J. M. Grow

Inductively coupled plasma etching of bulk 6H-SiC and thin-film SiCN in NF3 chemistries

A parametric study of the etching characteristics of 6H p+ and n+ SiC and thin-film SiC0.5N0.5 in inductively coupled plasma (ICP) NF3/O2 and NF3/Ar discharges has been performed. The etch rates in both chemistries increase monotonically with NF3 percentage and rf chuck power. The etch rates go through a maximum with increasing ICP source power, which is explained by a trade-off between the increasing ion flux and the decreasing ion energy. The anisotropy of the etched features is also a function of ion flux, ion energy and atomic fluorine neutral concentration. Indium-tin-oxide masks display relatively good etch selectivity over SiC (maximum of ∌70:1), while photoresist etches more rapidly than SiC. The surface roughness of SiC is essentially independent of plasma composition for NF3/O2 discharges, while extensive surface degradation occurs for SiCN under high NF3:O2 conditions. © 1998 American Vacuum Society.

Comparison of dry etch chemistries for SiC

SiC has generally been plasma etched in polymer-forming chemistries such as CHF3/O2 or CF4/O2, often with addition of H2 to achieve acceptable surface morphologies. We find that under high ion density conditions gases such as SF6, NF3, IBr, and Cl2 produce smooth surfaces that are free of hydrogen passivation effects. Etch rates in excess of 1500 A/min are achieved in electron cyclotron resonance (ECR) NF3 or Cl2/Ar discharges with low additional rf chuck powers (100–150 W); dc bias of −120 to −170 V. The rates are somewhat lower (factors of 2–4) with IBr and SF6 chemistries. Ion-induced damage is evident from Hall measurements for SiC exposed to rf powers >150 W (dc bias >−170 V) under ECR conditions and >250 W (dc bias >−275) under reactive ion etch conditions. Efforts to anneal damage at these higher powers reveals a major annealing stage is evident at ∼700 °C, with an activation energy of ∼3.4 eV, but there is significant damage remaining even after 1050 °C annealing. Hydrogen passivation is a problem...

High rate etching of SiC and SiCN in NF3 inductively coupled plasmas

Etch rates of ∌3,500 A…/min for 6H-SiC and ∌7,500 A…/min for SiC0.5N0.5 were obtained in inductively coupled plasmas with NF3-based chemistries. Similar etch rate trends were achieved with both NF3/O2 and NF3/Ar mixtures. The rates were strong functions of plasma composition, ion energy and ion fluxes, and were independent of conductivity type for SiC. Surface root-mean-square (RMS) roughness were 1-2 nm for etched SiC over a wide range of conditions indicating equi-rate removal of the SiFx and CFx etch products, but SiCN surfaces became extremely rough (RMS roughness g 20 nm) for F2-rich plasma conditions. The etched surfaces of SiC were chemically clean and stoichiometric, with small (l0.2 at%) quantities of N2- or F2- containing residues detected. © 1998 Elsevier Science Ltd. All rights reserved.

A comparative study of plasma enhanced chemically vapor deposited SiOH and SiNCH films using the environmentally benign precursor diethylsilane

Abstract The environmentally benign precursor diethylsilane (DES) was used with either N 2 O or NH 3 to synthesize SiOH or SiNCH films by plasma enhanced chemical vapor deposition (PECVD). The growth rates were observed to decrease with higher temperature while increasing with total pressure. Oxide films with optimal properties were synthesized at a deposition temperature of 300 °C, total pressure of 0.3 Torr, DES flow rate of 15 sccm, and N 2 O/DES flow rate ratio of 16. Comparative values of refractive index, stress, hardness and Youngs modulus are presented as a function of processing variables and related to film density and resulting film compositions.

Growth kinetics and characterization of low pressure chemically vapor deposited Si3N4 films from (C4H9)2SiH2 and NH3

Abstract The use of the environmentally benign precursor ditertiarybutylsilane (DTBS) with NH 3 to synthesize silicon nitride films by low pressure chemical vapor deposition was investigated. In the temperature range 600 to 700 °C, the growth rate is observed to follow an Arrhenius behavior with an activation energy of 50 kcal mol −1 , while above 700 °C, the rate decreases with higher temperatures primarily due to the gas phase decomposition of DTBS. The growth rate varied linearly with total pressure over the investigated range of 0.2 to 0.65 Torr and with DTBS flow rate up to a value of 20 sccm in agreement with a Langmuir-Hinshelwood mechanism. A rapid decrease in growth rate was observed with higher NH 3 DTBS ratios due to a reduction in the partial pressure of DTBS and its enhanced competition with NH 3 for available surface sites. All deposits were found to be essentially stoichiometric and to contain ≈ 10 at% carbon. The films were found in all cases to be amorphous and highly tensile. At deposition temperatures below 750 °C, values of the refractive index were near those reported for Si 3 N 4 . FTIR spectra revealed the presence of hydrogen for even the highest investigated deposition temperature (900 °C). The hardness and Youngs modulus of the films increased with higher deposition temperatures reaching values near 19 and 190 GPa, respectively, at 900 °C.

Plasma enhanced chemical vapor deposition of Si-N-C-H films from environmentally benign organosilanes

Abstract The environmentally benign precursors diethylsilane (DES) and di-t-butylsilane were used with NH 3 to synthesize hydrogenated silicon carbonitride films by plasma enhanced chemical vapor deposition. The growth kinetics and film properties were examined as a function of deposition temperature, pressure, and NH 3 /organosilane ratio. The growth rate was observed to decrease with higher temperature and higher NH 3 /organosilane ratio while increasing with higher total pressure. Values of index of refraction, stress, hardness, and Youngs modulus were measured as a function of processing variables and related to film density and resulting film compositions. Oxidation of the films was noted to occur at low deposition temperatures, low NH 3 / organosilane ratios, and high pressures. Carbon was present in all deposits and decreased slightly with higher NH 3 /organosilane flow ratios.

ICP etching of SiC

A number of different plasma chemistries, including NF3/O2, SF6/O2, SF6/Ar, ICl, IBr, Cl2/Ar, BCl3/Ar and CH4/H2/Ar, have been investigated for dry etching of 6H and 3C-SiC in a Inductively Coupled Plasma tool. Rates above 2,000 angstroms·cm-1 are found with fluorine-based chemistries at high ion currents. Surprisingly, Cl2-based etching does not provide high rates, even though the potential etch products (SiCl4 and CCl4) are volatile. Photoresist masks have poor selectivity over SiC in F2-based plasmas under normal conditions, and ITO or Ni are preferred.

Growth kinetics and properties of dielectric films synthesized by low pressure chemical vapor deposition from diethylsilane

Abstract Diethylsilane (DES) has been used to synthesize amorphous silicon carbide and silicon dioxide films by low pressure chemical vapor deposition. For silicon carbide, the deposition rate at 700°C was observed to vary linearly with flow rate and pressure while the stoichiometry of the deposits showed little variation from a composition of Si 0.6 C 0.4 . In the 600–700°C range, the growth rate was observed to follow an Arrhenius behavior with an activation energy of 41 kcal mol −1 . The stoichiometry became progressively richer in carbon with higher temperatures. The onset of crystallinity was observed to occur for the 850°C deposits and the films were found to be tensile in all cases. The silicon dioxide films were synthesized in the temperature range 350–475°C with the growth rate observed to follow an Arrhenius behavior with an apparent activation energy of 10 kcal mol −1 . The growth rate was seen to increase with higher pressure and to vary as a function of the square root of the DES flow rate and O 2 -to-DES ratio. In both the pressure and the O 2 -to-DES ratio studies conducted at 400°C, there were points of abrupt cessation in deposition. The density and index of refraction of the films were found to be 2.25 g cm −3 and 1.45 respectively, independent of deposition conditions. The etch rate of the films in a 25°C P-etch solution was observed to decrease with higher deposition or annealing temperatures, reflecting densification of the material. Despite severe aspect ratios, the films were seen to exhibit good step coverage.

LPCVD Of Silicon Carbide Films From The Organosilanes Diethylsilane And Di-T-Butylsilane

In this paper, the kinetics and properties of amorphous LPCVD silicon carbide films synthesized from the single organosilane precursors diethylsilane (DES) or di-tbutylsilane (DTBS) are discussed. For DES, the growth rate is observed to vary linearly with flow rate and pressure, while for DTBS, a square root dependency is seen as a function of these parameters. An Arrhenius type behavior was observed for both chemistries yielding activation energy values of 40 and 25 kcal/mol for DES and DTBS respectively. The elemental composition of the films became progressively richer in carbon as the deposition temperature increased with stoichiometry occurring near 750°C. The film stress was dependent on carbon content and became compressive at compositions near Si 0.35 C 0.65 . The hardness and Youngs modulus of the films increased with increasing carbon content reaching maxima near stoichiometry. Free-standing membranes produced under optimal processing conditions had a relatively low optical transmission due to excess carbon. Although, transmission characteristics were improved by adding NH 3 in the reaction chamber, the resulting silicon carbonitride films exhibited undesirably high values of tensile stress.

Analog Computer Simulation of Energy and the Environment

Energy education is becoming recognized as a “basic skill” or “survival skill.” Programs are needed to increase public awareness of the current energy situation. The Energy-Environment Simulator is a specially designed analog computer that simulates real-world conditions, focusing on the current energy problems and looking at possible energy futures. The Simulator is capable of varying a large number of parameters affecting either the supply of energy or the demand for energy, as well as determining the rate at which the energy from each source is supplied for the various demands. A digital clock, proceeding at the rate of a century a minute, allows the operator to make decisions about the allocation of energy resources in response to changing conditions on a continuous basis. Different types of presentations of the Simulator are possible, depending on the nature and size of the audience and time available for the program. The Simulator is found to be an excellent educational tool, serving as a visible demonstration that the combination of limited fossil fuels with continued growth in energy consumption can lead to serious future energy problems.