JPH02187017A - Formation of semiconductor layer into single crystal - Google Patents

Abstract

PURPOSE:To adjust a distance between both light beams and the intensity and spreading of each light beam by splitting laser light through a beam splitter(BS) into the two light beams, reflecting the respective light beams on a reflecting surface with a relative displacement of a fine angle, and irradiating a semiconductor layer through a second BS. CONSTITUTION:Laser light 11 emitted from a laser oscillator 10 in the Y- direction is reflected on a mirror M1 in the X-direction and splitted through a BS 12 through a lambda/2 plate 14 into X- and Y-direction light beams. The vertically polarized X-direction emitted light is reflected by mirrors M2-1, M2-2, M2-3 and is incident upon a second BS 13. On the other hand, the horizontally polarized Y-direction emitted light is reflected by mirrors M3-1, M3-2, M3-3 and is incident upon the BS 13. The emitted light combined through the BS 13 is reflected by a mirror M4, with which a unsingle crystal semiconductor layer is irradiated through a lens 15 and made a single crystal.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to shaping the cross-sectional shape of a laser beam used for single crystallization of a poly-Si layer, and aims to avoid changes in the shape of the irradiated beam due to vibrations, etc. A method for single-crystallizing a semiconductor layer is to split a laser beam output from one light source into two by a first beam splitter, and each optical path is composed of the same number of reflecting surfaces, having approximately equal distances, and with relative polarization planes. maintains the relationship,
By making a pair of reflective surfaces in one of the optical paths have a slight angle deviation, the combined cross-sectional shape of the two beams made parallel by the second beam splitter is made into a desired shape;
The method includes a process of sweepingly irradiating the non-single crystal semiconductor layer with the combined light flux.

[Industrial application field]

The present invention relates to the formation of a so-called SOI substrate in which a single crystal semiconductor layer is provided on an insulating substrate, and in particular SfO.

This process involves single crystallization of poly-Si deposited on a surface by laser irradiation.

! @ If a substrate provided with a single crystal semiconductor layer on edge material is used to form an integrated circuit (IC), no treatment is required to insulate between the various elements constituting the IC and the substrate.
Many advantages can be obtained, such as simplification of isolation between elements, resulting in higher integration, and higher performance of elements due to reduction in parasitic capacitance.

This type of substrate is SOI (semiconductor
For technical or economical reasons, the most commonly used type is one in which a SiO2 film is provided on the surface of a Sil board and a single crystal Si layer is provided thereon.

The Si/5iO7/Si type SOI substrate is produced by thermally oxidizing the surface of a single-crystalline (or polycrystalline) St wafer to form a SiO□ film, and then depositing polycrystalline Si (or amorphous Si, hereinafter generally referred to as polySt
It is formed by depositing a poly-Si layer (denoted as ) and single-crystallizing this poly-Si layer.

In the single crystallization process at that time, the poly-Si layer is once melted and then crystallized again to form a single crystal, but in order to avoid deformation of the St wafer that is the support, the poly-Si layer is gradually partially removed. Usually, it is melted and recrystallized.

In addition, high-energy beams such as laser beams are used to melt poly-St, and poly-Si is successively made into single crystals while being irradiated in a sweeping manner. However, when the molten St solidifies again, it is already In order to inherit the crystal orientation of the fused region and crystallize it, the temperature distribution of the molten region or the cross-sectional shape of the laser beam must satisfy the following conditions.

When a Si layer is irradiated with a normal laser beam to partially melt it, the temperature is highest at the center and lowest at the periphery. When the laser beam irradiation area is swept in this state, crystallization starts from the periphery, which is the lowest temperature region, and since the periphery is in contact with the polycrystalline region, many coarse crystal grains with different orientations are formed. easy to become

In order to avoid this situation and preferentially grow the single crystal region, it is necessary to lower the temperature in the center of the molten region, where single crystal growth progresses, and raise the temperature in the regions near the periphery. be. Therefore, as a means to realize such a temperature distribution, ■ make the energy distribution of the laser beam multimodal;
A method is known in which a light shielding film or an interference film is selectively provided on the poly-SiN surface to differentiate the amount of energy absorbed.

[Prior Art and Problems to be Solved by the Invention] Although the present invention relates to the multimodal laser beam described in (1) above, the intended energy distribution shape does not have to be concentric circles;
It is important that the energy distribution in the direction perpendicular to the sweep direction, that is, the temperature distribution of the molten St, be bimodal or multimodal.

An immediately conceivable method for realizing a bimodal energy distribution in a specific direction is to use two laser beams and irradiate the beam with their centers slightly shifted. More specifically, the laser beams output from two laser light sources are guided to adjacent points on poly-Si via independent optical paths, but in laser recrystallization treatment, the laser beams output from two laser light sources are guided to close points on poly-Si. Blur can lead to undesirable results, and by using two independent light sources and optical paths, the effects of blur can be doubled.

In order to avoid such problems, it is also known to obtain two beams of light using a single light source. For example, by passing a crystal birefringent plate, one laser beam can be made into two parallel beams of light. . If most of the optical path including the light source and sweeping operation is shared in this way, the negative effects of vibration can be reduced, but in order for this effect to be noticeable, the poly-Si layer must be decomposed immediately before irradiation, which requires energy consumption. The bimodal characteristic of the distribution is fixed by the birefringence plate, and there is no room to adjust the distance between the light beams, the intensity of each light beam, the spread, etc.

The purpose of the present invention is to divide a laser beam output from a single light source into parallel beams with almost no deviation due to vibration, etc. It is an object of the present invention to provide a light beam splitting method that can arbitrarily adjust such factors, and thereby to provide a processing method for converting a non-single crystal semiconductor layer into a single crystal.

For details of the above-mentioned conventional technology, please refer to, for example, Chapter 3.1 of "RSOI Structure Formation Technology" edited by Nibe Furukawa (Sangyo Tosho, 1987).

[Means to solve the problem]

In order to achieve the above object, the laser beam used in the laser recrystallization process of the present invention is such that the laser beam output from one light source is divided into two by a first beam splitter, and each optical path has a substantially equal distance. In addition, the relative relationship of polarization angles is maintained, and the two beams are made parallel by the second beam splitter by a method such as giving a minute angle deviation to a pair of reflecting surfaces in one of the optical paths. The optical axis of the light beam is shifted to give a desired composite cross-sectional shape.

[For production]

FIG. 1 is a principle diagram illustrating that the optical path division method according to the present invention is not easily affected by vibrations.

As shown by the solid line in FIG. 2(a), the input light 1 is separated by the beam splitter 2 into two beams with polarization planes perpendicular to each other, each reflected by the total reflection surface 4 or 5, and then transmitted to the second beam. The beam enters the beam splitter 3. Since the polarization conditions of both light beams remain the same and the optical path lengths are the same, both light beams are combined by the beam splitter, resulting in 2
The output lights 6 of the book are parallel to each other.

If we consider here a state in which the input lights are deviated from each other while being parallel, the input lights follow the optical path shown by the dotted line, so the situation in which the combined output lights are parallel to each other does not change. Furthermore, considering a state in which the input light is slightly tilted, the two combined output lights are kept parallel in this case as well, as shown by the dotted line in FIG. 1(b).

In other words, as long as the relative relationship of the polarization angles between the two light beams divided as shown in Figure 1 does not change, the optical path environment determined by the optical elements such as the beam splitter and reflective surface will be relative to each other. Unless the light changes to , it will be synthesized and return to the original luminous flux.

Next, consider a case in which more reflective surfaces are provided in the separated optical paths. FIG. 2 is also a diagram for explaining the present invention in detail, but here, each optical path has 4-1.4-2.4 reflecting surfaces.
~3, 5-1, 5-2, 5-3 are provided.

If all of the above reflecting surfaces are parallel to the reflecting surface of beam splitter 2 or 3, as shown by the solid line in FIG.
As in the case of FIG. 1, the light beams are combined into one beam and output.

Now, if we consider the case where reflective surfaces 5-2 and 5-3 are rotated by a small angle Δθ while keeping them parallel to each other, the light flux passing through the optical path including the reflective surfaces will be shifted by Δd from the original output position. The light is output from a shifted position and in a direction parallel to the original output light.

This condition is shown in FIG. 2 by dotted lines. If the reflective surface is rotated, a slight difference will occur in the optical path length, but this is a negligible value, and the reflective surface 4-1.4-2.
Luminous flux passing through 4-3 and reflecting surface 5-1.52.5-3
The light flux passing through is output as two parallel light fluxes having an interval of Δd.

As is clear from Figures 1 and 2, the optical path length of each divided optical path can be set as necessary, so it is possible to vary the interval between output lights or adjust the intensity and cross-sectional shape of each. Means can be provided.

According to the present invention, it is easy to make the energy distribution of laser light suitable for crystallization between semiconductor layers, and it is less affected by external disturbances such as vibrations.

〔Example〕

An embodiment of the invention is shown in FIG. The following description will be given with reference to the drawings.

For example, a laser beam 11 outputted in the Y direction from a laser oscillator 10, which is a multi-mode Ar ion laser, is turned to the X direction by a mirror M1, passes through a λ/2 plate 14, enters the beam splitter 12, and enters the beam splitter 12 in the X direction and -Y direction. is divided into a luminous flux of The λ/2 plate is used to adjust the polarization of input light and the relative intensity of both output lights.

The output light in the X direction, which is vertically polarized light, is turned to the -Y force direction by mirror M2-1, turned to the X direction by mirror M2-2, and then turned again to the -Y force direction by mirror M2-3, and then sent to the second beam splitter 13. Enter.

On the other hand, the output light in the Y force direction, which is horizontally polarized light, is from the mirror M3.
1 in the X direction, mirror M3-2 in the X direction, mirror M3-3 again in the X direction, and input to the second beam splitter 13.

The output light that has been combined into one beam by the beam splitter 13 is turned from the -Y force direction to the -ZX direction by the mirror M4.
The Si layer (not shown) is irradiated via the lens element 5. Here, for example, by rotating the mirrors M2-2 and 1-3 by a small angle while keeping them parallel, the output light in the -2 direction can be converted into two light beams shifted in the Y direction.

50 μm thick deposited on base oxide film (1.0 μm thick)
An example of processing conditions for single-crystallizing a poly-Si layer is as follows. The output of the Ar ion laser is, for example, 5 W, which is divided into two parts and used as a laser beam of 2.5 W each. The diameter of each light beam is 20 μm, the distance between the light beams is 15 μm, and the poly-Si layer is single crystallized at a sweep speed of 150 mm/sec. Set the sweep center line spacing to 35
If the thickness is μm, processing can be performed efficiently without leaving any poly regions.

〔Effect of the invention〕

As explained above, the laser beam used in the present invention has a bimodal energy distribution suitable for single crystallizing a semiconductor layer such as poly-Si, and the energy distribution can be easily changed. Not only that, but it is also less affected by external disturbances such as vibrations, so by sweepingly irradiating the non-single crystal semiconductor layer and turning it into a single crystal,
An SOI substrate suitable for forming semiconductor devices such as integrated circuits can be obtained.

Furthermore, according to the beam splitting method of the present invention, it is also possible to arrange the beam parallel to the sweep direction, and after melting polySt with the main beam, it is also possible to adjust the solidification conditions with the subsequent secondary beam. It is. Regarding such processing, since the invention of the present inventor has been patented as Japanese Patent Application No. 1986-286309, please refer to the specification.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams for explaining the present invention in detail, and FIG. 3 is a schematic diagram showing the configuration of an embodiment. 1 is a beam splitter, 3 is a second beam splitter, 4.4-1.4-2.4-3 is a reflection surface of the first optical path, 5
, 5-1, 5-2.5-3 are reflective surfaces of the second optical path,
6 is an output light, 10 is a laser oscillator, 11 is a laser beam, 12 is a first beam splitter, 13 is a second beam splitter, 14 is a 2/λ plate, 15 is a lens, Ml, M2-1. M2-2. M2-3. M3-
1. M3-2. M3-3. M4 is a mirror.

Claims (1)

[Scope of Claims] A laser beam output from a single light source is split into two beams, a first beam and a second beam, which are orthogonal to each other by a first beam splitter (2), and the first beam splits into a plurality of beams. The second beam is made to reach a second beam splitter (3) through a first optical path constituted by a total reflection surface of, and the second beam is approximately equidistant from the first optical path and The beam reaches the second beam splitter (3) via a second optical path that does not change the relative relationship of the polarization angle between the beam and the beam, and whose optical axis is shifted from that of the first optical path. The two beams are made parallel by a beam splitter.
1. A method for single-crystallizing a semiconductor layer, comprising a process of sweepingly irradiating a non-single-crystal semiconductor layer with a laser beam.