Deposition mechanism of trace metals on silicon wafer surfaces in ultra pure water

Spontaneous deposition of trace metal contaminants such as Cu onto silicon wafer surfaces in ultra pure water (UPW) was investigated, focusing upon the reaction pathways of their deposition processes. Scanning probe microscopy analysis revealed that 10-20 nm diameter Cu particles were formed by reductive deposition of ionic species to the metals, which was enhanced under deoxygenated condition. On the other hand, dissolved oxygen enhanced the formation of oxide layer at silicon surface as well as inclusion of the metal species into the layer to develop rougher surface. These variation in the characteristics of metal contaminants such as chemical state and dispersion condition in microscopic scale, caused by the difference in dissolved oxygen concentration, should be one of the significant issues to optimize precision device processes.