JP3402124B2 - Beam homogenizer and method for producing semiconductor thin film - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam homogenizer for controlling the cross-sectional intensity distribution of a light beam and a method for manufacturing a semiconductor thin film using the same.

[0002]

2. Description of the Related Art A cylinder array type beam homogenizer is composed of a front cylinder array, a rear cylinder array, and a focus lens. Each cylinder array is configured by arranging a plurality of equivalent convex cylindrical lenses in a direction perpendicular to the optical axis and the generatrix of the columnar surface. The optical axes of the respective cylindrical lenses of the cylinder array of the former stage are arranged so as to coincide with the optical axes of the corresponding cylindrical lenses of the cylinder array of the latter stage. In this specification, the optical axis of the cylindrical lens means an axis that is included in the plane of symmetry of the cylindrical lens and is orthogonal to the cylindrical surface.

When a bundle of rays parallel to the optical axis thereof is incident on the cylinder array in the preceding stage, the bundle of incident rays is converged by each cylindrical lens. Each converged ray bundle is again converged by each cylindrical lens of the cylinder array in the subsequent stage. In this way, the two cylinder arrays divide the incident ray bundle into as many small ray bundles as the number of cylindrical lenses.

The obtained light beam bundle becomes divergent light, parallel light, or convergent light depending on the relative positions of the two cylinder arrays. By superimposing each small ray bundle on a certain surface using the focus lens group, it is possible to make the light intensity distribution in the irradiation region uniform (homogenize).

There is known a technique in which an amorphous silicon film is irradiated with a pulsed laser beam homogenized by this beam homogenizer to polycrystallize it. Hereinafter, this polycrystallization technique will be described.

In this technique, usually two pairs of cylinder arrays are used. When considering an XY orthogonal coordinate system in the homogenizing plane, one pair of cylinder arrays homogenizes in the X-axis direction in the homogenizing plane, and another pair of cylinder arrays homogenizes in the Y-axis direction. The size of the irradiation area on the homogenized surface can be changed by changing the interval between each pair of cylinder arrays.

By adjusting the distance between each pair of cylinder arrays, the irradiation area on the homogenized surface forms a long beam which is long in the X-axis direction. The substrate on which the amorphous silicon film is formed is moved in the Y-axis direction so that this irradiation region partially overlaps the region irradiated by the previous pulse irradiation. In this way, a desired region of the amorphous silicon film can be polycrystallized by irradiating a wide range with laser light.

[0008]

The irradiation region on the amorphous silicon film has a length of 200 mm and a width of 0.5 m, for example.
It is an elongated area of about m. This region is moved in the width direction by 0.05 mm for each pulse. If the position of the irradiation area on the surface of the silicon film deviates from the desired position, the amount of overlap between the area irradiated by the pulse irradiation and the irradiation area this time changes, making it difficult to obtain a high-quality polycrystalline silicon film. become.

An object of the present invention is to provide a beam homogenizer with less fluctuation of the beam irradiation position and a method of manufacturing a semiconductor thin film using the same.

[0010]

According to one aspect of the present invention, when a parallel ray bundle is incident, the light intensity distribution in a cross section perpendicular to the optical axis of the incident ray bundle is made to approach uniformly, and the surface of the object to be irradiated is illuminated. Until it reaches the upper side, the light beam is not homogenized, and the second beam is long in the first direction on the surface of the object to be irradiated.
A homogenizing optical system for directly homogenized short linear region in the direction of the disposed on the incident side of the homogenizing optical system converts the angular magnification of the light beam, see <br/> including the optical axis of the light flux , At least an angular magnification conversion optical system having an angular magnification of less than 1 with respect to an imaginary plane parallel to the second direction.
The angular magnification conversion optical system reduces the angular magnification to less than 1.
A beam homogenizer is provided in which a bundle of rays is incident on the homogenizing optical system .

When the optical axis of the parallel ray bundle incident on the angular magnification conversion optical system is deviated from the reference direction, the deviation angle of the optical axis of the emitted parallel ray bundle from the reference direction is the deviation angle of the incident ray bundle. Will be smaller than. Therefore, it is possible to reduce the displacement of the irradiation region on the homogenized surface by the homogenizing optical system.

[0012]

Since the displacement of the irradiation area can be reduced,
Positional deviation of the laser light applied to the semiconductor thin film is reduced, and stable laser light irradiation is possible.

[0014]

1 shows a cross-sectional view of a beam homogenizer according to an embodiment of the invention. Xy with the z-axis being the direction parallel to the optical axis of the bundle of rays incident on the beam homogenizer
Consider the z Cartesian coordinate system. 1A is a cross-sectional view parallel to the xz plane, and FIG. 1B is a cross-sectional view parallel to the yz plane.
The beam homogenizer according to the embodiment includes an angular magnification conversion optical system AF and a homogenizing optical system HN. The homogenizing optical system HN includes cylinder arrays 1A, 1B, 2
A, 2B, a converging lens 3, and a relative position adjusting mechanism 5 are included.

As shown in FIG. 1A, each of the cylinder arrays 1A and 1B is composed of seven equivalent cylindrical lenses. The optical axis of each cylindrical lens is parallel to the z-axis, and the generatrix of the cylindrical surface is parallel to the y-axis.
Here, the optical axis of the cylindrical lens means an axis that is included in the plane of symmetry of the cylindrical lens of the image forming system and is perpendicular to the cylindrical surface. The cylindrical lenses arranged in this way are arranged along the virtual plane parallel to the xy plane with the edge surfaces in close contact with each other. The cylinder array 1A is arranged on the light incident side (left side in the drawing), and the cylinder array 1B is arranged on the emitting side (right side in the drawing). In addition, each cylindrical lens of the cylinder array 1A is
It is arranged so as to share the optical axis with the corresponding cylindrical lens of the cylinder array 1B.

As shown in FIG. 1B, each of the cylinder arrays 2A and 2B is composed of seven equivalent cylindrical lenses. The optical axis of each cylindrical lens is parallel to the z-axis, and the generatrix of the cylindrical surface is parallel to the x-axis.
The cylindrical lenses arranged in this way are arranged along the virtual plane parallel to the xy plane with the edge surfaces in close contact with each other. The cylinder array 2A is arranged on the incident side of the cylinder array 1A, and the cylinder array 2B is arranged between the cylinder arrays 1A and 1B. Further, each cylindrical lens of the cylinder array 2A is arranged so as to share the optical axis with the corresponding cylindrical lens of the cylinder array 2B.

The relative position adjusting mechanism 5 sets the distance between the cylinder arrays 1A and 1B and the distance between the cylinder arrays 2A and 2B to desired values.

A converging lens 3 is arranged on the exit side of the cylinder array 1B. The optical axis of the converging lens 3 is also parallel to the z axis.

An angular magnification conversion optical system AF is arranged in front of the homogenizing optical system HN. Angular magnification conversion optical system AF
Converts the angular magnification of the bundle of rays. The angular magnification γ is less than 1. A configuration example of the angular magnification conversion optical system AF will be described later.

With reference to FIG. 1 (A), the manner of propagation of a ray bundle in the xz plane will be described. In the xz plane,
Since the cylinder arrays 2A and 2B are equivalent to a simple flat plate, they do not affect the convergence and divergence of the light beam. A parallel light bundle 10 having an optical axis parallel to the z axis is an angular magnification conversion optical system AF.
Incident on. The angular magnification conversion optical system AF converts the angular magnification and emits the parallel light flux 11. The incident ray bundle 10 has, for example, a light intensity distribution that is strong in the central portion and weak in the peripheral portion.

The parallel light beam bundle 11 that has passed through the angular magnification conversion optical system AF passes through the cylinder array 2A and enters the cylinder array 1A. The incident ray bundle is divided by the cylinder array 1A into seven convergent ray bundles corresponding to the respective cylindrical lenses. In FIG. 1A, only the light fluxes at the center and both ends are shown as a representative. The ray bundle converged by the cylinder array 1A is further converged by the cylinder array 1B.

The seven convergent light bundles 12 converged by the cylinder array 1B are condensed in front of the converging lens 3, respectively. This condensing position is closer to the lens than the incident side focal point of the converging lens 3. Therefore, the seven ray bundles that have passed through the converging lens 3 become divergent ray bundles and overlap on the homogenizing surface 4.

X of each ray bundle illuminating the homogenized surface 4
The light intensity distribution in the axial direction is similar to the light intensity distribution of the corresponding portion of the light bundle 10. The light intensity of the ray bundle 10 is strong near the center and weak near the periphery, but by dividing this ray bundle 10 into small ray bundles and superimposing the respective ray bundles, the light intensity distribution in the irradiation region is made closer to uniform. You can (homogenize).

With reference to FIG. 1B, the manner in which the ray bundle propagates in the yz plane will be described. The incident ray bundle 10 enters the angular magnification conversion optical system AF. Angular magnification conversion optical system AF
Converts the angular magnification and emits a bundle of parallel rays 11.

The parallel ray bundle 11 enters the cylinder array 2A. The parallel ray bundle 11 is divided into seven convergent ray bundles corresponding to the respective cylindrical lenses by the cylinder array 2A. In FIG. 1B, only the light fluxes at the center and both ends are shown as a representative. In the yz plane, since the cylinder arrays 1A and 1B are equivalent to simple flat plates, they do not affect the convergence and divergence of the light flux.

Each ray bundle is condensed in front of the cylinder array 2B and becomes a divergent ray bundle and enters the cylinder array 2B. The respective bundles of rays that have entered the cylinder array 2 </ b> B are emitted at the same exit angle and enter the converging lens 3.

The bundles of rays that have passed through the converging lens 3 become bundles of convergent rays, which overlap on the homogenized surface 4. The light intensity distribution in the y-axis direction of the seven ray bundles that illuminate the homogenized surface 4 approaches a uniform distribution as in the case of FIG. Since each ray bundle transmitted through the convergent lens 3 is a convergent ray bundle, the length of the irradiation area on the homogenized surface 4 in the y-axis direction is shorter than the length in the x-axis direction.
Therefore, the light irradiation area on the homogenized surface 4 has a linear shape that is long in the x-axis direction and short in the y-axis direction.

The beam width on the homogenized surface, that is, the width W of the light irradiation region, is defined by the focal length of the converging lens 3 f _F , the combined focal length of the cylindrical lenses forming the cylinder array f _C , and each cylindrical structure forming the cylinder array. W = (f _{F where} d is the lens width of the lens
/ F _C ) d. The width of the light irradiation region can be changed by adjusting the interval between the corresponding cylinder arrays to change the combined focal length f _C of the cylinder arrays.

In the case of the beam homogenizer shown in FIGS. 1 (A) and 1 (B), by changing the distance between the cylinder arrays 1A and 1B, the length of the light irradiation region in the long axis direction is changed to change the cylinder length. The width in the minor axis direction can be changed by changing the distance between the arrays 2A and 2B.
By using the beam homogenizer shown in FIGS. 1A and 1B, a long axial region in the y-axis direction can be irradiated almost uniformly.

The traveling direction of the bundle of parallel rays 10 is z due to the vibration of the mirror constituting the optical resonator of the laser oscillator and the vibration of the optical system from the laser oscillator to the angular magnification conversion optical system AF.
It may deviate from the axis. Since the angular magnification conversion optical system AF has an angular magnification of less than 1, the deviation angle between the traveling direction of the parallel ray bundle 11 that has passed through the angular magnification conversion optical system AF and the z axis is the same as the traveling direction of the parallel ray bundle 10 and z. It is smaller than the angle of deviation from the axis.

When the traveling direction of the bundle of rays 11 entering the homogenizing optical system HN deviates from the z axis, the homogenizing surface 4
The upper irradiation position deviates from the reference position. Even if the traveling direction of the incident light bundle 10 is deviated from the z-axis, the deviation angle of the light bundle 11 can be reduced by the angular magnification conversion optical system AF. Therefore, the deviation amount of the irradiation position is reduced, and the positional stability of the irradiation region can be improved.

Even if the focal length of the converging lens 3 shown in FIGS. 1 (A) and 1 (B) is shortened, the displacement of the irradiation area can be reduced. However, if it is attempted to shorten the focal length of the converging lens 3 without changing the length of the irradiation region in the long axis direction, the angle of view in the long axis direction (in the xz plane) of the irradiation region becomes large, which is not preferable. Further, since it is necessary to shorten the distance between the homogenizing optical system HN and the homogenizing surface 4, there are many restrictions on the arrangement of the device.
By inserting the angular magnification conversion optical system AF as in the above embodiment, the positional stability of the irradiation region can be enhanced without shortening the focal length of the converging lens 3.

Next, a method for polycrystallizing an amorphous silicon film by using the beam homogenizer shown in FIGS. 1A and 1B will be described. A substrate having an amorphous silicon film formed on the surface thereof is arranged so that the surface thereof coincides with the homogenized surface 4. The converging lens 3
Within the range of the depth of field of, the homogenized surface may be shifted back and forth. By adjusting the distance between the cylinder arrays 1A and 1B and the distance between the cylinder arrays 2A and 2B, the irradiation area on the homogenized surface 4 is formed into a shape having a desired length and width. The substrate is moved in the y-axis direction so that the irradiation region of the laser light partially overlaps the irradiation region of the previous pulse irradiation. The laser-irradiated region of the amorphous silicon film is melted and solidified to be polycrystallized.

The deviation of the irradiation position due to the deviation of the traveling direction of the light bundle 10 can occur in both the major axis direction and the minor axis direction of the irradiation area. However, the misalignment in the long axis direction causes almost no problem when the amorphous silicon film is polycrystallized. Therefore, the angular magnification conversion optical system AF has an angular magnification of less than 1 on the yz plane shown in FIG.
The angular magnification with respect to the xz plane shown in FIG.

Next, an example of the configuration of the angular magnification conversion optical system will be described with reference to FIG. The xyz coordinates shown in FIGS. 2 (A) to 2 (D) are xy shown in FIGS. 1 (A) and 1 (B).
It is the same as the z coordinate.

FIG. 2A shows an example using a Kepler-type afocal system. Convex cylindrical lens 21
And 22 are arranged so as to form a confocal system with each other. The optical axes of the cylindrical lenses 21 and 22 are parallel to the z axis, and the generatrix of the cylindrical surface is parallel to the x axis.

A light shielding plate 23 is arranged along a focal plane including the confocal points of the cylindrical lenses 21 and 22.
The light shield plate 23 is provided with slits parallel to the x axis at positions corresponding to the optical axes of the cylindrical lenses 21 and 22. By making the focal length of the incident side cylindrical lens 21 shorter than the focal length of the exit side cylindrical lens 22, the angular magnification can be less than 1.

The incident ray bundle 10 usually contains a noise component other than the component parallel to its optical axis. The noise component is generated by the light source having a finite size, scattering by dust in the air, and the like. The noise component of the incident ray bundle 10 does not pass through its focal point even if it is converged by the cylindrical lens 21. A noise component that travels at a certain angle from the optical axis is shielded by the light shield plate 23 and does not reach the cylindrical lens 22. Therefore, the parallel ray bundle 11 that has passed through the angular magnification conversion optical system becomes a ray bundle having less noise components than the incident ray bundle 10. As described above, the Kepler-type angular magnification conversion optical system can have the function of reducing the noise of the incident light flux by arranging the light shielding plate in addition to converting the angular magnification.

A spherical lens may be used instead of the cylindrical lenses 21 and 22. In this case, a pinhole is provided at a position corresponding to the focal point of the light shielding plate 23.

FIG. 2B shows an example using a Galileo type afocal system. Concave cylindrical lens 25
And the convex cylindrical lens 26 are arranged so that the optical axis thereof is parallel to the z axis. The generatrices of the cylindrical surfaces of the cylindrical lenses 25 and 26 are parallel to the x axis. The concave cylindrical lens 25 is arranged on the incident side, and the convex cylindrical lens 26 is arranged on the emitting side.

Also in this case, as in the case of FIG. 2A, a spherical lens may be used instead of the cylindrical lens.

FIG. 2C shows an example using one prism 27, and FIG. 2D shows an example using two prisms 27 and 28. Each prism is arranged so that the incident light beam bundle enters obliquely and the output light beam bundle emits in the vertical direction. In the case of FIG. 2C, the traveling directions of the incident light beam bundle 10 and the outgoing light beam bundle 11 are different. In the case of FIG. 2D, the incident ray bundle 10 and the outgoing ray bundle 11 are decentered, but their traveling directions are parallel to each other.

If the angular magnification of the angular magnification conversion optical system is γ,
The beam size of the outgoing ray bundle 11 is 1 / γ times the beam size of the incident ray bundle 10. When the configuration is such that the angular magnification γ is less than 1, the beam size of the outgoing ray bundle 11 becomes larger than the beam size of the incoming ray bundle 10. It is preferable to design the angular magnification conversion optical system AF in consideration of the aperture of the homogenization optical system HN so that most of the light flux 11 transmitted through the angular magnification conversion optical system AF enters the homogenization optical system HN.

Taking these into consideration, the angular magnification γ is 1/1.
It is preferably about 5 to 1/3.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0046]

As described above, according to the present invention,
It is possible to suppress the positional deviation of the irradiation area on the homogenized surface due to the deviation of the traveling direction of the incident ray bundle. Since the position stability of the irradiation region is improved, the crystallinity of the semiconductor film can be stably improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a beam homogenizer according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a configuration example of an angular magnification conversion optical system of the beam homogenizer shown in FIG.

[Explanation of symbols]

1A, 1B, 2A, 2B cylinder array 3 Converging lens 4 Homogenized surface 5 Relative position adjustment mechanism 10 incident ray bundle 11, 12 ray bundle 21, 22, 25, 26 Cylindrical lens 23 Light shield 27, 28 prism

Claims (3)

(57) [Claims] 1. When a parallel ray bundle is incident, the light intensity distribution in a cross section perpendicular to the optical axis of the incident ray bundle is brought close to uniform, and the ray bundle is homogenized until it reaches the surface of the object to be irradiated. without, on the surface of該被irradiation object, the first direction
A homogenizing optical system for directly homogenized short linear region in a second direction long, arranged on the incident side of the homogenizing optical system converts the angular magnification of the light beam, it viewed including the optical axis of the light flux At least before
Serial angular magnification possess the angular magnification conversion optical system is less than 1 about the virtual plane parallel to the second direction, the angle magnification conversion optical
A ray bundle whose angular magnification is less than 1 by the academic system
A beam homogenizer that is incident on the optical system . 2. The step of arranging the object to be processed having a semiconductor thin film on the surface thereof so that the surface of the object to be processed is substantially coincident with the homogenized surface of the beam homogenizer according to claim 1. And a step of irradiating the semiconductor thin film with laser light homogenized by the beam homogenizer to change the crystallinity. 3. The angular magnification of the angular magnification conversion optical system is 1 / 1.5 to 1/3 with respect to a virtual plane that includes the optical axis of the light beam bundle and is parallel to the second direction. 1. The beam homogenizer according to 1.