JP2006351811A - Anisotropic etchant composition used for silicon microfabrication and etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an etchant composition having a high silicon etching speed and capable of reducing a silicon etching process time while maintaining etching characteristics such as an etching speed ratio depending on crystal surfaces and smoothness of an etching surface in silicon etching, and an etching method of silicon employing this etchant composition. <P>SOLUTION: The etchant composition used for silicon microfabrication contains inorganic alkali compound and ascorbic acid or glyoxylic acid. The inorganic alkali compound is at least one kind selected from among sodium hydroxide, potassium hydroxide, ammonia and hydrazine. Moreover, the compound contains at least one kind of alcohol, pyrocatechol, glycerol and glyceric derivative. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to etching of silicon members. Furthermore, since it is an aqueous solution of an alkali compound, it is used for microfabrication of a silicon member, a silicon anisotropic etching agent having a different etching rate with respect to the crystal plane orientation of the silicon surface, and an anisotropy using the anisotropic etching agent. The present invention also relates to an electronic device such as a MEMS (Micro Electro Mechanical Systems) such as a semiconductor pressure sensor and a speed sensor, which has a silicon wafer subjected to the etching method and further the anisotropic etching method.

  Conventionally, when etching a silicon single crystal substrate with a chemical solution, a method of etching with an acid-based etchant that is a mixed aqueous solution composed of components such as hydrofluoric acid, nitric acid, acetic acid, potassium hydroxide, tetramethylammonium hydroxide, There is a method of etching with an alkaline etching agent that is an alkaline aqueous solution such as an aqueous solution of hydrazine (see Non-Patent Documents 1 and 2). Of these, the acid-based etchant has an isotropic etching rate regardless of the crystal plane orientation of the silicon single crystal substrate, so that the chemical etching for uniformly etching the silicon substrate surface cut from the silicon single crystal ingot, etc. Many have been used. On the other hand, alkaline etching agents have an etching rate that depends on the crystal orientation of the silicon single crystal substrate, that is, they can be anisotropically etched, so they are used for silicon microfabrication in combination with photolithography technology. I came.

Many studies and studies have been made on silicon etching using an alkaline etching agent. Currently, the most widely used etching agent is an inorganic alkaline aqueous solution containing alcohols such as isopropyl alcohol, ethyl alcohol, and methyl alcohol to suppress undercut and smooth the unevenness of the etching pattern wall shape. Is. In Patent Document 1, by using an alkaline etching agent in which 0.5 to 1 volume of anhydrous ethylenediamine is mixed with 1 volume of hydrated hydrazine, the conventional silicon etching of potassium hydroxide, sodium hydroxide, and hydrazine is different. A technique for suppressing the generation of micro pyramids while maintaining the properties is disclosed. In patent document 2, the device which makes the etching rate in a processing tank uniform is disclosed when using the etching agent which consists of aqueous alkali solution and alcohol. Patent Document 3 discloses a silicon etchant composed of an alkali compound and a higher alcohol that does not etch a p-type doped region and etch other regions with high selectivity by using a temperature lower than the flash point. ing. In Patent Document 4, the etching surface is flat, the etching bottom surface is parallel to the main surface of the substrate, the silicon etching rate is high, and the degree of erosion of the silicon oxide film as a mask is extremely low 0.3% or more. An alkaline etching agent comprising three components of potassium hydroxide, hydrazine and water is disclosed. In Patent Document 5, an etching agent in which two or more alkalis having different crystal planes such as potassium hydroxide and ethylenediamine, potassium hydroxide and tetramethylammonium hydroxide, or potassium hydroxide and ammonia are mixed is mixed. Thus, a technique for obtaining a smooth etched wall surface is disclosed. Further, Patent Document 6 discloses a technique for improving the etching rate and obtaining a uniform etching surface by adding a reducing agent to a potassium hydroxide solution under pressure and performing silicon etching.
Sato, "Silicon Etching Technology", Surface Technology, Vol.51, No.8, 2000, P754-759 Esashi, “2003 Micromachine / MEMS Technology Encyclopedia”, p.109-114 JP 49-076479 JP 05-102124 A JP 08-31452 Japanese Patent No. 3444409 Japanese Patent No. 3525612 JP 2000-349063 A

  In the MEMS field, which has been growing rapidly in recent years, silicon microfabrication has been carried out by a combination of photolithography technology and anisotropic etching. Many different alkaline etchants have been developed, such as the ratio of the etching rate by the surface (for example, the ratio of the etching rate of the surface (100) to the etching rate of the surface (111)) and the smoothness of the etching surface (bottom surface, wall surface). in use.

  However, in response to the demand for improving MEMS productivity as demand grows, the process time of silicon etching using this alkaline etching agent is rate-limiting, and shortening of this process time has become a major issue. That is, in the silicon etching process in MEMS manufacturing, there are many processes for etching silicon to a depth of several hundred μm or more, and the etching rate varies slightly depending on the composition of the alkaline etching agent, but a long process time of 10 to 10 days. Is needed. This long process time is problematic because it deviates from the allowable range of time that can be spent on one process in the construction of a mass production system. In order to solve this problem, attempts have been made to shorten the silicon etching process time by changing the composition of the alkali-based etchant, but the difference in the etching rate depending on the crystal plane, the etching surface (bottom surface, side surface) It is not easy to review the composition of each company found based on many years of experience and many studies and examinations from the viewpoints of smoothness and chemical use restrictions from safety. The actual situation is that productivity is improved by increasing the number of etching apparatuses (tanks) while taking a long process time.

In view of the above problems, the object of the present invention is to maintain the etching characteristics such as the etching rate ratio by the crystal plane and the smoothness of the etching plane in the silicon etching, and the silicon etching rate is high and the silicon etching process time is shortened. It is another object of the present invention to provide an etching composition and a method for etching silicon using the etching composition, and further to provide an electronic apparatus having a silicon substrate processed by the etching method.

  As a result of intensive studies to solve the above problems, the present inventors have found that an alkaline etching composition having a composition in which ascorbic acid or glyoxylic acid is added to an inorganic alkaline aqueous solution is based on the conventional crystal plane of the alkaline aqueous solution. The inventors have found that there are excellent characteristics that the etching rate with respect to silicon is high while maintaining the etching characteristics such as the etching rate ratio and the smoothness of the etched surface, and the present invention has been completed. That is, this invention relates to the etching agent composition used for the silicon | silicone fine processing characterized by containing an inorganic alkali compound and ascorbic acid or glyoxylic acid.

  According to the present invention, it is possible to perform etching that is preferably used for fine silicon processing with a high etching rate. In particular, the ability to increase the etching rate while maintaining the basic alkali compound concentration, composition, and etching characteristics is extremely effective in a manufacturing process using silicon microfabrication technology.

The inorganic alkali compound used in the present invention can be used as long as it is a compound showing strong alkalinity, and a known alkali compound capable of obtaining desired etching characteristics may be used. Among them, sodium hydroxide, potassium hydroxide, Ammonia and hydrazine are preferred. The alkali compounds may be used alone or in combination of two or more kinds, and a combination of potassium hydroxide and ammonia may be used.
Moreover, it is also possible to use it in combination with an organic alkali compound as needed. Examples of the organic alkali compound include quaternary ammonium hydroxide, choline, and ethylenediamine.

  The concentration of the alkali compound used in the present invention may be a conventional alkali compound concentration that provides desired etching characteristics, but the solubility of the alkali compound in water, the concentration of reducing sugars in the etching agent composition, and other additions to be added It can also be appropriately determined depending on the agent concentration, and is preferably used in the range of 0.1 to 65% by weight, more preferably in the range of 1 to 40% by weight. If the concentration is lower than 0.1% by weight, the silicon etching rate is very slow or etching is not performed. If the concentration is higher than 65% by weight, crystal precipitation or solidification occurs in the etching agent composition. Absent.

  The ascorbic acid and glyoxylic acid of the present invention may be used alone or in combination of two kinds. The concentrations of ascorbic acid and glyoxylic acid are appropriately determined depending on the solubility in water, the concentration of the alkali compound in the etching composition, and the concentration of other additives added, but preferably 0.1 to 50% by weight. And more preferably in the range of 1 to 40% by weight. If the concentration is lower than 0.1% by weight, the desired silicon etching rate cannot be improved. If the concentration is higher than 50% by weight, crystals are precipitated and solidified in the etching agent composition, which makes it difficult to handle. .

  In addition to inorganic alkali compounds and ascorbic acid or glyoxylic acid, conventionally used additives may be added to the etching agent composition of the present invention. If desired, silicon may be dissolved in the etching agent composition, or a surfactant may be added to improve wettability. As the surfactant, for example, any of cationic, nonionic and anionic surfactants can be used. Or add decomposition additives to prevent decomposition of additives, additives to prevent damage to components other than silicon used for silicon microfabrication, or additives or organic solvents to control the etching rate of silicon Also good. Of these, alcohol, pyrocatechol, glycerin or glycerin derivatives are preferred. Examples of the alcohol include methanol, ethanol, isopropyl alcohol, n-propyl alcohol, isobutyl alcohol or n-butyl alcohol, and examples of the glycerol derivative include diglycerol and polyglycerol. Although the pH of the etching agent composition of this invention should just be an alkali higher than 7, pH11 or more is preferable.

  The etching method for microfabrication of silicon of the present invention is usually for immersing an etching object in a heated etching agent composition, taking it out after a predetermined time, and removing the etching agent composition from the etching object. A method of rinsing with water or the like and then drying is performed. The use temperature of the etchant composition is preferably from room temperature to below the flash point of the etchant composition from the viewpoint of equipment and safety. Moreover, when an etching agent composition does not have flash point, use at the temperature below normal temperature to a boiling point is preferable. However, when effective treatment is performed in the processing facility, use in a temperature range other than the above temperature range is also possible. Moreover, in order to obtain a faster etching rate by using it at higher temperature, you may use an etching agent composition under pressure.

  Since the etching composition of the present invention is characterized by its ability to etch silicon, it is mainly used for etching silicon single crystals. Since this silicon single crystal is crystalline, the etching rate differs depending on the crystal plane orientation. Isotropic etching characteristics can be utilized. Specifically, after a silicon oxide film or silicon nitride film is formed on a silicon substrate made of a silicon single crystal, the pattern is formed by etching the silicon oxide film or silicon nitride film using the resist patterned on the upper layer as a mask. After forming on a silicon substrate, anisotropic etching is given to a silicon substrate with the etching agent composition of the present invention. In addition, in an electronic device such as a speed sensor, anisotropic etching may be performed on a silicon substrate made of a silicon single crystal in which a metal such as aluminum used as a wiring or element is previously patterned. Furthermore, the etching agent composition in the present invention is not only anisotropic etching for silicon single crystals using the etching rate difference depending on the crystal plane orientation as described above, but also from the feature of improving the etching rate of silicon. Etching targets include amorphous polysilicon and amorphous silicon, doped polysilicon doped with these, doped amorphous silicon, and other silicon materials such as silicon oxide film, silicon nitride film, and silicon organic film It can also be applied to the etching.

  The etching method in the present invention is mainly applied to MEMS manufacturing having a deep silicon etching process using anisotropic etching, but can also be applied to manufacturing semiconductor integrated circuits, flat panel display devices, and the like. Examples of the electronic apparatus having a silicon substrate processed by using the etching method of the present invention include an acceleration sensor, an angular velocity sensor, a semiconductor pressure sensor, a flow rate sensor, and an ink jet printer head.

  The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. In the examples,% is% by weight. The sample used for the evaluation has a pattern of silicon thermal oxide film and silicon nitride film on one side of the wafer, and a silicon single crystal wafer having a protective film of silicon thermal oxide film and silicon nitride film on the other side is 1% fluorinated. After immersion in an aqueous hydrogen acid solution at room temperature for 3 minutes, rinse with UPW and dry to remove only the natural oxide film on the surface of the silicon single crystal, and use this evaluation sample for the following examples and comparative examples. It was.

Example 1
An aqueous solution containing 10% potassium hydroxide and 5% ascorbic acid was used as an etching agent, and an evaluation sample was immersed in this etching agent at 80 ° C. After immersion for 1 hour, the evaluation sample was taken out from the etching agent and dried after UPW rinsing. When the plane (100) direction and the plane (111) direction of the silicon single crystal were measured from this chemical-treated evaluation sample, the etching amount in the plane (100) direction was about 101 μm. Etching in the plane (111) direction was about 4 μm.

Example 2
When an aqueous solution containing 10% sodium hydroxide and 5% glyoxylic acid was used as an etching agent and the silicon etching amount was measured by performing the same treatment as in Example 1, the etching amount in the plane (100) direction was about 81 μm. . Etching in the plane (111) direction was about 1 μm.

Example 3
The amount of silicon etching was measured using the same treatment as in Example 1 except that an aqueous solution containing 10% potassium hydroxide and 5% glyoxylic acid was used as an etching agent and the treatment time was changed to 1 hour. The etching amount in the direction was about 80 μm. Etching in the plane (111) direction was about 1 μm.

Comparative Example 1
The amount of etching in the plane (100) direction was about 88 μm when the silicon etching amount was measured by performing the same treatment as in Example 1 using a 10% tetramethylammonium hydroxide aqueous solution as an etching agent. Etching in the plane (111) direction was about 3 μm.

Comparative Example 2
The amount of etching in the plane (100) direction was about 1 μm or less when the silicon etching amount was measured by performing the same treatment as in Example 1 using 5% ascorbic acid aqueous solution as an etching agent. The etching amount in the plane (111) direction was also about 1 μm or less.

Comparative Example 3
The amount of etching in the plane (100) direction was about 1 μm or less when the silicon etching amount was measured by performing the same treatment as in Example 1 using a 5% glyoxylic acid aqueous solution as an etching agent. The etching amount in the plane (111) direction was also about 1 μm or less.

Comparative Example 4
Using an aqueous solution containing 0.05% tetramethylammonium hydroxide and 0.05% ascorbic acid as an etchant, and performing the same treatment as in Example 1 and measuring the silicon etching amount, the etching amount in the plane (100) direction is about 1 μm or less. Met. The etching amount in the plane (111) direction was also about 1 μm or less.

Comparative Example 5
Using an aqueous solution containing 0.005% potassium hydroxide and 0.05% glyoxylic acid as an etchant and performing the same treatment as in Example 3, and measuring the silicon etching amount, the etching amount in the plane (100) direction was about 1 μm or less. It was. The etching amount in the plane (111) direction was also about 1 μm or less.

Comparative Example 6
The amount of etching in the plane (100) direction was about 66 μm when the silicon etching amount was measured by performing the same treatment as in Example 4 using 10% potassium hydroxide aqueous solution as an etching agent. Etching in the plane (111) direction was about 1 μm.
The thickness was about 2 μm.

Comparative Example 7
When an aqueous solution containing 10% potassium hydroxide and 5% tannic acid was used as an etching agent and the silicon etching amount was measured by performing the same treatment as in Example 4, the etching amount in the plane (100) direction was about 1 μm. . Etching in the surface (111) direction was about 1 μm or less.

Comparative Example 8
Using an aqueous solution containing 10% potassium hydroxide and 5% formaldehyde as an etching agent, the silicon etching amount was measured by performing the same treatment as in Example 4. The etching amount in the plane (100) direction was about 3 μm. Etching in the plane (111) direction was about 1 μm.

Comparative Example 9
When an aqueous solution containing 10% potassium hydroxide and 5% ammonium acetate was used as an etchant and the silicon etching amount was measured by performing the same treatment as in Example 4, the etching amount in the plane (100) direction was about 31 μm. . Etching in the plane (111) direction was about 2 μm.

As described above, by adding ascorbic acid and glyoxylic acid to potassium hydroxide, which is an alkali compound, tetramethylammonium hydroxide aqueous solution, potassium hydroxide aqueous solution, simple ascorbic acid aqueous solution of the same concentration, or a combination thereof. It can be seen that the etching rate in the surface (100) direction is improved from the diluted solution. In addition, when gallic acid or tannic acid, which is an organic acid other than ascorbic acid or glyoxylic acid, sorbitol, a saccharide, formaldehyde, an ammonium salt, ammonium acetate, or the like is added, an aqueous potassium hydroxide solution of the same concentration It can be seen that the etching rate in the plane (100) direction does not improve at all or is significantly reduced, and ascorbic acid and glyoxylic acid exhibit unique effects.

Claims (7)

An anisotropic etchant composition used for silicon microfabrication, which is an aqueous solution containing ascorbic acid or glyoxylic acid and an inorganic alkali compound. The anisotropic etchant composition according to claim 1, wherein the inorganic alkali compound is at least one selected from sodium hydroxide, potassium hydroxide, ammonia, and hydrazine. The anisotropic etchant composition according to claim 1, wherein the inorganic alkali compound is a mixture of potassium hydroxide and ammonia. The anisotropic etching agent composition according to any one of claims 1 to 4, wherein the inorganic alkali compound is 0.1 to 65% by weight, and ascorbic acid and glyoxylic acid are 0.1 to 50% by weight. Furthermore, the anisotropic etching agent composition in any one of Claims 1-4 containing at least 1 sort (s) of alcohol, pyrocatechol, glycerol, and a glycerol derivative. A method for etching silicon using the anisotropic etchant composition according to claim 1. An electronic apparatus having a silicon substrate processed by the etching method according to claim 6.