TWI581327B - Silicon anisotropic etching method - Google Patents

Description

Heterogeneous etching method

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

A method of manufacturing an acceleration sensor, a pressure sensor, an inkjet printing head, a thin film magnetic head, or the like by microfabrication applied to a ruthenium substrate is conventional. In such microfabrication, an anisotropic etching method in which the etching rate is different depending on the crystal plane orientation of the tantalum substrate is used.

In the past, the anisotropic etching method used an alkaline aqueous solution containing potassium hydroxide or tetramethylammonium hydroxide (TMAH) as an anisotropic etching solution. In terms of metal-free, it is preferable to use TMAH-containing.矽 Anisotropic etchant. For example, in Patent Documents 1 and 2, when an anisotropic etching is applied to a germanium substrate using a TMAH-containing anisotropic etching solution, the etching rate of the {100} plane is 6 to 100 of the etching speed of the {111} plane. Approximately doubling, and the TMAH-containing anisotropic etchant selectively etches {100} faces.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 7-45582

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2009-206335

However, in recent years, with the complication of processing technology, the anisotropic etching technique for activating the crystal face of germanium has attracted attention. For example, it has been attempted to immerse the ruthenium substrate provided with the etch mask in the etchant by providing an etch mask having an opening having a side along the <110> direction on the {100} plane of the ruthenium substrate, and facing the ruthenium substrate. The depth direction forms an inclined surface having an edge parallel to the <110> direction and an angle of 50 to 60° with respect to the {100} plane, that is, a {111} plane. However, the inventors of the present invention have judged that it is difficult to form the inclined surface itself when using an anisotropic etching liquid containing TMAH, and even if it is formed, the flatness of the formed inclined surface is poor.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a wet anisotropic etching method capable of forming an inclined surface having an excellent flatness at an angle of 50 to 60° with respect to a main surface of a substrate.

The inventors of the present invention have repeatedly conducted active research to solve the above problems. As a result, it has been found that the above problems can be solved by using a specific anisotropic etching solution, and thus the present invention has been completed.

That is, the anisotropic etching method of the present invention uses an etching rate of a {111} plane of a tantalum substrate at a temperature of 25 to 70 ° C including a quaternary ammonium hydroxide (except for tetramethylammonium hydroxide). An anisotropic etching solution for etching an erbium substrate with an etching selectivity ratio of 0.25 to 0.80 and an etching ratio of the {100} plane of the ruthenium substrate, and the method is included in the ruthenium substrate a step of providing an etch mask having an opening along a side of the <110> direction, wherein the ruthenium substrate provided with the etch mask is immersed in the anisotropic etchant The step of forming the inclined surface parallel to the <110> direction in the depth direction of the substrate and forming the inclined surface at an angle of 50 to 60° with respect to the above {100} plane.

Here, the {100} plane includes a (100) plane and a (010) plane, a (001) plane, a (-100) plane, a (0-10) plane, and (00) having equivalent symmetry with the (100) plane. -1) All of the faces. In addition, the <110> direction includes the [110] direction and the [011] direction, the [101] direction, the [-110] direction, the [0-11] direction, the [-101] direction, and the [110] direction equivalent to the [110] direction. 1-10] direction, [01-1] direction, [10-1] direction, [-1-10] direction, [0-1-1] direction, and [-10-1] direction.

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

1‧‧‧ etching mask

2‧‧‧矽 substrate

3‧‧‧Resist film

1a, 3a‧‧‧ openings

1b, 2b‧‧‧ Orientation plane

P1‧‧‧ main surface

P2‧‧‧ sloped surface

P3‧‧‧ bottom

Fig. 1 is a plan view showing an example of an etching mask used in carrying out the anisotropic etching method according to the embodiment of the present invention.

Fig. 2 is a partial cross-sectional view showing the vicinity of the opening 1a of the cut surface along the line A-A of Fig. 1 as a main step of the anisotropic etching method according to the embodiment of the present invention.

Fig. 3 is a flow chart showing the respective steps of the anisotropic etching method corresponding to the cross-sectional views shown in Figs. 2(a) to 2(g).

4 is a plan view showing a concave portion formed on the main surface P1 of the ruthenium substrate 2 by the anisotropic etching method shown in FIGS. 2 and 3, and the main surface P1.

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

First, an etching mask 1 used in carrying out the anisotropic etching method according to the embodiment of the present invention will be described with reference to Fig. 1 . The anisotropic etching method according to the embodiment of the present invention is a wet etching method using a chemical (an anisotropic etching liquid) having a liquid which dissolves the properties of cerium corrosion, and is formed by forming a fine sensor or the like. It is used when a diaphragm is used and a depression is formed to the same extent as the thickness of the crucible substrate. Moreover, the etch mask 1 is formed such that only a portion of the ruthenium substrate to be removed by the etching method is exposed to the chemical for the ruthenium substrate He was partially covered and hidden from exposure to chemicals. Specifically, the etching mask 1 is formed into a film on the entire main surface of the ruthenium substrate, and has an opening 1a in a portion of the ruthenium substrate to be etched and removed. 1 is a plan view of the main surface side of the germanium substrate, so that the germanium substrate 2 is formed from the opening 1a, and the other portion of the germanium substrate 2 is covered and hidden by the etching mask 1. Moreover, the outer shape of the crucible substrate 2 is equal to the outer shape of the etching mask 1.

Further, in the embodiment of the present invention, the ruthenium substrate 2 is formed of a disk-shaped silicon wafer in which an orientation flat 1b (notch) showing a [011] direction is formed, and the stack shown in FIG. The main surface of the substrate 2 after etching the mask 1 is a (100) plane. Of course, the germanium substrate 2 also includes a film other than a wafer, and includes a thick film made of a single crystal germanium formed on an insulator or the like, such as an SIO substrate.

The shape of the opening 1a shown in FIG. 1 is the main 4 having a direction parallel to the <110> direction, that is, the [011] direction, the [01-1] direction, the [0-1-1] direction, and the [0-11] direction. The square shape of the sides has a parallel precision of 1° before and after the crystal orientation of the main sides. Of course, the size or shape of the opening formed in the etching mask 1 is arbitrarily determined depending on the size or shape of the diaphragm or the engraving to be formed, and is not limited to the shape shown in FIG.

The material of the etching mask 1 may be any etching resistance to the anisotropic etching liquid. For example, cerium oxide (SiO ₂ ) or tantalum nitride (Si ₃ N ₄ ) may be used.

Next, an anisotropic etching solution used in the anisotropic etching method according to the embodiment of the present invention will be described. The anisotropic etchant contains a grade 4 ammonium hydroxide (except for tetramethylammonium hydroxide) and is The etching selectivity ratio of the etching rate of the {111} plane of the tantalum substrate to the etching speed of the {100} plane of the tantalum substrate at 25 ° C to 70 ° C is an anisotropic etching liquid having an etching selectivity of 0.25 to 0.80.

In the above anisotropic etching solution, the etching selectivity is usually 0.25 to 0.80, preferably 0.30 to 0.70°, by making the etching selectivity ratio 0.25 to 0.80, compared to tetramethylammonium hydroxide (TMAH). In the case of the anisotropic etching solution, the etching speed of the {111} plane and the etching speed of the {100} plane are close to each other. It is presumed that due to this influence, it is possible to easily form an inclined surface having an angle of 50 to 60° with respect to the main surface of the tantalum substrate and having good flatness. Further, it is presumed that a recess having four inclined surfaces and a flat bottom surface formed by the {100} plane can be easily formed.

Hereinafter, each component contained in the anisotropic etching solution will be described in detail.

[(A) Grade 4 ammonium hydroxide (except for tetramethylammonium hydroxide)]

The fourth-order ammonium hydroxide (except for the tetramethylammonium hydroxide) (the component (A)) is not particularly limited as long as the etching selectivity is obtained, and is, for example, 4 represented by the following general formula (1). Grade ammonium hydroxide.

(wherein R ₁ to R ₄ each independently represent a monovalent hydrocarbon group having 1 to 16 carbon atoms, but the total number of carbon atoms contained in R ₁ to R ₄ is 6 or more in total).

Since the fourth-order ammonium hydroxide represented by the above formula (1) has a total number of carbon atoms contained in R ₁ to R ₄ of 6 or more, it is bulky compared with tetramethylammonium hydroxide (TMAH). Hydrocarbyl group, reduced in basicity. It has been reviewed whether the decrease in alkalinity has an effect on the dissolution of hydrazine by an aqueous alkaline solution. The dissolution of hydrazine by the aqueous alkaline solution was carried out 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

From this formula, it is understood that if the basicity of the alkaline aqueous solution is weak, the hydroxide ions which react with hydrazine are reduced, so that the etching rate of the ruthenium substrate is lowered. At this time, the etching rate of the {100} surface is decreased by a larger amplitude than the {111} surface. It is easy to form an inclined surface having an angle of 50 to 60° with respect to the main surface of the substrate and having good flatness. It is considered that the etching rate on the {100} surface has a larger amplitude than the {111} surface. Further, it is easy to form a concave portion having four inclined faces and a flat bottom formed by the {100} face, and it is considered to be caused by the same influence.

The monovalent hydrocarbon group of R ₁ to R ₄ is exemplified by, for example, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, isopentyl, neopentyl, hexyl. , heptyl, octyl, decyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, etc.; vinyl; Alkenyl groups such as allyl groups; aryl groups such as phenyl and tolyl; aralkyl groups such as benzyl and phenethyl.

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) are tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH), diethyldimethylammonium hydroxide, hydrogen. Oxidized methyl triethylammonium, benzyltrimethylammonium hydroxide, cetyltrimethylammonium hydroxide. Among them, TEAH, TPAH, and TBAH are preferred, and TBAH is preferred. The component (A) may be used alone or in combination of two or more.

The concentration of the component (A) in the anisotropic etching solution is preferably in the range of 0.001 to 0.6 N. More preferably in the range of 0.002 to 0.5 N, preferably in the range of 0.003 to 0.4 N. By setting the concentration of the component (A) to a range of 0.001 to 0.6 N, the etching selectivity is likely to fall within the range of 0.25 to 0.80, and it is easy to form an angle of 50 to 60° to the main surface of the substrate and flatness. Good sloped surface.

[(B) water]

Water ((B) component) is usually used as the solvent component used in the anisotropic etching solution. The (B) component is preferably a highly purified purification such as ion-exchanged water or distilled water from the viewpoint of preventing impurities such as metal salts from being contained in the anisotropic etching solution to reduce the yield of the produced semiconductor article. water.

[Other ingredients]

Other components may be added to the anisotropic etching solution used in the present invention. The other components are listed as, for example, a dissolution auxiliary component ((C) component). (C) is composed of (C1) water-soluble organic solvent and (C2) boundary At least one component selected from the group consisting of surfactants. 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 (C2) component to the anisotropic etching solution, the solubility of the component (A), particularly TBAH, can be increased, and the precipitation temperature of the component (A) in the anisotropic etching solution can be lowered. By lowering the precipitation temperature of the component (A), precipitation of the component (A) in the anisotropic etching solution is suppressed, and the stability of the anisotropic etching solution is improved. In particular, when the anisotropic etching solution is in a concentrated state (when the concentration of the component (A) such as TBAH is high), the component (A) in a low temperature environment, particularly TBAH, is easily precipitated, so it is preferable to add it. The component (C) lowers the precipitation temperature of the component (A). 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 component (C) to the anisotropic etching solution, the solubility of the component (A) in the anisotropic etching solution can be improved, and the anisotropy can be suppressed. Precipitation of the component (A) in the etching solution. This effect is especially pronounced when the anisotropic etchant is in a concentrated state.

The component (C1) is not particularly limited as long as it is less damage to the ruthenium substrate or the etching mask, and is exemplified by methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, and second butanol. a monohydric alcohol such as tert-butanol, n-pentanol, isoamyl alcohol, second pentanol or third pentanol, ethylene glycol, propylene glycol, butylene glycol, 1,5-pentanediol, 1,6- Hexanediol, 1,2-hexane Alcohols such as alcohol, 2,4-hexanediol, hexanediol, 1,7-heptanediol, octanediol, glycerol, 1,2,6-hexanetriol, etc.; diisopropyl Ether, diisobutyl ether, diisoamyl ether, di-n-butyl ether, di-n-pentyl ether, di-second butyl ether, diisoamyl ether, di-second amyl ether, di-third Ethers such as ethers; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethyl Glycol ethers such as diol monopropyl ether and diethylene glycol monobutyl ether. In the above, it is preferable to increase the solubility of the quaternary substrate or the etching mask while etching, and to improve the solubility of the above-described fourth-order ammonium hydroxide, particularly TBAH, from the viewpoint of ethylene glycol, a dihydric alcohol such as propylene glycol, a trihydric alcohol such as glycerin, or an alcohol such as a monohydric alcohol such as isopropanol, n-butanol, isobutanol or second butanol; and more preferably, it is a dihydric alcohol. Class, 3 alcohols. The above-mentioned (C1) component can be used alone or in combination of two or more.

The content of the (C1) component in the anisotropic etching solution is preferably from 1 to 10% by mass. When the content of the component (C1) is 1% by mass or more, the precipitation of the component (A) in the anisotropic etching solution is effectively suppressed. This effect is particularly remarkable when the anisotropic etching solution is in a concentrated state. In addition, when the content of the component (C1) is 10% by mass or less, the influence of the component (C1) on the ruthenium substrate or the etching mask can be reduced. The content of the (C1) component in the anisotropic etching solution is preferably from 3 to 10% by mass, more preferably from 3 to 7% by mass. Further, as described above, the content of the component (C1) means the concentration in the anisotropic etching solution used for the development process, and does not mean the concentration in the anisotropic etching solution in the concentrated state.

‧(C2) surfactant

By adding a surfactant ((C2) component) to the anisotropic etching solution as the component (C), the solubility of the component (A) in the anisotropic etching solution can be improved, and the anisotropic etching can be suppressed. Precipitation of component (A) in the liquid. This effect is particularly remarkable especially when the anisotropic etchant is in a concentrated state. Further, when the component (C2) is added to the anisotropic etching solution, the effect of improving the wettability of the anisotropic etching solution and suppressing the etching residue and the like are obtained.

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

The anionic surfactant is not particularly limited, and a conventional surfactant having an anionic group can be used. Such an anionic surfactant may, for example, be a surfactant having a carboxylic acid group, a sulfonic acid group or a phosphoric acid group as an anionic group.

Specific examples thereof include higher fatty acids having a carbon number of 8 to 20, higher alkyl sulfates, higher alkyl sulfonic acids, higher alkyl aryl sulfonic acids, and other surfactants having a sulfonic acid group. Or higher alcohol phosphates, or such salts. Here, the anionic surfactant may have an alkyl group which may be linear or branched, or may have a pendant phenyl group or an oxygen atom in the branching chain, or may be substituted with a hydroxyl group or a carboxyl group. One of the hydrogen atoms.

Specific examples of the above higher fatty acid include dodecanoic acid, myristic acid, and stearic acid, and specific examples of the higher alkyl sulfate may be listed. Examples are mercaptosulfate, dodecyl sulfate, and the like. Further, examples of the above higher alkylsulfonic acid may be decanesulfonic acid, dodecanesulfonic acid, tetradecanesulfonic acid, pentadecanesulfonic acid, stearic acidsulfonic acid or the like.

Further, specific examples of the higher alkylarylsulfonic acid may, for example, be dodecylbenzenesulfonic acid or mercaptophthalic acidsulfonic acid.

Further, other surfactants having a sulfonic acid group may, for example, be an alkyl diphenyl ether disulfonic acid such as dodecyl diphenyl ether disulfonic acid or a dioxane such as dioctyl sulfosuccinate. Alkyl sulfosuccinate and the like.

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

Among the above anionic surfactants, a surfactant having a sulfonic acid group is preferably used, and specifically, an alkylsulfonic acid, an alkylbenzenesulfonic acid, an olefinsulfonic acid, or an alkyldiphenylethersulfonic acid is used. Alkylnaphthalenesulfonic acid, dialkyl sulfosuccinic acid, and the like. Among these, alkylsulfonic acid, alkylbenzenesulfonic acid, alkyldiphenylether disulfonic acid, and dialkylsulfosuccinate are preferably used. The average carbon number of the alkyl group of the alkylsulfonic acid is preferably from 9 to 21, more preferably from 12 to 18. Further, the alkyl group of the alkylbenzenesulfonic acid preferably has an average carbon number of from 6 to 18, more preferably from 9 to 15. The alkyl group of the alkyl diphenyl ether disulfonic acid preferably has an average carbon number of from 6 to 18, more preferably from 9 to 15. Further, the alkyl group of the dialkyl sulfosuccinate has an average carbon number of preferably 4 to 12, more preferably 6 to 10.

Among the above anionic surfactants, an alkylsulfonic acid having an alkyl group having an average carbon number of 15 and an alkylbenzenesulfonic acid having an alkyl group having an average carbon number of 12 are preferably used.

Polyoxyethylidene Ether, acetylene nonionic surfactant, and the like. The nonionic surfactant is preferably one having water solubility. The range of HLB 7~17 is preferred. When the HLB is small and the water solubility is insufficient, it may be mixed with other surfactants to make it water-soluble.

Further, one or two or more kinds of various surfactants may be added as the (C2) component to the anisotropic etching solution.

The content of the (C2) component in the anisotropic etching solution is preferably from 0.01 to 10% by mass. By setting the content of the component (C2) to 0.01% by mass or more, (A) formation in the anisotropic etching solution can be effectively suppressed. This effect is particularly remarkable when the anisotropic etching solution is in a concentrated state. In addition, when the content of the component (C2) is 10% by mass or less, the influence of the (C2) component on the ruthenium substrate or the etching mask can be reduced. The content of the (C2) component in the anisotropic etching solution is more preferably 0.02 to 1% by mass, still more preferably 0.03 to 0.5% by mass. Further, as described above, the content of the component (C2) means the concentration in the anisotropic etching solution actually used in the development process, and does not mean the concentration in the anisotropic etching solution in the concentrated state.

The anisotropic etching solution can be prepared by stirring and mixing, for example, a fourth-order ammonium hydroxide of the component (A), water of the component (B), and other components such as a dissolution auxiliary component of the component (C).

Next, a specific procedure of the anisotropic etching method according to the embodiment of the present invention will be described with reference to FIGS. 2 and 3 using the etching mask 1 and the anisotropic etching solution shown in FIG.

(1) First, in step ST1 of Fig. 3, the etching mask 1 shown in Fig. 1 is formed on the main surface of the germanium substrate 2. Specifically, first, in step ST11, as shown in FIG. 2(a), an etching mask 1 made of a SiO ₂ film having a film thickness of 1 μm or less is formed on the main surface P1 of the ruthenium substrate 2. Specifically, the etching mask 1 is formed on the main surface P1 in the same manner using a chemical vapor deposition (CVD) method or a thermal oxidation method.

(2) Proceeding to step ST12, as shown in FIG. 2(b), the resist film 3 is formed on the etching mask 1 by spin coating and baking. Proceeding to step ST13, exposure processing, development processing, post-baking, and the like are sequentially performed on the resist film 3, whereby the position corresponding to the opening 1a of Fig. 1 is selectively removed as shown in Fig. 2(c). The resist film 3 has an opening 3a formed in the resist film 3.

(3) Proceeding to step ST14, the etching mask 1 exposed from the opening 3a is selectively removed by a dry etching method such as reactive ion etching (RIE), and as shown in Fig. 2(d), in the etching mask 1 forms an opening 1a. In this manner, 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. 2(e), the ruthenium substrate 2 is exposed from the opening 1a, and the other portion is covered with the etch mask 1 to form the ruthenium substrate 2 in the state shown in FIG.

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

(5) Subsequently, in step ST21, the tantalum substrate 2 is drooped with respect to the liquid surface of the above-mentioned anisotropic etching liquid set at 25 to 70 ° C Etching is performed in a straight manner for a specific time. Next, after the ruthenium substrate 2 is lifted, the high-purity ion-exchanged water is applied with a sufficient flushing treatment, and the ruthenium anisotropic etching solution is washed with water and dried. Further, during the impregnation of the crucible substrate 2, the rotor is rotated at the bottom of the vessel of the anisotropic etching solution to sufficiently stir the anisotropic etching solution.

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

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

[Examples]

The embodiments of the present invention are described below, but the scope of the present invention is not limited to the embodiments.

<Examples 1 to 22, Comparative Examples 1 to 7> (1) Determination of etching selectivity ratio

A 4-stage ammonium hydroxide aqueous solution having the concentration shown in Table 1 was prepared and used as an anisotropic etching solution. Details of the grade 4 ammonium hydroxide in Table 1 are as follows. Further, the anisotropic etching solution of Example 19 contained 5% by mass of propylene glycol in addition to the fourth-order ammonium hydroxide and water.

TMAH: tetramethylammonium hydroxide (total of carbon numbers: 4)

TEAH: tetraethylammonium hydroxide (total of carbon numbers: 8)

TPAH: tetrapropylammonium hydroxide (total of carbon numbers: 12)

TBAH: tetrabutylammonium hydroxide (total of carbon numbers: 16)

DEDMAH: diethyldimethylammonium hydroxide (total of carbon numbers: 6)

MTEAH: methyltriethylammonium hydroxide (total of carbon number: 7)

BTMAH: benzyltrimethylammonium hydroxide (total of carbon numbers: 10)

HDTMAH: Cetyltrimethylammonium hydroxide (total of carbon numbers: 19)

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

After the etching treatment, the ruthenium substrate having the concave portion formed as shown in FIG. 4 was cut along the line A-A of FIG. 4, and an SEM photograph of the cross section near the concave portion was taken. The etching amount (nm) of the {111} plane and the {100} plane was measured using this SEM photograph, and the etching rate of each surface was calculated from the value of the measured value and the etching time. Further, 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.

As can be seen from Table 1, when the TMAH aqueous solution is used as the anisotropic etching solution, the etching speed of the {100} plane is much faster than the etching speed of the {111} plane, and the etching selectivity ratio is less than 0.25.

On the other hand, use TEAH, TPAH, TBAH, etc. An aqueous solution of a larger volume of a hydrocarbon-based 4- to ammonium hydroxide as a ruthenium anisotropic etchant, the etch rate of the {111} face is compared to {100} when using an aqueous solution of TMAH as an anisotropic etchant The etching speed of the faces becomes a value close to each other. The etching selectivity is 0.25 to 0.80 in the range of 0.001 to 0.6 N in the concentration of the 4-stage ammonium hydroxide.

(2) Evaluation of the flatness and inclination angle of the inclined surface P2

With respect to Examples 11, 13, and 17 to 19 and Comparative Examples 4, 6, and 7, the SEM photograph was used to visually observe the flatness of the inclined surface P2, and the inclination angle of the inclined surface P2, that is, the inclined surface P2 and the bottom surface P3 were measured. In terms of perspective. The results are shown in Table 2.

As is clear from Table 2, when the anisotropic etching liquids of Examples 11, 13, and 17 to 19 of the etching selection ratio of 0.25 to 0.80 were used, the flatness of the inclined surface P2 was good, and the inclination angle of the inclined surface P2 was 50 to 60. Within the range of °.

On the other hand, when the anisotropic etching liquid of Comparative Example 4 having an etching selectivity of less than 0.25 is used, the flatness of the inclined surface P2 is poor, and the bottom surface P3 is curved. Further, when the anisotropic etching liquid of Comparative Examples 6 and 7 having an etching selectivity of more than 0.80 was used, the flatness of the inclined surface P2 was good, but the inclination angle of the inclined surface P2 was outside the range of 50 to 60°.

P2‧‧‧ sloped surface

P3‧‧‧ bottom

2‧‧‧矽 substrate

2b‧‧‧ Orientation plane

Claims (5)

An anisotropic etching method using an etch rate of a {111} plane of a germanium substrate at 25 to 70 ° C using a quaternary ammonium hydroxide (except for tetramethylammonium hydroxide) An anisotropic etching method for etching a tantalum substrate with an etching selectivity ratio of 0.25 to 0.80, and an anisotropic etching solution containing no asymmetric tetraalkyl quaternary phosphonium salt The method includes: providing a etch mask having an opening having a side along the <110> direction on a {100} plane of the ruthenium substrate; and immersing the ruthenium substrate provided with the etch mask In the anisotropic etching liquid, a step of forming an inclined surface having an angle parallel to the <110> direction and an angle of 50 to 60° with respect to the {100} plane is formed toward the depth direction of the tantalum substrate. An anisotropic etching method using a quaternary ammonium hydroxide having a carbon number of 12 to 16 at an etching rate of a {111} plane of a germanium substrate at 25 to 70 ° C and a substrate of {100} The etch rate of the surface is an etch rate of 0.25 to 0.80, and an anisotropic etching method for etching the ruthenium substrate, the method comprising: providing the {100} surface of the ruthenium substrate a step of etching the mask having an opening along the side of the <110> direction; and immersing the germanium substrate provided with the etching mask in the anisotropic etching liquid toward the depth direction of the germanium substrate A step of forming an inclined surface having a parallel side parallel to the <110> direction and an angle of 50 to 60° with respect to the {100} plane is formed. The anisotropic etching method according to claim 1 or 2, wherein the anthotropic anisotropic etching solution comprises a quaternary ammonium hydroxide represented by the following general formula (1), (In the formula, R ₁ to R ₄ each independently represent a monovalent hydrocarbon group having 1 to 16 carbon atoms, but the total number of carbon atoms contained in R ₁ to R ₄ is 12 to 16 or more in total). An anisotropic etching method according to claim 1 or 2, wherein the concentration of the quaternary ammonium hydroxide in the anisotropic etchant is in the range of 0.001 to 0.6N. The anisotropic etching method according to claim 1 or 2, wherein the quaternary ammonium hydroxide is one or two selected from the group consisting of tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.