X-Ray Diffraction Analysis of Strain and Mosaic Structure in (001) Oriented Homoepitaxial Diamond Films
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with a -1 mm spot size. Nitrogen (at atomic concentrations of 0 ppm, 950 ppm, or 1800 ppm) was added to the feed gas. The C(001) HPHT substrates (-3 mm x 3 mm) were polished off-axis -5.55+- 0.50 in the [100] direction prior to film deposition. The off-axis angle and orientation were measured with Laue diffraction. A Philips HR1 x-ray diffractometer was used to perform x-ray analysis on the homoepitaxial diamond films. The x-ray tube generator was operated at 40 kV and 40 mA and produced CuKa radiation at a wavelength (%)of 1.54056 A. The radiation was conditioned by a Bartels [8] 4-crystal monochromator to produce radiation with AO=12 arcsec divergence and AV/,=2.3xl0-5 wavelength spread. The spot size of the x-ray beam at the sample was -0.5 mm x 5 mm. X-ray analysis performed with the 4-crystal monochromator is generally referred to as high-resolution x-ray diffraction (HRXRD). The x-ray diffractometer had a U-shaped (BonseHart) [9] analyzer crystal in front of the detector to limit the acceptance angle to -14arcsec, which allowed separation of lattice parameter and misorientation contributions to diffraction peak broadening. The x-ray diffracts off of seven crystals, including the sample, and thus is referred to as seven crystal x-ray diffraction. Both omega/2theta (0o/20) and omega (0o) rocking curves were recorded. The terminology reflects the configuration geometry of the sample, detector, and the optical axis of the x-ray source. During recording of an (o/20 rocking curve (also referred to as an 03/20 scan), both the detector (20) and the sample rock through the Bragg angle (0), with the detector moving twice the angular velocity of the sample. During an coscan, only the sample rocks through 0. The Wo/20 rocking curve is sensitive to lattice plane spacing [10]. The angular separation of the film and substrate peaks, Aco, are used to calculate the lattice mismatch through Bragg's law. Strain calculations were relative to the substrate lattice parameter. The co rocking curve is sensitive to lattice plane tilt or mosaic structure [10,11]. Micro-Raman analysis was performed using the 514.5 nm line from an Ar' ion laser operating at a power of 100 mW. The objective lens had a magnification of 80x and the spot size at the sample was -2 pLm. Cross-sectional micro-Raman analysis was performed to separate film and substrate contributions. A cross-section was prepared by mechanical polishing. RESULTS Figure 1A shows the (004) cW/20 rocking curve from an as received HPHT substrate. The full width at half maximum (FWHM) of this diamond standard was 33 arcsec; slightly broader than the (004) co/20 rocking curve from a (001) silicon wafer (8 arcsec) [not shown]. The diamond standard rocking curve indicates a Ad(oo4/d(w4) of -6x10"5 (Ad(oowd(oo4 ) = range of (004) lattice plane spacing). This range of lattice parameters is not surprising due to the variation in nitrogen content for different growth sectors. Rocking curves from three homoepitaxial films on HPHT substrates are shown in Figures 1B, IC, and ID. The experimenta
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