Reduction of metal oxide in a dual frequency etch chamber

Details Reduction of metal oxide in a dual frequency etch chamber Reduction of metal oxide in a dual frequency etch chamber

1998-05-21

2003-04-15

Alanko, Anita (Department: 1746)

Chemistry: electrical and wave energy

Processes and products

Processes of treating materials by wave energy

C216S013000, C216S078000, C148S565000

Reexamination Certificate

active

06547934

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to etch chambers. More particularly, the present invention relates to a process for cleaning copper oxides from a substrate using an etch chamber.
2. Background of the Related Art
As integrated circuit (IC) dimensions become increasingly smaller, the interface contact resistance between interconnect layers becomes significantly important. A particular contact resistance problem involves metal oxides that form when the substrate is exposed to air during the fabrication process. In the past, sputter etching has been utilized successfully to remove many metal oxides. However, as device dimensions and interconnect features shrink, sputter etching has become inadequate for removing metal oxides, particularly copper oxides, within the smaller interconnect features.
In order to fabricate a complete IC, typically several substrate processing systems are used, with each system performing a particular step or series of steps in the overall fabrication process. The substrates are transferred between the systems at ambient conditions. The ambient environment is maintained very clean to prevent contamination of the substrates as they are transferred between systems. The substrates may even be transferred in completely enclosed cassettes in order to further prevent contamination thereof. A problem, however, is that oxygen in the ambient air form oxides on the surfaces of the substrates, and in the case of copper deposits, copper oxides form on the surface of the deposited copper film. The surface oxide creates an interface having a high contact resistance with a subsequently deposited metal film and degrades the device performance because of the excess interface resistance. Thus, the surface oxides need to be removed or etched from the surfaces of the substrates, in a pre-processing cleaning or pre-clean step, before the substrates are subjected to subsequent processing, in order to assure a very low interface resistance with a subsequently deposited layer.
A pre-clean chamber cleans the surface of the substrate by removing the undesired layer of oxides.
FIG. 1
is a simplified cross sectional view of a pre-clean chamber. Generally, the pre-clean chamber
10
has a substrate support member
12
disposed in a chamber enclosure
14
under a quartz dome
16
. The substrate support member
12
typically includes a central pedestal plate
18
disposed within a recess
20
on a quartz insulator plate
22
. The upper surface of the central pedestal plate
18
typically extends above the upper surface of the quartz insulator plate
22
. A gap
24
, typically between about 5 mils and 15 mils, is formed between a bottom surface of the substrate
26
and the top surface of the quartz insulator plate
22
. During processing, the substrate
26
is placed on the central pedestal plate
18
and located thereon by positioning pin
32
. The peripheral portion of the substrate
26
extends over the quartz insulator plate
22
and overhangs the upper edge of the quartz insulator plate
22
. A beveled portion
28
of the quartz insulator plate
22
is disposed below this overhanging peripheral portion of the substrate
26
, and a lower annular flat surface
30
extends from the lower outer edge of the beveled portion
28
. The insulator plate
22
and the dome
16
may comprise other dielectric materials, such as aluminum oxide and silicon nitride, and the insulator plate
22
and the dome
16
are typically parts of a process kit that system operators periodically replace during routine maintenance. It is desirable that a process kit has a long useful lifetime so that the downtime of the system will be a small percentage of the overall processing time.
The process for cleaning the substrate
26
in the pre-clean chamber
10
generally involves a sputter-etching process using the substrate
26
as the sputtering target. Generally, a cleaning gas such as argon is flowed through the chamber
10
, and a plasma is struck in the chamber with a bias power applied to the substrate
26
in the range of about 150 W to about 450 W. Additionally, a RF power is applied to the chamber through coils disposed outside of the chamber. A DC bias of about −100 V to about −600 V, with a bias power of about 100 W to about 300 W, accelerates the ions toward the substrate
26
. The pressure in the pre-clean chamber
10
during sputtering is typically between about 0.4 mTorr and about 0.5 mTorr. Under these conditions, the pre-clean chamber
10
can typically remove about 150 Å to about 450 Å of the oxidized material at an etch rate of about 300 Å/min to about 600 Å/min. Typically, about 400 Å or less of oxidized material is removed from the surface of the substrates.
The primary purpose of the etch cleaning is to remove the oxidized materials that form on the surface of the substrate typically when the substrate was subjected to ambient air conditions while being transported between processing chambers of a processing system or from one processing system to another processing system. For cleaning of copper oxides that form on the surface of a deposited copper film on a silicon substrate, the substrate is processed in the pre-clean chamber
10
as described above. The etched material (i.e., copper oxides) sputters off the substrate surface and forms a film on the process kit. As the film forms on the process kit surfaces, its density may change, resulting in stress on the film. This stress, along with differences in the coefficients of expansion of the materials in the film and the process kit surfaces, can result in delamination, or flaking, of the film from the surface of the process kit and contamination of the substrate being processed. Because these particles can seriously damage the substrates and/or cause defects to form on the substrates, the process kit is typically replaced after a certain number of substrates have been cleaned in the system. However, replacement of the process kit is time consuming and reduces throughput of the system. Additionally, as long as a film is formed on the surfaces of the process kit, there is a risk of flakes of material falling onto a substrate and damaging the devices formed on the substrate.
Furthermore, where the copper oxide is formed on the bottom surface of an interconnect feature, such as a contact or a via, some of the sputtered copper oxide from the bottom of the interconnect feature deposits onto the side wall of the interconnect feature. The copper from the copper oxide may diffuse through the dielectric material that forms the side wall of the interconnect feature and degrade the device performance. Also, when a subsequent layer or a barrier layer, such as tantalum (Ta) or tantalum nitride (TaN), is deposited over the surfaces within the interconnect feature where the copper oxide has deposited, the film quality of the subsequent layer is compromised or degraded by the copper oxide that sputtered onto the side walls of the interconnect feature.
Therefore, there exists a need for an apparatus and a method of removing metal oxides, particularly copper oxides, from a substrate surface that prevents sputtering of copper oxides from the bottom of an interconnect feature onto the side walls of an interconnect feature. Furthermore, there is a need to eliminate sputtering of the copper oxides onto the process kit that may eventually flake off and cause defects on the substrate.
SUMMARY OF THE INVENTION
The invention generally provides an apparatus and a method of removing metal oxides, particularly copper oxides and aluminum oxides, from a substrate surface. Primarily, the invention eliminates sputtering of copper oxide from the bottom of an interconnect feature onto the side walls of an interconnect feature, thereby preventing diffusion of the copper atom through the dielectric material and degradation of the device. The invention also eliminates sputtering of the copper oxides onto the chamber side walls that may eventually flake off and cause defects

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