Reactor for epitaxial deposition and heating method thereof

Abstract

The present application relates to a reactor (1) for epitaxial deposition and a heating method thereof. The reactor (1) comprises a susceptor (2) and an inductor (4); the inductor (4) is suitable for heating the susceptor (2) by electromagnetic induction when it is powered on; the inductor (4) comprises a plurality of turns (41-47); during the heating of the susceptor (2) from a first temperature to a second temperature, one or more turns (43) of the inductor (4) change position relative to the susceptor (2) and other turns of the inductor (4). The turns (43) are actuated by means of a suitable actuation system (61, 62, 63).

Description

[0001] This application is a divisional application of an application with an application date of October 30, 2017, application number 201780067269.3, and invention name “Heating method for a reactor for epitaxial deposition and a reactor for epitaxial deposition”. Field of the Invention

[0002] The invention relates to a heating method of a reactor for epitaxial deposition and a reactor for epitaxial deposition. Prior art

[0003] Any epitaxial reactor comprises a heating system to heat the substrate to be epitaxially grown.

[0004] The stages of the epitaxial deposition process are preceded by a heating phase and followed by a cooling phase.

[0005] For example, the heating may be electromagnetic induction type heating.

[0006] Typically, in this case, the heating system directly heats the susceptor (which is located within the reaction chamber of the epitaxial reactor), and the substrate receives heat by conduction from the susceptor (which supports the substrate).

[0007] In this case, the heating system always comprises at least one inductor.

[0008] In the past, the applicant has provided the possibility that one or more turns of such an inductor are movable: patent document WO9610659A2.

[0009] According to this solution, the inductor comprises a plurality of rigid circles electrically and mechanically connected by flexible bridges; a single circle is moved by means of a single electric motor and a single translation actuator mounted on the motor shaft; the deformation caused by said actuator is entirely borne by the flexible bridges.

[0010] Before starting the heating operation, and therefore before starting the epitaxial deposition, the turns are positioned in the desired location; this positioning is one of the operations of the initial setup of the reactor.

[0011] This solution is also known from patent documents with publication numbers US2010059182, JP2003133245 and KR100978567.

[0012] The main goal of a heating system for an epitaxial reactor is to obtain a uniform temperature of the substrate during processing.

[0013] A second goal of a heating system for an epitaxial reactor is to reach the process temperature in a short time.

[0014] According to a solution known from patent publication No. JP2003133245, the entire inductor is brought close to the susceptor before the epitaxial deposition process to heat the susceptor faster, and the entire inductor is moved away from the susceptor after the epitaxial deposition process to cool the susceptor faster.

[0015] Overview

[0016] The Applicant has recognized through experiments carried out by him that a uniform temperature of the substrate from moment to moment not only during the process but also during the heating, or more precisely, during the heating preceding the epitaxial deposition process, is very advantageous; for example, this advantage can be associated with a reduction in thermal stresses and defects, in particular "slip lines".

[0017] The Applicant then set himself the goal of providing a solution making it possible to obtain a uniform temperature of the substrate during heating and subsequent epitaxial deposition.

[0018] The applicant also set itself the goal of providing a solution which makes it possible to reach the process temperature within a short time.

[0019] Finally, the applicant set himself the goal of providing a solution that is not only effective but also simple.

[0020] These objects are substantially achieved by means of a heating method for an epitaxial reactor and a reactor having the technical characteristics set out in the following items.

[0021] This application provides the following items:

[0022] 1. A method for heating a reactor for epitaxial deposition,

[0023] The reactor comprises a receiving container and a sensor;

[0024] wherein the inductor is adapted to heat the susceptor by electromagnetic induction when powered;

[0025] wherein the inductor comprises a plurality of turns;

[0026] Wherein, before the epitaxial deposition process, during the heating of the susceptor from the first temperature to the second temperature, the position of at least one first turn of the inductor is changed relative to the susceptor and relative to other turns of the inductor.

[0027] 2. The heating method according to item 1, wherein, before the epitaxial deposition process, during the heating of the susceptor from the first temperature to the second temperature, the position of at least one second turn of the inductor relative to the susceptor and relative to other turns of the inductor is changed.

[0028] 3. The heating method according to item 1 or 2, wherein, before the epitaxial deposition process, the position of the at least one turn and / or the at least one second turn is repeatedly changed during the heating of the susceptor from the first temperature to the second temperature.

[0029] 4. A heating method according to any one of the preceding items, wherein, before the epitaxial deposition process, during the heating of the susceptor from a first temperature to a second temperature, the position of the at least one turn and / or the at least one second turn is changed by means of "open loop control".

[0030] 5. The heating method according to any one of the preceding clauses, wherein, before the epitaxial deposition process, during the heating of the susceptor from the first temperature to the second temperature, the inductor is energized by means of “open loop control”.

[0031] 6. The heating method according to any of the preceding clauses, wherein the position of any of the turns of the inductor is not changed during the epitaxial deposition process.

[0032] 7. The heating method according to any of the preceding clauses, wherein during the epitaxial deposition process, the inductor is energized by means of "open loop control".

[0033] 8. The heating method according to any of the preceding items, wherein the first temperature corresponds to a loading temperature of an epitaxial deposition process, and / or wherein the second temperature corresponds to a process temperature of an epitaxial deposition process.

[0034] 9. The heating method according to item 8, wherein in at least one temperature interval between the first temperature and the second temperature, the position of any of the turns of the inductor is not changed.

[0035] 10. A reactor for epitaxial deposition, comprising: at least one susceptor having a disk-shaped portion, the susceptor being adapted to directly or indirectly support one or more substrates; and an inductor having turns, the inductor being adapted to heat the disk-shaped portion and being controlled by changing the position of the turns,

[0036] Characterized in that, the reactor comprises:

[0037] - a first electric motor adapted to change the position of at least one first turn of said inductor due to its movement,

[0038] - a first plurality of translation actuators adapted to act on a corresponding plurality of points of said at least one first turn ( Figure 3 ) and causing translation of the at least one first turn, and

[0039] - a first transmission adapted to transmit the movement of said first motor to said first plurality of actuators.

[0040] 11. The reactor for epitaxial deposition according to item 10, comprising:

[0041] - a second motor adapted to change, due to its movement, the position of at least one second turn of said inductor,

[0042] - a second plurality of translation actuators adapted to act on a corresponding plurality of points of said at least one second turn ( Figure 3 ) and causing translation of the at least one second turn, and

[0043] - a second transmission adapted to transmit the movement of the second electric motor to the second plurality of actuators.

[0044] 12. The reactor for epitaxial deposition according to item 10 and / or 11, wherein the first transmission device and / or the second transmission device comprises one and / or two belts or chains.

[0045] 13. A reactor for epitaxial deposition according to item 10 or 11 or 12, wherein the inductor comprises a continuous conductor in the form of a single elastic mechanical piece.

[0046] 14. A reactor for epitaxial deposition according to any one of items 10 to 13, comprising a potentiometer for detecting the rotation of the actuator.

[0047] 15. A reactor for epitaxial deposition, comprising means particularly suitable for implementing the heating method according to any one of items 1 to 9, and preferably comprising at least one motor, at least one plurality of actuators and at least one transmission.

[0048] List of Figures

[0049] The present invention will become more apparent from the following detailed definitions considered in conjunction with the accompanying drawings, in which:

[0050] Figure 1 shows a vertical cross-sectional view of a reaction chamber of an embodiment of an epitaxial reactor according to the prior art,

[0051] Figure 2 A vertical cross-sectional view showing a reaction chamber of an embodiment of an epitaxial reactor according to the present invention, and

[0052] Figure 3 Schematically shows Figure 2 Top view of the reactor's inductor.

[0053] It will be readily appreciated that there are various ways of implementing the invention in practice, the invention being defined in its main advantageous aspects in the items described above. Detailed Description

[0054] Figure 1 A vertical cross-sectional view of a reaction chamber of an embodiment of an epitaxial reactor 1 according to the prior art is shown.

[0055] The reaction chamber is provided with a cavity 10 which is delimited by an upper wall 11 (in particular made of transparent quartz), a lower wall 12 (in particular made of transparent quartz) and side walls (in particular made of transparent quartz) not shown in the figures.

[0056] The susceptor 2 is positioned within the chamber 10 and is adapted to support and heat the substrate during epitaxial deposition. Figure 1 In the case of the present invention, there is a single substrate 100, which is located on a support element 3 (having a disk-like shape, in particular a cylindrical shape with a height much smaller than the diameter, placed horizontally and made of graphite (which may be coated with SiC or TaC)), which in turn is located on a receiver 2 (having a disk-like shape, in particular a cylindrical shape with a height much smaller than the diameter, placed horizontally and made of graphite (which may be coated with SiC or TaC)), element 3 is not essential for the purpose of the present invention.

[0057] A heating system is provided, comprising: at least one inductor 4, adapted to heat a susceptor 2 by electromagnetic induction when it is powered; the inductor 4 is flat and comprises a plurality of turns 41-47 (particularly Figure 1 Seven concentric turns in the example). The system may include other inductors below the chamber, but typically has no inductors above the chamber.

[0058] Inside the cavity 10 is a horizontal inner wall 14 aligned with the base 100 .

[0059] The susceptor 2 is fixed about a vertical axis Z to a rotation shaft 5 .

[0060] The lower wall 12 has a hole and a sleeve 13 for the shaft 5 to pass through.

[0061] The inductor 4 is located below the lower wall 12 around the sleeve 13 .

[0062] Figure 2 The embodiment is Figure 1 or an improvement of a similar solution.

[0063] exist Figure 2In it some parts of the actuation system 6 for moving the turns of the inductor 4 can be seen: an electric motor 61 , a pair of actuators 62 with a corresponding pair of potentiometers (not shown in the figure) and a transmission 63 .

[0064] exist Figure 2 In the figure, a thermal imaging camera 7 is shown, which is located above the upper wall 11 and is suitable for measuring the temperature in the chamber, in particular the temperature of the substrate 100, in a thin bottom radial area; in particular, the radial area extends between the axis Z (or very close to it) and the edge of the substrate 100 (or very close to it); this measurement area is large enough because the holder and the substrate rotate.

[0065] exist Figure 2 In FIG. 8 , a computerized heating control system is shown; it may include one or more PLCs. The system 8 is electrically connected to the following items: the sensor 4 to provide power thereto; the system 6 (particularly the motor 61 and the potentiometer); the thermal imaging camera 7; and the user interface 9. The interface 9 allows an operator to input commands and retrieve information.

[0066] exist Figure 3 , an example situation is schematically shown, in which turns 43, 45 and 46 are movable; turns 45 and 46 constituting, for example, a "group" are moved by system 6 together with turn 43 and independently of turn 43; the movement of turn 43 is obtained with the help of three actuators 621, 622 and 623, which are, for example, 90° apart from each other; the movement of the group of turns 45 and 46 is obtained with the help of three pairs of actuators, which are, for example, 90° apart from each other, or with the help of three actuators 624, 625 and 626 (as shown in the figure, one actuator moves two points of two turns simultaneously). In order to make the figures clearer, Figure 2 Only the part of the device for moving the turn 43 is shown, the device for moving the turns 45 and 46 is not shown.

[0067] exist Figure 3 In the embodiment, each turn has a circular arc shape, for example, a circular arc shape of about 330°, and the turns are connected together, for example, by straight line segments.

[0068] According to the present invention, the reactor ( Figure 2 1) includes a turn ( Figure 2 Sensors (41-47) Figure 2 4), the inductor 4 is usually flat (or substantially flat) and is suitable for heating the receiving device ( Figure 2 2) and is suitable for modifying one or more turns ( Figure 2 The positions 41-47) in the figure are controlled.

[0069] Reactor( Figure 21) includes an actuation system, the actuation system comprising:

[0070] -First motor( Figure 2 61) (particularly an electric motor) which is adapted to modify the inductor ( Figure 2 4) of at least one first turn ( Figure 2 43) in the position (preferably only the axial position, i.e. the vertical position),

[0071] - a first plurality of translation actuators ( Figure 2 62), which is suitable for acting on the first turn ( Figure 2 43) at the corresponding multiple points (see Figure 2 and Figure 3 ), and causes a translation of the first turn (preferably only an axial translation, i.e. a vertical translation), and

[0072] -First transmission device ( Figure 2 63) (particularly a mechanical transmission device), which is suitable for the first motor ( Figure 2 The motion of 61) is transmitted to the first plurality of actuators ( Figure 2 62).

[0073] Thus, one turn (or group of turns) of the inductor can be moved independently of the other turns.

[0074] Two turns (or two groups of turns) of the inductor can move independently of each other and the other turns.

[0075] In this case, the actuation system also includes:

[0076] a second electrical machine (in particular an electric motor) suitable for modifying the position (preferably only the axial position, ie the vertical position) of at least one second turn of the inductor by the effect of its movement,

[0077] a second plurality of translation actuators adapted to act on a corresponding plurality of points of the second turn and to cause a translation (preferably only axial translation, ie vertical translation) of the second turn, and

[0078] A second transmission, in particular a mechanical transmission, is adapted to transmit the movement of the second motor to the second plurality of actuators.

[0079] Usually and typically, an inductor has several turns (or groups of turns) that can move independently of each other and other turns.

[0080] like Figure 3 As schematically shown in FIG. 1 , the first motor and / or the second motor may be adapted to modify a set of turns (eg, turns 45 and 46) of the inductor relative to the susceptor ( Figure 2 2) and the position relative to the other turns of the inductor.

[0081] The first transmission device ( Figure 2 64) and / or the second transmission means comprises one and / or two belts or chains; the belt is preferably toothed.

[0082] Preferably, the sensor ( Figure 2 and Figure 3 4) in which comprises a continuous conductor made of a single mechanical piece; said mechanical piece must be sufficiently elastic, i.e. not rigid, to allow the turns of the inductor to translate in the axial direction without causing significant displacement of adjacent turns; the reason being that the deformation caused by the actuator is distributed along the entire length of the turn.

[0083] Each actuator ( Figure 2 62) converts the rotation received from the motor via the transmission into a translation. Preferably, the actual translation of the actuator is measured to determine the positioning of the corresponding turns; for this purpose, a simple potentiometer is advantageously associated with the actuator and precisely measures the rotation corresponding to the translation produced by the actuator.

[0084] Then, with the reactor in place, it is necessary to calibrate the actuator mechanically and the potentiometer electrically.

[0085] The system 8 can then drive the motor as provided by one or more control laws and verify that the turn (or more precisely, its point) has moved as desired.

[0086] In particular, the function of the computerized system 8 is to control the heating of the reactor 1 and to control the cooling of the reactor 1 .

[0087] The system 8 may include means, in particular hardware means and software means, capable of implementing the heating method according to the invention, which will be described below.

[0088] According to the heating method of the present invention, in the susceptor ( Figure 2 2) during heating from the first temperature to the second temperature and before the epitaxial deposition process, modifying the inductor ( Figure 2 4) of at least one first turn ( Figure 2 43) or the first set of turns relative to the receiver and relative to the inductor ( Figure 2 4) in the position of the other turns; the second temperature is usually higher than the first temperature.

[0089] In many cases, it is advantageous to change at least one second turn or a second set of turns of the inductor relative to the susceptor and relative to the inductor during the heating of the susceptor from the first temperature to the second temperature and prior to the epitaxial deposition process. Figure 2 The positions of the other turns in 4).

[0090] The change in position of the second turn is typically independent of the change in position of the first turn.

[0091] The change in position may be a single one during the heating period, but, more typically, the position will change repeatedly.

[0092] In this way, it is possible to try to keep all substrates at a constant temperature even during temperature transitions. For example, all at 25°C at the beginning, all at 50°C after one minute, all at 75°C after another minute, all at 100°C after another minute, all at 100°C after another minute, ..., and finally all at 1150°C; thereafter, all at 1150°C during the epitaxial deposition cycle. It should be noted that in order to obtain temperature uniformity during temperature transitions, the thermal inertia of the susceptor must be taken into account. According to this example, the position of each turn of the inductor can be associated with each temperature transition interval (25-50°C, 50-75°C, 75-100°C, ..., 1125-1150°C).

[0093] For example, the previously mentioned first temperature can be between 0°C and 50°C, i.e. the "ambient temperature", or it can be between 100°C and 300°C, i.e. the "loading temperature"; depending on the reactor, a) one or more substrates, or b) one or more supporting elements with one or more substrates, or c) a receiver with one or more substrates can be loaded.

[0094] The second temperature may be between 500° C. and 2000° C., ie, the “process temperature” of the epitaxial deposition process.

[0095] Typically, during the entire heating cycle of the reactor from the first temperature to the second temperature, one or more turns will appropriately and repeatedly modify their position (moving them away from or closer to the susceptor) so that the temperature of the susceptor and the upper surface of the supported substrate is preferably uniform from moment to moment during the entire heating cycle.

[0096] Alternatively, one or more turns will modify their position appropriately and repeatedly (move them away from or closer to the susceptor) only within the temperature range between the first temperature and the second temperature. For example, if the first temperature is the "ambient temperature" (e.g., 25°C) or the "loading temperature" (e.g., 150°C), and if the second temperature is the "process temperature" (e.g., 1150°C), then one or more turns will modify their position appropriately and repeatedly, for example, only in the temperature interval between 500°C and the "process temperature"; in other words, in the temperature interval between the "ambient temperature" or the "loading temperature" and, for example, 500°C, the position of any one turn is not modified. This alternative may be useful, for example, in cases where a certain temperature inconsistency of the substrate is tolerable under certain conditions.

[0097] The (especially flat) geometry of the inductor corresponds to the (cylindrical with a height much smaller than the diameter) geometry of the susceptor.

[0098] Since the susceptor is rather thin, the temperature difference between the lower and upper surfaces is rather low (eg 50-100° C.), and the temperature of the susceptor can be represented schematically in a first approximation by a radial diagram.

[0099] These position changes usually occur under the control of a control system.

[0100] During heating and before deposition, the control of the position of the turns is preferably "open loop", and the electrical control of the inductor is preferably "open loop"; this is a simple control, but for this application, even better than "closed loop" control.

[0101] Preferably, during "open loop" control, the temperature can be measured, for example, by means of a thermal imaging camera. The control law can be stored, for example, in a table; each row corresponds to a different temperature (for example, the average temperature of the substrate measured by the thermal imaging camera), for each temperature the electrical power supplied to the inductor as, for example, the vertical position of the turns of the inductor. Starting from a first temperature (for example, the ambient temperature), a first power and a first position are set; when the thermal imaging camera measures a second temperature, a second power and a second position are set; and so on.

[0102] The data for the "open loop control" are usually obtained from one or more experimental campaigns. It has been observed that the best results are obtained when the position of the turns is modified according to an "experimental rule".

[0103] The advantage of using an "open loop" control is that, from process to process, only the final temperature of the "process recipe" (which can be considered the "process temperature") varies, in a first approximation, at a thermal level, and not the ramp to reach said temperature. Since it is necessary to achieve a temperature ramp that is always equal (or very similar) to itself, it is not worthwhile to include a "closed loop" control, since it is essentially excellent at managing a wide range of different and unforeseen situations. In this way, with just one experimental campaign, it is possible to discover the optimal law to eliminate the problem of thermal inertia of the susceptor and avoid dangerous instabilities of the controlled system.

[0104] During the epitaxial deposition process (ie after the heating phase and before the cooling phase) it is preferred to operate in a different manner.

[0105] During the epitaxial deposition process, the position of any one turn in the inductor is not modified, ie the position of each turn is maintained; the inductor is powered by means of a "closed loop control".

[0106] During "closed-loop" control, the temperature can be measured, for example, with the aid of a thermal imaging camera, and the electrical power to be supplied to the inductor is calculated based on the difference between the desired temperature (i.e., the process temperature set, for example, by an operator) and the temperature measured by the thermal imaging camera (e.g., the average temperature of the substrate).

[0107] In some applications, it may be preferable to keep the turns fixed and apply "closed loop" electrical control to the inductor during the final part of the heating operation (eg, during the last 50-100°C of heating).

Claims

1. A reactor (1) for epitaxial deposition, comprising: at least one susceptor (2) having a disc-shaped portion, the susceptor (2) being suitable for directly or indirectly supporting one or more substrates (100); and an inductor (4) having a plurality of turns (41-47), the inductor (4) being adapted to heat the disk-shaped portion and being controlled by changing the positions of the plurality of turns (41-47), Characterized in that, the reactor comprises: - a first motor (61) suitable for changing the position of at least one first turn (43) of the inductor (4) due to its movement, - a first plurality of translation actuators (62) adapted to act on a respective plurality of points of the at least one first turn (43) and to cause an axial translation of the at least one first turn (43), thereby moving the at least one first turn (43) away from or closer to the susceptor, and - a first transmission device (63) suitable for transmitting the movement of the first motor (61) to the first plurality of translation actuators (62), The inductor (4), the first motor (61), the first plurality of translation actuators (62) and the first transmission device (63) are completely located outside the reaction chamber of the reactor (1), and each turn of the plurality of turns has an arc shape and the plurality of turns are connected together by straight line segments, and each turn or each group of turns of the plurality of turns moves independently of other turns.

2. The reactor for epitaxial deposition according to claim 1, comprising: - a second motor adapted to change the position of at least one second turn (45, 46) of said inductor (4) due to its movement, - a second plurality of translation actuators adapted to act on a respective plurality of points of said at least one second turn (45, 46) and to cause a translation of said at least one second turn (45, 46), and - a second transmission adapted to transmit the movement of said second motor to said second plurality of translation actuators.

3. The reactor for epitaxial deposition according to claim 1, wherein the first transmission device (63) comprises one and / or two belts or chains.

4. The reactor for epitaxial deposition according to claim 2, wherein the second transmission device comprises one and / or two belts or chains.

5. A reactor for epitaxial deposition according to claim 1 or 3, wherein the inductor (4) comprises a continuous conductor in the form of a single elastic mechanical piece.

6. A reactor for epitaxial deposition according to claim 2 or 4, wherein the inductor (4) comprises a continuous conductor in the form of a single elastic mechanical piece.

7. A reactor for epitaxial deposition according to claim 2 or 4, comprising potentiometers for detecting rotation of the first plurality of translation actuators and the second plurality of translation actuators.

8. The reactor for epitaxial deposition of claim 6, comprising potentiometers for detecting rotation of the first plurality of translation actuators and the second plurality of translation actuators.

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