JPS6367726A - Vapor growth method for crystal thin film - Google Patents

Abstract

PURPOSE:To obtain a crystal thin film of extremely high purity without necessity of interposing an intermediate layer by laminating a crystal thin film made of the same element as an amorphous thin film on the amorphous thin film set to active state by heating the amorphous thin film to form a crystal thin film. CONSTITUTION:When a crystalline silicon film is formed on an amorphous glass substrate, a glass substrate 3 is first mounted, evacuated in vacuum, and a plasma is generated while introducing silane gas thereto. A voltage applied to an ion accelerating electrode 9 is initially reduced, silane ions are slightly accelerated, neutral particles neutralized by a neutralizer 10 are irradiated to the substrate 3 by a small impact energy to form an amorphous silicon thin film. Then, the voltage applied to the electrode 9 is increased to form silane ions of high speed wave, the impact energy of the particles neutralized by the neutralizer 10 is increased to set the surface of the thin film of silicon to liquid state to be rheotaxial growth and simultaneously grown with thin film of good crystallinity.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for forming a thin film with good crystallinity.

BACKGROUND OF THE INVENTION Conventionally, rheotaxial growth has been proposed as a method for forming a crystalline thin film on a substrate. In this method, when forming, for example, a silicon crystal thin film on a substrate, an intermediate layer of a low-melting metal liquid is interposed between the two so that the orientation direction of the substrate surface does not extend to the silicon thin film. That is, a thin film with good crystallinity can be obtained by first forming a low melting point metal intermediate layer on a substrate, turning the low melting point metal into a liquid state by heating, and growing a silicon thin film thereon.

Tin is said to be suitable for this low-melting metal intermediate layer because it has a low melting point and vapor pressure, and is inert to thin films (J, Appl, Phys, 2003).

48(9), 3937 (1937)).

Problems to be Solved by the Invention However, when forming a functional element such as a transistor using the above method, even though it is inert, the diffusion of tin contaminates the silicon and degrades the performance of the element. There was a problem with variations.

This is the same even when an element other than tin is used in the intermediate layer.

Means for Solving the Problems The present invention provides a process of forming an amorphous thin film, a process of heating the amorphous thin film to bring it into an activated state, and a process of forming the amorphous thin film on the heated amorphous thin film. This is a crystalline thin film vapor phase growth method that includes the process of forming a thin film made of the same element as an amorphous thin film.

Since the working base is an amorphous thin film, it is possible to obtain an extremely pure crystalline thin film at a low temperature, that is, in an activated state without being in a molten state9, without the need for an intermediate layer.

Examples Generally speaking, amorphous substances have their melting point (more precisely, their glass transition point)
is known to be lower than the melting point of the crystal.

In addition, antistatic particles such as electrons and ions can easily be accelerated to a few eV to several hundred eV in an electric field, and their kinetic energy is approximately 12,000 K per 1 eV when converted to temperature.
corresponds to That is, when a material is irradiated with high-velocity electrons or ions, the surface of the material is heated by the impact of particles with high kinetic energy.

Therefore, when high-velocity ions are irradiated onto an amorphous object,
The surface of an amorphous object is heated and turns into a liquid state. If film formation is performed in this state, rheotaxial growth can be performed.

Furthermore, in order to obtain a thin film with good crystallinity, it is necessary to raise the substrate temperature [for example, J, Appl, Ph
ys.

37(10), 3665 (1965)). FIG. 4 illustrates this situation, and shows the change in film quality with respect to the reciprocal of the film formation rate and substrate temperature. As mentioned above, the temperature of the surface of the υ substance increases due to irradiation with electrons and ions, so
Irradiates electrons and ions without heating the substrate, increasing its intensity.
That is, if the impact energy of electrons and ions is increased, the surface temperature of the substrate will increase. That is, the relationship shown in FIG. 4 shows the same tendency even when the reciprocal of the ion bombardment energy is used as the horizontal axis.

However, if the impact energy is too large, the film will be sputtered and the film formation rate will decrease. FIG. 6 shows this situation. From this, it is understood that irradiation with high-velocity electrons and ions has the effect of improving the crystallinity of thin films. However, when depositing an insulating thin film on an insulating substrate, ion irradiation will cause charge-up on the substrate.
This causes problems such as the ions slowing down and the impact being reduced, and dielectric breakdown of the thin film. In this case, if the ions that have been accelerated and given kinetic energy are neutralized and irradiated as neutral particles, the same effect as above can be achieved.

FIG. 1 shows an apparatus to which the thin film vapor phase epitaxy of the present invention is applied when forming a crystalline silicon film on an amorphous glass substrate. In FIG. 1, 1 is a plasma chamber, 2 is a film forming chamber, and 3 is a plasma chamber.
5 is a glass substrate, 4Vi silane gas inlet, and 5 is an exhaust port. Inside the plasma chamber 1, a filament 6 for emitting thermionic electrons, an anode 7, and an electromagnet 8 for generating a magnetic field are installed around the plasma chamber 1.
n+.

A plasma containing n=o~3) is generated. Reference numeral 9 denotes an ion accelerating electrode, and the acceleration of silane ions irradiated onto the substrate 3 is adjusted by its voltage. Furthermore, if the substrate is an insulator such as glass N, if the substrate is charged up by ions, not only will the film formation rate decrease, but the thin film will break down, so a neutralizer is required to neutralize the ions. 9 has been installed. However, if the substrate and the film-forming material are conductors, it is sufficient to ground them, and the 211 trizer 10 is not necessary. Even if Neutralizer-10 is used, there is no difference in that the kinetic energy of accelerated ions is used to improve crystallinity.

Next, the operation will be explained. First, after installing the glass substrate 3, the entire apparatus is evacuated and plasma is generated while disilane gas is introduced through the silane gas inlet 4. At first, by keeping the voltage applied to the ion accelerating electrode 9 low, the silane ions are slightly accelerated and the neutral particles neutralized by the neutralizer 10 are irradiated onto the glass substrate 3 with small impact energy to form an amorphous crystal. Deposit a high quality silicon thin film. This state corresponds to point A in FIG. Next, by increasing the voltage applied to the ion accelerating electrode 9, high-speed wave silane ions are created, and the impact energy of the neutral particles, which are neutralized by the neutralizer 10, is increased to produce amorphous silicon. At the same time, a thin film with good crystallinity can be grown in the state shown at point B in FIG.

In this embodiment, the ion bombardment energy was changed discontinuously from point A to point B in FIG. 5, but it may also be changed from natural point A to point B in a continuous manner.

In this first embodiment, the ions to be irradiated were ions containing an element that forms a thin film, but next, a second embodiment of the apparatus to which the present invention is applied is applied when the ions to be irradiated are inert gas ions. As shown in the figure. This second embodiment is used when both the substrate and the thin film have a certain degree of conductivity, such as when a crystalline silicon solar cell is fabricated by vapor deposition on a metal substrate.

In FIG. 2, 11 is a vacuum container, 12 is a conductive metal substrate, and is grounded by wiring 13.

14 is an exhaust port, 16 is a crucible containing silicon or n-type or p-type impurities, 17 and 18 are heaters, and 19 is an argon ion source.

First, after installing the substrate 12, the inside of the vacuum container 11 is evacuated, the argon ion source 19 is turned off, and the crucibles 15 and 16 are removed.
is heated to form a silicon thin film together with impurities. In this state, since the substrate temperature is low, an amorphous thin film is formed as shown at point C in FIG. 4. Next, while continuing film formation, the argon ion source 19 is turned on and the substrate is irradiated with argon ions, which turns the amorphous thin film into a liquid state, allowing rheotaxial growth and at the same time achieving state point B in FIG. As a result, thin films with good crystallinity can be grown.

Although the above embodiments were for ion irradiation, FIG. 3 shows an embodiment in which the present invention is applied to electron irradiation. The embodiment shown in FIG. 3 is for forming a metal thin film for wiring semiconductor elements. In order to reduce the electrical resistance of the wiring, it is desirable to have a thin film with few crystal grain boundaries that impede the movement of electrons within the wiring, that is, with good crystallinity.

In Fig. 3, 20 is a vacuum container, 21 is a gas inlet for supplying a gas containing a metal element for wiring, for example, trimethylaluminum (AI! (CH3)3) in the case of aluminum wiring, and 22 is an exhaust port. Mouth, 23 is an electron gun, 24
2 is a substrate grounded by wiring 25, and 26 is an accelerating electrode.

After the substrate 24 is installed, the inside of the vacuum container 20 is evacuated, a gas containing a metal element is introduced from the gas inlet 21, and electrons are emitted from the electron gun 23. Then, at first, the accelerating electrode 2
Did you lower the voltage applied to 6? )-8 heat and gas ≠;
It decomposes when the thunderbolt's palm hits it, forming a thin metal film on the substrate. In this case, most of the kinetic energy of the electrons is spent decomposing the gas, so the thin film cannot be bombarded with electrons, and an amorphous thin film is formed. Next, by increasing the voltage applied to the accelerating electrode 26, high-velocity electrons decompose the gas as before, and at the same time apply impact energy to the thin film, growing a thin film with good crystallinity as in the previous example. can be done.

Note that the present invention is not limited to cases where the substrate is amorphous such as glass. For example, it can be applied to the case where crystals of potassium, arsenic, etc. are formed on a single crystal silicon substrate.

Effects of the Invention According to the present invention, a thin film with good crystallinity can be obtained without using an intermediate layer such as a low melting point metal, and therefore without contaminating the thin film with such low melting point metals.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an apparatus embodying the growth method of the present invention;
Figures 2 and 3 are configuration diagrams of the same different equipment, Figure 4 is a diagram showing the relationship between the deposition rate and the reciprocal of substrate temperature on film quality, and Figure 5 is a diagram of the relationship between deposition rate and ion bombardment energy on film quality. It is a relationship diagram with a reciprocal number. 1... Plasma chamber, 2... Film forming chamber, 3
. . . Glass substrate, 9 . . . Ion accelerating electrode, 10 . . . Neutrizer. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 3
figure

Claims (5)

[Claims] (1) Forming an amorphous thin film, heating the amorphous thin film to bring it into an active state, and laminating a crystalline thin film made of the same element as the amorphous thin film on top of the activated amorphous thin film. A crystalline thin film vapor phase growth method characterized by forming a crystalline thin film. (2) The crystalline thin film vapor phase growth method according to claim 1, wherein the amorphous thin film layer is heated with an irradiator of ions or neutral particles containing elements that form the thin film. (3) The crystalline thin film vapor phase growth method according to claim 1, characterized in that the amorphous thin film is heated by an irradiator of electrons or inert gas ions. (4) forming an amorphous thin film and a laminated thin film in an activated state with an ion or neutral particle irradiator;
3. The crystalline thin film vapor phase growth method according to claim 1, wherein the amorphous thin film is heated by increasing the irradiation speed of the irradiator. (5) Forming an amorphous thin film and a laminated thin film in an activated state with an electron or inert gas ion irradiator, and heating the amorphous thin film by increasing the irradiation speed of the irradiator. A crystal thin film vapor phase growth method according to claim 1 or 3.