JP2007088402A - Etchant and etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an etchant and an etching method capable of smoothing an etching process surface of a silicon substrate after etching. <P>SOLUTION: The etchant used for wet-etching a silicon substrate is an alkaline solution added with gold (Au) of high concentration, more than 100ppb. The alkaline solution is KOH aqueous solution. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an etching solution and an etching method used when wet etching a silicon substrate.

  2. Description of the Related Art Conventionally, as an etching technique for a silicon substrate, an anisotropic etching technique that is performed using a difference in etching rate with respect to an alkaline solution of the silicon substrate is known. This anisotropic etching process is performed by forming a mask pattern of a predetermined shape made of an oxide film or the like on the surface of a silicon substrate and bringing an etching solution into contact with the silicon substrate exposed through this mask pattern.

  It is said that etching processing can be performed with higher accuracy than mechanical processing, and the etched silicon substrate is required to have a very smooth surface. It is used in devices such as a liquid jet head such as a pressure sensor diaphragm. The surface of a silicon substrate used in such an apparatus is required to be smoother, and conventionally, a method for further smoothing the etched surface of a silicon substrate has been studied.

  As an etchant that can smooth the surface, for example, a solution in which the concentration of a metal component that suppresses an etching reaction between an etched surface of a silicon substrate and an etching component is adjusted to a predetermined range has been proposed (Patent Document 1). reference). This etching solution is obtained by adding Cu, Mg, and Pb metal components to an alkaline aqueous solution, and smoothes or roughens the etched surface by adjusting the metal concentration.

  There is a need for an etchant that can further smooth the silicon substrate.

Japanese Patent No. 3081171 (Claims etc.)

  In view of such circumstances, it is an object of the present invention to provide an etching solution and an etching method that can extremely smooth an etched surface of a silicon substrate after etching.

A first aspect of the present invention that solves the above-mentioned problems is an etching solution used when wet etching a silicon substrate, and is made of an alkaline solution containing gold (Au) having a concentration higher than 100 ppb. In the liquid.
In the first aspect, by using an etching solution made of an alkaline solution containing gold (Au) having a concentration higher than 100 ppb, the etched surface can be smoothed when the silicon substrate is wet-etched.

According to a second aspect of the present invention, there is provided an etching liquid according to the first aspect, wherein the gold (Au) concentration is 200 ppb or more.
In the second aspect, by using an etching solution having a gold (Au) concentration of 200 ppb or more, the etched surface can be more effectively smoothed when the silicon substrate is wet-etched. Further, the etching time is shortened and the etching accuracy is improved.

According to a third aspect of the present invention, there is provided an etching liquid according to the second aspect, wherein the gold (Au) concentration is 500 ppb or more.
In the third aspect, by using an etching solution having a gold (Au) concentration of 500 ppb or more, the etched surface can be more effectively smoothed when the silicon substrate is wet-etched.

According to a fourth aspect of the present invention, there is provided the etching solution according to the third aspect, wherein the gold (Au) concentration is 1000 ppb or more.
In the fourth aspect, by using an etching solution having a gold (Au) concentration of 1000 ppb or more, the etched surface can be more effectively smoothed when the silicon substrate is wet-etched.

According to a fifth aspect of the present invention, in the etching liquid according to any one of the first to fourth aspects, the alkaline solution is a KOH aqueous solution.
In the fifth aspect, when the alkaline solution is an etching solution that is an aqueous KOH solution, the silicon substrate can be efficiently etched when the silicon substrate is wet-etched.

According to a sixth aspect of the present invention, there is provided an etching method characterized by wet etching a silicon substrate using an etching solution made of an alkaline solution containing gold (Au) having a concentration higher than 100 ppb.
In the sixth aspect, the etched surface can be smoothed by wet-etching the silicon substrate using an etching solution made of an alkaline solution containing gold (Au) having a concentration higher than 100 ppb.

According to a seventh aspect of the present invention, in the etching method according to the sixth aspect, the concentration of gold (Au) in the etching solution is 200 ppb or more.
In the seventh aspect, the etched surface can be more effectively smoothed by wet-etching the silicon substrate using an etching solution having a gold (Au) concentration of 200 ppb or more. Further, the etching time is shortened and the etching accuracy is improved.

An eighth aspect of the present invention is the etching method according to the seventh aspect, wherein the gold (Au) concentration in the etching solution is 500 ppb or more.
In the eighth aspect, the etched surface can be more effectively smoothed by wet etching the silicon substrate using an etching solution having a gold (Au) concentration of 500 ppb or more.

According to a ninth aspect of the present invention, in the etching method according to the eighth aspect, the concentration of gold (Au) in the etching solution is 1000 ppb or more.
In the ninth aspect, the etched surface can be more effectively smoothed by wet etching the silicon substrate using an etching solution having a gold (Au) concentration of 1000 ppb or more.

According to a tenth aspect of the present invention, in the etching method according to any one of the sixth to ninth aspects, the alkaline solution is a KOH aqueous solution.
In the tenth aspect, the silicon substrate can be efficiently etched by performing wet etching on the silicon substrate using an etching solution whose alkaline solution is a KOH aqueous solution.

Hereinafter, the present invention will be described in detail based on embodiments.
The etching solution of the present invention is an etching solution used when wet etching a silicon substrate (silicon single crystal substrate), and is made of an alkaline solution containing Au at a concentration higher than 100 ppb. That is, Au is added so that the Au concentration becomes higher than 100 ppb. By using an etching solution made of an alkaline solution containing gold (Au) having a concentration higher than 100 ppb, the etched surface can be extremely smoothed when the silicon substrate is wet-etched. For example, when etching is performed to form a concave portion on a silicon substrate having a surface orientation (110) using the etching solution of the present invention, the concave portion having a side surface of the surface orientation (111) and a bottom surface of the surface orientation (110) is silicon The etched surface, ie, the bottom surface, which is formed on the substrate and has the plane orientation (110), is extremely smoothed. The etching solution of the present invention is very suitably used when wet etching a silicon substrate having a surface orientation (110). For example, it is used for a silicon substrate having a surface orientation (100). There is no particular limitation.

  The etching solution of the present invention can improve the smoothness of the etched surface if Au is added so that the concentration of Au is higher than 100 ppb, preferably 500 ppb or more. As the concentration of increases, the surface of the silicon substrate after etching is more effectively smoothed. Note that when the concentration of Au in the etching solution exceeds a certain level, the smoothness of the silicon substrate surface hardly increases with respect to the concentration of Au in the etching solution.

  In the etching solution of the present invention, the content of Au that has a particularly remarkable effect on smoothing is such that the concentration of Au in the etching solution is, for example, 500 ppb or more, more preferably 1000 ppb or more. If the content of Au is the amount described above, the etched surface can be made extremely smooth.

  When a silicon substrate is etched using an etching solution that does not contain Au, the surface roughness Ra of the etched surface is about 500 nm, although it varies slightly depending on the concentration of the alkaline solution. On the other hand, if the silicon substrate is etched using an etching solution to which Au is added so that the concentration of Au is higher than 100 ppb, particularly 500 ppb or more, the etched surface is extremely smoothed. The surface roughness Ra is 200 nm or less. Further, when the silicon substrate is etched using an etching solution added with Au so that the Au concentration becomes 1000 ppb or more, the surface roughness Ra of the etched surface becomes 100 nm or less, and the Au concentration becomes 500 ppb or more. The surface of the silicon substrate is smoothed more effectively than the etching solution to which is added. When the concentration of Au in the etching solution is about 2000 ppb or more, the surface roughness Ra of the etched surface is smoothed to about 20 nm, and even if more Au is added, the surface roughness Ra is smoothed with respect to the concentration of Au in the etching solution. There is almost no increase in sex.

  That is, in order to obtain an extremely smooth silicon substrate surface, the silicon substrate is etched with an etching solution to which Au is added so that the concentration of Au in the etching solution is preferably 500 ppb or more, more preferably 1000 ppb or more. That's fine. If Au is added so that the Au concentration in the etching solution is 2000 ppb or more, sufficient smoothness can be obtained.

  Moreover, it is preferable to add Au to the etching liquid of this invention so that the density | concentration of Au may become 200 ppb or more in terms of an etching rate. When a silicon substrate is etched using an etching solution to which Au is added, the etching rate of silicon (Si) is improved as compared with an etching solution to which no Au is added. When the concentration of Au in the etching solution is 200 ppb or more, the etching rate of silicon (Si) hardly changes any more and is stabilized at a high etching rate. That is, when an etching solution having an Au concentration of 200 ppb or more is used, the etching time is shortened, and the etching rate is not changed by a concentration error, so that the etching accuracy is improved.

Note that the etching rate of silicon dioxide (SiO ₂ ) at this time is the same as the etching solution to which no Au is added. That is, by adding Au to the etching solution, only the etching rate of silicon (Si) is selectively improved.

  When the silicon substrate is etched using an etching solution added with Au so that the concentration of Au becomes 200 ppb or more, the etching processing surface can be extremely smoothed when the silicon substrate is wet etched. It is shortened and the etching accuracy is improved.

  Further, the alkaline solution according to the present invention is not particularly limited, and examples thereof include KOH, hydrazine, ethylenediamine pyrocatechol (EDP), tetramethylammonium hydroxide (TMAH), etc. Among them, a KOH aqueous solution is particularly used. preferable. In the etching solution of the present invention, the concentration of the alkaline solution is not particularly limited. As the concentration of the alkaline solution increases, the smoothness of the etched surface when the silicon substrate is etched increases. However, in the case of the etching solution of the present invention, an extremely smooth etched surface even if the concentration of the alkaline solution is decreased. There is an advantage that can be obtained. That is, by adding Au to a low-concentration alkaline solution so as to have a concentration higher than 100 ppb, an etching solution that can make the etched surface of the silicon substrate extremely smooth can be obtained. Therefore, the etching solution of the present invention does not need to use a high-concentration alkaline solution as in the prior art, and may be a low-concentration alkaline solution.

  Furthermore, since the etching solution of the present invention only needs to be added with Au so as to have a concentration higher than 100 ppb, when a standard solution containing Au is added to the alkaline solution, adjustment is strictly performed using a special apparatus or the like. There is no need, for example, it may be added with a micropipette or the like. For this reason, there also exists an effect that an etching liquid can be easily made cheaply.

  The etching solution of the present invention may contain other metals as long as the effect of containing Au at a concentration higher than 100 ppb is not hindered.

  By performing wet etching on the silicon substrate using the etching solution of the present invention as described above, the etched surface of the silicon substrate can be made extremely smooth.

  When the etching solution of the present invention is used, a very smooth groove can be formed on the etched silicon substrate surface, so that the degree of structural freedom is increased in microfabrication using a silicon structure.

  The etching method of the present invention wet etches a silicon substrate (silicon single crystal substrate) using an etching solution made of an alkaline solution containing Au at a concentration higher than 100 ppb. Here, the wet etching is anisotropic wet etching, and is performed using a difference in etching rate of the silicon single crystal substrate. For example, when a silicon single crystal substrate having a plane orientation (110) is immersed in an etching solution, the silicon single crystal substrate is gradually eroded and a first (111) plane perpendicular to the (110) plane of the surface is formed. A second (111) plane appears which forms an angle of about 70 degrees with the (111) plane of the surface and makes an angle of about 35 degrees with the (110) plane of the surface. Since the etching rate of the (111) plane is about 1/180 compared to the etching rate of the (110) plane, the etching is substantially terminated when the (111) plane appears. At this time, when etching is performed using the etching solution of the present invention, the (110) plane which is a plane parallel to the surface is extremely smoothed.

  Hereinafter, the etching method of the present invention will be described in detail based on embodiments.

  FIG. 1 is a diagram showing an etching process according to an embodiment of the present invention. First, as shown in FIG. 1A, after an oxide film 2 is formed on one surface of a silicon substrate 1 having a plane orientation (110), the oxide film 2 is patterned as shown in FIG. Thus, a mask pattern 3 having a predetermined shape is formed. Here, the mask pattern is formed by thermally oxidizing the silicon substrate 1 to form an oxide film 2 made of a silicon oxide film, and patterning the oxide film 2 into a predetermined shape by photolithography.

  Next, as shown in FIG. 1 (c), an etching solution made of an alkaline solution containing Au having a concentration higher than 100 ppb is brought into contact with one surface side of the silicon substrate 1, thereby opening the mask pattern 3 having a predetermined shape. The silicon substrate 1 exposed through the portion 3a is anisotropically etched to form a recess 4 having a bottom surface 4a (hereinafter, etched surface 4a) having a surface orientation (110) in the silicon substrate 1. This completes the etching of the silicon substrate.

  In this embodiment, the etching method for forming the recesses in the silicon substrate has been described. However, when the entire silicon substrate is thinned, the entire silicon substrate is etched without forming a mask pattern. When the entire silicon substrate is thinned using the etching method of the present invention, the entire silicon substrate can be extremely smoothed.

  By the etching method of the present invention as described above, the etched surface of the silicon substrate can be made extremely smooth. Further, the etching method of the present invention can be used suitably for thinning the entire silicon substrate because the silicon substrate can be made extremely smooth. By thinning the silicon substrate by etching using an etching solution made of an alkaline solution containing Au at a concentration higher than 100 ppb, a silicon substrate having a very smooth surface can be obtained, and the silicon substrate surface can be ground and mechanically processed. This is unnecessary, and the manufacturing process of the desired silicon substrate is reduced.

  The silicon substrate subjected to anisotropic etching by the etching method of the present invention is not only a member constituting a device such as a liquid jet head such as an ink jet recording head or a pressure sensor diaphragm, but also an acceleration sensor, an in-vehicle It can also be used as a member that constitutes a small switching device in the field of airbags, aircraft navigation systems, and telecommunications.

(Test Example 1)
In this test example, after a mask pattern having a predetermined shape was formed on a silicon substrate, the silicon substrate having a plane orientation (110) was etched using the etching solutions of Examples 1 to 4 and Comparative Examples 1 and 2 shown below. By carrying out, the recessed part which has a bottom face of a surface orientation (110) was formed, and the surface state of the bottom face of a recessed part was observed.

  This test example will be described with reference to FIG. First, as shown in FIG. 1A, after an oxide film 2 is formed on one surface of a silicon substrate 1 having a plane orientation (110), the oxide film 2 is patterned as shown in FIG. Thus, a mask pattern 3 having a predetermined shape was formed. Here, the mask pattern was formed by thermally oxidizing the silicon substrate 1 to form an oxide film 2 made of a silicon oxide film, and patterning the oxide film 2 into a predetermined shape by photolithography.

  Next, as shown in FIG. 1 (c), an etching solution of Examples 1 to 4 and Comparative Examples 1 and 2 shown below is brought into contact with one surface side of the silicon substrate 1 to form a mask pattern 3 having a predetermined shape. The silicon substrate 1 exposed through the opening 3a was anisotropically etched to form a recess 4 having a bottom surface 4a (hereinafter, etched surface 4a) having a surface orientation (110) in the silicon substrate 1. At this time, the temperature of the surface of the silicon substrate was 80 ° C.

  The etched surface formed from the above process was observed with an electron microscope, and the surface roughness Ra was obtained. The results are shown in FIGS.

Example 1
An etching solution obtained by adding Au to an aqueous KOH solution having a concentration of 37.5% so that the Au concentration was 500 ppb was used as the etching solution of Example 1.

(Example 2)
The same etching solution as in Example 1 was used as the etching solution in Example 2 except that Au was added so that the Au concentration was 1000 ppb.

(Example 3)
The same etching solution as in Example 1 was used as the etching solution in Example 3 except that Au was added so that the Au concentration was 2000 ppb.

Example 4
The same etching solution as in Example 1 was used as the etching solution in Example 4 except that Au was added so that the Au concentration was 3000 ppb.

(Comparative Example 1)
Etching solution similar to Example 1 was used as the etching solution of Comparative Example 1 except that Au was not added.

(Comparative Example 2)
The same etching solution as in Example 1 was used as the etching solution in Comparative Example 2 except that Au was added so that the Au concentration was 100 ppb.

(Summary of results)
An etched surface using Example 1 to which Au is added so that the Au concentration is 500 ppb (see FIG. 2), and an etched surface using Comparative Example 1 to which Au is not added (see FIG. 6) The surface roughness Ra of the etched surface using Example 1 is 174 nm, and the surface roughness Ra is smaller than that of the etched surface using Comparative Example 1 of 449 nm. It can be seen that the silicon substrate is smoothed. Moreover, when the etching process surface (refer FIGS. 2-4) using Examples 1-3 is compared, it turns out that surface roughness Ra becomes small as the density | concentration of Au in etching liquid becomes high. On the other hand, as shown in FIGS. 4 and 5, the etched surfaces using Example 3 and Example 4 in which the Au concentration in the etching solution is 2000 ppb or more have surface roughness Ra of 24 nm and 23 nm, respectively. There was no significant difference. In addition, an etched surface using Comparative Example 1 in which no Au was added (see FIG. 6) and an etched surface using Comparative Example 2 in which Au was added so that the Au concentration was 100 ppb (see FIG. 7). ) And no significant effect on smoothing.

  That is, the smoothness of the etched surface 4a is improved by adding Au to the alkaline solution so that the Au concentration is higher than 100 ppb. Further, if the concentration of Au in the etching solution becomes a certain amount or more, the smoothness of the etched surface 4a hardly changes any more because a sufficient amount for smoothing is added.

  The etching solution of the present invention contains a higher concentration of Au than 100 ppb, thereby extremely smoothing the etched surface of the silicon substrate. As the Au concentration in the etching solution increases, the smoothness of the bottom surface of the etched silicon substrate increases. When the Au concentration in the etching solution exceeds a certain amount, the smoothness of the bottom surface of the silicon substrate increases. There is almost no rise. By containing Au having a concentration of preferably 500 ppb or more, particularly preferably 1000 ppb or more, a remarkable effect on smoothing can be seen. In addition, if the Au concentration in the etching solution is a certain amount or more, specifically, Au having a concentration of 2000 ppb or more is contained, the amount is sufficient for smoothing.

(Test Example 2)
In this test example, using the etching solutions of Examples 5 to 7 and Comparative Examples 3 and 4 shown below, a silicon (Si) single crystal substrate with a plane orientation (100) and silicon dioxide with a plane orientation (110) ( The etching rate of each of the SiO ₂ ) substrates was measured. The result is shown in FIG.

(Example 5)
An etching solution obtained by adding Au to an aqueous KOH solution having a concentration of 28.5% so that the Au concentration was 200 ppb was used as the etching solution of Example 5.

(Example 6)
The same etching solution as in Example 5 was used as the etching solution in Example 6 except that Au was added so that the Au concentration was 500 ppb.

(Example 7)
The same etching solution as in Example 5 was used as the etching solution in Example 7 except that Au was added so that the Au concentration was 1000 ppb.

(Comparative Example 3)
The same etching solution as in Example 5 was used as the etching solution of Comparative Example 3 except that Au was not added.

(Comparative Example 4)
Etching solution similar to Example 5 was used as the etching solution of Comparative Example 4 except that Au was added so that the Au concentration was 100 ppb.

(Summary of results)
As shown in FIG. 8, in the etching solution of Comparative Example 4, the silicon etching rate was about 1.9 μm / min, but in the etching solution of Example 5, the silicon etching rate was about 2.0 μm / min. Improved. In addition, the etching solutions of Example 6 and Example 7 had a silicon etching rate of around 2.0 μm / min, which was almost the same as Example 5. That is, when the Au concentration is 200 ppb or more, the silicon etching rate is stabilized in a high state. Therefore, the etching time is shortened and the etching accuracy is improved.

In each example and each comparative example, the etching rate of the silicon dioxide (SiO ₂ ) substrate with the plane orientation (110) was about 37.5 Å / min, and no change was observed. On the other hand, the etching rate of the silicon (Si) single crystal substrate with the plane orientation (100) changed. That is, by adding Au to the etching solution, only the etching rate of silicon (Si) is selectively improved.

It is a figure which shows the process of the etching concerning one Embodiment of this invention. FIG. 3 is a diagram showing the surface state of the silicon substrate of Example 1. It is a figure which shows the surface state of the silicon substrate of Example 2. FIG. It is a figure which shows the surface state of the silicon substrate of Example 3. FIG. It is a figure which shows the surface state of the silicon substrate of Example 4. FIG. 6 is a view showing a surface state of a silicon substrate of Comparative Example 1. FIG. 6 is a view showing a surface state of a silicon substrate of Comparative Example 2. FIG. It is a figure which shows the relationship between the density | concentration of Au in an etching liquid, and an etching rate.

Explanation of symbols

1 silicon substrate, 2 oxide film, 3 mask pattern, 3a opening, 4 recess

Claims (10)

An etching solution used when wet etching a silicon substrate, comprising an alkaline solution containing gold (Au) having a concentration higher than 100 ppb. The etching solution according to claim 1, wherein the gold (Au) concentration is 200 ppb or more. 3. The etching solution according to claim 2, wherein the gold (Au) concentration is 500 ppb or more. 4. The etching solution according to claim 3, wherein the gold (Au) concentration is 1000 ppb or more. 5. The etching solution according to claim 1, wherein the alkaline solution is a KOH aqueous solution. An etching method comprising wet etching a silicon substrate using an etching solution made of an alkaline solution containing gold (Au) having a concentration higher than 100 ppb. 7. The etching method according to claim 6, wherein the concentration of gold (Au) in the etching solution is 200 ppb or more. 8. The etching method according to claim 7, wherein a concentration of gold (Au) in the etching solution is 500 ppb or more. 9. The etching method according to claim 8, wherein the concentration of gold (Au) in the etching solution is 1000 ppb or more. The etching method according to any one of claims 6 to 9, wherein the alkaline solution is a KOH aqueous solution.

Images