Experimental Analysis in Lithium Niobate CMP for Room Temperature Bonding

Lithium niobate (LN, LiNbO3) is a kind of artificial crystal with piezoelectricity, pyroelectricity and ferroelectricity, which has been widely used in electron components. The large difference in thermal expansion coefficients between Si and LN causes a serious thermal stress during the thermal-pressure bonding process. Therefore room temperature bonding would be the best candidate to make strong and stress-free interface between Si and LN. However, room temperature bonding requires lower surface roughness (Ra<2nm) and lower defects on the LN wafer surface than those of thermal bonding. Chemical mechanical polishing (CMP) process helps LN to obtain the high quality surface and thin wafer suited in room temperature bonding. The LN wafer was polished using colloidal silica slurry, resulting in high material removal rate (MRR) and fine surface quality under the condition of low pH, high abrasive concentration and low flow rate. The polishing mechanism of LN was discussed by mechanical, chemical and thermal analysis.