JPS6130049A - Method for laser scribing and device thereof - Google Patents

Abstract

PURPOSE:To prevent generating microcrack by scanning sub laser beam of low energy density before, or before and after main laser beam is scanned along a scribing line of a semiconductor wafer. CONSTITUTION:A wafer 2 is mounted on an X-Y table 1 and is shifted by shift signal MS in a controlling circuit 3. A power supply 5 of a laser oscillator 4 is started by signal KS and a flash light 6 illuminates and the illuminated pulse is condensed 7 and YAG laser 8 is irradiated, then optical excitation is performed. A excited laser beam is taken out through a resonant mirror 10 and Q-switch 11 and focused 16 on the wafer 2 through lenses 13, 14 and a total reflection mirror. A lens 16 is devided into A-C sections whose optical axises and focuses are different and each B and C area is about one third of A area. Passing beams are separated to 9a-9c and are focused to three points (a)-(c) respectively on a wafer. Main beam is beam 9a. As the wafer is pre-heated by the sub beam 9b or 9c, before being irradiated by the main beam 9a, microcrack is not generated by processing heat and also yield and quality are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a laser scribing method and apparatus for scribing a semiconductor wafer into chips using a laser beam.

[Technical background of the invention and its problems] Conventionally, in the manufacturing process of semiconductor devices, laser scribing technology has been used to cut out individual elements from a semiconductor wafer such as a sapphire substrate on which a large number of semiconductor elements are formed. .

FIGS. 2 and 3 of the accompanying drawings are explanatory diagrams of laser scribing. Laser scribing is performed by scanning a laser beam along lattice-like scribing lines that separate individual devices on the semiconductor wafer 2, and forming processing grooves of a constant depth between each semiconductor device. Incidentally, since sapphire substrates and the like have a low light absorption rate, in order to perform sufficient processing, it is necessary to increase the irradiation density by lowering the scanning speed of the laser beam or increasing the intensity of the laser beam. However, when scanning is performed with a laser beam of high irradiation density, microcracks inevitably occur on the side of the processed groove due to processing heat generated during laser beam irradiation. This causes the inconvenience of lowering the yield and quality of semiconductor devices.

Conventionally, these problems have been solved by (a) widening the width of the scribing line so that the influence of microcracks does not reach the semiconductor element, and (b) changing the scanning direction of the laser beam as shown in Figure 2. (C) The scanning direction of the laser beam is limited to specific directions in which microcracks are less likely to occur, determined by the crystal structure of the material that makes up the semiconductor wafer, as shown in the scanning order A to B and B to II. (d) When the direction in which the laser beam is scanned is in a direction where microcracks are less likely to occur, the laser beam is scanned at a normal speed, and in other directions it is scanned at a higher speed. Countermeasures have been considered, such as increasing the intensity of the laser beam for scanning, and lowering the intensity of the laser beam in other directions.

However, in method (a) above, as the scribing width on the semiconductor wafer 2 increases, the area on which semiconductor elements are formed decreases, so the number of semiconductor elements that can be produced with one wafer decreases. In the method (b), the time required for scribing increases, resulting in a decrease in the throughput of the scribing device. On the other hand, with methods (c) and (d), when the scanning speed of the laser beam is high or the intensity of the laser beam is low, it may not be possible to form a groove of sufficient depth on the surface of the semiconductor wafer. There were drawbacks.

[Purpose of the invention]

The present invention has been made in order to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a laser scribing method and apparatus that can prevent the occurrence of microcracks and improve the yield and quality of semiconductor devices. With the goal.

(Summary of the Invention) In order to achieve the above object, the present invention scans a main laser beam along the scribing line of a semiconductor evaporator, and at the same time scans a secondary laser beam with low energy density before or before scanning the main laser beam. A scanning laser scribing method and apparatus are provided.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 4 of the accompanying drawings. FIG. 1 is a block diagram of an apparatus for carrying out the laser scribing method according to the same embodiment.

A semiconductor wafer 2 (for example, a sapphire substrate) to be scribed is placed on the upper surface of the XY table 1, and the semiconductor wafer 2 is moved in a horizontal plane according to a movement control signal MS from a control circuit 3. The laser oscillator 4 is activated by the drive control signal KS from the control circuit 3.
The flash lamp 6 is caused to emit light, and the emitted light pulses from the flash lamp 6 are focused on the condensing lens barrel 7C and irradiated onto the YAG laser Otsudo 8 for optical excitation. The optically excited beam is extracted to the outside via a resonant mirror 10 and a Q switch 11, and is sent out as a laser beam 9. Note that the Q switch 11 is driven by a drive device 12. A laser beam 9 emitted from a laser oscillator 4 is reflected by a total reflection mirror 15 via a concave lens 13 and a convex lens 14, and is focused onto a desired spot by a condensing lens 16 and irradiated onto the semiconductor wafer 2.

FIG. 4 is an explanatory diagram of the laser beam irradiation shown in FIG.
(b) shows the state seen from the side, and (C) shows the state seen from the plane of the semiconductor wafer. As shown in FIG. 4(a), the condensing lens 16 has three parts A and B having different optical axes and focal points.

It is divided into C. When the laser beam 9 passes through the condensing lens 16, the light that has passed through each part A, B, and C is divided into three laser beams 9a and 9, respectively, as shown in FIG. 4(b).
The three points a and b on the semiconductor wafer 2 are divided into b and 9c.
, c, respectively. The areas of portions B and C of the condenser lens 16 are each approximately one-third of the area of portion A, and the laser beam 9a is the main beam, and the laser beams 9b and 9c are secondary beams, which focus on the semiconductor wafer. 2
is irradiated.

The points a, b, and c are arranged on a straight line as shown in FIG. Ru. The secondary laser beams 9b and 9c are placed on both sides of the main laser beam 9a so that the main laser beam 9a scans the area on the semiconductor wafer 2 before it scans it, regardless of the scanning direction. Laser beams 9b, 9c
This is to ensure that either one of them is irradiated. By doing so, it becomes possible to select the scanning direction of the laser beam depending on the crystal structure of the wafer. Furthermore, since either of the secondary laser beams is irradiated even after processing with the main laser beam, the processed portion will not cool down rapidly.

Next, the operation of the embodiment shown in FIGS. 1 and 4 will be explained. First, the semiconductor wafer 2 to be scribed is set on the XY table 1 in a predetermined orientation. In this state, according to the movement control signal MS from the control circuit 3, the laser beams 9a and 9b are moved.

The XY table 1 is moved so that 9C scans the scribing line. By simultaneously driving the laser oscillator 4, the scribing line on the semiconductor wafer 2 is irradiated with one of the secondary laser beams 9b and 9C, and then the main laser beam 9a is irradiated. In this way, since the semiconductor wafer 2 is preheated by the secondary laser beam before being processed by the main laser beam, microcracks etc. do not occur due to the influence of processing heat. Furthermore, since a powerful main laser beam can be used, productivity can be improved. Additionally, a powerful primary laser beam can create a deep enough marking on the semiconductor wafer 2 to facilitate mechanical separation.

Note that the method of dividing the condenser lens 16 is not limited to the example shown in FIG. It can also be implemented by changing the shape or method (for example, arranging them in concentric circles). Furthermore, instead of producing the main laser beam 9a and the secondary laser beams 9b and 9c from the same light source, a configuration may be adopted in which they are obtained from separate laser light sources.
A similar effect can be obtained. Further, in the above embodiment, the secondary laser beams 9b and 9c are arranged before and after the main laser beam 9a, but they may be arranged only in front of the main laser beam 9a.

〔Effect of the invention〕

As described above, according to the present invention, microcracks are generated due to the influence of processing heat by using a main laser beam and a secondary laser beam with lower energy density in laser scribing. It is possible to realize a laser scribing method and apparatus that makes it possible to suppress the above. As a result, it becomes possible to improve the production yield and quality of semiconductor devices.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an apparatus for implementing a laser scribing method according to an embodiment of the present invention, FIGS. 2 and 3 are plan views showing a laser beam scanning method, and FIG. 4 is similar to FIG. 1. FIG. 2 is an explanatory diagram of the optical path of a laser beam irradiated onto a semiconductor wafer in the example shown. 1...XY table, 2...semiconductor wafer, 3...
- Control circuit, 4... Laser oscillator, 9... Laser beam, 16... Condensing lens. Applicant's agent Kiyoshi Inomata Figure 1 Figure 3 Figure 2 Figure 4

Claims (1)

Claims: 1. A laser scribing method in which a main laser beam is scanned along a scribing line of a semiconductor wafer, and a secondary laser beam with low energy density is scanned before or after the main laser beam scan. 2. Laser beam generating means that generates a main laser beam with high energy density and a secondary laser beam with low energy density and focuses these laser beams on at least two points on a semiconductor wafer, and an imaging point of this laser beam. A laser scribing apparatus comprising: a scanning means for relatively moving the laser beam generating means and the semiconductor wafer so that the laser beam is placed on the scribing line of the semiconductor wafer.