Combined Room Temperature Photoluminescence and High Resolution X-Ray Diffraction Mapping of Semiconductor Wafers
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incorporated a room temperature PL spectrometer into our desk-side X-ray diffractometer [3]. This paper describes the characteristics of the instrument and presents exemplary data. X-RAY DIFFRACTION DESIGN In response to the requirement for a rapid, routine, high resolution double axis X-ray diffraction facility capable of being used in a clean-room, some years ago, Bede Scientific developed a desk-top double axis diffractometer suitable for 3" crystals, incorporating a miniature, air-cooled X-ray generator and fixed beam conditioning reference crystal. This instrument, the QC1 diffractometer, permitted the very rapid measurement of lattice mismatch as a function of position across the wafer with a minimum of operator adjustment and with minimal specimen contamination. The success of this instrument (later developed and marketed as the Philips PW1881) and the industry demand for area mapping over large wafers, led us to develop a new instrument, the QC2, suitable for complete area mapping of rocking curves over an industrystandard 150 mm dia. wafer [3]. With the more recent incorporation of a moving slit-collimated detector, the QC2a instrument is capable of measuring both symmetric and asymmetric diffraction rocking curves and performing low resolution reciprocal space maps in a quasi-triple axis mode. This latter capability has proved particularly useful for relatively imperfect materials such as those of the I1-VI compounds. The design criteria were: 555 Mat. Res. Soc. Symp. Proc. Vol. 406 © 1996 Materials Research Society
a) b) c) d) e) f)
a minimum of adjustments required of the operator, basic rocking curve precision of one arc second with 260 range, specimen repositioning over an angular range of 10 degrees in a time of less than a minute, rapid x-y positioning over all of a 150 mm diameter wafer, tilt adjustment for alignment of specimen with reference crystal in high resolution studies, rotation of specimen through 3600 without moving the point of measurement, for automated alignment, g) rotation of the detector over a 900 range, h) no adhesives to be applied to the specimen and the instrument to be clean-room compatible, i) no external services required except a 13A single-phase electrical supply. The requirements for the X-ray diffraction performance of the combined X-ray and PL instrument were identical to that of the QC2a. Since the mechanical precision and tolerances involved in achieving this were considered to be stricter than those required for the PL measurements, we opted to adapt the optical spectrometer to retain the X-ray instrument in almost its original form. PHOTOLUMINESCENCE DESIGN CHARACTERISTICS Room temperature PL emission spectra [1,4] are broad and the resolution requirements for the spectrometer are not particularly stringent and a resolution of about I nm suffices. This permitted the options of either a mechanically scanned, wavelength dispersive device or a Fourier transform spectrometer [4]. We opted for the former, both because this is common in other PL systems and because it r
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