Method and apparatus for endpoint detection for chemical mechanical polishing

A chemical mechanical polishing system for polishing films on a semiconductor wafer surface, the system comprising:

• a light source configured to generate light of a bandwidth;
• a polishing pad having a through-hole;
• a pad backer configured to hold the polishing pad;
• a rotatable wafer chuck configured to hold the semiconductor wafer against the polishing pad during a polishing process;
• a fiber optic cable assembly having a first end and a second end, the first end of the fiber optic cable assembly being disposed partially into the through-hole, wherein the fiber optic cable assembly is configured to propagate light from the light source to illuminate at least a portion of the wafer surface;
• a light sensor coupled to the second end of the fiber optic cable assembly, wherein the light sensor is configured to receive light reflected from the wafer surface through the fiber optic cable assembly, the light sensor being further configured to generate data corresponding to a spectrum of the reflected light;
• and
• a computer coupled to the light sensor, wherein the computer is configured to generate an endpoint signal as a function of the data from the light sensor.

A method of detecting an endpoint during chemical mechanical polishing of a wafer surface, the method comprising:

• providing a relative rotation between the wafer surface and a pad, the pad contacting the surface during a polishing process of the wafer surface;
• illuminating at least a portion of the surface with light having a spectrum while the wafer surface is being polished;
• generating reflected spectrum data corresponding to a spectrum of light reflected from the region while the wafer surface is being polished;
• and
• determining a value as a function of amplitudes of at least two individual wavelength bands of the reflected spectrum data.

An apparatus for detecting an endpoint during polishing of a wafer surface, the apparatus comprising:

• means for providing a relative rotation between the wafer surface and a pad, the pad contacting the surface during a polishing process of the wafer surface;
• means for illuminating at least a portion of the surface with light having a spectrum while the wafer surface is being polished;
• means for generating reflected spectrum data corresponding to a spectrum of light reflected from the region while the wafer surface is being polished;
• and
• means for determining a value as a function of amplitudes of at least two individual wavelength bands of the reflected spectrum data.