Intermediate gas phase precursors during plasma CVD of HMDSO

Abstract

In plasma enhanced chemical vapor deposition (PECVD) from complex molecules like hexamethyldisiloxan (HMDSO) often not the molecules themselves but intermediate and reactive radicals or molecules are the precursors for film growth. Additionally, such PECVD processes are volume or mass flow limited under many process conditions. In these cases growth rate and film homogeneity is mainly dominated by the precursor content and its spatial distribution in the gas or plasma phase. Therefore the identification of such intermediate precursors is an important task to optimize a PECVD process and also helps us to understand the plasma chemical reactions during PECVD. A combined mass spectrometry and IR absorption study is used to identify intermediate gas phase precursors in HMDSO/O 2 PECVD remote plasmas. For this study a microwave plasma CVD system was used with HMDSO/O 2 ratios between 0.1 and 1 at typical operating pressures between 20 and 70 Pa. Three reactive intermediate species are proposed to act as a precursor for SiO x film growth from HMDSO/O 2 plasmas. All three having a mass of 148 amu. The related reactive groups are the silanon (Si=O), silanol (Si–OH) and aldehyde (C=O) groups.