JP2003158124A - Method for forming carbon-based thin film on compound semiconductor - Google Patents

Abstract

(57) Abstract: To provide a method for forming a carbon-based thin film with uniform and high adhesion strength in forming an insulating film, a protective film, and a heat sink film on a compound semiconductor chemically sensitive to active hydrogen. With the goal. SOLUTION: A carbon-based thin film containing carbon or carbon as a main component is formed on a surface of a compound semiconductor chemically sensitive to active hydrogen by a sputtering method in a reaction chamber 6 in an inert gas atmosphere using solid carbon as a target 16. To form

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 an insulating film or a protective film on a compound semiconductor used in a compound semiconductor device (FET, radiation detector, etc.), and more particularly to a carbon film or carbon as a main component. The present invention relates to a method for forming a film.

[0002]

2. Description of the Related Art A compound semiconductor insulating film or protective film is
Since it is difficult to form it by thermal oxidation like SiO ₂ on silicon, conventionally, a thin film of silicon dioxide, silicon nitride, aluminum nitride or the like is formed by using a CVD method, a sputtering method or the like. However, such a protective film and an insulating film (silicon dioxide, silicon nitride, aluminum nitride) have a temperature of 200 ° C to 500 ° C.
It can be formed only at a temperature of ° C, and depending on the type of the compound semiconductor, the crystal may be thermally damaged in this process, which may adversely affect the performance of the device.

When the above-mentioned insulating film or protective film is crystalline, the film and the substrate may be separated from each other due to a mismatch in lattice constant between the film and the compound semiconductor as the substrate, a difference in thermal expansion, or the like. There is also a problem that defects occur at the interface of the device and cause deterioration of the device performance.

Further, when the above-mentioned protective film is formed by the CVD method, it is common to use a toxic gas such as silane and disilane, and the safety must always be taken into consideration in the film forming process. However, the process is complicated and the manufacturing cost tends to be high.

Therefore, if a heating process such as a heat treatment is not required in device fabrication, the silicon nitride film or the silicon dioxide film cannot always be said to be practical in view of the above-mentioned aspects. An insulating film or a protective film which has a mechanical strength and an adhesive strength to some extent at a lower temperature and which can be formed by a safe and simple film forming process is desired.

Amorphous carbon film or diamond-like carbon (DL) has been used as a material used for an insulating film or a protective film up to now.
There is a carbon film having an amorphous structure, which is called C), or a film containing carbon containing hydrogen, oxygen, nitrogen, etc. as a main component in the range of several% to several tens%.

These films are stable (chemical resistance) to acids and alkalis, have excellent wear resistance, slidability, electrical insulation, etc., and are used as cutting tools, drive parts for machines, diaphragms for speakers, etc. It is also used for coating decorative articles, optical parts, etc. because it has a property of transmitting light at a normal film thickness.

Since these films are amorphous materials, there are no problems such as lattice mismatch with the substrate, no poisonous gas is used in a relatively simple device, and the temperature is low from room temperature to about 100 ° C. It has advantages in practical use such as formation.

Therefore, application as an insulating film or a protective film on the compound semiconductor can be expected sufficiently. In fact, G
Attempts have been made to apply it as a heat sink film on an aAs substrate.

The carbon or the film containing carbon as a main component is generally formed by a plasma CVD method using a gas containing carbon as a raw material or a sputtering method using a solid containing carbon as a raw material. However, a problem in forming such a film is the adhesion strength of the film. Carbon or a film containing carbon as a main component has an amorphous structure containing sp ³ -bonded carbon, and generally, when the proportion thereof increases, the performance as an insulating film and a protective film such as electric insulation, thermal conductivity, and hardness. While the film thickness is improved, the internal stress in the film is increased, so that peeling from the substrate is observed. Therefore, in the actual film formation, hydrogen is added at the time of forming the thin film, and hydrogen is introduced into the film to control the terminal structure of the thin film to relieve the internal stress in the film and maintain the adhesive strength of the film. Such measures are taken.

[0011]

However, the above-mentioned conventional method has no particular problem with semiconductor materials such as silicon and GaAs, which have a relatively slow reaction with hydrogen, but can easily be used with hydrogen among compound semiconductors. C to react
In the case of a dTe semiconductor substrate, the active hydrogen contained in the gas causes alteration or etching of the crystal surface, which damages the crystal and causes the surface to become rough, resulting in a uniform and highly adherent carbon. It is difficult to form a film.

Therefore, at present, formation of amorphous carbon on such a compound semiconductor (CdTe or the like) that is chemically sensitive to active hydrogen has not been established, including the formation conditions.

In view of the above situation, the present invention provides a method for forming a uniform carbon-based thin film having high adhesion strength in forming an insulating film, a protective film and a heat sink film on a compound semiconductor which is chemically sensitive to active hydrogen. The purpose is to provide.

[0014]

In order to achieve the above object, the present invention provides [1] a method for forming a carbon-based thin film on a compound semiconductor, the surface of which is chemically sensitive to active hydrogen. First, carbon or a film containing carbon as a main component is formed by sputtering using solid carbon as a target in an inert gas atmosphere.

[2] In the method for forming a carbon-based thin film on the compound semiconductor according to the above [1], the semiconductor material that is chemically sensitive to active hydrogen is CdTe.

[3] The method for forming a carbon-based thin film on a compound semiconductor according to the above [2], which comprises performing sputtering on the surface of the CdTe crystal in a mixed gas atmosphere of an inert gas and a hydrogen gas. To use.

[4] The method for forming a carbon-based thin film on a compound semiconductor according to the above [3], which is performed in a mixed gas atmosphere of the above-mentioned inert gas and hydrogen gas.

[5] The method for forming a carbon-based thin film on a compound semiconductor according to the above [4], wherein a trace amount of the hydrogen gas is controlled.

[6] The method for forming a carbon-based thin film on a compound semiconductor according to the above [5], wherein the hydrogen partial pressure ratio of the hydrogen gas is 0.02% to 0.1%.

In the present invention, in the background as described in the conventional example, a carbon film or a film containing carbon as a main component is used as an insulating film or a protective film having sufficient adhesive strength, mechanical strength (hardness) and insulating property. , A method of forming a compound semiconductor (CdTe or the like) which is chemically sensitive to active hydrogen at a low temperature (room temperature to 150 ° C. or lower).

The formation of a carbon film or a film containing carbon as a main component (hereinafter referred to as a carbon-based thin film) on the compound semiconductor has been carried out by the conventional method for the reason described above. It is difficult to obtain a uniform film having high adhesion strength within the control range of partial pressure. Further, even when the film is formed in a hydrogen-free atmosphere, the internal stress of the carbon film increases and the film peels off. That is, to form a carbon-based thin film on the compound semiconductor as an insulating film and a protective film,
It is necessary to alleviate the reaction with the surface of the compound semiconductor, which is the formation surface, while relaxing the internal stress in the film and maintaining an appropriate adhesion strength.

Further, according to the present invention, in order to solve these problems, the carbon having a sufficient adhesion strength and mechanical strength (hardness) is obtained by controlling a minute amount of hydrogen, which has not been carried out in the prior art. The inventors have found that it is possible to form a system thin film on the compound semiconductor, and have completed the present invention.

In the present invention, the carbon thin film is formed by the sputtering method. This is because it is necessary to control the amount of hydrogen at the time of film formation in a minute amount as described above. CV
In the case of forming a carbon-based thin film by the D method, a hydrocarbon-based gas is mainly used as a raw material gas, and the control of the amount of hydrogen is limited by the ratio of carbon / hydrogen contained in the raw material gas, so that a very small amount of carbon is used. Film formation under hydrogenation or hydrogen-free environment is impossible.

Further, when the amount of hydrogen during film formation is made minute by increasing the ratio of the rare gas with the mixed gas of the rare gas and the hydrocarbon-based gas, the amount of the raw material gas is reduced. It takes a considerable amount of time to reduce the film forming speed and form a desired film thickness. This does not solve the problem because it increases the probability that hydrogen reacts with the surface of the compound semiconductor, which is the formation surface, as a result.

On the other hand, the sputtering method uses a solid raw material of simple carbon, and the amount of hydrogen can be controlled independently of the mixing ratio with the rare gas to be introduced. Can be controlled arbitrarily. This means that when the film forming conditions other than the hydrogen amount (high-frequency power, reaction pressure, substrate bias voltage, etc.) are changed, the optimum hydrogen amount for film formation can be easily changed. ing. That is, the sputtering method is a film forming method that is particularly effective for controlling a small amount of hydrogen, and is the most suitable method for the present invention.

In forming the carbon thin film by the sputtering method in the present invention, the minute amount of hydrogen is optimally controlled by adjusting the mixing ratio of the rare gas (helium gas or the like) and hydrogen gas introduced during film formation. (Hydrogen partial pressure ratio:
0.02% -0.1%. Here, the hydrogen partial pressure ratio is the ratio of the hydrogen partial pressure to the total gas pressure during film formation). further,
By this optimization, it was clarified that the required mechanical strength, insulating property, and adhesion strength can be obtained at a film thickness of about 10 nm to 100 nm.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

FIG. 1 is a block diagram of a carbon-based thin film forming apparatus showing an embodiment of the present invention. Here, a high frequency magnetron sputtering apparatus as an example for forming a carbon film or a film containing carbon as a main component is used. Shows.

As shown in this figure, in the introduction gas system 1, helium gas is supplied from the first introduction port 2, hydrogen gas is supplied from the second introduction port 3, flowmeters 4A and 4B, and valves 5A and 5B are connected. After that, it is introduced into the reaction chamber 6 through the nozzle 7.

The reaction chamber 6 was provided with a first electrode 8 and a second electrode 9. The second electrode 9 is normally grounded at the same potential as the reaction chamber 6. Electrical energy is applied between the pair of first electrode 8 and second electrode 9 from the high-frequency power source 10 through the matching circuit 11 to generate plasma.

The exhaust system 12 exhausts unnecessary gas through a pressure adjusting valve 13, an oil diffusion pump 14, and a rotary pump 15. The gas introduced into the reaction chamber 6 has a pressure of 0.00
1-1 Torr, typically 0.01-0.5 Torr
Energy is added to 0.1-1 kW by high frequency energy under r. Electrons in the plasma generated by obtaining high-frequency energy are accumulated in the second electrode 9 to cause self-bias, which causes the first electrode 8
Positive ions (for example, He ⁺ , H ⁺ ) are accelerated and collide with the graphite target 16 installed on the first electrode 8.

By this collision, carbon or particles in which carbon and hydrogen are bonded, which compose the graphite target 16, are knocked out into the reaction space, reach the substrate 17 installed on the second electrode 9, and C on the substrate 17 is reached. A carbon-based thin film having an amorphous structure including -C bond, C-H bond, and C = C bond is formed.

As an example of the present invention, an example in which a carbon-based thin film is formed as a protective film on a CdTe crystal which is a II-VI compound semiconductor will be shown.

In forming the carbon-based thin film thus configured, the semiconductor substrate 17 made of CdTe was placed on the second electrode 9. The reaction chamber 6 was evacuated to a high vacuum by an exhaust device. Since the CdTe semiconductor reacts with hydrogen gas and the surface of the substrate is roughened, it is necessary to optimize the mixing ratio of helium gas and hydrogen gas in order to form a film having high adhesion strength.

Therefore, the semiconductor substrate 17 made of CdTe is installed on the second electrode 9, and the reaction chamber 6 is evacuated to a high vacuum by an exhaust device, and then the degree of vacuum in the reaction chamber 6 is 0.4 Tor.
r, the reaction chamber 6 with the total gas flow rate kept at 40 SCCM
Helium and hydrogen gas were introduced by the flowmeters 4A and 4B so that the hydrogen partial pressure ratio inside was 0.03% to 0.065%. The second electrode 9 has the same potential (ground) as the reaction chamber 6 and is not particularly cooled or heated.

In such a state, the high-frequency magnetron sputtering device is operated to generate plasma in the reaction chamber 6 to perform sputtering, thereby performing CdTe.
A carbon-based thin film having a film thickness of about 10 to 100 nm is formed on the surface of the substrate 17.

At this time, the substrate is not particularly heated,
Ions (such as He ions) in plasma and carbon particles sputtered from the target collide with the substrate during film formation, so the substrate temperature is about 50 to 100 ° C., but at this temperature, the CdTe substrate is No thermal damage done.

FIG. 2 is a characteristic diagram of hardness of a carbon-based thin film formed by the method for forming a carbon-based thin film on a compound semiconductor according to the present invention with respect to a hydrogen partial pressure ratio. The axis shows hardness (GPa) and the total gas pressure is 0.
This is the case of 4 Torr.

The carbon-based thin film formed by the present invention is
As shown in FIG. 2, the hardness was 10-12 GPa, the optical gap was 1.0 eV, the resistivity was 1 × 10 ⁵ Ω · cm, and the adhesive strength was not observed by the adhesive tape peeling test. It was confirmed that the adhesion was sufficiently good.

From the above results, it was possible to form a carbon-based protective film having sufficient hardness and adhesive strength on a CdTe substrate at a low temperature (room temperature to 100 ° C. or lower).

The most important point in this example is the addition of a small amount of hydrogen during film formation. Under the above conditions, the hydrogen partial pressure ratio is 0.03% to 0.065%, and a very small amount of hydrogen is controlled.

As described above, in the range of hydrogen partial pressure ratio (1% to 100%) which has been conventionally performed, CdTe is obtained.
This is because it is not possible to form a carbon-based thin film having strong adhesion strength because the surface of the substrate becomes rough. In fact, a thin film formed with a hydrogen partial pressure ratio higher than 0.1% easily peeled off by a tape test.

The carbon-based thin film is further laminated on the film shown in the above embodiment by changing the film forming conditions (hydrogen amount, high frequency power, reaction pressure, substrate bias voltage, etc.), and the film as a whole is further It is possible to control the physical properties and the thickness in the range as shown in.

Hardness: 2 GPa to 20 GPa Optical gap: 1 eV to 3.5 eV Resistivity: 1 × 10 ⁵ Ω · cm to 1 × 10 ¹³ Ω · cm The present invention is not limited to the above embodiment,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0045]

As described above in detail, according to the present invention, an insulating film having sufficient adhesion strength, mechanical hardness, and insulating property on a compound semiconductor, particularly a compound semiconductor sensitively reacting with hydrogen. Further, a carbon-based thin film is formed as a protective film at a low temperature (room temperature to 150 ° C. or lower), and it must be noted when manufacturing a compound semiconductor device. No damage such as alteration (composition change, surface roughness) due to heat of the substrate is given.

Therefore, the device manufacturing process is 4
If performed below 00 ° C (temperature at which the carbon thin film can maintain a stable state) or below, insulation between wirings or electrodes or
It is effective for insulation and protection of parts other than the electrode when soldering to the electrode, and since no particularly toxic gas or the like is used, it is possible to provide a naturally gentle manufacturing method.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a carbon-based thin film forming apparatus showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram of hardness with respect to a hydrogen partial pressure ratio of a carbon-based thin film formed by the method for forming a carbon-based thin film on a compound semiconductor of the present invention.

[Explanation of symbols]

1 Introduced gas system 2 First inlet 3 Second inlet 4A, 4B flow meter 5A, 5B valve 6 Reaction chamber 7 nozzles 8 First electrode 9 Second electrode 10 high frequency power supply 11 Matching circuit 12 Exhaust system 13 Pressure control valve 14 Oil diffusion pump 15 Rotary pump 16 Graphite target 17 Substrate (CdTe)

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4K029 AA04 BA34 BD01 CA05 DC02                       DC35 DC39 EA05                 5F033 GG01 RR01 SS08                 5F058 BA20 BB01 BC20 BF12 BG01                       BG02 BG04

Claims (6)

[Claims] 1. A compound semiconductor which forms carbon or a film containing carbon as a main component on a surface of a compound semiconductor which is chemically sensitive to active hydrogen by sputtering using solid carbon as a target in an inert gas atmosphere. Of forming a carbon-based thin film of. 2. The method for forming a carbon-based thin film on a compound semiconductor according to claim 1, wherein the semiconductor material chemically sensitive to active hydrogen is CdTe. Method. 3. The method for forming a carbon-based thin film on a compound semiconductor according to claim 2, wherein the compound is formed by sputtering on the surface of the CdTe crystal in a mixed gas atmosphere of an inert gas and a hydrogen gas. A method for forming a carbon-based thin film on a semiconductor. 4. The method for forming a carbon-based thin film on a compound semiconductor according to claim 3, wherein the carbon-based thin film is formed on the compound semiconductor in a mixed gas atmosphere of the inert gas and hydrogen gas. . 5. The method for forming a carbon-based thin film on a compound semiconductor according to claim 4, wherein the carbon-based thin film is formed on a compound semiconductor for controlling a minute amount of the hydrogen gas. 6. The method for forming a carbon-based thin film on a compound semiconductor according to claim 5, wherein the carbon on the compound semiconductor has a hydrogen partial pressure ratio of the hydrogen gas of 0.02% to 0.1%. Method of forming a thin film.