Measuring apparatus

1. Apparatus for monitoring a fabrication process of a semiconductor wafer, the apparatus including:

a wafer support arranged to support the wafer;

a vibration exciting device arranged to vibrate the wafer; and

a measurement device which measures the wafer vibrations at one or more measurement positions and which compares frequencies of the wafer vibrations measured by the measurement device before and after the wafer is subjected to one or more treatment steps in the fabrication process to determine one or more properties of the wafer.

2. Apparatus according to claim 1 , wherein the wafer support and/or vibration exciting device includes a contact element for defining one or more boundary conditions on the wafer which constrain the modes of vibration.

3. Apparatus according to claim 2 , wherein the contact element is arranged on the wafer support to clamp the wafer around its periphery.

4. Apparatus according to claim 2 , wherein the contact element includes a guard ring arranged to contact the underside of the wafer to create independently vibratable localized sub-regions of wafer surface.

5. Apparatus according to claim 4 , wherein the guard ring comprises a vacuum clamp.

6. Apparatus according to claim 1 , wherein the vibration exciting device is arranged to excite vibrations at a plurality of localized measurement positions.

7. Apparatus according to claim 1 , wherein the vibration exciting means includes a pressure differential applicator arranged to create a pressure difference between opposite surfaces of the wafer.

8. Apparatus according to claim 1 , wherein the vibration exciting device includes a vibratable contact probe arranged to contact a point on the wafer in order to transmit vibrations into the wafer.

9. Apparatus according to claim 8 , wherein the vibration exciting device includes a movement mechanism for transferring the contact probe between each of the plurality of measurement positions.

10. Apparatus according to claim 9 , wherein the movement mechanism includes a tracking device arranged to determine the positional relationship between the wafer support and probe.

11. Apparatus according to claim 1 including a processor arranged to monitor the change in mass distribution of a semiconductor wafer caused by the one or more treatment steps in the fabrication process based on the measured wafer vibrations.

12. Apparatus according to claim 11 , wherein the processor is arranged to convert the measured vibrations into mass values.

13. Apparatus according to claim 12 , wherein the processor includes a non-uniformity profile generator arranged to calculate a non-uniformity profile for the wafer based on the determined change in mass distribution.

14. Apparatus according to claim 1 , wherein the wafer support comprises a housing having a ledge for the outer edge of the wafer to rest thereon in a substantially horizontal orientation.

15. Apparatus according to claim 14 , wherein the ledge defines an aperture through which the vibration exciting device is operable.

16. Apparatus according to claim 1 , wherein the wafer support is adapted to receive the wafer in a predetermined orientation.

17. Apparatus according to claim 1 , wherein the measurement device is arranged to detect a time-varying parameter of the vibrations at each measurement position.

18. Apparatus according to claim 17 , wherein the measurement device includes a non-contact sensor.

19. A method of monitoring a mass distribution of a semiconductor wafer during a fabrication process where the wafer is subjected to one or more treatment steps, the method including the steps of:

supporting the wafer on a wafer support;

vibrating the wafer;

measuring the frequency of vibrations at one or more measurement positions on the wafer; and

comparing the frequencies of the wafer vibrations measured before and after the wafer is subjected to the one or more treatment steps in the fabrication process to obtain a difference in mass distribution caused by the one or more treatment steps in the fabrication process.

20. A method according to claim 19 including applying boundary conditions to areas of the wafer before vibrating the wafer.

21. A method of monitoring a mass distribution of a semiconductor wafer during a fabrication process, the method comprising:

exciting and measuring a frequency of localized vibrations at a plurality of measurement positions on a wafer substrate before wafer treatment;

treating the wafer;

exciting and measuring a frequency of localized vibrations at a plurality of measurement positions on the substrate after wafer treatment; and

comparing the before wafer treatment measurement results with the after wafer treatment measurement results.