U.S. patent application number 14/356104 was filed with the patent office on 2014-09-25 for cvd reactor and substrate holder for a cvd reactor.
The applicant listed for this patent is AIXTRON SE. Invention is credited to Adam Boyd, Daniel Claessens, Hugo Silva.
Application Number | 20140287142 14/356104 |
Document ID | / |
Family ID | 47178621 |
Filed Date | 2014-09-25 |
United States Patent
Application |
20140287142 |
Kind Code |
A1 |
Boyd; Adam ; et al. |
September 25, 2014 |
CVD REACTOR AND SUBSTRATE HOLDER FOR A CVD REACTOR
Abstract
The invention relates to a CVD reactor, with a process chamber
(4) which is arranged therein and into which a process gas can be
fed by means of a gas inlet member (2), with a substrate holder (3)
which, on the upper side (3') thereof facing the process chamber
(4), has one or more pockets (5) which are designed in such a
manner that one substrate (7) in each case rests only on selected,
raised support regions (6), and with a heating system (9) which is
arranged below the substrate holder (3) and is spaced apart from
the lower side (3'') of the substrate holder (3), wherein the lower
side (3'') of the substrate holder (3) is configured differently in
a central region (b) with respect to the heat transmission from the
heating system (9) to the substrate holder (3), which central
region is located under a central zone of the pocket (5), than in a
surrounding region (a) which surrounds the central region (a) and
is located below a zone close to the edge of the pocket (5). The
heating system (9) is intended to be designed as a substantially
planar heat source. A gas flushing device (11) is provided in order
to flush the gap (12) with flushing gases of different heat
conductivity. The gap (12) has such a gap height (s, t), that, upon
a change of a first flushing gas with a first heat conductivity to
a second flushing gas with a second heat conductivity, the supply
of heat from the heating system (9) to the substrate holder (3)
changes differently in the circumferential region (a) than in the
central region (b).
Inventors: |
Boyd; Adam; (Kelmis, DE)
; Claessens; Daniel; (Aachen, DE) ; Silva;
Hugo; (Aachen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AIXTRON SE |
Hersogenrath 98 |
|
DE |
|
|
Family ID: |
47178621 |
Appl. No.: |
14/356104 |
Filed: |
November 2, 2012 |
PCT Filed: |
November 2, 2012 |
PCT NO: |
PCT/EP2012/071687 |
371 Date: |
May 2, 2014 |
Current U.S.
Class: |
427/255.28 ;
118/725 |
Current CPC
Class: |
H01L 21/68735 20130101;
C23C 16/455 20130101; C23C 16/458 20130101; H01L 21/67109 20130101;
C23C 16/46 20130101; H01L 21/6875 20130101; H01L 21/68771
20130101 |
Class at
Publication: |
427/255.28 ;
118/725 |
International
Class: |
C23C 16/458 20060101
C23C016/458 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 4, 2011 |
DE |
10 2011 055 061.5 |
Claims
1. A CVD reactor having a reactor housing (1), a process chamber
(4) arranged therein, into which at least one process gas can be
fed by means of a gas inlet body (2), having a substrate holder
(3), which has, on its top side (3') facing toward the process
chamber (4), one or more pockets (5), which are formed so that
respectively one substrate (7) only rests on selected support
regions (6) raised in relation to a base (5') of the one or more
pockets (5), having a heater (9) arranged underneath the substrate
holder (3), which is spaced apart by a gap (12) from a bottom side
(3'') of the substrate holder (3), wherein the bottom side (3'') of
the substrate holder (3) has a depression (8) in a central region
(b) lying under a middle zone of the one or more pockets (5) or has
a different reflectivity than in a surrounding region (a), which
surrounds the central region (b) and lies underneath an
edge-proximal zone of the one or more pockets (5), so that heat
transfer from a heater (9) to the substrate holder (3) is different
in the central region (b) than in the surrounding region (a),
characterized in that the heater (9) is implemented as an
essentially flat heat source, which extends underneath an entire
region of the substrate holder (3) occupied with the one or more
packets (5), a gas flushing unit (11) is provided to flush the gap
(12) with flushing gases of various thermal conductivities, and the
gap (12) has a gap height (s, t) such that in the event of a change
from a first flushing gas having a first thermal conductivity to a
second flushing gas having a second thermal conductivity, the heat
supply from the heater (9) to the substrate holder (3) changes
differently in the surrounding region (a) than in the central
region (b).
2. The CVD reactor according to claim 1, characterized in that the
gap height (t, t', t'') of the gap (12) under the central region
(b) is different from the gap height (s) under the surrounding
region (a).
3. (canceled)
4. The CVD reactor according to claim 1, characterized in that a
base (5', 8') of the one or more pockets (5) or the recess (8)
curves in a bowl shape.
5. The CVD reactor according to claim 4, characterized in that the
curve of the base (5', 8') is approximated by a stepped shape.
6. The CVD reactor according to claim 1, characterized in that the
bottom side (3') of the substrate holder (3) has a different
reflectivity in the central region (b) than in the surrounding
region (a).
7. The CVD reactor according to claim 1, characterized in that the
central region (b) and/or the surrounding region (a) is coated with
a reflective coating.
8. The CVD reactor according to claim 1, characterized in that the
heater (9) is formed by a heating wire (10) arranged in a
spiral.
9. A method for depositing a plurality of layers arranged one on
top of another in respectively one process step on a substrate (7)
in a CVD reactor, having a reactor housing (1), a process chamber
(4) arranged therein, into which at least one process as can be fed
by means of a gas inlet body (2), having a substrate holder (3),
which has, on its top side (3') facing toward the process chamber
(4), one or more pockets (5), which are formed so that respectively
one substrate (7) only rests on selected support regions (6) raised
in relation to a base (5') of the one or more pockets (5), having a
heater (9) arranged underneath the substrate holder (3), which is
spaced apart by a gap (12) from a bottom side (3'') of the
substrate holder (3), wherein the bottom side (3'') of the
substrate holder (3) has a depression (8) in a central region (b)
lying under a middle zone of the one or more pockets (5) or has a
different reflectivity than in a surrounding region (a), which
surrounds the central region (b) and lies underneath an
edge-proximal zone of the one or more pockets (5), so that heat
transfer from a heater (9) to the substrate holder (3) is different
in the central region (b) than in the surrounding region (a),
characterized in that the heater (9) is implemented as an
essentially flat heat source, which extends underneath an entire
region of the substrate holder (3) occupied with the one or more
pockets (5), a gas flushing unit (11) is provided to flush the gap
(12) with flushing gases of various thermal conductivities, and the
gap (12) has a gap height (s, t) such that in the event of a change
from a first flushing gas having a first thermal conductivity to a
second flushing gas having a second thermal conductivity, the heat
supply from the heater (9) to the substrate holder (3) changes
differently in the surrounding region (a) than in the central
region (b), wherein, in at least one first process step, a first
layer having a first composition is deposited at a first
temperature and, in at least one second process step, a second
layer having a second composition is deposited at a second
temperature, wherein the two compositions and the two temperatures
are different from one another, characterized in that, in the first
process step, a first flushing gas or flushing gas mixture is fed
into the gap (12) and, in the second process step, a second
flushing gas or flushing gas mixture is fed into the gap, wherein
the first flushing gas or flushing gas mixture differs from the
second flushing gas or flushing gas mixture at least by way of its
thermal conductivity.
10. The method according to claim 9, characterized in that, in the
first process step, the heat transport from the heater (9) to the
substrate holder (3) is heat-radiation-dominated and, in the second
step, it is heat-conduction-dominated, at least in one of the two
regions (a, b).
11. The method according to claim 9, characterized in that, in the
first process step, a mean temperature in a middle zone of the base
(5') of the one or more pockets (5) approximately corresponds to a
mean temperature of an edge region of the base (5') and, in the
second process step, these two temperatures are different from one
another.
12. A substrate holder having one or more pockets (5), which have a
support region, formed as a rib (6) running along their edges (5'')
which support region, is raised in relation to the base (5') of the
one or more pockets (5), for substrate (7), and from the edge (5'')
of which multiple projections (17) protrude into the one or more
pockets (5), to hold the edge (7') of the substrate (7) spaced
apart from the edge (5'') of the one or more pockets (5),
characterized in that the rib (6) is interrupted in regions of
proximate the projections (17).
13. The substrate holder according to claim 12, characterized in
that a circumferential length of the interruptions (16)
approximately corresponds to a circumferential length of the
projections (17).
Description
[0001] The invention primarily relates to a CVD reactor having a
reactor housing, a process chamber arranged therein, into which at
least one process gas can be fed by means of a gas inlet body,
having a substrate holder, which has, on its top side facing toward
the process chamber, one or more pockets, which are formed so that
respectively one substrate only rests on selected support regions,
which are raised in relation to the base of the pocket, having a
heater arranged underneath the substrate holder, which is spaced
apart by a gap from the bottom side of the substrate holder, the
bottom side of the substrate holder being designed differently in a
central region, which lies under a middle zone of the pocket, in
relation to the heat transfer from the heater to the substrate
holder than in a surrounding region, which surrounds the central
region and lies under an edge-proximal zone of the pocket.
[0002] Such a CVD reactor is described in JP 2002-146540 A. The
substrate holder has a pocket formed by a depression, which has a
further depression in its middle zone. The substrate rests on the
edge step thus formed, which is raised in relation to the central
zone of the base of the pocket. A heater, which is spaced apart
from the bottom side of the substrate holder by a gap, is located
underneath the substrate holder. The heater consists of multiple
circumferential sections, which are spaced apart from one another
by depressions. The bottom side of the substrate holder has a
depression in a central region lying under a middle zone of the
pocket, so that the gap height of the insulation gap is greater
there than in a circumferential region surrounding this central
region. A central heating element, using which the central region
can be heated, lies underneath the central region. Spaced apart
therefrom in the radial direction by a gap, a further heating
element surrounding the first heating element is located, which can
separately heat the surrounding region.
[0003] EP 0 160 220 B2 describes a substrate holder, in which the
substrates also only rest on one edge of a pocket.
[0004] U.S. 2011/0049779 A1 is concerned with the problem that
substrates, which are coated in a CVD reactor with different layers
at different temperatures, can curve as a result of different
properties of the layers. For example, if a layer having a greater
coefficient of thermal expansion than the substrate is deposited on
the substrate in the coating process and the substrate is brought
to a lower temperature or brought to a higher temperature in a
following process step, the substrate curves in one direction or
the other direction. Since the substrate is only supported on
selected support regions and in particular only at the edge and
otherwise extends freely over the base of the pocket, it is
essentially heated by heat conduction via the gas between substrate
and pocket base. In the case of a curve upward, the gas gap
enlarges in the middle region, so that less heat is transported to
the substrate there, with the consequence that the surface of the
substrate has a lower temperature there than in the edge region.
This has the consequence that the electrically--or
optically--active layers deposited on the substrate have different
properties from one another laterally. These inhomogeneities are
very disadvantageous in particular in the manufacturing of
light-emitting diodes and therein in the manufacturing of MQW
(multi-quantum wall).
[0005] DE 10 2006 018 514 A1 describes a substrate holder, in which
a rotationally-driven carrier, which can respectively carry one or
multiple substrates, lies in each of a plurality of pockets. The
substrates lie on the top side of the rotatable carrier. The
rotatable carrier is mounted on a gas cushion. The gas forming the
gas cushion can have various thermal conductivities. A recess is
located in the bottom side of the carrier, so that the gas cushion
between the base of the pocket and the bottom side of the carrier
has zones of various gap heights. By variation of the thermal
conductivity of the gas, the temperature profile on the top side of
the carrier and therefore the substrate temperature can be locally
influenced.
[0006] The invention is therefore based on the object of specifying
measures, using which the homogeneity of multilayer structures, in
particular made of elements of the III and V main groups, may be
improved.
[0007] The object is achieved by the invention specified in the
claims, wherein these are firstly and essentially based on the fact
that the heater is implemented as an essentially flat heat source.
The heater can be implemented in this case by a heating wire laid
in a spiral. The spacing of the individual winding threads can be
in the order of magnitude of the gap width. Such a flat heat source
delivers a homogeneous heating power in the direction of the
substrate holder over its entire area. The heat is transferred to
the substrate holder both via heat radiation and also via heat
conduction. A gas flushing unit is provided, to flush the gap with
flushing gases of various thermal conductivities. If the gap is
flushed with a flushing gas having a high thermal conductivity, for
example, hydrogen, the heat conduction thus dominates during the
heat transport. In contrast, if the gap is flushed with a flushing
gas having lower thermal conductivity, the heat radiation thus
dominates during the heat transport. According to the invention,
the gap has a gap height such that in the event of a change from a
first flushing gas having a first thermal conductivity to a second
flushing gas having a second thermal conductivity, the heat supply
from the heater to the substrate holder behaves differently in the
circumferential region than in the central region. As a result of
this design of the embodiment of the substrate holder, on the one
hand, and its arrangement in relation to a flat, essentially
homogeneous heat source, on the other hand, the heat flow
inhomogeneities to the substrate caused by the curve can be
compensated for. The compensation means is, according to the
invention, a heat transfer inhomogeneity from the heater to the
substrate holder, wherein locally different changes of the heat
flow are induced by the change of the thermal conductivity of the
flushing gas.
[0008] In a first variant, it is provided that the gap height of
the gap under the central region is different from the gap height
of the surrounding region. If the growth process is to be guided so
that the base of the pocket has the same temperature both in the
middle zone and also in the edge-proximal zone, a flushing gas
having low thermal conductivity is used. The heat transport from
the heater to the substrate holder is now dominated by the heat
radiation, so that different gap heights only have a slight
influence on the heat transport. In contrast, in the case of a
process step in which the center of the substrate curves downward,
if the reinforced heat transport due to the gap decreased therein
between pocket base and substrate is to be compensated for, in that
the middle zone of the pocket base obtains a somewhat lower
temperature than the surrounding region, the gap between heater and
substrate holder is thus flushed with a strongly heat-conductive
flushing gas, so that the heat transport is now dominated by the
heat conduction, which is less in the region of a high gap height
than in the region of smaller gap heights. The power of the heater
is readjusted accordingly. The bottom side of the substrate holder
can have a depression in the central region. However, it is also
possible that the bottom side of the substrate holder has a
material accumulation pointing toward the heater in the central
region, for example, a projection. The base of the pocket or the
base of the recess or an end face of a material accumulation
pointing toward the heater can be curved. This curve can be
implemented as stepped. In a second variant, which is also
combinable with the first variant, the bottom side of the substrate
holder has a different reflectivity in the central region than in
the surrounding region. For example, if the central region has a
high reflectivity, in the case of a heat transport dominated by
heat radiation, more heat is absorbed in the surrounding region
than in the central region, since the degree of absorption is
greater in the surrounding region than in the central region. It is
also conceivable that the central region has a higher degree of
absorption than the surrounding region. It then preferably has a
higher degree of reflection than the central region. The zones of
different reflectivity or different degrees of absorption can be
implemented by a coating of the substrate holder bottom side. In
the case of such a configuration, the base of the pocket obtains a
substantially laterally homogeneous temperature distribution when
the heat transport between heater and substrate holder is dominated
by heat conduction, i.e., hydrogen is used as a flushing gas, for
example. However, if the central zone of the base of the pocket is
to obtain a lower temperature than the surrounding region
underneath the substrate, a gas having a lower thermal
conductivity, for example, nitrogen, is thus used as a flushing
gas, so that now the heat transport is dominated by the heat
radiation.
[0009] The substrate holder of the CVD reactor is additionally
characterized in that the rib supporting the substrate runs along
the edge of the essentially circular pocket. In this case, the rib
can be spaced apart from the wall of the pocket. Furthermore, the
CVD reactor is characterized in that projections oriented inward
into the pocket originate from the edge of the pocket, to hold the
substrate resting on the rib with equal edge spacing to the pocket
wall over the entire circumference. Furthermore, the CVD reactor is
characterized in that the rib respectively has an interruption in
the region of the projections, which are preferably distributed
uniformly around the circumference. In the region in which the
substrate rests on the rib, the heat transport from the substrate
holder to the substrate occurs via heat conduction via the direct
material contact. In the region of the projections, an additional
contact surface of the substrate holder is added to the substrate.
However, a greater quantity of heat is at least locally transferred
to the substrate there in relation to the remaining circumference
due to the smaller spacing, so that local temperature increases can
occur there. To compensate for this locally elevated heat flow to
the substrate, the invention proposes as an independent refinement
of the prior art, that the rib is interrupted in the regions of the
projections. The circumferential length of the interruptions can
approximately correspond to the circumferential length of the
projections.
[0010] The substrate holder according to the invention can be
manufactured from graphite. However, it is also provided that the
substrate holder is manufactured from quartz, metal, or a
crystalline material. The heat source is preferably a resistor
through which current flows, in particular in the form of a heating
wire.
[0011] The substrate holder embodied according to the invention can
preferably have a circular shape and can be rotationally driven
about its center axis. It has multiple circular pockets arranged
around the center on its top side. One pocket can also lie in the
center. The heater does not also have to rotate, because it is
implemented so that it has an essentially homogeneous temperature
distribution over its entire area. The CVD reactor is therefore
additionally characterized in that the substrate holder is
rotationally-drivable by means of a rotational drive in relation to
the stationary heater associated with the reactor housing.
[0012] Exemplary embodiments of the invention will be explained
hereafter on the basis of the appended drawings. In the
figures:
[0013] FIG. 1 shows a top view of a substrate holder 3 having a
total of seven pockets 5, wherein six pockets are arranged
uniformly around a central pocket 5;
[0014] FIG. 2 shows a section along line II-II in FIG. 1;
[0015] FIG. 3 shows an illustration according to FIG. 2, but
enlarged in the region of a single pocket;
[0016] FIG. 4 shows an illustration according to FIG. 3 having
downwardly curved substrate
[0017] FIG. 5 shows a second exemplary embodiment according to FIG.
3 having upwardly curved substrate 7;
[0018] FIG. 6 shows a third exemplary embodiment of the invention
in an illustration according to FIG. 3;
[0019] FIG. 7 shows a fourth exemplary embodiment according to FIG.
3;
[0020] FIG. 8 shows a fifth exemplary embodiment according to FIG.
3;
[0021] FIG. 9 shows a sixth exemplary embodiment according to FIG.
3; and
[0022] FIG. 10 shows a single pocket in a top view.
[0023] FIG. 2 shows the cross section through a CVD reactor. It has
an externally gas-tight housing 1. A feed line 13 leads into the
housing 1. An exhaust line 14 leads back out of the housing.
Suitable process gases, which contain, for example, trimethyl
gallium, trimethyl indium, or trimethyl aluminum, can be introduced
into a gas inlet body 2 through the feed line 13. The gas inlet
body is only schematically shown. Not only starting materials which
contain elements of the III main group, but rather also starting
materials which contain elements of the V main group can be
introduced into the gas inlet body 2. The introduction of the
starting materials is respectively performed using a carrier gas,
which can be hydrogen, for example. The gas inlet body 2
schematically shown in FIG. 2 is a showerhead. It has a plurality
of gas outlet openings 15, through which the process gases can flow
into a process chamber 4 arranged underneath. Various chambers,
which are separate from one another, and which can each introduce a
process gas, are located in the gas inlet body 2. Therefore,
various process gases can be introduced into the process chamber 4
separately from one another.
[0024] In the exemplary embodiment (not shown), the gas inlet body
2 is designed differently, for example, as a central inlet body, so
that the process chamber has vertical flow through it.
[0025] The base of the process chamber 4 is formed by the top side
3' of a substrate holder made of graphite, for example. The
substrate holder 3 has a circular formation, like the gas inlet
body 2. A plurality of depressions 5 are incorporated in the top
side 3' of the substrate holder 3. FIG. 1 shows the spatial
arrangement of these depressions 5. The depressions 5 form circular
pockets. A rib 6 respectively runs radially inward from the walls
5'' of the pockets 5. This is a circular rib 6 in this case, on
which the edge section of a substrate 7 can rest. The rib top sides
are depressed somewhat in relation to the top side 3', so that the
substrate surface runs flush with the top side 3'.
[0026] The base 5' of the pocket 5 is formed flat in the first
exemplary embodiment shown in FIGS. 2 to 5, so that a gas gap forms
between substrate bottom side and pocket base 5', which has the
same gap height everywhere in the case of uncurved substrate.
[0027] The bottom side 3'' of the substrate holder 3 has recesses
8. In the exemplary embodiment shown in FIGS. 2 to 4, the recesses
8 have flat recess bases 8', which run parallel to the pocket base
5'. The pockets 8 have pocket walls 8'', which run on a circular
arc line, wherein the circular arc line of the wall 8' of the
recess 8 runs concentrically to the wall 5'' of the pocket 5. The
recess 8 only extends over a central region b which lies below a
middle zone of the pocket base 5'. The central region b is enclosed
by a surrounding region a, which extends under an edge region of
the pocket 5.
[0028] A heater 9 extends underneath the substrate holder 3
parallel to the substrate holder 3. The heater 9 is shown in
simplified form in the drawings. It is indicated that the heater 9
is formed by a heating wire 10 laid in a spiral. If a current flows
through the heating wire 10, it heats up. The heating power which
is emitted from this heating winding 10 is essentially constant
over the entire area of the heater 9, so that the heater 9 emits an
essentially homogeneous surface heating power. The heater 9 extends
underneath the entire region of the substrate holder 3 occupied
with pockets 5, specifically at a spacing of a few millimeters. In
this way, a heat transfer gap 12 forms between the bottom side 3''
of the substrate holder 3 and the top side 9' of the heater 9.
[0029] The gap width s of the gap 12 is of particular significance,
which will be described in greater detail hereafter.
[0030] Flushing gas inlets, using which a flushing gas can be
introduced into the gap 12, are indicated with the reference sign
11. This flushing gas can be a pure gas, for example, hydrogen,
nitrogen, argon, or helium. However, it can also be a mixture of
these or other gases, in particular inert gases. The gap width s is
selected so that at the process temperatures used, in the range
between 500.degree. C. and 1100.degree. C., the heat transport from
the heater 9 to the substrate holder 3 can only be changed by the
selection of the flushing gas between heat-conduction-dominated and
heat-radiation-dominated. If the heat transport is to be
heat-conduction-dominated, a gas having a high thermal
conductivity, for example, hydrogen, is thus introduced into the
gap 12. If the heat transport is to be heat-radiation-dominated, in
contrast, a gas having a lower thermal conductivity, for example,
nitrogen, is thus introduced into the gap 12.
[0031] The depth of the recess 8, i.e., the distance of the base 8'
from the bottom side 3'', is selected so that less thermal power is
transferred therein in the case of heat-conduction-dominated heat
transport than in the surrounding region.
[0032] The heat transported from the heater 9 to the substrate
holder 3 is dissipated from the substrate holder 3 via heat
radiation or heat conduction through the process chamber 4 to the
process chamber cover, which is cooled. In the exemplary
embodiment, the showerhead 2 has cooling channels (not shown) for
this purpose, through which a cooling medium flows, so that its
bottom side facing toward the process chamber 4 is cooled.
[0033] In the second exemplary embodiment shown in FIG. 5, the edge
section of the bottom side of the substrate holder 3 enclosing the
recess 8 is coated using a reflective surface 21.
[0034] In the third exemplary embodiment shown in FIG. 6, the base
5' of the pocket 5 is depressed like a shell. The base 5' forms a
stepped depression 18 there. The base 5' can alternatively thereto
also have a stepped curve in particular, however.
[0035] In the fourth exemplary embodiment shown in FIG. 7, the base
8' of the recess 8 is formed like a bowl. It forms a stepped
depression 19. In this way, the gap 12 has the gap height s, which
is the least, in the region of the surrounding region a. In the
central region b, i.e., in the region over which the recess 8
extends, the gap 12 has various gap heights t, t', t'', which are
each higher than the gap height s. An outward curve can also be
provided instead of an inward curve here.
[0036] In the fifth exemplary embodiment shown in FIG. 8, the
bottom side 3' of the substrate holder 3 has a high reflectivity in
the region of the central region b. Therein it has a region 20
having a strongly reflective surface. In this case, this can be a
coating, which strongly reflects infrared light, which is emitted
from the heater 9. The surface section 20 in the region of the
central region b at least reflects more strongly than the surface
of the bottom side 3' in the surrounding region a. The radiation
emitted by the heater 9 is more strongly absorbed therein than in
the central region b.
[0037] While in all exemplary embodiments, the substrate holder 3
is essentially radiation-opaque to the heat radiation emitted by
the heater 9, the substrate 7 can certainly be transmissive to heat
radiation, i.e., it can consist of sapphire, for example. The heat
transport from the base 5' of the pocket 5 to the substrate 7
therefore predominantly occurs via thermal conduction via the gas
which is located between the bottom side of the substrate 7 and the
base of the pocket 5.
[0038] In the sixth exemplary embodiment shown in FIG. 9, in
contrast to the fifth exemplary embodiment shown in FIG. 8, the
central region is not provided with a reflective surface 20, but
rather the surrounding region a is provided with a strongly
reflective surface 21, as also in the second exemplary embodiment
shown in FIG. 5.
[0039] FIG. 10 shows the top view of a pocket 5, for example, of
the first exemplary embodiment shown in FIGS. 2 to 5. The support
region, on which the edge region of the substrate 7 rests, is
formed by a circular rib 6, which leaves a clearance in the circle
interior and which has a small spacing to the wall 5'' of the
pocket. The rib 6 is interrupted at multiple points, which are
arranged distributed uniformly around the circumference of the rib
6. The rib 6 is therefore divided into multiple partial ribs, the
ends 6' of which are spaced apart by a spacing clearance 16. The
spacing clearance therefore forms an interruption of the rib 6.
[0040] In the region of these interruptions 16, projections 17
protrude radially inward from the edge 5'' of the pocket 5. The
extension of the projections 17 measured in the circumferential
direction essentially corresponds to the extension of the
interruptions 16 measured in the circumferential direction. Using
the projections 17, the edge 7' of the substrate 7 is held in a gap
spacing position to the edge 5'' of the pocket 5.
[0041] The rib 6 is spaced apart from the wall 5'' of the pocket 5
such that a channel forms between rib 6 and wall 5''.
[0042] The mode of operation of the device is as follows: [0043]
Using it, LED structures on a sapphire substrate may be turned off.
In a first preparation step, the substrate surface is heated to a
temperature of approximately 1100.degree. C. A nucleation layer is
deposited at a temperature which can be in the range between
500.degree. C. and 1000.degree. C. The gaseous starting materials,
for example, a metal-organic compound of an element of the III main
group and a hydride of an element of the V main group, are
introduced in this case through the feed line 13 and the gas inlet
body 2 into the process chamber 4. Gaseous reaction products and
the carrier gas exit again from the gas exhaust line 14. During the
deposition of the nucleation layer, the substrate 7 hardly sags, so
that the spacing between substrate bottom side and base 5' is
essentially equal everywhere in the exemplary embodiment shown in
FIG. 3. During this process step, nitrogen is introduced through
the flushing gas inlet 11 into the gap 12. The heat transport from
the heater 9 to the substrate holder 3 therefore occurs via heat
radiation, so that the surrounding region a and the central region
b heat up to approximately the same temperature.
[0044] In a following process step, at a temperature which can be
in the range between 1050.degree. C. and 1100.degree. C., firstly a
buffer layer made of GaN is deposited. An n-doped GaN layer is then
deposited on this layer. During this process, the substrate 7 sags
toward the pocket base 5' as shown in FIG. 4. This has the
consequence that a higher thermal power would be supplied to the
substrate 7 in the central region b than in the surrounding region
a, if the regions a, b had the same temperature. To keep the heat
transport approximately equal in both zones, measures according to
the invention are taken, to temporarily reduce the heat transport
from the heater 9 to the substrate holder 3 in the central region
b. For this purpose, a gas is introduced into the gap 12 through
the flushing gas inlet 11, for example, hydrogen, which has a high
thermal conductivity. As a consequence thereof, in the surrounding
region a, where the gap height s is least, more heat is transferred
per unit of time to the substrate holder 3 than in the central
region b, where the gap height t is greater than the gap height s.
As a consequence thereof, the pocket base 5' heats up in the
central region b to a somewhat lower temperature than in the
surrounding region a. From the substrate surface, the heat supplied
from the bottom is dissipated by heat radiation or heat conduction
to the process chamber cover, which is cooled.
[0045] A multi-quantum wall structure InGaN--GaN is then deposited
on the n-doped buffer layer. This MQW structure is deposited at
temperatures between 700.degree. C. and 800.degree. C. At this
temperature, the substrate rests essentially flatly on the ribs 6,
as shown in FIG. 3.
[0046] However, it can occur that the substrate 7 curves upward, as
shown in FIG. 5. To perform a compensation here by way of local
control of the heat flow, the central region b must be heated more
highly than the surrounding region a. This may be achieved, for
example, in that the heat supply in the surrounding region a is
reduced in the radiation-dominated heat transport region, which can
be implemented, for example, by a reflective surface 21. For
example, the substrate holder bottom side 3'' can be covered
therein with a reflective layer 21. By balancing out the mixing
ratio of two gases having coefficients of heat conduction which
strongly deviate from one another, the states shown in FIGS. 3 and
4 can then also be reached, in which surrounding region a and
central region b are heated equally strongly or the surrounding
region a is heated more strongly than the central region b.
[0047] In a last step, a p-contact layer, which consists of p-doped
AlGaN, is deposited on the MQW structure. This is performed at
process temperatures between 800.degree. C. and 950.degree. C. The
slight sag of the substrate 7 forming in this case toward the
pocket base 5' can be considered in the manner described above with
reference to FIG. 4.
[0048] All process steps can be carried out with permanently
rotating substrate holder 3. For this purpose, the substrate holder
3 is rotationally driven using drive means (not shown) about its
central axis Z. The substrate holder 3 then rotates in relation to
the heater 9, which is held stationary, at uniform spacing 12.
[0049] In the exemplary embodiments shown in FIGS. 8 and 9, the
surrounding region a and the central region b heat up in the
heat-conduction-dominated regime, i.e., uniformly with the use of a
strongly heat-conductive flushing gas. A local temperature
inhomogeneity in the region of the pocket base 5' results here in
the radiation-dominated regime, if nitrogen or another flushing gas
having low thermal conductivity is used as the flushing gas. Then,
in the fourth exemplary embodiment shown in FIG. 8, the surrounding
region a heats up more strongly than the central region b or, in
the fifth exemplary embodiment shown in FIG. 9, the central region
b heats up more strongly than the surrounding region a.
[0050] The substrate 7 resting on the support region 6 is heated
more strongly in the region of the support surface, i.e., in the
edge region, since it is in contact with the rib 6 here. A heat
supply flow also occurs from the pocket edge 5'' toward the
substrate holder edge 7'. This heat transport is increased in the
region of the projections 17, since the gap between projection 17
and substrate holder edge 7' is smaller here than the gap between
pocket edge 5'' and substrate holder edge 7'. To compensate for
this locally increased heat supply, the above-described
interruptions 16 are provided in the rib 6, which extend
essentially over the same length over which the projections 17
extend.
[0051] All disclosed features are essential to the invention (per
se). The contents of the disclosure of the associated/appended
priority documents (prior application) are hereby also incorporated
in their entirety in the contents of the disclosure of the
application, also for the purpose of incorporating features of
these documents in the claims of the present application. The
dependent claims characterize, in their optional, subordinate
version, independent refinements according to the invention of the
prior art, in particular to perform divisional applications on the
basis of these claims.
LIST OF REFERENCE SIGNS
[0052] 1 reactor housing [0053] 2 gas inlet body [0054] 3 substrate
holder [0055] 3' substrate holder top side [0056] 3'' substrate
holder bottom side [0057] 4 process chamber [0058] 5 pocket [0059]
5' pocket base [0060] 5'' pocket edge [0061] 6 support region, rib
[0062] 6' ends [0063] 7 substrate [0064] 7' substrate holder edge
[0065] 8 recess [0066] 8' base [0067] 8'' pocket walls [0068] 9
heater [0069] 10 heater winding [0070] 11 flushing gas inlet [0071]
12 gap [0072] 13 gas feed line [0073] 14 gas exhaust line [0074] 15
gas outlet opening [0075] 16 interruption [0076] 17 projection
[0077] 18 depression, shell-like [0078] 19 depression [0079] 20
reflective surface [0080] 21 reflective surface [0081] a
surrounding region [0082] b central region [0083] s gap height
[0084] t gap height
* * * * *