JP2003279884A - Optical device provided with multi cylindrical lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure for reducing the loss of light in an optical device uniformizing the intensity distribution of a laser beam. <P>SOLUTION: The optical device is provided with a multi cylindrical lens on which a pulse laser or a continuous laser is made incident, the multi cylindrical lens is composed by alternately arranging convex cylindrical lenses and concave cylindrical lenses and the boundary of the convex cylindrical lens and the concave cylindrical lens is smoothly continued. Thus the scattering of light generated conventionally at a boundary part between the cylindrical lenses is reduced. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The invention disclosed in this specification includes:
For example, the present invention relates to an optical device using a laser such as a device (laser annealing device) for performing an annealing process by irradiation with laser light. In particular, the present invention relates to an apparatus such as a laser annealing apparatus for irradiating a large area beam, which can obtain a uniform irradiation effect. Such a laser annealing apparatus is used in a semiconductor manufacturing process or the like.

A large-area laser beam is also used in an exposure device for forming a fine circuit pattern such as a semiconductor circuit. In particular, ultraviolet laser light is used to form a circuit having a submicron design rule.

[0003]

2. Description of the Related Art Conventionally, a technique of crystallization by irradiating an amorphous silicon film with laser light has been known. Also,
There is known a technique of irradiating a laser beam for recovering the crystallinity of a silicon film damaged by the implantation of impurity ions and activating the implanted impurity ions. These are called laser annealing techniques.

A typical example of the latter technique is an example of annealing the source and drain regions of a thin film transistor. In this method, after the impurity ions typified by phosphorus and boron are implanted into the region, the region is annealed by laser light irradiation.

The process of irradiating laser light as described above is characterized in that there is almost no thermal damage to the substrate. The feature that there is no problem of heat damage to the substrate is advantageous in reducing restrictions on the material to be processed and forming a semiconductor element on a substrate having low heat resistance such as glass. In particular, it becomes important in the case of manufacturing an active matrix type liquid crystal display device whose use range is expanding in recent years.

In the active matrix type liquid crystal display device, it is desired to use a glass substrate as a substrate in view of cost and a demand for large area. A glass substrate cannot withstand heat treatment at a high temperature of 600 ° C. or higher, or 700 ° C. or higher. As a technique for avoiding this problem, a technique in which the above-described crystallization of the silicon film and annealing after the impurity ions are performed by irradiating a laser beam is effective.

In the method using laser light irradiation,
Even when a glass substrate is used as the substrate, there is almost no heat damage to the glass substrate. Therefore, a thin film transistor using a crystalline silicon film can be manufactured using a glass substrate. It has also been proposed to use the laser light as coherent light as a light source for forming a fine circuit pattern. Particularly, by using an ultraviolet laser, a fine pattern of submicron or less can be obtained.

However, in general, laser light is generated from a laser device (hereinafter referred to as original beam).
Then, since the beam area is small, a method of processing a large area by scanning a laser beam is common, but in this case, the in-plane uniformity of the processing effect is low, and the processing takes time. Have problems such as. Especially, since a general original beam has a non-uniform light intensity distribution, if it is used as it is, there is a significant problem in terms of uniformity of processing effect.

Therefore, a technique has been proposed in which the original beam is processed into a beam as uniform as possible, and the size of the beam is changed according to the shape of the processing area.
The shape of the beam is generally rectangular or linear.
By doing so, it is possible to perform uniform laser annealing over a large area.

An example of a laser irradiation device for processing an original beam is shown in FIG. As the laser oscillator, for example, an excimer laser or the like is used. In this method, a predetermined gas is decomposed by high-frequency discharge, and an excited state called an excimer state is created to oscillate laser light.

For example, a KrF excimer laser obtains an excited state of KrF ^* by high pressure discharge using Kr and F as source gases. This excited state has a lifetime of several nanoseconds
Although it is not stable such as several μsec, the ground state, KrF, which is not stable, is an unstable state, and an inverted distribution occurs in which the excited state density is higher than the ground state density. This results in stimulated emission,
It is possible to obtain laser light with relatively high efficiency.

Of course, the laser oscillator is not limited to the excimer laser, but may be other pulse laser or continuous laser. Generally, a pulse laser is suitable for the purpose of obtaining a high energy density. As shown in FIG. 1A, the original beam emitted from the laser oscillator is processed into an appropriate size by a beam expander composed of a concave lens and a convex lens.

The beam then enters an optical device called a homogenizer. It has at least one lens device (multi-cylindrical lens) with a large number of cylindrical lenses (generally having a paraboloidal shape). The conventional multi-cylindrical lens is shown in Fig. 1.
As shown in (B), a plurality of cylindrical lenses 1 to
5 (both are convex lenses) are formed on one piece of glass.

Generally, two multi-cylindrical lenses are used and are arranged so as to be orthogonal to each other. Of course, the number of multi-cylindrical lenses may be one or three or more. With one multi-cylindrical lens, the non-uniformity of the original beam in one direction is dispersed. Further, if two or more multi-cylindrical lenses are formed in the same direction, the same effect as increasing the number of cylindrical lenses can be obtained.

By passing through the multi-cylindrical lens, it is possible to obtain a highly uniform beam with dispersed energy density. This principle will be described later.
After that, the beam is processed into a desired shape by a converging lens, or if necessary, the direction is changed by a mirror, and the sample is irradiated with the beam. (Fig. 1 (A))

[0016]

Next, the principle and problems of the conventional homogenizer (multi-cylindrical lens) will be described. This problem is the problem to be solved by the present invention. In the following, in order to avoid complexity, an optical consideration will be made on one surface. The laser light transmitted through the multi-cylindrical lens is as shown in FIG.

Here, the multi-cylindrical lens L
Has five convex cylindrical lenses l, and the light incident on each cylindrical lens is refracted by each cylindrical lens. After converging at the focus, the beam diverges. At that time, a portion (mixing area) in which all the lights that have passed through the respective cylindrical lenses are mixed is obtained.

By the way, it is assumed that the light intensity distribution of the beams is biased and the intensity of the light incident on each cylindrical lens is different. However, in the mixing area, the light that has passed through each cylindrical lens is mixed,
The bias is dispersed. That is, the light intensity is made uniform. In this way, a beam with a small light intensity distribution can be obtained. (Fig. 2 (A))

By the way, focusing on the optical path that has passed through the multi-cylindrical lens, this is at equal intervals (distance a).
The light is emitted from the point light sources F (that is, the focus) arranged in the. (Fig. 2 (B))

A similar effect is obtained by providing a space a on both sides of the glass substrate.
Apart from each other, and a convex cylindrical lens l _{1 on one} surface,
It can be obtained also when the convex cylindrical lens ₁₂ is arranged on the other surface. In FIG. 3A, the optical path passing through the cylindrical lens l ₁ is indicated by a solid line, and the cylindrical lens l 1
_The optical path passing through ₂ is indicated by a broken line. Also in this case, the mixed region is obtained as in the case of FIG. (Fig. 3 (A))

Further, focusing on the optical path that has passed through the multi-cylindrical lens, as shown in FIG.
It is the light emitted from the point light sources F ₁ and F ₂ (that is, the focus) of the kind. (Fig. 3 (B))

In the conventional multi-cylindrical lens shown above, since the end portion of each cylindrical lens (boundary with another cylindrical lens) is refracted, light is scattered at that portion and light loss occurs. Occurred. This means that the laser light cannot be effectively used, which causes a decrease in beam intensity.

[0023]

The present invention has been made in view of the above problems. In the present invention, in the multi-cylindrical lens, not only the convex cylindrical lens, but also the concave cylindrical lens is used, the convex cylindrical lens and the concave cylindrical lens are alternately arranged, and each cylindrical lens can be smoothly continuous. It is characterized by

A first aspect of the present invention is an apparatus for forming a laser beam having a linear or rectangular beam shape,
In the homogenizer inserted between the laser oscillator and the object to be irradiated, the multi-cylindrical lens having the above-mentioned configuration is used.

A second aspect of the present invention is a laser optical device having a laser oscillator and a homogenizer to which the laser light emitted from the laser oscillator is input, wherein the multi-cylindrical lens used in the homogenizer has the above-mentioned configuration. It is something to be done.

In the above multi-cylindrical lens, the curved surface state of the convex cylindrical lens and the curved surface state of the concave cylindrical lens may be the same. Also,
In the homogenizer, at least two multi-cylindrical lenses may be arranged, and the directions of the two multi-cylindrical lenses may be arranged orthogonally.

The form of the multi-cylindrical lens of the present invention is as shown in FIG. This is because all the conventional multi-cylindrical lenses are composed of convex cylindrical lenses 1 to 5 (FIG. 1 (B)).
On the other hand, it has concave cylindrical lenses 2 and 4 between convex cylindrical lenses 1 and 3, 3 and 5.
In addition, the boundaries of these cylindrical lenses are smoothly continuous. (Fig. 1 (C))

In order to smoothly connect the cylindrical lenses to each other, the concave cylindrical lens and the convex cylindrical lens adjacent to each other may have the same curvature (curved surface shape). When the cylindrical lens is a parabolic lens, it has a structure in which parabolic surfaces with different directions are combined. The optical path of the laser light in such a multi-cylindrical lens is shown in FIG. 4 as shown in FIGS. 2 and 3.

Here, the multi-cylindrical lens L
Has three convex cylindrical lenses l ₁ and two concave cylindrical lenses l ₂ as shown in FIG. 1 (C). The light incident on the convex cylindrical lens is converged at the focal point and then diffused. On the other hand, the light incident on the concave cylindrical lens is unilaterally diffused as if it is diffused from a certain point. As a result, a portion (mixing area) in which all the light transmitted through each cylindrical lens is mixed is obtained.

The above effects can be obtained similarly even when the convex cylindrical lens and the concave cylindrical lens have different curvatures (elements that determine the focal length or the curved surface shape of the lens). Moreover, in the multi-cylindrical lens having such a structure, since there is no structure for scattering light (non-smooth portions such as protrusions), light loss can be reduced. (Fig. 4 (A))

Focusing on the optical path that has passed through the multi-cylindrical lens, this is the light emitted from the two types of point light sources F ₁ and F ₂ (that is, the focus), as in the case shown in FIG. 3B. Can be considered. (Fig. 4 (B))

When the convex cylindrical lens and the concave cylindrical lens have the same curvature, the boundary of the optical path of the light passing through the concave cylindrical lens passes through the focal point F ₁ of the adjacent convex cylindrical lens. This will be described below. The fact that the convex cylindrical lens and the concave cylindrical lens have the same curvature means that the convergence angle in the former case (the divergence angle after passing the focus) and the divergence angle in the latter case are the same when parallel rays are incident.

That is, as shown in FIG. 5A, assuming that the focal length of the convex cylindrical lens l ₁ is x, the parallel rays transmitted through the concave cylindrical lens l ₂ are shown in FIG.
As shown in (B), a point F ₂ separated from the incident side by a distance x
It can be regarded as the light emitted from. Here, the convex cylindrical lens and the optical path F ₁ A of the light passing through the lower end of l _1, concave cylindrical lens optical path F ₂ of light passing through the upper end of the l ₂
Focusing on A and A, since the divergence angle and the convergence angle of the light passing through both lenses are the same, the straight line F ₂ A is the straight line F ₁ A
Overlap with. That is, the boundary of the optical path of the light passing through the concave cylindrical lens passes through the focal point F ₁ of the adjacent convex cylindrical lens. (Fig. 5)

[0034]

EXAMPLE An optical system of this example will be described. The basic structure of the laser irradiation apparatus of this embodiment is similar to that shown in FIG. The shape of the laser beam before entering the homogenizer is 6
It is cm × 5 cm. In this example, the homogenizer used one multi-cylindrical lens. Only the multi-cylindrical lens will be described below.

In the structure shown in this embodiment, the multi-cylindrical lens is composed of 6 concave cylindrical lenses (width 5 mm) and 5 convex cylindrical lenses (width 5 mm).
mm) are alternately arranged, and the incident laser light is divided into about 10 parts. The length of the cylindrical lens in the longitudinal direction was 7 cm. The multi-cylindrical lens is made of quartz.

In the present embodiment, the length of the linear laser beam to be finally irradiated is 12 cm in the longitudinal direction and the width is 0.
It is 5 mm. For this reason, after passing through the homogenizer, the laser light was enlarged twice in the longitudinal direction and reduced to 1/100 in the direction perpendicular to it. Both the convex cylindrical lens and the concave cylindrical lens were spherical lenses, and their curvatures were the same. The focal length of the convex cylindrical lens was 5 cm. (See Figure 1 (A))

[0037]

By utilizing the invention disclosed in this specification, it is possible to obtain a large-area and uniform laser beam required in a laser process used for manufacturing a semiconductor device or the like.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of an optical system of a laser irradiation device and an outline of a conventional and inventive multi-cylindrical lens.

FIG. 2 is a schematic diagram showing an optical path of a conventional multi-cylindrical lens.

FIG. 3 is a schematic view showing an optical path of a conventional multi-cylindrical lens.

FIG. 4 is a schematic diagram showing an optical path of a multi-cylindrical lens of the present invention.

FIG. 5 is a diagram showing an optical path of a convex lens and an optical path of a concave lens.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01S 3/101 G02B 27/00 E

Claims (8)

[Claims] 1. A multi-cylindrical lens on which a pulse laser is incident, wherein the multi-cylindrical lens is configured by alternately arranging a convex cylindrical lens and a concave cylindrical lens, wherein the convex cylindrical lens and the concave cylindrical lens are An optical device characterized in that the boundaries are smoothly continuous. 2. A multi-cylindrical lens into which a continuous laser is incident, wherein the multi-cylindrical lens comprises convex cylindrical lenses and concave cylindrical lenses arranged alternately, and the convex cylindrical lens and the concave cylindrical lens are An optical device characterized in that the boundaries are smoothly continuous. 3. A quartz multi-cylindrical lens into which a pulsed laser is incident, wherein the multi-cylindrical lens comprises convex cylindrical lenses and concave cylindrical lenses arranged alternately, and the convex cylindrical lens and the concave cylindrical lens. An optical device characterized in that the boundary with the lens is smoothly continuous. 4. A quartz multi-cylindrical lens into which a continuous laser is incident, the multi-cylindrical lens comprising convex cylindrical lenses and concave cylindrical lenses arranged alternately, wherein the convex cylindrical lens and the concave cylindrical lens are arranged. An optical device characterized in that the boundary with the lens is smoothly continuous. 5. At least two multi-cylindrical lenses on which a pulse laser is incident are provided, wherein the multi-cylindrical lenses have convex cylindrical lenses and concave cylindrical lenses arranged alternately, and the convex cylindrical lenses and the concave cylindrical lenses are arranged. An optical device characterized in that the boundary with the lens is smoothly continuous. 6. A multi-cylindrical lens having at least two continuous lasers incident thereon, wherein the multi-cylindrical lens comprises convex cylindrical lenses and concave cylindrical lenses arranged alternately, and the convex cylindrical lens and the concave cylindrical lens. An optical device characterized in that the boundary with the lens is smoothly continuous. 7. A multi-cylindrical lens on which a pulse laser is incident, wherein the multi-cylindrical lens has two convex cylindrical lenses and a concave cylindrical lens arranged between the two convex cylindrical lenses. An optical device, wherein a boundary between the two convex cylindrical lenses and the concave cylindrical lens is smoothly continuous. 8. A multi-cylindrical lens into which a continuous laser is incident, wherein the multi-cylindrical lens has two convex cylindrical lenses and a concave cylindrical lens arranged between the two convex cylindrical lenses. An optical device, wherein a boundary between the two convex cylindrical lenses and the concave cylindrical lens is smoothly continuous.