Wafer shape and flatness measurement apparatus and method
A semiconductor equipment architecture WGT for wafer shape and flatness measurement is disclosed. The semiconductor equipment architecture WGT includes a reflective air-bearing chuck and a hybrid wafer thickness gauge. Also disclosed are the corresponding methods of measuring wafer shape and flatness using the architecture, the air-bearing chuck and the hybrid wafer thickness gauge.
1. A wafer shape and flatness measurement apparatus comprising:
a large aperture interferometer, and
a reflective air bearing chuck comprising alternating vacuum nozzles and pressure nozzles arranged in a plurality of concentric rings and a distance between adjacent vacuum nozzle and pressure nozzle is substantially uniform for the vacuum nozzles and pressure nozzles on each concentric nozzle ring.
2. The wafer shape and flatness measurement apparatus of claim 1 , wherein the large aperture interferometer is one of a single Fizeau interferometer, a grating-based shearing interferometer, and a Michelson interferometer.
3. The wafer shape and flatness measurement apparatus of claim 1 , wherein the reflective air bearing chuck comprises a vacuum manifold layer, a pressure manifold layer, and a top chuck layer on top of both the vacuum manifold layer and the pressure manifold layer, the top chuck layer comprises the vacuum nozzles and the pressure nozzles.
4. The wafer shape and flatness measurement apparatus of claim 1 , wherein the pressure nozzles are configured to support the wafer to about 2-5 mm near an edge of the wafer.
5. The wafer shape and flatness measurement apparatus of claim 1 , wherein the reflective air-bearing chuck has a 5-30 um flying height to support a wafer and flatten a backside of the wafer for wafer flatness measurement by using the single Fizeau interferometer.
6. The wafer shape and flatness measurement apparatus of claim 5 , wherein the reflective air bearing chuck has a 60-350 um flying height to support the wafer while maintaining the original shape of the wafer for wafer shape measurement by using the single Fizeau interferometer.
7. The wafer shape and flatness measurement apparatus of claim 1 ,
wherein the reflective air bearing chuck is made of aluminum or ceramic; and
wherein the reflective air bearing chuck comprises a polished surface that is sufficiently flat to show interference fringes.
8. The wafer shape and flatness measurement apparatus of claim 1 ,
wherein large aperture interferometer comprises a transmission flat; and
wherein the reflective air bearing chuck and the transmission flat form an optical cavity that allows calibration to be perform.
9. The wafer shape and flatness measurement apparatus of claim 8 , wherein the calibration comprises removing any flatness imperfection of the transmission flat and the air bearing chuck.
10. The wafer shape and flatness measurement apparatus of claim 1 , wherein a diameter of the air bearing chuck is slightly larger than a diameter of a wafer supported by the air-bearing chuck.
11. The wafer shape and flatness measurement apparatus of claim 1 , wherein the reflective air bearing chuck is calibrated by using cavity data on one or more chuck surfaces.
12. The wafer shape and flatness measurement apparatus of claim 1 , wherein the reflective air bearing chuck is configured to provide high air flow to achieve high stiffness of air-bearing.
13. The wafer shape and flatness measurement apparatus of claim 1 , wherein alternating vacuum nozzles and pressure nozzles are spaced equally across the whole reflective air bearing chuck.
14. The wafer shape and flatness measurement apparatus of claim 1 , further comprising a capacitive sensor at a middle of the reflective air bearing chuck, the capacitive sensor configured to monitor air gap.
15. The wafer shape and flatness measurement apparatus of claim 14 , wherein the capacitive sensor is further configured for wafer recovery.
16. The wafer shape and flatness measurement apparatus of claim 1 , further comprising a position sensor and a capacitive sensor configured to measure a thickness of a wafer positioned between the position sensor and the capacitive sensor.
17. The wafer shape and flatness measurement apparatus of claim 1 , further comprising a Z-tip-and-tilt stage configured for chuck alignment and mechanical phase shifting.
18. The wafer shape and flatness measurement apparatus of claim 17 , wherein the Z-tip-and-tilt stage is further configured to measure highly warped wafers.
19. The wafer shape and flatness measurement apparatus of claim 18 , wherein the Z-tip-and-tilt stage is further configured to measure highly warped wafers with a thickness of 300 um.
20. The wafer shape and flatness measurement apparatus of claim 1 , wherein the reflective air bearing chuck comprises a mirror-finished surface >=N4 of ISO standards.