JPH05275333A - Manufacture of polycrystalline silicon thin film - Google Patents

Abstract

PURPOSE:To obtain a high quality polycrystalline silicon thin film by forming an amorphous silicon film so as to cover a region with dotted single crystal silicon followed by performing heat treatment on this amorphous silicon film. CONSTITUTION:A first amorphous silicon film 2 is formed on a supporting substrate 1 followed by patterning this for being dotted and irradiated with a laser beam 3 in order to make the dotted amorphous silicon film 2 a single crystal silicon region 2a. Next, a second amorphous silicon film 4 is formed on the surface of the supporting substrate 1 so as to cover the single crystal silicon region 2a. Then, heat is applied so as to polycrystallize the second amorphous silicon film 4 while having the dotted single crystal silicon regions 2a as nuclei in order to make a polycrystalline silicon thin film 5 of high quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a thin film transistor,
The present invention relates to a method for manufacturing a polycrystalline silicon thin film which is a base material of a solar cell.

[0002]

2. Description of the Related Art It is known that a polycrystalline silicon thin film generally shows better characteristics as the size of the crystal grains constituting the polycrystalline silicon thin film increases. To this end, while controlling these crystal grains from the growth stage. It is necessary to form a polycrystalline silicon thin film.

A method proposed as a method for forming a polycrystalline silicon thin film is, for example, JP-A-63-143.
869 and Applied Physics Vol. 57, No. 9 (1988) p.
1387 to 1392. FIG. 6 is an element structure diagram for each step of the proposed method for manufacturing a polycrystalline silicon thin film, which is manufactured according to the following procedure.

In the process shown in FIG. 1A, a quartz substrate (61) is used.
A polycrystalline silicon thin film (62) having a film thickness of 0.1 μm is formed thereon by a vacuum deposition method at a substrate temperature of 600 ° C.

Next, in the step shown in FIG. 1B, this polycrystalline silicon thin film is formed by a conventionally known photography method.
(62) is patterned on the quartz substrate (61) to have an island shape. The polycrystalline silicon thin film (62) divided in this way ...
Serves as a nucleus when polycrystallizing the amorphous silicon thin film in the subsequent heat treatment step. Hereinafter, the divided polycrystalline silicon thin films (62) ... Are referred to as polycrystalline silicon nuclei.

In the step shown in FIG. 6C, the film thickness of the polycrystalline silicon nuclei (62) ...
A 2 μm amorphous silicon film (63) is formed on the quartz substrate (61).

Then, in the next step shown in FIG.
These amorphous silicon thin films (63) have a thickness of 600 in a nitrogen atmosphere.
This amorphous silicon film (63) was subjected to heat treatment at ℃ for 20 hours.
Into a polycrystalline silicon thin film (64).

The heat-treated amorphous silicon film starts to be crystallized from the respective polycrystal silicon nuclei (62), and is gradually polycrystallized along the plane direction of the quartz substrate (61). Will proceed.

[0009]

However, in the method of manufacturing such a polycrystalline silicon thin film (64), polycrystalline silicon is used as a nucleus for polycrystallization of the amorphous silicon film (63). Since it is used, there is a limit to the degree of polycrystallization.

In particular, the quality of the initially formed polycrystalline silicon nuclei (62) determines the function of the nuclei, so that it is possible to obtain a polycrystalline silicon thin film having a quality higher than that of the nuclei in the first place. I can't.

The nucleus (62) is not only affected by the quality of the nucleus itself but also by the geometrical arrangement of the nucleus. That is, generally, the crystal grains forming the polycrystalline silicon thin film grow radially from the nucleus, but the growth is usually at a position in contact with another crystal grain grown from another adjacent nucleus. You can't stop and grow bigger than that. This means that the size of the crystal grain is relatively determined depending on the distance between adjacent nuclei. In addition, since a portion having a poor film quality generally called a grain boundary is formed at a portion where the crystal grains are in contact with each other, the position of the grain boundary is determined by the arrangement of the nuclei.

However, even if the polycrystalline silicon nuclei are scattered at a desired distance in consideration of the geometrical arrangement of the nuclei in the conventional method for producing a polycrystalline silicon thin film, the grain boundaries are well generated. It is not possible to control the position. This is because the polycrystalline silicon nuclei that originally function as nuclei originally have only random crystal planes, and therefore the polycrystalline silicon thin film grown from this nuclei cannot grow in an orderly manner.

[0013]

The feature of the method for producing a polycrystalline silicon thin film according to the present invention lies in that it is formed on the supporting substrate by the first method.
Forming an amorphous silicon film, patterning the first amorphous silicon film so as to be scattered on the supporting substrate, and applying an energy beam to the first amorphous silicon film. A step of forming a single crystal silicon region by irradiation, and a step of depositing and forming a second amorphous silicon film so as to cover the scattered single crystal silicon regions,
And a step of polycrystallizing the second amorphous silicon film by heat treatment, and the thickness of the first amorphous silicon film is 300 to 600 Å, Means that the pattern size of the first amorphous silicon film scattered on the supporting substrate is 3 μm □ or less.

[0014]

According to the manufacturing method of the present invention, since single crystal silicon is used as a nucleus for solid phase growth formed on a supporting substrate, a polycrystalline silicon thin film grown from this nucleus also has high quality. It can be a thin film.

Particularly, in the present invention, an amorphous silicon film is used as a starting material for this nucleus, and high quality single crystal silicon with few defects obtained by irradiating this with an energy beam is used as the nucleus. In particular, when the amorphous silicon film is single-crystallized, the film thickness and patterning size of 300 to 600 Å and 3 μm □ or less have a sufficient function as a nucleus. A single crystal silicon region can be obtained.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a structural drawing of an element according to steps of the manufacturing method of the present invention.

In the first step shown in FIG. 1A, a first amorphous silicon film (2) is formed on a supporting substrate (1) such as quartz or glass.
To form. In the embodiment, the amorphous silicon film (2) is formed by the conventionally known plasma CVD method. In this example, this film thickness was set to 500 Å. In the present invention, the film thickness of the first amorphous silicon film (2) and the patterning size of this film in the next step are important factors. These optimum values will be described later by showing experimental results.

Table 1 shows typical conditions for forming the amorphous silicon film (1).

[0019]

[Table 1]

Next, in a second step shown in FIG. 2B, this first amorphous silicon film (2) is patterned so as to be scattered at desired positions on the surface of the supporting substrate (1). The amorphous silicon film (2) formed by such patterning is
The size of the patterning of the amorphous silicon film (2) is an important second factor of the present invention because it becomes a single crystal silicon region that functions as a nucleus by irradiation with an energy beam in the next step.

Then, in the third step shown in FIG.
A laser beam (3) is applied to the interspersed amorphous silicon film (2).
Are irradiated, the amorphous silicon films (2) ... Become single crystal silicon regions (2a). Usually, the shape of this region (2a) is granular or film-like. As a result, the nuclei for polycrystallization can be arranged at a desired position on the supporting substrate (1) in the subsequent step. Table 2 shows typical conditions for the laser irradiation. Moreover, as this laser beam,
An rF (193 nm) excimer laser was used.

[0022]

[Table 2]

In particular, in the production of the nucleus according to the present invention, since the energy beam is used, the nucleus, that is, the single crystal silicon region (2a) can be firmly adhered to the supporting substrate (1).

In the fourth step shown in FIG. 3D, the supporting substrate is
The surface of (1) has a thickness of 5 so as to cover the single crystal silicon regions (2a) ... Interspersed with the second amorphous silicon film (4).
It is formed in the range of 00Å to 3000Å. As for the forming method, the same method as the first amorphous silicon (2) may be used.

Then, in the fifth step shown in FIG.
By applying heat, the second amorphous silicon film (4) is polycrystallized using the interspersed single crystal silicon regions (2a) ... as nuclei to form a polycrystalline silicon thin film (5). This polycrystallization progresses radially from the single crystal silicon regions (2a) ... Until eventually the similar polycrystallization from the adjacent single crystal silicon regions (2a). Normally, crystallization from these adjacent single crystal silicon regions (2a) progresses almost at the same level, so that the grain boundaries (6) are formed substantially in the middle of these single crystal silicon regions (2a).

In particular, according to the present invention, since the single crystal silicon having excellent crystallinity is used as the nucleus, the position of the grain boundary (6) can be sufficiently controlled, and the conventional method using the polycrystalline silicon as the nucleus is used. It is possible to suppress the generation of grain boundaries at random positions, which has occurred in the case of using a material, and as a result, a high quality polycrystalline silicon thin film can be obtained.

Therefore, according to the manufacturing method of the present invention, the second
Since the grain boundaries (6) can be formed at the positions reflecting the patterning shape of the first amorphous silicon film (2) performed in the step, the patterning shape of the first amorphous silicon film (2) can be changed. By taking this into consideration, the portion where no grain boundary (6) exists in this polycrystalline silicon thin film can be used as an active layer of various semiconductor devices. A specific example of this usage method will be described later.

Furthermore, in the polycrystalline silicon thin film produced by the manufacturing method of the present invention, the crystal structure of the portion surrounded by the grain boundaries (6) is ordered, so if such a portion is viewed locally, It can be said to be single crystal silicon (7). Therefore,
The polycrystalline silicon film according to the present invention is characterized by being a thin film composed of a large number of crystal grains made of single crystal silicon.

Next, the film thickness of the first amorphous silicon film (2), which is an important factor in the manufacturing method of the present invention, and its pattern size will be described. First, FIG. 2 shows the first
Film thickness of the amorphous silicon (2) and the single crystal silicon region obtained by the laser beam irradiation (3) in the third step
It is a characteristic view showing a relationship with the size of (2a). The pattern size of the first amorphous silicon film (2) used was 1
It was performed by irradiating an ArF excimer laser with an energy intensity of 300 mJ / cm ^{2 as a} laser and 128 pulses (about several tens Hz) under a substrate temperature of 400 ° C.

According to the figure, the grain size of the single crystal silicon region obtained by the laser irradiation is the largest when the thickness of the first amorphous silicon film is 300 to 600 Å, and according to the experiment, it is about 3 μm. There is a big thing to cross. On the other hand, outside this range, the particle size is rapidly reduced. Especially, if the film thickness is less than 300Å, the energy intensity is 30
Since a high irradiation intensity of about 0 mJ / cm ² was used, only a film having an insufficient crystalline property in which an amorphous phase and a crystalline phase were mixed was obtained. However, below this film thickness 300 mJ
It has been confirmed that even if the energy intensity is smaller than / cm ^2, only a single crystal silicon region having a size of 3000 to 4000 Å can be obtained.

Further, when the film thickness exceeds 600 Å, the particle size cannot be increased even if the energy intensity of laser irradiation is set large, and the particle size is saturated at a certain stage. The reason for this is not clear, but the present inventors presume as follows. That is, when the first amorphous silicon film (2) is irradiated with laser light, this film becomes a single crystal silicon region, but the single amorphous silicon film (2) is irradiated for single crystallization. It is preferable that the temperature of the entire film rises uniformly. In particular, since the supporting substrate (1) such as glass used has a relatively poor thermal conductivity, the heat due to laser light absorption loses its escape when the temperature of the entire first amorphous silicon film (2) rises. Therefore, the heat can be effectively utilized for single crystallization.

However, in the case of a thick film having a film thickness of 600 Å or more, the heat generated by the laser light is applied only to the vicinity of the surface of the first amorphous silicon film (2). Then, this heat does not stay near the surface but begins to conduct heat in the film depth direction of the first amorphous silicon film (2) which is still in a low temperature state. As a result, the heat generated by the laser light cannot be effectively utilized for single crystallization, and as a result, only a small single crystal silicon region can be formed.

In particular, when the excimer laser is used, the laser wavelength is relatively short, so that the absorption of the laser beam is only near the surface of the first amorphous silicon film (2). I think it's easy to concentrate.

From the above, the thickness of the first amorphous silicon film (2) is preferably in the range of 300 to 600Å,
In particular, a film thickness of about 500Å is most suitable for increasing the size of crystal grains.

Next, the pattern size of the first amorphous silicon film will be described. This first amorphous silicon film
(2) is a single crystal silicon region (2a) that is formed by the energy beam irradiation in the third step and functions as a nucleus for polycrystallization in the subsequent step, so that it is a high quality single crystal silicon. It is necessary to be.

In FIG. 3, the crystalline state after laser irradiation was observed by a scanning electron microscope when the pattern size of the first amorphous silicon film as the starting material of the single crystal silicon region was variously changed. It is a schematic diagram. The laser irradiation conditions are the same as those used in FIG. 2 except that the film thickness of the first amorphous silicon is about 500 Å, and the pattern size is five types from 0.5 to 7 μm. Shows. Further, the surface of the polycrystalline silicon thin film before observation is slightly secco-etched so that the observation under a scanning microscope can be clearly performed.

According to the figure, the pattern size is about 3.0.
When the size becomes larger than μm, the crystallization by laser irradiation does not reach the single crystal silicon region (31) and remains in the polycrystalline silicon (32), and some grain boundaries (33) exist in the film. Will be created. On the other hand, when the size is smaller than about 3.0 μm, good single crystal silicon
(31) is completed. In particular, according to the manufacturing method of the present invention, a high quality film can be obtained even when compared with a polycrystalline silicon thin film obtained by simply heat treating a conventional amorphous silicon film.

Next, various semiconductor devices using the polycrystalline silicon thin film formed by the manufacturing method of the present invention will be described. FIG. 4 is an element structure diagram for each step of a thin film transistor using this polycrystalline silicon thin film. The same figure (a)
Is a first amorphous silicon film (not shown) patterned on a supporting substrate (41) such as glass at equal intervals.
This is a single crystal silicon region (42) formed by single crystallizing with a energy beam.

Next, in the step shown in FIG. 4B, after forming a second amorphous silicon film (not shown), this amorphous silicon film is polycrystalline to the polycrystalline silicon (43). It has been transformed. As a result, a grain boundary (44) is formed substantially in the middle of the position where the single crystal silicon region is arranged as shown in the figure, and the three single crystal silicon (43a) surrounded by these grain boundaries (44) make a large number as a whole. This means that a crystalline silicon thin film is formed.

In the step shown in FIG. 3C, the grain boundary (44) is formed so that one thin film transistor is formed in the single crystal silicon (43a) existing in one area surrounded by the grain boundary (44). After dividing the single crystal silicon (43a) along the line (4), an element is formed according to a normal process as a thin film transistor. In the figure, (45) is a channel layer using this polycrystalline silicon thin film, (46) is a gate insulating film, (47) is a gate electrode, (48) is a source electrode, and (49) is a drain electrode. ing. Other than the polycrystalline silicon thin film according to the present invention, it is formed and patterned by a conventionally known method. In this embodiment, three thin film transistors are formed.

As shown in this example, since the position of the grain boundary of the polycrystalline silicon thin film of the present invention can be controlled in advance, the grain boundary (44) should not be included in the channel layer (45) of the thin film transistor. Therefore, a high-mobility transistor can be manufactured. In this example, only one transistor was manufactured for the portion sandwiched by the grain boundaries (44), but the use of the polycrystalline silicon thin film according to the present invention is not limited to this.
It goes without saying that a plurality of thin film transistors may be manufactured in one single crystal silicon (43a).

Next, an example of a photovoltaic device using a polycrystalline silicon thin film formed by the manufacturing method of the present invention will be described. FIG. 5 is a cross-sectional view of the element structure for each manufacturing step of the photovoltaic device. In the step shown in FIG. 3A, single crystal silicon regions (52) in the manufacturing method of the present invention are formed on a supporting substrate (51) made of quartz at desired intervals.

Next, in the step shown in FIG. 6B, after forming a second amorphous silicon film (not shown), this amorphous silicon film is expanded to a polycrystalline silicon thin film (53). The polycrystalline silicon thin film is made to be p-type by crystallization and further by an ion implantation method, a thermal diffusion method or the like. This polycrystalline silicon thin film
(53) is composed of single crystal silicon (55) surrounded by grain boundaries (54) as in the previous embodiment.

In the step shown in FIG. 5C, phosphorus is diffused on the surface of the polycrystalline silicon thin film (53) by an ion implantation method or a thermal diffusion method, and the surface is n-type polycrystalline silicon thin film (5).
3a).

In the step shown in FIG. 3D, the portion corresponding to the grain boundary (54) is etched from the surface thereof to expose the lower p-type polycrystalline silicon film (53), and then the portion. And a light incident side electrode (56) formed of a transparent conductive film on the p-type surface. The steps such as the diffusion of impurities such as phosphorus in this example are performed by a conventionally known method.

In this embodiment, since the portion of the grain boundary (54) which originally has poor film quality is used as the optical carrier extraction, the carrier can be extracted to the outside without crossing this grain boundary (54) in the first place. The loss of carriers due to so-called carrier recombination can be reduced.

Further, as in the case of the above-mentioned thin film transistor, the polycrystalline silicon film (53) formed by the manufacturing method of the present invention is replaced with the portion of single crystal silicon where the grain boundaries (54) do not exist by the light of the photovoltaic device. Since it can be used as an active layer, high conversion efficiency can be obtained.

Further, in this embodiment, Ar is used as the laser light source.
F excimer laser (193 nm) was used, but Kr
F excimer laser (248 nm) and XeCl excimer laser (3
The amorphous silicon film may be single-crystallized by using (08 nm) or the like.

Although the method of plasma CVD is used as the film formation in the fourth step in this embodiment, the manufacturing method of the present invention is not limited to this.
Method or thermal CVD method may be used. Further, as the gas used in these reaction methods, a fluorine-based gas may be used.

[0050]

According to the manufacturing method of the present invention, since a high quality single crystal silicon region is used as a nucleus, a polycrystalline silicon thin film grown on the basis of this becomes a high quality film. The crystal grains forming this film are made of single crystal silicon.

Further, according to the present invention, since the grain boundary can be arranged at the position reflecting the pattern position of the first amorphous silicon serving as the nucleus, the crystal grain of this polycrystalline silicon thin film can be arranged. Can be easily used as an active layer in various semiconductor devices.

In particular, according to the thickness and size of the first amorphous silicon film shown in the manufacturing method of the present invention, a high-quality single crystal silicon region with few crystal defects can be obtained without depending on an excessive laser irradiation intensity. be able to.

[Brief description of drawings]

FIG. 1 is a sectional view of an element structure for each step for explaining the manufacturing method of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a film thickness of a first amorphous silicon film used in the manufacturing method of the present invention and a single crystal silicon region.

FIG. 3 is a schematic view of a pattern size of a first amorphous silicon film used in the manufacturing method of the present invention and a crystalline state after laser irradiation, which is observed by a scanning electron microscope.

FIG. 4 is a sectional view of an element structure for each manufacturing step of a thin film transistor using a polycrystalline silicon thin film formed by the manufacturing method of the present invention.

FIG. 5 is a sectional view of an element structure for each manufacturing step of a photovoltaic device using a polycrystalline silicon thin film formed by the manufacturing method of the present invention.

FIG. 6 is a sectional view of a device structure for each step for explaining a conventional method for manufacturing a polycrystalline silicon thin film.

[Explanation of symbols]

(1) ... Support substrate (2) ... First amorphous silicon film (2a) ... Single crystal silicon region (4) ... Second amorphous silicon film

Claims (3)

[Claims] 1. A step of forming a first amorphous silicon film on a supporting substrate; a step of patterning the first amorphous silicon film so as to be scattered on the supporting substrate; A step of irradiating the amorphous silicon film of No. 1 with an energy beam to form a single crystal silicon region; and a step of depositing and forming a second amorphous silicon film so as to cover the scattered single crystal silicon regions. And a step of heat-treating the second amorphous silicon film to polycrystallize the second amorphous silicon film. 2. The method for producing a polycrystalline silicon thin film according to claim 1, wherein the first amorphous silicon film has a film thickness of 300 to 600 Å. 3. The production of a polycrystalline silicon thin film according to claim 1, wherein the pattern size of the first amorphous silicon film scattered on the supporting substrate is 3 μm □ or less. Method.