JPS5984423A - Energy radiation equipment - Google Patents

Abstract

PURPOSE:To obtain an energy radiation equipment with a wide light beam by a method wherein a concave or a convex is provided at the center of an optical lens and among the lights passing through the lens, the lights near the center are refracted out of the lens relatively to the lights passing through the circumference and the passing light is made to illuminate the target through a Quonset hut shape lens. CONSTITUTION:A concave 12 or a convex 13 is formed at the center of an optical lens 11 and the light 14 passing through the central part is given relatively large refraction toward the outside of the lens 11. Thus the energy intensity condensed at the center is dispersed to the circumference and the lights passing the lens are gathered at the focus 19 by a conventional convexed lens group or the like to obtain output light with a ring shape output light energy distribution. Moreover, a Quonset hut shape lens 15 is combined with the lens 11 and an oval shape, compressed to one direction, and flat output light energy distribution 17 is obtained near the synthesized focus 16 instead of the conventional Gaussian distribution. With this configuration, an irradiation equipment which does not give thermal damage to the substrate without reducing the output of the laser is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a high-energy beam irradiation used for modifying a surface layer, and particularly to an apparatus used for single crystallization of a semiconductor substrate.

Conventional Structures and Problems There are laser irradiation devices used for modification of metal surfaces, such as hardening, and for semiconductor devices, such as single crystallization of thin film polycrystals.

In such a laser irradiation device, the laser beam is guided through an optical system, and the output light is focused and irradiated onto the sample surface, but the energy distribution 1 generally has a Gaussian distribution as shown in Figure 1 (IL). . When a sample is irradiated with such output light, naturally only the peak position 20 is heated deeply and to a high temperature, and the surrounding area 3 is not heated much.

Therefore, in a beam with the shape shown in Figure 1, the high-temperature part of the beam is narrow (11"), and in order to uniformly heat treat a certain surface, the overlap must be made extremely large and a number of scans must be performed. . For example, in an extreme example of laser annealing for semiconductors, the diameter of the output light is 50 μm or more, but the diameter is shifted by 10 to 20 μm, that is, 60 to 80 μm.
The disadvantage is that the irradiation must be done with a % overlap. Moreover, because the peak is large, it has been pointed out that the substrate is instantaneously heated deep into the substrate, inducing thermal distortion and defects. Therefore, the so-called ring-shaped or donut-shaped output light energy distribution 4 shown in Fig. 2 is caused by this point. It is imagined that it will be excellent. In other words, in Figure 2, the area where the temperature is relatively high (the shaded area) is wide, and uniform heating can be performed over a wide range.The energy distribution shown in Figure 2 causes the laser beam to have a Gaussian distribution. It is known that it can be obtained by changing from multimode to single mode and changing to TEMo+ or TE M+o, but it is very difficult to adjust and the laser output drops to a large [1], for example, 1//F5
It has the disadvantage that it becomes ~1/1o.

Purpose of the Invention The present invention does not cause a decrease in the irradiation energy output of a laser etc., that is, even in a multi-mode laser etc., the IJ is wide.
The present invention provides a light energy irradiation device that realizes output light with uniform energy distribution and irradiates over a wide range without causing thermal distortion deep into the substrate.

Structure of the Invention The present invention uses an optical lens having a concave or convex portion in the center, and out of the light passing through this optical lens, the light passing near the center is relatively smaller than the light passing around the periphery. The light that passes through the optical lens is irradiated onto the object by greatly refracting the light to the outside of the lens, reducing the energy density at the center of the light beam exiting the optical system, and then passing through the semi-cylindrical lens to improve the light energy distribution. is compressed in one direction to make it into an ellipse.

DESCRIPTION OF THE EMBODIMENTS The present invention is achieved by providing a special optical lens in the middle of the optical system. That is, the optical lens used in the present invention has a concave portion 12 or a convex portion 13 in the center of the optical lens 11, as shown in FIG. 3 or 4, so that the light 14 passing through the center is relatively By refracting a large amount outward, the energy intensity concentrated in the center is dispersed to the periphery.
By concentrating the light that has passed through the lens 1 to a focal point using a normal convex lens (group), output light having a ring-shaped output light energy distribution as shown in FIG. 2 is obtained.

In addition to what is shown in FIGS. 3 and 4, this special optical lens 14 may have a conical shape on both sides as shown in FIG. 5, or may have an arcuate conical base as shown in FIG. may be subtracted. The point is that the light at the center of the lens is refracted to the outside more than with a normal concave or convex lens, so it does not need to be focused. Also, even if it is not a curved surface,
A similar effect can be obtained even if the structure is made of a flat surface such as a pentagonal pyramid.

Also, if it is a special convex lens like the one shown in Figure 7 (the concave part is extremely emphasized), a second lens will be placed near the focal point with one lens.
Output light having a light energy distribution as shown in the figure can be obtained.

Furthermore, if the special optical lens 11 illustrated in FIGS. 5 and 6 is combined with the semi-cylindrical lens 15 as shown in FIG. It is possible to realize an output light energy distribution 17 which is not a Gaussian distribution but is compressed in one direction, has an oval shape, and is flat, as shown in FIG. 9, which is preferable for heat treatment. That is, by scanning in the direction of the arrow 18 with such an elliptical laser beam having a relatively uniform energy distribution, the target object can be efficiently irradiated with energy.

Note that the composite focal point 16 shown in FIG.
It is preferable that the focal point 19 be located near the original focal point 19 of the transmitted light indicated by the broken line when there is no 2. The right side view of the lens 15 in FIG. 8 shows the side surface and shows that it has a semicylindrical shape.

The effects of the present invention will be explained using the results of application to a semiconductor element under severe conditions.

A very thick thermal oxide film of 2 μm was formed on a silicon substrate, and a polycrystalline silicon film of 0.5 μm was further formed thereon by LP (low pressure) CVD.

Usually, this polycrystalline silicon is annealed using a conventional laser beam irradiation device shown in FIG. 10 to form a single crystal or a large crystal grain. In FIG. 10, a laser beam 22 from a laser generator 21 is expanded ten times by a magnifier 23, and a mirror 24
The sample is bent at a right angle, apertured with a final lens (a normal convex lens with a focal length of 5 Qm) 25, and applied onto a sample (the substrate on which the polycrystalline silicon is formed) 26.

Using this conventional device, the laser output sW and the scanning speed 1o
At owtr, /S and a substrate temperature of 300°C, polycrystalline silicon with a width of about 20 μm melted and became a large crystal.

In order to further increase the grain size over the entire surface, it was necessary to increase the overlap of scans and send them in the lateral direction at a small pitch of 6 μm. Next, when the substrate was cracked after laser irradiation, it was found that the normal arm opening did not occur, but instead it cracked into shell-shaped pieces and was severely distorted. When the cross section was polished and etched, there were countless defects up to a depth of 5 μm, corresponding to the peak of the laser beam. When the hole 11 was inserted into the dot-dash line in Fig. 10, under the same conditions. However, the melting width increased to about 80 μm.

Therefore, the pitch can be set to 40 μm, which is a large non-electromagnetic method, and the scanning efficiency is improved by 4 to 8 times compared to the conventional method. Moreover, no thermal strain was observed on the substrate, and no defects such as those described above were observed.

Next, as shown in FIG. 11, a special lens 11 and a semi-cylindrical lens 15 were installed after the convex lens 25 to form the output light shown in FIG. 9 having an oval intensity. When a similar experiment was conducted using the configuration shown in Figure 11, the melting width was approximately 170 mm.
The pitch can be further increased to 100 μm, which is a great improvement. No thermal effect on the substrate was observed. It was also revealed that by combining two semi-cylindrical lenses at right angles, the width and length of the output light could be adjusted freely.

Effects of the Invention As is clear from the above explanation, according to the present invention, it is possible to obtain an energy irradiation device with a wide beam width without causing a decrease in laser output or causing thermal damage to the substrate. . It is clear that the present invention is applicable not only to silicon but also to all surface treatments.

[Brief explanation of drawings]

Figures 1a and 1b are frontal distribution diagrams and planar distribution diagrams of the laser output light energy distribution, and Figures 2a and 2b are frontal distribution diagrams of the energy distribution created by the lens of the present invention. ＋ ``l'
ml 5'f, -W'y A town. Air □1 ka, ka,
6. A diagram showing the special optical lens. Figure 8 is a diagram showing the laser optical path and the irradiation state of the output light when using a semi-cylindrical lens. Figures 9 a and b are energy distribution when using a semi-cylindrical lens. FIG. 10 is a schematic diagram of a conventional laser irradiation device, and FIG. 11 is a partial schematic diagram of a laser irradiation device to which the present invention is applied. 4.17...Energy distribution, 11...Special lens, 14...Light passing through the center, 15.
...Horse-shaped lens, 26...Sample. Name of representative Patent attorney Toshio Nakao and 1 other person 1st
Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (2)

[Claims] (1) A concave or convex portion is provided in the center of the optical lens, and among the light passing through the optical lens, light near the center is refracted to the outside of the lens to a large extent relative to surrounding light. An energy irradiation device characterized by irradiating a target object with light passing through an optical lens. (2) By providing a concave or convex portion in the center of the optical lens, the light near the center is refracted to the outside of the lens to a greater extent relative to the surrounding light, and the light is further passed through the semi-cylindrical lens to generate light energy. A light energy irradiation device characterized by compressing the distribution in one direction into an elliptical shape.