EFFECT OF ULTRAVIOLET-IRRADIATION UPON THE RECOMBINATION LIFETIME OF SILICON-WAFERS COVERED WITH A DIELECTRIC FILM

The effect of UV irradiation upon the recombination lifetime of silico n covered with chemical vapor deposition (CVD) oxide has been studied using a laser-microwave photoconductance (LM-PC) technique. It is foun d that the lifetime changes little after the first UV irradiation, but dramatically decreases following thermal annealing at 500 K for 1 h. Moreover, the lifetime can be cycled up and down by repeated irradiati on and thermal annealing. A comparison is made of the UV irradiation e ffect upon the lifetime of silicon wafers covered with a variety of di fferent dielectric films. It is suggested that UV rechargeable defects are present in a CVD oxide film, like in native oxide and CVD nitride , but are absent in thermal oxide. Finally, it is emphasized that the noncontact LM-PC technique can be a powerful tool to characterize the defects in dielectric films on silicon wafers.