From the Ingot to Finished Silicon Wafers
The ingots grown with the Czochralski or float-zone technique are ground to the desired diameter and cut into shorter workable cylinders with e. g. a band saw and ground to a certain diameter.An orientation flat is added to indicate the crystal orientation (schema right), while wafers with an 8 inch diameter and above typically use a single notch to convey wafer orientation, independent from the doping type.
Dicing With Inside Hole Saw (Annular Saw)
The wafers are sawed inside a circular blade whose cutting edge is filled with diamond splinters (schema right).After sawing, the wafer surfaces are already relatively flat and smooth, so the subsequent lapping of the surfaces takes less time and effort.However, only one wafer per annular saw can be cut at the same time, so this technique has a comparably low throughput which makes the wafers more expensive compared to wafers cut by a wire saw.
In order to increase throughput, wire saws with many parallel wires are used which cut many wafers at once (schema top).A long (up to 100 km) high-grade steel wire with a diameter of » 100 - 200 μm is wrapped around rotating rollers with hundreds of equidistant grooves at a speed of typically 10 m/s. The mounted silicon cylinder is drained into the wire grid and thus cut into single wafers.The wire is either coated with diamond splinters or wetted with a suspension of abrasive particles such as diamonds or silicon carbide grains, and a carrier (glycol or oil).The main advantage of this sawing method is that hundreds of wafers can be cut at a time with one wire. However, the attained wafer surface is less smooth and more bumpy as compared to wafers cut by an annular saw, so the subsequent lapping takes more time.
After dicing, the wafers are lapped on both sides in order to i) remove the surface silicon which has been cracked or otherwise damaged by the slicing process (e. g. grooves by the wire saw) and ii) thinned to the desired wafer thickness.
Wafer dicing and lapping degrade the silicon surface crystal structure, so subsequently the wafers are etched in either KOH- or HNO3/HF based etchants in order to remove the damaged surface.
After etching, both wafer surfaces appear like the rear side of finished single-side polished wafer. In order to attain the super-flat, mirrored surface with a remaining roughness on atomic scale, the wafers have to be polished.
Wafer polishing is a multi-step process using an ultra-fine slurry with 10 - 100 nm sized grains consisting of e. g. Al2O3, SiO2 or CeO2 which, combined with pressure, erode and mechanically and chemically smoothen the wafer surface between two rotating pads.
Finally, the wafers are cleaned with ultra-pure chemicals in order to remove the polishing agents thereby making them residual-free.
Our Technical Wafer Brochure
Our technical wafer brochure with information on the production and specification of silicon, quartz, fused silica and borosilicate glass wafers can be downloaded or ordered (for free) here.