Chemical vapor deposition system with a plasma chamber...

Details Chemical vapor deposition system with a plasma chamber... Chemical vapor deposition system with a plasma chamber...

2001-11-21

2003-04-29

Salimi, Ali R. (Department: 1648)

Cleaning and liquid contact with solids

Processes

Hollow work, internal surface treatment

C134S001100, C134S037000, C134S022180, C134S031000

Reissue Patent

active

RE038097

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of chemical vapor deposition systems, and more particularly, to apparatus and methods for cleaning the residue left by the process gas which has been injected into a plasma chamber of the system.
BACKGROUND OF THE INVENTION
Chemical vapor deposition (CVD) systems normally employ a chamber in which gaseous chemicals react. From these reactions, a substance is deposited on a wafer surface to form dielectric, conductor, and semiconductor film layers that constitute an integrated circuit, for example. In a chemical vapor deposition system, a process gas is injected into the plasma chamber in which a plasma is formed. Due to the ion bombardment within the plasma of the process gas, (SiH
4
(silane), for example) silicon will be deposited on a wafer which has been previously placed in the chamber. During this deposition step, the gas injection ports, also known as jet screws, typically clog with silicon-rich oxide residue formed by the combined SiH
4
(the process gas) and oxygen radicals flowing to the gas injection port. These oxygen radicals originate from the plasma chamber.
The residue coats the walls of the chamber, and also tends to clog the gas injection ports. The chamber, as well as the gas injection ports, needs to be cleaned periodically. This ensures that each wafer encounters the same environment so that the deposition process is repeatable. Since opening up the chamber (changing out the hardware) for cleaning is very labor intensive and costly, a method for removing the deposition from the chamber walls without opening the chamber itself has been previously developed. This “insitu” cleaning has been accomplished in the past using fluorine. The fluorine is injected into the chamber as NF
3
. Fluorine is known to etch silicon and silicon dioxide at high rates when it is accompanied by ion bombardment. Radio frequency (RF) power provides the energy for ion bombardment, with the NF
3
serving as the source of fluorine.
Typically, after a wafer is processed through deposition in the CVD system, the wafer is removed to a load lock. A cover wafer is then transferred to the chamber and placed on the chuck. The cover wafer is a standard silicon wafer that is coated with aluminum. It protects the chuck surface from the plasma cleaning and conditioning steps that follow.
The RF power is applied to the chamber and NF
3
is injected into the chamber. The walls will then be cleaned of oxide deposition. However, there may still be a significant amount of fluorine in the chamber and on the walls and free particles. For this reason, a pre-deposition conditioning step is often required. The conditioning step is essentially a deposition that getters the fluorine and tacks down particles onto the chamber walls. When this pre-deposition conditioning step is completed, the cover wafer is transported back to its cassette and the next wafer can then be processed.
In conventional systems for routing the gas to the chamber, injection ports are shared between the deposition process gas (SiH
4
) and the insitu cleaning gas (NF3). Such an arrangement is shown in prior art
FIG. 1
in which a portion of a process chamber is schematically depicted. The plasma chamber
10
injects oxygen at port
12
into the interior
14
of the plasma chamber. The oxygen radicals are formed within the plasma chamber
14
. The shared injection ports for the deposition process gas and the insitu clean gas are depicted as reference numeral
16
. During the deposition step, the gas injection ports (also known as “jet screws”) clog with silicon-rich oxide residue formed by the combined SiH
4
and the incoming oxygen radicals originating from the plasma chamber.
As stated earlier, the insitu cleaning gas is designed to chemically etch the SiO
2
(silicon dioxide) residue. However, high pressure caused by supersonic gas flows in front of the jet screws causes regions of scarce fluorine radicals that reduce fluorine induced etching of the SiO
2
.
FIG. 2
a schematic depiction of a detail of a jet screw. NF
3
gas is injected into the chamber
14
through the jet screw
16
. Within the jet screw, there is SiO
2
clogging, schematically depicted at point
18
at the jet screw
16
. The high pressure region
20
of scarce fluorine radicals caused by the supersonic gas flows in front of the jet screws
16
reduces the fluorine induced etching of the SiO
2
in this area, and in particular, prevents the jet screws
16
from being unclogged of the SiO
2
residue. All of the other chamber surfaces are typically cleaned except for the jet screw ports.
Due to the SiO
2
clogging of the jet screw ports, the jet screws are normally replaced after approximately 300 wafers have been processed. This process involves shutting down the chamber at high expense and loss of productivity. Another problem of the prior art arrangement is that the SiH
4
and NF
3
gases, if combined, are highly combustible so that routing the gases through the same injection ports can be relatively dangerous.
SUMMARY OF THE INVENTION
There is a need for a gas routing system and method for routing gas in a plasma chamber so as to unclog the jet screws through which deposition gas is injected into the chamber.
These and other needs are met by the present invention which provides an arrangement for insitu cleaning of a chamber in which process gas is injected into the chamber through gas injection ports. The arrangement comprises a chamber in which a process is performed, and at least a first gas injection port in the chamber through which the process gas is injectable into the chamber. At least a second gas injection port is provided in the chamber through which insitu cleaning gas is injectable into the chamber. The cleaning gas injected into the chamber also contacts the first gas injection port to clean the first gas injection port. The first and second gas injection ports are separate ports.
By re-routing of the cleaning gas through a separate, second gas injection port, the pressures within the jet screws are equalized with the pressure of the chamber. This allows higher fluorine dissociation and SiO
2
etching.
Another advantage of the present invention is the injection of the SiH
4
and NF3 gases through completely separate manifolds, thus providing a clear safety advantage.
A further advantage of the present invention is the reduction in the amount of maintenance required of the chamber. For example, using the gas routing system of the present invention, the chamber does not need to be maintained for approximately 3,000 wafers. This is a decided advantage over the prior art in which the jet screws needed to be replaced after only 300 wafers.
Another advantage of the present invention is that the insitu clean time is decreased due to more efficient cleaning of the jet screws. This provides a throughput advantage of, for example, two wafers per hour. Finally, another advantage is that plasma to surface arcing is completely eliminated in the jet screw area.
Another embodiment of the present invention satisfies the earlier stated needs by providing a method of routing gas to a plasma chamber comprising the steps of: injecting process gas into the plasma chamber through a first gas injection port, and injecting chamber gas into the plasma chamber through a second gas injection port. The second gas injection port is separate from the first gas injection port. The cleaning gas cleans the plasma chamber and the first gas injection port.
Another method of the present invention provides for unclogging jet screw ports in the chamber. The jet screw ports inject process gas into the chamber. This method comprises the steps of terminating injection of the process gas into the chamber and injecting cleaning gas into the chamber through openings separate from the jet screw ports to equalize pressure of the cleaning gas within the jet screw ports with pressure of the cleaning gas within the chamber.
In another embodiment of the present invention, an electron cyclotron resonance chemical vapor deposition sys

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