Hafnium Missing Induced SRAM HTOL Fail in Scaled HKMG Technologies

Static Random Access Memory (SRAM) test chip HTOL (High Temperature Operating Life) test was frequently used for new platform product qualification and bit cell qualification. The Vmin shift outliers occurred during HTOL stress induced Vmin fail spec in deep sub-micron High-K metal gate (HKMG) technology. All fail bits showed small particles across deformed gate and hafnium missing. These particles were deduced to exist before gate oxide formation, and could be significantly reduced by replacing dual-gate etch batch clean with single wafer cleaning process. Small particles should be carefully controlled at the beginning of platform development, especially in advanced tech nodes with high density SRAM that vulnerable to defects.