Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-08-24
2003-04-29
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C422S177000, C422S178000, C422S211000
Reexamination Certificate
active
06554970
ABSTRACT:
The present invention relates to improvements made with a view to enhancing vacuum in a very high vacuum system (ultrahigh vacuum), comprising a chamber which is capable of releasing gas at its surface.
In a metal system used as a heating chamber in which very high vacuum is generated (i.e. a vacuum of at least 10
−10
Torr 10
−8
Pa), even in the order of 10
−13
to 10
−14
(10
−11
to 10
−12
Pa)), the metal walls of the chamber constitute an inexhaustible source of gas. The hydrogen contained in the metal structure (for example stainless steel, copper, aluminium alloy) is freely dispersed in the thickness of the metal and is released at the surface defining the chamber. Similarly, when the walls of the vacuum chamber are bombarded by particles (synchrotron, electron or ion radiation)—as is the case in particle accelerators—heavier molecular species are expelled, such as CO, CO
2
, CH
4
, produced at the surface after dissociation of hydrocarbons, carbides and oxides.
The vacuum level obtained in the chamber is therefore defined by the dynamic equilibrium between the release of gas at the surface defining the chamber and the pumping rate of the pumps used. Producing high vacuum involves a dual requirement of ensuring that the surface of the chamber is extremely clean so as to reduce the emission of gas and applying a high pumping rate. In the case of vacuum systems for particle accelerators, in which the chambers are generally small in section, either the pumps must be arranged close to one another or pumping has to be applied continuously in order to overcome the conductance limitation.
Under these conditions, a known approach to obtaining as high a vacuum as possible is to supplement the vacuum produced by mechanical pumps by applying complementary pumping, in particular by means of a getter arranged inside the chamber: this material is capable of producing chemically stable compounds by a reaction with the gases present in the vacuum chamber (in particular H
2
, O
2
, CO, CO
2
, N
2
) and this reaction causes the molecular species concerned to disappear, which is tantamount to a pumping effect.
However, regardless of the pumping process used and irrespective of the distributed efficiency that can be achieved by using a non-evaporable getter, the vacuum level likely to be obtained in the chamber is still defined by the dynamic equilibrium between the pumping rate (regardless of the means used) and the rate at which gas is released from the metal surface of the chamber (irrespective of the cause); in other words, the vacuum level remains dependent on the rate of release of gas inside the chamber for any given pumping rate.
In order to improve the quality of the ultrahigh vacuum inside the chamber, it is therefore desirable to try to reduce significantly the rate at which gases are released at the surface of the metal wall of the chamber and whilst doing to so increase significantly the efficiency of the pumping means.
REFERENCES:
patent: 3630690 (1971-12-01), Coppola
patent: 4000335 (1976-12-01), Stahl
patent: 4528003 (1985-07-01), Dittrich et al.
patent: 01242134 (1989-09-01), None
patent: 03247778 (1990-02-01), None
Larson & Taylor PLC
McDonald Rodney G.
Organisation Europeenne pour la Recherche Nucleaire
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