JP3193332B2 - Method for manufacturing thin film transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is related to a method for manufacturing a thin film transistor such as an insulated gate field effect transistor
I do .

[0002]

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

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 an excimer laser, which is commonly used, has a problem that it is difficult to completely 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 method of manufacturing a thin film transistor using a laser annealing method which has solved the above-mentioned problems.

[0012]

SUMMARY OF THE INVENTION A thin film transistor according to the present invention.
The method for manufacturing a capacitor, the first to manufacture a semiconductor film on a glass substrate
A first step, a second factory for irradiating infrared light to the semiconductor film
And degree, the laser beam to the semiconductor film after the second step
A third step of irradiating and annealing.
A method of manufacturing a transistor, wherein the second step is performed after the second step.
The process is performed without exposing the glass substrate to the atmosphere until step 3.
It is characterized by the following.

[0013] The method for manufacturing a thin film transistor of the present invention having the above structure, prior to the step of crystallizing the amorphous semiconductor by irradiating a laser beam, is irradiated with infrared light in a vacuum or in an inert atmosphere non Heat annealing is performed at a temperature equal to or lower than the crystallization temperature of the crystalline semiconductor, 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.

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

Further, to perform the <br/> thermal annealing in a vacuum or in an inert atmosphere, unwanted film for example, an oxide film such as an amorphous semiconductor surface is to prevent the would be deposited.

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 a P-Si (polycrystalline) TFT having uniform characteristics can be formed on a large-area glass substrate. .

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 silicon semiconductor. This is based on the following experimental facts that were revealed in experiments performed by the present inventors.

That is, based on the experimental result that the crystallinity is remarkably improved as a result of irradiating an excimer laser (KrF 248 nm) to an amorphous silicon film which has been thoroughly dehydrogenated from a non-single-crystal silicon film. 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.

At this time, 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 that of laser light having a low energy density, which has been conventionally performed. 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, of a thin film transistor utilizing the apparatus of multi-chamber system for the amorphous semiconductor film surface after thermal annealing for dehydrogenation is performed following the laser crystallization step without being exposed to the atmosphere It relates to a manufacturing method.

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 irradiating infrared light to generate hydrogen, a chamber 4 for laser crystallization, and transport of a sample are shown. 1 shows an apparatus in which a sample loading chamber 1 and a sample unloading chamber 5 which are chambers are arranged in series.

Although not shown in FIG. 2, it goes without saying 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. Further, 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 impurity concentration, particularly the oxygen concentration, in the chamber in a vacuum state 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 .

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 aligned with the width of the glass base <br/> plate using an optical system, and the conveying direction of the glass substrate by using a beam cross section is rectangular, which is extended in the vertical direction, By slowly transporting the sample without moving the laser system, annealing can be performed efficiently if continuous irradiation is performed from the end of the sample.

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.

In this case, the laser irradiation was performed without heating the glass substrate, but the laser crystallization may be performed while maintaining the glass substrate temperature at the temperature of 500 ° C. before the laser crystallization. . Of course, the heating annealing temperature for dehydrating hydrogen is not limited to 500 degrees.

In the present 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 a Raman spectrum as shown by a curve A and the energy density of a laser beam during laser crystallization are considered as disadvantages. In the case where there is a relationship, since the crystallinity has little dependence on the laser intensity, a crystal film having uniform crystallinity without much influence of 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 exhibiting good crystallinity is useful.

FIG. 1 shows that the sample that has been heat-treated (heat-annealed for dehydrogenation) has been 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 thin film transistor using a polycrystalline silicon film having a small 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

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/20

Claims (2)

(57) [Claims] 1. A first method for forming a semiconductor film on a glass substrate .
And a second step of irradiating the semiconductor film with infrared light; and irradiating the semiconductor film with a laser beam after the second step.
Thin film transistor having a third step of annealing by annealing
The method according to any one of claims 1 to 3, wherein, from the second step to the third step, the glass substrate
Thin film tracing, which is performed without exposing the plate to the atmosphere
How to make transistors. 2. The method of claim 1, the irradiation of the laser beam irradiation section is rectangular Leh
The method for manufacturing a thin film transistor which is characterized in that by conveying the glass substrate perpendicularly to the long axis of Heather beam.