A detailed study on the growth of thin oxide layers on silicon using ozonated solutions

The oxidation of silicon using ozonated, deionized water solutions was inve stigated as a function of several parameters: reaction time, pH, ozone conc entration, temperature; and influence of anions. The oxidation of silicon w as dependent on ozone concentration especially near neutral pH. This concen tration dependence disappears at concentrations greater than 15 mg/L ozone. No temperature effect was found between 20 and 50 degrees C. Lowering the DH leads to a less pronounced concentration dependence with no specific ani on effect between HCl or HNO3. The oxidation of silicon by ozonated solutio ns does not lead to extensive roughening of the silicon surface as shown by atomic force microscopy measurements. Various thermal oxidation models wer e evaluated and the Fehnler expression represents the experimental data fai rly well. The overall oxidation thus follows logarithmic growth kinetics. I t is proposed that ozone dissociates at the SiO2/liquid interface in a one- step reaction forming the oxidizing species, namely, O-. This radical diffu ses through the SiO2 layer under the influence of an electric field which d evelops over the oxide layer. The field-imposed drift is the limiting facto r in the oxidation process. The bulk chemistry of the ozonated solutions is of no importance to the oxidation of silicon. The initial oxidation rate, defined at an oxidation time of 6 s, was dependent on the ozone concentrati on below 15 mg/L and leveled off above this concentration as it was limited by the field-imposed drift of the oxidation precursor. (C) 2000 The Electr ochemical Society. S0013-4651(99)06-013-9. All rights reserved.