Effects of Chemical Additives to Oxide Nitride Selectivity

At the operating pH (4-6) of most STI slurries, the oxide surface is negatively charged and the nitride surface is slightly positively charged. As shown in Fig. 13.13, a negatively charged surfactant or polyelectrolyte should enhance the selectivity of oxidemitride. 

Kang et al. [24] investigated the effect of anionic surfactants on the oxidemitride selectivity. As shown in Fig. 13.14, due to static repulsion, the addition of a low molecular weight anionic surfactant did not have any 

FIGURE 13.13 A typical chemical interaction between a surfactant and the STI wafer surface. 

FIGURE 13.14 Oxide film removal rate versus anionic surfactant concentration. 

FIGURE 13.15 Nitride film removal rate versus surfactant concentration. 

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EFFECTS OF CHEMICAL ADDITIVES TO OXIDE NITRIDE SELECTIVITY... 

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