Patent Document

BACKGROUND  
       [0001]     Semiconductor devices are built up using a number of material layers. Each layer is patterned to add or remove selected portions to form circuit features that will eventually make up an integrated circuit. Some layers can be grown from another layer; for example, an insulating layer of silicon dioxide can be grown over a layer of silicon by oxidizing the silicon surface. Other layers are formed using deposition techniques, typical ones being chemical vapor deposition (CVD), evaporation, and sputtering.  
         [0002]     Deposition methods form layers using vaporized materials that condense to form a film on the surface of interest. Unfortunately, the films thus formed are not limited to the surface of interest, but tend also to form on other surfaces within the reaction chamber. Thus, after substantial use, a thick film of the deposited material accumulates on components and surfaces within the reaction chamber. These films eventually become troublesome sources of contaminants. Etch processes also contaminate inside surfaces of reaction chambers, though by different mechanisms. In either case, the reaction chamber, including internal components, must be periodically cleaned or replaced.  
         [0003]     Many process contaminants are removed using hazardous liquids. Unfortunately, the storage, use, and disposal of hazardous liquids and their vapors are dangerous and expensive, particularly when these chemicals are used in large volumes. There is therefore a need for cleaning methods and systems that minimize the required amounts of hazardous chemicals.  
         [0004]     The difficulty and expense of dealing with hazardous chemicals are not the only problems encountered when cleaning semiconductor process equipment. Some forms of contamination are so stubbornly attached to the underlying material that removal of the contamination jeopardizes the part to be cleaned. Each of  FIGS. 1, 2 , and  3  (prior art) illustrates an exemplary component and is used to describe a particular cleaning problem addressed in the following disclosure.  
         [0005]      FIG. 1  (prior art) depicts a stainless-steel shield  100  used to contain titanium-bearing vapors during physical vapor deposition (PVD) processes used to deposit layers of titanium and titanium alloys on semiconductor wafers. In confining such vapors, the interior surface  105  of shield  100  becomes highly contaminated with layers of titanium and titanium species, such as titanium nitride. Exterior surface  110  of shield  100  also becomes contaminated, though to a lesser extent. Shield  100  must therefore be periodically cleaned or replaced.  
         [0006]     Conventional etchants that attack the titanium and titanium alloys also attack stainless steel. Immersing shield  100  in these etchants to remove the contaminants can therefore damage the underlying stainless steel. Exterior surface  110  is particularly vulnerable because that stainless steel lacks the thick contaminant layer of interior surface  105 , and is thus exposed to etchants for a longer time. Pitting and roughening of exterior surface  110  is undesirable for aesthetic purposes and because rough surfaces trap undesirable contaminants when shield  100  is returned to a process chamber. There is therefore a need for a method of effectively removing titanium contaminant species from shield  100  without damaging the underlying stainless steel.  
         [0007]      FIG. 2  (prior art) depicts an aluminum blocker plate  200  used to distribute gases evenly over a semiconductor surface. Blocker plate  200  is used, for example, to evenly distribute silicon-bearing gases (e.g. silane) over the surface of a semiconductor wafer during silicon deposition processes. Blocker plate  200  includes a constellation of small holes  205  through which pass the silicon-bearing gas. During such deposition processes, the surfaces of aluminum blocker plate  200 , including the inner surfaces of holes  205 , become contaminated with silicon and silicon oxides. Blocker plate  200  must therefore be periodically cleaned or replaced.  
         [0008]     Oxides of silicon are difficult to remove from aluminum because common silicon etchants vigorously attack aluminum. A similar problem exists for components of or layered with yttrium oxide or sprayed ceramic. Expensive components like blocker plate  200  are therefore discarded and replaced rather than cleaned and reused. There is therefore a need in the art for a way removing silicon and silicon-bearing contamination from expensive aluminum, yttrium oxide, and sprayed ceramic parts.  
         [0009]      FIG. 3  (prior art) depicts a diffusion tube employed in high-temperature furnaces to deposit polysilicon and silicon nitride on semiconductor wafers. Diffusion tube  300  can be of quartz or silicon carbide. During the deposition of polysilicon or silicon nitride, these deposited materials built up on the inner surfaces of diffusion tube  300 . After a period of use, the resulting contamination layers can begin to flake off, posing a serious threat of induced defects on the wafers being processed. It is therefore necessary to periodically clean or replace diffusion tube  300 .  
         [0010]     Unfortunately, current methods of cleaning diffusion tubes are inadequate. In a typical process, one or more “spray balls” are inserted up into a vertically positioned diffusion tube  300 . Etchants are then sprayed against the interior surfaces of diffusion tube  300  to dissolve away the accumulated contamination layers. Spray balls do not apply chemicals evenly; therefore contamination removal is slow and uneven. There is therefore a need of improved methods of restoring expensive diffusion tubes to a contamination-free state.  
         [0011]     The examples of  FIGS. 1-3  are in no way exhaustive of the problems encountered as a result of contaminated semiconductor-processing equipment or of the types of parts that can be cleaned. Many other expensive components pose difficult cleaning problems. For example, some titanium components become contaminated with titanium species, including titanium metal and titanium nitride. Known methods of removing titanium species are labor intensive and potentially damage the underlying titanium substrate. There is therefore a need for methods of removing titanium metal and titanium alloys from titanium substrates.  
       SUMMARY  
       [0012]     The present invention is directed to methods, systems, and chemistries for cleaning various components of semiconductor process equipment. These components are of different types of materials and suffer from different types of contamination. The embodiments described herein remove these contaminants using small amounts of chemicals and with minimal damage to the article being cleaned.  
         [0013]     A method in accordance with one embodiment cleans articles with differently contaminated interior and exterior surfaces by using those articles to separate a cleaning vessel into separate chambers, one chamber for the interior surface and one for the exterior surface. Different chemistries are then applied to the differently contaminated surfaces. This embodiment reduces the required volume of etchant, and consequently saves considerably on the purchase, handling, and disposal costs associated with the use of toxic chemicals. One embodiment further reduces the requisite etchant volume using one or more volume-displacement elements that displace some of the etchant volume.  
         [0014]     A method in accordance with another embodiment removes layers of stubborn silicon and silicon-nitride contamination from the interior surfaces of articles such as deposition tubes. In such embodiments, a tube to be cleaned is gently rolled on it side while a portion of the tube&#39;s interior surface is exposed to an etchant. The tube is only partially filled with etchant to reduce the requisite etchant volume, and the rolling motion evenly exposes the contaminated surfaces to the etchant.  
         [0015]     Another embodiment employs hydrofluoric acid to remove titanium species, including titanium metal and titanium nitride, from titanium substrates. Hydrofluoric acid chemistries are traditionally disfavored for such tasks, as hydrofluoric acid tends to attack the underlying titanium substrate. A chemistry in accordance with one embodiment includes a mixture of hydrofluoric acid and hydrogen peroxide that vigorously attacks deposited titanium and titanium nitride without significantly attacking the machined titanium alloys normally used to form titanium components for semiconductor processing. This chemistry can therefore be used to clean expensive titanium parts. In one embodiment, the chemistry found to remove titanium and titanium-bearing contaminants from a titanium substrate without significantly attacking the substrate is a mixture of less than about 2% hydrofluoric acid, from between about 6% and about 30% hydrogen peroxide, and the balance water. This mixture may be selectively applied to contaminated areas.  
         [0016]     In accordance with yet another embodiment, a hydrofluoric acid solution is employed to remove silicon species from aluminum, yttrium oxide, and sprayed ceramic substrates. Silicon oxides are relatively inert, and consequently resist most etchants. However, hydrofluoric acid has long been known to be effective at dissolving silicon oxide. Unfortunately, hydrofluoric acid strongly attacks aluminum, yttrium oxide, and sprayed ceramic, and consequently damages expensive components. Methods used in accordance with some embodiments remove silicon and silicon-bearing contaminants from aluminum using a mixture of hydrofluoric acid and anhydrous acetic acid. The hydrofluoric-acid solution used in one embodiment is 51% water and 49% hydrofluoric acid, so the etchant consists primarily of water, hydrofluoric acid, and anhydrous acetic acid.  
         [0017]     This summary does not limit the invention, which is instead defined by the claims. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0018]      FIG. 1  (prior art) depicts a stainless-steel shield  100  used to contain titanium-bearing vapors during physical vapor deposition (PVD) processes used to deposit layers of titanium and titanium alloys on semiconductor wafers.  
         [0019]      FIG. 2  (prior art) depicts an aluminum blocker plate  200  used to distribute gases evenly over a semiconductor surface.  
         [0020]      FIG. 3  (prior art) depicts a diffusion tube employed in high-temperature furnaces to deposit polysilicon and silicon nitride on semiconductor wafers.  
         [0021]      FIG. 4A  depicts a volume-efficient cleaning system  400  that addresses the problems of cleaning PVD shield  100  a  FIG. 1 .  
         [0022]      FIG. 4B  depicts a cleaning system  450 , in which three shields  100  are stacked within containment vessel  405  of tank  400  for cleaning.  
         [0023]      FIG. 5  depicts a cleaning system  500  in accordance with an embodiment that cleans tubes like tube  300  described above in connection with  FIG. 3 .  
         [0024]      FIGS. 6A and 6B  are respective side and front views of a cleaning system  600  in accordance with an embodiment used to clean quartz and silicon carbide tubes  300  of the type described above in connection with  FIG. 3 .  
         [0025]      FIGS. 7A and 7B  are respective side and front views of a cleaning system  700  in accordance with another embodiment used to clean quartz and silicon carbide tubes  300 .  
         [0026]      FIGS. 8A and 8B  are respective side and from views of a cleaning system  800  similar to system  600  of  FIGS. 6A and 6B , like-numbered elements being the same or similar.  
         [0027]      FIG. 9  depicts a cleaning system  900  in accordance with an embodiment adapted to clean a wafer boat  905 . 
     
    
     DETAILED DESCRIPTION  
       [0028]      FIG. 4A  depicts a volume-efficient cleaning system  400  that addresses the problems of cleaning PVD shield  100  a  FIG. 1 . Tank  400  includes a containment vessel  405 , of volume displacement element  410 , a first inlet  415 , and a second inlet  420 . Inlets  415  and  420  can double as drains, or separate inlets and drains can be provided. In this illustrative example, tank  400  is employed to remove titanium contaminant layers from stainless steel shields of the type depicted in  FIG. 1  and described above. The etchant used in the cleaning process includes a mixture of hydrofluoric acid (HF) and hydrogen peroxide (H 2 O 2 ). Specific etchant chemistries are detailed below.  
         [0029]     Containment vessel  405  and volume displacement element  410  are made of chemically resistant polypropylene, which is easy to clean and does not contribute significant amounts of contamination to the cleaning solution. Volume displacement element  410  is included to minimize the required etchant volume. This aspect of tank  400  is important, as highly pure etchants, such as hydrofluoric acid and hydrogen peroxide, are expensive. The expense of using hydrofluoric acid is exacerbated by the expense of disposal and compliance with environmental regulations that limit the amount of fluorine injected into local sewage systems.  
         [0030]      FIG. 4B  depicts a cleaning system  450 , in which three shields  100  are stacked within containment vessel  405  of tank  400  for cleaning. Each of shields  100  includes first and second open ends, the first of which is smaller in diameter than the second. Shields  100  are stacked so that the first open ends from adjacent shields meet and the second open ends from adjacent shields meet. The stacked shields  100  thus collectively form a somewhat cylindrical barrier separating an interior portion  455  of vessel  405  from an exterior portion  460 . Interior portion  455  and exterior portion  460  are simultaneously filled via respective inlets  420  and  415 , interior portion  455  with a titanium etchant and exterior portion  460  with deionized water. Interior and exterior portions  455  and  460  are filled until the levels of both portions reach the top of the uppermost shield  100 . The etchant is then allowed to dissolve or weaken the contamination on the interior surfaces of shields  100 .  
         [0031]     Filling interior and exterior portions  455  and  460  at the same rate to maintain substantially equivalent fill levels in the interior and external portions maintains an equivalent pressure in those portions, and consequently prevents excessive mixing the etchant and water. Such mixing can be further limited by providing a gasket material (not shown) between the bottom shield  100  and the bottom of vessel  405  and between adjacent shields  100 . Such sealing is not generally necessary, as a relatively dilute acid solution formed in exterior portion  460  is desirable to attack the relatively light titanium contamination on the exterior surfaces of shields  100 . Some embodiments prevent excessive etchant concentration in exterior portion  460  by circulating the water in and out of portion  460  during the cleaning process. The etchant chemistry can also be adjusted during the cleaning process as desired.  
         [0032]     As an added advantage, the jacket of water surrounding shields  100  prevents shields  100  from heating excessively in response to the exothermic reaction normally used to remove stubborn titanium deposits. In other embodiments, the temperature of the cleaning process is controlled up or down using a heat exchanger, such as coils of stainless steel or polypropylene tubing, in one or both of exterior portion  460  and interior portion  455 . Such embodiments provide the additional advantage of displacing some percentage of either the cleaning solution or the deionized water used in the respective interior and exterior portions, and consequently reduce the amount of chemicals needed for cleaning and the amount of chemicals required for handling and disposal. Though not shown, a cover can be placed over  450  to collect and evacuate hazardous vapors and to protect operators from splashed chemicals.  
         [0033]     Different types of cleaning solutions can be used depending on the type of contamination and the item being cleaned. In this embodiment, in which a stainless-steel substrate is contaminated with species of titanium, the use of a particular cleaning chemistry within interior portion  455  has been shown to provide excellent contamination removal while minimizing the damage to the underlying stainless steel. Also important, the chemistry uses a relatively low concentration of hydrofluoric acid, and consequently minimizes disposal costs and environmental impact. This chemistry includes about 60 parts hydrogen-peroxide solution to one part hydrofluoric-acid solution. The hydrogen-peroxide solution used in the chemistries discussed herein is purchased as a ratio of 30% hydrogen peroxide to 70% water, and the hydrofluoric-acid solution is purchased as a mixture of 49% hydrofluoric acid and 51% water. The 60 to 1 mixture is therefore about 29.5% hydrogen peroxide, less than 1% hydrofluoric acid, and the balance water. This mixture may include up to about 5% hydrofluoric acid and from about 6-30% hydrogen peroxide. To minimize the costs of chemicals and their disposal, the preferred ranges of hydrofluoric acid and hydrogen peroxide for removing titanium from stainless steel are from 1-2% hydrofluoric acid and from 10-29% hydrogen peroxide.  
         [0034]     Though the articles being cleaned in  FIG. 4B  are stainless steel, hydrofluoric acid chemistries in accordance with some embodiments are used to remove titanium species, including titanium metal and titanium nitride, from titanium substrates. Conventional methods of removing titanium and titanium nitride employ a combination of chemical and mechanical processes that are collectively very labor intensive. Chemical processes include the use of hydrofluoric acid, but these chemistries are disfavored for use in decontaminating titanium substrates because the chemistries attack the substrates. As a consequence of these shortcomings, very expensive titanium components are routinely discarded.  
         [0035]     Applicants discovered an etchant chemistry that removes deposited titanium and titanium nitride from titanium substrates without damaging those substrates. This important chemistry employs a mixture of hydrofluoric acid and hydrogen peroxide that vigorously attacks deposited titanium and titanium nitride without significantly attacking the machined titanium alloys normally used to form titanium components for semiconductor processing. Applicants speculate that the etchant attacks deposited titanium and titanium nitride much more aggressively than the underlying titanium alloy due to compositional differences, physical differences, or both.  
         [0036]     An etchant found to remove titanium and titanium-bearing contaminants from a titanium substrate without significantly attacking the substrate is a mixture of less than about 2% hydrofluoric acid, from between about 6% and about 30% hydrogen peroxide, and the balance water. This mixture may be selectively applied to contaminated areas.  
         [0037]      FIG. 5  depicts a cleaning system  500  in accordance with an embodiment that cleans tubes like tube  300  described above in connection with  FIG. 3 . System  500  operates using principles similar to those discussed above in connection with  FIGS. 4A and 4B  to expose contaminated surfaces to etchants while protecting other surfaces from the etchants, reducing the required volume of etchants, and controlling reaction temperature.  
         [0038]     System  500  includes a containment vessel  505  removably attached to a base  510 . An O-ring seal  515  prevents liquid from leaking from vessel  505 . A volume-displacement element  520  and optional gasket  525  are fixed to base  510 . Before cleaning and cooling solutions are added to vessel  505 , vessel  505  is removed from base  510  and tube  300  is placed over displacement element  520 . Tubes  300  can be heavy and expensive, so some versions of system  500  can be tilted to allow horizontal insertion of tube  300  over displacement element  520 . Once system  500  is assembled as shown in  FIG. 5 , deionized water or some dilute cleaning solution is injected into the region surrounding tube  300  via an inlet  530 . An etchant is also injected between the interior surface of tube  300  and volume-displacement element  520  via a second inlet  535 . A vent  527  and tube  540  allow air to escape as liquid is injected into containment vessel  505  and tube  300 . One or both of vent  527  and tube  540  can be vented for proper disposal of reaction gases.  
         [0039]     Gasket  525  prevents the interior and exterior solutions from mixing. A good seal is not necessarily important, however, as maintaining a similar fluid depth inside and outside of tube  300  prevents significant mixing of the interior and exterior fluids. In some embodiments, the fluid level on the outside of tube  300  is maintained somewhat higher than the fluid level inside tube  300  to prevent the etchant from flowing out of tube  300 .  
         [0040]     As noted above in connection with  FIG. 3 , typical contaminants on the inside of tube  300  include polysilicon and silicon nitride. These chemicals are conventionally removed using known hydrofluoric acid and nitric acid mixtures. The outside of tube  300  is exposed to deionized water in one embodiment, but other solutions might also be used. In embodiments in which tube  300  is of a different form, of a different material, or contaminated with different materials on different surfaces, the chemistries of the interior and exterior solutions can be changed accordingly.  
         [0041]      FIGS. 6A and 6B  are respective side and front views of a cleaning system  600  in accordance with an embodiment used to clean quartz and silicon carbide tubes  300  of the type described above in connection with  FIG. 3 . System  600  is adapted to evenly clean the interior surface of tube  300  to remove polysilicon and silicon nitride contamination layers using small volumes of etchants.  
         [0042]     System  600  includes a storage vessel  605 , typically of a chemically resistant polypropylene. Dams  610  are included at the bottom of vessel  605  to displace some of the etchant. The shape and configuration of dams can be modified as appropriate to optimize the level and amount of etchant and to accommodate different article shapes.  
         [0043]     Tube  300  rests on two sets of rollers  615  disposed on a corresponding pair of axles  620 . One of axles  620  includes a pulley  625  at one end, and pulley  625  is connected to a corresponding drive pulley  630  via a belt  635 . In the depicted embodiment, belt  635  is exposed to an acid-based etchant  640  and is therefore made of an acid-resistant material. In one embodiment belt  635  chemically resistant O-ring available from Dupont under the trademark KALREZ or from Greene Tweed Products under the trademark CHEMRAZ.  
         [0044]     A driveshaft  642  connected to a motor (not shown) within a motor housing  645  turns pulley  630  and consequently pulley  635 , axles  620 , and rollers  615 . Two sets of journals  650  support axles  620  and are mounted, in this embodiment, to dams  610 . The various components of system  600  are made of chemically resistant materials, such as polypropylene or TEFLON. Journals  650 , one of which is detailed in  FIG. 6B , include two parts joined using chemically inert bolts  655 . Finally, a perforated drainpipe  660  near the bottom of vessel  605  or some other form of drain is provided to facilitate removal of etchant  640 . Though not shown, vessel  605  can include a lid, and the lid may be vented in a manner that collects potentially harmful vapors.  
         [0045]     During operation, tube  300  is rotated slowly to evenly expose the interior surface of tube  300  to etchant  640 . An appropriate etchant for removing polysilicon and silicon nitride includes equal volumes of hydrofluoric and nitric acid solutions. Commercially available hydrofluoric and nitric acid solutions include a significant percentage of water.  
         [0046]      FIGS. 7A and 7B  are respective side and front views of a cleaning system  700  in accordance with another embodiment used to clean quartz and silicon carbide tubes  300 . System  700  is similar to system  600  of  FIGS. 6A and 6B , like-numbered element being the same or similar. In system  700 , dams  610  are eliminated; instead, a semi-cylindrical vessel  715  reduces the requisite etchant volume.  
         [0047]     In the embodiment of  FIGS. 6A and 6B , the rollers, bearings, and belt are exposed to the cleaning solution. In system  700 , a single axle  705  supports tube  300  in a manner that isolates the drive mechanism from etchant  640 . Tube  300  can be heavy, and axle  705  should be sufficiently rigid to support tube  300 . Though not shown, axle supports extending from housing  645  into tube  300  can be added if necessary. Rollers  710  of e.g. TEFLON can also be added to isolate axle  705  from the wet inner surface of tube  300 . In other embodiments, rollers  710  are replaced with a chemically inert sleeve that covers a rigid (e.g., stainless steel) axle  705 . Though optional, the two end rollers  710  are mildly cam-shaped to move etchant along the length of tube  300 . Further, stops can be added to prevent tube  300  from wandering too far on the rollers.  
         [0048]      FIGS. 8A and 8B  are respective side and from views of a cleaning system  800  similar to system  600  of  FIGS. 6A and 6B , like-numbered elements being the same or similar. A cover  805  attached to the bottom end of tube  300  contains etchant  810  so the outer surface of tube  300  is not exposed to etchants. Cover  805  can be of polypropylene and may include a chemically resistance O-ring (not shown) to prevent leakage. Chemically resistant fasteners  812  hold cover in place. A vent  815  may be used to fill and drain tube  300 , and additionally serves as a vent for allowing reaction gases to escape. In the depicted embodiment, cover  805  is tapered on the side facing into tube  300  from the outside diameter toward vent  815  to facilitate draining when tube  300  is placed upright. The outer vessel is protected from exposure to etchant, but still serves as secondary containment for spills and can contain e.g. water or a relatively mild cleaning solution to control process temperature and clean the outer surface of tube  300 .  
         [0049]     As noted above in connection with the discussion of  FIG. 2 , many expensive semiconductor-processing components are aluminum contaminated with silicon or silicon-bearing compounds. Eventually, this contamination will either impede gas flow or flake off, potentially damaging expensive semiconductor die.  
         [0050]     Oxides of silicon are relatively inert, and consequently resist most etchants. However, hydrofluoric acid has long been known to be effective at dissolving silicon oxides. Unfortunately, hydrofluoric acid strongly attacks aluminum, anodized aluminum, yttrium oxide, and sprayed ceramic. Hydrofluoric acid thus damages surfaces made from these materials. Some components can be cleaned using mechanical methods that scrape or blast away exterior silicon contamination, but such methods do not work well for hard-to-reach surfaces, such as the interior surfaces of holes  205  in blocker plate  200  of  FIG. 2 . Such methods may also remove or damage sensitive coatings, and are consequently difficult to apply to components coated with yttrium oxide or sprayed ceramics.  
         [0051]     Methods used in accordance with some embodiments to remove silicon and silicon-bearing contaminants from aluminum using a hydrofluoric-acid solution prepared by combining hydrofluoric acid with an anhydrous acid. The hydrofluoric acid used in one embodiment is 51% water and 49% hydrofluoric acid, so the etchant consists primarily of water, hydrofluoric acid, and an anhydrous acid.  
         [0052]     A possible explanation for the effectiveness of this solution at removing silicon oxides from aluminum substrates without damaging the aluminum is that the high concentration of anhydrous acid deprives the etchant of sufficient free water to attack the aluminum. Whatever the mechanism, this chemistry has been found to remove silicon oxides from aluminum, anodized aluminum, yttrium oxide, and sprayed ceramic surfaces without significantly damaging the underlying material. In one example, an aluminum blocker plate  200  with 0.025 to 0.030 inch diameter holes contaminated with silicon oxide was restored without any significant reduction in hole diameter.  
         [0053]     In one embodiment, the hydrofluoric acid solution for removing silicon from aluminum contains between 0.5% and 30% hydrofluoric acid and between 50% and 99% anhydrous acetic acid. If the only water added to the chemistry is provided with the commercially available hydrofluoric acid, then the etchant will typically contain less than about 25% water. A hydrofluoric acid solution is saturated with anhydrous citric acid in another embodiment. Citric acid crystals may, for example, be added.  
         [0054]      FIG. 9  depicts a cleaning system  900  in accordance with an embodiment adapted to clean a wafer boat  905 , typically of quartz or silicon nitride. The chemistries employed are conventional, but a displacement element  910  is added to a container  915  to displace a significant percentage of the liquid used in cleaning. In one embodiment, for example, disp lacement element  910  displaces over thirty gallons, reducing the liquid required to cover wafer boat  905  from over forty gallons to about seven gallons.  
         [0055]     While the present invention has been described in connection with specific embodiments, variations of these embodiments will be obvious to those of ordinary skill in the art. For example, while the contaminated articles are round in the forgoing examples, differently shaped parts and correspondingly shaped vessels and volume-displacement elements might also be used; and the methods described in connection with  FIGS. 5-8B  can be applied to other types of cylindrical and substantially cylindrical parts, including e.g. cylindrical shields conventionally used inside deposition tubes. Therefore, the spirit and scope of the appended claims should not be limited to the foregoing description.

Technology Category: 4