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Investigation on sidewall polymer contamination during metal etching in wafer fabrication

Metal 1 sidewall polymer contamination was investigated in wafer fabrication. SEM and EDX techniques were used to identify the root cause. After metal 1 etching, particle contamination was found on metal 1 lines. Cross sectional SEM results showed the contamination was at the side of the metal lines. EDX results showed that C and Cl elements were detected. Failure analysis results indicated that the contamination was most likely sidewall polymer introduced during metal etching. Further fab investigation found that the sidewall polymer contamination was due to gas flow drifting from set point during metal etches. The solution is that the mass flow control is calibrated using two set points (at 30 and 60 sccm). This new calibration procedure was able to detect the MFC linearity problem. After implementing the two point calibration method, the sidewall polymer contamination was eliminated.