JPH03280528A - Formation of polycrystalline semiconductor thin film - Google Patents

Abstract

PURPOSE:To prevent the random generation of seeds for crystal growth and to contrive the control of a crystal particle diameter by a method wherein crystallized regions formed at desired parts of an amorphous semiconductor thin film are used as the seeds for crystal growth. CONSTITUTION:An SiO2 film 12 is deposited on a substrate 11 and moreover, a polycrystalline Si film 13 is deposited on this film 12. Si<+> 14 is ion-implanted in the whole surface of the film 13 and the film 13 is turned into an amorphous Si film 15. Then, an excimer laser beam 16 of an energy of such a degree that the film 15 is not melted is selectively irradiated only on desired parts of the film 15. As this result, parts only, which are irradiated with the beam 16, of the film 15 are recrystallized and fine crystallized regions 17 are formed. Then, when a solid growth annealing of the film 15 is performed at a temperature of 600 deg.C or thereabouts, crystal particles 18 are formed corresponding to the regions 17 only and these crystal particles 18 have a large crystal particle diameter and an irregularity in the crystal particle diameter is also little.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for forming a polycrystalline semiconductor thin film used for manufacturing thin film transistors and the like.

(Summary of the Invention) The present invention provides a method for forming a polycrystalline semiconductor thin film as described above, in which crystal grain size is This makes it possible to form a polycrystalline semiconductor thin film with a large grain size and little variation in crystal grain size.

[Prior Art] Thin film transistors are used in liquid crystal displays, stacked CMO3 type O3AMs, and the like, and thin film transistors are generally formed in polycrystalline semiconductor thin films.

Therefore, in order to improve the performance of a thin film transistor by increasing the mobility or decreasing the threshold swing, it is necessary to increase the crystal grain size of the polycrystalline semiconductor thin film.

Therefore, a method is used in which a polycrystalline semiconductor thin film is temporarily made amorphous by ion-implanting Si'' or the like, and then this amorphous semiconductor thin film is subjected to solid phase growth annealing at a relatively low temperature of about 600°C. (For example, JP-A-61-127118
Publication No.).

[Problem to be solved by the invention]

However, the above-mentioned conventional method merely causes crystal growth using randomly generated nuclei in an amorphous semiconductor thin film as seeds. Therefore, the crystal grain size is around 2 μm at most, and the crystal grain size itself varies.

On the other hand, if the degree of amorphization is increased by increasing the dose of Si'', random nucleation can be suppressed and the crystal grain size can be increased.However, this time the nucleation time itself is extremely long and is not practical.

[Means for Solving the Problems] In the method for forming a polycrystalline semiconductor thin film according to the present invention, a crystallized region 17 is formed in a desired portion of an amorphous semiconductor thin film 15,
The amorphous semiconductor thin film 1 is grown using the crystallized region 17 as a seed.
5 to cause crystal growth.

[Function] In the method for forming a polycrystalline semiconductor thin film according to the present invention, the crystallized region 17 formed in a desired portion of the amorphous semiconductor thin film 15 is used as a seed for crystal growth, and the seeds for crystal growth are not randomly generated. Therefore, the crystal grain size can be controlled.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

In this embodiment, as shown in FIG. 1A, a substrate 11 made of quartz or the like is used.
On top, apply an iOz film 1 to a thickness of about 5000 by CVD.
2 is deposited, and a thickness of 80 mm is further deposited on this SiO□ film 12'.
A polycrystalline Si film 13 about the size of 0 people is deposited.

Then, Si”14 was heated to about 40 keV and 5
Polycrystalline Si film 1 with a dose of 1015 cl” or more
By implanting ions into the entire surface of the polycrystalline Si film 13, the polycrystalline Si film 13 is transformed into an amorphous Si film 15, as shown in FIG. 1B.

Next, as shown in FIG. 1B, only desired portions of the amorphous Si film 15 are selectively irradiated with excimer laser light 16 having an energy level that does not melt the amorphous Si film 15.

To perform such irradiation, thinning shots may be performed by step-and-repeat. Excimer laser light 1
6, XeCl or the like having a wavelength of 308 nm can be used.

As a result, only the portion of the amorphous Si film 15 irradiated with the excimer laser beam 16 is recrystallized, and a minute crystallized region 17 is formed.

Next, solid phase growth annealing of the amorphous Si film 15 is performed at a temperature of about 600°C. FIG. 2 shows the relationship between the Si'14 dose and crystallization in this solid phase growth annealing. The joint axis in FIG. 2 shows the peak of the reflectance in the ultraviolet wavelength range as a ratio of 100 to that of single crystal Si.

As is clear from this FIG. 2 and as stated above, Si”
If the dose of No. 14 is large, the time until random nucleation is long, and as a result, the crystal grain size is large and the rate of crystallization is high.

In this example, the dose of Si"14 was set to 5 as described above.
X 1015 cin-" or more, the time until random nucleation is extremely long. However, the amorphous Si film 1
5, a crystallized region 17 is formed in advance.

Therefore, if solid-phase growth annealing is performed at a temperature of about 600°C, crystal grains will grow using the crystallized region 17 as a seed, and it will take time until they come into contact with the crystal grains that have grown using the adjacent crystallized region 17 as a seed. In this case, it is possible to prevent the generation of nuclei between the crystallized regions +ti17.

As a result, as shown in FIG. 1C, crystal grains 18 are formed corresponding only to the crystallized region 17, and these crystal grains 18 have large crystal grain sizes and little variation in crystal grain size.

Therefore, polycrystalline 5iH19 consisting of such crystal grains 18
If a thin film transistor is formed using as an active layer,
This thin film transistor has high performance and less variation in characteristics.

In addition, in this example, the dose amount of Si"14 was set to 5×10"
ell-" or more, but lX101S~1x10"C
Similar effects can be obtained if the distance is about 11-''.

Further, in this embodiment, the polycrystalline 5ill13 was made amorphous 5ill15 by ion implantation of Si''14, but the amorphous Si film 15 is
If the film can be formed directly on the Sing film 12, ion implantation of Si'' 14 is not necessarily necessary.

〔Effect of the invention〕

In the method for forming a polycrystalline semiconductor thin film according to the present invention, since the crystal grain size can be controlled, a polycrystalline semiconductor thin film with a large crystal grain size and little variation in crystal grain size can be formed.

[Brief explanation of drawings]

Fig. 1 is a side sectional view sequentially showing one embodiment of the present invention;
The figure is a graph showing the relationship between the dose of Si" for a polycrystalline Si film and the crystallization of this polycrystalline Si film. In the symbols used in the drawing, 15 - ・---m---・- −−−−1−−−−−−
・-Amorphous 5il117−・−・−−−1−−−−−
・−・・−Crystallization region 19−−−−−−−−−−−
---...--Polycrystalline Si film.

Claims (1)

[Scope of Claims] A method for forming a polycrystalline semiconductor thin film, comprising forming a crystallized region in a desired portion of an amorphous semiconductor thin film, and growing crystals in the amorphous semiconductor thin film using the crystallized region as a seed.