Negative Oxide Charge in Thermally Oxidized Cr-Contaminated n-Type Silicon Wafers

Abstract

The evaluation of thermally oxidized Cr-contaminated Si surfaces, by an AC surface photovoltage (SPV) method, indicates that a certain amount of contaminating Cr atoms resides in the SiO2 thin film, resulting in the creation of a negative oxide charge in the form of a (CrOSi)- and/or CrO2- networks, which are postulated to be analogous to the (AlOSi)- network. For samples oxidized at temperatures between 550 and 700 °C for 10 min, the AC SPV gives evidence that the induced negative oxide charge causes a strongly inverted state of the Si surface. At oxidation temperatures higher than 700 °C and/or a longer oxidation time than 10 min, AC SPV is reduced, meaning that the strongly inverted state changes into a less depleted state, and finally, the AC SPV disappears. In this case, a collapse of the (CrOSi)- and/or CrO2- networks is expected with a possible change into Cr2O3.