Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
2001-05-02
2004-09-14
Hassanzadeh, Parviz (Department: 1763)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C438S905000, C156S345290
Reexamination Certificate
active
06790258
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to traps for collecting and removing condensable aluminum chloride vapor from a gas stream to control the build-up of aluminum chloride in vacuum pump lines, valves, and other components downstream from aluminum etching chambers, and more particularly to an improved aluminum chloride trap containing a disposable element for cooling and condensing condensable aluminum chloride vapor byproducts from an aluminum etch system and retaining the condensed aluminum chloride solids within the disposable element, wherein the disposable element can be easily and quickly removed for the safe and rapid removal and disposal of the condensed aluminum chloride solids.
2. Description of the Prior Art
In a typical aluminum etching process for producing components for semiconductor devices, a silicon wafer or other substrate having a film of aluminum on its top surface is positioned in a reaction chamber, and the chamber is evacuated to a vacuum of about 10 millitorr via a turbo pump and a mechanical pump which are connected to a reaction chamber via a foreline. A photoresist having a particular pattern is placed on the aluminum surface to protect part of the aluminum film. The exposed part of the aluminum film that is not protected by the photoresist is then etched by employing a reactive, chlorine-containing gas such as chlorine (Cl
2
) or boron trichloride (BCl
3
). Typically, the etching reaction is plasma-enhanced, where the reaction between the chlorine-containing gas and the aluminum film is enhanced by applying rf power to the reaction chamber to create a plasma comprising the atomic constituents of the reactive gas in high energy states in the chamber. The generation of the plasma also causes the reaction chamber to heat up, typically to a temperature of 100 to 150° C. or in some cases, 150-200° C. The plasma-assisted reaction between the aluminum film and the chlorine-containing reaction gas etches aluminum from the exposed areas of the aluminum film, resulting in the formation of condensable aluminum chloride vapor (AlCl
3
) byproducts. The reaction chamber effluent, which contains the condensable aluminum chloride vapor in addition to excess chlorine-containing reaction gas, is then removed from the reaction chamber by an applied vacuum from a vacuum pump. An exhaust line leading from the vacuum pump then directs the effluent to a scrubber, where the condensable aluminum chloride vapor and any excess chlorinated reaction gases are destroyed. A wet scrubber is often employed to treat the effluent with water to remove the condensable aluminum chloride vapor and excess chlorinated reaction gas from the effluent. Alternatively, a dry scrubber may be employed to destroy excess chlorine-containing reaction gases from the effluent, however, the dry scrubber is not able to destroy the condensable aluminum chloride vapor byproduct.
The condensable aluminum chloride vapor byproduct in the conventional aluminum etching systems described above cause problems downstream from the reaction chamber, because they condense, solidify, and deposit upon contact with cool surfaces, such as the cooler interior surfaces of the vacuum forelines and exhaust lines that are used to convey the effluent gas away from the reaction chambers, as well as in other components of the vacuum conduit system of the etching system. Such buildup of solid aluminum chloride downstream from the etching chamber can partially or even entirely clog the pipes, thus reducing vacuum conductance, and can cause piping, pumps, scrubbers and other equipment used in the etching system to be functionally impaired or inoperative and in need of frequent maintenance. Solid aluminum chloride buildup can also flake apart and fall off the piping surfaces and migrate back into the reaction process chamber to become a source of contamination in the semiconductor device manufacturing process.
Typically, the vacuum in the foreline of an aluminum etching system is approximately 500 millitorr, and consequently it is necessary to heat the forelines to a temperature of about 70° C. in order to keep condensable aluminum chloride vapor in the vapor phase so that the condensable aluminum chloride vapor can be removed from the chamber and the foreline by the applied vacuum. However, the pressure in the exhaust line between the pump and the scrubber is typically 760 torr, and therefore it is necessary to heat the exhaust lines to even higher temperatures, typically around 105° C., to keep the condensable aluminum chloride vapor in the vapor phase as the effluent flows through the exhaust lines. If either the foreline, the exhaust line, or both are not maintained at the proper temperature, the condensable aluminum chloride vapor will cool, condense, and solidify, and the condensed aluminum chloride solids will build up along the interior surfaces of the vacuum conduit system, resulting in the diminished function or clogging of the vacuum source.
In order to prevent condensation and solidification and build-up of condensed aluminum chloride solids in the forelines and exhaust lines in aluminum etching systems, heater jackets can be wrapped around such piping to maintain the forelines and exhaust lines at an elevated temperature, thereby preventing condensation and solidification of condensable aluminum chloride vapor on the inside surfaces of such piping. However, depending on the length of the forelines and exhaust lines in the etching system, the use of heating jackets can be quite costly. For example, in some etching systems the reaction chamber may be located on one floor of a building while the vacuum pump and scrubber may be located one or more floors above or below the reaction chamber. Consequently, the foreline, the exhaust line, or both may be 10 feet or longer. In such situations, the use of heating jackets could be cost prohibitive. Therefore, as a less costly alternative, heating tape is often used in place of heating jackets to heat the forelines and exhaust lines. However, the use of heating tape also has drawbacks in that it can be difficult to completely and effectively wrap the lines, and consequently gaps are often left between sections of the heating tape. Such gaps between sections of heating tape on a poorly wrapped pipe result in “cold spots,” where the condensable aluminum chloride vapor condenses on the inside of the pipe.
Additional measures used to control the buildup of solid aluminum chloride in vacuum forelines and exhaust lines in vacuum systems of etching systems can include installing a trap just after the heated section of the piping line for trapping and removing aluminum chloride vapors from the effluent gas flow. As a result, the condensable aluminum chloride vapor is condensed and collected in the trap instead of depositing and building up in the piping lines. The trap can then be removed from the piping line whenever necessary for cleaning and removal of the deposited solid aluminum chloride.
The use of traps to remove condensable vapor from piping lines is well-known in the art. Conventional traps for trapping condensable vapor are often designed on the principle that lowering the temperature of the condensable vapor in the trap will cause the condensable vapor to condense as a solid. For example, U.S. Pat. No. 5,422,081, issued to Miyagi et al., discloses a trap device for a vapor phase reaction apparatus having an adjustable number of interior surfaces upon which the condensable aluminum chloride vapor cools on contact with the interior surfaces and condense on such surfaces. However, the Miyagi et al. trap requires a plurality of plate-shaped members assembled in layers, which can be difficult and time-consuming to manufacture and assemble. In addition, the large number of parts makes the Miyagi et al. trap difficult and time-consuming to disassemble for cleaning and removal of condensed aluminum chloride solids. Further, the close proximity between the plate-shaped members and the intake opening can cause the trap to clog prematur
Cochran Freund & Young LLC
Hassanzadeh Parviz
MKS Instruments Inc.
Young James R.
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