Damaged-layer removal

To fully understand the formation of the N13S2 scale under certain gas conditions, a brief description needs to be given on the chemical aspects of the protective (chromium oxide) Ci 203/(nickel oxide) NiO scales that form at elevated temperatures. Under ideal oxidizing conditions, the alloy Waspaloy preferentially forms a protective oxide layer of NiO and Ci 203 The partial pressure of oxygen is such that these scales are thermodynamically stable and a condition of equilibrium is observed between the oxidizing atmosphere and the scale. Even if the scale surface is damaged or removed, the oxidizing condition of the atmosphere would preferentially reform the oxide scales. 

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 damaged layer can be determined by measuring its chemical resistance by a succession of short dips in diluted etching mixtures. When the etching rate reaches a constant value (corresponding to the bulk material) the damaged layer is removed. Figure 23 shows that both 0.1% HF and hot ammonia lead to the same thickness. 

In the case of the scrubberless approach, the damaged layer is in practice generally removed during the underetch particle removal process (ammonia... 

When using a scrubber without any etching step (HF), an additional etching bath can be implemented in order to remove the damaged layer. 

We must ensure that the etching steps performed during the cleaning processes are sufficient to remove the damaged layer as well. 

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. 

On a wet bench, a conventional SCI with megasonics to remove the particles followed by an HF dip to remove both the damaged layer and metallic contamination gives satisfactory results. 

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. 

The EBSD technique measures the top few monolayers of a sample to determine its crystal structure. However, most polishing techniques leave a damaged layer on the samples. Even 1 or 0.25 pm diamond polish is not sufficient. For EBSD work, a final polish with colloidal silica (grain size 0.05 pm) is often required to remove the damaged surface layers. 

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

This is illustrated in Fig. 1 the oxidation was carried out at a pressure of approximately 10" mm and at 900°C, at this temperature the oxide is volatile thus a pit is formed. Fig. 2 shows oxidation at a similar pressure on ill material although there are fewer oxidation pits in this picture, they are not found at dislocation sites. Oxidation in concentrated nitric acid had the advantage that the oxide layer left by the CP4 etch that was used to remove the damaged layer could be removed by HF. Many more oxide particles were formed on surfaces that did not have this oxide layer removed prior to oxidation. Thus we can say, at least for germanium, that the dislocations do not act as preferential sites for the nucleation of oxidation. 

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