JP3785463B2 - Microstructure fabrication method - Google Patents

Description

  The present invention does not require a complicated masking operation that has been conventionally performed when patterning single crystal silicon, and the height of the fine pattern to be formed depends on the processing conditions when performing micromachining of a predetermined shape. The present invention relates to a method for manufacturing a fine structure in which the control is adjusted.

  Conventionally, in semiconductor manufacturing, a photo-sensitive photoresist is applied to the surface of a thinly cut single crystal silicon wafer, and then this surface is covered with an exposure mask pattern to irradiate far ultraviolet rays to develop it. The mask pattern is transferred to the photoresist. Next, this is oxidized, and the pattern of the actual circuit is formed by etching the resist pattern thus formed. Such a technique is not limited to semiconductor manufacturing, and is widely used, for example, in the formation of minute members made of single crystal silicon.

In addition, the following patent document 1 by the present inventors exists as a technique which solved the problem to be solved by the invention shown below by a method different from the present invention.
JP 2002-64080 A

  As described above, when finely processing single crystal silicon by etching, it is necessary to perform a photoresist adhesion process, a mask pattern transfer operation by irradiation with far ultraviolet rays, an oxidation process, and the like, and it is necessary to perform complicated processes many times. Therefore, there is a problem that it takes a lot of work and time.

  In addition, in order to change the existing pattern, it is necessary to recreate the exposure mask, and there is also a problem that it is not suitable for fine structure manufacturing that requires a degree of freedom such as trial manufacture.

  Furthermore, when forming recesses and protrusions of various shapes on single crystal silicon, the masked portion must be formed as protrusions, so there is a problem that the method of forming the recesses and protrusions is limited. It was.

  Therefore, the present invention does not require photoresist processing, far-ultraviolet irradiation work, oxidation treatment, etc. when finely processing single-crystal silicon by etching. It is an object of the present invention to provide a fine structure manufacturing method capable of manufacturing a fine structure.

  2. Description of the Related Art Conventionally, research on micromachining technology using a scanning probe microscope (SPM) technique such as a friction force microscope (FFM) or an atomic force microscope (AFM) has been made. For example, as shown in FIG. 19, as a micro processing machine using the principle of a friction force microscope, a high-rigidity processing cantilever 4 is used instead of a flexible cantilever used in a conventional friction force microscope, and laser diode 1 is used. Is irradiated to the back surface of the tip of the processing cantilever 4 provided at the tip with diamond abrasive grains 5 in contact with the surface of the material 3 via the lens 2, and the reflected light is received by the four-divided photodetector 6. Is.

  The light reception signal is a signal obtained by detecting the state of the processing cantilever 4 by an optical lever system, and represents the state of deflection and twist of the processing cantilever 4. Deflection and torsion of the processing cantilever are calculated, compared with a preset value, an error signal is output to the tube-type PZT scanner 7, and the material 3 is moved in the X, Y, and Z directions to obtain a predetermined value. A predetermined shape can be processed while maintaining the depth of cut.

  The processing cantilever 4 is obtained by attaching diamond abrasive grains 5 having a tip as shown in an enlarged view in FIG. 1C to the tip of a lever 10, as shown in an enlarged view in FIG. Yes, this cantilever has high rigidity as described above. By using such a tool, the material surface is rubbed, and fine cutting can be performed with a nanometer-order cut.

  Using such a micro processing machine, fine cutting is performed with diamond abrasive grains along a predetermined masking shape. At this time, there is a disorder of crystallinity or residual stress on the surface after the cutting process, and a work-affected layer is formed. Masking action is performed for anisotropic etching using potassium oxide.

  It was discovered that this masking action varies depending on the concentration of the etching solution such as potassium hydroxide, and the invention as shown in Patent Document 1 has been reached, and the patent assessment has been finalized. The present inventors have further advanced this research and found that the above problems can be solved by other means, and by adjusting the height of the fine pattern to be formed in such fine processing, In addition, it was discovered that the height of the fine pattern to be formed can be adjusted only by adjusting the feed amount at the time of micromachining, without adjusting the concentration of the etching solution, and has led to the present invention. It is.

More specifically, in order to solve the above-described problem, the fine structure manufacturing method of the present invention performs a predetermined shape micromachining on the surface of a single crystal silicon material, and etches the material with an etching solution of an alkaline aqueous solution. In the microstructure manufacturing method for forming a fine pattern having a shape, the height of the formed fine pattern is adjusted by arbitrarily selecting the vertical load of the micromachined portion.

In another fine structure manufacturing method according to the present invention, a fine pattern of a predetermined shape is formed by performing micromachining of a predetermined shape on the surface of a single crystal silicon material and etching the material with an etching solution of an alkaline aqueous solution. in the microstructure manufacturing method, by arbitrarily selecting a feed amount during the micromachining, in which so as to adjust the height of the fine pattern to be formed.

  In another microstructure manufacturing method according to the present invention, the fine machining is performed by a mechanism of a friction force microscope.

  Further, another microstructure manufacturing method according to the present invention is the above-described micromachining, in which the tool tip is moderately blunted to form a work-affected layer on the surface without performing removal processing, and to form a fine pattern. It ’s what you get.

As described above, when etching is performed after FFM processing according to previous research results, it is known that the FFM processing region shows a masking effect, and a convex structure remains to be formed. It became clear that it was possible to produce a structure, and it was possible to arbitrarily form a concavo-convex shape depending on the concentration of the etching solution using this, but in the present invention, various experiments were further performed, In order to fabricate a three-dimensional microstructure having a controlled height direction, the influence of FFM processing conditions on the etching rate was investigated. as a result,
1) As the vertical load increases, the etching rate of the FFM processed portion decreases and the convex structure height increases.
2) When the scanning line feed amount is reduced, the influence of the scanning lines causes the mask layer to become stronger and the etching rate to decrease.
3) The change in the processing speed hardly affects the masking effect.
4) As the etching time increases, the height of the convex structure formed in the FFM processed portion increases, but the height of the convex structure hardly changes when the masking effect is lost.
5) By changing the processing conditions, it is possible to produce a three-dimensional microstructure having a controlled height direction.
6) When the tip of the tool is moderately dull, a work-affected layer having an action as an etching mask can be formed on the surface without removing the surface of the material.
It became clear that there existed these effects. Further, by controlling the processing conditions with higher accuracy, it becomes possible to manufacture a more complicated three-dimensional microstructure.

The present invention adopts the fine structure manufacturing method as described above, and does not require photoresist processing, far-ultraviolet irradiation work, oxidation treatment, etc. when finely processing single crystal silicon by etching, and it is simply micromachining. The height of the fine pattern to be formed can be arbitrarily adjusted by arbitrarily selecting the vertical load of the portion or by arbitrarily selecting the feed amount at the time of fine machining. There are advantages of the present invention.

The present invention does not require photoresist processing, far-ultraviolet irradiation work, oxidation treatment, etc. when finely processing single crystal silicon by etching, and simply having an arbitrary shape and an arbitrary height depending on conditions during the fine processing. In order to be able to manufacture a fine structure, a fine structure is produced by forming a fine pattern of a predetermined shape by subjecting the surface of a single crystal silicon material to a predetermined shape of micro machining and etching the material with an etching solution. In the method, the height of the fine pattern to be formed is adjusted by arbitrarily selecting the vertical load of the micromachined portion.

  Hereinafter, the present invention will be described in detail including the background to the present invention. As described above, when the FFM processed sample is etched with a KOH aqueous solution, the FFM processed surface exhibits a strong masking action, and it has been clarified that a convex structure is formed. This phenomenon is caused by an oxide layer having low crystallinity formed by FFM processing.

  In previous experiments, we could not refer to the surface before etching, so we could not fully study the strength of the masking effect due to processing conditions, but by introducing an etching rate calculation method based on the surface before etching. The etching rate can be measured accurately. Accordingly, an apparatus that is almost the same as the conventional processing apparatus shown in FIG. 19 is used. However, unlike the previous experiments, as shown in FIG. 10 was also used for processing experiments. As a result, it is possible to control the structure and thickness of the mask layer under the condition that the protuberance is generated without removing the processing region, and the etching rate can be controlled, so that the processing depth by FFM processing is reduced. Control of the height of the remaining convex structure is also facilitated.

FIG. 2 shows a method for calculating an etching rate necessary for confirming the operation and effect of the present invention. First, a silicon wafer for processing experiment in which a mask pattern of a SiO ₂ mask 22 is drawn on a single crystal silicon 21. 23 was produced. On the silicon wafer 23, numbers 00 to 99 were prepared as shown in FIG. 3 for identifying the processing marks, and a 40 × 40 μm square SiO ₂ mask pattern was prepared thereunder for height measurement. FFM processing is performed in the vicinity of the mask of the SiO ₂ film, and the depth of the processing mark is measured. Next, the silicon material 3 is put into the etching solution 14 by an apparatus shown in FIG. 1C to perform an etching process, and the height of the convex structure is measured. In the example shown in FIG. 1C, the internal water 13 is vibrated using the ultrasonic generator 12, and the etching process is performed under this vibration state, whereby the etching rate and the surface roughness are reduced. It is improving. Thereafter, the SiO ₂ mask is removed by hydrofluoric acid treatment, and the height of the mask portion is measured. From these values, the etching amount is given by the following equation.
E = Hm− (Hr + D) (1)
The etching rate can be calculated by dividing this value by the etching time.

In the first experiment, in order to investigate the influence of the processing conditions on the masking action, a single-crystal silicon wafer (100) surface was processed under the conditions shown in Table 1 using a sharp cantilever for processing, and then silicon with hydrofluoric acid. The natural oxide film on the wafer surface was removed, and the sample was etched while applying ultrasonic waves to the KOH aqueous solution under the conditions shown in Table 2. Finally, washing with running water was performed sufficiently, the surface was dried, and changes in the shape of the processed part were observed with an observation cantilever.

  FIG. 4 shows the relationship between the vertical load, the processed portion depth, and the etching rate. In the case of a minute vertical load (24 μN), a raised phenomenon occurs in the FFM processed portion, resulting in a convex shape. As the vertical load increases, the depth of the processed portion increases instead of the removal processing. The etching rate of the processed portion decreases as the vertical load increases. That is, it can be seen that the masking effect of the processed portion becomes stronger as the vertical load increases.

  FIG. 5 shows the relationship between the scanning line feed amount, the depth of the processed portion, and the etching rate. As the scanning line feed amount increases, the depth of the processed portion decreases and the etching rate of the processed portion increases. That is, it can be seen that the masking effect of the processed portion becomes stronger as the scanning line feed amount decreases. In this case, the surface roughness of the processed part is also reduced.

  Applying the relationship between FIG. 4 and FIG. 5, a three-dimensional microstructure was formed. FIG. 6 shows an example of forming a fine structure having a uniform height. A shape of a Chiba Prefecture map having an area of about 5 μm × 10 μm and a height of about 60 nm was created under the processing conditions of a vertical load of 180 μN and a scanning line feed amount of 40 nm. FIG. 4A is an AFM observation image (concave) immediately after processing, and FIG. 4B is an AFM observation image (convex) after etching.

  FIG. 7 shows an example of creating a staircase-like fine structure. Processing was performed at a vertical load of 90 μN in the A part, a vertical load of 225 μm in the B part, and a scanning line feed amount of 60 nm ((a) in the figure). After the etching process, a convex step with an A portion height of 68 nm and a B portion height of 104 nm was formed ((b) in the figure). The fact that the etching rate of the processed portion decreases as the vertical load increases is used.

  FIG. 8 shows an example of forming a three-dimensional fine structure whose height changes. A three-dimensional gear having an outer diameter of 10 μm, a convex base diameter of 7 μm, a shaft hole diameter of 4 μm, and a step having a convex base higher than the tooth portion was manufactured. The vertical load was 90 μN on the convex base part, 18 μN on the tooth part, and the scanning line feed amount was 60 nm. After the etching process under the conditions shown in Table 2, a three-dimensional gear as shown in FIG. FIG. 8B is a cross-sectional view of the three-dimensional gear. The tooth height is 65 nm and the height of the convex base is 77 nm.

  As a result of investigating the relationship between the etching rate of the FFM processed portion and the processing conditions as described above, the masking effect increases with increasing vertical load, and the masking effect increases with decreasing scanning line feed amount. confirmed.

In FFM processing, the relationship between the vertical load and the removal depth changes depending on the sharpness of the tip of the processing cantilever. Therefore, the following second experiment was also conducted using a processing cantilever with a moderately dull tip shape. It was. That is, in order to further confirm the above phenomenon, the following second experiment was also conducted. That is, in order to investigate the influence of the processing conditions on the masking action, the experiment was performed while changing the processing conditions of the vertical load processing speed and the scanning line feed amount according to the FFM processing conditions shown in Table 3 and the etching conditions shown in Table 4. .

  FIG. 9 shows changes in the etching rate, processing depth, and convex structure height with respect to the vertical load. When the vertical load was 372 μN or less, the removal process was not performed by the FFM process, and a protrusion having a height of about 1 to 2 nm was formed as shown in FIG. This phenomenon is attributed to a physicochemical phenomenon that occurs on the probe and the sample surface during FFM processing. This phenomenon disappeared as the vertical load increased, and removal processing was performed at 433 μN or more. On the other hand, the etching rate tended to decrease as the vertical load increased in the raised region. From this, it is considered that the crystallinity disorder of the FFM processed part is increased by the increase of the vertical load, and the masking effect is enhanced. On the other hand, under this condition, no significant change was observed in the etching rate in the removal processing region.

  FIG. 11 shows changes in the etching rate depending on the processing speed. As is apparent from this graph, there is almost no change in the etching rate depending on the processing speed, and the convex structure having almost the same height under any condition. Things are formed. Therefore, it is considered that there is almost no influence on the masking effect due to the change in the processing speed.

  FIG. 12 shows changes in the etching rate, processing depth, and convex structure height with respect to the scanning line feed amount. The vertical load was fixed at 310 μN, and the conditions were changed in the raised region shown in FIG. When the scanning line feed amount was 29 nm, which is the smallest, etching hardly progressed in the FFM processed portion, and a very high convex structure having a height of about 330 nm was formed. As the scanning line feed amount increased, the masking effect decreased and the etching rate increased.

  FIG. 13 is an AFM observation image when the scanning line feed amount is 29 and 469 nm. When the scanning line feed amount is 29 nm which is small, a strong mask layer is uniformly formed in the FFM processed region as shown in FIG. On the other hand, when the scanning line feed amount is increased, a masking effect appears on the scanning lines. However, since the masking effect does not appear between the scanning lines, the etching progresses and the FFM processing region becomes comb-like. Further, the interval between the comb-like peaks coincides with the scanning line feed amount.

  From the above, it is considered that when the scanning line feed amount is small, the work-affected layer is further affected by the adjacent scanning line during FFM processing, and the masking effect is enhanced.

  FIG. 14 shows changes in the etching rate and the height of the convex structure with respect to the etching processing time of the sample processed by FFM under the two kinds of conditions of the scanning line feed amount, 29 nm, and 59 nm where the difference in etching rate was large as described above. When the scanning line feed amount is 29 nm, which has a strong masking effect, the FFM processing region is hardly etched until the etching processing time reaches 40 minutes, the convex structure height increases almost linearly, and the convex shape of about 950 nm. A structure was formed. Thereafter, when reaching 60 minutes, the mask layer in the FFM processing region was eroded, so that the masking effect was weakened and the etching rate was rapidly increased.

  On the other hand, when the scanning line feed amount is 59 nm, the etching is not performed until the etching processing time is 5 minutes. However, when the scanning processing time is 10 minutes, the masking effect of the FFM processed portion is weakened, and thereafter the convex structure height is not changed. . FIG. 15 is an AFM observation image after 40 and 60 minutes of etching processing time of a sample processed with a scanning line feed amount of 29 nm. Compared with the etching time of 10 minutes, after 40 minutes, the upper surface of the convex structure is flat, but the shape of the processed region is slightly broken and the width is reduced. Further, in the sample 60 minutes after the masking effect is lowered, the upper surface of the convex structure is not flat, and the etching progresses, so that the surface is uneven.

  FIG. 16 shows the change in the etching rate with respect to the concentration of the KOH aqueous solution. The processing conditions were the same as described above. When the scanning line feed amount is 29 nm, the FFM processed region is hardly etched when the concentration is 20 wt% or less, and when the concentration is 20% or more, the etching rate increases as the concentration increases. When the scanning line feed amount is 59 nm, the masking effect is smaller than that of the scanning line feed amount 29 nm, but when the concentration is 5 wt%, etching is not performed in the FFM processing region. When the concentration was 10 wt% or more, the etching rate increased with increasing concentration, and no significant change was observed after the concentration of 15 wt%.

As described above, the etching rate of SiO ₂ depends on the KOH aqueous solution concentration. For this reason, when the KOH aqueous solution concentration increases, the mask layer disappears at the initial stage of etching, and the etching rate increases. On the other hand, since the mask layer is less likely to be eroded by KOH when the concentration is 5 wt%, etching is not performed under any processing conditions. From this, it is considered that a concentration of 10 to 20 wt% is appropriate for controlling the etching rate according to the processing conditions.

  Also from the above results, it was found that by controlling the FFM processing conditions, in particular, the vertical load and the scanning line feed amount, the masking effect of the FFM processed portion changes, and the height of the convex structure can be controlled. It can be seen that by applying this, it is possible to produce a three-dimensional microstructure.

  FIG. 17 shows a step-like structure manufactured by changing the vertical load stepwise. FFM processing was performed by changing the vertical load from the A side to (124), 248, and 372N. After the FFM processing, uplift processing is performed in the processing portion, but almost no change in height due to vertical load is seen. (B) is the result of performing an etching process for 10 minutes with a 10 wt% KOH aqueous solution after FFM processing. It can be seen from the figure that the larger the vertical load, the stronger the masking action and the higher the convex structure is formed.

  FIG. 18 shows a stepped structure produced by changing the vertical load more finely. The vertical load is produced by performing the same etching process at the stage of 124, 186, 248, 310, 372N from the A side of (a).

  From these results, it was found that it is possible to produce a three-dimensional microstructure having a height controlled by controlling the processing conditions. Also. It is considered that a highly accurate three-dimensional microstructure can be produced by controlling the processing conditions in more detail.

  Since the present invention can easily carry out extremely fine processing as described above, it can be used as ultra-precision processing of various devices used in the fields of the electronics industry, information industry, optical industry, and the like.

It is a perspective view which shows the outline | summary of the apparatus which implements this invention. It is a figure which shows the calculation method of the etching rate in this invention. It is a figure which shows the silicon wafer for a processing experiment used in this invention. It is a graph which shows the relationship between the vertical load in 1st experiment, and a process part etching rate. It is a graph which shows the relationship between the scanning line feed amount and the process part etching rate in 1st experiment. It is an example of the shape of the Chiba map produced in the first experiment. It is an example of creating a staircase-like microstructure manufactured in the first experiment. It is an example of creation of the three-dimensional gear manufactured in the first experiment. It is a graph which shows the change of the etching rate by a perpendicular load in the 2nd experiment. It is a figure which shows the AFM observation image of the protruding process trace in this invention in 2nd experiment. It is a graph which shows the change of the etching rate by processing speed in the 2nd experiment. It is a graph which shows the change of the etching rate by a scanning line feed amount in 2nd experiment. It is a figure which shows the shape change after the etching by the scanning line feed amount in this invention in 2nd experiment. It is a graph which shows the change of the etching rate by etching processing time in the 2nd experiment. It is a figure which shows the change of the shape by the etching processing time in this invention in 2nd experiment. It is a graph which shows the KOH aqueous solution density | concentration dependence of the sking effect in 2nd experiment. It is a figure which shows the three-step step-like structure created by the vertical load change in this invention in 2nd experiment. It is a figure which shows the five-step step-like structure created by the vertical load change in this invention in 2nd experiment. It is a schematic diagram of the apparatus which implements the fine structure manufacturing method proposed previously.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser diode 2 Lens 3 Material 4 Processing cantilever 5 Diamond abrasive grain 6 4 division | segmentation photodetector 7 Tube PZT scanner 8 Feedback control apparatus 10 Cantilever 11 Tip 12 Ultrasonic generator 13 Water 14 Etching liquid

Claims (4)

In a fine structure manufacturing method in which a fine pattern of a predetermined shape is formed by performing micromachining of a predetermined shape on the surface of a single crystal silicon material and etching the material with an etching solution of an alkaline aqueous solution, the vertical load of the micromachined portion A method for producing a fine structure, wherein the height of a fine pattern to be formed is adjusted by arbitrarily selecting. In a fine structure manufacturing method in which a fine pattern of a predetermined shape is formed by performing micromachining of a predetermined shape on the surface of a single crystal silicon material and etching the material with an etching solution of an alkaline aqueous solution, a feed amount during the micromachining A method for producing a fine structure, wherein the height of a fine pattern to be formed is adjusted by arbitrarily selecting. 3. The microstructure manufacturing method according to claim 1, wherein the fine machining is performed by a mechanism of a friction force microscope. 4. The fine machining according to claim 1, wherein in the fine machining, the tool tip portion is appropriately blunted to form a work-affected layer on the surface without performing removal processing, thereby obtaining a fine pattern. The fine structure manufacturing method as described in any one.

Images