IMPACT OF IRON CONTAMINATION AND ROUGHNESS GENERATED IN AMMONIA HYDROGEN-PEROXIDE MIXTURES (SC1) ON 5 NM GATE OXIDES

Immersion of hydrophobic (HF-last) silicon wafers into iron-contaminat ed ammonia peroxide mixtures (SC1 solution) results in the formation o f so-called clustered light point defects. At these sites, increased s urface microroughness and local higher iron concentrations are observe d. Also, device yield is strongly affected by the presence of iron con tamination into SC1 solutions. It is demonstrated that only dHF/dHCl c leans are capable of completely eliminating any yield loss resulting f rom iron-contaminated SC1 treatments. The experimental observations ca n be understood based on the following model. Hydrogen peroxide decomp osition is catalyzed by iron. Iron contamination (present in SC1 solut ion as insoluble hydroxide aggregates) deposits on the silicon wafer s urface upon immersion of the latter. While doing so, the adsorbed iron cluster continues to catalyze further hydrogen peroxide decomposition . Local hydrogen peroxide depletion exposes the bare silicon surface t o the etching activity of the ammonia. Local etching of the silicon cr eates microroughness. Additionally, iron becomes inhomogeneously incor porated into the bulk of the chemical oxide formed. Gate oxide integri ty degradation can be observed to correlate with these sites. A subseq uent acid clean is only efficient in eliminating the induced yield los s, if the oxide layer (with built-in iron) is completely removed.