Characterization in Silicon Processing

NMOS

device subthreshold leakage has been used to infer the presence of sur-

face

charge along the

sidewall.

56

'

58

Leakage along oxide

sidewalls

was 10-lOOx

higher

than

a LOCOS standard, whereas leakage along nitride

sidewalls

was 6-8

orders of magnitude higher.

58

Preclean Quality

The presence of the patterned mask complicates the precleaning process for

selec-

tive

epitaxial growth. First, formation of the window openings by plasma etch

processes can damage the silicon substrate or leave etch residues on the surface;

sacrificial

oxidation or HCl etch may be required to remove damage or resi-

dues.

59

'

60

Second, in situ precleaning of oxide maske ...