JPH0533812B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a film forming apparatus that uses a photo CVD method or a CVD method using excited neutral particles.

[Conventional technology] Photochemical reactions that have been carried out in the past, such as the photochemical reaction of amorphous silicon whose main raw material is silane gas.
In the CVD method, silane gas is only directly photodecomposed by ultraviolet light with a wavelength of 160 nm or less;
Since it is difficult to obtain a suitable light source that emits ultraviolet light at this wavelength, mercury-sensitized photochemical reactions using mercury as a catalyst have been used. However, in this method, mercury used as a catalyst may be mixed into the membrane, which may have an adverse effect, and there are also problems in managing mercury, which is toxic. On the other hand, when higher-order silanes such as disilane are used, direct photolysis is possible using light from a low-pressure mercury lamp without using mercury sensitization, and the negative effects of mercury can be eliminated, but higher-order silanes are expensive. Yes, and the deposition rate is 0.25Å/
This is about seconds, which is still insufficient from a practical standpoint.

A commonly used film formation method is to decompose and deposit silane using a high-frequency discharge of 13.56 MHz, but there are problems such as the deposited film being damaged by charged particles and impurities getting mixed into the film. Ta.

Therefore, as a film formation method that enables a high-quality, uniform thin film without the harmful effects of mercury and without impurities or load particle damage at a sufficiently fast deposition rate for practical use, we have developed a film-forming method using ultraviolet rays irradiated from a plasma. A film is formed by causing a photochemical reaction and depositing a reaction product on a substrate separated from the plasma. The film forming apparatus used in this optical CVD method has a plasma region formed by gas discharge and a substrate on which the film is formed in a single container, and a chemically reactive gas release mechanism is installed. A reaction area is provided.

Then, a film is formed by appropriately supplying an ultraviolet radiation gas and a photochemically reactive gas that effectively emit ultraviolet light having a wavelength of 160 nm or less. As a method for generating plasma, a method is used in which an electrode is disposed in a plasma region and a DC or low frequency AC voltage is applied to generate a gas discharge. In addition, a hot cathode is used for the electrode, which can input a large amount of power in order to obtain strong ultraviolet rays. Among them, alkaline earth metals, which have high thermal electron emission efficiency at relatively low temperatures, are used on the surface of the high-melting point metal coil. A coated filament hot cathode is used. Although this filament hot cathode is highly efficient, it is known that it is significantly degraded by reactive gases such as hydrogen and oxygen.

[Problems to be Solved by the Invention] As described above, in a film forming apparatus having a plasma region in which electrodes are disposed and a reaction region in which reactive gas is emitted in one container, the emitted ultraviolet rays There is a problem in that reactive gases such as hydrogen and oxygen contained in the radiation gas, reactive gas, or gases produced by-product during the film-forming reaction diffuse slightly into the plasma region, significantly shortening the life of the filament hot cathode. Ta.

In addition, when using a hot cathode made of triated tungsten, which is slightly less susceptible to deterioration due to reactive gases than a filament, the temperature must be raised to over 2000°C to maintain discharge, which requires extensive cooling of the device. When using a cold cathode, which is difficult to put into practical use and is less prone to deterioration due to reactive gases, a higher voltage is required to maintain discharge than a filament hot cathode, and the power supply is larger. However, there were problems such as difficulty in maintaining stable discharge at high power and low frequency.

In addition, when using electrodeless discharge as a plasma generation method using high frequency or microwave without using electrodes, the lifetime is long, but the luminous efficiency is lower than that of the electrode method under the reduced pressure where film formation is normally performed. There was a problem that the volume velocity was extremely low and a sufficient volume velocity could not be obtained.

The present invention has been made in order to solve these conventional problems, and is capable of forming a film with little deterioration of the electrode due to reactive gas, long life, fast film formation speed, and no damage to the deposited film due to charged particles. The purpose is to provide equipment.

[Means for Solving the Problems] In order to achieve the above object, the film forming apparatus of the present invention includes an electrode for applying a DC or low frequency AC voltage to a plasma region, and an introduction window for introducing microwaves. The device is configured to generate plasma by simultaneously applying a direct current or low frequency alternating current voltage applied to the electrode and microwave introduced into the introduction window.

[Function] With the above configuration, a stable plasma discharge can be obtained by the combination of the discharge between the electrodes and microwaves, and thereby the deposition rate of film formation can be significantly increased.

[Examples] Hereinafter, the present invention will be specifically described based on examples shown in the drawings.

In FIG. 1, the upper space inside the container 5 is the plasma region A, and the lower space is the reaction region B. In this plasma region A, a pair of electrodes 1, 1
are arranged facing each other, and a DC or low frequency AC voltage is applied thereto. At this time, one side of the electrode to which a negative voltage is applied operates as a cold cathode. A quartz introduction window 8 for introducing microwaves is arranged on the ceiling of the container 5, and microwaves MW are introduced through a waveguide 9. The material of the introduction window 8 is not limited to quartz, and may be made of other materials that transmit microwaves, or may be simply open without requiring any material. On the back of the electrode 1 on the upper side of the container 5,
Introductory holes 6, 6 for ultraviolet radiation gas _G1 are formed,
From this, an ultraviolet radiation gas G ₁ selected from a rare gas, hydrogen or deuterium, or a mixed gas containing these gases is introduced. The ultraviolet radiation gas G ₁ is ionized mainly in the vicinity of the introduction window 8 by the microwave MW. This ionized gas causes dielectric breakdown between the electrodes 1 and 1, and plasma P is formed between the electrodes 1 and 1, and light including ultraviolet rays emitted from this plasma P is transmitted to the reaction area below. B is irradiated. A substrate holder 3 is arranged in the reaction area B, and a substrate 4 on which a film is to be formed is placed thereon.
A ring-shaped pipe 2, which is a photochemically reactive gas discharge mechanism, is arranged slightly above this, and a photochemically reactive gas _G2 is discharged near the substrate 4 from its nozzle 2a. Therefore, the gas G ₂ is directly photodecomposed by the ultraviolet rays, and the reaction products are deposited on the substrate 4 to form a film. An exhaust port 10 is provided below the substrate holder 3, through which the gas inside is exhausted. It is also good to prevent flakes and the like from landing on the substrate by placing these upside down and placing the substrate on top.

A conductive partition wall 7 is preferably disposed between the region A and the region B in order to electrically separate the plasma region and the reaction region and to suppress the diffusion of charged particles into the reaction region. The partition wall 7 has an opening approximately equal to or slightly larger than the substrate 4, and this opening is covered with a conductive shielding net 7a, and both areas A and B are covered by the partitioning wall 7 and the shielding net 7a. It is sectioned. Of course, it may be partitioned by only the shield net 7a without arranging the partition wall 7, but if the area of the shield net 7a is made smaller by arranging the partition wall 7 as shown in the drawing, the gas G ₂ can be divided into the area A. Diffusion can be reduced.

These partition walls 7 and shield net 7a may be made of stainless steel, for example, but when amorphous silicon is deposited to form a film, it is preferable that they be made of silicon or that their surfaces be coated with a silicon film. This is because even if the shield net 7a and the like are exposed to plasma and a sputtering phenomenon occurs, and the sputtered material is incorporated into the film, the film quality will not deteriorate because the elements are the same.

In this embodiment, in order that plasma P generated by voltage application and microwaves can effectively act as a light source, region A contains rare gases, hydrogen, deuterium, and other gases as ultraviolet radiation gas _G1 . A mixed gas of _G2 is selected and supplied depending on the type of photochemically reactive gas G2. For example, when depositing amorphous silicon, if the gas G ₂ is silane, silane is deposited by direct photolysis with ultraviolet rays of 160 nm or less, so as G ₁ that effectively emits ultraviolet rays of 160 nm or less, Argon,
Krypton, xenon, etc. are selected. Incidentally, the emission wavelengths of argon are 104.8nm and 106.7nm, krypton is 123.6nm and 116.5nm, xenon is 147.0nm,
It is 129.6nm.

Furthermore, plasma P is generated by microwave MW,
Microwave MW is generated between electrodes 1 and 1 of cold cathode operation due to dielectric breakdown caused by ionized gas.
Compared to the case without using, high power discharge can be stably maintained at a sufficiently low applied voltage. Therefore, the electrodes are less likely to deteriorate due to reactive gases, resulting in a long life, and the power supply device can be made smaller.Furthermore, the luminous efficiency is higher than in electrodeless discharge, and a film can be formed more effectively. Further, a sufficient film formation rate can be obtained without relying on a photosensitization reaction due to mercury, and contamination due to mercury does not become a problem.

Furthermore, even if the charged particles of the plasma P try to diffuse into the region B, most of them are captured by the shield network 7a and do not reach the substrate 4, so the deposited film is not damaged by the charged particles and there is less contamination of impurities. It is possible to obtain a deposited film with excellent performance.

Next, an example of film formation using the film forming apparatus shown in Fig. 1 is shown.
When depositing a thin film of amorphous silicon under conditions of ℃, the ultraviolet radiation gas G ₁ is argon at a flow rate of 100 sccm, and the photochemically reactive gas G ₂ is silane at a flow rate of 100 sccm.
20 sccm flow, frequency from microwave introduction window 13
A microwave with a frequency of 2.45 GHz and a power of 400 W was introduced, and at the same time, a frequency of 50 Hz and a voltage was applied between electrodes 1 and 1.
When 230V is applied, discharge starts between electrodes 1 and 1, and the discharge voltage between electrodes 1 and 1 at this time is 180V,
The current is stable at 4A, plasma P is generated, and 1.1~
The film could be formed at a high deposition rate of 1.31 Å/sec. The obtained thin film was in good condition with no charged particle damage, the photoconductivity was σ _p =10 ^-4 S/cm, and the dark conductivity was σ _d =
10 ^-9 S/cm, resulting in a high quality thin film. Also,
The lifespan of the electrodes has been significantly extended.

Figure 2 shows the deposition rate versus microwave power, and shows that a sufficient deposition rate can be obtained with a small power of about 400W, which is the same as when using discharge light emission using only microwaves of the same power. This shows that the deposition rate can be dramatically increased by combining the electric discharge between the electrodes 1 and microwaves.

On the other hand, if you try to form a film by discharging only the cold cathode electrode without using microwaves, a high voltage of 600V or more is required to start the discharge.
Further, the discharge that occurred was unstable and stopped immediately, making it impossible to form a film.

In addition, if microwaves are introduced only when the first electrode discharge starts, and then the microwaves are stopped after the discharge starts and only the electrodes are operated, the plasma discharge will stop immediately when the microwaves are stopped.
It was not possible to form a film.

Incidentally, in the above embodiment, the reaction of the reactive gas is initiated by the ultraviolet rays emitted from the plasma.
Although we have mentioned CVD methods, but are not limited to them, reactive gases are diffused from _the plasma region by excited neutral particles, such as electronically excited argon _Ar ( ^3P2 ), etc. A similar effect can be obtained when applied to the excited species CVD method in which the reaction is initiated, and even more
A similar effect can be obtained when applied to the CVD method.

[Effects of the Invention] As explained above, the film forming apparatus according to the present invention has an electrode for applying a DC or low frequency AC voltage to a plasma region and an introduction window for introducing microwaves, and has an electrode for applying a DC or low frequency AC voltage to a plasma region. Plasma is generated by applying AC voltage and microwave simultaneously, so cold cathode operation electrodes that are less susceptible to deterioration due to reactive gases can be used, making it possible to generate stable plasma and have a long service life. It has many advantages, such as high-speed deposition, no impurity or charged particle damage to the deposited film, and the ability to deposit high-quality, uniform thin films.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a film forming apparatus showing an embodiment of the present invention, and Fig. 2 shows the deposition rate with respect to the change in microwave power when the power of the microwave introduced in the apparatus of Fig. 1 is changed. FIG. In the figure, 1... electrode, 2... pipe, 2a... nozzle,
3... Substrate holder, 4... Substrate, 5... Container, 6... Introduction hole, 7... Partition wall, 7a... Shield net, 8... Introduction window,
9... Waveguide, 10... Exhaust port, P... Plasma, G ₁
...gas for ultraviolet radiation, G ₂ ...photochemically reactive gas.

Claims (1)

[Scope of Claims] 1. Film formation having a plasma region formed by gas discharge and a reaction region provided with a reactive gas release mechanism in one container provided with a substrate for film formation. In the apparatus, an electrode for applying a DC or low frequency AC voltage to the plasma region and an introduction window for introducing microwaves are provided, and the DC or low frequency AC voltage applied to the electrode and the micro wave introduced to the introduction window are provided. 1. A film forming apparatus characterized by comprising means for generating plasma by simultaneously applying waves. 2. The film forming apparatus according to claim 1, wherein the reaction of the reactive gas is initiated by ultraviolet rays emitted from the plasma region. 3. The film forming apparatus according to claim 1, wherein the reaction of the reactive gas is initiated by excited neutral particles diffused from the plasma region.