Heating device such as an electrical heating plate used in the semiconductor industry

Abstract

The invention relates to a heating device comprising: - a heating plate (20) having a support face (20a) intended to receive an object to be heated and an opposite face referred to as inner face (20b), - a backplate (22) assembled on the heating plate (20), and - one or more heating elements (4, 5) fitted between the inner face (20b) of the heating plate (20) and the backplate (22). The invention is characterized in that the heating device further comprises at least one insert (31, 32) made of a thermally conductive material, having one or more grooves (8) intended to receive the heating element(s) (4, 5), the insert (31, 32) being fitted between the inner face (20b) of the heating plate (20) and the backplate (22).

Description

A heating device such as an electric heating plate used in the semiconductor industry

[0001] The present invention relates to the field of heating devices such as an electric heating plate used in the semiconductor industry. State of the art

[0002] Heating metal surfaces such as electric heating plates allow the heating of silicon wafers or wafers, on which the substrate required for etching electronic chips is deposited.

[0003] Such metal heating plates are capable of reaching high temperatures, for example in the order of 900 to 950°C, while ensuring very good thermal uniformity. These metal heating plates are used in vacuum deposition machines, for example PVD, CVD, ALD type, as a heated substrate holder for the manufacture of semiconductors.

[0004] These devices are highly technical and must have high thermal performance. In particular, the criterion of thermal homogeneity on the surface of the heated wafers is crucial for the quality of the substrate deposition. It is therefore important to offer a heating metal surface that has thermal homogeneity allowing this uniform heating of said wafers.

[0005] Typically, such a heating plate is made in the form of a disc with spiral grooves on the back, through which one or more heating elements such as mineral-insulated shielded heating cables run.

[0006] These plates can reach temperatures between 350°C and 950°C, or even higher in some cases, if necessary. The plate is made of a steel or nickel-based alloy, or ceramic. The heating elements, namely the heating cable(s), are plated at the bottom of the grooves and brazed as described in patent WO2020165452A1.Thus, the plate is in the form of a disc having a functional region of oval, circular or polygonal shape, which has:- on one side, a support face intended to receive for example the wafer(s) to be heated, and- on the other side, a so-called internal face on the surface of which are hollowed out a plurality of grooves substantially concentric to the functional region, in particular circular or forming one or more spirals; the step of producing the body comprising:- the insertion of the one or two heating elements into said grooves,- assembly and fixing on said internal face, in particular by sealed welding, of a counterplate which closes said grooves to thus form the housing(s) containing said heating elements.Then, the body is prepared, including the deposition of the brazing material in one or more casting tanks fixed to the counterplate, temporarily or forming a foot for fixing and / or supplying the conductors of the heating elements.

[0007] The process thus allows for an improved assembly between the body and the heating element(s). The latter are thus embedded in the liquid solder during the soldering operation, which is in intimate and continuous contact with both the heating elements and the body. The solder fills the voids and replaces the gaseous cavities with metallic material, on all accessible surfaces. This results in a single-piece heating device, in the sense that it has a continuous metallic material in which the heating elements are directly embedded. The heating plate thus produced allows for sufficient and uniform heat exchange, by total conduction between the heating elements and the mechanical assembly making up the body.

[0008] The process described in this document therefore makes it possible to produce a heating plate with homogeneity of the heating of the body, which improves the uniformity of its temperature. Such a heating plate also makes it possible to accelerate heat transfers over time and therefore reduce the reaction time during temperature adjustments. This facilitates the temperature adjustment and control processes, promoting the maintenance of a stable temperature over time and allowing rapid changes in the temperature obtained.

[0009] However, the presence of local temperature anomalies has been observed, linked in particular to the routing of the cables and the presence of thermocouples. The present invention therefore aims to overcome these drawbacks by proposing a heating plate of the type described in the prior art in which thermal uniformity is further improved while reducing as much as possible or even eliminating these local temperature anomalies on the surface of the plate.

[0010] To this end, the invention relates to a heating device comprising: - a heating plate having a support face intended to receive an object to be heated and an opposite face called the internal face, - a counterplate assembled on the heating plate, and - one or more heating elements housed between the internal face of the heating plate and the counterplate, characterized in that it further comprises at least one insert made of thermally conductive material, comprising one or more grooves intended to receive the heating element(s), said insert being housed between the internal face of the heating plate and the counterplate.

[0011] Such an insert makes it possible to diffuse the heat from the heating element(s), housed in the concentric and / or spiral grooves, towards the support face of the plate while “smoothing” the temperature on the surface of the plate. Advantageously, the heating plate according to the invention has improved thermal uniformity of the plate, local temperature anomalies attributable to the structure such as the routing of the cables, the presence of thermocouples being thus greatly reduced. The insert has a face intended to be housed against the internal face of the heating plate and its opposite face comprises the heating element(s).

[0012] The heating element(s) are fixed to said insert using a brazing material introduced during a brazing cycle. Thus, this or these insert(s) are chosen so as to have a high thermal conductivity but also so as to be able to withstand the conditions of implementation of a brazing cycle consisting of a high vacuum and a temperature rise of more than 1000°C. The insert(s) are thus made of materials such as metal such as copper and its alloys, nickel and its alloys, molybdenum and its alloys, or graphite and any other suitable material.

[0013] When using a heating plate in a wafer or wafer deposition process, transition steps in that process may require different thermal power zones such as overpower on an annular or other area of ​​the heating plate.

[0014] Indeed, during the deposition process on the wafers, thermal loads can change during operation. It is therefore necessary to be able to offer different surface temperature setpoints on the same heating plate in several locations or zones of said heating plate to compensate for localized and transient thermal losses and thus maintain a uniform surface temperature of the wafer. In these cases, surface temperature shifts between zones are sometimes required. It may therefore be necessary to provide for differences of up to 10% of the setpoint temperature between zones.

[0015] Thus, the heating plate has at least two thermal zones, each defined by an independent heating element whose temperature is controlled by a thermocouple and a regulator.

[0016] Preferably, these thermal zones are made possible by using several inserts respectively comprising an independent heating element, for example 2 or 3, controlled respectively by 2 or 3 thermocouples and 2 or 3 regulators. Thus, an insert and the heating element which is housed in its grooves, define a thermal zone whose temperature is controlled by the thermocouple and the regulator associated with the heating element. It is thus possible to define distinct thermal zones with two distinct heating elements, these zones, for example a central one and the other peripheral one, each having a different temperature from each other allowing temperature shifts to be achieved between thermal zones.

[0017] It is also possible to provide that a single insert and at least two heating elements which are housed in its grooves, thus define at least two thermal zones whose temperature is controlled by a thermocouple and a regulator associated with each heating element.

[0018] An insert has a disc shape whose dimensions are adapted to the heating plate when a single insert is provided and in the case of at least two inserts, said inserts consist of a central disc and concentric rings. It is thus possible to provide two or three inserts housed under a heating plate and which, associated respectively with a heating element, define distinct thermal zones.

[0019] In addition, in order to optimize these temperature shifts between thermal zones, a thermally insulating element is provided between two thermal zones of the heating plate to reduce radial heat flows between heating zones and limit thermal conduction from zone to zone.

[0020] Indeed, the compactness of the heating plate, the presence of solder around the heating elements and the insert(s) imply a strong thermal conduction and an independent adjustment of the temperature of each zone is very difficult or almost impossible. This thermally insulating element thus makes it possible to adjust the temperature of each thermal zone by reducing radial heat flows.

[0021] According to a preferred embodiment, several inserts are therefore provided in the form of a central disc and concentric rings, these discs and rings corresponding to the zones where a determined temperature is desired to achieve thermal uniformity. Thus, a thermal zone being defined by an insert and an associated heating element, an element made of thermally insulating material is inserted into a space reserved between two inserts defining two adjacent thermal zones, this space having for example a width of 3 to 10 millimeters, and the thermally insulating element making it possible to reduce the radial heat flows between heating zones.

[0022] This thermally insulating element forms a thermal barrier between each zone defined by an insert. This thermal barrier is thus obtained by placing, during assembly, a ring of thermally insulating material between the zones whose temperature must be individually controlled, by increasing the thermal resistance between said zones over their entire periphery.

[0023] The heat passage section between zones is thus reduced by 30 to 75%.

[0024] According to an alternative embodiment, an insert may comprise at least two heating elements each defining a different thermal zone. An element made of thermally insulating material is then inserted into a space reserved in the insert between the two thermal zones defined respectively by a heating element. The element made of thermally insulating material is thus positioned in a groove, preferably discontinuous, configured to separate the thermal zones. This facilitates the mounting of the insert in the plate, in the form of a single piece.

[0025] Thermally insulating materials such as moldable, embeddable, or machinable ceramics may be selected and used to form these thermal barriers. Preferably, these materials have a thermal conductivity between 0.1 and 0.6 W / m°C, such as those based on silica, alumina, or magnesia.

[0026] The material constituting this thermal barrier must therefore be both resistant to the high-temperature brazing process, thermally efficient (i.e., have very low thermal conductivity) and easy to install. Such materials are chosen from those based on silica, alumina or magnesia and have a thermal conductivity much lower than that of the base metals constituting the heating plate. In addition, such materials are chosen so as not to be impregnated by the brazing when it melts.

[0027] The invention also relates to a method for manufacturing such a heating device comprising the following steps:E1: manufacturing a heating plate and counterplate,E2: manufacturing the insert(s) and making the grooves, inserting heating elements into the grooves as well as one or more thermocouplesE3: inserting the insert(s) into the heating plate, E3': optionally, inserting a thermally insulating element between two heating elements defining two thermal zones,E4: filling casting reservoirs provided from the rear face of the counterplate, using a brazing material in a quantity determined to ensure the filling of all accessible volumes within the grooves, between the heating elements, and the heating plate, as well as the thermocouples,E5: preheating in the oven, until a uniform temperature is obtained within the entire assembly,at a temperature lower than the melting temperature of the brazing material,E6: casting heating, at a temperature higher than the melting temperature of the brazing material, for a determined period to allow the filling of all accessible volumes within the grooves, between the heating elements and the insert(s).,

[0028] The insertion of the thermally insulating element can be carried out by introducing it into a groove made in the insert or plate or during the molding of the insert.

[0029] The invention will be well understood and other aspects and advantages will appear clearly on reading the following description, given by way of example with reference to the attached drawing plate in which the figures represent:

[0030] a sectional view of a heating device according to the invention; and

[0031] a transparent view from above of the device

[0032] The heating device 1 according to the invention consists of a heating plate 20 of the type used to manufacture a semiconductor wafer or plate.

[0033] This heating plate 20 consists of a flat plate (possibly with local reliefs) intended to receive an object to be heated. Typically, the heating plate 20 is produced in the form of a single-piece disc provided with a peripheral rim 21.

[0034] The heating plate 20 thus has a support face 20a on which a semiconductor wafer can be deposited to be heated. Two heating elements 4 and 5 are arranged in the heating device 1 so as to constitute a heating element 4 called the inner heating element, forming at least one spiral, positioned substantially in the center of the heating plate 20, and a heating element 5 called the peripheral heating element, forming a circular loop or several spiral loops, which surrounds said inner heating element 4, in particular in a flat manner, parallel to the support surface and for example coplanar with each other.

[0035] These two heating elements 4 and 5 are preferably made of shielded heating cables with mineral insulation.

[0036] Against the inner face 20b of the heating plate 20 are arranged two inserts 31 and 32 made of a thermally conductive material. The first insert 31 placed centrally is disc-shaped. This insert 31 has dimensions similar to the central part of the inner face 20b of the heating plate 20. In the thickness of this insert 31 on its face opposite the plate 20, a plurality of grooves 8 are made, in a spiral, intended to receive the shielded heating cable with mineral insulation 4.

[0037] A second insert 32 has an annular shape and is positioned between the insert 31 and the peripheral rim 21 of the heating plate 20. In the thickness of this insert 32 on the face opposite the plate 20, a plurality of grooves 7 are made, for example spiral grooves, in which the second mineral-insulated shielded heating cable 5 is received.

[0038] These inserts 31 and 32 made of high thermal conduction material make it possible to improve the thermal uniformity of the heating plate by radially diffusing the heat to smooth the surface temperature of the heating plate 20.

[0039] The two heating zones delimited by the inserts 31 and 32 and the heating cables 4 and 5 define different thermal zones Z1 (central) and Z2 (peripheral), each controlled by a thermocouple 6 and an associated regulator. These two zones Z1, Z2 thus make it possible to impose different surface temperature setpoints for the heating plate 20, making it possible to compensate for localized and transient thermal losses, which may occur due to the local introduction of a gas to produce a plasma for example and thus maintain a uniform surface temperature of the treated wafer deposited on the heating plate 20.

[0040] Thus, as already mentioned above, the heating plate 20 has a support face 20a intended to receive the wafer to be heated, and a so-called internal face against which is housed the insert(s) 31, 32 on the surface of which are hollowed out a plurality of grooves 7, 8 which are substantially concentric, circular or forming one or more spirals. Once the heating elements 4, 5 are housed in the grooves 7, 8 of the inserts 31, 32, a counterplate 22 is assembled, in particular by sealed welding, which closes said grooves 7 to thus form the housing(s) containing said heating elements 4, 5.

[0041] A brazing material is then deposited in one or more casting tanks fixed to the counterplate 22.

[0042] Thus, such a heating plate can be manufactured according to the following steps: E1: manufacturing a heating plate 20 and counterplate, E2: manufacturing the insert(s) 31, 32 and making the grooves 8, inserting heating elements 4, 5 into the grooves 8 as well as one or more thermocouples E3: inserting the insert(s) 31, 32 into the heating plate 20, closing with the counterplate 22, E3': optionally, inserting a thermally insulating element 10 between two heating elements 4, 5 defining two thermal zones Z1, Z2, E4: filling casting reservoirs arranged on the rear face of the counterplate 22 using a brazing material in a quantity determined to ensure the filling of all the accessible volumes within the grooves 8, between the heating elements 4, 5, and the heating plate 20, as well as the thermocouples.

[0043] Then a heating step is carried out which comprises the following operations: E5: preheating in the furnace, until a uniform temperature is obtained within the entire assembly, at a temperature lower than the melting temperature of the brazing material. Optionally, the preheating comprises a degassing stage which is carried out under secondary vacuum, in its entirety or during a final part of the preheating. E6: casting heating, at a temperature higher than the melting temperature of the brazing material, for a determined duration to allow the filling of all the accessible volumes within the grooves, between the heating elements 4, 5 and the insert(s) 31, 32, the latter being thus embedded in the liquid brazing during the brazing operation, which improves the reaction time of each of the heating zones. The casting is carried out under secondary vacuum, that is to say at a pressure lower than 10-3 mbar (one millibar).

[0044] The brazing material forms a nickel-based metal alloy, particularly from the BNi family.

[0045] In order to be able to optimally regulate the temperature of the heating plate 20, according to the two defined thermal zones Z1, Z2, a thermal barrier consisting of a thermally insulating element 10, i.e. a material having low thermal conduction, is inserted between these two zones Z1, Z2, i.e. between two different heating elements 4, 5. This barrier is inserted into a groove provided on the internal face 20b of the heating plate 20 in an intermediate space reserved between the inserts 31, 32, i.e. between the heating zones Z1, Z2 to reduce the radial heat flows between these heating zones Z1, Z2. This intermediate space has a width of 3 to 10 millimeters. It is also possible to provide a single insert comprising two heating elements respectively defining a thermal zone, the insert comprising a groove in which a thermally insulating element can be housed.

[0046] The thermal barrier limits conductive heat flow by occupying an annular space in place of the base metal, solder, or insert.

[0047] Therefore, during assembly, a thermally insulating element 10 in the form of a ring, for example made of porous material or consisting of a gas layer, is inserted between each zone Z1, Z2 to be controlled individually. This material therefore forms the thermal barrier which increases the thermal resistance between zones over their entire periphery. The inserts 31, 32 do not cover the thermal barrier(s) so as not to counteract their wall effect on the heat flow. Thus, the two effects are combined: reinforced temperature uniformity in each zone but thermal independence from zone to zone.

[0048] This prevents thermal conduction linked to the compactness of the heating plate 20, the presence of solder around the heating elements 4, 5 and the inserts 31, 32 from disturbing the independent adjustment for each zone Z1, Z2.

Claims

Heating device comprising:- a heating plate (20) having a support face (20a) intended to receive an object to be heated and an opposite so-called internal face (20b),- a counterplate (22) assembled on the heating plate (20), and- one or more heating elements (4, 5) housed between the internal face (20b) of the heating plate (20) and the counterplate (22),characterized in that it further comprises at least one insert (31, 32) made of thermally conductive material, comprising one or more grooves (7, 8) intended to receive the heating element(s) (4, 5), said insert (31, 32) being housed between the internal face (20b) of the heating plate (20) and the counterplate (22). Heating device according to claim 1, characterized in that the insert(s) (31, 32) are made of materials having high thermal conductivity such as copper and its alloys, nickel and its alloys, molybdenum and its alloys, graphite. Heating device according to claim 1 or 2, characterized in that the heating plate (20) has at least two thermal zones (Z1, Z2) each defined by an independent heating element (4, 5) whose temperature is controlled by a thermocouple (6) and a regulator. Heating device according to claim 3, characterized in that an insert (31, 32) and the heating element (4, 5) which is housed in its grooves (7, 8), define a thermal zone (Z1, Z2) whose temperature is controlled by a thermocouple and a regulator associated with the heating element (4, 5). Heating device according to claim 3, characterized in that an insert (31, 32) and at least two heating elements (4, 5) which are housed in its grooves (7, 8), thus define at least two thermal zones (Z1, Z2) whose temperature is controlled by a thermocouple and a regulator associated with each heating element (4, 5). Heating device according to one of claims 1 to 4, characterized in that an insert (31, 32) has a disc or ring shape. Heating device according to one of claims 3 to 6, characterized in that a thermally insulating element (10) is provided between two thermal zones (Z1, Z2) of the heating plate (20). Heating device according to claim 7, characterized in that a thermally insulating element (10) is inserted into a space reserved between two inserts (31, 32) defining the two thermal zones (Z1, Z2). Heating device according to claim 7, characterized in that a thermally insulating element (10) is inserted into a space reserved on an insert (31, 32) between the two thermal zones (Z1, Z2) defined respectively by a heating element (4, 5). Heating device according to one of claims 7 to 9, characterized in that the thermally insulating element consists of a ring (6) made of thermally insulating material having a thermal conductivity between 0.1 and 0.6 W / m°C, such as those based on silica, alumina or magnesia. A method of manufacturing a heating device according to one of claims 1 to 9, comprising the following steps:E1: manufacturing a heating plate (20) and counterplate,E2: manufacturing the insert(s) (31, 32) and producing the grooves (8), inserting heating elements (4, 5) into the grooves (8) as well as one or more thermocouplesE3: inserting the insert(s) (31, 32) into the heating plate (20), closing with the counterplate (22),E4: filling casting tanks provided with a brazing material in a quantity determined to ensure the filling of all accessible volumes within the grooves (7, 8), between the heating elements (4, 5), and the heating plate (20), as well as the thermocouples,E5: preheating in the furnace, until a uniform temperature is obtained within the whole of the assembly, at a temperature lower than the melting temperature of the solder material,E6: casting heating,at a temperature above the melting temperature of the solder material, for a determined period of time to allow the filling of all accessible volumes within the grooves, between the heating elements and the insert(s). Method of manufacturing a heating device according to claim 11, characterized in that it comprises a step E3' of inserting a thermally insulating element (10) between two thermal zones (Z1, Z2).

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