JP3007525B2 - Method for producing impurity-doped polycrystalline silicon thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an impurity-doped silicon thin film by forming an amorphous silicon thin film containing impurities on a substrate, heating and melting the amorphous silicon thin film for crystallization. It is about the method.

[0002]

2. Description of the Related Art As a method of forming a semiconductor thin film doped with an impurity, a method of exposing the semiconductor thin film to an atmosphere containing an impurity gas and subjecting the semiconductor thin film to a heat treatment to diffuse the impurity into the semiconductor thin film or a method of forming a thin film. And a method of mixing a source gas with an impurity gas to form a semiconductor thin film by a CVD method or the like in a state in which the impurity gas is contained.

[0003] In addition to the above-mentioned method, a method of manufacturing a polycrystalline silicon thin film doped with impurities is as follows. An amorphous silicon thin film containing impurities is formed on a substrate and then heat-treated. There is a method of forming a polycrystalline silicon thin film. This method is generally called a solid phase growth method, and is a method of growing a crystal in a solid phase without melting an amorphous silicon thin film.

[0004] On the other hand, there is known a method in which a semiconductor thin film is once melted by heating and crystallized. As a method of such crystallization by melting, an amorphous silicon thin film having a film thickness of 0.1 μm or less is crystallized by using a short pulse laser of the order of nanoseconds such as an excimer laser and melting in a short time of the order of microseconds. There is known a method of forming a polycrystalline silicon thin film having high crystallinity.

[0005]

However, a technique for melting and crystallizing an amorphous silicon thin film having a film thickness of 0.1 μm or more has not been sufficiently studied, and particularly with respect to the distribution of impurity concentration in the thin film. Did not have sufficient knowledge. The present inventors have proposed such a film thickness of 0.1.
As a result of comparative study of the method of melting and crystallizing an amorphous silicon thin film of 1 μm or more under gravity and under zero gravity, the surface of the thin film was heated and melted under gravity and crystallized. It has been found that the impurity concentration is significantly reduced in the vicinity and near the interface with the substrate.

The present invention is based on such knowledge, and it is possible to manufacture an impurity-doped silicon thin film having a uniform impurity concentration in the thickness direction of the thin film under gravity as well as under zero gravity. It aims to provide a way to do it.

[0007]

The manufacturing method of the present invention comprises the steps of forming an amorphous silicon thin film containing impurities on a substrate, and heating and melting the amorphous silicon thin film for crystallization. comprising a method for producing a doped polycrystalline silicon thin film, can it set relatively higher than the impurity concentration of the impurity concentration in the film center portion of the substrate side near the interface and the film near the surface in the amorphous silicon thin film This amorphous silicon
By heating and melting the crystallization of the thin film,
Doped polycrystalline silicon with almost uniform impurity concentration in
It is characterized by forming a corn thin film .

In order to obtain a silicon thin film having a uniform impurity concentration in the thickness direction of the thin film according to the manufacturing method of the present invention, the impurity concentration in the vicinity of the interface on the substrate side and in the vicinity of the film surface should be adjusted at the center of the film. 1.5 to 2.5 times the impurity concentration of
It is preferable to form an amorphous silicon thin film approximately twice as large, and to crystallize the amorphous silicon thin film by heating and melting.

The thickness of the silicon thin film manufactured by the manufacturing method of the present invention is not particularly limited. However, in the case of a thin film having a thickness of 0.1 μm or more, the entire film can be formed in a short time using an excimer laser or the like. It is difficult to melt-crystallize a thick region, and from this point, the present invention is particularly useful for forming a silicon thin film having a thickness of 0.1 μm or more.

[0010]

According to the manufacturing method of the present invention, the impurity concentration in the vicinity of the interface on the substrate side and in the vicinity of the film surface is relatively lower than the impurity concentration in the central portion of the film due to crystallization by heating and melting. In order to prevent the impurity concentration distribution in the thickness direction of the thin film from becoming non-uniform, the impurity concentration in the vicinity of the substrate side interface and in the vicinity of the film surface of the amorphous thin film is relatively higher than that in the center of the film. You have set. Therefore, in a crystallized silicon thin film obtained by heating and melting and crystallizing an amorphous silicon thin film having such an impurity concentration distribution, the impurity concentration at the center of the film, the vicinity of the substrate side interface and the film surface The impurity concentration in the vicinity can be made substantially the same, and the impurity concentration can be made uniform in the thickness direction of the thin film.

[0011]

FIG. 2 is a sectional view showing an amorphous silicon thin film in one embodiment according to the manufacturing method of the present invention. Referring to FIG. 2, an amorphous silicon thin film 2 is formed on a substrate 1 made of an insulating material such as quartz or ceramics or a semiconductor material such as a single crystal silicon wafer by using a plasma CVD method. The amorphous silicon thin film 2 includes a film central portion 2b having a low impurity concentration and a substrate vicinity 2 near the substrate side interface having a high impurity concentration.
a and the film surface vicinity 2c. Although FIG. 2 is shown divided into three layers, the density distribution is actually gentle as described later with reference to FIG.

Such a change in the impurity concentration distribution is caused by
Temperature, RF power, reaction pressure and silane (SiH_Four) Flow
The amount is kept constant, and the dopant /
It can be realized by changing the flow rate ratio of silane
it can. Fig. 4 shows the reaction from the start of the thin film formation
FIG. 3 is a diagram showing a gas flow ratio of dopant / silane. Anti
Gas flow of dopant / silane at the start of reaction (t = 0)
X to quantity ratio₁And a dopant /
X gas flow ratio of silane₀Then X₁Is X ₀About
1.5 times to 2.5 times is preferable, and more preferably about 2 times.
Degrees. The portion near the substrate-side interface 2a shown in FIG.
When forming, the gas flow ratio of the dopant / silane is set to X
₁To X₀It gradually decreases until. The central part 2b of the membrane
When forming, the gas flow ratio of the dopant / silane is set to X
₀And constant. When forming the film surface vicinity 2c,
The gas flow ratio of dopant / silane is X₀To X_TwoUntil Xu
Increase each time. X_TwoIs preferably X₀About 1.5
It is about 2.5 times, and more preferably about 2 times.

The reaction time t ₁ for forming the substrate side interface vicinity 2a is １ ／ T to ＴT, where T is the total reaction time.
The degree is preferably, more preferably, about 1 / 3T. Further, a reaction time t at which the formation of the film central portion 2b is completed.
₂ is preferably about 1 / 2T to 4 / 5T, and more preferably 2 / 3T, assuming the total reaction time T.

Hereinafter, specific embodiments of the present invention will be described. <100> Plasma CVD on single crystal silicon wafer
A P (phosphorus) -doped amorphous silicon thin film having a thickness of 1 μm was formed by the method. The conditions for forming the thin film were as follows, and were constant during the formation of the thin film.

Reaction temperature: 550 ° C. RF power: 80 W Reaction pressure: 0.5 Torr Silane gas flow rate: 40 SCCM Phosphine (PH ₃ ) was used as a dopant gas.
The gas flow ratio of phosphine / silane was changed to X ₀ ,
X ₁ and X ₂ were adjusted such that X ₀ = 2.5 × 10 ⁻⁴ X ₁ = X ₂ = 2X ₀ = 5 × 10 ⁻⁴ .

The total reaction time T was 480 seconds, and FIG.
The times t ₁ and t ₂ shown in FIG.
0 and 320 seconds. As a result, an amorphous silicon thin film having an impurity concentration distribution as shown in FIG. 5 was obtained. In FIG. 5, C _MID = 1.5 × 10 ¹⁹ cm ⁻³ , C
_SUR = C _SUB = 3 × 10 ¹⁹ cm ⁻³ .

For comparison, as shown in FIG. 4 as a comparative example, amorphous silicon in which the gas flow ratio of dopant / silane was kept constant at X ₀ = 2.5 × 10 ^-4 from the start of the reaction to the end of the reaction. A thin film was prepared. Other conditions for forming the thin film were the same as those in the above embodiment. The obtained amorphous silicon thin film of the comparative example has an impurity concentration distribution as shown by a dotted line in FIG. 5, and C ₀ = 1.5 × from the film surface to the interface on the substrate side.
It was constant at 10 ¹⁹ cm ^-3 . FIG. 3 shows the structure of such an amorphous silicon thin film of a comparative example. An amorphous silicon thin film having a uniform impurity concentration distribution in the thickness direction is formed on a substrate 11 similar to the substrate 1 shown in FIG. A silicon thin film 12 is formed.

The amorphous silicon thin films of Examples and Comparative Examples obtained as described above were heated and melted to crystallize. The heating was performed at a high speed of 1200 to 1300 ° C. in 30 seconds by using an image furnace for condensing an infrared lamp light of 2 kW, and the temperature was kept at 1200 ° C. or higher for 6 seconds to melt and crystallize. In addition, another experiment confirmed that the melting points of the amorphous silicon thin films of the example and the comparative example were about 1190 ° C. As a result of such heat melting, a polycrystalline silicon thin film having a concentration distribution as shown in FIG. 1 was obtained.

As shown in FIG. 1, the polycrystalline silicon thin film of the comparative example has a low impurity concentration at the film surface and at the interface on the substrate side, whereas the polycrystalline silicon thin film of the embodiment according to the present invention has It can be seen that the concentration of phosphorus as an impurity in the thickness direction is 9 × 10 ¹⁸ cm ^−3, which is almost uniform.

Further, the surface resistance of the polycrystalline silicon thin film of the example was measured by a four-point probe method, and it was found that the surface resistance was 13 in the comparative example.
While it was about 0 Ω / □, the polycrystalline silicon thin film of the example was about 75 Ω / □, showing a low surface resistance.

In the above embodiment, phosphorus is used as an impurity. However, the present invention is also applicable to the case where other n-type dopants such as arsenic and antimony and p-type dopants such as boron, gallium and aluminum are doped. Can be.

[0022]

As described above, according to the present invention,
By setting the impurity concentration of the amorphous silicon thin film near the substrate-side interface and near the film surface relatively higher than the impurity concentration at the center of the film, the amorphous silicon thin film can be obtained by heating and melting under zero gravity. Similar to crystallized silicon thin film,
A crystallized silicon thin film having a uniform impurity concentration over the entire thin film can be obtained.

Further, since the crystallized silicon thin film obtained by the present invention is crystallized by heating and melting, the crystallized silicon thin film has better crystallinity than the crystallized silicon thin film obtained by the so-called solid phase growth method. be able to.

[Brief description of the drawings]

FIG. 1 is a view showing an impurity concentration distribution in a thickness direction of a polycrystalline silicon thin film obtained in an example according to the present invention.

FIG. 2 is a cross-sectional view schematically showing an amorphous silicon thin film in one embodiment according to the present invention.

FIG. 3 is a sectional view schematically showing an amorphous silicon thin film of a comparative example.

FIG. 4 is a diagram showing a change in a dopant / silane gas flow ratio in one embodiment according to the present invention.

5 is a view showing a dopant concentration distribution in a thickness direction of an amorphous silicon thin film obtained by changing a gas flow ratio of dopant / silane shown in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Amorphous silicon thin film 2a ... Near the interface on the substrate side 2b ... Central part of the film 2c ... Surface part of the film

────────────────────────────────────────────────── (5) Continuation of the front page (72) Inventor Kenichiro Wakisaka 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-60-29754 (JP, A) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) H01L 21/205 H01L 21/31

Claims (2)

(57) [Claims] 1. A doped Tayui comprising the steps of: an amorphous silicon thin film containing an impurity is formed on the substrate, and a step of crystallizing heat melted to the amorphous silicon film
The method of manufacturing a crystal silicon thin film, can you set relatively higher than the impurity concentration of the impurity concentration at the substrate side near the interface and the film near the surface before Kihi Si thin film layer center part, the non Amorphous silicon thin film
Is heated and melted to crystallize
Impurity-doped polycrystalline silicon thin film with nearly uniform pure concentration
Forming an impurity-doped polycrystalline silicon thin film. 2. The substrate side of the amorphous silicon thin film
The impurity concentration near the interface and near the film surface is
1.5 to 2.5 times the impurity concentration of
The impurity-doped polycrystalline silicon thin film according to claim 1,
Production method.