U.S. patent application number 10/568794 was filed with the patent office on 2007-03-29 for alkyl push flow for vertical flow rotating disk reactors.
This patent application is currently assigned to Veeco Instruments Inc.. Invention is credited to Eric A. Armour, Jonathan Cruel, Richard Hoffman, Lev Kadinski, Michael Murphy, Jeffrey C. Ramer.
Application Number | 20070071896 10/568794 |
Document ID | / |
Family ID | 34215342 |
Filed Date | 2007-03-29 |
United States Patent
Application |
20070071896 |
Kind Code |
A1 |
Murphy; Michael ; et
al. |
March 29, 2007 |
Alkyl push flow for vertical flow rotating disk reactors
Abstract
In a rotating disk reactor (1) for growing epitaxial layers on
substrate (3), gas directed toward the substrates at different
radial distances from the axis of rotation of the disk has
substantially the same velocity. The gas directed toward portions
of the disk remote from the axis (10a) may include a higher
concentration of a reactant gas (4) than the gas directed toward
portions of the disk close to the axis (10d), so that portions of
the substrate surfaces at different distances from the axis (14)
receive substantially the same amount of reactant gas (4) per unit
area. A desirable flow pattern is achieved within the reactor while
permitting uniform deposition and growth of epitaxial layers on the
substrate.
Inventors: |
Murphy; Michael; (Somerset,
NJ) ; Hoffman; Richard; (Clinton, NJ) ;
Murphy; Michael; (Somerset, NJ) ; Hoffman;
Richard; (Clinton, NJ) ; Cruel; Jonathan;
(Plano, TX) ; Kadinski; Lev; (Burghausen, DE)
; Ramer; Jeffrey C.; (Sunnyvale, CA) ; Armour;
Eric A.; (Pennington, NJ) |
Correspondence
Address: |
LERNER, DAVID, LITTENBERG,;KRUMHOLZ & MENTLIK
600 SOUTH AVENUE WEST
WESTFIELD
NJ
07090
US
|
Assignee: |
Veeco Instruments Inc.
100 Sunnyside Boulevard, Ste., B
Woodbury
NY
11797
|
Family ID: |
34215342 |
Appl. No.: |
10/568794 |
Filed: |
August 20, 2003 |
PCT Filed: |
August 20, 2003 |
PCT NO: |
PCT/US03/26112 |
371 Date: |
November 8, 2006 |
Current U.S.
Class: |
427/255.5 ;
118/715; 118/719 |
Current CPC
Class: |
C30B 25/12 20130101;
C30B 25/14 20130101; C23C 16/45565 20130101; C30B 25/08 20130101;
C23C 16/45578 20130101; C23C 16/52 20130101; C23C 16/4584 20130101;
C23C 16/458 20130101; C23C 16/45563 20130101; C30B 25/165 20130101;
C23C 16/455 20130101; C23C 16/45574 20130101 |
Class at
Publication: |
427/255.5 ;
118/715; 118/719 |
International
Class: |
C23C 16/00 20060101
C23C016/00 |
Claims
1. A reactor for treating a substrate comprising: a reaction
chamber; a substrate carrier mounted within the reactor chamber,
whereby at least one substrate can be mounted on the substrate
carrier; a plurality of gas inlets connected to said chamber; one
or more sources of a reactant gas connected to said inlets and one
or more sources of a carrier gas connected to at least one of said
inlets, said gas sources and said inlets being constructed and
arranged so that each inlet directs a gas stream into said chamber
toward said substrate carrier, the streams directed by said inlets
having different concentrations of said reactant gas and different
mass flow rates of said reactant gas but having substantially the
same velocity; and said inlets and said gas sources are arranged so
that the reactant gas mass flow rate of each gas stream is
proportional to the area of the associated zone of said treatment
surface.
2. A reactor as claimed in claim 1 wherein said substrate carrier
has a treatment surface incorporating a plurality of zones of
unequal area and said inlets are arranged so that each said gas
stream is associated with and impinges on a different one of said
zones.
3. A reactor as claimed in claim 2 wherein said inlets and said gas
sources are arranged so that a first one of said gas streams
impinges on a first one of said zones having a first area, a second
one of said gas streams impinges on a second one of said zones
having a second area greater than said first area, and so that said
second one of said gas streams has a reactant gas mass flow rate
greater than the reactant gas mass flow rate of said first gas
stream.
4. A reactor as claimed in claim 2 wherein said inlets and said gas
sources are arranged so that the reactant gas mass flow rate of
each gas stream is directly proportional to the area of the
associated zone of said treatment surface while constant total gas
velocity is maintained.
5. A reactor as claimed in claim 2 wherein said substrate carrier
is mounted for rotation about an axis, said treatment surface is
substantially perpendicular to said axis, and said inlets are
arranged to direct said gas streams in flow directions
substantially parallel to said axis.
6. A reactor as claimed in claim 5 wherein said inlets are disposed
at differing radial distances from said axis.
7. A reactor as claimed in claim 6 wherein said inlets are arranged
to direct said gas streams substantially along a common plane, said
common plane extending substantially radially from said axis.
8. A reactor as claimed in claim 1 further comprising an injection
plate having upstream and downstream faces, said injection plate
being at least partially porous, said injection plate being
disposed in said chamber between said inlets and said substrate
carrier with said upstream face facing said inlets so that gasses
passing from said inlets to said substrate carrier pass through
said injection plate to said downstream face and from said
downstream face toward said substrate carrier.
9. A reactor as claimed in claim 8 wherein at least one of said
inlets includes a reaction gas port connected to one of said one or
more reaction gas sources and a carrier gas port connected to one
of said one or more carrier gas sources, said ports opening to said
chamber so that reactant gas introduced through said reactant gas
port and carrier gas introduced through said carrier gas port mix
and form a combined gas stream exiting from said downstream face of
said injection plate.
10. A reactor as claimed in claim 1 wherein at least one of said
inlets includes a common port opening to said chamber and connected
to one of said one or more reaction gas sources and also connected
to one of said one of more carrier gas sources.
11. A reactor for treating a substrate comprising: a chamber; a
substrate carrier mounted for movement within the chamber, said
substrate carrier being adapted to hold one or more substrates; and
a gas stream generator arranged to deliver a gas stream having
substantially uniform velocity but different concentrations of a
reactant gas at different locations within the stream, said gas
stream generator being arranged to direct the gas stream within the
chamber toward the substrate carrier, said substrate carrier is
mounted for rotational movement about an axis and said gas stream
generator is adapted to supply said gas stream with different
concentrations of said reactant gas at different radial distances
from said axis.
12. A reactor as claimed in claim 11 wherein said gas stream
generator is adapted to supply said gas stream with concentrations
of said reactant gas at a rate directly proportional to the radial
distances of said gas stream generator from said axis.
13. A reactor as claimed in claim 11, wherein said gas streams
generator issues said gas streams downwardly into said chamber in
the axial direction parallel to said axis.
14. A reactor as claimed in claim 11 wherein said gas stream
generator includes a plurality of gas stream inlets spaced apart
from one another and different gas sources connected to said gas
stream inlets, said gas sources being arranged so that gases
supplied through different inlets have different concentrations of
said reactant gas while maintaining substantially constant total
gas velocity.
15. A reactor as claimed in claim 11 wherein said gas stream
generator includes a structure defining a carrier gas passage
having a downstream direction and a reactant gas passage having a
downstream direction, said reactant gas passage extending in
proximity to said carrier gas passage, a source of carrier gas
communicating with the interior of the chamber through said carrier
gas passage so that carrier gas entering the chamber will pass in
the downstream direction through the carrier gas passage, and a
source of reactant gas communicating with said chamber through said
reactant gas passage so that reactant gas entering the chamber will
pass in the downstream direction through the reactant gas passage,
each said passage having resistance to gas flow in the downstream
direction through the passage, the resistance of the carrier gas
passage increasing progressively in a radially outward direction
away from said axis, the resistance of the reactant gas passage
decreasing progressively in the radially outward direction.
16. A reactor as claimed in claim 15, further including a choke
structure comprising a plate, wherein said carrier gas passage is
in the form of a carrier gas slot extending through said plate,
said reactant gas passage is in the form of a carrier gas slot
extending through said plate, said each said slot having a width
transverse to the radially outward direction, the width of the
carrier gas slot decreasing progressively in the outward direction,
the width of the reactant gas slot decreasing progressively in the
inward direction.
17. A reactor for growing epitaxial layers on a substrate
comprising: a reaction chamber; a substrate carrier movably mounted
within the reactor chamber for rotation about an axis; whereby at
least one substrate can be mounted on the substrate carrier, a
first reactant gas source for supplying a first reactant gas at a
first reactant gas flow rate; a first carrier gas source for
supplying a first carrier gas at a first carrier gas flow rate;
said first gas inlet and said first carrier gas source being
connected to said chamber so that the first reactant gas and first
carrier gas enter the chamber as a first combined gas stream, said
first combined gas stream having a first combined stream velocity;
a second reactant gas source for supplying a second reactant gas at
a second reactant gas flow rate; a second carrier gas source for
supplying a second carrier gas at a second carrier gas flow rate;
said second reactant gas source and said second carrier gas source
being connected to said chamber so that said second reactant gas
and said second carrier gas enter said chamber as a second combined
gas stream, said second combined gas stream having a second
combined velocity substantially equal to said first combined
velocity; said reactant gas sources and carrier gas sources being
connected to said chamber so that said first combined gas stream
impinges on a first treatment area of said treatment, and said
second combined gas stream impinges on a second treatment area of
said treatment surface, said second treatment area unequal in area
to said first treatment area; and said first and second reactant
gas velocities being selected so that a ratio of said first
reactant gas flow rate to said first treatment area is equal to the
ratio of said second reactant gas flow rate to said second
treatment area.
18. A reactor as claimed in claim 16, further including a second
gas inlet wherein said second carrier gas source is connected to
said chamber so that the second reactant gas and second carrier gas
enter the chamber as a second combined gas stream, wherein said
first gas inlet and said second gas inlet issue said first combined
gas stream and said second combined gas stream respectively
downwardly into said chamber in the axial direction parallel to
said axis.
19. A reactor for treating a substrate, comprising: a chamber; a
substrate carrier rotatably mounted in said chamber for rotation
about an axis, said substrate carrier including a treatment surface
for holding one or more substrates to be treated; and gas supply
means for introducing a reactant gas and a carrier gas into said
chamber so that said gases flow within said chamber toward said
treatment surface in one or more streams at having substantially
uniform velocity but so that different portions of said treatment
source at different radial locations receive substantially the same
amount of said reactant gas per unit time per unit area; wherein
said gas supply means is operative to mix at least some of said
reactant gas with said carrier gas so that gas flowing toward
radially outward portions of said treatment surface has a higher
concentration of said reactant gas than gas flowing toward radially
inward portions of said treatment surface.
20. A reactor as claimed in claim 19, wherein said gas stream
generator issues said gas stream downwardly into said chamber in
the axial direction parallel to said axis.
21. A method of treating substrates comprising: rotating a
substrate support about an axis while supporting one or more
substrates on said support so that one or more surfaces of the
substrates to be treated lie substantially perpendicular to said
axis; and introducing a reactant gas and a carrier gas into said
chamber so that said gases flow within said chamber toward said one
or more surfaces in one or more streams having substantially
uniform velocity at different radial distances from said axis so
that different portions of said one or more surfaces at different
radial distances from said axis receive substantially the same
amount of said reactant gas per unit time per unit area; and,
mixing at least some of said reactant gas with said carrier gas so
that gas flowing toward radially outward portions of said one or
more surfaces has a higher concentration of said reactant gas than
gas flowing toward radially inward portions of said one or more
surfaces.
22. A method as claimed in claim 21 wherein said introducing step
includes discharging said gases into said chamber through a
plurality of inlets disposed at different radial distances from
said axis.
23. A method as claimed in claim 22 wherein mixing step is
performed so that as to mix the carrier gas with the reactant gas
prior to discharge from at least some of said inlets, and so that
streams having different concentrations of said carrier gas will be
discharged from different ones of said inlets.
24. A method as claimed in claim 21 further comprising the step of
maintaining reaction conditions in said chamber such that said
reactant gas reacts at said substrate to grow a layer including a
constituent derived from said reactant gas epitaxially on said one
or more surfaces.
25. A method as claimed in claim 24 wherein said reactant gas
includes a metal alkyl.
26. A method as claimed in claim 24 wherein said carrier gas
includes nitrogen.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to metal organic chemical
vapor phase deposition reactors. More particularly, the present
invention relates to rotating disk reactors in which one or more
gases are injected onto the surface of a rotating substrate to grow
epitaxial layers thereon.
BACKGROUND OF THE INVENTION
[0002] Vertical high-speed rotating disk reactors, in which the gas
or gases are injected downwardly onto a substrate surface rotating
within a reactor, are frequently employed for metal organic
chemical vapor deposition (MOCVD). Vertical disk-type CVD reactors,
in particular, have been found useful for wide varieties of
epitaxial compounds, including various combinations of
semiconductor single films and multilayered structures such as
lasers and LED'S. In these reactors, one or more injectors spaced
above a substrate carrier provide a predetermined gas flow, which
upon contact with the substrate, deposits layers of epitaxial
material on the surface of the substrate.
[0003] For larger wafers, rotating disk reactors employ several
injectors spaced above the substrate. The injectors are typically
spaced above the wafer in various positions along one or more
radial axes of the wafer, relative to the central axis of the
substrate carrier. Frequently, the rate of source reactant material
injected into the reactor varies from injector to injector to
permit the same molar quantity of reactant to reach the surface of
the substrate. Hence, some reactant injectors may have different
gas velocities than others. This variation in reactant velocity is,
in pertinent part, due to the relative placement of the injectors.
As the reactor carrier holding the substrate rotates at a
predetermined rate, the injectors near the outer edge of the
carrier cover a larger region of surface area on the carrier than
the injectors closer to the center of the carrier in any given time
period. Thus, the outer injectors typically employ a greater gas
velocity of reactant than the inner injectors in order to maintain
desired uniformity. For example, individual injector gas velocities
may differ by a factor of as much as three to four between adjacent
injectors.
[0004] While this variation in gas velocity helps to ensure a more
uniform layer thickness, it may also cause turbulence between the
injector flows due to their varying velocities. Also, the risk of
side effects such as uneven layer thickness, dissipation of
reactant, or premature condensation of reactant may be
increased.
DISCLOSURE OF THE INVENTION
[0005] One aspect of the invention provides a reactor. A reactor
according to this aspect of the invention preferably includes a
chamber and a substrate carrier mounted for movement within the
chamber, most preferably for rotational movement about an axis. The
substrate carrier is adapted to hold one or more substrates, most
preferably so that surfaces of the substrates to be treated lie
substantially perpendicular to the axis. The reactor according to
this aspect of the invention desirably includes a gas stream
generator arranged to deliver one or more gas streams within the
chamber directed toward the substrate carrier at a substantially
uniform velocity.
[0006] The gas stream generator most preferably is arranged so that
the one or more gas streams include a carrier gas and a reactant
gas, and so that different portions of the one or more gas streams
contain different concentrations of the reactant gas. Where the
substrate carrier is mounted for rotational movement about an axis,
the gas stream generator desirably is arranged to supply said one
or more gas streams with different concentrations of the reactant
gas at different radial distances from the axis. The gas directed
towards a portion of the substrate carrier near the axis desirably
includes a relatively large concentration of the carrier gas and a
relatively small concentration of the reactant gas, whereas the gas
directed towards a portion of the substrate carrier desirably
includes a high concentration of the reactant gas.
[0007] The gas stream generator may include a plurality of gas
inlets communicating with the chamber at different distances from
the axis, as well as one or more sources of a reactant gas
connected to the inlets and one or more sources of a carrier gas
connected to at least one of inlets.
[0008] A further aspect of the invention includes methods of
treating substrates. A method according to this aspect of the
invention desirably includes rotating a substrate support about an
axis while supporting one or more substrates to be treated on the
support so that surfaces of the substrates lie substantially
perpendicular to said axis. The method further includes introducing
a reactant gas and a carrier gas into the chamber so that said
gases flow within said chamber toward the surfaces in one or more
streams having substantially uniform velocity at different radial
distances from said axis.
[0009] The one or more gas streams are arranged so that different
portions of the substrate surfaces at different radial distances
from the axis receive substantially the same amount of said
reactant gas per unit time per unit area. Most preferably, the step
of introducing the carrier gas and reactant gas includes mixing at
least some of the reactant gas with the carrier gas so that gas
flowing toward radially outward portions of the substrate surfaces
has a higher concentration of the reactant gas than gas flowing
toward radially inward portions of the surfaces, close to the
axis.
[0010] Preferred reactors and methods according to the foregoing
aspects of the invention can provide uniform distribution of the
reactant gas over the treatment surface of a substrate carrier,
such as over the surface of a rotating disk substrate carrier,
while avoiding turbulence caused by differing reactant gas
velocities.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1A is a schematic view depicting a reactor according to
one embodiment of the present invention.
[0012] FIG. 1B is a top plan view of a substrate carrier used in
the embodiment of FIG. 1A.
[0013] FIG. 2 is a fragmentary sectional elevational view depicting
a reactor according to another embodiment of the invention.
[0014] FIG. 3 is a fragmentary view along line 3-3 in FIG. 2.
[0015] FIG. 4 is a fragmentary bottom plan view of a plate used in
a reactor according to a further embodiment of the invention.
[0016] FIG. 5A is a fragmentary sectional elevational view
depicting a reactor according to yet another embodiment of the
invention.
[0017] FIG. 5B is a sectional view along line 5B-5B in FIG. 5A.
[0018] FIGS. 6, 7 and 8 are view similar to FIG. 4 but depicting
portions of plates used in reactors according to additional
embodiments of the invention.
MODES FOR CARRYING OUT THE INVENTION
[0019] An apparatus according to one embodiment of the invention,
depicted schematically in FIG. 1, includes a reaction chamber 1 and
a substrate carrier 2. The chamber includes a top wall 16 and an
exhaust port 11. The substrate carrier 2 is mounted within the
chamber 1 for rotation about a central axis 14 and connected to a
rotary drive system 12 so that the substrate carrier 2 can be
rotated around the axis 14. The substrate carrier 2 defines a
treatment surface 18 in the form of a generally planar disc
perpendicular to axis 14 and facing toward top wall 16. Only a
portion of such surface 18 is depicted in FIG. 1. The reaction
chamber 1 is equipped with other conventional elements (not shown)
for facilitating the desired epitaxial growth reaction as, for
example, a heating system for maintaining the substrate carrier at
an elevated temperature, temperature monitoring devices and
pressure monitoring devices. These features of the apparatus may be
of the type used in reactors sold under the trademark
TURBODISC.RTM. by the Emcore Corporation of Somerset, N.J.
[0020] The reactor has a plurality of gas stream inlets 8a-8d
communicating with the interior of the chamber through top wall 16.
In the embodiment of FIG. 1, each inlet is in the form of a single
port directed downwardly in a direction parallel to central axis 14
towards the treatment surface 18 of the carrier, and the port of
each inlet is of the same size. Gas stream inlets 8a-8d are
arranged along a common plane which extends radially from central
axis 14. The common plane is a plane defined by axis 14 and a
radial line 17 extending perpendicular to axis 14. The gas stream
inlets 8a-8d are spaced apart from one another, for example, by a
uniform spacing distance h in the radial direction. Each inlet 8 is
aligned with a different annular zone of treatment surface 18.
Thus, outermost or first inlet 8a is aligned with an outermost zone
10a furthest from axis 14; inlet 8b is aligned with the next zone
10b; inlet 8c is aligned with zone 10c, and inlet 8d is aligned
with the innermost zone 10d, closest to axis 14. Although the zone
borders are indicated by broken lines in FIG. 1 for clarity of
illustration, these zones typically are not delineated by visible
features of the substrate carrier.
[0021] The reactor includes a plurality of reaction gas sources
6a-6d, each such source being adapted to supply a reaction gas at a
predetermined mass flow rate. Any device capable of providing the
reaction gas at a predetermined rate may be used. In the
arrangement illustrated, each reaction gas source 6a-6d is a flow
restricting device, and all of the sources are connected to a
common supply 4 of the reaction gas as, for example, a tank holding
such gas under pressure. The flow restricting device incorporated
in each gas sources 6a-6d may include any conventional flow control
structure such as a fixed orifice, a manually adjustable valve or
an automatically-controlled valve linked to a feedback control
system (not shown) or a metering pump. Where the reactant gas is
formed by vaporization from the liquid phase, each reactant gas
source may include a separate evaporator arranged to control the
rate of vaporization, or else each gas source may include a flow
restricting device as discussed above, all of these being connected
to a common evaporator.
[0022] The reactant gas may be any gas, vapor, or material desired
to be injected into the reactor to participate in the deposition of
a substrate within the reactor. More particularly, the reactant gas
may be any gas which is suitable for treating the substrate
surface. For example, where the desired treatment is growth of a
semiconductor layer such as epitaxial growth, the reactant gas
includes one or more constituents of the semiconductor to be grown.
For example, the reactant gas may include one or more metal alkyls
for deposition of a compound semiconductor. The reactant gas may be
a mixture of plural chemical species, and may include inert,
non-reactive components. Where the desired reaction includes
etching of a substrate surface, the reactant gas may include a
constituent reactive with the material of the substrate
surface.
[0023] The types of material systems to which the present invention
can be applied can include, for example, epitaxial growth of Group
mn-v semiconductors such as GaAs, GaP, GaAs.sub.1-x, P.sub.x,
Ga.sub.1-y Al.sub.yAs, Ga.sub.1-yIn.sub.yAs, AlAs, InAs, InP,
InGaP, InSb, GaN, InGaN, and the like. However, the invention can
also be applied to other systems. These include Group II-VI
compounds, such as ZnSe, CdTe, HgCdTe, CdZnTe, CdSeTe, and the
like; Group IV-IV compounds, such as SiC, diamond, and SiGe; as
well as oxides, such as YBCO, BaTiO, MgO.sub.2, ZrO, SiO.sub.2, ZnO
and ZnSiO; and metals, such as Al, Cu and W. Furthermore, the
resultant materials will have a wide range of electronic and
optoelectronic applications, including high brightness light
emitting diodes (LED's), lasers, solar cells, photocathodes, HEMT's
and MESFET's.
[0024] Carrier gas sources 7a-7d are also provided. The carrier gas
sources 7a-7d may be similar in structure to the reaction gas
sources, and may be connected to a common supply 5 of a carrier
gas.
[0025] Each gas stream inlet 8a-8d is connected to one reaction gas
source 6a-6d and to one carrier gas source 7a-7d. For example,
inlet 8a is connected to reaction gas source 6a and carrier gas
source 7a, whereas inlet 8d is connected to reaction gas source 6d
and carrier gas source 7d.
[0026] The carrier gas may be any carrier desired which does not
participate in the deposition reaction in the chamber given the
reactant gasses to be applied to the substrate, such as an inert
gas or a non-participating gas in the reaction, or, alternatively
the carrier gas may be, for example, itself a reactant gas which
serves as a non rate limiting participant in a reaction and thus
may be provided in any desired quantity so long as such quantity is
in excess of a rate limiting quantity in the reactor at the desired
temperature, pressure and conditions of reaction.
[0027] In a method according to one embodiment of the invention,
substrates 3 in the form of flat, thin discs are disposed on the
treatment surface 18 of the substrate carrier 2 so that the
substrates 3 overlay the treatment surface 18 and so that the
surfaces of the substrates 3 to be treated face upwardly, toward
top wall 16. Desirably, the exposed surfaces of the substrate 3 are
coplanar or nearly coplanar with the surrounding portions of the
treatment surface. For example, a substrate 3 in the form of a
relatively thin wafer placed on a treatment surface 18 will have an
exposed, upwardly facing surface elevated above the surrounding
portions of the treatment surface 18 by only the thickness of the
wafer 3. The treatment surface 18 of the substrate carrier 2 may
include pockets or depressions having a depth approximately equal
to the thickness of the wafer (not shown).
[0028] When the substrate carrier 2 and substrates 3 are at the
desired temperature for the reaction, and the interior of the
chamber 1 is at the desired subatmospheric pressure for the
particular reaction to be accomplished, the reaction gas sources
6a-6d and carrier gas sources 7a-d are actuated to supply gasses to
inlets 8a-8d. The reactant gas 4 and carrier gas 5 supplied to each
inlet mix to form a combined gas stream 9a-9d issuing from each
inlet 8a-8d. The gas streams 9a-9d issuing from the inlets flow
downwardly into the chamber, in the axial direction parallel to
axis 14, and impinge on the treatment surface and on the exposed
surfaces of the substrates 3. The gas streams 9a-9d from different
inlets 8a-8d impinge on different zones 10a-10d of the treatment
surface 18. For example, stream 9a issuing from inlet 8a impinges
predominantly on innermost zone 10a, whereas streams 9b, 9c and 9d
impinge predominantly on zones 10b, 10c and 10d, respectively.
Thus, although the streams 9a-9d merge with one another to form a
substantially continuous, radially elongated stream or curtain of
gas flowing towards the substrate carrier, the individual streams
9a-9d of from the various inlets 8a-8d pass to different zones
10a-10d of the treatment surface 18. Stated another way, the gas
impinging on innermost zone 10d of the treatment surface 18 is
composed principally of gas in stream 9d from inlet 8d, whereas the
gas impinging on zone 10b is composed principally of gas in stream
9b from inlet 8b, and so on. As the substrate carrier 2 rotates at
a predetermined rotation rate .alpha., different portions of the
carrier 2 at different circumferential positions around axis 14 are
brought into alignment with the gas streams 9a-9d, so that exposure
of the treatment surface 18 to the gas streams 9a-9d is the same at
all circumferential positions.
[0029] To provide equal reaction rates on the various regions of
the exposed substrate 3 surfaces, all regions 10a-10d of the
treatment surface 18 should be provided with equal amounts of
reactant gas 4 per unit area of treatment surface per unit time.
However, the zones 10a-10d supplied by the various gas outlets are
of unequal area. For example, zone 10a, adjacent the periphery of
the treatment surface, has a larger surface area than zone 10d,
adjacent the axis. Accordingly, the reactant gas flow rates
provided by sources 6a-6d are selected to provide different flow
rates of reactant gas in the streams 9a-9d issuing from the various
inlets 8a-8d. Unless otherwise indicated, the flow rates referred
to in this discussion are molar flow rates. The molar flow rate
represents the number of molecules of gas (or atoms in a monatomic
gas) per unit time. Source 6a is arranged to supply reactant gas at
a relatively large flow rate to inlet 8a for stream 9a, whereas
soirce 6d is set to supply reactant gas at a relatively small flow
rate to inlet 8d for stream 9d. Sources 6b and 6c supply the
reactant gas at intermediate flow rates. Stated another way, the
reactant gas flow rate increases in direct relation to the distance
between the central axis 14 of rotation for the substrate carrier 2
of the reactor 1 and the gas inlet 8a-8d to be supplied with
reactant gas.
[0030] Carrier gas sources 7a-7d are set to supply the carrier gas
5 at different flow rates to the various inlets 8a-8d. The flow
rates of the carrier gas are selected so that the velocities of the
various streams 9a-9d will be equal to one another. For inlets of
the same configuration--which provide streams of equal
cross-sectional area--the volumetric flow rate of the streams 9a-9d
issuing from each inlet 8a-8d should be equal.
[0031] As a first approximation, assuming that the gases are near
ideal gases, the volumetric flow rate of the gas in each stream is
directly proportional to the total molar flow rate in the strean,
i.e., to the sum of the reactant gas molar flow rate and the
carrier gas molar flow rate. Thus, to provide streams having equal
total molar flow rates and hence equal velocity, the carrier gas
molar flow rate supplied by source 7d to inlet 8d must be greater
than the carrier gas molar flow rate supplied by source 7a to inlet
8a. The greater carrier gas flow rate supplied to inlet 8d and
incorporated in stream 9d compensates for the smaller reactant gas
flow rate from reactant gas source 6d relative to that provided by
reactant gas source 6a to inlet 8a.
[0032] Stated another way, the various streams have the same total
volumetric flow rate but different concentrations of reactant gas.
Stream 9a impinging on the largest zone 10a has the highest
reactant gas flow rate, and the lowest carrier gas flow rate,
whereas stream 9d impinging on the smallest zone 10d has the lowest
reactant gas concentration, and hence the highest carrier gas flow
rate.
[0033] This arrangement is indicated graphically by bars 13a-13d in
FIG. 1. The overall length C of bar 13d represents the total molar
flow rate or volumetric flow rate of stream 9d issuing from inlet
8d. The length of the darkened portion of this bar represents the
reactant gas molar flow rate vain the stream, whereas the white
portion of the bar represents the carrier gas molar flow rate ia in
the same stream 9d. Bars 13a, 13b and 13c similarly represent the
composition and flow rate of streams 9a, 9b and 9c respectively.
The overall lengths C of all bars 13 are equal, but bars 13a, 13b
and 13c represent the progressively greater reactant gas molar flow
rates v.sub.c, v.sub.b and v.sub.a and progressively lower carrier
gas molar flow rates i.sub.c, i.sub.b, i.sub.a in streams 9c, 9b
and 9a. By supplying the various streams 9a-9d at different
concentrations of reactant gas but at the same total stream
velocity, the system avoids turbulence and other flow
irregularities which would be created by streams of different
velocities, and yet supplies substantially equal molar flow rates
of reactant gas per unt area to the various zones of the of the
treatment surface.
[0034] Thus, the exposed surfaces of the wafer 3 at all portions of
the treatment surface 18 receive substantially the same amount of
reactant gas per unit time per unit area. The reaction thus proceds
at a substantially uniform rate over all of the exposed wafer
surfaces 3. For example, where the reaction involves deposition of
a layer such as epitaxial growth, the deposited layer grows at a
substantially uniform rate on the various exposed surfaces.
[0035] The system can be varied to deliver unequal amounts of
reactant gas per unit surface area per unit time. For example, the
gas flow pattern within the reactor may include some flow in the
radially outward direction, away from axis 14 at or near the
treatment surface. Such flow may tend to carry some unreacted
reactant gas from the innermost zone 10d toward the outermost zone
10a. To compensate for this effect, the gas sources can be adjusted
to deliver slightly more reactant gas to the innermost zone, as by
increasing the reactant gas concentration in innermost stream 9d
above that which would be required to achieve exactly equal
reactant gas flow per unit time. In this case, the reactant gas
flow and reactant gas concentration will not be exactly
proportional to radial distance from axis 14. However, the system
still uses multiple gas streams of differing concentration but the
same velocity to provide a downwardly or axially flowing gas
curtain having substantially uniform velocity but unequal reactant
gas concentration at different radial locations.
[0036] In another variant, the reactant gas concentration in the
gas stream from the outermost inlet 8a may be 100%, so that the
downwardly-flowing gas impinging on the outermost zone consists
entirely of the reactant gas, with no carrier gas. In this
instance, carrier gas source 7a associated with inlet 8a may be
omitted. Also, the principles discussed above can be applied with
more or fewer gas inlets directed onto more or fewer zones.
[0037] In apparatus according to a further embodiment of the
invention, seen in FIG. 2 and 3, the gas stream inlets are not
disposed in a radial plane on one side of the axis of rotation as
discussed above with reference to FIG. 1. Instead, in the
embodiment of FIGS. 2 and 3, the outermost gas inlet 108a is
disposed on one side of the axis of rotation 114 of substrate
carrier 102, and at a large radial distance from the axis, whereas
the next gas inlet 108b lies on the opposite side of axis 114 but
at a lesser radial distance from the axis. Inlets 108c and 108d, at
lesser radial distances from axis 114, also lie on opposite sides
of the axis along a common diameter 219 (FIG. 3). Here again, the
different gas streams 109a-109d impinge on different zones of
treatment surface 118 having different areas. The carrier gas flows
from carrier gas sources 107a-107d and the reactant gas flows from
reactant gas sources 106a-106d are selected in the same manner as
described above, so as to provide gas streams 109a-109d with
different reactant gas concentrations and flow rates, but with the
same velocity. In a further variant, the gas inlets may be provided
as two complete sets, one on each side of the central axis, each
such set including a full complement of gas inlets adapted to
direct gas onto all of the zones of the treatment surface. More
than two sets of gas inlets may be provided as, for example, four
sets disposed on two diameters. In a further variant (FIG. 4) the
various gas inlets 36a 36g may be distributed along different radii
17a-17g, and at different radial distances from the central axis
114.
[0038] In the apparatus discussed above, each gas stream is formed
by mixing carrier gas and reactant gas prior to introducing the
mixed gases into the reaction chamber. However, this is not
essential. In the apparatus of FIGS. 5A and 5B, the innermost gas
inlet 208d includes two separate ports opening through reactor top
wall 216: a reactant gas port 230d and a carrier gas port 232d. The
reactant gas port 230d is connected to a reactant gas source 206d,
whereas the carrier gas port 232d is connected to a carrier gas
source 207d. Ports 230d and 232d are disposed adjacent to one
another, so that the carrier gas introduced through port 232d
merges with the reactant gas introduced through port 230d just
after the gases enter the interior of reaction chamber 201, and
form a combined gas stream passing downwardly onto the associated
zone of treatment surface 218. Each of the other inlets 208a-208c
is constituted by a similar pair of ports, and operates in the same
manner.
[0039] The apparatus of FIGS. 5A and 5B also includes a porous
plate 215 mounted within reaction chamber 210, between top wall 216
and the treatment surface. As discussed in greater detail in U.S.
Pat. No. 6,197,121, the disclosure of which is incorporated by
reference here, such a porous plate can include, for example, a
wire mesh screen supported by a set of coolant conduits. The porous
plate has an upstream or inlet side facing toward the top wall 216,
and has a downstream side facing toward substrate carrier 202
(toward the bottom of the drawing in FIG. 5A). The porous plate 215
is spaced from the top wall. A set of barrier walls 250 extend
between the top wall 216 and the porous plate 215 in the vicinity
of inlets 208a-208d. The barrier walls 250 subdivide the space
upstream of the porous plate into spaces 254a-254d. Each gas inlet
208a-208d opens into one such space. Additional walls 256 separate
spaces 254a-254d from other spaces 258 (FIG. 5B) disposed upstream
of the porous plate.
[0040] In operation, the carrier gas and reactin gas provided
through each inlet mix within the space 254 associated with that
inlet, and pass through a region of the porous plate aligned with
such space. For example, the combined gasses provided by inlet
208d, including reactant gas from port 230d and carrier gas from
port 232d, passes downstream through a region of the porous plate
215, and passes from the downstream side of the injection plate to
the treatment surface as a stream 209d, so that this stream
impinges principally on the innermost region 210d of the treatment
surface 218. In the same manner, the gases from inlets 208c, 208b
and 208d mix in spaces 254c, 254b and 254a, respectively, to form
streams 209c, 209b and 209a, which impinge on other regions of the
treatment surface. Although the individual streams are depicted
separately in FIG. 5A for clarity of illustration, in actuality the
streams spread radially and merge with one another enroute from the
porous plate 215 to the treatment surface. Here again, the flow
rates of the carrier gas and reaction gas supplied by each of the
gas sources are selected so that the total flow rate in each stream
209, and hence the velocity of each stream, is substantially equal,
but the concentration of reactant gas in the various streams is
unequal. In this arrangement as well, additional sets of inlets
208' for the carrier gas and reaction gas may be provided at other
locations spaced circumferentially around central axis 214. Each
such set is arranged in the same manner as inlets 208a-208d. Also,
other gases used in the growth process can be introduced through
additional inlets (not shown) connected to additional spaces 258.
Such other gases can be introduced at the same time as the carrier
gas and reactant gas, or at other times, during other stages of the
process.
[0041] A similar porous plate may be used with inlets such as those
discussed above with reference to FIGS. 1A and 2.
[0042] In apparatus according to a further embodiment (FIG. 6), the
ports constituting the inlets act to control the amounts of gases
in each gas steam. In this embodiment, the outermost gas inlet 308a
includes a reaction gas port 330a and a carrier gas port 332a,
whereas each of the other gas inlets 308b, 308c and 308d includes a
similar pair of ports. Here again, the ports constituting each gas
inlet are disposed adjacent to one another. The ports are arranged
along a common radial line 317. All of the reaction gas ports 330a,
330b, 330c and 330d are connected to a common conduit 306 which in
turn is connected to a supply of reactant gas, so that all of the
reactin gas ports are supplied with the reaction gas at
substantially the same pressure. Likewise, all of the carrier gas
ports 332a,332b,332c and 332d are connected to a common conduit
307, which in turn is connected to a supply of the carrier gas, so
that all of the carrier gas ports are supplied with the carrier gas
at substantially the same pressure. The sizes of the ports, and
hence the flow resistances of the ports, differ. Reactant gas port
330a of the outermost gas inlet 308a is relatively large, and has
relatively low flow resistance, whereas carrier gas port 332a of
the outermost gas inlet is relatively small, and hence has high
flow resistance. Accordingly, the gas stream issuing from these
ports and hence from gas inlet 308a will incorporate a large
proportion of reactant gas and a small proportion of carrier gas.
Conversely, reactant gas port 330d of the innermost gas inlet 308d
is relatively small, and has high flow resistance, whereas the
carrier gas port 332d of the same inlet is relatively large, and
has high flow resistance. The gas stream issuing from inlet 308d
will have a relatively large proportion of carrier gas. As will be
appreciated with reference to FIG. 6, the sizes of the reactant gas
ports 330 increase progressively in the radially outward direction,
away from axis 314, ie., in the direction from the smallest zone of
the treatment surface to the largest zone, so that the flow
resistance of the reactant gas ports decreases progressively in
this direction. Conversely, the flow resistance of the carrier gas
ports increases progressively in the same direction. The apparatus
thus will provide gas streams having substantially the same total
flow rate (carrier gas plus reactant gas) but differing
concentrations of reactant gas, impinging on the differing zones of
the treatment surface. Plural sets of ports as described above can
be provided along numerous radial lines, so as to provide a
plurality of such streams around the circumference of the
chamber.
[0043] In a further variant (FIG. 7) the separate ports and inlets
of are replaced by a carrier gas passage 432 and reactant gas
passage 430 extending through top plate 416. The downstream ends of
these passages (the ends of the passages opening into the reaction
chamber) are visible in FIG. 7. The passages are disposed
side-by-side. Carrier gas passage 432 is connected to carrier gas
conduit 407, whereas reactant gas passage 430 is connected to a
reactant gas conduit 406. Conduits 407 and 406 are connected to
supplies of carrier gas and reactant gas, respectively. The carrier
gas passage 432 has a width w432 which decreases progressively in
the radially outward direction away from axis 414. Thus, the
resistance of the carrier gas passage to flow of the carrier gas in
the downstream direction of the passage (the direction out of the
plane of the drawing in FIG. 7) increases progressively in the
radially outward direction. The reactant gas passage has a width
w430 which increases progressively in the radially outward
direction, so that the resistance of the reactant gas passage to
downstream flow of reactant gas decreases progressively in the
radially outward direction. In operation, a relatively large amount
of reactant gas passes through the radially outer portion of the
reactant gas passage 430 whereas a relatively small amount of
carrier gas passes through the radially outer portion of carrier
gas passage 432. Conversely, a small amount of reactant gas and a
large amount of carrier gas pass through the radially inner
portions of the passages. The carrier and reactant gases merge to
form a gas stream passing downstream (in the direction out of the
plane of the drawing in FIG. 7), such gas stream having a
substantially constant total flow rate per unit radial distance and
substantially constant velocity at all radial locations but having
progressively increasing reactant gas concentration in the radially
outward direction.
[0044] A reactor according to a further embodiment of the
invention, shown in FIG. 8, has a reactant gas passage 530 and
carrier gas passage 532 similar to the passages discussed above
with reference to FIG. 7. In the reactor of FIG. 8, however, the
passages have constant width over their radial extent.
[0045] Reactant gas passage 530 is filled with a mesh or other
porous structure 531 having progressively increasing porosity in
the radially outward direction, away from axis 514. Accordingly,
the resistance of passage 530 to downstream flow of reactant gas
decreases in the radially outward direction. The carrier gas
passage 532 is filled with a porous structure 533 having
progressively decreasing porosity, and hence progressively
increasing flow resistance, in the radially outward direction. The
net effect is the same as discussed with reference to FIG. 7. Other
features of the passageways can be varied to achieve similar
variations in flow resistance along the radial extent of the
passageways. For example, the passageways can include baffles or
partial obstructions disposed at various radial locations. In yet
another variant, each passage can have different lengths, in the
downstream direction of the passage, at its inner and outer edges.
For example, where a passage extends through a plate, the thickness
of the plate can vary in the radial direction so as to vary the
length of the passage, and hence the flow resistance of the
passage, in the radial direction.
[0046] Although the invention herein has been described with
reference to particular embodiments, it is to be understood that
these embodiments are merely illustrative of the principles and
applications of the present invention. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
invention as defined by the appended claims.
INDUSTRIAL APPLICABILITY
[0047] The present invention is applicable to the electronics
manufacturing industry and where it is desired to manufacture
electronics components in large number through the epitaxial growth
of materials thereon. The present invention is applicable to, for
example, vertical disk reactors for the epitaxial growth of
materials on silicon wafers for electronics components.
* * * * *