U.S. patent application number 11/014104 was filed with the patent office on 2005-05-19 for method and apparatus for providing and integrating a general metal delivery source (gmds) with atomic layer deposition (ald).
Invention is credited to Sneh, Ofer.
Application Number | 20050103269 11/014104 |
Document ID | / |
Family ID | 32297256 |
Filed Date | 2005-05-19 |
United States Patent
Application |
20050103269 |
Kind Code |
A1 |
Sneh, Ofer |
May 19, 2005 |
Method and apparatus for providing and integrating a general metal
delivery source (GMDS) with atomic layer deposition (ALD)
Abstract
A General Metal Delivery Source (GMDS) for delivery of volatile
metal compounds in gaseous form to processing apparatus has a
reaction chamber holding a solid metal source material and
connecting to the processing apparatus, and having an outlet for
provision of the volatile metal compounds, a source heater coupled
to the reaction chamber for heating said solid metal source
material, a gas source for providing a reactive gas, a gas delivery
conduit from the gas source to the reaction chamber for delivering
gas species to the reaction chamber; and a plasma generation
apparatus coupled to the gas delivery conduit. The plasma
generation apparatus dissociates reactive gas molecules providing
monatomic reactive species to the reaction chamber, and the
monatomic reactive species combine with metal from the heated solid
metal source material forming the volatile metal compounds.
Inventors: |
Sneh, Ofer; (Broomfield,
CO) |
Correspondence
Address: |
CENTRAL COAST PATENT AGENCY
PO BOX 187
AROMAS
CA
95004
US
|
Family ID: |
32297256 |
Appl. No.: |
11/014104 |
Filed: |
December 15, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11014104 |
Dec 15, 2004 |
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10295614 |
Nov 14, 2002 |
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6863021 |
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Current U.S.
Class: |
118/715 |
Current CPC
Class: |
C23C 16/4488 20130101;
C23C 16/405 20130101 |
Class at
Publication: |
118/715 |
International
Class: |
C23C 016/00 |
Goverment Interests
[0001] This invention was made with government support under
contract F33615-99-C-2961 awarded by the US Army Space and Missile
Defense Command. The United States Government may therefore have
certain rights to this invention.
Claims
What is claimed is:
1. A general metal delivery source for delivery of volatile metal
compounds in gaseous form to processing apparatus, comprising: a
reaction chamber holding a solid metal source material and
connecting to the processing apparatus, and having an outlet for
delivery of the volatile metal compounds to said processing
apparatus; a source heater within the reaction chamber for heating
said solid metal source material; a gas source for providing a
reactive gas; a gas delivery conduit from the gas source to the
reaction chamber for delivering gas species to the reaction
chamber; and a dissociation apparatus coupled to the gas delivery
conduit; wherein the dissociation apparatus dissociates the
reactive gas molecules providing at least a monatomic reactive
species to the reaction chamber, and the monatomic reactive species
combine with metal from the heated solid metal source material
forming the volatile metal compounds.
2. The general metal delivery source of claim 1 wherein the gas
delivery conduit and the reaction chamber comprise a common quartz
tubing.
3. The general metal delivery source of claim 1 wherein the gas
source is valved in a maimer that rapid pulses of reactive gas are
provided to the reaction chamber, providing thereby rapid pulses of
the volatile metal compounds at the reaction chamber outlet.
4. The general metal delivery source of claim 1 wherein the
dissociation apparatus comprises a plasma generator.
5. The general metal delivery source of claim 1 wherein the plasma
generation apparatus comprises a helical resonator.
6. The general metal delivery source of claim 1 wherein the solid
metal source material is Tantalum and the reactive gas is
Chlorine.
7. A method for providing volatile metal compounds at an outlet of
a reaction chamber, comprising steps of: (a) flowing a reactive gas
from a gas source into a gas delivery conduit connected to a heated
reaction chamber holding a solid metal source; (b) striking a
plasma in the flowing reactive gas, thereby forming at least a
monatomic species of the reactive gas; (c) forming the volatile
metal compound in the reaction chamber through chemical reaction
between the heated metal source and at least the monatomic reactive
gas; and (d) delivering the volatile metal compound at an outlet of
the reaction chamber.
8. The method of claim 7 wherein the reaction chamber and the gas
delivery conduit comprise a common quartz tubing.
9. The method of claim 7 wherein the gas source is valved in a
manner that rapid pulses of reactive gas are provided to the
reaction chamber, providing thereby rapid pulses of the volatile
metal compounds at the reaction chamber outlet.
10. The method of claim 7 wherein the plasma generation apparatus
comprises a helical resonator.
11. The method of claim 7 wherein the solid metal source material
is Tantalum and the reactive gas is Chlorine.
12. A processing system comprising: a heated hearth for supporting
a substrate in a process deposition chamber; apparatus for
exchanging substrates for sequential processing; an inlet port for
delivering a volatile metal compound as a precursor to the coating
chamber; and a general metal delivery source connected to the inlet
port, the general metal delivery source comprising: a reaction
chamber holding a solid metal source material and having an outlet
for delivery of the volatile metal compounds to said coating
chamber; a heater within the reaction chamber for heating said
solid metal source material; a gas source for providing a reactive
gas; a gas delivery conduit from the gas source to the reaction
chamber for delivering gas species to the reaction chamber; and a
plasma generation apparatus coupled to the gas delivery conduit;
wherein the plasma generation apparatus dissociates reactive gas
molecules, providing at least a monatomic reactive species to the
reaction chamber, and the monatomic reactive species combine with
metal from the heated solid metal source material forming the
volatile metal compounds delivered to the coating chamber.
13. The processing system of claim 12 wherein the gas delivery
conduit and the reaction chamber comprise a common quartz
tubing.
14. The processing system of claim 12 wherein the gas source is
valved in a manner that rapid pulses of reactive gas are provided
to the reaction chamber, providing thereby rapid pulses of the
volatile metal compounds at the reaction chamber outlet.
15. The processing system of claim 12 wherein the plasma generation
apparatus comprises a helical resonator.
16. The processing system of claim 12 wherein the solid metal
source material is Tantalum and the reactive gas is Chlorine.
17. The processing system of claim 12 configured for and dedicated
to chemical vapor deposition.
18. The processing system of claim 12 configured for and dedicated
to atomic layer deposition.
19. A chemical vapor deposition (CVD) system comprising: an inlet
port for delivering a volatile metal compound as a precursor for
CVD processing; and a general metal delivery source connected to
the inlet port, the general metal delivery source comprising a
reaction chamber holding a solid metal source material and having
an outlet for delivery of the volatile metal compounds to said
coating chamber, a heater within the reaction chamber for heating
said solid metal source material, a gas source for providing a
reactive gas, a gas delivery conduit from the gas source to the
reaction chamber for delivering gas species to the reaction
chamber, and a dissociation apparatus coupled to the gas delivery
conduit; wherein the plasma generation apparatus dissociates
reactive gas molecules, providing at least a monatomic reactive
species to the reaction chamber, and the monatomic reactive species
combine with metal from the heated solid metal source material
forming the volatile metal compounds delivered to the inlet
port.
20. An atomic layer deposition (ALD) system comprising: an inlet
port for repeated delivery of a volatile metal compound as a
precursor for ALD processing; and a general metal delivery source
coupled to the inlet port, the general metal delivery source
comprising a reaction chamber holding a solid metal source material
and having an outlet for delivery of the volatile metal compounds
to said coating chamber, a heater within the reaction chamber for
heating said solid metal source material, a gas source for
providing a reactive gas, a gas delivery conduit from the gas
source to the reaction chamber for delivering gas species to the
reaction chamber, and a dissociation apparatus coupled to the gas
delivery conduit; wherein the plasma generation apparatus
dissociates reactive gas molecules, providing at least a monatomic
reactive species to the reaction chamber, and the monatomic
reactive species combine with metal from the heated solid metal
source material forming the volatile metal compounds delivered to
the inlet port.
21. An apparatus for providing volatile metal compounds at an
outlet of a reaction chamber, comprising: a means for flowing a
reactive gas from a gas source into a gas delivery conduit
connected to a heated reaction chamber holding a solid metal
source; a means for striking a plasma in the flowing reactive gas,
thereby forming at least a monatomic species of the reactive gas; a
means for forming the volatile metal compound in the reaction
chamber through chemical reaction between the heated metal source
and at least the monatomic reactive gas; and a means for delivering
the volatile metal compound at an outlet of the reaction chamber.
Description
FIELD OF THE INVENTION
[0002] The present invention is in the field of CVD processes
including Atomic Layer Deposition (ALD), and pertains more
particularly to methods and apparatus for preparing at
point-of-process and delivering contaminant-free metal precursors
in such processes.
BACKGROUND OF THE INVENTION
[0003] Requirements for ever-thinner thin film deposition, improved
uniformity over larger surfaces, and higher production yields have
been, and still are, the driving forces behind emerging
technologies developed by the research community and commercialized
by equipment manufactures for coating wafers to make electronic
devices. As these devices become smaller and faster, the need for
improved uniformity and better defined layer thickness, as well as
film properties such as conductivity and the like, rises
dramatically.
[0004] Various technologies well known in the art exist for
applying thin films to wafers or other substrates in manufacturing
steps for integrated circuits (ICs). Among the more established
technologies available for applying thin films, Chemical Vapor
Deposition (CVD) is an often-used commercialized processes. Atomic
Layer Deposition (ALD), a variant of CVD, is now emerging as a
potentially superior method for achieving uniformity, excellent
step coverage, and cost effective scalability to substrate size
increase. ALD however, can exhibit a generally lower deposition
throughput (typically <100 {haeck over (A)}/min) than CVD, but
is suitable for ultrathin films, less than typically 100 {haeck
over (A)}.
[0005] CVD is a flux-dependent technique requiring specific and
uniform substrate temperature and stringent uniformity of
precursors (chemical species) flux in order to produce a desired
layer with uniform thickness and properties on a substrate surface.
These stringent requirements become more challenging as substrate
size increases, sometimes dictating additional chamber design
complexity and manifold complications to sustain adequate film
uniformity and properties. Another problem in CVD coating, wherein
reactants and the products of reaction coexist in a close proximity
to the deposition surface, is the probability of inclusion of
reaction products and other contaminants in each deposited layer.
Still further, highly reactive precursor molecules contribute to
homogeneous gas phase reactions that can produce unwanted
particles, which are detrimental to film quality and device
performance.
[0006] Another critical area of thin film technology is the ability
of a system to provide a high degree of uniformity and thickness
control over a complex topology, referred to as step coverage. In
the case of CVD, step-coverage typically exceeds typical physical
vapor deposition (PVD) performance. However, certain disadvantages
of CVD make ultrathin CVD films inadequate for many emerging
critical semiconductor applications. For example, film initiation
via nucleation deems CVD films discontinuous and practically
useless for many sub 50 {haeck over (A)} needs. Likewise, coating
high aspect ratio features with conformal CVD films while
maintaining film quality and adequate throughput is difficult.
[0007] ALD, although at present a slower process than CVD,
demonstrates a remarkable ability to deposit uniform, ultra-thin
films over complex topology. This robust and inherent property
comes from the flux independence of ALD. In addition, ALD
implementation requires time and space separated molecular
precursors which in turn circumvents gas phase reactions and
therefore enables utilization of highly reactive precursor.
Accordingly, ALD process temperatures are typically and
advantageously lower than typical conventional CVD process
temperatures.
[0008] ALD processes are executed by a series of self saturating
surface processes. Generally, ALD is a process wherein conventional
CVD processes are divided into single-monolayer depositions, in
which each separate deposition step theoretically goes to
saturation at a single molecular or atomic monolayer thickness and
self-terminates when the layer formation occurs on the surface of a
material. Generally, in the standard CVD process, the precursors
are fed simultaneously into a reactor. In an ALD process the
precursors are introduced into the reactor separately at different
steps. Typically the precursors are introduced separately by
alternating the flow of the precursor to combine with a carrier gas
being introduced into the reactor while coexistence of the
precursors in the reactor is suppressed by appropriately purging or
evacuating the reactor in between successive introduction of
precursors.
[0009] For example, when ALD is used to deposit a thin film layer
on a material layer, such as a semiconductor substrate, saturating
at a single molecular or atomic layer of thickness results in a
formation of a pure desired film and eliminates the extra atoms
that comprise the molecular precursors (or ligands). By the use of
alternating precursors, ALD allows for single layer growth per
cycle so that much tighter thickness controls can be exercised to
deposit an ultra thin film. Additionally, ALD films may be grown
with continuity with thickness that is as thin as a monolayer (3-5
Angstroms). This capability is a unique characteristic of ALD films
that makes them superior candidates for applications that require
ultrathin films. A good reference work in the field of Atomic Layer
Epitaxy, which provides a discussion of the underlying concepts
incorporated in ALD, is Chapter 14, written by Tuomo Suntola, of
the Handbook of in Crystal Growth, Vol. 3, edited by D. T. J.
Hurle, .COPYRGT. 1994 by Elsevier Science B. V. The Chapter title
is "Atomic Layer Epitaxy". This reference is incorporated herein by
reference as background information.
[0010] The unique mechanism of film formation provided by ALD
offers several advantages over previously discussed technologies.
One advantage derives from the flux-independent nature of ALD
contributing to some relaxed reactor design-rules and scaling.
Device technology is progressing at a rapid rate driving
improvements of commercial deposition-equipment technology. While
industry road maps for advanced and future device requirements are
fairly well established, some critical applications cannot be
realized by existing process technologies. For example, it is
desired that commercial viability be attained for high quality
dielectric laminate processes used in devices such as dielectric
memory capacitors, RF products, "systems on a chip" applications,
and advanced gate dielectrics with metal oxide gates.
[0011] ALD processes have often relied on solid source materials
that are heated (e.g. a Knudsen thermal vaporizer source from a low
vapor pressure Metal halide solid) to produce adequate precursor
exposure. However, high temperature sources dictate that all
manifolds located downstream to the hot sources are maintained at
(or above) the source temperature. These temperatures and their
maintenance are trivial to maintain throughout passive manifold
components such as tubings, diffusers etc. However, valves that are
necessary to produce time controlled pulsed introduction of
precursors, which are key for ALD, are typically limited in service
temperature, especially when corrosive precursors are involved.
Accordingly, usage of many desired solid precursors poses
insurmountable performance and reliability limitations on ALD
manifolds deeming them inadequate for semiconductor manufacturing.
Although several solid precursor delivery systems have been
proposed and are implemented with more or less success in research
and development, there are no known systems, thus far, that are
properly suitable for high volume manufacturing. Existing systems
are typically maintenance intensive, low throughput, contaminating
and inefficient.
[0012] To overcome the deficiencies of conventional heated solid
sources a General Metal precursor Delivery System (GMDS) technique
is described in this patent. This source is relatively generic and
capable of pulse delivering a variety of metal precursor into ALD
reactors. Preferably, GMDS is implemented by an embodiment that
maintains critical manifold components such as valves at
temperatures that are compatible with low maintenance operation.
Additionally, the GMDS is capable of providing high fluxes of low
vapor pressure precursors. Such a system may be integrated with ALD
deposition systems to enhance their capabilities.
SUMMARY OF THE INVENTION
[0013] In a preferred embodiment of the present invention a general
metal delivery source for delivery of volatile metal compounds in
gaseous form to a processing apparatus is provided, comprising a
reaction chamber holding a solid metal source material and
connecting to the processing apparatus, and having an outlet for
delivery of the volatile metal compounds to said processing
apparatus, a source heater within the reaction chamber for heating
said solid metal source material, a gas source for providing a
reactive gas, a gas delivery conduit from the gas source to the
reaction chamber for delivering gas species to the reaction
chamber, and a dissociation apparatus coupled to the gas delivery
conduit. The general metal delivery source is characterized in that
the dissociation apparatus dissociates the reactive gas molecules
providing at least a monatomic reactive species to the reaction
chamber, and the monatomic reactive species combine with metal from
the heated solid metal source material forming the volatile metal
compounds.
[0014] In some preferred embodiments the gas delivery conduit and
the reaction chamber comprise a common quartz tubing. Also in some
preferred embodiments the plasma generation apparatus comprises a
helical resonator. In some applications the solid metal source
material is Tantalum and the reactive gas is Chlorine. The gas
source in some embodiments may be valved in a manner that rapid
pulses of reactive gas are provided to the reaction chamber,
providing thereby rapid pulses of the volatile metal compounds at
the reaction chamber outlet. In some embodiments the dissociation
apparatus comprises a plasma generator.
[0015] In another aspect of the invention a method for providing
volatile metal compounds at an outlet of a reaction chamber is
provided, comprising the steps of (a) flowing a reactive gas from a
gas source into a gas delivery conduit connected to a heated
reaction chamber holding a solid metal source; (b) striking a
plasma in the flowing reactive gas, thereby forming monatomic
species of the reactive gas; (c) forming the volatile metal
compound in the reaction chamber through chemical reaction between
the heated metal source and the monatomic reactive gas; and (d)
delivering the volatile metal compound at an outlet of the reaction
chamber.
[0016] In some preferred embodiments the reaction chamber and the
gas delivery conduit comprise a common quartz tubing. Also in some
preferred embodiments the plasma generation apparatus comprises a
helical resonator.
[0017] In some applications the solid metal source material is
Tantalum and the reactive gas is Chlorine. Further, the gas source
may be valved in a manner that rapid pulses of reactive gas are
provided to the reaction chamber, providing thereby rapid pulses of
the volatile metal compounds at the reaction chamber outlet.
[0018] In yet another aspect of the invention a processing system
is provided, comprising a heated hearth for supporting a substrate
in a coating chamber, apparatus for exchanging substrates for
sequential processing, an inlet port for delivering a volatile
metal compound as a precursor to the coating chamber; and a general
metal delivery source connected to the inlet port, the general
metal delivery source comprising: a reaction chamber holding a
solid metal source material and having an outlet for delivery of
the volatile metal compounds to said coating chamber, a heater
within the reaction chamber for heating said solid metal source
material, a gas source for providing a reactive gas, a gas delivery
conduit from the gas source to the reaction chamber for delivering
gas species to the reaction chamber, and a plasma generation
apparatus coupled to the gas delivery conduit. The plasma
generation apparatus dissociates reactive gas molecules, providing
at least a monatomic reactive species to the reaction chamber, and
the monatomic reactive species combine with metal from the heated
solid metal source material forming the volatile metal compounds
delivered to the coating chamber.
[0019] In some preferred embodiments the gas delivery conduit and
the reaction chamber comprise a common quartz tubing. Also in some
preferred embodiments the plasma generation apparatus comprises a
helical resonator. In some applications the solid metal source
material is Tantalum and the reactive gas is Chlorine.
[0020] In some preferred embodiments the gas source is valved in a
manner that rapid pulses of reactive gas are provided to the
reaction chamber, providing thereby rapid pulses of the volatile
metal compounds at the reaction chamber outlet. Also in some
preferred embodiments the system may be configured for and
dedicated to chemical vapor deposition, or in other embodiments for
atomic layer deposition.
[0021] In yet another aspect of the invention a chemical vapor
deposition (CVD) system is provided, comprising an inlet port for
delivering a volatile metal compound as a precursor for CVD
processing, and a general metal delivery source connected to the
inlet port, the general metal delivery source comprising a reaction
chamber holding a solid metal source material and having an outlet
for delivery of the volatile metal compounds to said coating
chamber, a heater within the reaction chamber for heating said
solid metal source material, a gas source for providing a reactive
gas, a gas delivery conduit from the gas source to the reaction
chamber for delivering gas species to the reaction chamber, and a
dissociation apparatus coupled to the gas delivery conduit. Plasma
generation apparatus dissociates reactive gas molecules, providing
at least a monatomic reactive species to the reaction chamber, and
the monatomic reactive species combine with metal from the heated
solid metal source material forming the volatile metal compounds
delivered to the inlet port.
[0022] In still another aspect of the invention an atomic layer
deposition (ALD) system is provided, comprising an inlet port for
repeated delivery of volatile metal compound as a precursor for ALD
processing, and a general metal delivery source coupled to the
inlet port, the general metal delivery source comprising a reaction
chamber holding a solid metal source material and having an outlet
for delivery of the volatile metal compounds to said coating
chamber, a heater within the reaction chamber for heating said
solid metal source material, a gas source for providing a reactive
gas, a gas delivery conduit from the gas source to the reaction
chamber for delivering gas species to the reaction chamber, and a
dissociation apparatus coupled to the gas delivery conduit. The
plasma generation apparatus dissociates reactive gas molecules,
providing at least a monatomic reactive species to the reaction
chamber, and the monatomic reactive species combine with metal from
the heated solid metal source material forming the volatile metal
compounds delivered to the inlet port.
[0023] In embodiments of the invention taught in enabling detail
below, for the first time a general metal delivery source is
provided that can deliver, from solid sources, volatile precursors
bearing the metal, or in some cases non-metal elements, for a wide
variety of processes
BRIEF DESCRIPTION OF THE DRAWINGS FIGURES
[0024] FIG. 1 is a sectioned view of a plasma-based General Metal
Delivery System (GMDS) according to an embodiment of the present
invention.
[0025] FIG. 2 is a block diagram illustrating the GMDS of FIG. 1
connected to an ALD reactor according to an embodiment of the
present invention.
[0026] FIG. 3 is a process flow diagram illustrating basic process
steps using tantalum, chlorine, and argon in a Ta.sub.2O.sub.5 ALD
process according to an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] Solid metal source materials are being considered and
studied for a variety of film applications, such as insulators
(metal oxides), metal nitride and metal films. These efforts are
limited in execution because metal halide sources are desired, but
volatile halide metal sources are rare. Some metal organic liquid
sources have good volatility, but may or will provide carbon
contamination by parasitic incorporation into the film. Liquid
metal-organic sources may also be difficult to handle safely,
although industry uses them with the added cost of specialized
containment practices.
[0028] Apparatuses are used in CVD that deliver vapors from liquid
delivery lines and evaporate the liquid sources. These apparatuses
apply liquid delivery lines and evaporate the liquid in metered
fashion through a heatable nozzle or a heatable porous glass frit.
These delivery schemes are or may not be suitable for commercial
ALD applications due to a long time response.
[0029] Most metal halide precursors are highly corrosive. If these
materials are to be pulsed through conventional pneumatic or
solenoid valves at the temperature that is necessary to sustain
practical vapor pressure of these solid precursors, the valves may
substantially corrode leading to deterioration and breakdown. In
addition, limitation of ultra high purity (UHP) valves
specifications into the temperature range below .about.120.degree.
C. pose significant restriction over attainable vapor pressure of
non-volatile compounds.
[0030] ALD relies on pulsed flow of the precursors into the film
deposition chamber. The precursors must be introduced for short
periods of time. Corrosive solids with low vapor pressure must
typically be heated to high temperatures to achieve adequate vapor
pressures. The vapors are transferred through heatable lines into
the reaction chambers. These materials will clog and/or corrode any
type of valve. Therefore, creating flow pulses of these materials
is a technical challenge.
[0031] A solution for the delivery of low vapor pressure materials
is described in general by T. Suntola, Handbook of Crystal Growth
3, edited by D. T. J. Hurle, Elsevier, 1994, pp. 616-621, which is
incorporated into the present specification by reference. The
figure in this reference on p. 619 indicates source(s) that can
provide a heated (Knudsen cell-like) solid metal precursor source
(e.g. TaCl.sub.5). These ALD sources are controlled by a single low
temperature UHP valve that is capable of routing an inert gas into
the heated reactant source(s) when the source is at the "ON" state.
Advantageously, the source is using a single valve that is located
upstream to the Knudsen cell and can be maintained at relatively
lower temperatures. The "OFF" state of the source is maintained by
a side loop of inert gas flowing to the outlet of the Knudsen cell.
Since the inlet to the Knudsen cell is connected to a vacuum pump,
back flow of inert gas entering the cell from the outlet is
designed to prevent downstream flow of chemical by reversing the
flow and delivering the chemical into the vacuum pump. An
appropriately selected set of capillaries is set to maintain
material loss during the "OFF" state at minimum. This source was
widely implemented in research and development and has been capable
to deliver metal precursors requiring temperatures in excess of
250.degree. C. Unfortunately, under prolonged utilization that is
necessary in the production environment, it is quite difficult to
maintain conditions that prevent condensation and solidification of
the solid material and subsequent disadvantageous clogging of the
cold valve. This problem is mainly related to back-diffusion of
vapor into the stagnant leg (from the valve to the Knudsen cell)
when the source is at the "OFF" state. This leg is dictated by the
need to provide a thermal barrier between a hot Knudsen-cell and
the back capillary that are typically placed within a vacuum
enclosure and the inert gas valve that is typically placed outside
the vacuum and maintained at substantially cooler temperatures.
This limitation is believed to be generic to the prior-art source
and not to specific engineering of a particular system.
Accordingly, maintaining the source at optimum performance dictated
overhaul type maintenance with rather impractically frequent
schedule. In addition, frequent vacuum line (the backstreaming line
to the vacuum pump) clogging, typically makes this source even more
maintenance intensive. Finally, creeping of solid material into the
inlet line induces deterioration of the "OFF" state and the ALD
process. The deterioration of the "OFF" state was almost immediate
and was blamed for progressively increased CVD component in ALD
films.
[0032] A substantial design improvement and precursor delivery
methodology must be formulated and implemented. Such a general
metal deposition source (GMDS) is provided by the inventor and
disclosed in enabling detail below. The GMDS generates metal
precursors at the point of use. The challenge of generating
time-controlled pulses of non-volatile metal precursors is
addressed by the unique design of the GMDS that is described below.
The basic design is illustrated in the more detailed drawings
described below.
[0033] FIG. 1 is a sectioned view of a plasma-enhanced GMDS 25
according to an embodiment of the present invention. In GMDS 25
solid metal source 33 is combined with one or more elements
introduced as gases. In a preferred embodiment atoms or molecules
of the introduced elements are substantially dissociated or
otherwise excited prior to introduction to increase reactivity.
[0034] As an example for the use of GMDS 25, production of volatile
TaCl.sub.5 is described, using a solid tantalum source and
substantially dissociated Chlorine. GMDS 25 in this example
generates volatile TaCl.sub.5 at the point of use, beyond conduit
51 through fitting 53. The generation of timed pulses of the
reactive metal precursors is induced by a timed generation of
dissociated chlorine. The timed generation of reactive chlorine is
produced upstream to the source where cooler manifolds and valves
are operating at optimum conditions, eliminating the need to
operate valves at high temperatures. A plasma generator component
27 powered by a high-voltage, high frequency power supply 42 is
provided for the purpose of maintaining a constant plasma source
that breaks Cl.sub.2 molecules into more reactive Cl atoms for the
purpose of obtaining increased chemical reactivity in combining
with Ta to produce the volatile precursor, TaCl.sub.5. In a
preferred embodiment plasma generator 27 is a helical resonator
customized for this use. A furnace assembly 29 is provided and
adapted to heat a solid Ta metallic source 33 which is placed in a
quartz tube 31 adapted to contain both the source Ta 33 and the
generated plasma. Quartz tube 31 extends through both the plasma
generator and the heated region carrying the solid Ta source
material.
[0035] A heating element 35 provides a direct and adjustable heat
source to Ta 33. In a preferred embodiment, the furnace power is
regulated to control the temperature in the range from 200-400
degrees Celsius.
[0036] Furnace assembly 29 is a double walled enclosure separated
from component 27 by a flange 43 and likewise from the reactor side
by an end-flange 45. However, an unrestricted free flow capability
is maintained through the interior of shared tube 31. A
thermocouple housing 37 is provided and adapted to house
thermocouples for gauging oven temperature as is known in the art.
Furnace assembly 29 has a double containment exterior 36 adapted to
prevent leakage. A vent outlet 39 is provided and adapted to allow
venting of the system as is also known in the art. Fittings 53 and
47 provide connection to a deposition reactor and the upstream gas
delivery manifold respectively.
[0037] In a preferred embodiment of the present invention, a Noble
gas-halide mixture such as Cl.sub.2 and Ar is introduced for two
reasons. The first is that during the reactive phase TaCl.sub.5
precursor is generated very quickly and in large amounts within 5
to 40 msec. A time resolution for an ALD reactive phase is
approximately 100 msec. Therefore a dilution of the Cl.sub.2 by
mixing with a Noble gas is appropriate to protect against excessive
precursor generation. Secondly, using a Noble gas such as Ar, for
example, allows the plasma to be maintained continuously
eliminating plasma generation time. In this way, when Cl.sub.2 flow
is turned off, then etching of the Ta source (TaCl.sub.5
production) ceases even though plasma is kept on and maintained by
a continuous Ar flow. Alternatively, the plasma may, in some
instances, be timed to coincide with the introduction of Cl.sub.2
gas.
[0038] The Cl.sub.2/Noble mixture is introduced into tube 31
through fitting 47 by way of conduit 49 through flange 41. The
mixture is passed through the helical resonator (Plasma generation)
to produce the more reactive Cl atoms at a flow of approximately 20
standard cubic centimeters per minute (SCCM) in one embodiment. Cl
atoms are generated at approximately useful rates (e.g. at
approximately 30 sccm). The atoms react with Ta 33 in tube 31 to
etch the metal producing highly volatile TaCl.sub.5 (at the
temperature that furnace, 29, is maintained). Furnace 29 keeps Ta
33 heated to a high enough temperature to operate in a flux-limited
mode by desorbing the etch product molecules faster than generation
rate. The precursor is flowed into an ALD reactor through fitting
53.
[0039] A method for suppressing contaminant formation is also
utilized by GMDS 25 as is described below.
[0040] FIG. 2 is a cross sectional illustration presenting GMDS 25
of FIG. 1 interconnected to an ALD reactor 55 and gas sources
according to an embodiment of the present invention. Reactor 55 has
apparatus for maintaining a partial vacuum, and for supporting a
substrate, usually a silicon wafer, on a heated hearth during
deposition processes. GMDS 25 is approximately 18 inches in overall
length and compact enough to easily be fitted and integrated into
virtually any ALD or CVD system. In this example, GMDS 25 is
illustrated as connected to an ALD reactor 55.
[0041] During delivery of TaCL.sub.5 into reactor 55, it is
important that no solid precursor reforms on the walls of a
delivery line. Moreover, it is equally important that no Cl atoms
be allowed to pass into chamber 55 where they may become a source
of contamination. Adding a nickel-plated delivery line 59 and a
standard line heater 57 alleviates these concerns. Nickel plating
on the inside of line 59 acts to quench Cl atoms before they enter
reactor 55. In this way, no contamination results from chlorine
being inadvertently introduced into reactor 55. Line 59 is kept
heated to approximately 90.degree. C. effectively preventing
precursor from clogging line 59 and an associated pinch valve 61.
The preferred length of line 59 shall be sufficient enough to fully
quench Cl atoms. Moreover, since no TaCl.sub.5 is allowed to
solidify as a on the walls, no subsequent flaking of the solid
precursor will occur eliminating notorious upstream generation of
particles. Maintenance cleaning time is substantially reduced using
GMDS 25 due to the improvements cited above.
[0042] On the carrier-source end of GMDS 25, there are four
regulated gas lines illustrated, with each line responsible for
introducing a specific gas. The choice of reactive and Noble gas
types will depend upon the choice of solid source types and desired
precursor. Fluorine, Bromine, and other commonly known
metal-etching gases may also be used. Further, although use of
Noble gases is preferred, in some cases other gases, such as
Nitrogen, may be used.
[0043] It is important to regulate the upstream flow of reactive
and Noble gasses into GMDS 25. To that end, standard valves 63 are
provided in each separate line to enable turning the gas flow ON or
OFF. Flow restrictors 65 are similarly provided to restrict flow
rates and to provide measured, pulsed flow in ALD processes,
wherein the valves in each supply line are cycled alternately. Each
line has a mass flow meter (MFM) 67 to aid in adjusting flow as
well as upstream pressure regulators, 69. H.sub.2 may be used to
assist with plasma control as is known in the art. In preferred
embodiments control is by software dedicated to the process
purposes.
[0044] It will be apparent to one with skill in the art that the
unique implementation of GMDS 25 may be integrated with a wide
variety of ALD processes for a variety of films and applications,
as well as CVD applications without departing from the spirit and
scope of the present invention. As research continues regarding
optimum metallic sources and associated reactant gasses progresses,
new and future process materials and interaction paths may be
perfected for commercial use in the production of high quality
dielectrics and conducting films for electronic devices.
[0045] FIG. 3 is a process flow diagram illustrating basic process
steps using tantalum, chlorine, and argon in a Ta.sub.2O.sub.5 ALD
process according to an embodiment of the present invention.
Although the process steps represented herein describe a
self-terminating ALD cycle, continuous recursor flow may be used in
other applications such as with standard CVD.
[0046] In step 71, plasma is ignited and stabilized with a
continuous flow of argon. Alternatively, plasma may be timed to
pulse with the reactive gas. In step 73, reactive gas such as
Cl.sub.2 is introduced into a helical resonator (plasma
generation). In this step, Cl.sub.2 may be mixed with a Noble gas
such as Ar for reasons previously described.
[0047] In step 75 Cl atoms produced in plasma subsequently etch the
Ta source to produce highly volatile TaCl.sub.5, which in this
example is the desired precursor. In step 77 TaCl.sub.5 produced in
step 75 is pulsed into a suitable ALD reactor, or alternatively,
introduced as a continuous flow into a suitable CVD reactor.
Obviously, if the process is CVD, the oxygen containing precursor
would be introduced to the CVD reactor concurrently with the
TaCl.sub.5. For the sake of simplicity, FIG. 3 concentrates on the
ALD process.
[0048] In step 79, TaCl.sub.5 reacts with a prepared substrate
surface (OH) to produce a desired Ta.sub.2O.sub.5 layer. In step
81, separate purge (Ar) and surface reaction with H.sub.2O vapor is
performed to prepare the substrate surface for a next pulse of
metal precursor. The cycle repeats with step 83, which is the next
pulse of TaCl.sub.5.
[0049] The innovative design and implementation of an efficient and
contaminant free GMDS such as GMDS 25 greatly improves throughput
and quality in the fabrication of ALD films for various
applications. Solid metallic sources, which are more available in
pure and refined ingots, safer to handle, and more common than gas
or liquid metallic sources may now be conveniently used without
experiencing downtime delays associated with the need to control
particulate contamination and cleaning requirements which are
typical in prior-art applications that use solid compound sources.
Lower temperatures may be used for heating source metals and
shorter pulse intervals may be achieved due to higher reaction
rates. GMSD 25, as a process-independent chemical-delivery source,
may be used in general CVD as well as in ALD without departing from
the spirit and scope of the present invention.
[0050] In the above descriptions Tantalum (Ta) has been described
as a solid source, used with dissociated chlorine, preferably mixed
with a Noble gas, such as Argon. It was also described that the
choice of reactive and Noble gas types will depend upon the choice
of solid source types and desired precursor. Fluorine, Bromine, and
other commonly known metal-etching gases may be used. There are
similarly a variety of solid materials that may be used, depending
on the volatile precursor desired. For example, using the
well-known scientific notations for elements, the following may all
be considered as candidate solid sources in embodiments of the
invention: Ta, Zr, Hf, W, Nb, Mo, Bi, Zn, Pb, Mg, Ba, Sr, Cr, Co,
P, Sr, As, Ni, Ir and others.
[0051] It will also be apparent to anyone who is properly skilled
in the art that a variety of changes may be made in the embodiments
described above without departing from the spirit and scope of the
present invention. The apparatus used for dissociation (plasma
formation) and its power supply may be any of a number of
commercially available or custom made devices. Moreover, there are
a broad variety of metals that may be used, and source temperatures
and the like. In addition, there are elemental materials such as Ge
and Si which also form halides, and that may be used within the
operational and functional scope of the invention, even though
these materials may not be strictly classified as metals. Further
the devices described in various embodiments may be used for steady
flow CVD processes and also for interrupted flow (pulsed) ALD
processes. Still further, the gas streams may be combined with
other carrier gases, such as Nitrogen if inert in the operation of
the source, and may also be combined with or blended with other
inert gases in the downstream wafer reactor area and space.
Typically the GMDS of the invention will be attached upstream to an
ALD reactor or a CVD reactor, and typically these production
systems have apparatus for cycling a series of substrates
sequentially through the ALD or CVD reactor and a heated hearth for
supporting and heating a substrate in process. The spirit and scope
of the present invention is limited only by the claims that
follow.
* * * * *