Narendra Singh Mehta

Characterization of Low-Temperature Silicon Nitride LPCVD from Bis(tertiary-butylamino)silane and Ammonia

Low pressure chemical vapor deposition (LPCVD) of silicon nitride from bis(tertiary-butylamino)silane (BTBAS) and ammonia precursors has been demonstrated at 550-600°C in a 200 mm vertical batch furnace system. Deposition rates of 4-30 A/min are achieved with a film thickness variation below 2% 1-sigma. Silicon nitride depositions using BTBAS and NH 3 were found to retain a significant mass-transfer limiting component at temperatures <600°C. Substantial carbon and hydrogen incorporation are detected in low-temperature BTBAS silicon nitride, relative to dichlorosilane based silicon nitride deposited at higher temperature. These impurities result in the formation of a SiNCH solid solution with carbon substitution of nitrogen and disproportionate occupation of silicon and nitrogen sites by interstitial hydrogen. Optical and physical properties of silicon nitride are significantly altered by the addition of carbon and hydrogen impurities. Etch resistance of BTBAS-derived silicon nitride was found to diminish at elevated hydrogen levels. However, increasing etch resistance is observed in silicon nitride films with higher carbon levels. The data from this study indicate that carbon and hydrogen impurity concentrations may be tuned to produce silicon nitride with specific material properties.

Non-contact implant dose and energy metrology for advanced CMOS low-energy implants

Ultra Shallow Junctions are required to successfully improve device performance with scaling to have a better threshold voltage control, improve transistor performance, reduce CHC (Channel Hot Carrier) degradation and reduce parasitic capacitance. All these play an increasingly critical role as we move on to the 45 nm node and beyond to provide the required ac and dc device performance for CMOS devices. In the low energy implant regime, four point probe based sheet resistivity measurement becomes highly unreliable as does silicon damage based metrology systems used currently for advanced process control and monitoring. A non-contact metrology method is investigated based on leakage and tunneling currents in a non-conductive film that contains the implanted dose. These shallow implants damage the non-conductive film causing leakage paths to the silicon substrate. The implant damage is proportional to the dose and energy of the implanted species. Furthermore implanting the non-conductive film causes the top layers of the film to become conductive thus changing the electrical oxide thickness of this film. Excellent correlation was found among the implanted dose, energy to the equivalent oxide thickness. Results from controlled experiments indicate that this method has potential for use in low energy implanter qualification and ultra large scale integration process control and monitoring.