METHOD AND APPARATUS FOR MEASURING MINORITY CARRIER CONCENTRATION IN SEMICONDUCTOR MATERIALS

摘要

A contactless apparatus for measuring contaminants in a semiconductor specimen (24) includes a tunable microwave generator (26) coupled by a coaxial cable (36) to a tuned narrowband microstrip antenna (38) that defines a through hole (72). The antenna is placed in near field relationship to the specimen to direct microwave energy toward a first specimen surface (44). This proximity provides a substantially more powerful microwave field than prior art systems, and the specimen comprises an impedance termination for the microwave path that includes the microwave generator and antenna, thereby rendering system measurements substantially immune to mechanical vibration of the specimen. A pulsed laser (42) directs optical energy through the antenna through hole toward the first specimen surface (44). The optical energy generates minority carriers within the specimen that begin to recombine upon cessation of each pulse. Minority lifetime decay affects microwave energy reflecting from freed holes and electrons in the specimen, which energy is coupled from the antenna to a detector (46) and preferably a computer system (48) that controls the system and provides signal processing of the detector output. Because of the enhanced microwave sensitivity, measurements may be taken over a wide dynamic range of injected optical energy, thus permitting injection spectroscopic measurements. The computer system permits a display (50) that maps contaminant location and concentration within the specimen, based upon recombination lifetime data. Optionally the system permits measurements of a non-oxidized specimen disposed in an electrolytic bath (60) that passivates unoxidized surfaces to minimize surface recombination effects upon measurements.