Ion Beam Sputter Deposition of Refractory Metal Oxides
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heating of the substrate. The energetic ions hit almost exclusively the target. In contrast to RF sputtering no heating due to electron bombardment can occur. In the present work ion beams of a C0 2 -fed Kaufman-type gun were applied to the corresponding metal targets for oxide deposition. The resulting films were investigated for their optical properties inregard to optical coating applications. EXPERIMENTAL DETAILS Ion beam sputter deposition was carried out in a stainless steel vacuum chamber which was diffusion-pumped through aliquid nitrogen cooled baffle (base pressure 1.10-6 Torr). The system employs two Kaufinan-type ion guns (Veeco), a 3fold target holder and a rotatable watercooled sample stage. The substrate attached to it can either be turned towards the etch gun for sputter cleaning or towards the target which is in this arrangement beamed by the deposition gun. CO 2 was admitted to the chamber through the gun just in operation and stabilized to a pressure of 1.10 4 Torr by mass flow controlling. 2"-wafers of (100) silicon and (100)-InP were used as substrates for ion beam deposition of oxides. The corresponding metallic sputter targets Hf (purity 2N2), Nb (2N8), Ta (3N5), and Zr (2N2) were fixed at an angle of 450 relative to the ion beam. The substrate was arranged parallel to the beam in reflecting position to the target and could not be hit by primary ions. Deposition took place at 529 Mat. Res. Soc. Symp. Proc. Vol. 354 01995 Materials Research Society
a beam voltage of UB = 800 Volt and a current density ofjB = 1 mA/cm 2 throughout our investigations. To monitor the gas composition a residual gas analyser (RGA, Inficon, Quadrex 100) has been directly attached to the deposition chamber. The composition of the films was deducted from EPMA-measurements (JOEL, JXA8800M). XRD-analysis was performed with an 0-0-diffractometer (STOE). Refractive indices and extinction constants were determined by spectroscopic ellipsometry (S2000 UV-IR, Rudolph Research). THE C0 2 -PLASMA
Ionizing a molecular gas ina plasma results in an extensive fragmentation. Fig. 1 shows mass spectra of CO 2 obtained from the RGA at a chamber pressure of 1-10-4 Torr. Without plasma discharge the fragmentation pattern is typical for single electron impact processes which take place in the RGA itself (Fig. Ia). E 0 14
l
Beside a strong signal representing CO 2 + (mass 44) also CO+ (28), 0+ (16), and C (12)
are found with decreasing intensity. Starting the ion gun changes the current levels of the individual ion fragments. In addition a strong 02+ (32)-signal emerges (Fig. lb). As the gas the gun exceeds the value in the pressure chamber in by an order of magnitude a reaction 2 CO 2 -* 2 CO + 02 takes place and provides molecular oxygen.
Fig. 1 Mass spectrum of CO2 a) discharge off (upper curve) b) discharge on (lower curve)
SPUTTERING WITH CO2
The ion gun fed with CO 2 provides a total of 5 different ion species for sputtering, namely C0 2+, CO+, 02+, 0+, and C+. Most of the molecular ions undergo collisional dissociation and
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