JPH0793260B2 - Single crystal thin film forming equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement of a single crystal thin film forming apparatus used in the field of manufacturing a semiconductor device, and more specifically, to an amorphous film formed on an amorphous underlayer. The present invention relates to an apparatus for irradiating a non-single-crystal silicon thin film of high quality or polycrystal with CW laser light to melt the non-single-crystal silicon thin film to single crystal.

<Prior art> Amorphous or polycrystalline non-single-crystal silicon thin film is formed on an insulating film that is not crystalline, and the non-single-crystal silicon thin film is irradiated with an energy beam or a heater lamp, etc. A method for producing a single crystal thin film by heating and melting and recrystallizing it (so-called SOI (Silic
on on Insulator) technology) has been proposed.

As a conventionally proposed method, an insulating film 12 is formed on a silicon substrate 11 as shown in FIG. 6 (a), and an amorphous or polycrystalline non-single-crystal silicon thin film is further formed thereon.
After forming 13, the single crystallized film 14 is obtained by irradiating a laser beam having a Gaussian distribution or heating 15 by a heater or a lamp as shown in FIG. 6 (b).

However, the size of the crystal grains of the silicon single crystal film 14 obtained by this method is not large, and even if a transistor is formed in this film, good operating characteristics are not exhibited.

Therefore, as shown in FIG. 7, the insulating film 16 is formed on the non-single-crystal silicon thin film 13, and the non-single-crystal silicon thin film 17 is selectively formed on the insulating film 16 to improve the reflectance of the laser beam. By scanning a laser beam 15 having a Gaussian distribution in the direction of the arrow on the periodically changed one, the non-single crystal silicon thin film 13 grows as a nucleus immediately below the portion where the reflectance is maximum. As a result, a single crystal having a width of the portion having the maximum reflectance can be obtained.

<Problems to be solved by the invention> However, in the above-mentioned conventional method, when the deviation of the intensity from the Gaussian distribution of the laser beam occurs frequently, the temperature directly below the part where the reflectance is maximum is The phenomenon of lowness does not occur correctly, and grain boundaries and crystal defects are included in the single crystal portion, and a single crystal of an intended size cannot be obtained. Therefore, there is a problem that the transistor formed in this portion happens to malfunction.

The present invention has been devised in view of the above points, and the intensity distribution of the laser irradiated on the sample is relaxed to some extent even with frequent changes in the intensity distribution of the laser, and has a uniform intensity distribution. It is an object of the present invention to provide a single crystal thin film forming apparatus which enables recrystallization by laser light.

<Means for Solving the Problems> In order to achieve the above object, the present invention forms an insulating film and a first non-single-crystal silicon thin film on a single-crystal substrate, and further, the first non-single-crystal. A second non-single-crystal silicon thin film is selectively formed on the silicon thin film in the scanning direction of the laser beam through the insulating film, and the laser beam is irradiated from above the second non-single-crystal silicon thin film. In a single crystal thin film forming apparatus for melting and recrystallizing a first non-single crystal silicon thin film, in the optical path of the laser beam so that the light condensed in a circle having a diameter of 50 to 300 μm has a uniform intensity distribution, The first optical means is composed of a single convex lens, a central convex lens, and six convex lenses arranged around the convex lens. The six convex lenses are arranged so as to be perpendicular to the optical path of the light incident on the center thereof. Tilt and juxtaposed The light from the first optical means is configured to provide a second beam shape forming means combining optical means consisting of a lens group which is adapted to enter into the convex lenses.

That is, according to the present invention, a beam shape shaping means composed of a plurality of convex lenses is provided in a part of the irradiation optical path of the laser light so that the laser light irradiated to the sample has a nearly uniform distribution,
When a single crystal silicon thin film is obtained from a non-single crystal silicon thin film, a single crystal thin film that is stable and has few grain boundaries and crystal defects is obtained.

<Operation> By irradiating the sample with a beam shape shaping means that combines one convex lens and a lens group in which a plurality of convex lenses are juxtaposed to match the optical path in the optical path of a parallel laser beam with a diameter of about 30 mm, the sample is irradiated. The intensity distribution of the laser light on the surface is almost uniform, and even if the intensity distribution of the original laser light deviates from the Gaussian distribution, the deviation of the distribution of the surface irradiated on the sample becomes small.

Therefore, the phenomenon that the temperature immediately below the portion of the first non-single-crystal silicon thin film where the reflectance of the laser beam reflected by the second non-single-crystal silicon thin film is maximum is always low occurs correctly, and the intended size is increased. Can be obtained.

<Embodiment> An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a single crystal thin film forming apparatus according to an embodiment of the present invention, in which 1 is a laser light source, 2 is a reflection mirror,
3 is a beam shape shaping means provided in the optical path 4 of the laser according to the present invention, 5 is a thin film sample, 6 is a sample mounting table, and the laser light emitted from the laser light source 1 is set on the sample mounting table 6. The thin film sample 5 thus formed is irradiated and scanned. Thin film of the sample 5 has a polycrystalline or thin film to be a single crystal made of an amorphous silicon thin film which is produced by a conventionally known method, SiO ₂ on a silicon single crystal substrate
Is deposited through an insulating thin film such as.

On the laser light path 4 between the laser light source 1 and the sample 5, beam shape shaping means 3 for controlling the intensity distribution of the laser light is provided. As will be described later, the beam shape shaping means 3 is configured by combining a first optical means 7 composed of one convex lens and a second optical means 8 formed by arranging a plurality of convex lenses so as to match the optical path of the laser. The laser light emitted with the Gaussian distribution shown in FIG. 2 (a) is changed into a uniform intensity distribution as shown in FIG. 2 (b).

3 and 4 are the second for converting to the above intensity distribution.
It is a figure which shows the detailed structure of the optical means 8 and the 1st optical means 7 of this.

FIGS. 3 (a) and 3 (b) respectively show the second optical means 8 composed of seven convex lenses 81 to 87 which are the core of the present invention.
3A and 3B are a plan view and a cross-sectional view showing the detailed configuration of FIG. The second optical means 8 forms the beam shape shaping means 3 in combination with the first optical means 7 consisting of a single convex lens 71 shown in FIGS. As shown in FIGS. (A) and (b), out of the seven lenses 81 to 87, the outer six lenses 81 to 86 are the convex lenses 71 shown in FIGS. 4 (a) and (b). The laser beams that have passed through are aligned side by side so as to be perpendicular to the main axis of the optical section, in line with the optical path that focuses the light toward the inside.

Also, the seven lenses shown in FIGS. 3 (a) and 3 (b) above.
The focal lengths 81 to 87 are, as shown in FIG. 5, a diameter l after the laser light passing through the beam shaping means 3 is focused.
Is designed so that the beams of all seven lenses 81 to 88 overlap when the beam diameter becomes about 50 to 300 μm (for example, about 60 μm).

By configuring the laser beam shape shaping means 3 as described above, the intensity of a laser beam having a Gaussian distribution shown in FIG. 2 (a) or a distribution close thereto can be made uniform as shown in FIG. 2 (b). Light having a distribution is obtained, and as a result, single crystallization without grain boundaries or crystal defects is performed.

<Effects of the Invention> As described above, according to the present invention, it is possible to irradiate a sample with a laser beam having a nearly uniform distribution, even if the laser beam has a Gaussian distribution and a distribution deviating from the Gaussian distribution. Therefore, when the non-single-crystal silicon film is single-crystallized, crystal grains having larger crystal grains than those in the conventional case can be obtained. Further, when the beam shaping means according to the present invention is used, the light having a Gaussian distribution whose minimum value is 6% of the maximum value becomes a beam having a diameter of 50 to 300 μm with a uniformity of 7.5% or less. Light with a planar distribution whose value is 50% of the maximum is 15
%, The beam with a diameter of 50 to 300 μm has uniformity, so even if the intensity distribution of the laser light deviates from the Gaussian distribution, the deviation of the intensity distribution of the surface irradiated on the sample will be small. A single crystal silicon thin film that is stable and has few grain boundaries and crystal defects can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of the present invention, and FIG.
FIGS. 3A and 3B are diagrams showing laser light intensity distributions having a Gaussian shape and a uniform shape, respectively, and FIGS. 3A and 3B are concrete configuration examples of the second optical means in the present invention. And FIG. 4 (a) and FIG. 4 (b) are plan views and sectional views, respectively, showing a concrete configuration example of the first optical means in the present invention, and FIG. FIGS. 6 (a), 6 (b) and 7 show the focal length of the lens forming the beam shape shaping means in the example, and FIGS. 6 (a), 6 (b) and 7 are views for explaining the conventional single crystal thin film forming method. 1 ... Laser light source, 2 ... Reflection mirror, 3 ... Beam shape shaping means, 4 ... Laser optical path, 5 ... Thin film sample, 6 ... Sample mounting table, 7 ... First optical means, 8 ......
Second optical means, 11 ... Silicon substrate, 12 ... Insulating film,
13 …… Non-single crystal silicon thin film, 14 …… Single crystal silicon thin film.

Claims (1)

[Claims] 1. An insulating film and a first non-single-crystal silicon thin film are formed on a single crystal substrate, and the insulating film is further formed on the first non-single-crystal silicon thin film in the scanning direction of a laser beam. A single crystal in which a second non-single-crystal silicon thin film is selectively formed, and a laser beam is irradiated from above the second non-single-crystal silicon thin film to melt and recrystallize the first non-single-crystal silicon thin film. In the thin film forming apparatus, the first optical means consisting of one convex lens and the central convex lens are provided in the optical path of the laser beam so that the light condensed in a circle having a diameter of 50 to 300 μm has a uniform intensity distribution. It consists of 6 convex lenses arranged around the convex lens, and these 6 convex lenses are juxtaposed so as to be perpendicular to the optical path of the light incident on the center thereof, and the light from the first optical means is It enters the convex lens The lenses single crystal thin film forming apparatus characterized by comprising providing a beam shape forming means combining the second optical means consisting of a group.