Polysilicon, silicon oxide and silicon nitride CMP processes

During the fabrication of Micro-Electro-Mechanical Systems (MEMS), chemical mechanical planarization (CMP) is used to achieve planarity at each level of the multilevel structure. However, the large step heights of up to 5 mu in MEMS structures presents several challenges during CMP. One such challenge is to achieve a high polish rate of ∼0.5 mu/min of the top layer (typically polysilicon) to reduce the polish time, while simultaneously maintaining a high polish rate selectivity of > 50 over the underlying silicon dioxide (SiO 2) and silicon nitride (Si3N4) layers to prevent erosion of the underlying layers. In this work, robust polysilicon CMP processes have been designed using both colloidal silica and calcined ceria-based slurries with the amino acid additives, arginine and lysine mono hydrochloride. The role of these additives in the slurry towards achieving the desired removal rate selectivities of polysilicon over that of SiO2 and Si 3N4 is explained using zeta potential, Fourier Transform Infrared (FTIR) spectroscopy and contact angle data.; In the second part of this work, achieving a low SiO2 removal rate and a relatively high Si3N4 removal rate, which is both challenging and promising for emerging applications in integrated circuit chip fabrication, is investigated. Si3N4 has been widely used as an etch stop layer in shallow trench isolation (STI) CMP and the goal in this case has been to achieve a very low Si3N 4 removal rate and a high polish rate of SiO2. However, the reverse process of achieving a removal rate selectivity of SiO2 over Si3N4 to be lower than about one is now aimed at. This was thought to be impossible as the removal of Si3N4 follows a two-step mechanism of first being hydrolyzed to the SiO 2, and then removed during CMP and therefore additives normally used to suppress the SiO2 removal rate would tend to suppress the Si 3N4 removal rate as well.; In this work, we show that by using several different amino acid additives (arginine, lysine mono hydrochloride and picolinic acid) in colloidal silica slurries, a low SiO2 and relatively high Si3N4 removal can be achieved. The removal rates of both SiO2 and Si3N4 were highly tunable from ∼5 nm/min to ∼60 nm/min yielding selectivities of SiO2:Si3N4 that range from 1:1 to 1:8. This has been possible by identifying additives that significantly enhance SiO2 and Si3N4 removal rates and using them in combination with small amounts of other additives that suppress removal rates. Finally, selectivities as high as 1:20 and 1:78 have also been achieved using a zirconia slurry. Several factors which enable the high removal rate selectivities of Si3N4 over SiO 2 have been discussed in detail.; Finally, a fundamental investigation of the interaction of arginine and lysine mono hydrochloride additives with ceria and silica abrasives, SiO 2 and Si3N4 polishing films has been carried out to understand better the CMP of SiO2 and Si3N4 in the presence of these additives. FTIR and Thermo Gravimetric Analysis (TGA) have been performed to understand the adsorption behavior of these amino acids on abrasives and polishing films as a function of pH. The results show that only a small amount of these amino acids adsorbed on ceria abrasive and SiO2/Si3N4 polishing films is sufficient to effectively suppress the SiO2 and Si3N4 removal rates in the pH range of 2 to 10. It was also observed that despite strong electrostatic repulsive forces between arginine/lysine mono hydrochloride and ceria/Si3N4 at some pH, the additives were adsorbed on ceria and Si3N4. Based on these results, three patent applications have been filed and licensed to Ferro Corp. in 2006.