Defect reduction and cost savings through re-inventing RCA cleans

RCA cleans, (also referred to as SC1 and SC2 cleans) have been used in semiconductor manufacturing for decades. These solutions, as developed by Kern and Puotinen in 1965, are multi-purpose surface treatments. If used as originally developed, they are effective at both organic and metallic contamination control, and are viewed as innocuous to silicon based surfaces. Only recently have new processing conditions been explored. Historically, these mixtures of water, hydrogen peroxide, and either ammonium hydroxide (for the SC1 solution) or hydrochloric acid (for the SC2 solution), were mixed at a 5:1:1 and 6:1:1 ratio respectively and used at temperatures of 70-80 degrees C. This paper presents a comprehensive study using surface analysis and inspection techniques to test residue removal, silicon surface roughening, silicon dioxide etch rates, and particle removal efficiency due to the effects of chemical concentration and temperature. Impinging high-frequency sonic energy onto the wafer surface at different wafer to wafer spacing in the processing cassette is also studied. The authors have found that lower concentration SC1 and SC2 solutions, in concert with "megasonic" energy, leads to higher particle cleaning efficiency, excellent residue removal, reduced silicon surface roughening, and reduced chemical usage in several types of processing equipment. These effects add up to reduced semiconductor device defect densities at a net lower cost. Electrical test data on both DRAM and micro-processors are presented.