Characterization and Understanding of High Valued Polysilicon Resistor Resistance Variation Across a Resistor Bank With Parallel Resistor Fingers

High value poly resistor bank with multiple poly fingers causing a voltage divider circuitry to fail was investigated using atomic force nano-probing technique, process split matrix analysis, physical analysis, and CAD layout design analysis. The poly fingers exhibited a convex shape in resistance distribution across the resistor bank. The reduced resistance can be explained using the hydrogen diffusion model through the barrier nitride layer that capped the poly lines. The eroded LPCVD nitride corners at the top allowed hydrogen to diffuse through and passivated the traps in the poly grain boundary, resulting in significant resistance reduction. The hydrogen at metal-oxide interface at the bank edge correlated to the convex shape. Using the bank resistance distribution shape, a lateral hydrogen diffusion length in PECVD oxide film above poly was estimated to be about 30 μm . The resistivity of poly resistor was poly size dependent as a result of hydrogen diffusion through the nitride corners affecting design manual values.