System for in-situ monitoring of removal rate/thickness of top layer during planarization

A system for removing a top wafer layer during a chemical mechanical polishing (CMP) process, comprising:

• a light source for illuminating a top layer of a wafer;
• an optical detector for collecting time series data based on a reflected wavelength from the top layer;
• computer program instructions that determines a removal rate of the top layer based on a frequency of peak intensities in the time series data;
• computer program instructions that calculates a current thickness of top layer based on the removal rate;
• a process controller that discontinues the CMP process when the current thickness of the top layer is equal to or less than a target thickness;
• and
• an endpoint detection subsystem that performs a separate polishing process to remove an additional portion of the top layer.

A method for removing a top wafer layer during a chemical mechanical polishing (CMP) process, comprising the operations of:

• collecting time series data based on a reflected wavelength from a top layer of a wafer;
• applying a Fourier Transform to the time series data;
• analyzing a frequency of peak intensities in the Fourier Transform of the time series data to determine a peak magnitude in the frequency;
• determining a first removal rate o f the top layer based on the peak magnitude in the frequency;
• calculating a current thickness of top layer based on the first removal rate;
• discontinuing the CMP process when the current thickness of the top layer is equal to or less than a target thickness;
• and
• performing a separate polishing process to remove an additional portion of the top layer.