U.S. patent application number 10/900830 was filed with the patent office on 2005-01-20 for controlling the temperature of a substrate in a film deposition apparatus.
Invention is credited to Chiang, Tony P., Leeser, Karl F..
Application Number | 20050011457 10/900830 |
Document ID | / |
Family ID | 27559386 |
Filed Date | 2005-01-20 |
United States Patent
Application |
20050011457 |
Kind Code |
A1 |
Chiang, Tony P. ; et
al. |
January 20, 2005 |
Controlling the temperature of a substrate in a film deposition
apparatus
Abstract
A system and method for that allows one part of an atomic layer
deposition (ALD) process sequence to occur at a first temperature
while allowing another part of the ALD process sequence to occur at
a second temperature. In such a fashion, the first temperature can
be chosen to be lower such that decomposition or desorption of the
adsorbed first reactant does not occur, and the second temperature
can be chosen to be higher such that comparably greater deposition
rate and film purity can be achieved. Additionally, the invention
relates to improved temperature control in ALD to switch between
these two thermal states in rapid succession. It is emphasized that
this abstract is provided to comply with rules requiring an
abstract. It is submitted with the understanding that it will not
be used to interpret or limit the scope or meaning of the
claims.
Inventors: |
Chiang, Tony P.; (Santa
Clara, CA) ; Leeser, Karl F.; (Sunnyvale,
CA) |
Correspondence
Address: |
PATENT LAW GROUP LLP
2635 NORTH FIRST STREET
SUITE 223
SAN JOSE
CA
95134
US
|
Family ID: |
27559386 |
Appl. No.: |
10/900830 |
Filed: |
July 28, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10900830 |
Jul 28, 2004 |
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09854092 |
May 10, 2001 |
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09854092 |
May 10, 2001 |
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09812285 |
Mar 19, 2001 |
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6428859 |
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09854092 |
May 10, 2001 |
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09812352 |
Mar 19, 2001 |
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09854092 |
May 10, 2001 |
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09812486 |
Mar 19, 2001 |
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6416822 |
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60251795 |
Dec 6, 2000 |
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60254280 |
Dec 6, 2000 |
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Current U.S.
Class: |
118/724 ;
118/728; 257/E21.171; 257/E21.577; 257/E21.582; 427/248.1;
427/596 |
Current CPC
Class: |
C23C 16/45536 20130101;
C23C 16/46 20130101; C23C 16/483 20130101; C23C 16/481 20130101;
H01L 21/76838 20130101; H01L 21/76843 20130101; C23C 16/34
20130101; C23C 16/0227 20130101; C23C 16/08 20130101; C23C 16/463
20130101; H01L 21/28562 20130101; C23C 16/466 20130101; C23C 16/511
20130101; H01L 21/76873 20130101; C23C 16/45538 20130101; C23C
16/45527 20130101; C23C 16/45544 20130101; C23C 16/401 20130101;
C23C 16/45525 20130101 |
Class at
Publication: |
118/724 ;
427/248.1; 427/596; 118/728 |
International
Class: |
C23C 016/00; C23C
014/30 |
Claims
1-15. (Canceled)
16. A method for affecting a temperature of a substrate on a
pedestal in a film deposition apparatus comprising: increasing a
temperature of said substrate by irradiating said substrate with an
energy source and having a heat transferring gas between said
pedestal and said substrate at a low pressure; and decreasing a
temperature of said substrate by not having said energy source
irradiating said substrate and having said heat transferring gas
between said pedestal and said substrate at a high pressure.
17. The method of claim 16, wherein said heat transferring gas is
argon.
18. The method of claim 16, wherein said heat transferring gas is
helium.
19. The method of claim 16, wherein said high pressure is between
about 3 and 10 torr.
20. The method of claim 16, wherein said high pressure is between
about 3 and 20 torr.
21. The method of claim 16, wherein said low pressure is less than
3 torr.
22. The method of claim 16, wherein said low pressure is less than
1 torr.
23. The method of claim 16, wherein said energy source is selected
from a group consisting of a rapid thermal processor, a laser, an
electron beam source, and an x-ray source.
24. The method of claim 16, wherein said substrate temperature is
additionally affected by resistively heating said pedestal.
25. The method of claim 16, wherein said substrate temperature is
additionally affected by flowing a chilled fluid through said
pedestal.
26-51. (Cancelled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/251,795, filed Dec. 6, 2000, U.S. Provisional
Application No. 60/254,280, filed Dec. 6, 2000 and U.S. Utility
Applications Ser. Nos. 09/812,285, 09/812,352, and 09/812,486; all
filed Mar. 19, 2001.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to the field of film
deposition, and more particularly, to a method and apparatus for
improving and enhancing temperature control in atomic layer
deposition (ALD).
[0004] 2. Description of the Background Art
[0005] The present invention relates generally to the field of
advanced thin film deposition methods commonly used in the
semiconductor, data storage, flat panel display, as well as allied
and other industries. More particularly, the present invention
relates to improved atomic layer deposition whereby the kinetics of
the adsorption of the first precursor and the subsequent reaction
with the second precursor are decoupled. By decoupling, we mean
causing the reaction (i.e., adsorption) of the first precursor to
occur at a different temperature state than the temperature state
required for the reaction with the second precursor. More
importantly, methods and apparatus for improved temperature control
in ALD are disclosed that can switch between these two thermal
states in rapid succession.
[0006] The disadvantages of conventional ALD are additionally
discussed in copending applications with the same assignee entitled
"Sequential Method For Depositing A Film By Modulated Ion-Induced
Atomic Layer Deposition (MII-ALD)", "System and Method for
Modulated Ion Induced Atomic Layer Deposition (MII-ALD)", and
"Continuous Method For Depositing A Film By Modulated Ion-Induced
Atomic Layer Deposition (MII-ALD)" which are hereby incorporated by
reference in their entirety and may be found as copending utility
applications, application Ser. Nos. 09/812,285, 09/812,352,
09/812,486 respectively.
[0007] As integrated circuit (IC) dimensions shrink and the aspect
ratios of the resulting features increase, the ability to deposit
conformal, ultra-thin films on the sides and bottoms of high aspect
ratio trenches and vias becomes increasingly important. These
conformal, ultra-thin films are typically used as "liner" materials
to enhance adhesion, prevent inter-diffusion and/or chemical
reaction between the underlying dielectric and the overlying metal,
and promote the deposition of a subsequent film.
[0008] In addition, decreasing device dimensions and increasing
device densities has necessitated the transition from traditional
CVD tungsten plug and aluminum interconnect technology to copper
interconnect technology. This transition is driven by both the
increasing impact of the RC interconnect delay on device speed and
by the electromigration (i.e., the self-diffusion of metal along
interconnects, thereby affecting reliability) limitations of
aluminum based conductors for sub 0.25 .mu.m device generations.
Copper is preferred due to its lower resistivity and higher (more
than 10 times) electromigration resistance as compared to aluminum.
A single or dual damascene copper metallization scheme is used
since it eliminates the need for copper etching and reduces the
number of integration steps required. However, the burden now
shifts to the metal deposition step(s) as the copper must fill
predefined high aspect ratio trenches and/or vias in the
dielectric. Electroplating has emerged as the copper fill technique
of choice due to its low deposition temperature, high deposition
rate, and potential low manufacturing cost.
[0009] Two major challenges exist for copper wiring technology: the
barrier and seed layers. Copper can diffuse readily into silicon
and most dielectrics. This leads to electrical leakage between
metal wires and poor device performance. An encapsulating barrier
layer is needed to isolate the copper from the surrounding material
(e.g., dielectric, Si), thus preventing copper diffusion and/or
reaction with the underlying material (e.g., dielectric, Si). In
addition, the barrier layer also serves as the adhesion or glue
layer between the patterned dielectric trench or via and the copper
used to fill it. The dielectric material can be a low dielectric
constant i.e., low-k material (used to reduce inter- and intra-line
capacitance and cross-talk) which typically suffers from poorer
adhesion characteristics and lower thermal stability than
traditional oxide insulators. Consequently, this places more
stringent requirements on the barrier material and deposition
method. An inferior adhesion layer will, for example, lead to
delamination at either the barrier-to-dielectric or
barrier-to-copper interfaces during any subsequent anneal and/or
chemical mechanical planarization (CMP) processing steps leading to
degradation in device performance and reliability. Ideally, the
barrier layer should be thin, conformal, defect free, and of low
resistivity so as to not compromise the conductance of the copper
metal interconnect structure.
[0010] In addition, electroplating fill requires a copper seed
layer, which serves to both carry the plating current and act as
the nucleation layer. The preferred seed layer should be smooth,
continuous, of high purity, and have good step coverage with low
overhang. A discontinuity in the seed layer will lead to sidewall
voiding, while gross overhang will lead to pinch-off and the
formation of top voids.
[0011] Both the barrier and seed layers which are critical to
successful implementation of copper interconnects require a means
of depositing high purity, conformal, ultra-thin films at low
substrate temperatures.
[0012] Physical vapor deposition (PVD) or sputtering has been
adopted as the preferred method of choice for depositing conductor
films used in IC manufacturing. This choice has been primarily
driven by the low cost, simple sputtering approach whereby
relatively pure elemental or compound materials can be deposited at
relatively low substrate temperatures. For example, refractory
based metals and metal compounds such as tantalum (Ta), tantalum
nitride (TaN.sub.x), other tantalum containing compounds, tungsten
(W), tungsten nitride (WN.sub.x), and other tungsten containing
compounds which are used as barrier/adhesion layers can be sputter
deposited with the substrate at or near room temperature. However,
as device geometries have decreased, the step coverage limitations
of PVD have increasingly become an issue since it is inherently a
line-of-sight process. This limits the total number of atoms or
molecules which can be delivered into the patterned trench or via.
As a result, PVD is unable to deposit thin continuous films of
adequate thickness to coat the sides and bottoms of high aspect
ratio trenches and vias. Moreover, medium/high-density plasma and
ionized PVD sources developed to address the more aggressive device
structures are still not adequate and are now of such complexity
that cost and reliability have become serious concerns.
[0013] Chemical vapor deposition (CVD) processes offer improved
step coverage since CVD processes can be tailored to provide
conformal films. Conformality ensures the deposited films match the
shape of the underlying substrate, and the film thickness inside
the feature is uniform and equivalent to the thickness outside the
feature. Unfortunately, CVD requires comparatively high deposition
temperatures, suffers from high impurity concentrations which
impact film integrity, and have higher cost-of-ownership due to
long nucleation times and poor precursor utilization efficiency.
Following the tantalum containing barrier example, CVD Ta and TaN
films require substrate temperatures ranging from 500.degree. C. to
over 800.degree. C. and suffer from impurity concentrations
(typically of carbon and oxygen) ranging from several to tens of
atomic % concentration. This generally leads to high film
resistivities (up to several orders of magnitude higher than PVD),
and other degradation in film performance. These deposition,
temperatures and impurity concentrations make CVD Ta and TaN
unusable for IC manufacturing, in particular for copper
metallization and low-k integration.
[0014] Chen et al. ("Low temperature plasma-assisted chemical vapor
deposition of tantalum nitride from tantalum pentabromide for
copper metallization", J. Vac. Sci. Technol. B 17(1), pp. 182-185
(1999); and "Low temperature plasma-promoted chemical vapor
deposition of tantalum from tantalum pentabromide for copper
metallization", J. Vac. Sci. Technol. B 16(5), pp. 2887-2890
(1998)) have demonstrated a plasma-assisted (PACVD) or
plasma-enhanced (PECVD) CVD approach using tantalum pentabromide
(TaBr.sub.5) as the precursor to reduce the deposition temperature.
Ta and TaN.sub.x films were deposited from 350.degree. C. to
450.degree. C. and contained 2.5 to 3 atomic % concentration of
bromine. Although the deposition temperature has been reduced by
increased fragmentation (and hence increased reactivity) of the
precursor gases in the gas phase via a plasma, the same
fragmentation leads to the deposition of unwanted impurities.
Gas-phase fragmentation of the precursor into both desired and
undesired species inherently limits the efficacy of this
approach.
[0015] Recently, atomic layer chemical vapor deposition (AL-CVD) or
atomic layer deposition (ALD) has been proposed as an alternative
method to CVD for depositing conformal, ultra-thin films at
comparatively lower temperatures. ALD is similar to CVD except that
the substrate is sequentially exposed to one reactant at a time.
Conceptually, it is a simple process: a first reactant is
introduced onto a heated substrate whereby it forms a monolayer on
the surface of the substrate. Excess reactant is pumped out. Next a
second reactant is introduced and reacts with the first reactant to
form a monolayer of the desired film via a self-limiting surface
reaction. The process is self-limiting since the deposition
reaction halts once the initially adsorbed (physi- or chemisorbed)
monolayer of the first reactant has fully reacted with the second
reactant. Finally, the excess second reactant is evacuated. The
above sequence of events comprises one deposition cycle. The
desired film thickness is obtained by repeating the deposition
cycle the required number of times.
[0016] In practice, ALD is complicated by the painstaking selection
of a process temperature setpoint wherein both: 1) at least one of
the reactants sufficiently adsorbs to a monolayer and 2) the
surface deposition reaction can occur with adequate growth rate and
film purity. If the substrate temperature needed for the deposition
reaction is too high, desorption or decomposition of the first
adsorbed reactant occurs, thereby eliminating the layer-by-layer
process. If the temperature is too low, the deposition reaction may
be incomplete (i.e., very slow), not occur at all, or lead to poor
film quality (e.g., high resistivity and/or high impurity content).
Since the ALD process is entirely thermal, selection of available
precursors (i.e., reactants) that fit the temperature window
becomes difficult and sometimes unattainable. Due to the
above-mentioned temperature-related problems, ALD has been
typically limited to the deposition of semiconductors and
insulators as opposed to metals.
[0017] Continuing with the TaN example, ALD of TaN films is
confined to a narrow temperature window of 400.degree. C. to
500.degree. C. , generally occurs with a maximum deposition rate of
0.2 .ANG./cycle, and can contain up to several atomic percent of
impurities including chlorine and oxygen. Chlorine is a corrosive,
can attack copper, and lead to reliability concerns. The above
process is unsuitable for copper metallization and low-k
integration due to the high deposition temperature, slow deposition
rate, and chlorine impurity incorporation.
[0018] In conventional ALD of metal films, gaseous hydrogen
(H.sub.2) or elemental zinc (Zn) is often cited as the second
reactant. These reactants are chosen since they act as a reducing
agent to bring the metal atom contained in the first reactant to
the desired oxidation state in order to deposit the end film.
Gaseous, diatomic hydrogen (H.sub.2) is an inefficient reducing
agent due to its chemical stability, and elemental zinc has low
volatility (e.g., it is very difficult to deliver sufficient
amounts of Zn vapor to the substrate) and is generally incompatible
with IC manufacturing. Unfortunately, due to the temperature
conflicts that plague the ALD method and lack of kinetically
favorable second reactant, serious compromises in process
performance result.
[0019] In order to address the limitations of traditional thermal
or pyrolytic ALD, radical enhanced atomic layer deposition (REALD,
U.S. Pat. No. 5,916,365) or plasma-enhanced atomic layer deposition
has been proposed whereby a downstream radio-frequency (RF) glow
discharge is used to dissociate the second reactant to form more
reactive radical species which drives the reaction at lower
substrate temperatures. Using such a technique, Ta ALD films have
been deposited at 0.16 to 0.5 .ANG./cycle at 25.degree. C., and up
to 1.67 .ANG./cycle at 250.degree. C. to 450.degree. C. Although
REALD results in a lower operating substrate temperature than all
the aforementioned techniques, the process still suffers from
several significant drawbacks. Higher temperatures must still be
used to generate appreciable deposition rates. However, such
temperatures are still too high for some films of significant
interest in IC manufacturing such as polymer-based low-k
dielectrics that are stable up to temperatures of only 200.degree.
C. or less. REALD remains a thermal or pyrolytic process similar to
ALD and even CVD since the substrate temperature provides the
required activation energy for the process and is therefore the
primary control means for driving the deposition reaction.
[0020] In addition, Ta films deposited using REALD still contain
chlorine as well as oxygen impurities, and are of low density. A
low density or porous film leads to a poor barrier against copper
diffusion since copper atoms and ions have more pathways to
traverse the barrier material. Moreover, a porous or under-dense
film has lower chemical stability and can react undesirably with
overlying or underlying films, or with exposure to gases commonly
used in IC manufacturing processes.
[0021] Another limitation of REALD is that the radical generation
and delivery is inefficient and undesirable. RF (such as 13.56 MHz)
plasma generation of radicals used as the second reactant such as
atomic H is not as efficient as microwave plasma due to the
enhanced efficiency of microwave energy transfer to electrons used
to sustain and dissociate reactants introduced in the plasma.
Furthermore, having a downstream configuration whereby the radical
generating plasma is contained in a separate vessel located
remotely from the main chamber where the substrate is situated and
using a small aperture to introduce the radicals from the remote
plasma vessel to the main chamber body significantly decreases the
efficiency of transport of the second radical reactant. Both
gas-phase and wall recombination will reduce the flux of desired
radicals that can reach the substrate. In the case of atomic H,
these recombination pathways will lead to the formation of diatomic
H.sub.2, a far less effective reducing agent. If the plasma used to
generate the radicals was placed directly over the substrate, then
the deposition of unwanted impurities and particles can occur
similarly to the case of plasma-assisted CVD.
[0022] Finally, ALD (or any derivative such as REALD) is
fundamentally slow since it relies on a sequential process whereby
each deposition cycle is comprised of at least two separate
reactant flow and evacuation steps which can occur on the order of
minutes with conventional valve and chamber technology. Significant
improvements resulting in faster ALD are needed to make it more
suitable for commercial IC manufacturing.
SUMMARY OF THE INVENTION
[0023] A method for depositing a film on a substrate in a chamber
comprising adjusting a temperature of said substrate to a first
temperature, introducing a first reactant gas into said chamber,
adsorbing substantially at least one monolayer of said first
reactant gas onto said substrate, evacuating any excess of said
first reactant gas from said chamber, adjusting a temperature of
said substrate to a second temperature, introducing a second
reactant gas into said chamber to react with said first reactant
gas to produce said film on said substrate, and evacuating any
excess of said second reactant gas from said chamber; and adjusting
a temperature of said substrate to a third temperature.
[0024] A system for depositing a film on a substrate in a chamber
comprising a means for adjusting a temperature of said substrate to
a first temperature, a means for introducing a first reactant gas
into said chamber, a means for adsorbing substantially at least one
monolayer of said first reactant gas onto said substrate, a means
for evacuating any excess of said first reactant gas from said
chamber, a means for adjusting a temperature of said substrate to a
second temperature, a means for introducing a second reactant gas
into said chamber to react with said first reactant gas to produce
said film on said substrate, a means for evacuating any excess of
said second reactant gas from said chamber, and a means for
adjusting a temperature of said substrate to a third
temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 shows the relative timing diagram of the sequence for
the improved ALD method incorporating two (or more) discrete
temperature states;
[0026] FIG. 2 shows the relative timing diagram of an alternative
sequence for the improved ALD method incorporating two (or more)
discrete temperature states;
[0027] FIG. 3 is the ALD system schematic incorporating a lamp
array for rapidly heating, and a chilled electrostatic chuck (ESC)
for rapidly cooling, the substrate;
[0028] FIG. 4 is the ALD system schematic incorporating a
mechanically-scanned laser (coupled with wafer rotation) for
rapidly heating, and a chilled electrostatic chuck (ESC) for
rapidly cooling, the substrate; and
[0029] FIG. 5 shows the relative timing diagram of substrate
temperature response to irradiation and state-dependent control of
backside gas pressure.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The present invention resolves the ALD temperature dilemma
revolving around the use of a single, fixed substrate temperature
setpoint as the principal means of controlling or driving the
deposition reaction. The present invention does this by allowing
one part of the ALD process sequence (e.g., adsorption of the first
reactant) to occur at a first temperature (typically lower) while
allowing another part of the ALD process sequence (e.g., reaction
between the second reactant with the adsorbed first reactant) to
occur at a second temperature (typically higher). In such a
fashion, the first temperature can be chosen to be a lower level
such that decomposition or desorption of the adsorbed first
reactant does not occur, and the second temperature can be chosen
to be of a higher level such that comparably greater deposition
rate and film purity can be achieved. More importantly, the
invention relates to methods and apparatuses for improved
temperature control in ALD that can switch between these two
thermal states in rapid succession. Via these methods and
apparatuses, the limitations in precursor choice can be resolved
while improving process performance and deposition rate. In
particular, precursor choice can be expanded to include metals--a
highly desirable class of materials previously not viable with
conventional ALD.
[0031] Since ALD is by definition a slow process, introducing a
second temperature state would typically compete with the desire to
increase processing speed, i.e., the ALD
flow-evacuate-flow-evacuate sequence would take even longer. This
would be especially true in a conventional, isothermal hot-wall or
resistively heated pedestal reactor system commonly used for ALD.
This is because the reactor or pedestal must be heated to a higher
temperature and then cooled to a lower temperature, which can take
several minutes, or greater, due to the large thermal masses
involved. Since each deposition cycle results in a film thickness
of at most one monolayer, the process would be extremely slow (much
slower than even conventional ALD and its derivatives) and highly
unfavorable for IC device manufacturing. However, methods exist to
rapidly impart energy into a substrate (which may be a "bare"
substrate, e.g., a silicon wafer before any films have been
deposited, or it may be a substrate which may already have had one
or more films deposited on its surface), either globally or in a
focused or otherwise localized fashion, causing a transient, rather
than quasi-static, change in substrate temperature. The substantial
process benefits of employing such methods, in particular improved
adsorption and stability of the first reactant plus substantially
increased deposition rate, significantly outweigh the increased
complexity.
[0032] FIG. 1 shows a sequence for an improved ALD method
incorporating two (or more) discrete temperature states. In the
variant of the method shown in FIG. 1, the substrate temperature is
ramped 134 during the evacuation 124 of the first reactant. Note
that the time axis is not to scale. FIG. 2 shows an alternative
sequence for an improved ALD method incorporating two (or more)
discrete temperature states. In the variant of the method shown in
FIG. 2, the substrate temperature is ramped 234 during the flow 212
of the second reactant. Again, note that the time axis is not to
scale.
[0033] An improved ALD sequence incorporating the aforementioned
invention is as follows:
[0034] 1. First exposure 100, 200: A substrate heated (or cooled)
to a first temperature, T.sub.1 132, 232, is exposed 102, 202 to a
first gaseous reactant, allowing a monolayer of the reactant to
form on the surface.
[0035] 2. First evacuation: The excess reactant is removed by
evacuating 124, 224 the chamber with a vacuum pump. An inert gas
purge (e.g., Ar, H.sub.2, He) can be used in conjunction to speed
evacuation/removal of any excess first reactant.
[0036] 3. Second exposure 110, 210: The substrate is then heated
(or cooled) to a second temperature, T.sub.2 136, 236, where
T.sub.2 136, 236 is not equal to T.sub.1 132, 232. A second gaseous
reactant is introduced 112, 212 into the reactor chamber and onto
the substrate. The first and second (chemi- or physi-sorbed)
reactants react to produce a solid thin monolayer of the desired
film. The reaction between the first and second reactants is
self-limiting in that the reaction between them terminates after
the initial monolayer of the first reactant is consumed.
[0037] 4. Second evacuation 126, 226: The excess second reactant is
removed by again evacuating 126, 226 the chamber with the vacuum
pump. An inert gas purge (e.g., Ar, H.sub.2, He) can be used in
conjunction to speed evacuation/removal of any excess first
reactant. The substrate is then cooled (or heated) back to a first
temperature, T.sub.1 139, 239.
[0038] 5. Repeat: The desired film thickness is built up by
repeating the entire process cycle (steps 1-4) many times.
[0039] Additional precursor gases may be introduced and evacuated
as required for a given process to create tailored films of varying
compositions or materials.
[0040] Preferably, T.sub.2 136, 236 is greater than T.sub.1 132,
232. The first temperature, T.sub.1 132, 232, needs to be low
enough so that the first reactant sufficiently forms a monolayer
and does not decompose or desorb from the substrate. However,
T.sub.2 136, 236 must be high enough in order to drive the
deposition reaction and improve film purity. Typically, T.sub.1
132, 232 can range from 20.degree. C. or lower up to 300.degree.
C., but more preferably less than 200.degree. C. , while T.sub.2
136, 236 can range from 200.degree. C. to 600.degree. C. or
greater. The temperatures chosen depend on the reactants used and
the types of films being deposited. Of course, T.sub.1 132, 232
could be the ambient temperature state of the substrate initially
and, as such, would not be initially heated.
[0041] The temperature ramp up rate 134, 234 during heating, a, is
preferably at least 200.degree. C./sec, and more preferably,
higher. The temperature ramp down rate 138, 238 during cooling,
.beta., is preferably at least 100.degree. C./sec, and more
preferably higher. In practice, .alpha. is larger than .beta..
[0042] The methods of the present invention can toggle the
substrate surface quickly between two or more temperatures to yield
properly decoupled reactions. The energy may be delivered by ions,
electrons, photons, or by a thermal energy means that primarily
affects the top surface of the substrate undergoing deposition in a
transient fashion. Sources for imparting such energy may come from
rapid thermal processing (RTP) or laser irradiation. An electron
beam may similarly be used. Any of these energy-inducing methods
serve to cause a rapid, transient heating of the substrate.
[0043] FIG. 3 shows an ALD system schematic incorporating a lamp
array 310 for rapidly heating a substrate 360 and a chilled ESC 370
for rapidly cooling the substrate 360. Means for valving and
controlling 345 the pressure of the backside gas 340 are also
shown. FIG. 3 shows a preferred method of heating the substrate in
the manner described herein by rapid thermal processing. RTP refers
to a process in which the heating cycle is very rapid and is
typically performed via radiant heating 310 utilizing graphite
heaters, plasma arc, tungsten halogen lamps, or other means well
known in the art. This RTP system 300 is coupled to the substrate
360 such that the substrate 360 surface is brought up to required
temperature in seconds (as opposed to minutes for typical
isothermal processes) with typical temperature ramp rates of
100-300.degree. C./sec.
[0044] FIG. 4 shows an ALD system schematic incorporating a
mechanically-scanned laser 410 (coupled with wafer 360 rotation)
for rapidly heating a substrate 360 and a chilled ESC 370 for
rapidly cooling the substrate 360. Means for valving and
controlling 345 the pressure of the backside gas 340 are also
shown. FIG. 4 shows an alternative embodiment where an infrared
(IR), ultraviolet (UV), or deep ultraviolet (DUV) laser 410 may be
employed to rapidly heat a substrate 360 , whereby the beam is
scanned rapidly over the entire area of the substrate 360.
Alternatively, other forms of irradiation such as
extreme-ultraviolet (EUV) or other radiation forms such as x-rays
may be employed.
[0045] The scanning means is accomplished by methods that are well
known in the art. Alternatively, the substrate 360 can be moved
with respect to the laser 410 (such as rotating the substrate with
respect to a laser line source or point source) so that uniform
irradiation of the substrate 360 will occur or the laser 410 may
simply scan the entire surface. Laser 410 heating methods may
locally heat a substrate 360 with temperature ramp rates of
200-700.degree. C./sec or greater--typically, higher than RTP.
[0046] These rapid heating methods reduce the overall thermal
budget of the ALD process since the substrate 360 is only at a peak
temperature for a short duration of time (on the order of seconds
or less). This reduces the overall thermal budget of the process
and enables the use of peak temperatures greater than if the
substrate 360 was held at a constant temperature for longer periods
of time.
[0047] Regardless of the energy source used for heating the
substrate 360, the substrate 360 must be rapidly cooled, preferably
through the use of a cooled pedestal. A cooled pedestal is a
substrate 360 holder that retains the wafer 360 or other substrate
360 against a cooled surface and introduces a "backside" gas 340,
typically at pressures of 3-10 torr, as a thermal heat transfer
medium in the space 365 between them (i.e., the substrate and the
cooled pedestal). Thermal coupling between the substrate and
pedestal generally increases for increasing gas pressure, but
saturates at an upper limit, typically around 10-20 torr depending
on gas species, gap spacing, and geometry of the interface. Typical
gases used are Ar and He. Although pedestals incorporating clamp
rings for retaining the wafer can be used, electrostatic chucks
370, are preferred. ESCs 370 use electrostatic attraction to retain
the wafer with a minimal substrate-pedestal gap distance and
therefore attain better heat transfer than clamp ring systems. It
is known that ESCs 370 can be designed with cooling capacities of
approximately 200-350 W/m.sup.2.degree.K.
[0048] In order to achieve the fast temperature ramp up rates
discussed previously, the substrate 360 must at times be thermally
decoupled from the cooled pedestal so that the energy input is not
wasted in heating up the large thermal mass of the pedestal.
However, during fast temperature ramp downs, they must be coupled
so that the cooled pedestal can efficiently remove heat from the
substrate. Since the existence of a backside gas 340 is the primary
means of heat transfer between the substrate 360 and the rest of
the system in a vacuum or reduced atmosphere environment, a key
part of this invention then is this state-based presence of the
backside gas 340, or more specifically, the state-based pressure
control 345 of the backside gas 340. With suitable valving and
pressure control 345, application of wafer 360 backside gas 340
will facilitate thermal coupling between the wafer 360 and a cooled
pedestal enabling the low temperature state. Valving off the
backside gas 340 thermally decouples the substrate 360 from the
cooled pedestal so that a high temperature state can be quickly
achieved during RTP lamp 310 or laser 410 irradiation. This method
is particularly effective in the semiconductor wafer processing
industry since the thermal mass of the substrate 360 is very small,
especially compared to a typical cooled pedestal, and the heat
fluxes are so large. This sequence is illustrated in FIG. 5.
[0049] FIG. 5 shows substrate temperature 520 response to
irradiation 500 and state-dependent control of backside gas
pressure 510. FIG. 5 illustrates how the backside gas 340 in
conjunction with irradiation 500 can be used to cause the substrate
temperature 520 to rapidly change from a low temperature to a high
temperature and back to a low temperature state. The cooled
pedestal can be cooled via chilled water, gases, or refrigerants to
a steady state temperature near or significantly below room
temperature (e.g., -40.degree. C. to 20.degree. C. ). The pedestal
can also be simply maintained at a desired low temperature state
greater than room temperature by, for example, resistively warming
the heater. In either case, the heat transferring backside gas 340
is used to toggle between the low temperature state 522 (backside
gas 340 is "high" 514, e.g., 3-10 torr) of the pedestal to the high
temperature state 524 (backside gas 340 is "low" 512, e.g., much
less than 3 torr) during RTP 310 or laser 410 irradiation.
[0050] It may be conceivable to perform the sequences described in
FIGS. 1 and 2 in separate RTP and ALD chambers. However, processing
speed would be compromised. A preferable embodiment would be for
the sequences described in FIGS. 1 and 2 to be carried out in a
single chamber.
[0051] From the description of the preferred embodiments of the
process and apparatus set forth herein, it will be apparent to one
of ordinary skill in the art that variations and additions to the
embodiments can be made without departing from the principles of
the present invention.
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