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A New Approach for Improved Uniformity of Thin Thermal Oxides Using Water Vapor: A Case Study
By Richard Mee and Jeffrey Spiegelman
A combination of steam and oxygen has proven to meet uniformity standards and reduce growth time
When growing 1000 Å or thinner thermal oxides on 300 mm wafers, uniformity can be a problem with wet oxidation, so dry oxidation is frequently used. WRS Materials was able to meet their uniformity standards for thin oxides and reduce process time by a combination of steam at a flow rate of 50 slm and oxygen at 30 slm. Uniformity was better than 2% load-to-load and oxidation time was reduced from 100 minutes using oxygen to 13 minutes with the steam/oxygen recipe.
To determine optimum oxidation conditions a new parameter—Oxidation Thickness Saturation factor (OTS)— was defined as the quotient of the time to reach target oxidation thickness divided by saturation time to 99% partial pressure of oxidants in the furnace tube. For 50 slm with 100% steam, the OTS was 1.7, whereas for an 80 slm mixed flow of steam and oxygen the OTS was 4.5. To achieve better than 2% standard deviation across the wafer load, we recommend an OTS value of 4 or greater.
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