Approach to reducing oversaturated boron content in plate poly layer of DRAM

In this paper, we studied how to lower the boron content in the plate poly layer of DRAM. The plate poly layer is composed of a SiGe film and the boron is used as a precursor. When the boron content is reduced in an oversaturated SiGe film, the Ge relative ratio to Si and the Ge-Ge bond amount increased in the film. Therefore, when Ammonium Peroxide Mixture (APM) + HF wet cleaning was performed to remove particles generated during the back-end-of-line (BEOL) process, the SiGe film was melted and the “mushroom-shaped” defect occurred. This occurred because the Ge-rich film reacted with H₂O₂ in the APM solution and HF, leading to oxidation and dissolution. To solve this problem, the Si content was increased because compared to Ge, Si underwent less oxidation and can act as a passivation layer in HF solution. This resulted in a decrease in grain size and an increase in wet resistance. Ultimately, this approach serves as a crucial clue for the continued scaling of DRAM devices.