Abstract A range of amorphous hydrogenated silicon-carbide films have been produced using the plasma-enhanced chemical-vapour deposition technique with silane and methane diluted in hydrogen as the parent molecules. The air-exposed and sputter-cleaned surfaces of these films have been investigated by means of X-ray photoelectron spectroscopy. Auger electron spectroscopy, secondary-ion mass spectrometry, Raman spectroscopy and reflection-electron diffraction. The structural and chemical nature of the films has been determined as a function of the methane: silane ratio by a combination of the above techniques. X-ray photoelectron spectroscopy and Auger electron spectroscopy have been used to determine the carbon content of the films also as a function of the methane: silane ratio.
We investigate in situ dry etch monitoring via reflectometry. We present two approaches, the choice depending on the presence of layers (if any) deposited on the substrate. Firstly, we present a model of the normal incidence reflectance of a multilayer stack (of any number of layers) as a function of etch depth based on electrical transmission line theory. We have applied this model to the reactive ion etching of an InP/InGaAsP multilayer structure using CH4/H2/O2, and a GaAs/AlAs multilayer structure using SiCl4. In the case of the InP-based material, use of the model enabled us to distinguish individual 10.24 nm InGaAsP quantum wells. In the case of the GaAs-based structure, use of the model allowed us to determine the induction time for the removal of the native gallium oxide and to tell which AlAs quantum well had been reached during the etch, enabling cessation of the etch process just after the last well with no overetch. Agreement between the model and observed behavior of the reflectance was extremely good in both cases. Secondly, we have extended this approach to model the reflectance from a wafer with a suitable patterned dry etch mask and a laser beam covering both masked and etched areas, allowing the study of interference between the reflected beams from the two areas. We have compared the modeled and observed reflectance from a sample of NiCr masked bulk SiO2 and found agreement to be within 20 nm in a total etch depth of 1 μm.
The damage introduced into an InGaAs/InGaAsP quantum well structure during CH4/H2 reactive ion etching (RIE) processes was measured, for plasma powers from 20 to 100 W, using low temperature photoluminescence. The damage depth profile is estimated to be around 12–70 nm after annealing at 500 °C for 60 s using a rapid thermal annealer. A reduced damage RIE process has been developed to fabricate InGaAs/InGaAsP multiquantum well ridge waveguide lasers. The performance of these lasers has been compared to that of lasers fabricated from the same epilayer using wet etching to form the ridge. The resultant threshold currents were essentially indistinguishable, being 44.5 and 43 mA, respectively, for dry and wet etched lasers with 500 μm long laser cavities.
The loss associated with a mirror in an InP-based waveguide has been investigated. Mirror roughness and non-verticality were both significant sources of loss. Mirrors with only 1 dB loss have been produced through novel fabrication techniques.
We report on the use of CHF3, C2F6, and SF6 as etch gases for deep reactive ion etch processing of germano-boro-silicate glass films prepared by flame hydrolysis deposition (FHD). The glass film under study had a composition of 83 wt % SiO2, 12 wt % GeO2, and 5 wt % B2O3. The scope of the study was to identify the benefits and drawbacks of each gas for fabrication of deep structures (>10 μm) and to develop an etch process in each gas system. The etch rate, etch profile, and surface roughness of the FHD glass films were investigated for each gas. Etch rates and surface roughness were measured using a surface profiler and etch profiles were assessed using a scanning electron microscope. It was found that SF6 had the highest FHD glass etch rate and nichrome mask selectivity (>100:1) however, it had the lowest photoresist mask selectivity (<1:2) and highest lateral erosion. CHF3 had the lowest FHD glass etch rate but high selectivity over both nichrome (>80:1) and photoresist (>10:1) and the etch profile was found to be smooth and vertical. C2F6 had a similar etch profile to that of CHF3, but the selectivity over both mask materials was lower than in CHF3. Fused silica was used as a reference material where it was found the percentage drop in etch rate in C2F6, SF6, and CHF3 was −12%, −15%, and −37%, respectively. From the results presented here CHF3 proved to be the most versatile etch process as either photoresist or nichrome masks could be used to attain depths of 20 μm, or more.
Arrays of 40 - 50 nm quantum dots were fabricated from Si- Si1-xGex single quantum well and superlattice structures grown by molecular beam epitaxy. The dots showing strong luminescence were studied by synchrotron source x-ray diffraction. Some of the dots were coated with SiNx films containing different build-in stresses. It was found that the luminescence intensity depends strongly on the amount of stress in the SiNx coating, being strongest when the stress was close to zero. A strain symmetrization process occurred in the bright dots. Although an exact physical origin is not yet available, it is exciting that these quantum dot diodes work at room temperature and that the whole fabrication procedure is compatible with Si- technology.
The damage produced during CH/sub 4//H/sub 2/ reactive ion etching (RIE) processes has been measured using low temperature photoluminescence. The damage depth profile was estimated and a low level damage RIE process has been developed. The process has been used to fabricate InGaAs/InGaAsP ridge waveguide lasers containing 5 quantum wells with threshold currents, 43-45 mA for 500 /spl mu/m lasers, that are indistinguishable from those of wet-etched devices.
David Simpson's article on high-tech manufacturing industry in Scotland emphasized the high level of optoelectronics and photonics research in the country (August pp57–58).
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
