EP1513598A1

EP1513598A1 - Cold trap with rapid regeneration

Info

Publication number: EP1513598A1
Application number: EP03756032A
Authority: EP
Inventors: Jean-Pierre Desbiolles; Gloria Sogan; Sébastien Munari; Emmanuelle Veran
Original assignee: Alcatel CIT SA; Alcatel SA
Current assignee: Alcatel Lucent SAS
Priority date: 2002-05-30
Filing date: 2003-05-30
Publication date: 2005-03-16
Also published as: JP2005527366A; FR2840232A1; FR2840232B1; US20050235656A1; WO2003101576A1; US7370482B2

Abstract

The invention relates to a cold trap comprising a hollow body (3) with an inlet valve (2) and an outlet valve (6). The aforementioned hollow body (3) houses a cold core (11) which is associated with a plate (13) with low thermal inertia which can move between a trap position in which it is in contact with the cold core (11) and a regeneration position in which it is moved away from said cold core (11) and brought into contact with a heating ring (14). According to the invention, the plate (13) is in contact with the gases to be trapped and prevents said gases from moving towards the cold core (11). The regeneration requires the heating of the single plate (13) bearing the condensed, solidified gases and is therefore faster.

Description

FAST REGENERATION CRYOGENIC TRAP

TECHNICAL FIELD OF THE INVENTION The chambers of semiconductor component manufacturing installations contain gases originating from airlocks or process chambers.

These gases must be removed to avoid subsequent pollution of the semiconductor wafers introduced into the transfer chambers before or after their treatment. The gases are evacuated by mechanical pumping, often associated with a cryogenic trap, by performing selective pumping.

A cryogenic trap comprises a contact surface, brought and maintained at very low temperature by a cold source, and placed in contact with the pumped gases. The pumped gases thus condense and solidify on said contact surface, and are therefore removed from the interior atmosphere.

Commonly used cryogenic traps include a cold mass placed in contact with the gases in the chamber, and cooled by a cold finger thermally connected to a cold generator. The contact surface is the surface of the cold mass itself.

The problem is that the gases by condensing, in particular water, produce on the cryogenic trap a thick layer of ice which remains stationary and progressively reduces the freezing capacity of the cryogenic trap and its capacity to trap the gases to be eliminated.

It is therefore necessary to regenerate the cryogenic trap periodically, by heating it to make the ice disappear. For regeneration, warm the mass and cold finger. During this reheating step, the trap is inactive, and releases the previously trapped materials into the interior atmosphere. This results in a relatively long period, approximately two hours, between two successive operational states, to remove the ice and return the cryogenic trap to operation at low temperature. The entire installation must be shut down to avoid faults due to backward pollution resulting from the non-functioning of the cryogenic trap and the release of the trapped materials. In current systems, this rules out being able to regenerate the trap frequently. We must then be satisfied with a reduced effectiveness of the trap. To ensure faster regeneration of a cryogenic trap, the document JP 10 077967 A provides a movable contact surface in the form of a deformable diaphragm whose periphery is fixed to the wall of the hollow body and which carries an intermediate ring biased in displacement towards and away from a cold core by shape memory coils. The diaphragm is permanently thermally connected on the one hand to the peripheral wall of the hollow body, and on the other hand to the shape memory coils which themselves are heated by the passage of an electric current brought by an electric conductor. . During the regeneration stages, the diaphragm is heated by the heat released in the shape memory coils. The assembly thus has a relatively high thermal inertia. In addition, the presence of the diaphragm requires the provision of additional pumping means to balance the gas pressures on either side of the diaphragm. Such a system is thus complex, and does not allow regeneration fast enough to be carried out in masked time between successive stages of activity of a device for manufacturing semiconductor components.

Document US 4,763,483 describes a reverse solution, in which the contact surface is fixed, consisting of a central sleeve with fins connected to a coaxial peripheral tube by a connection zone provided with a heating ring. The cold core moves inside the cylindrical winged sleeve, to be in contact with or separated from the winged sleeve. In such a device, the contact surface has a high thermal inertia, and it is permanently in thermal contact with the heating means constituted by the heating ring. As a result, the regeneration is not fast enough to be carried out in masked time between successive stages of activity of a device for manufacturing semiconductor components. STATEMENT OF THE INVENTION

The invention aims to avoid the drawbacks of the systems of the prior art, firstly by eliminating more quickly the ice trapped on the cryogenic trap, then by bringing the cryogenic trap back to low temperature more quickly to make it operational again.

It is sought to achieve regeneration, the duration of which is of the order of one to a few minutes, in order to be able to perform regenerations in masked time between successive stages of activity of the device for manufacturing semiconductor components.

In this way it is possible to maintain optimum efficiency of the cryogenic trap, without harming the rates of use of the chambers, and without increasing the risk of retrograde pollution. The essential idea of the invention is to produce a cryogenic trap whose surface which is in contact with the gases to be trapped has two states, comprising a first state with high thermal inertia for the gas trapping steps, and a second state with low thermal inertia for the regeneration stages. To achieve these and other objects, the cryogenic trap according to the invention comprises, in a hollow body with a peripheral wall, a contact surface disposed in contact with the gases to be trapped, means for generating cold to cool the surface of contact at a suitable temperature to condense and solidify the gases to be trapped, and heating means for periodically heating the contact surface and thus eliminating the layer of ice which is deposited on the contact surface during trapping; according to the invention:

- the contact surface is a thermally insulated element and itself has low thermal inertia,

the contact surface is thermally connected to the means for generating cold by means of thermal transmission means having:

a first state with high conductance, for the gas trapping steps,

A second state with low conductance, for the regeneration steps, - the heating means are permanently separated from the cold generation means and are provided for selectively heating the contact surface during the regeneration steps, - isolation means are provided for keeping the gases to be trapped at away from the means of cold generation.

In this way, during the regeneration step, only the insulated contact surface with low thermal inertia is heated, requiring a lower heating energy than known devices. The cold generation means, thermally isolated from the contact surface, are not substantially heated and remain at operating temperature, thus reducing the cooling energy necessary to return the cryogenic trap to operating condition, and reducing the time required for it. And during the trapping step, the heating means are isolated from the contact surface and from the cold generation means and are not cooled, while the contact surface is rapidly cooled. According to an advantageous embodiment:

the contact surface is the exposed surface of a plate with low thermal inertia and isolated from the peripheral wall of the hollow body, movable between a trapping position in which the plate is in contact with the means for generating cold while being isolated heating means, and a regeneration position in which the plate is away from the cold generation means while being in contact with the heating means,

displacement means are provided for selectively displacing the plate between its two positions,

- The heating means are provided for selectively heating the tray when it is in the regeneration position.

In practice, the general structure of the cryogenic trap can be such that the hollow body comprises an interior cavity with a proximal zone and a distal zone, the proximal zone being in communication with a main inlet by an access valve, the distal zone containing the cryogenic trap and being in communication with the proximal zone which separates it from the main entrance.

Preferably, the proximal zone is in communication with pumping means by an outlet valve.

Preferably, the cryogenic trap must maintain a high thermal inertia, in order to be as quickly as possible in working condition after a regeneration step. For this, it can advantageously be provided that the cold generation means comprise a cold core with high thermal inertia, placed in the distal zone, and arranged so that the plate comes to bear on the cold core in the trapping position, the cold core itself being thermally coupled to external means for generating cold by a cold finger. In this case, it is advantageous to provide that:

the plate moves in a cylindrical portion of the cavity of the hollow body with a small peripheral space between the peripheral edge of the plate and the wall of the cavity,

- Neutral gas injection means create in said low peripheral space a flow of neutral gas circulating from the distal zone towards the proximal zone, said flow of neutral gas opposing the passage of the gases to be trapped towards the cold core.

According to one embodiment, the displacement means can advantageously comprise said means for generating a flow of neutral gas in said small peripheral space from the distal zone towards the proximal zone, said means for generating a gas flow neutral then being adapted to selectively generate a flow of neutral gas at a higher flow rate which moves the plate to the regeneration position.

According to another embodiment, the displacement means comprise an actuator connected to the plate by one or more insulating rods integral with the plate.

SUMMARY DESCRIPTION OF THE DRAWINGS Other objects, characteristics and advantages of the present invention will emerge from the following description of modes of specific embodiments, made in relation to the attached figures, among which:

- Figure 1 is a schematic view of a cryogenic trap structure according to an embodiment of the present invention, in the trapping position;

- Figure 2 illustrates the state of the device and the circulation of neutral gas in the trapping position; FIG. 3 illustrates the state of the device during the intermediate stage of heating the heating means in the form of a heating ring; FIG. 4 illustrates the state of the device during the intermediate step of injecting a flow of neutral gas to lift the tray; FIG. 5 illustrates the state of the device in the regeneration position; and

- Figure 6 is a schematic view of a cryogenic trap structure according to another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the embodiments illustrated in the figures, the cryogenic trap comprises a hollow body 3 with peripheral wall 3a having a main inlet 4 and an outlet 5, both located in a proximal zone 16 of the hollow body 3 The main inlet 4 is connected by an access valve 2 to a main chamber 1 from which it is desired to extract and trap the gases. The outlet 5 is connected by an outlet valve 6 to an outlet pipe 7 connected to pumping means not shown.

A contact surface 13a is arranged at the interface between the proximal zone 16 and a distal zone 17 of the interior cavity of the hollow body 3, so as to be in contact with the gases to be trapped which penetrate into the proximal zone 16 through the main entrance 4.

The cryogenic trap includes means for generating cold to cool the contact surface 13a to a temperature suitable for condensing and solidifying the gases to be trapped. The cold generation means comprise a cold core 11 with high thermal inertia, coupled to external cold generation means 12a by a cold finger 12 which passes through the peripheral wall 3a of the hollow body 3. The cold core 11 is located in the distal zone 17, opposite the proximal zone 16 relative to the contact surface 13a.

In the illustrated embodiments, the contact surface 13a is the proximal surface of a plate 13 with low thermal inertia, which is associated with the cold core 11, and which is thermally insulated from the peripheral wall 3a of the hollow body 3 by a peripheral space 15.

The plate 13 is movable, in the interface between the proximal zone 16 and the distal zone 17 of the cavity, between a trapping position, illustrated in FIGS. 1 to 4, and a regeneration position illustrated in FIG. 5.

In the trapped position, the plate 13 is in contact with the cold core 11, along a large contact surface, so that the large contact surface constitutes a thermal transmission means having a high conductance, ensuring good cold transmission from the cold core 11 to the contact surface 13a or proximal surface of the plate 13.

In the regeneration position, the plate 13 is away from the cold core 11, from which it is separated by an insulating air gap 23 occupied by the gases at very low pressure contained in the hollow body 3. In this way, in this position of regeneration, the air gap 23 constitutes means of thermal transmission having a low conductance. For its movement between the trapping and regeneration positions, the plate 13 is guided by guide means such as, for example in FIGS. 1 to 5, a guide pin 21 integral with the plate 13 and sliding in guides passing through the cold core 11. In trapping position as illustrated in the figure

1, the gases to be trapped penetrate into the proximal zone 16 and come into contact with the cold contact surface 13a. They thus condense on the contact surface 13a. However, it is necessary to avoid that the same gases circulate around the cold core 11, because they would also deposit on the cold core 11, producing a layer of ice over the entire external surface of the cold core 11, and in particular on its proximal surface against which must come in contact the plate 13. To prevent the gases to be trapped circulating around the cold core 11, provision is made for a circulation of a neutral gas such as nitrogen which causes a flow of neutral gas from the distal zone 17 towards the proximal zone 16 of the hollow body 3. For this in the embodiment of FIGS. 1 to 5, a source of neutral gas 18 such as nitrogen is connected to the distal zone 17 by pipes 18a and control valves 9 and 10, for let neutral gas enter through a neutral gas inlet 8 located in the distal zone 17 away from the proximal zone 16. A first control valve 9 ensures a low flow of neutral gas, while a second control valve 10 ensures a greater flow of neutral gas.

In trapping mode, as illustrated in FIG. 2, the access valve 2 is open to admit the gases to be trapped from the chamber 1 towards the proximal zone 16. The outlet valve 6 is open. The opening of the first control valve 9 and the closing of the second control valve 10 produce a weak flow FI of neutral gas, which circulates in the small peripheral space 15 between the periphery of the plate 13 and the wall 3a of the hollow body 3. This weak IF flow of neutral gas is opposed to the passage of trapped gases from the proximal zone 16 to the distal zone 17 containing the cold generation means 11, 12. However, the weak IF flow of neutral gas is not not sufficient to cause displacement of the plate 13, which thus remains in contact with the cold core 11 and, by its low temperature, condenses the gases in the form of a layer of ice 22.

The cryogenic trap also comprises means for moving the plate 13 between its trapping and regeneration positions. In the embodiment illustrated in Figures 1 to

5, the displacement means comprise said means for generating a neutral gas flow in said peripheral space 15 from the distal zone 17 in the direction of the proximal zone 16. Thus, to move the plate 13 from the trapping position (FIGS. 1 and 2) until in the regeneration position (FIG. 5), the second control valve 10 is opened, possibly closing the first control valve 9, to produce a flow of neutral gas at higher flow rate F2 in the small peripheral space 15 from the distal zone 17 towards the proximal zone 16, as shown in FIGS. 4 and 5. The flow at higher flow rate F2 moves the plate 13 up to in the regeneration position, away from the cold core 11 (Figure 5).

In other embodiments, the means for moving the plate 13 can be means, mechanical, pneumatic, electromagnetic, for example.

This is so in the embodiment of Figure 6. In this figure, we find the essential elements of a cryogenic trap of the previous embodiment of Figures 1 to 5, and these elements are identified by the same reference numerals. The hollow body 3 is limited by a peripheral cylindrical wall 3a, inside which the other elements of the trap are placed, namely the cold core 11 supplied by the cold finger 12, the plate 13 movable by axial sliding in the body hollow 3 and constituting the contact surface 13a, and a neutral gas inlet pipe 18a for causing neutral gas to enter the distal zone 17 through a neutral gas inlet 8 and thereby generating a neutral gas flow FI circulating in the small peripheral space 15 between the periphery of the plate 13 and the wall 3a of the hollow body 3.

In this embodiment, the means for moving the plate 13 comprise an actuator 30 such as a screw jack, a hydraulic jack, a stepping motor or any other known type of actuator, connected to the plate 13 by one or several insulating rods such as rods 21, 21a and 21b which pass freely through the cold core 11.

The actuator 30 is arranged opposite the plate 13 relative to the cold core 11, in the distal zone 17 of the hollow body 3.

In the illustrated embodiment, the three rods 21, 21a and 21b are integral with the plate 13, and their presence prevents any rotation of the plate 13 around the longitudinal axis of the hollow body 3.

Preferably, the insulating rods 21, 21a and 21b are stressed by the actuator 30 by means of a plate support 31 and respective elastic means 32, 32a and 32b interposed between the distal ends of the insulating rods 21, 21a and 21b and the support plate 31.

Preferably, the insulating rods 21, 21a and 21b are separable from the actuator 30 during the gas trapping steps, that is to say when the support plate 31 is in the position of maximum deviation from the cold core 11, the plate 13 then resting on the contact face 11a of the cold core 11. This reduces the thermal inertia of the assembly formed by the plate 13 and the insulating rods 21, 21a and 21b.

The cryogenic trap according to the invention furthermore comprises heating means 14 for selectively heating the plate 13 when it is in the regeneration position.

In the embodiments illustrated in the figures, in particular FIG. 1 and FIG. 6, the heating means comprise a heating ring 14 disposed in the cavity of the hollow body 3 facing the contact surface 13a of the plate 13, so that the plate 13 comes into contact with the heating ring 14 through its peripheral zone when it is in the regeneration position. Thus, the heating ring 14 is placed in the proximal zone 16 of the cavity of the hollow body 3, near the distal zone 17, but at a distance from the cold core 11.

The heating ring 14 may for example be a ring consisting of an electrical resistance supplied by a supply 19 of electrical energy. The heating ring 14 is placed away from the cold core 11, at a suitable distance to define the air gap 23 (FIG. 5) between the plate 13 and the cold core 11 when the plate 13 is in contact with the heating ring 14 in regeneration position. Means can also be provided to promote the thermal connection between the plate 13 and the cold core 11 when the plate 13 is in the trapping position. One difficulty is in fact to ensure a good thermal connection while the plate 13 and the cold core 11 are bathed in a gaseous atmosphere at very low pressure, and therefore thermally insulating. Such a means can consist in injecting helium into the zone between the cold core 11 and the plate 13, the helium being a good thermal conductor.

Another means is to provide a film of thermally conductive material interposed between the cold core 11 and the plate 13, for example fixed on one or the other of the elements.

The cryogenic trap as illustrated in FIG. 1 further comprises control means 20 which sequentially control the operation of the displacement means such as the means for injecting neutral gas 9, 10, of the access valve 2, heating means 14 by their supply 19, and the outlet valve 6.

In a permanent trapping regime, illustrated in FIG. 2, the neutral gas current FI is weak, and only opposes the passage of trapped gas from the proximal zone 16 of the cavity towards the cold generation means 11, 12. The access valve 2 is open for the passage of the gases to be trapped. The outlet valve 6 is in principle open, to favor the presence of a gas stream from the chamber 1 to the proximal zone 16 of the cavity. After the trapping step, in FIG. 3, an intermediate step of heating the heating ring 14 is undertaken: the access valve 2 is closed, and the heating ring 14 is supplied with electrical energy by the supply 19 ( figure 1). The weak IF flow of neutral gas can continue. In FIG. 4, an intermediate stage of lifting the plate 13 is then undertaken: the access valve 2 remains closed, the outlet valve 6 remains open, the heating ring 14 remains supplied with electrical energy, the control valve is opened 10 to admit a flow of neutral gas at a high flow rate F2 into the distal zone 17 of the cavity and into the peripheral space 15. The flow F2 is chosen to be sufficient to take off the plate 13 and lift it away from the cold core 11.

During regeneration, the neutral gas circulation F2 remains strong, and pushes the plate 13 against the heating ring 14. The plate 13 thus lifted is therefore thermally isolated from the cold core 11 by the air gap 23. It is on the other hand in contact with the heating ring 14 which is itself electrically heated. One then obtains a rapid sublimation of the ice 22 previously formed on the contact surface 13a of the plate 13. The access valve 2 remains closed, while the outlet valve 6 remains open to evacuate the sublimed gases 24. The flow of neutral gas F2 such as nitrogen makes it possible to dilute the vapors resulting from the sublimation of the ice 22, and to evacuate them by the outlet pipe 7.

When the regeneration is complete, the plate is returned to the initial position against the cold core 11 by closing the control valve 10, and due to its low thermal inertia it cools very quickly in contact with the cold core 11.

As a result, the regeneration procedure is very rapid, and the system can find itself in correct operating condition with the contact surface 13a at a temperature suitable for trapping after a very short duration, of the order of one to a few minutes.

The control means 20 comprise for example a microcontroller or a microprocessor programmed so as to sequentially control the control valves 9 and 10, the access valve 2, the outlet valve 6 and the supply 19 according to the sequence of steps described above.

In the embodiment of FIG. 6, the neutral gas is introduced through a pipe 18a which opens out through at least one neutral gas inlet 8, preferably placed in the central zone of the contact face 11a of the cold core 11. This face contact 11a of the cold core 11 is shaped to allow the diffusion of neutral gas under the plate 13 when the latter is in the regeneration position, pressing against the contact face 11a of the cold core 11. At the periphery of this contact face 11a, a crown 11b in relief provided with radial grooves 11 is provided, as illustrated in enlarged detail in detail A. Raised support zones 11d are scattered on the contact surface 11a, to distribute the support of the plate 13.

In this way, a neutral gas such as nitrogen escapes through the inlet of neutral gas 8, diffuses over the entire lower surface of the plate 13 to ensure good thermal transmission between the plate 13 and the cold core 11 in position of regeneration, then escapes towards the proximal zone 16 by producing the flow F1 in the peripheral space 15 around the plate 13, opposing the penetration of the gases pumped from the proximal zone 16 towards the distal zone 17 and the cold core 11. In this embodiment, thanks to the displacement of the plate 13 by a mechanical actuator, it is possible to ensure effective guiding of the plate, so as to reduce the peripheral space 15, thus reducing the flow F1 of neutral gas necessary to ensure l '' stop of pumped gases. The reduced flow F1 makes it possible to further reduce the thermal bond between the plate 13 and the peripheral wall 3a of the hollow body 3, ensuring low thermal inertia of the plate 13.

In addition, the fact that the neutral gas escapes through a central neutral gas inlet 8 improves the thermal contact between the plate 13 and the cold core 11 in the trapping position.

One can also provide an elastic return means of the plate 13 towards the trapping position, to ensure better contact between the plate 13 and the cold core 11. The present invention is not limited to the embodiments which have been explicitly described , but it includes the various variants and generalizations which are within the reach of those skilled in the art.

Claims

CLAIMS 1 - Cryogenic trap comprising, in a hollow body (3) with peripheral wall (3a), a contact surface (13a) arranged in contact with the gases to be trapped, means for generating cold (11, 12) to cool the contact surface (13a) at a temperature suitable for condensing and solidifying the gases to be trapped, and heating means for periodically removing the layer of ice (22) which is deposited on the contact surface (13a) during trapping, characterized in that: - the contact surface (13a) is an element (13) thermally insulated and itself having low thermal inertia,

- the contact surface (13a) is thermally connected to the cold generation means (11, 12) by means of thermal transmission means having: 'a first state with high conductance, for the gas trapping steps,' a second low conductance state (23), for the regeneration steps,

the heating means (14) are permanently separated from the cold generation means (11, 12) and are provided for selectively heating the contact surface (13a) during the regeneration steps,

- Isolation means (F1) are provided to keep the gases to be trapped away from the cold generation means (11, 12). 2 - Cryogenic trap according to claim 1, characterized in that:

the contact surface (13a) is the exposed surface of a plate (13) with low thermal inertia and isolated from the peripheral wall (3a) of the hollow body (3), movable between a trapping position in which the plate ( 13) is in contact with the cold generation means (11, 12) while being isolated from the heating means (14), and a regeneration position in which the plate (13) is away from the generation means cold (11, 12) while being in contact with the heating means (14),

displacement means (F2) are provided for selectively displacing the plate (13) between its two positions, - The heating means (14) are provided for selectively heating the plate (13) when it is in the regeneration position.

3 - Cryogenic trap according to claim 2, characterized in that the hollow body (3) has an interior cavity with a proximal region (16) and a distal region (17), the proximal region (16) being in communication with a main entrance ( 4) by an access valve (2), the distal zone (17) containing the cryogenic trap and being in communication with the proximal zone (16) which separates it from the main entrance (4).

4 - Cryogenic trap according to claim 3, characterized in that the proximal zone (16) is in communication with pumping means by an outlet valve (6).

5 - cryogenic trap according to one of claims 3 or 4, characterized in that the cold generation means (11, 12) comprise a cold core (11) with high thermal inertia, placed in the distal zone (17), and arranged so that the plate (13) comes to bear on the cold core (11) in the trapping position, the cold core (11) itself being thermally coupled to external means for generating cold (12a) by a finger cold (12).

6 - Cryogenic trap according to claim 5, characterized in that:

the plate (13) moves in a cylindrical portion of the cavity of the hollow body (3) with a small peripheral space (15) between the peripheral edge of the plate (13) and the wall of the cavity,

- neutral gas injection means (9, 10) create in said small peripheral space (15) a flow of neutral gas (Fl) flowing from the distal zone (17) towards the proximal zone (16), said neutral gas flow (Fl) opposing the passage of the gases to be trapped towards the cold core (11).

7 - cryogenic trap according to claim 6, characterized in that the displacement means comprise said means for generating a flow of neutral gas in said small peripheral space (15) from the distal zone (17) towards the proximal zone (16), said means for generating a flow of neutral gas being adapted to selectively generate a flow of neutral gas at higher flow rate (F2) which moves the plate (13) to the regeneration position.

8 - Cryogenic trap according to claim 6, characterized in that the displacement means comprise an actuator (30) connected to the plate (13) by one or more rods (21, 21a, 21b) insulating integral with the plate (13).

9 - Cryogenic trap according to claim 8, characterized in that the rod (s) (21, 21a and 21b) pass through the cold core (11), and the actuator (30) is arranged opposite the plate (13) relative to the cold core (11).

10 - Cryogenic trap according to claim 9, characterized in that the rods (21, 21a, 21b) are separable from the actuator (30) during the gas trapping steps.

11 - Cryogenic trap according to one of claims 7 or 8, characterized in that it comprises control means (20) which sequentially control the operation of the displacement means (9, 10, 30, 21, 21a, 21b) , the access valve (2), heating means (14) and the outlet valve (6).

12 - cryogenic trap according to any one of claims 2 to 11, characterized in that the heating means comprise a heating ring (14) disposed in the cavity of the hollow body (3) facing the contact surface (13a ) of the plate (13) so that the plate (13) comes into contact with the heating ring (14) through its peripheral zone when it is in the regeneration position.

13 - Cryogenic trap according to any one of claims 2 to 12, characterized in that it comprises means for promoting the thermal connection between the plate (13) and the cold core (11) when the plate (13) is in trapping position.