Metal Organic Chemical Vapor Deposition of Co-, Mn-, Co-Zr and Mn-Zr Oxide Thin Films
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EXPERIMENT Co(C 5H5 )2 and Mn(C 5F6 HO 2)2(THF) 2 has been obtained by following procedure well developed in our institute [6]. The MOCVD system was a normal hot walls apparatus and the growth parameters were adjusted as reported in the table I. Table L Growth conditionfor Co-, Mn-, Zr-oxides.
Material Source temperature Pressure N2 carrier flux 0 2 -H20 flux Growth time H2 0 consumption Substrates
Co oxide 60 0 C 19.4 Torr 8 scc/min 25 scc/min 4 hr 1.83 g Polished stainless steel, Si (100), glass
ZrO 2-Co oxide Mn oxide 85 0 C 115 °C 5 Torr 0.6 Torr 8 scc/min 8 scc/min 25 scc/min 25 scc/min 1.5 hr 1 hr 2.12 g 1.10 g Aluminum, Si (100) glass I II
ZrO 2-Mn oxide 110 OC 0.75 Torr 8 scc/min 25 scc/min 40 min 0.62 g Si (100)
69 Mat. Res. Soc. Symp. Proc. Vol. 606 0 2000 Materials Research Society
RESULTS Deposition of Co-oxide thin films Co(C5H 5 ) 2 has been preferred as precursor to CO- based volatile compounds in view of its appreciable volatility [4,5] and absence of toxicity. It can be easily prepared and purified by sublimation. Our deposition experiments have been carried in the 450-550 'C temperature range. The best results have been obtained at 475 'C. It must be noted that only at a pressure higher than 19 Torr an oxide deposit was obtained, while at lower pressure the precursor was collected unchanged in a cooled trap after the reaction chamber. Moreover by using only fill) dry 02 as a reactant gas the deposits
were inhomogeneous; their quality im-
,
proved substantially by using a mixture of 0 2-H 20 vapor instead of pure 02. The deposits resulted nanocrystalline
(l22)
and were characterized unequivocally as
22) 311)
, ""()
Fig. 1. XRD pattern of Co034 deposited at 475 'C on glass.
of CoO pre4 with no evidence sent as shown by XRD analysis [Fig. 1]. The substrates influenced both the crysand the tallographic orientation dimension of the crystallites [23 nm on stainless steel; 50 nm on silicon (100) and 63 nm on glass]; see table II. CO3 0
Table IT XRD for Co30 4 film on different substrate.
Crystall.
I (%)
I (%)
I (%)
Planes (111) (220) (311) (222) (400) (422) (511) (440)
Stainless Steel 30,57 47.60 100.00 15.55 12.06 8.38 21.64 23.56
Si (100) 17.06 32.71 100.00 10.10 14.15 7.24 21.51 25.16
Glass 100.00 38.54 27.87 53.97 0.68 4.41 18.67 17.13
The XPS spectra [Fig. 2] show the presence of only carbon, cobalt and oxygen in the film surface, but after a 5 min. sputter cleaning the C atomic percentage is reduced from about 30% to below the XPS detection limit. This proves that carbon arises only by atmospheric contamination and is not due to residuals of undecomposed precursor incorporated in the oxide matrix. Hence, this confirms that the Co(C 5H5)2 has a clean decomposition pattern in presence of oxygen and moisture. The Co 2p surface peak shows a shape and BE position similar for all the cobalt oxide films [Fig. 3]. The BE (780.1-780.3 eV) values are close to those already reported
70
Z
(a)
COLMM
Cis Co3p S Co3s
(b) .
I
200
0
......................... I
400
600
I
I
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