Etching effect

Selective removal of the less noble constituent has been demonstrated by chemical analysis in the case of nickel-rich alloys in fused caustic soda or fused fluorides ", and by etching effects and X-ray microanalysis for Fe-18Cr-8Ni steels in fused alkali chlorides. This type of excessive damage can occur with quite small total amounts of corrosion, and in this sense its effect on the mechanical properties of the alloy is comparable with the notorious effect of intercrystalline disintegration in the stainless steels. 

Other transport limitations, such as diffusion-controlled reactions, can lead to localized depletion of etchant, which results in a number of observable etch effects. The size and density of features can influence the etch rate at different locations on a single wafer, thus producing "pattern sensitivity." Depletion across a wafer produces a "bulls eye" effect, while depletion across a reactor is indicated by the fact that the leading wafer edge etches faster than the trailing edge. Similar effects are noted when product removal is transport-limited. Most of these effects can be reduced... 

Gold can be etched effectively with C2CI2F4 76) or with CCIF3 (77), while CF4/O2 etching causes staining. The observed staining is believed to be gold oxides, whose formation is enhanced by the presence of atomic fluorine (77). 

Fig. 5.1 Field ion image of a Pt surface showing the image contrast of vacancies on the 012 planes. These vacancies are however produced by a field induced chemical etching effect, not equilibrium thermal vacancies.

The surfaces of polypropylene mouldings may be etched effectively by exposure to trichlorethylene vapour under controlled conditions. The temperature of the solvent should be kept below its boiling point and the period of exposure to the vapour determined according to the thickness and other dimensions of the mouldings (it may be in the range from a half second to a few minutes). 

Also visible in Fig.2(a) are diffusely etched bands coincident with and extending beyond the rays containing the slip bands. This etching effect represents a type of kink band (20), i. e., an area at die edges of which the orientation changes abruptly. Similar kink bands have also been observed in abraded surfaces of zinc (37), and can be expected to be general. 

Initial processing experiments showed however, that under typical O2 RIE conditions (power 0.1 to 0.2 W/cm self-bias — —250 to —350 V, pressure — 5 to 20 mTorr O2), these resists are not very resistant, particularly under prolonged etching. Effective pattern transfer may require etch times of 15 to 30 min (11,12). which are sufficient to cause extensive degradation of the resist. Such behavior is reminiscent of poly (olefin sulfone)s such as the well-known PBS e-beam resist, which is etched 5-7 times faster than polystyrene in an oxygen plasma (5). 

The oxidizing and etching effects that help in particle removal may lead to a rougher surface on the substrate such as poly-Si [37,38]. Therefore, a balance must be maintained between the need for greater etching depth to remove... 

Photoetching processes do not always consist of a simple superposition of an anodic and a cathodic partial process and may exhibit various types of complications. Firstly, even in the simple case of the photoetching of GaP single crystals in alkaline OBr solutions, the situation is actually more complex than depicted above, since at n-type crystals, it appears that the photoetching process itself induces a hole injection reaction and hence and electroless etching effect [24]. Initially, OBr is reduced at the GaP surface via the current-doubling mechanism (as is concluded from photocurrent measurements at p-type samples) ... 

The role of illumination consists in creating electron-hole pairs, which are necessary for the partial reactions. During the reduction of OBr" ions, Br radicals are formed as intermediates (cfr. reaction (55)), which appear to initiate an autocatalytic reaction mechanism surface states are formed, through which holes are injected into the valence band (at least at not too high OBr concentrations). These surface states, which are experimentally detected as a peak in the capacitance-potential plot [24, 81], are believed to be associated with adsorbed OBr. Furthermore, voltammetric experiments demonstrate that these surface states can be annihilated by a sufficiently large concentration of holes at the surface. The latter explains why this induced electroless etching effect is not observed at p-GaP, since in this case the holes are present at the surface in a quasi-equilibrium cloud of majority carriers, in contrast to the case of n-GaP. 

Bhalla, A. S., Tongson, L. L. and Newnham, R. E. Relationship of crystallographic polarity to piezoelectric, pyroelectric and chemical etching effects in LijGeOs and LiGa02 single crystals. J. Appl. Cryst. 16, 138-140 (1983). 

Cu " salts. Show an etching effect in ammoniacal solution preferentially on W(IOO) faces (Millner-Sass solution). 

Sputtered material can be spread over the surface, and selective etching effects can influence the measured compositions. These effects will be discussed further in the results section. 

---