Method and configuration for conditioning a polishing pad surface
A method and a configuration for conditioning a polishing pad surface are described. The method includes measuring a rotation table current or voltage as an input for a motor driving the rotation of the polishing pad versus a rotating conditioning head. The electrical power input is used as a measure of an actual abrasion effective in regenerating the polishing pad. Since the polishing pad commonly deteriorates by repeated usage, i.e. debris settles down onto its surface, the abrasion efficiency decreases. The method issues a warning signal, in response to the electrical power input exceeding a limit, to take actions for maintaining the uniformity of the conditioning process. The polishing pad rotation can be accelerated or the conditioning head pressure force or rotation can be increased in response to the warning signal. Therefore, the polishing pad can be conditioned.
1. A method for conditioning a polishing pad surface of a polishing pad used for chemical mechanical polishing of semiconductor wafers, which comprises the steps of:
setting a limit to an electrical power input of a motor rotating a rotation table supporting the polishing pad;
applying a rotating conditioning head having a conditioning pad to the polishing pad surface with a pressure force, the rotating conditioning head oscillating in a cycle across the polishing pad surface from a center position of the polishing pad to an edge of the polishing pad and back to the center position;
rotating the rotation table with the polishing pad surface using the motor having the electrical power input for abrading the polishing pad against the conditioning pad;
measuring the electrical power input to the motor for each oscillation cycle resulting in a measured electrical power input;
comparing the measured electrical power input with the limit of the electrical power input; and
issuing a warning signal if, upon comparing a motor current to the limit, the measured electrical power input exceeds the limit.
2. The method according to claim 1 , which comprises adjusting the electric power input for setting a rotation table angular velocity to be within a tolerance range.
3. The method according to claim 1 , which comprises:
terminating the conditioning of the polishing pad; and
replacing one of the conditioning pad the polishing pad in response to the warning signal.
4. The method according to claim 2 , which comprises adjusting the tolerance range of the rotation table angular velocity in response to the warning signal, such that the electrical power input is adjusted and remains within the limit for providing a uniform abrasion rate.
5. The method according to claim 1 , which comprises adjusting the pressure force of the conditioning head in response to the warning signal, such that the electrical power input remains within the limit for providing a uniform abrasion rate.
6. The method according to claim 1 , which comprises adjusting a rotation rate of the conditioning head in response to the warning signal, such that the electrical power input remains within the limit for providing a uniform abrasion rate.
7. A configuration for chemical-mechanical polishing of wafers, comprising:
a rotation table;
a conditioning head having a conditioning pad disposed on one side of said rotation table, said conditioning head oscillating in a cycle across a surface of said rotation table from a center position to an edge of said rotation table and back to said center position;
a polishing pad having a surface and mounted on said rotation table;
a motor coupled to and rotating said rotation table, said motor receiving an electrical energy supply;
a current measurement device measuring the electrical energy supply received by said motor for each oscillation cycle of said conditioning head; and
a control unit connected to said current measurement device and to said motor.