Systems and methods for remote plasma clean

Details Systems and methods for remote plasma clean Systems and methods for remote plasma clean

2001-06-29

2004-12-28

Markoff, Alexander (Department: 1746)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

With plasma generation means remote from processing chamber

C156S345240, C134S001100, C438S905000

Reexamination Certificate

active

06835278

ABSTRACT:

BACKGROUND
1. Field of the Invention
The present invention generally relates to cleaning semiconductor processing chambers, and more particularly, to systems and methods for cleaning a semiconductor processing chamber using a remote plasma source.
2. Description of the Related Art
Conventional techniques for removing undesired deposits, films, and residues from the surfaces of hardware located inside a processing chamber typically involve so-called direct plasma clean methods. In such methods, cleaning gases are injected and plasmas are generated directly within the processing chamber. Plasma-activated species then react with the unwanted deposits to form a volatile by-product that is pumped out of the processing chamber. These cleaning methods are desirable in that they reduce the potential for contamination by removing deposits that may shed particles on the substrate being processed. Furthermore, a more stable processing environment may be realized by removing accumulated materials that may interfere with the control of processing conditions. Direct plasma clean methods, however, have the disadvantage in that plasma generated ions continuously bombard internal surfaces of the processing chamber and can cause damage to associated hardware, such as susceptors, heater blocks, lift pins, gas lines, viewports, showerheads, thermal shields, susceptors, and temperature measuring probes such as optical pyrometers and thermocouples. In addition, direct plasma clean methods may not completely clean peripheral areas of the processing chamber or areas that are difficult to access such as underneath susceptors, places around robotic parts such as lift pins, or within gas distribution showerheads.
In order to overcome these disadvantages, remote plasma clean methods have been developed to avoid many of the problems encountered with direct plasma cleaning. In a Remote Plasma Clean (RPC) process, a plasma is ignited from gases fed into a chamber that is located remotely from the processing chamber. Plasma-activated species from the RPC chamber then flow through a delivery line towards the processing chamber. Because the plasma is generated remotely and in a separate compartment from the processing chamber, there is less opportunity for ion bombardment and plasma radiation to damage hardware within the processing chamber. Once delivered to the processing chamber, the activated species can then react with the unwanted deposits and residues, and the volatile by-products can be removed from the processing chamber.
Although remote plasma cleaning methods alleviate many of the problems encountered with direct plasma cleaning, there are still many challenges to be addressed. One such challenge is the phenomenon of recombination, which occurs when activated species generated in the RPC chamber recombine while flowing to the processing chamber. The activated species may comprise, for example, neutral fluorine radicals, which can recombine into a non-reactive form. Of course, not all the radicals recombine on their way to the processing chamber, but any recombination that does occur lowers the overall efficiency of the remote cleaning process, and requires an increased flow of feed gases to the RPC chamber to make up for the loss of efficiency. This recombination of activated species is undesirable because the cleaning gas is expensive, and disposing of the chemically inactive recombined radicals can be environmentally unfriendly.
One cause of excessive recombination occurs when the gas delivery system exhibits a low gas conductance. A low gas conductance results in higher pressures in the delivery system, which increases the likelihood of a collision between two (rarely more) activated species to form a non-reactive molecule. A low conductance delivery system can also substantially increase the operating pressure within the RPC chamber. This pressure is often referred to as backpressure from the point of view of the RPC chamber, since this is the pressure against which the remote plasma source is forced to deliver activated species. High backpressure in the RPC chamber requires high RF plasma power to generate sufficient plasma-activated species for effective clean rates. This high power consumption results in low cleaning efficiencies and affects the overall cost of performing the clean.
Another problem associated with RPC processes occurs when gases present during substrate processing travel from the processing chamber to the RPC chamber through the delivery system in a reverse direction. This diffusion of process gases into the RPC chamber is undesirable due to the potential for the RPC chamber to become contaminated. Moreover, an open RPC delivery system presents a larger deposition volume (represented by the volume of the delivery line and RPC chamber). This increase in volume may influence and interfere with processing conditions in the processing chamber (e.g., chamber pressure and gas flows) during substrate processing.
Other problems typically encountered with remote plasma cleaning operations involve the difficulty in cleaning various regions of the processing chamber. For example, the plasma-activated species may be unable to reach areas underneath the susceptor, places around robotic parts such as the lift pins used to raise and lower the substrate during substrate transport, and cavities within the showerhead used to supply and distribute process gases to the processing chamber. Furthermore, chambers adjacent to the processing module, such as substrate transfer chambers, vacuum loadlocks, and the isolation doors between them are typically not addressed by conventional RPC processes. Further problems occur when plasma-activated species from the RPC chamber react with materials that comprise the deposition gas delivery system (materials such as stainless steel), thereby causing some of those materials to flow into the processing chamber and contaminate the substrate being processed. Still further problems involve determining the point at which the cleaning process is complete.
Therefore, in light of the deficiencies with conventional approaches, there is a need for systems and methods that can efficiently and effectively clean semiconductor processing chambers using improved remote plasma cleaning techniques.
SUMMARY OF THE INVENTION
Aspects of the present invention provide a Remote Plasma Cleaning (RPC) system for cleaning the interior of a separate processing chamber or reactor. The RPC system may include a RPC chamber coupled to a gas supply and power supply for igniting and sustaining a cleaning plasma within the RPC chamber. The RPC plasma may be generated from a mixture of gases including, but not limited to, NF
3
and Ar. A high conductance delivery system couples the RPC chamber to a processing chamber and enables activated species to flow from the RPC chamber to the processing chamber. The activated species are preferably introduced into the processing chamber via a dedicated inlet port, such as an opening formed in a wall of the processing chamber. The inlet port substantially increases the conductance of the RPC delivery system compared to delivering the RPC gas through a conventional showerhead, reducing the backpressure experienced by the RPC chamber. The RPC chamber may also be arranged close to and below the processing chamber to reduce the length (and further increase the conductance) of the RPC delivery system, while allowing unobstructed access to a top portion of the processing chamber. These aspects of the present invention enable the conductance of the delivery system to be greater than about 40 liters per second when measured with a process chamber pressure greater than or equal to 1 Torr, and a RPC feed gas flow rate of about 2,000 sccm. These aspects also allow the power supplied to the RPC chamber to be maintained at a level less than about three kilowatts (3 kW).
Other aspects of the present invention incorporate an isolation valve in the delivery system for selectively isolating the RPC chamber from the processing chamber. For example, the isolation valve may

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