CN114226960A

CN114226960A - Ultrafast laser cutting method for silicon wafer

Info

Publication number: CN114226960A
Application number: CN202111668437.9A
Authority: CN
Inventors: 蒋仕彬
Original assignee: Hangzhou Yinhu Laser Technology Co ltd
Current assignee: Hangzhou Yinhu Laser Technology Co ltd
Priority date: 2021-12-31
Filing date: 2021-12-31
Publication date: 2022-03-25

Abstract

The invention discloses an ultrafast laser cutting method of a silicon wafer, which is characterized by comprising the following steps: the method comprises the steps of adopting a fiber laser with the output optical wavelength of 1900-2300 nanometers as a light source, focusing a laser beam into the silicon wafer to be cut, enabling the diameter of a light spot of a focusing point to be smaller than 10 micrometers, generating longitudinal microcracks near the focusing point, moving the focusing point along a cutting track to form cutting envelope, and then separating the silicon wafer to be cut through external force to finish cutting. The invention can adopt the recessive method to carry out laser cutting on the silicon chip, and has the advantages of high speed, less pollution, less loss and high cutting quality compared with the prior scheme.

Description

Ultrafast laser cutting method for silicon wafer

Technical Field

The invention relates to a silicon wafer cutting method, in particular to a processing method for realizing concealed cutting of a silicon wafer.

Background

Single crystal silicon is a hard and brittle material with diamond lattices, and has wide applications in the semiconductor industry, the photovoltaic industry and the like. The silicon material has high hardness and strong brittleness, and the traditional diamond sheet machining mode has the defects of poor cutting precision, low efficiency, large surface damage, high material loss and the like. With the development of science and technology, the requirements on the aspects of silicon wafer cutting quality, efficiency, material loss and the like are higher and higher, and the technology of cutting silicon wafers by laser is gradually applied. The laser cutting has the characteristics of no contact, no cutting force, small heat influence, environmental protection, no pollution and the like. The laser spot can realize micron-level tight focusing, thereby realizing precise and ultra-precise micro-nano machining. In addition, the laser system is well compatible with a computer control system, automatic silicon wafer cutting can be rapidly realized, and the production efficiency is greatly improved compared with that of the traditional process.

At present, the laser silicon wafer cutting process is mainly divided into two types: the first is a fusion cutting method, which utilizes laser thermal effect to melt and gasify near a surface focus point, and adopts means such as high-speed airflow to remove slag to form a processing curve; the other is a thermal cracking method, namely, laser is adopted to irradiate the silicon wafer, a temperature gradient field is generated, and the silicon wafer with controllable crack tracks is cracked through thermal stress. The hot cracking method has the advantages that the high-temperature surface of the material can not appear, and the cutting quality, the material loss and the like are better than those of the hot melting method. However, the existing silicon wafer cutting methods still have the problems of particle contamination, wide cut and the like, and cannot meet further requirements.

The laser wavelength for cutting the silicon wafer is usually between 193nm and 1064 nm. For example, the ' study on 355nm all-solid-state ultraviolet laser cutting silicon wafer ' of Zhang Fei et al at the national conference on semiconductor integrated circuit silicon materials ' uses 355nm ultraviolet laser to cut silicon wafers, but the wavelength of YAG laser (1064 nm) is considered to be well used for silicon with electronic band gap (1.11 eV or 1117 nm), so that 1064nm YAG laser is generally adopted by the current commercial silicon wafer laser cutting equipment.

One consideration for further improving the cutting quality is to use a stealth method, i.e., laser penetrates the surface of the material and forms a high power density convergence point inside the material to form thermal stress and other effects, while the laser does not generate any effect at the surface because of the low power density. After that, cutting is completed by splitting. However, the silicon material has an absorption efficiency of 1064nm wavelength of 60% or more and a low material transmittance, and thus is inferior in the effect if it is used in the stealth method.

Disclosure of Invention

The invention aims to provide an ultrafast laser cutting method of a silicon wafer, which realizes low-loss, pollution-free and high-quality cutting of the silicon wafer.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows: a ultrafast laser cutting method of a silicon wafer adopts a fiber laser with an output optical wavelength of 1900 nm to 2300 nm as a light source, focuses a laser beam into the silicon wafer to be cut, generates a longitudinal micro-crack near a focusing point with a spot diameter of less than 10 microns, moves the focusing point along a cutting track to form a cutting envelope, and then separates the silicon wafer to be cut by external force to finish cutting.

According to a further technical scheme, the laser beam is a pulse laser beam, the width of each pulse is 50 femtoseconds to 500 picoseconds, and the peak power of each pulse is more than 200 kilowatts.

In order to better focus the laser beam inside the silicon wafer, the surface of the silicon wafer facing the input of the laser beam is a polished surface.

In the above technical solution, one method for moving the focus point along the cutting trajectory is to fix the silicon wafer to be cut on a displacement device, and move the displacement device to realize the movement of the focus point in the silicon wafer to be cut.

In another method, the focus point is moved along the cutting path by providing a galvanometer in the optical path of the laser beam and controlling the galvanometer to move the focus point.

And the displacement device and the galvanometer can be matched to realize the movement of the focusing point.

In the technical scheme, the method for separating the silicon wafer to be cut by external force is heating cracking or liquid adding cracking.

Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:

1. the invention changes the traditional thinking that the laser beam with the wavelength below 1064 nanometers is conventionally adopted to cut the silicon wafer in the field, and adopts the optical fiber laser with the optical wavelength between 1900 nanometers and 2300 nanometers to cut the silicon wafer, and the silicon wafer has higher transmittance to the wave band, and can form a focus point in the silicon wafer without influencing the surface property, thereby being capable of adopting the recessive method to carry out laser cutting on the silicon wafer and having the advantages of higher speed, less pollution, less loss and high cutting quality compared with the prior scheme.

2. The invention can effectively ensure the cutting efficiency by adopting the pulse laser with the width of 50 femtoseconds to 500 picoseconds.

Drawings

FIG. 1 is a schematic flow chart of a method of an embodiment of the present invention;

fig. 2 is a schematic structural diagram of an apparatus according to an embodiment of the present invention.

Detailed Description

The invention is further described with reference to the following figures and examples:

the first embodiment is as follows: referring to the attached figure 1, the ultrafast laser cutting method of the silicon wafer adopts a fiber laser with 1950 nm output optical wavelength as a light source, outputs pulse laser with the pulse width of 200 femtoseconds, focuses laser beams into the silicon wafer to be cut, generates longitudinal microcracks near a focus point, moves the focus point along a cutting track to form a cutting envelope, and finishes cutting by heating the cracks, wherein the peak power of each pulse is more than 200 kilowatts.

To ensure the processing effect, the surface of the silicon wafer facing the input of the laser beam may be first polished.

An apparatus which can be used to carry out the above method is shown in FIG. 2. The fiber laser 101 generates a pulse train laser beam 501, which uses thulium doped fiber as a gain medium, the laser output center wavelength 1950 nm, the pulse width 200 femtoseconds, the single pulse energy 50 nanojoules, the pulse interval 25 nanoseconds, each pulse train containing 2 pulses, each second containing 5 million equidistant pulse trains. The laser beam 501 passes through the lens and the vibrating mirror 201, the diameter of a light spot on the surface of the polished silicon wafer 301 exceeds 30 microns, no physical and chemical effect is generated, and the silicon wafer is transparent to the 1950 nanometer laser and low in transmission loss, so that the light spot with the diameter of 3 microns is converged inside the silicon wafer 301, and microcracks along the transmission direction of the light beam are generated. The silicon chip realizes the relative displacement of light spots through the matching work of the vibrating mirrors in the displacement devices 401 and 201, the cutting envelope is formed, and then the silicon chip is split by heating. Because the internal recessive cutting mode is adopted, no debris is generated, the pollution is less, the surface edge breakage is less, the material loss is less, and the high-quality high-speed silicon wafer cutting is realized.

Claims

1. An ultrafast laser cutting method of a silicon wafer is characterized in that: the method comprises the steps of adopting a fiber laser with the output optical wavelength of 1900-2300 nanometers as a light source, focusing a laser beam into the silicon wafer to be cut, enabling the diameter of a light spot of a focusing point to be smaller than 10 micrometers, generating longitudinal microcracks near the focusing point, moving the focusing point along a cutting track to form cutting envelope, and then separating the silicon wafer to be cut through external force to finish cutting.

2. The ultrafast laser cutting method of silicon wafer according to claim 1, wherein: the laser beam is a pulse laser beam, the width of each pulse is 50 femtoseconds to 500 picoseconds, and the peak power of each pulse is more than 200 kilowatts.

3. The ultrafast laser cutting method of silicon wafer according to claim 1, wherein: the surface of the silicon wafer facing the input of the laser beam is a polished surface.

4. The ultrafast laser cutting method of silicon wafer according to claim 1, wherein: the method for moving the focus point along the cutting track is to fix the silicon slice to be cut on a displacement device, and to move the displacement device to realize the movement of the focus point in the silicon slice to be cut.

5. The ultrafast laser cutting method of silicon wafer according to claim 1, wherein: the method for moving the focus point along the cutting track is to arrange a galvanometer in the light path of the laser beam and to move the focus point by controlling the galvanometer.

6. The ultrafast laser cutting method of silicon wafer according to claim 1, wherein: the method for separating the silicon slice to be cut by external force is heating splinter or adding liquid splinter.