Method and apparatus for polishing control with signal peak analysis

An apparatus for control of a chemical mechanical polishing process with signal peak analysis comprising:

• a chemical mechanical polishing machine comprising a polishing pad, a polishing pad drive means for driving said polishing pad, a polishing head for holding an object to be treated, a polishing head drive means, loading means for creating contact pressure between said object and said polishing pad, and polishing slurry supply means;
• electroacoustic sensing means for sensing changes in said object, said electroacoustic sensing means having an output that generates operating data signals in response to said changes;
• a signal control and monitoring system for processing said operating data signals and for generating a control signal, comprising:
• a signal conditioning unit having an input connected to said output of said electroacoustic sensing means, said signal conditioning unit generating a conditioned signal;
• a signal analyzer connected to said signal conditioning unit;
• and a control unit having an input connected to said signal analyzer and an output connected to said chemical mechanical polishing machine;
• said signal analyzer comprises:
• an integrating unit for generating an average level of said conditioned signal, said integrating unit having an input and output, said input of said integrating unit being connected to said signal conditioning unit;
• a peak detector having an input and output, said input of said peak detector being connected to said signal conditioning unit;
• and a comparator having an output, a first input connected to said output of said integrating unit, and a second input connected to said output of said peak detector, said output of said comparator being connected to said control unit.

A method for polishing control with signal peak analysis comprising the steps of:

• providing a polishing machine for polishing an object, fixed in a polishing head, with the use of a polishing tool, said polishing machine having means for moving said polishing tool, means for moving said polishing head together with said object, loading means for creating contact pressure between said object and said polishing tool, and polishing slurry supply means, said polishing machine being equipped with sensing means and with a control and monitoring system connected to said polishing machine via a feedback line;
• initiating an operation of polishing said object with said polishing tool while maintaining said polishing head and said polishing tool in contact and moving at least one of said polishing head and said polishing tool for creating a relative motion;
• detecting by said sensing means acoustic waves generated in said contact between said object and said polishing tool and generating operating electroacoustic data signals by said sensing means in response to said acoustic waves, said operating electroacoustic data signals corresponding to intensity of said operation of polishing;
• processing said operating electroacoustic data signals in said control and monitoring system for obtaining conditioned signals;
• detecting and analyzing peaks of said operating electroacoustic data signals;
• determining a peak level and an average level of said operating electroacoustic data signals;
• determining a ratio of said peak level to said average level for generating a ratio signal;
• generating a control signal based on said ratio signal and said average level;
• and
• sending said control signal to said polishing machine via said feedback line for controlling said operation of polishing.