Growth of Mon X by Reactive Laser ablation
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Mat. Res. Soc. Symp. Proc. Vol. 388 0 1995 Materials Research Society
angle of 45" to the surface. A laser fluence of 6 J/cm 2 was used. The ambient gas (N2 with 10% H 2) input pressure was regulated to a dynamic equilibrium (-10 sccm) by a solenoid-activated leak valve controlled by a capacitance manometer with the chamber under gated or throttled pumping. The substrates were washed with ethanol, attached to the substrate heater with silver paste and maintained -6 cm from the target. The film compositions and thicknesses were determined by Rutherford Backscattering Spectroscopy (RBS) with 6 MeV He 2 +. X-Ray diffraction (XRD) patterns were collected using a rotating anode source and a conventional 0-20 geometry, and indexed using a least squares fit of the data. Rocking curve full width at half maximum of o scans, reported as F (FWHM) for the (200) peak (for the cubic films) or the (006) peak (for the hexagonal films), was measured by fixing 20 at the peak maximum and scanning through 0. Temperature-dependent resistance (R(T)) measurements were performed by a standard ac fourpoint probe measurement. RESULTS AND DISCUSSION A series of MoNx films were grown simultaneously on (100) MgO and amorphous fused silica under varied growth conditions. The N2 (+10% H 2 ) reactive gas pressure was varied from 40 to 120 mTorr and substrate temperatures were either 500 or 600 *C. The structures of the deposited films were determined by XRD, the electrical properties were measured by R(T), and the compositions (N/Mo ratios) were found by RBS. The results are summarized in Table I.
XRD Results The crystal structure adopted by the MoNx films was dependent on the substrate identity, deposition pressure and deposition temperature. Deposition on amorphous substrates led to the growth of films with poor crystallinity while growth on single crystal MgO promoted the formation of highly oriented material. This is illustrated in Figure 2, where XRD patterns are shown of two MoNx films grown simultaneously at a pressure of 60 mTorr and substrate temperature of 600 °C on substrates of (a) fused silica and (b) (100) MgO. The XRD pattern of the film grown on fused silica was indexed as a poorly crystalline cubic material with broad weak reflections from (111) and (200) planes consistent with a lattice parameter of a-4.19 A. The film grown on MgO was indexed as a highly oriented (1-F(FWHM)=0. 10 *) hexagonal material with only the (001) reflections present in the XRD pattern, producing a calculated c lattice parameter equal to 6.00 A. The effect of substrate temperature on the structure of the deposited film was demonstrated by growing a film at the same pressure (60 mTorr) but at a lower substrate temperature (500 "C). Table I. Summary of Mo] Substrate Crystalline Symmetry
Growth and Characterization Results Lattice F (FWHM) Tc (onset) Parameter(s) (A) c_O) (K) a--4.24 0.14 4.8
P (N2)
Tsub
(mTorr) 40
(K) 600
MgQ
Cub
40
600
SiO 2
Amor
NM
60
600
MQO
Hex
60
600
MQ)
Hex
60
600
SiO 2
60
500
120
600
N/Mo Ratio 0.65
NM
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