WO2017150628A1

WO2017150628A1 - Microscopic three-dimensional structure forming method, and microscopic three-dimensional structure

Info

Publication number: WO2017150628A1
Application number: PCT/JP2017/008171
Authority: WO
Inventors: 田中　宏幸; 淳也来見田; ソマワンクンプアン; 史朗原
Original assignee: 国立研究開発法人産業技術総合研究所
Priority date: 2016-03-02
Filing date: 2017-03-01
Publication date: 2017-09-08
Also published as: JP6856225B2; TW201826375A; TWI646598B; JPWO2017150628A1

Abstract

The present invention addresses the problem of forming, rapidly and faithfully to a design, a microscopic three-dimensional structure carved in a vertical direction and having smooth side surfaces at low cost. As a solution, a microscopic three-dimensional structure forming method is provided, comprising: the step (1) of forming a resist pattern drawn on a substrate by mask-less exposure; an isotropic etching step (2A) of forming a recess in the substrate by isotropic etching; a plasma deposition step (2B) of depositing a protective film on the resist pattern and the inner walls of the recess; a removal step (2C) of removing the protective film on the bottom surface of the recess by anisotropic etching; and the step (2) of sequentially reiterating the isotropic etching step (2A), the plasma deposition step (2B) and the removal step (2C), thereby forming a microscopic depression in the substrate.

Description

Fine three-dimensional structure forming method and fine three-dimensional structure

The present invention relates to a method for forming a fine three-dimensional structure and a fine three-dimensional structure.

It is required to accurately form fine three-dimensional structures on the order of micrometers for three-dimensional mounting of semiconductors, optical waveguides, microchannels, microreactors, nanoimprint molds, etc. A method for forming a fine three-dimensional structure using lithography and etching has been studied.

In lithography for forming a fine three-dimensional structure, exposure with high resolution is required to obtain a resist having a uniform film thickness. When the exposure resolution is low, the vicinity of the boundary of the resist pattern formed after development is blurred and the resist becomes thin, so that the so-called resist has a skirt. FIG. 15A shows a resist 401 formed on the silicon substrate W with a skirt. In the etching process, the resist is also etched to some extent with the silicon substrate. When etching is performed using this resist as a mask, the bottom of the resist gradually disappears as the etching progresses, and etching is performed on the portion of the silicon substrate where the resist has disappeared. Begins (FIG. 15B), and the silicon substrate is finally etched into a trapezoidal shape (FIG. 15C). Therefore, lithography for forming a fine three-dimensional structure requires a resist with a uniform film thickness so that etching proceeds in the vertical direction, and exposure with high resolution is required.

Usually, a mask is used for exposure, but the mask is very expensive and takes a long time to manufacture the mask itself. Therefore, an exposure method that does not use a mask for printing computer image data as it is called maskless exposure has been proposed (see Patent Document 1). FIG. 16 shows a schematic diagram of light intensity in an exposure spot of maskless exposure and a schematic diagram of a film thickness after development of a pattern subjected to maskless exposure. In maskless exposure, light from a light source is condensed and exposed by a reduction projection lens, so that the light intensity at the exposure spot is strong at the center and weak at the periphery. For this reason, in the maskless exposure, the resist formed after development has a bottom. Maskless exposure is considered to be unsuitable for forming a fine three-dimensional structure because exposure with high resolution cannot be performed and etching in the vertical direction is difficult. Note that maskless exposure is mainly used for printed circuit boards that have a wide pattern width of about 100 μm and do not require high resolution, and is rarely used for fine pattern formation.

Further, in order to form a fine three-dimensional structure by etching, it is necessary to perform etching smoothly in the vertical direction faithfully to the developed resist pattern.
As described above, even when exposure with high resolution is performed and etching is performed using a resist having a uniform film thickness as a mask, the resist is side-etched little by little. When deep etching is carried out over time, the resist width is narrowed by side etching as the etching progresses, so that the substrate is etched in a slightly oblique direction and cannot be accurately etched in the vertical direction.

Here, Patent Document 2 proposes an etching method called a Bosch process as a deep digging technique for manufacturing a device having a large three-dimensional structure with a resolution of MEMS or the like of about 10 μm.
FIG. 17 shows a process diagram of the Bosch process. In the Bosch process, isotropic etching is performed on the silicon substrate W having the resist 401 on the surface (FIG. 17A), and a protective film 403 is deposited on the side and bottom surfaces of the recess 402 formed by etching (FIG. 17). 17 (b)), a process in which the three steps of removing the protective film on the bottom surface of the depression by anisotropic etching (FIG. 17C) are repeated as one cycle. In the Bosch process, during the isotropic etching, the side surface of the depression protected by the protective film is not etched, and the isotropic etching proceeds from the bottom of the depression from which the protective film is removed. By repeating isotropic etching on the bottom surface of the depression, etching proceeds only in the vertical direction, and a hole having a depth of 100 μm or more can be formed in the vertical direction (FIG. 17D).

However, in the Bosch process, since the etching proceeds at a uniform speed in all directions in the isotropic etching process, the substrate is cut into a spherical shape. Therefore, irregularities synchronized with the repetition cycle of etching called scallop (Scallop 404) are formed on the side surface of the hole, and a hole with a smooth side surface cannot be manufactured. If the time required for one cycle of the Bosch process (hereinafter also referred to as cycle time) is shortened, the scallop can be reduced. However, since the exhaust time of the etching gas and the protective film forming gas requires at least about 4 seconds each, The time is 8 seconds or more. If the other gas is introduced before one gas is completely exhausted, the cycle time can be shortened. However, a sufficient protective film is not formed on the side surface of the hole, and the side surface is removed in the isotropic etching process. It is etched and a hole cannot be formed in the vertical direction.

That is, in a normal Bosch process that sufficiently replaces the gas, the cycle time cannot be shorter than 8 seconds, and a scallop is formed during the etching of 4 seconds including the exhaust, so the scallop is inevitable. Occurs. Further, in the formation of holes by the Bosch process, it is required to reduce the number of cycles necessary for forming holes in order to shorten the processing time, and isotropic etching is set so as to perform large etching. Therefore, in a normal Bosch process, a hole having a scallop depth of 500 nm or more formed on the side surface is formed.

In order to obtain a hole with a smooth side surface using the Bosch process, as proposed in Patent Document 3, a flattening process such as dry etching for flattening the scallop is required. For the planarization process, oxide film formation, neutral particle beam etching, and the like are used, but the size of the hole changes in any method. Furthermore, the normal Bosch process has a large mask undercut of 500 nm or more. That is, in the etching by the Bosch process, the mask undercut is large, and the size of the hole is changed by the flattening process. Therefore, it is difficult to form a hole having a desired designed size.

As described above, in normal etching, deep digging in the vertical direction cannot be performed, and a trapezoidal shape whose side surfaces are oblique is formed. In addition, the Bosch process can dig deeply in the vertical direction, but since a scallop is formed, it cannot obtain a smooth side surface, and it is difficult to form a hole of a size faithful to the design. is there.
That is, it has been very difficult to form a fine three-dimensional structure having smooth side surfaces dug in the vertical direction by etching, faithfully to the design.

JP 2005-123234 A International Publication No. 94/14187 JP 2007-311584 A

An object of the present invention is to form a fine three-dimensional structure having smooth side surfaces dug in the vertical direction at a low cost and promptly and faithfully to the design.

1. Forming a resist pattern drawn by maskless exposure on a substrate (1);
An isotropic etching step (2A) for forming a depression in the substrate by isotropic etching;
A plasma deposition step (2B) of depositing a protective film on the inner wall of the recess and the resist pattern;
A removal step (2C) for removing the protective film on the bottom surface of the depression by anisotropic etching;
A step (2) of forming a fine recess in the substrate by sequentially repeating an isotropic etching step (2A), a plasma deposition step (2B), and a removal step (2C);
A method for forming a fine three-dimensional structure, comprising:
2. The maskless exposure is a multiple exposure. The method for forming a fine three-dimensional structure according to 1.
3. When the widths at the 10% depth position, 50% depth position, and 90% depth position of the fine recess are W10, W50, and W90, respectively, the coefficient of variation (W10 to W90) of W10, W50, and W90 is 5%. 1. It is characterized by the following. Or 2. The method for forming a fine three-dimensional structure according to 1.
4). 1. A scallop period P on the side surface of the fine recess is 100 nm or less. ~ 3. The method for forming a fine three-dimensional structure according to any one of the above.
5. The depth D of the scallop on the side surface of the fine recess is 30 nm or less. ~ 4. The method for forming a fine three-dimensional structure according to any one of the above.
6). The substrate has a diameter of 0.5 inch. ~ 5. The method for forming a fine three-dimensional structure according to any one of the above.
7). 1. Cycle time is 0.5 second or more and 6 seconds or less ~ 6. The method for forming a fine three-dimensional structure according to any one of the above.
8). 5. The coefficient of variation (W10 to W90) is 3.5% or less. Or 7. The fine three-dimensional structure described in 1.
9. 5. The scallop depth D is 12 nm or less. ~ 8. The fine three-dimensional structure according to any one of the above.
10. A fine recess having a depth of 20 μm or less and a width of 3 μm or more on the substrate;
When the widths at the 10% depth position, 50% depth position, and 90% depth position of the fine recess are W10, W50, and W90, respectively, the coefficient of variation (W10 to W90) of W10, W50, and W90 is 5%. A fine three-dimensional structure characterized by:
11. 9. The scallop period P on the side surface of the fine recess is 100 nm or less. The fine three-dimensional structure described in 1.
12 9. The scallop depth D is 30 nm or less. Or 11. The fine three-dimensional structure described in 1.
13. A fine convex portion adjacent to the fine concave portion;
Having a resist covering the top of the fine protrusions;
9. The film thickness at the edge of the resist is thinner than the film thickness at the center. ~ 12. The fine three-dimensional structure according to any one of the above.
14 12. The width of the mask undercut at the upper end portion of the fine convex portion is 30 nm or less. The fine three-dimensional structure described in 1.
15. 9. The diameter of the substrate is 0.5 inch. ~ 14. The fine three-dimensional structure according to any one of the above.
16. 15. The coefficient of variation (W10 to W90) is 3.5% or less. The fine three-dimensional structure described in 1.
17. 15. The depth D of the scallop is 12 nm or less. Or 16. The fine three-dimensional structure described in 1.

Since the method for forming a fine three-dimensional structure of the present invention draws a resist pattern by maskless exposure, an expensive mask is unnecessary. Since maskless exposure can be easily drawn using a computer, according to the method for forming a fine three-dimensional structure of the present invention, a fine three-dimensional structure can be manufactured in a small lot, and a variety of products can be produced in small quantities. Suitable for maid production and on-demand production. In addition, by performing multiple exposure, a smooth pattern can be drawn in the horizontal direction.

The fine three-dimensional structure forming method of the present invention performs etching by a so-called Bosch process. In the Bosch process, the resist is less likely to be etched by about 10 times compared to normal etching. The resist pattern drawn by maskless exposure is thinner near the boundary than the center of the pattern. However, by using the Bosch process, the initial shape of the maskless exposed resist can be reduced during the etching process. Almost no change including the part. Therefore, even if the resist has a non-uniform film thickness, etching can be performed in the vertical direction along the drawn resist pattern, and fine concave portions whose width hardly changes in the depth direction can be formed. Further, by finely repeating isotropic etching in the Bosch process, it is possible to form a fine recess having a small scallop depth and a smooth side surface.

The fine three-dimensional structure forming method of the present invention can form fine concave portions having smooth side surfaces without performing an additional planarization step. Further, the width of the fine recesses actually obtained has a very small error from the design dimension, and a fine three-dimensional structure that is almost faithful to the pattern drawn by maskless exposure can be formed.

The processing gas in the Bosch process can be replaced at high speed by using a half-inch silicon substrate, reducing the volume of the chamber for generating plasma, and using an exhaust device having sufficient exhaust capacity with respect to the chamber capacity. . Therefore, the Bosch process can be repeated while sufficiently replacing the processing gas with a cycle time of 6 seconds or less that could not be achieved conventionally. By performing the Bosch process with a cycle time of 6 seconds or less, it is possible to form a fine recess having a more vertical and smooth side surface. In addition, since the cycle time is short, even if the Bosch process is repeated several hundred cycles, the processing time of the fine three-dimensional structure is short and the productivity is excellent.

The fine three-dimensional structure of the present invention is superior in the verticality and smoothness of the side surface as compared with a fine three-dimensional structure having a fine recess having a depth of 20 μm or less that has been reported conventionally. Since the unevenness on the side surface is small with respect to the wavelength of light and the perpendicularity of each surface is excellent, there is little attenuation when light is reflected, and it can be suitably used as an optical waveguide. Since an error from the design dimension is small and a desired shape can be formed, it can be suitably used as a diffraction grating or a hologram.
Further, since the liquid can flow smoothly, it is also suitable as a microchannel or a microreactor. Furthermore, the fine three-dimensional structure of the present invention having a small side scallop depth is suitable as a mold for nanoimprinting because it has little catch when transferring and peeling the structure.

The schematic diagram of DLP exposure which is maskless exposure. The schematic diagram of the light intensity at the time of performing the multiple exposure four times by shifting the exposure spot of maskless exposure. Sectional drawing which shows the structural example of a plasma etching apparatus. The schematic diagram of the depth direction cross section of the fine recessed part formed with the fine three-dimensional structure formation method of this invention. The figure explaining the shape of the fine recessed part formed with the fine three-dimensional structure formation method of this invention. The schematic diagram of the cross section of the depth direction of one embodiment of the fine three-dimensional structure of this invention. A cross-sectional image of a resist pattern drawn in Experiment 1 with a line and space of 4 μm by a scanning electron microscope. The bird's-eye view image by the scanning electron microscope of the resist pattern drawn in Experiment 1 whose curve width is 4 micrometers. The bird's-eye view image by the scanning electron microscope of the micro three-dimensional structure which was created in Experiment 1, and the curve width is 4 micrometers. A cross-sectional image obtained by a scanning electron microscope having a fine three-dimensional structure having a line and space of 4 μm created in Experiment 1. FIG. 3 is a cross-sectional image obtained by a scanning electron microscope having a fine three-dimensional structure having a line and space of 2 μm created in Experiment 1. FIG. A cross-sectional image of a resist pattern drawn in Experiment 2 with a line and space of 4 μm by a scanning electron microscope. The bird's-eye view image by the scanning electron microscope of the fine three-dimensional structure whose curve width created in Experiment 2 is 4 micrometers. A cross-sectional image obtained by a scanning electron microscope having a fine three-dimensional structure having a line and space of 4 μm created in Experiment 2. FIG. The figure explaining the progress of the etching when the resist which pulled the skirt is used as a mask. The schematic diagram of the light intensity in the exposure spot of maskless exposure. The figure explaining the process of a Bosch process.

W Silicon substrate 100 Fine three-dimensional structure 110 Fine concave portion 111 Opening portion 112 Bottom surface 113 Side surface 114 Scallop 120 Resist pattern 130 Fine convex portion
201 Light source 202 DMD
203 Reduction projection lens
300 Plasma Etching Device 301 Chamber 302 Gas Supply Mechanism 303 Coil 304 Coil Power Supply Mechanism 305 Base 306 Base Power Supply Mechanism 307 Exhaust Device
401 resist 402 dent 403 protective film 404 scallop

The present invention is completely different in industrial application, that is, maskless exposure with poor resolution, which is mainly used for patterning printed circuit boards, and Bosch process in which scallops are formed on the side surfaces used for etching during MEMS manufacturing. This is a method for forming a fine three-dimensional structure by combining techniques used for applications.

Hereinafter, the present invention will be described along the steps.
(1) Maskless exposure First, a resist pattern drawn by maskless exposure is formed on a silicon substrate. The resolution of maskless exposure is preferably small, preferably 0.5 μm or less, and more preferably 0.25 μm or less. The width of the resist pattern can be, for example, 0.25 μm or more and 10 μm or less. The shape of the resist pattern is not particularly limited, and for example, any of dots, lines, surfaces, or a combination thereof can be drawn. As the substrate, not only silicon but also germanium, gallium arsenide, gallium arsenide phosphorus, silicon carbide, gallium nitride, sapphire, diamond, or the like can be used.

As maskless exposure, light from a light source is reflected according to pattern data using a digital micromirror device (hereinafter referred to as DMD) in which hundreds to thousands of micromirrors of about 10 μm square are arranged vertically and horizontally. Can be used. FIG. 1 shows a schematic diagram of DLP exposure (Digital Light Processing) as an example of maskless exposure.
The DLP exposure is a method in which light from the light source 201 is reflected by the DMD 202 and the light reflected by the DMD is exposed on the silicon substrate W through the reduction projection lens 203. In DLP exposure, a fine pattern is formed by irradiating light condensed by a reduction projection lens onto a photoresist film, so that a light irradiation range is narrow and scanning scanning for moving the irradiation range is necessary. Further, the shape of the exposure spot projected on the silicon substrate is substantially square. Therefore, a smooth pattern can be drawn in a direction parallel to the scanning direction, but only a pattern having a jagged step can be drawn in the scanning direction and the oblique direction.

By performing multiple exposure, jagged steps in a plane parallel to the silicon substrate surface can be reduced. For example, when the exposure spot is 0.5 μm square, the step can be set to 0.1 μm by exposing the pixel in five. When the resolution of light is 0.3 μm (for example, i-line is 0.365 μm), a step of 0.1 μm unit, which is equal to or less than the wavelength of light, is drawn dull, so the step disappears and is smooth. Pattern.

Here, as described above, in the DLP exposure, the light condensed by the reduction projection lens is irradiated. Therefore, the light intensity at the exposure spot is not uniform, being strong at the center and weak at the periphery. When multiple exposure is performed, the number of times of light irradiation at the center of the pattern is a plurality of times, whereas the number of times of light irradiation at the pattern boundary is only once. FIG. 2 shows a schematic diagram of the light intensity when the maskless exposure exposure spot is shifted and multiple exposure is performed four times. In FIG. 2, the light intensity in one exposure spot is shown as the same for simplification. Therefore, when multiple exposure is performed, the difference in light intensity between the center portion and the boundary portion of the pattern becomes larger. That is, the resist pattern drawn by maskless exposure is in a state where the pattern central portion is thick, the pattern boundary portion is thin, and the skirt is drawn regardless of the presence or absence of multiple exposure.

Since DLP exposure is performed while scanning scanning, it takes more time to expose the entire surface of the silicon substrate than mask exposure. For example, it takes about 100 hours to perform DLP exposure on a wafer having a diameter of 300 mm. is required. Furthermore, if multiple exposures are performed with 5 divisions in the vertical and horizontal directions, 2500 hours (100 × 5 × 5) are required.
The problem that it takes a long time to expose a single wafer, which is a drawback of DLP exposure, can be solved by reducing the size of the wafer. For example, by using a half-inch size (diameter: 12.5 mm) wafer, the wafer area can be reduced to about 1/700 compared to a 300 mm diameter wafer. Therefore, the five-division multiple exposure that required 2500 hours can be completed within 2 hours, which is 1/1000 or less. Further, by increasing the speed of the DMD and the scanning mechanical mechanism, five-division multiple exposure can be performed in about 40 minutes.

(2) Bosch Process Next, an isotropic etching step (2A) for forming a recess in the silicon substrate by isotropic etching, and a plasma deposition step (2B) for depositing a protective film on the inner wall of the recess and the resist pattern layer. And a removal step (2C) of removing the protective film on the bottom surface of the depression by anisotropic etching, a fine recess is formed in the silicon substrate by a so-called Bosch process. (Hereinafter, the isotropic etching step (2A) and the removal step (2C) are also referred to as an etching step.)

FIG. 3 shows a configuration example of a plasma etching apparatus that performs the Bosch process. The plasma etching apparatus 300 includes a cylindrical chamber 301 that generates plasma and performs plasma processing, a gas supply mechanism 302 that supplies a processing gas to the chamber, a coil 303 disposed outside the chamber, and a coil A coil power supply mechanism 304 for supplying high-frequency power, a base 305 for placing the silicon substrate W, a base power supply mechanism 306 for supplying high-frequency power to the base, and an exhaust for exhausting the gas in the chamber Device 307.

As the processing gas, an etching gas such as SF ₆ , CF ₄ , C ₃ F ₈ , SiF ₄ , or NF ₃ and a protective film forming gas such as C ₄ F ₈ or C ₅ F ₈ are used. By switching on / off of the bias power to the base 305 by the base power supply mechanism 306, the removal process (2C) which is anisotropic etching and the isotropic etching process (2A) can be switched. .

In the fine three-dimensional structure forming method of the present invention, a protective film is deposited not only on the inner wall of the recess but also on the resist pattern in the plasma deposition step (2B). Since a protective film is deposited on the resist pattern, the resist is very difficult to etch as compared with normal etching. Even if the etching resistance of the resist is a ratio of resist: etching target material = 1: 10, the ratio is improved to about 1: 100 by depositing a protective film on the resist pattern.

The protective film is slightly etched in the etching process, but is repaired by depositing the protective film in the plasma deposition process (2B). In the fine three-dimensional structure forming method of the present invention, a resist pattern having a non-uniform film thickness is formed by maskless exposure. However, since the resist pattern is protected by a protective film throughout the entire Bosch process, the initial resist shape is It is maintained including the skirt and the thin part does not disappear. Since etching can be performed while maintaining the drawn resist pattern, it is possible to form a fine recess that faithfully reflects the resist pattern in the horizontal plane.

In FIG. 4, the schematic diagram of the cross section of the depth direction of the fine recessed part formed with the fine three-dimensional structure formation method of this invention is shown. The shape of the fine recesses in the horizontal plane is not particularly limited, and the horizontal recesses other than the convex portions such as circular holes, square holes, straight and curved ridges, cylinders, quadrangular columns, ridges, etc. Almost the entire surface can be a fine recess.
The fine recess 110 is formed in the silicon substrate W and has an opening 111, a bottom surface 112, and a side surface 113, and a scallop 114 having a period P and a depth D is formed on the side surface 113. The height position of the opening of the fine recess is equal to the surface of the silicon substrate before processing. In addition, the silicon substrate has a resist pattern 120 on the surface, and this resist pattern is drawn by maskless exposure. Therefore, the film thickness is not uniform, thick at the center, and thin at the boundary. In FIG. 4, the scallop 114 is exaggerated from the actual one.

In the Bosch process, when the width of the fine recess becomes narrower or the depth of the fine recess becomes deeper, the processing gas hardly enters the inside of the fine recess and the etching rate tends to decrease. By making the width of the fine recesses 3 μm or more and the depth 20 μm or less, it is possible to suppress a decrease in the etching rate. The width of the fine recess is preferably 3 μm or more, more preferably 4 μm or more, and further preferably 5 μm or more. Similarly, the depth of the fine recess is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 12 μm or less.

微細 By suppressing the decrease in the etching rate in the Bosch process, it is possible to dig fine recesses in the vertical direction. Specifically, when the widths of the fine recesses at the 10% depth position, 50% depth position, and 90% depth position are W10, W50, and W90, respectively, the standard deviations of W10, W50, and W90 are average values. The divided variation coefficient (W10 to W90) can be 5% or less. By setting the coefficient of variation to 5% or less, for example, when an optical waveguide is used, the reflecting surfaces facing each other are excellent in parallelism, and a long distance can be transmitted while repeating total reflection at the interface. The coefficient of variation (W10 to W90) is preferably 3.5% or less, more preferably 3% or less, further preferably 2.7% or less, and most preferably 2% or less. preferable. Here, the width of the fine concave portion is based on a line connecting the portions where the scallop is dug most in the horizontal direction. In addition, when the shape in the horizontal direction surface of a fine recessed part is not linear, as the width | variety of a fine recessed part, the 1st side surface of the fine recessed part in a depth direction cross section and the nearest 8 micrometers or more away from the 1st side surface The distances from the second side surface at the 10% depth position, 50% depth position, and 90% depth position are W10, W50, and W90, respectively.

Furthermore, the depth D of the scallop formed on the side surface of the fine recess can be reduced by reducing the depth of the recess formed in the one isotropic etching step (2A). The depth of the depression formed in one isotropic etching step (2A) varies depending on various conditions such as the frequency and power of the high-frequency power, the pressure and flow rate of the processing gas, and the time of the etching step, in particular, It is easy to adjust by the time of the isotropic etching step (2A) in which no bias power is applied to the base. By repeating the formation of the shallow depression, the scallop depth D is shallow, and a fine recess having a smooth side surface can be formed. The depth of the recess formed in one isotropic etching step (2A) corresponds to the scallop period P.

The scallop period P, which is the depth of the depression formed in one isotropic etching step (2A), is preferably 100 nm or less, more preferably 60 nm or less, still more preferably 40 nm or less, and most preferably 20 nm or less. . In order to obtain a smoother side, the scallop period P is preferably smaller. However, since the time taken to form the fine recesses is longer, the scallop period P is preferably 1 nm or more, and preferably 3 nm or more. Is more preferable, and more preferably 5 nm or more.

The scallop depth D is preferably 30 nm or less, more preferably 20 nm or less, further preferably 12 nm or less, and most preferably 5 nm or less. When the scallop period P is set to 40 nm or less, the scallop protrusion is flattened while the Bosch process is repeated, and the unevenness cannot be visually recognized in the electron microscope image, and the scallop may actually disappear.
Further, by reducing the scallop depth D, the width of the mask undercut, which is the distance between the upper end of the side surface of the fine recess and the end of the resist, can be made equal to the scallop depth D.

Further, the shape of the fine recess of the present invention will be described in detail with reference to FIG. In FIG. 5, the side surface shape is exaggerated for the sake of explanation. The top of the side surface of the fine recess is H0, the depth of the fine recess is h0, the intermediate height point of the side surface is H1, the height of H1 is h1 (= h0 / 2), and the straight line l passing through H0 and H1 and the bottom surface The point of intersection is O, the point of intersection between the perpendicular line passing through O and the side is H2, the height of H2 is h2, and the height of the side of the fine recess is h3 (= h2 / e, where e is the base of natural logarithm) Let it be H3. The angle between the straight line 1 and the bottom surface is a taper angle θ, and the distance between H2 and H3 in the direction parallel to the bottom surface is a tailing length L. In addition, H1, H2, and H3 are located on the line which connects the part where the scallop was dug most in the horizontal direction.

According to the method for forming a fine three-dimensional structure of the present invention, a fine recess having a taper angle θ of 85 degrees or more and 89.99 degrees or less can be formed. Furthermore, by setting the depth of the recess formed in one isotropic etching step (2A) to 100 nm or less, it is possible to form a fine recess having a skirt length L of 2 μm or less. That is, according to the method for forming fine recesses of the present invention, it is possible to form fine recesses that are dug in the vertical direction and whose side surfaces rise sharply from the bottom. Here, when the width of the fine concave portion at the 95% depth position is W95, the fine concave portion obtained by the fine concave portion forming method of the present invention is dug in the vertical direction and has a short tail at the bottom portion. Variations in W50, W90, and W95 are small, and variation coefficients (W10 to W95) of W10, W50, W90, and W95 are smaller than variation coefficients (W10 to W90) of W10, W50, and W90. The coefficient of variation (W10 to W95) is preferably 3.5% or less, more preferably 3.2% or less, further preferably 2.5% or less, and 1.8% or less. Most preferably it is.
In addition, each above-mentioned value can be calculated | required by analyzing electron microscope images, such as SEM, TEM, and STEM, using attached or commercially available image analysis software. However, as described above, the scallop cannot be confirmed, and the scallop period P and the depth D may not be obtained. In this case, the scallop period P can be calculated from the depth of the formed fine recess and the number of cycles of the Bosch process. In some cases, the period P and depth D of the scallop can be measured by observing with an atomic force microscope (AFM) instead of the electron microscope.

Here, by using a half-inch size (diameter: 12.5 mm) wafer, the volume of the chamber can be reduced to 500 mL or less. By using an exhaust device having a chamber capacity (V) of 500 mL or less and an exhaust capacity (100 V / second or more) 100 times or more of the chamber volume per second, the processing gas can be replaced at high speed, and the cycle time Can be shortened. The exhaust capacity of the exhaust device is preferably 150 times or more, more preferably 200 times or more of the chamber volume per second.
By replacing the processing gas at high speed, switching between the etching step and the deposition step (2B) in a short time and digging up little by little, a fine concave portion having a smoother side surface can be formed. Specifically, by digging so that the scallop period P is 40 nm or less, the scallop depth D is 12 nm or less, the coefficient of variation (W10 to W90) is 3.3% or less, and the coefficient of variation (W10 to W95). ) Of 3.1% or less, taper angle of 88.6 degrees or more, and skirt length of 0.8 μm or less.

The time for the etching step is preferably 3.5 seconds or less, more preferably 2 seconds or less, and even more preferably 1 second or less. What is necessary is just to adjust suitably the ratio of the time of an isotropic etching process (2A) in the etching process, and the time of a removal process (2C) in the range of 90:10 or more and 10:90 or less. Further, the ratio of the time of the isotropic etching step (2A) and the time of the removal step (2C) may be constant throughout the Bosch process or may be changed. Further, the time of the plasma deposition step (2B) is preferably 3.5 seconds or less, more preferably 2 seconds or less, and further preferably 1 second or less. Furthermore, the cycle time, which is the time required for the isotropic etching step (2A), plasma deposition step (2B) and removal step (2C), is preferably 6 seconds or less, more preferably 4 seconds or less, and 2 seconds or less. Is more preferable. Since the gas cannot be sufficiently replaced and the processing gas is mixed, the cycle time is preferably 0.5 seconds or more.

For example, using a half-inch wafer and changing the processing gas at high speed to set the cycle time to 2 seconds, the Bosch process can be performed 300 cycles in just 10 minutes (600 seconds). At this time, by adjusting the depth of the recess formed in one isotropic etching step (2A) to 33.3 nm, the depth is 10 μm in 10 minutes, and the scallop depth D is 12 nm or less. It is possible to form a fine concave portion.

The number of cycles of the Bosch process in the fine three-dimensional structure method of the present invention is not particularly limited. However, in order to form a fine concave portion having a smooth side surface with a small scallop depth D, it is preferable to form a fine concave portion having a desired depth by a Bosch process of 200 cycles or more. The number of cycles is more preferably 300 cycles or more, further preferably 500 cycles or more, and most preferably 1000 cycles or more. However, the depth of the recess formed in one isotropic etching step (2A) is 100 nm or less.

Here, by using a half-inch wafer (diameter: 12.5 mm), the inner diameter of the chamber of the plasma generating portion can be set to 20 mm or more and 60 mm or less. By reducing the space for generating plasma, it is possible to reduce the size and power consumption of equipment required for plasma generation. For example, 50 W, which requires permission for installation of equipment according to the Japanese Radio Law. The output can be lower than.

The so-called skin layer near the inner wall of the chamber where plasma is generated is a region where plasma is not generated by the skin effect when high-frequency power is supplied to the coil. The skin layer is thinner in the radial direction as the frequency of the high-frequency power is higher, and is thicker as the frequency of the high-frequency power is lower. Therefore, when the frequency of the high frequency power is small, the skin layer becomes too thick, and a region where plasma is generated is not sufficiently secured. However, plasma can be generated even in a narrow region by setting the frequency of the high-frequency power to 40 MHz or more. Moreover, the generated plasma can be stably maintained by setting the magnitude of the high-frequency power to 2 W or more. By setting the frequency of the high-frequency power to 40 MHz or more, which is larger than the general 13.56 MHz, even if the high-frequency power is as small as 2 W, sufficient energy for separating the plasma can be given. Furthermore, since the etching rate is reduced when the high-frequency power is reduced, the depth of the groove formed in one isotropic etching step (2A) is reduced, which is suitable for forming fine concave portions having smooth side surfaces.

As described above, according to the fine three-dimensional structure forming method of the present invention using maskless exposure and the Bosch process, a fine three-dimensional structure having a vertical and smooth side surface and faithful to the drawn resist pattern can be formed. In addition, the fine three-dimensional structure formation method of this invention can perform additional processes, such as protective layer formation processes, such as an oxide film, a nitride film, and metal plating, a dicing process, as needed.

`` Fine three-dimensional structure ''
The schematic diagram of the cross section in the depth direction of one embodiment of the fine three-dimensional structure of the present invention is shown in FIG. The fine three-dimensional structure 100 according to an embodiment has a fine concave portion 110 formed on a silicon substrate W and made of a portion from which silicon is removed, and a period P is 100 nm or less and a depth D is formed on a side surface of the fine concave portion. A scallop (not shown) having a thickness of 30 nm or less is formed.
In the fine three-dimensional structure of the present invention, the fine recess is formed by etching the silicon substrate in the vertical direction. The portion where the silicon substrate remains without being etched constitutes the fine protrusion 130. Therefore, the fine concave portion and the fine convex portion are adjacent to each other, and the fine convex portion and the silicon substrate are made of the same continuous material and have no interface. The shape of the fine three-dimensional structure is not particularly limited, and examples thereof include a cylinder, a quadrangular column, a circular hole, a square hole, a linear or curved ridge, a groove, or a combination thereof.

The fine recess has a depth of 20 μm or less and a width of 3 μm or more. The depth of the fine concave portion, that is, the height of the fine convex portion is more preferably 15 μm or less, and further preferably 12 μm or less. The depth of the fine concave portion (height of the fine convex portion) is preferably 500 nm or more, more preferably 1 μm or more, and further preferably 2 μm or more. Further, the width of the fine recess is preferably 4 μm or more, and more preferably 5 μm or more.
The fine concave portion is dug almost vertically, and the fine convex portion stands upright substantially perpendicular to the silicon substrate. Specifically, when the widths at the 10% depth position, 50% depth position, and 90% depth position of the fine recess are W10, W50, and W90, respectively, the variation coefficient (W10 to W90) is 5% or less. is there. The coefficient of variation (W10 to W90) is preferably 3.5% or less, more preferably 3% or less, further preferably 2.7% or less, and most preferably 2% or less. preferable. When the width at the 95% depth position is W95, the coefficient of variation (W10 to W95) of W10, W50, W90, and W95 is preferably 3.5% or less, and is preferably 3.2% or less. More preferably, it is more preferably 2.5% or less, and most preferably 1.8% or less.

The scallop period P on the side surface of the fine recess is 100 nm or less, preferably 60 nm or less, more preferably 40 nm or less, still more preferably 30 nm or less, and most preferably 20 nm or less. The scallop depth D is 30 nm or less, preferably 20 nm or less, more preferably 15 nm or less, still more preferably 12 nm or less, and most preferably 5 nm or less.
Furthermore, the taper angle θ of the fine recess is preferably 86 degrees or more, more preferably 88 degrees or more, further preferably 89 degrees or more, and most preferably 89.5 degrees or more. . The skirt length L is preferably 2 μm or less, more preferably 1.5 μm or less, further preferably 1 μm or less, and most preferably 0.6 μm or less.
In addition, each above-mentioned value can be calculated | required by analyzing electron microscope images, such as SEM, TEM, and STEM, using attached or commercially available image analysis software. However, the scallop cannot be confirmed from the electron microscope image, and the scallop period P and depth D may not be obtained. In this case, the scallop period P can be calculated from the depth of the formed fine recess and the number of cycles of the Bosch process. In some cases, the period P and depth D of the scallop can be measured by observing with an atomic force microscope (AFM) instead of the electron microscope.

By using a half-inch (diameter: 12.5 mm) wafer as the silicon substrate, the cycle time of the Bosch process when forming the fine recesses can be reduced to 6 seconds or less. By shortening the cycle time, the digging can be carried out little by little, so that the scallop depth D becomes smaller and the side surface can be further smoothed. The scallop period P can be 40 nm or less, and the depth D can be 12 nm or less. Further, the coefficient of variation (W10 to W90) can be 3.4% or less, the coefficient of variation (W10 to W95) can be 3.1% or less, the taper angle is 88.6 degrees or more, and the tailing length is 0.8 μm or less. .

The fine three-dimensional structure of the present invention is not limited to the above-described embodiment. For example, the top of the fine protrusions may be covered with a maskless exposed resist. At this time, in the resist, the film thickness at the center is larger than the film thickness at the boundary, and the width of the mask undercut is 30 nm or less. Moreover, it can also be set as the fine three-dimensional structure which has the fine recessed part from which depth differs, and the fine convex part from which height differs by performing the fine three-dimensional structure formation method of this invention in multiple times.

The fine three-dimensional structure of the present invention has smoother side surfaces, superior verticality of each surface, and is faithful to the drawn resist pattern as compared with the conventional one. The use of the fine three-dimensional structure of the present invention is not particularly limited. For example, since the scallop period P and the depth D are sufficiently smaller than the wavelength of light, and the perpendicularity of the fine three-dimensional structure is excellent, the attenuation when light is reflected at the interface is small. Can be suitably used. Further, since a desired shape can be formed faithfully to the resist pattern, it is suitable as an optical element such as a diffraction grating or a hologram. Furthermore, since the side surface is smooth and the resistance when the liquid flows is small, it can be used as a microchannel or a microreactor. At this time, since there are few unevenness | corrugations of a side surface and it is hard to catch a solid substance, it is especially suitable for the use which flows a cell, microorganisms, etc. In addition, it can also be used as an imprint mold, MEMS, NEMS (Nano Electro Mechanical Systems), and the like.

Experiment 1
A negative photoresist was spin-coated on a half-inch silicon wafer so that the film thickness after drying was 1 μm, and dried.
After exposure once with a DLP exposure apparatus, development was performed to draw a resist pattern. The shape of the exposure spot is 0.5 μm square.
Using a plasma etching apparatus having a chamber capacity of 500 ml and an exhaust speed of 80 L / sec, 300 cycles of a Bosch process with a cycle time of 2 seconds were performed for 1 second each for the etching process and the plasma deposition process (2B) under the following conditions. The etching process is an isotropic etching process (2A) of 0.6 seconds and a removal process (2C) of 0.4 seconds, and the total time of the Bosch process is 600 seconds (= 2 seconds × 300 cycles).
Pressure: 10Pa
High frequency power frequency: 100 Hz
Size of high frequency power: 25W
Bias power: 2W
Etching: _SF 6, 8ml / min
Plasma deposition: C ₄ F ₈ , 8 ml / min
Thereafter, the resist pattern was removed using an asher device to form a fine three-dimensional structure.

The drawn resist pattern and the created fine three-dimensional structure were observed with a scanning electron microscope. A cross-sectional image and a bird's-eye view image of a resist pattern having a line and space of 4 μm are shown in FIGS. 9 to 11 show an overhead image of a fine three-dimensional structure, a cross-sectional image of a part having a line and space of 4 μm, and a cross-sectional image of a part having a line and space of 2 μm, respectively.

The resist pattern had a skirt due to non-uniformity of light irradiation in maskless exposure. Further, the resist pattern has a jagged step in the scanning direction and the oblique direction. When this resist pattern is etched as a mask, a fine three-dimensional structure in which the jagged step is directly reflected can be formed.

A fine recess having a depth of 12.0 μm could be formed at a line and space of 4 μm. Even when the cross-sectional image was magnified 500,000, scallops could not be confirmed. For this reason, the depth D of the scallop formed on the side surface is 12 nm or less. The scallop period P calculated from the depth of the fine recesses and the number of cycles is 40.0 nm.
The fine recesses W10, W50, and W90 were 5.00 μm, 4.77 μm, and 4.69 μm, respectively, and the variation coefficient (W10 to W90) was 3.34%. W95 was 4.69 μm, and the coefficient of variation (W10 to W95) was 3.06%. The taper angle was 88.6 degrees and the skirt length was 0.59 μm. Table 1 shows the measured values.
The portion where the line and space was 4 μm could be etched in a substantially vertical direction and stood up sharply from the bottom. Moreover, the scallop was not confirmed and the side surface was smooth.

A fine recess having a depth of 11.0 μm could be formed in the portion where the line and space was 2 μm. Even when the cross-sectional image was magnified 500,000, scallops could not be confirmed. For this reason, the depth D of the scallop formed on the side surface is 12 nm or less. The calculated scallop period P is 36.7 nm.
The fine recesses W10, W50, and W90 were 3.09 μm, 2.85 μm, and 2.61 μm, respectively, and the coefficient of variation (W10 to W90) was 8.06%. W95 was 2.61 μm, and the coefficient of variation (W10 to W95) was 8.24%. The taper angle was 88.5 degrees and the skirt length was 0.40 μm. Table 1 shows the measured values.
In the part where the line and space is 2 μm, the etching rate was gradually decreased because the width of the space was narrow and the processing gas did not easily enter the inside. For this reason, the coefficient of variation (W10 to W90) was larger than that of the line and space portion of 4 μm. The taper angle at the line and space portions of 4 μm and 2 μm hardly changed. This is because the difference between W10 and W50 (W10−W50) in the portions where the line and space is 4 μm and 2 μm is almost the same as 0.23 μm and 0.24 μm, respectively. However, the difference between W50 and W90 (W50-W90) in the part where the line and space is 4 μm and 2 μm is significantly different from 0.08 μm and 0.24 μm. When the line and space is 2 μm, the fine concave portion becomes deeper. The etching rate continued to decrease gradually.

Experiment 2
A fine three-dimensional structure was formed in the same manner as in Experiment 1 except that multiple exposure (5 divisions each in vertical and horizontal directions) was performed with a DLP exposure apparatus and a resist pattern was drawn. Multiple exposure was performed by shifting an exposure spot of 0.5 μm square by 0.1 μm vertically and horizontally. Note that the total exposure energy integration amount of the multiple exposure is equal to the exposure energy of the first embodiment.

The drawn resist pattern and the created fine three-dimensional structure were observed with a scanning electron microscope. FIG. 12 shows a cross-sectional image of a resist pattern having a line and space of 4 μm. In addition, an overhead image of a fine three-dimensional structure and a cross-sectional image of a portion having a line and space of 4 μm are shown in FIGS. 13 and 14, respectively.

When the maskless exposure was subjected to multiple exposure, the resist pattern had a tail.
In addition, since the jagged steps of the resist pattern were reduced by the multiple exposure, it was possible to form a very smooth fine three-dimensional structure in the horizontal plane as compared with the fine three-dimensional structure of Experiment 1.

A fine recess having a depth of 10.2 μm could be formed at a line and space of 4 μm. Even when the cross-sectional image was magnified 500,000, scallops could not be confirmed. For this reason, the depth D of the scallop formed on the side surface is 12 nm or less. The calculated scallop period P is 34.0 nm.
The fine recesses W10, W50, and W90 were 4.83 μm, 4.64 μm, and 4.59 μm, respectively, and the variation coefficients (W10 to W90) were 2.70%. W95 was 4.59 μm, and the coefficient of variation (W10 to W95) was 2.45%. The taper angle was 89.1 degrees and the skirt length was 0.76 μm. Table 1 shows the measured values.
Even when a resist pattern drawn by maskless exposure was used, etching was able to proceed in a substantially vertical direction in a portion where the line and space was 4 μm, and the bottom portion also stood up sharply. Moreover, the scallop was not confirmed and the side surface was smooth.

Experiment 3
Instead of the Bosch process, a fine three-dimensional structure was formed in the same manner as in Experiment 2 except that etching gas and protective film forming gas were simultaneously flowed and etching was performed under the following conditions. Etching conditions are as follows.
Etching time: 600 seconds Pressure: 10 Pa
High frequency power frequency: 100 Hz
Size of high frequency power: 25W
Bias power: 2W
Etching: _SF 6, 4ml / min
Plasma _{_{deposition: C 4 F 8, 4ml /}} min

When the portion of the created fine three-dimensional structure having a line and space of 4 μm was observed with a scanning electron microscope, a fine recess having a depth of 5.12 μm could be formed. In Experiment 3, since the Bosch process is not used, a scallop is not formed.
W10, W50, and W90 of the fine recesses were 5.23 μm, 5.56 μm, and 5.23 μm, respectively, and the variation coefficient (W10 to W90) was 3.57%. W95 was 4.26 μm, and the coefficient of variation (W10 to W95) was 11.08%. The taper angle was 94.3 degrees and the skirt length was 0.48 μm. Table 1 shows the measured values.
In Experiment 3, the conditions for etching and deposition were poor, the taper angle was 94.3 degrees, and etching could not be performed in the vertical direction, and the width was the widest at 5.80 μm near the 80% depth position of the fine recess.

Claims

Forming a resist pattern drawn by maskless exposure on a substrate (1);
An isotropic etching step (2A) for forming a depression in the substrate by isotropic etching;
A plasma deposition step (2B) of depositing a protective film on the inner wall of the recess and the resist pattern;
A removal step (2C) for removing the protective film on the bottom surface of the depression by anisotropic etching;
A step (2) of forming a fine recess in the substrate by sequentially repeating an isotropic etching step (2A), a plasma deposition step (2B), and a removal step (2C);
A method for forming a fine three-dimensional structure, comprising:
2. The method for forming a fine three-dimensional structure according to claim 1, wherein the maskless exposure is multiple exposure.
When the widths at the 10% depth position, 50% depth position, and 90% depth position of the fine recess are W10, W50, and W90, respectively, the coefficient of variation (W10 to W90) of W10, W50, and W90 is 5%. The method for forming a fine three-dimensional structure according to claim 1 or 2, wherein:
The method for forming a fine three-dimensional structure according to any one of claims 1 to 3, wherein a scallop period P on the side surface of the fine concave portion is 100 nm or less.
The method for forming a fine three-dimensional structure according to any one of claims 1 to 4, wherein a scallop depth D on the side surface of the fine concave portion is 30 nm or less.
6. The method for forming a fine three-dimensional structure according to claim 1, wherein the diameter of the substrate is 0.5 inch.
The method for forming a fine three-dimensional structure according to any one of claims 1 to 6, wherein the cycle time is 0.5 seconds or more and 6 seconds or less.
The fine three-dimensional structure according to claim 6 or 7, wherein the coefficient of variation (W10 to W90) is 3.5% or less.
The fine three-dimensional structure according to any one of claims 6 to 8, wherein a depth D of the scallop is 12 nm or less.
A fine recess having a depth of 20 μm or less and a width of 3 μm or more on the substrate;
When the widths at the 10% depth position, 50% depth position, and 90% depth position of the fine recess are W10, W50, and W90, respectively, the coefficient of variation (W10 to W90) of W10, W50, and W90 is 5%. A fine three-dimensional structure characterized by:
The fine three-dimensional structure according to claim 10, wherein a scallop period P on the side surface of the fine concave portion is 100 nm or less.
The fine three-dimensional structure according to claim 10 or 11, wherein a depth D of the scallop is 30 nm or less.
A fine convex portion adjacent to the fine concave portion;
Having a resist covering the top of the fine protrusions;
The fine three-dimensional structure according to any one of claims 10 to 12, wherein a film thickness at an end portion of the resist is thinner than a film thickness at a central portion.
The fine three-dimensional structure according to claim 13, wherein the width of the mask undercut at the upper end of the fine convex portion is 30 nm or less.
The fine three-dimensional structure according to any one of claims 10 to 14, wherein a diameter of the substrate is 0.5 inches.
The fine three-dimensional structure according to claim 15, wherein the coefficient of variation (W10 to W90) is 3.5% or less.
The fine three-dimensional structure according to claim 15 or 16, wherein a depth D of the scallop is 12 nm or less.