U.S. patent application number 13/830322 was filed with the patent office on 2014-09-18 for silane or borane treatment of metal thin films.
This patent application is currently assigned to ASM IP HOLDING B.V.. The applicant listed for this patent is ASM IP HOLDING B.V.. Invention is credited to Suvi Haukka, Eric Shero.
Application Number | 20140273428 13/830322 |
Document ID | / |
Family ID | 51503937 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140273428 |
Kind Code |
A1 |
Shero; Eric ; et
al. |
September 18, 2014 |
SILANE OR BORANE TREATMENT OF METAL THIN FILMS
Abstract
The negative effect of oxygen on some metal films can be reduced
or prevented by contacting the films with a treatment agent
comprising silane or borane. In some embodiments, one or more films
in an NMOS gate stack are contacted with a treatment agent
comprising silane or borane during or after deposition.
Inventors: |
Shero; Eric; (Phoenix,
AZ) ; Haukka; Suvi; (Helsinki, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASM IP HOLDING B.V. |
Almere |
|
NL |
|
|
Assignee: |
ASM IP HOLDING B.V.
Almere
NL
|
Family ID: |
51503937 |
Appl. No.: |
13/830322 |
Filed: |
March 14, 2013 |
Current U.S.
Class: |
438/592 |
Current CPC
Class: |
H01L 21/02271 20130101;
H01L 21/28088 20130101; H01L 21/321 20130101; C23C 16/56 20130101;
H01L 21/76841 20130101; H01L 21/02211 20130101; Y10S 438/932
20130101; H01L 21/28562 20130101; H01L 21/3105 20130101; H01L
29/4966 20130101; H01L 29/517 20130101 |
Class at
Publication: |
438/592 |
International
Class: |
H01L 21/28 20060101
H01L021/28; H01L 21/02 20060101 H01L021/02 |
Claims
1. A method for forming a gate stack comprising: providing a
substrate comprising a dielectric material and a first
metal-containing thin film over the dielectric material; contacting
the first metal-containing thin film with a silane or borane
compound; after contacting the substrate with the silane or borane
compound, depositing a second metal-containing thin film over the
first thin film.
2. The method of claim 1, wherein the first thin film comprises a
metal selected from Ti, Ta, Hf, V, Nb, and Zr.
3. The method of claim 1, wherein the first metal-containing thin
film is an etch stop layer or barrier layer and the second
metal-containing thin film is a workfunction setting layer.
4. The method of claim 1, wherein the first metal-containing thin
film is a TiN, TiAlN, TaN or TiAlCN thin film.
5. The method of claim 1, wherein the second metal containing thin
film comprises an n-type metal.
6. The method of claim 1, wherein the second metal containing thin
film comprises TiAl, TaC, HfC, TaAlC, TiAlSiC, TiAlB, TaAlB,
TiAlSiB, TaAl, SiAlSiC or HfAlSiB.
7. The method of claim 1, wherein the second metal-containing thin
film is a titanium carbide film.
8. The method of claim 1, wherein contacting the first
metal-containing thin film with a silane or borane compound
comprises exposing the first metal-containing thin film to the
silane or borane compound for a duration of between about 1 second
and about 2 minutes.
9. The method of claim 1, additionally comprising contacting the
second metal-containing thin film with a silane or borane
compound.
10. The method of claim 1 wherein depositing the second
metal-containing thin film comprises an atomic layer deposition
process comprising multiple deposition cycles.
11. The method of claim 10, wherein the substrate is exposed to a
silane or borane compound in each deposition cycle.
12. The method of claim 1, additionally comprising depositing a
third metal-containing thin film over the second metal-containing
thin film.
13. The method of claim 12, wherein the substrate is contacted with
a silane or borane compound during or after depositing the second
metal-containing thin film and prior to depositing the third
metal-containing thin film.
14. The method of claim 12, wherein the substrate is contacted with
a silane or borane compound during or after deposition of the third
metal-containing thin film.
15. The method of claim 14, additionally comprising depositing a
metal thin film over the third metal-containing thin film.
16. The method of claim 15, wherein the metal thin film is a
tungsten thin film.
17. The deposition method of claim 1, wherein the silane or borane
is selected from the group consisting of monosilane, disilane,
trisilane, borane, diborane, and triborane.
18. The deposition method of claim 17, wherein the silane or borane
is trisilane.
19. The deposition method of claim 1, wherein the first and second
metal-containing thin films are deposited in situ.
20. A method for forming an NMOS stack, the method comprising,
sequentially: providing a substrate comprising a previously
deposited dielectric material and an etch stop layer; contacting
the etch stop layer with a silane or borane compound; and
depositing a metal-containing layer over the first etch stop
layer.
21. The method of claim 20, wherein the etch stop layer is a
titanium nitride layer and the metal-containing layer comprises an
n-type metal.
22. The method of claim 21, wherein the metal-containing layer
comprises TiAl, TaC, HfC, TaAlC, TiAlSiC, TiAl B, TaAlB, TiAlSiB,
TaAl, TiAlSiC TaAlSiB, or HfAlSiB.
23. The method of claim 20, further comprising contacting the
metal-containing layer with a silane or borane compound.
24. The method of claim 20, wherein the metal-containing layer is
deposited by an atomic layer deposition process comprising multiple
deposition cycles, and wherein the substrate is contacted with a
silane or borane compound during at least one of the deposition
cycles.
25. The method of claim 24, wherein the silane or borane is
selected from the group consisting of monosilane, disilane,
trisilane, borane, diborane, and triborane.
26. The deposition method of claim 20, wherein contacting the etch
stop layer with a silane or borane compound does not increase the
thickness first metal nitride layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present application relates generally to processes for
providing a protective treatment to metal thin films. In some
embodiments, thin films used in metal gate and metal electrode
applications in metal oxide semiconductor field effect transistors
(MOSFETs), such as n-channel MOSFETs (NMOS) are treated either
during or after deposition in order to prevent or reduce the
effects of oxidation.
[0003] 2. Description of the Related Art
[0004] Oxidation of a metal thin film can easily occur during many
steps in processing, such as by exposure to atmospheric water or
oxygen. In a multi-step fabrication process oxidation may occur
between the deposition of each thin film, such as when transferring
a wafer or substrate between deposition modules. Oxidation poses a
problem in that it can affect the workfunction of a given thin film
or an entire stack. And oxidation in one thin film may lead to
oxidation of the interface between that film and a second film or
even oxidation of the second film itself if the oxygen is able to
diffuse through the first film to the second film.
[0005] For example, in a typical fabrication process of a MOSFET,
oxidation of the etch-stop layer can easily occur after formation
of a PMOS stack and before formation of an NMOS stack. Oxidation of
the etch-stop layer can affect the workfunction of the subsequently
formed NMOS stack, as it may lead to a shift in the workfunction,
for example, from n-type to p-type. Other layers deposited during
formation of a gate stack can also be exposed to oxygen, for
example between deposition of each of the various thin films.
[0006] Referring to FIG. 1, a typical NMOS stack 100 is
illustrated. The stack 100 includes a dielectric layer 102, a first
metal nitride layer 104, a metal carbide layer 106--in which the
interface 108 between the first metal nitride layer 104 and the
metal carbide layer 106 includes oxidized portions represented by
the presence of oxygen ("0") atoms--a second metal nitride layer
110, and a metal layer 112. The presence of oxygen at the interface
108 between the first metal nitride layer 104 and the metal carbide
layer 106 can undesirably shift the workfunction of the stack 100
from n-type to p-type.
[0007] Oxidation of the various layers can occur in a variety of
ways during formation of the stack; however, it is common for the
first metal nitride layer 104 to have already been oxidized prior
to the deposition of the metal carbide layer 106. Even if the metal
carbide layer 106 is able to be deposited without the presence of
oxygen so as to achieve a relatively pure layer of a metal carbide,
oxygen present in the first metal nitride layer 104 is capable of
diffusing up into the metal carbide layer 106. Oxygen in the metal
carbide layer 106 and particularly at the interface 108 can
undesirably shift the work function of the overall stack 100.
SUMMARY OF THE INVENTION
[0008] According to some embodiments of the present disclosure,
methods for forming a gate stack include providing a substrate
having a dielectric material and a first metal-containing thin film
over the dielectric material, contacting the first thin film with a
silane or borane compound, and depositing a second metal-containing
thin film over the first metal-containing thin film. In some
embodiments, the first thin film comprises a metal selected from
Ti, Ta, Hf, V, Nb, and Zr. In some embodiments, the first
metal-containing thin film is an etch stop layer or barrier layer
and the second metal-containing thin film is a workfunction setting
layer. The first metal-containing thin film in some embodiments is
a TiN, TiAlN, TaN or TiAlCN thin film.
[0009] According to some embodiments, the second metal containing
thin film comprises an n-type metal. And in some embodiments, the
n-type metal (or n-metal) film comprises a metal carbide, such as
TaC, TiC, HfC, TaAlC, TiAlSiC, or SiAlSiC. In some embodiments, the
n-type metal is TiAl, TiAlB, TaAlB, TiAlSiB, TaAl, or HfAlSiB. The
second metal-containing thin film in some embodiments is a titanium
carbide film. In some embodiments the metal in the first
metal-containing thin film is different from the metal in the
second metal-containing thin film.
[0010] According to some embodiments of a method for forming a gate
stack, contacting the first metal-containing thin film with a
silane or borane compound comprises exposing the first
metal-containing thin film to the silane or borane compound for a
duration of between about 1 second and about 2 minutes. Some
methods further include contacting the second metal-containing thin
film with a silane or borane compound. In some methods, depositing
the second metal-containing thin film comprises an atomic layer
deposition process comprising multiple deposition cycles.
[0011] According to some embodiments, the substrate is exposed to a
silane or borane compound in each deposition cycle. Some methods
further include depositing a third metal-containing thin film over
the second metal-containing thin film. The third metal-containing
thin film may comprise a different metal from the second-metal
containing thing film. In some methods, the substrate is contacted
with a silane or borane compound during or after depositing the
second metal-containing thin film and prior to depositing the third
metal-containing thin film. And in some methods, the substrate is
contacted with a silane or borane compound during or after
deposition of the third metal-containing thin film. Some methods
further include depositing a metal over the third metal-containing
thin film. The metal in some embodiments is tungsten.
[0012] According to some embodiments, the silane or borane is
selected from the group consisting of monosilane, disilane,
trisilane, borane, diborane, and triborane. And in some
embodiments, the silane or borane is trisilane. According to some
methods, the first and second metal-containing thin films are
deposited in situ.
[0013] Some embodiments of methods for forming an NMOS stack
according to the present disclosure include, sequentially,
providing a substrate comprising a previously deposited dielectric
material and an etch stop layer, contacting the etch stop layer
with a silane or borane compound; and depositing a metal-containing
layer over the first etch stop layer.
[0014] In some methods, the etch stop layer is a titanium nitride
layer and the metal-containing layer comprises an n-type metal. The
metal-containing layer in some methods comprises TiAl, TaC, HfC,
TaAlC, TiAlSiC, TiAl B, TaAlB, TiAlSiB, TaAl, TiAlSiC TaAlSiB, or
HfAlSiB. Some methods also include contacting the metal-containing
layer with a silane or borane compound. The metal-containing layer
in some methods is deposited by an atomic layer deposition process
comprising multiple deposition cycles, and the substrate is
contacted with a silane or borane compound during at least one of
the deposition cycles. In some embodiments, the silane or borane is
selected from the group consisting of monosilane, disilane,
trisilane, borane, diborane, and triborane. And contacting the etch
stop layer with a silane or borane compound in some methods does
not increase the thickness first metal nitride layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention will be better understood from the Detailed
Description of the Preferred Embodiments and from the appended
drawings, which are meant to illustrate and not to limit the
invention, and wherein:
[0016] FIG. 1 is a schematic cross-sectional side view of a gate
stack containing an oxidized portion;
[0017] FIG. 2 is a schematic cross-sectional side view of an
electrode structure, comprising an NMOS stack that includes a
dielectric layer, a first metal nitride layer, a metal carbide
layer, a second metal nitride layer, and a metal layer, according
to some embodiments of the invention; and
[0018] FIGS. 3A-C are flow charts generally illustrating protective
treatment of a dielectric layer or titanium nitride layer during a
process of forming a thin film stack, in accordance with some
embodiments.
[0019] FIGS. 4A-C are flow charts generally illustrating protective
treatment of a titanium nitride or titanium carbide layer during a
process of forming a thing film stack, in accordance with some
embodiments.
[0020] FIG. 5 is a flow chart illustrating methods of forming a
thin film by ALD, in which supply of a protective treatment follows
removal of excess second reactant and by-products, in accordance
with some embodiments.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] The present disclosure provides methods for reducing or
preventing undesirable effects of oxidation in one or more thin
films comprising metal. The thin films can be deposited using known
vapor deposition processes, such as atomic layer deposition (ALD)
or chemical vapor deposition (CVD) processes. In some embodiments
the methods for reducing oxidation can comprise an oxygen barrier
material or a preventative treatment applied to a deposited thin
film. In some embodiments however, a protective treatment may be
provided as a part of an ALD or CVD method used to form the thin
film. A protective treatment may comprise exposing the film to be
treated to a silane or a borane compound. The treatment may reduce
or substantially prevent oxidation of the thin film and the
possible buildup of oxygen at the interface of the thin film and an
overlying layer.
[0022] Oxidation resistance is important in many contexts. For
example, in a gate stack even a minor amount of oxygen in the stack
could change the stack's electrical properties, namely eWF, making
it unsuitable for its intended purpose. Moreover, processing,
including deposition of films and film stacks, without exposure to
air or ambient moisture can be costly, difficult, and/or too
complex. The application of a preventative treatment during or
after deposition of one film in a manufacturing process may not
only reduce or prevent oxidation of that film but also of overlying
films during subsequent processing steps. Thus, using a protective
treatment can simplify processing while also controlling costs.
[0023] In addition, although described as preventative, the
treatment may also reduce the deleterious effects of oxygen that is
already present in a film, such as from previous processing steps
or transport. The material used in the treatment may remove or
isolate oxygen that may be present in a thin film or on the surface
of a thin film. In some embodiments, treatment of one thin film may
benefit subsequent layers or films in that the treatment may
prevent oxygen from migrating up into those layers.
[0024] Without being held to any particular theory, the silicon or
boron introduced into a metal film during treatment with silane or
borane reduces bonds between oxygen and the metal by formation of
silicon oxide or boron oxide. The oxygen may be present in the film
at the time of treatment, or the film may subsequently be exposed
to oxygen. For example, if an oxidized TiN film is treated with
silane or borane, the TiON is reduced back to TiN. The presence of
Si and/or B in a treated metal film can also act as a barrier to
oxidation, such as during subsequent processing steps, by allowing
the oxygen to preferentially bond with the Si and/or B, relative to
the metal of the metal film.
[0025] In some embodiments, a silane or borane treatment can be
used to reduce the resistivity of a thin metal film, such as a
titanium carbide film.
[0026] In some embodiments, a metal thin film is deposited and
subsequently receives a protective treatment, which may comprise
exposure to a silane or a borane. For example a metal thin film may
be formed by a known deposition process, such as by a CVD process
and then exposed to a borane or silane, such as trisilane or
disilane.
[0027] In some embodiments, the protective treatment may be
provided during deposition of the metal film, rather than, or in
addition to, the treatment being applied after deposition. That is,
the treatment may be applied intermittently during deposition. For
example, a substrate may be exposed to silane or borane
intermittently in an atomic layer deposition process for forming a
metal thin film, such as a metal nitride or metal carbide thin
film. In some embodiments the substrate is exposed to the silane or
borane in each deposition cycle, after a certain number of
deposition cycles, or after all the deposition cycles have been
completed.
[0028] In some embodiments the thin film that is treated comprises
one or more metals selected from the group consisting of Ti, Ta, W,
In some embodiments the thin film that is treated comprises Ta, Ti,
or W, such as a TaN film, a TiC film, or a W film. In some
embodiments the thin film that is treated comprises TiAl, TaC, HfC,
TaAlC, TaAlB, TaAl, SiC, HfAlSiB, etc. In some embodiments the thin
film comprises an n-type metal, such as titanium. In some
embodiments the thin film is deposited during integrated circuit
processing, such as during formation of a gate stack, as described
in more detail below. Although generally described herein with
reference to films deposited during fabrication of NMOS
transistors, the skilled artisan will recognize that the methods
described herein can be used in other contexts where
metal-containing films are or could be exposed to oxygen.
[0029] In some preferred embodiments, the treatment agent comprises
one or more silane or borane, or a mixture of silanes and boranes.
The silane or borane may be selected from the following: borane,
diborane, triborane, silane, monosilane, disilane, trisilane, or a
mixture of two or more of these. The treatment agent may be
provided as a brief pulse, such as during one or more ALD cycles,
or may be provided for longer periods of time, such as when a
previously deposited film is being treated. The length of time can
be controlled to achieve the desired amount of silicon or boron in
the thin film.
[0030] In some embodiments, the pressure within a reaction chamber
during a protective treatment is between about 0.1 torr and about
50 torr, though the pressure can be between about 0.5 torr and
about 5 torr.
[0031] In some embodiments, the temperature within a reaction
chamber is between about 350.degree. C. and about 450.degree. C.,
though it can be between about 380.degree. C. and about 420.degree.
C. or, preferably, between about 390.degree. C. and about
420.degree. C.
[0032] In some embodiments, the duration of exposure to the
treatment agent may be from about 1 second and to about 60 seconds
or more. Longer periods, such as at least about 10 seconds, may be
desired if treating a thicker film, such as where a completed film
has already or previously been deposited prior to a protective
treatment. And shorter periods, such as about 1, 2 or 3 seconds,
may be desired when incorporating a treatment step into a
deposition cycle. In some embodiments, treatment may comprise
exposure to the treatment agent for less than 1 second.
Gate Stack Applications
[0033] The processes disclosed herein may be applied in a variety
of contexts where protecting a layer from oxidation or reducing the
effect of oxygen on the properties of an oxidized layer may be
beneficial. Although primarily illustrated in the context of the
fabrication of NMOS transistors, which may include planar
"replacement gate" devices as well as multiple gate transistors,
such as FinFETs, the skilled artisan will be aware of other
relevant contexts in which the disclosed methods could be utilized,
such as metal electrodes for memory structures where an n-type
metal is needed.
[0034] In the context of the present disclosure, a protective
treatment refers to exposing a thin film comprising metal on a
substrate to a treatment agent comprising silane or borane. The
treatment agent may react with oxygen that may be present on or in
the thin film or with oxygen upon subsequent exposure of the thin
film to oxygen or oxidizing agents. In some cases, at least some
oxygen is bound to metal atoms in the thin film, and with exposure
to the treatment agent comprising silane or borane the metal oxygen
bonds are reduced by preferential formation of silicon oxide or
boron oxide. The silane or borane agent may also bind oxygen that
is not bound to metal, such as oxygen that may be present in the
form of contaminants such as water, hydroxyl groups, etc.
[0035] As mentioned above, the treatment agent comprises one or
more silanes and/or boranes, such as monosilane, disilane,
trisilane, borane, diborane, and triborane.
[0036] The treatment agent may be applied in vapor or liquid form.
However, the treatment is typically carried out by providing a
vapor phase pulse of the treatment agent The length of time that
the treatment agent is applied may vary, for example depending on
the thickness of the film being treated and the amount of oxidation
or the anticipated exposure to oxidizing agents. In some
embodiments the treatment agent is contacted with the film for a
period of about 1 second to about 10 minutes, from about 2 second
to about 5 minutes, from about 10 seconds to about 2 minutes or
from about 20 seconds to about 60 seconds. However, shorter or
longer exposures can be utilized. For example, in some embodiments
the treatment agent may be applied as a relatively short pulse,
such as less than about 1 second. In some embodiments a partially
or completely deposited film is soaked in the treatment agent, such
as for 1 second or more, 10 seconds or more, 20 seconds or more, 30
seconds or more, or 60 seconds or more. In some embodiments the
soak may be for at least one minute, two minutes, five minutes, ten
minutes or more. Specific treatment times can be determined by the
skilled artisan depending on the particular circumstances such as
the type of film, thickness of the film, amount of existing
oxidation of the film and the type of exposure to oxidizing agents
that is anticipated.
[0037] In some embodiments the protective treatment does not add to
the thickness of a thin film, such that a thin film (or plurality
of thin films) that has received a protective treatment is not
appreciably thicker than a thin film that has not received such a
treatment.
[0038] In some embodiments, a thin film comprising a metal is
deposited according to a known process, such an ALD or a CVD
process. A protective treatment can then be applied to the thin
film after the thin film has been fully deposited. However, in some
embodiments, the protective treatment forms a part of the
deposition process. For example, where an ALD process is used, the
protective treatment may comprise one step of at least one ALD
cycle. In some cases, the protective treatment is provided in a
certain number of ALD cycles or all of the ALD cycles. For example,
the protective treatment may be provided as a separate pulse in
every ALD cycle, or provided every 2, 3, 4, 5, 10, 20 or more ALD
cycles. For CVD deposition, the CVD deposition process may be
interrupted one or more times during deposition to provide the
treatment agent. In some embodiments, the protective treatment is
applied as the last pulse or exposure in the deposition
process.
[0039] In some embodiments, the protective treatment is applied to
the substrate prior to the deposition of a thin film that is to be
protected from oxidation. For example, treatment of an oxidized
film on a substrate surface may prevent migration of oxygen from
that film to a film that is subsequently deposited over the treated
film and that will benefit from being protected from oxidation.
[0040] As discussed above, in addition to reducing metal oxide and
thus addressing previous exposure to an oxidizing agent, the use of
a protective treatment may also protect a metal thin film from
being oxidized by subsequent exposure to oxygen. The use of a
protective treatment may also at least partially protect one or
more films that are deposited over a treated thin film.
[0041] Referring to FIG. 2, an exemplary embodiment of an NMOS
stack 200 is illustrated. The stack 200 includes a dielectric layer
202, such as hafnium oxide, a first etch stop layer or bottom
barrier layer 204, such as a titanium nitride (TiN) layer, a first
n-type metal layer, here illustrated as a metal carbide layer 206,
such as tantalum carbide (TaC), a second metal nitride layer 208,
and a metal layer 210, such as a tungsten (W) layer. The presence
of silicon 212 derived from a protective treatment is illustrated
as being contained within the first metal nitride layer 204. While
the silicon 212 may form a part of or be contained in any one of or
more than one of the illustrated layers, FIG. 2 illustrates that
the silicon 212 is located more or less at the interface of the
first metal nitride layer 204 and the n-type metal layer 206.
Without being tied to any particular theory, it is believed that
this interface or near-interface region may determine or influence
the workfunction of the overall stack 200. Thus, limiting the
migration of materials such as oxygen or aluminum--which can occur
more easily as the layers become thinner--may help protect the
workfunction or another characteristic of the stack 200.
Accordingly, in some embodiments, such as the one illustrated here,
it may be particularly beneficial to provide a protective treatment
as a part of the deposition of the etch stop layer 204 or prior to
the deposition of the n-metal layer 206, where the protective
treatment may provide silicon 212 (or boron), at least at or near
the interface between the etch stop and n-metal films (the first
metal nitride layer 204 and the metal carbide layer 206 as
illustrated). In some embodiments, a protective treatment is
applied to the first etch stop layer 204 once the substrate has
been placed in a chamber for depositing the n-metal layer but
before deposition of the n-metal layer has begun. Of course,
treatment may be utilized to provide Si or B at the interface
between any two layers.
[0042] In some embodiments, an etch-stop layer (or bottom barrier
layer) that receives a protective treatment could comprise TiN,
TaN, or other materials known in the art. And materials other than
TaC could be used as then n-type metal layer, including other
oxygen sensitive n-type metal films, such as TiAl, TiC, HfC, TaAlC,
TaAlB, TaAl, SiC, HfAlSiB. Other types of films that would benefit
from the treatment will be apparent to the skilled artisan.
[0043] The use of a protective treatment can bind up at least some
of the oxygen that may be present initially, or upon subsequent
exposure, such as during transport from one chamber to another. The
use of a protective treatment may also reduce at least some of the
previously oxidized portions of a thin film, such as the first
metal nitride layer 204. For example, substrates may be received
that already contain an etch stop layer (or bottom barrier layer),
such as a TiN layer, and that layer can be treated as described
herein by exposure to a treatment agent prior to subsequent
processing.
[0044] The thicknesses of the various layers in the stack 200 may
vary, though in some embodiments, such as the one illustrated in
FIG. 2, the first metal nitride layer 204 may be from about 5 .ANG.
to about 20 .ANG. thick, for example about 15 .ANG. thick, and the
second metal nitride layer may be about 30 .ANG. to about 50 .ANG.
thick. The use of a protective treatment as presently disclosed can
have particular utility where the thicknesses of the various layers
in a stack, such as stack 200, are reduced to achieve smaller
electronic devices and circuitry.
[0045] The protective treatments disclosed herein could be applied
to any one or more of the layers 202, 204, 206, 208, or 210 before,
during, or after the deposition of each thin film. In some
embodiments, it is preferable to treat one or both of layers 204
and 206. In some embodiments, it may be preferable to treat one or
more of layers 204, 206, and 208. The use of a protective treatment
before or during the formation of the NMOS workfunction setting
layer (the n-metal layer 206 as illustrated) has been mentioned;
however a treatment agent could also or alternatively be applied
before or during the deposition of the first etch stop layer (the
first metal nitride layer 204). In some embodiments, the use of a
protective treatment on the first metal nitride layer 204 may
eliminate or reduce the need for such a treatment of any subsequent
layers or at least the NMOS workfunction setting layer 206.
Similarly, the use of a protective treatment before, during, or
after the formation of the n-metal layer 206 may eliminate or
reduce the need for a similar treatment to subsequent layers,
particularly if a treatment applied to the n-metal layer 206
preserves the work function of the overall stack 200 irrespective
of moderate oxidation of the subsequent layers 208 or 210.
[0046] However, in some embodiments, it may be beneficial to treat
the second metal nitride layer 208 and/or the metal layer 210. As
with the lower layers, a protective treatment may reduce oxidized
portions of those layers, scavenge oxygen contaminates, and/or
prevent subsequent oxidation when exposed to contaminates or the
atmosphere.
[0047] Irrespective of the layer being discussed, the same methods
for applying the protective treatment can be used. In some
embodiments the treatment agent is provided as a pulse as a part of
a deposition cycle. In some embodiments a deposited film, or
portion of a deposited film is soaked in the treatment agent. For
example, a protective treatment could be incorporated into an ALD
process for forming any one of the layers 204, 206, 208, or 210.
And the treatment agent could be provided in every ALD cycle or
just in some cycles. With a CVD process, the treatment could be
incorporated during the deposition process as other precursors are
being exposed to the substrate or could be provided after
deposition of the film has been completed and all the precursors
have reacted with the substrate and excess reactants have been
purged from the reaction space. In some embodiments CVD may be used
to deposit film to a first thickness, CVD can be stopped and the
reaction chamber purged, that thickness can be exposed to a
treatment agent, and CVD can be continued to add additional
thickness to the film. This can be repeated as many times as
desired to obtain a film with the desired thickness. Again, a final
treatment can be applied after the final deposition.
[0048] With reference again to FIG. 2, in some embodiments a first
metal nitride layer 204 is deposited over the dielectric layer 202,
which may comprise a dielectric material such as hafnium oxide. A
protective treatment may be applied before, during, and/or after
the deposition of the first metal nitride layer 204. In some
embodiments, it is desirable to apply a protective treatment to a
completed first etch stop layer, such as a TiN layer, prior to the
deposition of the NMOS workfunction setting layer, such as
then-metal layer 206, even if a protective treatment was used in
the deposition of the first etch stop layer. For example, if some
time has passed from the time the first metal nitride layer 204 was
deposited and the time when the n-metal layer 206 is deposited.
Such a delay may increase the chances that the first metal nitride
layer will be exposed to water, air, etc.
[0049] FIG. 3A illustrates one possible process where a substrate
having a dielectric material is provided at step 302, and a metal
nitride layer, such as a titanium nitride etch stop layer, is
deposited over the dielectric layer at step 304. A protective
treatment is then applied to the completed titanium nitride etch
stop layer at step 306. The protective treatment applied at step
306 may be applied as a soak, and may reduce TiON and/or bind to
free oxygen in the TiN layer, particularly near the surface. The
duration of step 306 may be, for example, from about 30 seconds to
about 4 minutes. The duration may depend on the thickness of the
titanium nitride layer and may be adjusted by the skilled artisan
based on the particular circumstances. In some embodiments, the
duration can be shortened if step 306 is performed at a higher
pressure and/or a higher temperature.
[0050] FIG. 3B illustrates a process where a substrate having a
dielectric material is provided at step 312, and a protective
treatment is applied to the dielectric layer at step 314. A
titanium nitride is then deposited by a known method at step 316.
In this process, free oxygen that may have been present in or on
the dielectric layer may be bound up by the protective treatment so
that it is not available to oxidize the titanium deposited in step
316. In some embodiments where the dielectric material receives a
protective treatment, the protective treatment may not prevent
subsequent oxidation of additional layers, but it may prevent
oxygen in the dielectric from diffusing up into the additional
layers.
[0051] FIG. 3C illustrates one process where a substrate having a
dielectric material is provided at step 322, and a titanium nitride
film is deposited by an ALD method at step 324 in which a
protective treatment is incorporated into one or more of the
deposition cycles. The protective treatment may be provided in only
one deposition cycle or may comprise a step in a certain number of
cycles, such as every other cycle or every third, fourth, fifth,
sixth, seventh cycle, etc.
[0052] In some embodiments, the deposition of the titanium nitride
layer at step 324 may comprise an ALD process having the following
steps: [0053] 1. providing a titanium precursor, such as a titanium
halide, to the reaction space; [0054] 2. substantially purging
and/or evacuating excess titanium precursor and reaction
byproducts; [0055] 3. providing a nitrogen-contributing reactant to
the reaction space, such as NH.sub.3, hydrazine, or radicals/ions
of N and H (such as in a PEALD process); [0056] 4. substantially
purging and/or evacuating excess nitrogen-contributing reactant and
reaction byproducts; and [0057] 5. providing a protective treatment
agent comprising a silane or borane, to the reaction space.
[0058] Step 5 can be included in each ALD cycle or only some of the
ALD cycles. Thus, steps 1-4 can be repeated several times before
step 5 is introduced. Step 5 may also be used prior to any ALD
cycle or only as the first step in the first ALD cycle.
[0059] Again referring to FIG. 2, the n-metal carbide layer 206 can
be deposited over the first metal nitride layer 204. A protective
treatment may be applied before, during, and/or after the
deposition of the n-metal layer 206. FIG. 4A illustrates one
possible process where a titanium nitride layer is provided at step
402, and an n-type metal layer, such as a titanium carbide layer,
is deposited over the titanium nitride layer at step 404. A
protective treatment is then applied to the completed titanium
carbide layer at step 406. In some embodiments, application of a
protective treatment during or before the deposition of the work
function setting n-metal layer 206 may help minimize the presence
of oxygen in the film while the n-metal layer 206 awaits the second
metal nitride layer 208 in a clustered or declustered process. The
protective treatment applied at step 406 may comprise soaking the
deposited titanium carbide layer in a treatment agent comprising
silane or borane. The protective treatment may reduce or bind to
oxygen contaminates in the TiC film.
[0060] FIG. 4B illustrates one process where a titanium nitride
layer is provided at step 412, and a protective treatment is
applied to the titanium nitride layer at step 414. A titanium
carbide is then deposited by a known method at step 416. In this
process, free oxygen that may have been present in or on the
titanium nitride layer may be bound up by the protective treatment
agent so as to prevent or reduce oxidation of the titanium carbide
deposited in step 416.
[0061] Other materials may also benefit from the application of a
protective treatment according to the present disclosure. All NMOS
workfunction layers, such as pure metals like Al and Ti, or
transition metal nitrides, carbides, borides, silicides, etc. may
suffer from oxygen incorporation making them more p-type.
Accordingly, a protective treatment could be applied to films
comprising any of such materials.
[0062] FIG. 4C illustrates one process where a titanium nitride is
provided at step 422, and a titanium carbide is deposited by an ALD
method at step 424 in which a protective treatment is incorporated
into one or more of the deposition cycles. For example, the
protective treatment may comprise a step in only one cycle or may
comprise a step in a certain number of cycles, such as every other
cycle or every third, fourth, fifth, sixth, seventh cycle, etc.
[0063] In some embodiments, the deposition of the titanium carbide
layer at step 424 may comprise an ALD process having the following
steps: [0064] 1. providing a titanium precursor, such as a titanium
halide (or other transition metal halides), to the reaction space;
[0065] 2. substantially purging and/or evacuating excess titanium
precursor and reaction byproducts; [0066] 3. providing a
carbon-contributing reactant to the reaction space, such as
compounds containing metal-carbon bonds including metalalkyl
compounds (e.g., TTBA and TMA); [0067] 4. substantially purging
and/or evacuating excess carbon-contributing reactant and reaction
byproducts; and [0068] 5. providing a protective treatment agent
comprising a silane or borane, to the reaction space.
[0069] Step 5 can be included in each ALD cycle or only in some of
the ALD cycles. Thus in some embodiments steps 1-4 can be repeated
several times before step 5 is introduced. Step 5 may also be used
prior to any ALD cycle or only as the first step in the first ALD
cycle. Application of a protective treatment prior to any ALD cycle
for depositing the n-metal layer 206 may be desirable where the
first metal nitride layer 204 has already been oxidized, such as
where the first metal nitride layer has served as an etch-stop
layer in a prior process. In such cases, it may be desirable to
apply the protective treatment as a soak of a treatment agent
comprising silane or borane prior to depositing the n-metal layer
206. In some embodiments where the TiN layer 204 is treated,
protective treatment during or after the deposition of the n-metal
layer 206 is not utilized. However, in some embodiments where the
first metal nitride layer 204 has been treated, it may still be
desirable to apply a protective treatment during or after the
deposition of the n-metal carbide layer 206.
[0070] In some embodiments, NMOS stacks containing n-metal thin
films fabricated using the methods disclosed herein exhibit a
leakage (J.sub.g) (at -1V stress) of less than about 10.sup.-2
A/cm.sup.2, less than about 10.sup.-3 A/cm.sup.2, or less than
about 3*10.sup.-4 A/cm.sup.2.
[0071] In some embodiments of the present disclosure, n-metal thin
films can be formed in which the equivalent oxide thickness, or
EOT, of the thin films can be less than about 1.3 nm, less than
about 1.2 nm, preferably less than about 1.1 nm, or less than about
1.05 nm.
[0072] In some embodiments of the present disclosure, n-metal films
can be formed in which the effective workfunction, or eWF, can be
from about 4.0 to about 4.4 eV, from about 4.05 to about 4.35 eV,
or from about 4.1 to about 4.25 eV.
[0073] In some embodiments, the use of a protective treatment such
as a silane (e.g., disilane or trisilane) can reduce the
resistivity of an n-metal thin film relative to a TiC film to which
a protective treatment is not exposed. In some embodiments, the
resistivity is reduced up to or as much as about 30%, up to or as
much as about 40%, or up to or as much as about 50%. In some
embodiments, such as where a protective treatment is applied as
soak after deposition, resistivity reduction may be as much as
about 5%, as much as about 10%, or as much as about 20%.
[0074] Again referring to FIG. 2, a metal layer 210 may be
deposited by any known method. A protective treatment may be
applied before, during, and/or after deposition of the metal layer
210. In some embodiments, a second metal nitride layer 208 is
provided, and the metal layer 210 is deposited over the metal
nitride layer 208. The second metal nitride layer 208 can be
deposited over the n-metal layer 206. A protective treatment may be
applied before, during, and/or after the deposition of the second
metal nitride layer 208, similar to the first metal nitride layer
212. In this process, free oxygen that may have been present in or
on the second metal nitride layer 208 may be bound up by the
protective treatment so as to not oxidize the subsequently
deposited tungsten. Reducing the amount of free oxygen in the
second metal nitride layer 208 may have the added benefit of
diminishing the amount of oxygen that could diffuse down into the
stack 200 during subsequent processes, such as downstream thermal
processing, diffusion that could actually reach the workfunction
layer (i.e., the n-metal layer 206 or another suitable layer such
as TaC).
[0075] A protective treatment may be applied to the completed metal
layer 210. The protective treatment may be applied as a soak to the
deposited metal film. In some embodiments, a metal layer is
deposited by an ALD method in which a protective treatment is
incorporated into one or more of the deposition cycles. For
example, the protective treatment may comprise a step in only one
deposition cycle or may comprise a step in a certain number of
cycles, such as every fifth, tenth, twentieth cycle, etc.
[0076] Again, while illustrated in the context of treating thin
films in an NMOS stack, other metal-containing films can be treated
as well. The exact composition of metal thin films produced and/or
treated using the methods and materials disclosed herein may vary.
For example, titanium carbide films fabricated according to the
present disclosure may contain a number of differing elemental
components including, but not limited to titanium, aluminum,
carbon, silicon and/or boron depending in part on the type of
protective treatment used.
[0077] In some embodiments, the atomic percentage of silane or
borane present in a film after treatment could be greater than
about 10%, greater than about 25%, or greater than about 35%. In
embodiments where the protective treatment is applied as soak, the
silane or borane may be very concentrated at those surfaces that
were treated, with the concentration dropping off rapidly below
those surfaces. In embodiments where the protective treatment is
applied as a part of a deposition process, such as in an ALD
process, the silane or borane concentration may be from about 5% to
about 50%.
Deposition Methods
[0078] As discussed above, in addition to the treatment of
deposited films, methods presented herein allow treatment during
deposition of conformal metal thin films on substrate surfaces.
[0079] According to some embodiments, an ALD or quasi-ALD process
is used in which a material, such as silicon or boron, is
incorporated into a metal thin film and protects the film from
oxidation. In some embodiments, the protective treatment is
incorporated into one or more cycles of the deposition process. In
some embodiments, the protective treatment is applied to a metal
thin film after all the deposition cycles have been completed. In
some embodiments, the protective treatment is applied prior to a
deposition process in order to prepare an underlying surface or as
the first step in a deposition process.
[0080] According to some embodiments, an ALD or quasi-ALD process
is used to form a metal film. For example, one or more films in an
NMOS stack can be formed. An exemplary NMOS stack may comprise a
dielectric layer, such as a hafnium oxide (HfO.sub.2) layer, a thin
layer of a first metal-containing film, such as a metal nitride,
for example titanium nitride (TiN), over the dielectric, a second
metal-containing film, such as a carbide, for example titanium
carbide (TiC), over the first metal-containing film, a third
metal-containing film, such as a metal nitride, for example TiN,
over the second metal-containing film, and a layer of metal, such
as tungsten, over the third metal-containing film. In some
embodiments, one or more additional elements may be present in one
or more of these layers. For example, one or more layers may
further comprise silicon or boron, such as following treatment.
[0081] In some embodiments an NMOS stack comprises a dielectric
layer, a first metal nitride layer over the dielectric layer, a
metal carbide layer over the first metal nitride layer, a second
metal nitride layer over the metal carbide layer, and a metal layer
over the second metal nitride layer. In some embodiments each of
the overlying layers is deposited directly on and contacting the
underlying layer.
[0082] In some embodiments an NMOS stack comprises a dielectric
layer, such as HfO.sub.2, a first titanium nitride layer over the
dielectric, a titanium carbide layer over the first titanium
nitride layer, a second titanium nitride layer over the titanium
carbide layer, and a tungsten layer over the second titanium
nitride layer.
[0083] A protective treatment may be used in the deposition process
of one or more of these respective thin films of the NMOS stack. In
some embodiments, a protective treatment is used prior to the
deposition of one or more thin films. In some embodiments, a
protective treatment is used after the deposition of one or more
thin films. Of course other metal films may be deposited by ALD or
quasi-ALD processes comprising one or more treatment steps.
[0084] In some embodiments, the protective treatment does not
increase the thickness of the thin film. This is particularly
beneficial as thinner and thinner films become more and more
desirable and necessary, as one problem with thinner films is that
oxygen can more easily diffuse through and oxidize them as compared
to thicker films in which only the upper portions would be
oxidized. It will be readily appreciated by those of skill in the
art, that protective treatments can provide benefits to many
different functional thin films.
[0085] According to some embodiments of the present disclosure, the
use of a protective treatment in the fabrication of multiple thin
films, such as to form an NMOS stack, can result in a lower
resistivity of the films--as much as about 30% less--compared to
films fabricated without the use of a protective treatment. In some
embodiments, the presence of silicon or boron--a component of the
protective treatment--may serve to reduce the overall resistivity
of the film or films.
[0086] In some embodiments, the use a protective treatment may
eliminate or reduce the need to utilize an in situ or clustered
fabrication process. In some embodiments, the use of a protective
treatment may allow for fabrication processes performed at lower
vacuum than ordinary processes. However, in some embodiments, high
vacuum, clustered, and/or in situ processes are desirably combined
with a protective treatment.
[0087] In some embodiments, some of the variables that can be
controlled to achieve a desirable result include, but are not
limited to, pressure, temperature, duration, and quantity of the
protective treatment used. In some embodiments, the pressure within
a reaction chamber is between about 0.1 torr and about 10 torr. In
some embodiments, the pressure is between about 0.5 torr and about
5 torr. In some embodiments, the temperature within a reaction
chamber is between about 350.degree. C. and about 450.degree. C. In
some embodiments, the temperature is between about 380.degree. C.
and about 420.degree. C. and, preferably, between about 390.degree.
C. and about 420.degree. C.
[0088] According to some embodiments, the duration of a treatment,
cycle step, pulse, or soak using a protective treatment is between
about 1 second and about 60 seconds. Longer periods, such as at
least about 10 seconds, may be desired if treating a thicker film,
such as where a completed film has already or previously been
deposited prior to a treatment with a protective treatment. And
shorter periods, such as about 2-3 seconds or less, may be desired
when incorporating a treatment step into a deposition cycle, such
as in the formation of a metal carbide or metal nitride layer. The
duration of a treatment step may also depend on the reactor
conditions. For example, where a reaction chamber tends to not hold
pressure over time, it may be desirable to perform the treatment as
a plurality of short pulses in order to maintain a relatively
constant concentration within the reaction. However, in a reactor
that can maintain pressure longer, longer single pulses or soaks
may be desirable.
Metal Carbide Films
[0089] According to some embodiments, an ALD type process is used
to form metal thin films on a substrate. For example, metal carbide
thin films, such as titanium carbide can be deposited on an
integrated circuit workpieces. Other suitable metal carbide thin
films include, but are not limited to, TaC, HfC, TaAlC, SiC, etc.
The ALD process may comprise at least one deposition cycle in which
a treatment agent comprising silane and or borane is provided. The
surfaces on which the thin titanium carbide (TiC) films are
deposited can take a variety of forms. Examples include, but are
not limited to silicon, silicon oxide (SiO.sub.2), coated silicon,
dielectric materials, low-k materials, metals--such as copper and
aluminum--metal alloys, metal oxides and various nitrides, such as
transition metal nitrides and silicon nitride or a combination of
said materials.
[0090] In a some embodiments, a substrate or workpiece is placed in
a reaction chamber and subjected to alternately repeated surface
reactions. In particular, thin films are formed by repetition of an
ALD cycle. Each ALD cycle is typically self-limiting. In the case
of compound metallic thin film deposition, at least two different
source chemicals are alternatively employed. One reactant will form
no more than about one monolayer on the substrate surface and
includes a metal species desired in the layer being deposited. This
reactant, also referred to herein as "the metal reactant," is
preferably a titanium halide, and thus the deposited monolayer is
terminated with halogen ligands.
[0091] A second reactant preferably contributes carbon. In some
embodiments, the second reactant comprises a metal and carbon, such
as trimethylaluminum (TMA) or triethylaluminum (TEA). In some
embodiments, the second reactant is a metal-containing source
chemical comprising at least one ligand, such as a metalorganic
compound. Further, in some embodiments the second reactant can also
leave some amount of metal in the film being deposited. For
example, in the case of TMA or TEA, some amount of aluminum may be
left in the film, depending on the particular reaction
conditions.
[0092] In some embodiments according to the present disclosure, a
third reactant that is the protective treatment agent is provided
every cycle, after a certain number of cycles, or after deposition
of the metal carbide film is complete. The third reactant may
comprise a silicon compound, such as a silane, or a boron compound,
such as a borane. The protective treatment agent is preferably more
reactive to oxygen than is titanium and thus is capable of reducing
the amount of titanium oxide in the film. In some cases, little or
no oxygen is actually removed from the thin film; however, the
protective treatment acts to reduce titanium oxide by breaking the
bonds between titanium and oxygen to return the titanium to its
pure titanium carbide form. In such cases, although, the oxygen has
not actually been removed from the film, it is bound up by the
protective treatment so as to not impede the workfunction of the
thin film. Accordingly, it could also be said that application of a
protective treatment increases the amount of TiC compared to the
amount of TiOC in the film. Moreover, in some embodiments the third
reactant also provides a species desired in the thin film, such as
silicon or boron.
[0093] The protective treatment agent may be selected from the
group consisting of monosilane, disilane, trisilane, borane,
diborane, triborane, or any other suitable material that readily
reacts with oxygen to reduce titanium. The protective treatment may
be supplied in vapor or liquid form, and may be applied as a
relatively short pulse every cycle or intermittently in the
deposition process or as a relatively longer soak to a partially or
completely formed titanium carbide layer.
[0094] The protective treatment may be provided before one or more
ALD cycles, in each ALD cycle, at intervals during the deposition
process, or after the deposition process has been completed. For
example, in some embodiments the protective treatment is provided
every one to four ALD cycles. In some embodiments, at the time the
protective treatment is provided, the film grown in the most recent
ALD cycles is preferably thin enough that the protective treatment
can penetrate the film. In some embodiments, such as situations
where more than one deposition cycle has been completed prior to
exposure to the protective treatment, the amount of silane/borane
penetration in the films can be controlled by the quantity or
concentration of the agent used or the duration of the
exposure.
[0095] The protective treatment may be provided as a part of one or
more cycles or may be applied after one or more cycles have been
completed. Thus, in some embodiments, the deposition of a metal
carbide film, such as TiC, is considered to be a cycle in an ALD
process independent of the application of a protective treatment.
In such cases, the cycle is repeated as many times as desired, and
the silane/borane treatment is applied after some or all of the
cycles. However, in some embodiments, the protective treatment is
applied during one or more cycles (as a part of an ALD cycle) as
well as after one or more cycles (separate from an ALD cycle).
[0096] In one phase of an ALD cycle ("the titanium phase" or the
"first phase"), the reactant or source chemical comprising titanium
is supplied to the reaction chamber and chemisorbs to the substrate
surface. The reactant supplied in this phase is selected such that,
under the preferred conditions, the amount of reactant that can be
bound to the surface is determined by the number of available
binding sites and by the physical size of the chemisorbed species
(including ligands). The chemisorbed layer left by a pulse of the
titanium reactant is self-terminated with a surface that is
non-reactive with the remaining chemistry of that pulse. This
phenomenon is referred to herein as "self-saturation." One of skill
in the art will recognize that the self-limiting nature of this
phase makes the entire ALD cycle self-limiting. Excess reactant and
reactant byproducts (if any) are removed from the reaction space,
for example by purging with an inert gas and/or evacuation.
[0097] In the next phase of the cycle, a pulse of a second source
chemical is provided that reacts with the molecules left on the
substrate surface by the preceding pulse. In some embodiments the
source chemical preferably comprises carbon that is to be
incorporated in the thin film. The carbon is incorporated into the
thin film by the interaction of the source chemical with the
monolayer left by the metal reactant. This phase is referred to
herein as "the second phase" or the "carbon-contributing phase." In
some embodiments, the second source chemical is a carbon containing
compound and its reaction with the chemisorbed metal species
produces a metal carbide layer on the substrate. In some
embodiments the second source chemical also comprises a second
metal, such as aluminum, and the second metal is incorporated into
the growing film along with the carbon. In some embodiments the
species-contributing source chemical comprises metal and carbon and
may be, for example, TTBA, TMA, or TEA. The second source chemical
may or may not be self-limiting when deposited on the
substrate.
[0098] Excess second source chemical and reaction byproducts, if
any, are removed from the reaction space by purging and/or
evacuation.
[0099] In some embodiments, a third phase of the ALD cycle
comprises providing the protective treatment. In the some
embodiments the protective treatment removes oxygen from the
growing thin film and/or reacts with oxygen preferentially relative
to the other metals in the growing film. In some embodiments, the
protective treatment may also remove or isolate other contaminants.
In addition, the protective treatment may comprise a species that
may be incorporated into the thin film, such as boron or silicon.
This is referred to as the "third phase" or the "oxygen isolation
phase."
[0100] Although referred to as the "first phase," the "second
phase" and the "third phase," these labels are for convenience and
do not indicate the actual order of the phases in each ALD cycle.
Thus, the initial ALD cycle may be started with any of the three
phases described above. However, one of skill in the art will
recognize that if the initial ALD cycle does not begin with the
metal reactant phase, at least two ALD cycles will typically need
to be completed to deposit about a monolayer of the desired metal
carbide thin film.
[0101] In addition, the order of the phases may be changed. That
is, in some embodiments the protective treatment may be the next
reactant provided after the second reactant, while in other
embodiments the protective treatment may be the next reactant
provided after the first metal source reactant. And in some
embodiments, the protective treatment may be supplied after only
some cycles or after all cycles have been completed. For example,
in some embodiments the third phase (provision of the protective
treatment) may immediately follow the first phase (provision of the
reactant comprising a metal species), which in turn is followed by
the carbon-contributing phase. And in some embodiments, the third
phase may be supplied as a "soak," liquid or vapor, after the thin
film has been completely formed. That is, the deposited film is
exposed to a silane or a borane in liquid or vapor form for a
period of time. A phase is generally considered to immediately
follow another phase if only a purge or other reactant removal step
intervenes.
[0102] In some embodiments the protective treatment is not provided
in every ALD cycle. Rather, a partially or completely deposited
titanium carbide film may be treated with a protective treatment
agent. This may the case, for example, where a first film has been
formed using TiCl.sub.4 and TEA but the resulting TiAlC film has
been oxidized by water, air, or some other contaminant source to
form a layer that is essentially TiAlOC. A protective treatment can
be applied to the first film to reduce the TiAlOC layer back to
essentially TiAlC with only the minor presence of impurities.
[0103] In one embodiment, an ALD cycle comprises: [0104] 1.
providing a titanium halide to the reaction space; [0105] 2.
substantial purging and/or evacuation of excess titanium halide and
reaction byproducts; [0106] 3. providing a carbon-contributing
reactant to the reaction space, such TEA or TMA; [0107] 4.
substantially purging and/or evacuation of excess second reactant
and reaction byproducts; and [0108] 5. providing a protective
treatment to the reaction space.
[0109] Step 5 can be included in each ALD cycle, or steps 1-4 can
be repeated several times before step 5 is introduced. In some
embodiments steps 1-4 are repeated up to 10 times before step 5 is
included. In other embodiments steps 1-4 are repeated up to 100 or
even 1000 or more times before step 5 is included. In some
embodiments, a complete film of desired thickness is deposited
prior to step 5.
[0110] With reference to FIG. 5, in an embodiment of the invention,
after initial surface termination, if necessary, a first reactant
or source chemical pulse is supplied 502 to the substrate or
workpiece. In the illustrated embodiment, the first reactant is a
metal halide, and the thin film being formed comprises a metal
carbide. In accordance with a preferred embodiment, the first
reactant pulse comprises a carrier gas flow and a volatile titanium
halide species that is reactive with the workpiece surfaces of
interest. Accordingly, the halogen-containing titanium species
adsorbs upon the workpiece surfaces. The first reactant pulse
self-saturates the workpiece surfaces such that any excess
constituents of the first reactant pulse do not further react with
the monolayer formed by this process. Self-saturation results due
to halide tails terminating the monolayer, protecting the layer
from further reaction.
[0111] The first reactant is then removed 504 from the reaction
space. Step 504 may entail merely stopping the flow of the first
reactant or chemistry while continuing to flow a carrier gas for a
sufficient time to diffuse or purge excess reactants and reactant
by-products from the reaction space. Preferably the removal 504
comprises continuing to flow purge gas for between about 0.1
seconds and 20 seconds after stopping the flow of the first
reactant pulse. Inter-pulse purging is described in co-pending U.S.
Pat. No. 6,511,539, entitled "IMPROVED APPARATUS AND METHOD FOR
GROWTH OF A THIN FILM," the disclosure of which is incorporated
herein by reference. In other arrangements, the chamber may be
pumped down between alternating chemistries. See, for example, PCT
publication number WO 96/17107, published Jun. 6, 1996, entitled
"METHOD AND APPARATUS FOR GROWING THIN FILMS," the disclosure of
which is incorporated herein by reference. Together, the adsorption
502 and reactant removal 504 represent a first phase 505 in an ALD
cycle. The first phase in the illustrated ALD cycle is thus the
metal phase.
[0112] With continued reference to FIG. 5, a second reactant or
source chemical pulse is then supplied 506 to the workpiece. The
second chemical reacts with the monolayer left by the first
reactant. In the illustrated embodiment, this second reactant pulse
506 comprises supplying a carrier gas with the second source gas to
the workpiece. In particular, where the first reactant comprises a
titanium halide, the second reactant, such as TMA or TEA, comprises
carbon and a second, different metal. In the case of TEA or TMA the
second reactant leaves no more than about a monolayer of TiCAl. The
second reactant preferably removes at least some halide ligands
from the adsorbed first reactant. The second reactant pulse 506
also leaves a surface termination that operates to limit the
deposition in a saturative reaction phase.
[0113] After a time period sufficient to completely saturate and
react the monolayer with the second reactant pulse 506, any excess
second reactant is removed 508 from the workpiece. As with the
removal 504 of the first reactant, this step 508 may comprise
stopping the flow of the second chemistry and continuing to flow
carrier gas for a time period sufficient for excess reactants and
volatile reaction by-products from the second reactant pulse to
diffuse out of and be purged from the reaction space. Together, the
second reactant pulse 506 and removal 508 represent a second phase
509 in the illustrated process, and can also be considered a carbon
and metal species-contributing phase.
[0114] When the excess reactants of the second reactant pulse have
been removed 508 from the chamber, a third reactant or source
chemical pulse may be supplied to the workpiece 510. The third
reactant can be a protective treatment agent or oxygen barrier
material capable of removing halides and/or reacting with oxygen in
the growing film. Examples of suitable agents include silanes and
boranes, including monosilane, disilane, trisilane, borane, and
diborane. The oxygen barrier material or protective treatment may
be provided with an inert carrier gas. Temperature and pressure
conditions can be adjusted to control the level of diffusion of the
protective treatment through the monolayer.
[0115] After a time period sufficient to achieve a desired level of
saturation of the third reactant in the monolayer, excess unreacted
oxygen barrier material and any reaction by-products (which may
also be volatile) are removed 512 from the reaction space, for
example by a purge gas pulse. The removal can be as described for
step 204. Together, the protective treatment pulse 510 and removal
512 represent a third phase 513 of the illustrated ALD process,
which can also be referred to as the oxygen isolation phase.
[0116] The combination of first phase 505, second phase 509, and
third phase 513, can be considered as a single deposition cycle
515. In some embodiments, the ordering of the third phase 513
actually precedes either or both the first phase 505 and the second
phase 509. In some embodiments, the third phase 513 is included in
only some or only one deposition cycle 515.
[0117] In some embodiments, supplying a protective treatment
immediately follows the step of removing excess first reactant and
by-products. After a time period sufficient to react the monolayer
with the protective treatment, excess unreacted protective
treatment materials and reaction by-products are removed from the
reaction space, possibly by a purge gas pulse. The removal step is
followed by supply of the second reactant pulse.
[0118] In some embodiments of the disclosure (not shown), the steps
of supplying the protective treatment and removing any excess
protective treatment materials and by-products precede the step of
supplying the first reactant. In some embodiments, the protective
treatment is not provided in every cycle or may be provided after
all the cycles are complete.
[0119] In some embodiments, the step of supplying a protective
treatment takes the form of a soak occurring after some or all of
the titanium carbide deposition cycles have been completed. In some
cases, a soak of trisilane occurring after deposition of a TiC film
is completed has been found to achieve suitable results.
[0120] In one embodiment, a process for forming a titanium carbide
film comprises: [0121] 1. providing a titanium halide, such as a
titanium chloride, to the reaction space; [0122] 2. substantially
purging and/or evacuation of excess titanium halide and reaction
byproducts; [0123] 3. providing a second carbon and
aluminum-contributing reactant, such as TEA or TMA, to the reaction
space; [0124] 4. substantially purging and/or evacuation of excess
second reactant and reaction byproducts; [0125] 5. repeating steps
1 through 4 for either a desired number of cycles or until a film
of a desired thickness has been achieved; and [0126] 6. subjecting
the product of step 5 to a soak with a protective treatment
agent.
[0127] The soak of Step 6 can be configured to achieve a particular
level of interaction between any oxygen present in the film and the
protective treatment. For example, the soak may last long enough to
substantially diffuse throughout the film or the soak's duration
may be kept shorter so as to reach only a partial depth in the
film. In some embodiments, a soak may serve to "coat" a thin film
with an oxygen barrier by providing silicon or boron in the film.
In some embodiments, the protective treatment is applied as a soak
is trisilane.
[0128] The foregoing embodiments will be discussed in the context
of specific thin film chemistries.
[0129] Carbon containing metal films or metal carbides have varying
applications, such as gate electrodes, electrodes in capacitors and
barrier layers in damascene and dual damascene structures.
[0130] In some embodiments, a general pulsing sequence for
carbon-containing metal or metal carbide thin film deposition
is:
(M.sup.1X.sub.y+purge+M.sup.2R.sub.3+purge+protective
treatment+purge).times.m.sub.1
or
(M.sup.1X.sub.y+purge+protective
treatment+purge+M.sup.2R.sub.3+purge).times.m.sub.1,
[0131] wherein m.sub.1 is the number of total cycles.
[0132] M.sup.1 is a metal atom, preferably selected from the group
consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W. And in some
embodiments M.sup.1 is selected from the group consisting of Fe,
Mn, Ni, Co, Cu, Zn, Cd, Ge, Si, Sn, Sb, Ga, Ru, Ir, Pd, Pt, Au, Rh,
Re, B, In and Al.
[0133] M.sup.2 is a metal atom, preferably selected from the group
consisting of B, Al, In, Sn, Bi, Sn, Zn, Pb, Sb and Ga. R is a
ligand for M.sup.2 and can be any ligand, preferably a metalorganic
ligand, more preferably an organometallic ligand, most preferably
an alkane ligand, such as ethyl ligand.
[0134] X.sub.y is one or more ligands for M.sup.1. Each X may be a
halogen ligand selected from the group consisting of I, Br, Cl and
F. However, in some embodiments at least one X can be a
metalorganic ligand, such as a cyclopentadienyl (for example,
cyclopentadienyl, methylcyclopentadienyl,
pentamethylcyclopentadienyl, ethylcyclopentadienyl,
isopropylcyclopentadienyl, tertbutylcyclopentadienyl, and indenyl),
alkoxide (for example, methoxide, ethoxide, isopropoxide, and
tertbutoxide), alkyl (for example, methyl, ethyl, propyl, and
butyl), carbonyl, cyclo-octadiene, benzene or hydrogen ligand. In
other embodiments X.sub.y may comprise mixtures thereof. However,
at least one of the X.sub.y ligands is preferably a halogen. As an
example, bis(cyclopentadienyl)hafnium dichloride or
bis(cyclopentadienyl)tantalum(V)trichloride, can be used as a metal
precursor in some embodiments.
[0135] The protective treatment may comprise exposure to a
treatment agent selected from the group consisting of monosilane,
disilane, trisilane, borane, diborane, triborane, etc. In some
embodiments, the protective treatment is a disilane or a trisilane
that is applied during or after each layer is deposited, before any
layers are deposited, after only some layers are deposited, or
after all the layers have been deposited. The protective treatment
can be applied in a pulse or as a soak and as a liquid or as a
vapor.
[0136] In preferred embodiments, M.sup.2 is a metal, preferably
aluminum, and R is a carbon-containing ligand. M.sup.2R.sub.3
preferably has at least one metal-to-carbon bond. In some
embodiments, M.sup.2R.sub.3 may be considered a carbon source
chemical. In some embodiments, M.sup.2R.sub.3 is selected from the
group consisting of TMA and TEA.
[0137] One benefit of the ALD processes of some embodiments is that
the growth rate is extremely high for an ALD process or a quasi-ALD
process. For example, the growth rate for TaC formation can be over
2 .ANG./cycle. Further, annealing can be performed after the metal
carbide deposition for enhancing the properties of the film.
Suitable atmospheres, such as N.sub.2 or forming gas
(N.sub.2/H.sub.2), may be used during annealing.
[0138] Exemplary pulsing sequences for TiC film formation
include:
(TiCl.sub.4+purge+trimethylaluminum (TMA) or triethylaluminum
(TEA)+purge+protective treatment+purge)].times.m.sub.2
and
(TiCl.sub.4+purge+protective treatment+purge+TMA or
TEA+purge)].times.m.sub.2,
[0139] wherein m.sub.2 is the number of total cycles and the
protective treatment is selected from the group consisting of
monosilane, disilane, trisilane, borane, diborane, triborane,
etc.
[0140] Films deposited using the above exemplary pulsing sequence
contained, based on an atomic basis, about 17-20% Ti, about 17-27%
Al, about 16-42% Si, and about 21-39% C. In some films, Al may be
as much as about 40% on an atomic basis. These values were
determined using Rutherford backscattering spectrometry, or
RBS.
[0141] In other embodiments, a protective treatment is not utilized
every cycle but only in some of the cycles. In this situation, a
general pulsing sequence for carbon-containing metal thin film
deposition can be:
[n.sub.3.times.(M.sup.1X.sub.y+purge+M.sup.2R.sub.3+purge)+m.sub.3.times-
.(protective treatment+purge)].times.k.sub.3,
[0142] wherein n.sub.3 is the number of carbide cycles in one total
cycle, m.sub.3 is the number of cycles in which a protective
treatment is used in one total cycle, and k.sub.3 is the number of
total cycles.
[0143] M.sup.1 is preferably Ti but may be a metal atom selected
from the group consisting of Zr, Hf, V, Nb, Ta, Cr, Mo, W, Si and
Al. In other embodiments M.sup.1 can be selected from the group
consisting of Fe, Mn, Ni, Co, Cu, Zn, Cd, Ge, Si, Sn, Sb, Ga, Ru,
Ir, Pd, Pt, Au, Rh, Re, B, In. M.sup.2 is preferably Al but may be
a metal atom selected from the group consisting of B, Al, In, Sn,
Bi, Zn, Pb, Sb and Ga. R is a ligand for M.sup.2 and can be any
ligand.
[0144] X.sub.y is one or more ligands for M.sup.1. Each X is
preferably a halogen ligand selected from the group consisting of
I, Br, Cl and F. However, in some embodiments at least one X can be
a metalorganic ligand, such as a cyclopentadienyl (for example,
cyclopentadienyl, methylcyclopentadienyl,
pentamethylcyclopentadienyl, ethylcyclopentadienyl,
isopropylcyclopentadienyl, tertbutylcyclopentadienyl, and indenyl),
alkoxide (for example, methoxide, ethoxide, isopropoxide, and
tertbutoxide), alkyl (for example, methyl, ethyl, propyl, and
butyl), carbonyl, cyclo-octadiene, benzene or hydrogen ligand. In
other embodiments X.sub.y may comprise mixtures thereof. However,
at least one of the X.sub.y ligands is preferably a halogen. As an
example, bis(cyclopentadienyl)hafnium dichloride or
bis(cyclopentadienyl)tantalum(V)trichloride, can be used as a metal
precursor in some embodiments.
[0145] Use of a protective treatment as disclosed herein has the
potential of providing a thin film, such as a TiC, with resistance
to oxidation during subsequent processing. Without being tied to
any particular theory, it is believe that resistance to oxidation
is increased in part because the protective treatment tends to
decrease the amount of carbon in the thin film as it is partially
replaced by silicon or boron or some other element comprising the
protective treatment.
Metal Nitride Films
[0146] According to some embodiments, an ALD or quasi-ALD process
is used to form titanium nitride thin films on substrates, such as
integrated circuit workpieces. The surfaces on which the thin
titanium nitride (TiN) films are deposited can take a variety of
forms. Examples include, but are not limited to, hafnium oxide,
silicon, silicon oxide (SiO.sub.2), coated silicon, dielectric
materials, low-k materials, metals--such as copper and
aluminum--metal alloys, metal oxides and various nitrides, such as
transition metal nitrides and silicon nitride or a combination of
said materials.
[0147] In a some embodiments, a substrate or workpiece is placed in
a reaction chamber and subjected to alternately repeated surface
reactions. In particular, thin films are formed by repetition of an
ALD cycle. Each ALD cycle is typically self-limiting, though, as
discussed above, the reaction conditions may be modified to achieve
a quasi-ALD process, such as where a true ALD process would require
an undesirable amount of time to perform. In the case of compound
metallic thin film deposition, at least two different source
chemicals are alternatively employed. One reactant may form no more
than about one monolayer on the substrate surface and includes a
metal species desired in the layer being deposited. This reactant,
also referred to herein as "the metal reactant," is preferably a
titanium halide, and thus the deposited layer is terminated with
halogen ligands.
[0148] A second reactant preferably contributes nitrogen. In some
embodiments, the second reactant comprises NH.sub.3, hydrazine, or
radicals/ions of N and H (for example in a PEALD process) or other
known nitrogen compound for use in ALD.
[0149] In some embodiments according to the present disclosure, a
third reactant is provided every cycle, after a certain number of
cycles, or after deposition of the TiN film is complete. The third
reactant may be a protective treatment agent, and may comprise a
silicon compound or a boron compound, preferably one that can
reduce at least a portion of any oxidized TiN. In other words, the
protective treatment may act to reduce titanium-oxygen bonds to
restore the titanium-nitride bonds. In some embodiments the third
reactant comprises a silane or a borane, such as monosilane,
disilane, trisilane, borane, diborane, triborane, etc.
[0150] The protective treatment is more reactive to oxygen than is
titanium and thus is capable of reducing the amount of titanium
oxide in the film. In some cases, little or no oxygen is actually
removed from the thin film; however, the protective treatment acts
to reduce titanium oxide by breaking the bonds between titanium and
oxygen to return the titanium to its pure titanium carbide form. In
such cases, although, the oxygen has not actually been removed from
the film, it is bound up by the protective treatment so as to not
impede the workfunction of the TiN film or a film deposited prior
or subsequent to the TiN film. Accordingly, it could also be said
that application of a protective treatment increases the amount of
TiN compared to the amount of TiON in the film. Moreover, in some
embodiments the third reactant also provides a species desired in
the thin film, such as silicon or boron.
[0151] The protective treatment may be provided in each ALD cycle,
at intervals during the deposition process, or after the deposition
process has been completed. For example, in some embodiments the
protective treatment is provided every one to four ALD cycles. In
some embodiments, at the time the protective treatment is provided,
the film grown in the most recent ALD cycle is preferably thin
enough that the protective treatment can penetrate the film. In
some embodiments, such as situations where more than one deposition
cycle have been completed prior to exposure to the protective
treatment, the amount of penetration or diffusion in the films can
be controlled any number of factors, such as duration, temperature,
pressure, selection of the protective treatment, quantity or
concentration of the barrier material used, etc.
[0152] The protective treatment may be provided as a part of one or
more cycles or may be applied after one or more cycles have been
completed. Thus, in some embodiments, the deposition of a metal
nitride film, such as TiN, is considered to be a cycle in an ALD
process independent of the application of a protective treatment.
In such cases, the cycle is repeated as many times as desired, and
the treatment using a protective treatment is applied after some or
all of the cycles. However, in some embodiments, the protective
treatment is applied during one or more cycles (as a part of an ALD
cycle) as well as after one or more cycles (separate from an ALD
cycle).
[0153] In one phase of an ALD cycle ("the titanium phase" or the
"first phase"), the reactant or source chemical comprising titanium
is supplied to the reaction chamber and chemisorbs to the substrate
surface. The reactant supplied in this phase is selected such that,
under the preferred conditions, the amount of reactant that can be
bound to the surface is determined by the number of available
binding sites and by the physical size of the chemisorbed species
(including ligands). The chemisorbed layer left by a pulse of the
titanium reactant is ideally self-terminated with a surface that is
non-reactive with the remaining chemistry of that pulse. This
phenomenon is referred to herein as "self-saturation." One of skill
in the art will recognize that the self-limiting nature of this
phase makes the entire ALD cycle self-limiting. Excess reactant and
reactant byproducts (if any) are removed from the reaction space,
for example by purging with an inert gas and/or evacuation.
[0154] However, in some embodiments, the purge step may be
insufficiently long to fully clear the reaction space of precursors
before the next precursor is pulsed through the reaction space. In
some cases, full evacuation or purging may require a period of time
that is not economical or efficient. Moreover, some precursors may
actually decompose or partially decompose within the reaction
space.
[0155] In the next phase of the cycle, a pulse of a second source
chemical is provided that reacts with the molecules left on the
substrate surface by the preceding pulse. In some embodiments the
source chemical preferably comprises nitrogen that is to be
incorporated in the thin film. The nitrogen is incorporated into
the thin film by the interaction of the source chemical with the
monolayer left by the metal reactant. This phase is referred to
herein as "the second phase" or the "nitrogen-contributing phase."
In some embodiments, the second source chemical is a
nitrogen-containing compound and its reaction with the chemisorbed
metal species produces a metal nitride layer on the substrate.
[0156] Excess second source chemical and reaction byproducts, if
any, are removed from the reaction space by purging and/or
evacuation.
[0157] In some embodiments, a third phase of the ALD cycle
comprises providing the protective treatment agent. In the some
embodiments the protective treatment agent removes or isolates
oxygen from the growing thin film and/or reacts with oxygen
preferentially relative to the other metals in the growing film. In
addition, the protective treatment agent may comprise a species
that may be incorporated into the thin film, such as boron or
silicon. This is referred to as the "third phase" or the "oxygen
isolation phase."
[0158] Although referred to as the "first phase," the "second
phase" and the "third phase," these labels are for convenience and
do not indicate the actual order of the phases in each ALD cycle.
Thus, the initial ALD cycle may be started with any of the three
phases described above. However, one of skill in the art will
recognize that if the initial ALD cycle does not begin with the
metal reactant phase, at least two ALD cycles will typically need
to be completed to deposit about a monolayer of the desired metal
nitride thin film.
[0159] In addition, the order of the phases may be changed. That
is, in some embodiments the protective treatment may be the next
reactant provided after the second reactant, while in other
embodiments the protective treatment may be the next reactant
provided after the first metal source reactant. In some
embodiments, the protective treatment is supplied before any other
reactants and may be supplied only initially as compared to as a
part of cycle or after all the cycles are completed. And in some
embodiments, the protective treatment may be supplied after only
some cycles or after all cycles have been completed. For example,
in some embodiments the third phase (provision of the protective
treatment) may immediately follow the first phase (provision of the
reactant comprising a metal species), which in turn is followed by
the nitrogen-contributing phase. And in some embodiments, the third
phase may be supplied as a "soak," after the thin film has been
completely formed. That is, the deposited film is exposed to a
silane or a borane for a more extended period of time. A phase is
generally considered to immediately follow another phase if only a
purge or other reactant removal step intervenes.
[0160] In some embodiments the protective treatment agent is not
provided in every ALD cycle. Rather, a partially or completely
deposited titanium nitride film may be treated with a protective
treatment. This may be the case, for example, where a first TiN
film has been formed by has been or is likely to be oxidized by
water, air, or some other contaminant source to form a layer that
is essentially TiON. A protective treatment can be applied to the
first film to reduce the TiON layer back to essentially TiN with
only the minor presence of impurities, such as oxygen, or to
prevent oxidation of the Ti in the layer.
[0161] In one embodiment, an ALD cycle comprises: [0162] 1.
providing a titanium halide to the reaction space; [0163] 2.
substantially purging and/or evacuation of excess titanium halide
and reaction byproducts; [0164] 3. providing a
nitrogen-contributing reactant to the reaction space, such as
NH.sub.3; [0165] 4. substantially purging and/or evacuation of
excess second reactant and reaction byproducts; and [0166] 5.
providing a protective treatment to the reaction space.
[0167] Step 5 can be included in each ALD cycle, or steps 1-4 can
be repeated several times before step 5 is introduced. In some
embodiments steps 1-4 are repeated up to 10 times before step 5 is
included. In other embodiments steps 1-4 are repeated up to 100 or
even 1000 or more times before step 5 is included. In some
embodiments, a complete film of desired thickness is deposited
prior to step 5.
[0168] With reference again to FIG. 5, in an embodiment of the
invention, after initial surface termination, if necessary, a first
reactant or source chemical pulse is supplied 502 to the substrate
or workpiece. In the illustrated embodiment, the first reactant is
a metal halide, and the thin film being formed comprises a metal
nitride. In accordance with a preferred embodiment, the first
reactant pulse comprises a carrier gas flow and a volatile titanium
halide species that is reactive with the workpiece surfaces of
interest. Accordingly, the halogen-containing titanium species
adsorbs upon the workpiece surfaces. The first reactant pulse
self-saturates the workpiece surfaces such that any excess
constituents of the first reactant pulse do not further react with
the monolayer formed by this process. Self-saturation results due
to halide tails terminating the monolayer, protecting the layer
from further reaction.
[0169] The first reactant is then removed 304 from the reaction
space. Step 504 may entail merely stopping the flow of the first
reactant or chemistry while continuing to flow a carrier gas for a
sufficient time to diffuse or purge excess reactants and reactant
by-products from the reaction space. Preferably the removal 504
comprises continuing to flow purge gas for between about 0.1
seconds and 20 seconds after stopping the flow of the first
reactant pulse. Together, the adsorption 502 and reactant removal
504 represent a first phase 505 in an ALD cycle. The first phase in
the illustrated ALD cycle is thus the metal phase.
[0170] With continued reference to FIG. 5, a second reactant or
source chemical pulse is then supplied 506 to the workpiece. The
second chemical reacts with the monolayer left by the first
reactant. In the illustrated embodiment, this second reactant pulse
506 comprises supplying a carrier gas with the second source gas to
the workpiece. In particular, where the first reactant comprises a
titanium halide, the second reactant, may be a nitrogen compound
such as NH.sub.3. The second reactant preferably removes at least
some halide ligands from the adsorbed first reactant leaving no
more than about a monolayer of TiN. The second reactant pulse 506
also leaves a surface termination that operates to limit the
deposition in a saturative reaction phase.
[0171] After a time period sufficient to completely saturate and
react the monolayer with the second reactant pulse 506, any excess
second reactant is removed 308 from the workpiece. As with the
removal 504 of the first reactant, this step 508 may comprise
stopping the flow of the second chemistry and continuing to flow
carrier gas for a time period sufficient for excess reactants and
volatile reaction by-products from the second reactant pulse to
diffuse out of and be purged from the reaction space. Together, the
second reactant pulse 506 and removal 508 represent a second phase
509 in the illustrated process, and can also be considered a
nitrogen-contributing phase.
[0172] According to some embodiments, a residual amount of a metal,
such as aluminum, is present in the chamber during the
nitrogen-contributing phase. The metal may have been used in a
previous phase. Because it is present during the
nitrogen-contributing phase, it is possible for it to be
incorporated into the resulting metal nitride layer. For example,
the deposition of a TiN layer may actually produce at least some
TiAlN.
[0173] When the excess reactants of the second reactant pulse have
been removed 508 from the chamber, a third reactant pulse may be
supplied to the workpiece 510. The third reactant can be a
protective treatment agent capable of removing halides and/or
reacting with oxygen in the growing film. Examples of suitable
protective treatment agents include silanes and boranes, for
example in the form of monosilane, disilane, trisilane, borane,
diborane, triborane, etc. The protective treatment agent may be
provided with an inert carrier gas. Temperature and pressure
conditions can be adjusted to control the level of diffusion of the
protective treatment agent through the monolayer.
[0174] After a time period sufficient to achieve a desired level of
saturation of the third reactant in the monolayer, excess unreacted
protective treatment agent and any reaction by-products (which may
also be volatile) are removed 512 from the reaction space, for
example by a purge gas pulse. The removal can be as described for
steps 504 or 508. Together, the protective treatment pulse 510 and
removal 512 represent a third phase 513 of the illustrated ALD
process, which can also be referred to as the oxygen isolation
phase.
[0175] The combination of first phase 305, second phase 509, and
third phase 513, can be considered as a single deposition cycle
515. In some embodiments, the ordering of the third phase 513
actually precedes either or both the first phase 505 and the second
phase 509. In some embodiments, the third phase 513 is included in
only some or only one deposition cycle 515.
[0176] In some embodiments, supply of a protective treatment agent
immediately follows the step of removing excess first reactant and
by-products. After a time period sufficient to react the monolayer
with the protective treatment agent, excess unreacted protective
treatment materials and reaction by-products are removed from the
reaction space, possibly by a purge gas pulse. The removal step is
followed by supply of the second reactant pulse.
[0177] In some embodiments of the disclosure (not illustrated), the
steps of supplying the protective treatment and removing any excess
protective treatment materials and by-products precede the step of
supplying the first reactant. In some embodiments, the protective
treatment is not provided in every cycle or may be provided after
all the cycles are complete.
[0178] In some embodiments, the step of supplying a protective
treatment agent takes the form of a soak occurring after some or
all of the titanium nitride deposition cycles have been completed.
In some cases, a soak of trisilane occurring after deposition of a
TiN film is completed has been found to achieve suitable
results.
[0179] In one embodiment, a process for forming a titanium nitride
film comprises: [0180] 1. providing a titanium halide, such as a
titanium chloride, to the reaction space; [0181] 2. substantial
purging and/or evacuation of excess titanium halide and reaction
byproducts; [0182] 3. providing a second reactant or a
nitrogen-contributing reactant, such as NH.sub.3, hydrazine, or
radicals/ions of N and H (used in a PEALD process), to the reaction
space; [0183] 4. substantially purging and/or evacuation of excess
second reactant and reaction byproducts; [0184] 5. repeating steps
1 through 4 at least once or for either a desired number of cycles
or until a film of a desired thickness has been achieved; and
[0185] 6. subjecting the product of step 5 to a soak with a
protective treatment agent comprising silane and/or borane.
[0186] The soak of Step 6 can be configured to achieve a particular
level of interaction between any oxygen present in the film and the
protective treatment agent. For example, the soak may last long
enough to substantially diffuse throughout the film or the soak's
duration may be kept shorter so as to reach only a partial depth in
the film. In some embodiments, a soak may serve to "coat" a thin
film with an oxygen barrier by providing silicon or boron in the
film. In some embodiments, the protective treatment applied as a
soak is trisilane.
[0187] According to some embodiments, it may be desirable to
subject a thin film, such as metal nitride, to a protective
treatment well after the film has been deposited but before
proceeding with a subsequent deposition process whether or not the
subsequent process itself includes an oxygen barrier treatment.
[0188] In at least some of the aforesaid embodiments, any element
used in an embodiment can interchangeably be used in another
embodiment unless such a replacement is not feasible.
[0189] It will be appreciated by those skilled in the art that
various other omissions, additions and modifications may be made to
the methods and structures described above without departing from
the scope of the invention. All such modifications and changes are
intended to fall within the scope of the invention, as defined by
the appended claims.
* * * * *