × 30 (pieces) = 900 (pieces) unit cells.

Next, in the central 2 × 2 unit cell (density distribution mask: 6 μm × 6 μm on the density distribution mask, 1.2 μm × 1.2 μm in the actual pattern), cell No. 1 (all chromium remaining) ). Cell No. 80 (no chrome remaining portion) is arranged at the four corners of the lens. The “opening area” corresponding to each “gradation” is made to correspond to the cells of No. 1 to No. 80 during this time. This relationship is obtained from the exposure process and the resist sensitivity curve. Of course, it is necessary to grasp the sensitivity curve each time the resist material or process is different. In this way,
MLA density distribution mask Creates CAD data of the density distribution mask. In the present embodiment, a CAD program was manufactured using an equation based on the relationship between the sensitivity curve, the Cr film thickness, and the light transmittance.

(Production of Concentration Distribution Mask) The CAD data created as described above was irradiated with laser light using a laser light irradiation apparatus (manufactured by Ricoh Optical Co., Ltd.) shown in FIG. . In this laser beam irradiation, an optimal beam shape can be determined according to a desired shape, and a polygonal shape, a circular shape, or the like can be shaped by an aperture. The laser power may be changed by changing the current value supplied to the laser or by inserting a neutral density filter on the light emission side.

The laser beam irradiation device shown in FIG. 10 includes a laser beam oscillator 1, a beam splitter 2 for dividing the laser beam from the laser beam oscillator 1 into a plurality of laser beams, a mirror 3 for bending the optical path of the laser beam, and a mirror. 3
The optical modulator 4 modulates the laser light bent by the optical modulator 4. The optical modulator 4 controls the optical modulator 4 by a signal from the data bus to control ON / OFF of each laser light. A light deflector 6 for deflecting the laser light, an objective lens 7 for condensing the laser light on the resist material layer, and a mask blank placed thereon in the X direction and Y direction.
It is composed of main components such as an XY stage 8 that moves in the direction, and a control device 9 that controls the operation of the optical deflector 6 and the operation of the XY stage 8.

This laser beam irradiation apparatus controls the operation of the XY stage 8 according to the design data, and controls the ON / OFF and deflection of each laser beam so that a desired mask is formed on the resist material layer of the mask blank. Draw a pattern. That is, a laser beam is radiated to the resist material layer by the laser beam irradiating device to two-dimensionally form a light transmitting region or a light shielding region in each unit cell so as to have a desired transmittance distribution. Further, a substrate surface height detector (AF function) is attached, and the focal position is changed by slightly displacing the AF surface from the AF surface.

In this embodiment, the diameter of the laser beam is 0.
2 μm, alignment accuracy 0.05 μm, focal position accuracy 0.5
The measurement was performed at 1 μm. The laser power at the time of drawing is not changed little by little, and the entire surface is exposed once with a low exposure power of about 1/4 power, and then the necessary parts are overlapped twice, three times, and four times according to the design. Exposure (multi-stage drawing).
Thereby, the energy control at the time of exposure and the depth of the photosensitive material are changed. The unit cell shape and the grid shape may be appropriately selected depending on the intended product.

The CAD data created as described above is installed in the laser beam irradiation apparatus shown in FIG. 10, and while controlling the ON / OFF of the XY stage and the laser beam, the beam irradiation position and the number of times of drawing, The mask blanks were exposed by a predetermined method. Then, development and rinsing were performed by a predetermined method to pattern the resist material layer. Thereafter, the Cr film was patterned by dry etching. By controlling the number of times of beam writing using a laser beam writing method, higher reproducibility than the electron beam writing method can be obtained. If the drawing area is circular,
Laser beam writing method has a writing area diameter of 0.2 μm
In the above case, very high reproducibility can be obtained. When the diameter of the drawing area is smaller than 0.2 μm, the reproducibility deteriorates. However, in the electron beam drawing method, when the dimension of the drawing area is smaller than 0.5 μm, the reproducibility deteriorates. Is excellent. However, in the present invention, it can be realized by laser or electron beam drawing.

The prediction of the "adjacent effect" depends on the shape of the unit cell and the method of changing the density. When the unit cell shape is a square or a rectangle, it can be accurately drawn by circular dots, so that the adjacent effect can be predicted by calculation. In the following specific example, a CAD program was created using a circular dot shape (a method of increasing the laser beam irradiation portion concentrically from the center). In this manner, a density distribution mask having a target opening size and a density distribution was manufactured.

(Specific Example of Concentration Distribution Mask Production) Fabrication of MLA for Liquid Crystal: Concentration Distribution Mask In producing a concentration distribution mask, a positive resist material TGMR-950BE (Tokyo Ohka Co., Ltd.) was used as a resist material as a photosensitive material. Co., Ltd.) was used. The density distribution mask was formed of unit cells divided into squares, and the amount of light transmission or light shielding in each unit cell was controlled. Of course, an optimum unit cell may be determined according to a desired shape and manufactured with optimum dots. Here, for the sake of simplicity, the description will be made using a square. As a method of controlling the amount of light transmission, there is a method of combining the control of the Cr opening area and the control of the Cr film thickness. Here, the following method was adopted.

The “unit cell pattern N” prepared separately
o. Relationship between the thickness of the photosensitive material and the thickness of the removed photosensitive material (may be the remaining thickness) "," Relationship between the Cr film thickness and the amount of light transmission "," Number of drawing times and the removed thickness of the photosensitive material (may be the remaining thickness) " , "Optical density and Cr pattern", "optical density and Cr film thickness distribution", etc., and design a density distribution mask unit cell arrangement for manufacturing a desired shape by a design simulator.

To produce a concentration distribution mask, a Cr film having a thickness of, for example, 150 nm is formed on a transparent glass substrate.
The above resist material is applied thereon. The resist material was irradiated with laser light using the laser light irradiation apparatus shown in FIG. 10 to perform drawing. Thereafter, a mask pattern was formed on the resist material layer through development and rinsing, and the Cr film was dry-etched using the resist pattern as an etching mask, thereby patterning the Cr film to produce a concentration distribution mask.

The completed density distribution mask is shown in FIG.
As shown in (3), the unit cells in which the light transmittance changes continuously are arranged on the entire surface and the density distribution as a whole is obtained, or as shown in FIG. 5, the change in the light transmittance of the grid is a random arrangement. The unit cells are arranged on the entire surface and have a concentration distribution as a whole.

When exposure is performed using such a density distribution mask, as shown in FIG. 11, the light intensity distribution of the transmitted light has a shape that is small at the center and large at the periphery. Therefore, when a positive photosensitive material is exposed using this concentration distribution mask, the photosensitive material pattern obtained after development has a convex shape that is thicker at the center and thinner at the periphery.

(Specific Example 1 of Manufacturing Micro Dimension MLA for Liquid Crystal)
Using the density distribution mask manufactured by the above-described liquid crystal micro-size MLA, a reduction projection exposure apparatus (1/1) shown in FIG.
An example of an MLA for a liquid crystal projector manufactured by exposing using a 5 stepper) to form a resist pattern and transferring it to a material for an optical device will be described.

First, the reduction projection exposure apparatus will be described. Light from the light source lamp 30 is condensed by the condenser lens 31 and irradiates the exposure mask 32 manufactured according to the present invention. The light transmitted through the mask 32 is incident on an imaging lens 33 having a reduction magnification, and a reduced image of the mask 32, that is, a reduced image of the transmittance distribution, is formed on the surface of the optical device material 37 placed on the stage 34. Is imaged. The stage 34 on which the optical device material 37 is placed is a step motor 3
By the action of 5, 36, it can be displaced in two directions perpendicular to each other in a plane perpendicular to the optical axis of the imaging lens 33, and the position of the optical device material 37 can be shifted with respect to the optical axis of the imaging lens 33. It can be positioned.

The reduced image of the mask 32 by the imaging lens 33 is formed on the surface of the photoresist layer of the optical device material 37. This exposure is performed densely over the entire surface of the optical device material 37. In order to manufacture an MLA for a liquid crystal projector, a neoceram substrate was prepared, and the above-mentioned TGMR-950BE resist was formed on this substrate at 8.56 μm.
To a thickness of Next, prebaking was performed on a hot plate at 100 ° C. for a baking time of 180 seconds.

This substrate was exposed with a 1/5 stepper shown in FIG. The following exposure conditions were continuously performed. Defocus: +4 μm, light irradiation amount: 390 mW ×
0.44 sec Defocus: +2 μm, light irradiation amount: 390 mW ×
0.44 sec Defocus: +0 μm, light irradiation amount: 390 mW ×
0.13 seconds Under these conditions, the total exposure is 390 mW x light irradiation.
1.02 seconds (illuminance: 394 mJ). Here, the sign of + in the display of the defocus amount means that the focus is above the resist surface.

After exposure under these conditions, PEB (post-exposure bake) was performed at 60 ° C. for 180 seconds. Next, the photosensitive material was developed and rinsed. Thereafter, the resist was hardened by evacuating while irradiating with ultraviolet light for 180 seconds using an ultraviolet curing device. The ultraviolet curing device irradiates light with a wavelength that can cure the resist at a shorter wavelength than the wavelength used for exposing the resist. By this operation, the plasma resistance of the resist is improved, and the resist can be processed in the next step. At this time, the resist height was 7.5 μm. Due to the defocus effect, the shape could be manufactured without any particular step.

Thereafter, the substrate is set in a TCP (inductively coupled plasma) dry etching apparatus, and the degree of vacuum is set as follows:
^{1.5 × 10 -3 Torr, CHF3:} 5.0sccm, C
F ₄ : 50.0 sccm, O ₂ : 15.0 sccm, substrate bias power: 600 W, upper electrode power: 1.25 kW,
Dry etching was performed at a substrate cooling temperature of -20 ° C. At this time, the etching was performed while changing the substrate bias power and the upper electrode power over time, and changing the selectivity to decrease with time. The average etching rate of the substrate was 0.67 μm / min,
The actual etching time required 11.0 minutes. The lens height after the etching was 5.3 μm.

(Specific Example 2 of Production of Micro Dimension MLA for Liquid Crystal)
Here, an aspheric MLA was manufactured. The same density distribution mask as that of the specific example 1 of the above-mentioned micro-size MLA manufacturing for liquid crystal was used, and the exposure conditions in the stepper device were changed using the density distribution mask. The following exposure conditions were continuously performed. Defocus: +3 μm, light irradiation amount: 390 mW ×
0.16 sec. Defocus: +2 μm, light irradiation amount: 390 mW ×
0.23 sec. Defocus: +1 μm, light irradiation amount: 390 mW ×
0.23 sec. Defocus: +0 μm, light irradiation amount: 390 mW ×
0.30 seconds Under these conditions, the total exposure is 390 mW x light irradiation.
0.92 seconds (illuminance: 359 mJ).

After exposure under these conditions, the photosensitive material PEB,
Development and rinsing were performed. Next, the micro dimensions for liquid crystal ML
Hardening of the resist was performed under the same conditions as in Example 1 of Production A. The resist height at this time was 7.7 μm. Due to the defocus effect, the shape could be manufactured without any particular step. After that, the substrate was set in a TCP dry etching apparatus, and dry etching was performed by changing O ₂ from 15.0 sccm to 0.9 sccm among the conditions in the specific example 1 for manufacturing the micro dimensions MLA for liquid crystal. The average etching rate of the substrate is
It was 0.55 μm / min, but the actual etching time required was 14.0 minutes. The lens height after the etching was 7.4 μm. The MLA manufactured according to the specific example 2 can realize an MLA having a shorter focal length than the MLA prepared according to the specific example 1.

[0062]

According to the present invention, the drawing of the mask blank on the photosensitive material is divided into a plurality of drawing steps over the entire surface, and the mask blanks are obtained based on the three-dimensional structural design values of the photosensitive material pattern to be formed. According to the light transmission amount distribution and the sensitivity characteristics of the photosensitive material of the mask blank, a density distribution mask is manufactured by a multi-step exposure method in which the number of times of writing is set for each unit cell. An analog mask having a light transmission density distribution in the original direction can be manufactured at high speed and at low cost without using a special device.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a method of manufacturing a concentration distribution mask according to the present invention.

FIGS. 2A to 2D are diagrams showing multi-stage drawing, in which FIGS. 2A to 2D show drawing areas for each time, and FIG. 2A shows a drawing pattern when all four times are drawn.

FIG. 3 is a cross-sectional view of a unit cell showing a process of developing and rinsing a drawn mask blank and etching a light shielding film.

FIG. 4 is a sectional view of a unit cell comparing the method of the reference and the method of the present invention.

FIG. 5 is a diagram showing a unit cell light transmittance arrangement showing an example in which a unit cell is divided into grids to form a light transmission density distribution, wherein (A) shows a unit cell of 30/100 gradation and (B) )
Shows an example in which unit cells of 60/100 gradations are combined, and (C) shows an example in which unit cells of 0/100 gradations, 30/100 gradations, and 60/100 gradations are combined.

FIG. 6 is a diagram showing examples of six types of unit cell shapes.

FIG. 7 is a diagram illustrating an example of a unit cell arranged on a concentration distribution mask of an MLA.

FIG. 8 is a diagram showing an initial pattern serving as a starting point of an increase or decrease of a light transmitting area or a light shielding area in a unit cell and a method of changing a light transmitting amount or a light shielding amount.

9A and 9B are diagrams illustrating a method of increasing or decreasing a light transmitting area or a light shielding area in a unit cell. FIG. 9A illustrates an example in which the unit cell is rectangular, and FIG. 9A illustrates an example in which the unit cell is regular hexagonal. is there.

FIG. 10 is a schematic configuration diagram showing an example of a laser beam irradiation apparatus used for manufacturing a concentration distribution mask.

FIG. 11 is a diagram showing a light intensity distribution of transmitted light and a cross-sectional shape of a positive photosensitive material pattern obtained when exposure is performed using a concentration distribution mask of one example.

FIG. 12 is a schematic configuration diagram illustrating an example of a reduction projection exposure apparatus.

[Explanation of symbols]

 12 Material substrate of mask blanks 14 Light shielding film 16 Cross-sectional view of photosensitive material pattern after development

Claims (8)

[Claims] 1. A concentration distribution mask used in a process for forming a photosensitive material pattern having a three-dimensional structure on a substrate, wherein a region used for exposure is divided without gaps by unit cells having an appropriate shape and size. At least some of the unit cells include a light-shielding pattern whose light transmission amount or light-shielding amount is set to a value corresponding to the height of a corresponding position of the photosensitive material pattern, A density distribution mask, wherein the light shielding pattern has a predetermined optical density by changing light transmittance from the center of the unit cell to the periphery. 2. The density distribution mask according to claim 1, wherein the light-shielding pattern has a light-transmitting portion whose cross-sectional shape changes smoothly and the light transmittance changes continuously. 3. In a concentration distribution mask used in a process for forming a photosensitive material pattern having a three-dimensional structure on a substrate, a region used for exposure is divided without gaps by unit cells having an appropriate shape and size. At least some of the unit cells include a light-shielding pattern whose light transmission amount or light-shielding amount is set to a value corresponding to the height of a corresponding position of the photosensitive material pattern, A density distribution mask, wherein the light-shielding pattern divides a unit cell into grids, and the light transmittance in the grid changes discontinuously so that the entire unit cell has a predetermined light transmission amount. 4. The unit cell having a light-shielding pattern in which a light transmission amount or a light-shielding amount is set has a transmittance of 0% and 100%.
% Having a grid with a light transmittance in the middle of
4. The density distribution mask according to claim 3, wherein the grid is arranged so that the light transmittance changes discontinuously in the unit cell, and the total light transmission amount of the unit cell is controlled to realize halftone. . 5. A method of manufacturing a density distribution mask used in a photoengraving process for forming a photosensitive material pattern having a three-dimensional structure on a substrate, wherein a light-shielding film is formed on a transparent substrate, and a photosensitive film is further formed thereon. Prepare a mask blank on which a photosensitive material film is formed, divide the writing of the mask blank on the photosensitive material into a plurality of drawing steps by light or electron beams over the entire surface, and perform the tertiary of the photosensitive material pattern to be formed. According to a light transmission amount distribution obtained based on the original structure design value and a sensitivity characteristic of the photosensitive material of the mask blank, a multi-step exposure method of setting the number of times of writing for each unit cell is performed, Manufacturing method of distribution mask. 6. The method of manufacturing a density distribution mask according to claim 5, wherein a focal depth is made different for each writing step of said writing. 7. The method of manufacturing a density distribution mask according to claim 5, wherein a beam diameter is changed for each writing step of the writing. 8. The method for manufacturing a density distribution mask according to claim 5, comprising the following steps (A) to (E). (A) A region in which a density distribution mask is to be generated is divided without gaps by unit cells of an appropriate shape and size, and each unit is divided based on the light transmission amount distribution and a sensitivity curve obtained by formulating the sensitivity characteristic. (B) determining the number of drawing of each unit cell on the CAD based on the light transmitting region or the light blocking region determined in step (A), and determining the light transmitting region or the light blocking region of the cell. (C) calculating the depth of focus and beam diameter and converting the data into data; (C) irradiating the photosensitive material of the mask blank with light based on the data obtained in step (B) to perform drawing; Developing the subsequent mask blanks to form a photosensitive material pattern having a three-dimensional structure; and (E) transferring the photosensitive material pattern to the light shielding film by etching. Step.