Stoichiometric Dependence of Physical and Electrical Properties of Silicon Nitride

Student’s name: Daniel Teleshevsky Home Institution: Cornell University NNCI Site: CNF @ Cornell University REU Principal Investigator: Huili (Grace) Xing REU Mentor: Philip Infante Abstract: In recent years, nitride transistors have received much attention in the semiconductor device research community due to their wide bandgap, high thermal conductivity, and polarization properties. Two important performance metrics of these devices are the suppression of leakage current through the gate dielectric and its resilience under repeated use. Previous studies [1] have shown that these properties can be improved in SiNx (a common gate dielectric for nitride transistors) by changing the stoichiometry of the dielectric deposition. This investigation entails the physical and electrical characterization of silicon nitride (SiNx) thin films deposited on silicon substrates by low-pressure chemical vapor deposition (LPCVD). Films were deposited at temperatures of 775oC, 750oC, and 725oC, and dichlorosilene to ammonia gas flow ratios of 5:1, 5:2, and 1:4, yielding a total of nine samples. Physical characterization measurements, including stress and index of refraction, were conducted on each film. The films with the lowest Si content showed the most stress and lowest index of refraction. Aluminum contacts were deposited on the silicon nitride using CNF’s CVC SC4500 Thermal Evaporation System and patterned by contact lithography in a metal-first process to form MOS capacitors. Capacitance-voltage behavior of the fabricated capacitors was measured at a DC probe station to determine the dielectric properties of the SiNx . The leakage current through the capacitors under applied bias was also measured as a function of time to determine the time-dependent dielectric breakdown of each film.