Cleaning method

Abstract

The present invention provides a method for cleaning a component for use in an ultra-high vacuum. The method may comprise the steps of placing the component to be cleaned in a vacuum furnace chamber; plasma cleaning the component at a temperature of greater than about 80° C.; and evacuating the chamber to a pressure of less than about 10E-5 mbar. Apparatus for performing such methods and kits comprising said components are also provided.

Claims

1. A method, the method comprising the steps of: a) placing an ultra-high vacuum component in a vacuum furnace chamber; b) plasma cleaning the ultra-high vacuum component at a temperature from 80° C. to 125° C. and at a pressure greater than 10E-06 mbar to remove hydrocarbons from the ultra-high vacuum component, wherein during plasma cleaning, the temperature is prevented from exceeding 125° C.; and c) ceasing plasma cleaning and then evacuating the vacuum furnace chamber to reduce a pressure in the vacuum furnace chamber to less than 10E-06 mbar to cause the ultra-high vacuum component to outgas, wherein during evacuating, the temperature is prevented from exceeding 125° C.

2. The method according to claim 1, further comprising evacuating the vacuum furnace chamber to a pressure of less than 10E-6 mbar, after step a) but before step b).

3. The method according to claim 1, further comprising repeating steps b) to c), from 2 to 12 times.

4. The method according to claim 1 wherein a gas for forming the plasma is introduced to a pressure of from 0.1E+00 mbar to 1E+00 mbar, and/or at flow rate from 5 sccm to 20 sccm.

5. The method according to claim 1 wherein the vacuum furnace chamber has a volume of from 250 liters to 350 liters.

6. The method according to claim 1 wherein following step c) the component is cooled and nitrogen is introduced into the vacuum furnace chamber.

7. The method according to claim 1 wherein a plasma generator is used with a voltage frequency from 20 kHz to 40 kHz.

8. The method according to claim 1 wherein step b) lasts from 15 minutes to 35 minutes.

9. The method according to claim 1 wherein steps a), b) and c) together lasts from 15 minutes to 40 minutes.

10. The method according to claim 1 wherein step c) lasts from about 2 to about 4 hours.

11. The method according to claim 1 wherein the component is cleaned with a solvent before it is placed in the vacuum furnace chamber.

12. The method according to claim 1 wherein gas for forming the plasma is selected from the group consisting of oxygen, air, nitrogen, helium and argon.

13. The method according to claim 12 wherein the gas is oxygen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred features of the present invention will now be described, by way of example, with reference to the accompanying figures, in which:

(2) FIG. 1 discloses a vacuum furnace according to the invention.

(3) FIG. 2 discloses a vacuum furnace according to the invention.

(4) FIG. 3 provides a comparison between a sample treated according to the invention and an untreated sample.

(5) FIG. 4 provides a further comparison between a sample treated according to the invention and an untreated sample.

DETAILED DESCRIPTION

(6) The present invention provides a method for cleaning a component for use in an ultra-high vacuum. The method comprises the steps of placing the component to be cleaned in a vacuum furnace chamber; plasma cleaning the component at a temperature of greater than about 80° C., preferably from about 80° C. to about 125° C.; and evacuating the chamber to a pressure of less than about 10E-5 mbar, preferably less than about 10E-06 mbar. The invention further provides a vacuum furnace for use in the method.

(7) For the purpose of the invention a vacuum furnace is a temperature controlled vacuum chamber. As discussed elsewhere in the application, the chamber may include both heating and cooling elements so that the chamber and/or component to be cleaned can be maintained at a predetermined temperature or within a predetermined temperature range. Heating is typically provided by the plasma itself, whereas cooling is, typically, used at the end of the process to facilitate removing the parts from the vacuum furnace. The temperature of the vacuum furnace chamber may be monitored by a probe with an exchangeable radiation absorber, whereas each rig within the chamber that holds a component may also have their temperature monitored by optical cable. Typically, heating will be automatically stopped when a desired temperature is reached. The chamber surface may also be monitored by separate temperature probe.

(8) FIGS. 1 and 2 show front and rear views of two vacuum furnaces (1, 2) according to the invention. The vacuum furnaces (1, 2) are located in a clean room. Each vacuum furnace includes a vacuum chamber (3, 4), a turbomolecular pump (5, 6), and a plasma generator (7, 8). A rotary pump (9) is connected to the turbomolecular pump (6) for quickly pumping down the chamber (4) to a rough vacuum during evacuation steps before the chamber (4) is evacuated to ultra-vacuum pressures. Suitable turbomolecular pumps are available from Edwards Vacuums™. Suitable vacuum furnaces are available from Termobit™. The vacuum furnace further comprises a temperature probe for monitoring the temperature within the chamber, and heating and cooling elements (not shown) for controlling the temperature within the vacuum furnace, in particular during the plasma cleaning step.

(9) The illustrated vacuum chambers further comprise observation windows (10, 11) for viewing the content of the chambers (3, 4) during the process of the invention. The second vacuum furnace (2) contains a shelving unit (12) onto which components are placed for cleaning. The vacuum chambers (3, 4) are leak-tight to a pressure of less than about 10E-8 mbar.

(10) The illustrated vacuum furnaces further comprise displays (13, 14) for controlling the vacuum furnaces (1, 2) and/or indicating the progress of the vacuum furnace (1, 2) during the cleaning process. Typically, the vacuum furnace (1, 2) performs the cleaning process automatically with each step being performed for a predetermined length of time in predetermined sequence. Typically, the user will make a single “start” input to initiate the process. The vacuum furnace will then perform the cleaning process and indicate to the user by a visual and/or audible signal that the process is complete. The cleaned components may then be employed in an ultra-high vacuum. The length and sequence of steps required to clean specific components adequately can be determined by experimentation and may vary depending upon plasma power and flow, temperature, evacuation pressure, the initial amount of hydrocarbon contamination and/or the level of cleanliness required.

(11) The working gas (e.g. oxygen) used to form the plasma enters the chamber through a flow-controlled vent (not shown). The nitrogen used for purging the vacuum furnace once the evacuation step is complete enters through a separate vent (not shown).

(12) The invention will now be described with reference to the example, which is not intended to be limiting.

EXAMPLE

(13) A purpose built vacuum furnace per the invention was assembled. The vacuum furnace comprised a 300 litre vacuum chamber [Termobit™], turbomolecular pump [Edwards™ Plasma Purifier 300 Twin], plasma generator, and a temperature control system.

(14) In a clean room, the previously unused rotors and stators of four Edwards™ nEXT™ turbomolecular pumps were cleaned using CHEMACID 5000; USF3 to remove dust, cutting agents and other surface contamination.

(15) The components of two of the turbomolecular pumps were then placed inside the vacuum furnace. The chamber was sealed and evacuated to 10E-6 mbar to remove the air from the chamber. The chamber was then filled with working gas (oxygen) to a pressure of 0.5 mbar and the sample was plasma cleaned at a flow rate of 10 sscm for 30 minutes at an elevated temperature of 80° C. with the plasma generator set to a frequency of 35 kHz and 3 kW of power.

(16) Following the plasma cleaning, the chamber was evacuated to 1E-06 mbar to remove the working gas. Once the chamber was so evacuated, the sample was cooled and nitrogen was introduced into the chamber before the temperature of the chamber dropped below about 50° C. When the chamber was at atmospheric pressure and room temperature, the vacuum chamber was opened and the clean components removed.

(17) Edwards™ nEXT™ Turbomolecular pumps were then assembled: some with plasma cleaned components, others with untreated components. All were connected to separate vacuum chambers that were leak-tight to 10E-8 mbar.

(18) Of the turbomolecular pumps, two (one plasma cleaned, one untreated) were then each connected to a separate gas-chromatographer/mass-spectrometer (GCMS) [2010 Plus and 2010 Ultra] and the remaining two were each connected to separate residual gas analysers (RCA) [Hiden Analytical HAL201]. The turbomolecular pumps were then initiated and an ultra-high vacuum of 10E-8 mbar obtained. The GCMS and RCA monitored the output of the pumps as they degassed.

(19) As shown in FIG. 3, which shows the RGA results, in the case of the plasma cleaned turbomolecular pump, the peak for AMU55 (C.sub.4H.sub.7) reached the minimum detection limit of the apparatus (i.e. 1.00E-14 Torr) in less than 2 hours, whereas the untreated apparatus took approximately 18 hours.

(20) Likewise, as shown in FIG. 4, the plasma cleaned turbomolecular pump was sufficiently clean for use in mass-spectrometry after approximately 4 hours, whereas the untreated pump took about 48 hours of hot running to be similarly clean.

(21) More than 30 vacuum assemblies were back to back tested to confirm the results. All plasma cleaned vacuum assemblies had highly reduced outgassing time compared to standard untreated assemblies.

(22) It will be appreciated that various modifications may be made to the embodiments shown without departing from the spirit and scope of the invention as defined by the accompanying claims as interpreted under patent law.

(23) Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

(24) Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.