US3512369A - Ultrahigh-vacuum enclosure - Google Patents

Description

May 19,1970 I A. HOUYVET ETAL 3,512,369

ULTRAHIGH-VACUUM ENCLOSURE Filed Dec. 13, 1968 v 4/ FIG?) 42 United States Patent 3,512,369 ULTRAHIGH-VACUUM ENCLOSURE Alain Houyvet, Clamart, and Pierre Noe, Palaiseau, France, assignors to Commissariat a lEnergie Atomique, Paris, France Filed Dec. 13, 1968, Ser. No. 783,628 Claims priority, applicatiogsFrance, Jan. 5, 1968,

0 9 Int. Cl. F25b 27/00; B01d 5/00 US. Cl. 62-55.5 9 Claims ABSTRACT OF THE DISCLOSURE An ultrahigh-vacuum enclosure comprising a casing having a generally cylindrical shape formed of a lateral shell and two parallel end-walls, one end-wall being provided with a circular opening surmounted by a removable bell-housing which limits the volume of said enclosure. A cylindrical skirt is mounted opposite to the circular opening and means are provided for displacing the skirt in sliding motion through the opening. The skirt is provided in its outer surface with seals which are intended to be applied against raised bearing surfaces formed in the endwalls of the casing so as to define a closed annular chamber and a cryogenic pump is mounted within said annular chamber.

This invention relates to a sealed enclosure within which a high vacuum is produced for the main purpose of carrying out within said enclosure the deposition of metallic films on a substrate by vacuum evaporation, although other applications may be contemplated.

It is known that very low pressures cannot be produced within a sealed enclosure unless the wall of said enclosure or the objects contained therein are completely degassed. It is also known that the evaporation of any substance in a vacuum and at high temperature releases large quantities of gas which have to be removed progressively in order to maintain the pressure at its initial value. Finally, it is known that, in order to develop within an enclosure of this type a pressure which corresponds to the ultrahigh vacuum range, it is essential to utilize very high pumping speeds which can attain several thousand liters per second.

In order to obtain pumping speeds of this order, different types of high-vacuum pumps may be adopted. Among these can be mentioned the oil vapor pumps, the ionization pumps and especially the cryogenic pumps or so-called cold traps of the helium circulation type which are the most suitable for the purpose of producing both very low pressures and high outputs While requiring only limited space as well as being acceptable from the point of View of capital cost. However, in the case of the pump of the type last mentioned, it is an advantage to make provision within the enclosure for means which prevent heating of the trap, especially when a particular application makes it necessary to open the enclosure and consequently to expose this latter to the surrounding air at frequent intervals, the object achieved by such means being to avoid any unnecessary power consumption in the production of very low temperatures.

The present invention is directed to an ultrahigh-vacuum enclosure which makes it possible to achieve the object referred-to above by isolating the cryogenic pump or cold trap which is associated with said enclosure each time this latter is opened, the structure of the pump being additionally determined so that the conventional geometry of the enclosure is not modified.

To this end, the ultrahigh-vacuum enclosure in accordance with the invention which comprises a casing having a generally cylindrical shape formed of a lateral shell and ice two parallel end-walls, one end-wall being provided with a circular opening surmounted by a removable bell-housing which delimits the volume of said enclosure, is characterized in that it comprises a cylindrical skirt which is adapted to move along the axis of said casing through said opening, said skirt having a height which is substantially equal to that of said casing and provided in the outer surface thereof with seals which are intended to be applied against bearing surfaces formed in relief in the end-walls of said casing while defining a closed annular chamber, a cryogenic pump mounted within said annular chamber and means for producing the displacement of said skirt with respect to said casing.

Preferably, said cryogenic pump comprises a first annular reservoir containing a liquefied gas and forming an outer thermal shield for a second annular reservoir which contains another liquefied gas. Advantageously, said first reservoir surrounds said second reservoir on three sides, said second reservoir being provided in the outer surface which is directed towards the axis of said casing with flat circular plates forming condensation trays which are oriented at right angles to said axis. In addition, and in accordance with another characteristic feature, said second reservoir is insulated from the central portion of said casing by means of a cooled inner shield comprising a plurality of metallic fins which prevent radiation in the direction of said annular chamber.

Finally, in accordance with another characteristic feature, the means for controlling said cylindrical skirt are constituted by at least one pneumatic jack, the motion of said jack being imparted to a rod which traverses the endwalls of said casing and which is rigidly fixed to said skirt. Small columns which are parallel to the axis of said casing are adapted to cooperate with runner-wheels carried by bearing-brackets which are rigidly fixed to said skirt so as to guide said skirt in its movement of displacement relative to said casing.

Further properties of an ultrahigh-vacuum enclosure as constructed in accordance with the invention will also appear from the following description of one exemplified embodiment which is given by way of indication without any implied limitation, reference being made to the accompanying drawings, in which:

FIG. 1 is a diagrammatic axial sectional view of an enclosure in accordance with the invention;

FIGS. 2 and 3 illustrate two alternative forms of construction of a detail of one of the portions of said enclosure.

As shown in FIG. 1, the enclosure under consideration which is primarily intended for the deposition of metals by evaporation under vacuum, essentially comprises a casing 1 formed of a lateral cylindrical shell 2 and of two parallel end-walls 3 and 4 which are suitably joined to the ends of said shell with interposition of seals 5. The upper end-wall 3 is provided at its center with a circular opening 6, a skirt 7 which is also of cylindrical shape being placed opposite to said opening. Circular flanges 8 and 9 are provided respectively at each end of said skirt and adapted to accommodate seals which are designated respectively by the references 10 and 11. The height of the skirt 7 is chosen so as to be substantially equal to that of the shell 2. Thus, by virtue of the fact that the skirt can be subjected to a movement of displacement along the axis of the casing 1 under the action of control means described hereinafter, said skirt is accordingly capable of closing said casing internally and of duplicating the shell 2, there being consequently formed between said shell and the end-walls 3 and 4 an annular chamber 12 which surrounds the axis of the casing. With this objective, the annular flanges 8 and 9 together with their respective seals 10 and 12 are capable of cooperating with two bearing surfaces 13 and '14 which are formed in relief in the end-walls 3 and 4 so as to ensure leaktightness of the annular chamber 12 with respect to the central portion of the casing.

There is mounted within said annular chamber 12 a cryogenic pump or cold trap which is advantageously constituted by a first reservoir 15 of annular shape which is filled with a liquefied gas and especially liquid nitrogen by means of a double duct 16 which traverses the endwall 3. Said first reservoir 15 has a central portion 17 which duplicates the shell 2 towards the exterior of the casing and two lateral portions 18 and 19 which are parallel to the end-walls 3 and 4, thus surrounding on three sides a second reservoir 20 which is in turn filled with a second liquefied gas such as liquid helium. The first reservoir 15 thus constitutes a thermal shield for the second reservoir 20 and insulates this latter from the outer wall of the casing 1, thereby preventing any loss of refrigeration towards the exterior. In addition, a thin metallic shield 21 is advantageously placed between the casing and the first reservoir so as to provide this latter with thermal protection against direct radiation from the casing wall, the outer face of which is at ambient temperature. The second reservoir 20 is provided in the outer surface which is directed towards the axis of the casing 1 with flat circular plates 22 forming condensation trays; furthermore, this reservoir can be thermally insulated from the internal region of the casing 1 by means of a second shield 49 which is fixed between the lateral portions 18 and 19 of the reservoir 15 and formed by an assembly of flat metallic fins of which two particular profiles are illustrated in FIGS. 2 and 3. In the case of FIG. 2, said flat fins 23 are endowed with relatively high thermal conductivity whereas in the case of FIG. 2, the fins 24 have a herringbone configuration, which endows them with a greater degree of opacity but reduces the pumping speed in proportion.

The equipment of the ultrahigh-vacuum enclosure under consideration is completed by means of small spacing columns 25 which are disposed between the end-walls 3 and 4 of the casing I. Said columns serve in particular to transmit forces which arise from atmospheric pressure to the two end-walls while preventing any deformation or compression within the annular chamber 12 when the interior of the chamber is evacuated. In addition, said chamber is limited externally by a bell-housing 26 having a flange 27 fitted with a seal 28 which is intended to be fitted within a groove 29 formed in the end-wall 3, said bell-housing which is shown partially in FIG. 1 being adapted to cover the entire opening 6 of the skirt 7. The second end-wall 4 is rigidly fixed by means of screws 30 to a support plate 31 in which is formed a passage 32 for a rod 33, one end of which is fitted with a device 34 for fastening the rod to the skirt 7. In the outer region of the enclosure and beyond the point at which the rod 33 passes through the opening 32, said rod is provided with an enlarged portion forming a piston 50 which is mounted within a sleeve 35, said sleeve being secured to the underface of the support plate 31 with interposition of a seal 36. In addition, an O-ring seal 51 is fitted in the top face of said piston 50 in order to isolate the internal portion of the sleeve 35 from the enclosure when the skirt 7 is located in the top position thereof. As an advan tageous feature, the piston 50 can be duplicated by a second piston 37, both pistons being fitted with sealing rings 38 in order to isolate the interior of the enclosure from the outer atmosphere which is in contact with the extremity of the sleeve 35. Beyond the pistons 50 and 37, the rod 33 is keyed to a plate 39 which is fastened by means of screws 40 to the rods 41 and 42 of two pneumatic jacks 43 and 44 which are fixed beneath the support plate 31. Said two jacks are operated in synchronism and permit the displacement of the skirt 7 along the axis of the casing 1. The skirt is guided during its movement by means of small columns 45 which are mounted between the support plate 31 and a top plate 46 through the end-walls 3 and 4, said columns being intended to cooperate with runner-wheels 47 carried by bearing-brackets 48 which are fixed against the inner surface of the skirt 7.

The operation of the ultrahigh-vacuum enclosure as hereinabove described can now be readily deduced: during the normal period of utilization, a vacuum is first created within the enclosure by means of a conventional pump set such as a backing pump coupled with a highvacuum diffusion pump, whereupon the skirt is lifted and the pressure is reduced and maintained in the ultrahigh region by the cryogenic pump or cold trap which is constituted by the reservoirs 15 and 20 and more especially by the condensation trays 22 of the second reservoir 20, the fins 23 and 24 and the shield 21 being intended to prevent direct radiation from any heat sources towards the cold surface of the trap which is thus provided. The skirt 7 is in the top position thereof; the bell-housing 26 is tightly applied against the end-wall 3.

Should it prove necessary for any reason to gain access to the interior of the enclosure by carrying out the removal of the bell-housing 26, the annular chamber 12 which contains the cold trap is first sealed in order to maintain the low temperature which has been produced and to prevent unnecessary heating of said trap by the surrounding atmosphere. To this end, the jacks 43 and 44 are actuated in the direction which results in the downward movement of the rod 33 and consequently of the skirt 7 until this latter comes into abutment in the bottom position thereof with its seals 10' and 11 applied against the bearing surfaces 13 and 14 of the end-walls 3 and 4,

thereby totally closing the chamber 16. From this moment, the pressure within the enclosure can be progressively increased until it is possible to remove the bellhousing 26. Once the necessary operations have been carried out within the enclosure, the bell-housing is replaced and the pressure is again reduced by the pump set to a value at which the cryogenic pump can be operated efiiciently. At this moment, the displacement of the skirt 7 is produced in the opposite and upward direction so as to open the chamber 16 and permit the pressure to attain its normal operating value.

Among the advantages secured by the ultrahigh-vacuum enclosure considered, emphasis can be laid on those which arise from the fact that the design structure of the pump makes it possible to retain the conventional geometry of the enclosure while offering a large surface area on which its efiiciency is primarily dependent. In fact, the dimensions of the casing are not at all critical, the pump being integrated in the enclosure proper and so designed as to produce by means of its trays the immediate condensation of the gases to be removed. Furthermore, the structure which has been adopted and which is of revolution about the axis of the apparatus makes it possible to provide a central opening of large size. A further noteworthy advantage arises from the special arrangement which is adopted in the case of the jacks which cause the displacement of the skirt relative to the casing, whereby the interior of the enclosure can be completely isolated from the control portion proper, the leak-tight assembly of the rod which is attached to the skirt within a sleeve located outside the enclosure being such as to dispense with the need for any degassing of components which form part of the control means themselves.

As will be readily understood and as has in any case been brought out by the foregoing, the invention is not limited to the example of construction which has been more especially contemplated but extends on the contrary to all alternative forms. In particular, although the ultrahigh-vacuum enclosure considered finds an advantageous application in the deposition of metals by vacuum evaporation, it will be apparent that other applications could also be contemplated each time it proves necessary to employ an enclosure which makes it possible to carry out operations under a vacuum within a short period of time while nevertheless retaining the possibility of opening the enclosure or even of increasing the pressure at frequent intervals.

What we claim is:

1. An ultrahigh-vacuum enclosure comprising a casing having a generally cylindrical shape formed of a later- 211 shell and two parallel end-Walls, one end-wall being provided with a circular opening surmounted by a removable bell-housing 'which delimits the volume of said enclosure, characterized in that it comprises a cylindrical skirt which is adapted to move along the axis of said casing through said opening, said skirt having a height which is substantially equal to that of said casing and provided in the outer surface thereof with seals which are intended to be applied against bearing surfaces formed in relief in the end-walls of said casing while defining a closed annular chamber, a cryogenic pump mounted within said annular chamber and means for producing the displacement of said skirt with respect to said casing.

2. An ultrahigh-vacuum enclosure in accordance with claim 1, characterized in that said cryogenic pump comprises a first annular reservoir containing a liquefied gas and forming an outer thermal shield for a second annular reservoir which contains another liquefied gas.

3. An ultrahigh-vacuum enclosure in accordance with claim 2, characterized in that said first reservoir surrounds said second reservoir on three sides, said second reservoir being provided in the outer surface which is directed towards the axis of said casing with flat circular plates forming condensation trays which are oriented at right angles to said axis.

4. An ultrahigh-vacuum enclosure in accordance with claim 2, characterized in that said second reservoir is insulated from the central portion of said casing by means of a cooled inner shield comprising a plurality of metallic fins which prevent radiation in the direction of said annular chamber.

5. An ultrahigh-vacuum enclosure in accordance with claim 4, characterized in that said fins are flat.

6. An ultrahigh-vacuum enclosure in accordance with claim 4, characterized in that said fins have a herringbone profile.

7. An ultrahigh-vacuum enclosure in accordance with claim 1, characterized in that the means for displacing said cylindrical skirt are constituted by at least one pneumatic jack whose motion is imparted to a rod which traverses the end-walls of said casing and which is rigidly fixed to said skirt.

8. An ultrahigh-vacuum enclosure in accordance with claim 7, characterized in that said rod is provided externally of said casing with at least one enlarged portion forming a piston which is displaceable in leak-tight manner within a fixed sleeve, said rod being secured at one end to a plate and said plate being adapted to cooperate with two jacks which are operated in synchronism.

9. An ultrahigh-vacuum enclosure in accordance with claim 1, characterized in that small columns which are parallel to the axis of said casing are adapted to cooperate with runner-wheels carried by bearing-brackets Which are rigidly fixed to said skirt so as to guide said skirt in its movement of displacement relative to said casing.

References Cited UNITED STATES PATENTS 2,737,779 3/1956 Lawrence 62-383 X 3,3 27,491 6/ 1967 Andonian 62--45 3,360,949 1/1968 Blanchard et a1. 62-555 ROBERT A. OLEARY, Primary Examiner A. W. DAVIS, IR., Assistant Examiner U.S. Cl. X.R.

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