Double-Edged Effect of Aqueous Hydrofluoric Acid (HF) on Silicon Interface Quality

RCA (Radio Corporation of America) clean remains as one of the most prevalent cleaning schemes in semiconductor manufacturing ever since it was developed by Kern in the 1960s [1], [2]. A plethora of studies have affirmed the cleaning mechanism and effectiveness of SC1 & SC2 in removing organic and metallic impurities from the wafer surface. However, less emphasis was placed on investigating the interplay between RCA cleaning sequence with the silicon surface reaction at the interface in the aqueous HF (hydrofluoric acid). In this interesting work, some compelling findings observed during our study to improve the wafer-edge yield at the top quadrant on 0.13um BiCMOS wafers are presented. Our analysis unveiled the predominance of "HF -last" in the cavity RCA clean and its immersion time effect when coupled with the interaction of SC2 on the silicon interface. A remarkable breakthrough was then demonstrated invariably in the wafer-edge performance by skipping SC2 compounded with a shorter "HF -last" immersion time. These insights not only brought in an innovative process sequence optimization, which had proclaimed an astounding wafer-edge yield improvement, but also food for thought on processes in which the interface quality poses a concern for the downstream integration. Our work is also reckoned to eventually lead to cost and chemical waste reduction in response to environmental sustainability.