JPH01115117A - Beam uniformized optical device - Google Patents

Abstract

PURPOSE:To uniformize the intensity distribution of beams by branching laser beams into two optical paths by a first beam splitter, mounting an optical system, sectional intensity distribution of which is weakened and increased in the periphery, to one optical path, collecting these optical paths and optical system by a second beam splitter and obtaining parallel beams having uniform intensity distribution. CONSTITUTION:Circularly polarized parallel monochromatic beams are passed through a first beam splitter 81, and one of beams emitted branched into two optical paths from the first beam splitter 81 is passed through optical systems 91, 92 constituted so that sectional intensity distribution is weakened at the center and increased in the periphery. Beams emitted branched to the other optical path from the first beam splitter 81 and beams emitted from the optical systems 91, 92 are passed through a second beam splitter 82, and parallel beams having uniform intensity distribution are acquired from the second beam splitter 82. Accordingly, the intensity distribution of parallel laser beams projected from a device is brought close, and the displacement of a surface applied to a sample is reduced even when the intensity distribution of original laser beams is displaced from Gaussian distribution.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an improvement in an optical device for irradiating a beam such as a laser in a single-crystal thin film forming apparatus used in the field of manufacturing semiconductor devices. This invention relates to the improvement of optical equipment in a single crystal thin film forming apparatus by irradiating a CW laser onto a non-single crystal silicon thin film such as amorphous or polycrystalline silicon formed on an amorphous base to melt the non-single crystal silicon thin film. be.

Conventional technology: Conventionally, an amorphous or polycrystalline non-monocrystalline silicon thin film is formed on an insulating film that does not have any crystallinity, and this non-monocrystalline silicon thin film is irradiated with an energy beam. A method (so-called 5OI (
Silicon on Insulator technology) has been proposed.

A conventionally proposed method is to form an insulating film 12 on a silicon substrate 11 as shown in FIG. 5(a),
Further, after forming an amorphous or polycrystalline non-single-crystal silicon thin film 13 thereon, irradiation with a laser beam having a Gaussian distribution or heating 15 with a heater or lamp is performed as shown in FIG. 5(b). A single crystallized film 14 is obtained. However, the crystal grain size of the silicon single crystallized film 14 obtained by this method is not large, and even if a transistor is formed in this film, it does not exhibit good operating characteristics.

Therefore, the non-single crystal silicon thin film 1 shown in FIG.
By forming an insulating film [6] on 3 and selectively forming a non-single-crystal silicon thin film 17 on top of the insulating film 6, the reflectance of the laser beam is periodically changed, and a Gaussian distribution is formed on the film. By scanning the laser beam 15 in the direction of the arrow, the non-single-crystal silicon thin film 13 grows crystals with the core directly under the part where the reflectance is maximum.
A single crystal is obtained having a width equal to the distance between the parts where the reflectance is maximum.

<Problems to be solved by the invention> However, in the conventional method described above, when a deviation in intensity from the Gaussian distribution of laser light occurs, which occurs quite frequently, the The phenomenon that the temperature is low becomes incorrect, grain boundaries and crystal defects enter the single crystal part, and a single crystal of the intended size cannot be obtained. For this reason, there were problems such as a transistor fabricated in this portion accidentally malfunctioning.

The present invention was devised in view of the above points, and even with frequent changes in the intensity distribution of the laser, the changes in the intensity distribution of the laser irradiated onto the sample are alleviated to a certain extent.
The purpose of the present invention is to provide a beam uniformizing optical device suitable for use in forming a single crystal thin film that enables recrystallization with a laser beam having a -like intensity distribution. 〉 In order to achieve the above object, the beam homogenizing optical device of the present invention passes circularly polarized, t-parallel monochromatic light through a first beam spitter, and branches it into two optical paths from this first beam spitter. One of the emitted lights is configured so that the cross-sectional intensity distribution is weak at the center and strong at the periphery, and passed through a constant optical system, and the light is branched into the other optical path of the above-mentioned il beam spitter and emitted from the above-mentioned optical system. The light emitted from the beam is passed through a second beam spitter, and is configured to obtain parallel light with a more uniform intensity distribution than the second beam spitter.

That is, the beam homogenizing optical device of the present invention, when trying to make the intensity distribution of a cross section of parallel monochromatic light such as a laser beam uniform, can be used to make parallel light that remains parallel even after equalization, but circularly polarized light. Laser light is transmitted through an IL beam splitter such as a birefringent plate.
An optical system (for example, a pair of conical prisms) is inserted into one optical path so that the cross-sectional intensity distribution is weak at the center and strong at the periphery, and then these two optical paths are divided into two optical paths using a birefringent plate, etc. The configuration is such that parallel light with a uniform intensity distribution is obtained by combining the two intensity distributions into one by a second beam splitter and adding them.

In the embodiment of the present invention, as will be described later, parallel laser beams with a diameter of 1 m or more are made to have a uniform intensity distribution, and even after being emitted from the beam shape shaping means, the light path remains parallel. After placing a 1/4 wavelength plate in a part of the optical system, the optical system is split into two optical paths by a birefringent plate, and one optical path has a pair of conical prisms with their tips facing each other. After inserting the laser beam, the intensity distribution is made weaker at the center and stronger at the periphery.After passing through a beam homogenizing optical device that combines these two optical paths into one using a birefringent plate, the laser beam is focused using a converging lens. A single crystal thin film is obtained by irradiating a thin non-single crystal silicon film formed on the surface of a single crystal substrate covered with an insulating film.

That is, in an embodiment of the present invention, a beam homogenizing optical device that combines a 1/4 wavelength plate, a birefringent plate, a pair of conical prisms, and a birefringent plate to form an S is provided in a part of the optical path of the laser beam. The parallel laser light that is emitted has a nearly uniform distribution. ! : When a single crystal silicon thin film is obtained from a non-single crystal silicon thin film, a stable single crystal thin film f: with few grain boundaries and crystal defects is obtained.

Effect> An advantage is to insert a beam homogenizing optical device consisting of a combination of a 1/4 wavelength plate, a birefringent plate, a pair of conical prisms, and a birefringent plate into the optical path of a parallel laser beam with a diameter of 1 cm or more. , the intensity distribution of the parallel laser beam emitted from the device becomes nearly uniform, and even if the intensity distribution of the original laser beam deviates from the Gaussian distribution, the deviation in the distribution of the surface irradiated to the sample will be small. .

Embodiment> Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a single crystal thin film forming apparatus using a beam uniformizing optical device according to an embodiment of the present invention, where l is a laser light source, 2 is a reflecting mirror, 10 is a converging lens, and 3 is a main body. According to the invention, a beam homogenizing optical device is provided in the optical path 4 of the laser, 5 is a thin film sample, 6 is a sample mounting table, and the laser beam irradiated from the laser light source 1 is set on the sample mounting table 6. The light is irradiated onto the thin film sample 5 and scanned.

The thin film of sample 5 was fabricated by a conventionally known method, and had a thin film to be made into a single crystal, consisting of a polycrystalline or amorphous silicon thin film, and was made by depositing SiO2 on a laser conductor single crystal substrate.
It is attached via an insulating thin film such as.

A beam homogenizing optical device 3 for controlling the intensity distribution of the laser beam is provided on the laser optical path 4 between the laser light source l and the converging lens lO, and this beam homogenizing optical device 13 will be described later. The device consists of an I/4 wavelength plate 7, two birefringent plates 81, 82, and a pair of conical prisms 91, 92 in one optical path, and has the L-shaped Gaussian distribution shown in Fig. 2 (a). Figure 2 shows the emitted laser light (
c) The light is converted into light having a uniform intensity distribution as shown in FIG.

Figure 3 shows the basic configuration of the beam homogenizing optical device of the present invention, which divides the laser beam into two optical paths to convert the intensity distribution into a uniform intensity distribution and stores one beam in one optical path. FIG.

In FIG. 3, laser light (incident light) 21, which is a Gaussian type, direct magnetically polarized, parallel, monochromatic light, is passed through a quarter-wave plate 7. By using this quarter wavelength plate 7, the linearly polarized laser light 21 can be changed into circularly polarized light.

The laser beam exiting the quarter-wave plate 7 is passed through a birefringent plate 8I, which is a first beam splitter, and the light on one optical path is split into two optical paths 18 and 19. Also, optical path 19
Inside is a pair of conical prisms 91, as shown in FIG.
92 are arranged with their tips facing each other so that the cross-sectional intensity distribution is weak in the center and strong in the periphery, and an optical system is inserted.Then, the light in the two optical paths 18 and 19 is Birefringent plate 82 constituting the second beam splitter
The light passes through 9, is combined into one light, and is emitted as one optical path F output light 22. In this way, the birefringent plate 82
By mixing the light with a Gaussian distribution on the optical path 18 shown in FIG. 2(a) and the light with a concave center emerging from the optical system (91°92) shown in FIG. 2(b), By adding up the two intensity distributions, one parallel beam having a uniform distribution as shown in FIG. 2(c) can be obtained.

It is possible to configure the laser beam homogenizing optical device 3 in the above manner, or to arrange a plurality of laser beam homogenizing optical devices 3 in series in the optical path in order to further increase the uniformity. Figure 2 (c)
), it is possible to obtain a laser beam having a near-uniform intensity distribution, and as a result, in the structure shown in FIG. 1, a single crystallized film that is less likely to have grain boundaries or crystal defects can be obtained.

<Effects of the Invention> As described above, according to the present invention, even if the laser beam has not only a Gaussian distribution but also a neat distribution, it is possible to always generate a laser beam with a nearly uniform distribution. Since the sample can be irradiated with irradiation, it can be used when converting non-single crystal silicon films into single crystals to obtain stable single crystal silicon thin films with few grain boundaries and crystal defects.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the entire configuration of a single-crystal thin film forming apparatus using a beam-uniforming optical device according to an embodiment of the present invention, and FIG.
a) is a diagram showing the laser light intensity distribution of the original optical path 4 and the first optical path 18, FIG. Figure 3 shows a structural example of the beam homogenizing optical device according to the present invention; Figure 4 shows the shape and arrangement of a pair of conical prisms in detail. 5(a), 5(b), and 6 are detailed diagrams each illustrating a conventional method for forming a single crystal thin film. 1...Laser light source, 2...Reflecting mirror, 3...
Beam homogenizing optical device, 4... Laser optical path, 5.
... Thin film sample, 6... Sample mounting table, 7... Quarter wavelength plate, 81°82... Birefringent plate, 91.92... Conical prism, 10... Converging lens, 18 ...1st optical path, 19...2nd optical path〇 Agent Patent attorney Takeshi Sugiyama (1 other person) Figure 1

Claims (1)

[Scope of Claims] 1. Pass circularly polarized parallel monochromatic light through a first beam spitter, and send one of the lights that are split into two optical paths and exit from the first beam spitter so that the cross-sectional intensity distribution is at the center. The light is transmitted to an optical system configured to be weak at the edges and strong at the periphery, and the light branched to the other optical path of the first beam spitter and the light output from the optical system are passed through the second beam spitter. . A beam homogenizing optical device, characterized in that the second beam spitter is configured to obtain parallel light with a uniform intensity distribution.