Product Code: ICAL09_M1105

Cutting Performance Comparison Between Low Power LPSS and sm Fiber Laser for Mono and Polycrystalline Silicon Wafers
Authors:
Mohammed Naeem, GSI Group, Inc. - Laser Division; Rugby Great Britain
Presented at ICALEO 2009

Silicon is widely used in a number of industries but primarily in solar cells and in semiconductor manufacture, with growing applications in jewelry and entertainment goods. In the majority of applications the source material is in the form of wafers which are typically 0.2-1.5mm (thick and 100-300mm diameter. From the flat faces of the octagons they laser cut a flat rectangular wafer that is then further processed to become a solar cell. Cutting speed and yield are important to reducing costs. Silicon wafers are conventionally diced off by a thin diamond blade into individual IC chip, before they are packaged. The problems encountered in blade dicing include chipping, kerf-loss and low productivity. Currently green wavelength (frequency doubled) and microjet are been used but both of these processes are slow and expensive to operate. Milliseconds low power pulsed Nd: YAG lasers and high beam quality continuous wave fiber lasers are being used to cut these materials but the cut quality is poor i.e. microcracking due to excessive heat input, which can lead to failure of some components during process steps and associated reduction in yields.. The length of microcracks can range from 15µm to 100µm depending on the laser source being used. The main requirements for cutting of silicon wafers are dross and crack free cut edges in a range of thicknesses. The cutting trials have been performed in a range of thicknesses with two different laser sources i.e. with a high beam quality CW single mode fiber laser and also with a high beam quality pulsed Nd: YAG laser. Considering the differences in beam quality and pulsed performance between the two types of laser, there are different operating regimes for the two types of laser. The lamp-pumped YAG laser is characterised by long high-energy pulses but poorer beam quality, and the fiber laser with high repetition rate on-off type modulation, single-mode beam quality but low pulse energy. From an applications perspective, both these regimes have their advantages and these are discussed in the following sections.