Device for heat transmission under vacuum with grains

p0001The present invention relates to a heat transfer device under vacuum between a hot or cold thermal source and an object by means of intermediate grains disposed therebetween.

p0002Microelectronics or superconductors, we feel indeed often the need to make deposits or crystallization under vacuum at elevated temperature, eg oxides or metals on substrates in thin layers. We can reciprocally want to cool the substrate on which the layers are deposited in order to hinder their crystallization. In both cases, the problem is the same: to ensure the heat transfer between a source and the substrate.

p0003This transmission can occur by radiation, but this method is usually not very effective, especially as the substrate on which the crystals are deposited can be transparent to radiation emitted by the penny thermal rce. Transmission can also occur through solid carriers between the source and the substrate, which may include the frame on which the substrate is fixed to keep the middle of the vacuum chamber. This process is not so effective either because the contact surfaces between the substrate and the frame are small, and in addition, it can prevent the occurrence of thermal gradients in the substrate because the heat transmission is easier near the border.

p0004It was once thought to delineate between the substrate and the source, within the vacuum chamber, a sealed sub-enclosure in which a gas is introduced or possibly a low vapor pressure liquid.

p0005A general disadvantage of such techniques is that there must be vis-à-vis the vacuum chamber sealing, which is not easy when working at high temperatures at which the seals are not provided. In the case of liquefied solids such as gallium or indium, must accept some consumption of these expensive products and pollution are inevitable.

p0006These drawbacks are avoided according to the invention by interposing between the substrate and the heat source a particulate material which ensures the transmission of heat uniformly, through multiple paths, while creating no sealing problem. More specifically, the invention comprises a support in the vacuum chamber provided with means for mounting the object there, the carrier, the object and a wall part of the heat source, that is to say a wall heated or cooled, delimits a cavity filled with heat conducting grains. The heat source can then be of any suitable type and in particular, in the case of a heat source, a heating resistor disposed on the other side of the wall; this resistor is installed in another cavity which can be filled with electrically insulating fluid and thermal conductor.

p0007It is also essential that the grains are fine enough to ensure good uniformity of heat transfer between the source and the substrate, especially as the temperature changes can cause irregular shape deformations to which the intermediate grains should s' adapt. It is therefore preferred to use spherical beads of diameter less than or equal to 2 mm.

p0008Furthermore, it may provide the vacuum chamber secured to the cavity and communicating with a reservoir in which is maintained the grains when no heating takes place. We can then conveniently mount or dismount the object to be heated without seeing flow grain outside.

p0009The invention will now be described using the following appended figures of illustration and not limitation:<ul><li>Figure 1 is an overall sectional view of the device, and</li><li>Figure 2 is a partial view taken along section II-II of Figure 1 and showing the conformation of the support for the object to be heated or to be cooled and in particular the grain tank.</li></ul>

p0010Figures 1 and 2, the vacuum chamber is referenced by 1. The vacuum is established during operation by a vacuum pump 2 disposed outside of the chamber 1 and opening into the interior of the -this. The chamber 1 is also pierced on two opposing walls through a door 3 of relatively large dimensions and a sleeve 4. The seals 5 are disposed to the contours of the chamber 1.

p0011The sleeve 4 expands within the vacuum chamber 1 by a ring 6 provided with a peripheral shoulder 7. It is here that a fixed support 8 of the object to be heated or cooled by additional peripheral shoulder 9. the shoulders 7 and 9 are fixed by screws 10.

p0012The sleeve 4 and the support 8 then delimit a thermal source cavity 11 in which is located the heat source 12, here constituted by a heating resistor. Other solutions are of course possible and may for example consider establish a forced circulation of fluid for heating or cooling. With the resistor 12, the vacuum can prevail in the thermal source or cavity 11, which leads to better thermal conduction, this cavity 11 may be filled with an electrically insulating fluid such as air. In the first case, it is necessary to provide a seal by a plug which closes the sleeve 4 between the resistor 12 and a supply 13 thereof; the cap is referenced by 14. In the second case, sealing is performed with respect to the vacuum chamber 1 by interposing a seal 15 between the peripheral shoulders 7 and 9.

p0013The wall 20 of the support 8 in contact with the thermal source cavity 11 thus constitutes a floor heating or cooling. It is now to transmit this energy to the object to be heated located outside the cavity of heat source 11; this object is typically a planar substrate 21 mounted on the support 8, maintained parallel to the wall 20 and at some distance therefrom, and, an external face 22 opposite the wall 20 supports thin layered over the seed which is to be intervene.

p0014The substrate 21 may be concretely made of glass, quartz, silicon garnet or gadolinium gallium, and thin films of barium hexaferrite, nitrides, borides, oxides, without these being limiting lists. The substrate 21 is held in place between a peripheral bearing surface 23 which rises from the wall 20 and a ring 24 clamped on the end of the peripheral bearing surface 23 by screws 25. The wall 20, the substrate 21 and the range device 23 define a cavity 26 it is difficult to seal to fill gas to enhance heat transmision. The substrate 21 is in fact in contact with the bearing surface 23 and the ring 24 as a small width of its periphery and it is therefore difficult to install seals at this location. In the invention, the vacuum thus prevails in the cavity 26.

p0015The cavity 26 is generally closed except at one end where it may advantageously result in a tank 27. During the treatment, the cavity 26 is filled with heat-conductive granular material which can be advantageously constituted of balls 30 of about 1 mm in diameter. The reservoir 27 is then above the cavity 26, so that the balls 30 tend to fill the latter with pressure on its walls determined by the weight of the balls 30. If the substrate 21 is deformed as a result of its heating the flow of balls 30 that ensues can be adapted to this change in form.

p0016In addition, the heat transfer from the wall 20 is made by winding multiple thermal paths defined by the contact points between balls 30 and is uniformly over the entire surface of the substrate 21, even if there is a thermal gradient on the wall 20, allowing overheating both more regular and greater than if the heat had to go through the peripheral range 23.

p0017These various benefits also explain the superiority of grains such as ball 30 to other intermediate sound that we could have adopted, for example rollers, pads or blocks that did not follow the thermal expansion of the substrate 21, would been more difficult to install with correct tolerances and would have produced less uniform heat transfer.

p0018The beads 30 may advantageously be contituées the same material as the substrate 21 in order to avoid pollution by contact.

p0019It has been found in a specific example, the wall 20 being at a temperature of 560 ° C, the temperature of the substrate 21 was elevated to 130 ° C when the balls 30 were introduced into the cavity 26.

p0020When the treatment is completed, atmospheric pressure is restored in the chamber 1 and the door 3 is removed; screws 10 are then removed and the carrier can be unlocked 8. The substrate 21 is then removed to the outside by removing the ring 24. In the meantime, the holder 8 has been returned so as to locate the reservoir 27 beneath the cavity 26, so that the balls 30 flowed back into the reservoir 27 and that it is not necessary to worry more about them before removing the substrate 21.

p0021The installation of a new substrate 21 in the vacuum chamber 1 is made by inverse operations.