Vapour phase etching

The silicon is etched away in the window 6 down to and exposing the sapphire surface 7. The surface 7 is cleaned and a buffer layer 8 of CdTe is grown. In the next step two layers 9 and 10 of HgCdTe are grown by metal-organic vapour phase epitaxy, MOVPE. The layers 9 and 10... 

The depth of the recrystallised layer is very small, of the order of 0.01 -0.1 pm. Thus, a possible way to eliminate its effect on p-n junction properties is to perform a drive-in diffusion of aluminium from the epitaxial layer. Unfortunately, the diffusivity of aluminium from an epitaxial layer is extremely slow in SiC. The diffusivity is 3 - 5 orders of magnitude lower than that observed for diffusing aluminium from the vapour phase [70]. The authors of [69] had to employ very high diffusion temperatures, over 2500 °C. The anneal produced a shift of the p-n junction into the crystal bulk and the electrical properties were substantially improved. However, this could not provide the elimination of the weak points of the junctions. The characteristics of the p-n junctions were worse than those with the recrystallised layer removed by sublimation etching. In addition, the surface evaporation and graphitisation at temperatures above 2500 °C severely reduces the reproducibility of the results. 

Applications that are relevant to the topic of adhesion include the determination of the growth kinetics and densification of polymer films at surfaces, quahty control of anodization and other surface-modification pre-treatments, measurement of adsorption and determination of molecular orientation and compaction of adsorbed layers and Lang-muir-Blodgett films, detection of surface damage in plasma-etching processes and measurements of thinning of lubricant films. Metallization from the solution or vapour phase can be studied up to the stage at which the metal becomes opaque (around 40-nm thick for most metals). 

Etching of the sacrificial oxide by vapour-phase HF etch to release comb and ring/disk structures... 

Figure 18.12(a) shows the roughness of the epi-poly layer after deposition and Figure 18.12(b) shows a detail of the interdigital capacitors of the drive structure after poly-Si CMP, DRIB and vapour-phase HF release etch of the sacrificial oxide layer. Only the smooth surface after CMP allows the precision etch of the capacitor spaces <1 pm. 

Maia MD, de Vasconcelos EA, Conceigao de Mascena Diniz Maia PF, da Costa Maciel J, Rizzardi Cajueiro KR, da Paz Carvalho da Silva M, da Silva Jr EF, Fireman Dutra RA, Freire VN, de Filho JL (2007) Immobilization of urease on vapour phase stain etched porous silicon. Process Biochem 42(3) 429 33... 

Fig. 4.2 shows a polished and etched section of a production clinker. Crystals of alite and belite are embedded in a matrix of aluminate and ferrite phases. If HF vapour is properly used, the alite is yellowish brown, the belite is blue or red, and the aluminate is grey the ferrite, which is unattacked, is... 

There should be little free lime. What there is should occur as rounded grains, typically 10-20 pm in size, and associated with alite and interstitial material. Lime appears cream in sections etched with HF vapour. Its presence may be confirmed by a microchemical test using White s reagent (5 g of phenol in 5 ml of nitrobenzene + 2 drops of water) long, birefringent needles of calcium phenate are formed. The test also responds to CH. Alkali sulphates occur in the clinker pore structure they are etched black with HF vapour, and inhibit the etching of silicate phases with which they are in contact. 

In addition small-scale exposures at 870"C were used to study further the role of water vapour with 20 vol.-% and 30 vol.-% water vapour in air in an alumina tube furnace. Phase morphology was studied with scanning electron microscope (SEM). To distinguish between the glassy and crystalline phases some samples were etched in 2-% HF-solution. Phase composition was determined by a quantitative X-ray diffraction (XRD) analysis based on the internal standard, Cap2, method. The chemical composition of the amorphous phase in the binder was determined locally with EDS analysis in SEM. A bulk chemical analysis of the amorphous phases in binder was performed by Induction Coupled Plasma Mass-Spectrometry (ICP-MS). The samples were crushed powders of as-received and 500 h at water vapour bulk exposed (w) materials. The glassy phase was dissolved in HF-HNO3 solution. Open porosity, apparent and bulk densities of each specimen were determined by Archimedes method before and after the tests. 

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