U.S. patent application number 11/530375 was filed with the patent office on 2007-02-01 for method of thermally oxidizing silicon using ozone.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to Vedapuram ACHUTHARAMAN, Mehran BEHDJAT, Cory CZARNIK, Christopher OLSEN, Sundar RAMAMURTHY, Yoshitaka YOKOTA.
Application Number | 20070026693 11/530375 |
Document ID | / |
Family ID | 37071127 |
Filed Date | 2007-02-01 |
United States Patent
Application |
20070026693 |
Kind Code |
A1 |
YOKOTA; Yoshitaka ; et
al. |
February 1, 2007 |
Method of Thermally Oxidizing Silicon Using Ozone
Abstract
A method and apparatus for oxidizing materials used in
semiconductor integrated circuits, for example, for oxidizing
silicon to form a dielectric gate. An ozonator is capable of
producing a stream of least 70% ozone. The ozone passes into an RTP
chamber through a water-cooled injector projecting into the
chamber. Other gases such as hydrogen to increase oxidation rate,
diluent gas such as nitrogen or O.sub.2, enter the chamber through
another inlet. The chamber is maintained at a low pressure below 20
Toir and the substrate is advantageously maintained at a
temperature less than 800.degree. C. Alternatively, the oxidation
may be performed in an LPCVD chamber including a pedestal heater
and a showerhead gas injector in opposition to the pedestal.
Inventors: |
YOKOTA; Yoshitaka; (San
Jose, CA) ; RAMAMURTHY; Sundar; (Fremont, CA)
; ACHUTHARAMAN; Vedapuram; (San Jose, CA) ;
CZARNIK; Cory; (Mountain View, CA) ; BEHDJAT;
Mehran; (San Jose, CA) ; OLSEN; Christopher;
(Fremont, CA) |
Correspondence
Address: |
LAW OFFICES OF CHARLES GUENZER;ATTN: APPLIED MATERIALS, INC.
2211 PARK BOULEVARD
P.O. BOX 60729
PALO ALTO
CA
94306
US
|
Assignee: |
APPLIED MATERIALS, INC.
3050 Bowers Avenue
Santa Clara
CA
|
Family ID: |
37071127 |
Appl. No.: |
11/530375 |
Filed: |
September 8, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11099082 |
Apr 5, 2005 |
|
|
|
11530375 |
Sep 8, 2006 |
|
|
|
Current U.S.
Class: |
438/795 ;
257/E21.284; 257/E21.285 |
Current CPC
Class: |
H01L 21/67109 20130101;
H01L 21/02238 20130101; H01L 21/02255 20130101; H01L 21/02249
20130101; H01L 21/0214 20130101; H01L 21/31662 20130101; H01L
21/67115 20130101; H01L 21/31658 20130101 |
Class at
Publication: |
438/795 |
International
Class: |
H01L 21/00 20060101
H01L021/00 |
Claims
1. A method of treating a surface of a substrate to be formed into
an integrated circuit, comprising the steps of: maintaining a
processing surface of said substrate at a temperature; and flowing
from a first gas port into a processing chamber accommodating said
substrate an oxygen-based gas mixture containing at least 30%
ozone.
2. The method of claim 1, wherein said gas mixture contains at
least 50% ozone.
3. The method of claim 2, wherein said gas mixture contains at
least 70% ozone.
4. The method of claim 3, wherein said gas mixture contains at
least 90% ozone.
5. The method of claim 1, wherein said substrate comprises a
silicon-containing material and said ozone oxidizes the
silicon-containing material.
6. The method of claim 5, further comprising flowing into said
processing chamber hydrogen.
7. The method of claim 6, wherein said hydrogen flows into said
processing chamber through a second port.
8. The method of claim 5, further comprising flowing oxygen gas
into said chamber through a second port.
9. The method of claim 5 wherein the temperature is less than
800.degree. C.
10. The method of claim 9, wherein the temperature is less than
600.degree. C.
11. The method of claim 10, wherein the temperature is less than
400.degree. C.
12. The method of claim 1, wherein the gas mixture is not excited
into a plasma adjacent said substrate.
13. The method of claim 1, wherein the maintaining step is
performed by radiant lamps directed at the substrate.
14. The method of claim 1, wherein said flowing step includes
flowing said gas mixture into a said processing chamber through an
injector projecting into said processing chamber and further
comprising cooling said injector with a cooling liquid.
15. The method of claim 1, wherein the maintaining step includes
electrically heating a pedestal accommodated within said processing
chamber and supporting the substrate.
16. The method of claim 15, wherein said flowing step includes
flowing said gas mixture into a gas manifold separated from the
processing chamber by a showerhead including a plurality of
apertures therethough and disposed in opposition to the
pedestal.
17. The method of claim 1, further comprising flowing molecular
oxygen gas through an ozonator external of the chamber to produce
said oxygen-based gas mixture.
18. The method of claim 1, wherein a pressure within the processing
chamber is maintained no higher than 20 Torr.
19. The method of claim 18, where the pressure is maintained no
higher than 5 Torr.
20. The method of claim 1, further comprising flowing another
processing gas into the processing chamber from a port different
than a port admitting said oxygen-based gas into said processing
chamber.
Description
RELATED APPLICATION
[0001] This application is a division of Ser. No. 11/099,082, filed
Apr. 5, 2005.
FIELD OF THE INVENTION
[0002] The invention relates generally to fabrication of integrated
circuits. In particular, the invention relates to thermal oxidation
of and other oxygen-based treatment of electronic materials such as
silicon.
BACKGROUND ART
[0003] The fabrication of silicon integrated circuits typically
includes one or more steps of forming layers of silicon dioxide,
having a general composition of SiO.sub.2, although some variation
in its stoichiometry is possible. In some applications, dopants are
added. For brevity, this material may hereafter be referred to as
oxide. Silicon dioxide is a rugged material that bonds well with
silicon and is electrically insulating, that is, dielectric.
Thicker layers of oxide are typically deposited by spin-on glasses
or by chemical vapor deposition, particularly when they form
inter-level dielectric layers, which may be formed over metal and
other oxide features. However, thin oxide layers formed over
silicon maybe formed by oxidizing the silicon to form silicon
oxide. The silicon to be oxidized may be monocrystalline silicon of
the wafer or polysilicon deposited as a layer on the wafer in a
multi-level structure. Gate oxide layers may be formed by oxidation
of typically about 1 nm or less. Pads and STI (shallow trench
isolation) liners may similarly be formed to thicknesses of
typically 5 to 10 nm. The oxide layer not only electrically
insulates the underlying silicon but also passives the
silicon/dielectric interface.
[0004] Oxidation is conventionally performed by heating the silicon
surface to approximately 1000.degree. C. to 1200.degree. C. or
higher and exposing it to gaseous oxygen for dry oxidation or to
steam (H.sub.2O) for wet oxidation. Such thermal oxidation may
conventionally be performed in a furnace accommodating large number
of wafers, but furnaces have in part been superseded by
single-wafer processing chambers utilizing a process called rapid
thermal oxidation (RTO), a form of rapid thermal processing (RTP).
In RTO, high-intensity incandescent lamps rapidly heat a silicon
wafer to very high temperatures and oxygen is flowed into the RTP
chamber to react on the surface of the hot wafer to react with the
silicon and produce a layer of silicon oxide on top of the wafer.
Gronet et al. disclose oxidation in an RTP chamber in U.S. Pat. No.
6,037,273, incorporated herein by reference in its entirety. One
advantage of RTO is that the walls of the RTP chamber are typically
much cooler than the wafer so that oxidation of the chamber walls
is reduced. Gronet et al. disclose injecting oxygen and hydrogen
gases into the RTP chamber to react near the hot wafer surface for
in situ generation of steam.
[0005] It has been recognized that oxygen radicals O* provide
several advantages in silicon oxidation. The oxygen radicals more
easily react than oxygen gas so that the oxidation rate is
increased for a given temperature. Further, the radicals promote
corner rounding, an important feature in STI.
[0006] Oxygen plasmas have been used for oxidation, but they are
felt to subject the semiconducting silicon and dielectric layers to
damage particularly when the oxygen species is charged, e.g.
O.sup.- or O.sup.=.
[0007] Ozone (O.sub.3) is an unstable form of oxygen gas that may
be considered an oxygen radical since O.sub.3 spontaneously
dissociates into O.sub.2 and O*, particularly when exposed to
surfaces held at temperatures of greater than 400.degree. C. It is
known to use ozone in silicon oxidation, see U.S. Pat. No.
5,294,571 to Fujishiro et al. and U.S. Pat. No. 5,693,578 to
Nakanishi et al. However, most known prior art for ozone-assisted
oxidation occurs at relatively high temperatures and low ozone
concentrations.
[0008] Another approach for low temperature oxidation supplies the
reactor chamber with a gas mixture of oxygen gas O.sub.2 and ozone
O.sub.3, as disclosed in U.S. Pat. No. 5,330,935 to Dobuzinsky et
al. (hereafter Dobuzinsky). Ozone is a metastable form of oxygen
that may be generated in a microwave or UV generator and which
readily dissociates into O.sub.2 and the oxygen radical O*.
Dobuzinsky supplies the ozone-rich mixture into a thermal reactor
operated at a relatively low temperature but including additional
RF plasma excitation of the ozone. However, Dobuzinsky's reactor is
still a hot-wall reactor so that the ozone quickly dissociates
inside the chamber and equally reacts with the chamber walls.
Dobuzinsky does however mention the possibility of RTO after their
plasma oxidation.
[0009] More recent technology has imposed different constraints
upon silicon oxidation processes. In view of the very thin layers
and shallow doping profiles in advanced integrated circuits, the
overall thermal budget and maximum processing temperatures are
reduced. That is, the typical oxidation temperatures of greater
than 1000.degree. C. are considered excessive even when used with
the rapid temperature ramp rates available in RTP. Furthermore, the
gate oxide thickness are decreasing to well below 1 nm, for
example, 0.3 to 0.6 nm in the near future. However, to prevent
dielectric breakdown and increase reliability, the gate oxides must
be uniformly thick and of high quality. Plasma oxidation may be a
low temperature process because it produces oxygen radicals O*
which readily react with silicon at low temperatures. However,
charging and other effects on the fragile thin oxide prevent plasma
oxidation from being widely adopted. The fabrication of advanced
integrated circuits is not only constrained by a reduced thermal
budget, they it is also facing decreasing limits in the maximum
temperature to which the ICs may be exposed even for short times.
The known prior art of ozone oxidation does not satisfy the more
recent requirements.
[0010] It is felt that the prior art insufficiently utilizes the
advantages of ozone for low temperature oxidation without the use
of plasmas.
[0011] Furthermore, ozone is considered explosive. Safety concerns
are greatly alleviated if the pressure within a chamber containing
ozone is held at a pressure of no more than 20 Torr. Such low
pressures, however, disadvantageously decrease the oxidation
rate.
SUMMARY OF THE INVENTION
[0012] Silicon or other material in a semiconductor substrate is
oxidized by exposing it to a high concentration of ozone at a
relatively low temperature, for example, between 400 and
800.degree. C. in a plasma-free process. Even lower temperatures
are possible. The processing chamber may be maintained at a
relatively low pressure, for example, less than 20 Torr, which low
pressure simplifies the safety requirements. The pressure maybe
even lower, for example, less than 10 Torr or even less than 5
Torr. The invention is particularly useful for growing a gate oxide
or a passivation layer on silicon.
[0013] The ozone may be produced in an ozonator, which includes
several types of apparatus producing ozone from oxygen. The
ozonator should be capable of producing a stream of
oxygen-containing gas that is at least 30% ozone, more preferably
70% ozone, still more preferably at least 80%, and even more
preferably at least 90%.
[0014] The ozone may be combined with a diluent gas such as oxygen
gas or nitrogen.
[0015] The ozone/oxygen mixture may be combined with hydrogen to
increase the oxidation rate. The hydrogen may be essentially pure
hydrogen gas or be a forming gas of H.sub.2/N.sub.2, for example,
having 7% hydrogen.
[0016] The ozone/oxygen mixture may be combined with a nitriding
gas such as nitrous oxide or ammonia so that the oxidation product
is a silicon oxynitride.
[0017] The oxidation may be performed in a rapid thermal processing
(RTP) chamber including an array of incandescent lamps or a scanned
laser source to radiantly heat the substrate.
[0018] The ozone is preferably introduced into the RTP processing
chamber in a first inlet port separate and offset from a second
inlet port supplying the diluent gas of oxygen or nitrogen,
hydrogen, and nitriding gas. Preferably, the two ports are
angularly spaced on the chamber wall with a separation of between
15.degree. and 120.degree., 90.degree. being a preferred
separation. The first inlet port for the ozone preferably includes
a cooled injector that projects into the processing chamber and is
cooled by water or other cooling fluid.
[0019] Alternatively, the oxidation may be performed in a
low-pressure chemical vapor deposition (LPCVD) chamber including an
electrically heated pedestal supporting and heating the substrate
and a showerhead positioned in opposition to the substrate. The
showerhead includes a supply manifold in which the ozone/oxygen gas
and other gases may be mixed and a large number of apertures
between the manifold and the processing chamber over an area
approximately covering the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a cross-sectional view schematically illustrating
a rapid thermal processing (RTP) chamber capable of performing
ozone-based thermal oxidation.
[0021] FIG. 2 is an exploded orthographic view of a water-cooled
gas injector.
[0022] FIG. 3 is a sectioned orthographic view of the injector of
FIG. 2.
[0023] FIG. 4 is a cross-sectional view of the injector of FIG.
2.
[0024] FIG. 5 is an axial plan view of the injector of FIG. 2.
[0025] FIG. 6 is a schematic cross-sectional view of the RTP
chamber taken along its central axis.
[0026] FIG. 7 is a cross-sectional view schematically illustrating
a low-pressure chemical vapor deposition (LPCVD) chamber configured
for ozone-based thermal oxidation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The invention in part concerns the thermal oxidation of
silicon or other materials in the presence of ozone in an RTP
(rapid thermal processing) chamber or in a chamber adapted for
chemical vapor deposition.
[0028] FIG. 1 schematically illustrates in cross section an RTP
chamber 10 described by Ranish et al. in U.S. Pat. No. 6,376,804,
incorporated herein by reference. The chamber 12 is generally
representative of the Radiance RTP chamber available from Applied
Materials, Inc. of Santa Clara, Calif. The RTP chamber 10 includes
a vacuum chamber 12, a wafer support 14 located within the chamber
12, and a lamphead 16 or heat source assembly located on the top of
the chamber 12, all generally symmetrically arranged about a
central axis 18.
[0029] The vacuum chamber 12 includes a chamber body 20 and a
window 22 resting on the chamber body 20. The window 22 is composed
of a material that is transparent to infrared light, for example,
clear fused silica quartz.
[0030] The chamber body 20 may be made of stainless steel and be
lined with a quartz liner (not shown). An annular channel 24 is
formed symmetrically about the central axis 18 near the bottom of
the chamber body 20. The wafer support 14 includes a magnetic rotor
26 placed within the channel 24, a quartz tubular riser 28 resting
on or otherwise coupled to the magnetic rotor 26, and an edge ring
30 resting on the riser 28. The edge ring 30 may be composed of
silicon, silicon-coated silicon carbide, opaque silicon carbide, or
graphite. During processing, a wafer 34 or other substrate rests on
the edge ring 30 in opposition to the window 22. A purge ring 36
outside and below the edge ring 30 supplies a purge gas such as
argon to the back of the wafer 34. A magnetic stator 40 located
externally of the magnetic rotor 26 is magnetically coupled through
the chamber body 20 to the magnetic rotor 26. The rotor 26 may be
mechanically supported on ball bearings or be magnetically
levitated by the magnetic rotor 26. When an unillustrated motor
rotates the magnetic stator 34 about the central axis 18, it
induces rotation of the magnetic rotor 26 and hence of the edge
ring 30 and the supported wafer 34 about the central axis 18.
[0031] The quartz window 22 rests on an upper edge of the chamber
body 20 and an O-ring 44 located between the window 22 and the
chamber body 20 provides a vacuum seal between them. A lamphead
body 46 of the lamphead 16 rests on the window 20. Another O-ring
48 located between the window 20 and lamphead body 46 provides a
vacuum seal between them when a clamp 49 presses together the
chamber body 20 and the lamphead body 46 with the window 22 and
O-rings 40, 48 sandwiched between them. A vacuum-sealed processing
space 50 is thereby formed within the chamber body 20 below the
window 22 and encompasses the wafer 34 to be processed. The wafer
34 is transferred into and out of the processing chamber by means
of an unillustrated wafer port in the sidewall of the chamber body
20, a slit valve selectively sealing the wafer port, a wafer paddle
insertable through the wafer port, and lift pins in a bottom wall
52 of the chamber body 20 which selectively raise the wafer 34
above the edge ring 30 and the paddle. The top surface of the
bottom wall 52 may be coated with a reflective layer to act as a
reflector plate defining one side of a black body cavity 54 on the
backside of the wafer 34.
[0032] The lamphead 16 includes a plurality of lamps 56 loosely
disposed in respective downwardly directly lamp holes 58. The lamps
56 are supported by and electrically powered through electrical
sockets 60. The lamps 56 are preferably incandescent bulbs that
emit strongly in the infrared such as tungsten halogen bulb having
a tungsten filament inside a quartz bulb 62 filled with a gas
containing a halogen gas such as bromine and diluted with an inert
gas to clean the inside of the quartz bulb 62. The upper portion of
each bulb 62 and its socket 60 are potted into its lamp hole 58
with a ceramic potting compound 64, which is relatively porous. The
lamps 56 are located inside the reflective walls of the vertically
oriented cylindrical lamp holes 58 within the lamphead body 46 to
form respective light pipes. The open ends of the lamp holes 58 of
the lamphead body 46 are located adjacent to but separated from the
window 20.
[0033] Interconnected cooling channels 66 are defined within the
lamphead body 40 by upper and lower lamphead chamber walls 68, 70
and cylindrical walls 72 surrounding each of the lamp holes 58 as
well as an exterior side wall 74 of the lamphead body 46. A
recirculating coolant, such as water, introduced into the chambers
66 via an inlet 76 and removed at an outlet 78 cools the lamphead
body 46 and traveling adjacent the lamp holes 58 cools the lamps
56. Baffles may be included to ensure proper flow of the coolant
through the cooling channels 66.
[0034] A thermally conductive gas, such as helium, is supplied from
a pressurized gas source 84 and metered by a mass flow controller
86 to be delivered to the lamphead 16 to facilitate thermal
transfer between the lamps 56 and the cooling channels 66. The
helium is supplied through a port 88 to a manifold 90 formed in
back of the lamp bases between the lamp holes 58 and a lamphead
cover 92. Opening the mass flow controller 86 causes the thermal
transfer gas to flow into the manifold 90 and further flow through
the porous potting compound 64 around the sides of the bulb 62 of
each lamp 56 to cool by heat convectively transferred through the
thermal transfer gas to the cooling water in the channels 66.
[0035] A vacuum pump 100 reduces the pressure within the lamphead
body 46, particularly when the processing chamber 50 within the
chamber 12 is vacuum pumped so that the reduced pressure in the
lamphead body 46 reduces the pressure differential across the
quartz window 20. The vacuum pump 100 is connected to the air
passages in the lamp holes 58 surrounding the lamps 56 through a
port 102 including a valve 104. The pumping of the vacuum pump 100
must be balanced with the supply of helium from the gas source 84
to maintain the desired pressure of helium within the lamphead 16
for promoting thermal transfer.
[0036] Thermal sensors such as seven pyrometers 110 (only two of
which are shown) are supported bythe chamber body 20 and are
optically coupled to light pipes 112 disposed in respective
apertures 114 in the bottom wall 52. The pyrometers 110 detect
respective temperatures or other thermal properties at different
radial portion of the lower surface of the wafer 34 or of the edge
ring 30, as described in U.S. Pat. No. 5,755,511 to Peuse et al.
The pyrometers 110 supply temperature signals to a power supply
controller 116, which controls the power supplied to the infrared
lamps 56 in response to the measured temperatures. The infrared
lamps 56 may be controlled in radially arranged zones, for example,
fifteen zones, to provide a more tailored radial thermal profile to
compensate for thermal edge effects. All the pyrometers 110
together provide signals indicative of a temperature profile across
the wafer 34 to the power supply controller 116, which controls the
power supplied to each of the zones of the infrared lamps 56 in
response to the measured temperature profile.
[0037] The chamber body 20 of the processing chamber 12 includes
two perpendicularly arranged processing gas inlet ports 120, 122
(inlet port 122 is not illustrated in FIG. 1). In use, the pressure
within the process space 50 can be reduced to a sub-atmospheric
pressure prior to introducing a process gas through the gas inlet
ports 120, 122. The process space 50 is evacuated by a vacuum pump
124 pumping through a pump port 126 arranged diametrically opposite
the first inlet port 120. The pumping is largely controlled by a
butterfly valve 128 disposed between the pump port 126 and the
vacuum pump 124. The pressure may be reduced to between about 1 and
160 Torr. However, for reasons to be described below, the chamber
pressure is preferably maintained at less than 20 Torr.
[0038] Although the RTP chamber 10 represents the most prevalent
type of RTP chamber in use today, advanced RTP chambers are being
developed using one or more lasers whose beams are scanned over the
substrate, as has been disclosed by Jennings et al. in U.S. Patent
Application Publication US 2003/0196996 A1, incorporated herein by
reference in its entirety.
[0039] According to one aspect of the invention involving
oxidation, a gas source 130 supplies oxygen gas (O.sub.2) through a
mass flow con troller 122 to an ozonator 134, which converts a
large fraction of the oxygen to ozone gas (O.sub.3). The resultant
oxygen-based mixture of O.sub.2 and O.sub.3 and perhaps some oxygen
radicals O* and ionized oxygen atoms or molecules is delivered
through a process gas supply line 136 to the first inlet port 120
and into the processing chamber 50, The oxygen-based gas reacts
within the processing chamber 50 with the surface of the wafer 34,
which has been heated to a predetermined, preferably low
temperature by the infrared lamps 56. Ozone is a metastable
molecule which spontaneously quickly dissociates in the reaction
O.sub.3.fwdarw.O.sub.2+O* where O* is a radical, which very quickly
reacts with whatever available material can be oxidized. In
general, ozone dissociates on any surface having a temperature
greater than 400.degree. C. although it also dissociates at a lower
rate at lower temperatures.
[0040] The ozonator 134 may be implemented in a number of forms
including a capacitively or inductively coupled plasma or a UV lamp
source. It is preferred that the ozonator be capable of a stream of
gas containing at least 70% ozone, more preferably at least 80%,
and most preferably at least 90%. Even an ozone concentration of at
least 30% would provide advantages over the prior. An capable of
producing the higher ozone concentrations is commercially available
from Iwatami International Corp. of Osaka, Japan as Model
AP-800-LR. Other ozonators and sources of ozone may be used with
the invention.
[0041] At these high ozone concentrations, the wafer need not be
heated very much to achieve relatively high oxidation rates. The
high ozone concentration also allows the ozone partial pressure to
be reduced. Safety rules in place in many countries require that
special procedures and equipment be implemented whenever ozone is
present at pressures of greater than 20 Torr. Below 20 Torr, the
strict rules do not apply. Accordingly, a high ozone fraction
allows the ozone oxidation to be performed at pressures of less
than 20 Torr.
[0042] Highly concentrated ozone maybe used not only to oxidize
bare silicon but may be used in a two-step process. In the first
step, a thin oxide is grown perhaps using only oxygen at a
relatively low temperature. In the second step, concentrated ozone
is used to treat the preexisting oxide film and to increase its
thickness to a reliable level. The concentrated ozone may also be
used to treat and possibly increase the thickness of a metal oxide
film, such as tantalum oxynitride (TaNO). Similarly, high-k
dielectric films, for example, of perovskite material, maybe
treated with concentrated ozone to stabilize them and for other
reasons.
[0043] One problem with ozone oxidation is that a high temperature,
for example, above 400.degree. C., of any surface to which the
ozone is exposed promotes the dissociation of ozone before it
reaches the hot wafer surface. As a result, the ozone should be
maintained relatively cool except adjacent the wafer being
oxidized. An RTP chamber is advantageous for ozone oxidation
because it may be considered to be a cold-wall reactor in which the
chamber walls are typically much cooler than the radiantly heated
wafer. In contrast, in a hot-wall reactor such as an annealing
furnace, the wafer temperature is no more than the temperature of
the surrounding furnace wall or liner. Although high wafer
temperatures are achievable in RTP chambers, a sidewall 138 of the
processing chamber 50 and the window 22 are typically maintained at
much lower temperatures, particularly if the thermal process
performed over a relatively short period. Nonetheless, even the
walls of an RTP chamber become somewhat warm and any ozone adjacent
the warm walls is likely to dissociate far from the wafer and
perhaps oxidize the chamber wall rather than the wafer.
[0044] To reduce the effect of a warm chamber, the ozone is
supplied into the chamber through an injector 140 which projects
from the chamber sidewall 138 towards the center 18 of the
processing chamber 50 parallel and above the surface of the wafer
34. In one embodiment, the nozzle tip of the injector 140 is
radially spaced about 2.5 cm outwardly of the edge of the wafer 34.
Furthermore, the injector 140 is preferably water cooled or
otherwise temperature controlled by a fluid.
[0045] One embodiment of the injector 140 is illustrated in the
orthographic view of FIG. 2, the sectioned orthographic view of
FIG. 3, and the cross-sectional view of FIG. 4. A base 142 can be
screwed to the exterior of the chamber sidewall 138 and sealed to
it in a configuration having an tubular body 144 of a length of
about 5cm projecting into the processing chamber 50. A washer 146
is welded to the end of the tubular body 144 to seal the end of the
tubular body 144 except for an injector nozzle 148 penetrating
through and welded to the hole of the washer 146. A plan view of
the tubular body 144 shown in FIG. 5 is taken along line 5-5 of
FIG. 4 along the axis of the tubular body 144. For clarity, the
views of FIGS. 3, 4, and 5 omit the washer 146.
[0046] A central gas line 150 is machined in the tubular body 144
and terminates at the injector nozzle 148 at its distal end. A
supply tube 152 is fixed to thebase 142 and communicates with the
central gas line 150. A gland 154 captures the end of the supply
tube 152 and is threaded onto the gas supply line 136 from the
ozonator 134 of FIG. 1. Two circular axially extending liquid lines
158, 160 are bored into the tubular body 144 offset from the tube's
central axis but stop before reaching the bottom of the base 142.
Instead, two obliquely oriented fluid lines 162, 164 are bored from
the outside of the base 142 to meet with the axial liquid lines
158, 160 on their inner ends and to be mated with corresponding
tubes and glands on their outer ends and thereby be coupled by two
recirculating chilling lines 166, 168, illustrated in FIG. 1, to
the two ports of a chiller 170. The chiller 170 either supplies
cold water or recirculates cooling water or other cooling liquid or
fluid refrigerant through the injector 140 to cool it and the
injected ozone.
[0047] Returning to FIGS. 2-5, two axially extending, arc-shaped
apertures 180, 182 are machined in the distal portion of the
tubular body 144 to be respectively connected to the two axial
liquid lines 158, 160. A septum 184 separates the two arc-shaped
apertures 180, 182, and the distal end of the gas line 150 is
formed within the septum 184. An annular ledge 186 is machined into
the distal end of the tubular body 144 at a level slightly above
the end surface of the septum 184. The washer 146 rests on the
ledge 186 and is welded to the outer portion of the tubular body
144 and to the injector nozzle 148. Thereby, cooling water supplied
by one liquid line 158 flows through one arc-shaped aperture 180
surrounding almost half of the distal portion of the gas supply
line 160, flows through the gap between the end surface of the
septum 184 and the washer 146 and into the other arc-shaped
aperture 182 surrounding most of the other half of the distal
portion of the tubular body 144 before flowing out through the
other liquid line 160.
[0048] The liquid-chilled injector 140 cools the ozone and injects
it closer to the wafer 34, thereby decreasing the likelihood of
premature dissociation and oxidation of other chamber parts. It
also tends to cool the chamber wall 138 in its immediate
vicinity.
[0049] A cross-sectional view of FIG. 6 taken along the chamber
axis 18 schematically illustrates the RTP chamber 10 in the
vicinity of the processing space 50. The second gas inlet port 122
may be located 90.degree. about the axis 18 from the first gas
inlet port 120 supplying the ozone through the water-chilled
injector 140. The angular separation, preferably in the range of
15.degree. and 115.degree., between the two processing gas inlets
120, 122 delays the mixing of the ozone with the other gases. The
injector 140 for the ozone is located downstream from the inlet
port 122 for the other gases as referenced to the rotation
direction of the wafer 34. The second gas inlet 120 is
diametrically disposed from the pump port 126 and placed above the
unillustrated wafer port in the chamber wall 138. Diluent,
nitriding, and hydrogen gases are supplied through the second gas
inlet port 122 so as to reduce any back pressure in the injector
140 and in the gas supply line 136 supplying the ozone to it. The
second gas inlet 122 does not require cooling so that it may be
conventionally formed of a gas supply line terminating in a recess
190 in the chamber wall 138, thus not interfering with the wafer
port or its slit valve.
[0050] Gaseous hydrogen from a gas source 192 is metered by a mass
flow controller 194 into the processing chamber 50 via the second
gas inlet 122 to increase the oxidation rate, if desired, in a
process similar to in situ steam generation. The hydrogen gas may
either be essentially pure hydrogen or be part of a mixture, such
as a forming gas having about 7% hydrogen and 93% nitrogen. It has
been found that pure hydrogen supplied with the highly concentrated
ozone to a fraction of 33 provides the desired high oxidation rate.
It is believed that hydrogen increases the concentration of oxygen
radicals.
[0051] Gaseous oxygen may be supplied from the oxygen gas source
130 through another mass flow controller 198 to the second gas
inlet 122 to act as a diluent to reduce the oxidation rate, which
may be desired for very thin gate oxides. While it is possible for
the ozonator 134 to pass additional gaseous oxygen to the first gas
inlet 120, the additional flow would increase the back pressure in
the injector 140 and its supply line. An alternative diluent gas is
nitrogen supplied from a gas source 200 through a mass flow
controller 202 to the second gas inlet 122. The nitrogen is also
used to purge the processing chamber 50. Other diluent gases may be
used, for example, argon or helium.
[0052] Other processing gases may be used. For example, nitrous
oxide (N.sub.2O) supplied from a gas source 204 through a mass flow
controller 206 acts as a nitriding gas. The nitrous oxide may be
used when a film of silicon oxynitride is desired as the oxidation
product. It may also be supplied separately from the ozone to
effect a forming anneal. Gaseous ammonia (NH.sub.3) may
alternatively be used as the nitriding gas, or other nitriding
gases may be substituted.
[0053] Although the gas distributions from both the first and
second gas inlets 120, 122 are non-uniform across the wafer 34, the
wafer 34 is rotating about the axis 18 fast enough to time-average
out the non-uniformity.
[0054] The RTP chamber illustrated in FIG. 1 is illustrative only.
Other RTP chambers maybe used with the invention. Other types of
thermal processing equipment may be also use. For example, Jennings
et al. describe in U.S. Patent Application Publication US
2003/0196996 a thermal processing apparatus that scans a narrow
beam of laser light across the surface of the wafer.
[0055] High-concentration ozone oxidation has been verified in an
RTP chamber. The resultant oxide films have been observed to
exhibit many fewer interfacial defects, presumably arising from
dangling bonds, than oxide grown with oxygen radicals formed in a
steam generator. Ozone oxidation has been observed at wafer
temperatures down to 600.degree. C. and reasonable oxidation rates
should occur at lower temperatures, for example, down to
400.degree. C. However, 800.degree. C. appears more workable at the
present time. Wafer temperatures of 1000.degree. C. produce very
low defects densities. It is contemplated that future generations
of integrated circuits will require oxidation temperatures even
lower than 400.degree. C., perhaps even room temperature. Chamber
pressures of between 3 and 5.5 Torr have been used, far below the
safety limit of 20 Torr. Even lower pressures maybe used.
Ozone-based oxidation with 33% hydrogen has been observed to
produce a 2 nm oxide thickness for 1 minute of processing. Ozone
flow rates need to be maximized to achieve high oxidation
rates.
[0056] The relatively low process temperatures achievable with
high-concentration ozone allows the use of a chamber resembling an
LPCVD (low pressure chemical vapor deposition) chamber 210,
schematicallyillustrated in cross section in FIG. 7. A vacuum
chamber 212 is pumped to, for example, less than 10 Torr by the
vacuum pump 124 through the pump port 126 formed in an annular
pumping manifold 214 formed near its bottom wall. A pedestal heater
216 is configured to a support the wafer 34 across a processing
space 218 in opposition to a showerhead 220 in the upper wall of
the chamber 212. A supply gas manifold 222 is formed on top of the
chamber 210 to receive the highly concentrated ozone through one
gas inlet port 224 and the steam generating gas H.sub.2 through a
second gas inlet port 216. If required, a diluent gas, such as
oxygen or nitrogen or other nitriding gas may also be controllably
supplied, either through the second gas inlet poit 226 or through
separate ones. The gases mix and equilibrate in the gas supply
manifold 222 before passing through a large number, typically at
least 100, of small apertures 228 formed through the showerhead 220
in an area overlying the wafer 34. The processing space 218 between
the showerhead 220 and the wafer 34 may have a thickness of about
500 mils (1.2 cm) in comparison to a wafer diameter of 200 or 300
mm. The pedestal heater 216 includes a resistive heater 230 powered
by an electrical power supply 232 to heat the pedestal heater 216
to a relatively low temperature, for example, 400 to 700.degree.
C., needed for high-concentration ozone oxidation. Other types of
electrical heating are known, such as RF susceptors. The
temperatures of the showerhead 220 and the manifold 222 need to be
maintained at relatively low levels, for example, less than
400.degree. C. and preferably substantially lower, by for example
water cooling to prevent the premature dissociation of the
ozone.
[0057] The planar geometry made possible in the LPCVD chamber 210
by the narrow processing space 218, the wide showerhead 222, and
the annular pumping manifold 214 provides good uniformity for
ozone-based oxidation without the need to rotate the pedestal 216.
The high-concentration of ozone allows relatively low oxidation
temperatures provided by a simple resistivelyheated pedestal. As a
result, the ozone-based oxidation may be performed in a relatively
simple and inexpensive chamber and not impose particularly high
temperatures on the wafer 34.
[0058] Although oxidation of silicon is the most widespread use of
the invention, the invention is not so limited and different
aspects of the invention can be applied to oxidizing other
materials.
[0059] The gas injector of the invention is not limited to
injecting ozone or other oxidizing gases and may be used with other
types of CVD.
* * * * *