Filtering technique for CVD chamber process gases

Details Filtering technique for CVD chamber process gases Filtering technique for CVD chamber process gases

1999-05-20

2001-12-11

Gulakowski, Randy (Department: 1746)

Cleaning and liquid contact with solids

Processes

Hollow work, internal surface treatment

C156S345420, C438S905000

Reexamination Certificate

active

06328043

ABSTRACT:

This application relies for priority upon Korean Patent Application No. 98-18166, filed on May 20, 1998, and Korean Patent Application No. 98-19872, filed on May 29, 1998, the contents of both of which are herein incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor. More particularly, the present invention relates to a method and apparatus for removing particulate contamination in a tungsten silicide deposition process.
2. Discussion of the Related Art
In providing electrical connections to silicon for microelectronic applications, it is frequently desired to provide a conductive interface between a metallization layer, such as aluminum (Al), and a portion of a silicon substrate or layer to be electrically connected to the aluminum, in order to prevent the direct contact of the aluminum with the silicon. The reason for this is that if aluminum were to be directly deposited onto the silicon, various problems may arise.
One significant problem in depositing aluminum directly on silicon is that the aluminum acts as a P-type dopant, and any migration of aluminum atoms into a silicon region would dope the silicon region with P-type impurities. This is especially significant when the aluminum contacts an N-type silicon region, where the migration of P-type aluminum atoms into the silicon region would result in an undesired rectifying contact.
One way to overcome the problems mentioned above is to form one or more interface layers over the silicon before the deposition of an aluminum metallization layer. This type of process is generally described in U.S. Pat. No. 3,777,364 to Schinella et al., although numerous other patents describe similar processes. In such a process, a refractory metal, such as tungsten, molybdenum, palladium, platinum, or tantalum, is deposited over and reacts with an exposed silicon (or polysilicon) substrate or layer to form a silicide layer. Once this silicidation process is completed, top portion of the deposited refractory metal that has not reacted with the silicon, may then be removed. Aluminum is then deposited over the silicide layer.
The resulting silicide layer formed between the aluminum and silicon acts as a barrier to the aluminum atoms, preventing migration of the aluminum into the silicon. The silicide layer also provides a low resistivity contact between the aluminum and the silicon. In addition, this type of process slightly reduces the step height of the resulting device.
A problem with the above method of forming a silicide layer is that, when tungsten silicide is used, for example, as the interface layer between aluminum and silicon, and a chemical vapor deposition (CVD) process employing tungsten hexafluoride(WF
6
) as a reactant gas is used, the high temperatures involved in the CVD process can cause the hot CVD chamber walls to react with the WF
6
gas. This results in a lowering of the deposition rate of the tungsten onto the surface of the wafer.
To avoid these problems, a cold-wall radiantly-heated chemical vapor deposition (CVD) system is preferably used to deposit the refractory metal. In such a system, each wafer is heated by, for example, a broad band light source. As a result, the deposition of the refractory metal onto the wafer to form a barrier layer between the silicon substrate and an aluminum layer will not be limited by any reaction of process gases (e.g., WF
6
) with high-temperature chamber walls.
A representative CVD system is shown in FIG.
1
. The CVD system includes an Ar-
1
gas line
12
, an NF
3
cleaning gas line
18
, an Ar-
2
carrier gas line
20
, a WF
6
reaction gas line
24
, an Ar-
3
carrier gas line
26
, an SiH
4
source gas line
32
, and an Ar-
4
gas line
36
. The gas lines are engaged with a gas tank (not shown) containing each gas. The gas lines have valves
38
,
40
,
42
,
46
,
50
,
102
,
104
,
106
and
108
, and a mass flow controller (MFC)
44
, activated by a controller (not shown), to control the flow and flow rate of the various gases.
The gas lines
12
,
18
,
20
,
24
,
26
, and
32
also include a plurality of filters
48
, which filter gas passing through the gas lines
12
,
18
,
20
,
24
,
26
,
28
, and
32
. A holding apparatus (not shown), e.g., a chuck, is provided to load the wafers to be processed and is set up in the chamber
10
. An apparatus for controlling the pressure, such as a pump
52
and valve
54
, is also provided to control the pressure within the chamber
10
. Through the SiH
4
source gas line
32
, SiH
4
silicon source gas is supplied to the chamber
10
.
A different kind of silicon source gas, such as dichlorosilane (SiH
2
Cl
2
or DCS), may also be used in accordance with this process. Thus a gas line
28
for DCS may be formed parallel to the source gas line
32
. Such a gas line
28
will also have valves
42
,
46
, and
50
, as well as an MFC
44
.
The Ar-
1
, Ar-
2
, Ar-
3
, and Ar-
4
gas lines
12
,
36
,
20
, and
26
, each provide argon (Ar) gas into the chamber
10
. The Ar-
1
and Ar-
2
gas lines
12
and
20
supply argon gas into the upper part of the chamber
10
; the Ar-
3
gas line
26
supplies argon gas into the middle part of the chamber
10
; and the Ar-
4
gas line
36
supplies argon gas into the lower part of the chamber
10
.
An argon carrier gas is supplied to the chamber
10
with the SiH
4
source gas and the DCS gas through the Ar-
3
carrier gas line
26
, which is connected to the SiH
4
gas line
32
. The Ar-
4
gas line
36
diverges from the Ar-
3
carrier gas line
26
to provide a second source of argon gas to the chamber
10
. The Ar-
4
gas line
36
is constructed to be divided from the Ar-
3
carrier gas line
26
prior to when the Ar-
3
gas line
26
connects with the SiH
4
source gas line
32
and the DCS gas line
28
.
The WF
6
reacfion gas line
24
, the Ar-
2
carrier gas line
20
, and the NF
3
cleaning gas line
18
are all coupled to the Ar-
1
carrier gas line
12
. An argon (Ar) carrier gas is supplied to the chamber
10
through the Ar-
2
carrier gas line
20
, and the Ar-
1
carrier gas line
12
, which is coupled to upper part of the chamber
10
. The NF
3
cleaning gas is supplied to the chamber
10
through gas lines
18
and
12
.
To ensure the purity of a deposition film, the chamber
10
is conventionally cleaned by forming plasma using NF
3
after the deposition process. Despite the fact that the chamber
10
is cleaned before the deposition process, a contamination problem on deposifion film of the wafer by unknown particulate contaminant continuously happens during deposition process. As a result, residual gas in the chamber is analyzed by a residual gas analyzer (not shown) in order to find any source of particulate contaminant. By making use of the residual gas analyzer, the pressure of each compound of the residual gas is measured.
FIG. 2
is a graph detecting the pressure of gas in the chamber
10
by making use of a residual gas analyzer. The fluctuation of the pressure of SiH
4
silicon source gas is shown in a regular pattern in which the pressure of the SiH
4
rises during the deposition step and remains at a constant level (e.g., 1×10
−4
Torr) during the cleaning step. However, the pressure of NF
3
experiences an irregular pattern in some regions such as during the initial deposition step. Especially sudden ascents of the pressure of NF
3
(shown in the circles “A” and “B” in
FIG. 2
) in the initial deposition step means that some NF
3
gas remains in the gas line connected with the chamber
10
after the cleaning step.
The NF
3
gas is used to clean the chamber
10
by forming the plasma and may remain in the chamber
10
and gas line
12
rather than being completely eliminated from the chamber. In this case, during as initial deposition step, residual NF
3
gas in the gas line
12
will be inserted in the chamber with other gas and will react with SiH
4
to produce SiF
x
, which acts as a particulate contaminant during the tungsten silicide deposition process.
It

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