Effect of Oxide Thickness by Metallic Residue during Radical Oxidation Using Vertical Batch-Type Furnace Equipment on 300-Mm-Diameter Silicon Substrates

Abstract

Metallic residues have a detrimental effects on device performance as well as retard gate oxide growth rate to induce unintended thinner oxide layer. In this study, we found that oxide thickness could be subjective to metallic residues on the edge of silicon substrate. Hydrogen-assisted radical oxidation was investigated using vertical batch-type furnace equipment for a 300-mm wafer fab. Radical oxidation has been used to improve gate oxide quality overcoming the disadvantages of conventional wet or dry thermal oxidation for some applications. Since the radical oxidation method reduces dangling bonds and defects in the oxide layer due to activated oxygen radicals, a high-quality oxide film can be formed. It also helps improve reliability due to reduced dependence on the silicon crystal direction of oxidation, enabling uniform membrane deposition of stress-focused corner rounding oxidation. In addition, it has excellent throughput as it is possible to process up to 100 wafers simultaneously. This study has shown that as the number of wafers with metallic residues in the dummy pattern on the edge due to the wafer edge exposure (WEE) difference for each photo step increases in the same batch for radical oxidation, the median thickness has decreased. When the silicon wafer with the metallic residue was included within the same batch of the furnace equipment, the thickness of the oxide layer was reduced by 1.8% compared to when the metallic residue-free silicon wafer was included. The radical oxygen have a tendency to react to tungsten rather than silicon, which reduces the O2 value required to form SiO2 and lowers the thickness, which is due to the difference in electronegativity between silicon and tungsten, 1.9 and 2.36 respectively. The study is expected to improve gate oxide quality by controlling metal residues on the wafer edge or backside during the fab process.