Abstract
Ga contamination in wafers analyzed by a dual beam FIB was investigated. For a milled wafer, the following has been found. Surface sensitive methods, TRXRF and TRXPS, indicated that the Ga contamination level is of the order of 10(10) atoms/cm(2) and is insensitive to injected dosage. ICP-MS analysis, which detects species in surface layers of about 5m thick over a whole wafer, detected Ga of 1.1x10(13) atoms/wafer against a 71 min.nA dose and 5.1x10(13) atoms/wafer against a 567 dose. These are related to dosage. Most of the irradiated Ga will charge up in the bottom of milling crater and only a very small fraction of them will contaminate the surface area. The WDX analysis indicated that Ga distributes mostly within the area of 200m centered on the milled crater. The AES analysis also showed similar results. The lateral Ga distribution was surveyed by TRXRF for a total of 49 spots of 10 mm, including the milled spot and its neighboring spots. Ga was detected in 2 spots. Taking into account it, we should regard that the area within 200 mm is contaminated and the rest of the surface is clean. A further investigation is necessary in order to determine whether a milled wafer can be returned to a production line or not. For a wafer tested without ion milling, no Ga was detected by either ICP-MS or TRXPS. The wafer tested without ion milling can be returned to a production line.