Dry cleaning by atomic F of a Si surface placed vertical and floating in a high pressure plasma created in a barrel reactor

Abstract

Summary form only given. A novel dry plasma cleaning process for cleaning the Si surface is proposed including the removal of native oxide using low electron energy (high pressure) plasma of CF/sub 4//H/sub 2/ gas mixture (NF/sub 3/ can also be used) created in a barrel reactor at 1 Torr pressure and 70 W RF power. Atomic F created in such a plasma is found not only to remove the native oxide, but also clean the Si surface. The effectiveness of the cleaning process is judged by growing dry thermal SiO/sub 2/ in 20% O/sub 2/-N/sub 2/ oxidation ambient at 1100/spl deg/C on the cleaned Si surface and studying the interface properties of the MOS capacitor formed on it and annealed in forming gas for 8 min at 450/spl deg/C. The average fixed oxide charge density, N/sub f/, obtained over 45 C-V dots on the cleaned wafer was 2.13/spl times/10/sup 10//cm/sup 2/ with a standard deviation of 1.96/spl times/10/sup 10/ cm/sup -2/. The average interface trap level density, N/sub it/, obtained by the high-low frequency method was in 2-3/spl times/10/sup 11//cm/sup 2/ eV/sup 1/ range and the same obtained by a conductance technique after correcting for series resistance was around 1/spl times/10/sup 11//cm/sup 2/ eV/sup 1/. These can be compared tothe mean N/sub f/ obtained over 56 C-V dots formed on the uncleaned Si sample (control) as 2.05/spl times/10/sup 12/ cm/sup -2/ with a standard deviation of 1.56/spl times/10/sup 12/ cm/sup -2/. The comparison clearly demonstrates that the proposed method of cleaning is effective based on the fact that oxidation kinetics is known to be affected by the Si surface clean condition and consequently affects the Si/SiO/sub 2/ interface properties.