Page 326 - A Practical Guide from Design Planning to Manufacturing

296 Chapter Nine

B

A
No mask required
Silicide
Silicide Silicide
Poly
O
O
O
O
iO
S S S S Si S S S S Si S S S S Si iO 2 2 2 2 2 2 2 2 2
O
iO
O
O
O
O
O
O
O
O
O
O
O
O
S S SiiO 2
P+ N+
P-well N-well
D eposit re f ractory meta l
Deposit refractory metal
Silicide Silicide
O
O
O
O
O
O
O
O
O
O
iO
S S S S SiiO
iO
O
O
O
O
iO
S S S S Si S S S S Si
S S S S SiiO S S S S Si S S S S Si iO
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
N+ N+ 2 2 2 2 2 2 2 2 2 2 P+ P+ N+ N+ 2 2 2 2 2 2 2 2 2 2 P+ P+
P-well N-well P-well N-well
Figure 9-28 Silicide formation.
After contacts have been formed the first level of metal wires is created.
Copper is the metal of choice for interconnects but has the disadvantage
of diffusing very easily through SiO 2 and silicon. Copper atoms will con-
taminate the silicon and cause excessive leakage currents in the transis-
tors unless carefully contained. To avoid this, copper wires are formed
using a damascene process. Damascene refers to decorative designs (in the
B
B A
A
Poly
B
O
O
O
O
O
O
O
O
O
O
S S S S SiO
S S S S Si S S S S Si O 2 2 2 2 2 2 2 2 2 2 2
O
O
O
O
O
O
P+ N+
Etch P-well N-well
Tungsten
PR PR
o
o
P P Poooly
o
P P P
o
P P P Po o oly l l l y y y y y y y y y y P P P P P Pooly l l l y y y y y y y y y y P P P P P Poooly l l l y y y y y y y y y y P P P P P P P P P Poolly ly l l y y y y y y y y y y
o
o
o
oly
o
ol
o
P P P Po
o
P P P Po
o
oly
o
o
o
O
O
O
O
O
O
O
O
O
O
O
O
O
O
S S S S Si S S S S Si
S S S S Si S S S S Si
S S S S SiiO 2 2 2 2 2 2 2 2 2 2 2 S S S S SiiOO 2 2 2 2 2 2 2 2 2 2 2
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
iO
iO
iO
iO
A A
N+ N+ P+ P+ N+ N+ P+ P+
P-well N-well P-well N-well
Figure 9-29 Contacts.