SILICON SURFACES TREATED BY CF4, CF4 H-2, AND CF4/O-2 RF PLASMAS - STUDY BY IN-SITU FOURIER-TRANSFORM INFRARED ELLIPSOMETRY/

The reaction layer formed on a silicon substrate in a CF4 rf plasma an d in its admixtures with hydrogen and oxygen has been investigated by Fourier transform infrared phase-modulated spectroscopic ellipsometry (FTIR-PMSE). The results are compared with x-ray photoelectron spectro scopy spectra of the surface. It is shown that by using FTIR-PMSE, a s ignificant gain in sensitivity is obtained as compared to ordinary ref lection absorption measurements. In the case of a CF4 plasma, a large difference in the reaction layer at rf and the grounded electrode has been found. Samples treated on the rf electrode have a thin reaction l ayer consisting of SiFx (x = 1, 2, 3, and 4). The reaction layer of sa mples treated on the grounded electrode also contain CFx species. In t he case of a 50% CF4 50% H-2 plasma, a thick carbon layer is formed on both the rf and the grounded electrode. While the layer formed on the grounded electrode contains a high amount of CFx (x = 1, 2, and 3) bo nds, that on the powered electrode does not contain as much. In the ca se of a 50% CF4 50% O-2 plasma, a thin siliconoxide layer is formed. O n the grounded electrode, it takes slightly longer to build up, but th e final reaction layer on rf and grounded electrodes is the same. Smal l amounts of SiF4 are also present in the layer. (C) 1997 American Vac uum Society.