Local Cross-sectional Profiling of Multilayer Thin Films with an Atomic Force Microscope for Layer Thickness Determinati
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Local cross-sectional profiling of multilayer thin films with an atomic force microscope for layer thickness determination J. R. LaGraff a) and J. M. Murduck Superconducting Electronics Organization, TRW Space and Defense, One Space Park Drive, Redondo Beach, California 90278 (Received 3 January 1997; accepted 4 April 1997)
A new essentially nondestructive cross-sectional method is described for measuring the individual thicknesses of multilayer YBa2 Cu3 O7 (YBCO) and SrTiO3 (STO) thin films using off-axis ion milling and the atomic force microscope (AFM). Since the ion-milling is done during routine patterning of a thin-film device and the AFM requires only a small area for imaging, no additional sample preparation is required. This is a significant improvement over traditional cross-sectional techniques which often require lengthy and destructive sample preparation. Also, there is no a priori reason that this technique would not be amenable to other multilayer thin-film systems. Proper calibration of thin-film deposition techniques and subsequent interpretation of the electrical properties of a patterned device require accurately knowing the thickness of the constituent layers, preferably by an easy-to-use, nondestructive method. A number of characterization techniques are already in use to measure and track thin-film thicknesses, including optical methods such as ellipsometry and interferometry,1 and crosssectional methods in combination with scanning electron microscopy (SEM), transmission electronic microscopy (TEM), or profilometry.2 In addition to the individual strengths of these methods, each has its own particular set of weaknesses, broadly including, resolution limits, materials specific techniques, and often complicated and lengthy sample preparation procedures. For example, cross-sectional techniques —one of the most direct measures of film thickness—are typically destructive, requiring the fabrication of “test” or “witness” pieces which are not reusable for device fabrication. Recently, the atomic force microscope (AFM) has been applied to the characterization of thin-film devices, primarily as a high resolution profilometer for measuring edge angles, step heights, surface microstructure and roughness,3 and in measuring lateral variations in dopant profiles.4 In addition, the AFM and the scanning tunneling microscope (STM) have been used to resolve individual layers of multilayer thin films,5–8 including FeySi,5 mixed lead-thallium oxide superlattices,6 and GaAs.7,8 However, these AFM and STM cross-sectional profiling techniques5–8 are destructive, involving some
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Electronic mail: [email protected] J. Mater. Res., Vol. 12, No. 8, Aug 1997
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combination of cutting, cleaving, polishing, or chemical etching of an unpatterned multilayer thin film. While sample preparation is often simpler than thinning specimens for TEM analysis, it still destroys significant portions of a thin film. In this communi
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