Abstract
Effects associated with the incorporation of chlorine during the thermal growth of SiO2 (500-1400A) on <100> Si are investigated as a function of additive species (HCI, CI2), additive concentration, and oxidation temperature (900°-1150°C). Chlorine profiles are measured mainly by nuclear backscattering spectroscopy, and oxide thicknesses and refractive index changes by ellipsometry. The highest chlorine concentrations in unannealed oxides always occur at the Si-S1O2 interface. Under otherwise similar conditions, the use of Cl2 results in higher, more evenly distributed chlorine levels (up to 1.2 X 1021 at cm-3). The incorporated chlorine is gradually removed by annealing at temperatures in excess of 1100°C, as well as under conditions where further oxide growth takes place without the presence of HCI or Cl2. Additional oxide formation in steam effectively removes all the incorporated chlorine. MOS capacitors made from oxides grown in HCI or Cl2 show fixed charge levels lower than 1011 cm-2 and mobile charge levels less than 1010 cm-2. When biased at high fields (>6 MV/cm) significant shifts in the flatband potential of Si were observed. Chlorine-grown oxides exhibit positive and negative shifts attributed to a mobile species; the smaller negative shifts in HCl oxides are attributed to interface states. Other electrical data of intentionally Na-contaminated HCl oxides suggest that only a constant fraction of the Na is trapped. © 1975, The Electrochemical Society, Inc. All rights reserved.