Batch process for forming metal plugs in a dielectric layer...

Details Batch process for forming metal plugs in a dielectric layer... Batch process for forming metal plugs in a dielectric layer...

1998-09-30

2001-06-05

Tsai, Jey (Department: 2812)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S672000, C438S675000, C438S908000

Reexamination Certificate

active

06242345

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to the processing of semiconductor wafers and, more particularly, to a batch process for forming metal plugs in dielectric layers of semiconductor wafers.
The prior art process, of which the present invention is an improvement, is described in “A 3-Level, 0.35 &mgr;m interconnection process using an innovative, high pressure aluminum plug technology” (Z. Shterenfeld-Lavie, I. Rabinovich, J. Levy, A. Haim, C. Dobson, K. Buchanan, P. Rich and D. J. Thomas, Twelfth International VLSI Multilevel Interconnection Conference, Jun. 27-29, 1995, Session II Paper C), which is incorporated by reference for all purposes as if fully set forth herein. Briefly, holes for contacts and vias are etched in a dielectric layer on a semiconductor wafer; a layer of soft metal, typically aluminum, at least as thick as the holes are wide is deposited above the holes, typically by sputtering; and external isostatic pressure is applied to the wafer to force the metal into the holes. According to the prior art process, all of these steps are performed in vacuum chamber cluster machines such as the one shown schematically in FIG.
1
.
The particular configuration of a vacuum chamber cluster machine
10
shown in
FIG. 1
is used for the deposition and external pressure steps. Cluster machine
10
includes a central hexagonal dealer
12
to which are attached three vacuum chambers
14
,
14
′ and
14
″, a high pressure chamber
16
, and two vacuum cassette handlers
18
. The machine is controlled by a control system
20
. Vacuum cassettes holding semiconductor wafers are introduced to cluster machine
10
and removed from cluster machine
10
via vacuum cassette handlers
18
, and moved counterclockwise from chamber to chamber for processing by dealer
12
. In vacuum chamber
14
, the wafer is preheated to 450° C. to outgas it, and a soft sputter etch precleaning is performed to clean the surface of the dielectric layer. In vacuum chamber
14
′, a 200 Å layer of titanium and a 500 Å layer of titanium nitride are deposited. In vacuum chamber
14
″, the aluminum layer is deposited. In high pressure chamber
16
, the wafer is heated to about 430° C. and an inert gas such as argon, under a pressure of 700 atmospheres, forces the aluminum into the holes previously etched in the dielectric layer below. Finally, the wafer is returned to vacuum chamber
14
′ and a 450 Å layer of titanium nitride is deposited as an anti-reflective coating.
This prior art process suffers from certain inefficiencies associated with the need to operate under both vacuum and high pressure conditions within the same machine. The cluster machine of
FIG. 1
processes one wafer at a time, and most of the time is spent raising and lowering the pressure of chamber
16
, not actually processing the wafer. In addition, the design and construction of cluster machine
10
is significantly more complex than the design and construction of cluster machines that do not mix vacuum chambers and high pressure chambers, reflecting the special requirements associated with safely cycling between vacuum and high pressure every few minutes.
There is thus a widely recognized need for, and it would be highly advantageous to have, a method, of forming metal plugs in dielectric layers of semiconductor wafers by external pressure, that is more efficient and safer than the presently known methods.
SUMMARY OF THE INVENTION
According to the present invention there is provided an improved process for forming metal plugs in a dielectric layer of at least one semiconductor wafer, at least one hole being etched in the dielectric layer, a layer of the metal being deposited over the at least one hole, and external pressure being applied to the layer of metal, the etching and the deposition being effected in a vacuum chamber cluster machine, the improvement consisting of the step of: removing the at least one wafer from the cluster machine, prior to applying the external pressure.
According to the present invention there is provided an improved process for forming metal plugs in the dielectric layers of a plurality of semiconductor wafers, at least one hole being etched in each of the dielectric layers, a layer of the metal being deposited over the at least one hole, and external pressure being applied to the layer of metal, the improvement comprising the steps of: providing a high pressure chamber; and placing the plurality of wafers inside the high pressure chamber the application of external pressure being effected within the high pressure chamber.
Surprisingly, it has been found that the application of pressure to the wafer, to force the metal into the dielectric layer, may be performed successfully after the deposition of the titanium nitride anti-reflective coating. According to the present invention, the step of applying isostatic pressure to the wafer is performed, not in a vacuum chamber cluster machine such as cluster machine
10
, but in a separate high pressure chamber. After the deposition of the aluminum layer in vacuum chamber
14
″, a layer of titanium nitride, having a thickness between about 200 Å and about 400 Å, is deposited above the aluminum layer in vacuum chamber
14
′. This layer of titanium nitride serves as the anti-reflective coating, and also serves to protect the aluminum layer from oxidation when the wafer is removed from the cluster machine. The wafer is removed from the cluster machine after the deposition of the aluminum layer and placed in the high pressure chamber. An inert gas under high pressure is pumped into the high pressure chamber long enough to force the aluminum into the holes in the underlying dielectric layer. The high pressure is released, and the wafer is removed from the chamber.
The wafer now may be returned to the same cluster machine, or to a different cluster machine, for further processing under vacuum. Because the aluminum layer has already been covered with titanium nitride before the application of high pressure, however, the wafer need not be returned to a vacuum chamber at this point, but may be subjected immediately to further conventional processing steps, such as photolithography, that are performed at atmospheric pressure.
One high pressure chamber serves several cluster machines, processing several (from 6 to 100) wafers at a time, so that the pressure is cycled up and down for several wafers simultaneously instead of separately for each wafer. It is in this sense that the present invention is a batch process.


REFERENCES:
patent: 4951601 (1990-08-01), Maydan et al.
patent: 5019234 (1991-05-01), Harper
A 3-Leve, 0.35 um interconnection process using an innovative, high pressure aluminum plug technology, Shterenfeld-Lavie, etc., VMIC Conference, pp. 31-36, Jun. 27-29, 1995.*
“A 3-Level, 0.35 um interconnection process using an innovative, high pressure aluminum plug technology”, Shterenfeld-Lavie, etc., VMIC Conference, Jun. 27-29, 1995, pp.31-36.

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