JPH0220137B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides laser irradiation for forming a high-quality SOI structure by combining two laser beams using an optical system to form a beam with a bimodal energy distribution. It is about the method.

Conventional configurations and their problems In most cases, laser irradiation devices conventionally used in laser annealing devices, etc., have a mechanism that irradiates one laser beam using one laser light source. Ta. Generally, the most stable and high-energy mode of a laser beam is the TEM ₀₀ mode, and the power intensity distribution in this case has a Gaussian distribution with the maximum power density at the beam center.
It is known that when a laser beam with such a Gaussian power distribution is applied, for example, to the melting and recrystallization technology of a silicon layer, ie SOI, on an amorphous insulating substrate, it becomes an aggregate of fine small crystal grains. ing.

When such a recrystallized layer is used as a base material for a semiconductor device, the influence of grain boundaries causes serious deterioration of the electrical characteristics of the device, such as an increase in leakage current and a deterioration of mobility. Therefore, in order to eliminate such problems, one way to obtain a large-grained or single-crystal silicon layer is to change the beam power distribution of the laser beam to a donut-shaped beam with a lower intensity at the center than at the periphery.
A composite beam of TEM ₀₁ mode and TEM ₁₀ mode, or a beam with multiple local maxima, e.g.
Attempts have been made to irradiate with beams such as TEM ₀₁ mode. In fact, it has been reported that such beam irradiation results in large crystal grains near the center of the beam scan, ie, in a portion where the power is lower than in the periphery.

However, as a laser oscillation mode,
In the TEM ₀₁ and TEM ₁₀ modes that deviate from the TEM ₀₀ mode, the beam oscillation is extremely unstable and the output power is also small. Therefore, in order to use it stably as a laser light source, it is desirable to oscillate in TEM ₀₀ mode.

Therefore, it is desired to develop a laser irradiation method that eliminates the above-mentioned drawbacks and includes the development of a stable, high-energy laser beam irradiation device that can control a desired power distribution.

Purpose of the Invention The present invention overcomes the drawbacks of the conventional laser beam used for recrystallization and annealing of SOI by laser irradiation, and provides a laser beam that can control the intensity distribution of the laser beam to obtain a desired distribution. The present invention provides a laser irradiation method for forming a high-quality SOI using a laser beam with a desired energy distribution using an irradiation device.

Structure of the Invention The present invention uses two laser light sources to combine and control two laser beams having stable Gaussian energy, for example, TEM ₀₀ mode, using an optical system, and then directs the combined laser beam to a desired target. A beam power distribution is applied to the silicon layer on the insulating substrate to melt and recrystallize the silicon layer.

A configuration of the present invention using two laser light sources will be described below.

For example, a continuous wave Ar _ion laser is used as the laser light source. The laser beam from the light source is
For example, it becomes a linearly polarized P wave. The first laser light from the first laser light source enters the beam expander as a P wave, and then its power is adjusted by a Glan-Taylor prism and enters a polarizing beam splitter that transmits most of the P waves. do. P of the second laser beam from the second laser light source
The wave is parallel to the first laser beam and is converted into an S wave after passing through a half-wave plate. After that, the second laser beam is reflected from the incident direction by a total reflection mirror.
It is reflected in a 90° direction and enters the polarizing beam splitter in the vicinity where the first laser beam is transmitted. A polarizing beam splitter reflects most of the S waves and bends them at 90 degrees with respect to the direction of incidence. The second laser beam leaving the polarizing beam splitter is therefore parallel to the initial direction. Furthermore, as mentioned above, most of the first laser light passes through the polarizing beam splitter, so the light that exits the polarizing beam splitter is almost combined into a single beam. . By making the total reflection mirror that reflects the second laser beam slightly movable in parallel with the optical axis of the second laser beam, the combined beam that exits the polarizing beam splitter will travel the distance that this total reflection mirror moves. The center of the second laser beam is separated from the center of the first laser beam by the same distance as . Therefore, by arbitrarily changing this moving distance, you will have an intensity distribution in which two beams with a Gaussian intensity distribution are superimposed, resulting in a two-peak beam with close peaks or an intensity distribution with an almost flat center. A composite beam with .

Thereafter, the beam is narrowed to a desired size using an aperture lens, and the silicon layer on the insulating substrate is irradiated while being scanned, melting and recrystallizing to obtain a high-quality SOI structure. On the silicon layer, the interval between the two energy peaks of the laser beam is controlled with high precision.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing the concept of the optical system up to the front of the aperture lens, which is used to obtain a beam having a bimodal energy distribution according to the present invention.

The first laser light L1, which is a linearly polarized P wave, emitted from the first laser light source ₁ is a laser light whose beam diameter is, for example, 10 times larger after passing through the beam expander 4.
L ₁₂ , and after passing through Glan-Taylor prism 6 to adjust the power, the laser beam with the desired power
L ₁₃ and enters the polarizing beam splitter 8. Since the polarizing beam splitter 8 is of a transmission type for P waves, the laser beam L ₁₃ is hardly attenuated and a laser beam L ₁₄ is obtained after passing through the polarizing beam splitter 8. Since the optical axes of the optical system are aligned, the first laser beams L ₁ , L ₁₂ , L ₁₃ , and L ₁₄ are all on the same straight optical axis.

Next, P of the linearly polarized light emitted from the second laser light source 2
The second laser beam _L2 , which is a wave, passes through the half-wave plate 3 and is converted into a linearly polarized S-wave. This second laser beam _L21 , which has become an S wave, passes through the beam expander 5 and has a beam diameter of 10
The laser beam L ₂₂ becomes twice as strong, passes through the Glan-Taylor prism 7, and becomes the laser beam L ₂₃ with the desired power.
The light then enters the total reflection mirror 9. The laser beams L ₂ , L ₂₁ , L ₂₂ , and L ₂₃ emitted from the second laser light source 2 are all on the same straight optical axis, and the first laser beam
L ₁ , L ₁₂ , and L ₁₃ are parallel. Further, the total reflection mirror 9 can be slightly moved on the optical axes of the second laser beams L ₂ , L ₂₁ , L ₂₂ , and L ₂₃ in parallel to the optical axes.

The second laser beam L ₂₄ totally reflected by the total reflection mirror 9 has an optical axis at an angle of 90° with respect to the optical axis of the laser beams L ₂ , L ₂₁ , L ₂₂ , and L ₂₃ . The angle of the total reflection mirror 9 is adjusted so that The position of the total reflection mirror 9 is adjusted so that the second laser beam L ₂₄ is incident near the position A of the polarizing beam splitter 8 through which the first laser beam L ₁₃ is transmitted. Since the second laser beam L ₂₄ is an S wave, almost all the optical energy is reflected in the right angle direction by the polarizing beam splitter 8, and the first laser beam 14 that has passed through the polarizing beam splitter 8
A laser beam L ₂₅ whose optical axes are parallel to each other and almost close to each other emerges from the polarizing beam splitter 8. Therefore, the laser beams L ₁₄ and L ₂₅ exiting the polarizing beam splitter 8 are parallel beams whose optical axes are very close to each other, so that they appear to be combined into one beam.

The manner in which the second laser beam L ₂₃ is reflected and combined with the first laser beam L ₁₃ by the polarizing beam splitter 8 and appears as one laser beam will be briefly explained according to Fig. 2. .

When the total reflection mirror 9 is at position B, the reflected light L ₂₄ of the second laser beam L ₂₃ enters the polarization beam splitter 8 at position A. This point A is the point at which the first laser beam L ₁₃ passes through the polarizing beam splitter 8. Next, by moving the total reflection mirror 9 by a distance d parallel to the optical axis of the second laser beam L ₂₃ , the reflected light L ₂₄ is reflected by the polarizing beam splitter 8 and then transferred to the first laser beam. d from the optical axis of L ₁₄
The laser beam L ₂₅ has parallel optical axes separated by the same distance, and the beam synthesized by the first laser beam L ₁₄ and the second laser beam L ₂₅ has a power each having two peaks in a Gaussian power distribution. distribution. Furthermore, the distance d between these two peaks can be set to any desired value by finely adjusting the total reflection mirror 9.

Therefore, it is possible to obtain a laser beam that has a stable bimodal peak and the distance between the peaks can be set to any desired value.

After this, by narrowing down the laser beam with an appropriate aperture lens system, a laser beam having a bimodal energy distribution in cross section as shown in Fig. 3 can be obtained on the silicon layer formed on the insulating substrate. The distance between the two maximum beam intensity points of this bimodal beam can be controlled with high precision. Therefore, if the silicon layer is melted and recrystallized using this laser light, the recrystallized silicon layer can be made into a crystal layer with large crystal grains, resulting in a high-quality crystal layer.
SOI structure can be obtained.

Effects of the Invention By concentrating the laser beam according to the present invention on a silicon layer whose sample structure is a silicon island using an appropriate aperture lens system, it is possible to obtain twin beams with a desired energy distribution through highly accurate beam spacing control required for optimal crystallization. A peak-shaped beam can be obtained, and if this laser light is used for melting and recrystallizing silicon in an SOI structure, the recrystallized silicon layer can be made into a crystal layer with large crystal grains. By irradiating a silicon layer whose sample structure is a silicon island with the laser beam according to the present invention, the entire silicon island can become almost single-crystalline, making it possible to provide an excellent SOI device and a high-performance, highly integrated semiconductor. The effect on the realization of IC is extremely large.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram of an embodiment of the apparatus for the optical system part until obtaining the bimodal beam of the present invention, Fig. 2 is a detailed explanatory diagram of the part for obtaining the composite beam, and Fig. 3 is the apparatus of the present invention. Figure 3a is a schematic diagram of the power distribution of the laser beam irradiated onto the silicon layer formed on the insulating substrate after focusing the combined beam obtained from the
is a planar power distribution diagram, and b is a cross-sectional power distribution diagram. 1, 2... Laser light source, 3... 1/2 wavelength plate, 4,
5... Beam expander, 6, 7... Glan-Taylor prism, 8... Polarizing beam splitter, 9... Total reflection mirror, L ₁ , L ₁₂ , L ₁₃ , L ₁₄ ...
...first laser beam, L ₂ , L ₂₁ , L ₂₂ , L ₂₃ , L ₂₄ ,
L ₂₅ ...Second laser beam.

Claims (1)

[Claims] 1 Each first optical device is arranged so that the first laser beam passes through a beam splitter via a first beam expander, and the second laser beam passes through a half-wave plate. After passing through a second beam expander and being refracted by a total reflection mirror, the beam is incident on the beam splitter at right angles to the first laser beam. When the first and second laser beams are combined into one beam by an optical system in which second optical devices are arranged so as to pass through an optical path that is refracted so as to be parallel to the light, the first and second laser beams are combined into one beam. 1. The second laser beam has a stable Gaussian energy distribution, and the energy distribution of the combined beam has two maximum values, and by moving the total reflection mirror, the two After finely adjusting the mutual distance between the positions where the energy maximum value is obtained and obtaining a composite beam having the desired energy distribution, the distance between the two maximum values of the composite beam is controlled through an aperture lens, and the distance between the two maximum values of the composite beam is controlled. irradiates the silicon layer formed on the substrate to melt and recrystallize the silicon layer.
A laser irradiation method for SOI formation, characterized by forming an SOI structure.