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Applied Optics

Applied Optics


  • Vol. 37, Iss. 22 — Aug. 1, 1998
  • pp: 5116–5125

Determining the optical constants of read-write sliders during flying-height testing

Peter de Groot, Ara Dergevorkian, Tod Erickson, and Russell Pavlat  »View Author Affiliations

Applied Optics, Vol. 37, Issue 22, pp. 5116-5125 (1998)

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Flying-height testers for rigid disk drives employ a transparent glass substrate in place of the magnetic disk and use optical interferometry to measure the flight properties of the read-write slider. Because of the material phase change on reflection, the effective optical constants n and k of the slider play an important role in the measurement. We describe an instrument that determines the optical constants simultaneously with flying height, using polarization interferometry. This in situ analysis of n and k obviates the need for independent ellipsometry, while avoiding the problematic retract calibration characteristic of traditional flying-height test equipment. The rms uncertainty for n and k are 0.04, resulting in height uncertainties that range from 3 nm for 250-nm flying heights down to 0.5 nm at contact. We verify these results by use of a variety of experimental techniques on both laboratory samples and actual read-write sliders.

© 1998 Optical Society of America

OCIS Codes
(120.2130) Instrumentation, measurement, and metrology : Ellipsometry and polarimetry
(120.2830) Instrumentation, measurement, and metrology : Height measurements
(120.3180) Instrumentation, measurement, and metrology : Interferometry
(120.4530) Instrumentation, measurement, and metrology : Optical constants
(120.4640) Instrumentation, measurement, and metrology : Optical instruments
(120.5410) Instrumentation, measurement, and metrology : Polarimetry

Original Manuscript: November 5, 1997
Revised Manuscript: March 31, 1998
Published: August 1, 1998

Peter de Groot, Ara Dergevorkian, Tod Erickson, and Russell Pavlat, "Determining the optical constants of read-write sliders during flying-height testing," Appl. Opt. 37, 5116-5125 (1998)

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  1. B. Bhushan, Tribology and Mechanics of Magnetic Storage Devices (Springer-Verlag, New York, 1990) pp. 765–797.
  2. W. Stone, “A proposed method for solving some problems in lubrication,” The Commonwealth Engineer (1November1921), pp. 115–122.
  3. J. M. Fleischer, C. Lin, “Infrared laser interferometer for measuring air-bearing separation,” IBM J. Res. Develop. 18, 529–533 (1974). [CrossRef]
  4. T. Ohkubo, J. Kishegami, “Accurate measurement of gas-lubricated slider bearing separation using laser interferometry,” Trans. ASME 110, 148–155 (1988). [CrossRef]
  5. C. Lacey, J. A. Adams, E. W. Ross, A. Cormier, “A new method for measuring flying height dynamically,” Proceedings of DiskCon ’92 (International Disk Drive Equipment and Materials Association, Sunnyvale, Calif., 1992), pp. 27–42.
  6. T. E. Erickson, J. P. Lauer, “Multiplexed laser interferometer for non-dispersed spectrum detection in a dynamic flying height tester,” U.S. patent5,673,110 (30September1997).
  7. P. de Groot, L. Deck, J. Soobitsky, J. Biegen, “Polarization interferometer for measuring the flying height of magnetic read-write heads,” Opt. Lett. 21, 441–443 (1996). [CrossRef] [PubMed]
  8. P. de Groot, J. Biegen, L. Deck, A. Dergevorkian, T. Erickson, J. Morace, R. Pavlat, J. Soobitsky, “Polarization interferometer for flying height testing,” in Proceedings of Future Dimensions in Storage Symposium (International Disk Drive Equipment and Materials Association, Sunnyvale, Calif., 1997), pp. 89–94.
  9. P. de Groot, “Optical gap measuring apparatus and method,” U.S. patent5,557,399 (17September1996).
  10. F. Muranushi, K. Tanaka, Y. Takeuchi, “Estimation of zero-spacing error due to a phase shift of reflected light in measuring a magnetic head slider’s flying height by light interference,” Adv. Info. Storage Syst. 4, 371–379 (1992). The same paper was presented at the ASME Winter Annual Meeting, Atlanta, Ga., 1991.
  11. The calculations for Table 1 also appear in the paper “Interferometric measurement of disk/slider spacing: the effect of phase shift on reflection,” by C. Lacey, R. Shelor, A. Cormier, R. E. TalkeIEEE Trans. Magn. MAG-29, 3906–3910 (1993).
  12. M. Born, E. Wolf, Principles of Optics (Pergamon, New York) p. 40.
  13. Following Born and Wolf, we prefer to use the n + ik definition of the complex index, rather than the more common n - ik.
  14. P. de Groot, “Optical properties of alumina titanium carbide sliders used in rigid disk drives,” (submitted to Appl. Opt.).
  15. R. Pavlat, “Flying height measurement systems and slider absorption,” IDEMA Insight 7, 1 (1994).
  16. Y. Li, “Flying height measurement on Al2O3 film of a magnetic slider,” presented at the American Society of Mechanical Engineers Tribology Conference, paper 96-TRIB-61 (San Francisco, Calif., 13–17 October 1996).
  17. K. Lue, C. Lacey, F. E. Talke, “Measurement of flying height with carbon overcoated sliders,” IEEE Trans. Magn. 30, 4167–4169 (1994). [CrossRef]
  18. G. Sommargren, “Flying height and topography measuring interferometer,” U.S. patent5,218,424 (8June1993).
  19. Generally, it is not possible to calculate a film thickness as well as the optical constants from a single ellipsometric measurement; hence the need for three or more flying heights for proper n and k calibration. See, for example, R. M. A. Azzam, N. M. Bashara, Ellipsometry and Polarized Light (Elsevier, Amsterdam, 1987), p. 317.
  20. P. de Groot, “Birefringence in rapidly-rotating glass disks,” J. Opt. Soc. Am. A 15, 1202–1211 (1998). [CrossRef]
  21. P. de Groot, “Method and apparatus for measuring and compensating birefringence in rotating disks,” U.S. patent5,644,562 (1July1997).
  22. W. H. Press, S. A. Teukolsky, W. T. Vetterling, B. P. Flannery, Numerical Recipes in C, 2nd ed. (Cambridge U. Press, Cambridge, UK, 1992) p. 680.
  23. Not everyone agrees that interference phase information is essential for n and k. K. H. Womack and A. Butler have proposed to calculate the two parameters n and k using only the intensity reflectivity at normal incidence, together with off-site characterization of the material. Their paper, entitled “In-situ n & k phase compensation in an interferometric flying height tester,” is available from Phase Metrics Corporation, 10260 Sorrento Valley Road, San Diego, Calif. 92121.
  24. P. de Groot, “Homodyne interferometric receiver and calibration method having improved accuracy and functionality,” U.S. patent5,663,793 (2September1997).
  25. C. P. Brophy, “Effect of intensity error correlation on the computed phase of phase-shifting interferometry,” J. Opt. Soc. Am. A 7, 537–541 (1990). [CrossRef]
  26. Another way to express the uncertainty in the optical constants would be to calculate the ratios Δk/k and Δn/n. However, this would create the misleading impression that the uncertainty improves for larger values of n and k. It would also create the false impression that measurement of k on a dielectric has an undefined uncertainty because the k is zero.
  27. P. de Groot, L. Deck, J. Soobitsky, J. Biegen, “Optical flying-height testing of magnetic read-write heads,” in Lasers, Optics, and Vision for Productivity in Manufacturing I, C. Gorecki, ed., Proc. SPIE2782, 47–57 (1996).
  28. C. Lacey, C. Durán, K. Womack, R. Simmons, “Optical measurement of flying height,” in Proceedings of Future Dimensions in Storage Symposium (International Disk Drive Equipment and Materials Association, San Diego, 1997), pp. 81–88.
  29. C. A. Durán, “Error analysis of a multiwavelength dynamic flying height tester,” IEEE Trans. Magn. 32, 3720–3723 (1996). [CrossRef]
  30. R. B. Edwards, “Three-color laser interferometer,” IBM Technical Disclosure Bulletin 16, 595–596 (1973).
  31. T. Fukuzawa, T. Hisano, T. Morita, K. Ikarugi, “Method and apparatus for measuring the flying height of a magnetic head above a disk surface at three wavelengths,” U.S. patent5,502,565 (26March1996).
  32. G. Sommargren, “Distance measuring interferometer and method of use,” U.S. patent4,606,638 (19August1986).
  33. C. Lacey, C. Duran, “Full surface detection of flying height with in-situ n & k measurement,” IDEMA Insight, 9(6), 1, 9 (1996).
  34. P. de Groot, J. Biegen, L. Deck, R. Smythe, “Calibration standard for optical gap measuring tools,” U.S. patent5,724,134 (3March1998).
  35. A similar arrangement for establishing known gaps for calibration appears in U.S. patent5,220,408 to M. Mager, entitled “Method and apparatus for calibration of optical flying-height testers” (15June1993).
  36. Our technique does require an estimated value for the scattered light loss, in the form of the μ factor. However, the effect of an incorrect μ on the ZSE is small. It serves primarily to simplify comparison of our technique with traditional ellipsometry.

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