Principal Residual Strains as a function of Depth for Sputter Deposited Mo Thin Films
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substrates. The sputtering power was 308 watts (-83 A/minute deposition rate) and the chamber was pumped to a base pressure of 5x10- 6 to 7x10-6 Torr. The chamber was then back-filled with Ar and maintained at a pressure of -10 mTorr. The samples were mounted face-down 5 inches above the sputter source in a horizontal carousel which rotated at 20 rpm. The target was presputtered onto the shutter for at least I minute to prevent oxides or contaminants from being sputtered on to the wafers. The GIXS experiments were conducted under standard conditions (3 GeV and 60 mA at fill) on the eight-pole focused wiggler station BL 7-2 at SSRL. A Si (111) double-crystal monochromator was used to select the incident x-ray wavelength of 1.24 A (10 keV) from the continuous spectrum. The horizontal and vertical divergence of the beam on BL 7-2 is 3 mrad and 0.2 mrad, respectively. Slits 1 mm x 1 mm were used for the incoming beam and 1 mrad Soller slits were used for the diffracted beam to limit vertical divergence. The diffracted beam was detected with a scintillation counter. The samples were mounted on an automated Huiber 5020 four-circle goniometer and a beam-line computer was dedicated to control the goniometer motions, the shutter, and the photon counting. The experiments were conducted in the "dose" mode by
putting a scintillation counter in the path of the incident beam because the current in the synchrotron ring decreased linearly with time. Two different scattering geometries were used to collect the data: symmetric and highly asymmetric GIXS, as illustrated in Figure 1.8 Note that the strains obtained from symmetric GIXS will be referred to as in-plane strains and the strains obtained from highly asymmetric GIXS will be referred to as out-of-plane strains. For each sample, the {110), {200}, {211), {310}, {222), {321}, and {400) diffraction peaks were collected in the symmetric GIXS geometry and the {110), {200), and {211) peaks were collected in the asymmetric GIXS geometry at four penetration depths from the free surface. The penetration depths were varied by changing the angle of the incoming radiation near the critical angle for total external reflection. 5 The depths for the -500 A film include 140 A, 220 A, 440 A, and 500 A; the penetration depths for the -1000 A film include 220 A, 530 A, 750 A, and 1000 A. The upper limit for the error in the penetration depths was ±100 A, except very near the critical angle, where the uncertainty was
±300 A.
Q
S20B
(b)
(a)
Figure 1. Schematics of (a) symmetric GIXS geometry and (b) highly asymmetric GIXS geometry. The incident radiation is denoted as ko, the diffracted radiation as k, and the scattering vector as Q. In symmetric GIXS the scattering planes are nearly perpendicular to the sample surface, and in highly asymmetric GIXS they are inclined.
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RESULTS AND DISCUSSION The diffraction data was fit with a Voigt or Gaussian function to determine the location of each peak, 20, which was then used to determine the interplanar spacings for each {hkl} family of planes,
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