JPH10116795A - Equipment for manufacturing semiconductor material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve uniformity of the in-plane distribution of crystallinity and crystal grain size of a semiconductor film by transferring a sample without exposing to the atmosphere between a chamber for heat treating an amorphous semiconductor at a temperature lower than the crystallization temperature and a chamber for irradiating the semiconductor with laser light. SOLUTION: After thermal annealing for dehydrogenation, a laser crystallization process is effected without exposing the surface of an amorphous semiconductor to the atmosphere. A plasma CVD system 2 for depositing a starting film, i.e., an amorphous silicon film, a thermal annealing furnace 3 for dehydrogenation, a laser crystallization chamber 4, a sample carry-in chamber 1 and a sample carry-out chamber 5 are arranged in series. The chamber 3 is a thermal annealing furnace for dehydrogenation and the chamber 4 is a laser annealing chamber. A laser beam is matched with the width of a substrate using the optical system and a rectangular beam extending perpendicularly to the carrying direction of substrate is employed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing apparatus for obtaining a polycrystalline semiconductor used for a thin film device such as an insulated gate field effect transistor by laser irradiation.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing a polycrystalline silicon semiconductor thin film used for a thin film device such as a thin film type insulated gate field effect transistor (TFT), amorphous silicon formed by a plasma CVD method or a thermal CVD method is used. A method of crystallizing a film by irradiating the film with a laser beam is known.

In general, in order to crystallize an amorphous silicon film using a laser beam, a low energy density laser beam is applied to the amorphous silicon film in order to separate hydrogen contained in the amorphous silicon film as a starting film from the film. Thereafter, a step of crystallizing the amorphous silicon film by irradiating a laser beam having a threshold energy density (the minimum energy density necessary for melting silicon) or more is performed.

The reason why hydrogen in an amorphous silicon film is released by irradiating a low energy laser beam first is mainly to solve the following two problems.

The first problem is that when a laser beam having an energy density equal to or higher than the threshold energy density is suddenly irradiated on the amorphous silicon film, a large amount of hydrogen existing in the amorphous silicon film is rapidly ejected from the film surface. However, when the insulating film is provided on the surface of the crystallized silicon film later, a level is generated at the interface between the silicon film and the insulating film. The problem is that an interface state cannot be obtained.

A second problem is that a large amount of hydrogen existing in an amorphous silicon film is ejected to the surface by a laser beam having a high energy density higher than a threshold energy density, and at the same time, a large amount of hydrogen is melted in the silicon film. Since it moves with kinetic energy, there is a problem that crystallization of silicon is hindered.

Therefore, a laser beam having a low energy density, which is conventionally referred to as pre-laser annealing, is used to sufficiently remove hydrogen from the film, and then a laser beam for crystallization is irradiated to crystallization of the hydrogen in the film. The influence on the conversion was eliminated as much as possible.

[0008]

However, the above-mentioned conventional methods have the following problems. First, there is a problem that the efficiency is low because laser irradiation is performed in two separate steps, which is not suitable for large-area processing.

In addition, a pulse shot laser typified by a commonly used excimer laser has a problem that it is difficult to thoroughly remove hydrogen because the laser irradiation time is short.

[0010] Furthermore, a laser device used for laser annealing necessarily has non-uniformity of laser beam and fluctuation of output, so that in the process of dehydrogenation, hydrogen distribution in the film is inevitably non-uniform. There is a problem that it causes non-uniformity of the crystal grain size after the formation.

The present invention relates to a laser annealing method which solves the above-mentioned problems.

[0012]

According to the present invention, there is provided a chamber for subjecting an amorphous semiconductor to a heat treatment at a temperature lower than its crystallization temperature, and a chamber for irradiating the semiconductor with a laser beam. The sample is transported between the two chambers without being exposed to the atmosphere.

The apparatus having the above structure is a step of crystallization of an amorphous semiconductor by irradiating a laser beam, and the crystallization temperature of the amorphous semiconductor in a vacuum or an inert atmosphere before the laser irradiation. Heat annealing is performed at the following temperature, and laser irradiation is performed in a vacuum or an inert atmosphere to crystallize the heat-annealed amorphous semiconductor.

Although an excimer laser is generally used as a laser, the structure of the present invention does not limit the kind of laser at all, and it goes without saying that any laser may be used.

As the amorphous semiconductor, a silicon semiconductor is generally used, but another semiconductor may be used. In the embodiments of the present specification, description will be made using a silicon semiconductor as an example.

The reason why the amorphous semiconductor is heat-annealed at a temperature lower than the crystallization temperature of the amorphous semiconductor in a vacuum or inert atmosphere is to dehydrogenate the amorphous semiconductor. However, if heat annealing is performed at a temperature higher than the crystallization temperature, the amorphous semiconductor will be crystallized, and sufficient crystallization cannot be performed in the subsequent crystallization by laser irradiation. It is important to perform annealing.

The reason why the heat annealing is performed in a vacuum or an inert atmosphere is to prevent an unnecessary thin film such as an oxide film from being formed on the surface of the amorphous semiconductor.

By annealing this amorphous semiconductor at a temperature lower than the crystallization temperature, uniform and thorough dehydrogenation can be performed in the film. As a result, the in-plane distribution of crystallinity of the semiconductor film and the uniformity of the crystal grain size are improved, and P-type semiconductors having uniform characteristics are formed on a large-area substrate.
It becomes possible to form a Si (polycrystalline) TFT.

Irradiating a laser beam for crystallization in a vacuum or an inert atmosphere to crystallize the amorphous semiconductor is performed by dangling bonds (dangling bonds) of the amorphous semiconductor generated as a result of dehydrogenation. This is to prevent the bond (ring bond) from binding to oxygen, hydrogen, or nitrogen in the air, which is an active gas.

The present invention is characterized in that crystallization is promoted by forming a large number of dangling bonds in an amorphous semiconductor. This is based on the following experimental facts that were revealed in experiments performed by the present inventors.

That is, based on an experimental result that the crystallinity was remarkably improved as a result of irradiating an excimer laser (KrF 248 nm) to an amorphous silicon film in which dehydrogenation of a non-single-crystal silicon film was thoroughly performed. Things.

An amorphous silicon film generally contains a large amount of hydrogen, and this hydrogen neutralizes dangling bonds.

However, the present inventors have recognized from the above experimental facts that the existence of dangling bonds is extremely important in the crystallization from the amorphous state in the molten state. The present inventors have found a method of promoting instantaneous crystallization in a molten state by intentionally forming a paired bond.

In this case, if an oxide film or the like is formed on the surface of the semiconductor film by exposing the surface of the semiconductor film to air, the dangling bonds that have been formed are neutralized. It is very important to perform crystallization by laser irradiation in an active atmosphere.

The temperature lower than the crystallization temperature of the amorphous semiconductor is a temperature at which the amorphous semiconductor starts to crystallize by heat annealing.

In the structure of the present invention, the heat annealing before crystallization by laser irradiation at a temperature equal to or lower than the above-mentioned crystallization temperature is performed even if the silicon film once crystallized is irradiated with laser light. This is based on an experimental result that almost no improvement in crystallinity was observed, and the crystallinity was significantly lower than that of a film crystallized by irradiating laser light in an amorphous state.

Therefore, it is extremely important that hydrogen is removed from the amorphous semiconductor film at a temperature lower than the crystallization temperature of the amorphous semiconductor film. However, in the structure of the present invention, it is extremely important to thoroughly remove hydrogen from the amorphous semiconductor film and generate as many dangling bonds in the film as possible. It is preferable to perform annealing for dehydration at a temperature as high as possible.

The desorption of hydrogen by heating is different from the laser beam of low energy density which has been conventionally used, and has a great feature that the dehydration can be performed uniformly and thoroughly. As a result, a polycrystalline semiconductor film having a large particle size and a uniform particle size can be obtained. Hereinafter, the configuration of the present invention will be described in detail with reference to examples.

[0029]

EXAMPLE This example relates to a multi-chamber type apparatus for performing the next laser crystallization step without exposing the surface of an amorphous silicon semiconductor film to the atmosphere after heat annealing for dehydrogenation.

FIG. 2 schematically shows an apparatus used in the present embodiment. In the drawing, a plasma CVD apparatus 2 for forming an amorphous silicon film as a starting film, a heating annealing furnace 3 for dehydrogenation, a chamber 4 for laser crystallization, and a sample loading chamber 1 as a sample transfer chamber. , A sample discharge chamber 5 is arranged in series.

Although not shown in FIG. 2, it is needless to say that each of the chambers # 1 to # 5 is provided with a system for introducing an active or inert gas and a system for transporting a sample as necessary. . Each chamber is provided with a vacuum exhaust device in which a turbo-molecular device and a rotary pump are connected in series, so that the concentration of impurities in the chamber in a vacuum state, particularly the concentration of oxygen, is minimized.

In order to further reduce the impurity concentration, it is effective to additionally provide a cryopump.

The multi-chamber apparatus shown in FIG. 2 is provided with a gate valve 6 for partitioning each chamber. For example, a reactive gas in a chamber 2 which is a plasma CVD apparatus is mixed in a heating annealing furnace 3 for dehydrogenation. Was prevented.

The chamber 3 is a heating annealing furnace for dehydrogenation, and the heating was performed using an infrared lamp heating device. Of course, another heating device, for example, a method of performing heating by a heater may be used.

The chamber 4 is a chamber for performing laser annealing. Irradiation of laser light is performed through an external laser generator and an optical system through a quartz window provided in the upper part of the chamber.

The laser beam is adjusted to the width of the substrate by using an optical system, and the sample is transported slowly without moving the laser system using a rectangular beam extended in a direction perpendicular to the transport direction of the substrate. Thus, if the irradiation is continuously performed from the end of the sample, the annealing can be efficiently performed.

In the case where the apparatus shown in FIG. 2 is used, it is preferable to continuously perform heat annealing and laser crystallization of the sample in a vacuum without breaking the vacuum state. By not breaking the vacuum state, the dangling bonds are not neutralized, and therefore the threshold energy for crystallization is reduced. Therefore, a polycrystalline silicon film having a large grain size is efficiently used in the laser crystallization process. Can be formed.

In this embodiment, each chamber is provided one by one in series. However, a plurality of chambers are provided according to the processing time of the sample in each chamber, and the chambers are directly connected. Instead, it is also possible to increase the productivity by providing a common sample transfer chamber in each chamber and performing a plurality of processes simultaneously using a time difference.

In this embodiment, an apparatus for forming a film by the plasma CVD method is shown. However, other film forming methods such as a sputtering method and a thermal CVD method may be used. A film forming apparatus for forming an insulating film may be connected, and a structure necessary for a series of steps can be taken.

REFERENCE EXAMPLE This reference example is intended to show, based on experimental results, the effect of heat annealing for dehydrogenation in laser crystallization of amorphous silicon (crystallization by laser light irradiation). is there.

First, a silicon oxide film as a base protective film is
Plasma CVD on a glass substrate with a thickness of 00 mm
100 n of amorphous silicon film (a-Si film)
A film is formed to a thickness of m under the following conditions.

Two kinds of the above samples were produced. One type has no heat treatment, and one type has been heated and annealed at a temperature of 500 ° C. for 1 hour in an N ₂ atmosphere which is an inert gas. And a wavelength of 248 nm for both in a vacuum.
Was irradiated with a KrF excimer laser to crystallize the a-Si film. This laser crystallization was performed only for one shot while changing the energy density of the laser.

At this time, the substrate was irradiated with the laser without being heated. However, the laser crystallization may be performed while maintaining the substrate temperature at the temperature of the heat annealing at 500 ° C. before the laser crystallization. Of course, the heating annealing temperature for dehydrating hydrogen is not limited to 500 degrees.

In this embodiment, the heating annealing is performed at a temperature of 500 ° C. for one hour. However, it is natural that the heating temperature and the heating time are changed depending on the process and the type of the semiconductor film.

Raman spectra were measured to examine the crystallinity of the two types of samples prepared as described above. FIG. 1 is a graph showing the relationship between the peak of the Raman spectrum of a sample heat-annealed at a temperature of 500 ° C. for 1 hour before the laser crystallization indicated by the curve A and the energy density of the laser irradiated during crystallization. 5A and 5B are graphs showing the relationship between the peak of the Raman spectrum of the sample not heat-annealed before the laser crystallization indicated by the curve B and the energy density of the laser irradiated during crystallization.

Referring to curve A in FIG. 1, the peak of single-crystal silicon is obtained even when the energy density of the laser is low by performing the heat annealing before the laser crystallization.
A value close to 21 cm ^-1 was found, indicating that good crystallinity was exhibited. In general, it is known that the closer the Raman spectrum peak of a film obtained by crystallizing an amorphous silicon film to 521 cm ⁻¹ which is the peak of the Raman spectrum of single crystal silicon, the larger the crystal grain size of this film is. ing. This indicates that a larger crystal grain size can be formed by heat annealing for dehydration.

From the curve B, if heat annealing for dehydration is not performed, the crystallinity greatly depends on the energy density of the irradiation laser at the time of laser crystallization.
Moreover, it is understood that good crystallinity cannot be obtained unless a laser beam having a large energy density is irradiated.

In general, the energy density of an excimer laser is liable to fluctuate and lacks stability. However, the peak of the Raman spectrum as shown by a curve A and the energy density of the laser light during laser crystallization are considered as disadvantages. If there is a relationship, since the crystallinity has little dependence on the laser intensity, a crystal film having uniform crystallinity without being greatly affected by the instability of the excimer laser (polycrystalline silicon in this reference example). Membrane) can be obtained.

However, in the case of the curve B, that is, when heat annealing for dehydration is not performed, a polycrystalline film having non-uniform crystallinity is formed due to a change in the energy density of the laser beam.

Considering that a major problem is how to fabricate a device having uniform characteristics in the actual fabrication process, as shown by the curve A, a stable device is obtained without depending on the energy density of the laser beam. The laser crystallization step that can obtain a polycrystalline film showing good crystallinity is useful.

Referring to FIG. 1, it can be seen that the sample subjected to the heat treatment (heating annealing for dehydrogenation) is crystallized by a laser beam having a low energy density as shown by a curve A. From this, it is concluded that the minimum energy density (threshold energy density) for causing crystallization by performing heat annealing for dehydration is low.

From the above, the present inventors have made it possible to thoroughly remove hydrogen from an amorphous silicon film and to form a large number of dangling bonds, thereby lowering the threshold energy density for crystallization. We have come to the conclusion that we can.

[0053]

According to the constitution of the present invention, the heat annealing in an inert or vacuum atmosphere at a temperature lower than the crystallization temperature and the subsequent irradiation with a laser beam in the inert or vacuum atmosphere provide high crystallinity. A polycrystalline silicon film having little dependence on the energy density of the laser and having excellent uniformity was obtained.

[Brief description of the drawings]

FIG. 1 shows the relationship between the peak of the Raman spectrum of a polycrystalline semiconductor film and the energy density of laser irradiation.

FIG. 2 shows a multi-chamber type apparatus shown in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Loading chamber of sample 2 ... Plasma CVD apparatus 3 ... Heat annealing furnace 4 ... Laser annealing furnace 5 ... Sample loading chamber 6 ... Gate valve

Claims (2)

[Claims] 1. An apparatus for manufacturing a semiconductor material, comprising: a chamber for irradiating a semiconductor film provided on a substrate with infrared light; a chamber for laser annealing the semiconductor film; Means for transporting the semiconductor material without being carried out. 2. An apparatus for manufacturing a semiconductor material, comprising: a chamber for irradiating a semiconductor film provided on a substrate with infrared light; a chamber for laser annealing the semiconductor film; Means for transporting the semiconductor film by using a rectangular beam having a long axis arranged perpendicular to the direction of transport of the substrate, fixing the beam, and transporting the substrate. An apparatus for producing a semiconductor material, wherein laser annealing is performed.