Microcrystalline silicon thin films deposited by matrix-distributed electron cyclotron resonance plasma enhanced chemical vapor deposition using an SiF4 /H2 chemistry. (21st June 2016)

• Record Type: Journal Article
• Authors: Wang, Junkang; Bulkin, Pavel; Florea, Ileana; Maurice, Jean-Luc; Johnson, Erik
• Is Part Of: Journal of physics. Volume 49:Number 28(2016)
• Publication Date: 2016-06-21
• Subjects: hydrogenated microcrystalline silicon -- matrix-distributed electron cyclotron resonance -- substrate temperature -- ion bombardment energy -- seed layer; Physics -- Periodicals; 530
• DOI: 10.1088/0022-3727/49/28/285203
• Languages: English
• ISSNs: 0022-3727

Abstract

Abstract: For the growth of hydrogenated microcrystalline silicon ( μ c-Si:H) thin films by low temperature plasma-enhanced chemical vapor deposition (PECVD), silicon tetrafluoride (SiF4 ) has recently attracted interest as a precursor due to the resilient optoelectronic performance of the resulting material and devices. In this work, μ c-Si:H films are deposited at high rates (7 Å s −1 ) from a SiF4 and hydrogen (H2 ) gas mixture by matrix-distributed electron cyclotron resonance PECVD (MDECR-PECVD). Increased substrate temperature and moderate ion bombardment energy (IBE) are demonstrated to be of vital importance to achieve high quality μ c-Si:H films under such low process pressure and high plasma density conditions, presumably due to thermally-induced and ion-induced enhancement of surface species migration. Two well-defined IBE thresholds at 12 eV and 43 eV, corresponding respectively to SiF + ion-induced surface and bulk atomic displacement, are found to be determinant to the final film properties, namely the surface roughness, feature size and crystalline content. Moreover, a study of the growth dynamics shows that the primary challenge to producing highly crystallized μ c-Si:H films by MDECR-PECVD appears to be the nucleation step. By employing a two-step method to first prepare a highly crystallized seed layer, μ c-Si:H films lacking any amorphous incubation layer have been obtained. A crystalline volume fraction of 68% is achieved with a substrate temperature as low as 120 °C, which is of great interest to broaden the process window for solar cell applications.