Damaged-layer effects

A damaged layer between 1 to 10 nm thick according to the material and the polishing conditions is generated by the CMP process. This layer would seem to have to be removed as it presents poorly defined physical properties, for example, in terms of contamination, internal stress, insulating characteristics, and the like. Nevertheless the detrimental effects of this layer still have to be clearly demonstrated. 

The simple scrubber process is very efficient to eliminate slurries but does not remove the metallic contamination or the damaged layer. The simplest additional process is to use an HF-based step which removes both of them. The use of an HF-compatible scrubber saves an additional wet bench with a dryer and a wafer transfer. The chemistries used must avoid loading effects. 

The efficient scrubberless alternative consists in using hot diluted ammonia in a specific bath with very high megasonic power. In this case, the backside surface must be protected with an oxide or nitride layer to prevent a severe silicon roughening effect from occurring. Then an HF-HCl dip enables the metallic contamination and damaged layer to be removed. HCl turns the respective zeta potentials into favorable conditions that limit the particle redeposition. 

It should be noted that dielectric and optical properties of the near-the-surface layer of a semiconductor, which vary in a certain manner under the action of electric field, depend also on the physicochemical conditions of the experiment and on the prehistory of the semiconductor sample. For example, Gavrilenko et al (1976) and Bondarenko et al. (1975) observed a strong effect of such surface treatment as ion bombardment and mechanical polishing on electroreflection spectra. The damaged layer, which arises in the electrode due to such treatments, has quite different electrooptic characteristics in comparison with the same semiconductor of a perfect crystalline structure (see also Tyagai and Snitko, 1980). 

GaN H3P04 (85%) 180 0.27 - - Kim [8] Effectively removes damage layer from... 

The strain energy release rate can be effectively calculated if instead of the damaged laminate one considers the equivalent laminate, in which the damaged layer is replaced with an equivalent homogeneous one with degraded stiffness properties. The residual stiffness matrix [Q] of the equivalent layer is a function of the relative delamination area D = i and the... 

The final effect to be considered is radiation induced segregation (RIS). The creation and annihilation of point defects can be spatially separated. This leads to defect fluxes or an equivalent atom flux that depends on which alloy element is involved. When this leads to a non-uniform distribution of elements within a previously homogeneous alloy it is called RIS. It is an active area of research, particularly for alloys used in nuclear power plants, which has been reviewed recently (39). The effect can be strong enough to produce phase separation and growth under ion bombardment. Depths affected are of the same order as RID because they both involve thermally activated processes which can produce effects well beyond the ion damage layer at elevated temperatures. 

Deposition of metals is not reversible, even with catalyst regeneration. The metals may come into the system via additives, such as silicon compounds used in coke drums to reduce foaming, or feedstock contaminants such as Pb, Fe, As, P, Na, Ca, Mg, or as organometallic compounds in the feed primarily containing Ni and V. The deposition of Ni and V takes place at the pore entrances or near the outer surface of the catalyst, creating a rind layer - effectively choking off access to the interior part of the catalyst, where most of the surface area resides. Metals deposition can damage the acid sites, the metal sites, or both. 

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