Note: Descriptions are shown in the official language in which they were submitted.
2080~28
APPARATUS FOR MANUFACTURING SEMICONDUCTOR WAFERS
his invention relates to apparatus for
manufacturing semiconductor wafers.
In the manufacture of semiconductor wafers for
electronic or optoelectronic usage, a susceptor carries a
substrate for the wafer in a reactor vessel. Gaseous
lo reactants are caused to flow into contact with an exposed
surface of the wafer and form deposits on the substrate as
crystalline layers. The composition of the gaseous
reactants determines the composition of the deposited
layers.
In one type of apparatus, the wafer is carried by
its susceptor with its exposed surface facing upwardly.
~- The wafer is caused to rotate about a vertical axis during
the deposit of the crystalline layers. Rotation is
provided in an attempt to maximize uniformity in depth and
material deposition of the layers. As each wafer carries
many, e.g., thousands, of semiconductor devices during
their manufacture by crystalline layer or epitaxy
deposition, uniformity in composition and thickness of the
layers is important to produce the desired characteristics
in the maximum number of devices. A problem which exists,
however, with this arrangement is that foreign bodies
-~ within the reactor vessel have been known to settle within
" the layers during deposition.
In another type of apparatus, a susceptor carries
a stationary wafer which has its exposed surface facing
downwardly and the gaseous reactants are caused to flow
beneath the wafer and to impinge upon the exposed surface
to achieve crystalline layer deposition. This provides an
improvement in uniformity of composition and thickness even
though the wafer is stationary and this effect is believed
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to be at least partly because of the manner in which the
gases flow beneath the wafer.
The present invention provides an apparatus which
in use seeks to improve uniformity of composition and
thickness of deposition of crystalline layers upon a
substrate.
Accordingly, the present invention provides an
lo apparatus for manufacturing semiconductor wafers comprising
a susceptor for carrying a substrate during gaseous
deposition of crystalline layers onto a surface of the
wafer, the susceptor comprising:- an annular rotor having
an outwardly directed annular flange and an inwardly
directed seating surface means for supporting edge regions
of the substrate, the rotor defining an opening inwardly of
the seating surface means; and a susceptor body having
aperture means for rotatably carrying the annular rotor in
a position with the seating surface means at a lower end of
the rotor and facing upwardly for supporting edge regions
of the substrate while a major surface of the substrate is
exposed downwardly through the opening for forming
crystalline layers thereon, and with the outwardly directed
; flange disposed upwardly from the seating surface means and
overlying the body, the body having means for directing a
flow of rotor driving gas upwardly to impinge upon an
~ underside of the flange and cause rotation of the rotor.
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In use of the above apparatus according to the
- 30 invention, because the wafer is caused to face downwardly,
this m;nim;zes the quantity of foreign bodies which may
embed themselves into crystalline layers formed upon the
wafer and also provides desirable uniformity in thickness
and composition of materials in the layer.
In a preferred arrangement, the underside of the
rotor flange is provided with a plurality of
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circumferentially spaced and radially extending impingement
surfaces against which the flow of driving gas may be
directed by the flow directing means at a particular angle
to the axis of the rotor and cause rotor rotation. It is
also to be preferred that the rotor and the susceptor body
are rotatably sealable together to prevent the rotor
driving gas from descending to the seating surface means,
the susceptor having an outlet means for the driving gas
- from underneath the flange. The outlet means may be
lo provided by orifices in the flange of the rotor.
Preferably however the outlet means is provided by regions
of the flange which are outward from the impingement
surfaces, these outward regions being spaced from the
~- susceptor body to form an outlet for the gas.
The invention also includes an apparatus for
manufacturing semiconductor wafers comprising a susceptor
;~ and a reactor vessel, the susceptor comprising:- an
~' annular rotor having an outwardly directed annular flange
and an inwardly directed seating surface means for
- supporting edge regions of the substrate, the rotor
defining an opening inwardly of the seating surface means;
and a susceptor body having aperture means for rotatably
carrying the ~nn~ r rotor in a position with the seating
~ 25 surface means at a lower end of the rotor and facing
'. upwardly for supporting edge regions of the substrate while
~- a major surface of the substrate is exposed downwardly
through the opening for forming crystalline layers thereon
~' and with the outwardly directed flange disposed upwardly
~ 30 from the seating surface means and overlying the body, the
body having means for directing a flow of rotor driving gas
. upwardly to impinge upon an underside of the flange and
cause rotation of the rotor; and the reactor vessel having
a reactant gas flow passage with an inlet and an outlet, a
station for location of the susceptor with the major
surface of the substrate exposed downwardly at the top of
the flow passage.
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In the apparatus according to the invention as
defined in the last preceding paragraph, it is preferable
that a first connection means is provided for connecting
the inlet to a source of the reactant gas, the inlet and
the first connection upon assembly forming between them a
first part spherical joint, and a second connection means
is provided for connecting the susceptor to a source of the
rotor driving gas through a second part spherical joint
upon assembly, the second connection means comprising a
connecting tube formed at least partly as a compression
spring. For this arrangement a means to apply end pressure
upon the tube is also provided whereby upon assembly with
the first and second part spherical joints formed, the
pressure applying means applies pressure to the tube so
that the compression spring retains each of the spherical
joints assembled.
One embodiment of the invention will now be
described by way of example, with reference to the
accompanying drawings, in which:-
FIGURE 1 is a cross-sectional view through a
- susceptor according to the embodiment;
~ FIGURE 2 is a view taken in the direction of arrow
:- 25 II in FIGURE 1 and on a smaller scale onto a part of the
~ susceptor;
:~ FIGURE 3 on a reduced scale is a plan view of a
reactor vessel carrying the susceptor of the embodiment;
FIGURE 4 is a cross-sectional view taken along
line IV-IV in FIGURE 3 of the reactor vessel and susceptor;
FIGURE 5 is a side elevational cross-sectional
view of an apparatus including the reactor vessel and
susceptor in use; and
-~ FIGURE 6 is a cross-sectional view through the
~ 35 apparatus of FIGURE 5 taken along line VI-VI in FIGURE 5.
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As shown by FIGURE 1, a susceptor 10 for carrying
a wafer substrate during gaseous deposition of crystalline
layers onto a surface of the substrate is formed from high
purity carbon and comprises a susceptor body 12 and an
annular rotor 14. The susceptor body 12 has a circular
aperture 16 extending between opposite major faces for
receiving a cylindrical portion 18 of the annular rotor to
enable the rotor to be rotated within the body. In
assembled condition of the susceptor and in a position for
lo use, an inwardly directed seating surface means of the
rotor is disposed at the lower end of the cylindrical
portion 18. This seating surface means comprises an
annular flange 20 for supporting edge regions of a
substrate 22 with a major surface of the substrate exposed
in a downward direction through an opening 24 lying
radially inwardly of the flange 20. A short cylindrical
plug 25 fits inside the cylindrical portion 18 as shown in
-: FIGURE 1 to provide weight and heat or thermal contact to
the substrate and hold it in position within the rotor
during formation of crystalline layers upon the under
surface of the substrate.
At the other end of the cylindrical portion 18,
the annular rotor is provided with an outwardly directed
annular flange 26. This flange overlies an annular portion
of the body 12 which immediately surrounds the aperture 16.
The body 12 has means for directing a flow of rotor driving
' gas upwardly so as to impinge upon the underside of the
.
'~r flange and to cause rotation of the rotor. This means
comprises an annular recess 28 formed in the upper surface
of the body 12 and underlying edge regions of the flange
26. A flow of driving gas, i.e., air, is delivered to the
annular recess 28 through an entrance passage 30 extending
; inwards from one end of the body 12 as shown. The
underside surface of the edge region of the flange 26 is
- formed with a plurality of spaced apart concavely surfaced
~ shallow recesses 32 which extend around the edge region as
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shown by FIGURE 2. The rotor is provided also with aplurality of circumferentially spaced radially extending
impingement surfaces against which the flow of driving air
is to be directed. These surfaces are provided by radially
extending end surfaces 34 of the recesses, the radially
extending end surfaces being disposed at the same ends of
the recesses so as to face circumferentially in the same
direction of the rotor.
lo The flow directing means also directs the flow of
driving air at an angle to the rotor axis so as to impinge
upon the surfaces 34 thereby causing rotor rotation. This
orientation of driving air is provided by annular disk 36
which is inserted into the top of the recess 28 so as to
substantially seal against the sides of the recess, the
disk having a plurality of spaced apart apertures 38 which
extend through the disk at an inclined angle. Hence a flow
of gas passing through the recess 28 will pass through the
apertures 38 in a direction inclined to the axis of the
' 20 rotor and impinge upon the surfaces 34 so as to rotate the
- rotor in the aperture 16.
The rotor 14 and the body 12 are rotatably sealed
together to prevent the driving gas after it passes through
the apertures 38 from passing radially inwardly. This
prevents it from passing between the aperture 16 and the
~; cylindrical portion 18 so that the driving gas cannot move
into contact and mix with the reactant gas which is to form
~ crystalline layers on the undersurface of the substrate 22.
- 30 This sealing arrangement is provided by a plurality of
annular and downwardly extending ribs 40 of the flange 26,
the ribs having a common centre, i.e., around the axis of
rotation of the rotor, and lying in mesh with complimentary
ribs 42 extending upwardly from the body 12. AS the body
and the rotor are both formed from high purity carbon, the
meshed ribs may be substantially in intimate contact with
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each other and move in sliding engagement during rotor
rotation.
The rotor is provided with a means to allow for
escape of the driving gas while directing it radially
outwardly away from the aperture 16. This means comprises
regions of the flange 26 outwardly of the impingement
surfaces 34, these regions 44 being inclined downwardly
towards the body 12 while forming a narrow gap 46 together
lo with a body 12 to allow for the escape of the driving gas
after it has entered the recesses 32 and applied the
driving force against the surfaces 34.
; As shown by FIGURES 3 and 4, the susceptor 10 is
to be mounted onto a quartz reactor vessel 50 which has a
main parallel sided part 51 of generally rectangular cross-
section terminating at one end in a tapered rectangular
cross-sectional part 52 which has an inlet end 54 which
forms the male part of a part spherical joint for
connection to a source of reactant gas as will be
-' described. As shown by FIGURE 4, opposite side edges of
the body 12 of the susceptor are formed with shoulders 56
which are supported upon inwardly flanged sides 58 of the
reactor vessel 50, the susceptor being slidably moveable
along the flanges of the sides 58 from the opposite end 60
'; of the vessel to the male part 54 of the spherical joint.
The driving gas is introduced into the passage 30 to
proceed to the annular recess 28 through a quartz inlet
tube 62 extending into the passage 30. As shown by FIGURE
5, the reactor vessel is provided with an upwardly inclined
baffle 64 which extends beneath the location for the
substrate so as to direct reactor gases proceeding through
the chamber of the reactor vessel upwardly towards the
substrate.
In use, the assembly of susceptor 10 and the
-. reactor vessel 50 is carried with the reactor vessel
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horizontal within a cylindrically formed quartz chamber 70
provided to hold a gas pressure lower than ambient
pressure. One end of the chamber is sealed to and carries
an inlet tube 72 for the reactant gases, the inlet tube
having an end 74 forming a female part of the spherical
joint against which the male part 54 is sealably engageable
to introduce the reactant gases into the reactor vessel.
The other end of the chamber 70 is sealed around its edges
to a bulkhead 84 with the open end of the chamber forming
an outlet for the driving air and the reactant gases to a
gas collection facility (not shown~. The tube 62 is
connectable to an upstream quartz tube 76 also through a
part spherical joint formed between part spherical mating
end parts 78 and 79 on the tubes 62 and 76. The tube 76 is
formed partly as a helical compression spring 80 and the
upstream end 82 of the tube proceeds through the bulkhead
84 of the mounting apparatus and is mounted within a plate
86 which during assembly of the parts, is urged by a screw
thread mounting (not shown) towards the bulkhead 84. The
~; 20 plate 86 is mountable in position by the screw threaded
- mounting so as to force the plate 86 towards the bulkhead
84, i.e., in the left-hand direction as shown in FIGURE 5.
In assembled condition, the plate 86 and bulkhead 84 are
sealed together to prevent gases from escaping to outside
atmosphere and to ensure that the gases flow to the gas
collection facility.
--- To assemble the susceptor mounted upon the reactor
vessel 50 into the chamber 70, the reactor vessel is slid
into the chamber 70 upon quartz guiderails 88 extending
inwardly from the chamber 70. The tube 72 is secured into
another bulkhead 90 opposing the bulkhead 84. Thus the
reactor vessel is moved along the guides 88 so that the
male part 54 forms a part spherical joint with the female
part 74. Subsequently, ~he tube 76 is introduced into the
chamber 70 as the plate 86 is moved towards the bulkhead
84. Upon the plate 86 being screwed towards the bulkhead,
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the other part spherical joint is formed between the mating
end parts 78 and 79 on the two tubes 62 and 76. Continued
inwards movement of the plate 86 towards the bulkhead
applies a compressive force upon the compression spring 80
of the tube 76 so that the spring 80 applies the spring
force against each of the part spherical joints and holds
each of the joints assembled and in sealed condition. Thus
the spring 80 operates to apply a constant load
horizontally to hold the two spherical joints under end
lo pressure and provide the required seal at each joint.
During use of the apparatus described above, the
~' reactant gases are deflected upwardly as they pass through
:~ the reactor vessel, by the baffle 64 towards the major
undersurface of the substrate so as to deposit layers of
crystalline material as required upon the substrate.
During this procedure, pressurized driving air passes
through the tube 62, into the chamber 28 and upwardly
through the apertures 38 so as to drive the rotor in the
body 12 of the susceptor. Because of this rotation, a
desirable uniformity in thickness and composition of the
layers of crystalline material is achieved across the
substrate. Further to this, because the substrate faces
'' downwardly, then there is little or no possibility of any
'' 25 foreign bodies adhering to the substrate surface and
-~ becoming embedded in the crystalline layers. Further, the
- driving gas is prevented from mixing with the reactant
gases because the driving gas is directed outwards through
- the annular gap 46 between the rotor and the body 12 so as
'' 30 to be emitted outwardly from the reactor vessel whereas the
reactor gases move through the reactor vessel and pass into
contact with the substrate before issuing from an outlet
end 92 of the reactor vessel.
In addition to the above advantages, the method of
assembly of the apparatus into the chamber 70 is
particularly unique and offers distinct advantages because
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of the ease of assembly and disassembly and the m;n;m~l
time required for these operations. AS may be seen from
the above description, the reactor vessel is easily
assembled into the chamber 70 and the joints for the flow
5 of reactor gas and for the driving air are easily formed by
simply moving the plate 86 towards the bulkhead 84 under
pressure, e.g., as by a screw thread means, the spring 80
then operating continuously to apply an end force to the
part spherical joints so as to maintain the sealing
o operation.
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