JP2003257964A - Method of forming metal oxide thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate the formation of a high-quality metal oxide thin film on a compound semiconductor substrate using a simple and low-cost apparatus, and to facilitate the selective formation of a thin film on the surface of the substrate with a high degree of freedom in selection of the compound semiconductor substrate. <P>SOLUTION: A liquid phase film formation method wherein the compound semiconductor substrate is dipped in a solution containing a fluorine compound and then a thin film of a metal oxide is formed on the compound semiconductor substrate by chemical reaction in the solution comprises steps of (S1) preparing a saturated solution containing a fluorine compound, (S2) for surface reformation, irradiating plasma containing oxygen on the surface of the compound semiconductor substrate, (S3) after the surface reformation, dipping the compound semiconductor substrate in the solution, and then forming the thin film of a metal oxide on the substrate. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a metal oxide thin film on a compound semiconductor by liquid phase film formation.

[0002]

2. Description of the Related Art Conventionally, for this type of film formation, a vapor deposition method or a sputtering method is generally used, and FIGS. 3 and 4 show a schematic configuration of the film forming apparatus.

FIG. 3 is a sectional view schematically showing the structure of an electron beam heating vapor deposition apparatus. In the figure, 1 is a substrate on which a film is formed, 2 is a shutter, 3 is an electron gun, 4 is an evaporation material as a raw material for forming a film, and is contained in a crucible 5.
Reference numeral 6 denotes a vacuum chamber connected to a vacuum pump (not shown) in which the above-mentioned components are arranged.

In this apparatus, the vacuum chamber 6 is evacuated to about 10 ⁻³ Pa, an evaporation material 4 which is a raw material for forming a film as an evaporation source is placed in a crucible 5, and this is irradiated with an electron beam generated from an electron gun 3. It is heated and evaporated, and the evaporated substance is condensed on the substrate 1 placed facing each other with a certain distance.

FIG. 4 is a sectional view schematically showing the structure of a sputtering film forming apparatus. In the figure, 11 is a sputtering target, which is cooled by cooling water. 1
2 is a shutter, 13 is a substrate stage which serves as an anode, 14
Is a substrate on which a film is to be formed, 15 is a shield plate, 16 is a vacuum chamber connected to a vacuum pump (not shown), each of the above components is arranged inside, and Ar (gas) is introduced. 17
Is a flow meter for measuring the introduced amount of Ar.

[0006] In this apparatus, after the vacuum chamber 16 is evacuated to a pressure of at least 10 ^-3 Pa or less using a vacuum pump, Ar is introduced into the vacuum chamber 16 to discharge between the target 11 and the substrate stage 13. It is what causes it. As a result of the electric discharge, Ar ions in the vacuum chamber 16 are struck by the target 11, and the substance forming the target 11 is repelled and adheres to the substrate 14 arranged opposite to the target.

In this way, it is known that a metal oxide such as silicon oxide or titanium oxide can be formed on a compound semiconductor substrate.

Further, Japanese Patent Application Laid-Open No. 67-196744 and Japanese Patent Publication No. 63-65621 propose a method of forming a silicon oxide film in a liquid phase. In this method, a glass substrate is immersed in a hydrosilicofluoric acid aqueous solution saturated with silicon oxide powder, the solution in the system is filtered and circulated while dropping boric acid, and silicon oxide is formed on the substrate by a chemical reaction. I'm trying to film. A method using a weakly acidic aqueous solution of ammonium silicofluoride is also disclosed in JP-A-10-158.
No. 010 publication.

Similarly, by reacting an aqueous solution of titanium hydrofluoric acid or an aqueous solution of ammonium titanium fluoride with boric acid, a titanium oxide film can be formed on a substrate, as disclosed in Japanese Patent Publication No. 7-35268 and Japanese Patent No. 2785433. Proposed.

[0010]

However, in the conventional vapor phase film forming technique as described above, the material to be formed is incident on the substrate from one direction. There is a problem that a uniform film thickness cannot be obtained. Further, since these methods perform film formation in a vacuum, a complicated and expensive apparatus for producing the vacuum is required. In addition, when the film forming substance is a compound of a substance having a significantly different vapor pressure, in order to form the film while maintaining the stoichiometric ratio, the film formation is performed while introducing the component gas of the film forming substance. It must be made.

Further, particularly in the case of the sputtering film forming apparatus, since the film forming substance is struck against the substrate, damage to the substrate, that is, so-called plasma damage cannot be avoided. In addition, the substrate may be heated during film formation, which may damage the photoresist,
There is a problem that the substrate has no selectivity and a film is formed on the entire surface of the substrate.

Further, in JP-A-57-196744 and JP-A-63-65621, the above problems can be avoided, but the material of the substrate on which the silicon oxide film can be formed is glass, silicon or the like surface. However, there is a problem that it is not possible to freely form a film on various substrates because it is limited to those having a stable hydrophilic group.

The present invention has been made in view of the above problems, and it is possible to easily produce a good quality metal oxide thin film on a compound semiconductor substrate at a low temperature using a simple and inexpensive apparatus. It is an object of the present invention to provide a method for forming a metal oxide thin film, which is capable of forming a compound semiconductor substrate with a high degree of freedom in selection and which can selectively form a thin film on the substrate surface.

[0014]

The method for forming a metal oxide thin film according to the present invention is configured as follows.

(1) A method of liquid phase film formation in which a compound semiconductor substrate is immersed in a solution containing a fluorine compound and a metal oxide thin film is formed on the compound semiconductor substrate by a chemical reaction in the solution. Before the film formation, the surface of the compound semiconductor substrate is subjected to a surface modification treatment by irradiation with plasma containing oxygen.

(2) In the above (1), the surface modification treatment by irradiating the plasma containing oxygen is performed by oxygen partial pressure of 0.1 P.
a to 100 Pa, processing time 30 seconds or more, antenna power 1
It was performed under the conditions of 0 W or more and the substrate temperature of 0 ° C to 90 ° C.

(3) In the above (1) or (2),
The fluorine compound was made to contain at least one of SiF ₆ ²⁻ , TiF ₆ ²⁻ , and ZrF ₆ ²⁻ .

(4) In any one of (1) to (3) above, the metal oxide is at least one of silicon oxide, titanium oxide and zirconium oxide.

(5) In any one of (1) to (4) above, the compound semiconductor is a compound semiconductor containing gallium,
At least one of a compound semiconductor containing indium and a compound semiconductor containing zinc is used.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a liquid-phase film forming method for forming a film of oxide oxide, titanium oxide or zirconium oxide on a compound semiconductor surface in a liquid phase. A method of liquid-phase film formation in which a thin film of a metal oxide is formed on the compound semiconductor substrate by a chemical reaction in a solution containing the compound semiconductor substrate, the surface of the compound semiconductor substrate being formed before the film formation. Is subjected to surface modification treatment by irradiation with plasma containing oxygen.

FIG. 1 shows an essential part of a film forming process according to the present invention. After preparing a saturated solution containing a fluorine compound (S1) and performing a surface modification treatment on the compound semiconductor substrate (S2),
A compound semiconductor substrate is immersed in the above solution (S3) to form a metal oxide thin film on the substrate.

More specifically, it contains a compound semiconductor that does not have a stable hydrophilic group on the surface that serves as a foothold for reaction, such as gallium nitride (GaN), gallium arsenide (GaAs) or gallium phosphide (GaP). The surface of a compound semiconductor, a compound semiconductor containing indium represented by indium nitride (InN), and a compound semiconductor containing zinc oxide represented by zinc oxide (ZnO),
The metal oxide thin film is formed at a low temperature on the above compound semiconductor by the above liquid phase film forming method by performing the modification treatment by irradiating the plasma containing oxygen.

As an example of the film forming liquid used for the above film formation, S
A solution containing a fluorine compound containing at least one of iF ₆ ²⁻ , TiF ₆ ²⁻ , and ZrF ₆ ²⁻ is desirable, and a solution containing silicic acid (Si
O ₂ · nH ₂ O) powder is dissolved to a saturated state, hydrofluoric acid (H ₂ SiF ₆ ) aqueous solution, ammonium silicofluoride ((NH ₄ ) ₂ SiF ₆ ) aqueous solution, titanium ammonium fluoride ((NH ₄ ) ₂ TiF ₆ ) aqueous solution or the like may be used, depending on the case, a boric acid aqueous solution or a solution containing aluminum and an aluminum compound as a reaction accelerator.

The metal oxide thin film that can be produced by the present invention is made of silicon dioxide (SiO ₂ ), titanium oxide (Ti
O ₂ ), zirconium oxide (ZrO ₂ ) and the like depending on the film forming liquid.

First, when forming a film on the compound semiconductor, a surface modification treatment of the compound semiconductor is performed by plasma containing oxygen. The condition is that the oxygen partial pressure is 0.1 Pa to 10 Pa.
0 Pa, preferably 0.5 Pa to 5 Pa, processing time 3
0 seconds or more, antenna power 10 W or more, RF frequency 13.
56MHz, substrate temperature 0 ℃ ~ 90 ℃, desirably 20 ℃
~ 30 ° C.

Then, the surface of the compound semiconductor is subjected to a surface modification treatment with plasma containing oxygen, and then the above film forming solution is added from 0.5 mol / l to 3.0 mol / l, preferably 1.0 mol / l. Dilute from 1 to 3.0 mol / l and immerse the substrate in this solution for 30 minutes or longer, preferably 30 minutes to 10 hours, and keep the liquid temperature at 15 ° C or higher, preferably from room temperature to 60 ° C to form a film. I do. At this time,
It is preferable to circulate the film-forming solution and insert a filter in the circulation path to remove dust mixed with the solution and fine particles that precipitate.

At the time of the above film formation, it is considered that the following chemical reactions occur in the film forming liquid.

H ₂ SiF ₆ + 2H ₂ O ⇔ SiO ₂ + 6HF (Equation 1) This reaction is performed when a substrate having a stable hydrophilic group on the surface, such as glass or a silicon wafer, is immersed in a film forming solution. The reaction intermediate adsorbed on the surface is a hydrophilic group on the surface, for example, surface O
Proceeding while causing a dehydration bond reaction with the H-group, a silicon oxide (SiO ₂ ) film is formed on the substrate.

In the case of forming a film on the surface of a compound semiconductor, which is the object of the present invention, the surface of the compound semiconductor substrate is previously irradiated with plasma containing oxygen to modify the surface, and a stable hydrophilic group that becomes a foothold for the reaction is formed. To form. At this time, if a mask is applied to the surface of the substrate, hydrophilic groups are formed on the portions other than the mask, so that the film can be selectively formed on the surface of the substrate. The method of masking the surface of the substrate may be any method as long as the damage by plasma containing oxygen, such as the deposition of a photoresist or a metal thin film, does not matter.

The film forming method of the present invention will be described in detail below with reference to examples.

Example 1 3.1 mol / l silicofluorination
Silicic acid (SiO ₂・ N
H₂O) 12 g of powder was melt | dissolved and the saturated solution was produced.
2 inch diameter GaN is selected as the compound semiconductor for film formation.
And irradiating the surface of the GaN substrate with plasma containing oxygen.
Surface treatment was applied.

The processing conditions are as follows: ICP (Inductive)
Coupled Plasma: Inductively coupled plasma)
Oxygen partial pressure 1.0Pa, oxygen flow rate 5
0sccm, processing time 10 minutes, antenna power 800W,
The RF frequency was 13.56 MHz and the substrate temperature was 25 ° C.

This GaN substrate was immersed in a film forming solution prepared by diluting the above-mentioned saturated silica solution to 1.4 mol / l and kept at 40 ° C. When the film was pulled up from the film forming solution after 5 hours, SiO ₂ was formed on the GaN surface. The film thickness of this film was 200 when measured with a step gauge.
was nm.

The SiO ₂ film thus produced is
It has excellent characteristics as an insulating film. Fig. 2 shows a 200 nm Si film formed on the surface of a GaN substrate by the sputtering method.
O ₂ thin film and Si formed on the GaN substrate surface in Example 1
O ₂ thin film of current - voltage characteristics thereof are shown.

It can be seen that the film formation of this example makes it possible to form a film having an insulation property equivalent to or higher than that of the SiO ₂ film formed by the conventional sputtering method. FIG. 2 is a diagram showing current-voltage characteristics of the SiO ₂ film produced by the liquid phase film forming method and the sputtering method.

As described above, in this embodiment, a good quality metal oxide thin film can be easily formed on a compound semiconductor substrate at a low temperature of 60 ° C. or lower by using a simple and inexpensive apparatus by chemical reaction. Further, a thin film can be formed with good conformity even on a substrate having irregularities, and the degree of freedom in selecting a compound semiconductor substrate is high. Furthermore, by forming a pattern on the compound semiconductor substrate surface using a mask, a thin film can be selectively formed on the substrate surface.

Example 2 Similar to the above, 3.1 mol /
1 to 200 ml of a hydrosilicofluoric acid aqueous solution
(SiO₂・ NH₂O) 12 g of powder is dissolved and saturated solution
Was produced. Furthermore, this is diluted to 2.5 mol / l
A film-forming solution is prepared and plasma containing oxygen is used.
Immerse 2 inch diameter GaAs substrate with surface modification treatment
And kept at 40 ° C. After 3 hours, it was pulled up from the film-forming solution
On the surface of the GaAs substrate, SiO ₂The membrane is made
I was there. The thickness of this film was measured using a step gauge.
It was 200 nm.

The SiO ₂ film formed in this manner has excellent characteristics similar to those of the SiO ₂ film formed in the above-mentioned embodiment, and not only can it be used as an insulating film when manufacturing an LED element, for example. It can also be widely used as a dielectric film, a protective film, an optical film, and the like.

[0039]

As described above, according to the present invention,
Using a simple and inexpensive device, a good quality metal oxide thin film can be easily formed on a compound semiconductor substrate at low temperature,
In addition, the compound semiconductor substrate has a high degree of freedom in selection, and there is an effect that a film can be selectively formed on the substrate surface.

[Brief description of drawings]

FIG. 1 is a diagram showing a film forming process according to the present invention.

FIG. 2 is a diagram showing the voltage-current characteristics of the SiO ₂ film produced in the example.

FIG. 3 is a sectional view showing the structure of an electron beam heating vapor deposition apparatus.

FIG. 4 is a sectional view showing the structure of a sputtering film forming apparatus.

[Explanation of symbols]

1 substrate 2 shutter 3 electron gun 4 Evaporation material 5 crucibles 6 vacuum tank 11 targets 12 shutters 13 Substrate stage 14 board 15 Shield plate 16 vacuum tank 17 Flowmeter

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Manami Uezuka, inventor             2-9-13 Nakameguro, Meguro-ku, Tokyo             NLE Electric Co., Ltd. (72) Inventor Masami Awai             2-9-13 Nakameguro, Meguro-ku, Tokyo             NLE Electric Co., Ltd. F term (reference) 5F058 BA09 BB01 BB02 BC02 BC03                       BE10 BF41 BF44

Claims (5)

[Claims] 1. A liquid phase film formation method comprising immersing a compound semiconductor substrate in a solution containing a fluorine compound and forming a thin film of a metal oxide on the compound semiconductor substrate by a chemical reaction in the solution, A method for forming a metal oxide thin film, characterized in that the surface of the compound semiconductor substrate is subjected to a surface modification treatment by irradiation with plasma containing oxygen in a pre-stage of film formation. 2. The surface modification treatment by irradiating the plasma containing oxygen includes oxygen partial pressure of 0.1 Pa to 100 Pa, treatment time of 30 seconds or more, antenna power of 10 W or more, and substrate temperature of 0.
The method for forming a metal oxide thin film according to claim 1, wherein the method is performed under the condition of ℃ to 90 ℃. 3. The fluorine compound is SiF ₆ ²⁻ , Ti
The method for forming a metal oxide thin film according to claim 1, comprising at least one of F ₆ ²⁻ and ZrF ₆ ²⁻ . 4. The method for forming a metal oxide thin film according to claim 1, wherein the metal oxide is at least one of silicon oxide, titanium oxide and zirconium oxide. 5. The compound semiconductor according to claim 1, wherein the compound semiconductor is at least one of a compound semiconductor containing gallium, a compound semiconductor containing indium, and a compound semiconductor containing zinc. A method for forming a metal oxide thin film.