ADE Phaseshift技术方向介绍

OPTI 696C Practical Optics SeminarTerm paperTaeyoung ChoiADE Phaseshift is a company that specializes in metrology, inspection and process control. ADE Phaseshift was merged with KLA-Tencor in 2006 and now became an ADE division of KLA-Tencor. The application fields are silicon wafer manufacturing, semiconductor manufacturing, magnetic data storage, and optics/precision-engineered surfaces. The consumers of their instruments are semiconductor equipment manufacturers, wafer manufacturers, data storage companies like Seagate and Hoya, precision-optics companies, or tribology companies like Alcoa, GE, Apple. The competitors are Veeco, Zygo, Taylor Hobson, Fogale, SNU precision and so forth.The presentation and tour were based on some of their best-selling metrology instruments for small systems and large systems. The technology developed for small optical systems is used for producing large optics metrology instruments.1. Optical profiler (MicroXAM)MicroXAM is a 3D non-contact surface profiler for surface analysis and roughness. An Michelson-type optical profilometer uses two low magnification (for 2.5X, 5X) objective lenses. One is focused on the reference and the other focused on the sample. A Mirau interferometer is used with high magnification (>10X) objective lenses. The advantage of the Mirau type is that it is a common path after the beamsplitter, and the disadvantage is that the objective lens should have a long working distance to have a beamsplitter. [1] A beamsplitter and a reference plate are placed inside the microscope objective as shown in Fig. 1. There are two operation modes: phase shifting interferometry (PSI) and vertical step interferometry (VSI). In general, PSI has accuracy, but limited dynamic range. [2] In phase-shifting interferometers, the height difference between two adjacent data points must be less than λ/4, because of π-phase ambiguities. VSI overcomes this phase ambiguity problem by using multiple wavelengths or preferably white light and sensingthe coherence peak during vertical scan. Therefore, VSI provides wide dynamic range with reduced vertical resolution.In MicroXAM, the PSI mode uses a narrow bandpass-filtered colored light, has the maximum height of about 200nm, and has a vertical resolution of 0.01nm. On the other hand, the VSI mode uses a white light and has the max. vertical scanning range of about 2mm. The vertical resolution of VSI is 1nm, and the step size is around 10um. The lateral resolution is about 1um, but it depends on numerical aperture (NA) of the objective lens used.Fig. 1 Mirau interferometer used for high magnification objective lenses. A beam splitter and a reference are placed inside the microscope objective.2. MiniFiz Laser interferometer (MiniFiz )A MiniFiz is a Fizeau interferometer for testing flat, concave or convex surfaces and wavefront transmission by phase shifting, as shown in Fig. 2. Phase shift for small optics is achieved with a PZT. For large optics, however, they use wavelength shifting instead of a PZT. Wavelength shifting is realized using an external cavity laser diode with λ=635nm and P=1mW. A grating in the laser is rotated by a PZT to tune the wavelength. The amount of tuning required to introduce a certain amount of optical path length difference (OPD) is calculated by dividing the wavelength, λ, by the OPD. That is, OPD λ∆λ= An external cavity diode laser (ECDL) used for phase shifting in MiniFiz is furtherstudied. Figures 2(a) and (b) schematically show external cavity diode lasers (ECDLs) inLittrow and Littman configurations, which are the most common types of ECDLs that use a simple diffraction grating as a tunable filter. [3,4] In both types of ECDLs, the front facet of the laser diode is antireflection(AR)-coated with one or more dielectric layers in order to suppress the internal cavity modes. In the Littrow configuration ECDL, the emitted light from the AR-coated front facet is collimated and directed to the reflection grating. The grating is aligned to return its first order diffraction beam to the laser cavity. The zeroth order beam is used as output. So, the wavelength of the output beam is determined by the total cavity length, which consists of the cavity of the original laser chip and the external cavity between the laser front facet and the grating surface. Rotating the grating about an axis changes not only the external cavity length, but also the incident angle of the beam on the grating, which shifts the external cavity modes and the peak wavelength of the filter. Then, the output wavelength is forced to occur where one of the external cavity modes matches the filter peak. One drawback of the Littrow configuration is that the rotation of the grating results in an angular change of the output beam or a parallel shift when a beam correction mirror is placed on the output side of the grating, as shown in Fig. 2 (b). The Littman configuration ECDL is similar to the Littrow ECDL, except for the fact that it has a larger incidence angle onto the grating and tunes the wavelength by rotating the mirror with the grating fixed. So, the output beam is in a fixed direction, regardless of mirror rotation for tuning.MiniFiz can measure surface flatness, homogeneity, index variation. In addition, it can measure a plane parallel plate that has the pseudo-reflection from the back surface when using the wavelength-shifting technique. The reflected light from the second surface will be filtered out in an algorithm. Another unique feature is saturation insensitivity in CCD pixels. With CCD pixels saturated, we can still get accurate measurements of a surface. An algorithm in the analysis procedure solves the pixel saturation problem.Reference[1] B. Bhushan, J. C. Wyant, and C. L. Koliopoulos, "Measurement of surface topography of magnetic tapes by Mirau interferometry," Appl. Opt. 24, 1489- (1985) [2] J. C. Wyant, OPTI513R classnote on “White light interferometry,”/jc wyant/pdf/Meeting_papers/WhiteLight Interferometry.pdf [2] Zorabedian, P., “Tunable external cavity semiconductor lasers,” in Tunable Lasers Handbook, F. J. Duarte, Ed. (Academic Press, San Diego, 1995).[3] Sacher Lasertechnik Group: /ExternalCavity.php。