JP2642587B2 - Method of forming polycrystalline thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a polycrystalline thin film, and more particularly, to a method for forming a polycrystalline thin film formed in a thin film transistor and other semiconductor devices.

[0002]

2. Description of the Related Art Some semiconductor devices have a thin film of amorphous silicon, polysilicon, or the like. For example, amorphous silicon or polysilicon is used as an operation semiconductor layer of a thin film transistor (TFT) provided for driving a liquid crystal display device. The silicon is required to be uniformly formed on a large-area insulating substrate made of quartz or glass. Since the silicon thin film greatly depends on the crystallinity of the underlying layer, it is formed in an amorphous state or a polycrystalline silicon state on an insulating substrate made of quartz or glass.

By the way, the transistor characteristics of a TFT are as follows:
It is better to apply polycrystalline silicon having a large grain size and large carrier mobility as the operating semiconductor layer. 1000 ° C. as the material of the TFT base
A quartz substrate that can be heated up to about 500 ° C., a heat-resistant glass substrate that can be heated up to about 500 ° C., and a low-melting glass substrate that has a heating upper limit of 200 ° C. can be considered.

In general, a silicon film is grown by thermal CVD or plasma CVD using SiH ₄ as a reaction gas. According to the thermal CVD method, the film grows at 550 ° C. or higher, and according to the plasma CVD method, the film grows at a normal temperature or higher. Whichever growth method is used, the crystallinity of silicon is determined by the growth temperature. In general, silicon grows amorphous at a temperature of 550 ° C. or less, while polycrystallization progresses at a temperature of 600 ° C. or more.

Therefore, when a polycrystalline silicon film is formed by a thermal CVD method, for example, a quartz substrate 1 is used to form a SiH ₄ film.
Is thermally decomposed at a temperature of 600 ° C. or more to grow silicon. In this case, the higher the temperature, the better the crystallinity, and a large grain size can be obtained. The growth process is shown in Fig. 5 (a),
As shown in (b), insulating substrate 1 by flashing of SiH ₄
5 (c), and the growth of grains around the nucleation site 2 (de) as shown in FIG.
The film formation is performed in two stages of film formation according to position). The nucleation step is very important and causes nuclei 2 which are not normally present on the smooth insulating substrate 1 to be formed. Note that long-time annealing may be used for grain growth as shown in FIG. The size of the grain size obtained by this is about several hundred nm to several nm.

On the other hand, when the plasma CVD method is used,
For example, as shown in FIGS. 6A and 6B, a glass substrate 4 is used to decompose SiH ₄ at a temperature of 400 ° C. to grow an amorphous silicon film 5 thereon. A polycrystalline silicon film 6 is formed as shown in FIG. As a method of polycrystallization, there is a method of applying ultraviolet energy or heat energy after the formation of the amorphous silicon film 5. Examples of a method for applying the energy include lamp annealing, laser annealing, and excimer laser annealing. When laser annealing is used, FIG.
As shown in (d), the laser is applied to the amorphous silicon film 5.
The crystallinity can be improved by a kind of liquid phase epitaxial growth method in which the film is melted and solidified while scanning along the surface. The size of the grain size thus obtained is about several μm to several tens μm.

In FIG. 6D, reference numeral 5a denotes a recrystallization portion, and 5b denotes a melting portion.

[0008]

However, from the viewpoint of cost reduction and ease of manufacture of a liquid crystal display device using a TFT,
Since it is desired to obtain a silicon thin film having good crystallinity by a process at a temperature of about 500 ° C. or less, the film growth method and materials are restricted. Further, after growing a film at a low temperature, the method of improving the crystallinity by a laser beam or the like,
This is not a practical method because the throughput is low and the manufacturing cost increases.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a method for forming a polycrystalline thin film which is simple and surely obtains a film having good crystallinity.

[0010]

Means for Solving the Problems The object of the present invention is to provide a first invention, a step of spraying or applying crystalline fine particles on a surface of a base at a constant distribution density, and the step of spraying the crystalline fine particles, Alternatively, a semiconductor-containing gas is supplied on the applied base, and the semiconductor-containing gas is thermally decomposed or plasma-decomposed to grow semiconductor crystals with the crystal fine particles as crystal nuclei, thereby forming a semiconductor film on the base. And a method for forming a polycrystalline thin film, the method comprising:
The method of forming a polycrystalline thin film according to the first aspect of the present invention includes a step of annealing the semiconductor film at a temperature of 500 ° C. or less. Or a semiconductor substrate having an amorphous layer formed thereon, which is solved by the method of forming a polycrystalline thin film according to the first aspect, and is a fourth aspect of the present invention, wherein hydrogen is applied before the formation of the semiconductor film. The semiconductor-containing gas, which is solved by the method for forming a polycrystalline thin film according to the first invention, comprising a step of increasing the activity of the fine particles by performing a plasma treatment, and which is a fifth invention, And a silane-based gas, wherein the semiconductor film is a silicon film, and is solved by the method of forming a polycrystalline thin film according to the first invention.

Alternatively, as shown in FIG. 1D, after the semiconductor film 13 is formed, the semiconductor film 13 is
This is achieved by a method for forming a polycrystalline thin film, comprising a step of annealing at a temperature of 0 ° C. or lower. Or
As illustrated in FIG. 1 or FIG. 4, the underlayer is achieved by a method of forming a polycrystalline thin film, which is a glass substrate 11 or a semiconductor substrate on which an amorphous layer is formed.

Alternatively, before forming the semiconductor film 13,
This is achieved by a method for forming a polycrystalline thin film, comprising a step of increasing the activity of the fine particles 12 by performing a hydrogen plasma treatment. Alternatively, the semiconductor-containing gas is a silane-based gas, and the semiconductor film is a silicon film, which is achieved by a method for forming a polycrystalline thin film.

[0013]

In the present invention, crystalline fine particles are adhered to the surface of an underlayer such as a glass substrate at a constant distribution, and the semiconductor particles are formed on the underlayer using these as crystal nuclei. In this method, nucleation is artificially performed in advance on the surface of the substrate,
With this in mind, crystalline fine particles are used as crystal nuclei.

According to this, since the crystalline fine particles are scattered or applied, fine particles of single crystal silicon or the like having good crystallinity can be used as the crystalline fine particles. The crystallinity of the crystal film grown from the crystal nuclei of the crystalline fine particles having good crystallinity is improved. Further, since crystal nuclei having an optimum size and a constant size can be used, it is possible to suppress the occurrence of irregularities on the entire surface of the grown semiconductor film. Further, since the crystal nuclei are distributed by spraying or coating, the distribution density of the crystal nuclei can be optimized, and the distribution density can be made uniform. At this time, the grown semiconductor film exhibits crystallinity corresponding to the distribution density of the fine particles, and the smaller the density, the larger the grain size. This makes it possible to form a polycrystalline film having a large grain size, small irregularities on the entire surface of the grown film, and good crystallinity. In addition, since crystal nuclei can be easily formed on an amorphous and smooth surface such as a glass substrate, a semiconductor-containing gas decomposed by heat or plasma is supplied to the crystal nuclei, and the crystal nuclei are centered. By growing a semiconductor by solid phase epitaxy, a semiconductor film having a large grain size and good crystallinity can be formed.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a sectional view showing a first embodiment of the polycrystalline thin film forming method of the present invention. First, FIG. 1 (a), FIG.
As shown in (b), for example, crystalline fine particles 12 are adhered on a glass substrate 11 as a TFT base.

There are several methods for attaching the fine particles 12. For example, a solution in which fine particles 12 are dispersed in a liquid such as alcohol is used, the glass substrate 11 is immersed in the solution, the glass substrate 11 is pulled up, and a gas such as nitrogen is blown to dry the surface. Method or
In this method, a solution containing the fine particles 12 is applied onto the glass substrate 11 by a spin coating method, and the alcohol is volatilized and dried. In the case of using the spin coating method, the adhesion density of the fine particles 12 is determined by the amount of dispersion in alcohol, the number of revolutions of spin coating, and the like, so that an arbitrary value can be selected.

Incidentally, fine particles having a diameter of 10 nm or less are used, and examples thereof include silicon fine particles, silicon carbide fine particles, and diamond fine particles. They are CV
It is produced by Method D, crystallized at the time of production, and these fine particles themselves have a certain crystal orientation. For example, silicon carbide is β-crystallized. Since these fine particles are used industrially, they are easily available. In order to uniformly disperse the fine particles in the solution, stirring by ultrasonic vibration is effective.

[0018] Thus, after depositing the fine particles randomly on the surface of the glass substrate 11, 500 ° C. by a plasma CVD method using _{SiH 4, Si 2 H 6,} Si 3 silane-based gas such as H ₈
Silicon is applied to the glass substrate 1 at the following temperature, for example, 400 ° C.
1 and a polycrystalline silicon film 13 is formed as shown in FIG. When the polycrystalline silicon film 13 is grown, fine particles 12 such as silicon, silicon carbide, and diamond serve as crystal nuclei. When a silane-based gas is used, silicon grows around the crystal nucleus in a solid phase epitaxy manner. Then, a crystal corresponding to the density of the fine particles is shown.

Since an amorphous and smooth surface such as the surface of the glass substrate 11 generally does not have any nucleation centers, it does not crystallize without a nucleation treatment. Although nuclei can be formed by a method of forming fine powder of silicon on the glass substrate 11 by flushing with SiH _4, polycrystalline silicon having a large grain size cannot be obtained due to its crystallinity and density. The fine powder particles are of the order of tens to hundreds of nm.

On the other hand, in the present embodiment, the fine particles 12 having a crystal orientation of about 10 nm in diameter are formed on the glass substrate 11, so that the crystal grows around the fine particles 12 and a large grain size is formed. Polycrystalline silicon can be grown. A large number of fine particles 12 are randomly dispersed on the glass substrate 11, and as shown in FIG. 2, when the size of the fine particles 12 is on the order of 10 nm, silicon grains 14 of several tens to several hundreds of nm are formed. In such a case, no irregularities are generated on the surface.

The relationship between the density of the fine particles 12 and the grain size is shown in FIG. 3. As shown in FIG. 3, the size of the grains 14 increases as the distance between the fine particles 12 increases and the particle density decreases. For example, the fine particles 12 have a diameter of 10 nm to 3
0 nm, and the distance between the fine particles is 0.1 μm to 0.3 μm.
In the case of μm, a polycrystalline silicon film having a grain size of 50 to 100 nm in diameter can be obtained. Note that the diameter is 10 nm to 30 nm.
Examples of the fine particles of nm include β-crystal silicon carbide powder (manufactured by Sumitomo Cement Co., Ltd.).

The grain size of the crystalline fine particles 1
2 is a function of the size, average spacing, and film thickness. Since crystallization proceeds more easily in the lateral direction, when the distance between the fine particles 12 is about 10 times the size, the plane shape is about 10 times the grain size even if the film thickness is about the same as the fine particles 12. become. After the polycrystalline silicon film 13 is formed, as shown in FIG.
Annealing at a temperature of 00 ° C. or less, for example, 400 ° C., further improves the crystallinity. Before the formation of the silicon film 13, the surface of the glass substrate 11 may be subjected to hydrogen plasma treatment to increase the activity of the fine particles 12 and improve the crystallinity. Second Embodiment In the above embodiment, the polycrystalline silicon film 13 is formed on the glass substrate 11 on which the fine particles 12 are adhered by the plasma CVD method. Good. When the thermal CVD method was used to thermally decompose the silane-based gas at a low temperature of 500 ° C. or less to grow polycrystalline silicon, the grain size was almost the same as that of the first embodiment. (Third Embodiment) In the above embodiment, a large number of crystalline fine particles 12 are adhered on a glass substrate 11 and a polycrystalline silicon film 13 is further formed thereon. 4A and 4B, if an amorphous silicon film 15 is formed on the glass substrate 11 as shown in FIGS. 4A and 4B, silicon, silicon carbide, and the like as shown in FIG. The attachment of the fine particles 12 such as diamond is facilitated. Thereafter, as shown in FIG. 4D, when the polycrystalline silicon film 13 is formed by a plasma CVD method or a thermal CVD method, a grain size similar to that of the first embodiment can be obtained.

The material of the base for forming the fine particles and the polycrystalline silicon film is not limited to glass. For example, in the manufacture of a down-gate type TFT, fine particles are deposited on a gate insulating film, and then the above-described polycrystalline silicon film having a large grain size is formed thereon, and this is used as an operating semiconductor layer. Will use. In the case of manufacturing an up-gate type TFT, a polycrystalline silicon film having a large grain size is formed after fine particles are deposited on a conductive film serving as a source / drain electrode.

Further, the base of the polycrystalline silicon film 13 is
It may be a silicon oxide film, a silicon nitride film, or another insulating layer.

[0025]

As described above, according to the present invention, crystalline fine particles are adhered to a surface of a base such as a glass substrate at a constant distribution, and a semiconductor film is formed on the base using these as crystal nuclei. doing. According to this, since crystal nuclei are easily formed on an amorphous and smooth surface such as a glass substrate,
By supplying semiconductor-containing gas decomposed by heat or plasma to fine particles that are crystal nuclei, semiconductors are grown in a solid phase epitaxy centered on the crystal nuclei, forming a semiconductor film with large grain size and good crystallinity. it can.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a process of a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a crystalline state of a silicon film formed by the steps of the first embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a difference in crystallinity of a silicon film due to a difference in fine particle density in the first embodiment of the present invention.

FIG. 4 is a sectional view showing a process of a third embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a first method for forming a conventional silicon film.

FIG. 6 is a cross-sectional view showing a second conventional method for forming a silicon film.

[Explanation of symbols]

 11 Glass substrate (underlying) 12 Fine particles (crystalline fine particles) 13 Polycrystalline silicon film (semiconductor film) 14 Grain 15 Amorphous silicon film (underlying)

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Claims (5)

(57) [Claims] A step of spraying or applying the crystalline fine particles on the surface of the base at a predetermined distribution density; and supplying a semiconductor-containing gas onto the base on which the crystalline fine particles are sprayed or applied. Thermally decomposing or plasma decomposing the semiconductor-containing gas to grow a semiconductor crystal using the crystal fine particles as a crystal nucleus, and forming a semiconductor film on the underlayer. Method. 2. The method according to claim 1, further comprising a step of annealing the semiconductor film at a temperature of 500 ° C. or less after forming the semiconductor film. 3. The method according to claim 1, wherein the underlayer is a glass substrate or a semiconductor substrate on which an amorphous layer is formed. 4. The method for forming a polycrystalline thin film according to claim 1, further comprising a step of performing a hydrogen plasma treatment to increase the activity of the fine particles before forming the semiconductor film. 5. The method according to claim 1, wherein the semiconductor-containing gas is a silane-based gas, and the semiconductor film is a silicon film.