Page 101 - Sami Franssila Introduction to Microfabrication

80 Introduction to Microfabrication

(a) (b) (c) (d) (e)
Abrupt Interfacial layer Diffused Reacted Pitted
<Si>/<CoSi > Si/native oxide/Al SiO /Cu Si/Ti Si/Al
2
2
Figure 7.6 Possible interface structures: (a) abrupt; (b) interfacial layer; (c) diffused; (d) reacted and (e) pitted
Weight per cent silicon
10 20 30 40 50 60 70 80 90

Wt-% Si
0.5 1.0 1.5 2.0
700
600 577° 1500
(Al) 1.59
(1.65) ∼1430°
500 1400

400 1300
0.16 (0.17)
300 1200
Temperature (°C) 200 (Al) + Si 1100

1000
100
0 630 REF 31 900
0.5 1.0 1.5 610
At-%Si
800
590
577.2°
700 12.1 (12.5)
660° 570
5 10 15
At-% Si
600 577°
11.3 Si
(Al) (11.7)
500
400
0 10 20 30 40 50 60 70 80 90 100
Al Atomic per cent silicon Si
Figure 7.7 Aluminium/silicon phase diagram. Reproduced from Hansen, M. & K. Anderko (1958), by permission of
McGraw Hill

cobalt/silicon dioxide reaction is positive, and cobalt are encountered in epitaxy; but other methods, CVD,
does not reduce the oxide. This means that titanium PVD and electrochemical deposition, also produce
silicide and cobalt silicide formation reactions are very almost ideally sharp interfaces. Native oxides are almost
different from interfacial oxide point of view. universally encountered on interfaces (Figure 7.6(b));
Interface types also vary significantly. Abrupt inter- however, in many cases, those ca. 1 nm films do not
faces (Figure 7.6(a)) are not the only idealizations: they destroy the device functionality.