U.S. patent application number 09/747649 was filed with the patent office on 2001-05-31 for radical-assisted sequential cvd.
Invention is credited to Sneh, Ofer.
Application Number | 20010002280 09/747649 |
Document ID | / |
Family ID | 23020817 |
Filed Date | 2001-05-31 |
United States Patent
Application |
20010002280 |
Kind Code |
A1 |
Sneh, Ofer |
May 31, 2001 |
Radical-assisted sequential CVD
Abstract
A new method for CVD deposition on a substrate is taught wherein
radical species are used in alternate steps to depositions from a
molecular precursor to treat the material deposited from the
molecular precursor and to prepare the substrate surface with a
reactive chemical in preparation for the next molecular precursor
step. By repetitive cycles a composite integrated film is produced.
In a preferred embodiment the depositions from the molecular
precursor are metals, and the radicals in the alternate steps are
used to remove ligands left from the metal precursor reactions, and
to oxidize or nitridize the metal surface in subsequent layers. A
variety of alternative chemistries are taught for different films,
and hardware combinations to practice the invention are taught as
well.
Inventors: |
Sneh, Ofer; (Branchburg,
NJ) |
Correspondence
Address: |
CENTRAL COAST PATENT AGENCY
PO BOX 187
AROMAS
CA
95004
US
|
Family ID: |
23020817 |
Appl. No.: |
09/747649 |
Filed: |
December 22, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09747649 |
Dec 22, 2000 |
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09267953 |
Mar 11, 1999 |
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6200893 |
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Current U.S.
Class: |
427/255.28 ;
118/723R; 257/E21.17; 257/E21.272; 257/E21.274; 257/E21.28;
257/E21.292; 427/255.31; 427/255.39; 427/404 |
Current CPC
Class: |
C23C 16/45536 20130101;
H01L 21/02274 20130101; H01L 21/31641 20130101; H01L 21/31616
20130101; H01L 21/318 20130101; C23C 16/452 20130101; H01L 21/31691
20130101; C23C 16/44 20130101; C23C 16/4554 20130101; H01L 21/0228
20130101; H01L 21/02178 20130101; H01L 21/31637 20130101; H01L
21/28556 20130101; H01L 21/31604 20130101; H01L 21/31645 20130101;
H01L 21/28562 20130101 |
Class at
Publication: |
427/255.28 ;
427/255.39; 427/255.31; 427/404; 118/723.00R |
International
Class: |
C23C 016/06; B05D
001/36; C23C 016/34; C23C 016/40 |
Claims
What is claimed is:
1. A method for depositing a metal on a substrate surface in a
deposition chamber, comprising steps of: (a) depositing a monolayer
of metal on the substrate surface by flowing a molecular precursor
gas or vapor bearing the metal over a surface of the substrate, the
surface saturated by a first reactive species with which the
precursor will react by depositing the metal and forming reaction
product, leaving a metal surface covered with ligands from the
metal precursor and therefore not further reactive with the
precursor; (b) terminating flow of the precursor gas or vapor; (c)
purging the precursor with inert gas; (d) flowing at least one
radical species into the chamber and over the surface, the radical
species highly reactive with the surface ligands of the metal
precursor layer and eliminating the ligands as reaction product,
and also saturating the surface, providing the first reactive
species; and (e) repeating the steps in order until a metallic film
of desired thickness results.
2. The method of claim 1 wherein the radical species is atomic
hydrogen.
3. The method of claim 1 wherein the precursor gas bearing the
metal is tungsten hexafluoride and the metal deposited is
tungsten.
4. The method of claim 1 wherein the precursor gas bearing the
metal is tantalum pentachloride and the metal deposited is
tantalum.
5. The method of claim 1 wherein the precursor gas bearing the
metal is one of trimethylaluminum or aluminum trichloride and the
metal deposited is aluminum.
6. The method of claim 1 wherein the precursor gas bearing the
metal is one of titanium tetrachloride or titanium tetraiodide and
the metal deposited is titanium.
7. The method of claim 1 wherein the precursor gas bearing the
metal is molybdenum hexafluoride and the metal deposited is
molybdenum.
8. The method of claim 1 wherein the precursor gas bearing the
metal is zinc dichloride and the metal deposited is zinc.
9. The method of claim 1 wherein the precursor gas bearing the
metal is hafnium tetrachloride and the metal deposited is
hafnium.
10. The method of claim 1 wherein the precursor gas bearing the
metal is niobium pentachloride and the metal deposited is
niobium.
11. The method of claim 1 wherein the precursor gas is copper
chloride Cu.sub.3Cl.sub.3 and the metal deposited is copper.
12. A method for depositing a metal oxide on a substrate surface in
a deposition chamber, comprising steps of: (a) depositing a
monolayer of metal on the substrate surface by flowing a metal
molecular precursor gas or vapor bearing the metal over a surface
of the substrate, the surface saturated by a first reactive species
with which the precursor will react by depositing the metal and
forming reaction product, leaving a metal surface covered with
ligands from the metal precursor and therefore not further reactive
with the precursor; (b) terminating flow of the precursor gas or
vapor; (c) purging the precursor with inert gas; (d) flowing a
first radical species into the chamber and over the surface, the
radical species highly reactive with the reaction product and
combining with the reaction product to create volatile species and
saturate the surface with the first radical species; (e) flowing
radical oxygen into the chamber to combine with the metal monolayer
deposited in step (a), forming an oxide of the metal; (f) flowing a
third radical species into the chamber terminating the surface with
the first reactive species in preparation for a next metal
deposition step; and (g) repeating the steps in order until a
composite film of desired thickness results.
13. The method of claim 12 wherein the first and third radical
species are both atomic hydrogen, and the metal surface in step (f)
is terminated with hydroxyl species reactive with the metal
precursor to deposit the metal.
14. The method of claim 13 wherein the oxygen and hydrogen atomic
steps (e) and (f) are repeated to improve film quality.
15. The method of claim 12 wherein steps (e) and (f) are combined
into one step wherein the surface is reacted with hydrogen and
oxygen atoms simultaneously.
16. The method of claim 12 wherein the metal precursor is tantalum
pentachloride and the film is tantalum pentoxide.
17. The method of claim 12 wherein the metal precursor is
trimethylaluminum or aluminum trichloride and the film is aluminum
oxide.
18. The method of claim 12 wherein the metal precursor is titanium
tetrachloride or titanium tetraiodide and the film is titanium
oxide.
19. The method of claim 12 wherein the metal precursor is niobium
pentachloride and the film is niobium pentoxide.
20. The method of claim 12 wherein the metal precursor is zirconium
tetrachloride and the film is zirconium oxide.
21. The method of claim 12 wherein the metal precursor is hafnium
tetrachloride and the film is hafnium oxide.
22. The method of claim 12 wherein the metal precursor is zinc
dichloride and the film is zinc oxide.
23. The method of claim 12 wherein the metal precursor is
molybdenum hexafluoride or molybdenum pentachloride and the film is
molybdenum oxide.
24. The method of claim 12 wherein the metal precursor is manganese
dichloride and the film is manganese oxide.
25. The method of claim 12 wherein the metal precursor is tin
tetrachloride and the film is tin oxide.
26. The method of claim 12 wherein the metal precursor is indium
trichloride or trimethylindium and the film is indium oxide.
27. The method of claim 12 wherein the metal precursor is tungsten
hexafluoride and the film is tungsten oxide.
28. The method of claim 12 wherein the metal precursor is silicon
tetrachloride and the film is silicon dioxide.
29. The method of claim 12 wherein the first radical species is
atomic hydrogen and steps (e) and (f) are united to one step using
OH radicals, and the metal surface in step (f) is terminated with
hydroxyl species reactive with the metal precursor to deposit the
metal.
30. A method for depositing a metal nitride on a substrate surface
in a deposition chamber, comprising steps of: (a) depositing a
monolayer of metal on the substrate surface by flowing a metal
precursor gas or vapor bearing the metal over a surface of the
substrate, the surface saturated by a first reactive species with
which the precursor will react by depositing the metal and forming
reaction product, leaving a metal surface covered with ligands from
the metal precursor and therefore not further reactive with the
precursor; (b) terminating flow of the precursor gas or vapor; (c)
purging the precursor with inert gas; (d) flowing a first radical
species into the chamber and over the surface, the atomic species
highly reactive with the surface ligands of the metal precursor
layer and eliminating the ligands as reaction product and also
saturating the surface; (e) flowing radical nitrogen into the
chamber to combine with the metal monolayer deposited in step (a),
forming a nitride of the metal; (f) flowing a third radical species
into the chamber terminating the surface with the first reactive
species in preparation for a next metal deposition step; and (g)
repeating the steps in order until a composite film of desired
thickness results.
31. The method of claim 30 wherein the first and third atomic
radical species are both atomic hydrogen, and the metal surface in
step (f) is terminated with amine species reactive with the metal
precursor to deposit the metal.
32. The method of claim 31 wherein steps (e) and (f) are combined
to one step wherein the surface is reacted with hydrogen and
nitrogen atoms simultaneously.
33. The method of claim 30 wherein the metal precursor is tungsten
hexafluoride and the film is tungsten nitride.
34. The method of claim 30 wherein the metal precursor is tantalum
pentachloride and the film is tantalum nitride.
35. The method of claim 30 wherein the metal precursor is aluminum
trichloride or trimethylaluminum and the film is aluminum
nitride.
36. The method of claim 30 wherein the metal precursor is titanium
tetrachloride and the film is titanium nitride.
37. The method of claim 30 wherein the metal precursor is silicon
tetrachloride or dichlorosilane and the film is silicon
nitride.
38. The method of claim 30 wherein the metal precursor is
trimethylgallium and the film is gallium nitride.
39. The method of claim 30 wherein the first radical species are
atomic hydrogen and steps (e) and (f) are united to one step using
one or both of NH and NH.sub.2 radicals, and the metal surface in
step (f) is terminated with amine species reactive with the metal
precursor to deposit the metal.
40. A process for building a metal, metal oxide, or metal nitride
film on a substrate surface, wherein deposition steps comprising
flowing a metal precursor gas or vapor over the surface with the
surface terminated with a first chemical species reactive with the
metal precursor to deposit the metal, are alternated with steps
comprising flowing radical species over the freshly deposited metal
layers to remove the ligands from the deposition steps and to
provide the first chemical species to terminate the substrate
surface preparatory to the next deposition reaction.
41. The process of claim 40 wherein a metal nitride film is built
up by a step sequence of metal deposition by reacting a metal
precursor gas with a surface terminated by amine species, then
alternating exposure of the surface with atomic radical hydrogen,
nitrogen and hydrogen again, thereby volatilizing products
remaining from the metal deposition chemistry, nitridizing the
deposited metal monolayer, then terminating the metal surface with
amine species again in preparation for a next metal deposition
step.
42. The process of claim 40 wherein a metal oxide film is built up
by a step sequence of metal deposition by reacting a metal
precursor gas with a surface terminated by hydroxyl species, then
alternating exposure of the surface with atomic radical hydrogen,
oxygen and hydrogen again, thereby volatilizing products remaining
from the metal deposition chemistry, oxidizing the metal monolayer,
then terminating the metal surface with hydroxyl species again in
preparation for a next metal deposition step.
43. A method for depositing a compound film on a substrate surface
in a deposition chamber, comprising steps of: (a) depositing a
monolayer of metal on the substrate surface by flowing a metal
molecular precursor gas or vapor bearing the metal over a surface
of the substrate, the surface saturated by a first reactive species
with which the precursor will react by depositing the metal and
forming reaction product, leaving a metal surface covered with
ligands from the metal precursor and therefore not further reactive
with the precursor; (b) terminating flow of the precursor gas or
vapor; (c) purging the precursor with inert gas; (d) flowing a
first radical species into the chamber and over the surface, the
radical species highly reactive with the reaction product and
combining with the reaction product to create volatile species and
saturate the surface with the first radical species; (e) flowing
nonmetal radical species into the chamber to combine with the metal
monolayer deposited in step (a), forming a compound film of the
metal; (f) flowing a third radical species into the chamber
terminating the surface with the first reactive species in
preparation for a next metal deposition step; and (g) repeating the
steps in order until a composite film of desired thickness
results.
44. The method of claim 43 wherein the first and third radical
species are both atomic hydrogen, and the metal surface in step (f)
is terminated with hydride species of the nonmetallic element that
are reactive with the metal precursor to deposit the metal.
45. The method of claim 43 wherein the non-metallic and hydrogen
atomic steps (e) and (f) are repeated to improve the film
quality.
46. The method of claim 43 wherein steps (e) and (f) are combined
into one step wherein the surface is reacted with hydrogen and
non-metallic atoms simultaneously.
47. The method of claim 43 wherein the metal precursor is
molybdenum hexafluoride or molybdenum pentachloride, the non
metallic element is sulfur and the film is molybdenum
disulfide.
48. The method of claim 43 wherein the metal precursor is zinc
dichloride, the non metallic element is sulfur and the film is zinc
sulfide.
49. A radical-assisted sequential CVD reactor, comprising: a
chamber with controlled gas inlets for introducing gases in
sequential steps and a heated substrate support for holding a
substrate and exposing a surface of the substrate to incoming
gases; and a plasma generation apparatus for generating radical
atomic species for use in the reactor; wherein an aggregate metal
layer is formed by depositing a monolayer of metal on the substrate
surface by flowing a precursor gas or vapor bearing the metal over
a surface of the substrate, the surface terminated by a first
reactive species with which the precursor will react by depositing
the metal and forming reaction product, leaving a metal surface not
further reactive with the precursor, terminating flow of the
precursor gas or vapor, flowing at least one atomic radical species
into the chamber and over the surface, the atomic species highly
reactive with the reaction product and combining with the reaction
product, and also terminating the surface, providing the first
reactive species, and repeating the steps in order until a
composite film of desired thickness results.
50. The reactor of claim 49 wherein the atomic radical species is
atomic hydrogen.
51. The reactor of claim 49 wherein the precursor gas bearing the
metal is tungsten hexafluoride and the metal deposited is
tungsten.
52. The reactor of claim 49 wherein the plasma generation apparatus
comprises an electrode within the reactor chamber and a high
frequency power supply connected to the electrode.
53. The reactor of claim 49 further comprising a showerhead-type
gas distribution apparatus, and wherein a plasma is generated
within the showerhead apparatus to produce the atomic radical
species.
54. The reactor of claim 49 wherein the atomic radical species is
produced in a remote plasma generator, and the species are
delivered to the reactor.
Description
FIELD OF THE INVENTION
[0001] The present invention is in the area of chemical vapor
deposition, and pertains more particularly to new methods and
apparatus for depositing films by atomic layer deposition.
BACKGROUND OF THE INVENTION
[0002] In the manufacture of integrated circuits, deposition of
thin films of many pure and compound materials is necessary, and
many techniques have been developed to accomplish such depositions.
In recent years the dominant technique for deposition of thin films
in the art has been chemical vapor deposition (CVD), which has
proven to have superior ability to provide uniform even coatings,
and to coat relatively conformably into vias and over other
high-aspect and uneven features in wafer topology. As device
density has continued to increase and geometry has continued to
become more complicated, even the superior conformal coating of CVD
techniques has been challenged, and new and better techniques are
needed.
[0003] The approach of a variant of CVD, Atomic Layer Deposition
has been considered for improvement in uniformity and conformality,
especially for low temperature deposition. However the practical
implementation of this technology requires a solution to higher
purity and higher throughput. This patent addresses these
requirements.
[0004] Atomic Layer Deposition
[0005] In the field of CVD a process known as Atomic Layer
Deposition (ALD) has emerged as a promising candidate to extend the
abilities of CVD techniques, and is under rapid development by
semiconductor equipment manufacturers to further improve
characteristics of chemical vapor deposition. ALD is a process
originally termed Atomic Layer Epitaxy, for which a competent
reference is: Atomic Layer Epitaxy, edited by T. Suntola and M.
Simpson, published by Blackie, Glasgo and London in 1990. This
publication is incorporated herein by reference.
[0006] Generally ALD is a process wherein conventional CVD
processes are divided into single-monolayer deposition steps,
wherein each separate deposition step theoretically goes to
saturation at a single molecular or atomic monolayer thickness, and
self-terminates.
[0007] The deposition is the outcome of chemical reactions between
reactive molecular precursors and the substrate. In similarity to
CVD, elements composing the film are delivered as molecular
precursors. The net reaction must deposit the pure desired film and
eliminate the "extra" atoms that compose the molecular precursors
(ligands). In the case of CVD the molecular precursors are fed
simultaneously into the CVD reactor. A substrate is kept at
temperature that is optimized to promote chemical reaction between
the molecular precursors concurrent with efficient desorption of
byproducts. Accordingly, the reaction proceeds to deposit the
desired pure film.
[0008] For ALD applications, the molecular precursors are
introduced into the ALD reactor separately. This is practically
done by flowing one precursor at a time, i.e. a metal
precursor--ML.sub.x (M.dbd.Al, W, Ta, Si etc.) that contains a
metal element--M which is bonded to atomic or molecular ligands--L
to make a volatile molecule. The metal precursor reaction is
typically followed by inert gas purging to eliminate this precursor
from the chamber prior to the separate introduction of the other
precursor. An ALD reaction will take place only if the surface is
prepared to react directly with the molecular precursor.
Accordingly the surface is typically prepared to include
hydrogen-containing ligands--AH that are reactive with the metal
precursor. Surface--molecule reactions can proceed to react with
all the ligands on the surface and deposit a monolayer of the metal
with its passivating ligand:
substrate--AH+ML.sub.x.fwdarw.substrate--AML.sub.y+HL, where HL is
the exchange reaction by-product. During the reaction the initial
surface ligands--AH are consumed and the surface becomes covered
with L ligands, that cannot further react with the metal
precursor--ML.sub.x. Therefore, the reaction self-saturates when
all the initial ligands are replaced with--ML.sub.y species.
[0009] After completing the metal precursor reaction the excess
precursor is typically removed from the reactor prior to the
introduction of another precursor. The second type of precursor is
used to restore the surface reactivity towards the metal precursor,
i.e. eliminating the L ligands and redepositing AH ligands.
[0010] Most ALD processes have been applied to deposit compound
films. In this case the second precursor is composed of a desired
(usually nonmetallic) element--A (i.e. O, N, S), and hydrogen
using, for example H.sub.2O, NH.sub.3, or H.sub.2S. The reaction:
--ML+AH.sub.z.fwdarw.--M--- AH+HL (for the sake of simplicity the
chemical reactions are not balanced) converts the surface back to
be AH-covered. The desired additional element--A is deposited and
the ligands L are eliminated as volatile by-product. Again, the
reaction consumes the reactive sites (this time the L terminated
sites) and self-saturates when the reactive sites are entirely
depleted.
[0011] The sequence of surface reactions that restores the surface
to the initial point is called the ALD deposition cycle.
Restoration to the initial surface is the keystone of ALD. It
implies that films can be layered down in equal metered sequences
that are all identical in chemical kinetics, deposition per cycle,
composition and thickness. Self-saturating surface reactions make
ALD insensitive to transport nonuniformity either from flow
engineering or surface topography (i.e. deposition into high aspect
ratio structures). Non uniform flux can only result in different
completion time at different areas. However, if each of the
reactions is allowed to complete on the entire area, the different
completion kinetics bear no penalty.
[0012] As is often the case with process development, the initial
promised advantages of a new technique do not, in the end, attain
their full initial promise. Unfortunately, ALD has a serious
fundamental problem. Unlike CVD reactions that are of a continuous
steady state nature, ALD reactions follow kinetics of
molecular-surface interaction. Kinetics of molecular-surface
reactions depends on the individual reaction rate between a
molecular precursor and a surface reactive site and the number of
available reactive sites. As the reaction proceeds to completion,
the surface is converted from being reactive to non-reactive. As a
result the reaction rate is slowing down during the deposition. In
the simplest case the rate, dN/dt is proportional to the number of
reactive sites, dN/dt=--kN, where N is the number of reactive sites
and k is the (single site) reaction rate. Eliminating reactive
sites (or growing of the already-reacted sites) follows an
exponential time dependence kN(t)=kN.sub.0exp(--kt). This
fundamental property of molecule-surface kinetics was named after
the great scientist Langmuir, and is quite well-known in the
art.
[0013] The interpretation of Langmuirian kinetics limitations
illustrates a serious drawback of ALD and a severe deviation from
the ideal picture. Accordingly, the self-terminating reactions
never really self-terminate (they would require an infinite time
because the rate is exponentially decreasing). It means that under
practical conditions the surface is never entirely reacted to
completion after a deposition cycle. If the surface is not
completely reacted there are leftover undesired elements in the
film. For example, if the ML.sub.x reaction cannot totally consume
the surface--AH sites, the film will have H incorporation.
Likewise, if the AH.sub.y reaction is not carried to completion,
undesired L incorporation is inevitable. Clearly, the quality of
the film depends on the impurity levels. The throughput-quality
tradeoff is of particular concern because it carries an exponential
throughput penalty to attain a reduction of impurity levels.
[0014] In conventional atomic layer deposition one must accept low
throughput to attain high-purity film, or accept lower-purity films
for higher throughput. What is clearly needed is an apparatus and
methods which not only overcome the Langmuirian limitations but
simultaneously provide higher-purity films than have been available
in the prior art methods. Such apparatus and methods are provided
in embodiments of the present invention, taught in enabling detail
below.
SUMMARY OF THE INVENTION
[0015] In a preferred embodiment of the present invention a method
for depositing a metal on a substrate surface in a deposition
chamber is provided, comprising steps of (a) depositing a monolayer
of metal on the substrate surface by flowing a molecular precursor
gas or vapor bearing the metal over a surface of the substrate, the
surface saturated by a first reactive species with which the
precursor will react by depositing the metal and forming reaction
product, leaving a metal surface covered with ligands from the
metal precursor and therefore not further reactive with the
precursor; (b) terminating flow of the precursor gas or vapor; (c)
purging the precursor with inert gas; (d) flowing at least one
radical species into the chamber and over the surface, the radical
species highly reactive with the surface ligands of the metal
precursor layer and eliminating the ligands as reaction product,
and also saturating the surface, providing the first reactive
species; and (e) repeating the steps in order until a metallic film
of desired thickness results.
[0016] In many such embodiments the radical species is atomic
hydrogen. Using atomic hydrogen a broad variety of pure metals may
be deposited, such as tungsten, tantalum, aluminum, titanium,
molybdenum, zinc, hafnium, niobium and copper.
[0017] In another aspect of the invention a method is provided for
depositing a metal oxide on a substrate surface in a deposition
chamber, comprising steps of (a) depositing a monolayer of metal on
the substrate surface by flowing a metal molecular precursor gas or
vapor bearing the metal over a surface of the substrate, the
surface saturated by a first reactive species with which the
precursor will react by depositing the metal and forming reaction
product, leaving a metal surface covered with ligands from the
metal precursor and therefore not further reactive with the
precursor; (b) terminating flow of the precursor gas or vapor; (c)
purging the precursor with inert gas; (d) flowing a first radical
species into the chamber and over the surface, the radical species
highly reactive with the reaction product and combining with the
reaction product to create volatile species and saturate the
surface with the first radical species; (e) flowing radical oxygen
into the chamber to combine with the metal monolayer deposited in
step (a), forming an oxide of the metal; (f) flowing a third
radical species into the chamber terminating the surface with the
first reactive species in preparation for a next metal deposition
step; and (g) repeating the steps in order until a composite film
of desired thickness results.
[0018] In this method the first and third radical species may be
both atomic hydrogen, and the metal surface in step (f) is
terminated with hydroxyl species reactive with the metal precursor
to deposit the metal. In another embodiment the oxygen and hydrogen
atomic steps (e) and (f) are repeated to improve film quality. In
still another embodiment steps (e) and (f) are combined into one
step wherein the surface is reacted with hydrogen and oxygen atoms
simultaneously.
[0019] In various embodiments for depositing oxides the oxides can
be tantalum pentoxide, aluminum oxide, titanium oxide, niobium
pentoxide, zirconium oxide, hafnium oxide, zinc oxide, molybdenum
oxide, manganese oxide, tin oxide, indium oxide, tungsten oxide and
silicon oxide, among others.
[0020] In some embodiments the first radical species is atomic
hydrogen and steps (e) and (f) are united to one step using OH
radicals, and the metal surface in step (f) is terminated with
hydroxyl species reactive with the metal precursor to deposit the
metal.
[0021] In still another aspect of the invention a method for
depositing a metal nitride on a substrate surface in a deposition
chamber is provided, comprising steps of (a) depositing a monolayer
of metal on the substrate surface by flowing a metal precursor gas
or vapor bearing the metal over a surface of the substrate, the
surface saturated by a first reactive species with which the
precursor will react by depositing the metal and forming reaction
product, leaving a metal surface covered with ligands from the
metal precursor and therefore not further reactive with the
precursor, (b) terminating flow of the precursor gas or vapor; (c)
purging the precursor with inert gas; (d) flowing a first radical
species into the chamber and over the surface, the atomic species
highly reactive with the surface ligands of the metal precursor
layer and eliminating the ligands as reaction product and also
saturating the surface; (e) flowing radical nitrogen into the
chamber to combine with the metal monolayer deposited in step (a),
forming a nitride of the metal; (f) flowing a third radical species
into the chamber terminating the surface with the first reactive
species in preparation for a next metal deposition step; and (g)
repeating the steps in order until a composite film of desired
thickness results.
[0022] In this method the first and third atomic radical species
may both be atomic hydrogen, and the metal surface in step (f) may
be terminated with amine species reactive with the metal precursor
to deposit the metal. Further, steps (e) and (f) may be combined
into one step wherein the surface is reacted with hydrogen and
nitrogen atoms simultaneously.
[0023] In variations of this embodiment a variety of different
nitrides may be produces, including, but limited to tungsten
nitride, tantalum nitride, aluminum nitride, titanium nitride,
silicon nitride and gallium nitride.
[0024] In another variation the first radical species may be atomic
hydrogen and steps (e) and (f) may be united into one step using
one or both of NH and NH.sub.2 radicals, and the metal surface in
step (fi is terminated with amine species reactive with the metal
precursor to deposit the metal.
[0025] In yet another aspect of the invention a process for
building a metal, metal oxide, or metal nitride film on a substrate
surface is provided, wherein deposition steps comprise flowing a
metal precursor gas or vapor over the surface with the surface
terminated with a first chemical species reactive with the metal
precursor to deposit the metal, are alternated with steps
comprising flowing radical species over the freshly deposited metal
layers to remove the ligands from the deposition steps and to
provide the first chemical species to terminate the substrate
surface preparatory to the next deposition reaction.
[0026] In this process a metal nitride film is built up by a step
sequence of metal deposition by reacting a metal precursor gas with
a surface terminated by amine species, then alternating exposure of
the surface with atomic radical hydrogen, nitrogen and hydrogen
again, thereby volatilizing products remaining from the metal
deposition chemistry, nitridizing the deposited metal monolayer,
then terminating the metal surface with amine species again in
preparation for a next metal deposition step. A metal oxide film is
built up by a step sequence of metal deposition by reacting a metal
precursor gas with a surface terminated by hydroxyl species, then
alternating exposure of the surface with atomic radical hydrogen,
oxygen and hydrogen again, thereby volatilizing products remaining
from the metal deposition chemistry, oxidizing the metal monolayer,
then terminating the metal surface with hydroxyl species again in
preparation for a next metal deposition step.
[0027] In yet another aspect of the invention a method for
depositing a compound film on a substrate surface in a deposition
chamber is provided, comprising steps of (a) depositing a monolayer
of metal on the substrate surface by flowing a metal molecular
precursor gas or vapor bearing the metal over a surface of the
substrate, the surface saturated by a first reactive species with
which the precursor will react by depositing the metal and forming
reaction product, leaving a metal surface covered with ligands from
the metal precursor and therefore not further reactive with the
precursor; (b) terminating flow of the precursor gas or vapor; (c)
purging the precursor with inert gas; (d) flowing a first radical
species into the chamber and over the surface, the radical species
highly reactive with the reaction product and combining with the
reaction product to create volatile species and saturate the
surface with the first radical species; (e) flowing nonmetal atomic
species into the chamber to combine with the metal monolayer
deposited in step (a), forming a compound film of the metal, (f)
flowing a third radical species into the chamber terminating the
surface with the first reactive species in preparation for a next
metal deposition step; and (g) repeating the steps in order until a
composite film of desired thickness results.
[0028] In this method the first and third radical species may be
both atomic hydrogen, and the metal surface in step (f) is
terminated with hydride species of the nonmetallic element that are
reactive with the metal precursor to deposit the metal. In a
variation the non-metallic and hydrogen atomic steps (e) and (f)
are repeated to improve the film quality. In another variation
steps (e) and (f) are combined into one step wherein the surface is
reacted with hydrogen and non-metallic atoms simultaneously. A
variety of films may be produced by practicing this variation of
the invention as well, including but not limited to molybdenum
disulfide and zinc sulfide.
[0029] In yet another aspect of the invention a radical-assisted
sequential CVD (RAS-CVD) reactor is provided, comprising a chamber
with controlled gas inlets for introducing gases in sequential
steps and a heated substrate support for holding a substrate and
exposing a surface of the substrate to incoming gases; and a plasma
generation apparatus for generating radical atomic species for use
in the reactor. In this reactor an aggregate metal layer is formed
by depositing a monolayer of metal on the substrate surface by
flowing a precursor gas or vapor bearing the metal over a surface
of the substrate, the surface terminated by a first reactive
species with which the precursor will react by depositing the metal
and forming reaction product, leaving a metal surface not further
reactive with the precursor, terminating flow of the precursor gas
or vapor, flowing at least one atomic radical species into the
chamber and over the surface, the atomic species highly reactive
with the reaction product and combining with the reaction product,
and also terminating the surface, providing the first reactive
species, and repeating the steps in order until a composite film of
desired thickness results.
[0030] In various embodiments the atomic radical species is atomic
hydrogen. The precursor gas bearing the metal may be tungsten
hexafluoride and the metal deposited tungsten.
[0031] In some embodiments the plasma generation apparatus
comprises an electrode within the reactor chamber and a high
frequency power supply connected to the electrode. In other
embodiments the plasma generation apparatus comprises a
showerhead-type gas distribution apparatus, and a plasma is
generated within the showerhead apparatus to produce the radical
species. In still other embodiments the atomic radical species is
produced in a remote plasma generator, and the species are
delivered to the reactor.
[0032] In the various embodiments of the invention a new process is
provided wherein films of many sorts, including pure metals, oxides
of metals, nitrides of metals, and other films, may be produced
quickly and efficiently, with very high purity and with superior
conformity to substrate topography and coverage within vias and
other difficult surface geometries.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a generalized diagram of a reactor and associated
apparatus for practicing a radical-assisted sequential CVD process
according to an embodiment of the present invention.
[0034] FIG. 2 is a step diagram illustrating the essential steps of
an atomic layer deposition process.
[0035] FIG. 3 is a step diagram illustrating steps in a
radical-assisted CVD process according to an embodiment of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] The inventor has developed an enhanced variation of ALD
which alters the conventional surface preparation steps of ALD and
overcomes the problems of conventional ALD, producing high
throughput without compromising quality. The inventor terms the new
and unique process Radical-Assisted Sequential CVD (FAS-CVD).
[0037] FIG. 1 is a generalized diagram of a system 11 for
practicing RAS-CVD according to an embodiment of the present
invention. In this exemplary system a deposition chamber 13 has a
heatable hearth for supporting and heating a substrate 19 to be
coated, and a gas distribution apparatus, such as a showerhead 15,
for delivering gaseous species to the substrate surface to be
coated. Substrates are introduced and removed from chamber 13 via a
valve 21 and substrate-handling apparatus not shown. Gases are
supplied from a gas sourcing and pulsing apparatus 23, which
includes metering and valving apparatus for sequentially providing
gaseous materials. An optional treatment apparatus 25 is provided
for producing gas radicals from gases supplied from apparatus
23.
[0038] The term radicals is well-known and understood in the art,
but will be qualified again here to avoid confusion. By a radical
is meant an unstable species. For example, oxygen is stable in
diatomic form, and exists principally in nature in this form.
Diatomic oxygen may, however, be caused to split to monatomic form,
or to combine with another atom to produce ozone, a molecule with
three atoms. Both monatomic oxygen and ozone are radical forms of
oxygen, and are more reactive than diatomic oxygen. In many cases
in embodiments of the present invention the radicals produced and
used are single atom forms of various gases, such as oxygen,
hydrogen, and nitrogen, although the invention is not strictly
limited to monatomic gases.
[0039] FIG. 2 is a step diagram of a conventional Atomic Layer
Deposition process, and is presented here as contrast and context
for the present invention. In conventional ALD, as shown in FIG. 2,
in step 31 a first molecular precursor is pulsed in to a reactor
chamber, and reacts with the surface to produce (theoretically) a
monolayer of a desired material. Often in these processes the
precursor is a metal-bearing gas, and the material deposited is the
metal; Tantalum from TaCl.sub.5, for example.
[0040] In step 33 in the conventional process an inert gas is
pulsed into the reactor chamber to sweep excess first precursor
from the chamber.
[0041] In step 35 in the conventional system a second precursor,
typically non-metallic, is pulsed into the reactor. The primary
purpose of this second precursor is to condition the substrate
surface back toward reactivity with the first precursor. In many
cases the second precursor also provides material from the
molecular gas to combine with metal at the surface, forming
compounds such as an oxide or a nitride with the freshly-deposited
metal.
[0042] At step 37 the reactor chamber is purged again to remove
excess of the second precursor, and then step 31 is repeated The
cycle is repeated as many times as is necessary to establish a
desired film.
[0043] FIG. 3 is a step diagram illustrating steps in a
radical-assisted CVD process according to an embodiment of the
present invention. In the unique process illustrated by FIG. 3 the
first steps, steps 41 and 43, are the same as in the conventional
process. A first precursor is pulsed in step 41 to react with the
substrate surface forming a monolayer of deposit, and the chamber
is purges in step 43. The next step is unique. In step 45 single or
multiple radical species are pulsed to the substrate surface to
optionally provide second material to the surface and to condition
the surface toward reactivity with the first molecular precursor in
a subsequent step. Then step 41 is repeated. There is no need for a
second purge, and the cycle is repeated as often as necessary to
accomplish the desired film.
[0044] Step 45 may be a single step involving a single radical
species. For example, the first precursor may deposit a metal, such
as in W from WF.sub.6, and the radical species in step 45 may be
atomic hydrogen. The atomic hydrogen very quickly and effectively
neutralizes any remaining F to HF, and terminates the surface with
atomic hydrogen, providing reactive surface for the next pulse of
WF.sub.6.
[0045] In many cases step 45 will be a compound step comprising
substeps involving different radical species. A good example is a
sequence of atomic hydrogen followed by atomic oxygen, followed by
atomic hydrogen again. The first hydrogen step neutralizes Cl or
other remaining ligand, the atomic oxygen provides an oxide of the
freshly-deposited metal, and the second atomic hydrogen terminated
the surface with (OH) in preparation for the next metal precursor
step.
[0046] There are a broad variety of materials and combinations in
step 45, and many are disclosed in more detail below, along with a
more complete explanation of process chemistry.
[0047] In RAS-CVD, following the metal precursor reaction, highly
reactive radical species are introduced to quickly react with
products of the metal precursor reaction and to prepare the surface
for the next metal precursor reaction. Radical species, as
introduced above, are reactive atoms or molecular fragments that
are chemically unstable and therefore are extremely reactive. In
addition, radicals chemisorb to surfaces with virtually 100%
efficiency. Radicals may be created in a number of ways, and plasma
generation has been found to be an efficient and compatible means
of preparation.
[0048] RAS-CVD processes use only a single molecular precursor, in
many cases a metal precursor. Surface preparation as well as the
deposition of nonmetallic elements are accomplished by atom-surface
reactions. Following the metal precursor reaction, The --ML
terminated surface is reacted with hydrogen atoms to convert the
surface into --MH and eliminate HL by-product. Unlike
molecule-surface reactions, atom-surface reactions do not depend on
the number density of reactive sites. Most atoms (except for noble
gases) stick very efficiently to surfaces in an irreversible
process because atomic desorption is usually unfavorable. The atoms
are highly mobile on non-reactive sites and very reactive at
reactive sites. Consequently, atom-surface reactions have linear
exposure dependence, as well as high rates.
[0049] The --MH surface can be reacted with A atoms to yield a
--M--A-- surface. In this case some of the H ligands can be
eliminated as AH.sub.y. For example the --MH surface can be reacted
with oxygen atoms to deposit oxide compound. Alternatively, --MH
surface can be reacted again with ML.sub.x for atomic layer
controlled deposition of M metal films. For the deposition of
nitride compound films, A is atomic nitrogen. The surface after the
A atomic reaction is terminated with A-- and AH. At this point an
additional atomic reaction with hydrogen converts the surface to
the desired AH ligands that are reactive towards the metal
precursor. Alternatively, the MH surface can be reacted with a
mixture of A and H atoms to convert the surface into --AH
terminated surface with one less step. All the above described
reactions are radical-surface reactions that are fast and efficient
and depend linearly on exposure. In addition, the final hydrogen
reaction results in a complete restoration to the initial surface
without any incorporation of impurities.
[0050] Another throughput benefit of RAS-CVD is that a single purge
step after the metal precursor step is needed, rather than the two
purge steps needed in the conventional process. Purge steps are
expected by most researchers to be the most significant
throughput-limiting step in ALD processes. Another advantage is
that RAS-CVD promises longer system uptime and reduced maintenance.
This is because atomic species can be efficiently quenched on
aluminum walls of the deposition module. Downstream deposition on
the chamber and pumping lines is therefore virtually eliminated.
RAS-CVD eliminates the use of H.sub.2O and NH.sub.3 that are
commonly applied for oxides and nitrides deposition (respectively)
in the prior art. These precursors are notorious to increase
maintenance and downtime of vacuum systems.
[0051] According to the above a typical RAS-CVD cycle for a metal
oxide film will comprise steps as follows:
[0052] 1. Metal precursor reaction with --OH (hydroxyl) terminated
surface to attach --O--ML.sub.y and eliminate the hydrogen by HL
desorption. The surface becomes covered with L ligands, i.e. in the
case of TaCl.sub.5 the surface becomes covered with Cl atoms.
[0053] 2. Purge with inert gas to sweep away excess metal
precursor.
[0054] 3. Atomic hydrogen step--eliminates the ligands L by HL
desorption and terminates the surface with hydrogen.
[0055] 4. Atomic oxygen step--reacts with monolayer of metal to
form oxide. Atomic hydrogen again to leave hydroxyl saturated
surface for next metal precursor step.
[0056] At this point the quality of oxide films (i.e. insulation
properties, dielectric strength, charge trapping) can be improved
by running steps 4+5 for multiple times. For example:
Al.sub.2O.sub.3 RAS-CVD can be realized from trimethylaluminum
Al(CH.sub.3).sub.3, hydrogen and oxygen exposures.
Al(CH.sub.3).sub.3 reacting with --OH terminated surface will
deposit --OAl(CH.sub.3).sub.x concurrent with the desorption of
methane (CH.sub.4). The --OAl(CH.sub.3).sub.x (x=1,2) surface will
be treated with H atoms to eliminate x number of methane molecules
and terminate the surface with --OAlH. This surface after
consecutive (or concurrent) reaction with 0 atoms and H atoms will
be terminated --OAl--OH which is the restoration state. At this
point, the RAS-CVD process can proceed by applying another
Al(CH.sub.3).sub.3 reaction. Alternatively, the --OAl--OH surface
can be exposed to another cycles of 0 and H atoms. At temperature
above 100.degree.C. this process will exchange OH groups and
Al--O--Al bridge sites and the resulted --OAl--OH surface will be
more thermodynamically favorable than the beginning surface,
because the process eliminates the more strained (Al--O--).sub.n
ring structures as well as titrating away defects and broken
bonds). Since the atomic reactions are rather fast, these quality
improvements are not expected to be a major throughput concern. In
fact, ultimate quality may be achieved by applying the O, H cycles
for several times. Following, a given number of O, H atomic
reactions the sequence will continue with the next
Al(CH.sub.3).sub.3 reaction.
[0057] 6. Repeat steps from 1.
[0058] For metal nitrides atomic nitrogen is substituted for
oxygen. For pure metal depositions the oxygen/nitrogen step may be
eliminated in favor of a single atomic hydrogen step, such as for
tungsten films. The hydrogen saturated surface after the first
atomic hydrogen step is reactive with WF.sub.6 to produce the pure
metal.
[0059] The generic nature of RAS-CVD is advantageous for multiple
layer combination films of different oxides, different nitrides,
oxides with nitrides, different metals and metals with compound
films.
[0060] In another unique process, useful for barrier layers, the WN
process may be combined with the pure W process to produce
alternating W and WN layers in a variety of schemes to suppress
polycrystallization and to reduce the resistivity of the barrier
layer. Other properties, such as electromigration may be controlled
by an ability to provide a graded layer of WN with reduced nitrogen
content at the copper interface for such applications.
[0061] In embodiments of the invention a broad variety of process
chemistries may be practiced, providing a broad variety of final
films. In the area of pure metals, for example, the following
provides a partial, but not limiting list:
[0062] 1. Tungsten from tungsten hexafluoride.
[0063] 2. Tantalum from tantalum pentachloride.
[0064] 3. Aluminum from either aluminum trichloride or
trimethylaluminum.
[0065] 4. Titanium from titanium tetrachloride or titanium
tetraiodide.
[0066] 5. Molybdenum from molybdenum hexafluoride.
[0067] 6. Zinc from zinc dichloride.
[0068] 7. Hafnium from hafnium tetrachloride.
[0069] 8. Niobium from niobium pentachloride.
[0070] 9. Copper from Cu.sub.3Cl.sub.3
[0071] In the area of oxides the following is a partial but not
limiting list:
[0072] 1. Tantalum pentoxide from tantalum pentachloride.
[0073] 2. Aluminum oxide from trimethylaluminum or aluminum
trichloride.
[0074] 3. Titanium oxide from titanium tetrachloride or titanium
tetraiodide.
[0075] 4. Niobium pentoxide from niobium pentachloride.
[0076] 5. Zirconium oxide from zirconium tetrachloride.
[0077] 6. Hafnium oxide from hafnium tetrachloride.
[0078] 7. Zinc oxide from zinc dichloride.
[0079] 8. Molybdenum oxide from molybdenum hexafluoride or
molybdenum pentachloride.
[0080] 9. Manganese oxide from manganese dichloride.
[0081] 10. Tin oxide from tin tetrachloride.
[0082] 11. Indium oxide from indium trichloride or
trimethylindium.
[0083] 12. Tungsten oxide from tungsten hexafluoride.
[0084] 13. Silicon dioxide from silicon tetrachloride.
[0085] In the area of nitrides, the following is a partial but not
limiting list:
[0086] 1. Tungsten nitride from tungsten hexafluoride.
[0087] 2. Tantalum nitride from tantalum pentachloride.
[0088] 3. Aluminum nitride from aluminum trichloride or
trimethylaluminum.
[0089] 4. Titanium nitride from titanium tetrachloride.
[0090] 5. Silicon nitride from silicon tetrachloride or
dichlorosilane.
[0091] 6. Gallium nitride from trimethylgallium.
[0092] Hardware Requirements
[0093] Another advantage of RAS-CVD is that it is compatible in
most cases with ALD process hardware. The significant difference is
in production of atomic species and/or other radicals, and in the
timing and sequence of gases to the process chamber. Production of
the atomic species can be done in several ways, such as (1) in-situ
plasma generation, (2) intra-showerhead plasma generation, and (3)
external generation by a highdensity remote plasma source or by
other means such as UV dissociation or dissociation of metastable
molecules referring again to FIG. 1, these methods and apparatus
are collectively represented by apparatus 25.
[0094] Of the options, in-situ generation is the simplest design,
but poses several problems, such as turn on--turn off times that
could be a throughput limitation. Intra-showerhead generation has
been shown to have an advantage of separating the atomic specie
generation from the ALD space. The preferable method at the time of
this specification is remote generation by a high-density source,
as this is the most versatile method. The radicals are generated in
a remote source and delivered to the ALD volume, distributed by a
showerhead over the wafer in process.
[0095] It will be apparent to the skilled artisan that there are a
variety of options that may be exercised within the scope of this
invention as variations of the embodiments described above some
have already been described. For example, radicals of the needed
species, such as hydrogen, oxygen, nitrogen, may be generated in
several ways and delivered in the process steps. Further, ALD
chambers, gas distribution, valving, timing and the like may vary
in many particulars. Still further, many metals, oxides nitrides
and the like may be produced, and process steps may be altered and
interleaved to create graded and alternating films.
[0096] In addition to these variations it will be apparent to the
skilled artisan that one may, by incorporating processes described
herein, alternate process steps in a manner that alloys of two,
three or more metals may be deposited, compounds may be deposited
with two, three or more constituents, and such things as graded
films and nano-laminates may be produced as well. These variations
are simply variants using particular embodiments of the invention
in alternating cycles, typically in-situ. There are many other
variations within the spirit and scope of the invention, so the
invention is limited only by the claims that follow.
* * * * *