Identification of Critical Process Parameters and Improvement of the Wafering Process by Measuring of Mechanical Load

© Fraunhofer CSP

The loads (forces, moments) acting on the silicon block in three spatial directions can be measured and recorded by using 4 sensors.

© Fraunhofer CSP

Draws in the wire direction for a slurry-based wire saw cut.

The determination of critical process steps can be done at the Fraunhofer Center for Silicon Photovoltaic CSP by performing wafering and wire wear experiments. The goal of decreasing the process time and consumables could be reached by higher feed speed and less wire consumption. Four load sensors for forces and moments (figure at the top, Fig. 1) are used for an inline force detection in three dimensions to determine process limits. As an example the figure below (Fig. 2) is showing the load in wire movement direction of each sensor. In general, the wafering process can be separated into three parts, the cutting-in and cutting-out process and the main sawing period in the middle of process time. By the analysis of force curves an improvement of the cutting-in and cutting-out process is possible in order to decrease the amount consumables and to increase the wafer surface quality or surface damage. The variation of load during the main sawing process is almost constant.

Any changes of these homogeneous conditions could influence the wafer geometry. Furthermore, the wire wear can be observed according to the position in the wire web because of the position of forces sensors. The wire usage is increasing from sensor 1 to sensor 4. The figure shows a slightly change of forces in wire direction that are depending on a decrease of wire abrasion properties. This combination of different investigations enables an optimization of wire usage and wire consumption. Finally the influence of process parameters can be analyzed regarding the running process itself but also to the wafer specifications. This unique measurement system is used basic research like the abrasion mechanisms of silicon, as well as questions of high-volume production in industry.