Effect of ultraviolet irradiation upon the recombination lifetime of silicon wafers covered with a dielectric film

Abstract

The effect of UV irradiation upon the recombination lifetime of silicon covered with chemical vapor deposition (CVD) oxide has been studied using a laser-microwave photoconductance (LM-PC) technique. It is found 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 irradiation and thermal annealing. A comparison is made of the UV irradiation effect upon the lifetime of silicon wafers covered with a variety of different 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.