Apparatus and method for in-situ chamber cleaning in a compound semiconductor etching system

Abstract

This invention consists of an apparatus and method of permitting automatic, in-situ cleaning of the process chamber and condensation trap of the vacuum pumping system used for etching Gallium Arsenide and other materials producing toxic and condensable etching by-products. This automated cleaning greatly reduces the danger of human exposure to the toxic materials and by-products of the etching. There are two key features. First, the process chamber and condensation trap are designed so that all components are vacuum-sealed to each other (or may be purged with inert gas) such that during wafer processing gas phase species from the process environment cannot condense in narrow spaces between components in the chamber. The surfaces of all parts that come in contact with, and may react to, enchant byproducts, process gases, or any cleaning liquid, are covered with nickel, or Teflon or other highly chemically inert coating. The second feature is that a liquid cleaning cold wall condensation trap is used to capture etching byproducts. The reactor and trap are cleaned separately or simultaneously by injecting water, with or without, liquid cleaner(s) into the process chamber through a set of injection holes. Said liquid cleaner may contain acidic, caustic or other reagents. The wet cleaning step dissolves or converts to soluble form any arsenic (or other toxic) compounds condensed in the process chamber or trap. In addition the flushing action of the liquids aids in the dislodging and removal of any insoluble or low soluble deposits. Liquid cleaning is typically followed with a heated air or nitrogen flow to evaporate any remaining liquid. Said cleaning process may have multiple steps. In a typical clean sequence the chamber and trap are flushed with water-based cleaning compounds that may be acidic or basic. This may be followed by a water-based rinse to rinse away all condensates or remnant compounds from the etching process. The next step may be a rinse with an alcohol or non-aqueous liquid with higher vapor pressure to scavenge or drive out remaining water. And finally, the system may be purged with a drying gas such as nitrogen to remove remnant traces of liquid. The result of such flushing is the virtually complete removal of traces of arsenic and its compounds from the system so as to greatly improve the safety of any ensuing manual chamber clean or replacement of parts. This cleaning process also maintains a more consistent process environment for process stability and reduces particulate that can affect yield.

Description

RELATED APPLICATION [0001] This application is based upon Provisional Application No. 60 / 472,279, filed May 20, 2003, the priority of which is claimed.BACKGROUND OF THE INVENTION [0002] The etching of many arsenic containing III-V compound semiconductors, including Gallium Arsenide, produces toxic reaction products such as Arsenic Chloride. These etch reaction products have modest vapor pressures at room temperature and may condense on the walls of the etching reactor and in the vacuum pumping system used to exhaust the etching chamber. This condensate material and materials formed by reaction of condensates with atmospheric gases or moisture are hazardous to the health of the worker who does periodic cleaning or maintenance of the reactor. Previous methods of cleaning reactors used for gallium arsenide etching used gas phase cleaning followed by manual cleaning. While in-situ gas phase cleaning does not expose workers to the chamber interior, manual cleaning does expose workers. Ma...

AI Technical Summary

Benefits of technology

[0004] The invention uses an automatic method of wet cleaning both the process chamber and the closely positioned cold trap with its associated plumbing. The invention also provides for the blowout and rapid drying time of the vacuum parts to so that total cleaning time is less then by conventional means.

[0005] This improved method and apparatus for the wet cleaning of etch systems having toxic residues, utilizes the physical and chemical cleaning properties of flowing water and water-based chemicals which also can wash away toxic and gritty residues, coupled with the properties of solvents to remove water and other contaminants. The invention provides for normally flat horizontal surfaces to be sloped in order to reduce liquid residue after cleaning, and also provides for liquid shields and appropriately designed O-ring seals to prevent cleaning liquids from entering cracks and other areas that would be difficult to dry.

[0006] To eliminate water (and other cleaning fluids) from leaking into the vacuum system, multiple valves are used. The valves isolate water pressure from a water drain, and the water source, as well as from leaking into the vacuum system. Multiple valves are used in series to isolate liquids from vacuum. Since no seal is perfect, an additional valve may be connected to the plumbing line that is located between the two series valves with its exhaust port pointed down so that it vents to the floor of the room (or to a catch tray). Thus, even with very leaky valve seals, no liquid can build up between the two series valves, and thus no liquid can enter the vacuum system through the valve that provides the vacuum seal. Any liquid that exits the plumbing via the valve placed between the two series valves can trigger an alarm to indicate that service is required.

[0007] To minimize the drying time of system parts after automatic wet cleaning, water-scavenging solvents (which may include alcohol) may be passed through the system, followed by hot gas (typically air) being blown through the system. Heating the chamber parts can also assist in reducing the time required for complete drying. The heating of the chamber parts also helps reduce the build up of condensates during the etching process. A modest chamber temperature of 50° to 80° C. is all that is required.

[0008] Accordingly, several objects and advantages of the invention are to provide for a cleaning method that is safe for personnel as well as faster than combined gas phase cleaning followed by manual cleaning. It is also an object of the invention to provide a better and faster method of etch chamber cleaning that greatly reduces human exposure to arsenic while avoiding the problems associated with virtual leaks when vacuum to liquid seals are required. Still further objects and advantages will become apparent from the study of the following description and accompanying drawings.

Problems solved by technology

The etching of many arsenic containing III-V compound semiconductors, including Gallium Arsenide, produces toxic reaction products such as Arsenic Chloride.

This condensate material and materials formed by reaction of condensates with atmospheric gases or moisture are hazardous to the health of the worker who does periodic cleaning or maintenance of the reactor.

While in-situ gas phase cleaning does not expose workers to the chamber interior, manual cleaning does expose workers.

Normally, gas-phase in-situ chamber cleans, which can be very slow and time consuming, still leave hazardous amounts of toxic arsenic compounds condensed in the process chamber and pumping system.

Due to this, manual cleaning of the chamber and pumping system for III-V etching systems is done at substantial expense (and some risk) by personnel using hazardous material apparatus.

In this case there will be a great deal more toxic material deposited on the chamber walls than during conventional etching.

In addition, there will tend to be large amounts of condensed toxic compounds in vacuum system components such as throttle valves and isolation valves.

This will necessitate much more frequent manual cleaning of the chamber and pumping system than is currently performed on such etching chambers—with a substantial increase in operating cost per wafer etched.

One alternative, sometimes used in some etching systems where condensation of reaction products in the process chamber is undesirable, is to heat the chamber walls and internal components.

Heating such large subsystems to this level is often not possible, and when it is possible, it tends to increase the downtime associated with manual chamber cleans.

Downtime is increased because it is difficult to design a process chamber and pumping system components that work reliably over extended periods at such temperatures.

One difficulty is the substantial thermal expansion of the metal chamber relative to the support structure and the interfacing wafer handling system.

Another is that many seals fail prematurely at elevated temperatures.

This elevated temperature also makes working on, or near, the system more difficult and / or more hazardous to all personal.

When these reactants condense in the pumps the pumps become very hard to keep in proper operating condition or require frequent and hazardous cleaning.

It is very difficult to get the efficiency needed in such a trap while maintaining high gas conductance at low operating pressures.

There is a tendency for condensation in the lines, and pump, to be unacceptably high.

Thus, even with very leaky valve seals, no liquid can build up between the two series valves, and thus no liquid can enter the vacuum system through the valve that provides the vacuum seal.

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