Mechanical and chemical-mechanical planarizing processes (collectively "CMP") are used in the manufacturing process of microelectronic devices to form a flat surface on semiconductor wafers, field emission displays, and many other microelectronic-device substrates and substrate assemblies. FIG. 1 is a partially schematic, isometric view of a conventional web-format planarizing machine 10 that has a platen 20. A sub-pad 11 is attached to the platen 20 to provide a flat, solid workstation for supporting a portion of a web-format polishing pad 16 in a planarizing zone "A" during planarization. The polishing pad 16 has a rear surface 19 that engages the sub-pad 11 and a planarizing surface 18 facing opposite the rear surface 19 to planarize a substrate 12.
The planarizing machine 10 also has a pad-advancing mechanism, including a plurality of rollers, to guide, position and hold the polishing pad 16 over the sub-pad 11. The pad-advancing mechanism generally includes a supply roller 24, first and second idler rollers 21a and 21b, first and second guide rollers 22a and 22b, and a take-up roller 23. As explained below, a motor (not shown) drives the take-up roller 23 and the supply roller 24 to advance and retract the polishing pad 16 over the sub-pad 11 along a travel path T--T. The first idler roller 21a and the first guide roller 22a press an operative portion of the polishing pad 16 against the sub-pad 11 to hold the polishing pad 16 stationary during operation.
The planarizing machine 10 further includes a carrier assembly 30 to translate the substrate 12 over the polishing pad 16. In one embodiment, the carrier assembly 30 has a head 31 to pick up, hold and release the substrate 12 at appropriate stages of the planarizing process. The carrier assembly 30 also has a support gantry 32 and a drive assembly 33 that can move along the gantry 32. The drive assembly 33 has an actuator 34, a drive shaft 35 coupled to the actuator 34, and an arm 36 projecting from the drive shaft 35. The arm 36 carries the head 31 via a terminal shaft 37. The actuator 34 orbits the head 31 about an axis B--B (as indicated by arrow R.sub.1) and can rotate the head 31 about an axis C--C (as indicated by arrow R.sub.2) to move the substrate 12 over the polishing pad 16 while a planarizing fluid 17 flows from a plurality of nozzles 38 in the head 31. The planarizing fluid 17 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the substrate 12, or the planarizing fluid 17 may be a non-abrasive planarizing solution without abrasive particles. In most CMP applications, conventional CMP slurries are used on conventional polishing pads, and planarizing solutions without abrasive particles are used on fixed-abrasive polishing pads.
In the operation of the planarizing machine 10, the carrier assembly 30 presses the substrate 12 against the planarizing surface 18 of the polishing pad 16 as the carrier head 31 moves the substrate 12 over the planarizing surface 18. The polishing pad 16 moves across the sub-pad 11 along the pad travel path T--T either during or between planarizing cycles to change the particular portion of the polishing pad 16 in the planarizing zone A. For example, the supply and take-up rollers 24, 23 can drive the polishing pad 16 between planarizing cycles such that a point P moves incrementally across the sub-pad 11 to a number of intermediate locations I.sub.1, I.sub.2, etc. Alternatively, the rollers 24, 23 may drive the polishing pad 16 between planarizing cycles such that the point P moves all the way across the sub-pad 11 toward the take-up roller 23 to completely remove a used or post-operative portion of the polishing pad 16 from the planarizing zone A. The rollers 24, 23 may also continuously drive the polishing pad 16 at a slow rate during a planarizing cycle such that the point P moves continuously across the sub-pad 11 during planarization.
The planarizing machine 10 can also include a planarizing surface cleaner 40 (shown schematically in FIG. 1) positioned between the platen 20 and the take-up roller 23 to clean the post-operative portion of the polishing pad 16. The planarizing surface cleaner 40 can include a brush 41 having bristles that contact the planarizing surface 18 of the polishing pad 16 and a liquid dispenser 42 positioned proximate to the brush 41 to dispense a cleaning liquid on the planarizing surface 18. Accordingly, the planarizing surface cleaner 40 can clean the post-operative portion of the polishing pad 16 as it moves off the platen 20 along the travel path T--T. Once the post-operative portion of the polishing pad 16 has been cleaned, it can be translated back onto the platen 20 along the travel path T--T and into the planarizing zone A for another planarizing cycle.
One drawback with the apparatus 10 shown in FIG. 1 is that the rear surface 19 of the polishing pad 16 can become contaminated with debris (such as liquid and/or particulate matter) during the planarizing process and/or the cleaning process. The debris can become trapped between the polishing pad 16 and the sub-pad 11, causing a local bump or other non-uniformity to form in the planarizing surface 18. The non-uniformity in the planarizing surface 18 can create a non-uniformity in the substrate 12 and/or can cause the polishing pad 16 to wear in a non-uniform manner.
A further drawback is that liquid on the rear surface 19 of the polishing pad 16 can form an adhesive bond between the polishing pad 16 and the sub-pad 11. The adhesive bond can inhibit relative movement between the polishing pad 16 and the sub-pad 11 when the polishing pad 16 moves along the travel path T--T. In one conventional method, the idler rollers 21a, 21b and/or the guide roller 22a move the polishing pad 16 normal to the upper surface of the sub-pad 11 to break the adhesive bond. However, the action of the rollers against the polishing pad 16 may not be effective to separate the polishing pad 16 from the sub-pad 11. Furthermore, if the polishing pad 16 is dragged over the sub-pad 11, the frictional contact between the two can abrade particulate matter from the polishing pad 16 and/or the sub-pad 11, which can cause a bump or other non-uniformity to form in the planarizing surface 18, as discussed above.