Effects of post oxidation of SiO2/Si interfaces in ultrahigh vacuum below 450 °C

Growing SiO2 layer by wet-chemical oxidation of Si surfaces before growth of
another insulating film(s) is a used method to passivate Si interfaces in
applications (e.g., solar cell, photodiode) at low temperatures (LT) below 450
oC. We report on potential of LT ultrahigh-vacuum (UHV) treatments combined
with the wet-chemical oxidation, by investigating effects of LT-UHV oxidation
after the wet-chemical growth of SiO2 and before growing Al2O3 film on top of
SiO2/Si. This method modifies the SiO2/Si and is found to (i) decrease defect-
level density, (ii) increase negative fixed charge density, and (iii) increase carrier
lifetime for Al2O3/SiO2/p-Si, as compared to state-of-the-art SiO2/p-Si reference interfaces without LT-UHV. X-ray photoelectron spectroscopy shows that the LT-UHV treatment decreases amount of Si+3 oxidized atoms in chemically grown SiO2 and also amount of carbon contamination. In order to pave the way for further tests of LT-UHV in silicon technology, we present a design of simple UHV instrument. The above-described benefits are reproduced for 4-inch silicon wafers by means of the instrument, which is further utilized to make LT-UHV treatments for complementary SiO2/Si interfaces of the native oxide at silicon diode sidewalls to decrease the reverse bias leakage current of the diodes.