JPH081891B2 - Method for recrystallizing semiconductor film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] When a polycrystalline silicon film is irradiated with a laser beam and a part of the film in the film thickness direction is melted, it usually occurs on the film surface when the entire film thickness is melted. Taking advantage of the fact that irregularities with a period of several tens of μm do not appear, the polycrystalline silicon film is melted in advance from its surface to a depth of about 1/2 of the film thickness, and then a cap layer is formed on the surface to form the entire film thickness. By melting, a silicon film having a smooth surface is obtained.

[Industrial applications]

The present invention relates to a method for manufacturing a semiconductor device having an SOI (Silicon-on-Insulator) structure.

[Conventional technology]

When polycrystal silicon deposited on an insulator is recrystallized by irradiation with an energy ray such as a laser beam to enlarge crystal grains, unevenness of a few tens of μm cycle generated in the recrystallized silicon film is prevented. For this purpose, it is effective to provide a cap layer made of silicon dioxide (SiO2) on the surface.

[Problems to be solved by the invention]

On the other hand, on the surface of the polycrystalline silicon film as it is formed on the insulator, there are minute irregularities corresponding to the columnar crystals forming the polycrystalline silicon film. Therefore, the fine irregularities are preserved as they are on the surface of the recrystallized silicon film in contact with the cap layer formed thereon.
The size of this minute unevenness is about 200 to 300Å in the height direction,
The horizontal period is about 0.1 μm corresponding to the grain size. Even if an element such as a transistor is formed on the recrystallized film while leaving such unevenness, there is a problem that an element having desired characteristics cannot be obtained.

[Means for solving problems]

The inventors of the present invention did not melt the entire polycrystalline silicon film having a cap layer provided in the film thickness direction by irradiating it with a laser beam and left the layer in contact with the underlying insulator as non-melted. In other words, it was found that no large unevenness having a period of about several tens of μm, which occurs when melted over the entire film thickness, appears. On the other hand, the unevenness smaller than this, which is caused by the columnar crystal structure of the polycrystalline silicon film, disappears due to this melting because the cap layer is not provided.

Therefore, the problem in the structure of the conventional SOI structure transistor as described above is that the manufacturing method of the present invention utilizing the above-mentioned finding, that is, the surface of the polycrystalline silicon film formed on the insulator is irradiated with a laser beam. Then, a step of melting from the surface to a predetermined depth smaller than the film thickness, a step of forming a cap layer made of an insulating film on the surface of the silicon film which is solidified after the melting, and a polycrystal having the cap layer formed And a laser beam is applied to the surface of the silicon film to melt the silicon film over its entire thickness.

[Action]

In recrystallizing a polycrystalline semiconductor film in the manufacture of a semiconductor device having an SOI structure, the polycrystalline semiconductor film is irradiated with an energy beam to melt it to a predetermined depth, and then a cap layer is formed on this surface. After that, the polycrystalline semiconductor film is melted and recrystallized over the entire film thickness to obtain a semiconductor film having a smooth surface.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

1 (a) to 1 (d) are cross-sectional views showing steps of a method for recrystallizing a polycrystalline semiconductor film according to the present invention. As shown in FIG. 3A, an insulating layer 2 made of, for example, SiO 2 and having a thickness of about 1.0 μm is formed on the surface of a substrate 1 such as a silicon wafer by a method such as thermal oxidation.

As shown in FIG. 1B, a polycrystalline silicon film 3 having a thickness of about 0.5 μm is formed on the insulating layer 2 by using, for example, a normal chemical vapor deposition method (CVD). At this time, the surface of the polycrystalline silicon film 3 has minute irregularities 30 of about 200 to 300 Å.

As shown in FIG. 1 (c), the surface of the polycrystalline silicon film 3 is irradiated with an energy beam 4 having a relatively low energy such as an Alcon laser having an output of about 4 watts. With this energy, the polycrystalline silicon film 3 has a predetermined depth from its surface smaller than the film thickness, for example, 0.2 μm of the drug.
To the extent melted. In the figure, reference numeral 31 is the polycrystalline silicon film 3 being melted by the irradiation of the energy beam 4.
Indicates the part. The energy beam 4 is scanned in the direction of arrow A, and the surface of the polycrystalline silicon film 3 is flattened in the scanned region. Numerical examples of the scanning pitch of the energy beam 4 and the diameter of the melted portion due to this are 10 μm and 15 μm, respectively.

Due to the partial melting in the film thickness direction, the relatively large irregularities of several tens of μm cycle that occur when the entire film thickness is melted do not appear because the molten silicon is well wetted with the solid silicon. It is considered that the lateral movement of the is suppressed. On the other hand, it is due to the surface tension acting on the surface of the molten silicon that the fine irregularities that existed before the partial melting disappear.

As described above, a predetermined region is melted by the scanning of the energy beam 4, and as a result, the flattened polycrystalline silicon film 3 is provided with a thickness of 300 Å, respectively, as shown in FIG. 1 (d). The SiO2 layer 5 and the silicon nitride (S
i3N4) layer 6 is formed. These formation methods are
You can use D. The SiO2 layer 5 and the Si3N4 layer 6 form not only a cap layer but also an antireflection film for a laser beam described later.

The surface of the polycrystalline silicon film 3 on which the cap layer is formed as described above is irradiated with an energy beam 7 having a relatively high energy, such as an argon laser having an output of about 8 watts. This energy is sufficient to melt the polycrystalline silicon film throughout its thickness. In FIG. 1 (d), reference numeral 32 indicates a portion of the polycrystalline silicon film 3 which is being melted by the irradiation of the energy beam 7.
The energy beam 7 is scanned in the direction of arrow A, for example, to recrystallize a predetermined region of the polycrystalline silicon film 3 in sequence. Numerical examples of the diameter of the scanning bitch and the melting part of the energy beam 7 are 30 μm and 40 μm, respectively.

〔The invention's effect〕

According to the present invention, in a recrystallized silicon film used for a transistor having an SOI structure, it is possible to suppress the occurrence of both minute irregularities with a pitch of about 0.1 μm and irregularities with a large period of about 2 to 40 μm. There is an effect that a high-performance transistor can be manufactured with a high yield.

[Brief description of drawings]

1 (a) to 1 (d) are cross-sectional views showing steps of a method for recrystallizing a polycrystalline semiconductor film according to the present invention. In the figure, 1 is a substrate, 2 is an insulating layer, 3 is a polycrystalline silicon film, 4
And 7 are energy beams, 5 is SiO2 layer, 6 is Si3N4 layer, 30
Is a minute unevenness, and 31 and 32 are molten portions.

Claims (3)

[Claims] 1. A step of irradiating the surface of a semiconductor film formed on an insulator with an energy beam to melt the surface of the semiconductor film to a predetermined depth smaller than the film thickness, and the step of melting and solidifying the semiconductor film. A semiconductor comprising: a step of forming an insulating film on the surface; and a step of irradiating the surface on which the insulating film is formed with an energy beam to melt the semiconductor film over its entire thickness. Membrane recrystallization method. 2. The method for recrystallizing a semiconductor film according to claim 1, wherein the semiconductor film is a silicon film. 3. The recrystallization of the semiconductor film according to claim 2, wherein the insulating film is a single layer or a multilayer film including a silicon dioxide film which is in contact with at least the surface of the semiconductor film. Method.