Plasma diagnostic approach for the low-temperature deposition of silicon quantum dots using dual frequency PECVD

Abstract

Although studies of silicon (Si) quantum dots (QDs) were started just a few years ago, progress is noteworthy concerning unique film properties and their potential application for devices. In particular, relating to the Si QD process optimization, it is essential to control the deposition environment by studying the role of plasma parameters and atomic and molecular species in the process plasmas. In this work, we report on advanced material processes for the low-temperature deposition of Si QDs by utilizing radio frequency and ultrahigh frequency dual frequency (DF) plasma enhanced chemical vapor deposition (PECVD) method. DF PECVD can generate a very high plasma density in the range ~9 × 1010 cm−3 to 3.2 × 1011 cm−3 at a very low electron temperature (Te) ~ 1.5 to 2.4 eV. The PECVD processes, using a reactive mixture of H2/SiH4/NH3 gases, are carefully studied to investigate the operating regime and to optimize the deposition parameters by utilizing different plasma diagnostic tools. The analysis reveals that a higher ion flux at a higher plasma density on the substrate is conducive to enhancing the overall crystallinity of the deposited film. Along with high-density plasmas, a high concentration of atomic H and N is simultaneously essential for the high growth rate deposition of Si QDs. Numerous plasma diagnostics methods and film analysis tools are used to correlate the effect of plasma- and atomic-radical parameters on the structural and chemical properties of the deposited Si QD films prepared in the reactive mixtures of H2/SiH4/NH3 at various pressures.