U.S. patent application number 12/563764 was filed with the patent office on 2011-03-24 for defect-free junction formation using octadecaborane self-amorphizing implants.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to Bruce E. Adams, Aaron Muir Hunter, Jiping Li, Stephen Moffatt, Theodore Moffitt.
Application Number | 20110070724 12/563764 |
Document ID | / |
Family ID | 43756972 |
Filed Date | 2011-03-24 |
United States Patent
Application |
20110070724 |
Kind Code |
A1 |
Li; Jiping ; et al. |
March 24, 2011 |
DEFECT-FREE JUNCTION FORMATION USING OCTADECABORANE
SELF-AMORPHIZING IMPLANTS
Abstract
A method and apparatus for implanting a semiconductor substrate
with boron clusters. A substrate is implanted with octadecaborane
by plasma immersion or ion beam implantation. The substrate surface
is then annealed to completely dissociate and activate the boron
clusters. The annealing may take place by melting the implanted
regions or by a sub-melt annealing process.
Inventors: |
Li; Jiping; (Palo Alto,
CA) ; Hunter; Aaron Muir; (Santa Cruz, CA) ;
Adams; Bruce E.; (Portland, OR) ; Moffitt;
Theodore; (Hillsboro, OR) ; Moffatt; Stephen;
(US) |
Assignee: |
APPLIED MATERIALS, INC.
Santa Clara
CA
|
Family ID: |
43756972 |
Appl. No.: |
12/563764 |
Filed: |
September 21, 2009 |
Current U.S.
Class: |
438/530 ;
257/E21.328 |
Current CPC
Class: |
H01L 21/2658 20130101;
H01L 21/26513 20130101; H01L 21/26566 20130101 |
Class at
Publication: |
438/530 ;
257/E21.328 |
International
Class: |
H01L 21/26 20060101
H01L021/26 |
Claims
1. A method of treating a substrate, comprising: implanting boron
macromolecules into a surface of the substrate; melting the surface
of the substrate implanted with the boron macromolecules;
resolidifying the surface of the substrate implanted with the boron
macromolecules; and annealing the surface of the substrate.
2. The method of claim 1, wherein the boron macromolecules comprise
clusters containing at least sixteen boron atoms.
3. The method of claim 1, wherein melting the surface of the
substrate implanted with boron macromolecules comprises directing
heating energy to portions of the substrate surface to increase a
temperature of the substrate surface to a point at or above the
melting point of the substrate surface.
4. The method of claim 3, wherein the heating energy comprises
electromagnetic energy.
5. The method of claim 3, wherein the heating energy comprises
laser light.
6. The method of claim 5, wherein the laser light is continuous
wave radiation.
7. The method of claim 5, wherein the laser light is pulsed.
8. The method of claim 1, wherein resolidifying the surface of the
substrate comprises cooling the surface at a rate less than
200.degree. C./sec.
9. The method of claim 1, wherein resolidifying the surface of the
substrate comprises cooling the surface at a rate selected to
eliminate crystal defects from the surface of the substrate.
10. The method of claim 1, wherein annealing the surface of the
substrate comprises maintaining the substrate surface at a
temperature of at least 400.degree. C. for at least 1 minute.
11. The method of claim 1, wherein the boron macromolecules
comprise octadecaborane.
12. A method of treating a substrate, comprising: implanting
octadecaborane into the surface of the substrate; and annealing
implanted regions of the substrate by repeatedly heating and
cooling the implanted regions.
13. The method of claim 12, wherein the octadecaborane is implanted
at an energy level less than about 1 keV.
14. The method of claim 12, wherein repeatedly heating and cooling
the implanted regions comprises directing laser energy toward the
implanted regions.
15. The method of claim 14, further comprising pre-heating the
substrate.
16. The method of claim 14, wherein repeatedly heating and cooling
the implanted regions comprises maintaining a temperature of the
implanted regions at a temperature less than a melting temperature
of the implanted regions.
17. The method of claim 12, wherein repeatedly heating and cooling
the implanted regions comprises exposing the implanted regions to
pulses of electromagnetic radiation.
18. The method of claim 17, wherein the electromagnetic radiation
comprises laser light.
19. The method of claim 18, wherein each implanted region is
exposed to at least 30 pulses of electromagnetic radiation.
20. The method of claim 19, wherein each pulse of electromagnetic
radiation has a duration from about 1 nsec to about 10 .mu.sec.
Description
FIELD
[0001] Embodiments described herein relate to semiconductor
manufacturing methods. More specifically, embodiments of the
invention encompass methods of doping semiconductor substrates.
BACKGROUND
[0002] As semiconductor technology progresses, devices formed on
semiconductor substrates grow smaller. As devices grow smaller,
manufacturers are continually challenged to develop productive
processes for making the devices. Currently, manufacturing
processes are being deployed to make devices having critical
dimension of 45 nm. Researchers are busy developing next generation
processes for devices having critical dimension of 20 nm or less.
At these extreme dimensions, implanting dopants in a substrate
becomes forbidding. In a traditional boron doping process, for
example, boron atoms are directed toward a substrate with
sufficient energy to penetrate the crystal lattice to a desired
depth, and the substrate is then annealed to distribute the boron
and activate it (attach it to the crystal network). As device
dimensions grow smaller, control of implantation depth becomes more
critical. Next generation devices are expected to have junctions no
more than about 50 atomic layers deep.
[0003] Implantation problems arise as junction depth diminishes.
Because the ions must travel more slowly to avoid implanting too
deeply, the repulsive charge among like-charged ions forces them to
diverge from their intended path. To compensate for this effect,
fast-moving ions are magnetically decelerated near the surface of
the substrate. Beam deceleration, however, results in "energy
contamination," arising from exchange of charge between fast-moving
ions and fugitive neutral particles during or prior to
deceleration. The fast-moving neutralized particles are unaffected
by the beam decelerator and implant deeply into the substrate.
[0004] Small ions also channel through the crystal lattice. Because
the crystal lattice has open spaces large enough for many ions to
pass unimpeded, more ions will travel down these "channels",
resulting in highly variable implant depth. To reduce the tendency
to channel, many manufacturers have resorted to "pre-amorphizing"
the substrate surface to remove any opportunity for channeling.
Pre-amorphization may also improve implant dose by opening more
space within the solid matrix for ions to penetrate. Pre-amorphized
substrates require more annealing, however, to activate dopants
because the crystal structure is completely disrupted to a
considerable depth and must be repaired. This leads to unwanted
dopant diffusion and residual EOR damage.
[0005] Thus, there is a continuing need for better methods of
implanting dopants in a shallow junction with high dopant dose and
activation, low sheet resistance, and even distribution of
dopants.
SUMMARY
[0006] Embodiments described herein provide a method of treating a
substrate, comprising implanting boron macromolecules into a
surface of the substrate, melting the surface of the substrate
implanted with the boron macromolecules, resolidifying the surface
of the substrate implanted with the boron macromolecules, and
annealing the surface of the substrate. In some embodiments, the
boron macromolecules comprise boron clusters having at least
sixteen boron atoms.
[0007] Other embodiments provide a method of treating a substrate,
comprising implanting octadecaborane into the surface of the
substrate, and annealing implanted regions of the substrate by
repeatedly heating and cooling the implanted regions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] 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 and
are therefore not to be considered limiting in scope, because other
equally effective embodiments may be devised.
[0009] FIG. 1A is a schematic cross-sectional view of an apparatus
according to one embodiment.
[0010] FIG. 1B is a perspective view of the apparatus of FIG.
1A.
[0011] FIG. 2 is a flow diagram summarizing a method according to
one embodiment.
[0012] FIG. 3 is a flow diagram summarizing a method according to
another embodiment.
[0013] FIG. 4 is a schematic illustration of an anneal system that
may be used to practice embodiments described herein.
[0014] FIG. 5 is a schematic illustration of a top view of a
substrate that contains forty square shaped dice that are arranged
in an array.
[0015] FIG. 6 is a flow diagram summarizing a method according to
another embodiment.
[0016] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that elements
disclosed in one embodiment may be beneficially utilized on other
embodiments without specific recitation.
DETAILED DESCRIPTION
[0017] Embodiments described herein generally provide methods of
doping a semiconductor substrate with boron. A substrate is
provided to an implant chamber. A gas mixture containing boron
macromolecules is provided to the chamber. The boron macromolecules
are ionized and accelerated toward the substrate with energy
selected to accomplish a shallow implant of the boron
macromolecules into a surface of the substrate. The boron
macromolecules penetrate and amorphize the substrate surface and
break apart into atoms or small clusters. The boron dopant is then
activated using an anneal process.
[0018] FIG. 1A depicts a plasma reactor 100 that may be utilized to
practice ion implantation, oxide layer formation, and capping layer
formation according to one embodiment of the invention. One
suitable reactor which may be adapted to practice the invention is
a P3i.TM. reactor, available from Applied Materials, Inc., of Santa
Clara, Calif. Another reactor which may be adapted to practice the
invention is described in U.S. patent application Ser. No.
11/608,357. It is contemplated that the methods described herein
may be practiced in other suitably adapted plasma reactors,
including those from other manufacturers.
[0019] The plasma reactor 100 includes a chamber body 102 having a
bottom 124, a top 126, and side walls 122 enclosing a process
region 104. A substrate support assembly 128 is supported from the
bottom 124 of the chamber body 102 and is adapted to receive a
substrate 106 for processing. A gas distribution plate 130 is
coupled to the top 126 of the chamber body 102 facing the substrate
support assembly 128. A pumping port 132 is defined in the chamber
body 102 and coupled to a vacuum pump 134. The vacuum pump 134 is
coupled through a throttle valve 136 to the pumping port 132. A gas
source 152 is coupled to the gas distribution plate 130 to supply
gaseous precursor compounds for processes performed on the
substrate 106.
[0020] The reactor 100 depicted in FIG. 1A further includes a
plasma source 190 best shown in the perspective view of FIG. 1B.
The plasma source 190 includes a pair of separate external
reentrant conduits 140, 140' mounted on the outside of the top 126
of the chamber body 102 disposed transverse to one another (or
orthogonal to one another, as shown in the exemplary embodiment
depicted in FIG. 1B). The first external conduit 140 has a first
end 140a coupled through an opening 198 formed in the top 126 into
a first side of the process region 104 in the chamber body 102. A
second end 140b has an opening 196 coupled into a second side of
the process region 104. The second external reentrant conduit 140b
has a first end 140a' having an opening 194 coupled into a third
side of the process region 104 and a second end 140b' having an
opening 192 into a fourth side of the process region 104. In one
embodiment, the first and second external reentrant conduits 140,
140' are configured to be orthogonal to one another, thereby
providing the two ends 140a, 140a', 140b, 140b' of each external
reentrant conduits 140, 140' disposed at about 90 degree intervals
around the periphery of the top 126 of the chamber body 102. The
orthogonal configuration of the external reentrant conduits 140,
140' allows a plasma source distributed uniformly across the
process region 104. It is contemplated that the first and second
external reentrant conduits 140, 140' may be configured as other
distributions utilized to provide uniform plasma distribution into
the process region 104.
[0021] Magnetically permeable torroidal cores 142, 142' surround a
portion of a corresponding one of the external reentrant conduits
140, 140'. The conductive coils 144, 144' are coupled to respective
RF plasma source power generators 146, 146' through respective
impedance match circuits or elements 148, 148'. Each external
reentrant conduit 140, 140' is a hollow conductive tube interrupted
by an insulating annular ring 150, 150' respectively that
interrupts an otherwise continuous electrical path between the two
ends 140a, 140b (and 140a', 104b') of the respective external
reentrant conduits 140, 140'. Ion energy at the substrate surface
is controlled by an RF plasma bias power generator 154 coupled to
the substrate support assembly 128 through an impedance match
circuit or element 156.
[0022] Referring back to FIG. 1A, process gases including gaseous
compounds supplied from the process gas source 152 are introduced
through the overhead gas distribution plate 130 into the process
region 104. RF plasma source power generator 146 is coupled from
the power applicator to gases supplied in the conduit 140, which
creates a circulating plasma current in a first closed torroidal
path including the external reentrant conduit 140 and the process
region 104. Also, RF plasma source power generator 146' may be
coupled from the other power applicator to gases in the second
conduit 140', which creates 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 140' and the process region 104. The
plasma currents in each of the paths oscillate (e.g., reverse
direction) at the frequencies of the respective RF plasma source
power generators 146, 146', which may be the same or slightly
offset from one another.
[0023] In one embodiment, the process gas source 152 provides
different process gases that may be utilized to provide ions
implanted to the substrate 106. The power of each plasma source
power generator 146, 146' is operated so that their combined effect
efficiently dissociates the process gases supplied from the process
gas source 152 and produces a desired ion flux at the surface of
the substrate 106. The power of the RF plasma bias power generator
154 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 106 with desired ion concentration. For
example, with relatively low RF power, such as less than about 50
eV, relatively low plasma ion energy may be obtained.
[0024] A gas mixture comprising boron macromolecules is provided to
a chamber having a substrate disposed therein. Embodiments of the
invention may also be practiced using a QUANTUM.RTM. X Plus
implanter available from Applied Materials, Inc., of Santa Clara,
Calif., or equivalent devices from other manufacturers. The boron
macromolecules may comprise any mixture of stable boron
macromolecules, including but not limited to the boron hydrides
B.sub.xH.sub.y, wherein x is between about 6 and about 20, and y is
between about 12 and about 24. In many embodiments, boron clusters
or macromolecules used for implantation will have at least 16 boron
atoms each. Some exemplary boron hydride macromolecules include
octadecaborane (B.sub.18H.sub.22), decaborane (B.sub.10H.sub.14),
hexaborane (B.sub.6H.sub.10), octaborane (B.sub.8H.sub.12), and
hexadecaborane (B.sub.16H.sub.20). Octadecaborane is preferred
because it may be ionized without decomposing under processing
conditions. Octadecaborane also transports a high quantity of boron
to a substrate at very low energy without the difficulties
enumerated above. Because octadecaborane ions have a high
mass-to-charge ratio, the tendency for the ions to diverge is
sharply reduced, allowing low energy implant with none of the
challenges described above.
[0025] In one embodiment, octadecaborane (B.sub.18) is vaporized by
heating to a sublimation temperature. B.sub.18 may be vaporized
using a Clusterlon.RTM. vaporizer available from SemEquip, Inc., of
North Billerica, Mass., or equivalent source systems available from
other manufacturers. The B.sub.18 vapor is then provided to a
chamber or device for implanting into a surface of a substrate.
[0026] In a plasma-immersion type device, the B.sub.18 vapor is
provided to an ionizing zone formed inside a gas distribution
apparatus. RF power is coupled to the ionizing zone to ionize the
B.sub.18. Typically, flow of a carrier gas will be established at
between about 1,000 sccm and about 5,000 sccm, such as between
about 2,000 sccm and about 4,000 sccm, for example about 3,000
sccm. The carrier gas may be any gas non-reactive under processing
conditions, such as helium or argon. RF power is coupled into the
gas flow, and then a pulse of B.sub.18 vapor is provided to the
chamber to form a gas mixture in the gas distribution apparatus.
The pulse of B.sub.18 vapor may be provided for about 1 second at a
flowrate between about 500 sccm and about 2,000 sccm, such as
between about 700 sccm and about 1,200 sccm, for example about
1,000 sccm. The ionizing RF power may be coupled into the ionizing
zone at between about 100 W and about 500 W, such as between about
200 W and about 400 W, for example about 300 W. The RF power may be
coupled into the ionizing zone by use of capacitative coupling
using, for example, parallel plate electrodes, or by inductive
coupling. In some embodiments, greater than 90% of the B.sub.18
molecules are ionized, such as greater than 95%, for example
greater than 99%.
[0027] The B.sub.18 ions flow through the ionizing zone into the
chamber through the gas distribution apparatus. In some
embodiments, the B.sub.18 ions may be accelerated toward the
substrate surface by application of an electrical bias to the gas
distributor, the substrate support, or both. The bias may be a DC
bias or an RF bias. Some embodiments use no electrical bias,
allowing the B.sub.18 ions to drift toward the substrate with the
gas flow. In embodiments wherein an electrical bias is used, a bias
of 100 V to 300 V DC or root-mean-square RF at a power level of 10
W to 500 W may be used. In some embodiments, 200 V DC is provided
at 100 W of power.
[0028] In an ion implanter device, B.sub.18 vapor is passed through
an ionizing zone in which an electric field ionizes the B.sub.18
molecules. A magnetic mass selector produces a beam of B.sub.18
ions which are focused and directed toward the substrate. Each
boron cluster will generally have kinetic energy between about 2
keV and about 20 keV, which is equivalent to each boron atom having
kinetic energy between about 0.1 keV and about 1.1 keV. The beam
current may be between about 0.1 mA and about 5.0 mA to deliver
equivalent ion current between about 2 mA and about 100 mA of
individual boron ions.
[0029] Octadecaborane ions disrupt the crystal structure of a
substrate surface as they implant, and are thus self-amorphizing.
The large ions impact the substrate surface, substantially melting
the surface in the immediate vicinity of the impact. As the ions
pass into the surface, they form tiny impact craters, substantially
disrupting the crystal lattice. Hydrogen atoms are stripped from
the ion and diffuse out of the substrate, leaving the boron cluster
to barrel through successive layers of the crystal surface. As the
large clusters move through the crystal, fragments of boron break
off from the main cluster. These fragments may be single boron
atoms or clusters of a few boron atoms. The small clusters are
better able to penetrate the crystal lattice with low energy by
channeling through the empty spaces, but because the large cluster
is amorphizing its immediate environment, movement of most small
clusters is diverted laterally, causing lateral dispersion of boron
atoms.
[0030] The inventors have found that annealing processes involving
melting the surface of the substrate, and sub-melt annealing
processes involving rapid repeated heating and cooling are more
effective for activating boron macromolecule implants than
traditional sub-melt anneal processes. While not wishing to be
bound by theory, it is thought that implantation of B.sub.18
clusters amorphize the surface of the substrate to a degree much
greater than implantation of smaller particles, so that standard
sub-melt anneal processes do not fully recrystallize the substrate.
Additionally, B.sub.18 clusters do not necessarily fragment
entirely into individual boron atoms upon implantation, so melting
assists in completing the fragmentation in-situ. In some
embodiments, due to the ability of B.sub.18 clusters to amorphize
the surface of a substrate without creating EOR defects,
ultra-shallow junctions having little or no leakage due to EOR
defects may be created using B.sub.18 implantation followed by melt
annealing.
[0031] FIG. 2 summarizes a method 200 of doping a substrate with
boron according to one embodiment of the invention. Boron
macromolecules are implanted into the surface of the substrate at
202. Octadecaborane or other stable macromolecules containing a
large amount of boron, such as, but not limited to, icosaborane
(B.sub.20H.sub.26), triantaborane (B.sub.30H.sub.x), and
sarantaborane (B.sub.40H.sub.x) may be useful for certain
embodiments. Combinations or mixtures of the above may also be
used. Implantation may be accomplished using a plasma immersion
apparatus or a beam implant apparatus to ionize the boron clusters
and direct them toward the substrate. A DC or RF bias may be
applied to the substrate to tune the implant energy.
[0032] The implanted portion of the substrate surface is melted at
204. A melt heating process suitable for treatment of substrates
implanted with octadecaborane may be administered using any
convenient source of energy. A substrate may be heated by
conduction or by radiant heating with electromagnetic radiation.
The substrate may be disposed on a heated support or may be
subjected to irradiation with visible, infrared, or microwave
radiation. A heated support may be heated using resistive heating
embedded within the support, or by providing conduits within the
support for flowing hot fluids. The radiation may be coherent or
incoherent, focused or unfocused, monochromatic or polychromatic,
or polarized or unpolarized to any degree. The radiation may be
delivered by any combination of one or more lasers, flash lamps,
arc lamps, or filament lamps. In some embodiments, the entire
substrate may be treated at once, while in other embodiments,
portions of the substrate may be treated consecutively. In some
embodiments, an energy absorbing film, such as a carbon film, may
be applied over the substrate to improve application of energy to
the substrate surface, and to reduce loss of boron from sublimation
as the substrate is heated. In some embodiments, the substrate
surface may be heated with radiant energy while the bulk of the
substrate is cooled using a cool support.
[0033] The portion of the substrate implanted with octadecaborane
is heated to a temperature at or above the melting point of the
implanted portion. In some embodiments, only the implanted surface
is melted, while the bulk of the substrate remains crystalline. Due
to the extent of amorphizing accompanying octadecaborane
implantation in some embodiments, it may be sufficient to heat the
surface to a temperature at or above the melt temperature of the
amorphous material, which will generally be less than that of the
corresponding crystalline material. For embodiments in which a
silicon substrate is treated, a temperature of 1,200.degree. C. or
more may suffice to melt the amorphized portion of the surface.
Because amorphous silicon melts at a lower temperature than
crystalline silicon, the amorphized portion melts at this
temperature, but the underlying crystalline phase does not. To
minimize any substrate damage due to thermal stress, it may be
advantageous to heat the bulk of the substrate to an intermediate
temperature. In an exemplary embodiment, the substrate support may
heat the substrate to a temperature of 500.degree. C. or more, and
a radiant energy source may be used to heat portions of the
substrate to the melt temperature. Very fast heating of the melt
zone is generally preferred to achieve melting of the amorphous
phase before it crystallizes. In some embodiments, nanosecond
pulsed lasers having pulse duration from a few nanoseconds to about
200 nanoseconds, such as between 10 nsec and 100 nsec, for example
20 nsec, may be used to melt the amorphous phase.
[0034] After melting, the melted portions of the substrate are
recrystallized at 206. In many embodiments, the recrystallization
is performed in a way that promotes formation of a crystal lattice
including the implanted boron atoms. In this way, the
recrystallization is similar to an annealing process. To promote
crystal formation, it is generally preferred to cool the melted
portions at a rate slower than would be achieved through normal
conductive or radiative cooling. In some embodiments, it may be
advantageous to maintain the temperature of the substrate at
500.degree. C. or more for up to 10 minutes, such as between about
1 minute and about 10 minutes, for example about 3 minutes,
following melting. In other embodiments, it may be useful to cool
the implanted portion of the substrate surface at a rate not higher
than about 100.degree. C./sec, such as between about 1.degree.
C./sec and about 50.degree. C./sec, for example about 10.degree.
C./sec. In still other embodiments, a slow cooling rate may be
combined with periods of constant temperature to accomplish the
recrystallization.
[0035] A substrate to be implanted as described herein may be
subjected to a preclean process. The solution may have a
concentration of about 0.1 to about 10.0 weight percent HF and be
used at a temperature of about 20.degree. C. to about 30.degree. C.
In an exemplary embodiment, the solution has about 0.5 weight
percent of HF and a temperature of about 25.degree. C. In another
exemplary embodiment, the solution has about 1.0 weight percent of
HF and a temperature of about 25.degree. C. The substrate may be
exposed to the HF solution form a duration from about 10 seconds to
about 60 seconds. Any unwanted oxide is removed from the substrate
by the etching action of the HF solution. A brief exposure of the
substrate to the solution may be followed by a rinse step in
de-ionized water and a bake step. The bake step may be performed
under an inert atmosphere, such as nitrogen gas, helium, or argon,
at a temperature selected to volatilize any remaining fugitive
species from the surface of the substrate. In one embodiment, the
substrate may be exposed to a temperature of between about
200.degree. C. and about 600.degree. C. for about 60 seconds.
[0036] A substrate implanted with boron as described herein may be
subjected to a stripping process following the anneal process to
remove any residual high surface concentration of boron. In some
embodiments, the substrate is exposed to a hydrogen-containing gas
to generate volatile hydrides. In some embodiments, the
hydrogen-containing gas may be a plasma. For example, hydrogen gas
or ammonia, with or without plasma, may be used to convert dopants
at the surface of the substrate into volatile hydrides. Boron may
react to form various volatile boron hydrides such as borane,
diborane, or other volatile borane oligomers. In one exemplary
embodiment, the substrate may be exposed to a hydrogen plasma for
between about 10 seconds and about 30 seconds, such as about 15
seconds, at a temperature of between about 100.degree. C. and about
300.degree. C., such as about 200.degree. C., to reduce the surface
concentration of dopants. The hydrogen plasma may be generated
in-situ or remotely, and may accompany a non-reactive carrier gas
such as argon or helium. The carrier gas flow may be established at
a rate between about 1,000 sccm and about 2,000 sccm, such as about
1,500 sccm, and a pulse of hydrogen gas added. The pulse of
hydrogen gas may be supplied at a flow rate between about 100 sccm
and about 500 sccm, such as about 300 sccm, for an interval of
about 10 seconds to about 30 seconds, such as about 15 seconds.
Following exposure, the hydrogen gas is stopped and the carrier gas
purges any remaining volatile hydrides from the chamber. The
chamber may also be pumped-down to a low pressure to remove any
remaining fugitive hydrides.
[0037] FIG. 3 summarizes a method 300 according to another
embodiment of the invention. A substrate is disposed in a
processing chamber at 302. Flow of a carrier gas is established at
304. The carrier gas may be any non-reactive gas, such as helium,
argon, or nitrogen gas. In some embodiments, the carrier gas flow
rate may be between about 1,000 sccm and about 5,000 sccm, such as
between about 2,000 sccm and about 4,000 sccm, for example about
3,000 sccm. A precursor comprising boron macromolecules is added at
306. The boron precursor may be added to the carrier gas stream
outside the processing chamber or may be added directly to the
processing chamber. The boron precursor may be provided at a flow
rate between about 100 sccm and about 500 sccm, such as between
about 200 sccm and about 400 sccm, for example about 300 sccm. The
boron precursor will generally be provided at or above a
vaporization temperature to maintain the boron precursor in a vapor
state. For B.sub.18, the boron precursor may be provided at a
temperature between about 100.degree. C. and about 400.degree. C.,
such as about 250.degree. C.
[0038] The carrier gas and boron precursor flow into one or more
ionizing zones near or within the processing chamber. At 308,
ionizing energy is applied to ionize the boron precursor without
decomposing the boron macromolecules, which then emerge through a
gas distributor into the processing chamber. In some embodiments,
the ionizing energy may be applied by coupling an electric field
into the ionizing zones. The electric field may be static, such as
a DC bias, or varying, such as that generated by application of RF
power, and may be coupled into the ionizing zones by capacitative
or inductive means. In one embodiment, inductive ionizing zones are
provided outside the processing chamber, with one or more conduits
to carry gas to the ionizing zones from the processing chamber. An
electric field is coupled into each ionizing zone by providing one
or more torroidal cores disposed around the ionizing zones. The one
or more torroidal cores are energized with RF power to generate an
electric field inside the ionizing zones. For most embodiments, the
ionizing energy may be provided at a power level of between about
100 W and about 500 W, such as about 300 W.
[0039] At 310, an electric field may be applied to accelerate the
ionized boron macromolecules toward the substrate surface. This may
be a static field, such as a DC bias applied to the substrate
support, the gas distributor, or both, or it may be a varying field
such as an RF-driven field. Application of an electric field is an
optional step used to adjust the energy of the ionized boron
macromolecules as they travel toward the substrate surface. Some
embodiments may allow the ions to drift toward the surface. If an
electric field is used, it will preferably be a weak field, applied
at a power level between about 50 W and about 500 W, such as about
100 W. In some embodiments, the ionized boron macromolecules will
travel toward the substrate surface with kinetic energy between
about 100 eV and about 2,000 eV. Individual embodiments may
energize the ions with any particular value or range of kinetic
energy between these two values. A single embodiment may also
feature ions with a distribution of energies within this range. For
example, a first portion of the ionized boron macromolecules may
have higher kinetic energy than a second portion of the ionized
boron macromolecules due to thermal, pressure, or electrical
gradients or fluctuations.
[0040] The ionized boron macromolecules impact the substrate
disposed on the substrate support at 312, implanting into the
substrate surface. The macromolecules generally carry enough
kinetic energy to disrupt the crystal matrix of the substrate
surface as they impact, amorphizing the surface. Additionally, the
boron macromolecules fragment as they bore into the substrate
surface. The fragments generally diverge laterally from the main
macromolecule due to the amorphizing process, resulting in an
as-implanted concentration profile that is relatively abrupt. In
some embodiments, the maximum concentration of as-implanted boron
may be between about 5 and 15 nm below the surface, such as about
10 nm below the surface, and may be between about 10.sup.19
cm.sup.-3 and about 10.sup.21 cm.sup.-3 at that depth. The
as-implanted concentration will generally fall at a rate of 2-20
nm/dec., depending on the implant energy. The implant layer will
generally be between about 30 nm and about 150 nm thick, such as
about 50 nm thick. The resulting implant layer will be completely
amorphized by action of the boron macromolecules, with boron atoms
or small boron clusters of 2 to 4 boron atoms each, dispersed
through the layer.
[0041] At 314, heating energy is applied to one or more implanted
portions. The heating energy is selected to raise the temperature
of the implanted area to the melting point, or above. The heating
energy may be applied in any convenient way. For example,
electromagnetic energy or radiant energy may be projected toward
the implanted area to melt portions thereof. Additionally,
background heating may be applied to pre-heat the implanted area,
an area of the substrate containing the implanted area to be
melted, or the entire substrate. For example, a heated substrate
support may apply conductive heating energy to the substrate to
raise its temperature to between about 400.degree. C. and about
700.degree. C., maintaining that temperature while individual
implanted areas are melted by application of incremental heating
energy. Radiant energy for melting implanted areas may be delivered
by laser, heat lamp, flash lamp, or the like, and may be pulsed or
continuous, coherent or incoherent, monochromatic or polychromatic,
polarized or unpolarized to any degree. Portions of the substrate
may be irradiated consecutively, or the entire substrate irradiated
simultaneously. The implanted portions may be heated to a
temperature between about 1,100.degree. C. and about 1,400.degree.
C., depending on the embodiment. Melting of amorphized silicon
generally occurs at a lower temperature than melting of crystalline
silicon, so embodiments wherein the substrate material is
predominantly silicon may feature heating implanted portions to
about 1,200.degree. C. The melt temperature is selected to melt the
amorphous layer without melting the underlying crystalline layer.
It is generally desired to heat the portions to be melted at a high
rate, so that the amorphous portion is heated faster than heat can
be conducted away by the substrate material, and is melted before
it can recrystallize. When amorphous silicon is slowly heated to
near its melting point, it undergoes solid phase epitaxy,
converting to crystalling silicon with a higher melting point. Very
rapid heating may melt the amorphous portion before it can
recrystallize.
[0042] At 316, the temperature of the melted portions of the
implanted surface is maintained above the melting temperature for a
period of time to allow complete dissociation of remaining boron
fragments and some diffusion of boron out of the maximum
concentration layer. Most embodiments using nanosecond pulsed
lasers will feature melt duration from tens to hundreds of
nanoseconds. In some embodiments, however, melt duration may be
between a few milliseconds and about 0.5 seconds, such as about 10
msec.
[0043] At 318, the heated portions of the substrate surface are
cooled at a controlled rate to recrystallize or resolidify the
substrate surface. In general this cooling rate will be slower than
would be experienced through simple de-energizing of the heating
apparatus to allow controlled recrystallization. This controlled
recrystallization process effectively activates the boron dopant
atoms derived from the implanted boron macromolecules by moving
them to crystal lattice positions and freezing them in place. In
some embodiments, heating energy may be applied to melted implant
areas control the rate of cooling of melted implant by adjusting
the energy-time profile of the heating source. For example, the
profile of the pulse of a nanosecond laser may be adjusted using
pulse modification optics, or the shape of a discharge voltage
pulse applied to one or more flash lamps may be adjusted. The
heating energy may be electromagnetic energy or radiant energy
according to any of the methods described above. In other
embodiments, heating energy may be applied to the entire substrate
to maintain its temperature at an intermediate temperature for a
period of time to accomplish the recrystallization process. For
example, a substrate may be recrystallized by maintaining its
temperature between about 400.degree. C. and about 700.degree. C.
for between about 1 minute and about 10 minutes. For example, in
one embodiment, a substrate may be recrystallized by maintaining
its temperature at about 500.degree. C. for about 60 seconds. The
controlled cooling process anneals the substrate surface to
eliminate crystal defects from the substrate surface, distribute
the dopants, and activate the dopants.
[0044] FIG. 4 schematically illustrates an anneal system 400 that
may be used to practice embodiments of the present invention. The
anneal system 400 comprises an energy source 420 which is adapted
to project an amount of energy on a defined region, or an anneal
region 412, of a substrate 410 to preferentially melt certain
desired regions within the anneal region 412.
[0045] In one example, as shown in FIG. 400, only one defined
region of the substrate 410, such as an anneal region 412, is
exposed to the radiation from the energy source 420 at any given
time. The substrate 410 moves relative to the energy source 420 so
that other regions on the substrate 410 may be sequentially exposed
to the energy source 420.
[0046] In one aspect of the invention, multiple areas of the
substrate 410 are sequentially exposed to a desired amount of
energy delivered from the energy source 420 to cause the
preferential melting of desired regions of the substrate 410.
[0047] In general, the areas on the surface of the substrate 410
may be sequentially exposed by translating the substrate 410
relative to the output of the energy source 420 (e.g., using
conventional X/Y stages, precision stages) and/or translating the
output of the energy source 420 relative to the substrate 410.
[0048] The substrate 410 may be positioned on a heat exchanging
device 415 configured to control over all temperature of the
substrate 410. The heat exchange device 415 may be positioned on
one or more conventional electrical actuators 417 (e.g., linear
motor, lead screw and servo motor), which may be part of a separate
precision stage (not shown), configured to control the movement and
position of substrate 410. Conventional precision stages that may
be used to support and position the substrate 410, and the heat
exchanging device 415, may be purchased from Parker Hannifin
Corporation, of Rohnert Park, Calif.
[0049] In one aspect, the anneal region 412 is sized to match the
size of the die 413 (e.g., 40 dice are shown in FIG. 4), or
semiconductor devices (e.g., memory chip), that are formed on the
surface of the substrate 410. In one aspect, the boundary of the
anneal region 412 is aligned and sized to fit within the "kurf" or
"scribe" lines 410A that define the boundary of each die 413.
[0050] Sequentially placing anneal regions 412 so that they only
overlap in the naturally occurring unused space/boundaries between
die 413, such as the scribe or kurf lines 410A, reduces the need to
overlap the energy in the areas where the devices are formed on the
substrate 410 and thus reduces the variation in the process results
between the overlapping anneal regions 412.
[0051] In one embodiment, prior to performing the annealing process
the substrate 410 is aligned to the output of the energy source 420
using alignment marks typically found on the surface of the
substrate 410 and other conventional techniques so that the anneal
region 412 can be adequately aligned to the die 413.
[0052] The energy source 420 is generally adapted to deliver
electromagnetic energy to preferentially melt certain desired
regions of the substrate surface. Typical sources of
electromagnetic energy include, but are not limited to an optical
radiation source (e.g., laser), an electron beam source, an ion
beam source, and/or a microwave energy source.
[0053] In general, the substrate 410 is placed within an enclosed
processing environment (not shown) of a processing chamber (not
shown) that contains the heat exchanging device 415. The processing
environment within which the substrate 410 resides during
processing may be evacuated or contain an inert gas that has a low
partial pressure of undesirable gases during processing, such as
oxygen.
[0054] In one embodiment, it may be desirable to control the
temperature of the substrate 410 during thermal processing by
placing a surface of the substrate 410, illustrated in FIG. 4, in
thermal contact with a substrate supporting surface 416 of the heat
exchanging device 415. The heat exchanging device 415 is generally
adapted to heat and/or cool the substrate 410 prior to or during
the annealing process. In this configuration, the heat exchanging
device 415, such as a conventional substrate heater available from
Applied Materials Inc., Santa Clara, Calif., may be used to improve
the post-processing properties of the annealed regions of the
substrate 410.
[0055] In one embodiment, the substrate may be preheated prior to
performing the annealing process so that the energy required to
reach the melting temperature is minimized, which may reduce any
induced stress due to the rapid heating and cooling of the
substrate 410 and also possibly reduce the defect density in the
resolidified areas of the substrate 410. In one aspect, the heat
exchanging device 415 contains resistive heating elements 415A and
a temperature controller 415C that are adapted to heat a substrate
410 disposed on the substrate supporting surface 416. The
temperature controller 415C is in communication with the controller
421.
[0056] In one aspect, it may be desirable to preheat the substrate
to a temperature between about 20.degree. C. and about 750.degree.
C. In one embodiment, where the substrate is formed from a silicon
containing material it may be desirable to preheat the substrate to
a temperature between about 20.degree. C. and about 500.degree. C.
In another embodiment, where the substrate is formed from a silicon
containing material it may be desirable to preheat the substrate to
a temperature between about 200.degree. C. and about 480.degree. C.
In another embodiment, where the substrate is formed from a silicon
containing material it may be desirable to preheat the substrate to
a temperature between about 250.degree. C. and about 300.degree.
C.
[0057] In another embodiment, it may be desirable to cool the
substrate during processing to reduce any diffusion due to the
energy added to the substrate during the annealing process and/or
increase the regrowth velocity after melting to increase the
amorphization of the various regions during processing. In one
configuration, the heat exchanging device 415 contains one or more
fluid channels 415B and a cryogenic chiller 415D that are adapted
to cool a substrate disposed on the substrate supporting surface
416. In one embodiment, a conventional cryogenic chiller 415D,
which is in communication with the controller 421, is adapted to
deliver a cooling fluid through the one or more fluid channels
415B. In one aspect, it may be desirable to cool the substrate to a
temperature between about -240.degree. C. and about 20.degree.
C.
[0058] During a pulsed laser anneal process, a substrate being
processed moves relative to an energy source so that portions of
the substrate are exposed to the energy source sequentially. The
relative movement may be a stepping motion. For example, the
substrate may be moved to and maintained at a first position so
that a first area on the substrate is aligned with the energy
source. The energy source then projects a desired amount of energy
toward the first area on the substrate. The substrate is then moved
to a second position to a second area with the energy source. The
relative movement between the substrate and the energy source is
stopped temporarily when the energy source projects energy to the
substrate so that the energy is projected precisely and uniformly
to a desired area. However, this stepping motion involves
accelerating and decelerating in every step which significantly
slows the down the process.
[0059] FIG. 5 schematically illustrates a top view of a substrate
410 that contains forty square shaped dice 413 that are arranged in
an array. The dice 413 are separated from one another by areas
marked by scribe lines 410A. Energy projection region 520A
indicates the area over which energy source 420 (shown in FIG. 4)
is adapted to deliver an energy pulse. In general, the energy
projection region 520A may cover an area equal to or greater than
the area of each die 413, but smaller than the area of each die 413
plus the area of the surrounding scribe lines 410A, so that the
energy pulse delivered in the energy projection region 520A
completely covers the die 413 while not overlapping with the
neighboring dice 413.
[0060] To perform the annealing process on multiple dice 413 spread
out across the substrate surface, the substrate and/or the output
of the energy source 420 needs to be positioned and aligned
relative to each die. In one embodiment, curve 520B illustrates a
relative movement between the dies 413 of the substrate 410 and the
energy projection region 520A of the energy source 420, during a
sequence of annealing process as that are performed on each die 413
on the surface of the substrate. In one embodiment, the relative
movement may be achieved by translating the substrate in x and y
direction so that they follow the curve 520B. In another
embodiment, the relative movement may be achieved by moving the
energy projection region 520A relative to a stationary substrate
410.
[0061] Additionally, a path different than 520B may be used to
optimize throughput and process quality depending on a particular
arrangement of dies.
[0062] In one embodiment, during an annealing process, the
substrate 410 moves relative to the energy projection region 520A,
such as shown by curve 520B of FIG. 5. When a particular die 413 is
positioned and aligned within the energy projection region 520A,
the energy source 420 projects a pulse of energy towards the
substrate 410 so that the die 413 is exposed to a certain amount of
energy over a defined duration according to the particular anneal
process recipe. The duration of the pulsed energy from the energy
source 420 is typically short enough so that the relative movement
between the substrate 410 and the energy projection region 520A
does not cause any "blur", i.e. non uniform energy distribution,
across each die 413 and it will not cause damage to the
substrate.
[0063] A substrate implanted with B.sub.18 ions may be annealed
using a sub-melt anneal process involving rapid repeated heating
and cooling of implanted regions. FIG. 6 is a flow diagram
summarizing a method 600 according to another embodiment. At 602, a
substrate surface is implanted with boron macromolecules according
to any desired embodiment. At 604, the implanted portion is
annealed by exposure to pulses of electromagnetic energy. The
pulses of electromagnetic energy rapidly heat and cool the
implanted portion repeatedly to anneal the substrate.
[0064] In one embodiment, the pulses of electromagnetic energy
comprise at least about 30 pulses of electromagnetic energy of
substantially the same energy flux and duration. In one embodiment,
the number of pulses may be at least about 30, or at least about
50, or at least about 100, such as between about 30 and about
100,000 pulses, or between about 50 and about 10,000 pulses, or
between about 100 and about 1,000 pulses, or between about 200 and
about 500 pulses. In one embodiment, the energy flux of each pulse
is between about 0.1 J/cm.sup.2 and about 2.0 J/cm.sup.2, such as
between about 0.2 J/cm.sup.2 and about 1.0 J/cm.sup.2, for example
about 0.25 J/cm.sup.2. In one embodiment, the pulses comprise laser
light. Each pulse may have duration between about 1 nsec and about
10 .mu.sec, such as between about 10 nsec and about 100 nsec, for
example about 20 nsec. The number of pulses needed will generally
be inversely proportional to the fluence and duration of each
pulse.
[0065] Each pulse of electromagnetic energy accomplishes a
micro-anneal cycle in the energized area of the substrate.
Unfragmented boron clusters are broken up, and individual boron and
silicon atoms are moved fractions of a unit cell dimension with
each pulse. Boron and silicon atoms occupying crystal lattice
positions do not receive enough energy from each pulse to dislodge
them, but those atoms occupying spaces between crystal lattice
locations are moved incrementally toward unoccupied lattice
positions. Incident energy flux between pulses declines to allow
energy from each pulse to dissipate through the crystal lattice
before the next pulse is delivered. In one embodiment, incident
energy flux may decline to near zero between pulses. In another
embodiment, incident energy flux declines to allow net energy flux
out of the anneal zone. Thus, while standard sub-melt techniques
require exposing boron-doped substrates to spikes of radiation
lasting 20 .mu.sec or more, repeated short pulses may accomplish an
anneal process at much lower total durations and power
requirements. The period of time between each pulse relative to the
duration of each pulse may be between about 50% and about 200%,
such as between about 100% and about 150%, for example about 125%.
A rest period below about 100% of pulse duration allows the net
energy balance of the implanted region to decline to a non-zero
level below the peak energy density experienced during a pulse
before the next pulse begins. A rest period above about 125% of a
pulse duration allows the net energy balance to return to a rest
state prior to the next pulse.
[0066] In one example, a substrate was implanted with B.sub.18 ions
to a dose of 2.times.10.sup.15 cm.sup.-2 at an equivalent boron ion
energy of 500 eV. After 30 pulses with a 20 nsec laser delivering
0.234 J/cm.sup.2 at a wavelength of 532 nm over a total duration of
about 1.4 .mu.sec, R.sub.s was about 500.OMEGA.. After 1000 pulses
over a duration of about 45 .mu.sec, R.sub.s was about 400
.OMEGA..
[0067] In another example, a substrate was implanted with B.sub.18
ions at a similar dose and ion energy. After 300 pulses with a 20
nsec laser delivering 0.234 J/cm.sup.2 at a wavelength of 532 nm
over a total duration of about 13.5 .mu.sec, boron ion
concentration of 10.sup.19 cm.sup.-3 was found at a depth of about
147 .ANG., with concentration profile at that depth of about 5
.ANG./dec.
[0068] While the foregoing is directed to embodiments of the
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.
* * * * *