JPH06260418A - Pretreatment for film formation - Google Patents

Abstract

PURPOSE:To provide a method for forming a PCVD thin film, which is constituted of particles having a large particle diameter on the average, using a plasma CVD method. CONSTITUTION:Evacuation in a reaction chamber 10 is performed and the temperature of a glass substrate 22 is set at 300 deg.C. Then, SiF4 gas of 300 to 500sccm and H2 gas of 0 to 700sccm are respectively introduced in the chamber 10 and the total pressure in the chamber 10 is controlled at a pressure of 100 to 400Pa. Then, a high frequency of 13.56MHz is applied at an rf plasma density of 50 to 100W to plasma-discharge the gases introduced in the chamber 10 for 5 to 10 minutes. Then, as the SiF4 and H2 gases are continuously introduced, the SiH4 gas of 10sccm is introduced and the gases are again plasma-discharged with the introduction amount of the H2 gas as 500sccm and a polysilicon film is deposited on the substrate 22 in a thickness of about 400nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a plasma CVD method (hereinafter, also referred to as PCVD method) to form a four-coordinate semiconductor or an alloy thin film containing a four-coordination semiconductor on a substrate provided in a reaction chamber ( Hereinafter, it is also referred to as a PCVD thin film).

[0002]

2. Description of the Related Art Conventionally, in order to form a driving circuit integrating transistors, research and development of a method for forming a thin film such as polycrystalline silicon (polysilicon) having a large electron mobility on a large area transparent substrate such as glass. Is being actively conducted. An annealing method is known as a well-known method for forming a polycrystalline silicon thin film. The annealing method includes a laser annealing method and a solid phase growth method.

In the laser annealing method, after an amorphous silicon film (hereinafter also referred to as α-Si) film is formed on a glass substrate, the α-Si film is locally heated by a laser. To recrystallize the α-Si film into a polycrystalline silicon film. However, this method has the following problems. Since precise control of the laser beam shape and beam scanning is required, expensive laser annealing equipment must be used. In addition, thermal distortion occurs in the recrystallized polycrystalline silicon film. In addition, a homogeneous polycrystalline silicon film cannot be obtained. In addition, there is a large damage to the underlying film.

On the other hand, in the solid phase growth method, the entire α-Si film formed on the glass substrate is annealed by heating at a high temperature of 600 ° C. or higher to recrystallize the α-Si film into a polycrystalline silicon film. I am trying to Using this method, a glass substrate
Since it is exposed to a high temperature of 00 ° C. or higher for a long time, there is a problem that an expensive quartz substrate must be used as a glass substrate.

Therefore, a group of researchers including the inventor of the present application, in a reference: "Japanese Patent Application Laid-Open No. 3-250624", uses a PCVD method instead of an annealing method to form a polycrystalline silicon film on a glass substrate or the like. It proposes a method of forming a film directly on the lower surface of. According to the technique disclosed in this document, when forming a polycrystalline silicon film on an underlayer using the PCVD method, the source gas is tetrafluorosilane (Si).
F ₄ ), silane (SiH ₄ ) and hydrogen (H ₂ ) can be directly deposited on the underlayer at a low temperature of about 300 ° C. by adjusting the film forming conditions such as a mixing ratio of hydrogen (H ₂ ). it can.

[0006]

[Problems to be Solved by the Invention] However, PCV
When a PCVD thin film, for example, a polysilicon thin film is formed by using the D method, the average grain size of the polysilicon forming the polysilicon thin film becomes smaller than that when the annealing method is used. When the average grain size of polysilicon is small, the electron mobility of the polysilicon thin film is low. Therefore, when the thin film of the device is formed by the PCVD method, there is a problem that the operating speed of the device becomes slow.

Therefore, the object of the present invention is to provide a plasma CV.
An object of the present invention is to provide a method for forming a PCVD thin film having a large average particle diameter of particles forming the thin film by using the D method.

[0008]

In order to achieve this object, according to the method for forming a semiconductor thin film of the present invention, a four-coordinate semiconductor thin film is formed on a base placed in a reaction chamber by using a plasma CVD method. Alternatively, in a pretreatment method for forming a thin film of an alloy containing a four-coordinated semiconductor, SiF ₄ gas, a mixed gas of SiF ₄ and H ₂ , a F ₂ gas and a SiF ₂ H ₂ gas are formed before starting the thin film formation. While introducing at least one type of gas selected from the group of gases (hereinafter, also referred to as plasma cleaning gas) into the reaction chamber,
The selected gas is subjected to high-frequency plasma discharge to clean the inside of the reaction chamber (hereinafter, this pretreatment for film formation is also referred to as plasma cleaning).

Further, even after plasma discharge, it is advisable to continuously introduce a selected gas such as SiF ₄ into the reaction chamber until the film formation of the PCVD thin film is started.

[0010]

According to the method of forming a semiconductor thin film of the present invention, P
Before forming the CVD thin film, SiF ₄ gas, SiF
While introducing at least one gas selected from the gas group consisting of a mixed gas of ₄ and H ₂ , F ₂ gas and SiF ₂ H ₂ gas into the reaction chamber, the selected gas is subjected to high frequency plasma. The interior of the reaction chamber is plasma cleaned by discharging. Mass analysis of the exhaust gas from the plasma-cleaned reaction chamber confirmed that moisture and hydrocarbons in the reaction chamber were reduced. From this, it is considered that the plasma cleaning reduces the impurities that become the crystal nuclei on the substrate, and as a result, the grain size of polysilicon or the like forming the PCVD thin film increases.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the pretreatment method for film formation of the present invention will be described below with reference to the drawings. It should be noted that the drawings referred to below only schematically show the sizes, shapes, and arrangement relationships of the respective constituent components to the extent that the present invention can be understood. Therefore, it is obvious that the present invention is not limited to the illustrated examples.

FIG. 1 is a schematic diagram of a PCVD apparatus used in this embodiment. Since the structure of the device itself is conventionally known, a detailed description thereof will be omitted. However, for convenience of description of the present invention, the structure will be briefly described. This apparatus has a lower electrode 12 and an upper electrode 14 provided in a reaction chamber 10. The lower electrode 12 can be rotated by a motor 16, and the lower electrode 12 is provided with a heater 20 controlled by a heater control 18. Also,
On the surface of the lower electrode 12 facing the upper electrode side 14, a glass substrate 22 as a base or the like can be placed. On the other hand, the upper electrode 14 has a gas introduction part 24.
And is connected to a gas for plasma cleaning the reaction chamber 10 and a thin film source gas introduction system 26. The gas introduction system 26 has a structure capable of introducing gas into the reaction chamber 10 from the gas blowing hole of the upper electrode 14. In this embodiment, SiH is used as the gas introduction system 26.
₄ gas introduction system 26a, SiF ₄ gas introduction system 26b and H
₂ gas introduction system 26c is provided, and each gas introduction system 26a
Mass flow controller (MFC) for ~ c
The gas flow rate can be individually controlled by 28a to 28c. Further, the reaction chamber 10 is evacuated by the rotary pump 32 and the oil diffusion pump 34 through the exhaust system 30. Further, the upper electrode 14 is connected to a high frequency power source 38 via a matching circuit 36, and has a structure capable of supplying rf power at a normal 13.56 MHz to the reaction space of the reaction chamber 10.

Next, an embodiment of the pretreatment method for film formation of the present invention will be described. In this example, a pretreatment method for forming a polysilicon thin film as a PCVD thin film on a glass substrate 22 as a base will be described.

First, the glass substrate 22 is put into the reaction chamber 10 of the PCVD apparatus, and then the reaction chamber 10 is evacuated by the rotary pump 32 and the oil diffusion pump 34 to bring the temperature of the glass substrate 22 to 300 ° C. Next, after evacuating only the rotary pump 32, 300 to 300 SiF ₄ gas is introduced into the reaction chamber 10.
Introduce 500 SCCM and 0 to 700 SCCM of H ₂ gas respectively, and set the reaction chamber 1 by the conductance valve 40.
The total pressure of 0 is adjusted to 100 to 400 Pa. Then 1
A high frequency of 3.56 MHz is applied with an rf power of 50 to 100 W to plasma discharge the gas introduced into the reaction chamber 10.

Reaction chamber 1 after plasma discharge for 5 to 10 minutes
After plasma cleaning 0, turn off high frequency discharge,
With SiF ₄ and H ₂ gas continuously introduced, SiH ₄ is newly introduced at a flow rate of 10 SCCM, and further H
_With the amount of ₂ introduced at 500 SCCM, the introduced gas is plasma-discharged again to change the polysilicon into the glass substrate 22.
Deposit on top. After depositing about 400 nm of polysilicon, the grain size of the polysilicon forming the polysilicon thin film was measured using an atomic force microscope (AFM).
The average particle size of polysilicon was 106 nm. This particle size is about 1.8 times the average particle size (60 nm) when a film is formed under the same conditions without plasma cleaning.

As described above, it was confirmed that the average particle size of polysilicon was increased by performing the plasma cleaning. By the way, the electron mobility in a polysilicon thin film is almost proportional to the average grain size of polysilicon. Therefore, if plasma cleaning is performed to form a thin film of the device, the operating speed of the device can be expected to double.

When the plasma cleaning is performed, the polysilicon thin film is formed on the glass substrate 2 for a certain reason.
It was found that it was difficult to peel off from No. 2 and the adhesion between the polysilicon thin film and the glass substrate 22 was improved.

In the above-described embodiments, the present invention has been described with reference to an example in which a specific material is used and which is formed under specific conditions, but the present invention can be modified and modified in many ways. For example, although a polysilicon thin film is formed in the above-described embodiments, the present invention may be used as a pretreatment for forming a thin film of polysilicon germanium, polygermanium or polysilicon carbide.

[0019]

According to the pretreatment method for film formation of the present invention, the grain size of polysilicon or the like constituting the PCVD thin film increases. As a result, the electron mobility in the PCVD thin film is increased, and the operating speed of the device having the PCVD thin film can be expected to be increased. Further, by performing plasma cleaning, it is possible to improve the adhesion between the base and the PCVD thin film.

Further, the pretreatment method for film formation of the present invention is a preferable method, particularly prior to the formation of the semiconductor thin film used for the formation of the drive circuit of the liquid crystal display and the image sensor.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a PCVD apparatus used for explaining an example of a pretreatment method for film formation according to the present invention.

[Explanation of symbols]

 10: Reaction chamber 12: Lower electrode 14: Upper electrode 16: Motor 18: Heater control 20: Heater 22: Glass substrate 24: Gas introduction part 26, 26a-26c: Gas introduction system 28a-28c: Mass flora controller 30: Exhaust system 32: Rotary pump 34: Oil diffusion pump 36: Matching circuit 38: High frequency power supply 40: Conductance valve

Claims (1)

[Claims] 1. A pretreatment method for forming a four-coordinated semiconductor thin film or a thin film of an alloy containing a four-coordinated semiconductor on an underlayer placed in a reaction chamber by using a plasma CVD method. Before film formation, SiF ₄ gas, SiF ₄ and H
A mixed gas of _2, while introducing at least one kind of gas selected from among a gas group consisting of F ₂ gas and SiF ₂ H ₂ gas into the reaction chamber, to a high-frequency plasma discharge the selected gas A pretreatment method for film formation, which comprises cleaning the reaction chamber.