U.S. patent application number 16/347251 was filed with the patent office on 2019-08-22 for heating method for a reactor for epitaxial deposition and reactor for epitaxial deposition.
The applicant listed for this patent is LPE S.p.A.. Invention is credited to Vincenzo OGLIARI, Franco PRETI, Silvio PRETI.
Application Number | 20190256999 16/347251 |
Document ID | / |
Family ID | 58266022 |
Filed Date | 2019-08-22 |
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United States Patent
Application |
20190256999 |
Kind Code |
A1 |
OGLIARI; Vincenzo ; et
al. |
August 22, 2019 |
HEATING METHOD FOR A REACTOR FOR EPITAXIAL DEPOSITION AND REACTOR
FOR EPITAXIAL DEPOSITION
Abstract
The present invention relates to a heating method for a reactor
(1) for epitaxial deposition; the reactor (1) comprises a susceptor
(2) and an inductor (4); the inductor (4) is adapted to heat the
susceptor (2) by electromagnetic induction when it is electrically
powered; the inductor (4) comprises a plurality of turns (41-47);
during heating of the susceptor (2) from a first temperature to a
second temperature, the position of one or more turns (43) of the
inductor (4) with respect to the susceptor (2) and to the other
turns of the inductor (4) is changed. The turns (43) are actuated
by means of an appropriate actuation system (61,62, 63).
Inventors: |
OGLIARI; Vincenzo;
(Baranzate (MI), IT) ; PRETI; Silvio; (Baranzate
(MI), IT) ; PRETI; Franco; (Baranzate (MI),
IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LPE S.p.A. |
Baranzate (MI) |
|
IT |
|
|
Family ID: |
58266022 |
Appl. No.: |
16/347251 |
Filed: |
October 30, 2017 |
PCT Filed: |
October 30, 2017 |
PCT NO: |
PCT/IB2017/056720 |
371 Date: |
May 3, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 16/52 20130101;
C30B 25/10 20130101; C23C 16/46 20130101 |
International
Class: |
C30B 25/10 20060101
C30B025/10; C23C 16/46 20060101 C23C016/46; C23C 16/52 20060101
C23C016/52 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 4, 2016 |
IT |
102016000111143 |
Claims
1. Heating method for a reactor for epitaxial deposition; wherein
the reactor comprises a susceptor and an inductor; wherein the
inductor is adapted to heat the susceptor by electromagnetic
induction when electrically powered; wherein the inductor comprises
a plurality of turns; wherein, during heating of the susceptor from
a first temperature to a second temperature, before an epitaxial
deposition process, the position of at least one first turn of the
inductor with respect to said susceptor and with respect to other
turns of the inductor is changed.
2. Heating method according to claim 1, wherein, during heating of
the susceptor from a first temperature to a second temperature,
before an epitaxial deposition process, the position of at least
one second turn of the inductor with respect to said susceptor and
with respect to other turns of the inductor is changed.
3. Heating method according to claim 1, wherein, during heating of
the susceptor from said first temperature to said second
temperature, before an epitaxial deposition process, the position
of said at least one turn and/or of said at least one second turn
is changed repeatedly.
4. Heating method according to claim 1, wherein, during heating of
the susceptor from a first temperature to a second temperature,
before an epitaxial deposition process, the position of said at
least one turn and/or of said at least one second turn is changed
through an open loop control.
5. Heating method according to claim 1, wherein, during the heating
of the susceptor from a first temperature to a second temperature,
before an epitaxial deposition process, said inductor is
electrically powered through an open loop control.
6. Heating method according to claim 1, wherein, during an
epitaxial deposition process, the position of none of the turns
(41-48) of said inductor is changed.
7. Heating method according to claim 1, wherein, during an
epitaxial deposition process, said inductor is electrically powered
through a closed loop control.
8. Heating method according to claim 1, wherein said first
temperature corresponds to a loading temperature of an epitaxial
deposition process, and/or wherein said second temperature
corresponds to a process temperature of an epitaxial deposition
process.
9. Heating method according to claims 8, wherein, in at least one
temperature interval between said first temperature and said second
temperature, the position of none of the turns of said inductor is
changed.
10. Reactor for epitaxial deposition comprising at least one
susceptor with a disk-like portion adapted to directly or
indirectly support one or more substrates, and an inductor with
turns adapted to heat said disk-like portion and to be controlled
by changing the position of the turns, the reactor comprising: a
first motor adapted to change the position of at least one first
turn of said inductor as a result of its motion, a first plurality
of translating actuators adapted to act on a corresponding
plurality of points (FIG. 3) of said at least one first turn and
causing translations thereof, and a first transmission adapted to
transmit the motion of said first motor (61) to said first
plurality of actuators.
11. Reactor for epitaxial deposition according to claim 10,
comprising: a second motor adapted to change the position of at
least one second turn of said inductor as a result of its motion, a
second plurality of translating actuators adapted to act on a
corresponding plurality of points (FIG. 3) of said at least one
second turn and causing translations thereof, and a second
transmission adapted to transmit the motion of said second motor to
said second plurality of actuators.
12. Reactor for epitaxial deposition according to claim 10, wherein
said first transmission and/or said second transmission consists of
one and/or two belts or chains.
13. Reactor for epitaxial deposition according to claim 10, wherein
said inductor comprises a continuous conductor in a single elastic
mechanical piece.
14. Reactor for epitaxial deposition according to claim from 10,
comprising potentiometers used to detect rotations of said
actuators.
15. Reactor for epitaxial deposition adapted to implement the
heating method according to claim from 1 and comprising at least
one motor (61), at least one plurality of actuators (62) and at
least one transmission (63).
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a heating method for a
reactor for epitaxial deposition and a reactor for epitaxial
deposition.
STATE OF THE ART
[0002] Any epitaxial reactor comprises a heating system to heat the
substrates to be subjected to epitaxial growth.
[0003] A phase of an epitaxial deposition process is preceded by a
heating phase and it is followed by a cooling phase.
[0004] Heating can be, for example, of the electromagnetic
induction type.
[0005] Often, in this case, the heating system directly heats a
susceptor (which is located inside the reaction chamber of the
epitaxial reactor), and the substrates receive heat by conduction
from the susceptor (which supports them).
[0006] Always, in this case, the heating system comprises at least
one inductor.
[0007] In the past, the present Applicant had provided the
possibility that one or more of the turns of such an inductor be
movable: the patent document WO9610659A2.
[0008] According to this solution, the inductor consisted of a
plurality of rigid circles connected electrically and mechanically
by flexible bridges; a single circle was moved by means of a single
electric motor and a single translating actuator mounted on the
shaft of the motor; the deformation caused by said actuator was
entirely borne by the flexible bridges.
[0009] The turns were positioned in desired positions before
starting the heating operation and hence well before starting
epitaxial deposition; this positioning was one of the operations of
the initial setting of the reactor.
[0010] Solutions of this kind are also known from the patent
documents with publication number US2010059182, JP2003133245 and
KR100978567.
[0011] The main objective of a heating system for epitaxial reactor
was and is to obtain a uniform temperature of the substrate during
the process.
[0012] A secondary objective of a heating system for epitaxial
reactor was and is to reach the process temperature in a short
time.
[0013] According to the solution known from the patent document
having publication number JP2003133245, an entire inductor is
approached to a susceptor to heat it more rapidly before an
epitaxial deposition process and to move an entire inductor away
from a susceptor to cool it more rapidly after an epitaxial
deposition process.
SUMMARY
[0014] The Applicant has realised, through experiments that it
conducted, that it is very advantageous for the temperature of the
substrate to be uniform not only during the process, but also
during heating, or, rather, instant by instant during heating that
precedes the epitaxial deposition process; the advantage can be
tied, for example, to the reduction of thermal stresses and
defects, in particular "slip lines".
[0015] The Applicant then set itself the objective of providing a
solution that makes it possible to obtain a uniform temperature of
the substrate both during heating and during the subsequent
epitaxial deposition.
[0016] The Applicant also set itself the objective of providing a
solution that makes it possible to reach the process temperature in
a short time.
[0017] Lastly, the Applicant has set itself the objective of
provide a solution that is not only effective, but also simple.
[0018] These objectives are substantially achieved thanks to the
heating method and to the reactor for epitaxial reactor having the
technical features set forth in the accompanying claims
LIST OF FIGURES
[0019] The present invention shall become more readily apparent
from the detailed definition that follows to be considered together
with the accompanying drawings in which:
[0020] FIG. 1 shows a vertically sectioned schematic view of a
reaction chamber of an embodiment of an epitaxial reactor according
to the prior art,
[0021] FIG. 2 shows a vertically sectioned schematic view of a
reaction chamber of an embodiment of an epitaxial reactor according
to the present invention, and
[0022] FIG. 3 schematically shows a top view of an inductor of the
reactor of FIG. 2.
[0023] As is easily understandable, there are various way of
implementing in practice the present invention which is defined in
its main advantageous aspects in the appended claims.
DETAILED DESCRIPTION
[0024] FIG. 1 shows a vertically sectioned schematic view of a
reaction chamber of an embodiment of an epitaxial reactor 1
according to the prior art.
[0025] The reaction chamber is provided with a cavity 10 defined by
an upper wall 11 (in particular made of transparent quartz), a
lower wall 12 (in particular made of transparent quartz) and
lateral walls (in particular made of transparent quartz) not shown
in the figure.
[0026] A susceptor 2 is positioned within the cavity 10 and it is
adapted to support and heat substrates during epitaxial deposition.
In the case of FIG. 1, there is a single substrate 100 that is laid
on a support element 3 (with disk-like shape, specifically of a
cylinder with far smaller height than diameter, positioned
horizontally and made of graphite which may be coated with SiC or
TaC) which, in turn, is laid on the susceptor 2 (with disk-like
shape, specifically of a cylinder with far smaller height than
diameter, positioned horizontally and made of graphite which may be
coated with SiC or TaC), the element 3 is not indispensable for the
purposes of the present invention.
[0027] A heating system is provided that comprises at least one
inductor 4 adapted to heat the susceptor 2 by electromagnetic
induction when it is supplied electrical power; the inductor 4 is
flat and it comprises a plurality of turns 41-47 (in particular
seven concentric turns in the example of FIG. 1), typically
connected electrically in series. The system can comprise other
inductors under the chamber, but, typically, nothing over the
chamber.
[0028] Inside the cavity 10 are horizontal inner walls 14 aligned
to the substrate 100.
[0029] The susceptor 2 is fastened to a rotating shaft 5 around a
vertical axis Z.
[0030] The lower wall 12 has a hole and a sleeve 13 for the passage
of the shaft 5.
[0031] The inductor 4 is situated under the lower wall 12 around
the sleeve 13.
[0032] The embodiment of FIG. 2 is an improvement of the solution
of FIG. 1 or of similar solutions.
[0033] In FIG. 2, some components of an actuation system 6 to move
the turns of the inductor 4 are 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.
[0034] In FIG. 2, a thermographic camera 7 is shown, located above
the upper wall 11 adapted to measure temperature in the chamber, in
particular of the substrate 100, in a thin underlying radial area;
in particular, the radial area extends between the axis Z (or very
close thereto) and the edge of the substrate 100 (or very close
thereto); this measurement area is sufficient because the susceptor
and the substrate rotate.
[0035] In FIG. 2, a computerised heating control system is shown;
it can comprise one or more PLCs. The system 8 is connected
electrically: to the inductor 4 to supply power to it, to the
system 6 (in particular, to the motor 61 and to the
potentiometers), to the thermographic camera 7, and a user
interface 9. The interface 9 allows an operator to enter commands
and to extract information.
[0036] In FIG. 3, the exemplifying case in which the turns 43, 45
and 46 are movable is shown schematically; the turns 45 and 46,
which constitute for example a "group", are moved by the system 6
together with and independently from the turns 43; the movement of
the turn 43 is obtained by means of three actuators 621, 622 and
623 situated, for example, 90.degree. from each other; the movement
of the group of turns 45 and 46 is obtained by means of three pairs
of actuators situated, for example, 90.degree. from each other, or
of three actuators 624, 625 and 626 (an actuator simultaneously
moves two points of two turns, as in the figure). In FIG. 2, for
greater clarity of the drawing, only parts of the devices that
allow to move the turn 43 are shown, and none of the devices that
allow to move the turns 45 and 46 is shown.
[0037] In FIG. 3, each of the turns has the shape of an arc of a
circle, for example of approximately 330.degree., and the turns are
jointed together for example by a rectilinear segment.
[0038] According to the present invention, the reactor (1 in FIG.
2) comprises an inductor (4 in FIG. 2) with turns (41-47 in FIG.
2), that is typically flat (or substantially flat), adapted to heat
a susceptor (2 in FIG. 2) and to be controlled by modification of
the position of one or more turns (41-47 in FIG. 2).
[0039] The reactor (1 in FIG. 2) comprises and actuation system
that comprises: [0040] a first motor (61 in FIG. 2) (in particular
an electric motor) adapted to modify the position (preferably, only
the axial, i.e. vertical position) of at least one first turn (43
in FIG. 2) of the inductor (4 in FIG. 2) by effect of a motion
thereof, [0041] a first plurality of translating actuators (62 in
FIG. 2) adapted to act on a corresponding plurality of points (see
both FIG. 2 and FIG. 3) of the first turn (43 in FIG. 2) and
causing translations thereof (preferably only the axial, i.e.
vertical translation), and [0042] a first transmission (63 in FIG.
2) (in particular a mechanical transmission adapted to transmit the
motion of the first motor (61 in FIG. 2) to the first plurality of
actuators (62 in FIG. 2).
[0043] Hence, it is possible that a turn (or a group of turns) of
the inductor can be moved independently of the other turn.
[0044] It is possible that two turns (or two groups of turns) of
the inductor can be moved independently of each other and of the
other turn.
[0045] In this case, the actuation system further comprises: [0046]
a second motor (in particular an electric motor) adapted to modify
the position (preferably, only the axial, i.e. vertical position)
of at least one second turn of the inductor by effect of a motion
thereof, [0047] a second plurality of translating actuators adapted
to act on a corresponding plurality of points of the second turn
and cause translations thereof (preferably only the axial, i.e.
vertical translations), and [0048] a second transmission (in
particular a mechanical transmission) adapted to transmit the
motion of the second motor to the second plurality of
actuators.
[0049] In general and typically, there are several turns (or groups
of turns) of the inductor that can move independently of each other
and of the other turns.
[0050] As shown schematically in FIG. 3, the first and/or the
second motor can be adapted to modify the position of a group of
turns (for example, the turns 45 and 46) of the inductor with
respect to the susceptor (2 in FIG. 2) and with respect to the
other turns of the inductors.
[0051] The first transmission (64 in FIG. 2) and/or the second
transmission consists of one and/or two belts or chains; the belts
are preferably toothed.
[0052] The inductor (4 in FIG. 2 and FIG. 3) preferably consists of
a continuous conductor made of a single mechanical piece; said
mechanical piece must be sufficiently elastic, i.e. not rigid, to
allow translating a turn thereof in axial direction without causing
appreciable displacement of the adjacent turns; the reason is that
the deformation caused by the actuators is distributed along the
entire length of the turn.
[0053] Each actuator (62 in FIG. 2) transforms rotations received
from a motor, through a transmission, into translations. It is
preferable to measure the actual translations of an actuator to be
certain of the positioning of the corresponding turns; for this
purpose, it is advantageous to associate a simple potentiometer
with an actuator and precisely to measure the rotations that it
effects which correspond to translations that it generates.
[0054] Then the reactor is put in place, it will be necessary to
calibrate the actuators mechanically and the potentiometers
electrically.
[0055] The system 8 is then able to drive a motor as provided by
one or more control laws and to verify that a turn (more precisely,
its points) has moved as desired.
[0056] The function of the computerised system 8 is, inter alia, to
control the heating of the reactor 1 as well as to control the
cooling of the reactor 1.
[0057] The system 8 can comprise means, in particular hardware
means and software means, able specifically to implement the
heating method according to the present invention that will be
described below.
[0058] According to the heating method according to the present
invention, during the heating of the susceptor (2 in FIG. 2), from
a first temperature to a second temperature, and before a process
of epitaxial deposition, the position of at least one first turn
(43 in FIG. 2), or of a first group of turns, of the inductor (4 in
FIG. 2) with respect to the susceptor and with respect to the other
turns of the inductor (4 in FIG. 2) is modified; typically, the
second temperature is higher than the first temperature.
[0059] In many cases, it will be advantageous that during the
heating of the susceptor, from the first temperature to the second
temperature, and before a process of epitaxial deposition, the
position of at least one second turn, or of a second group of
turns, of the inductor with respect to the susceptor and with
respect to the other turns of the inductor (4 in FIG. 2) is
changed.
[0060] The change in position of the second turn will typically be
independent from the change in position of the first turn.
[0061] The change in position can be a single one during said
heating, but, more typically, the position will be change
repeatedly.
[0062] In this way, it is possible to try to have all the substrate
at constant temperature even during temperature transitions. For
example, at the start, all at 25.degree. C., after one minute all
at 50.degree. C., after another minute all at 75.degree. C., after
another minute all at 100.degree. C., after another minute all at
100.degree. C., . . . , at the end all at 1150.degree. C.;
thereafter, during the period of the epitaxial deposition, all at
1150.degree. C. It should be noted that, to obtain temperature
uniformity during temperature transitions, it will be necessary to
take into account the thermal inertia of the susceptor. According
to this example, to each temperature interval of the transition
(25-50.degree. C., 50-75.degree. C., 75-100.degree. C., . . . ,
1125-1150.degree. C.) could be associated a position for each of
the turns of the inductor.
[0063] The first temperature mentioned previously can be for
example between 0.degree. C. and 50.degree. C., i.e. "ambient
temperature", or it can be between 100.degree. C. and 300.degree.
C., i.e. "loading temperature"; depending on the reactors, it is
possible to load a) one or more substrates or b) one or more
supporting elements with one or more substrates or c) a susceptor
with one or more substrates.
[0064] The second temperature mentioned above can be between
500.degree. C. and 2000.degree. C., i.e. "process temperature" of a
process of epitaxial deposition.
[0065] In general, one or more turns will appropriately and
repeatedly modify their position (moving them away from or
approaching them to the susceptor) during the entire heating period
of the reactor from the first temperature to the second temperature
so that the temperature of the upper face of the susceptor and of
the supported substrates is uniform preferably instant by instant
during the entire heating period.
[0066] Alternatively, one or more turns will appropriately and
repeatedly modify their position (moving them away from or
approaching them to the susceptor) only in a temperature range
between the first temperature and the second temperature. For
example, if the first temperature is the "ambient temperature" (for
example 25.degree. C.) or the "loading temperature" (for example
150.degree. C.) and if the second temperature is the "process
temperature" (for example 1150.degree. C.), one or more turns will
appropriately and repeatedly modify their position for example only
in the temperature interval between 500.degree. C. and the "process
temperature"; in other words, the position of no turn will be
modified in the temperature interval between the "ambient
temperature" or the "loading temperature" and, for example,
500.degree. C. This alternative can be useful, for example, in the
cases in which a certain temperature inconsistency of the substrate
in certain conditions is tolerable.
[0067] The geometry (in particular flat) of the inductor has a
correspondence with the geometry (cylindrical with far smaller
height than diameter) of the susceptor.
[0068] Since the susceptor is rather thin, the temperature
difference between lower face and upper face is rather low (e.g.
50-100.degree. C.), and the temperature of the susceptor can be
schematically represented, in first approximation, with a radial
diagram.
[0069] These position changes will typically take place under the
control of a control system.
[0070] During heating and before deposition, control of the
position of the turns is preferably "open loop" and the electrical
control of the inductor is preferably "open loop"; it is a simple
control, but even better than the "closed loop" control for this
application. Preferably, during "open loop" control, the
temperature can be measured for example by means of a thermographic
camera. The control law can be for example stored in a table; each
row corresponds to a different temperature (for example the average
temperature of the substrate measured by the thermographic camera),
for each temperature, an electrical power to be supplied to the
inductor is provided as are, for example, vertical positions of the
turns of the inductor. Starting from the first temperature (for
example ambient temperature) the first power and the first
positions are set; when the thermographic camera measures the
second temperature, the second power and the second positions are
set; and so on.
[0071] The data for the "open loop control" derive typically 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 law".
[0072] 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") changes
at the thermal level in first approximation, and not the ramp to
reach said temperature. Since a temperature ramp that is always
identical to itself (or very similar) has to be realised, it is not
worthwhile to include a "closed loop" control, which, by its
nature, is excellent in managing ever different and unforeseen
situations. In this way, through just one experimental campaign, it
is possible to identify an optimal law, to obviate the problem of
the thermal inertia of the susceptor and to avoid dangerous
instabilities of the controlled system.
[0073] During epitaxial deposition processes (i.e. after the
heating phase and before the cooling phase) it is preferable to
operate in a different way.
[0074] During an epitaxial deposition process, the position of no
turn of the inductor is modified, i.e. the position of each turn is
maintained; the inductor is supplied electrical power by means of a
"closed loop control".
[0075] During the "closed loop" control, the temperature can be
measured for example by means of a thermographic camera, and the
electrical power to be supplied to the inductor is calculated on
the basis of the difference between the desired temperature (i.e.
the process temperature for example set by the operator) and the
temperature measured by the thermographic camera (for example the
average temperature of the substrate).
[0076] In some applications, during the final part of the heating
operation (e.g. during the last 50-100.degree. C. of heating), it
can be preferable to maintain the turn fixed and implement a
"closed loop" electrical control of the inductor.
* * * * *