Student project

Characterization and Optimization of Silicon Nitride Thin Films

Ten runs of silicon nitride LPCVD (Low Pressure Chemical Vapor Deposition) depositions were performed with a different recipe for each run. The goal of this work was to examine properties of silicon nitride and their variation with regards to the deposition parameters, which are : the ratio between dichlorosilane or DCS (SiH2CL2) and ammonia (NH3), the total gas flow, the pressure and the temperature. The ratio and the temperature are the two most considered parameters. The temperature was varied between 776 C, 800 C or 838 C, pressure is 135 or 200 mTorr, the ratio of DCS:NH3 is between 1:6 and 6:1 and total gas flow is 132 or 200 sccm (standard cubic centimeters per minute). The affected properties we look at are: the stoichiometry of the silicon nitride layer, the internal stress, the roughness, the uniformity in thickness, the refractive index and the deposition rate. By varying the four deposition parameters, we could obtain different set of properties. The obtained ranges are shortly exposed: Si/N ratio varied from 0.84 to 1.04, stress from 168 to 1127 MPa, roughness from 0.18 to 7.55 nm, refractive index from 1.99 to 2.14, uniformity in thickness varies from 0.39 to 1.81 % and deposition rate from 2.4 to 6.6 nm/min.

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