JP2011079690A - Laser thermal stress dividing of thick plate glass using diffraction grating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus where a surface scribe having a depth of around 200 μm is made by CO<SB>2</SB>laser beam irradiation on glass being used as a solar cell substrate and having a thickness of around 5 mm and where dividing is attained by following machine breaking. <P>SOLUTION: In the glass surface scribing apparatus with a cooling unit where the cross-sectional shape of a CO<SB>2</SB>laser beam is converted to a line beam by a diffraction grating optical element, the line beam is radiated on a glass surface with scanning and the rear of the scanning laser beam is subjected to tracking scanning at the same speed, by lowering the scanning speed to a region of 10-20 mm from a scribe starting point at the edge of the class, the scribe depth in the region is increased to a depth of 3-4 mm, the machine breaking in a following step in the region is made easy, once started breaking is developed over another shallower region being a scribe depth of 200 μm and the thick plate glass having a thickness of 5 mm is divided by using a laser output of 70 W and at a speed of 50 mm/s. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a method for cleaving thermal stress of brittle materials, especially glass for solar cell substrates and glass for flat panel displays. Hereinafter, although the case of glass will be introduced as an example of a workpiece, the present invention can be applied to all brittle materials.

Recently, in the glass cleaving, the thermal stress cleaving method by laser light irradiation has been used in place of the diamond chip mechanical method which has been used for the past several centuries.

  According to this method, defects inherent in the mechanical method, that is, a decrease in glass strength due to the occurrence of microcracks, contamination due to the occurrence of cullet at the time of cleaving, existence of a lower limit value of the applied plate thickness, etc. can be eliminated.

As a result, according to the thermal stress cleaving method, polishing and cleaning, which are subsequent processes of mechanical cleaving, are not required, a mirror surface having a surface roughness of 1 μm or less is obtained, and the product external dimension accuracy is ± 25 μm or more. This method is currently used for glass for flat panel displays having a thickness of 0.7 mm, but in the future, it is desired to use it for glass for solar cell substrates having a thickness of 5 mm.

  The principle of this method is as follows. The glass is heated to the extent that cracks, melting, vaporization, etc. do not occur by laser irradiation locally. At this time, the glass heating section tries to expand thermally, but cannot sufficiently expand due to the reaction from the surrounding glass, and compressive stress is generated around the irradiation point. Even in the peripheral non-heated region, the peripheral portion is further distorted by the expansion from the heating portion, and as a result, compressive stress is generated. These compressive stresses are radial. By the way, when an object has a compressive stress, a tensile stress related to the Poisson's ratio is generated in the orthogonal direction. Here, the direction is a tangential direction. This is shown in FIG.

This figure shows the change of the radial stress component σx and the tangential stress component σy depending on the location when there is a temperature rise in the Gaussian distribution centered at the origin. The former is compressive stress from the beginning to the end (negative value in the figure), while the latter is compressive stress at the heating center, but changes to tensile stress (positive value in the figure) when leaving the center. Based on the stress distribution shown in the figure, a general temperature distribution can be handled as a linear superposition of the stress distribution. Even in that case, there is no difference that compressive stress and tensile stress are generated in the orthogonal direction at each point on the glass plate.

Of these stresses, the tensile stress is directly related to the cleaving. When the stress exceeds the fracture toughness value, which is a material specific value, fracture occurs everywhere and cannot be controlled. This is a destructive phenomenon, not processing. In the case of the thermal stress cleaving as in the present invention, the tensile stress is selected to be equal to or less than the same value, so this fracture does not occur.

However, if there is a crack at the position where the tensile stress is present, stress expansion occurs at the tip, and if this amplified tensile stress exceeds the fracture toughness value of the material, the crack expands. That is, as the progress of the crack, controlled cleaving as processing occurs. By scanning the laser beam irradiation point, the crack can be extended. In this thermal stress cleaving, the fractured surface is similar to the cleavage plane of the crystal, so there is no generation of microcracks and cullet, and the disadvantages of the mechanical method described above can be eliminated, and the glass processing method is extremely excellent. Will have.

  There are two types of thermal stress cleaving shown in FIG. As shown in FIG. 3A, as a result of the heating 2 and the cooling 3, the crack 4 occurs only in the surface layer (for example, a depth of 100 μm) of the workpiece 1 and is generally called a surface scribe. 5 indicates the scribe direction.

On the other hand, what is shown in FIG. 3B is one in which cracks occur over the entire thickness of the workpiece and is generally referred to as full cut. 5 indicates a cleaving direction, and 6 indicates a cleaving line. In the case of the full cut shown in the figure, cooling is not performed. Of course, cooling is advantageous for forming the tensile stress, but there is no method for cooling the work in bulk. Both have advantages and disadvantages. The former requires a break process after scribing, which is the biggest drawback. This process is not necessary for the latter, but the technique has a drawback of a so-called size effect such that the cleaving speed is lowered for a large workpiece and the cleaving position accuracy is lowered near the end of the workpiece.

  This surface scribing technology by laser irradiation of glass has been vigorously developed by Kondratenco Bradymier Stepanovic, and the Japanese Patent of Patent Document 1 has been established. This patent is also established as a European patent and a US patent in Patent Documents 2 and 3. He selected CO2 laser light as the laser light.

Similarly, a Japanese patent of Patent Document 4 has been established in which a surface sliver is performed using a CO2 laser, and a technique of converting a circularly symmetric laser beam into a plurality of beam spot arrays arranged in a straight line by a beam splitter.

In order to eliminate the above-mentioned defects, the full-cut technology development shown in FIG. 3 (b) was pursued for the above surface scribing patent. A patent has been granted.

  Whether the thermal stress cleaving becomes a full cut or a surface scribe depends on whether the workpiece heating is a surface phenomenon or a bulk phenomenon (by the laser of Non-Patent Document 1), the thermal stress is applied only to the surface layer. Depending on whether it occurs or occurs over the entire thickness of the workpiece. As described above, since both have merits and demerits, they may be properly used according to the purpose. This patent is a technical improvement in surface scribe so that the glass plate thickness can be about 5 mm for solar cells.

Kondratenko V.S., method for cutting brittle non-metallic materials, Japanese Patent No. 3027768 Kondratenko Vladimir S., Method of splitting non-metallic materials, EP0633867B1 Kondratenko Vladimir S., Method of splitting non-metallic materials, USP5609284 Tsutomu Teramoto, cutting device, Japanese Patent No. 3792639 Hiroshi Miura, Norio Kabebe, Cleaving method and apparatus for brittle materials, Japanese Patent No. 4179314

Vladimir V. Fedorov et al. 3.77-5.05 μm Tunable Solid-State Lasers Based on Fe2 + -Doped ZnSeCrystals Operating at Low and Room Temperatures, IEEE Journal of Quantum Electronics, Vol. 42, No. 9, pp 906-917, September ( 2006).

The thermal stress cleaving due to laser light irradiation or the like is characterized by a higher quality processing method than a mechanical method. On the other hand, this processing method also has drawbacks. One drawback of surface scribe is that it cannot be applied to thick glass. At present, this technique is used for cleaving glass for flat panel displays, and the glass plate thickness in this case is usually 0.7 mm. When the glass surface is irradiated with CO2 laser light, 99% of the incident energy is absorbed by the surface layer having a depth of 3.7 μm. For this reason, the sliver depth is usually limited to about 200 μm. If the plate thickness is 0.7 mm, a subsequent mechanical break is possible with a scribe depth of 200 μm. However, when the plate thickness is about 5 mm, a mechanical break is not possible at this scribe depth. With today's scribe technology, laser cutting of solar cell glass is not performed.

In order to solve this problem, the present invention uses the stress intensity phenomenon at the crack tip. When there is a surface scribe having a depth of 200 μm in a glass having a thickness of 5 mm, the crack cannot be propagated in the vertical direction all at once.

However, a mechanical break is executed only in a limited area near the edge of the glass in the thickness direction, and then the mechanical break is advanced in the direction along the scribe line. Just do it. A mechanical break is relatively easy to continue once it can be started, but is difficult to start first. For this reason, the scribe depth is not limited to 200 μm in the above-described region of the glass edge portion, and it is necessary to make the scribe depth almost the same as the total plate thickness.

ADVANTAGE OF THE INVENTION According to this invention, object plate | board thickness can be increased to 5 mm of the glass for solar cells, implement | achieving the high quality which a thermal stress cleaving has. Laser glass breaking has many great technical advantages in processing quality, but has not been able to replace the diamond tip mechanical system that has been used over the past centuries. The present invention changes such a situation.

The advantages of the thermal stress cleaving of glass realized by the present invention include the following.
1) Cleaving can be realized at a significantly higher speed than the conventional method.
2) No post-process such as polishing or cleaning after cleaving is required.
3) There is no generation of micro cracks in the vicinity of the fractured surface, and the material strength of the workpiece is high.
4) There is no adhesion of cullet on the cut surface and it is clean.
5) The cleaving position accuracy is increased.
6) The fractured surface is sufficiently perpendicular to the glass surface.
7) The fractured surface is a mirror surface and the surface roughness is good.
9) The cleaving can be automated.

Schematic diagram of ideal scribe depth distribution that facilitates mechanical breakage of thick glass. The generated thermal stress distribution diagram by Gaussian temperature distribution. Schematic diagram of surface scribe (a) and full cut (b) by laser irradiation of glass. The stress intensity factor distribution map by scanning laser spot heating. Conversion of Gaussian laser beam to line beam by DOE.

  FIG. 1 is a schematic diagram showing how the surface scribe depth changes in the scribe line direction enabling the present invention. The figure shows a case of soda glass having a thickness of 5 mm, which is the thickness of a normal solar cell glass. The vertical direction corresponds to the glass plate thickness and the surface scribe depth, and the horizontal direction is the scribe direction. As shown in the figure, the scribe depth is as deep as about 3-4 mm in a certain length range (from about 10 mm to 20 mm in the inventor's demonstration experiment) from the scribe start point of the glass edge, and thereafter, FIG. As shown in FIG. 4, the normal squibing depth is gradually reduced to 200 μm. The laser scanning speed was 30-53 mm / S when the irradiation laser output was 70 W, but it was effective to reduce the speed to 20 mm / S to obtain a deep scribe at the glass edge.

  When the sliver depth has such a distribution, a mechanical break can be easily performed over the entire plate thickness by limiting the region to the deep portion. Even when the scribe depth is as shallow as 200 μm beyond the region, it is easy to gradually advance the mechanical break in the scribe direction. Thus, the scribe depth along the scribe line is as shown in FIG. 1, and a thick plate of about 5 mm can be mechanically broken over the entire length.

  As described above, the method of creating the scribe distribution shown in FIG. 1 is to reduce the laser beam scanning speed in order to increase the scribe depth. Here, it will be described with reference to FIG. 4 that the scribing depth becomes deeper at the glass end portion than at the end portion due to the thermal stress generation mechanism. FIG. 4 shows a change in the stress intensity factor K1 induced in the glass plate in the laser beam scanning direction with respect to glass heating by laser beam irradiation under certain conditions. Laser beam scanning is performed continuously. In FIG. 4, the stress intensity factor distribution when the beam reaches seven points is shown together with the heating temperature distribution. Here, we focus only on changes in the stress intensity factor that are directly related to the scribe depth. In FIG. 4, it can be seen that the stress intensity factor distribution when the laser beam position is three positions of 10 mm, 30 mm, and 100 mm from the end portion has a large value in the vicinity of the glass end portion in any case. This increase in stress distribution is directly linked to the increase in scribe depth. FIG. 4 shows data under certain heating conditions, but the trend shown here is general.

Now, examples will be described. The present invention belongs to the surface scribe shown in FIG. Accordingly, the surface of the glass is scanned by heating by CO2 laser light irradiation and the cooling means by spraying the cooling liquid behind the glass surface. Moreover, the initial crack is provided in the glass edge part from which scribing is started. The principles and methods of these techniques are now well known.

  In FIG. 3 (a), the laser beam shows a case where the cross-sectional shape is a small circle. However, in the case where the scribe is linear or if the depth is to be increased, the heating time of the glass is increased. Laser light having a cross-sectional shape of a line beam may be used. Since the laser light emitted from the laser oscillator is usually a Gaussian beam having a circular cross-sectional shape, the cross-sectional shape of the beam must be converted by various methods.

One method is shown in FIG. It uses a Gaussian laser beam 8 emitted from a laser oscillator 7 converted into a line beam using a diffraction grating type optical element (DOE) 9 as a line beam homogenizer. FIG. 5 is a schematic diagram showing the state of this conversion. In FIG. 5, reference numeral 10 denotes a laser beam after passing through the DOE, and a line beam 11 which is a design specification is realized at a predetermined position. As this line beam, a beam having a width of about 0.1-1 mm and a length of about 25 mm is typically used. In this case, the intensity distribution is uniform in the length direction, but the width direction can be uniform or Gaussian. Also, the intensity distribution can be changed by adjusting the incident laser beam diameter, position, and the like. In the case of the present embodiment, the cleaving position accuracy can be further increased and the surface scribe depth can be further increased.

After these steps, a machine break is performed along the scribe line.

What has been described above are several embodiments for realizing the functions of the present invention, and it goes without saying that the spirit of the present invention can be realized in many other ways.

In this way, if the thermal stress cleaving of glass is introduced into the manufacturing process of solar cells and flat panel displays, the effect is immeasurable in improving processing speed, processing quality, economy, etc., and overcoming the weaknesses of conventional technologies. Become a thing. These processes are currently performed with a diamond cutter, which presents problems such as the necessity of a cleaning step after cutting for generating cullet and a reduction in material strength due to the presence of microcracks. Such a problem can be solved by the thermal stress cleaving according to the present invention.

1 Work
2 Heating 3 Cooling 4 Surface scribing 5 Scribe direction or cleaving direction 6 Cleavage line 7 Laser oscillator 8 Gaussian laser beam 9 Diffraction grating type optical element (DOE)
10 Laser beam after passing through DOE 11 Line beam cross-sectional shape

Claims (1)

A glass surface scriber device with a cooling unit that converts CO2 laser light into a line beam by a diffraction grating optical element, irradiates the glass surface with scanning, and follows and scans the scanning laser beam at the same speed. In this case, the scribing depth is increased by reducing the scanning speed near the scribe start point at the glass edge, facilitating a subsequent mechanical break in the same region, Characterized by progressing over an area.

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