Ion Assisted ETP-CVD a-Si:H at Well Defined Ion Energies
- PDF / 116,813 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 56 Downloads / 185 Views
1153-A17-06
Ion Assisted ETP-CVD a-Si:H at Well Defined Ion Energies M. A. Wank1, R. A. C. M. M. van Swaaij1 and M. C. M. van de Sanden2 1 Delft University of Technology, Electrical Energy Conversion Unit/DIMES, P. O. Box 5053, 2600 GB Delft, the Netherlands 2 Eindhoven University of Technology, Department of Applied Physics, P. O. Box 513, 5600 MB Eindhoven, the Netherlands ABSTRACT Hydrogenated amorphous silicon (a-Si:H) was deposited with the Expanding Thermal Plasma-CVD (ETP CVD) method utilizing pulse-shaped substrate biasing to induce controlled ion bombardment during film growth. The films are analyzed with in-situ real time spectroscopic ellispometry, FTIR spectroscopy, as well as reflection-transmission and Fourier transform photocurrent spectroscopy (FTPS) measurements. The aim of this work is to investigate the effect ion bombardment with well defined energy on the roughness evolution of the film and the material properties. We observe two separate energy regimes with material densification and relatively constant defect density below ~ 120-130 eV and a constant material density at increasing defect density > 120-130 eV substrate bias. We discuss our results in terms of possible ion – surface atom interactions and relate our observations to reports in literature. INTRODUCTION Hydrogenated amorphous silicon (a-Si:H) thin films can be deposited with the expanding thermal plasma chemical vapor deposition (ETP-CVD) technique at growth rates of up to 10 nm/s [1]. At these high growth rates, substrate temperatures > 300°C are required to obtain material with good optoelectronic properties for device applications, however in solar-cell applications this imposes thermal stress on the previously deposited p-layer, leading to reduced solar-cell performance. Sinusoidal radio-frequency (RF) substrate biasing has been successfully utilized to provide the growing film with additional energy via induced ion bombardment (e. g. Smets et al. [2]). In this work, we report on a-Si:H thin film deposition utilizing a different kind of substrate biasing introduced by Wang et al. [3], refer to as pulse-shaped biasing (PSB). Utilizing a specially tailored waveform, a constant, negative potential is created on the sample holder resulting in a very narrow ion energy distribution function (IEDF) contrary to the broad and bimodal IEDF obtained from RF biasing [3]. This allows studying the effect of separate ion energies on material properties. EXPERIMENT The ETP-CVD technique has been described in detail before [1]: a schematic representation is shown in Fig. 1. It is based on an Ar-H2-SiH4 plasma that expands into a low pressure reactor chamber. The SiH4 is dissociated mainly into SiH3 radicals that are transported to the temperature controlled substrate holder where the film is deposited. The PSB setup connected to our ETP-CVD reactor has been previously described by Wang et al. [3] and has been adapted for our reactor setup. The whole setup can be seen in Fig. 1b. The non-sinusoidal waveform is created by an arbitrary waveform ge
Data Loading...
