Abstract:
The present invention provides an improved apparatus and method for removing condensates, such as chlorides, from a dry etch, vacuum effluent stream. Dry etching of metallizations under vacuum conditions, using RF plasma and other techniques, is used in the processing of semiconductor devices and other applications. The apparatus and method remove accumulated chloride deposits that would otherwise restrict and ultimately plug the pipe that carries the vacuum effluent stream. The present invention utilizes an inner tube that is placed on the interior of the pipe and magnetically coupled to an outer tube that surrounds the exterior of the pipe. Translation of the outer tube causes translation of the inner tube, thereby removing accumulated condensate from the pipe. The apparatus may be configured so as to sense the accumulation of the condensate and automatically actuate the apparatus to remove the accumulated condensate.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to an apparatus and method for removing metal chloride condensate, such as condensable aluminum chloride vapor, that is being exhausted through the exhaust lines of a dry metal etching system in order to control the build-up of such condensate and prevent the eventual clogging of vacuum pump lines, valves, and other components downstream from the etching system. The invention comprises an apparatus that may be automatically translated through the interior of such lines to remove accumulated condensate. Further, the apparatus may be configured so as to sense the accumulation of the condensate and automatically actuate the apparatus to remove the accumulated condensate.  
           [0003]    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 using various well-known vacuum pumping mechanisms, such as for example, a combination of a turbo pump and a mechanical vacuum pump which are connected to the reaction chamber via a foreline. A photoresist that defines the desired metallization 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 removed by etching through the introduction of a low pressure, 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 radio frequency (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. 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 a condensable aluminum chloride vapor (AlCl 3 ) reaction byproducts. The reaction chamber effluent, which contains the condensable aluminum chloride vapor in addition to excess chlorine-containing reaction species, is removed from the reaction chamber by the application of a vacuum using well-known vacuum pumping techniques. An exhaust line  2  leading from the vacuum pump then directs the effluent  4  to a scrubber  6 , where the condensable aluminum chloride vapor and any excess chlorinated reaction gases are collected as shown in FIG. 1. A wet scrubber employing water is often employed to combine the gaseous aluminum chloride vapor and excess chlorinated reaction gas effluent with water to produce various aqueous species that can be treated using well-known waste treatment methods.  
           [0004]    The condensable chloride 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. As shown in FIG. 2, a buildup of solid aluminum chloride  8  downstream from the etching chamber can partially or even entirely clog the pipes.  
           [0005]    As shown in FIG. 3, it is well known to heat the vacuum conduit  2  used to exhaust the reaction chamber using a heater, such as heating tape  10 , to prevent the condensation of the gaseous species  4  created in the etching reaction. For example, typically, the vacuum in the foreline of an aluminum etching system is approximately 500 millitorr, and consequently it is necessary to heat the vacuum conduit to a temperature of about 70° C. in order to keep condensable species, such as aluminum chloride vapor, in the vapor phase so that they 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 much higher, for example 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. In addition, in the region adjacent to the scrubber  6 , there is also typically a partial pressure of water vapor available for the etching reaction by-products to react with, yielding additional condensable reaction products that can condense and clog the exhaust lines. If either the foreline, the exhaust line, or both are not maintained at the proper temperature, the condensable species  8  will cool, condense, and solidify, and species such as 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.  
           [0006]    Additional measures used to control the buildup of solid aluminum chloride in vacuum forelines and exhaust lines in vacuum systems of etching systems are known, including various forms of traps. However, since it is difficult to maintain all parts of an entire vacuum conduit system of an aluminum etching system at the proper temperature to ensure that condensation does not occur, or to efficiently trap condensable etching by-products with conventional traps, the buildup of solid aluminum chloride will inevitably occur throughout the vacuum conduit system of an aluminum etch system, particularly near the interface with the wet scrubber. Consequently, in spite of the heating jackets, heating tape, and various types of traps already available, there is still a need for an improved apparatus and method to prevent the accumulation of condensable species.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is an apparatus for removing deposits from a pipe, comprising: a reversible drive means; a drive screw having a longitudinal axis, said drive screw located adjacent to an exterior surface of the pipe such that a longitudinal axis of the pipe and the longitudinal axis of the drive screw are substantially parallel, said drive screw rotatably attached to said drive means; a ball nut that is translatably affixed to said drive screw, said ball nut having an anti-rotation means for limiting the rotation of the ball nut in conjunction with rotation of the ball screw; a first tube that is fixedly attached to said ball nut and capable of being magnetized, said first tube adapted to be translated over an outer surface of the pipe and having a longitudinal axis that is substantially parallel to the longitudinal axis of the pipe; a second tube that is adapted to be translatably positioned on the interior of the pipe and capable of being magnetized having an outer diameter adapted to permit said second tube to be positioned inside the pipe such that an exterior surface of the second tube is adjacent an interior surface of the pipe, and having a longitudinal axis that is substantially parallel to the longitudinal axis of the pipe. Preferably, the drive means is an electric motor. The apparatus may also include a controller, such as a microcomputer controller, for controlling the motor that is in signal communication with said electric motor; a pressure sensor for sensing the pressure in the pipe that is in signal communication with the controller; and at least two position sensors that are adapted to sense the position of the apparatus. The apparatus can sense an increase in the ambient pressure within the pipe and through the controller energize the motor to rotate the ball screw, thereby translating the ball nut and the first tube along the length of the ball screw. The second tube is magnetically attracted to the first tube and is thereby translated inside the pipe in conjunction with the translation of the first tube. The position sensors are used to detect the position of the apparatus through the controller. These position signals may be used to determine the travel limits of the apparatus.  
           [0008]    The apparatus described above may be controlled using the method of sensing the ambient pressure within the pipe; communicating a signal indicative of the ambient pressure within the pipe to the controller; monitoring the signal indicative of the ambient pressure within the pipe using the controller so as to identify changes in the ambient pressure; communicating a drive signal from the controller to the drive means in response to a change in the ambient pressure, so as to cause the apparatus to be translated along the pipe; sensing one of the first or second positions using respectively one of the first or second position w sensors; communicating a signal indicative of the position of the apparatus to the controller; and communicating a drive signal from the controller to the drive means in response to the signal from the position sensor. The drive signal may be a signal to stop the motor or to cause the motor direction to be reversed. In the case where the motor is reversed, the method may further comprise sensing the other of the first or second positions using respectively the other of the first or second position sensors; communicating a signal indicative of the position of the second tube to the controller; and communicating a drive signal from the controller to the drive means in response to the signal from the position sensor. The steps of the method may be repeated a number of times or cycles until the pressure sensor detects that the pressure in the pipe has returned to a desired ambient pressure and the position sensors indicate that the apparatus is in a desired stop position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a schematic description of some of the elements of a typical etching exhaust system that includes a wet scrubber to remove various by-products of the etching process.  
         [0010]    [0010]FIG. 2 is a schematic illustration of the accumulation of various etching by-products in a typical etching exhaust system during use of the system.  
         [0011]    [0011]FIG. 3 is a prior art apparatus for preventing the accumulation of etching by-products.  
         [0012]    [0012]FIG. 4 is a cross-sectional view of the apparatus of the present invention.  
         [0013]    [0013]FIG. 4A is a cross-sectional view of the apparatus of FIG. 4 along line AA.  
         [0014]    [0014]FIG. 5 is a second cross-sectional view of the apparatus of FIG. 4 illustrating the translation of the apparatus.  
     
    
     DESCRIPTION OF THE INVENTION  
       [0015]    Referring to FIG. 4, the present invention comprises an apparatus  12  for removing deposits from a pipe  14 , tube or similar structure. The present invention is preferably suitable for removing condensed etching by-products from a vacuum conduit of a dry etching system of the type described above, but is not so limited. It is believed to be generally applicable for the removal of deposits from pipes  12 , tubes or similar structures. As described above, the apparatus of the present invention is particularly suited for use in a vacuum conduit of a dry etching system in a region immediately adjacent the connection between the vacuum conduit and a scrubber used for the accumulation and treatment of the etching by-products, such as a wet scrubber, where condensation of the etching by-products is most likely to occur. Since vacuum conduits of the type referred to herein are typically assembled in flanged sections, it is preferred that the elements of the apparatus be assembled to a flanged section of pipe  14  of a length sufficient to encompass the portion of the conduit system that is most susceptible to the accumulation of the condensed etching by-products. It is also preferred that the elements of the apparatus be arranged so as to remove the condensed etching byproducts by pushing them into the scrubber, or alternately, into a trap such that they may be removed from the vacuum conduit system. Pipe  14  is preferably a non-magnetic material, including various non-metallic materials, such as glass or ceramic, but may also comprise various non-magnetic metals.  
         [0016]    Referring again to FIG. 4, apparatus  12  comprises a reversible drive means  16 . Reversible drive means  16  is preferably an electric motor, but other suitable reversible drive means may be used, such as a hydraulic motor, or a combination of a reversible electric motor, drive belt or chain, and pulley arrangement. Reversible drive means  16  is rotatably connected to drive screw  18 . By rotatably connected, it is meant to include all manner of connection of drive screw  18  that permits the transmission of the rotational energy of the motor to be coupled to drive screw  18 , including all manner of fixed connections, as well as various forms of clutches that would limit the amount of energy transmitted to drive screw  18 . Drive screw  18  is preferably a ball screw of a type well known in the art. Drive screw  18  has a longitudinal axis  20  and is located adjacent to an exterior surface of pipe  14  such that a longitudinal axis  22  of pipe  14  and longitudinal axis  20  of drive screw  18  are substantially parallel. As used herein, substantially parallel means sufficiently parallel considering the engineering tolerances of the related elements of apparatus  12  so as to permit the movement of the apparatus without undue parasitic losses due to misalignment of these elements. The end of drive screw  18  opposite reversible drive means  16  is supported by a bearing (not shown) or other mechanism known in the art sufficient to permit the free rotation of the screw while also providing support to that end of drive screw  18 .  
         [0017]    Apparatus  12  also comprises ball nut  24  of a type well known in the art that is translatably affixed to drive screw  18 . Ball nut  24  has an anti-rotation means  26  for limiting the rotation of ball nut  24  in conjunction with rotation of ball screw  18 . The anti-rotation means may be any suitable means, such as a bushing or bearing that is affixed to the ball nut and an associated guide rod having a longitudinal axis that is substantially parallel to longitudinal axis  20  of ball screw  18 .  
         [0018]    A first tube  28  is fixedly attached to ball nut  24  and capable of being magnetized. First tube may be a permanent magnet or an electromagnet. First tube  28  is adapted to be translated over an outer surface of pipe  14  and has longitudinal axis  30  that is substantially parallel to longitudinal axis  22  of pipe  14   
         [0019]    Second tube  32  is adapted to be translatably positioned on the interior of the pipe and capable of being magnetized having an outer diameter adapted to permit said second tube to be positioned inside the pipe such that an exterior surface of the second tube is adjacent an interior surface of the pipe, and having longitudinal axis  34  that is substantially parallel to longitudinal axis  22  of pipe  14 . Because of the corrosive environment and the need to provide a surface with a low coefficient of friction, second tube  32  preferably comprises a first portion that is adapted to be magnetized, such as iron or steel, and a second portion that encapsulates the first portion to protect the first portion from the corrosive environment and provide a low coefficient of friction relative to the inner surface of pipe  14 , such as an engineering thermoplastic or thermoset material. One such material is polytetrafluoroethylene (PTFE).  
         [0020]    Referring to FIG. 4A, first tube  28  and second tube  32  must be magnetized in such a way as to be magnetically attracted to one another. This magnetic attraction must be sufficiently strong to maintain a magnetic coupling between first tube  28  and second tube  32  as first tube  28  is translated along pipe  14 , taking into consideration the parasitic losses due to friction between the inner surface of pipe  14  and the outer surface of second tube  32 , including losses associated with removing accumulated condensate from the inner surface of pipe  14 . The apparatus  12  may also be surrounded by a heat jacket  44  of a type known in the art in order to provide additional protection against the accumulation of condensate within the pipe. The elements of the invention described herein will vary in size depending on many factors, including the diameter of pipe  14 , the materials used for first tube  28  and second tube  32 , and particularly the strength of the magnetic fields between them. However, if pipe  14  has a diameter of 15-20 cm and a zone over which condensation may occur of approximately 30-40 cm, second tube  32  may have a length of approximately 5-10 cm. In addition, it may be desirable to design second tube  32  such that the leading edge, the edge which is oriented toward the portion of pipe  14  where condensation is most likely to occur, is comprised entirely of the material used to encapsulate the magnetic portion to provide additional protection to the magnetic portion.  
         [0021]    Apparatus  12  may be operated in variety of modes, including a manual mode, whereby the translation of ball nut  24  and first tube  28  is observed by an operator and the direction of motor  16  is reversed manually when ball nut  24  reaches an end of travel limit. In order to automate the operation of apparatus  12 , it may also comprise controller  36 , such as a microcomputer controller of a type well known in the art, for controlling the electric motor that is in signal communication with electric motor. Controller  36  is utilized in conjunction with pressure sensor  38  that is in signal communication with controller  36 . Pressure sensor  38  is adapted to sense the pressure within pipe  14 . Controller  36  should also be utilized in conjunction with at least two position sensors  40 , first position sensor  40  and second position sensor  42 , that are in signal communication with controller  36 , said position sensors are adapted to sense the position of said second tube within pipe  14  and are spaced apart along pipe  14  to define a range of travel of apparatus  12 .  
         [0022]    One method of automated operation comprises defining predetermined intervals of operation of apparatus  12  within controller  36 , for example intervals ranging from 1 to 30 minutes. At the predetermined intervals, apparatus  12  is energized and reversible drive means  16  translates the apparatus along pipe  14  from first position sensor  40  to second position sensor  42 . When apparatus  12  reaches second position sensor  40 , the direction of rotation of reversible drive means  16  is reversed and apparatus  12  is translated along pipe  14  in the direction of first position sensor  40 . When apparatus  12  reaches first position sensor  40 , the apparatus may be shut off until the next predetermined interval of operation, or alternately, the method may be repeated for a predetermined number of times or cycles, a cycle being defined as the translation from the first position sensor to the second position sensor and back. The predetermined intervals of operation may be of the same duration, or may be varied according to a predetermined schedule. In addition, the pressure sensor  38  may be utilized to detect the pressure within the pipe  14 . If a sensed pressure is detected that is greater than the ambient operating pressure, such as for example a sensed pressure that is ≧10% above the ambient operating pressure, the speed of drive means  16  may be increased to apply more energy toward the removal of the accumulated condensate.  
         [0023]    A second method of automated operation comprises: sensing the ambient pressure within pipe  14  with the pressure sensor  38 ; communicating a signal indicative of the ambient pressure within pipe  14  from the pressure sensor  38  to controller  36 ; monitoring the signal indicative of the ambient pressure within pipe  14  from pressure sensor  38  using controller  36  so as to identify changes in the ambient pressure; and communicating a drive signal from controller  36  to drive means  16  in response to a sensed pressure that is above the ambient pressure, so as to cause drive means  16  to be energized and apparatus  12  to be translated along pipe  14 . As the apparatus is translated along pipe  14 , the method may also include sensing one of the first or second positions using respectively the first  40  or second  42  position sensor; communicating a signal indicative of the position of apparatus  12  to controller  36 ; and communicating a drive signal from the controller to the drive means in response to the signal from the first  40  or second  42  position sensor. At this point, the drive signal may simply be a command to drive means  16  to stop the translation of apparatus  12 . Alternately, the method may additionally include: sensing the other of the first or second positions using respectively the other of the first  40  or second  42  position sensors; communicating a signal indicative of the position of apparatus  12  to controller  36 ; and communicating a drive signal from controller  36  to drive means  16  in response to the signal from the other of the first  40  or second  42  position sensors. This method describes the automatic operation of the apparatus and interaction of its elements as it is translated from one position sensor to the other and back again. This defines one cycle of the apparatus. The method may be repeated for a plurality of cycles as necessary so long as the sensed pressure is above the ambient pressure during which operation, the method may include sensing the pressure in pipe  14  during the operation of apparatus  12 ; and communicating a drive signal from controller  36  to stop drive means  16  in response to the signal from the position sensor indicating that apparatus  12  is in a desired stop position and a signal from the pressure sensor that the sensed pressure in the pipe is the ambient pressure. While the invention has been described with respect to certain preferred embodiments and exemplifications thereof, these are not intended to limit the scope of the invention thereby, but solely by the claims appended hereto.