US3446422A

US3446422A - Ultra-high vacuum device

Info

Publication number: US3446422A
Application number: US649339A
Authority: US
Inventors: Josette Bailleul-Langlais; Robert Veilex
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1966-06-27
Filing date: 1967-06-27
Publication date: 1969-05-27
Anticipated expiration: 1986-05-27
Also published as: GB1194582A; DE1628443A1; FR1494152A; BE700515A; NL6708746A

Description

May 27, 1969 J. BAILLEUL-LANGLAIS ET AL 3,446,422

ULTRAHIGH VACUUM DEVICE Filed June 27, 1967 Sheet at s .INVENTORS oscnr BAILLEUL- LANGLAIS JEAN NEUW BY ROBERT V5"??? y 1969 J. BAlLLEUL-LANGLAIS ET AL 3, 22

7. ULTRA-HIGH VACUUM DEVICE FIG.2

INVENTORS JOSETTE BAILLEUL-LANGLMS EAN NEUVI J BY ROBERT VEI L Y AGENT May 27, 1969 J. BAILLEUL-LANGLAIS ET AL 3,446,422

ULTRA-HIGH VACUUM DEVICE Filed June 27. 1967 Sheet 3 of3 IN VENTORfi BY ROBERT Vflfi QZM z. AGENT LINGLNS 3,446,422 ULTRA-HIGH VACUUM DEVICE Josette Bailleul-Langlais, Suresnes, Jean Neuville,

Gentilly, and Robert Veilex, Paris, France, assignors, by mesne assignments, to US. Philips Corporation, New York, N.Y., a corporation of Delaware Filed June 27, 1967, Ser. No. 649,339 Claims priority, application France, June 27, 1966,

67,078 Int. Cl. F04!) 41/06, 37/10; F04d 25/16 U.S. Cl. 23045 7 Claims ABSTRACT OF THE DISCLOSURE for establishing an ultra-high vacuum in one region and subsequently providing a preliminary vacuum in the regions without exposing the entire preliminary pump means to atmospheric pressure; also the effect on evacuation of out-gassing of a work piece within the chamber is substantially reduced.

This invention relates to an improvement in devices having a closed chamber in which operations take place which require a very high vacuum corresponding to pressures less than 1() Pascal. It is known that certain operations such as, for example, the vapour deposition of thin layers, must be effected in ultra-high vacuum so that the various elements employed are protected :from any contamination, or to obtain beams of molecules or electrons under the conditions desired. To obtain an ultra-high vacuum in the chamber in which the said operations take place, use is preferably made of pumps operating on the fixation of gas molecules, ion pumps, cryogenic pumps, etc., which are made operative with the use of a preliminary vacuum which is usually obtained with a suitable pumping system comprising a primary pump, a secondary diffusion pump, a system of shields and an adsorption or condensation trap.

To bring about and maintain ultra-high vacuum in a given chamber by means of the above-mentioned devices one generally encounters several difficulties such as residual leaks, out-gassing or degasification of the elastic packings, interference degasifications of certain products employed, reflux beyond the pumping system, desorption of the walls of the duct or chambers provided between the ultra-high vacuum and the pumping system of the said kind. The disadvantages of the elastic packings can be obviated by using metallic packings, but these can be used only if numerous dismantlings have to be carried out.

Residual leaks can be decreased by known so-called double-walled devices. These devices comprise two chambers one of which, the inner chamber, is intended for the ultra-high vacuum and the other chamber of which envelopes the inner chamber at least in part and in which a preliminary vacuum, for example from 10- to 10* Pascal, is maintained: leaks through packings which depend upon the diiference between the pressures prevailing on each side thereof are thus found to be reduced considerably. However, these devices have the drawback that two pumping systems are required, one for each chamber, at least one pumping system having to reduce the pressure nited States Patent in the inner chamber from the atmospheric pressure to the ultra-high vacuum, which involves very long periods of pumping. However, these devices do not mitigate the disadvantage of the degasification of the products employed, for example in depositing thin layers on a substrate, during which process the latter must be protected from the evaporation of impurities of the initial product and of the container for the latter.

Devices for the vapour deposition in vacuo are also known which do not have the last-mentioned disadvantage. These devices include two chambers one of which contains the products to be evaporated and the other of which contains the elements or substrates on which there must be deposited, apertures to allow passage of useful jetsof molecules being provided between the two chambers. However, these devices again have the disadvantage that two pumping systems are needed, at least one of which must reduce the pressure in the chamber containing the substrates from the atmospheric pressure to the ultrahigh vacuum, which likewise involves very long periods of pumping.

The reflux beyond a diffusion pump cannot be eliminated completely by shields and traps of known type which are usually provided between the chamber and the pumping system. Further the packings, the ducts and all the elements located between the chamber and the pumping system liberate a certain amount of gas after each entry of air, which gas is added to possible molecular leaks, resulting in an impermissible residue atmosphere being formed. Even if removal thereof is possible, a considerable loss of time is involved due to lengthening of the pumping period.

The present invention provides a solution for the problems attended with the above-mentioned difliculties by making it possible in a closed chamber rapidly to obtain ultra-high vacuum and proceed in this chamber without influencing by interference evaporations, degasifications and the reflux of gas molecules beyond the pumping system.

According to the invention the ultra-high vacuum device includes a closed chamber which communicates with first pumping means for bringing the pressure in the whole chamber to a value corresponding to a preliminary high vacuum, and includes second pumping means for increasing the high vacuum to ultra-high vacuum in one region of the chamber. The invention is characterized in that the device includes a valve by which the region of the chamber into which the first pump is connected can momentarily be separated from the second region communicating with the second pumping means. The valve part in its closed position permits passages between the regions which allow a flow which is small enough to rapidly establish and maintain high vacuum in the second region, whereas in its open position the valve allows a large flow which is sufficient to make the first pumping means operate eificiently in the whole chamber.

Advantageously, valve seat means co-acting with the said valve part are provided and supported by the wall of the chamber through which the duct empties. This valve and seat provide connection of the duct to the first pumping means, and the valve in a third position insulates the whole chamber relative to the first pumping means.

In one modified embodiment of the invention the device includes a second wall which is integral with the valve part in the closed position thereof, and in this second closed position the valve can co-act with the valve seat supported by the wall of the chamber, in order to insulate the whole chamber relative to these pumping means. The valve part preferably has the shape of a disc and is displaced along its axis by means of a pin, the pin passing hermetically through the wall of the duct which connects the chamber to the first pumping means.

The movement of the valve part is advantageously ob tained by arranging a piston at the end of the pin located opposite the disc. The piston can reciprocate in a cylinder by creating suitable pressure difierences in the cylinder on each side of the piston, the pressures required being chosen of the lowest possible vaiues.

It will be appreciated that the valve part according to the invention, since in its closed position it divides the chamber into two distinct regions, permits the ultra-high vacuum region to be insulated from any contamination originating either from the other region of the chamber, or the ducts, or the pumping system comprising the first pumping means, or even the products employed in this second region.

In its open position this valve part leaves a passage which permits effective pumping in the whole chamber, a cryogenic trap advantageously being arranged close to the valve part in the region intended for the preliminary vacuum.

The valve part constitutes, together with the aforementioned second wall, a seal between the chamber and the first pumping means. This possibility of sealing is used prior to each new entry of air into the chamber; the entry of air is thus limited to the chamber only, the volumes comprising the traps, the deflectors, the ducts and the pumps being held under vacuum. To obtain again ultrahigh vacuum, it sufiices to create vacuum again only in the chamber itself without the whole remainder of the installation having to be exhausted and degasified.

If the second pumping means comprise an ion pump, this pump can be used with the device according to the invention under better conditions than with devices hitherto known. The relevant ion pump is put into operation only at a pressure corresponding to the preliminary high vacuum, which is attended with a much smaller consumption of energy for the said pump, resulting in a less important supply device and a much longer lifelength.

If the second pumping means is of the diffusion type instead of the fixation type, the ultra-high vacuum can be reached in a device according to the invention within a short time. In fact, when the whole chamber is exhausted to preliminary high-vacuum with the aid of the first pumping means, the diffusion pump which in this case forms the second means can be insulated from the chamber by a suitable regulating cock and it is not contaminated.

In order that the invention may be readily carried into effect, it will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIGURE 1 shows a partial cross section of a device according to the invention,

FIGURE 2 shows a partial cross section of a modification of a device according to the invention;

FIGURE 3 shows an assembly diagram of an ultra-high vacuum installation according to the invention.

FIGURE 1 shows an ultra-high vacuum device according to the invention including a valve 2a which divides the chamber 1 into two regions, one region 1a for the ultra-high vacuum and the other region 1b for the preliminary high-vacuum. The plate-shaped, preferably circular, movable valve 2a is fitted on a pin 7 and can coact in position 2a by its conical peripheral surface 6 with a fixed seating 2b; this results in an adequate seal being obtained between the regions 10 and 1b without the interposition of an elastic or metallic packing. It will be evident that the sealing surface between the valve and its seating need not be conical and can be spherical or toroidal.

The region 1a of the chamber includes an ion pump 3 which is shown, by way of example, as a means for improving the vacuum in the region 1a to the desired ultrahigh vacuum. This region of the chamber further includes a port-hole 4 and a device 5 for measuring the ultra-high vacuum 11, all these and any further elements required being secured in an air-tight manner, possibly with the interposition of only metallic packing. A removable elastic packing may be provided, for example at 18, between the region 1b of the chamber and the atmosphere, in order to permit easier access to the two regions upon dismantling, but on the condition that this packing is actually provided between the region 1b and the atmosphere and not between the region In and the atmosphere.

A duct 10 of large diameter opens into the region 1b of the chamber and is lengthened, preferably at right angles thereto, with another duct 8, substantially of the same diameter, which is connected to a pumping system, not shown. This pumping system comprises a primary pump, a secondary diffusion pump, possibly a vacuum container, and a cooled trap or an absorption trap, such as zeolites, all these elements being connected in a manner as usual in such a case.

Around the aperture through which the duct 10 opens into the region 1b there is provided an annular elastic packing 9 which is placed and matched so that the valve 2a in its position 2:1 can push on this packing by a rectilinear movement of the pin 7, so that the chamber and the duct 10 are completely insulated from each other.

In order that, on the one hand, the supporting surface 6 between the valve 211 and its seating 2b and, on the other hand, the supporting of the valve 2a by the packing 9 are evenly divided throughout their peripheries, the pin 7 is guided in a bearing 11 which is integral with the duct 10 and placed as close as possible to the surface of the packing 9.

A duct 20 which is connected to the primary pump of the pumping system or to the vacuum container opens into the region 1b of the chamber in order to be able, after an entry of air, to create a preliminary vacuum in the whole of the preliminary chamber before it is brought into communication with the high-vacuum duct 10.

The pin 7 passes through the wall of the duct 10 so that its rectilinear movement can be brought about by operating an outer part thereof. This passage must, of course, be hermetic. An advantageous form of a hermetic passage is formed by a bearing 17, which in turn is hermetically secured in line with the duct 10 which includes two

toroidal packings

17a and 17b between which a chamher through which the pin 7 passes is maintained under vacuum due to a duct 21 which is connected to the primary pump or the vacuum container.

In the device of FIGURE 1 the movement of the valve 2a is obtained by means of the following device: a piston 12 is secured to the end of the pin 7 and can hermetically reciprocate in a closed cylinder which is divided by the piston into two

sections

13 and 14. Two

ducts

15 and 16 each provided at one end of the cylinder may be connected, independently of each other, either to the primary vacuum, or the atmosphere, or a source of slightly cornpressed air.

Due to the exhaustion of the volume 14 and an entry of air at 13, the valve 2a is brought into the position Za which insulates the chamber from the duct 10. The entry of air into the chamber further produces an advantageous effect by increasing the pressure on the packing 9. Due to the exhaustion of the volume 13 and the entry of air, possibly compressed, at 14, the valve 2a is brought into the position 2a which separates the two regions 1a and 1b from each other. The open position 20 of the valve, located between the two previous positions, is obtained by suitably dosing the entries of air at 13 and 14 or by any other pneumatic, mechanical or electrical device for moving the pin7 and the piston 12.

To improve the vacuum conditions in the chamber during the preliminary pumping process, a tubing 19 preferably cooled by the circulation of liquid nitrogen is arranged close to the valve 2a in the region 1b of the chamber. This tubing constitutes a very effective trap for water vapour. All the elastic packings of the device of FIGURE 1, such as the

packings

9, 17a, 17b and 18, preferably consist of a material which is sold commercially under the name Viton, the degasification of which is negligible to pressures below Pascal.

FIGURE 2 shows a second embodiment of the invention which is suitable especially for the vapour deposition of thin layers. The vacuum chamber is divided two regions 31a and 31b by a valve 32a which can co-act, for example, by polished conical surfaces 33, with a fixed seating 32b.

The region 31a which is intended for the ultra-high vacuum, is connected to an ion pump 34, a pressure gauge 36, and a port-hole 35, but it will be evident that any other expedient required, for example electrode passage, cryogenic pump, could be provided, all the packings required having to be of metal, in order to prevent any impermissible degassing flow.

The valve 320 is secured to a pin 37 on which a plate 38 is also fixed at a distance suflicient for placing evaporating devices, crucibles and heating means in the volume between the valve 32a and the plate 38. Rectiliuear move ment of the pin 37 causes the plate 38 to engage an annular elastic packing 39 provided on a wall of the chamber 31; the chamber is thus insulated from a duct 40 Which in turn is connected through a duct 44 to the pumping system. The assembly comprising the valve 32a and the plate 38 can further occupy an intermediary position which leaves a passage between these elements and the wall of the chamber 31b sufficient to permit eflicient pumping of the whole chamber. The region 3112 of the cham* ber includes a removable packing 41 of which the position shown is not limiting, since the said region can have any form other than that shown without passing beyond the scope of the invention.

Elements which correspond to those of FIGURE 1 are found again in the device of FIGURE 2: a bearing 42 for guiding a pin 37, a duct 43 for the preliminary pumping and the re-entry of air, a double packing 47 at the lead-through of the pin .37, having an intermediate chamber which can be exhausted through a duct 45, a piston 46 which can reciprocate in a cylinder 48,

connections

49 and 50 for the preliminary vacuum and air respectively, and a tubing 51 which constitutes a cryogenic trap in the regoion 31b.

If the device in FIGURE 2 is used for the vapour deposition of thin layers, the trap 53 must be designed for passing jets of molecules under optimum conditions, said jets emerging from the initial products arranged between the said valve and the plate 38 and being directed onto the substrate to be coated which is arranged under ultrahigh vacuum in the region 31a. It is possible, for example, to provide threaded holes 30 into which tubes having a double wall or provided with heating or cooling agents can be screwed; the sole condition being that the total area of resulting apertures shall be sufficiently small, for maintaining the ultra-high vacuum in the region 31 of the chamber by means of the pump 34, making allowance for leakage through faults in the packing 33.

The cycle of operations necessary for the use of an improved ultra-high vacuum device according to the invention will now be described with reference to the diagram shown in FIGURE 3. This diagram relates to a device similar to that of FIGURE 1 to which a device for evaporating thin layers has been added.

In this diagram the region In of the chamber constitutes the ultra-high vacuum chamber including an ion pump 3 and a pressure gauge 5, which is insulated from the region 1b by the valve 2a which can occupy the positions 2:1 2:1 and 2a When the valve first of all occupies position 2:2 a preliminary vacuum is created in the regions 1a and 1b and also in the chamber 4 in which the initial products in the crucibles with their heating means are arranged. The preliminary vacuum is obtained by means of a primary pump 52, a trap 53,

cocks

64, 65 and the duct 20, The preliminary vacuum is also obtained in a container 54, and a high vacuum is obtained in the

ducts

8 and 10 using deflectors 56 and a trap 55 by means of a diffusion pump 57. The preliminary vacuum is also created in a chamber 17 through the duct 21 and in a chamber 14 through the duct 16, dependent upon the position of a cock 62. With a suitably chosen position of a cock 63 the chamber 13 communicates with the atmosphere through the duct 15 whereby the valve 2a is pushed on the packing 9.

When the vacuum in the chamber 1a, 1b is adequate, which may be tested by means of a pressure gauge 60, liquid hydrogen is introduced into the tubing 19 by a pump 59 and the cock 63 is turned in order to create vacuum in the chamber 13 until the valve has assumed the position 211 the cock 65 then being closed. A similar pressure as in the region lb can be obtained in the chamber 4 through the duct 66 of high conduction, and a high vacuum may be obtained in the whole of the chamber by means of the diffusion pump.

The necessary out-gassing and descriptions take place in the chamber 4 and the region 1a. The pump 3 is put into operation. The valve 2a is then brought into the position 2a by supplying, at 14, air at a pressure above atmospheric pressure by means of a pump 61, the cock 62 then having to occupy the desired position. The ultrahigh vacuum is obtained in the region 1a in which the vapour deposition process is carried out. The valve is subsequently moved back to the position 2:1 and air can re-enter into the chamber by means of the cock 65.

It will be evident that modifications can be made to the embodiments described, notably by using equivalent technical means, without passing beyond the scope of the invention.

What is claimed is:

1. In an apparatus including a housing defining therein a chamber, and first and second pump means for sequentially establishing in said chamber a preliminary vacuum and an ultra-high vacuum the improvement in combination therewith comprising:

(a) a first junction means including a. first valve seat for connecting the first pump means to the chamber;

(b) a second junction means remote from the first for connecting the second pump means to the chamber;

(c) a second valve seat located in the chamber inbetween the first and second junction means for dividing the chamber into first and second regions communicating directly with the first and second pump means respectively;

(d) a valve comprising a plate corresponding to said valve seats and a rod extending therefrom, the plate being movable: (1) to a first position in pressuresealing contact with said first valve seat, thereby closing the first junction from the first pump means while leaving the two regions in communication with each other, (2) to a second position in pressure-sealing contact with said second valve seat, thereby dividing the chamber into the first and second regions while leaving the first junction open to said first pump means, and (3) to a third position between the first and second valve seats, thereby leaving the first junction open and the two regions in communication with each other;

(e) means coupled to the rod for driving the valve plate selectively to its three positions; and

(f) a third junction means for connecting the first pump means to said first region for creating a preliminary vacuum in the regions when the first junction is closed.

2. Apparatus as defined in claim 1, further comprising a cylinder, a piston movable therein and connected to the rod of the valve for driving the valve plate between its positions, first and second duct means connected to the cylinder, and fluid means for applying pressure through said ducts for driving the piston axially in the cylinder.

3. Apparatus as defined in claim 2 wherein said fluid means comprises said first pumping means for applying negative pressure to the piston and atmospheric air for applying positive pressure to the opposite side of the piston.

4. Apparatus as defined in claim 1 wherein the chamber includes a wall portion having two spaced apertures therethrough, one aperture being associated with said first junction means, the apparatus further comprising a bearing mounted in said second aperture through which extends said valve rod.

Apparatus as defined in claim 1 further comprising 1 a coil of a hollow tubing disposed in said chamber and means for flowing liquid nitrogen through the coil, whereby water vapor is condensed and trapped on the coil. 6. Apparatus as defined in claim 1 further comprising control means for selectively operating elements of the apparatus in sequence including:

(a) moving the valve to its third position, (b) drawing a preliminary vacuum in said first and second regions by the first pump means, ('0) moving the valve to its second position, (d) drawing an ultra-high vacuum on said second region only by said second pump means, (e) moving the valve to its first position for maintaining said high vacuum in the first pump means,

(*5) opening the chamber whereby atmospheric air may enter,

(g) closing said chamber for re-evaouation,

(h) opening the third junction means for drawing a preliminary vacuum in said first and second regions,

(i) moving the valve to its third position for further evacuation of said regions, and

(j) moving the valve to its second position for again drawing an ultra-high vacuum in the second region.

-7. Apparatus as defined in claim 1 wherein the second pumping means comprises an ion pump.

References Cited UNITED STATES PATENTS 2,806,644 9/1957 Warren 230-401 2,826,353 3/1958 Auwarter et al. 230-101 XR 2,935,243 5/1960 Sadler 230- 3,144,199 8/ 1964 Ipsen 230-45 ROBERT M. WALKER, Primary Examiner.

US. Cl. X.R. 230*-10l, 227