JPH0917733A - Forming method for porous silicon thin film - Google Patents

Abstract

PURPOSE: To make it possible to form a high-quality porous silicon thin film on a substrate by a CVD method by applying a bias of a specified voltage by using a mixed gas of both oxygen gas and silane-based plasma gas by a specified pressure and microwave power under resonance by an electron cyclotron. CONSTITUTION: A silicon substrate is placed on a substrate holder of a CVD equipment, a bias of 0 to 200V is applied to the silicon substrate, and the substrate is held to a predetermined temperature. Moreover, microwave is introduced by a square wave wave guide, and a predetermined magnetic field is applied to a magnetic coil 3. Next, SiH4 gas and O2 gas are introduced to a reaction chamber of a plasma generating chamber 2, a total pressure is kept to 10<-1> to 103 Pa, plasma is generated with 0.1 to 5kW power, and a porous silicon thin film is formed on the silicon substrate. When the silicon substrate forming the porous silicon thin films is irradiated with laser, clear lighting of the laser radiating portion can be confirmed.

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 porous silicon thin film, and more particularly to a light emitting diode, a light emitting element such as a laser, a neural network, an optical wiring in a silicon chip, an optical connection such as three-dimensional integration. The present invention relates to a method for forming a porous silicon thin film that can be used in the integration technology used.

[0002]

2. Description of the Related Art Silicon semiconductors have abundant resources and high crystal manufacturing technology and device design / manufacturing technology. Therefore, electronic devices can be used from high power control to high-speed processing of electric signals. Is widely used as. However, since single crystal silicon is an indirect transition type semiconductor having an energy gap of 1.1 eV, it does not emit light in the visible light region, and the activity as an optical element has been confined to compound semiconductors.

However, in 1990, it was observed that a porous silicon thin film formed on the surface of a silicon substrate when anodized in a hydrofluoric acid solution emits visible light at room temperature due to photoexcitation or electron injection (Applied Physics Letters). 57,
1990 p1046). This is because the crystal size is smaller than the spread of de Broglie wave packet of electrons in silicon, the energy level is quantized, the energy gap is increased, and the conduction band is changed. If this is applied, it becomes possible to fuse an electronic device and an optical device by using a single electronic material called silicon, and it is expected to promote high integration, and thus the industrial value is extremely high.

In order to put this porous silicon thin film into practical use as an element material for optoelectronics, matching with other manufacturing processes is indispensable, but the most popular porous silicon forming method is anodization. The method has a major drawback in that it is a wet process using hydrofluoric acid. Therefore, as a method for achieving consistency with other manufacturing processes, a manufacturing method using only a dry process is strongly required.

At present, as a manufacturing method only by a dry process, Si particles are evaporated in a mixed gas of Ar 99% and O ₂ 1% under a vacuum of a gas pressure of 6 Torr, and this is vapor-deposited on a substrate to form silicon. A method of forming a thin film is also proposed (Proceedings of the 54th SPSJ Academic Lecture Meeting 29SZL9). However, in this method, only a silicon thin film in which passivation due to oxygen is incomplete can be obtained. When such a silicon thin film is used, there is a problem that the emission intensity is reduced by about one digit.

Further, there has been proposed a method of forming a silicon thin film by sputtering a target having a Si piece placed on SiO ₂ with Ar gas at a high frequency of 13.56 MHz (The 54th Annual Meeting of the Applied Physics Society of Japan). Meeting Proceedings 29
SZL10). However, in the method of forming a silicon thin film by such a method, since Ar is used for sputtering with high energy, there is a problem that Ar ions are mixed in the silicon thin film and the emission intensity is reduced by two digits or more. It was

Further, in these physical vapor deposition (PVD) methods such as the vacuum vapor deposition method and the sputtering method, there is a problem in the stable supply of the raw material when the silicon thin film is formed.
The present invention has been made in view of the above problems, and provides a method for forming a porous silicon thin film by which a high quality porous silicon thin film is formed by a dry process, particularly a chemical vapor deposition (CVD) method. To aim.

[0008]

According to the present invention, a silane-based gas plasma-converted under electron cyclotron resonance (ECR) at a pressure of 10 ^-1 to 10 ³ Pa and a microwave power of 0.1 to 5 kW is used. 0 using a mixed gas with oxygen gas
Provided is a method for forming a porous silicon thin film, which comprises forming a porous silicon thin film on a substrate to which a bias of -200 V is applied.

In the method of manufacturing the porous silicon thin film of the present invention, the electron cyclotron resonance plasma CVD method is used. That is, a high-density plasma is generated by combining an ECR ion source and a divergent magnetic field, thereby forming a high-quality porous silicon thin film. The CVD apparatus used at this time is usually ECR plasma CVD.
There is no particular limitation as long as it is an apparatus used in the method. Conditions in this manufacturing method, for example, the pressure is 10
It is preferably ⁻¹ to 10 ³ Pa. If it exceeds 10 ³ Pa, the gas temperature in the plasma rises and the substrate temperature rises, which is not preferable. Also, 10 ^-1 P
If it is less than a, film formation becomes impossible, which is not preferable.

The microwave power in the microwave generator is preferable because the larger the power, the higher the film formation rate and the lower the defect density. However, considering the equipment of the ECR plasma CVD apparatus, the microwave power is preferably about 5 kW or less. Also, 0.
If it is 1 kW or less, the obtained porous silicon thin film becomes amorphous, which is not preferable. The microwave frequency is not particularly limited, but is preferably about 2.45 GHz.

Further, the divergent magnetic field used in the present invention is not particularly limited, but is, for example, 875 G.
The degree of aus is mentioned. In the present invention, a mixed gas of silane-based gas and oxygen gas is used as the source gas. The silane-based gas is not particularly limited, and examples thereof include monosilane, disilane, trisilane, and tetrasilane, with monosilane being preferred. These raw material gases are preferably introduced into the apparatus while appropriately adjusting the pressure in the apparatus to be held, the microwave power, the reaction time, the mixing ratio of the silane-based gas and the oxygen gas, and the like. Gas is 1 ~ 1000scc
m and oxygen gas are preferably introduced at 0.1 to 100 sccm. Further, the mixing ratio of the silane-based gas and the oxygen gas at this time is preferably about 1: 1 to 1000: 1.

As the substrate on which the porous silicon thin film is formed, a light emitting diode, a light emitting element such as a laser, a neural network, a silicon chip, or the like can be appropriately selected according to its use. For example, a glass substrate or a plastic substrate. , A metal substrate, a compound semiconductor substrate such as GaAs or InGaAs, and a silicon substrate can be used. Of these, a silicon substrate is preferable. It is preferable that a negative bias of about 0 to -200 V is applied to the substrate for forming the porous silicon thin film so that the plasma ions of silicon are effectively accelerated. Further, the temperature of the substrate at that time is preferably maintained at about 100 ° C. or higher. If the temperature is lower than 100 ° C., it becomes difficult to form a film efficiently and uniformly with plasma ions.

The porous silicon thin film formed on the substrate under the above conditions means a silicon thin film formed of microcrystalline silicon having a grain size of several nm to several tens of nm and the surface of which is passivated with oxygen. . When forming such a porous silicon thin film, the film forming time can be appropriately adjusted depending on the film thickness of the porous silicon thin film to be obtained, microwave power, etc. When obtaining a porous silicon thin film, the film formation time is preferably about 3 hours.

Further, in the present invention, under electron cyclotron resonance, a pressure of 10 ^-1 to 10 ³ Pa and a pressure of 0.1 to 5 are used.
It is preferable to treat the porous silicon thin film formed on the substrate with a gas containing oxygen which has been turned into plasma with a microwave power of kW. As the gas containing oxygen, for example, various gases such as air, nitric oxide, nitrogen dioxide, carbon monoxide, carbon dioxide, a mixed gas of an inert gas and an oxygen gas, a mixed gas of a nitrogen gas and an oxygen gas, etc. Can be used. The proportion of oxygen contained in this case is not particularly limited and can be appropriately adjusted depending on the introduction amount of oxygen-containing gas, microwave power, substrate temperature, etc. -10
It is preferable that the content of oxygen ions is about 0%. Specifically, there is a case where nitrogen dioxide containing about 30% oxygen gas is introduced at 10 to 50 sccm. The irradiation time at this time is preferably about 10 minutes to 1 hour.

[0015]

According to the present invention, under electron cyclotron resonance,
A mixed gas of a silane-based gas and an oxygen gas, which has been turned into plasma with a microwave power of 0.1 to 5 kW and a pressure of 10 ⁻¹ to 10 ³ Pa, is used to perforate a substrate on which a bias of 0 to −200 V is applied. Since the thin silicon film is formed, the film surface is less damaged and a large-area film can be easily formed. In other words, the electrons in the plasma make a circular motion due to the Lorentz force in the magnetic field, but if the frequency at that time and the frequency of the introduced microwaves are matched, the microwave energy is efficiently converted into the kinetic energy of the electrons by resonance absorption. (For example, 100 to 1000 times), the temperature of electrons rises, ionization of gas molecules is promoted, and the density of generated plasma rises. Therefore, the source gas is excited at a low temperature and is stacked on the substrate, so that the film surface is less damaged. Further, since the temperature rise in the plasma generation chamber is suppressed and the low pressure can be maintained, uniform plasma is generated and the area can be easily increased.

Further, after forming the porous silicon thin film,
Further, when the porous silicon thin film is irradiated with oxygen plasma under the same conditions, the surface of the obtained porous silicon thin film is almost completely passivated, so that the porous silicon thin film having higher brightness can be obtained.

[0017]

Embodiments of the method for forming a porous silicon thin film according to the present invention will be described below with reference to the drawings. First, the CV used for forming the porous silicon thin film in this example.
The D device will be described with reference to FIG.

This CVD apparatus has a chamber 3 mainly composed of a plasma generation chamber 1 and a reaction chamber 2, a microwave oscillator 6 connected to the plasma generation chamber 1 via a rectangular waveguide 5, and a plasma generation chamber 1 surrounded by a microwave oscillator 6. The installed magnetic coil 4,
It is composed of an exhaust gas treatment device 8 connected to the chamber 3, a source gas introduction port 7, and a decompression device 9. Also, chamber 3
A substrate holder 10 for placing a substrate and capable of rotating and moving up and down is provided in the interior of the. Example 1 A silicon substrate is placed on the substrate holder of the above CVD apparatus,
A bias of −50 V was applied to the silicon substrate and the substrate temperature was kept at 200 ° C. Further, a microwave of 2.45 GHz was introduced from the rectangular waveguide, and a magnetic field of 875 Gauss was applied to the magnetic coil 3. Then, 50 s of SiH ₄ gas was introduced into the reaction chamber of the plasma generation chamber 2.
introducing ccm and O ₂ gas 5sccm with 10P total pressure
While maintaining at a, plasma was generated with a power of 1.2 kW, and a porous silicon thin film with a film thickness of about 1 μm was formed on the silicon substrate for 1 hour.

When a He--Cd laser (wavelength: 3250Å) was irradiated on the silicon substrate on which the porous silicon thin film was formed, the laser irradiation portion was clearly illuminated. Also,
Ar laser (wavelength 488) was added to the obtained porous silicon thin film.
The photoluminescence spectrum when irradiated with 0Å) is shown in FIG. Example 2 On the silicon substrate on which the porous silicon thin film obtained in Example 1 was formed, further, in the above CVD apparatus, 3
By introducing 0 sccm of N ₂ O gas, the pressure inside the apparatus was adjusted to 10
It was kept at 0 Pa and irradiated with electron cyclotron resonance plasma at 1.2 kW for 30 minutes. FIG. 3 shows the photoluminescence spectrum when the treated porous silicon thin film was irradiated with Ar laser (wavelength 4880Å). As is clear from FIG. 3, when the porous silicon thin film formed under the above conditions is further irradiated with plasma, it is found that the emission intensity is about twice as high as that of the porous silicon thin film. It was

[0020]

According to the method for forming porous silicon of the present invention, since the formation of the porous silicon thin film can be performed only by the dry process, good compatibility with other electronic device manufacturing processes can be obtained. You can Therefore, as compared with the conventional wet process such as the anodization method, various optoelectronic devices can be more advantageously realized. Further, it is possible to obtain a high-quality porous silicon thin film which is uniform over a large area and has less damage as compared with other dry processes.

Further, after forming the porous silicon thin film,
Further, when the porous silicon thin film is irradiated with oxygen plasma under the same condition, the passivation is further promoted, so that the porous silicon thin film having higher brightness can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a CVD apparatus used in an example of a method for forming porous silicon according to the present invention.

FIG. 2 is a first example of a method for forming porous silicon according to the present invention.
3 is a photoluminescence spectrum of the porous silicon obtained in 1.

FIG. 3 is a second example of the method for forming porous silicon according to the present invention.
3 is a photoluminescence spectrum of the porous silicon obtained in 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma generation chamber 2 Reaction chamber 3 Chamber 4 Magnetic coil 5 Waveguide 6 Microwave oscillator 7 Raw material gas inlet 8 Exhaust gas treatment device 9 Pressure reduction device 10 Substrate holder 10

Claims (3)

[Claims] 1. Under electron cyclotron resonance, 10 ^-1 to 1
A porous silicon thin film was formed on a substrate to which a bias of 0 to -200 V was applied using a mixed gas of a silane-based gas and an oxygen gas, which were made into plasma with a pressure of 0 ³ Pa and a microwave power of 0.1 to 5 kW. A method for forming a porous silicon thin film, which comprises forming the thin film. 2. The method for forming a porous silicon thin film according to claim 1, wherein the liquid volume mixing ratio of the silane-based gas and the oxygen gas is O ₂ / SiH ₄ = 1/1000 to 1/1. 3. Further, under electron cyclotron resonance, 1
Using a gas containing oxygen, which has been plasmatized with a microwave pressure of 0.1 to 5 kW and a pressure of 0 ⁻¹ to 10 ³ Pa,
The method for forming a porous silicon thin film according to claim 1, wherein the porous silicon thin film formed on the substrate is treated.