U.S. patent application number 14/330433 was filed with the patent office on 2014-10-30 for chemical vapor deposition with energy input.
The applicant listed for this patent is Veeco Instruments Inc.. Invention is credited to Eric A. Armour, Joshua Mangum, William E. Quinn.
Application Number | 20140318453 14/330433 |
Document ID | / |
Family ID | 41429649 |
Filed Date | 2014-10-30 |
United States Patent
Application |
20140318453 |
Kind Code |
A1 |
Mangum; Joshua ; et
al. |
October 30, 2014 |
CHEMICAL VAPOR DEPOSITION WITH ENERGY INPUT
Abstract
Methods of depositing compound semiconductors onto substrates
are disclosed, including directing gaseous reactants into a
reaction chamber containing the substrates, selectively supplying
energy to one of the gaseous reactants in order to impart
sufficient energy to activate that reactant but insufficient to
decompose the reactant, and then decomposing the reactant at the
surface of the substrate in order to react with the other
reactants. The preferred energy source is microwave or infrared
radiation, and reactors for carrying out these methods are also
disclosed.
Inventors: |
Mangum; Joshua; (Sarasota,
FL) ; Armour; Eric A.; (Pennington, NJ) ;
Quinn; William E.; (Whitehouse Station, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Veeco Instruments Inc. |
Plainview |
NY |
US |
|
|
Family ID: |
41429649 |
Appl. No.: |
14/330433 |
Filed: |
July 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12587228 |
Oct 2, 2009 |
8815709 |
|
|
14330433 |
|
|
|
|
61195093 |
Oct 3, 2008 |
|
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Current U.S.
Class: |
118/723MW |
Current CPC
Class: |
C30B 25/105 20130101;
C23C 16/45551 20130101; C30B 29/406 20130101; C23C 16/303 20130101;
C23C 16/511 20130101; C30B 29/403 20130101; C23C 16/483
20130101 |
Class at
Publication: |
118/723MW |
International
Class: |
C23C 16/511 20060101
C23C016/511 |
Claims
1. A chemical vapor deposition reactor comprising: (a) a reaction
chamber; (b) a substrate carrier mounted within said reaction
chamber for rotation about an axis of rotation extending in
upstream and downstream directions, said substrate carrier being
arranged to hold one or more substrates so that surfaces of said
substrates face generally in the upstream direction; (c) a flow
inlet element disposed upstream of the substrate carrier, said flow
inlet element having a plurality of discharge zones disposed at
different locations in directions transverse to said axis of
rotation, said flow inlet element being arranged to discharge
different gases through different ones of said plurality of
discharge zones so that said discharged gases are directed
generally downstream toward said substrate carrier in substantially
separate streams at different locations relative to said axis of
rotation; and (d) selective energy input apparatus arranged to
supply energy selectively at locations between said flow inlet
element and said substrate carrier aligned with a selected one of
said substantially separate streams to thereby supply energy
selectively to said gas associated with said selected one of said
substantially separate streams.
2. The reactor of claim 1 wherein said selective energy input
apparatus is selected from the group consisting of microwave and
infrared energy generators.
3. The reactor of claim 1 wherein said selective energy input
apparatus is arranged to supply said energy at a wavelength which
is substantially absorbed by said gas associated with said selected
one of said substantially separate streams.
4. The reactor of claim 1 wherein said energy is substantially not
absorbed by the others of said substantially separate streams.
5. The reactor of claim 1 wherein said selective energy input
apparatus is arranged to direct beams of said energy along one or
more beam paths having components in directions transverse to said
axis of rotation.
6. The reactor of claim 5 wherein said one or more beam paths are
arranged to intercept said selected one of said separate streams
adjacent to said surface of said substrate carrier.
7. The reactor of claim 1 wherein said selective energy input
apparatus is arranged to direct beams of said energy along one or
more beam paths having components in directions parallel to said
axis of rotation.
8. The reactor of claim 1 wherein said selective energy input
apparatus is arranged to direct beams of said energy along one or
more beam paths having components in directions at an angle between
about 0.degree. and 90.degree. with respect to said axis of
rotation.
9. The reactor of claim 1 wherein said selective energy input
apparatus is arranged to direct beams of said energy along one or
more beam paths having components in a direction at an angle of
about 90.degree. with respect to said axis of rotation.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional of U.S. patent
application Ser. No. 12/587,228, filed Oct. 2, 2009, which claims
the benefit of the filing date of U.S. Provisional Patent
Application No. 61/195,093 filed Oct. 3, 2008, the disclosure of
which is hereby incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to chemical vapor
deposition methods and apparatus.
BACKGROUND OF THE INVENTION
[0003] Chemical vapor deposition involves directing one or more
gases containing chemical species onto a surface of a substrate so
that the reactive species react and form a deposit on the surface.
For example, compound semiconductors can be formed by epitaxial
growth of a semiconductor material on a substrate. The substrate
typically is a crystalline material in the form of a disc, commonly
referred to as a "wafer." Compound semiconductors such as III-V
semiconductors commonly are formed by growing layers of the
compound semiconductor on a wafer using metal organic chemical
vapor deposition or "MOCVD." In this process, the chemical species
are provided by a combination of gases, including one or more metal
organic compounds such as alkyls of the Group III metals gallium,
indium, and aluminum, and also including a source of a Group V
element such as one or more of the hydrides of one or more of the
Group V elements, such as NH.sub.3, AsH.sub.3, PH.sub.3 and
hydrides of antimony. These gases are reacted with one another at
the surface of a wafer, such as a sapphire wafer, to form a III-V
compound of the general formula
In.sub.XGa.sub.YAl.sub.ZN.sub.AAs.sub.BP.sub.CSb.sub.D where
X+Y+Z=approximately 1, and A+B+C+D=approximately 1, and each of X,
Y, Z, A, B, C, and D can be between 0 and 1. In some instances,
bismuth may be used in place of some or all of the other Group III
metals.
[0004] In this process, the wafer is maintained at an elevated
temperature within a reaction chamber. The reactive gases,
typically in admixture with inert carrier gases, are directed into
the reaction chamber. Typically, the gases are at a relatively low
temperature, as for example, about 50.degree. C. or below, when
they are introduced into the reaction chamber. As the gases reach
the hot wafer, their temperature, and hence their available energy
for reaction, increases.
[0005] As used in this disclosure, the term "available energy"
refers to the chemical potential of a reactant species that is used
in a chemical reaction. The chemical potential is a term commonly
used in thermodynamics, physics, and chemistry to describe the
energy of a system (particle, molecule, vibrational or electronic
states, reaction equilibrium, etc.). However, more specific
substitutions for the term chemical potential may be used in
various academic disciplines, including Gibbs free energy
(thermodynamics) and Fermi level (solid state physics), etc. Unless
otherwise specified, references to the available energy should be
understood as referring to the chemical potential of the specified
material.
[0006] According to U.S. Patent Publication No. 2007/0256635, CVD
reactors are disclosed in which an ammonia source is activated by
UV light within the reactor. In the downflow reactors shown in this
application, the UV source activates the ammonia as it enters the
reactor. These applicants also indicate that lower temperature
reactions in their vacuum reactors can be achieved thereby.
[0007] As is shown in U.S. Patent Publication No. 2006/0156983 and
other such disclosures, it is known in plasma reactors of various
types that high frequency power can be applied to the electrodes
therein in order to ionize at least a portion of the reactive gas
to produce at least one reactive species.
[0008] It is also known that lasers can be utilized to assist in
chemical vapor deposition processes. For example, in Lee et al.,
"Single-phase Deposition of a .alpha.-Gallium Nitride by a
Laser-induced Transport Process," J. Mater. Chem., 1993, 3(4),
347-351, laser radiation occurs parallel to the substrate surface
so that the various gaseous molecules can be excited thereby. These
gases can include compounds such as ammonia. In Tansley et al.,
"Argon Fluoride Laser Activated Deposition of Nitride Films," Thin
Solid Films, 163 (1988) 255-259, high energy photons are again used
to dissociate ions from a suitable vapor source close to the
substrate surface. Similarly, in Bhutyan et al., "Laser-Assisted
Metalorganic Vapor-Phase Epitaxy (LMOVPE) of Indium Nitride (InN),"
phys. stat.sol. (a) 194, No. 2, 501-505 (2002), ammonia
decomposition is said to be enhanced at optimum growth temperatures
in order to improve the electrical properties of MOVPE-grown InN
films. An ArF laser is used for this purpose for photodissociation
of ammonia as well as organic precursors, such as trimethylindium
and the like.
[0009] The search has thus continued for improved CVD reaction
processes in which reactants such as ammonia can be more
effectively utilized in greater percentages and improved films can
be produced at the same reactor conditions as are currently
employed.
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, these and other
objects have now been realized by the discovery of a method of
depositing a compound semiconductor on a substrate comprising the
steps of (a) maintaining the substrate in a reaction chamber; (b)
directing a plurality of gaseous reactants within the reaction
chamber from a gas inlet in a downstream direction toward a surface
of the substrate, the plurality of gaseous reactants being adapted
to react with one another at the surface of the substrate so as to
form a deposit on the substrate; (c) selectively supplying energy
to one of the plurality of gaseous reactants downstream of the gas
inlet and upstream of the substrate so as to impart sufficient
energy to activate the one of the plurality of gaseous reactants
but not sufficient to decompose the one of the plurality of gaseous
reactants; and (d) decomposing the plurality of gaseous reactants
at the surface of the substrate. Preferably, the selectively
supplied energy is selected from the group consisting of microwave
energy and infrared energy.
[0011] In accordance with one embodiment of the method of the
present invention, the selectively supplied energy is supplied at
the resonant frequency of the one of the plurality of gaseous
reactants.
[0012] In accordance with another embodiment of the method of the
present invention, the method includes directing the one of the
plurality of gaseous reactants to a preselected area of the
substrate and simultaneously selectively supplying the energy only
to the preselected area of the substrate.
[0013] In accordance with another embodiment of the method of the
present invention, the step of directing the plurality of gaseous
reactants includes directing the reactants toward the substrate so
that the plurality of gaseous reactants remain substantially
separate from one another in at least a part of a flow region
between the inlet and the surface of the substrate, and maintaining
the substrate in the reaction chamber includes the maintaining the
substrate in motion. Preferably, the step of maintaining the
substrate in motion includes rotating the substrate about an axis
of rotation in the reaction chamber so that the plurality of
gaseous reactants impinge on a surface of the substrate which is
parallel to the axis of rotation. In a preferred embodiment, the
step of directing the plurality of gaseous reactants includes
directing the reactants into separate zones of the reaction chamber
and the step of selectively supplying energy includes supplying
energy to only those zones where the one of the plurality of
gaseous reactants is supplied and not to those zones where others
of the plurality of gaseous reactants are supplied.
[0014] In accordance with one embodiment of the method of the
present invention, the selectively applied energy is applied to the
one of the plurality of reactants at an angle of between 0.degree.
and 90.degree. with respect to the axis of rotation. In one
embodiment, the angle is about 0.degree. with respect to the axis
of rotation. In another embodiment, the angle is about 90.degree.
with respect to the axis of rotation. In other embodiments, the
angle may be between 0.degree. and 90.degree. with respect to the
axis of rotation.
[0015] In accordance with the present invention, a method has also
been discovered of depositing a compound semiconductor on a
substrate comprising the steps of: (a) maintaining the substrate in
a reaction chamber; (b) directing a plurality of gaseous reactants
including a Group V hydride and an organic compound of a Group III
metal within the reaction chamber from a gas inlet in a downstream
direction toward a surface of the substrate; (c) selectively
supplying energy to the Group V hydride downstream of the inlet and
upstream of the substrate so as to impart sufficient energy to
activate the Group V hydride but not sufficient to decompose the
Group V hydride; and (d) decomposing the plurality of gaseous
reactants at the surface of the substrate. In a preferred
embodiment, the selectively supplied energy is selected from the
group consisting of microwave energy and infrared energy.
[0016] In accordance with one embodiment of the method of the
present invention, the selectively supplied energy is supplied at
the resonant frequency of the Group V hydride. Preferably, the
Group V hydride comprises ammonia. In a preferred embodiment, the
methods includes directing the Group V hydride to a preselected
area of the substrate and simultaneously selectively supplying the
energy only to the preselected area of the substrate. In a
preferred embodiment, the Group III metal is gallium, indium or
aluminum. Preferably, the step of directing the plurality of
gaseous reactants includes directing the reactants toward the
substrate so that the plurality of gaseous reactants remain
substantially separate from one another in at least a part of a
flow region between the inlet and the surface of the substrate, and
maintaining the substrate in the reaction chamber includes
maintaining the substrate in motion. Preferably, the step of
maintaining the substrate in motion includes rotating the substrate
about an axis of rotation in the reaction chamber so that the
plurality of gaseous reactants impinge on a surface of the
substrate transverse to the axis of rotation.
[0017] In accordance with one embodiment of the method of the
present invention, the selectively applied energy is applied to the
Group V hydride at an angle of between 0.degree. and 90.degree.
with respect to the axis of rotation. In one embodiment, the angle
is about 0.degree. with respect to the axis of rotation. In another
embodiment, the angle is about 90.degree. with respect to the axis
of rotation. In other embodiments, the angle can be an angle
between 0.degree. and 90.degree. with respect to the axis of
rotation. In a preferred embodiment, the step of directing the
gaseous reactants includes directing the reactants into the
separate zones of the reaction chamber and the step of selectively
supplying energy includes supplying energy to only those separate
zones where the Group V hydride is supplied and not to those zones
where the organic compound of a Group III metal is supplied. In a
preferred embodiment, the Group III metal comprises indium.
[0018] In accordance with the present invention, a chemical vapor
deposition reactor has been invented comprising (a) a reaction
chamber; (b) a substrate carrier mounted within the reaction
chamber for rotation about an axis of rotation extending in
upstream and downstream directions, the substrate carrier being
arranged to hold one or more substrates so that surfaces of the one
or more substrates face generally in the upstream direction; (c) a
flow inlet element disposed upstream of the substrate carrier, the
flow inlet element having a plurality of discharge zones disposed
at different locations in directions transverse to the axis of
rotation, the flow inlet element being arranged to discharge
different gases through different ones of the plurality of
discharge zones so that the discharged gases are directed generally
downstream toward the substrate carrier in substantially separate
streams at different locations relative to the axis of rotation and
(d) selective energy input apparatus arranged to supply energy
selectively at locations between the flow inlet element and the
substrate carrier aligned with a selected one of the substantially
separate streams to thereby supply energy selectively to the gas
associated with the selected one of the substantially separate
streams. In a preferred embodiment, the selective energy input
apparatus is a microwave or infrared energy generation. Preferably,
the selective energy input apparatus is arranged to supply the
energy at a wavelength which is substantially absorbed by the gas
associated with the selected one of the substantially separate
streams. Preferably, the energy is substantially not absorbed by
the others of the substantially separate streams.
[0019] In accordance with one embodiment of the reactor of the
present invention, the selective energy input apparatus is arranged
to direct a beam of the energy along one or more beam paths having
components in directions transverse to the axis of rotation. In a
preferred embodiment, the one or more beam paths are arranged to
intercept the selected streams adjacent to the surface of the
substrate carrier.
[0020] In accordance with one embodiment of the reactor of the
present invention, the selective energy input apparatus is arranged
to direct beams of the energy along one or more beam paths having
components in directions parallel to the axis of rotation. In
another embodiment, the selective energy input apparatus is
arranged to direct beams of the energy along one or more beam paths
having components in directions at an angle between about 0.degree.
and 90.degree. with respect to the axis of rotation. In yet another
embodiment of the apparatus of the present invention, the selective
energy input apparatus is arranged to direct beams of the energy
along one or more beam paths having components in directions at an
angle of about 90.degree. with respect to the axis of rotation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The present invention can be more fully appreciated with
reference to the following detailed description, which in turn
refers to the Figures in which:
[0022] FIG. 1 is a side, elevational, partial, sectional view of a
reactor in accordance with the present invention;
[0023] FIG. 2 is a bottom, elevational view of a portion of the
reactor shown in FIG. 1;
[0024] FIG. 3 is a partial, enlarged, elevational view of a portion
of the gas inlet in a reactor in accordance with the present
invention;
[0025] FIG. 4 is a partial, side, perspective view of a portion of
the internal reactor in accordance with the present invention;
and
[0026] FIG. 5 is a top, elevational representational view of a
portion of the rotating disk of a reactor in accordance with the
present invention.
DETAILED DESCRIPTION
[0027] The present invention particularly refers to the selective
application of energy to one or more of the gaseous reactants
utilized in MOCVD apparatus for the formation of compound
semiconductors. In particular, the present invention specifically
utilizes microwave or IR radiation for this purpose. Microwave
energy is generally known to refer to electromagnetic waves having
wavelengths ranging from as long as one meter down to as short as
one millimeter or equivalently with frequencies between 300
megahertz and 300 gigahertz. Infrared radiation, on the other hand,
is generally known to be electromagnetic radiation with wavelengths
longer than that of visible light (400 to 700 nm) but shorter than
that of terahertz radiation (100 .mu.m to 1 mm) and microwaves. In
accordance with the present invention, the term microwave radiation
is thus intended to specifically include terahertz radiation;
namely, thus including the area between about 300 gigahertz and 3
terahertz corresponding to the sub-millimeter wavelength range from
about 1 mm, which is usually referred to as the high frequency edge
of the microwave band, and 100 micrometer (which is the long
wavelength edge of the far infrared light band).
[0028] One form of MOCVD apparatus which is commonly employed in
formation of compound semiconductors is depicted schematically in
FIG. 1. This apparatus includes a reaction chamber 10 having a
spindle 12 rotatably mounted therein. The spindle 12 is rotatable
about an axis 14 by a rotary drive mechanism 16. Axis 14 extends in
an upstream direction U and a downstream direction D. A substrate
carrier, typically in the form of a disc-like wafer carrier 18, is
mounted on the spindle for rotation therewith. Typically, the
substrate carrier and spindle rotate at about 100-2000 revolutions
per minute. The substrate carrier is adapted to hold numerous
disc-like wafers 20 so that surfaces 22 of the wafers are in a
plane perpendicular to axis 14 and face in the upstream direction.
A heater 26, as for example, a resistance heating element, is
disposed within the reaction chamber for heating the wafer carrier.
A flow inlet element 28 is mounted upstream of the substrate
carrier and spindle. The flow inlet element is connected to sources
30, 32, and 34 of the gases used in the process. The flow inlet
element directs streams of the various gases into the reaction
chamber. In a region of the reaction chamber near the flow inlet
element 28, referred to herein as the "flow region" 37, the streams
of gases pass generally downstream toward the substrate carrier 18
and wafers 20. Preferably, this downward flow does not result in
substantial mixing between separate streams of downwardly flowing
gas. Desirably, the flow in flow region 37 is laminar. As the
substrate carrier 18 is rotating rapidly, the surface of the
substrate carrier and the surfaces of the wafers are likewise
moving rapidly. The rapid motion of the substrate carrier and
wafers entrains the gases into rotational motion around axis 14,
and radial flow away from axis 14, and causes the gases in the
various streams to mix with one another within a boundary layer
schematically indicated at 36 in FIG. 1. Of course, in actual
practice, there is a gradual transition between the generally
downstream flow regime denoted by arrows 38 in the flow region 37
and the rapid rotational flow and mixing in the boundary layer 36.
However, the boundary layer can be regarded as the region in which
the gases flow substantially parallel to the surfaces of the
wafers. Under typical operating conditions, the thickness t of the
boundary layer is about 1 cm or so. By contrast, the distance d
from the downstream face of flow inlet element 28 to the surfaces
22 of the wafers commonly is about 5-8 cm.
[0029] The thickness of the boundary layer is thus substantially
less than the distance d between the flow inlet element 28 and the
substrate carrier 18, so that the flow region 37 occupies the major
portion of the space between the flow inlet element 28 and the
substrate carrier. The rotational motion of the substrate carrier
pumps the gases outwardly around the peripheral edges of the wafer
carrier, and hence the gases pass downstream to an exhaust system
40. Typically, the reaction chamber is maintained under absolute
pressures from about 25-1000 Torr, and most typically at about
100-760 Torr. Furthermore, in connection with the disassociation of
Group III hydrides and alkyls of the Group V metals, such as is the
production of InGaN and GaN LEDs, the reaction chambers are
maintained at temperatures from 500 to 1,100.degree. C.
[0030] The flow inlet element 28 is maintained at a relatively low
temperature, typically about 60.degree. C. or less, although higher
temperatures can be used, to inhibit the decomposition or other
undesired reactions of the reactants, in the flow inlet element and
in the flow region. Also, the walls of reaction chamber 10 are
typically cooled to about 25.degree. C. It is desirable to minimize
the rate of any reactions of the gases in the flow region 38 remote
from the substrate carrier 18. Because the residence time of the
gases in the boundary layer 36 is brief, it is desirable to promote
rapid reaction between the gases in the boundary layer 36, and
particularly at the surfaces of the wafers. In a conventional
system, the energy for reaction, as for example, the energy for
dissociation of a Group V hydride such as NH.sub.3 to form reactive
intermediates such as NH.sub.2 and NH, is provided substantially
only by heat transfer from the substrate carrier and wafers. Thus,
higher temperatures of the substrate carrier and wafers tend to
increase the speed of the reaction.
[0031] However, increasing the temperature of the wafer carrier and
wafers also tends to increase dissociation of the deposited
compound semiconductors, as for example, resulting in the loss of
nitrogen from the semiconductor. This phenomenon is particularly
severe in the case of indium-rich compounds such as InGaN and InN.
Thus, in this case these compounds have a high equilibrium N.sub.2
vapor pressure making higher temperature growth far more difficult.
The nitrogen thus prefers to be in the gas phase in the form of
N.sub.2, and this problem increases with increased temperature,
resulting in N-vacancies shortening the lifetime of the devices and
reducing their performance.
[0032] In addition, in connection with these devices the residence
time for the various components at the substrate surface is
extremely short. The shorter the residence time, the more
inefficient the process becomes. Thus, the amount of Group V
hydrides such as ammonia required to deposit sufficient N on the
substrate becomes greater and greater, and the amount of unreacted
NH.sub.3 becomes concomitantly greater. On the other hand, longer
residence times are also inefficient. Thus, with longer residence
times the probability of a gas phase reaction between the
reactants, such as, for example, a Group V hydride and an alkyl of
a Group III metal compound can occur, forming adducts which can
eventually form particles and thus eliminate these materials from
the reactants.
[0033] In accordance with the present invention, the selective
activation of, for example, the Group V hydride, such as NH.sub.3,
and increasing the available energy of this reactant is intended to
improve the decomposition efficiency at low residence times and
thus improve the decomposition at the surface of the substrate to
provide greater radical N-containing species to form stoichiometric
GaN, for example, and to reduce the N-vacancies in the ultimate
product. Increasing the residence time is undesirable because the
earlier breakdown of the hydride results in the formation of
N.sub.2 and H.sub.2, for example (from ammonia), so that the N is
no longer available for incorporation into the substrate. N.sub.2
and H.sub.2 gases are thus far too stable to react with the Group
III metal organic compounds. The concept of the present invention
is thus to prevent premature decomposition of the Group V hydride
compounds as they flow towards the substrate, but at the same time
to maximize such decomposition as close to the surface of the
substrate as possible during the short residence time of the gas
streams at that surface. This is accomplished in accordance with
the present invention by selective activation either by microwave
or infrared radiation specific to these compounds, so that as these
compounds approach the substrate surface their available energy
increases, and the energy necessary for their decomposition
decreases. Decomposition is thus readily triggered at these
surfaces by the increased temperatures at that location. In other
words, the infrared or microwave radiation is applied selectively
to the selected reactant, such as the Group V hydride compounds, so
that insufficient energy is applied by these sources themselves to
decompose these compounds, but sufficient energy is applied to
activate them. This is believed to occur by causing vibration of
these molecules generating heat thereby.
[0034] Application of this energy in the form of infrared or
microwave radiation is carried out in a manner such that the energy
can selectively impact the desired species of gases which are
intended to be activated at or near the surface of the substrate.
The direction of application of this energy, however, is not a
critical limitation. That is, the energy can be applied at an angle
of from 0.degree. to 90.degree. with respect to the substrate
surfaces, or with respect to the axis of rotation of the wafer
carrier. The energy can thus be applied parallel to the surface at
or near the substrate or significantly above the boundary layer, or
it can be applied at a transverse angle to the substrate surface,
or it an be applied directly perpendicular to the substrate
surface. Because the particular beams of energy comprising infrared
or microwave radiation in connection with the present invention
possess energies which are low enough so that surface degradation
will generally not be an issue, the energy can, for example, be
applied directly perpendicular to the substrate surface without
serious concerns. In connection with various other forms of energy,
such as UV light, for example, beams directed directly
perpendicular to the substrate surface could be detrimental to the
reaction process because of their high energy. As noted, however,
on the other hand, it is also possible to use transverse beams or
beams directed parallel to the substrate surface in connection with
the present invention.
[0035] Turning once again to FIG. 1, energy in the form of
microwave or infrared radiation is applied to the Group V hydride,
for example, from an energy activator such as energy activator 31a
or energy activator 31b, as shown in FIG. 1. The energy can thus be
applied from energy activator 31a from directly above the wafer
carrier 18 in a direction parallel to the axis of rotation U of the
carrier and thus directly perpendicular to the surfaces of the
wafers 20. Alternatively, this energy can be applied from energy
activator 31b in a direction parallel to the surface of the wafer
carrier 18 and thus perpendicular to the axis of rotation U across
the surface of the wafers 20. In an alternate embodiment which is
discussed below with reference to FIG. 5, the energy can also be
applied from energy activators located at alternate positions
between energy activators 31a and 31b so as to be applied
transverse or angularly with respect to the axis of rotation U at
angles from about 0.degree. to 90.degree. with respect to that axis
of rotation against the surface of the wafer carrier 18 and thus
that of the wafers 20 themselves.
[0036] Selective application of the energy to one or more of the
gases without applying it to all of the gases is facilitated by
introducing the gases separately in different regions of the
reactor. For example, the flow inlet element 28 may be arranged as
seen in FIG. 2. FIG. 2 is a view looking upstream toward the flow
inlet element, in the direction indicated by line 2-2 in FIG. 1. In
this arrangement, the flow inlet element 28 has elongated discharge
zones 50 extending generally radially with respect to the axis 14.
These discharge zones are used to discharge the organometallic
reactant, typically in admixture with a carrier gas such as
nitrogen. For example, the flow inlet element may have elongated
slot-like discharge openings or rows of small circular discharge
openings extending within the elongated zones 50. The flow inlet
element 28 also has further discharge zones 52 generally in the
form of quadrants of a circular pattern arranged around axis 14,
these zones being indicated by the cross-hatched areas in FIG. 2.
For example, the flow inlet elements may have numerous discharge
ports arranged within each of these zones. In operation, streams of
downwardly flowing organometallic gases are present in those
portions of the flow region 37 (FIG. 1) aligned with zones 50,
whereas streams of downwardly flowing hydrides such as ammonia are
present in those areas of the flow region 37 aligned with the
hydride discharge zones 52. Energy can be selectively applied to
the hydride by directing the energy only into those portions of the
flow region aligned with discharge zones 52. For example, a
microwave or infrared source (not shown) may be arranged to apply
microwave or infrared energy only within a radiation region or
energy application zone 54, as shown in FIG. 2, or within a smaller
energy application region 56, also depicted in FIG. 2. Although
only two radiation regions are depicted in FIG. 2, a typical
reactor would incorporate a radiation region aligned with each of
the discharge zones 52.
[0037] As shown schematically in FIG. 3, a flow inlet element 128
may have numerous discharge zones in the form of elongated strips
or stripes extending along the flow inlet element 128 (FIG. 3) in
directions transverse to the axis 14. The flow inlet has elongated
zones 150, used in this embodiment for supplying a gas containing
the metal organic. The flow inlet element also has elongated
discharge zones 152, which in this embodiment are used for
supplying the Group V hydride. The elongated discharge zones are
interspersed with one another, and extend parallel to one another.
Each such elongated discharge zone may include an elongated slot
for discharging the appropriate gas or a set of holes or other
discrete openings arranged along the direction of elongation of the
zone. Although only a few of the zones are depicted in FIG. 3, the
pattern of flow inlet zones may encompass most or all of the area
of the flow inlet element.
[0038] The flow inlet element may also include additional elongated
discharge zones 154, which are connected to a source of an inert
gas. As used in this disclosure, the term "inert gas" refers to a
gas which does not substantially participate in the reaction. For
example, in deposition of a III-V semiconductor, gases such as
N.sub.2, H.sub.2, He or mixtures of these gases may serve as inert
gases. Inert gases are also referred to herein as "carrier gases."
The discharge zones 154, used for discharging the inert or carrier
gases, are interspersed with the discharge zones 150 and 152 used
for the other gases, so that a discharge zone 154 for carrier gas
is positioned between each discharge zone 150 for the
organometallic gases and the next adjacent discharge zone 152. The
gases discharged from these various discharge zones pass downwardly
through the flow region 37 of the reactor as generally slab-like
streams of gas flowing generally in parallel planes without mixing
with one another. An idealized representation of such a flow is
seen in FIG. 4, which shows a flow of metal organic gas 250 moving
downstream within the flow region 37 in parallel with a flow of
hydride 252, and with a flow of carrier gas 254 disposed between
them. In this figure, the feature indicated as "purge/curtain" may
indicate the optional carrier gas discharge zones and the flow
extending from them. In the alternative, solid barriers may extend
downstream somewhat from the flow inlet element, denoted "cold
plate (top flange)."
[0039] Where microwave or IR energy is directed into one of the
flows of gases, it is desirable to apply that energy in such a
manner that the radiant energy reaches regions of the flowing gas
disposed at various radial distances from the axis of rotation 14.
However, this radiant energy which is applied typically has a
wavelength which is selected so that the radiant energy is
substantially interactive with the species to be energized. Thus,
the radiant energy will be strongly absorbed by the flowing gas
containing that species. As seen in FIG. 5, the flow inlet element
is arranged to provide two streams of first gas 352, commonly in
the form of a quadrant. The gas in stream 352 may be, for example,
ammonia or another hydride. Here again, the flow inlet element is
arranged to provide streams 350A and 350B of another, second gas
such as a metal organic. These streams may extend along the borders
of the streams 352. The flow inlet element may also be arranged to
provide further streams 354 of a further, carrier gas, also
arranged to occupy quadrants about the axis of rotation 14. As
shown, the radiant energy sources, such as microwave or IR
radiation sources, may be arranged to direct radiant energy which
is at a wavelength that is strongly absorbed by the gas in stream
352 but which is not strongly absorbed by the gases in streams 350
and 354. This radiant energy may be directed through streams 354
and 350 so as to impinge on borders 360 of streams 352, which
borders have a substantial radial extent, towards and away from the
central axis 14, or the axis of rotation. The radiant energy passes
through the streams 350 and 354, but is not substantially absorbed
by the gases in those streams. Because the radiant energy impinges
on borders 360 along their radial extent, the radiant energy is
absorbed by portions of the gas lying at all radial distances from
central axis 14. As further discussed below, it may be desirable to
assure that the radiant energy is absorbed by an interaction with a
gas stream near the lower end of the flow region, and near the
upper boundary of the boundary layer 36. In the embodiment of FIG.
5, the radiant energy sources 356 direct the beams of radiant
energy in directions which lie in a plane perpendicular to the axis
of rotation 14, i.e., a plane generally parallel to the surfaces 22
of the wafers (FIG. 1) and the upper surface of the substrate
carrier 18. It is not essential that the beams of radiant energy be
directed exactly in such a plane, but in the embodiment of FIG. 5,
it is desirable that the direction of the radiant energy have a
substantial component in such a plane. Therefore, the radiant
energy beams may be directed in a plane transverse to the central
axis 14, so that they intersect borders 360 near the boundary layer
36. If the radiant energy is directed in a plane generally parallel
to the surfaces of the wafers, it is possible to avoid directing
the radiant energy onto the surfaces of the wafers. This limits or
avoids undesired effects of the radiant energy on the wafer
surfaces. However, as discussed above, with the relatively low
energy sources described here, there will be minimal adverse effect
on the wafer surface. This permits one to again apply the energy at
a range of angles with respect to the axis of rotation of the
substrate carrier of from 0.degree. to 90.degree..
[0040] In a variant of this arrangement, streams 350B may be
omitted, whereas streams 350A are arranged as shown. Thus, each
stream 352 of the first reactant gas borders a stream 354 of the
inert or carrier gas at one radially-extensive border 360B. The
radiant energy is directed through the streams 354 of the inert or
carrier gas, and enters the streams of first gas through borders
360B. In this variant, the radiant energy passes into the first gas
352 without passing through a stream 350 of the second reactant
gas. This arrangement may be used, for example, where the second
reactant gas would substantially absorb the radiant energy. For
example, IR light at wavelengths which will specifically excite
NH.sub.3 can be employed. Thus, the IR light can be coupled
directly to the residence frequency of ammonia, which may or may
not be the same residence frequency for the metal organics. This
will, of course, depend on the specific metal organics which are
being utilized. They can be selected so that they will not absorb
the IR light at the particular wavelength utilized. On the other
hand, in the case of microwave energy, since metal organics and
ammonia are both nonpolar, they will both absorb the same
frequencies of microwave energy, while polar molecules such as
nitrogen and hydrogen will not absorb microwave energy. Once again,
these factors can be utilized to select the optimum IR or microwave
energy to be utilized in any particular case.
[0041] As depicted schematically in FIG. 4, the radiant energy R
may be directed into the reaction chamber through one of the planar
streams of gas 250, 254, which do not substantially interact with
the radiant energy, and may be directed at an oblique angle to the
theoretical plane of the target gas stream 252 which is to absorb
the radiant energy. The radiant energy R enters stream 252 near the
boundary layer 36, and hence near the lower end of the flow region
37, and hence the radiant energy is absorbed near the boundary
layer.
[0042] Typically, the reactants are introduced into the reaction
chamber at a relatively low temperature, and hence have low
available energy, well below that required to induce rapid reaction
of the reactants. In a conventional process, there may be some
heating of the reactants by radiant heat transfer as the reactants
pass downstream from the inlet towards the boundary layer. However,
most of the heating, and hence most of the increase in available
energy of the reactants, occurs within the boundary layer.
Moreover, all of the heating depends upon the temperature of the
substrate carrier and wafers. By contrast, in the embodiments
discussed above, substantial energy is supplied to at least one of
the reactants while the reactant is in the flow region, such energy
being supplied by means other than heat transfer from the substrate
carrier, substrates, and reactor walls. Further, the location where
the energy is applied can be controlled. By applying the energy to
the reactant or reactants near the transition between the flow
region and the boundary layer, the time between the moment that a
given portion of a reactant reaches a high available energy and the
time when that portion encounters the wafer surface can be
minimized. This, in turn, can help to minimize undesired side
reactions. For example, ammonia having high available energy may
spontaneously decompose into species such as NH.sub.2 and NH, and
then these species in turn may decompose to monatomic nitrogen,
which very rapidly forms N.sub.2. N.sub.2 is essentially
unavailable for reaction with a metal organic. By applying the
energy to the ammonia just before or just as the ammonia enters the
boundary layer, the desired reactions which deposit the
semiconductor at the surface, such as reaction of the excited
NH.sub.3 with the metal organic or reaction of NH.sub.2 or NH
species with the metal organic at the wafer surface, can be
enhanced, whereas the undesirable side reaction can be
suppressed.
[0043] Moreover, because energy is applied to one or more of the
reactants by means other than energy transfer such as heat transfer
from the substrate carrier and wafers, the available energy of the
reactants can be controlled, at least to some degree, independently
of the temperature of the substrates. Thus, the available energy of
the reactants in the boundary layer can be increased without
increasing the temperature of the wafers and the substrate carrier,
or conversely, the wafers and the substrate carrier can be
maintained at a lower temperature while still maintaining an
acceptable level of available energy. Of course, there is typically
some energy input from the substrate carrier and from the wafers to
the reactants.
[0044] When applying microwave energy in accordance with the
present invention, the energy can be applied as either a coherent
or diffuse beam. The beam can be applied parallel to the surface of
the substrate, at a location near the substrate or significantly
above the boundary layer, or can be perpendicular to the substrate,
or at any angle between the perpendicular and parallel positions
with respect to the substrate. The microwave energy can be applied
at various heights from the substrate surface. Furthermore,
microwaves can originate from one or a number of sources and these
can be controlled in order to interact with more than one of the
reactants. Thus, for example, in the case of Group V hydrides and
alkyls of Group III metals, microwave sources can be controlled to
interact with one or more of these sources.
[0045] Similarly, in the case of infrared energy, it can also be
applied as a coherent or diffuse beam, again either parallel to the
substrate, perpendicular to the substrate, or at any angle
therebetween. Once again, infrared energy can be applied at varying
heights from the substrate surface independent of the orientation
of the beam, and it can originate from one or more sources and can
be controlled to interact with one or more of the reactants.
[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.
* * * * *