JPH0688149B2 - Light processing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a selective processing method for performing direct drawing with linear ultraviolet light without using a thin film photoresist used for solar cells, display devices and the like.

"Prior art" YAG laser light (wavelength 1.06μ) is used as a laser processing technology for optical processing without using thin film photoresist.
The m) method is mainly used.

In the laser processing method using this wavelength, a spot-shaped beam is applied to the workpiece and the beam is scanned in the processing direction to form open grooves in a chain of continuous dots. Therefore, the scanning speed of this beam and the energy density required for processing interact very delicately in addition to the thermal conductivity and sublimability of the workpiece. Therefore, there is a drawback that the margin for ensuring the optimum quality is small while improving the productivity in industrialization.
Furthermore, the optical energy of the laser light is 1.23 eV (1.06 μV
m) only On the other hand, a work piece formed on a glass substrate or a semiconductor, for example, a transparent conductive film (hereinafter referred to as CTF) has an optical energy band width of 3 to 4 eV.
Therefore, CTFs such as tin oxide, indium oxide (including ITO), and zinc oxide (ZnO) do not have sufficient light absorption properties for YAG laser light. Also, the Q of YAG laser
In the laser processing method using switch oscillation, the pulsed light has strong average light energy of 0.5 to 1 W (optical diameter 50 μm, focal length 40 mm, pulse frequency 3 KHz, pulse width 60 nsec) at a scanning speed of 30 to 60 cm / min. Must be added and processed in. As a result, the CTF can be processed by this laser light, but at the same time, a microcrack is generated on the substrate provided below it, for example, the glass substrate,
I have damaged it.

[Problems to be solved by the invention] In this processing method using the YAG laser, spot-shaped beams are applied while being repeatedly scanned, so that minute cracks generated in the base substrate have a shape similar to the outer shape of the laser beam. It has a "scale" shape.

In addition, the method using the Q switch oscillation of the YAG laser is likely to cause variations in the peak value output of the laser beam during long-term use, and it is necessary to check with a monitor each time it is used.

Furthermore, it has been completely impossible to selectively form a large number of fine patterns having a width of 10 to 50 μm on the same plane. In addition, after the irradiation, the CTF material in the processed portion was not sufficiently made into an insulator, so it was necessary to perform etching with an acid solution (hydrogen fluoride solution) to completely insulate it.

In addition, when processing a thin film solar cell or other laminated thin film of different materials with a YAG laser, processing selectivity is required for each laminated layer, but when using a YAG laser Has a very small margin of selectivity, and damages even the lower layer of the target work piece, and particularly in solar cells and the like, the use of the YAG laser causes a problem that the device characteristics deteriorate. .

"Means for Solving Problems" The present invention is to solve the above problems and, as its irradiation light, irradiates a pulse laser having a wavelength of 400 nm or less (energy is 3.1 eV or more), 20-200 μm width (eg 150 μm) and length, not a 50 μφ beam spot
A linear pattern of 10 to 60 cm, for example, 30 cm is irradiated with a pulse once or several times at the same location to form a linear pattern. Thus, by linearly irradiating the pulsed light of the wavelength of 400 nm or less (pulse width of 50 nsec or less) shown in the present invention, the absorption efficiency of the optical energy in the CTF is increased by the YAG laser (1.
06μm) and more than 100 times higher, resulting in a processing speed of 10
It is more than twice as fast.

Further, as the initial light, an excimer laser light is used in the present invention, instead of a circular YAG laser having a Gaussian light intensity distribution. Therefore, the initial light irradiation surface has a rectangular shape,
Further, its strength is also substantially uniform on the irradiation surface. For this reason, an optical system such as a so-called beam expander that widens the width of light is used to enlarge the area into a rectangle. After that, the laser beam is condensed in a slit shape by a rod-shaped lens on the cylinder, that is, a cylindrical lens along one of the X or Y directions. However, in order to reduce the width of this condensed light to 50 μm or less, the spherical aberration of this cylindrical lens (rod-shaped condensing lens) cannot be ignored. For this reason, a region where the intensity is weakened according to the Gaussian distribution is generated in the peripheral portion of the condensed light, and the break at the end of the line of the condensed light becomes unclear. Therefore, it becomes further impossible to form a linear groove having a width of 10 to 30 μm, for example, 20 μm. Therefore, in the present invention, before entering the laser light to the cylindrical lens, through the slit, after converging the incident light to a width where the spherical aberration of the cylindrical lens can be ignored, it is condensed by the cylindrical lens, and the width is 10 to 30 μm. Moreover, it is possible to irradiate a laser beam with a sharp edge.

Furthermore, when processing is performed using such a narrow laser beam, the surface to be processed is irradiated with this laser light a plurality of times to perform selective processing that does not damage the underlying layer of the surface to be processed at all. It is characterized by doing.

[Operation] An optical system in which a linear groove is processed over a length of 10 to 60 cm, for example, 30 cm by irradiating the same position with pulsed light once or several times, and the groove width can be ignored for spherical aberration. Can be used to make an extremely fine shape of 10 to 30 μm. Further, since the pulsed light laser is used instead of the Q switch method of YAG laser light, the intensity of the peak value can be precisely controlled.

As a result, it becomes possible to selectively remove the slit open groove of the work piece, for example, CTF, without damaging the glass substrate that is the base substrate, and at the same time, vacuum, clean air, or a space between the mask and the work piece. By injecting nitrogen, it is possible to positively drop flying objects generated by laser light irradiation of the work piece to prevent it.

Further, powdery residuals remaining in the processed portion after forming the open groove can be sufficiently removed by ultrasonic cleaning with a cleaning liquid such as alcohol or acetone, so-called resist coating, etching of the processed material, resist Many processes such as removal have been completely eliminated, and the use of pollution materials has been eliminated.

In addition, since the slit is incorporated in the optical system before focusing the laser light, there is almost no damage to the slit by the laser light. Further, the mechanical processing accuracy with respect to the slit interval need not be so severe, and the shape of the beam is determined by being condensed by the cylindrical lens.

Example 1 FIG. 1 shows a system diagram of laser processing of the present invention using an excimer laser. Excimer laser (1) (wavelength 248nm, Eg =
5.0 eV) was used. Then, as shown in FIG. 2 (A), the initial light beam (20) has a size of 16 mm × 20 mm, and the efficiency is 3%, so that it has 350 mJ. Further, the beam expander (2) made the beam longer or larger. That is, it was enlarged to 16 mm x 300 mm (Fig. 2 (21)). Energy density of 5.6 × 10 ^-2 mJ / mm ² was obtained in this device.

Next, the laser beam is transmitted through a slit (3) having a distance of 2 mm × 300 mm to obtain a laser beam (22) of 2 mm × 300 mm. (FIG. 2 (C)) Furthermore, the cylindrical lens (4) made of synthetic quartz was focused so that the groove width on the processed surface was 20 μm. (FIG. 2 (D)) The width of the slit used at this time is not particularly determined, but it is necessary to narrow the laser beam to such an extent that the spherical aberration of the cylindrical lens does not affect it. Further, the groove width of the workpiece can be arbitrarily selected depending on the performance of the cylindrical lens.

As shown in FIG. 3, a slit-shaped beam (23) having a length of 30 cm and a width of 20 μ is linearly irradiated to the workpiece (11) on the substrate (10) to perform processing, and the open groove (5 ) Was formed.

In the case of this example, an excimer laser (manufactured by Questec Inc.) was used for a substrate (10) having a transparent conductive film on glass (Eg = 3.5 eV) as a surface to be processed.

The pulsed light was 248 nm light from a KrF excimer laser.
This is because the optical energy band width of the light is 5.0 eV, so that the object to be processed absorbs light sufficiently and only the transparent conductive film can be selectively processed.

Pulse width 20nsec, repetition frequency 1-100Hz, eg 10H
z, and tin oxide (SnO ₂ ) which is CTF (translucent conductive film) on a glass substrate was used as the work piece.

When this coating was processed, the open groove (5 CTFs) was completely turbid and turned into fine powder by the irradiation of the linear pulsed light only once. This was subjected to ultrasonic cleaning (frequency: 29 KHz) with an aqueous acetone solution for about 1 to 10 minutes to remove this CTF. The underlying soda glass was not damaged at all.

FIG. 2 shows the shape of the laser beam light in FIG. That is, the state of being irradiated with laser light is the second
It becomes a rectangle (20) in the figure (A). This is expanded (21) in the length direction by a beam expander to obtain FIG. 2 (B).
Furthermore, the slit narrows the shorter side of the laser beam (22). After that, the shorter side is condensed by the cylindrical lens, and the beam shape (23) shown in FIG.
Becomes

FIG. 3 shows that a substrate is irradiated with slit-shaped pulsed light to form a plurality of open grooves (5, 6, 7, ... N). Thus, one open groove is formed only by irradiating the pulse once. After that, change the Y table (Fig. 1 (25)) to, for example, 15
Move mm and add the next pulse (6). Move 15 mm further and add the next pulse (7). Thus, by applying the pulse n times, the plurality of open grooves are divided into n over a large area.

Example 2 In this example, the same laser light and optical system as in Example 1 were used, but a thin film solar cell having an integrated structure was used as the workpiece. The method of the present invention was used for the third laser scribing process of a thin film solar cell having a sectional structure as shown in FIG. That is, as shown in FIG. 4, a transparent electrode (27) patterned by the method of Example 1 is provided on a glass substrate (26), and the entire surface thereof is further subjected to a known plasma CVD method to form a PIN type amorphous silicon semiconductor (28). After forming, the second LS processing (31) is performed by a laser scribing method using a known YAG laser. At this time, the laser processing method using a YAG laser processed the transparent electrode (27) which is the base of the amorphous silicon semiconductor (28) which is the object to be processed, but had little influence on the characteristics of the element.

Next, aluminum is formed as the back surface electrode (29) and the third electrode is formed.
The LS processing (32) was performed using the same laser light and optical system as in Example 1.

The third LS processing (32) was carried out by irradiating the laser light applied at this time not only with one pulse but also a plurality of times, preferably 2 to 5 times. FIG. 5 shows a graph plotted against the number of times of laser light irradiation that adds the photoelectric conversion efficiency of the thin film solar cell thus formed.

As is clear from the figure, the photoelectric conversion efficiency is improved when the laser light irradiation is performed more than once.

It can also be seen that the efficiency is reduced again when it is added more than 6 times.

As is clear from these, the efficiency is improved when the laser light is irradiated twice or more and five times or less.

In this case, the back electrode (29) when the laser light is irradiated once
Is not sufficiently insulated, and a decrease in efficiency is expected due to the generation of a large amount of leakage current. Also, when irradiated 6 times or more, the surface of the underlying amorphous silicon semiconductor (28) is crystallized. Therefore, similarly, it is expected that the leakage current is generated and the efficiency is reduced. Further, FIG. 6 shows the results of changing the energy of the laser light applied with the number of times of laser light irradiation being twice.

As is clear from the figure, in this case, the characteristics were the best in the energy range of 0.85 to 1.5 J / cm ² .

From this range, it is possible to raise the energy density even more difficult in practice, but in that case, it was necessary to further increase the number of times of laser light irradiation.

Practically, this range had good processing characteristics.

[Effect] According to the present invention, in laser processing of a thin film solar cell or the like, a processing margin is increased in selective processing with an underlayer, and processing can be performed more easily.

When producing a large number of linear grooves according to the present invention, for example, 15
If you manufacture a width of 20μ at mm intervals, and if it is 10Hz / pulse,
It was possible in 0.8 minutes. As a result, compared to the case of patterning using a photoresist by the conventional mask align method, the number of steps is 7 steps to 2 steps (light irradiation, cleaning), and the working time is 5 minutes to 10 minutes. It is possible and extremely low cost when making a large number of linear grooves,
High productivity was achieved.

In the present invention, the case where the width between the open grooves (the area to be left without processing) is large is described. However, by connecting the light irradiations side by side, it is possible to make the remaining area 20 μm and the removed portion 400 μm, for example.

Further, in the optical system of the present invention, an integrator, a condenser lens, and a projection lens may be inserted in parallel between the beam expander and the surface to be processed in order to make the optical system more accurate.

[Brief description of drawings]

FIG. 1 shows an outline of the optical processing method of the present invention. FIG. 2 shows the beam shape of the laser light. FIG. 3 shows a manufacturing process of the groove on the substrate. FIG. 4 shows a sectional view of the workpiece. FIG. 5 and FIG. 6 show the characteristics of the solar cell formed by the method of the present invention.

Claims (1)

[Claims] 1. An excimer laser beam is expanded in area by a beam expander, passed through a slit, and then passed through a cylindrical lens to form a slit-shaped beam, and the slit-shaped beam is applied to a workpiece. An optical processing method, characterized in that an open groove is formed in the workpiece by doing so.