Free-abrasive machining is more popularly known as lapping. Lapping has been the tried and true method of obtaining extreme wafer flatness through a simple, straightforward methodology. The simplicity of lapping lends itself to the complexities of obtaining minimal thickness variation and stress-free surfaces as wafer sizes increase from 200mm to 300mm.
Lapping of silicon is performed using lapping plates (iron composite), an abrasive material (usually aluminum oxide) and a lapping slurry additive. The lapping slurry additive suspends the abrasive + water mixture, creating a slurry. The slurry is pumped from a source via a non-shear pump to the top lapping plate where it is dispersed through to the silicon interface. The lapping slurry should be stable for at least an eight hour shift. The slurry must also exhibit film strength to keep the wafers from breaking; corrosion protection to keep the plate from rusting; and detergency to keep the wafers from staining as they are removed from the plate.
The use of lapping is increasing at 300mm silicon wafer manufacturing facilities. Where once it was thought that a combination of surface grinding and lapping was best, it is now known that only lapping can consistently produce flat, stress-free, low damage wafers economically and efficiently. The use of Intersurface Dynamics’ Vector HTS Series of lapping slurry additives is critical for producing scratch-free, stain-free ultra-flat wafers, from 100mm, 150mm, 200mm, 300mm and beyond.