JPH06340500A - Recrystallization method by irradiation with neutral particle beam - Google Patents

Abstract

PURPOSE:To form a single crystal film by irradiating an amorphous thin film with the beam of a low-energy inert gas, low-activity neutral atom or neutral atom at a specified temp. from the direction vertical to plural different closest- packed crystal faces. CONSTITUTION:A silane is decomposed to deposit amorphous Si 2 on a quartz substrate 1 by plasma CVD. The substrate 1 is then heated by a heater 7 and kept at a temp. where the amorphous Si 2 is not crystallized. An inert gas such as Ar is introduced into an ion source 3 from a duct 4 to form an ion beam by an electron beam in the source, the ion beam is collided with a reflex plate 5 at an incident angle of 45 deg., reflected twice, discharged as a neutral Ar atom current and projected on the amorphous Si 2 face of the substrate 1 through a collimator 6. The amorphous Si 2 is irradiated from the direction vertical to >=2 different closest-packed crystal faces, hence the Si is crystallized, and a single crystal film having a specified crystal orientation is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recrystallization method by beam irradiation of neutral particles suitable for manufacturing a semiconductor thin film used for a thin film transistor of liquid crystal display, a single crystal thin film used for a three-dimensional LSI, and the like.

[0002]

2. Description of the Related Art Conventionally, melt recrystallization and lateral solid phase epitaxy have been used for single crystallization of polycrystalline semiconductor thin films and amorphous semiconductor thin films.

[0003]

According to the former method, in general, in the case of a high melting point substance, a large thermal strain occurs in the substrate,
The physical and electrical properties of the substance to be used are impaired. In addition, since the electron beam or laser beam is used for melting, and the method of scanning the entire surface of the substrate is used,
It takes a very long time and costs a lot.

Further, according to the latter method, the crystal growth method of the material of the substrate is apt to be influenced, the growth rate is slow, and it takes 10 hours or more for the growth of about 10 microns, and when the growth progresses to some extent, a lattice defect occurs. However, the growth of the single crystal stops and it is difficult to obtain large crystal grains.

In any case, the seed crystal needs to be brought into contact with the polycrystalline film or the amorphous film, and the crystal growth is also in the lateral direction. Therefore, the crystal growth distance becomes long and various obstacles occur during the growth. enter. For example, when the substrate is an amorphous material such as glass, since the lattice has no regularity, this irregularity affects the growth of the single crystal, and the grain shape is large, but the polycrystal grows.

As described above, in the case of the lateral solid phase epitaxy, it takes a long time to obtain a large crystal, but as a method of improving it, the growth in the vertical direction of the film is used to increase the growth distance. Attempts have also been made to shorten the growth time and thereby the growth time.

That is, a method has been tried in which a seed crystal is brought into contact with the entire surface of a polycrystalline thin film or an amorphous thin film to carry out solid phase epitaxy growth in the vertical direction, but the seed crystal and the amorphous film are partially brought into contact with each other, and from this portion. Only lateral epitaxy growth occurred.

Further, since the seed crystal and the grown single crystal film adhere to each other, it is very difficult to separate them,
If it is forcibly separated, the grown film may be separated from the substrate and adhere to the seed crystal side in some cases.

In view of this, the inventor of the present invention uses a physical seed crystal in the vertical growth method of solid phase epitaxy, because it becomes difficult for the grown single crystal thin film and the seed crystal to adhere and separate. Instead of using a seed crystal with a virtual large area, it has the same effect as the seed crystal adheres to the entire surface, and at the same time it says that nothing physically adheres to the single crystal surface when the growth ends. It has been found that such a virtual seed crystal should be obtained.

The present invention solves the above-mentioned various problems,
An object of the present invention is to provide a recrystallization method for efficiently crystallizing an amorphous thin film of a predetermined substance already formed on a substrate surface in the thickness direction so as to have a desired crystal orientation.

[0011]

To achieve this object, the present invention forms an amorphous thin film of a predetermined substance on a substrate and then converts the substance film into a single crystal film having a desired crystal orientation. Therefore, an inert gas having a relatively low energy from the direction perpendicular to two or more different close-packed dense crystal planes in the crystal orientation at a high temperature not higher than the temperature at which crystallization of the substance does not occur, or a low activity It is characterized by irradiating a beam of neutral atoms of gas.

[0012]

In an amorphous thin film of a predetermined substance already formed on the surface of a substrate, two or more different maximum densities in a desired crystallographic orientation of the substance at high temperatures below a temperature at which crystallization of the substance does not occur. When a neutral atom beam of a relatively low energy or a gas of low activity is irradiated from a direction perpendicular to the crystal plane, the irradiation causes at least the desired crystallographic orientation in the vicinity of the film surface, and Grows inward and crystallizes in the entire thickness direction of the film.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings.

Reference numeral 1 is a quartz substrate, 2 is amorphous silicon deposited by a plasma CVD method, and the thickness of the amorphous silicon 2 is about 2000 angstroms.

Reference numeral 3 denotes a cage-type ion source. The ion source 3 introduces argon gas from a conduit 4, ionizes the inside of the ion source 3 by an electron beam to form plasma, and only the argon ions are extracted at an extraction electrode. I take it out and make an ion beam. The cage type ion source 3 has a diameter of 10 cm and can accelerate argon ions to 200 V to 600 V.
Its current density is 1 to 9 ma / cm ² .

Reference numeral 5 is a reflection reduction plate, 6 is a collimator,
The reflection reduction plate 5 is composed of two (1, 0, 0) plane silicon single crystal plates having a diameter of 15 cm, and the collimator 6 has different atoms even if it is sputtered by a neutral atomic flow. 2c, silicon 6b is vapor-deposited on both sides of the aluminum plate 6a so that the aluminum does not reach the substrate and the aluminum is not exposed. The corrugated and flat aluminum plates are alternated as shown in FIG. 2b. Figure 2 (a)
As described above, thirty corrugated and flat aluminum plates are superposed, and the flow of atoms passing between these aluminum plates is aligned in the range of ± 0.5 degrees to remove charged particles. In addition, 7 is a heater for heating the substrate, and the substrate temperature is 60
Can be raised to 0 ° C.

Next, the single crystallization by the above apparatus will be described.

First, a quartz substrate 2 having a thickness of 1.5 mm is decomposed from silane using plasma CVD, and amorphous silicon is broken out and mounted on the substrate 2. Then, the substrate 2 is maintained at a temperature of 550 degrees by the heater 7. Amorphous silicon does not crystallize at this temperature.

Next, argon gas is introduced into the ion source 3 from the conduit 4 to form an ion beam inside the ion source 3 as described above, and the ion beam is applied to the reflection reduction plate 5 at an incident angle of 45 degrees. , After being reflected twice by these reflectors, it becomes a neutral argon atomic flow and goes out,
It passes through the collimator 6 and reaches the surface of the substrate 2.

Here, one neutral argon atom flow irradiates the amorphous silicon surface from the angle of 35 degrees with respect to the normal line of the substrate 2, that is, the direction of the densest crystal axis of the single crystal, and the other neutral atom. The flow is also at an angle of 35 degrees with respect to the normal, and the amorphous silicon surface is irradiated from a direction such that the irradiation directions of both beams are on the same plane.

As a result, in the first stage, as shown in FIG. 3 (a), only the vicinity of the surface is the single crystal 8, but in the second stage, this single crystal 8 grows toward the inside, and as shown in FIG. 3 (b). Similarly, the entire film becomes the single crystal 8.

According to the experiments conducted by the inventor, the acceleration voltage of the ion source is 2000 V, and the current density is about 2 ma / cm ² , about 2
When it was irradiated for 0 seconds, the dark brown color peculiar to amorphous silicon disappeared in the irradiated central part, and it changed to a transparent yellowish color. Among them, about 1 cm ² is X
The line and directional etching revealed that (1,
It was found to be a single crystal having the (1,0) axis in the substrate normal direction.

To determine the crystal orientation, the crystal plane is covered with a silicon dioxide film, a small hole is formed in this oxide film, and etching is performed with potassium hydroxide, and the etching pits are hexagonal. , 0) axis was confirmed to be a single crystal.

The reason for irradiating neutral atoms from a direction perpendicular to two or more different close-packed crystal planes in different crystal orientations at a temperature not higher than the above-mentioned temperature at which crystallization of the substance does not occur is as follows. by.

That is, the desired amorphous thin film already formed on the surface of the substrate does not crystallize immediately below the crystallization temperature, but is very unstable and starts to crystallize when some disturbance is given. It proceeds in a chain reaction. When a relatively low energy, for example, an ion beam of several tens of electron volts or a neutral atom beam is irradiated from one direction at this temperature, in the vicinity of the surface, a plane perpendicular to this irradiation direction is regarded as a densest crystal plane. Crystallization proceeds. This is known as Bravais's law.

Irradiation from a direction perpendicular to two or more close-packed dense crystal planes in different crystal states of the substance to obtain a single crystal causes rotation of the crystal around the irradiation direction during crystallization. The degree of freedom disappears, the crystal orientation is uniquely determined, and a crystal having a desired crystal orientation is obtained.

In this case, if a charged particle beam is used,
Due to the repulsive force due to static electricity between particles, the beam spreads and the directivity is lost, an insulating substrate is used, and when the resistivity of the substance is high, charges accumulate on the film surface, which is due to the repulsive force of the accumulated charges. The beam does not reach the film surface more than a certain amount. However, in the case of the neutral atom beam, such a repulsive force is not received, the parallel beam reaches the film surface, and crystallization proceeds smoothly.

A neutral molecular beam such as N ₂ may be used as the irradiation beam.

[0029]

As described above, according to the present invention, an amorphous thin film of a predetermined substance already formed on the surface of a substrate has two crystal orientations of the substance at a temperature not higher than a temperature at which crystallization of the substance does not occur. Since the neutral atom beam having relatively low energy is irradiated from the directions perpendicular to the different closest dense crystal planes, a semiconductor thin film used for a thin film transistor of liquid crystal display or a single crystal used for a three-dimensional LSI A wide range of thin films, etc. can be easily obtained without raising the temperature of the substrate so much. Further, conventionally known metal vapor deposition films generally have many vacancy points and the quality of the film is poor, so that it is suitable for wiring of electronic circuits. When it is used, it often causes a migration phenomenon and breaks. However, the present invention has an effect of preventing such a failure.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a device according to a first embodiment of the present invention.

FIG. 2A is a perspective view showing the structure of a collimator.

FIG. 2 (b) is an enlarged perspective view of a part thereof.

FIG. 2 (c) is an enlarged perspective view of a part thereof.

FIG. 3A is an enlarged cross-sectional view of the film in a state where the ion beam irradiation is started.

FIG. 3B is an enlarged cross-sectional view of the film after the ion beam irradiation.

[Explanation of symbols]

 1 Substrate 2 Amorphous thin film 3 Ion source 5 Reflection reduction plate 6 Collimator 7 Heater

Claims (1)

[Claims] 1. Since an amorphous thin film of a predetermined substance is formed on a substrate and then the substance film is converted into a single crystal film having a desired crystal orientation, a temperature below a temperature at which crystallization of the substance does not occur. Irradiation with a beam of neutral gas or neutral molecule of relatively low energy inert gas or low activity gas from a direction perpendicular to two or more different close-packed crystal planes in the crystal orientation at high temperature. A method for recrystallizing neutral particles by beam irradiation.