Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
2000-10-10
2003-04-08
Utech, Benjamin L. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S711000, C438S714000, C438S715000, C438S719000, C438S720000
Reexamination Certificate
active
06544896
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a fabrication process for manufacturing semiconductor devices. More particularly, the present invention relates to a method and etchant useful for etching TiSi
x
.
2. Background
Titanium silicide (TiSi
x
) is a material likely to be used with increasing frequency in semiconductor devices. In particular, TiSi
x
is a candidate for use as a gate material in memory devices such as DRAMs and SRAMs, because it favorably has a lower resistivity than materials presently used as gate materials in such devices, such as tungsten silicide (WSi
x
) and polysilicon. This lower resistivity allows faster devices, i.e., devices having a smaller RC delay, to be fabricated. Moreover, it is becoming possible to fabricate memory devices having dimensions smaller than about 0.25 microns. At this small scale, the resistance of the conventional gate electrode composed of polysilicon and tungsten silicide (WSi
x
) will be high enough to cause significant delay in signal transmission. Substituting TiSi
x
for the WSi
x
is expected to advantageously mitigate such delay.
Many desirable applications require the ability to anisotropically etch TiSi
x
. It is known to anisotropically etch TiSi
x
using Cl
2
or HBr in an inductively coupled plasma (ICP) etcher. See Soda et al., “Correlation between Etching Characteristics of Titanium Silicide and its Crystal Structure under Cl
2
or HBr Plasma Etching,”
Dry Process Symposium
, 33, 1997, (“Soda”) which is hereby incorporated by reference in its entirety. However, it has been observed that such etching may leave a residue due to the presence of Si nodules in the TiSi
x
. See Soda. This residue is very difficult to remove, and may interfere with device performance. In addition, the Si nodules may act as “micro-masks” that shield underlying TiSi
x
from the etching process, which can lead to roughness in the profile of the etched surface. Also, many process conditions may lead to undercutting, due to isotropic etching of the sidewall.
SUMMARY OF THE INVENTION
A method of etching TiSi
x
is provided. A patterned mask is provided on top of a layer of TiSi
x
. The TiSi
x
is exposed, through the patterned mask, to a plasma etchant. The plasma etchant comprises (i) at least one fluorine containing gas, such as SF
6
, NF
3
, C
x
F
y
(where x ranges from about 1 to about 10), and compatible mixtures of such gases; and (ii) a gas selected from the group consisting of HBr, Cl
2
, and combinations thereof.
Conventional methods of etching TiSi
x
use Cl
2
or HBr as the plasma etchant. However, these methods can lead to undesirable residues, due to the presence of silicon nodules in the present TiSi
x
. While not intending to be limited to any explanation as to why the present invention works, it is believed that the conventional Cl
2
or HBr plasma chemistry has a selectivity for TiSi
x
, relative to Si nodules, significantly greater than 1, ie., the plasma etches TiSi
x
at a faster rate than Si nodules that are often present in TiSi
x
. Since the Si nodules are not etched as quickly as the TiSi
x
, they act as “micro-masks,” by shielding underlying TiSi
x
from the etching process. The Si nodules may also act as micro-masks for other layers, such as a layer of polysilicon underlying the TiSi
x
. Note that the Si nodules are not polysilicon, and are etched at rates significantly different from polysilicon. The difference in the etch rate of the Si nodules and TiSi
x
is more pronounced when Cl
2
is used as the etchant than when HBr is used. As a result, the residue and micro-masking effect are more severe when Cl
2
is used as the etchant. The present invention overcomes the residue problem by adding a fluorine containing gas to the plasma etchant, which is then able to effectively etch the Si nodules so that the undesirable residue is not formed.
REFERENCES:
patent: 4659426 (1987-04-01), Fuller et al.
patent: 4680086 (1987-07-01), Thomas et al.
patent: 4778563 (1988-10-01), Stone
patent: 5014217 (1991-05-01), Savage
patent: 5118387 (1992-06-01), Kadomura
patent: 5143866 (1992-09-01), Matsutani
patent: 5160407 (1992-11-01), Latchford et al.
patent: 5342476 (1994-08-01), Cain
patent: 5429070 (1995-07-01), Campbell et al.
patent: 5591301 (1997-01-01), Grewal
patent: 5605601 (1997-02-01), Kawasaki
patent: 5698072 (1997-12-01), Fukuda
patent: 5738756 (1998-04-01), Liu
patent: 5792710 (1998-08-01), Yoshida et al.
patent: 5843226 (1998-12-01), Zhao et al.
patent: 5854137 (1998-12-01), Kuo
patent: 5958801 (1999-09-01), Langley
patent: 6103631 (2000-08-01), Soda et al.
patent: 0516043 (1992-12-01), None
E. Soda et al., “Correlation between Etching Characteristics of Titanium Silicide and its Crystal Structure under Cl2or HBr Plasma Etching”,Dry Process Symposium(1997), pp. 33-38.
Q. Xu et al., “Reactive ion etching of TiSi2
+polysilicon polycide structure for very large scale integrated application”,J. Vac. Sci. Technol.B, vol. 8, No. 5 (1990), pp. 1058-1061.
PCT Search Report for PCT/US 00/05730, mailed Aug. 22, 2000.
Kusuki Takakazu
Qian Xueyu
Xu Songlin
Applied Materials Inc.
Bach Joseph
Church Shirley L.
Tran Binh X
Utech Benjamin L.
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