Polycrystalline ingot cutting system
When you are in the solar cell business (polycrystalline silicon) or semiconductor business (monocrystalline), silicon ingots and boules – the source of your vital wafers – can be a considerable expense. The knack is to get as many wafers as possible out of each ingot or boule. But, many companies involved with wafer production get frustrated because the waste created when the ingot is sliced may be equal to or more than the amount in the wafer itself. Fraunhofer’s Institute for Mechanics of Materials (IWM) is working to whittle down this waste.
Wafers are made by slicing the ingot with a fine wire operating at high speeds. A cutting-slurry mix, often made with silicon carbide, is used to facilitate the wire’s work.
A typically resultant wafer thickness might be 180 µm. Unfortunately, it would also be typical for the wire to create a saw gap of 180 µm, too. The saw gap is a function of several factors, including the wire size and the abrasion interaction between the slurry and the ingot.
According to Rainer Kübler, business unit manager at IWM, Fraunhofer researchers “want to achieve smaller saw gap widths of around 100 µm, which are also suitable for industrial applications.”
IWM is using computer modeling to simulate different configurations. They think the main questions are related to determining the optimal level of wire wetting, slurry grain size and slurry grain distribution. “We want to answer all these questions and ultimately arrive at optimal wire and slurry systems,” said Kübler.
A report on the IWM website says that researchers are currently striving to achieve gap widths of 90 µm, an efficiency gain that would be a major step forward.
Their work is being funded by Germany’s federal ministry for the environment.