Patent Application
20070280834
Referring to
Vacuum enclosure 3 is connected to a connecting flange 5 for connecting pump 1 with a chamber to be evacuated and is provided with a high voltage electric feedthrough 7 for pump connection to a power supply.
Primary magnets 9a, 9b are located external to vacuum enclosure 3, at opposite ends of the cylindrical anode pump cells, for producing a magnetic field parallel to the pump cell axes.
In accordance with the invention, in order to achieve a high pumping speed even at low pressures, a secondary magnet assembly 11, comprising one or more magnets, is provided on one side only of pump cells housed within enclosure 3. More particularly, in the illustrated example, secondary magnet assembly 11 is provided only on the bottom side of enclosure 3, opposite to connecting flange 5.
The magnets in secondary magnet assembly 11 (or secondary magnets) are arranged so as to produce a magnetic field in orthogonal direction to the field produced by primary magnets 9a, 9b, thereby reducing the edge effects of the primary magnets. Preferably, secondary magnets 11 are permanent magnets.
As shown in
Referring in particular to
Referring to
As it is clearly apparent, the provision of secondary magnets 11 results in a considerable increase in magnetic field strength. More particularly, due to secondary magnets 11, there is a considerable increase in the region where the transversal magnetic field component exceeds a critical value (0.14 Tesla in the illustrated example), above which the maximum efficiency of the pump cells is achieved.
It is known that two different pumping modes are associated with sputter ion pumps, namely a high magnetic field (HMF) mode and a low magnetic field (LMF) mode. If the magnetic field inside the ion pump falls below a critical value, the transition from HMF pumping mode to LMF pumping mode occurs, with a consequent reduction in the pumping speed. The critical value of the magnetic field is a function of pressure and, more particularly, it is increases as pressure decreases, so that remaining above the critical value as pressure decreases is progressively more difficult.
Thus, a stronger magnetic field (in particular above 0.14 Tesla, in the illustrated example) results in maintaining HMF pumping mode also at very low pressures, consequently improving the pumping speed.
In this respect, in
The main difference can however be appreciated in the pressure range 10−8 to 10−9 mbars (10−6 to 10−7 Pa). In the case of the pump in accordance with the invention, the pumping speed decreases as pressure decreases, but the pumping speed loss keeps limited. On the contrary, without secondary magnets, the pumping speed suffers from an extremely strong reduction. Consequently, at pressures close to 10−9 mbars (10−7 Pa), the pumping speed of a pump in accordance with the invention is about twice the pumping speed of a pump lacking secondary magnets, but otherwise identical.
Turning now back to
Thus, as stated above, a sputter ion pump with satisfactory pumping speed even at low pressures can be obtained by using a reduced number of secondary magnets disposed on a single side of the pump cells and, consequently, by keeping the size, the weight and the manufacturing costs limited as compared to the ion pump disclosed in the U.S. Pat. No. 6,835,048.
Turning now to
In
It is clear that the above description has been given by way of non-limiting example and that several changes and modifications can be included within the inventive principle upon which the present invention is based. By way of example, a number of secondary magnets other than two could be provided, or the secondary magnets could be disposed on a different side of the vacuum enclosure, without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06425377.6 | Jun 2006 | EP | regional |
