Thermal Laser Seperation with Deep Scribe for Silicon Wafer Dicing

TLS-Dicing (Thermal Laser Separation) is a unique technology for separating wafers into single chips in semiconductor back end processing. TLS-Dicing uses thermally induced mechanical stress to separate brittle semiconductor materials, like silicon (Si) and silicon carbide (SiC) wafers. TLS is a two-step TLS-Dicing method consisting of scribing and cleaving. The scribing is used to create a starting point of the second step - the cleaving step. A continuous wave laser in combination with water spray cooling generates a thermal distribution. This leads to a mechanical stress capable to guide one defined crack along the dicing street which leads to the separation of the material. This work investigates a new scribing method - the Deep Scribe - in detail. While using Deep Scribe a pulsed laser beam of near infrared wavelength is focused with an objective into the silicon. This generates a line of subsurface material modification. By using this scribe technique no particles occur at the surface. Additionally, straightness and the bending strength of separated silicon chips can be improved in comparison with state of the art dicing technologies. In this presentation, we will discuss the latest developments in Deep Scribe TLS with focus on the physical effects of the interaction between laser beam and material, as well the requirements for generation of a Deep Scribe. We will investigate the influence of adjusting parameters such as focus position, duration of laser pulse and laser power, on position and size of the modified area. We will also study the effects of thermal laser separation with Deep Scribe on bending strength of diced chips, a crucial parameter for wafer thinning applications. For comparison, similar wafers were cut with current state-of-the-art mechanical blade dicing.