Feature-scale charging simulations during gate electrode overetching in high-density plasmas reveal that the thickness of the insulating mask plays a critical role in charging damage. When thinner masks are used, the electron irradiance of the conductive part of the sidewalls increases, causing the charging potentials of the polysilicon lines to decrease, thus reducing the probability for catastrophic tunneling currents through the underlying oxide. Simultaneously, changes in the charging potential distribution at the bottom SiO2 surface cause a significant perturbation in the local ion dynamics which, in turn, adversely affects notching. Notches are predicted to form everywhere in a line-and-space structure, even when the lines are electrically isolated. The results suggest that the trend toward thinner (hard) masks—to keep the aspect ratio low as device dimensions shrink—should reduce oxide failure but at the cost of more severe notching.

1.
K.
Hashimoto
,
Jpn. J. Appl. Phys.
32
,
6109
(
1993
);
K.
Hashimoto
,
Jpn. J. Appl. Phys.
33
,
6013
(
1994
).
2.
G. S.
Hwang
and
K. P.
Giapis
,
J. Vac. Sci. Technol. B
15
,
70
(
1997
).
3.
N.
Fujiwara
,
T.
Maruyama
, and
M.
Yoneda
,
Jpn. J. Appl. Phys.
34
,
2095
(
1995
);
N.
Fujiwara
,
T.
Maruyama
, and
M.
Yoneda
,
Jpn. J. Appl. Phys.
35
,
2450
(
1996
).
4.
T.
Nozawa
,
T.
Kinoshita
,
T.
Nishizuka
,
A.
Narai
,
T.
Inoue
, and
A.
Nakaue
,
Jpn. J. Appl. Phys.
34
,
2107
(
1995
).
5.
G. S.
Hwang
and
K. P.
Giapis
,
J. Appl. Phys.
82
,
566
(
1997
).
6.
G. S. Hwang and K. P. Giapis, J. Vac. Sci. Technol. B (in press).
7.
M. S.
Barnes
,
J. C.
Foster
, and
J. H.
Keller
,
IEEE Trans. Plasma Sci.
19
,
240
(
1991
).
8.
G. S.
Hwang
and
K. P.
Giapis
,
Appl. Phys. Lett.
70
,
2377
(
1997
).
9.
This conjecture is based on maintaining the substrate potential close to 0 V.
10.
G. S.
Hwang
,
C. M.
Anderson
,
M. J.
Gordon
,
T. A.
Moore
,
T. K.
Minton
, and
K. P.
Giapis
,
Phys. Rev. Lett.
77
,
3049
(
1996
).
11.
No overetching time is stated because it is impossible to calibrate the reactive ion flux without an etching experiment of a structure similar to the simulated one.
12.
When the mask is conductive, the steady-state potential of the lines becomes slightly negative, while that of the trench bottom remains large. The potential distribution along the trench bottom surface exhibits symmetric and equal peaks—with respect to the trench centerline—next to the sidewall feet, a situation reminiscent of the case of electrically connected poly-Si lines (see Ref. 2). Thus, symmetric notches will appear at both sidewalls of all but the outermost lines. The outer sidewall of the latter usually exhibits inward tapering but no notching because the potential of the bottom surface next to it cannot increase due to the lack of electron shadowing next to the open area.
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