JP2005037648A - Laser patterning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of high equipment costs and long manufacturing days in both cases of (1) to use an optical system of a high NA or (2) to use a laser of a short wavelength when fine groove working is performed since a light condensing diameter shorter than a diffraction limit can not be obtained. <P>SOLUTION: A non-linear effect of a non-linear optical material 6 is caused by using a laser beam having ≥2.2 MW output and the beam having light condensing diameter equal to or shorter than the diffraction limit and a thin film material 7 are relatively moved to perform the fine groove working. The non-linear optical material 6 is preferably quartz. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a laser patterning method.

  The laser oscillator having a high peak output in the prior art can be obtained by reducing the width of the oscillation pulse. Lasers with pulse widths of nanoseconds from the 1960s and femtoseconds with titanium sapphire lasers and supersaturated absorption mirrors have been developed and marketed since the 1990s, and have been used in various fields.

  In recent years, it has been marketed as a product that is excited and oscillated by a laser medium using a semiconductor laser in the picosecond and femtosecond region, and is easy to use for non-laser experts. Such a laser having a short pulse and a high peak output is considered to be suitable for fine processing such as thin film processing and resin processing with little thermal damage to a workpiece. Conventionally, there have been fine processing using a nanosecond laser and ablation processing using ultraviolet light from an excimer laser, but thermal damage cannot be denied due to the large pulse width of these lasers. Therefore, micromachining with a laser with a short pulse and high peak output is characterized by a good machined surface. However, the focused diameter of the beam can ideally be focused only up to its diffraction limit.

  In general, when the laser beam is ideally TEM00, and the laser beam is condensed to the diffraction limit, the condensing diameter d is

  Indicated by Where λ is the laser wavelength, f is the focal length of the condenser lens, and w is the beam diameter at the condenser lens. In order to obtain a small condensing diameter from the formula (1), it is conceivable to use a large beam with a short wavelength laser with a small λ or a lens with a large NA and a small focal length. However, if a large beam is used indiscriminately, the minimum condensing diameter may not be obtained due to the aberration of the condensing lens, and the depth of focus decreases in proportion to the square of NA, so the distance from the specific work material is adjusted. However, a processing method is required.

  Expression (1) is an expression representing only the laser condensing diameter, and when the workpiece is actually irradiated, the size differs depending not only on the energy of the laser but also on the absorption characteristics, shape, and surface state of the material depending on the wavelength.

  FIG. 5 shows a conventional processing system. (For example, refer nonpatent literature 1). A laser oscillator 101 (hereinafter referred to as “short pulse laser oscillator”) having a pulse width of nanoseconds or less is a laser oscillator having a femtosecond or picosecond pulse width. The output of the light emitted from the short pulse laser oscillator 101 is controlled by the attenuator 111. The attenuator 111 controls the output by rotating the plane of polarization by the half-wave plate 102 and the polarizing plate 103 and allowing light of only a certain polarization direction to pass. The output can be fed back by monitoring the output laser light and adjusting the rotation angle of the half-wave plate 102. The output is controlled in this way, and the controlled light becomes light having a unidirectional polarization. Further, this light is collimated and expanded by the beam expander 104. In a commercial product, the enlargement ratio can be 2 to 8 times. Thereafter, the laser light passes through the aperture 107. The diameter of the aperture is variable. Normally, the aperture is used when the shape is formed into stray light or laser light itself.

  Further, it is necessary to adjust the optical axis with a HeNe laser or the like so that the laser beam passes through the center with respect to the aperture. The laser light that has passed through the aperture 107 is condensed by the condenser lens 108 and the substrate 110 loaded on the stage 109 is processed. In order to reduce the condensing diameter d from FIG. 5 and formula (1), the wavelength λ is reduced. Bring NA closer to 1. This increases the magnification of the beam expander 104 (that is, increases w) and decreases the focal length f of the condenser lens 108.

  However, even if there is a lens with NA = 1, for example, the minimum diameter can be condensed only at a wavelength of 1.22 times. If the laser beam emits visible light and the wavelength is 800 nm, only a beam diameter of 976 nm can be obtained. However, in such a high NA condensing system, the depth of focus becomes small, and it is necessary to install an autofocus function or the like for adjusting the focal length. As seen in the exposure apparatus, it is necessary to adjust the focus direction, tilt, etc. to adjust the position of the condenser lens and the wafer.

In lithography, a fine pattern is formed using a laser wavelength of 200 nm or less and NA = 0.65.
Masayuki Ikeda et al. "Laser Process Technology Handbook" Asakura Shoten, April 1992, P479, Fig. 3, 2, 46

  However, in the above-described configuration, since a condensing diameter less than the diffraction limit cannot be obtained, when fine groove processing is performed, either an optical system with a high NA or a short wavelength laser is used. In a fine processing method using an optical system with a high NA, since the depth of focus is small, focus adjustment is necessary, and the equipment cost is high. Although it is not rare to use a short-wavelength laser for miniaturization, an ultraviolet laser is more expensive than a laser for the visible and infrared regions, and requires maintenance.

  As for optical parts, visible and infrared optical parts are far more common, and durability is higher than that for ultraviolet parts, and costs are low. An apparatus corresponding to a wavelength and a high NA eventually becomes expensive.

  On the other hand, there are two methods for fine pattern processing: a method of forming a pattern by performing simultaneous processing by beam splitting and directly drawing, and a method of forming a collective pattern by lithography. Even in the case of beam splitting, a short wavelength laser and a high NA optical system are required to obtain a condensing diameter less than the above-mentioned diffraction limit, and in the case of lithography, expensive equipment and pattern formation are required. In addition, a mask is required, and the production days and costs are further increased.

  The present invention solves the above-described conventional problems, and an object thereof is to provide a laser patterning method capable of forming a fine groove.

  In order to solve this problem, the present invention is a method for forming a fine groove in a thin film material on a substrate with a laser beam having a peak output of 2.2 MW or more, and a beam that expands the laser beam into a parallel beam Using an expander and a condensing lens for condensing the laser beam expanded and collimated, and a non-linear optical material installed near the focal position of the laser light condensed by the condensing lens, A substrate is provided with a gap, the nonlinear optical material is caused to have a nonlinear effect by the laser light of 2.2 MW or more, and a fine groove is formed by relative movement with the thin film material with a beam condensing diameter less than the diffraction limit. It is characterized by processing.

  According to this method, the beam is self-focused due to the nonlinear effect of the nonlinear optical material in the high-energy region in the nonlinear optical material and in the vicinity of the focusing position, and the beam is constant due to self-constraint due to the balance between diffraction and self-focusing. The thin film material is processed with a small diameter at or near the end of the nonlinear material. As described in the second claim of the present invention, the nonlinear optical material is quartz, and the quartz causes a nonlinear optical effect when the peak output is 2.2 MW or more. Thereby, the thin film material is processed with a minute diameter.

  On the other hand, when forming a pattern, there are a case where one light beam is processed by relative movement with a thin film material and a case where a pattern is formed by dividing into multiple light beams and relative movement. In the latter case, a beam splitting means for splitting the expanded and collimated laser beam into a plurality of beams is provided, and an F-theta lens is used in place of the condensing lens to collect each beam while splitting the plurality of beams. The light beam is relatively moved by a plurality of light beams having a beam diameter less than a diffraction limit by a nonlinear optical material.

  Further, the light beam divided into a plurality of beams is condensed by a condensing lens to cause interference, and by using the light intensity due to the interference, the optical axis or the glass substrate on which the thin film material is formed is relatively moved. It is characterized by.

  This is patterning by a so-called interference exposure method. According to this, an interference fringe is formed and patterning is performed by relative movement between the fringe and the thin film material.

  From the above, according to the present invention, in the high energy region in the vicinity of the condensing position, the beam is self-focused due to the nonlinear effect, and the beam is fixed by a self-constraint due to the balance between diffraction and self-focusing. Since the nonlinear optical material is propagated with a small diameter, the thin film material can be processed with a minute diameter at or near the end of the nonlinear material.

  FIG. 1 is a diagram showing a configuration according to the first embodiment of the present invention. Hereinafter, the operation specifications of the present embodiment will be described with reference to FIG. Laser light emitted from the laser oscillator 1 having a peak output of 2.2 MW or more is bent at a desired angle by two mirrors 2a and 2b, and is incident on a beam expander 3 that expands the beam in parallel. Thereafter, the beam is bent by the bending mirror 4 and is incident on the condenser lens 5. Nonlinear optical materials placed near the focal point produce nonlinear effects due to the high energy density of the laser. In general, the refractive index n of a substance is

It becomes. Here, I is the energy density (cm ² / MW) of incident light, n0 is the initial refractive index, and n2 is a nonlinear coefficient. n2 * I exhibits nonlinearity when I exceeds a threshold value (2.2 MW for quartz).

  Therefore, as shown in FIG. 2, in FIG. 2A, for example, when the laser peak output is 2.2 MW or less, the nonlinear optical material is once condensed near the focal point (the beam diameter is greater than the diffraction limit). ) Expand again. However, when the peak output is 2.2 MW or more, as shown in FIG. 2 (b), the beam is condensed below the diffraction limit according to the equation (2) for high peak output.

  Here, when the action of spreading by the diffraction of light (broken line in FIG. 2B) and the action of focusing by the non-linear effect (self-focusing) are balanced, the light maintained its diameter at a beam diameter below the diffraction limit. Propagates through the nonlinear optical material. The thin peak material 7 installed at the end of the nonlinear optical material 6 can be processed by this high peak output laser beam. The thin film material is formed on the substrate 8.

  In this case, the thin film material 7 and the substrate 8 are loaded on the stage, and the pattern of the thin film material can be formed by moving the optical axis and the substrate 8 relative to each other.

  By using quartz as the nonlinear optical material 6 as an embodiment of the second invention of the present invention, the thin film material 8 can be processed with a peak output of 2.2 MW.

  FIG. 3 shows an embodiment of the third invention of the present invention. The laser light emitted from the laser oscillator 1 having a peak output of 2.2 MW is bent by the two mirrors 2a and 2b and is incident on the beam expander 3 that expands the beam in parallel. Thereafter, the beam is bent by the bending mirror 4 and incident on the beam splitter 9 to be split into a plurality of beams. Each beam (light beam) is condensed and propagated vertically from the position where it enters by the F-theta lens 10, and each enters the nonlinear optical material 6.

  In this case, the peak output of each beam needs to be 2.2 MW or more that causes a non-linear effect, and a laser output proportional to the number of divisions in the case of division is necessary. Each beam processes the thin film material 8 below the diffraction limit. In the figure, reference numeral 11 denotes a driving means having a biaxial tilting function for relatively moving the beam and the thin film material, and the beam can be moved by tilting the folding mirror 4.

  FIG. 4 shows a fourth embodiment of the present invention. The laser light emitted from the laser oscillator 1 having a peak output of 2.2 MW is bent by the two mirrors 2a and 2b and is incident on the beam expander 3 that expands the beam in parallel. Thereafter, the beam is bent by the bending mirror 4 and incident on the beam splitter 9 to be split into a plurality of beams. Each beam (light beam) is collimated by the condenser lens 10 and condensed again. The resulting interference occurs in the nonlinear optical material 6.

  In this case, the peak output of each interference beam is required to be 2.2 MW or more that causes a nonlinear effect, and a laser output proportional to the number of divisions when divided is required. Each beam processes the thin film material 8 below the diffraction limit.

Schematic showing the first embodiment of the present invention The figure which shows the basic principle which concerns on the 1st Embodiment of this invention. Schematic showing the third embodiment of the present invention Schematic showing the fourth embodiment of the present invention Diagram showing conventional laser patterning method

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser oscillator 2a Mirror 2b Mirror 3 Beam expander 4 Bending mirror 5 Condensing lens 6 Nonlinear optical material 7 Thin film material 8 Substrate

Claims (4)

A method of forming a fine groove in a thin film material on a substrate with a laser beam having a peak output of 2.2 MW or more, wherein a beam expander that expands the laser beam into a parallel beam and an expanded collimated laser beam Using a condensing lens for condensing, and a non-linear optical material installed in the vicinity of the focal position of the laser light collected by the condensing lens, a substrate is installed with a close contact or gap with the non-linear optical material, A laser patterning method, wherein a nonlinear effect of the nonlinear optical material is generated by a laser beam of 2.2 MW or more, and a fine groove is formed by relative movement with the thin film material with a beam condensing diameter less than a diffraction limit. . The laser patterning method according to claim 1, wherein the nonlinear optical material is quartz. Beam splitting means for splitting the expanded and collimated laser light into a plurality of beams, and by using an F-theta lens instead of the focusing lens, each of the plurality of light beams is condensed and below the diffraction limit by a nonlinear optical material. The laser patterning method according to claim 2, wherein a plurality of light beams having a beam diameter of 10 mm and a glass substrate on which the thin film material is formed are relatively moved. The light beam divided into a plurality of light beams is condensed by the condensing lens, interference is generated, and light intensity due to the interference is utilized to relatively move the optical axis or the glass substrate on which the thin film material is formed. The laser patterning method according to claim 2, wherein:

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