Chemical/mechanical polishing endpoint detection device and method
AssigneeMomentum Technical Consulting, Inc.
InventorFu Zhang
Life of this patent
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Abstract
A device (28) and method for detecting endpoints (Ep1, Ep2) of a chemical-mechanical polishing (CMP) process for semiconductor wafers (14). A carrier current signal driving a polishing carrier motor is received and detected, the carrier current signal is modified, and the modified carrier current is analyzed to detect at least one endpoint of the polishing process. The device (28) includes a detector (40), a logic circuit (42) and storage (44).
Claims15
An endpoint detector for use in a polishing apparatus of the type having an electric motor that rotates a polishing carrier relative to an item to be polished, the detection device comprising;
- a detector for receiving and detecting the motor current signal;
- and
- a logic circuit for
- (a) establishing a baseline current signal threshold,
- (b) defining a time window of the current signal,
- (c) calculating the standard deviation of the current signal within said window, calculating the mean of the current signal within said window, and calculating the ratio of said standard deviation to said mean;
- and
- (d) analyzing the ratio to detect at least one endpoint, Ep1 or Ep2, of the polishing.
A method of detecting an endpoint of a polishing process which is effected by an electric motor rotating a polishing carrier relative to an item to be polished, which method comprises:
- (a) receiving and detecting the motor current signal;
- (b) establishing a baseline current signal threshold;
- (c) calculating the standard deviation of the current signal within a time window;
- (d) calculating the mean of the current signal within said window;
- (e) determining the ratio of said standard deviation to said mean;
- and
- (f) analyzing the ratio to detect an endpoint of the polishing.
An algorithm for detecting endpoints of a semiconductor wafer chemical-mechanical polishing (CMP) process, comprising:
- receiving and detecting a current signal driving a polishing carrier motor;
- establishing an endpoint baseline threshold level;
- calculating the standard deviation of the current signal within a time window;
- calculating the mean of the current signal within said window;
- determining a modified current signal by calculating the ratio of said standard deviation to said mean;
- and
- analyzing the ratio to detect at least one endpoint of the polishing process.
In a polishing process which is effected by an electric motor rotating a polishing carrier relative to a first layer residing on top of a layer, the layers defining an irregular interface therebetween, the polishing initially removing the first layer and then reaching the interface to remove increasingly larger portions of the second layer as it is exposed at the interface, a method of determining when polishing of the interface begins, which method comprises:
- (a) determining a threshold baseline value Y by calculating for a selected time during polishing of the first layer before the interface is reached the ratio of (1) the standard deviation of the motor current (2) the mean value of the motor current;
- (b) following determination of the value of Y, determining successive values of X, by calculating during successive time intervals of the same selected duration the ratio of (1) the standard deviation of the motor current to (2) the mean value of the motor current
- for each value of X determine if
- [(X−Y)/Y]>K,
- where K is a selected quantity, a negative determination indicating that polishing of the interface has not begun and a positive determination indicating that polishing of the interface has begun.
Dependencies are inferred from the claim text.