System and method for end-point detection in a multi-head CMP tool using real-time monitoring of motor current

A substrate planarization process endpoint detection system comprising:

• a motor current monitoring circuit adapted to receive an input signal indicative of a motor current signal for at least one motor responsible for a component of relative movement between said semiconductor wafer and a polishing pad;
• a processor receiving said input signal and generating a fourier transform of said input signal;
• identification logic identifying at least one frequency component of said input signal identifying a periodic mechanical oscillation arising from operational effects independent from planarization process step completion indicators;
• a filter for filtering said at least one identified frequency component to suppress said periodic oscillations from said input signal and generating a filtered signal in which motor current variations indicative of said planarization process step completion are preserved and more readily detectable relative to motor current at times other than said planarization process step endpoint;
• and
• a detection circuit for detecting said planarization process step completion as a change in the filtered motor current signal;
• said fourier transform and filtering at said identified frequency component ensuring that an undesirable oscillation in the monitored motor current are minimized to thereby provide better reliability and higher precision of said planarization process step completion detection.

A method for detecting a planarization process step endpoint of a semiconductor wafer planarization operation in a CMP planarization process, said method comprising:

• monitoring a plurality of motor current signals for at least one platen motor and one head motor responsible for a component of relative movement between said semiconductor wafer and a polishing pad;
• performing a fourier transform analysis of the monitored motor current signals to identify at least one motor current signal frequency component and harmonics thereof of said signal identifying periodic mechanical oscillation arising from platen and head rotation offsets independent from planarization process step completion indicators;
• filtering said identified frequency components to suppress said periodic oscillations from said motor current signals and generating filtered motor current signals in which motor current signal variations indicative of said planarization process step completion are preserved and more readily detectable relative to motor current at times other than said planarization process step endpoint;
• and
• detecting said planarization process step completion as a change in one or more of the filtered motor current signals;
• said fourier transform analysis and filtering at said identified frequency component ensuring that an undesirable oscillation in the monitored motor currents are minimized to thereby provide better reliability and higher precision of said planarization process step completion detection;
• at least one of said plurality of frequency components comprises a frequency corresponding to the rotational velocity of a polishing pad platen, and at least one of said plurality of frequency components comprises a frequency corresponding to the rotational velocity of a single polishing head.