Abnormal redeposition of silicate from Si3N4 etching onto SiO2 surfaces in flash memory manufacturing

• Published in: Journal of materials science Vol. 55; no. 3; pp. 1126 - 1135
• Main Authors: Teng, Kai-Wen, Tu, Sheng-Hung, Hu, Ssu-Wei, Huang, You-Xin, Sheng, Yu-Jane, Tsao, Heng-Kwong
• Format: Journal Article
• Language: English
• Published: New York Springer US 2020; Springer Nature B.V
• Subjects: Agitation; Characterization and Evaluation of Materials; Chemical etching; Chemistry and Materials Science; Classical Mechanics; Confined spaces; Crystallography and Scattering Methods; Deposition; Electronic Materials; Etching; Flash memory (computers); Mass transfer; Materials Science; Moisture content; Organic chemistry; Phosphoric acid; Polymer Sciences; Silicon dioxide; Silicon nitride; Solid Mechanics
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-019-04119-x

The Si 3 N 4 layers in a 3D NAND flash patterned wafer are generally removed by hot phosphoric acid. However, the abnormal deposition of silicate which is the by-product from Si 3 N 4 etching onto the neighboring SiO 2 layers will cause a serious problem in the subsequent process. In this work, the abnormal deposition phenomenon was investigated by a simple system containing a narrow gap (~ 80 μm) between two blanket wafers. To understand the mechanism, the influences of various factors on the chemical etching dynamics were examined, including the water content and the extent of mechanical agitation. It is found that the growth rate of SiO 2 decreases as the water content or the extent of agitation is increased. Our experimental results reveal that the abnormal growth on SiO 2 layers is a consequence of the competition between chemical deposition and mass transfer in a confined space (reaction–diffusion system).