M. Heintze

Amorphous and microcrystalline silicon by hot wire chemical vapor deposition

Amorphous hydrogenated silicon (a‐Si:H) was deposited by SiH4 decomposition on a hot tungsten filament. The substrate temperature was held at 400 °C for all samples, maintaining conditions where material combining a low defect density and a low hydrogen content is obtained. A systematic study of the effects of gas pressure, substrate‐to‐filament distance, and filament temperature on film properties is presented, allowing insight into the growth condition required for this material as well as the significance of secondary gas phase reactions. Material of good optoelectronic quality is obtained at high growth rates. The stability with respect to light degradation was compared to typical plasma deposited films. Conditions for the transition from amorphous to microcrystalline films, observed under gas phase dilution with hydrogen, were investigated. By in situ ellipsometry and atomic force microscopy the nucleation and film morphology were shown to be significantly different from those for plasma‐chemical vap...

New diagnostic aspects of high rate a-Si:H deposition in a VHF plasma

An a-Si:H deposition plasma operated in the wide frequency range from 32 to 180 MHz was investigated to identify frequency effects on the plasma bulk (density, power dissipation) and on the sheaths. Results are presented on the electron density, plasma impedance and power coupling efficiency, as well as measurements of the flux of ions to a growth surface and their energetic distribution. The results help to explain the observed increased film growth rate in a very high frequency plasma.

Properties of amorphous boron nitride thin films

Abstract Amorphous boron nitride films were prepared by very high frequency plasma chemical vapour deposition. The material obtained was stoichiometric and the choice of preparation conditions (substrate temperature, gas phase pressure) critically affected hydrogen concentration and bonding. The films showed a bandgap of typically 5 eV. A considerable density of electronic states in the bandgap and fairly flat band tails were revealed by photothermal deflection spectroscopy. The electric break-through field strength was about 2.2 MV/cm. From the dependence of the infrared absorption on the substrate temperature, an IR absorption band at 910 cm −1 was attributed to the wagging mode of the BH vibration. The amorphous phase of BN consists almost exclusively of sp 2 bonding. In samples which contain sp 3 bonding also the formation of a crystalline phase is detected by X-ray diffraction.

Deposition of a-Si:H with the hot-wire technique

Amorphous hydrogenated silicon (a-Si:H) was deposited by SiH 4 decomposition on a bot tungsten filament. A substrate temperature of T s =400 o C was chosen since an improved degradation behaviour is expected is expected as a result of low hydrogen incorporation. The effects of gas pressure, substrate-to-filament distance d s-f and filamenttemperature T f on film properties are discussed. Material of good optoelectronic quality is obtained at high deposition rates

Control of a-Si:H deposition by the ion flux in a VHF plasma

Abstract Excitation frequencies in the VHF range have been applied for the plasma CVD of a-Si:H at high rates as well as in other processes. An ion flux increasing with excitation frequency is known to enhance the formation of a stable structure. In the present contribution we show that SiH4 decomposition is only slightly enhanced with f. Not only the film properties but also the deposition rate is determined by the ion flux to the growth surface. Ions strongly affect surface processes due to their large kinetic energy, typically ≥ 20eV as compared to thermal energies for neutrals.

Surface controlled plasma deposition and etching of silicon near the chemical equilibrium

Abstract In this study we present investigations of silicon growth and etching in a dilute SiH4/H2 plasma near the partial chemical equilibrium in order to study nucleation processes at the growth surface in plasma CVD. μc-Si:H and a-Si:H deposited on Corning 7059 glass substrates was simultaneously exposed to an extremely diluted SiH4 in H2 VHF plasma at a frequency of 100 MHz. Under conditions used in our study simultaneous growth of μc-Si:H and etching of a-Si:H is observed. The results support the μc-Si:H growth model in which the net growth rate is the difference of a deposition and an etch rate.

Infrared spectroscopy during hydrogen effusion of a-Si:H, a-SiGe:H and a-Ge:H

The effusion of hydrogen from a-Si:H, a-SiGe:H and a-Ge:H was studied in-situ by infrared spectroscopy. This allows monitoring of Si-H (Ge-H) bond breaking in different configurations. Additional information is obtained from changes in refractive index and from the wavelength shift of absorption bands upon tempering. Already before the onset on H-effusion changes in hydrogen binding are observed. During effusion film density increases as a result of crosslinking in voids. Information on bond angle distribution and crystallisation is obtained from Raman measurements.

Laser induced nucleation and growth of polycrystalline silicon

We present a new method for growing large area polycrystalline silicon films from amorphous silicon at temperatures below 550°C, based on the selective creation of point-like polycrystalline nucleation seeds using laser crystallization and subsequent lateral growth by thermal crystallization. The growth rate depends on the laser intensity used to create the seed, as well as on the doping concentration and the thickness. Atomic force microscopy reveals grains of average diameter 60 nm in the thermally crystallized areas.

Thermally induced changes of conductivity in undoped and doped amorphous germanium

Reversible changes of the electrical properties in undoped and doped a-Ge:H by thermal quenching and subsequent annealing have been investigated. For undoped a-Ge:H the dark conductivity σ d shows two regimes, separated by the equilibration temperature T E of about 170°C. Above this temperature σ d becomes independent of thermal history, indicating that the structure is in thermal equilibrium and a unique function of T. Below 170°C σ d exhibits a pronounced downward kink in the Arrhenius plot and becomes dependent on the cooling rate. Relaxation behaviour can be described with a stretched exponential and the time constant for equilibration τ E follows a thermal activated form with an activation energy of 1.1eV. Heavily boron-doped films show the opposite effect, namely an increased conductivity after fast quenching.

Amorphous hydrogenated silicon carbon from VHF deposition

Amorphous hydrogenated silicon carbon (a-SiC:H) has been deposited in a very high frequency (VHF) glow discharge (GD) and compared to an optimized material from a DC-GD. It turns out that good quality material is obtained at high deposition rates (r d =17 A/s), when hydrogen dilution is applied. An increase of frequency from 50 to 180MHz has a negligible influence on film properties although r d is increased by about four times. A detailed analysis of microstructure by IR and PDS shows a better incorporation of carbon into the Si-matrix for VHF than for DC samples, i.e. less CH 3 groups at the same bandgap. The investigations of the plasma confirm that the CH 4 feed gas is dissociated by excited SiH x radicals in VHF and by electron impact in DC