JP2760449B2 - Semiconductor thin film manufacturing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor thin film which can be used particularly for an active region of a thin film transistor on an insulating substrate.

2. Description of the Related Art Thin-film transistors on insulating substrates can be used not only as active matrix elements in liquid crystal display devices but also as load elements in latch-up-free CMOS circuits and high-performance SRAM memory cells. And is of great interest.

Generally, a polycrystalline semiconductor thin film is used as an active region of the thin film transistor. Improvement is the biggest challenge. As one means for increasing the crystal grain size, there is a method in which after forming an amorphous semiconductor thin film, heat treatment (annealing) is performed at a low temperature to cause solid phase growth to obtain a polycrystalline semiconductor thin film.

As an example, a conventional method of manufacturing a semiconductor thin film for obtaining a large-grain polysilicon thin film will be described below with reference to FIGS. 5 and 6. After a silicon oxide film 12 is formed on a silicon substrate 11 as shown in FIG. 5 (a), and then an amorphous silicon thin film 13 is formed as shown in FIG. 5 (b). As shown in FIG. 1, annealing was performed, and an amorphous silicon thin film 13 was solid-phase grown to obtain a large grain polysilicon thin film 14 to produce a semiconductor thin film. FIG. 6 is an enlarged plan view of the semiconductor thin film obtained in this manner. Reference numeral 15 surrounded by a dotted line indicates an active region where a thin film transistor is formed. 16 is a crystal grain boundary.

In such a conventional method of manufacturing a semiconductor thin film, each crystal grain constituting the large-grained polysilicon thin film 14 that has been solid-phase grown by annealing is positioned at an arbitrary position in the amorphous silicon thin film 13. , Are formed at random positions as shown in FIG. For this reason, when a thin film transistor is formed in the polysilicon thin film 14, a portion to be an active region of the thin film transistor (hereinafter, referred to as an active region) 15 is composed of a plurality of polysilicon crystal grains. Since it is not possible to control the position of the active region 15 of the thin film transistor and the number of polysilicon crystal grains,
The variation causes a variation in the characteristics of the manufactured thin film transistor, which has a disadvantage that the overall characteristics of the integrated circuit are deteriorated.

The present invention solves the above-mentioned problems, and by controlling the number of polysilicon crystal grains formed by solid phase growth by annealing and the position of an active region, the active region of a thin film transistor with very little characteristic variation can be obtained. It is an object of the present invention to provide a method for manufacturing a semiconductor thin film that can be formed.

Means for Solving the Problems In order to achieve the above object, the present invention provides a step of forming an amorphous silicon thin film on an insulating substrate, and the step of forming silicon ions in a region other than the active region of the silicon thin film. Implanting the silicon thin film, and annealing the silicon thin film, wherein the amount of silicon ions implanted into a region other than the active region of the silicon thin film is N (
/ cm ² ), and the time when the amorphous silicon thin film is completely converted to a polysilicon thin film when the silicon ions are not implanted is t ₁ , and the silicon ion implantation amount N
When the (pieces / cm ²⁾ crystallization start time of the amorphous silicon thin film when implanting silicon ions was t _2, the semiconductor thin film, characterized by satisfying the t ₁ <t ₂ the relationship It is characterized by a manufacturing method.

According to the present invention, the amorphous semiconductor thin film in the ion-implanted region becomes the active region of the thin-film transistor because the solid-phase growth start time by annealing is delayed with an increase in the amount of implanted ions. Even when a part of the amorphous semiconductor thin film is completely crystallized by solid-phase growth by annealing, it is possible to keep the region other than the active region of the thin film transistor amorphous. As a result, it is possible to control a portion to be an active region of the thin film transistor and to be unaffected by crystallization from other regions.
It is composed of a single crystal grain with excellent uniformity and no crystal grain size.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1, 2, and 3. FIG.

FIGS. 1 (a) and 1 (b) show exactly the same steps as the conventional example shown in FIGS. 5 (a) and 5 (b). That is, as shown in FIG. 2A, a silicon oxide film is formed on the silicon substrate 11 by thermal oxidation.
12 and then disilane (Si) as shown in FIG.
_A non-doped amorphous silicon thin film 13 is formed by low-temperature LPCVD at about 480 ° C using 2H ₆ ) as a source gas.
Deposit to a thickness of 50-150 nm. Thereafter, as shown in FIG. 3 (c), an acceleration of about 100 keV is applied to a region other than the active region of the thin film transistor by using the photoresist mask 1 formed on the active region forming portion of the thin film transistor. Energy (3-5) x 10 ¹⁵ / c
Implant silicon ions of about m ² . Next, as shown in FIG. 3D, after removing the photoresist mask 1, annealing is performed at a low temperature of about 600 ° C. for about 20 hours in a nitrogen atmosphere. As a result, as shown in the enlarged plan view of the amorphous silicon thin film 13 in FIG. 2, only the active region 15 of the thin film transistor surrounded by the dotted line becomes the polysilicon thin film 2.

Meanwhile, there is a relationship as shown in FIG. 3 between the amount N of silicon ions implanted into the amorphous silicon thin film 13 and the crystallization ratio. Here, t ₀ is the crystallization start time when silicon ions are not implanted, t ₁ is the time for completely forming a polysilicon thin film, and t ₂ is the time of amorphous silicon thin film implanted with N / cm ² silicon ions. This is the crystallization start time. By selecting the silicon ion implantation amount N that satisfies t ₁ <t ₂ , crystallization of the active region 15 of the thin film transistor can be completed before crystallization of a portion other than the active region of the thin film transistor starts. According to such a manufacturing method, the active region 15 of the thin film transistor is not affected by the crystallization from the peripheral portion because the polysilicon does not crystallize in other regions, and therefore, as shown in FIG. The active region 15 of the thin film transistor can be formed by a semiconductor thin film made of a single crystal grain.

Next, another embodiment will be described with reference to FIGS. 4 (a) to 4 (d).

The difference from the embodiment of FIG. 1 is that, instead of using the photoresist mask 1 to implant silicon ions into regions other than the active region 15 of the thin film transistor in the step (c) of the embodiment of FIG. In the embodiment shown in FIG.
The point is that a silicon oxide film 1a of about 3000 to 5000 ° is used as a mask for ion implantation. The silicon oxide film 1a serving as an implantation mask is subjected to the annealing temperature (about 60
The temperature may be lower than 0 ° C.) by a normal pressure CVD method or a plasma CVD method.

According to the embodiment of FIG. 4, similar to the embodiment of FIG.
Not only can the active region 15 of the thin film transistor be formed by a semiconductor thin film composed of a single crystal grain as shown in FIG. 2, but also if the silicon oxide film 1a is used as a source and drain implantation mask, Only the amorphous semiconductor thin film can be used as a source and a drain. That is, only the semiconductor thin film composed of a single crystal grain can be reliably used as the active region of the thin film transistor. In the above embodiment, the case where the silicon substrate 11 on which the silicon oxide film 12 is formed is used. However, the present invention is also applicable to the case where a semiconductor thin film is formed on an insulating substrate such as glass, quartz, and ceramic. Although the case of silicon as the amorphous material has been described, the present invention can be applied to semiconductor materials in general.

Effects of the Invention As is apparent from the above embodiments, according to the present invention, the crystallization of the active region of the semiconductor thin film is completed before the crystallization of the portion other than the active region in the semiconductor thin film starts. Therefore, the position of the active region of the semiconductor thin film can be controlled, and the active region of the semiconductor thin film consisting of a single crystal grain can be formed without being affected by crystallization from the periphery of the active region. It has an excellent effect that it can be formed.

[Brief description of the drawings]

1 (a) to 1 (d) are cross-sectional views showing a manufacturing process of a semiconductor thin film according to an embodiment of the present invention, FIG. 2 is a partially enlarged plan view of the semiconductor thin film obtained in FIG. 1, and FIG. FIG. 4 (a) to FIG. 4 (a) are diagrams showing the time change of the crystallization ratio due to the annealing in the step of FIG.
5D is a sectional view of a semiconductor thin film manufacturing process according to another embodiment of the present invention, FIGS. 5A to 5C are sectional views of a conventional semiconductor thin film manufacturing process, and FIG. FIG. 4 is an enlarged plan view of a portion of the conventional semiconductor thin film obtained. 11: silicon substrate (insulating substrate), 12: silicon oxide film (insulating substrate), 13: amorphous semiconductor thin film, 15: active area.

Claims (1)

(57) [Claims] A step of forming an amorphous silicon thin film on an insulating substrate; a step of implanting silicon ions into a region other than an active region of the silicon thin film; and a step of annealing the silicon thin film. The amount of silicon ions implanted into a region other than the active region of the silicon thin film is set to N (pieces / cm ² ), and the silicon thin film is completely amorphous in the case where the silicon ions are not implanted. the time the silicon thin film and t _1, when the crystallization start time of the amorphous silicon thin film when implanting silicon ions implantation amount N (pieces / cm ²⁾ of the silicon ions was t _2, t _A method for producing a semiconductor thin film, wherein a relationship of ₁ <t ₂ is satisfied.