Methods and systems for interferometric analysis of surfaces and related applications
A method for determining a spatial property of an object includes obtaining a scanning low coherence interference signal from a measurement object that includes two or more interfaces. The scanning low coherence interference signal includes two or more overlapping low coherence interference signals, each of which results from a respective interface. Based on the low coherence interference signal, a spatial property of at least one of the interfaces is determined. In some cases, the determination is based on a subset of the low coherence interference signal rather than on the entirety of the signal. Alternatively, or in addition, the determination can be based on a template, which may be indicative of an instrument response of the interferometer used to obtain the low coherence interference signal.
1. A method comprising:
providing an interference signal produced by an interferometer for each of multiple spatial locations of a test object comprising a thin film having a thickness of 1000 nm or less; and
determining a surface topography for the object in the presence of the thin film based on the interference signals and a template indicative of a response of the interferometer.
2. The method of claim 1 , wherein the interference signals for the test object are low coherence interference signals.
3. The method of claim 1 , wherein the interferometer is a low coherence scanning interferometer.
4. The method of claim 3 , wherein the low coherence scanning interferometer comprises a multi-element detector for collecting data corresponding to the interference signals from the multiple spatial locations of the test object.
5. The method of claim 1 , wherein the object comprises a wafer and thin film is photoresist coating the wafer.
6. The method of claim 1 , wherein the template corresponds to a truncated portion of a reference low coherence interference signal.
7. The method of claim 1 , further comprising comparing the template and the low interference signal for each spatial location to determine a corresponding surface height for the determined surface topography.
8. The method of claim 7 , wherein the comparing comprises cross-correlating the template with each of the low coherence interference signals.
9. The method of claim 8 , wherein the cross-correlating comprises normalizing based upon a shape of the low coherence interference signal.
10. The method of claim 8 , wherein the cross-correlation is a partially complex cross-correlation.
11. The method of claim 1 , further comprising determining the template based on at least one interference signal obtained by the interferometer from a reference object having a known surface topography.
12. The method of claim 1 , further comprising determining the template based on interference signals obtained from multiple spatial locations of a reference object, wherein the reference interference signals are processed and then averaged to determine the template.
13. The method of claim 12 , wherein the processing of the reference interference signal comprises removing a linear phase component in the frequency domain removing surface height variations among the processed reference interference signals.
14. The method of claim 1 , further comprising using the interferometer to produce the interference signals.
15. The method of claim 1 , wherein the object is a semiconductor chip.
16. A method comprising:
determining a surface topography for an object based on low-coherence interference signals corresponding to multiple spatial locations of the object and a template indicative of a response of a low-coherence interferometer used to produce the low coherence interference signals.
17. An apparatus comprising:
a computer readable medium configured to cause a processor to determine a surface topography for an object in the presence of the object based on low coherence interference signals corresponding to multiple spatial locations of the object and a template indicative of a response of a low coherence interferometer used to produce the low coherence interference signals.
18. A system comprising:
a low-coherence interferometer configured to produce multiple low-coherence interference signals corresponding to different spatial locations of a test object; and
an electronic processor coupled to the low-coherence interferometer and configured to determine a surface topography for the test object based on the low coherence interference signals and a template indicative of a response of the low-coherence interferometer.
19. The system of claim 18 , wherein the template corresponds to a truncated portion of a reference low coherence interference signal.
20. The system of claim 18 , wherein the processor is further configured to compare the template to each of the interference signals in order to determine the surface topography.
21. The system of claim 20 , wherein the comparing configured to be performed by the processor comprises cross-correlating the template with each of the low coherence interference signals.
22. The system of claim 21 , wherein the cross-correlating comprises normalizing based upon a shape of the low coherence interference signal.
23. The system of claim 21 , wherein the cross-correlation is a partially complex cross-correlation.
24. The system of claim 18 , wherein the processor is further configured to determine the template based on one or more interference signals obtained by the interferometer from a reference object.
25. The method of claim 1 , further comprising outputting information about the determined surface topography.