JP3117663B2 - Method for forming polycrystalline silicon thin film - Google Patents

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 polycrystalline silicon thin film used for, for example, a thin film transistor.

[0002]

2. Description of the Related Art Generally, a polycrystalline silicon thin film has a high mobility of several tens to several hundreds of cm ² and is used as a switching element of a pixel of a display panel, a driving circuit element, or the like.

As a method of forming such a polycrystalline silicon thin film, a laser annealing method, a low pressure CVD method, and the like are conventionally known.

In the laser annealing method, for example, an amorphous silicon film is formed on an insulating substrate and is annealed at a temperature of about 600 ° C., thereby causing the amorphous silicon film to grow in a solid phase and to improve the orientation. This is a method of depositing a polycrystalline silicon thin film.

On the other hand, in the low pressure CVD method, for example, while the substrate temperature is kept at 550.degree.
An LPCVD film is deposited under a pressure of 1 Torr using a monosilane gas or the like diluted in water as a raw material, and then heat-treated at a temperature of 600 ° C. in an N ₂ atmosphere to form an oriented polycrystalline silicon thin film. Is the way.

[0006]

In the conventional methods of forming a polycrystalline silicon thin film such as the laser annealing method and the low pressure CVD method described above, the surface temperature of the substrate is set to 550 ° C.
Alternatively, since epitaxial growth cannot be performed unless the temperature is considerably increased to about 600 ° C., the orientation of a substrate of all materials, for example, a normal glass substrate (there is a restriction that heating can be performed only up to about 600 ° C.). There has been a problem that it is difficult or impossible to form a polycrystalline silicon thin film having the same.

The present invention has been made in view of the above circumstances, and is intended to form a polycrystalline silicon thin film having excellent electric characteristics and high mobility under a lower temperature condition than conventional methods. It is an object of the present invention to provide a method capable of forming a high-quality polycrystalline silicon thin film on the surface of an ordinary glass substrate or the like.

[0008]

In order to achieve the above object, a method of forming a polycrystalline silicon thin film according to the present invention comprises a method of forming a polycrystalline silicon thin film on a substrate surface using a sputtering method. Prior to the sputter deposition process,
A buffer layer is formed in advance on the surface of the substrate on which the polycrystalline silicon film is to be formed, and in the sputter deposition step, a step of applying a voltage to the target electrode to generate plasma near the target to perform sputtering, By alternately or simultaneously repeating the step of applying energy by microwave discharge from an electrode other than the target electrode to the vicinity of the surface of the layer, a polycrystalline silicon thin film having an orientation along the orientation of the buffer layer is formed. (Claim 1).

Here, in the present invention, it is desirable that the substrate temperature in the above-mentioned sputter deposition step be 350 ° C. or more and 500 ° C. or less (claim 2).

The material of the buffer layer used in the present invention includes a material capable of forming a polycrystalline film at about 300 ° C.
For example, it is preferable to use ZnS, Ni, AlN, Mo, or the like.

In the film forming method of the present invention, energy from an electrode other than the target electrode (hereinafter referred to as an assist electrode) serves to increase the reactivity of the sputtered particles, and after the sputtered particles adhere to the buffer layer. Until it becomes stable, its reactivity can be increased. Accordingly, it is possible to grow a polycrystalline silicon thin film having an orientation along the orientation of the buffer layer and a high mobility under a lower temperature condition than the conventional film forming method.

According to the film forming method of the present invention, after applying a voltage such as a high frequency to the target electrode to generate plasma near the target and perform sputtering, the microelectrode from the assist electrode is formed near the surface of the buffer layer. Since the process of applying energy by microwave discharge is repeated, or the process of applying energy by microwave discharge from the assist electrode to the vicinity of the surface of the buffer layer at the same time as applying voltage to the target electrode is performed repeatedly, After the sputtered particles such as adhere to the buffer layer on the substrate, it is possible to repeatedly increase the reactivity of the adhered particles to the buffer layer until the next sputtered particle arrives. High-mobility polycrystalline silicon thin film can be formed at a low temperature and in alignment with the buffer layer. .

That is, by supplying energy from an electrode (assist electrode) other than the target electrode to the crystal growth surface, epitaxial growth can be performed at a low temperature, and
The speed of growth can be increased.

In the method of the present invention capable of performing epitaxial growth at a low temperature as described above, the substrate temperature in the sputtering step is set to a temperature range of 350 ° C. or more and 500 ° C. or less, as described in claim 2. It has been confirmed that such a high-quality polycrystalline silicon thin film can be obtained.

[0015]

FIG. 1 is a schematic sectional view showing the structure of a sputtering apparatus used in an embodiment of the present invention.

The sputtering apparatus shown in FIG. 1 employs a method of introducing microwave plasma into the vacuum processing chamber 1 in an auxiliary manner.

In the vacuum processing chamber 1, a sputtering target 2 made of silicon is placed on one side thereof.
The surface on the opposite side is placed in close contact with the target electrode 3 while being exposed inside. The target electrode 3 is connected to an RF power supply 5 via a matching box 4 for impedance matching.

A substrate support 6 is disposed in the vacuum processing chamber 1 so as to face the target 2 between two electrodes, and a glass substrate 7 on which a polycrystalline silicon thin film is to be formed is placed on the substrate support 6. Attached to. Note that, on the glass substrate 7, a buffer layer 7a is formed in advance on a surface on which a polycrystalline silicon thin film is to be formed, as described later.

On the outside of the vacuum processing chamber 1, permanent magnets are alternately and concentrically arranged so that the two poles of the target 2 are adjacent to each other, and that the N pole and the S pole are adjacent to each other from inside to outside of the target 2. 8 are arranged. With this permanent magnet 8,
A magnetic field as shown by a broken line in FIG. 1 is formed in the vacuum processing chamber 1.

At substantially the center of the two-pole target 2, a coaxial tube 9 is opened toward the inside of the vacuum processing chamber 1. The coaxial tube 9 communicates with a magnetron (not shown) and receives a microwave. It is configured to introduce plasma into the vacuum processing chamber 1. Reference numeral 9a denotes an antenna for plasma discharge provided on the coaxial tube 9, which protrudes by １ ／ λ from the target surface.

An assist electrode 10 is provided around the opening of the coaxial tube 9 toward the vacuum processing chamber 1. The assist electrode 10 is connected to the magnetron through the coaxial tube 9. The energy by the microwave discharge of 45 GHz can be applied to the vicinity of the surface of the glass substrate 7 mounted on the substrate support 6.

Next, a specific method for forming a polycrystalline silicon thin film on the surface of the glass substrate 7 using the above-described sputtering apparatus will be described.

Before mounting the glass substrate 7 on the substrate support 6 in the vacuum processing chamber 1, for example, ZnS, Ni, AlN is formed on the surface of the glass substrate 7 where the polycrystalline silicon film is to be formed.
Alternatively, the buffer layer 7a is formed using a material such as Mo that forms a polycrystalline film at about 300 ° C.

After the glass substrate 7 on which the buffer layer 7a is formed is mounted on the substrate support 6 in the vacuum processing chamber 1, the inside of the vacuum processing chamber 1 is evacuated, and then a sputtering gas such as an argon gas is supplied. The glass substrate 7 is introduced into the vacuum processing chamber 1 through a supply pipe (not shown), and the surface temperature of the glass substrate 7 is heated to about 350 to 500 ° C.

Next, as shown in a time chart of the applied voltage to the target electrode 3 and the applied voltage waveform to the assist electrode 10 in FIG. Generating a plasma in the vicinity of the surface 2 and applying 2.45 G to the assist electrode 10.
The step of applying a microwave of Hz is alternately repeated.

The voltage application cycle to each electrode is, for example, about 10 to 100 μs for the target electrode 3 and about 50 to 200 μs for the assist electrode 10.

In the above operation, a high frequency voltage is applied to the target electrode 3 to generate plasma near the surface of the target 2 between the two electrodes. At this time, electrons emitted from the cathode are generated by the magnetic field of the permanent magnet 8 in the cyclotron. It moves and collides with gas molecules in the plasma with a high probability to create a large number of ions, and efficiently sputters the target 2 between the two poles. As shown schematically in FIG. The sputtered particles P adhere to the buffer layer 7a of the glass substrate 7.

In this state, the energy from the assist electrode 10 is applied to the vicinity of the buffer layer 7a of the glass substrate 7 until the next sputtering, so that it adheres to the buffer layer 7a as shown in FIG. The sputtered particles P move along the orientation of the buffer layer 7a and are stabilized. Thereafter, the above-described sputtering and the application of energy from the assist electrode 10 are repeated, whereby FIG.
As shown in (D), the orientation of the underlying buffer layer 7a (1
11, 110), the polycrystalline silicon thin film F is formed. That is, even under a low temperature condition of 350 to 500 ° C., silicon can be epitaxially grown on the buffer layer 7 a by the action of energy from the assist electrode 10, and the growth rate can be increased. .

In the above embodiment, after applying a high-frequency voltage to the target electrode 3 to generate plasma near the surface of the target 2 between the two electrodes and perform sputtering, the 2.45 GHz from the assist electrode 10 is applied. Although the operation of alternately repeating the operation of applying microwave energy to the vicinity of the surface of the glass substrate 7 by performing the microwave discharge has been described, FIG.
As shown in the time chart of the voltage waveform applied to each electrode, the application of the high-frequency voltage to the target electrode 3 and the application of the energy from the assist electrode 10 can be performed simultaneously.

In the above embodiment, a high-frequency voltage is applied to the target electrode 3 from the RF power supply 5.
Of course, it is possible to use this as a DC voltage. In short, it is sufficient to apply an optimal voltage to obtain a film quality according to the purpose.

[0031]

As described above, according to the present invention, in the sputter deposition step of silicon, a step of applying a voltage to the target electrode to generate plasma near the target to perform sputtering, By alternately or simultaneously repeating the step of applying energy by microwave discharge from an electrode other than the target electrode to the vicinity of the surface of the formed buffer layer, the reactivity of sputtered particles including silicon atoms is increased, Facilitating the particles to move along the orientation of the buffer layer,
Practical epitaxial growth of silicon was made possible under a lower temperature condition of about 500 ° C. as compared with the related art. As a result, even if the substrate temperature is as low as about 350 to 500 ° C., it is possible to form a polycrystalline silicon thin film having excellent mobility along the orientation of the buffer layer, and to be 550 to 600 ° C. or less. It has become possible to easily form a high-quality polycrystalline silicon thin film on a glass substrate or the like whose heating is limited to a certain extent.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a configuration of a sputtering apparatus used in an embodiment of the present invention.

FIG. 2 shows a target electrode 3 according to the embodiment of the present invention.
Chart showing a voltage waveform applied to the electrode and a voltage waveform applied to the assist electrode 10

FIG. 3 is an explanatory diagram of a behavior of sputtered particles P in the embodiment of the present invention.

FIG. 4 is a time chart showing a voltage waveform applied to a target electrode 3 and a voltage waveform applied to an assist electrode 10 according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum processing chamber 2 Target between 2 poles 3 Target electrode 5 RF power supply 6 Substrate support 7 Glass substrate 7a Buffer layer 8 Permanent magnet 9 Coaxial tube 10 Assist electrode P Sputtered particle F Polycrystalline silicon thin film

Claims (2)

(57) [Claims] In a method of forming a polycrystalline silicon thin film on a substrate surface by using a sputtering method, a buffer layer is formed in advance on a substrate surface on which a polycrystalline silicon film is to be formed, prior to a silicon sputter deposition step. In the sputter deposition process, a voltage is applied to the target
The process of generating plasma near the get and performing sputtering
And the vicinity of the surface of the buffer layer
The process of applying energy by microwave discharge from the pole
A method for forming a polycrystalline silicon thin film, comprising forming a polycrystalline silicon film having an orientation in accordance with the orientation of the buffer layer by repeating alternately or simultaneously . 2. The method according to claim 1, wherein the substrate temperature in said sputter deposition step is 350 ° C. or more and 500 ° C. or less.
The method for forming a polycrystalline silicon thin film according to claim 1.