Interferometric measuring microscopy applied to miniature machines, structures, and surface features John Roth, Eric Felkel and Peter de Groot Zygo Corporation, Middlefield, CT 06455 INTRODUCTION - THE NEED FOR 3D SURFACE ANALYSIS MEMS are complex microstructures such as data storage read-write heads, accelerometers, ink jet printer heads, sensors and micro-mirror arrays. Typically, measuring microscopes control and monitor MEMS fabrication, including the silicon micro-machining process. Metrology tools measure a wide variety of devices at various stages of device fabrication, including wafer, die, and packaged-level, and require flexibility and automation to meet the varied needs of R&D and production [1]. The large diversity of devices, materials, and processes, and the wide range of surface parameters create unique challenges for MEMS metrology tools. The physical dimensions and geometries of MEMS encompass a large range, from tens of millimeters down to the angstrom level. Ideally, surface characterization yields quantitative information over a variable field-of-view covering the x, y and z dimensions. Additional procedures and controls characterize mechanical parameters such as deformations. For the past decade, optical profilers based on scanning white light interferometry (SWLI) have enabled leading edge development and commercial success of advanced MEMS devices. We review the special requirements for MEMS metrology, the general principles of SWLI microscopy, and show several examples of expanded capabilities including integrated lateral metrology, long working distance objectives, and closed- loop deflection measurement. SCANNING WHITE LIGHT INTERFEROMETRIC MICROSCOPY A natural candidate for non-destructive 3D surface structure analysis of a MEMS device is an interference microscope, which provides surface height detail with sub-nm resolution. The instrument of choice is the scanning white light interferometer or SWLI microscope [2]. SWLI, also known as coherence scanning or vertical scanning interferometry, is fundamentally a multiple-wavelength technique, relying on a spectrally broadband source to remove the interference fringe order ambiguity characteristic of the previous generation of monochromatic interferometers. In a typical application (Figure 1), a PZT or similar mechanical transducer scans an interference objective towards or away from the object surface, gathering data by electronic camera during the scan. The data are then transformed by coherence and phase analysis into a surface profile. The scan direction orthogonal to the part surface can be several mm in length, accommodating tall step heights and disconnected regions characteristic of MEMS devices. SWLI has the interesting and important property that it has the sub-nm resolution of conventional interferometers on polished surfaces [3], but is nonetheless capable of handling rough surface textures that generate complex speckle patterns that traditionally were considered inaccessible