Polishing system including a hydrostatic fluid bearing support
View Patent ↗A polishing system such as a chemical mechanical belt polisher includes a hydrostatic fluid bearing that supports polishing pads and incorporates one or more of the following novel aspects. One aspect uses compliant surfaces surrounding fluid inlets in an array of inlets to extend areas of elevated support pressure around the inlets. Another aspect modulates or reverses fluid flow in the bearing to reduce deviations in the time averaged support pressure and to induce vibrations in the polishing pads to improve polishing performance. Another aspect provides a hydrostatic bearing with a cavity having a lateral extent greater than that of an object being polished. The depth and bottom contour of cavity can be adjusted to provide nearly uniform support pressure across an area that is surrounded by a retaining ring support. Changing fluid pressure to the retaining ring support adjusts the fluid film thickness of the bearing. Yet another aspect of the invention provides a hydrostatic bearing with spiral or partial cardiod drain grooves. This bearing has a non-uniform support pressure profile but provides a uniform average pressure to a wafer that is rotated relative to the center of the bearing. Another aspect of the invention provides a hydrostatic bearing with constant fluid pressure at inlets but a support pressure profile that is adjustable by changing the relative heights of fluid inlets to alter local fluid film thicknesses in the hydrostatic bearing.
1. A method for polishing a wafer, comprising:
supporting a polishing pad with a fluid bearing that includes inlets and outlets, wherein the inlets conduct into the fluid bearing a fluid flow that supports the polishing pad and the outlets sink the fluid flow;
placing the wafer in contact with the polishing pad; and
altering the flow of fluid to change support pressures from the fluid flow on the polishing pad while the wafer is in contact with the polishing pad.
2. The method of claim 1 , wherein the polishing pad is attached to a belt and the method further comprises rotating the belt so that the belt slides between the fluid bearing and the wafer and the polishing pads polishes the surface of the wafer.
3. The method of claim 1 , wherein altering the flow comprises switching fluid flow direction in the bearing so that, during polishing, the outlets conduct into the fluid bearing the fluid flow that supports the polishing pad and the inlets sink the fluid flow.
4. The method of claim 1 , wherein altering the flow comprises modulating pressure in the fluid flow to cause vibrations of the polishing pad.
5. The method of claim 4 , wherein modulating the pressure in the fluid flow comprises vibrating an agitator in the fluid to induce transmission of vibratory energy through the fluid.
6. The method of claim 1 , wherein altering the flow comprises inducing acoustical pressure variations in the fluid flow which cause vibrations of the polishing pad.
7. The method of claim 1 , wherein altering the flow comprises altering a pressure from a source of the fluid flow.
8. The method of claim 1 , wherein altering the flow comprises repeatedly alternating between a first state where the inlets conduct the fluid into the fluid bearing and a second state where the outlets conduct the fluid into the fluid bearing.
9. The method of claim 1 , further comprising moving the wafer relative to the fluid bearing and over an area of the belt supported by the fluid bearing.
10. The method of claim 9 , wherein moving the wafer comprises rotating the wafer about an axis perpendicular to the area supported by the fluid bearing.