U.S. patent application number 12/028423 was filed with the patent office on 2009-08-13 for novel method for conformal plasma immersed ion implantation assisted by atomic layer deposition.
Invention is credited to Seon-Mee Cho, Majeed A. Foad, HIROJI HANAWA.
Application Number | 20090203197 12/028423 |
Document ID | / |
Family ID | 40939240 |
Filed Date | 2009-08-13 |
United States Patent
Application |
20090203197 |
Kind Code |
A1 |
HANAWA; HIROJI ; et
al. |
August 13, 2009 |
NOVEL METHOD FOR CONFORMAL PLASMA IMMERSED ION IMPLANTATION
ASSISTED BY ATOMIC LAYER DEPOSITION
Abstract
Embodiments of the invention provide a novel apparatus and
methods for forming a conformal doped layer on the surface of a
substrate. A substrate is provided to a process chamber, and a
layer of dopant source material is deposited by plasma deposition,
atomic layer deposition, or plasma-assisted atomic layer
deposition. The substrate is then subjected to thermal processing
to activate and diffuse dopants into the substrate surface.
Inventors: |
HANAWA; HIROJI; (Sunnyvale,
CA) ; Cho; Seon-Mee; (Santa Clara, CA) ; Foad;
Majeed A.; (Sunnyvale, CA) |
Correspondence
Address: |
PATTERSON & SHERIDAN, LLP - - APPM/TX
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Family ID: |
40939240 |
Appl. No.: |
12/028423 |
Filed: |
February 8, 2008 |
Current U.S.
Class: |
438/513 ;
257/E21.473; 427/525; 427/569 |
Current CPC
Class: |
C23C 16/505 20130101;
C23C 16/45536 20130101; H01L 21/2236 20130101; C23C 16/56
20130101 |
Class at
Publication: |
438/513 ;
427/525; 427/569; 257/E21.473 |
International
Class: |
C23C 14/12 20060101
C23C014/12; H01L 21/42 20060101 H01L021/42 |
Claims
1-8. (canceled)
9. A method of processing a substrate, comprising: disposing the
substrate in a process chamber; providing a process gas mixture to
the process chamber, wherein the process gas mixture comprises a
dopant precursor; ionizing the dopant precursor into a plasma
comprising dopant ions inside the process chamber; generating a
weak electrical bias; and depositing the dopant ions conformally on
the substrate.
10. The method of claim 9, wherein the dopant precursor comprises a
boron compound, a phosphorus compound, an arsenic compound, a metal
compound, a fluorine compound, or a mixture thereof.
11. The method of claim 9, further comprising annealing the
substrate.
12. The method of claim 9 wherein the weak electrical bias is
generated by applying an electrical bias to a gas distributor.
13. The method of claim 12 wherein the electrical bias is applied
to the gas distributor by coupling RF power to the gas
distributor.
14. The method of claim 13 wherein the RF power is less than about
100 watts.
15. The method of claim 9, wherein the plasma is generated by
applying power less than about 1000 W to an inductively coupled
plasma source.
16. The method of claim 9, wherein the process gas mixture further
comprises a purge gas.
17. The method of claim 11, wherein annealing the substrate
comprises heating one or more portions of the substrate to a
temperature between about 700.degree. C. and about 1410.degree.
C.
18-20. (canceled)
21. A method of implanting dopants into a substrate in a processing
chamber, comprising: positioning the substrate having high aspect
ratio features on a substrate support in the processing chamber;
forming a dopant precursor plasma comprising ions in the processing
chamber by inductively coupling RF power into a dopant precursor;
attracting the ions from the dopant precursor plasma to the
substrate by applying an electrical bias at a power level less than
about 500 W; depositing the dopant ions conformally on a surface of
the substrate; and annealing the substrate.
22. The method of claim 21, wherein the dopant precursor comprises
a boron compound, a phosphorus compound, an arsenic compound, a
metal compound, a fluorine compound, or a mixture thereof.
23. The method of claim 22, wherein the dopant precursor further
comprises a purge gas.
24. The method of claim 21, wherein the RF power is coupled into
the dopant precursor at a power level less than about 1000 W.
25. The method of claim 24, wherein annealing the substrate
comprises selectively melting portions of the substrate
surface.
26. The method of claim 21, wherein the electrical bias is an RF
bias.
27. The method of claim 26, wherein depositing the dopant ions
conformally on a surface of the substrate comprises propelling ions
into the high aspect ratio features of the surface before they
deposit on the surface.
28. The method of claim 21, wherein annealing the substrate
comprises heating the substrate to a temperature between about
700.degree. C. and about 1,410.degree. C. in the processing
chamber.
29. The method of claim 28, wherein the dopant precursor comprises
a purge gas and a component selected from the group consisting of a
boron compound, a phosphorus compound, an arsenic compound, a metal
compound, a fluorine compound, and combinations thereof.
30. A method of processing a substrate having high aspect ratio
features formed therein, comprising: disposing the substrate on a
substrate support in a processing chamber; providing a gas mixture
to the processing chamber through a gas distributor disposed above
the substrate support in the processing chamber, the gas mixture
comprising a purge gas and a dopant component selected from the
group consisting of a boron compound, a phosphorus compound, an
arsenic compound, a metal compound, a fluorine compound, and
combinations thereof; ionizing the gas mixture to form a plasma by
inductively coupling RF power into the gas mixture at a power level
less than about 1,000 W; attracting ions from the plasma toward the
substrate by applying a weak electrical bias; depositing dopants
from the plasma conformally over the substrate surface; annealing
the substrate in the processing chamber by heating the substrate
surface to a temperature between about 700.degree. C. and about
1,410.degree. C.; and removing dopants from the substrate
surface.
31. The method of claim 30, wherein the weak electrical bias is a
DC bias applied at a power level less than about 500 W.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] Embodiments of the present invention generally relate to the
fabrication of semiconductor devices and particularly to the
formation of doped regions on a substrate by use of plasma
implantation assisted by atomic layer deposition.
[0003] 2. Description of the Related Art
[0004] In the semiconductor fabrication process, it is often
necessary to impart impurities into a pure material. Called
"doping," this process invests the material with desirable
properties, such as enhanced electrical conductivity. In many
processes, it is advantageous to implant various atoms or ions into
a semiconductor or semiconductor derivative substrate. For example,
boron, phosphorus, and arsenic atoms or ions are routinely
implanted into silicon substrates to create "doped" regions to
serve as source and drain regions for solid state transistors. In
some cases, the substrate is prepared prior to doping by
"amorphizing" the region of the substrate to be doped. The crystal
structure of the substrate is disrupted by bombardment with
silicon, germanium, or argon atoms, creating channels for dopants
to penetrate deeper into the substrate. In other applications,
nitrogen, oxygen, hydrogen, carbon, fluorine, and various metals,
such as indium, antimony, cobalt, and nickel, may be used as
dopants to control electrical conductivity or diffusion at
interfaces.
[0005] Dopants are generally implanted in two ways. In some
processes, dopants may be implanted on the surface of a substrate
and then heat treated to cause them to diffuse into the substrate.
In other processes, dopants may be ionized into a plasma and then
driven energetically into the substrate using an electric field.
The substrate is then heat treated to normalize distribution of
dopants and repair disruption to the crystal structure caused by
ions barreling through at high speed. In both types of processes,
the heat treatment anneals the substrate, encouraging dopant and
ambient atoms located at interstitial positions in the crystal to
move to lattice points. This movement "activates" dopants in
applications involving control of electrical properties by making
the electrical properties of the dopants communicable through the
crystal lattice, and it generally strengthens the crystal, which
may be important for diffusion control applications.
[0006] Even distribution of dopants throughout the target region is
generally desired. For applications involving control of electrical
conductivity, even distribution of dopants ensures uniform
properties throughout the target region. For applications involving
control of diffusion, even distribution of dopants ensures no open
diffusion pathways for unwanted migration of atoms. For
applications involving amorphization, even distribution of dopants
ensures uniform density of pathways for subsequent dopants. Heat
treatment after implanting promotes even distribution of dopants
through the target region.
[0007] For more than half a century, the semiconductor industry has
followed Moore's Law, which states that the density of transistors
on an integrated circuit doubles about every two years. Continued
evolution of the industry along this path will require smaller
features patterned onto substrates. Stack transistors currently in
production have dimensions of 50 to 100 nanometers (nm). The next
generation of devices may have dimensions of about 40 nm, and
design efforts are being directed toward devices with dimension of
20 nm and smaller. As devices grow smaller, the aspect ratio (ratio
of height to width) of features patterned on substrates grows.
Devices currently in production may have features with aspect ratio
up to about 4:1, but future devices will require aspect ratios
potentially up to 100:1 or higher.
[0008] Increasing aspect ratios and shrinking devices pose
challenges to dopant implantation processes. It is frequently
necessary, for example, to implant dopants at the bottom and on the
sides of trenches in a field region of a substrate to form
features. Energetic implantation processes are directional, with
the electric field tending to drive ions in a direction orthogonal
to the surface of the substrate. Ions readily impinge on the field
region on the substrate, and may penetrate into trenches a short
distance, but the electrical bias will drive the ions toward the
surface of the field region or side walls of the trenches,
preventing them from penetrating to the bottom of the trench. High
energy implantation may drive ions to the bottom of the trench, but
generally will not achieve conformal implantation and may result in
over-implantation in the bottom of the trench and in field areas as
compared to side walls.
[0009] FIGS. 1A-1D illustrate substrates subjected to conventional
implantation techniques. FIG. 1A illustrates substrate 100
featuring field regions surrounding implantation process. A process
free of plasma will implant a layer 102 primarily on the field
regions, and may implant a layer 104 in the bottoms of the
trenches, but any implantation on the side walls will be slow to
occur, and layers 102 will grow toward each other as implantation
occurs, reducing the opportunity for entry into trenches. FIG. 1C
illustrates the implanted layers 102 and 104 after annealing
(layers 106 and 108, respectively). Layers 106 feature bulges
frequently encountered with conventional implantation, and layers
108 illustrate the tendency of implanted materials to collect in
corners. In some processes, the substrate may be rotated to change
the angle of incidence, as shown in FIG. 1D, such that the
opportunity for precursor materials to penetrate trenches is
enhanced. This may result in increased implantation 110 on a
portion of sidewall 112. However, any such benefit is minimal,
particularly for very high aspect ratio structures, because
electric field lines driving the motion of ions are orthogonal to
the surface. Thus, stage rotation does not result in conformal
implantation or doping.
[0010] Therefore, there is a need for a method of conformal doping
of high aspect ratio structures on substrates.
SUMMARY OF THE INVENTION
[0011] Embodiments of the present invention generally provide a
method of processing a substrate, comprising disposing the
substrate in a process chamber; providing a first precursor
material to the process chamber; reacting the first precursor
material to form a layer of the first precursor on the substrate;
providing a second precursor material to the process chamber;
reacting the second precursor material to form a layer of dopant
atoms on the substrate; repeating the cycle until the layer of
dopant atoms reaches a target thickness; and diffusing the layer of
dopant atoms into the substrate by heating the substrate.
[0012] Embodiments of the present invention further provide a
method of processing a substrate having trenches, comprising
disposing the substrate in a process chamber; providing a process
gas mixture to the process chamber, wherein the process gas mixture
comprises a dopant precursor; ionizing the dopant precursor into a
plasma comprising dopant ions inside the process chamber;
generating an electric field configured to maximize penetration of
the dopant ions into the trenches of the substrate; and depositing
the dopant ions conformally on the substrate.
[0013] Embodiments of the present invention further provide a
method of forming a doped region on a surface of a semiconductor
substrate, comprising disposing the substrate in a process chamber;
providing a catalytic precursor to the process chamber; ionizing
the catalytic precursor into an isotropic plasma; reacting the
catalytic precursor to form a layer of catalytic precursor on the
substrate; providing a purge gas to the process chamber; providing
a dopant precursor to the process chamber; ionizing the dopant
precursor into an isotropic plasma; reacting the dopant precursor
to form a layer of dopants on the substrate; repeating the cycle of
precursors until the layer of dopants reaches a target thickness;
and diffusing the layer of dopants into the substrate by heating
the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0015] FIGS. 1A-1D illustrate a substrate treated according to
prior art doping processes.
[0016] FIG. 2 is a process flow diagram according to one embodiment
of the invention.
[0017] FIG. 3 is a process flow diagram according to another
embodiment of the invention.
[0018] FIG. 4 is a process flow diagram according to another
embodiment of the invention.
[0019] FIGS. 5A-5C illustrate a substrate treated according to any
of the processes depicted in FIGS. 2-4.
[0020] FIG. 6A is a cross-sectional side view of an apparatus for
processing a substrate according to one embodiment of the
invention.
[0021] FIG. 6B is a perspective view of a plasma source according
to one embodiment of the invention.
[0022] For clarity, identical reference numerals have been used,
where applicable, to designate identical elements that are common
between figures. It is contemplated that features of one embodiment
may be incorporated in other embodiments without further
recitation.
DETAILED DESCRIPTION
[0023] Embodiments of the invention contemplate methods of
conformal doping of a substrate. Such methods generally provide for
conformal deposition of a dopant source on a substrate followed by
treatment with electromagnetic energy to diffuse the dopants into
the substrate and activate them. Deposition may be by any process
designed to achieve conformal deposition of thin dopant source
layers on a substrate having high aspect ratio features, such as
greater than about 3:1 by atomic layer deposition (ALD), chemical
vapor deposition enhanced by weak plasma (WPCVD), or
plasma-assisted atomic layer deposition (PAALD) of dopants on the
substrate followed by anneal. Processes for manufacturing
semiconductor devices are increasingly challenged to produce
conformally doped regions on substrates with ultra-high aspect
ratio holes or trenches formed in field regions. ALD is a
successful procedure for forming conformal layers on high aspect
ratio features heretofore used in metal and dielectric deposition
processes. Embodiments of the current invention provide processes
that adapt ALD techniques to conformal deposition of dopant atoms
on a substrate, with or without the assistance of plasma.
[0024] Embodiments of the present invention use ALD processes to
deposit conformal layers of dopants in a doping process. In one set
of embodiments, a conformal layer of dopants is deposited on a
substrate, which may have very high aspect ratio holes or trenches
formed thereon. The dopants are then driven into the substrate in
an anneal process designed to diffuse the dopants into the
substrate and "activate" them, or encourage them to occupy
positions at lattice points in the crystal structure. The
deposition process may be an ALD process, a WPCVD process, or a
PAALD process. The anneal process may be a rapid thermal process,
in which the substrate is quickly heated to a target temperature,
held at that temperature for a predetermined amount of time, and
then quickly cooled. The anneal process may also be a spike anneal
process, in which the substrate is subjected to a temperature
spike, a laser anneal process, a pulsed electromagnetic energy
anneal process, or a furnace anneal process.
Conformal Doping By Ald
[0025] ALD processes typically feature execution of self-limiting
surface-catalyzed chemical "half-reactions" wherein a first
precursor reacts with the substrate and is deposited thereon, and
then a second precursor reacts with the deposited first precursor
to yield an atomic layer of the desired component deposited on the
substrate. These techniques have commonly been used to deposit
metal layers, metal oxide layers, metal nitride layers, and metal
derivative layers of more complex chemistry by sequential pulsing
of precursors containing the desired elements in binary, tertiary,
quaternary, or higher-order cycles.
[0026] Generally, a first precursor is provided to a reaction
chamber in a pulse, depositing on the surface of a substrate
disposed in the reaction chamber. The first precursor is generally
a catalytic species selected to promote formation of a conformal
monolayer on the surface. The first precursor reacts with reaction
sites on the surface of the substrate until all such reaction sites
are consumed, after which reaction stops. A monolayer of catalytic
species is generally left on the surface. Any excess of the first
precursor is removed from the reaction chamber by purging with a
non-reactive gas. A second precursor is then provided to the
reaction chamber in a pulse. The second precursor may be another
catalytic species, or a precursor to the species to be deposited on
the surface, such as a dopant precursor. The second precursor
reacts with adsorbed catalytic species to yield a monolayer of the
second precursor, which may be a catalytic species or the target
deposition species, such as a metal species or dopant species.
Further precursor steps may be used to progress the formation of a
deposited monolayer in multiple self-limiting deposition steps.
Monolayer after monolayer may then be deposited in repeated cycles
until a smooth conformal layer of the desired thickness has been
formed.
[0027] In metal oxide deposition processes, the first precursor is
generally an oxygen-containing compound selected to terminate the
surface with hydroxyl groups. The hydroxyl groups serve to catalyze
reaction with a metal-containing compound to deposit a conformal
monolayer of a metal oxide on the surface. The second precursor is
generally a metal-containing compound featuring relatively massive
ligands, such as alkyl amino groups for example, that may be
liberated by relatively facile reactions. The second precursor
deposits on the substrate when the metal complexes with local Lewis
base sites, such as the adsorbed hydroxyl groups, on the substrate,
liberating some of the ligands as volatile compounds.
[0028] After all the available sites have been consumed, reaction
stops and any excess metal precursor is removed from the reaction
chamber. ALD is said to be "self-limiting" because the reaction
does not proceed beyond deposition of a single layer due to
consumption of available reaction sites for the surface-catalyzed
reaction. This enables deposition of conformal layers on very high
aspect ratio structures.
[0029] Oxygen precursor is then provided in a pulse, and reacts
with adsorbed metal precursor to yield a monolayer of metal oxide
on the surface of the substrate, liberating remaining ligands and
leaving a catalytic hydroxyl group on the surface. Again, when the
available reaction sites are consumed, reaction stops. The metal
precursor/oxygen precursor cycle may then be repeated, depositing
monolayer after monolayer, until a smooth, conformal layer of the
desired thickness has been formed.
[0030] Pathways are known, as well, for depositing metals by ALD
processes. The catalytic species is generally a reducing agent that
terminates the surface with hydrogen atoms. The surface is prepared
by treating with the reducing agent. A metal precursor is then
adsorbed onto a substrate, after which the reducing agent is pulsed
into the reactor. The reducing agent leaves a monolayer of metal on
the substrate.
[0031] In one set of embodiments, a substrate is conformally doped
by an ALD process followed by an anneal process. FIG. 2 illustrates
a conformal doping process 200 using an ALD method according to one
embodiment of the invention. A conformal dopant source layer is
deposited on the surface of the substrate to a desired thickness
and driven into the substrate and activated, if necessary, by the
anneal process. The dopant source layer may be a phosphorus,
arsenic, fluorine, boron, metal, or silicate layer, depending on
the embodiment and the desired dopant. A capping layer may be used
in some embodiments to facilitate the anneal process, which may be
a rapid or spike thermal process, a laser or pulsed electromagnetic
energy process, or a furnace anneal process.
[0032] A boron, phosphorus, or arsenic source layer may be
deposited by an ALD process in some embodiments of the invention. A
substrate to be doped is provided to a process chamber and
positioned on a substrate support in step 202. The substrate may be
held in place by vacuum or electromagnetic means. The substrate
support may be configured to deliver a compound to the back side of
the substrate through the surface of the substrate support for
thermal control or control of back-side and edge deposition.
Additionally, the substrate support may itself be heated or cooled
resistively or by flowing a thermal control medium through conduits
in the support for direct thermal control of the back side of the
substrate. The substrate may have very high aspect ratio fholes or
features, such as greater than about 10:1. The process chamber may
be configured to perform one or more deposition, cleaning, thermal,
or electromagnetic energy processes. The surface of the substrate
may optionally be pre-treated in step 204 to condition it for
processing. For example, the surface may be cleaned using a liquid
composition or plasma pre-clean process. It may also be treated to
deposit reactive sites on the surface prior to the first ALD
cycle.
[0033] A first precursor, which may be a catalytic precursor, is
provided to the process chamber containing the substrate to be
doped in step 206. If the first precursor is an oxidizing agent, it
will react to form a terminal hydroxyl group layer, liberating
remaining ligands bonded to the dopant on the surface. If the first
precursor is a nitriding agent, terminal amino groups may be left
in a similar fashion. If a silicate layer is to be the dopant
source, such as borosilicate glass (BSG), phosphosilicate glass
(PSG), or borophosphosilicate glass (BPSG) for example, a
silicon-containing compound may be provided as the first precursor.
Precursors useful for this step include, but are not necessarily
limited to, oxygen (O.sub.2), ozone (O.sub.3), nitrous oxide
(N.sub.2O), water (H.sub.2O), alcohols (e.g., ROH, where R is an
aliphatic, cyclic, or aromatic organic functional group), peroxides
(organic and inorganic), carboxylic acids, and radical oxygen
compounds (e.g., O, O.sub.2, O.sub.3, and OH radicals), which may
be generated by heat, hot wires, and/or plasma. Suitable nitrogen
precursors include, but are not necessarily limited to, ammonia
(NH.sub.3), nitrogen gas (N.sub.2), hydrazines (e.g.,
N.sub.2H.sub.4 or MeN.sub.2H.sub.3), amines (e.g., RR'R''N, where
R, R', and R'' may each be hydrogen or the same or different
organic functional groups), anilines (e.g.,
C.sub.6H.sub.5NH.sub.2), organic and inorganic azides (e.g.,
MeN.sub.3, Me.sub.3SiN.sub.3, NaN.sub.3 or CP.sub.2CoN.sub.3), and
radical nitrogen compounds (e.g., N.sub.3, N.sub.2, N, NH, or
NH.sub.2 radicals), which may be formed by heat, hot-wires, and/or
plasma. Suitable silicon precursors include, but are not
necessarily limited to, silanes, functionalized silanes (e.g.,
alkyl-, alkoxy-, or alkylamino-silanes), silanols, and
functionalized silanols.
[0034] A second precursor, which may be a dopant precursor, is
provided to the process chamber containing the substrate to be
doped in step 208. The second precursor may be a boron containing
compound, a phosphorus containing compound, an arsenic containing
compound, a metal containing compound, or a fluorine containing
compound. In general, compounds useful in this regard are hydrides
such as boranes, phosphines, or arsines, organic moieties such as
alkyl-, cyclic alkyl-, or aryl-boranes, borides, borates,
phosphines, phosphides, phosphates, arsines, arsenides, or
arsenates. Additionally, moieties featuring heterosubstituted
groups may also be useful, such as amino-, alkylamino-, or
arylamino-dopant precursors. In general, compounds may be selected
for an ALD process based on their usability in standard CVD
processes and their ability to adhere to a substrate surface under
reasonable process conditions. Two exemplary precursors that may be
used for depositing a phosphorus dopant source layer are
trimethylphosphide and trimethylphosphate.
[0035] The boron, phosphorus, or arsenic containing compound may be
provided to the reaction chamber in one or more pulses and allowed
to adhere to the substrate. An organoboron compound, for example,
may adhere to a hydroxyl-terminated substrate surface, liberating
some organic components. After substantially all reaction sites are
consumed by the precursor, excess may be purged or pumped from the
chamber in preparation for the next phase of the cycle.
[0036] The second precursor reacts with the first precursor
adsorbed onto the surface of the substrate until reaction sites are
substantially consumed. The second precursor may then be purged
from the reaction chamber. If a simple oxide or nitride layer is
desired as the dopant source, a complete monolayer of dopant source
material will cover the substrate surface conformally after the
second precursor deposits. If higher chemistry layers are desired,
subsequent precursors are provided to complete the step-wise ALD
process.
[0037] The precursor cycles may be repeated until the desired
thickness of the dopant source layer is reached, as illustrated by
step 210. After the desired thickness is reached, the substrate is
subjected to an annealing treatment to diffuse the dopants into the
substrate, activate the dopants, and repair crystal lattice damage
in step 212. Step 212 may be performed in one or more treatment
cycles, such as by rapidly heating the substrate to a target
temperature, holding that temperature for a predetermined time, and
cooling the substrate rapidly to an ambient temperature, or by
subjecting the substrate to a temperature spike. In alternate
embodiments, the treatment cycles may be the same or different.
[0038] Multiple embodiments of the ALD process described above may
be useful. It may be advantageous, in some embodiments, to
pump-down or evacuate the chamber entirely between precursor cycles
by closing all inlet pathways and applying vacuum. In some
embodiments, the precursor pathways may also be purged with a
non-reactive gas between precursor deposition cycles. In still
other embodiments, purge gas may flow through one or more precursor
pathways into the process chamber continuously, and the process
chamber may be purged of excess precursor by stopping flow of the
precursor gas while continuing flow of the purge gas. Still other
embodiments may combine these features. Any of these embodiments
may be used to deposit conformal dopant layers on substrates.
Conformal Doping By Plasma Deposition
[0039] Conformal doping may be performed using a plasma-enhanced
deposition process. FIG. 3 illustrates such a process. The process
300 begins by positioning a substrate having high aspect-ratio
features on a substrate support in a process chamber in step 302.
The substrate may be held in place by vacuum or electromagnetic
means, and the substrate support may be configured as described
above for thermal control of the substrate. As also described
above, the process chamber may be configured to perform one or more
deposition, cleaning, thermal, or electromagnetic energy
processes.
[0040] A dopant precursor material is provided to the process
chamber in step 304. The dopant precursor is selected to adhere to
the substrate surface when activated by ionizing into a plasma.
Dopant precursors useful for this purpose include, but are not
necessarily limited to, boron compounds (i.e. boranes, borates, or
borides), phosphorus compounds (i.e. phosphines, phosphates, or
phosphides), arsenic compounds (i.e. arsines, arsenates, or
arsenides), silicon compounds (i.e. silanes, siloxanes, silanols),
nitrogen compounds (N.sub.2, NH.sub.3, N.sub.2O), hydrogen
(H.sub.2), oxygen (O.sub.2). Some exemplary compounds which may be
useful for conformal doping embodiments such as process 300 are
borane, diborane, phosphine, arsine, silane, nitrogen (N.sub.2),
hydrogen (H.sub.2), and oxygen (O.sub.2).
[0041] The dopant precursor is ionized into a plasma in step 306.
The plasma may be capacitatively, or preferably inductively,
coupled. An inductively coupled plasma may be generated by creating
an electric field through which a portion of the reaction mixture
passes. The field is usually generated by passing an oscillating
electric current through a coil disposed around a passage
containing the material, such as the dopant precursor, to be
ionized. The oscillating electric field is preferably generated at
relatively low power, such as less than about 1000 Watts (W), and
most preferably below about 500 W. Such a low-power plasma, or weak
plasma, enhances the tendency of the precursors to react with or
adsorb onto the substrate, while minimizing unwanted deposits on
process apparatus. The frequency of the oscillating electric field
is normally about 13.56 MHz, which is radio frequency (RF). An
inductively-coupled plasma of this type may be generated inside the
process chamber, in a loop adjacent to the process chamber, or in a
remote plasma generation apparatus.
[0042] Generating an inductively coupled plasma by application of
RF power through an inductor coupled to a portion of the chamber
may additionally be accompanied by application of an electrical
bias, as in step 308. Electrical bias may be generated by applying
RF power with a high- or low-pass filter, or DC power, to one or
more components bordering the reaction space, such as the gas
distributor, substrate support, or chamber wall. The bias is
preferably oriented such that ions are propelled toward the
substrate, and is preferably weak (i.e. less than 500 W) such that
charged particles will penetrate deeply into trenches before
veering toward the side walls, and so that charged particles will
deposit on the surface of the substrate rather than implanting into
the surface. Although an isotropic reaction mixture is preferred,
application of a weak electrical bias encourages ions to penetrate
into trenches without discouraging deposition on side walls. In
this way, conformal implantation and doping is achieved.
[0043] In addition to inductive coupling, plasma may be generated
by capacitative coupling, wherein the electric field is generated
between the plates of a capacitor. Similar to the method described
for generating electrical bias in the process chamber described
above, voltage may be applied to one or more components of the
reaction chamber to generate the electric field. RF power is
generally used, but DC power may also be used. A weak plasma is
preferred in such an embodiment.
[0044] Following deposition of dopant source material on the
surface of the substrate in step 310, the substrate is annealed in
step 312 to activate the dopants and diffuse them into the crystal
structure of the substrate.
Plasma-Assisted Ald
[0045] Some conformal doping embodiments may benefit from the use
of a plasma-assisted ALD (PAALD) method. In a PAALD process,
reaction of the precursors with the substrate, or with other
precursors adsorbed onto the substrate, is encouraged or enhanced
by ionization of precursor species. A plasma is produced which
reacts more readily to deposit layers of dopant. Plasma may be
inductively or capacitatively coupled, with or without electrical
bias applied.
[0046] FIG. 4 is a process flow diagram illustrating a PAALD
process 400 according to one embodiment of the invention. A
substrate having high aspect-ratio features is provided to a
process chamber and disposed on a substrate support, such as those
discussed above, in step 402. Portions of the surface of the
substrate may optionally be pre-treated in step 404 to clean or
condition the surface of the substrate, such as wet cleaning,
plasma cleaning, or functional termination (i.e. hydroxyl, amino,
or hydrogen termination). In step 406, a first precursor, which may
be a catalytic precursor as described above, is provided to a
process chamber. The chamber may be purged or evacuated before the
first precursor is provided, as also described above.
[0047] The first precursor, which may be a catalytic precursor, may
be ionized into a plasma to aid deposition in step 408. The plasma
may be generated by capacitative, or preferably by inductive
coupling, and may be generated inside the process chamber, or in an
apparatus adjacent to or remote from the process chamber. RF power
is applied at a frequency of 13.56 MHz to generate the plasma. As
described above, the RF power preferably generated at power levels
less than 1000 W, and most preferably below 200 W, is applied to an
inductor disposed around a passage containing the material to be
ionized, such as the first precursor. A weak plasma will aid
deposition of precursors onto the substrate surface. The plasma may
be biased, but is preferably unbiased or electrically neutral. An
unbiased plasma is most likely to be isotropic throughout the
process chamber, leading to conformal doping. A weak bias, such as
that generated by less than 500 W of power, may result in
substantially conformal deposition for high aspect ratio strictures
as well.
[0048] RF power may be applied to one or more precursors, if
desired, to enhance results. For example, a dopant precursor may be
activated by RF power, if desired, and the RF power discontinued
during application of the oxygen or nitrogen source, or other
catalytic precursor. The catalytic precursor may also be activated
or ionized by RF power into a plasma. An oxygen or nitrogen plasma
may be formed thereby. In embodiments featuring more than two
precursors, it may be advantageous to apply RF power to the various
precursors in many different combinations.
[0049] RF power may be continued during purge steps 410 and 416 as
well, if desired. RF power during purge steps may have the added
benefit of reducing the presence of precursors that may have
adsorbed onto the walls and piping of the reaction chamber. Purge
gases ionized into a weak plasma may be effective in removing such
deposits from the walls and from the chamber. Purge steps may also
be performed after discontinuing RF power.
[0050] As with any ALD process, deposition proceeds in cycles. The
precursors may be sequentially provided to the process chamber,
with or without plasma in specific cases, to form a dopant layer or
dopant source layer of the desired thickness. As illustrated by
step 418, if the target thickness is not reached, deposition cycles
may be repeated. Plasma may be used to varying degrees, if desired,
to further tune the deposition process. For example, alternate
cycles may feature plasma.
[0051] When the target thickness of the dopant source layer
deposited on the substrate is reached in step 418, the substrate
may be annealed to complete process 400. The substrate is annealed
in step 420 to diffuse dopants from the dopant source layer into at
least portions of the surface of the substrate, and may be used to
activate the dopants, and repair crystal lattice damage. Annealing
may be performed in one or more thermal treatment cycles, such as
rapid thermal processing, spike annealing, laser or pulsed laser
annealing, flash or pulsed flash lamp annealing, or furnace
annealing, which may be the same or different.
[0052] FIGS. 5A-5C illustrate a substrate at various stages
corresponding to process steps discussed above. FIG. 5A illustrates
a substrate 500 with high aspect-ratio features. It is desired to
produce a conformal doping on the top surfaces 500A, sidewalls
500B, and in the trenches 500C of substrate 500. FIG. 5B
illustrates the substrate 500 at an intermediate stage when a
dopant source material is being conformally deposited. A precursor
material 502 is illustrated distributed isotropically through the
process chamber, such that concentration of precursor is
substantially the same near the top surfaces 500A, the sidewalls
500B, and the trenches 500C of the substrate. A conformal layer of
dopant source material 504 grows over substrate 500. FIG. 5C
illustrates the effect after thermal treatment. Conformal layer 504
has been driven into substrate 500 and activated to form conformal
doped layer 506.
Activation
[0053] Dopant source material deposited on the surface of a
substrate must be treated to promote diffusion into the substrate
and to activate the dopants. Conformal doping embodiments also
include activation steps. Any dopant diffusion process may be used
to accomplish activation, such as rapid thermal processing or
annealing, spike annealing, laser annealing, flash, pulse, or
furnace annealing, or the like. In some embodiments, a capping
layer may be used advantageously to promote the diffusion and
activation process. The capping layer may be deposited over the
entire substrate, or only over portions of the substrate, to
achieve the desired thermal treatment result.
[0054] A substrate with deposited dopant source material may be
treated by thermal or electromagnetic annealing in the same chamber
used to deposit the dopant source material or in one or more
different chambers. For example, dopant source material may be
deposited in a chamber configured to perform a PAALD process, and
then transferred to a thermal treatment chamber for annealing. The
thermal treatment chamber may be configured to heat or cool the
entire substrate, using heat lamps for example, or only a portion
of the substrate, as with lasers or flash lamps or back-side
cooling configurations. The substrate support may be temperature
controlled to facilitate annealing.
[0055] Dopant atoms in the dopant source layer are energized by the
treatment and move into the substrate. In some embodiments, it may
be advantageous to apply a capping layer before annealing to
prevent escape of fugitive dopants during thermal processing. Use
of a capping layer may also serve to equalize thermal load on the
tops and sidewalls of structural features on the surface of the
substrate. Portions of the substrate are generally heated to a
temperature selected to encourage movement of dopants into the
substrate and ordering of the substrate crystal structure. The
target temperature may be from about 700.degree. C. to about
1410.degree. C., and may be selected to partially melt portions of
the substrate. Selective melting may be used to encourage local
rearrangement of dopant and substrate atoms to facilitate the
activation and diffusion process. The substrate may be controlled
at an ambient temperature between about 100.degree. C. and about
700.degree. C. between heating cycles to facilitate rapid heating.
Heating and cooling cycles are preferably rapid to facilitate
control of diffusion and activation. For example, a heating cycle
that raises the temperature of the substrate too slowly may result
in over-diffusion of dopants into the substrate or liberation of
previously activated dopants. Temperature ramp rates exceeding
400.degree. C./second are generally preferred. Cooling cycles
generally follow heating cycles to solidify or freeze migrated or
activated dopant or substrate atoms in place.
[0056] Following the anneal process, small amounts of the dopant
source layer may be left on the surface of the substrate. In
general, anneal processes will result in a concentration gradient
of dopants in the surface of the substrate, with the highest
concentration being near the surface. In some embodiments, a dopant
source layer on the surface of the substrate, and a
high-concentration dopant layer just below the surface of the
substrate, may be removed after annealing. A cleaning process, such
as an etching, plasma cleaning, or plasma etching process, may be
used to remove the unwanted species.
Appartus
[0057] FIG. 6A is a schematic cross-section diagram of an apparatus
according to one embodiment of the invention. The apparatus
illustrated is configured to perform plasma-assisted processes such
as plasma implantation of dopants in a substrate. The plasma
reactor 600 includes a chamber body 602 having a bottom 624, a top
626, and side walls 622 enclosing a process region 604. A substrate
support assembly 628 is supported from the bottom 624 of the
chamber body 602 and is adapted to receive a substrate 606 for
processing. A gas distributor 630 is coupled to the top 626 of the
chamber body 602 facing the substrate support assembly 628. A
pumping port 632 is defined in the chamber body 602 and coupled to
a vacuum pump 634. The vacuum pump 634 is coupled through a
throttle valve 636 to the pumping port 632. A gas source 652 is
coupled to the gas distributor 630 to supply gaseous precursor
compounds for processes performed on the substrate 606. In some
embodiments, gas distributor 630 may be a showerhead.
[0058] The reactor 600 depicted in FIG. 6A further includes a
plasma source 690 best shown in the perspective view of FIG. 6B.
The plasma source 690 includes a pair of separate external
reentrant conduits 640 and 640', which may be curved tubes, mounted
on the outside of the top 626 of the chamber body 602 disposed
transverse to one another (or orthogonal to one another, as shown
in the exemplary embodiment depicted in FIG. 6B). The first
external conduit 640 has a first end 640a coupled through an
opening 698 formed in the top 626 into a first side of the process
region 604 in the chamber body 602. A second end 640b has an
opening 696 coupled into a second side of the process region 604.
The second external reentrant conduit 640' has a first end 640a'
having an opening 694 coupled into a third side of the process
region 604 and a second end 640b' having an opening 692 into a
fourth side of the process region 604. In one embodiment, the first
and second external reentrant conduits 640, 640' are configured to
be orthogonal to one another, with the ends 640a, 640a', 640b,
640b' of each external reentrant conduits 640, 640' disposed at
about 90 degree intervals around the periphery of the top 626 of
the chamber body 602. The orthogonal configuration of the external
reentrant conduits 640, 640' allows a plasma source distributed
uniformly across the process region 604. It is contemplated that
the first and second external reentrant conduits 640, 640' may be
reconfigured if other distributions are desired to provide uniform
plasma distribution into the process region 604.
[0059] Magnetically permeable torroidal cores 642, 642' surround a
portion of a corresponding one of the external reentrant conduits
640, 640'. The conductive coils 644, 644' are coupled to respective
RF plasma source power generators 646, 646' through respective
impedance match circuits or elements 648, 648'. Each external
reentrant conduit 640, 640' is a hollow conductive tube interrupted
by an insulating annular ring 650, 650' respectively that
interrupts an otherwise continuous electrical path between the two
ends 640a, 640b (and 640a', 604b') of the respective external
reentrant conduits 640, 640'. Ion energy at the substrate surface
is controlled by an RF plasma bias power generator 654 (FIG. 6A)
coupled to the substrate support assembly 628 through an impedance
match circuit or element 656.
[0060] Referring back to FIG. 6A, process gases including gaseous
compounds supplied from the process gas source 652 are introduced
through the overhead gas distributor 630 into the process region
604. RF source plasma power 646 is coupled to gases supplied in the
conduit 640 by conductive coil 644 and torroidal core 642, creating
a circulating plasma current in a first closed torroidal path
including the external reentrant conduit 640 and the process region
604. Also, RF source power 646' (FIG. 6B) may be coupled to gases
in the second conduit 640' by conductive coil 644' and torroidal
core 642', creating a circulating plasma current in a second closed
torroidal path transverse (e.g., orthogonal) to the first torroidal
path. The second torroidal path includes the second external
reentrant conduit 640' and the process region 604. The plasma
currents in each of the paths oscillate (e.g., reverse direction)
at the frequencies of the respective RF source power generators
646, 646', which may be the same or slightly offset from one
another.
[0061] In one embodiment, the process gas source 652 provides
different process gases that may be utilized to provide dopants to
the substrate 606. The power of each plasma source power generators
646, 646' may be operated to dissociate the process gases supplied
from the process gas source 652 and produce a desired ion flux at
the surface of the substrate 606. The power of the RF plasma bias
power generator 654 is controlled at a selected level at which the
ion energy dissociated from the process gases may be accelerated
toward the substrate surface and implanted at a desired depth below
the top surface of the substrate 606 with desired ion
concentration, or deposited on the surface of substrate 606. For
example, with relatively low RF power applied to bias generator
654, such as less than about 50 eV, relatively low plasma ion
energy may be obtained. Dissociated ions with low ion energy may be
implanted at a shallow depth between about 0 .ANG. and about 600
.ANG. from the substrate surface, or merely deposited on the
surface of substrate 606. Alternatively, dissociated ions with high
ion energy provided and generated from high RF power, such as
higher than about 50 eV, may be implanted into the substrate having
a depth substantially over 100 .ANG. depth from the substrate
surface.
[0062] As has been discussed above, for conformal doping
applications, it is preferable to generate at most weak electrical
bias in the chamber. Strong bias, while maintaining vigorous
activation of deposition species, results in heavy deposition on
field regions and less deposition than desired in holes and
trenches. Weak field regions, so better penetration into trenches
is achieved. With no electrical bias, composition of the plasma is
isotropic, and deposition is conformal on field regions and in
trenches. In weak bias applications, RF bias generator 654 is
preferably operated at a frequency of 13.56 MHz, and may be
operated to best effect at a bias power level less than about 1000
W, or more preferably less than about 500 W, such as less than
about 100 W.
[0063] Bias power generator 654 is shown coupled to substrate
support 628 through matching network 656, with gas distributor 630
grounded. Bias power generator 654 applies a monopolar RF-driven
electrical bias to plasma generated by external reentrant conduits
640 and 640'. In alternate embodiments, bias power generator 654
may be coupled to gas distributor 630, or separate bias circuits
may be independently coupled to both gas distributor 630 and
substrate support 628.
[0064] The combination of the controlled RF plasma source power and
RF plasma bias power dissociates ions in the gas mixture having
sufficient momentum and desired ion distribution in the plasma
reactor 600. The ions are biased and driven toward the substrate
surface, thereby implanting ions into the substrate with desired
ion concentration, distribution and depth from the substrate
surface, if sufficiently energized. Lower energy plasma bias power
may result in deposition on the surface of the substrate with
little penetration, as will generally be preferred in conformal
doping applications. Furthermore, the controlled ion energy and
different types of ion species from the supplied process gases
facilitates ions implanted in, or deposited on, the substrate 606,
forming desired device structure, such as gate structure and source
drain region on the substrate 606.
[0065] Plasma reactor 600 may further comprise a chamber liner (not
shown). Chamber liners are commonly provided to protect chamber
walls from reactive components during processing. Such liners may
be made of ceramic, silicon, or other protective materials, and may
be designed to be replaced periodically. In alternate embodiments,
the chamber may be chemically lined by depositing a silicon or
oxide layer on the inside surface of the chamber prior to
processing. An in-situ chamber liner of this sort serves the same
function, and may be removed and replaced by etching or cleaning
processes.
[0066] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *