Method and system for analyzing low-coherence interferometry signals for information about thin film structures Number:7,321,431 from the United States Patent and Trademark Office (PTO) owispatent Methods and systems are disclosed for analyzing a scanning interferometry signal. A scanning interferometry signal is provided that is produced by a scanning interferometer for a first location of a test object (e.g., a sample having a thin film). A model function of the scanning interferometry signal is provided which is produced by the scanning interferometer. The model function is parametrized by one or more parameter values. The model function is fit to the scanning interferometry signal for each of a series of shifts in scan position between the model function and the scanning interferometry signal by varying the parameter values. Information is determined about the test object (e.g., a surface height or height profile, and/or a thickness or thickness profile for a thin film in the test object) at the first location based on the fitting.<H interferometry, information, Method, and, syst, 7321431.html, Patent, pto, 7321431

Title: Method and system for analyzing low-coherence interferometry signals for information about thin film structures

Abstract: Methods and systems are disclosed for analyzing a scanning interferometry signal. A scanning interferometry signal is provided that is produced by a scanning interferometer for a first location of a test object (e.g., a sample having a thin film). A model function of the scanning interferometry signal is provided which is produced by the scanning interferometer. The model function is parametrized by one or more parameter values. The model function is fit to the scanning interferometry signal for each of a series of shifts in scan position between the model function and the scanning interferometry signal by varying the parameter values. Information is determined about the test object (e.g., a surface height or height profile, and/or a thickness or thickness profile for a thin film in the test object) at the first location based on the fitting.

Patent Number: 7,321,431 Issued on 01/22/2008 to De Groot

Inventors: De Groot; Peter (Middletown, CT)
Assignee: Zygo Corporation (Middlefield, CT)

Appl. No.: 11/437,002

Filed: May 18, 2006

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
60682742	May., 2005

Current U.S. Class: 356/497 ; 356/504; 356/511

Current International Class: G01B 11/06 (20060101)

Field of Search: 356/479,497,503,504,511-514

References Cited [Referenced By]

U.S. Patent Documents


4355903	October 1982	Sandercock
4576479	March 1986	Downs
4618262	October 1986	Maydan et al.
4660980	April 1987	Takabayashi et al.
4818110	April 1989	Davidson
4999014	March 1991	Gold et al.
5042949	August 1991	Greenberg et al.
5042951	August 1991	Gold et al.
5112129	May 1992	Davidson et al.
5129724	July 1992	Brophy et al.
5133601	July 1992	Cohen et al.
5135307	August 1992	de Groot et al.
5301010	April 1994	Jones et al.
5398113	March 1995	de Groot
5587792	December 1996	Nishizawa et al.
5589938	December 1996	Deck
5602643	February 1997	Barrett
5774224	June 1998	Kerstens
5900633	May 1999	Solomon et al.
6242739	June 2001	Cherkassky
6249351	June 2001	de Groot
H1972	July 2001	Inoue
6259521	July 2001	Miller et al.
6275297	August 2001	Zalicki
6377349	April 2002	Fercher
6500591	December 2002	Adams
6507405	January 2003	Grek et al.
6545763	April 2003	Kim et al.
6597460	July 2003	Groot et al.
6636322	October 2003	Terashita
6721094	April 2004	Sinclair et al.
6940604	September 2005	Jung et al.
7018271	March 2006	Wiswesser et al.
2002/0135775	September 2002	de Groot et al.
2002/0196450	December 2002	Olszak et al.
2003/0112444	June 2003	Yang et al.
2004/0085544	May 2004	de Groot et al.
2004/0185582	September 2004	Kueny
2004/0189999	September 2004	de Groot et al.
2005/0057757	March 2005	de Lega et al.
2005/0068540	March 2005	de Groot et al.
2005/0073692	April 2005	de Groot et al.
2005/0078318	April 2005	de Groot
2005/0078319	April 2005	de Groot
2005/0088663	April 2005	de Groot et al.
2005/0146727	July 2005	Hill
2005/0237534	October 2005	Deck
2006/0012582	January 2006	de Lega

Foreign Patent Documents


4108944	Sep., 1992	DE
4309056	Sep., 1994	DE
0 929 094	Jul., 1990	EP
0 397 388	Nov., 1990	EP
0 549 166	Jun., 1993	EP
0 617 255	Sep., 1994	EP
2385417	Aug., 2003	GB
WO 97/44633	Nov., 1997	WO
WO 02/082008	Oct., 2002	WO
WO 03/062802	Jul., 2003	WO

Other References

C Akcay et al., "Spectral shaping to improve the point spread function in optical coherence tomography", Optics Letters, vol. 28 No. 20, pp. 1921-1923 (Oct. 15, 2003). cited by other .
R.M.A. Azzam et al., "Reflection and Transmission of Polarized Light by Stratified Planar Structures", Ellipsometry and Polarized Light, Elsevier Science B.V. ISBN 0 444 87016 4 (Paperback) pp. 267-363 (1987). cited by other .
R.M.A. Azzam et al., "Ellipsometric function of a film-substrate system: Applications to the design of reflection-type optical devices and to ellipsometry", Journal of the Optical Society of America, vol. 5, No. 3, pp. 252-260, (1975). cited by other .
M. Bashkansky et al., "Signal Processing for Improving Field Cross-correlation Function in Optical Coherence Tomography", Supplement to Optics & Photonics News, 9(5) (May 1998). cited by other .
Berman et al., "Review of In Situ & In-line Detection for CMP Applications", Semiconductor Fabtech--8.sup.th Edition, pp. 267-274, (1998). cited by other .
A. Bosseboeuf et al., "Application of microscopic interferometry techniques in the MEMS field", Proceedings of SPIE, vol. 5145, pp. 1-16 (2003). cited by other .
M. Davidson et al., "An Application of Interference Microscopy to Integrated Circuit Inspection and metrology", Proceedings SPIE, vol. 775, pp. 233-247 (1987). cited by other .
T. Dresel et al., "Three-dimensional sensing of rough surfaces by coherence radar", Applied Optics, vol. 31, No. 7, pp. 919-925 (Mar. 1, 1992). cited by other .
J.E. Greivenkamp, "Generalized data reduction for heterodyne interferometry", Optical Engineering., vol. 23 No. 4, pp. 350-352 (Jul./Aug. 1984). cited by other .
P. de Groot et al., "Signal modeling for low coherence height-scanning interference microscopy", Applied Optics, vol. 43 No. 25, pp. 4821-4830 (Sep. 1, 2004). cited by other .
P. de Groot, "Derivation of algorithms for phase-shifting interferometry using the concept of a data sampling window", Appl. O.pt., 34(22), p. 4723-4730 (1995). cited by other .
P. de Groot et al., "Signal modeling for modern interference microscopes", SPIE Proceedings, 5457-4 (2004). cited by other .
Peter de Groot et al., "Determination of fringe order in white-light interference microscopy", Appl. Opt., 41(22) pp. 4571-4578 (2002). cited by other .
Feke, Gilbert D. et al., "Interferometric back focal plane microellipsometry", Applied Optics, vol. 37, No. 10, pp. 1796-1802 (Apr. 1, 1998). cited by other .
P.A. Flournoy et al., "White-light interferometric thickness gauge", Appl. Opt., 11(9), pp. 1907-1915 (1972). cited by other .
G. Hausler et al., "Coherence Radar and Spectral Radar--New Tools for Dermatological Diagnosis", Journal of Biomedical Optics, vol. 3, No. 1, pp. 21-31 (Jan. 1998). cited by other .
R.D. Holmes et al., "Scanning microellipsometry for extraction of true topograpy", Electronics Letters, vol. 31, No. 5, pp. 358-359 (Mar. 2, 1995). cited by other .
Kim, Seung-Woo et al., "Thickness-profile measurement of transparent thin-film layers by white-light scanning interferometry", Applied Optics, vol. 38, No. 28, pp. 5968-5973 (Oct. 1, 1999). cited by other .
Kino, Gordon S. et al., "Mirau correlation microscope", Applied Optics, vol. 29, No. 26, pp. 3775-3783 (Sep. 10, 1990). cited by other .
Kieran G. Larkin, "Efficient nonlinear algorithm for envelope detection in white light interferometry", Journal of the Optical Society of America A, vol. 13, No. 4, pp. 832-843 (1996). cited by other .
Kujawinska, Malgorzata, "Spatial Phase Measurement Methods", Interferogram Analysis: Digital Fringe Pattern Measurement Techniques, IOP Publishing Ltd. 1993, pp. 141-193. cited by other .
Lee et al., "Profilometry with a coherence scanning microscope", Appl. Opt., 29(26), pp. 3784-3788 (1990). cited by other .
I. Lee-Bennett, "Advances in non-contacting surface metrology", OF&T Workshop, paper OTuC1 (2004). cited by other .
K. Leonhardt et al., "Micro-Ellipso-Height-Profilometry", Optics Communications, vol. 80, No. 3, 4, pp. 205-209 (Jan. 1, 1991). cited by other .
Y. Liu et al., "Common path interferometric microellipsometry", SPIE, vol. 2782, pp. 635-645 (1996). cited by other .
Lyakin et al., "The interferometric system with resolution better than coherence length for determination of geometrical thickness and refractive index of a layer object", Proceedings of the SPIE--The International Society for Optical Engineering SPIE-INT. Soc. Opt. Eng USA, vol. 4956, pp. 163-169 (Jul. 2003). cited by other .
C.J. Morgan, "Least-Squares estimation in phase-measurement interferometry", Optics Letters, 7(8), pp. 368-370 (1982). cited by other .
Ngoi et al., "Phase-shifting interferometry immune to vibration", Applied Optics, vol. 40, No. 19, pp. 3211-3214 (2001). cited by other .
A.V. Oppenheim et al., "10.3: The time-dependent Fourier Transform", Discrete-Time Signal Processing, 2.sup.nd Edition, pp. 714-722 (Prentice Hall, New Jersey, 1999). cited by other .
M.C. Park et al., "Direct quadratic polynomial fitting for fringe peak detection of white light scanning interferograms", Optical Engineering, vol. 39, No. 4, pp. 952-959 (2000). cited by other .
S. Pettigrand et al., "Mesures 3D de topographies et de vibrations a l'echelle (sub)micrometrique par microscopie optique interferometrique", Proc. Club CMOI, Methodes et Techniques Optiques pour l'Industrie, (2002). cited by other .
M. Pluta, "Advanced light microscopy", vol. 3, PWN--Polish Scientific Publishers (Elsevier, Amsterdam), pp. 265-271 (1993). cited by other .
W.H. Press et al., "Linear Correlation", Numerical Recipes in C, Cambridge University Press, 2.sup.nd Edition, pp. 636-639 (1992). cited by other .
Rosencwaig, Allan et al., "Beam profile reflectometry: A new technique for dielectric film measurements", Applied Physics Letters, vol. 60, No. 11, pp. 1301-1303 (Mar. 16, 1992). cited by other .
P. Sandoz et al., "Optical implementation of frequency domain analysis for white light interferometry", Proceedings SPIE, vol. 2545, pp. 221-228 (Jun. 1995). cited by other .
P. Sandoz et al., "High-resolution profilometry by using phase calculation algorithms for spectroscopic analysis of white-light interferograms", Journal of Modern Optics, vol. 43, No. 4 , pp. 701-708 (1996). cited by other .
Sandoz, Patrick, "Wavelet transform as a processing tool in white-light interferometry", Optics Letters, vol. 22, No. 14, pp. 1065-1067 (Jul. 15, 1997). cited by other .
P. Sandoz et al., "Processing of white light correlograms: simultaneous phase and envelope measurements by wavelet transformation", SPIE, vol. 3098, pp. 73-82 (1997). cited by other .
U. Schnell et al., "Dispersive white-light interferometry for absolute distance measurement with dielectric multilayer systems on the target", Optics Letters, vol. 21, No. 7, pp. 528-530 (Apr. 1996). cited by other .
J. Schwider et al., "Dispersive interferometric profilometer", Optics Letters, vol. 19, No. 13, pp. 995-997 (Jul. 1994). cited by other .
C.W. See et al., "Scanning optical microellipsometer for pure surface profiling", Applied Optics, vol. 35, No. 34, pp. 6663-6668 (Dec. 1, 1996). cited by other .
Shatalin, S.V. et al., "Reflection conoscopy and micro-ellipsometry of isotropic thin film structures", Journal of Microscopy, vol. 179, Part 3, pp. 241-252 (Sep. 1995). cited by other .
M. Totzeck, "Numerical simulation of high-NA quantitative polarization microscopy and corresponding near-fields", Optik, vol. 112, No. 9, pp. 399-406 (2001). cited by other .
R. Tripathi et al., "Spectral shaping for non-Gaussian source spectra in optical coherence tomography", Optics Letters, vol. 27, No. 6, pp. 406-408 (Mar. 15, 2002). cited by other .
D. Willenborg et al., "A novel micro-spot dielectric film thickness measurement system", SPIE, vol. 1594, pp. 322-333 (1991). cited by other.

Primary Examiner: Turner; Samuel A.
Attorney, Agent or Firm: Fish & Richardson P.C.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATIONS

Under 35 U.S.C. .sctn. 119(e), the present application claims priority to U.S. Provisional Patent Application Ser. No. 60/682,742, filed May 19, 2005 and entitled "METHOD AND SYSTEM FOR ANALYZING LOW-COHERENCE INTERFEROMETRY SIGNALS FOR SURFACE TOPOGRAPHY MEASUREMENT OVER THIN FILM STRUCTURES," the contents of which is incorporated herein by reference.

Claims

What is claimed is:

1. A method comprising: providing a scanning interferometry signal produced by a scanning interferometer for a first location of a test object; providing a model function of the scanning interferometry signal produced by the scanning interferometer, wherein the model function is parametrized by one or more parameter values; fitting the model function to the scanning interferometry signal for each of a series of shifts in scan position between the model function and the scanning interferometry signal by varying the parameter values; and determining information about the test object at the first location based on the fitting.

2. The method of claim 1, further comprising: providing a scanning interferometry signal produced by the scanning interferometer for each of additional locations of the test object; fitting the model function to each of the scanning interferometry signals corresponding to the additional locations of the test object for each of a series of shifts in scan positions between the model function and the respective scanning interferometry signal by varying the parameter values; and determining information about the test object at the additional locations based on the additional fitting.

3. The method of claim 2, wherein the interferometry signal for each location of the test object is expressible as comprising an intensity value for each of a series of global scan positions of the scanning interferometer.

4. The method of claim 3, wherein the model function is expressible as comprising an intensity value for each of a series of local scan positions, and wherein the fitting comprises fitting the model function to each of the interferometry signals with the model function centered on each of the global scan positions corresponding to the series of shifts in scan position between the model function and the respective scanning interferometry signal by varying the parameter values.

5. The method of claim 4, wherein, for each of the locations of the test object, the fitting comprises determining which of the series of shifts in scan positions between the model function and the respective scanning interferometry signal produces an optimum fit.

6. The method of claim 5, wherein the determining information comprises determining a surface height profile for the test object based on the shift in scan position corresponding to the optimum fit for each of the locations.

7. The method of claim 5, wherein the test object comprises a thin film, and wherein the determining information comprises determining a thickness profile for the thin film based on the shift in scan position corresponding to the optimum fit for each of the locations.

8. The method of claim 5, wherein the determining which of the series of shifts in scan positions produces the optimum fit comprises comparing the model function and the respective interferometry signal to determine the degree of similarity between the model function and the respective interferometry signal.

9. The method of claim 8, wherein determining which of the series of shifts in scan positions produces the optimum fit comprises calculating a metric indicative of the degree of similarity between the model function and the respective interferometry signal.

10. The method of claim 9, wherein determining which of the series of shifts in scan positions produces the optimum fit comprises determining a shift in scan position for which the corresponding metric indicates a high degree of similarity between the model function and the respective interferometry signal.

11. The method of claim 9, wherein, for each of the locations on the test object, the metric is related to a sum .times..function. ##EQU00018## where I.sub.z is the intensity value of the interferometer signal at the z.sup.th member of the set of global scan positions, f.sub.z is the intensity value of the model function at the z.sup.th member of the set of global scan positions, and g is some function which depends on I.sub.z and f.sub.z.

12. The method of claim 11 wherein the metric is related to the sum of the squares of the differences between the intensity value of the model function and the intensity value of the interferometer signal at each of the series of global scan positions.

13. The method of claim 11 wherein and the metric is related to the absolute value of the difference between the intensity value of the model function and the intensity value of the interferometer signal at each of the series of global scan positions.

14. The method of claim 9, wherein the metric is additionally based on the magnitude of the model function.

15. The method of claim 4, wherein the test object comprises a thin film; wherein the fitting comprises, for each of the locations, determining a first shift of the series of shifts of scan position which corresponds to a first optimal fit and determining a second shift of the series of shifts of scan position which corresponds to a second optimal fit; and wherein the determining information comprises determining a thickness profile for the thin film based on the first and second shifts in scan position for each of the locations.

16. The method of claim 5, wherein, for each of the locations, the fitting further comprises determining an estimate for one or more the parameter values based on the optimum fit.

17. The method of claim 16, wherein the determining of the information about the test object is based on the shift in scan position and at least one of the parameter value estimates corresponding to the optimum fit for each of the locations.

18. The method of claim 1, wherein the parameter values comprise a phase value, an average magnitude value, and an offset value.

19. The method of claim 2, wherein, for each of the locations, the fitting comprises determining an estimate for one or more the parameter values based on an optimum fit of the model function to the respective interferometry signal.

20. The method of claim 19, wherein the fitting determines an estimate for an average magnitude parameter value for each of the locations, and the determining information about the test object comprises determining a fringe-free image of the test object based on the estimates for the average magnitude parameter values.

21. The method of claim 20, wherein the fitting further provides surface height information for the test object, and wherein the information about test object comprises the fringe-free image and a surface height profile.

22. The method of claim 20, wherein the fitting further provides thickness profile information for a thin film in the test object, and wherein the information about test object comprises the fringe-free image and the thickness profile.

23. The method of claim 2, wherein the test object comprises a first and second interface.

24. The method of claim 23, wherein the first interface is an outer surface of the object and the second interface is beneath the outer surface, wherein the outer surface is an outer surface of a layer of photoresist overlying a substrate and the second interface is defined between the outer surface of the photoresist and the substrate.

25. The method of claim 24, comprising determining a spatial property of the outer surface based on the fitting and modifying a relative position of the object and a photolithography system based on the spatial property.

26. The method of claim 23, wherein the first interface is an outer surface of the object and the method comprises: prior to the providing the scanning interferometer signal, removing a material from the outer surface of the object; determining a spatial property of the outer surface of the object based on the fitting; and removing additional material from the outer surface of the object based on the spatial property.

27. The method of claim 23, wherein the first and second interfaces are interfaces of a liquid crystal cell.

28. The method of claim 23, comprising: prior to providing the scanning interferometer signal, irradiating the object with a laser to form a scribe line; determining a spatial property of a portion of the object including the scribe line based on the fitting; and performing additional scribing of the same object or a different object based on the spatial property.

29. The method of claim 23, comprising: prior to providing the scanning interferometer signal, forming the first and second interfaces during a solder bump process.

30. The method of claim 2, further comprising controlling the operation of a semiconductor process tool based on the information determined about the test object at each location.

31. The method of claim 2, further comprising controlling a semiconductor process based on the information determined about the test object at each location.

32. An apparatus comprising: a scanning interferometer configured to provide a scanning interferometry signal for each of multiple locations of a test object; and an electronic processor configured to analyze the interferometry signals, the electronic processor configured to fit a model function of the scanning interferometry signal produced by the scanning interferometer to the scanning interferometry signal corresponding to each of one or more of the locations of the test object, for each of a series of shifts in scan position between the model function and the respective scanning interferometry signal, by varying one or more parameter values parametrizing the model function, and determine information about the test object based on the fit.

33. The apparatus of claim 32, wherein the electronic processor is configured to fit the model function to the interferometry signal corresponding to each of multiple locations of the test object.

34. The apparatus of claim 32, wherein the parameter values comprise a phase value, an average magnitude value, and an offset value.

35. The apparatus of claim 33, wherein the model function is expressible as comprising an intensity value for each of a series of local scan positions, and wherein the fitting comprises fitting the model function to each of the interferometry signals with the model function centered on each of the global scan positions corresponding to the series of shifts in scan position between the model function and the respective scanning interferometry signal by varying the parameter values.

36. The apparatus of claim 35, wherein, for each of the locations of the test object, the fitting comprises determining which of the series of shifts in scan positions between the model function and the respective scanning interferometry signal produces an optimum fit.

37. The apparatus of claim 36, wherein the determining information comprises determining a surface height profile for the test object based on the shift in scan position corresponding to the optimum fit for each of the locations.

38. The apparatus of claim 36, wherein the test object comprises a thin film, and wherein the determining information comprises determining a thickness profile for the thin film based on the shift in scan position corresponding to the optimum fit for each of the locations.

39. The apparatus of claim 36, wherein the determining which of the series of shifts in scan positions produces the optimum fit comprises comparing the model function and the respective interferometry signal to determine the degree of similarity between the model function and the respective interferometry signal.

40. The apparatus of claim 39, wherein determining which of the series of shifts in scan positions produces the optimum fit comprises calculating a metric indicative of the degree of similarity between the model function and the respective interferometry signal.

41. The apparatus of claim 40, wherein determining which of the series of shifts in scan positions produces the optimum fit comprises determining a shift in scan position for which the corresponding metric indicates a high degree of similarity between the model function and the respective interferometry signal.

42. The apparatus of claim 35, wherein the test object comprises a thin film; wherein the fitting comprises, for each of the locations, determining a first shift of the series of shifts of scan position which corresponds to a first optimal fit and determining a second shift of the series of shifts of scan position which corresponds to a second optimal fit; and wherein the determining information comprises determining a thickness profile for the thin film based on the first and second shifts in scan position for each of the locations.

43. An apparatus comprising a computer readable medium storing a program configured to cause a processor to fit a model function of a scanning interferometry signal produced by a scanning interferometer to a scanning interferometry signal corresponding to each of one or more of locations of the test object measured by the scanning interferometer, for each of a series of shifts in scan position between the model function and the respective scanning interferometry signal, by varying one or more parameter values parametrizing the model function, determine information about the test object based on the fit.

44. An apparatus comprising: a means for providing an interferometry signal for each of multiple locations of a test object; and a means for processing configured to analyze the interferometry signals, the means for processing configured to fit a model function of the interferometry signal produced by the means for providing to the interferometry signal corresponding to each of one or more of the locations of the test object, for each of a series of shifts in scan position between the model function and the respective interferometry signal, by varying one or more parameter values parametrizing the model function, and determine information about the test object based on the fit.

45. The method of claim 1, further comprising: outputting information related to the determined information about the test object.

46. The apparatus of claim 44, wherein the program is further configured to cause the processor to output information related to the determined information about the test object.

Description

BACKGROUND

The invention relates to using scanning interferometry to measure surface topography and/or other characteristics of objects having complex surface structures, such as thin film(s), discrete structures of dissimilar materials, or discrete structures that are underresolved by the optical resolution of an interference microscope. Such measurements are relevant to the characterization of flat panel display components, semiconductor wafer metrology, and in-situ thin film and dissimilar materials analysis.

Interferometric techniques ate commonly used to measure the profile of a surface of an object. To do so, an interferometer combines a measurement wavefront reflected from the surface of interest with a reference wavefront reflected from a reference surface to produce an interferogram. Fringes in the interferogram are indicative of spatial variations between the surface of interest and the reference surface.

A scanning interferometer scans the optical path length difference (OPD) between the reference and measurement legs of the interferometer over a range comparable to, or larger than, the coherence length of the interfering wavefronts, to produce a scanning interferometry signal for each camera pixel used to measure the interferogram. A limited (or "low") coherence length can be produced, for example, by using a broadband light source (e.g., a white light source), which is referred to as scanning white light interferometry (SWLI). A typical scanning white light interferometry (SWLI) signal is a few fringes localized near the zero optical path difference (OPD) position. The signal is typically characterized by a sinusoidal carrier modulation (the "fringes") with bell-shaped fringe-contrast envelope. The conventional idea underlying SWLI metrology is to make use of the localization of the fringes to measure surface profiles. Low-coherence interferometry signals can also be produced with narrow band light that illuminates an object over a wide range of angles.

Techniques for processing low-coherence interferometry signals include two principle trends. The first approach is to locate the peak or center of the envelope, assuming that this position corresponds to the zero optical path difference (OPD) of a two-beam interferometer for which one beam reflects from the object surface. The second approach is to transform the signal into the frequency domain and calculate the rate of change of phase with wavelength, assuming that an essentially linear slope is directly proportional to object position. This latter approach is referred to as Frequency Domain Analysis (FDA). In the presence of thin film structures, the analysis can be more complicated.

U.S. patent applications published as US-2005-0078318-A1 entitled "METHODS AND SYSTEMS FOR INTERFEROMETRIC ANALYSIS OF SURFACES AND RELATED APPLICATIONS" and US-2005-0078319-A1 entitled "SURFACE PROFILING USING AN INTERFERENCE PATTERN MATCHING TEMPLATE, both by Peter J. de Groot, disclose additional techniques for analyzing low-coherence interferometry signals from a thin film sample. One of the disclosed techniques identifies the portion of a scanning white light interferometry (SWLI) signal corresponding to the top-surface profile of a thin film structure. For a thin enough film, the individual signals corresponding to the upper and lower interfaces of the film are inseparable, in the sense that the fringe contrast has only one peak; nonetheless, we can argue on physical grounds that the first few fringes on the right most closely relate to the top-surface profile. This technique identifies the trumpet-shaped leading edge of the signal, and ascribes this to the top surface profile. A further technique disclosed in these published applications describes one way of locating the leading edge or other segment of a signal by using a pattern matching technique, one example of which is referred to as correlation template analysis (CTA). Both of said published applications are commonly owned with the present applications and are incorporated herein by reference.

SUMMARY

Preferred embodiments disclosed herein feature a sliding-window least-squares (LSQ) procedure for analyzing low-coherence interferometry signals. The procedure can be used to accurately identify portions of the low-coherence interferometry signals of interest. The procedure performs a fit sequentially through the scan by means of a least-squares optimization. The first step is to create a fitting function based on a model of the signal that we expect to see, then using one or more variable parameters, including an interference phase value, to optimize the fit to the actual signal at each scan position. The scan position for which the LSQ fit is most successful locates the signal, and the phase at this point is the desired final result.

More generally, we now summarize some general aspects, features, and advantages of the invention.

In general, in one aspect, the invention features a method including: providing a scanning interferometry signal produced by a scanning interferometer for a first location of a test object (e.g., a sample having a thin film); providing a model function of the scanning interferometry signal produced by the scanning interferometer, wherein the model function is parametrized by one or more parameter values; fitting the model function to the scanning interferometry signal for each of a series of shifts in scan position between the model function and the scanning interferometry signal by varying the parameter values; and determining information about the test object (e.g., a surface height or height profile, and/or a thickness or thickness profile for a thin film in the test object) at the first location based on the fitting.

Embodiments of the method may further include any of the following features.

The method may further include: providing a scanning interferometry signal produced by the scanning interferometer for each of additional locations of the test object; fitting the model function to each of the scanning interferometry signals corresponding to the additional locations of the test object for each of a series of shifts in scan positions between the model function and the respective scanning interferometry signal by varying the parameter values; and determining information about the test object at the additional locations based on the additional fitting.

For example, the interferometry signal for each location of the test object can be expressed as including an intensity value for each of a series of global scan positions of the scanning interferometer. Furthermore, for example, the model function can be expressed as including an intensity value for each of a series of local scan positions, and wherein the fitting includes fitting the model function to each of the interferometry signals with the model function centered on each of the global scan positions corresponding to the series of shifts in scan position between the model function and the respective scanning interferometry signal by varying the parameter values. Wherein, for each of the locations of the test object, the fitting includes determining which of the series of shifts in scan positions between the model function and the respective scanning interferometry signal produces an optimum fit.

In certain embodiments, for example, the series of global scan positions and the series of local scan positions each correspond to a consecutive series of equal scan increments.

Thereafter, for example, the determining of the information may include determining a surface height profile for the test object based on the shift in scan position corresponding to the optimum fit for each of the locations and/or determining a thickness profile for a thin film in the test object based on the shift in scan position corresponding to the optimum fit for each of the locations.

In some embodiments, the determining which of the series of shifts in scan positions produces the optimum fit includes comparing the model function and the respective interferometry signal to determine the degree of similarity between the model function and the respective interferometry signal. For example, in some embodiments, determining which of the series of shifts in scan positions produces the optimum fit includes determining a shift in scan position for which the corresponding metric indicates a high degree of similarity between the model function and the respective interferometry signal.

In some embodiments, determining which of the series of shifts in scan positions produces the optimum fit includes calculating a metric indicative of the degree of similarity between the model function and the respective interferometry signal. In some embodiments, the metric is additionally based on the magnitude of the model function.

For example, in some embodiments, for each of the locations on the test object, the metric may be related to a sum

.times..times..function. ##EQU00001## where I.sub.z is the intensity value of the interferometer signal at the z.sup.th member of the set of global scan positions, f.sub.z is the intensity value of the model function at the z.sup.th member of the set of global scan positions, and g is some function which depends on I.sub.z and f.sub.z

In further embodiments, for example, the metric is related to the sum of the squares and/or the absolute value of the differences between the intensity value of the model function and the intensity value of the interferometer signal at each of the series of global scan positions.

In some embodiments, the test object includes a thin film. The fitting includes, for each of the locations, determining a first shift of the series of shifts of scan position which corresponds to a first optimal fit and determining a second shift of the series of shifts of scan position which corresponds to a second optimal fit. The determining information includes determining a thickness profile for the thin film based on the first and second shifts in scan position for each of the locations.

In some embodiments, the information about the test object includes a surface height profile for the test object. In some embodiments, the test object includes a thin film, and the information about the test object comprises a thickness profile for the thin film.

In some embodiments, the test object includes a first interface and a second interface. In some embodiments, for example, the first interface is an outer surface of the test object, and the second interface is beneath the test object. In some embodiments, the first and second interfaces are separated by 1000 nm or less.

For each of the locations, the fitting may further include determining an estimate for one or more the parameter values based on the optimum fit. For example, the determining of the information about the test object may be based on the shift in scan position and at least one of the parameter value estimates corresponding to the optimum fit for each of the locations.

The parameter values may include one or more of a phase value, an average magnitude value, and an offset magnitude value. For example, the parameter values may include a phase value, an average magnitude value, and an offset magnitude value.

The fitting may include a least squares optimization.

The model function may be determined theoretically or it may be determined based on empirical data from the scanning interferometer. In either case, in some embodiments, the model function may be a truncated asymmetric function.

The scanning interferometer is typically a low coherence scanning interferometer having a coherence length, and the interferometry signal for the test object typically spans a range larger than the coherence length of the low coherence scanning interferometer.

For each of the locations, the fitting may include determining an estimate for one or more the parameter values based on an optimum fit of the model function to the respective interferometry signal.

The fitting may determine an estimate for an average magnitude parameter value for each of the locations, and the determining of the information about the test object may include determining a fringe-free image of the test object based on the estimates for the average magnitude parameter values. The fitting may further provide surface height information for the test object, and the information about the test object may include the fringe-free image and a surface height profile. Alternatively, or in addition, the fitting may further provide thickness profile information for a thin film in the test object, and the information about the test object may include the fringe-free image and the thickness profile. In some embodiments, the thin film may include a first and second interface separated, for example, by less than 1000 nm.

In some embodiments, the test object includes a first and second interface. For example, the first interface may be an outer surface of the object and the second interface may be beneath the outer surface. In some embodiments, the first and second interfaces may be interfaces of a liquid crystal cell.

In further embodiments, the outer surface is an outer surface of a layer of photoresist overlying a substrate and the second interface is defined between the outer surface of the photoresist and the substrate. In some embodiments, determining a spatial property of the outer surface based on the fitting and modifying a relative position of the object and a photolithography system based on the spatial property.

In further embodiments where the first interface is an outer surface of the object the method may further include, prior to the providing the scanning interferometer signal, removing a material from the outer surface of the object; determining a spatial property of the outer surface of the object based on the fitting; and removing additional material from the outer surface of the object based on the spatial property.

In yet further embodiments where the test object includes a first and second interface, the method may further include, prior to providing the scanning interferometer signal, irradiating the object with a laser to form a scribe line; determining a spatial property of a portion of the object including the scribe line based on the fitting; and performing additional scribing of the same object or a different object based on the spatial property.

In yet further embodiments where the test object includes a first and second interface the method may further include, prior to providing the scanning interferometer signal, forming the first and second interfaces during a solder bump process.

In some embodiments, the method may further include controlling the operation of a semiconductor process tool based on the information determined about the test object at each location. For example, the semiconductor process tool may include one or more of a diffusion tool, rapid thermal anneal tool, a chemical vapor deposition tool (low pressure or high pressure), a dielectric etch tool, a chemical mechanical polisher, a plasma deposition tool, a plasma etch tool, a lithography track tool, and a lithography exposure tool.

In some embodiments, the method may further include controlling a semiconductor process based on the information determined about the test object at each location. For example, the semiconductor process may include one of: trench and isolation, transistor formation, and interlayer dielectric formation (such as dual damascene).

In general, in another aspect, the invention features a system including: a scanning interferometer configured to provide a scanning interferometry signal for each of multiple locations of a test object; and an electronic processor configured to analyze the interferometry signals. The electronic processor is configured to: i) fit a model function of the scanning interferometry signal produced by the scanning interferometer to the scanning interferometry signal corresponding to each of one or more of the locations of the test object, for each of a series of shifts in scan position between the model function and the respective scanning interferometry signal, by varying one or more parameter values parametrizing the model function; and ii) determine information about the test object based on the fit.

Embodiments of the system may further include any of the features described above in connection with the method.

In general, in another aspect, the invention features an apparatus including a computer readable medium storing a program configured to cause a processor to: i) fit a model function of a scanning interferometry signal produced by a scanning interferometer to a scanning interferometry signal corresponding to each of one or more of locations of the test object measured by the scanning interferometer, for each of a series of shifts in scan position between the model function and the respective scanning interferometry signal, by varying one or more parameter values parametrizing the model function; and ii) determine information about the test object based on the fit.

Embodiments of the apparatus may further include any of the features described above in connection with the method.

The techniques disclosed herein may be applicable to any of the following applications: i) simple thin films (e.g., the variable parameter of interest may be the film thickness, the refractive index of the film, the refractive index of the substrate, or some combination thereof); ii) multilayer thin films; iii) sharp edges and surface features that diffract or otherwise generate complex interference effects; iv) unresolved surface roughness; v) unresolved surface features, for example, a sub-wavelength width groove on an otherwise smooth surface; and v) dissimilar materials.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All patents, patent applications, and references mentioned herein are incorporated herein by reference; in case of conflict, the definitions in the present document control.

Other features, objects, and advantages of the invention will be apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an interferometry system.

FIG. 2 is a simulated plot of the intensity signal from a typical SWLI system.

FIG. 3 is a schematic diagram of a measurement object featuring multiple interfaces along with a corresponding SWLI signal.

FIG. 4 is a plot of a simulated SWLI signal featuring distinguishable contributions from two interfaces.

FIG. 5 depicts a truncated model signal fit to a simulated SWLI signal.

FIG. 6 depicts a model signal used in a sliding window LSQ pattern matching technique and a simulated SWLI signal.

FIG. 7 is a flow chart showing the flow of an exemplary embodiment of the sliding window LSQ pattern matching technique.

FIG. 8a is a schematic diagram showing a top down view of an object 30 which includes a substrate, e.g., a wafer, 32 and an overlying layer, e.g., photoresist layer 34.

FIG. 8b is a schematic diagram showing a side on view of the object 30.

FIG. 9a is a schematic showing a device 500 exemplary of the film structure resulting from the deposition of a dielectric 504 over copper features 502 deposited on a substrate 501.

FIG. 9b is a schematic diagram of the device 500 shown in FIG. 9a after undergoing chemical mechanical processing.

FIG. 10a is a schematic diagram of a structure 1050 suitable for use in solder bump processing.

FIG. 10b is a schematic diagram of the structure 1050 from FIG. 10a after solder bump processing has occurred.

FIG. 11 is a schematic diagram of a passive matrix LCD 450 is composed of several layers.

FIG. 12 is a plot of a simulated SWLI measurement signal 1201.

FIG. 13a is a plot of the system characterization spectrum derived from measurement signal 1201.

FIG. 13b is a plot of phase data for the system characterization spectrum derived from measurement signal 1201.

FIG. 14 is a plot of averaged system characterization data derived from measurement signal 1201.

FIG. 15a is a plot of the model signal for use in a sliding windows LSQ pattern matching analysis of measurement signal 1201.

FIG. 15b is a plot of the windowed model signal for use in a sliding window LSQ pattern matching analysis of measurement signal 1201.

FIG. 16a is a plot showing the result of the LSQ pattern matching analysis of measurement signal 1201.

FIG. 16b is a plot of the merit function obtained from the LSQ pattern matching analysis of measurement signal 1201.

FIG. 17a is a plot of the normal resolution top surface height profile obtained from the LSQ pattern matching analysis of measurement signal 1201.

FIG. 17b is a plot of the high resolution top surface height profile obtained from the LSQ pattern matching analysis of measurement signal 1201.

FIG. 18 is a plot of averaged system characterization data from example 2.

FIG. 19a is a plot of the asymmetric model signal for use in the sliding windows LSQ pattern matching analysis described in example 2.

FIG. 19b is a plot of the windowed asymmetric model signal for use in the sliding windows LSQ pattern matching analysis described in example 2.

FIG. 20a is a plot showing the result of the LSQ pattern matching analysis described in example 2.

FIG. 20b is a plot of the merit function obtained from the LSQ pattern matching analysis described in example 2.

FIG. 21a is a plot of the normal resolution top surface height profile obtained from the LSQ pattern matching analysis described in example 2.

FIG. 21b is a plot of the high resolution top surface height profile obtained from the LSQ pattern matching analysis described in example 2.

FIG. 22a is a plot showing the result of the LSQ pattern matching analysis described in example 3.

FIG. 22b is a plot of the merit function obtained from the LSQ pattern matching analysis described in example 3.

FIG. 23a is a plot of the normal resolution top surface height profile obtained from the LSQ pattern matching analysis described in example 3.

FIG. 23b is a plot of the high resolution top surface height profile obtained from the LSQ pattern matching analysis described in example 3.

FIG. 24 is a schematic diagram of measurement object 2400 composed of a 600 nm think layer of conformal photoresist 2401 over a pair of square aluminum pads 2402 on a silicon substrate 2403.

FIG. 24a is a plot showing the result of the LSQ pattern matching analysis of the SWLI signal from a point on measurement object 2400.

FIG. 25a is a plot of the normal resolution top surface height profile obtained from the LSQ pattern matching analysis of the SWLI signal from measurement object 2600.

FIG. 25b is a plot of the high resolution top surface height profile obtained from the LSQ pattern matching analysis of a SWLI signal from measurement object 2400.

FIG. 26 is a schematic diagram of measurement object 2600 which features a 10-micron wide, 440-nm deep trench 2601 in a nominal 940-nm thickness of silicon dioxide 2602 on a silicon substrate 2603.

FIG. 27 is a plot showing the result of the LSQ pattern matching analysis of the SWLI signal from a point on measurement object 2600.

FIG. 28a is a plot of the normal resolution top surface height profile obtained from the LSQ pattern matching analysis of the SWLI signal from measurement object 2600.

FIG. 28b is a plot of the high resolution top surface height profile obtained from the LSQ pattern matching analysis of the SWLI sign