JP5960511B2 - Silicon anisotropic etching method - Google Patents

Description

  The present invention relates to a wet silicon anisotropic etching method for forming an inclined surface having an angle of 50 to 60 ° with respect to a main surface of a silicon substrate.

  A method of manufacturing an acceleration sensor, a pressure sensor, an ink jet printer head, a thin film magnetic head, and the like through microfabrication performed on a silicon substrate is known. In such fine processing, a silicon anisotropic etching method using the fact that the etching rate varies depending on the crystal plane orientation of the silicon substrate is used.

  Conventionally, in the silicon anisotropic etching method, an alkaline aqueous solution containing potassium hydroxide, tetramethylammonium hydroxide (TMAH) or the like is used as the silicon anisotropic etching solution, and TMAH is not included in the point that it does not contain a metal. A silicon anisotropic etching solution containing is preferably used. For example, in Patent Documents 1 and 2, when anisotropic etching is performed on a silicon substrate using a silicon anisotropic etchant containing TMAH, the {100} plane etching rate is the same as the {111} plane etching rate. It is disclosed that the silicon anisotropic etchant containing TMAH is about 6 to 100 times and selectively etches the {100} plane.

Japanese Patent Laid-Open No. 7-45582 JP 2009-206335 A

  By the way, in recent years, with the complexity of processing techniques, attention has been focused on anisotropic etching techniques that make use of silicon crystal planes. For example, by providing an etching mask having an opening having a side along the <110> direction on the {100} plane of the silicon substrate, and immersing the silicon substrate provided with the etching mask in an etching solution, the <110> direction An inclined surface having a side parallel to the {100} plane and forming an angle of 50 to 60 ° with respect to the {100} plane, that is, a {111} plane, is attempted toward the depth direction of the silicon substrate. Yes. However, when the present inventors examined, when the silicon anisotropic etching liquid containing TMAH was used, formation of inclined surface itself was difficult, and even if it could be formed, the formed inclined surface is inferior in flatness. There was found.

  The present invention has been made in view of such conventional circumstances, and can form an inclined surface having an angle of 50 to 60 ° with respect to the main surface of the silicon substrate and good flatness. An object of the present invention is to provide a wet silicon anisotropic etching method.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, it has been found that the above problem can be solved by using a specific silicon anisotropic etching solution, and the present invention has been completed.

  That is, the silicon anisotropic etching method according to the present invention includes a quaternary ammonium hydroxide (excluding tetramethylammonium hydroxide), and the {111} plane of the silicon substrate at 25 to 70 ° C. The silicon substrate is etched using a silicon anisotropic etchant having an etching selectivity of 0.25 to 0.80, which is the ratio of the etching rate of the silicon substrate and the etching rate of the {100} plane of the silicon substrate. A step of providing an etching mask having an opening having a side along the <110> direction on the {100} plane of the silicon substrate; and the silicon substrate provided with the etching mask as the silicon anisotropic etching solution. By dipping, it has a side parallel to the <110> direction and an angle of 50 to 60 ° with respect to the {100} plane. The to the inclined surfaces and forming along the depth direction of the silicon substrate.

  Here, the {100} plane includes the (100) plane and the (010) plane, (001) plane, (-100) plane, (0-10) plane having symmetry equivalent to the (100) plane, and All of the (00-1) planes are included. The <110> direction includes the [110] direction and the [011] direction, [101] direction, [−110] direction, [0-11] direction, [−101] direction equivalent to the [110] direction, All of [1-10] direction, [01-1] direction, [10-1] direction, [-1-10] direction, [0-1-1] direction, and [-10-1] direction are included. It is.

  According to the present invention, it is possible to provide a wet silicon anisotropic etching method capable of forming an inclined surface having an angle of 50 to 60 ° with respect to a main surface of a silicon substrate and good flatness. it can.

It is a top view which shows an example of the etching mask used when enforcing the silicon anisotropic etching method which concerns on embodiment of this invention. It is a fragmentary sectional view of the opening 1a vicinity along the AA cut surface of FIG. 1 which shows the main processes of the silicon anisotropic etching method which concerns on embodiment of this invention. It is a flowchart which shows each procedure of the silicon anisotropic etching method corresponding to sectional drawing shown to Fig.2 (a)-FIG.2 (g). FIG. 4 is a plan view of the main surface P1 showing a recess formed in the main surface P1 of the silicon substrate 2 by the silicon anisotropic etching method shown in FIGS. 2 and 3.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  First, with reference to FIG. 1, the etching mask 1 used when implementing the silicon anisotropic etching method which concerns on embodiment of this invention is demonstrated. A silicon anisotropic etching method according to an embodiment of the present invention is one of wet (wet) etching methods using a liquid chemical (silicon anisotropic etching solution) having a property of corrosive dissolution of silicon, It is used when a diaphragm used for a fine sensor or the like is formed, or when a digging similar to the thickness of a silicon substrate is formed. The etching mask 1 is formed to expose only the portion of the silicon substrate that is desired to be removed by the etching method to chemicals and to cover other portions of the silicon substrate from the chemicals. Specifically, the etching mask 1 is deposited in a film shape on the entire main surface of the silicon substrate, and has an opening 1a in a portion of the silicon substrate that is desired to be removed by etching. Since FIG. 1 is a plan view seen from the main surface side of the silicon substrate, the silicon substrate 2 appears from the opening 1 a and the other part of the silicon substrate 2 is covered with the etching mask 1. Further, the outer shape of the silicon substrate 2 and the outer shape of the etching mask 1 are equal.

  In the embodiment of the present invention, the silicon substrate 2 is made of a disk-shaped silicon wafer in which an orientation flat 1b (notch) indicating the [011] direction is formed, and the etching mask 1 shown in FIG. 1 is deposited thereon. The main surface of the silicon substrate 2 is a (100) plane. Of course, the silicon substrate 2 includes a substrate other than a wafer, and includes, for example, a thick film made of single crystal silicon formed on an insulator, such as an SOI substrate.

  The shape of the opening 1a shown in FIG. 1 has four main directions parallel to the <110> direction, that is, the [011] direction, the [01-1] direction, the [0-1-1] direction, and the [0-11] direction. It has a square shape with one side, and the parallel accuracy with respect to the crystal direction of each major side is within 1 °. Of course, the size and shape of the opening formed in the etching mask 1 are arbitrarily determined according to the diaphragm to be formed and the size and shape of the engraving, and are not limited to the shape shown in FIG.

The material of the etching mask 1 may be any material having an etching resistance against a silicon anisotropic etching solution, and for example, silicon dioxide (SiO ₂ ) or silicon nitride (Si ₃ N ₄ ) is used. can do.

  Next, a silicon anisotropic etching solution used in the silicon anisotropic etching method according to the embodiment of the present invention will be described. The silicon anisotropic etching solution contains quaternary ammonium hydroxide (excluding tetramethylammonium hydroxide), and the etching rate of the {111} plane of the silicon substrate and the silicon substrate at 25 to 70 ° C. This is a silicon anisotropic etching solution having an etching selectivity ratio of 0.25 to 0.80, which is a ratio to the etching rate of the {100} plane.

In the silicon anisotropic etching solution, the etching selectivity is usually 0.25 to 0.80, preferably 0.30 to 0.70. When the etching selectivity is 0.25 to 0.80, the {111} plane etching rate and {100} are compared with the case of silicon anisotropic etching solution containing tetramethylammonium hydroxide (TMAH). The etching rates of the surfaces are close to each other. Due to the influence, it is presumed that an inclined surface having an angle of 50 to 60 ° with respect to the main surface of the silicon substrate and having good flatness is easily formed. Moreover, it is estimated that the recessed part which has such four inclined surfaces and the flat bottom face which consists of {100} surface is formed easily.
Hereinafter, each component contained in the silicon anisotropic etching solution will be described in detail.

[(A) Quaternary ammonium hydroxide (excluding tetramethylammonium hydroxide)]
The quaternary ammonium hydroxide (excluding tetramethylammonium hydroxide) (component (A)) is not particularly limited as long as it provides the above-described etching selectivity. The quaternary ammonium hydroxide represented by Formula (1) is mentioned.

（式中、Ｒ_１〜Ｒ_４はそれぞれ独立に炭素数１〜１６の１価炭化水素基を示す。但し、Ｒ_１〜Ｒ_４に含まれる炭素数の合計は６以上である。）

(In the formula, R _{1 to} R ₄ each independently represent a monovalent hydrocarbon group having 1 to 16 carbon atoms. However, the total number of carbon atoms contained in R _{1 to} R ₄ is 6 or more.)

The quaternary ammonium hydroxide represented by the above general formula (1) has a total number of carbons contained in R _{1 to} R ₄ of 6 or more, so it is compared with tetramethylammonium hydroxide (TMAH). It has a bulky hydrocarbon group and the basicity is lowered. The influence of the decrease in basicity on the dissolution of silicon by an aqueous alkali solution will be examined. Dissolution of silicon by the aqueous alkali solution proceeds according to the following chemical reaction formula.
Si + 2OH ⁻ + 2H ₂ O → Si (OH) ₄ + H ₂ + 2e ⁻
→ [SiO ₂ (OH) ₂ ] ² + 2H ₂
As can be seen from this equation, if the basicity of the alkaline aqueous solution is weakened, the hydroxide ions that react with silicon are reduced, and the etching rate of the silicon substrate is thus reduced. At this time, the {100} surface has a larger etching rate reduction than the {111} surface. An inclined surface having an angle of 50 to 60 ° with respect to the main surface of the silicon substrate and having good flatness is easily formed because the width of the etching rate reduction is smaller on the {100} surface than on the {111} surface. It seems that the large size has an influence. Moreover, it is thought that it is due to the same influence that the recessed part which has such 4 inclined surfaces and the flat bottom face which consists of {100} planes is formed easily.

Examples of the monovalent hydrocarbon group for R _{1 to} R ₄ include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group, Hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, alkyl group such as tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group; alkenyl group such as vinyl group, allyl group; phenyl group, An aryl group such as a tolyl group; and an aralkyl group such as a benzyl group and a phenethyl group.

The total number of carbon atoms contained in R _{1 to} R ₄ is 6 or more, preferably 8 to 20, more preferably 12 to 16.

  Specific examples of the component (A) include tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH), diethyldimethylammonium hydroxide, methyltriethylammonium water. Examples thereof include oxide, benzyltrimethylammonium hydroxide, and hexadecyltrimethylammonium hydroxide. Among them, TEAH, TPAH, and TBAH are preferable, and TBAH is preferable. (A) A component can be used 1 type or in combination of 2 or more types.

  The concentration of the component (A) in the silicon anisotropic etching solution is preferably in the range of 0.001 to 0.6N. More preferably, it is the range of 0.002-0.5N, and the range of 0.003-0.4N is the most preferable. When the concentration of the component (A) is in the range of 0.001 to 0.6N, the etching selectivity is likely to be in the range of 0.25 to 0.80, and 50 to 50% of the main surface of the silicon substrate. It becomes easy to form an inclined surface having an angle of 60 ° and good flatness.

[(B) Water]
As the solvent component used in the silicon anisotropic etching solution, water ((B) component) is usually used. From the viewpoint of preventing the yield of a semiconductor product to be manufactured from being reduced by including an impurity such as a metal salt in the silicon anisotropic etching solution, the component (B) is ion-exchanged water or distilled water. Thus, it is preferable to use highly purified water.

[Other ingredients]
Other components may be added to the silicon anisotropic etching solution used in the present invention. Examples of other components include a solubilizing component (component (C)). The component (C) is at least one component selected from the group consisting of (C1) a water-soluble organic solvent and (C2) a surfactant. In other words, the component (C) is one or more components selected from the group consisting of (C1) a water-soluble organic solvent and (C2) a surfactant. By adding the component (C2) to the silicon anisotropic etching solution, the solubility of the component (A), particularly TBAH, is increased, and the deposition temperature of the component (A) in the silicon anisotropic etching solution is lowered. be able to. By lowering the deposition temperature of the component (A), the deposition of the component (A) in the silicon anisotropic etching solution is suppressed, and the stability of the silicon anisotropic etching solution is improved. In particular, when the silicon anisotropic etching solution is in a concentrated state (when the concentration of the component (A) such as TBAH is high), the component (A), particularly TBAH, tends to precipitate in a low temperature environment. It is preferable that the precipitation temperature of (A) component becomes low by addition of C) component. Hereinafter, each component added as the component (C) will be described.

-(C1) Water-soluble organic solvent By adding a water-soluble organic solvent ((C1) component) as the (C) component to the silicon anisotropic etching solution, the (A) component is dissolved in the silicon anisotropic etching solution. And the precipitation of the component (A) in the silicon anisotropic etching solution can be suppressed. Such an effect is particularly remarkable when the silicon anisotropic etching solution is in a concentrated state.

  The component (C1) is not particularly limited as long as it causes little damage to the silicon substrate or the etching mask. Methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol , N-amyl alcohol, isoamyl alcohol, sec-amyl alcohol, monohydric alcohol such as tert-amyl alcohol, ethylene glycol, propylene glycol, butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2 Alcohols such as polyhydric alcohols such as hexanediol, 2,4-hexanediol, hexylene glycol, 1,7-heptanediol, octylene glycol, glycerin, 1,2,6-hexanetriol; Sopropyl ether, diisobutyl ether, diisopentyl ether, di-n-butyl ether, di-n-pentyl ether, di-sec-butyl ether, diisopentyl ether, di-sec-pentyl ether, di-tert-amyl ether, etc. Examples of such ethers include: glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, and diethylene glycol monobutyl ether. Among these, from the viewpoint of sufficiently improving the solubility of the quaternary ammonium hydroxide, particularly TBAH, while suppressing damage to the silicon substrate and etching mask during etching, ethylene glycol, propylene glycol Preferred examples include dihydric alcohols such as glycerol, trihydric alcohols such as glycerin, and alcohols such as monohydric alcohols such as isopropanol, n-butanol, isobutanol and sec-butanol. Among them, dihydric alcohols, 3 More preferable examples are monohydric alcohols. The component (C1) can be used alone or in combination of two or more.

  The content of the component (C1) in the silicon anisotropic etching solution is preferably 1 to 10% by mass. When the content of the component (C1) is 1% by mass or more, precipitation of the component (A) in the silicon anisotropic etching solution is effectively suppressed. This effect is significant when the silicon anisotropic etching solution is in a concentrated state. In addition, when the content of the component (C1) is 10% by mass or less, it is possible to reduce the influence of the component (C1) such as damage to the silicon substrate or the etching mask. The content of the component (C1) in the silicon anisotropic etching solution is more preferably 3 to 10% by mass, and further preferably 3 to 7% by mass. As described above, the content of the component (C1) here refers to the concentration in the silicon anisotropic etching solution that is actually used in the development process, and is a concentrated silicon anisotropic etching solution. It does not refer to the concentration at.

-(C2) Surfactant By adding a surfactant ((C2) component) as the (C) component to the silicon anisotropic etching solution, the solubility of the (A) component in the silicon anisotropic etching solution is increased. It can be increased, and precipitation of the component (A) in the silicon anisotropic etching solution can be suppressed. Such an effect is particularly remarkable when the silicon anisotropic etching solution is in a concentrated state. Further, when the (C2) component is added to the silicon anisotropic etching solution, the wettability of the silicon anisotropic etching solution is improved, and the effect of suppressing etching residue and the like is obtained.

  The component (C2) is not particularly limited, and a conventionally known surfactant can be used. Specifically, nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants can be used.

  The anionic surfactant is not particularly limited, and a conventionally known surfactant having an anionic group can be used. Examples of such an anionic surfactant include a surfactant having a carboxylic acid group, a sulfonic acid group, or a phosphoric acid group as an anionic group.

  Specifically, higher fatty acids having an alkyl group having 8 to 20 carbon atoms, higher alkyl sulfates, higher alkyl sulfonic acids, higher alkyl aryl sulfonic acids, other surfactants having sulfonic acid groups, or higher alcohol phosphoric acids Examples thereof include esters or salts thereof. Here, the alkyl group possessed by the anionic surfactant may be either linear or branched, and a phenylene group or an oxygen atom may be interposed in the branched chain. Some of the hydrogen atoms may be substituted with a hydroxyl group or a carboxyl group.

  Specific examples of the higher fatty acid include dodecanoic acid, tetradecanoic acid and stearic acid. Specific examples of the higher alkyl sulfate include decyl sulfate and dodecyl sulfate. Examples of the higher alkyl sulfonic acid include decane sulfonic acid, dodecane sulfonic acid, tetradecane sulfonic acid, pentadecane sulfonic acid, and stearic acid sulfonic acid.

  Specific examples of higher alkylaryl sulfonic acids include dodecylbenzene sulfonic acid and decylnaphthalene sulfonic acid.

  Furthermore, examples of other surfactants having a sulfonic acid group include alkyl diphenyl ether disulfonic acids such as dodecyl diphenyl ether disulfonic acid, and dialkyl sulfosuccinates such as dioctyl sulfosuccinate.

  Examples of higher alcohol phosphates include palmityl phosphate, castor oil alkyl phosphate, coconut oil alkyl phosphate, and the like.

  Among the above anionic surfactants, it is preferable to use a surfactant having a sulfonic acid group. Specifically, alkylsulfonic acid, alkylbenzenesulfonic acid, olefinsulfonic acid, alkyldiphenylethersulfonic acid, alkylnaphthalenesulfonic acid. And dialkylsulfosuccinate. Among these, it is preferable to use alkylsulfonic acid, alkylbenzenesulfonic acid, alkyldiphenyl ether disulfonic acid, and dialkylsulfosuccinate. The average carbon number of the alkyl group of the alkyl sulfonic acid is preferably 9 to 21, and more preferably 12 to 18. Moreover, it is preferable that it is 6-18, and, as for the average carbon number of the alkyl group of alkylbenzenesulfonic acid, it is more preferable that it is 9-15. The average carbon number of the alkyl group of the alkyldiphenyl ether disulfonic acid is preferably 6-18, and more preferably 9-15. Furthermore, 4-12 are preferable and, as for the average carbon number of the alkyl group of dialkyl sulfosuccinate, 6-10 are more preferable.

  Among the above anionic surfactants, it is preferable to use alkylsulfonic acid having an alkyl group having an average carbon number of 15 and alkylbenzenesulfonic acid having an alkyl group having an average carbon number of 12.

  Examples of nonionic surfactants include polyoxyethylene alkyl ethers and acetylenic nonionic surfactants. As the nonionic surfactant, those having water solubility are desirable. The range of HLB7-17 is good. When HLB is small and water solubility is insufficient, it may be made water-soluble by mixing with other surfactants.

  In addition, 1 type, or 2 or more types of various surfactant can be added to a silicon anisotropic etching liquid as (C2) component.

  The content of the component (C2) in the silicon anisotropic etching solution is preferably 0.01 to 10% by mass. When the content of the component (C2) is 0.01% by mass or more, precipitation of the component (A) in the silicon anisotropic etching liquid is effectively suppressed. This effect is significant when the silicon anisotropic etching solution is in a concentrated state. Moreover, when the content of the component (C2) is 10% by mass or less, it is possible to reduce the influence such as damage to the silicon substrate and the etching mask due to the component (C2). The content of the component (C2) in the silicon anisotropic etching solution is more preferably 0.02 to 1% by mass, and most preferably 0.03 to 0.5% by mass. As described above, the content of the component (C2) here refers to the concentration in the silicon anisotropic etching solution that is actually used in the development processing, and is a concentrated silicon anisotropic etching solution. It does not refer to the concentration at.

  Silicon anisotropic etching liquid is, for example, (A) component quaternary ammonium hydroxide, (B) component water, and, if necessary, other components such as (C) component solubilizing component Can be prepared by stirring and mixing with a stirrer or the like.

  Next, referring to FIG. 2 and FIG. 3, the silicon anisotropic etching method according to the embodiment of the present invention using the etching mask 1 shown in FIG. A simple procedure will be described.

(1) First, the etching mask 1 shown in FIG. 1 is formed on the main surface of the silicon substrate 2 in step ST1 of FIG. Specifically, first, in step ST11, as shown in FIG. 2A, an etching mask 1 made of a SiO ₂ film having a thickness of 1 μm or less is formed on the main surface P1 of the silicon substrate 2. Specifically, the etching mask 1 is uniformly formed on the main surface P1 using a chemical vapor deposition (CVD) method or a thermal oxidation method.

(2) Proceeding to step ST12, as shown in FIG. 2B, a resist film 3 is uniformly formed on the etching mask 1 by spin coating and baking. Proceeding to step ST13, the resist film 3 is sequentially subjected to exposure processing, development processing, post-baking, etc., so that the resist film 3 at a position corresponding to the opening 1a in FIG. 1 is formed as shown in FIG. By selectively removing, an opening 3 a is formed in the resist film 3.

(3) Proceeding to step ST14, the etching mask 1 exposed from the opening 3a is selectively removed by using a dry etching method such as a reactive ion etching (RIE) method, for example, as shown in FIG. Thus, an opening 1 a is formed in the etching mask 1. In this way, after the resist pattern (opening 3a) is transferred to the etching mask 1, the process proceeds to step ST15, and the resist film 3 is entirely removed. As a result, as shown in FIG. 2E, the silicon substrate 2 is exposed from the opening 1a, and the other portions are covered with the etching mask 1 to form the silicon substrate 2 in the state shown in FIG. .

(4) Next, proceeding to step ST2, crystal anisotropic etching of the silicon substrate 2 provided with the etching mask 1 is performed. Specifically, first, a natural oxide film formed on the main surface P1 of the silicon substrate 2 exposed from the opening 1a is removed with a diluted hydrofluoric acid aqueous solution, and rinsed with high-purity ion exchange water.

(5) Then, in step ST21, the silicon substrate 2 is etched by being immersed for a predetermined time so as to be perpendicular to the liquid surface of the above-mentioned silicon anisotropic etching solution set at 25 to 70 ° C. Then, after the silicon substrate 2 is pulled up, the silicon anisotropic etching solution is washed away and dried by sufficiently performing running water rinsing using high-purity ion exchange water. While the silicon substrate 2 is immersed, the rotator is rotated at the bottom of the silicon anisotropic etching solution container to constantly stir the silicon anisotropic etching solution.

(6) Next, proceeding to step ST3, the entire etching mask 1 is removed from the main surface P1 of the silicon substrate 2 as shown in FIG. 2 (g), for example, by immersing the silicon substrate 2 in a hydrofluoric acid aqueous solution. To do.

  Next, the concave portion formed in the main surface P1 of the silicon substrate 2 by the silicon anisotropic etching method shown in FIGS. 2 and 3 will be described. As shown in FIGS. 4 and 2 (g), in the same manner as the four sides provided in the opening 1a of FIG. 1, the side parallel to the <110> direction and the main surface P1 of the silicon substrate 2 is provided. An inclined surface P2 having an angle of 50 to 60 ° is formed in the depth direction of the silicon substrate 2. Specifically, the recess formed in the main surface P1 of the silicon substrate 2 has sides parallel to the [011] direction, the [01-1] direction, the [0-1-1] direction, and the [0-11] direction. Each has four inclined surfaces P2 having an angle of 50 to 60 ° with respect to the main surface P1, and a bottom surface P3 made of the same (100) plane as the main surface P1. In the recess, the inclined surface P2 is excellent in flatness, and the bottom surface P3 is also flat.

  Examples of the present invention will be described below, but the scope of the present invention is not limited to these examples.

<Examples 1 to 22 and Comparative Examples 1 to 7>
(1) Measurement of etching selectivity A quaternary ammonium hydroxide aqueous solution having the concentration shown in Table 1 was prepared and used as a silicon anisotropic etching solution. The details of the quaternary ammonium hydroxide in Table 1 are as follows. In addition, the silicon anisotropic etching liquid of Example 19 contains 5 mass% propylene glycol in addition to the quaternary ammonium hydroxide and water.
TMAH: Tetramethylammonium hydroxide (total carbon number: 4)
TEAH: tetraethylammonium hydroxide (total carbon number: 8)
TPAH: Tetrapropylammonium hydroxide (total carbon number: 12)
TBAH: Tetrabutylammonium hydroxide (total carbon number: 16)
DEDMAH: diethyldimethylammonium hydroxide (total carbon number: 6)
MTEAH: Methyltriethylammonium hydroxide (total carbon number: 7)
BTMAH: benzyltrimethylammonium hydroxide (total carbon number: 10)
HDTMAH: Hexadecyltrimethylammonium hydroxide (total carbon number: 19)

  The silicon substrate 2 shown in FIG. 1 was etched using the prepared anisotropic silicon etchant. The specific procedure of the etching process was as described in FIGS. 2 and 3 and the description of these figures. The removal of the natural oxide film in step ST2 in FIG. 3 was performed by immersing the silicon substrate 2 provided with the etching mask 1 in a 0.485 mass% hydrofluoric acid aqueous solution for 40 seconds at room temperature. The temperature during etching was set as shown in Table 1. The etching time was set so that the etching amount on the {111} plane was the same in all examples and comparative examples. A specific etching amount is 57 nm. This value corresponds to the amount of etching on the {111} plane in Comparative Example 4 when etching is performed for 10 minutes using a 0.26N aqueous TMAH solution at 40 ° C.

  After the etching process, a silicon substrate having a recess formed as shown in FIG. 4 was cut along the line AA in FIG. 4, and an SEM photograph of a cross section in the vicinity of the recess was taken. Using this SEM photograph, the etching amount (nm) of the {111} plane and {100} plane was measured, and the etching rate of each plane was calculated from the measured value and the etching time value. Moreover, the etching selectivity was calculated by dividing the etching rate of the {111} plane by the etching rate of the {100} plane. The results are shown in Table 1.

＊５質量％のプロピレングリコールを含む以外は、実施例１７のシリコン異方性エッチング液と同一の組成

* The same composition as the silicon anisotropic etching solution of Example 17 except that 5% by mass of propylene glycol is contained.

As can be seen from Table 1, when the TMAH aqueous solution is used as the silicon anisotropic etching solution, the etching rate of the {100} plane is much higher than the etching rate of the {111} plane, and the etching selectivity is 0. Less than .25.
On the other hand, when an aqueous solution of a quaternary ammonium hydroxide having a bulky hydrocarbon group such as TEAH, TPAH, TBAH, etc. is used as the silicon anisotropic etching solution, Compared with the case where the etching solution was used, the etching rate on the {111} plane and the etching rate on the {100} plane were close to each other. The etching selectivity was 0.25 to 0.80 when the concentration of the quaternary ammonium hydroxide was within the range of 0.001 to 0.6N.

(2) Flatness of inclined surface P2 and evaluation of inclination angle For Examples 11, 13, and 17 to 19 and Comparative Examples 4, 6, and 7, the flatness of the inclined surface P2 was visually observed using the SEM photograph. And the inclination angle of the inclined surface P2, that is, the angle formed by the inclined surface P2 and the bottom surface P3 was measured. The results are shown in Table 2.

＊底面Ｐ３が湾曲していたため、傾斜面Ｐ２の傾斜角度を測定することができなかった。

* Because the bottom surface P3 was curved, the inclination angle of the inclined surface P2 could not be measured.

As can be seen from Table 2, when the silicon anisotropic etching liquids of Examples 11, 13, and 17-19 having an etching selectivity of 0.25 to 0.80 are used, the flatness of the inclined surface P2 is good. The inclination angle of the inclined surface P2 was in the range of 50 to 60 °.
On the other hand, when the silicon anisotropic etching solution of Comparative Example 4 having an etching selection ratio smaller than 0.25 was used, the flatness of the inclined surface P2 was poor and the bottom surface P3 was curved. Further, when the silicon anisotropic etching liquids of Comparative Examples 6 and 7 having an etching selection ratio larger than 0.80 were used, the flatness of the inclined surface P2 was good, but the inclination angle of the inclined surface P2 was good. Was outside the range of 50-60 °.

DESCRIPTION OF SYMBOLS 1 Etching mask 2 Silicon substrate 3 Resist film 1a, 3a Opening 1b, 2b Orientation flat P1 Main surface P2 Inclined surface P3 Bottom surface

Claims (5)

Including quaternary ammonium hydroxide (excluding tetramethylammonium hydroxide), the etching rate of {111} plane of silicon substrate and the etching rate of {100} plane of silicon substrate at 25-70 ° C. The silicon anisotropy is obtained by etching a silicon substrate using a silicon anisotropic etching solution that does not contain an asymmetric tetraalkyl quaternary phosphonium salt, and the etching selectivity ratio is 0.25 to 0.80. An etching method comprising:
Providing an etching mask having an opening having a side along the <110> direction on the {100} plane of the silicon substrate;
By immersing the silicon substrate provided with the etching mask in the silicon anisotropic etching solution, the substrate has sides parallel to the <110> direction and an angle of 50 to 60 ° with respect to the {100} plane. A step of forming an inclined surface in the depth direction of the silicon substrate;
An anisotropic silicon etching method comprising: Etching selection which includes a quaternary ammonium hydroxide having 12 to 16 carbon atoms and a ratio of the etching rate of the {111} plane of the silicon substrate to the etching rate of the {100} plane of the silicon substrate at 25 to 70 ° C. A silicon anisotropic etching method for etching a silicon substrate using a silicon anisotropic etching solution having a ratio of 0.25 to 0.80,
  Providing an etching mask having an opening having a side along the <110> direction on the {100} plane of the silicon substrate;
  By immersing the silicon substrate provided with the etching mask in the silicon anisotropic etching solution, the substrate has sides parallel to the <110> direction and an angle of 50 to 60 ° with respect to the {100} plane. A step of forming an inclined surface in the depth direction of the silicon substrate;
An anisotropic silicon etching method comprising: The silicon anisotropic etching method according to claim 1 or 2, wherein the silicon anisotropic etching solution contains a quaternary ammonium hydroxide represented by the following general formula (1).

(In the formula, R _{1 to} R ₄ each independently represents a monovalent hydrocarbon group having 1 to 16 carbon atoms, provided that the total number of carbon atoms contained in R _{1 to} R ₄ is 12 to 16 ). The silicon anisotropic etching according to any one of claims 1 to 3 , wherein a concentration of the quaternary ammonium hydroxide in the silicon anisotropic etching solution is in a range of 0.001 to 0.6N. Method. The silicon according to any one of claims 1 to 4, wherein the quaternary ammonium hydroxide is one or two selected from the group consisting of tetrapropylammonium hydroxide and tetrabutylammonium hydroxide. Anisotropic etching method.

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