In semiconductor industry, wafers are mostly obtained by so-called multi-wire sawing process, in which metal wires perform cutting actions against semiconductor ingots in a continuous loop or a to-and-fro motion. The precious semiconductor material, which are usually of very high purity, removed by the cutting-away action of the wires, ends up as a dust from the ingot and is suspended in the liquid producing a mud-like sludge, the so-called “kerf-loss”, which is unavoidable at present. In the case of Silicon-based PV industry, this loss accounts for 40-50% of the ingot’s total mass and constitutes the most important economic loss in the PV production value chain today.
In order to extract the valuable semiconductor material from the sawing sludge at high purity and reasonable cost, several technology challenges across different technology fields must be taken into account, such as organic chemistry, micro-particle handling, vacuum technology, metallurgy etc.
After years of co-development with research and industry partners, Plus MAT has integrated dedicated, flexible and proprietary industrial processes, to recycle and reclaim the valuable semiconductor materials from kerf-loss, with high purity at low cost.
Example 1 – Silicon recycling from diamond wire PV-wafering kerf-loss: dedicated wet-chemical and metallurgical routes have been designed to reclaim the Silicon in the kerf-loss into PV-feedstock.
(Steps 2 & 3 are in collaboration with RoSi SAS)
Example 2 – Germanium recycling from slurry PV-wafering kerf-loss: micro-bubble floatation is developped to selectively float Germanium particles from the mixture with SiC abrasives and sawing additives such as PEG or mineral oil.