David C. Liu

‘‘Diamondlike’’ carbon films: Optical absorption, dielectric properties, and hardness dependence on deposition parameters

An rf plasma deposition system was used to prepare amorphous ‘‘diamondlike’’ carbon films. The source gases for the rf system include methane, ethylene, propane, and propylene, and the parameters varied were power, dc substrate bias, and postdeposition anneal temperature. Films were deposited on various substrates. The main diagnostics were optical absorption in the visible and in the infrared, admittance as a function of frequency, hardness, and Auger and ESCA spectroscopy. Band gap is found to depend strongly on rf power level and band gaps up to 2.7 eV and hardness up to 7 Mohs were found. There appears to be an inverse relationship between hardness and optical band gap.An rf plasma deposition system was used to prepare amorphous ‘‘diamondlike’’ carbon films. The source gases for the rf system include methane, ethylene, propane, and propylene, and the parameters varied were power, dc substrate bias, and postdeposition anneal temperature. Films were deposited on various substrates. The main diagnostics were optical absorption in the visible and in the infrared, admittance as a function of frequency, hardness, and Auger and ESCA spectroscopy. Band gap is found to depend strongly on rf power level and band gaps up to 2.7 eV and hardness up to 7 Mohs were found. There appears to be an inverse relationship between hardness and optical band gap.

Optical and interfacial electronic properties of diamond-like carbon films

Abstract We have been preparing hard semitransparent carbon films on oriented polished crystal wafers of silicon, indium phosphide and gallium arsenide, as well as on KBr and quartz. Properties of the films were determined using IR and visible absorption spectroscopy, ellipsometry, conductance-capacitance spectroscopy and α particle-proton recoil spectroscopy. Preparation techniques include r.f. plasma decomposition of methane (and other hydrocarbons), ion beam sputtering and dual-ion-beam sputter deposition. Optical energy band gaps as large as 2.7 eV and extinction coefficients lower than 0.1 at long wavelengths are found. Electronic state densities at the interface with silicon as low as 10 10 states eV -1 cm -2 were found.

An enhanced sensitivity null ellipsometry technique for studying films on substrates - Application to silicon nitride on gallium arsenide

General considerations are applied to optimize the sensitivity of ellipsometric measurements for thin films on a substrate. s‐ or p‐wave suppression conditions are found to give maximum sensitivity. Approximate values of the optical parameters of the films and substrate are used to calculate discrete film thicknesses for the s‐ or p‐wave suppression to occur. For null fixed‐wavelength ellipsometry, these calculations are limited to experimentally available wavelengths, e.g., at strong emission lines from a Hg lamp. Films with thicknesses near the calculated ones are then deposited on the substrate. The ellipsometric parameters ψ and Δ are obtained at multiple angles of incidence and wavelengths, and a least‐squares procedure is used for the analysis. The method has been applied to silicon nitride films on GaAs. The problem of correlation between the calculated optical parameters of the system is addressed. It is shown that the multiple‐wavelength analysis decreases significantly the correlations as compar...

Plasma deposited hydrogenated carbon on GaAs and InP

The properties of ‘‘diamondlike’’ carbon films grown by glow discharge 30 kHz plasma using methane are reported. The C ls XPS line shape of films showed localized hybrid carbon bonds ranging from as low as 40% to as high as 97% percent of the total carbon bonds. Infrared spectroscopy and N15 nuclear reaction profiling data indicated 35% to 42% hydrogen, depending inversely on deposition temperature. The deposition rate of films on Si falls off exponentially with substrate temperature, and nucleation does not occur above 200 °C on GaAs and InP. Optical data of the films showed band gap values of 2.0 to 2.4 eV increasing monotonically with methane flow rate.

InP MIS structures with diamondlike amorphous carbon films deposited by ion-beam sputtering and from plasma

Abstract The interfacial electronic properties of diamondlike carbon on both n -InP and p -InP have been studied. These measurements include conductance and capacitance versus frequency or bias voltage for metal-insulator-semiconductor structures. Carbon was deposited by both ion-beam sputtering, and from an rf plasma. We find that interface electronic state densities range from 10 11 to 10 13 states/eV cm 2 , depending on sample and preparation procedures. Normalized conductance versus frequency data show an unusual behavior, namely, two loss peaks having greatly differing voltage dependencies. We speculate on the physical origins of the two peaks.

Plasma deposition of amorphous hydrogenated carbon films on III-V semiconductors

Abstract Amorphous hydrogenated carbon films were grown on GaAs, InP and fused silica substrates using plasmas generated from hydrocarbon gases. Methane and n -butane sources were utilized. The effects of flow rate and power density on film growth were investigated. Carbon was the major constituent in the films. The degree of asymmetry at the carbon-semiconductor interface was approximately independent of the power density. Different HC bonding configurations were detected by the technique of secondary ion mass spectrometry. Band gaps up to 3 eV were obtained from optical absorption studies. Breakdown strengths as high as 6 × 10 8 V m −1 were measured.