JP2694615B2 - Method for forming single crystal semiconductor thin film - Google Patents

Description

The present invention relates to a method for forming a single crystal semiconductor thin film for forming a single crystal semiconductor thin film on an insulating film.

[Conventional technology]

Generally, an insulating film is formed on a single crystal semiconductor substrate, a groove in which the substrate is exposed is formed in the insulating film, an amorphous semiconductor thin film is formed on the insulating film and the groove, and the substrate exposed in the groove is used as a seed. There is a method of sequentially monocrystallizing this thin film from the groove in the solid phase by heat treatment, which is called recrystallization method,
(Silicon On Insulator) It is a useful technique in the technology and is drawing attention.

By the way, in the case of forming a single crystal semiconductor thin film by such solid phase growth, taking Si as an example, the amorphous Si thin film undergoes a phase transition from the contact portion with the substrate in the groove to the single crystal, and first, the upper surface of the substrate is In the vertical direction (vertical direction), single crystallization progresses, and then in the parallel direction (horizontal direction) parallel to the upper surface of the substrate, the amorphous Si thin film becomes single crystallization over the entire area.

However, the solid-phase growth distance greatly differs between the case where the amorphous Si thin film contains impurities and the case where the amorphous Si thin film does not contain impurities. It has been conventionally practiced to increase the solid-phase growth distance by using this region as a seed, and an example thereof is a method described in JP-A-63-60517 (H01L21 / 20).

This is because a plurality of high-concentration regions of impurities are provided in parallel in a direction orthogonal to the groove on a non-doped amorphous semiconductor thin film formed on the insulating film and on the groove, and the substrate in the groove and this high-concentration region are used as seeds for non-doping. The amorphous semiconductor thin film is crystallized into a single crystal.

[Problems to be solved by the invention]

In the method described in the above-mentioned publication, in the non-doped region surrounded by the two high-concentration regions and the groove, single crystallization proceeds in a V shape, so that finally the crystal subgrains of a rhombic complicated pattern are formed. Since a boundary is formed and it is necessary to form the channel of the device while avoiding this crystal sub-grain boundary in terms of the characteristics of the device, there is a problem that the area where the device can be effectively formed is limited.

The present invention has been made with the above points in mind, and it is an object of the present invention to extend the solid phase growth distance of a non-doped amorphous semiconductor region so that the effective area for forming a device can be expanded.

[Means for solving the problem]

In order to achieve the above object, in the method for forming a single crystal semiconductor thin film of the present invention, an insulating film is formed on a single crystal semiconductor substrate, a groove in which the substrate is exposed is formed in the insulating film, and the insulating film is formed on the insulating film. And forming a first amorphous semiconductor thin film on the groove, doping the first amorphous semiconductor thin film with a high concentration of impurities, and then crystallizing the first amorphous semiconductor thin film into a single film. A crystalline semiconductor thin film is formed, and the single crystalline semiconductor thin film is removed by etching, leaving a strip-shaped portion parallel to the groove and a groove parallel to the groove. An amorphous semiconductor thin film is formed, and the second amorphous semiconductor thin film is monocrystallized.

[Action]

With the above-described structure, when the flattened second amorphous semiconductor thin film is single-crystallized, the high-concentration regions of the single-crystallized impurities on the groove and the strip are used as seeds for single-crystallization. , The solid-phase growth distance can be increased, and a crystal sub-grain boundary is formed in parallel with the groove at an almost intermediate position between the groove and the band-like portion, and the crystal sub-grain boundary does not have a complicated pattern as in the past. The effective area for device formation can be expanded.

〔Example〕

 Embodiments will be described with reference to the drawings.

First, the step of forming a single crystal Si thin film will be described with reference to FIGS. 1 and 2. Note that Fig. 1 shows the final single crystal.
Perspective view of a state in which a Si thin film is formed, FIG. 2 (a), (b)
[Fig. 3] is a perspective view in the middle of formation.

Now, as shown in FIG. 2 (a), a SiO ₂ film (2) is formed as an insulating film on a single crystal Si substrate (1), and a groove in which the substrate (1) is exposed is formed in the SiO ₂ film (2). Forming (3), SiO ₂
A first amorphous Si thin film (hereinafter referred to as a first a-Si film) (4) is formed on the film (2) and the groove (3).

Then, the first a-Si film (4) is formed by the ion implantation method.
After doping phosphorus [P] with a high concentration of ³ to 5 × 10 ²⁰ (cm ^-3 ), heat treatment is performed at 600 ° C. for 16 hours in a nitrogen atmosphere to form a first a-Si film (4). Is crystallized to form a first single crystal Si thin film (5).

Here, since the first a-Si film (4) is heavily doped, the solid phase growth distance changes according to the heat treatment time as shown by the solid line in FIG. The heat treatment time that maximizes the growth distance is set to 16 hours, and the solid-phase growth distance at this time is about 30 μm. The saturated region in FIG. 3 is a region where polycrystallization occurs.

Next, as shown in FIG. 2 (b), the Si thin film (5) is removed by etching, leaving the band-shaped Si thin film (5) on the groove (3) and parallel to the groove (3). As shown in FIG. 1, Si thin film (5) on the SiO ₂ film (2) and remaining
An undoped second amorphous Si thin film (hereinafter referred to as the second a-
Si film) is formed, and the second a-Si film is subjected to heat treatment at 600 ° C. for 8 hours in a nitrogen atmosphere.
The a-Si film of 1 is crystallized to form a second single crystal Si thin film (6), and then the Si thin film (6) is flattened,
The single crystal Si thin films (5) and (6) are formed on the SiO ₂ film (2) to form the SOI film (7).

By the way, when the non-doped second a-Si film is single-crystallized, the high-doped single-crystal Si on the groove (3) and on the strip portion is used.
As single crystallization progresses using the thin film (5) as a seed, the solid phase growth distance changes according to the heat treatment time as shown by the one-dot chain line in Fig. 3, and the maximum growth distance is 600 ° C for 8 hours. About 8 by heat treatment
.mu.m, which is almost twice as large as that of the conventional 4-5 .mu.m.

At this time, single crystallization of the second a-Si film progresses from both sides in parallel with the Si thin film (5) on the groove (3) and the Si thin film (5) in the band-shaped portion, and therefore, in FIG. The groove (3), as shown by the dashed line
A crystal sub-grain boundary (8) is formed in a straight line parallel to the groove (3) at a substantially intermediate position between the sub-grain boundary and the strip portion, and the sub-grain boundary (8) does not have a complicated pattern as in the conventional case.

The layout of the gate (G), drain (D), and source (S) when forming a MOS transistor on the obtained SOI film (7) is as shown in FIG.
A MOS transistor (9) is formed in the vicinity of the first single crystal Si thin film (5) in the band-shaped portion with the direction perpendicular to the band-shaped portion as a long direction, and the p-MOS transistor (10) is formed in the groove (3). The channel may be formed in the vicinity of the first single crystal Si thin film (5) in parallel with the groove, and the channel may be formed while avoiding the crystal sub-grain boundary (8) in the middle of the groove (3) and the band portion. With such an arrangement
The device formation region of the SOI film (7) can be effectively used.

At this time, the source contact region (Cs) of the n-MOS transistor (9) is a highly doped first single crystal of the band-shaped portion.
It is formed on the Si thin film (5) to reduce the source contact resistance.

Therefore, according to the above embodiment, the undoped second a
Since the highly doped first single crystal Si thin film (5) on the groove (3) and the band portion is used as a seed when the -Si film is single-crystallized, the solid phase growth distance of the second a-Si film is It is possible to greatly expand the size compared to the conventional one, and the crystal grain boundary does not have a complicated pattern as in the conventional one, and the effective area for the device shape can be expanded.

In addition, in the above-described embodiment, the case of forming the single crystal Si thin film has been described, but the present invention is not limited to this.

〔The invention's effect〕

Since the present invention is configured as described above,
The following effects are obtained.

Since the second amorphous semiconductor thin film is single-crystallized by using the high-doped single crystal semiconductor thin film remaining on the groove and the strip portion as a seed, the solid-phase growth distance of the non-doped second amorphous semiconductor thin film is set to Can be greatly expanded, and the crystal sub-grain boundary is formed in a straight line parallel to the groove at an almost intermediate position between the groove and the band-shaped portion. It is possible to expand an effective area for forming a device without forming a pattern, which is very advantageous in obtaining an SOI film having a large effective area for a device.

[Brief description of the drawings]

The drawings show one embodiment of the method for forming a single crystal semiconductor thin film of the present invention. FIG. 1 is a perspective view of a state in which a single crystal semiconductor thin film is formed, and FIGS. 2 (a) and 2 (b) are in the process of being formed. 3 is a perspective view of FIG. 3, FIG. 3 is a relationship diagram between a heat treatment time and a solid phase growth distance, and FIG. 4 is a plan view showing a device arrangement pattern. (1) ... Single-crystal Si substrate, (2) ... SiO ₂ film, (3) ...
… Grooves, (5), (6) …… First and second single crystal Si thin films.

Claims (1)

(57) [Claims] 1. An insulating film is formed on a single crystal semiconductor substrate, a groove in which the substrate is exposed is formed in the insulating film, and a first amorphous semiconductor thin film is formed on the insulating film and the groove. After doping the first amorphous semiconductor thin film with a high concentration of impurities, the first amorphous semiconductor thin film is monocrystallized to form a single crystal semiconductor thin film, and the single crystal semiconductor thin film is formed on the groove and the groove by etching. The single crystal semiconductor thin film is removed leaving parallel strips, a non-doped second amorphous semiconductor thin film is formed on the insulating film and the remaining single crystal semiconductor thin film, and the second amorphous is formed. A method for forming a single crystal semiconductor thin film, which comprises crystallizing a thin semiconductor film.