THERMOGRIND

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

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 Obiettivo del progetto (Objective)

'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'

Introduzione (Teaser)

The global market for discrete light-emitting diodes (LEDs) is growing rapidly, yet small EU enterprises have trouble competing due to high manufacturing costs. EU-funded scientists developed technology to put them in the game.

Descrizione progetto (Article)

White and blue LEDs are typically produced on wafers made of silicon carbide (SiC) or sapphire (aluminium oxide (Al2O3)). The most expensive and time-consuming steps are lapping and polishing. Lapping to remove surface scratches and saw marks takes place immediately after cutting the ingots into wafers. Polishing comes next, usually with two or three recursions, on very high-precision machines.

Replacing lapping with conventional grinding would reduce processing time and enable better surface quality, consequently reducing time required for polishing. To date, this has been difficult to accomplish because the grinding of sapphire wafers is subject to large variability and there is no direct way to monitor process parameters at the contact zone between the grinding wheel and the wafer. Partners working on the EU-funded project THERMOGRIND solved this issue with innovative technology to measure and control grinding temperature, one of the key variables for process control.

Researchers exploited sapphire's optical transparency to infrared (IR) radiation by using sapphire to form the core element of an IR-transparent hollow spindle wafer-clamping system (vacuum chuck). A sensor detects IR radiation from the sapphire wafer that is transmitted through the chuck, enabling optical access to any preferred position on the wafer. After analysing in detail the dependency of the temperature signals on various parameters and operating conditions, scientists determined thermal control criteria for the grinding process. From the correlations, they developed the machine tool integrated loop control system.

THERMOGRIND scientists have developed an innovative solution to the problems of expense and time required for the production of blue and white LEDs on sapphire wafers. EU small and medium-sized enterprises (SMEs) will now be in a strong position to compete with foreign manufacturers in this huge global market. In addition, the modular technology should boost sales of individual components for other applications by the partner SMEs manufacturing them.