The study was done on the four-inch<100>GaAs wafers. The wafers were measured so that the total thickness variations (TTV) before and after grinding were less than 5 microns. All wafers were wax-mounted on the sapphire disk by the Logitech bonding machine.
The wet etch recipe used for this test was: 1(36.5% HCl): 4 (30% H2O2): 40 (DI), with an etch rate of about 0.3 microns per minute at room temperature.
the test wafers were loaded on the 12” Lap Master polishing machine. The wafer was rotated on the polishing pad. Polishing slurry was supplied to the pad and the removal rate was 1.2 microns per minute.
The Wafer Strength Measurements were taken by using an AIKO material strength tester manufactured by AIKO Engineering Inc. in Japan.The accuracy of the wafer strength measurement is+/- 0.01 lbs. 应力测试设备和精度要求。
urface roughness (Ra) [*]measurements by Chapman machine (model MP2100 non-contact measurement system)
The lowering of surface roughness is a major factor for wafer strength improvement, the smoother is the surface, the stronger is the wafer. The smooth surface will help preventing breakage during the wafer demounting and solvent cleaning. It is very important to do polishing instead of wet etching process in the wafer thinning operation to minimize the thickness variation, and reduce the surface roughness to improve the wafer strength. By implementing the polishing process in our high volume production line the wafer breakage rate was reduced from 9.13% to 0.59%.