Reliability testing is commonly used to verify the wafer manufacturing process. Among others, High Temperature Operating Life (HTOL) testing is one of the techniques used to simulate a device's operating condition in an accelerated manner by subjecting the device to specified conditions of bias and temperature over an extended time period such that the quality and reliability of the device can be demonstrated. This work aims at eliminating HTOL reliability fallouts through the eradication of the W oxidation problem arising from wafer transportation time between platens in the Tungsten CMP (WCMP) production process on the Applied Materials Mirra Polisher. These rejects were observed after HTOL 48hrs reliability testing and Failure Analysis into typical rejects showed oxide residual on the top of the via. This phenomenon was seen at random via-layers. Oxide at the Plug/Metal interface acts as an unwanted insulator, resulting in reliability failures. An investigation was launched to ascertain the root cause of the oxide formation and it was discovered that delay in transportation time between the final W polishing and oxide touch-up steps allowed W oxide to form on via top. The subsequent oxide touchup step was not be able to completely remove all the oxidation due to variations in its Removal Rate (RR), wafer profile/density and also the variation in speed of the Tungsten oxide formation. Solution to the reliability failure comes in the form of wafer cleaning after W removal and the reduction in transportation time prior to the next polishing step, thus preventing W oxide formation at the Via top caused by the oxidizing agent Hydrogen Peroxide (H{sub}2O{sub}2), commonly found in W slurry. Verification experiments and Reliability testing done without the aforementioned delay time showed that the unwanted formation of oxide film at via top is eliminated, improving reliability performance.
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