Jörg Schille

Study of fast laser induced cutting of silicon materials

We report on a fast machining process for cutting silicon wafers using laser radiation without melting or ablating and without additional pretreatment. For the laser induced cutting of silicon materials a defocused Gaussian laser beam has been guided over the wafer surface. In the course of this, the laser radiation caused a thermal induced area of tension without affecting the material in any other way. With the beginning of the tension cracking process in the laser induced area of tension emerged a crack, which could be guided by the laser radiation along any direction over the wafer surface. The achieved cutting speed was greater than 1 m/s. We present results for different material modifications and wafer thicknesses. The qualitative assessment is based on SEM images of the cutting edges. With this method it is possible to cut mono- and polycrystalline silicon wafers in a very fast and clean way, without having any waste products. Because the generated cracking edge is also very planar and has only a small roughness, with laser induced tension cracking high quality processing results are easily accessible.

Laser processing inside transparent materials: dependence on pulse length and wavelength

In this paper processing of transparent materials by laser radiation from various sources with short (nanoseconds) and ultrashort (femtoseconds) pulse lengths at different wavelengths is discussed. The investigations were carried out with a short pulse Nd:YVO4 laser (1064 nm, 532 nm) and a high repetition rate femtosecond fiber laser (1030 nm). In our experiments the laser beam was guided across the probe either through the motion of a coordinate table or through a laser scanner with an f-theta-objective. In our study we investigated in detail the influence of important process parameters like wavelength, pulse width, and irradiation regime upon micro defect generation inside bulk glass (BK glass, fused silica) and polymers (polymethylmethacrylate, polycarbonate, cyclo-olefin-copolymers). By applying an irradiation regime with optimal process parameters these locally confined material defects can be aligned as to yield cut surfaces for the excision of 3d parts that consist of transparent material with bulk properties. Especially for the production of irregularly shaped 3d parts a CAD-CAM software tool was developed that automatically converts geometry data into a processing program.