THERMOGRIND · Thermally Controlled Rotational Grinding of Sapphire Wafers for Highly Efficient Manufacturing of Modern White LED Light Sources

The market for discrete light emitting diodes (LEDs) is very fast growing. Basic materials for white and blue LEDs are wafers of Silicon Carbide (SiC) and Sapphire (Al2O3). Today European enterprises, most of them SMEs, hold less than 5% of worldwide wafer production due to high production costs compared to the main producers Russia, USA and Japan.The most time consuming and therefore expensive process steps in production of sapphire wafers are lapping and polishing. This process chain can be significantly shortened by substituting lapping by grinding as grinding allows for a much better surface quality in a shorter time. As a result the time needed for polishing will be diminished as well. This will be a decisive step for the European wafer manufacturers to gain significant shares in a highly profitable market.As grinding of silicon wafers, basic material for red and yellow LEDs, today is state of the art, grinding of sapphire wafers fails due to the variability and the interaction of individual effects during the grinding process. Due to this reasons, a direct measurement of the in-process parameters within the contact zone between work piece and grinding wheel is of eminent interest for developing a stable grinding process.ThermoGrind will allow the measurement of one of the key process parameters, the grinding temperature. For this, the optical transparency of sapphire for infrared radiation initiated in the contact zone will be exploited. Following this principle, ThermoGrind develops an innovative infrared transparent wafer clamping system (chuck) that allows temperature measurement by capturing the infrared radiation transmitted through wafer and clamping system. As a second step ThermoGrind will develop a temperature based loop control of the grinding process in order to achieve optimal process stability under mass production conditions