Abstract:
A vacuum trap, a plasma etch system using the vacuum trap and a method of cleaning the vacuum trap. The vacuum trap includes a baffle housing; and a removable baffle assembly disposed in the baffle housing, the baffle assembly comprising a set of baffle plates, the baffle plates spaced along a support rod from a first baffle plate to a last baffle plate, the baffle plates alternately disposed above and below the support rod and alternately disposed in an upper region and a lower region of the baffle housing.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of vacuum systems; more specifically, it relates to a vacuum trap for a vacuum system and a plasma etch system including a vacuum system having the vacuum trap. 
       BACKGROUND 
       [0002]    In plasma etch tools that use fluoro-carbon and/or sulfur-fluorine compounds as the reactant gases, fluorine containing polymers build up on the vacuum pump lobes and vacuum pump exhaust port reducing the pump rates and requiring expensive cleaning and tool downtime. Accordingly, there exists a need in the art to mitigate the deficiencies and limitations described hereinabove. 
       SUMMARY 
       [0003]    A first aspect of the present invention is an apparatus, comprising a baffle housing; and a removable baffle assembly disposed in the baffle housing, the baffle assembly comprising a set of baffle plates, the baffle plates spaced along a support rod from a first baffle plate to a last baffle plate, the baffle plates alternately disposed above and below the support rod and alternately disposed in an upper region and a lower region of the baffle housing. 
         [0004]    A second aspect of the present invention is a system comprising: a plasma etch tool and a vacuum pump; a vacuum trap disposed between an exhaust port of the plasma etch tool and a pumping port of a vacuum pump, the vacuum trap comprising: a baffle housing; and a removable baffle assembly disposed in the baffle housing, the baffle assembly comprising a set of baffle plates, the baffle plates spaced along a support rod from a first baffle plate to a last baffle plate, the baffle plates alternately disposed above and below the support rod and alternately disposed in an upper region and a lower region of the baffle housing. 
         [0005]    A third aspect of the present invention is a method, comprising: providing a plasma etch tool and a vacuum pump; placing a vacuum trap in a pumping line between an exhaust port of the plasma etch tool and a pumping port of the vacuum pump, the vacuum trap comprising: a baffle housing; a removable baffle assembly disposed in the baffle housing, the baffle assembly comprising a set of baffle plates, the baffle plates spaced along a support rod from a first baffle plate to a last baffle plate, the baffle plates alternately disposed above and below the support rod and alternately disposed in an upper region and a lower region of the baffle housing; and removable polymeric seals on edges of the baffle plates adjacent to internal walls of the baffle housing, the polymer seals touching the internal walls of the baffle housing; periodically removing the baffle housing and the baffle assembly from the pumping line and removing the baffle assembly from the baffle housing; cleaning the baffle housing and the baffle assembly by placing the baffle housing in an oven heated to a temperature above room temperature to melt and thereby remove any polymeric residue from surfaces of the baffle housing and the baffle assembly; removing the baffle housing and the baffle assembly from the oven; and after the cleaning, re-inserting the baffle assembly into the baffle housing and re-inserting the baffle housing into the pumping line. 
         [0006]    These and other aspects of the invention are described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein: 
           [0008]      FIG. 1  is a cross-sectional view of a vacuum trap according to an embodiment of the present invention; 
           [0009]      FIG. 2A  is a side view and  FIG. 2B  is end view of the baffle housing of the vacuum trap according to an embodiment of the present invention; 
           [0010]      FIG. 3A  is a side view and  FIGS. 3B and 3C  are opposite end views of the end caps of the vacuum trap according to an embodiment of the present invention; 
           [0011]      FIGS. 4 and 5  are side views of the baffle of the vacuum trap according to an embodiment of the present invention; 
           [0012]      FIG. 6  is an isometric view of the baffle of the vacuum trap according to an embodiment of the present invention; 
           [0013]      FIGS. 7A and 7B  illustrate the seal between the baffle and the baffle housing of the vacuum trap according to an embodiment of the present invention; 
           [0014]      FIG. 8  illustrates the proper alignment of baffle plates to the end caps of the vacuum trap according to an embodiment of the present invention; 
           [0015]      FIGS. 9A and 9B  illustrate the use of the vacuum trap according to an embodiment of the present invention; 
           [0016]      FIG. 10  illustrates a method of cleaning the vacuum trap according to an embodiment of the present invention; and 
           [0017]      FIG. 11  is a schematic diagram of an exemplary plasma etch system including the vacuum trap according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Vacuum traps according to embodiments of the present invention are designed to collect polymeric by-products and other residues generated by a plasma etch tool. Vacuum traps according to embodiments of the present invention are suitable for use at ambient room temperature. Vacuum traps according to embodiments of the present invention do not need to be cooled below ambient room temperature in order to trap polymer by-products or other residues. In one example, ambient room temperature is between about 20° C. and about 25° C. Vacuum traps according to embodiments of the present invention do not require mechanical cooling by any (e.g., forced refrigerated or room temperature gas or liquid flow directed to the body, endcaps or baffle assembly of the vacuum trap). However, mechanical cooling is optional. The baffles used by the vacuum traps according to embodiments of the present invention are not helical but present multiple collection surfaces that are perpendicular to the pumping direction. 
         [0019]      FIG. 1  is a cross-sectional view of a vacuum trap according to an embodiment of the present invention. In  FIG. 1 , a vacuum trap  100  includes a baffle housing  105 , two end caps  110 , a baffle assembly  115  and quick release clamps  135  for holding end caps  110  to body  115 . Quick release clamps  135  allow quick removal of vacuum trap  100  from the plasma etch system and removal of end caps  110  from baffle housing  105 . Baffle housing  105  has a cylindrical body  125  of uniform diameter bore  130  of diameter D 1  open at opposite ends and integral flanges  135  proximate to the ends of body  105  for clamping of body  105  to end caps  110 . End caps  110  include a cylindrical body  140  of uniform diameter bore  145  of diameter D 2  open at opposite ends, an integral flange  150 , and an integral flange plate  155  for joining end caps  110  to body  105 . Bore  145  is offset from the longitudinal axes  147  of baffle housing  105  so bore  145  aligns with only the upper half of bore  130 . Flange  150  is provided to clamp end caps  110  to other pipes or units of a vacuum system. A bracket  160  is attached to the surface of flange plate  155  for aligning baffle assembly  115  within baffle housing  105 . Baffle assembly  115  includes a central rod  165  having rod handles  170 A and  170 B attached at opposite ends of rod  165 . Attached to rod  165  are baffle plates  175 A,  175 B,  175 C,  175 D and  175 E. Baffle plates  175 A,  175 B and  175 E are disposed in an upper region of bore  130  that is aligned with bores  145  of end caps  110 . Baffle plate  175 B is disposed between baffle plates  175 A and  175 C. Baffle plate  175 D is disposed between baffle plates  175 C and  175 E. Baffle plates  175 B and  175 D are disposed in a lower region of bore that is not aligned with bores  145  of end caps  110 . Baffle plates  175 A and  175 E are spaced a distance S 1  from respective ends of baffle housing  105 . Baffle plates  175 A and  175 C are spaced a distance S 2  apart. Baffle plates  175 C and  175 E are spaced a distance S 2  apart. Baffle plates  175 A and  175 C are spaced a distance S 2  apart. Disposable seals  180  are provided on the circular edges of baffle plates  175 A,  175 B,  175 C,  175 D and  175 E to provide a seal between the baffle plates and the inside wall of baffle housing  105 . O-ring seals  185  are provided to seal flanges  135  to flange plates  155 . Baffle assembly is removeable from body  105  after disconnecting end caps  110  from baffle housing  105 . While five baffle plates are illustrated, there may be as few as three or more than five, with odd numbers of baffle plates being preferred when vacuum trap  100  is assembled as illustrated in  FIG. 1 . However, even numbers of baffle plates may be used if the first end cap  110  is mounted to baffle housing  105  and rotated 180° relative to the second baffle plate  110  so the respective bores  145  are not aligned (i.e., an axis passing through the centers of bores  145  is not parallel to axis  147  of  FIG. 1  but crosses axis  147 ). Then at least two baffle plates may be used. 
         [0020]    Bracket  160  along with the length of rod  165  and the orientation of rod handles  170 A and  170 B relative to baffle plates  175 A,  175 B,  175 C,  175 D and  175 E prevent the baffle plates of baffle assembly  115  from being assembled with the baffle plates rotated out of proper alignment relative to bores  145  of end caps  110 . Bracket  160  also forces the longitudinal axes  148  of bores  145  of end caps  110  to be aligned. Vacuum trap  100  cannot be assembled until end caps  110  and baffle assembly  115  are aligned properly. 
         [0021]    In one example, D 1  is about equal to the bore of the pump intake and exhaust ports of the vacuum pump. In one example D 2  is equal to about half D 1 . In one example, S 1  is about equal to D 2 . In one example, S 2  is equal to about twice S 1  so the distance between all adjacent pairs of baffle plates is about S 1 . Thus, for a three inch vacuum system, S 1  and D 2  are about three inches and D 1  and S 2  are about six inches. In one example, baffle housing  105  and end caps  110  are aluminum. In one example, baffle assembly  115  is stainless steel and rod  165  and handles  170 A and  170 B and baffle plates  175 A,  175 B,  175 C,  175 D and  175 E are welded together. In one example, seals  180  are formed from a polymer, examples of which include, but are not limited to, polyvinyl chloride, polyethylene, silicone, polyurethane and fluoro-polymers. 
         [0022]      FIG. 2A  is a side view and  FIG. 2B  is end view of the baffle housing of the vacuum trap according to an embodiment of the present invention. In  FIGS. 2A and 2B  baffle housing  105  is an open ended cylinder having flanges  135  at opposite ends of body  125 . 
         [0023]      FIG. 3A  is a side view and  FIGS. 3B and 3C  are opposite end views of the end caps of the vacuum trap according to an embodiment of the present invention. In  FIG. 3A , bracket  160  is mounted to the inside wall  186  of flange plate  155  just below bore  145 . In  FIG. 3B , flange plate  155  is divided into quadrants by mutually perpendicular axes  187  and  188  passing through the center of flange plate  155 . The point where axes  187  and  188  cross is longitudinal axis  147  of  FIG. 1 . The perimeter of bore  145  is proximate to axis  187  and is bisected by axis  188 . Bore  145  and flange  150  are divided into quadrants by mutually perpendicular axes  189  and  188  passing through the center of flange plate  155 . The point where axes  188  and  189  cross is longitudinal axis  148  of  FIG. 1 . Axes  187  and  189  are parallel and axis  188  is perpendicular to axes  187  and  189 . Axes  187 ,  188  and  147  of  FIG. 1  are mutually orthogonal. Axes  188 ,  189  and  148  of  FIG. 1  are mutually orthogonal. In  FIG. 3C , bracket  160  is mounted to flange plate  155  with its length parallel to and below axis  187 . 
         [0024]      FIGS. 4 and 5  are side views of the baffle of the vacuum trap according to an embodiment of the present invention. In  FIG. 4 , baffle plates  175 A,  175 B,  175 C,  175 D and  175 E are semi-circular plates located on alternate sides of rod  165 . Handle  170 A (and handle  170 B) have their respective longitudinal axes parallel to the flat edges of baffle plates  175 A,  175 B,  175 C,  175 D and  175 E. Rod  165  has a diameter D 3  and baffle plates  175 A,  175 B,  175 C,  175 D and  175 E have a thickness T. It is preferable that rod  165  has a diameter of less than about 1/10 the diameter of bore  130  of baffle housing  105  (see  FIGS. 2A and 2B ) so as not to restrict the exhaust path through the baffle housing. In one example, D 3  is about ½ of an inch. In one example, T is about 3/16 of an inch.  FIG. 5  is  FIG. 4  rotated 90° about longitudinal axis  147 . 
         [0025]      FIG. 6  is an isometric view of the baffle of the vacuum trap according to an embodiment of the present invention. In  FIG. 6 , curved edges  182  of baffle plates  175 A,  175 C and  175 E are aligned to each other and curved edges  182  of baffle plates  175 B and  175 D are aligned to each other. The flat edges  183  of all baffle plates  175 A,  175 B,  175 C,  175 D and  175 E and the longitudinal axes of handles  170 A and  170 B are aligned in parallel. In the example of  FIG. 6 , baffle plates  175 A,  175 B,  175 C,  175 D and  175 E are solid and contain no openings. 
         [0026]      FIGS. 7A and 7B  illustrate the seal between the baffle and the baffle housing of the vacuum trap according to an embodiment of the present invention.  FIG. 7B  is rotated 90° from  FIG. 7A . In  FIGS. 7A and 7B , an exemplary baffle plate  175 X has a radius R which is less than half the diameter of bore D 1  to accommodate seals  180 . Seals  180  not only seal alternate sections of the vacuum trap from each other, but help keep the baffle assembly aligned in bore  130  of baffle housing  125  (see  FIG. 1 ) as the baffle assembly is inserted into and removed from the bore. Also, seals  180  allow rotational adjustment along axis  147  (see  FIG. 1 ) of baffle assembly  125  without scratching the surfaces of bore  130 . 
         [0027]      FIG. 8  illustrates the proper alignment of baffle plates to the end caps of the vacuum trap according to an embodiment of the present invention. In  FIG. 8 , the flat edges of baffle plates  175 A and  175 B are aligned with axis  147  within bore  130  (of the baffle housing) and baffle plate  175 A is in line with bore  145  (of the end cap). Thus, looking straight into bore  145 , baffle plate  175 A would be visible while baffle plate  175 B would not be visible. 
         [0028]      FIGS. 9A and 9B  illustrate the use of the vacuum trap according to an embodiment of the present invention. In  FIG. 9A , as the exhaust from the plasma tool passes through vacuum trap  100 , by-products  190 A of the plasma etch process (polymers, vapors, particles and other residues and particles) impinge on front surfaces of baffle plates  175 A,  175 B,  175 C,  175 D and  175 E facing the exhaust port of the plasma tool, baffle plate  175 A being closet to the exhaust port. In  FIG. 9B , the entire vacuum trap  100  has been removed from the pumping line, and re-inserted in a reversed position into the pumping line with baffle plate  175 E closet to the exhaust port of the plasma system and by-products  190 B are collected on the back surfaces of the baffle plates. Baffle assembly  115  has not been removed from baffle housing  105  nor have the endcaps  110  (see  FIG. 1 ) been removed from the baffle housing. This procedure does not disturb polymer built up on the interiors surfaces of vacuum trap  100  and is the reason that the two end caps  110  are the same design. Vacuum trap  100  may be cleaned after collecting by-product  190 A and not re-positioned as in  FIG. 9B  or cleaned after collecting both by-product  190 A and  190 B. 
         [0029]      FIG. 10  illustrates a method of cleaning the vacuum trap according to an embodiment of the present invention. In  FIG. 10 , an oven  200  includes a chamber  205  having a door  210  and a heater  215 . A rack  220  is provided in a tray  225 . An exhaust port  230  and optional purge gas inlet  235  are also provided to chamber  205 . To clean the vacuum trap, the vacuum trap is removed from the plasma etch system (see  FIG. 11 ), end caps  110  removed from baffle housing  105 , baffle assembly  115  is removed from baffle housing  105 , seals  180  (see  FIGS. 1 ,  7 A and  7 B) removed and discarded and the baffle housing, baffle assembly and end caps placed on rack  220 . Oven  200  is heated to about 180° C. and the by-product collected (some collects on baffle housing  105  and end caps  110  as well as on baffle assembly  115 ) melts and drips into tray  225 . The temperature of oven  200  is less than the temperature that the collected by-products will decompose at to avoid releasing fluorine compounds. After cleaning, new seals are placed on the baffle plates and the baffle assembly is re-installed on the plasma etch system. Alternatively, if polymer build-up makes disassembly of the vacuum trap difficult, the entire assembled vacuum assembly (baffle housing, baffle assembly and both endcaps) can be placed in the oven, and after most of the polymer is removed, the vacuum trap can be disassembled as and the individual parts placed in the oven as described supra. 
         [0030]      FIG. 11  is a schematic diagram of an exemplary plasma etch system including the vacuum trap according to an embodiment of the present invention. In  FIG. 11 , a plasma etch system  250  includes a plasma etch tool  255  having one or more gas inlets  260  and an exhaust port  262 . Plasma etch tool  255  includes an RF generator and a DC power supply (not shown). An optional heated fore line  265  is placed between the input side end cap  110  of vacuum trap  100  and heated fore line  265 . In one example, heated fore line  265  is heated to about 85° C. The output side end cap  110  is connected to the pumping port of vacuum pump  270  through a throttling valve  275 . The exhaust port  280  of vacuum pump  270  is connected to an input port of silencer  285  by an optional heated exhaust line  280 . The output port of silencer  285  is connected to an exhaust fan  295 . While no scrubber is required, a scrubber after exhaust fan  295  may be provided. While forced cooling of vacuum trap  100  is not required, an optional cooling coil  300  may be provided around baffle housing  105 , though if cooled to too low a temperature enough polymer may be collected on the walls of the baffle housing to make disassembly of the vacuum trap difficult. 
         [0031]    While the baffle housing has been described as having an annular ring cross-section with the baffle assembly and end-caps configured to fit a baffle housing having n annular ring cross-section, baffle bodies may have other cross-sections, such as square or rectangular with the baffle assembly and end-caps configured to fit baffle bodies having square or rectangular or other cross-sections. However, a baffle housing having an annular ring cross-section is preferred because of ease of construction and reduced cost and weight. 
         [0032]    The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.