Abstract

With gate oxide thickness getting thinner and thinner, the possibility of pinholes, thickness variations, and surface irregularity is greatly increasing. Gate oxide integrity (GOI) tests are done to ensure product quality and uniformity of the gate oxide layer. Five percent (5%) Choline OH is normally used to remove bulk silicon in backside analysis, but oftentimes if gate oxide punch through is not the cause of the failure, further layer analysis of the sample is extremely difficult and sometimes impossible. When samples fail due to current leakage it most often means that a photoemission is given off and can be detected for defect localization. But not all devices that fail due to current leakage are caused by gate oxide punch through. Metal bridging or contact interface contaminates can often be the root cause of the failure. Sample de-layering is the only way to find such defects, so backside bulk silicon removal would not be appropriate. Many times when there is a problem with the gate oxide, punch through or pinhole, the size of the hole would be very useful information. Heated KOH is often used to remove poly silicon but it etches so rapidly that the silicon substrate is often over etched and the gate oxide is destroyed leaving a large square hole. Choline OH is a slow selective etch that can be controlled very easily and does not damage the oxide.

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