Method for manufacturing silicon wafers
This silicon wafer production process comprises in the order indicated a planarization step, in which the front surface and the rear surface of a wafer are ground or lapped, a single-wafer acid etching step, in which an acid etching liquid is supplied to the surface of the wafer while spinning and the entire wafer surface is etched to control the surface roughness Ra to 0.20 μm or less, and a double-sided simultaneous polishing step, in which the front surface and the rear surface of the acid etched wafer are polished simultaneously. The process may comprise a single-sided polishing step, in which the top and bottom of the acid etched wafer are polished in turn, instead of the double-sided simultaneously polishing step.
1. A method for manufacturing silicon wafers, the method comprising, in the order indicated:
a planarization step of grinding or lapping a front surface and a rear surface of a silicon wafer which is in a form of a thin disk and is obtained by slicing a silicon single crystal ingot;
a single-wafer acid etching step of supplying an acid etching liquid to the surface of the planarized single silicon wafer while spinning the single silicon wafer, thereby spreading the supplied acid etching liquid over the entire wafer surface due to centrifugal force generated by spinning, and etching the entire wafer surface so as to control the surface roughness Ra of the wafer surface to 0.05 μm or less; and
a double-sided simultaneous polishing step of polishing both of the front surface and the rear surface of the acid-etched single silicon wafer simultaneously,
wherein the acid etching liquid is an aqueous solution containing hydrofluoric acid, nitric acid and phosphoric acid respectively,
the mixing ratio as percents by weight of the hydrofluoric acid, nitric acid, phosphoric acid and water in the aqueous solution is such that hydrofluoric acid:nitric acid:phosphoric acid=4.5% to 10.5%:25.5 to 40.0%:30.0 to 45.5%,
the spinning speed at which the wafer is spun in the single-wafer acid etching step is 500 to 2000 rpm, and
the viscosity of the acid etching liquid is 10 to 35 mPa·sec.
2. The method for manufacturing silicon wafers according to claim 1 , wherein the surface tension of the acid etching liquid is 55 to 60 dyne/cm.
3. A method for manufacturing silicon wafers, the method comprising, in the order indicated:
a planarization step of grinding or lapping a front surface and a rear surface of a silicon wafer which is in a form of a thin disk and is obtained by slicing a silicon single crystal ingot;
a single-wafer acid etching step of supplying an acid etching liquid to the surface of the planarized single silicon wafer while spinning the single silicon wafer, thereby spreading the supplied acid etching liquid over the entire wafer surface due to centrifugal force generated by spinning, and etching the entire wafer surface so as to control the surface roughness Ra of the wafer surface to 0.05 μm or less; and
a single-sided polishing step of polishing one of the front surface and the rear surface of the acid-etched single silicon wafer, and then polishing the other one,
wherein the acid etching liquid is an aqueous solution containing hydrofluoric acid, nitric acid and phosphoric acid respectively,
the mixing ratio as percents by weight of the hydrofluoric acid, nitric acid, phosphoric acid and water in the aqueous solution is such that hydrofluoric acid:nitric acid:phosphoric acid=4.5% to 10.5%:25.5 to 40.0%:30.0 to 45.5%,
the spinning speed at which the wafer is spun in the single-wafer acid etching step is 500 to 2000 rpm, and
the viscosity of the acid etching liquid is 10 to 35 mPa·sec.
4. A method for manufacturing silicon wafers according to claim 3 , wherein the surface tension of the acid etching liquid is 55 to 60 dyne/cm.