Curved grooving of polishing pads
View Patent ↗A method is provided for forming grooves in a polishing pad useful for planarizing a substrate in a chemical mechanical planarization process. The method maintains average velocity as a function of bit diameter to enable groove formation using a rotating bit, whereby grooves can be formed at a higher rate while maintaining high groove quality and low defectivity.
1. A method for forming grooves in a polymeric polishing pad useful for the chemical mechanical planarization of a substrate, the substrate being at least one of magnetic, optical and semiconductor substrates comprising:
rotating a cutting bit about an axis in a z-direction, the cutting bit rotating at a rate of at least 60,000 revolutions per minute, the rate being sufficient to melt the polymeric polishing pad upon low velocity contact with the polishing pad without cooling and having at least one cutting edge for cutting groove depth in the z-direction into the polymeric polishing pad;
cutting the polishing pad in an x-direction and a y-direction to form at least one curved groove in the polymeric polishing pad, the x-direction and y-direction being perpendicular in a single plane and orthogonal to the z-direction, said cutting occurring by contacting the rotating cutting bit with a portion of the polymeric polishing pad, the at least one curved groove having polymeric sidewalls;
ejecting cut debris from the polishing pad within the at least one groove with at least one flute in the rotating cutting bit; and
varying velocity of the cutting in at least one of the x-direction or y-direction with a program-generated signal to guide the cutting through a curved path and to provide the at least one groove with a curved configuration in the polymeric polishing pad, the program-generated signal sending the cutting on a curved path while maintaining the velocity of the rotating bit to maintain a calculated chip thickness at a factor of 0.02 to 0.6 of a diameter of the rotating cutting bit and to reduce melting of the polymeric sidewalls of the polymeric polishing pad.
2. The method of claim 1 wherein the ejecting includes the at least one flute being a single flute and the single flute has a volume greater than forty percent of volume formed by rotating a cutting end of the rotating cutting bit about its axis.
3. The method of claim 1 comprising the additional step of cooling at least one of the rotating cutting bit and a region of the polishing pad proximate the cutting bit.
4. The method of claim 3 wherein the step of cooling comprises providing compressed gas, flowing the compressed gas through at least one small aperture nozzle and allowing the gas to expand.
5. The method of claim 1 wherein the rotating cutting bit rate maintains the calculated chip thickness at a factor of 0.04 to 0.4 of the diameter of the rotating cutting bit.
6. The method of claim 1 wherein the cutting forms a groove having a depth of at least twice a diameter of the rotating cutting bit.
7. The method of claim 1 wherein the rotating cutting bit has a corkscrew shape with less than two complete turns in its cutting end.
8. The method of claim 1 wherein the rotating is performed by a rotating spindle attached to the rotating cutting bit supported with an air bearing.
9. The method of claim 1 wherein the polymeric polishing pad is a non-porous polyurethane polishing pad.
10. The method of claim 1 wherein the polymeric polishing pad is a porous polyurethane polishing pad.