Dual Gate oxide reliability improved by Spacer and Salicide process optimisation

During the qualification phase of a 0.25 mum technology node for power and RF applications, the reliability test was degraded on the voltage breakdown (Vbd) of the gate oxide, with a potential root cause due to oxide itself. A partitioning has been done on common root causes without any result: gate oxide thinning on shallow trench isolation (STI) corner, charging during a process operation, poly-silicon deposition, gate oxide pre-clean. Failure analysis on the bad parts was not successful to solve the problem. Therefore a specific test method has been developed in order to identify the leaky parts without destroying them whereas the reliability test does. Failure analysis has confirmed that the breakdown was coming at the edge of the poly-silicon gate, and that the gate oxide has a good integrity. Data analysis with the implementation of the new test has pointed out the silicide module. Then salicide and spacer module experiments have been done and the fixes were spacer oxide deposition pressure and bridging removal.