Oxygen Diffusion in Tantalum Oxide Metal-Oxide-Metal Capacitor Structures
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1E-02
oxidized
1E-05
Ta
-
I1E-08
E-8r TiN/Ti 80C
TaN/Ta
IE-11
30
IE-14 0
10
20
30
40
50 36
Voltage (V)
Figure 5. Leakage current measured Al/Ta20 5 barrier/metal capacitors (160 micron in area). Replacing TiN/Ti with TaN/Ta results in two orders of magnitude improvement inthe leakage current.
32
28
Binding Energy (WV)
24
Figure 6. Evolution of the photoemission of Ta(4f) from a Ta2O5/Wsample during insitu vacuum heating. The appearance of W inthe surface layer after high temperature treatment highlights the importance of metal-diffusion barrier.
By examining the free energies of formation of the various metal oxides, one would predict [12] that neither W nor Pt could reduce Ta 2Os because in either case the reduction/oxidation reaction is endothermic. The same energy considerations [12] indicate that Ti, Al, and Si could reduce Ta 2O5, although the thermodynamic values say nothing about the
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kinetic feasibility of the reactions. Our experiments show that Ti and Al do, in fact, reduce Ta 205 at low temperatures. To the limits of our experimental detection (_
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