JP4543216B2 - Etching method of diamond structure and manufacturing method of power semiconductor device or electron emission source using the same. - Google Patents

Description

The present invention is a method of processing diamond by dry etching, an etching method characterized by a high etching selectivity with a mask material, a method of realizing a high aspect ratio, and an average roughness of the etched surface Relates to the realization of a processed structure of 2 nm or less. The processed diamond body of the present invention can be used as a power semiconductor device, an electron emission source, an electrode, a diamond electronic device such as MEMS, and a biodevice.

Various devices using diamond semiconductor characteristics, mechanical properties, high hardness, and chemical stability have been proposed, but have not yet been put into practical use. One of the causes is that diamond cannot be formed into a desired structure. Regarding the formation of a diamond structure, it has been reported that a structure is formed by depositing diamond on a silicon mold formed by etching (see Non-Patent Document 1). However, it has been difficult to achieve integration, miniaturization, sidewall perpendicularity, or a high aspect ratio.

For miniaturization and integration, (1) high etching selectivity with mask material, (2) flat etching surface formation, (3) high sidewall perpendicularity (high aspect ratio) technology can be realized. Development is necessary. (1) From the viewpoint of a high etching selectivity between a mask material and diamond, formation of a structure is reported by processing by oxygen plasma etching (see Patent Document 1). However, etching using only oxygen gas has a problem that a needle-like structure is formed on the diamond etching surface, and a flat etching surface cannot be formed. Further, it is impossible to form a highly perpendicular side wall. (2) Although the flatness of the etched surface is improved by introducing a fluorine-based gas such as CF _{4, the} problem remains that the selectivity ratio between the mask material and the diamond is small (Patent Document 2). reference). Therefore, although it is possible to form a side surface inclination angle of 78 ° or more, it is difficult to control the shape and area of the upper surface of the structure (see Patent Document 2).
Furthermore, a high aspect could not be realized due to damage of the mask. (3) It has been reported that high sidewall verticality and high aspect structure can be formed by using capacitive coupling (CCP) plasma etching (see Non-Patent Document 2). However, etching with oxygen alone has a high selectivity, but it is difficult to form a flat etching surface, and a flat etching surface can be formed by introducing a fluorine-based gas, but the selectivity is low. In other words, the existing diamond etching technique has not been developed as an etching technique that solves all of the above three problems.

On the other hand, in the field of silicon, a method widely known as “Bosch process” by Laermer et al. In this process, (1) silicon etching and (2) polymer sidewall protection film formation are repeated, so that high sidewall perpendicularity, high aspect structure, and high selectivity can be realized. On the other hand, in the etching of diamond, since a chemical reaction by oxygen is used, the polymer film cannot be used as a protective film, and a similar process has not been developed so far.

JP-A-6-132254 JP 2002-226290 A Yamada et al., IEICE Journal J81-C-II (1998), p181. D. S. Hwang et al. , Diam. Relat. Mater. 13 (2004) 2207

  In the present invention, the etching selectivity ratio between the mask and the diamond structure in which the flatness of the etching surface is 2 nm or less and the inclination angle of the side surface, which is the angle formed between the side surface of the upper surface and the bottom surface, is in the range of 60 ° to 100 °. Provides a diamond etching method that can be in the range of 10-80.

In order to form a high etching selectivity with a mask material, a flat etching surface, and a high side wall perpendicularity, the present inventors have studied conventional problems and performed a process of a diamond etching step and a cleaning step of the etching surface. I found it to repeat.
(1) In the diamond etching process, plasma etching is performed using only oxygen .
(2) The reason why the flat etching surface cannot be formed, such as the formation of needle-like structures, is thought to be due to redeposition of mask material and contamination from the chamber side wall, so fluorine gas such as gas containing CF ₄ or SF ₆ Clean the etched surface.
It was found that by repeating the steps (1) and (2), a high etching selectivity, a high sidewall vertical structure, and a flat etching surface can be realized.
That is, the present invention
A silicon oxide film, a metal oxide mask selected from aluminum oxide, titanium oxide, tungsten oxide, and molybdenum oxide is applied on the diamond substrate . First, plasma etching using only oxygen gas is performed, followed by oxygen. This is a diamond etching method in which a flattening plasma etching in which 0.01 to 5% of a fluorine-based gas is added to the gas and the bias power to the substrate is 0 is alternately repeated a plurality of times .
In the present invention, the fluorine-based gas can be CF ₄ or SF ₆ .
Furthermore, in the present invention, the diamond can be a diamond selected from single crystal diamond, polycrystalline diamond, homoepitaxial diamond, heteroepitaxial diamond, and nanodiamond.
Furthermore, in the present invention, a mask made of a metal oxide selected from a silicon oxide film, aluminum oxide, titanium oxide, tungsten oxide, and molybdenum oxide is provided on a diamond substrate, and only oxygen gas is used. Production of power semiconductor device using diamond etching method that repeats plasma etching and then planarizing plasma etching with oxygen gas 0.01% to 5% in addition to oxygen gas and zero bias power to the substrate alternately several times Is the method.
Furthermore, in the present invention, a mask of a metal oxide selected from a silicon oxide film, an aluminum oxide, a titanium oxide, a tungsten oxide, and a molybdenum oxide is provided on a diamond substrate, and only oxygen gas is used. Production of electron emission source using diamond etching method that repeats plasma etching and then flattening plasma etching by alternately adding fluorine gas 0.01-5% to oxygen gas and bias power to substrate 0. Is the method.

The diamond etching process of the present invention is basically performed by exposing diamond to plasma using only oxygen. Oxygen-only gas prevents damage and reduction of the mask material.

The plasma etching method of the present invention includes various known plasmas such as parallel plate plasma, RF plasma, direct current plasma, magnetron plasma, microwave plasma, electron cyclotron resonance (ECR) plasma, helicon wave plasma, and inductively coupled plasma. Is available.

In the etching surface cleaning process for forming a flat etching surface of the present invention, in order to prevent damage or reduction of the mask due to physical etching such as sputtering of the mask material, the bias power is reduced to 0 W or 0 W as much as possible, The etching selectivity between the material and diamond can be increased.

In the etching surface cleaning process for forming a flat etching surface of the present invention, parallel plate type plasma, RF plasma, DC plasma, magnetron plasma, microwave plasma, electron cyclotron resonance (ECR) plasma, helicon wave plasma, inductively coupled type Various known plasmas such as plasma can be used.

In the etching surface cleaning process for forming a flat etching surface of the present invention, the diamond etching surface is damaged by mainly using a chemical reaction for etching a redeposit from a silicon oxide film or aluminum as a mask material. Cleaning can be done without giving. Therefore, fluorine gas CF ₄ or SF ₆ which is an etching gas for silicon or silicon oxide film is used.
Typically, in the reactive etching process, the following are generated, and it is considered that silicon and aluminum in the deposit can be vaporized and removed.
Si + F → SiF
Si + 2F → SiF ₂
Si + 3F → SiF ₃
Si + 4F → SiF ₄
2Si + 6F → Si ₂ F ₆
3Si + 8F → Si ₃ F ₈

Al + F → AlF
Al + 3F → AlF ₃
2Al + 3F → Al ₂ F ₃

In the etching surface cleaning process for forming a flat etching surface of the present invention, parallel plate type plasma, RF plasma, direct current plasma, magnetron plasma, microwave plasma, direct current plasma, electron cyclotron resonance (ECR) plasma, helicon wave plasma, Various known plasmas such as inductively coupled plasma can be used.

In the etching surface cleaning process for forming a flat etching surface of the present invention, the diamond etching surface is damaged by mainly using a chemical reaction for etching a redeposit from a silicon oxide film or aluminum as a mask material. Cleaning can be done without giving. Therefore, it is possible to use a chlorine-based gas such as Cl ₂ and BCl _3.
Typically, in the reactive etching process, the following are generated, and it is considered that silicon and aluminum in the deposit can be vaporized and removed.

Si + Cl → SiCl
Si + 2Cl → SiCl ₂
Si + 3Cl → SiCl ₃
Si + 4Cl → SiCl ₄
2Si + 6Cl → Si ₂ Cl ₆
3Si + 8Cl → Si ₃ CL ₈

Al + Cl → AlCl
Al + 3CL → AlCl ₃
2Al + 3Cl → Al ₂ Cl ₃

In the above etching surface cleaning process for forming a flat etching surface, parallel plate plasma, RF plasma, DC plasma, magnetron plasma, microwave plasma, electron cyclotron resonance (ECR) plasma, helicon wave plasma, inductively coupled plasma Various known plasmas such as can be used.

In the etching surface cleaning process for forming a flat etching surface, the etching of redeposits from the silicon oxide film or aluminum that is the mask material is mainly used by chemical reaction, so that the diamond etching surface is not damaged. Cleaning can be performed.

The present invention is a method of processing diamond by etching, an etching method having an etching selectivity with a mask material in the range of 10 to 80, and a processed structure having an average surface roughness of 2 nm or less on the etched surface. Can be created.
Since diamond can be controlled to have a desired structure according to the present invention, it can be used as a power semiconductor device, an electron emission source, an electrode, a diamond electronic device such as MEMS, and a biodevice. That is, it is possible to form a structure such as a diamond electronic device or a micromachine.

A mask of a silicon oxide film, an oxide-forming metal such as aluminum or titanium, or a hard metal such as tungsten or molybdenum is formed on the surface of the single crystal diamond by photolithography, electron beam lithography, or the like. The mask can be formed by dry etching, wet etching, lift-off process, or the like.

The diamond used in the diamond etching process of the present invention is not limited to single crystal diamond, but may be polycrystalline diamond, homoepitaxial diamond, heteroepitaxial diamond, or nanodiamond.

In the diamond etching process, the diamond is exposed to a plasma containing only oxygen. In order to prevent damage and reduction of the mask material, oxygen-only gas is most suitable.

In the etching surface cleaning process for forming a flat etching surface, the etching of redeposits from the silicon oxide film or aluminum that is the mask material is mainly used by chemical reaction, so that the diamond etching surface is not damaged. Cleaning can be performed. Cleaning can be performed by exposing to a plasma containing fluorine-based gas such as CF ₄ or SF ₆ . By adding a small amount of fluorine-based gas such as CF ₄ or SF ₆ to the oxygen gas, it is possible to form a flat diamond etching surface and prevent damage and reduction of the mask. Flat etching surface formation and high etching selection Ratio can be realized. The fluorine gas flow rate is preferably in the range of 0.01 to 5%, more preferably in the range of 0.01 to 2% with respect to the oxygen gas flow rate.

The plasma etching method includes various known plasmas such as parallel plate plasma, RF plasma, DC plasma, magnetron plasma, microwave plasma, electron cyclotron resonance (ECR) plasma, helicon wave plasma, and inductively coupled plasma. Available.

As the diamond substrate, high pressure synthetic type Ib single crystal diamond (100) or (111) was used. After the silicon oxide film is formed by sputtering, patterning is performed by a photolithography technique, and a silicon oxide film mask is formed by dry etching or wet etching.

The diamond used in the diamond etching step is not limited to the high-pressure synthetic Ib type single crystal diamond (100) or (111), the plane orientation may be (110), and the single crystal diamond may be natural diamond. Further, it may be Ia type, IIa type or IIb type. The diamond may be polycrystalline diamond, homoepitaxial diamond, heteroepitaxial diamond, or nanodiamond.

Diamond dry etching was performed by ICP etching. The process conditions are as shown in Table 1 below, and 10 cycles were performed with the diamond etching step and the cleaning step taken as one cycle. The etching rate was calculated by measuring the level difference, and the etching surface was observed by a scanning electron microscope and an atomic force microscope.
The etching selectivity between the silicon oxide film and diamond was calculated to be 10. The etching selectivity was calculated by [Diamond etching rate / Mask etching rate].
As a result of observation with a scanning electron microscope, as shown in FIG. 1, the etching surface was remarkably flat, and a structure having a height of 12 to 13 μm or more was successfully formed. The average surface roughness in the atomic force microscope was in the range of 0.1 to 2.0 nm (Fig. 2).

The above-mentioned plasma etching method is not limited to ICP etching, and various known plasmas such as parallel plate plasma, RF plasma, DC plasma, magnetron plasma, microwave plasma, electron cyclotron resonance (ECR) plasma, helicon wave plasma, etc. Etching using can be used.

High-pressure synthetic Ib type single crystal diamond (100) , (111) was used as the diamond substrate. After the silicon oxide film is formed by sputtering, patterning is performed by a photolithography technique, and a silicon oxide film mask is formed by dry etching or wet etching.

The diamond used in the diamond etching step is not limited to the high-pressure synthetic Ib type single crystal diamond (100) or (111), the plane orientation may be (110), and the single crystal diamond may be natural diamond. Further, it may be Ia type, IIa type or IIb type. The diamond may be polycrystalline diamond, homoepitaxial diamond, heteroepitaxial diamond, or nanodiamond.

The above diamond dry etching was performed by ICP etching. The process conditions are as shown in Table 2 below, and the diamond etching process and the cleaning process were performed as one cycle, and 10 cycles were performed. The etching rate was calculated by measuring the level difference, and the etching surface was observed by a scanning electron microscope and an atomic force microscope.
The etching rate ratio between the silicon oxide film and diamond was calculated to be 26-30. As a result of observation by a scanning electron microscope and an atomic force microscope, almost the same flatness of the etched surface as in Example 1 was realized.

The above-mentioned plasma etching method is not limited to ICP etching, and various known plasmas such as parallel plate plasma, RF plasma, DC plasma, magnetron plasma, microwave plasma, electron cyclotron resonance (ECR) plasma, helicon wave plasma, etc. Etching using can be used.

As the diamond substrate, high pressure synthetic type Ib single crystal diamond (100) or (111) was used. After the silicon oxide film is formed by sputtering, patterning is performed by a photolithography technique, and a silicon oxide film mask is formed by dry etching or wet etching.

In the diamond etching step, not only the high-pressure synthetic Ib type single crystal diamond (100) or (111), the plane orientation may be (110), and the single crystal diamond may be natural diamond. Further, it may be Ia type, IIa type or IIb type. The diamond may be polycrystalline diamond, homoepitaxial diamond, heteroepitaxial diamond, or nanodiamond.

The above diamond dry etching was performed by ICP etching. The process conditions are as shown in Table 3 below, and 10 cycles were performed with the diamond etching step and the cleaning step taken as one cycle. The etching rate was calculated by measuring the level difference, and the etching surface was observed by a scanning electron microscope and an atomic force microscope.
The etching rate ratio between the silicon oxide film and diamond was calculated to be 26-30. As a result of observation by a scanning electron microscope and an atomic force microscope, almost the same flatness of the etched surface as in Example 1 was realized. Succeeded in forming a structure with a height of 12-13μm or more

The above plasma etching methods are not limited to ICP etching, but include parallel plate plasma, RF plasma, DC plasma, magnetron plasma, microwave plasma, DC plasma, electron cyclotron resonance (ECR) plasma, and helicon wave plasma. Etching using plasma can be used.

(Reference example)
As the diamond substrate, Ib type single crystal diamond (100) was used. After depositing Al by vacuum deposition, patterning is performed by photolithography, and a silicon oxide film mask is formed by dry etching or wet etching.

The diamond used in the diamond etching step is not limited to the high-pressure synthetic Ib type single crystal diamond (100) or (111), the plane orientation may be (110), and the single crystal diamond may be natural diamond. Further, it may be Ia type, IIa type or IIb type. The diamond may be polycrystalline diamond, homoepitaxial diamond, heteroepitaxial diamond, or nanodiamond.

The above diamond etching and ICP etching were performed. The process conditions are as shown in Table 2, and the diamond etching process and the cleaning process were performed as one cycle, and 20 cycles were performed. The etching rate was calculated by measuring the level difference, and the etching surface was observed by a scanning electron microscope and an atomic force microscope.
The etching rate ratio between Al thin film and diamond was calculated as 70-75. As a result of observation by a scanning electron microscope and an atomic force microscope, almost the same flatness of the etched surface as in Example 1 was realized. A structure with a height of 25μm or more was successfully formed. Furthermore, a very vertical structure with an inclination angle of 87 ° on the side surface of the diamond structure could be formed. It was also found that the side surface inclination angle can be controlled in the range of 65 ° to 87 ° by controlling the time of the diamond etching process and the cleaning process. It was found that the tilt angle of the side surface can be controlled in the range of 80 ° to 100 ° by controlling the bias power in the diamond etching process.

The above-mentioned plasma etching method is not limited to ICP etching, and various known plasmas such as parallel plate plasma, RF plasma, DC plasma, magnetron plasma, microwave plasma, electron cyclotron resonance (ECR) plasma, helicon wave plasma, etc. Etching using can be used.

In contrast to these examples, as shown in the following comparative examples, it is difficult to form a flat etching surface only by the diamond etching process. Furthermore, a high selection ratio with the mask material cannot be realized.

Comparative Example 1:
As the diamond substrate, Ib type single crystal diamond (100) was used. After the silicon oxide film is formed by sputtering, patterning is performed by a photolithography technique, and a silicon oxide film mask is formed by dry etching or wet etching.
The diamond structure was manufactured by ICP etching. The process conditions are as shown in Table 4.
The etching rate was calculated by measuring the level difference, and the etching rate ratio between the silicon oxide film and diamond was calculated to be 5-6.

Comparative Example 2:
As the diamond substrate, Ib type single crystal diamond (100) was used. After the silicon oxide film is formed by sputtering, patterning is performed by a photolithography technique, and a silicon oxide film mask is formed by dry etching or wet etching.
The diamond structure was manufactured by ICP etching. The process conditions are as shown in Table 5.
The etching rate is calculated by measuring the level difference, and the etching rate ratio between the silicon oxide film and diamond is as large as 25 to 30. / Microscopic protrusions are unintentionally formed.

  The diamond structure and diamond etching method of the present invention are not only a very important technique for producing a diamond semiconductor, but also can be widely applied, and industrial applicability is immeasurable.

The observation result by the scanning electron microscope of the diamond structure of Example 1. Observation results of average surface roughness with an atomic force microscope. The observation result by the scanning electron microscope of the diamond structure of the comparative example 2.

Claims (5)

A silicon oxide film, a metal oxide mask selected from aluminum oxide, titanium oxide, tungsten oxide, and molybdenum oxide is applied on the diamond substrate . First, plasma etching using only oxygen gas is performed, followed by oxygen. A diamond etching method in which a flattening plasma etching in which 0.01 to 5% of a fluorine-based gas is added to a gas and a bias power to the substrate is set to 0 is alternately repeated a plurality of times . The diamond etching method according to claim 1 , wherein the fluorine-based gas is CF ₄ or SF ₆ . The diamond etching method according to claim 1 or 2 , wherein the diamond is a diamond selected from single crystal diamond, polycrystalline diamond, homoepitaxial diamond, heteroepitaxial diamond, and nanodiamond. A silicon oxide film, a metal oxide mask selected from aluminum oxide, titanium oxide, tungsten oxide, and molybdenum oxide is applied on the diamond substrate, and then plasma etching using only oxygen gas is performed. A method of manufacturing a power semiconductor device using a diamond etching method in which a flattening plasma etching in which a fluorine-based gas of 0.01 to 5% is added to a gas and a bias power to a substrate is set to 0 is alternately repeated a plurality of times. A silicon oxide film, a metal oxide mask selected from aluminum oxide, titanium oxide, tungsten oxide, and molybdenum oxide is applied on the diamond substrate, and then plasma etching using only oxygen gas is performed. A method of manufacturing an electron emission source using a diamond etching method in which a flattening plasma etching in which 0.01 to 5% of a fluorine gas is added to a gas and a bias power to the substrate is set to 0 is alternately repeated a plurality of times.