JPH03276662A - Wafer cutting method - Google Patents

Abstract

PURPOSE:To cut off a wafer without producing any evaporated particles at all by a method wherein the wafer surface is irradiated with laser beams focussed by an optical system such as a lens and then the wafer is scanned along a prospected cutting line in the proper mean power density and at the scanning rate to produce no surface evaporation nor removal so that the cracking may be induced and propagated by thermal stress to cut off the wafer. CONSTITUTION:The continuously oscillating YAG laser beams are focussed by a quartz glass lens. When a wafer is scanned in the (011) direction and the (011) direction (a direction making 45 deg. with the (011) direction), in the relation between a sliceable irradiating laser power and the scanning rate, both factors shall be on the lower side of the curves respectively displayed by solid lines preferably on the curves. That is, the wafer can be cut off without evaporating the material meeting the requirements that in the (011) direction, the laser power exceeds 40W but not exceeding 70W, while in the (011) direction, the laser power exceeds 50W but not exceeding 70W, and the scanning rate not exceeding 8mm/s. At this time, cutting crack is generated at the position slightly deviated out of the central position of the laser spot but in the deviated amount not exceeding 0.2mm in the (011) direction also not exceeding 0.3mm in the (011) direction. Accordingly, the optimum requirements of the irradiation laser power exceeding 40W but not exceeding 70W as well as the laser scanning rate not exceeding 15mm/s can be selected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of cleaving a wafer by utilizing crack generation and propagation due to thermal stress during laser beam irradiation.

[Conventional technology] In the so-called dicing process, in which integrated circuits are formed on a silicon wafer and then divided into individual chips, conventionally, the peripheral blade cutting method or the grooving/pushing method using laser drilling (laser stari-pin) has been used in practice. has been made into The peripheral blade cutting method is a method of cutting the wafer into a dice shape using a thin-bladed diamond grindstone with a blade thickness of several tens of micrometers or more.Practically speaking, it is currently the most commonly used method, and it requires a large cutting allowance and processing fluid. Post-processing is troublesome, the cutting speed is slow, and a decline in machining performance due to grindstone wear is unavoidable.
There are other problems. On the other hand, pulse mode laser scribing is a method in which a YAG laser is focused on a minute spot and scanned to continuously drill minute holes in the form of perforations, but it is easy to cause contamination due to re-deposition of evaporated particles. It hasn't been used much lately.

[Problems to be Solved by the Invention] As mentioned above, all conventional wafer dicing methods involve material removal, so chips and evaporated particles may adhere to the integrated circuits formed on the wafer F or be processed. Contamination from the liquid was likely to occur, which was a major cause of lower production yields.

The present invention has been made to solve these problems, and provides a method of dividing a wafer using laser light without generating evaporated particles.

[Means for Solving the Problems] In order to achieve the above object, the present invention irradiates the wafer surface with a laser beam focused by an optical system such as a lens, and uses an appropriate average power that does not cause evaporation or removal of the surface. The method is characterized in that it scans along the planned dividing line at a high density and scanning speed to induce crack generation and propagation due to thermal stress, thereby causing the cutting.

In the present invention, specifically, the above-mentioned irradiation laser power is
0W or less and 40W or more and laser scanning speed]5+nm
It is preferable to keep it below /s.

[Operation] According to the above-mentioned cleaving method, since evaporated particles and molten particles are not generated or scattered, the particles do not re-adhere to the wafer surface and contaminate it, so the product yield of formed integrated circuits is improved. I can do it. Additionally, since no machining fluid is used, there is no need for cleaning, and the machining environment can be kept clean.

[Example] Fig. 1 is a basic configuration diagram of the laser cutting method, in which a laser beam 1 emitted from a laser oscillator is passed through an optical system 2, 2' such as a lens.
This is a method in which the beam is focused and irradiated onto the Si wafer 3 to be cut from a substantially perpendicular direction.

Lapping-finished Si single crystal with a thickness of 0.8 mm (1
An example will be described regarding the case of cutting a 00) plane wafer.

Cutting is possible when a continuous wave YAG laser is focused with a quartz glass lens to a spot diameter of 0.2 to 0.3 mmφ and scanned in the <011> direction and (001) direction (45 degrees from (011)). The relationship between the irradiation laser power and the scanning speed is shown in FIG. The conditions under which the cutting is possible are below the curves shown by solid lines, preferably on the curves. That is, in the <011> direction, the racer power is 40W or more and 70W.
W or less, the scanning speed is 11 mm/s or less, and in the (001> direction, the laser power is north of 50 W and is 70 W or less and the scanning speed is 8
Under conditions of mm/s or less, cutting can be performed without causing evaporation of the material. The occurrence position of the cutting crack is slightly shifted from the center position of the laser spot, but the amount of shift is less than 0.2 mm in the <011> direction and 0.3[[1 m] in the (001) direction.
It is as follows.

The laser used is not limited to the YAG laser, but any laser that causes light absorption on the Si surface can be used. Pulse oscillation may be used as the laser oscillation mode, but continuous oscillation is preferable in order to increase thermal stress and facilitate crank generation. Further, the laser spot/shape may be focused in a circle using a spherical lens, or may be focused on a line using a circumferential lens and scanned so that the scanning direction coincides with the longitudinal direction of the laser spot.

Although the above embodiments were carried out in the air, it is also effective to forcibly cool the vicinity of the laser irradiation part to facilitate the occurrence of cracks. Specifically, 02. N2. A
It is practical to spray a gas such as r, He, etc. onto the laser irradiation section. Of course, it is also effective to expose the Si wafer to a coolant such as liquid nitrogen to cool the entire wafer and then irradiate it with laser.

Furthermore, in order to facilitate the occurrence of cracks, it is also effective to add a mechanical tensioning mechanism or a bending mechanism so that tensile stress is applied in advance in a direction perpendicular to the planned fracture surface.

It is desirable that the Si surface can be cut even in a mirror-like state, or that it be a rough surface in order to improve absorption of laser light. It is also effective to irradiate laser light from the back side that has been lapped or ground.

[Effects of the Invention] As explained above, according to the cleaving method of the present invention, a Si wafer can be shunted without removing any material, thereby preventing the integrated circuits formed on the wafer from becoming contaminated by the adhesion of scattered particles. Product defects can be eliminated without any problems. In addition, processing efficiency is high and post-processing is not required, so a significant improvement in production efficiency is expected.

[Brief explanation of drawings]

Figure 1 shows the basic structure of the tree cutting method, and Figure 2 shows the S
FIG. 3 is a diagram showing the relationship between laser power and laser scanning speed that enable laser cutting of an i wafer. 1... Irradiation laser beam, 2, 2'... Optical system for focusing laser beam, 3... Si single crystal wafer

Claims (1)

[Claims] 1. After forming an integrated circuit on a silicon wafer, in the processing step (usually called dicing) for dividing it into individual circuit chips, laser light is irradiated along the planned dividing line.
A wafer cutting method characterized by scanning and generating thermal stress to generate and propagate cracks that reach the back surface of the wafer along the planned dividing line, thereby dividing the wafer. 2. The wafer cutting method according to claim 1, wherein the optimum conditions are selected such that the irradiation laser power is 70 W or less and 40 W or more and the laser scanning speed is 15 mm/s or less.