POLISHING APPARATUS
A polishing apparatus has a polishing pad, a top ring for holding a semiconductor wafer, and a vertical movement mechanism operable to move the top ring in a vertical direction. The polishing apparatus also has a distance measuring sensor operable to detect a position of the top ring when a lower surface of the top ring is brought into contact with the polishing pad, and a controller operable to calculate an optimal position of the top ring to polish the semiconductor wafer based on the position detected by the distance measuring sensor. The vertical movement mechanism includes a ball screw mechanism operable to move the top ring to the optimal position.
1 . A polishing apparatus comprising:
a polishing table for hold a polishing pad on its surface, the polishing table being rotatable about a shaft, the shaft being vertical to an upper surface of the polishing table; and
a top ring having an elastic membrane provided to a holding surface of the top ring so as to form chambers and to press a substrate against a polishing pad held on the upper surface of the polishing table by pressured fluids in the chambers,
wherein a distance between the holding surface of when the top ring is in a polishing position and a surface of the polishing pad held on the upper surface of the polishing table is kept constant.
2 . The polishing apparatus according to claim 1 , wherein the distance between the holding surface of the top ring and the polishing pad is determined based on a height of the top ring being in contact with the polishing pad at a portion outside of the elastic membrane.
3 . The polishing apparatus according to claim 1 , further comprising a movement mechanism configured to move the top ring toward the polishing pad,
wherein the movement mechanism moves the top ring to the polishing position according to the distance between the holding surface of the top ring and the polishing pad.
4 . The polishing apparatus according to claim 3 , wherein when the top ring is in contact with the polishing pad for determining the distance, the elastic membrane is prevented from contact with the polishing pad.
5 . The polishing apparatus according to claim 1 , wherein the distance is determined when the top ring holds a substrate.
6 . The polishing apparatus according to claim 1 , wherein the distance is determined when the top ring does not hold a substrate.
7 . The polishing apparatus according to claim 1 , wherein the distance is determined when the top ring presses against the polishing pad by gravity acting on the top ring.
8 . The polishing apparatus according to claim 1 , wherein a height of the top ring in the polishing position follows an amount of wear of the polishing pad.
9 . The polishing apparatus according to claim 1 , wherein an edge of the plastic membrane has a shape curved upward and inward.
10 . The polishing apparatus according to claim 1 , wherein an inner surface of the elastic membrane has a ripple portion leading obliquely upward.