U.S. patent application number 13/194552 was filed with the patent office on 2012-12-27 for novel thermal processing apparatus.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to Bruce E. Adams, Douglas E. Holmgren, Samuel C. Howells, Aaron Muir Hunter, Jiping Li, Stephen Moffatt, Edric Tong.
Application Number | 20120325784 13/194552 |
Document ID | / |
Family ID | 47360854 |
Filed Date | 2012-12-27 |
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United States Patent
Application |
20120325784 |
Kind Code |
A1 |
Moffatt; Stephen ; et
al. |
December 27, 2012 |
NOVEL THERMAL PROCESSING APPARATUS
Abstract
The present invention generally relates to an optical system
that is able to reliably deliver a uniform amount of energy across
an anneal region contained on a surface of a substrate. The optical
system is adapted to deliver, or project, a uniform amount of
energy having a desired two-dimensional shape on a desired region
on the surface of the substrate. An energy source for the optical
system is typically a plurality of lasers, which are combined to
form the energy field.
Inventors: |
Moffatt; Stephen; (St.
Brelade, JE) ; Holmgren; Douglas E.; (Portland,
OR) ; Howells; Samuel C.; (Portland, OR) ;
Tong; Edric; (Sunnyvale, CA) ; Adams; Bruce E.;
(Portland, OR) ; Li; Jiping; (Palo Alto, CA)
; Hunter; Aaron Muir; (Santa Cruz, CA) |
Assignee: |
APPLIED MATERIALS, INC.
Santa Clara
CA
|
Family ID: |
47360854 |
Appl. No.: |
13/194552 |
Filed: |
July 29, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61500727 |
Jun 24, 2011 |
|
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Current U.S.
Class: |
219/121.61 ;
219/121.67 |
Current CPC
Class: |
B23K 26/03 20130101;
B23K 26/04 20130101; B23K 26/0622 20151001; B23K 2103/56 20180801;
B23K 26/127 20130101; H01L 21/477 20130101; B23K 26/0608 20130101;
B23K 26/354 20151001; B23K 26/08 20130101; H01S 3/0057 20130101;
B23K 26/0006 20130101; B23K 26/032 20130101; F27B 5/14 20130101;
H01L 21/268 20130101; B23K 2101/40 20180801 |
Class at
Publication: |
219/121.61 ;
219/121.67 |
International
Class: |
B23K 26/00 20060101
B23K026/00 |
Claims
1. An apparatus for thermally processing a substrate, comprising: a
source of electromagnetic energy operable to produce pulses of
electromagnetic energy; an optical system comprising a pulse
combiner, a pulse shaper, a homogenizer, and an aperture member
positioned to receive pulses of electromagnetic energy from the
source; a substrate support operable to move a substrate with
respect to the optical system; and an imaging system operable to
view the substrate along an optical path of the optical system.
2. The apparatus of claim 1, wherein the pulse combiner comprises a
first polarizer for polarizing a first pulse, a second polarizer
for polarizing a second pulse, and a combining optic with a
polarizing surface, wherein the first pulse and the second pulse
are directed to opposite sides of the polarizing surface.
3. The apparatus of claim 1, wherein the imaging system comprises a
reflector that selectively reflects light reflected from a
substrate to a viewing optic.
4. An apparatus for combining pulses of electromagnetic energy,
comprising: a first energy input; a second energy input; a first
optic for imparting a first property to the first energy; a second
optic for imparting a second property to the second energy; a
selecting surface that reflects or transmits energy based on the
first property and the second property; a steering optic for
steering the first energy to a first location on a first side of
the selecting surface and the second energy to a second location on
a second side of the selecting surface opposite the first side of
the selecting surface, wherein the first location and the second
location are aligned; and a diagnostic module optically coupled to
the selecting surface.
5. The apparatus of claim 4, wherein the diagnostic module
comprises an energy detector and an intensity profile detector.
6. A thermal processing system, comprising: a plurality of laser
energy sources, each having an active q-switch coupled to an
electronic timer; at least two combiners optically coupled to the
laser energy sources, each combiner having a selecting optic, the
selecting optic having a selecting surface; an optical system to
direct light from the laser energy sources to opposite sides of the
selecting surface; and a homogenizer comprising at least two
microlens arrays.
7. The thermal processing system of claim 6, wherein each of the at
least two combiners combines two energy pulses into one energy
pulse, and the combined energy pulses are separated by a distance
less than a dimension of one of the combiners.
8. A system for processing a substrate comprising: a source of
electromagnetic energy; an optical system for focusing the
electromagnetic energy; and an aperture member having a reflective
portion embedded therein, the reflective portion having an opening
through which the electromagnetic energy projects, a surface of the
reflective portion positioned at a focal plane of the
electromagnetic energy.
9. The system of claim 8, wherein the aperture member is quartz and
the reflective portion is a dielectric mirror.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. Provisional Patent
Application Ser. No. 61/500,727 filed Jun. 24, 2011, which is
herein incorporated by reference.
FIELD
[0002] Embodiments described herein relate to apparatus and methods
of thermal processing. More specifically, apparatus and methods
described herein relate to laser thermal treatment of semiconductor
substrates.
DESCRIPTION OF THE RELATED ART
[0003] Thermal processing is commonly practiced in the
semiconductor industry. Semiconductor substrates are subjected to
thermal processing in the context of many transformations,
including doping, activation, and annealing of gate source, drain,
and channel structures, siliciding, crystallization, oxidation, and
the like. Over the years, techniques of thermal processing have
progressed from simple furnace baking, to various forms of
increasingly rapid thermal processing such as RTP, spike annealing,
and laser annealing.
[0004] Conventional laser annealing processes use laser emitters
that may be semiconductor or solid state lasers with optics that
focus, defocus, or variously image the laser light into a desired
shape. A common approach is to image the laser light into a line or
thin rectangle image. The laser light is scanned across a substrate
(or the substrate moved beneath the laser light) to process the
entire surface of the substrate.
[0005] As device geometry continues to decline, semiconductor
manufacturing processes such as thermal processing are challenged
to develop increased precision. In many instances, pulsed laser
processes are being explored to reduce overall thermal budget and
reduce depth and duration of energy exposure at the substrate.
Challenges remain, however, in creating laser pulses having a
temporal shape that affords the desired processing performance,
with the uniformity needed for uniform processing across the
surface of a substrate. Thus, there is a continuing need for new
apparatus and methods for thermal processing of semiconductor
substrates.
SUMMARY OF THE INVENTION
[0006] A system is disclosed for thermal processing of substrates.
The system has an energy source, typically a plurality of lasers,
for generating an energy field to be applied to the substrate. The
energy is combined and metered using a pulse control module to form
combined energy pulses. Temporal shape of the combined energy
pulses is adjusted in a pulse shaping module. Spatial distribution
of the energy is adjusted in a homogenizer. The adjusted energy
pulses then pass through an imaging system for viewing the
substrate along the optical pathway of the energy pulses.
[0007] Each energy source typically delivers a high power energy
pulse at least about 10 MW over a duration of about 100 nsec or
less. The pulse control module has a combining optic that combines
two energy pulses into one energy pulse, along with attenuators for
each pulse pathway. A diagnostic module measures the energy content
and temporal shape of pulses for feedback to a controller that
sends control signals to the attenuators. The combined pulses are
temporally adjusted in a pulse shaper with optical splitters that
divide each pulse into a plurality of sub-pulses and mirror paths
that send the sub-pulses along optical paths that have different
lengths, recombining the sub-pulses at the exit. The pulses are
spatially adjusted in a homogenizer that has at least two microlens
arrays. The imaging system has an optical element that captures
light reflected from the substrate and sends it to an imager. The
processing modules described herein may provide a shaped energy
field that is temporally decorrelated and has a spatial standard
deviation of energy intensity no more than about 4%.
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 of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0009] FIG. 1 is a schematic diagram of a thermal processing
apparatus according to one embodiment.
[0010] FIGS. 2A and B are plan views of pulse controllers according
to two embodiments.
[0011] FIGS. 2C-E are schematic views of different configurations
of pulse controllers and energy sources according to three
embodiments.
[0012] FIG. 3A is a schematic view of a pulse shaper according to
one embodiment.
[0013] FIGS. 3B and 3C are graphs showing pulse timing and pulse
energy profile using the pulse shaper of FIG. 3A.
[0014] FIG. 3D is a schematic view of the pulse shaper of FIG. 3A
according to another embodiment.
[0015] FIGS. 3E and 3F are graphs showing pulse timing and pulse
energy profile using the pulse shaper of FIG. 3D.
[0016] FIG. 3G is a schematic view of a pulse shaper according to
another embodiment.
[0017] FIGS. 4A and 4B are schematic views of homogenizers
according to two embodiments.
[0018] FIG. 5 is a side view of an aperture member 500 according to
another embodiment.
[0019] FIG. 6 is a schematic view of an imaging system 600
according to another embodiment.
[0020] 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
[0021] FIG. 1 is a plan view of a system 100 for laser processing
of substrates. The system 100 comprises an energy module 102 that
has a plurality of pulsed laser sources producing a plurality of
pulsed laser pulses, a pulse control module 104 that combines
individual pulsed laser pulses into combination pulsed laser
pulses, and that controls intensity, frequency characteristics, and
polarity characteristics of the combination pulsed laser pulses, a
pulse shaping module 106 that adjusts the temporal profile of the
pulses of the combined pulsed laser pulses, a homogenizer 108 that
adjusts the spatial energy distribution of the pulses, overlapping
the combination pulsed laser pulses into a single uniform energy
field, an aperture member 116 that removes residual edge
non-uniformity from the energy field, and an alignment module 118
that allows precision alignment of the laser energy field with a
substrate disposed on a substrate support 110. A controller 112 is
coupled to the energy module 102 to control production of the laser
pulses, the pulse control module 104 to control pulse
characteristics, and the substrate support 110 to control movement
of the substrate with respect to the energy field. An enclosure 114
typically encloses the operative components of the system 100.
[0022] The lasers may be any type of laser capable of forming short
pulses, for example duration less than about 100 nsec., of high
power laser radiation. Typically, high modality lasers having over
500 spatial modes with M.sup.2 greater than about 30 are used.
Solid state lasers such as Nd:YAG, Nd:glass, titanium-sapphire, or
other rare earth doped crystal lasers are frequently used, but gas
lasers such as excimer lasers, for example XeCl.sub.2, ArF, or KrF
lasers, may be used. The lasers may be switched, for example by
q-switching (passive or active), gain switching, or mode locking. A
Pockels cell may also be used proximate the output of a laser to
form pulses by interrupting a beam emitted by the laser. In
general, lasers usable for pulsed laser processing are capable of
producing pulses of laser radiation having energy content between
about 100 mJ and about 10 J with duration between about 1 nsec and
about 100 .mu.sec, typically about 1 J in about 8 nsec. The lasers
may have wavelength between about 200 nm and about 2,000 nm, such
as between about 400 nm and about 1,000 nm, for example about 532
nm. In one embodiment, the lasers are q-switched frequency-doubled
Nd:YAG lasers. The lasers may all operate at the same wavelength,
or one or more of the lasers may operate at different wavelengths
from the other lasers in the energy module 102. The lasers may be
amplified to develop the power levels desired. In most cases, the
amplification medium will be the same or similar composition to the
lasing medium. Each individual laser pulse is usually amplified by
itself, but in some embodiments, all laser pulses may be amplified
after combining.
[0023] A typical laser pulse delivered to a substrate is a
combination of multiple laser pulses. The multiple pulses are
generated at controlled times and in controlled relationship to
each other such that, when combined, a single pulse of laser
radiation results that has a controlled temporal and spatial energy
profile, with a controlled energy rise, duration, and decay, and a
controlled spatial distribution of energy non-uniformity. The
controller 112 may have a pulse generator, for example an
electronic timer coupled to a voltage source, that is coupled to
each laser, for example each switch of each laser, to control
generation of pulses from each laser.
[0024] The plurality of lasers are arranged so that each laser
produces pulses that emerge into the pulse control module 104,
which may have one or more pulse controllers 105. FIG. 2A is a plan
view of a pulse controller 200A according to one embodiment. The
one or more pulse controllers 105 described above in connection
with FIG. 1 may each be a pulse controller such as the pulse
controller 200A shown in FIG. 2A. Using optics contained in an
enclosure 299 to prevent light pollution, the pulse controller 200A
combines a first input pulse 224A received from the energy module
102 and a second input pulse 224B received from the energy module
102 into one output laser pulse 238. The two input laser pulses
224A/B enter the pulse controller 200A through input lenses 202A
and 202B disposed in openings of the enclosure 299. In the
embodiment of FIG. 2A, the two input lenses 202A/B are aligned
along one surface of the enclosure 299, with the laser pulses
224/A/B entering the enclosure 299 in a substantially parallel
orientation.
[0025] The two input pulses 224A/B are directed to a combining
optic 208 that combines the two pulses into one pulse 238. The
combining optic has a first entry surface 207A oriented
perpendicular to the entry path of the incident pulse 226A and a
second entry surface 207B oriented perpendicular to the entry path
of the incident pulse 226B to avoid any refraction of the input
pulses 226A/B upon entering the combining optic 208. The combining
optic 208 of FIG. 2A is a crystal that has a selecting surface 209
oriented such that first and second incident pulses 226A/B each
strike the selecting surface 209 at an angle of approximately
45.degree.. The selecting surface 209 interacts with light
selectively depending on the properties of the light. The selecting
surface 209 of the combining optic 208 may reflect the first
incident pulse 226A and transmit the second incident pulse to
create the combined pulse 228. To facilitate combination of the
pulses, each of the incident pulses 226A/B may be tailored to
interact with the selecting surface 209 in a particular way.
[0026] In one embodiment, the selecting surface 209 is a polarizing
surface. The polarizing surface may have a linear axis of polarity,
such that polarizing the incident pulse 226B parallel to the axis
of the polarizing surface allows the incident pulse 226B to be
transmitted by the polarizing surface, and polarizing the incident
pulse 226A perpendicular to the axis of the polarizing surface
allows the incident pulse 226A to be reflected by the polarizing
surface. Aligning the two incident pulses 226A/B to the same spot
on the polarizing surface creates the combined pulse 228 emerging
from a first exit surface 207C of the combining optic 208
perpendicular to the surface 207C to avoid any refraction of the
combined pulse 228. Alternately, the selecting surface 209 may be a
circular polarizer, with the incident pulse 226A circularly
polarized opposite the sense of the circular polarizer for
reflection, and the incident pulse 226B circularly polarized in the
same sense as the circular polarizer for transmission. In another
embodiment, the incident pulses 226A/B may have different
wavelengths, and the selecting surface 209 may be configured to
reflect light of one wavelength and to transmit light of another
wavelength, such as with a dielectric mirror.
[0027] In a polarization embodiment, polarization of the incident
pulses 226A/B is accomplished using polarizing filters 206A/B. The
polarizing filters 206A/B polarize the input pulses 224A/B to be
selectively reflected or transmitted by the selecting surface 209
of the combining optic 208. The polarizing filters 206A/B may be
wave plates, for example half-wave plates or quarter-wave plates,
with polarizing axes oriented orthogonal to each other to produce
the orthogonally polarized light for selective reflecting and
transmission at the selecting surface 209. The axis of each
polarizing filter 206A/B may be independently adjusted, for example
with rotational actuators 205A/B, to precisely align the
polarization of the incident pulses 226A/B with the polarization
axis of the selecting surface 209, or to provide a desired angle of
deviation between the polarization axis of an input pulse 226A/B
and the polarization axis of the selecting surface 209.
[0028] Adjusting the polarization axis of the incident pulses
226A/B controls intensity of the combined pulse 228, because a
polarizing filter transmits incident light according to Malus' Law,
which holds that the intensity of light transmitted by a polarizing
filter is proportional to the incident intensity and the square of
the cosine of the angle between polarization axis of the filter and
polarization axis of the incident light. Thus, rotating the
polarizing filter 206A so that the polarization axis of the
polarizing filter 206A deviates from an orientation perpendicular
to the polarization axis of the selecting surface 209 results in a
portion of the incident pulse 226A being transmitted through the
selecting surface 209. Likewise, rotating the polarizing filter
206B so that its polarization axis deviates from an orientation
parallel to the axis of the selecting surface 209 results in a
portion of the incident pulse 226B being reflected from the
selecting surface 209. This "non-selected" light from each of the
incident pulses 226A/B is combined into a rejected pulse 230 that
exits the combining optic 208 through a second exit surface 207D
into a pulse dump 210. In this way, each of the polarizing filters
acts as a dimmer switch to attenuate the intensity of pulses
passing through the polarizing filters.
[0029] It should be noted that the two pulses 226A/B that are to be
combined by the combining optic 208 are directed toward opposite
sides of the selecting surface 209 for selective reflection and
transmission. Thus, the first input pulse 202A is directed along a
path that brings the first input pulse 202A toward a reflecting
side of the selecting surface 209 by a reflector 204, while the
second input pulse 202B is directed toward transmitting side of the
selecting surface 209. Any combination of reflectors may naturally
be used to steer light along a desired path within the pulse
control module 104.
[0030] The combined pulse 228 interacts with a first splitter 212
that splits the combined pulse 228 into the output pulse 238 and a
sampled pulse 232. The splitter 212 may be a partial mirror or a
pulse splitter. The sampled pulse 232 is directed to a diagnostic
module 233 that analyzes properties of the sampled pulse 232 to
represent properties of the output pulse 238. In the embodiment of
FIG. 2A, the diagnostic module 233 has two detectors 216 and 218
that detect the temporal shape of a pulse and the total energy
content of a pulse, respectively. A second splitter 214 forms a
first pulse 236 and a second pulse 234 for input to the respective
detectors. The temporal shape detector 216 is an intensity monitor
that signals intensity of light incident on the monitor in very
short time scales. Light pulses incident on the temporal shape
detector may have total duration from 1 picosecond (psec) to 100
nsec, so the temporal shape detector, which may be a photodiode or
photodiode array, renders intensity signals at useful subdivisions
of these time scales. The energy detector 218 may be a pyroelectric
device, such as a thermocouple, that converts incident
electromagnetic radiation to voltage that can be measured to
indicate the energy content of the energy sample pulse 234. Because
the first and second splitters 212 and 214 sample a known fraction
of incident light based on the transmitting fraction of the first
and second splitters 212 and 214, the energy content of the output
pulse 238 may be calculated from the energy content of the energy
sample pulse 234.
[0031] Signals from the diagnostic module 233 may be routed to the
controller 112 of FIG. 1, which may adjust the laser operation or
the pulse control operation to achieve desired results. The
controller 112 may adjust an electronic timer coupled to an active
q-switch of each laser to control pulse timing in response to
results from the temporal shape detector 216. Cycling the active
q-switch faster makes shorter pulses, and vice versa. The
controller 112 may be coupled to the rotational actuators 205A/B to
adjust the intensity of the output pulse 238, based on results from
the energy detector 218, by adjusting the polarization angle of
light passing through the polarizing filters 206A/B. In this way,
the duration and energy content of the output pulse 238 may be
independently controlled. The controller 112 may also be configured
to adjust power input to each laser.
[0032] The output pulse 238 may be interrupted by a shutter 220, if
desired. The shutter 220 (shown schematically in FIGS. 2A and 2B)
may be provided as a safety device in the event the laser energy
emerging from the pulse control module 104 is to be interrupted to
make an adjustment to a component subsequent to the pulse control
module 104. The output pulse 238 exits the pulse control module 104
through an output lens 222.
[0033] The output pulse 238 is a combination of the two incident
pulses 226A/B. As such the output pulse 238 has properties that
represent a combination of the properties of the two incident
pulses 226A/B. In the polarization example described above, the
output pulse 238 may have an elliptical polarization representing
the combination of two orthogonally polarized incident pulses
226A/B having different intensities according to the degree of
transmission/reflection of each of the incident pulses 226A/B at
the selecting surface 209. In an example using incident wavelength
at the selecting surface 209 to combine two pulses, the output
pulse 238 will have a wavelength representing the combined
wavelength of the two incident pulses 226A/B according to their
respective intensities.
[0034] For example, a 1,064 nm reflecting dielectric mirror may be
disposed at the selecting surface 209 of the combining optic 208.
The incident pulse 226A may have wavelength of approximately 1,064
nm with intensity A for reflecting from the selecting surface 209,
and the incident pulse 226B may have a wavelength of 532 nm with
intensity B for transmitting through the selecting surface 209. The
combined pulse 228 will be a co-propagating bi-pulse of two photons
having the wavelengths and intensities of the incident pulses
226A/B, with total energy content that is the sum of the two pulse
energies.
[0035] FIG. 2B is a plan view of a pulse control module 200B
according to another embodiment. The one or more pulse controllers
105 described above in connection with FIG. 1 may each be a pulse
controller such as the pulse controller 200B or the pulse
controller 200A. The pulse controller 200B is the same as the pulse
controller 200A, with the following differences. In the embodiment
of FIG. 2B, the input lens 202A is not located adjacent to the
input lens 202B on the same surface of the enclosure 299. In FIG.
2B, the input lens 202A is located on a surface of the enclosure
299 that is substantially orthogonal to the surface on which the
input lens 202B is located, in this embodiment on an adjacent wall
of a rectangular enclosure. Thus, the first input pulse 224A enters
through the first input lens 202A (in a direction into the page of
FIG. 2B) and is diverted into the plane of FIG. 2B by a reflector
that is obscured by the first input lens 202a in the view of FIG.
2B. Reflectors 240 and 242 position the input pulse 224B for entry
into the polarizer 206B, illustrating the use of reflectors to
position pulses on any desired path. Steering pulses around the
pulse control module 104 may be helpful in cases where locating the
laser energy sources is space constrained.
[0036] FIGS. 2C and 2D are schematic views showing embodiments that
have multiple pulse controllers 200A/B. In the embodiment of FIG.
2C, two pulse controllers of the configuration of the pulse
controller 200A of FIG. 2A are aligned with four laser sources
102A-D to form two combined pulses 238. In the embodiment of FIG.
2D, two combined pulses 238 are formed having a desired distance
"d" between them. Two pulse controllers 200C/D accept input pulses
from two energy sources 102A and 102C along the plane of FIG. 2D
and perpendicular to the plane of FIG. 2D from two energy sources
not visible in the view of FIG. 2D. The two pulse controllers
200C/D are the same as the pulse controller 200B, with the
following differences. The pulse controller 200D is configured to
direct an output pulse 244 through an output lens 246 using an
output reflector 254. The output lens 246 directs the output pulse
244 into an input lens 248 of the pulse controller 200C to a
reflector 250 and an output lens 252 of the pulse controller 200C.
In this way, the two output pulses 238 may be positioned any
desired distance "d" from each other on exiting the pulse control
module 104 (FIG. 1). For most embodiments, the distance "d" will be
between about 1 mm and about 1,000 mm, such as less than 50 mm, for
example about 35 mm. As shown in FIG. 2D, the distance "d" may be
less than a dimension of the pulse controller 200C.
[0037] FIG. 2E is a schematic top view of the apparatus of FIG. 2D,
showing an embodiment wherein the energy sources 102 are configured
in a right-angle relationship. The energy sources 102B/D visible in
FIG. 2E were not visible in the view of FIG. 2D. The energy sources
102A/B produce input pulses 224A/B for processing in pulse
controller 200C, while the energy sources 102C/D produce input
pulses 224C/D for processing in pulse controller 200D. The output
pulses of the pulse controllers 200C/D are arranged as shown in
FIG. 2D separated by a desired distance "d", which is not visible
in the view of FIG. 2E. It should be noted that the pulse
controllers 200A-200D may be pulse combiners in some
embodiments.
[0038] One or more pulses exit the pulse control module 104 and
enter the pulse shaping module 106, which has one or more pulse
shapers 107, as shown schematically in FIG. 1. FIG. 3A is a
schematic illustration of one embodiment of a pulse shaper 306. The
one or more pulse shapers 107 of the pulse shaping module 106 may
each be a pulse shaper such as the pulse shaper 306. The pulse
shaper of FIG. 3A may comprise a plurality of mirrors 352 (e.g., 16
mirrors are shown) and a plurality of splitters (e.g., reference
numerals 350A-350E) that are used to delay portions of a laser
energy pulse to provide a composite pulse that has a desirable
characteristics (e.g., pulse width and profile). In one example, a
laser energy pulse 302 entering the pulse shaping module may be
spatially coherent. A pulse of laser energy is split into two
components, or sub-pulses 354A, 354B, after passing through the
first splitter 350A. Neglecting losses in the various optical
components, depending on the transmission to reflection ratio in
the first splitter 350A, a percentage of the laser energy (i.e., X
%) is transferred to the second splitter 350B in the first
sub-pulse 354A, and a percentage of the energy (i.e., 1-X %) of the
second sub-pulse 354B follows a path A-E (i.e., segments A-E) as it
is reflected by multiple mirrors 352 before it strikes the second
splitter 350B.
[0039] In one example, the transmission to reflection ratio of the
first splitter 350A is selected so that 70% of the pulse's energy
is reflected and 30% is transmitted through the splitter. In
another example the transmission to reflection ratio of the first
splitter 350A is selected so that 50% of the pulse's energy is
reflected and 50% is transmitted through the splitter. The length
of the path A-E, or sum of the lengths of the segments A-E (i.e.,
total length=A+B+C+D+E as illustrated in FIG. 3A), will control the
delay between sub-pulse 354A and sub-pulse 354B. In general by
adjusting the difference in path length between the first sub-pulse
354A and the second sub-pulse 354B a delay of about 3.1 nanoseconds
(ns) per meter of path length difference can be realized.
[0040] The energy delivered to the second pulse 350B in the first
sub-pulse 354A is split into a second sub-pulse 356A that is
directly transmitted to the third splitter 350C and a second
sub-pulse 356B that follows the path F-J before it strikes the
third splitter 350C. The energy delivered in the second sub-pulse
354B is also split into a third sub-pulse 358A that is directly
transmitted to the third splitter 350C and a third sub-pulse 358B
that follows the path F-J before it strikes the third splitter
350C. This process of splitting and delaying each of the sub-pulses
continues as each of the sub-pulses strikes subsequent splitters
(i.e., reference numerals 350D-E) and mirrors 352 until they are
all recombined in the final splitter 350E that is adapted to
primarily deliver energy to the next component in the thermal
processing apparatus 100. The final splitter 350E may be a
polarizing splitter that adjusts the polarization of the energy in
the sub-pulses received from the delaying regions or from the prior
splitter so that it can be directed in a desired direction.
[0041] In one embodiment, a waveplate 364 is positioned before a
polarizing type of final splitter 350E so that its polarization can
be rotated for the sub-pulses following path 360. Without the
adjustment to the polarization, a portion of the energy will be
reflected by the final pulse splitter and not get recombined with
the other branch. In one example, all energy in the pulse shaper
306 is S-polarized, and thus the non-polarizing cube splitters
divide incoming pulses, but the final splitter, which is a
polarizing cube, combines the energy that it receives. The energy
in the sub-pulses following path 360 will have its polarization
rotated to P, which passes straight through the polarizing pulse
splitter, while the other sub pulses following path 362 are
S-polarized and thus are reflected to form a combined pulse.
[0042] In one embodiment, the final pulse splitter 350E comprises a
non-polarizing splitter and a mirror that is positioned to combine
the energy received from the delaying regions or from the prior
splitter. In this case, the splitter will project part of the
energy towards a desired point, transmit another part of the energy
received towards the desired point, and the mirror will direct the
remaining amount of energy transmitted through the splitter to the
same desired point. One will note that the number of times the
pulse is split and delayed may be varied by adding pulse splitting
type components and mirrors in the configuration as shown herein to
achieve a desirable pulse duration and a desirable pulse profile.
While FIG. 3A illustrates a pulse shaper design that utilizes four
pulse delaying regions with splitters and mirrors, this
configuration is not intended to be limiting as to the scope of the
invention.
[0043] FIG. 3B illustrates an example of an energy versus time
graph of various sub-pulses that have passed through a two pulse
delaying region pulse shaper, which is similar to the first two
pulse delaying regions of the pulse shaper illustrated in FIG. 3A.
As shown in FIG. 3B, the pulse train pattern 307 delivered to the
input of the pulse shaper (FIG. 3A) has an individual pulse
duration equal to t.sub.1. In this case, pattern 307A is the first
pulse train, pattern 307B is the second pulse train, pattern 307C
is the third pulse train, and pattern 307D is the fourth pulse
train that exits the pulse shaper 306 of FIG. 3A. In general, the
duration of each of the sub-pulses will be about t.sub.1, since
this property of the pulses of the original pattern 307 will remain
relatively unchanged due to the pulse shaping process illustrated
in FIG. 3A. Referring to FIG. 3B, it follows that the pulses of
pattern 307A traveled the shortest distance and the pulses of
pattern 307D will have traveled the longest distance through the
pulse shaper 306. In one example, the sum of the four patterns will
deliver a composite energy profile 312 with pulses that have
duration t.sub.2, which is longer than the duration t.sub.1 of the
initial pulse. The composite energy profile 312 will also have a
lower average energy per unit time than the original pulse 307.
FIG. 3C illustrates a plot of the expected temperature profile of a
surface region of a substrate exposed to pulse energy having the
profile 312 as a function of time. It should be noted that
depending on the transmission to reflection ratio of each of the
selected splitters in the system, the energy of the sub-pulses may
be adjusted to deliver a desired pulse profile. For example, by
selecting a more transmissive, rather than reflective, combination
of splitters the profile of the composite energy profile 312 will
have a higher starting energy that will drop off towards the end of
the composite profile pulse 312. It should be noted that while FIG.
3B illustrates rectangular shaped pulses that have the same
amplitude this is not intended to be limiting as to the scope of
the invention, since other pulse shapes may be used to deliver a
composite energy profile 312 that has a more desirable profile.
[0044] FIG. 3D schematically illustrates another embodiment of the
present invention that is used to deliver a desirable pulse profile
by utilizing two or more synchronized energy sources (e.g., laser
sources 102A-D) with output routed through the pulse control module
106 and to pulse shaper 306, which are each discussed above in
conjunction with FIGS. 1-3C. In this configuration, the controller
112 synchronizes the output of the laser sources 102A-D to form
synchronized pulses 304 as input to the pulse shaper 306 so that
composite pulses 312 emerging from the pulse shaper 306 will have a
desirable profile. The composite pulse 312 may contain a composite
of each of the sub-pulses created in the pulse stretcher assembly
306 for each of the synchronized pulses delivered from each of the
laser sources 102A-D. The profile, or shape, of the composite pulse
312 shown in FIG. 3C formed from sub-pulses 307A-D is not intended
to be limiting as to the scope of the invention since any pulse
profile can be used to provide an optimized anneal process.
Alternate composite pulse shapes may be realised by changing the
synchronization of pulses, as illustrated in FIGS. 3E and 3F, which
show a different synchronization of pulses and a different
composite pulse shape 312 and temperature profile 311.
[0045] FIG. 3G schematically illustrates another embodiment of a
pulse shaper 320 showing a further technique for pulse shaping. In
the pulse shaper 320 of FIG. 3G, at least some of the reflectors
are displaced from a datum 322 or 324 to vary the optical path of
light through the pulse shaper 320. The displacement of a mirror
may be set a desired distance "x" to achieve a certain temporal
displacement for a sub-pulse. Typically the mirrors will be
displaced in pairs, each mirror in a given mirror pair having a
nearly identical displacement from the datum. The displacements of
pairs of mirrors may naturally be different to achieve any desired
pulse shape. In one embodiment, the displacement x.sub.1 of a first
mirror pair is about 10 mm, the displacement x.sub.2 of a second
mirror pair is about 7.5 mm, the displacement x.sub.3 or a third
mirror pair is about 20 mm, and the displacement x.sub.4 of a
fourth mirror pair is about 15 mm.
[0046] In another embodiment, all pulses emanating from a plurality
of lasers may be directed into a pulse shaper without passing
through a combiner first. Optics may be used to bring the pulses
into close physical proximity such that they all strike the first
splitter of the pulse shaper (e.g. 350A or 306A in FIGS. 3A and
3D). The pulses may be arranged in a configuration, for example a
square configuration, having a dimension less than a
cross-sectional dimension of the first splitter of the pulse
shaper, such that the pulses all travel through the first
splitter.
[0047] Shaped pulses from the pulse shaping module 106 are routed
into a homogenizer 108. FIG. 4A is a schematic view of a
homogenizer 400 according to one embodiment. The homogenizer 108 of
FIG. 1 may be the homogenizer 400 of FIG. 4A. A beam integrator
assembly 410 contains a pair of micro-lens arrays 404 and 406 and a
lens 408 that homogenize the energy passing through this integrator
assembly. It should be noted that the term micro-lens array, or
fly's-eye lens, is generally meant to describe an integral lens
array that contains multiple adjacent lenses. As designed, the beam
integrator assembly 410 generally works best using an incoherent
source or a broad partially coherent source whose spatial coherence
length is much smaller than a single micro-lens array's dimensions.
In short, the beam integrator assembly 410 homogenizes the beam by
overlapping magnified images of the micro-lens arrays at a plane
situated at the back focal plane of the lens 408. The lens 408 may
be corrected to minimize aberrations including field
distortion.
[0048] The size of the image field is a magnified version of the
shape of the apertures of the first microlens array, where the
magnification factor is given by F/f.sub.1 where f.sub.1 is the
focal length of the microlenses in the first micro-lens array 404
and F is the focal length of lens 408. In one example, a lens 408
that has a focal length of about 175 mm and a micro-lenses in the
micro-lens array have a 4.75 mm focal length is used to form an 11
mm square field image.
[0049] Although many different combinations for these components
can be used, generally the most efficient homogenizers will have a
first micro-lens array 404 and second micro-lens array 406 that are
identical. The first micro-lens array 404 and a second micro-lens
array 406 are typically spaced a distance apart so that the energy
density (Watts/mm.sup.2) delivered to the first micro-lens array
404 is increased, or focused, on the second micro-lens array 406.
This can cause damage, however, to the second micro-lens array 406
when the energy density exceeds the damage threshold of the optical
component and/or optical coating placed on the optical components.
Typically the second micro-lens array 406 is spaced a distance
d.sub.2 from the first micro-lens array 404 equal to the focal
length of the lenslets in the first micro-lens array 404.
[0050] In one example, each the micro-lens arrays 404, 406 contains
7921 micro-lenses (i.e., 89.times.89 array) that are a square shape
and that have an edge length of about 300 microns. The lens 408, or
Fourier lens, is generally used to integrate the image received
from the micro-lens arrays 404, 406 and is spaced a distance
d.sub.3 from the second micro-lens array 406.
[0051] In applications where coherent or partially coherent sources
are used, various interference and diffraction artifacts can be
problematic when using a beam integrator assembly 410, since they
create high intensity regions, or spots, within the projected
beam's filed of view, which can exceed the damage threshold of the
various optical components. Therefore, due to the configuration of
the lenses or the interference artifacts, the useable lifetime of
the various optical components in the beam integrator assembly 410
and system has become a key design and manufacturing
consideration.
[0052] A random diffuser 402 may be p laced in front of or within
the beam homogenizer assembly 400 so that the uniformity of
outgoing energy A.sub.5 is improved in relation to the incoming
energy A.sub.1. In this configuration, the incoming energy A.sub.l
is diffused by the placement of a random diffuser 402 prior to the
energy A.sub.2, A.sub.3 and A.sub.4 being received and homogenized
by the first micro-lens array 404, second micro-lens array 406 and
lens 408, respectively. The random diffuser 402 will cause the
pulse of incoming energy (A.sub.1) to be distributed over a wider
range of angles (.alpha..sub.1) to reduce the contrast of the
projected beam and thus improve the spatial uniformity of the
pulse. The random diffuser 402 generally causes the light passing
through it to spread out so that the irradiance (W/cm.sup.2) of
energy A.sub.3 received by the second micro-lens array 406 is less
than without the diffuser. The diffuser is also used to randomize
the phase of the beam striking each micro-lens array. This
additional random phase improves the spatial uniformity by
spreading out the high intensity spots observed without the
diffuser. In general, the random diffuser 402 is narrow angle
optical diffuser that is selected so that it will not diffuse the
received energy in a pulse at an angle greater than the acceptance
angle of the lens that it is placed before.
[0053] In one example, the random diffuser 402 is selected so that
the diffusion angle .alpha..sub.1 is less than the acceptance angle
of the micro-lenses in the first micro-lens array 404 or the second
micro-lens array 406. In one embodiment, the random diffuser 402
comprises a single diffuser, such as a 0.5.degree. to 5.degree.
diffuser that is placed prior to the first micro-lens array 404. In
another embodiment, the random diffuser 402 comprises two or more
diffuser plates, such as 0.5.degree. to 5.degree. diffuser plates
that are spaced a desired distance apart to further spreading out
and homogenize the projected energy of the pulse. In one
embodiment, the random diffuser 402 may be spaced a distance
d.sub.1 away from the first micro-lens array 404 so that the first
micro-lens array 404 can receive substantially all of the energy
delivered in the incoming energy A.sub.1.
[0054] FIG. 4B is a schematic view of a homogenizer 450 according
to another embodiment. The homogenizer 108 of FIG. 1 may be the
homogenizer 450 of FIG. 4B. The homogenizer 450 is the same as the
homogenizer 400, except in the following respects. Instead of using
a random diffuser 402 to improve uniformity of the outgoing energy,
a third microlens array 412 may be used.
[0055] Referring again to FIG. 1, energy from the homogenizer 108
is typically arranged in a pattern, such as a square or rectangular
shape, that approximately fits an area to be annealed on the
surface of a substrate. The processing and rearranging applied to
the energy results in an energy field having intensity that varies
from an average value by no more than about 15%, such as less than
about 12%, for example less than about 8%. Near the edges of the
energy field, however, more significant non-uniformities may
persist due to various boundary conditions throughout the
apparatus. These edge non-uniformities may be removed using an
aperture member 116. The aperture member 116 is typically an opaque
object having an opening through which the energy may pass in
cross-section shaped like the opening.
[0056] FIG. 5 is a side view of an aperture member 500 according to
one embodiment. The aperture member 116 of FIG. 1 may be the
aperture member 500 of FIG. 5. The aperture member 500 has a first
member 502 that is substantially transparent to selected forms of
energy, such as light or laser radiation having a selected
wavelength. An energy blocking member 504, which may be opaque or
reflective, is formed over a portion of a surface of the first
member 502 defining an opening 508 through which energy will pass
in the shape of the opening 508. A second member 506 is disposed
over the first member 502 and the energy blocking member 504,
covering the opening 508. The second member 506 is also
substantially transparent to the energy to be transmitted through
the aperture member 500, and may be the same material as the first
member 502. The edges of the aperture member 500 are enclosed by a
covering 510 that ensures particulates do not enter the opening
508.
[0057] The aperture member 500 is positioned such that the energy
blocking member 504 is at a focal plane 512 of the energy incident
on the aperture member 500, ensuring a precise truncation of the
energy field. Because the opening 508 is positioned at the focal
plane of the energy, any particles that collect in the opening, for
example on the surface of the first member 502, cast shadows in the
transmitted energy field that lead to non-uniform processing of a
substrate. Covering the opening 508 with the second member 506 and
enclosing the edges of the aperture member 500 ensures that any
particles adhering to the aperture member 500 are far enough from
the focal plane to be out of focus in the final energy field so
that variation in intensity of the final energy field due to the
shadows of the particles is reduced.
[0058] The first and second members 502 and 506 are typically made
from the same material, usually glass or quartz. The energy
blocking member 504 may be an opaque or reflective material, such
as metal, white paint, or a dielectric mirror. The energy blocking
member 504 may be formed and shaped, and the formed and shaped
energy blocking member 504 applied to the first member 502 using an
appropriate adhesive, such as Canada balsam. Alternately, the
energy blocking member 504 may be deposited on the first member 502
and then etched to provide the opening 508. The second member 506
is typically applied to the energy blocking member 504 using
adhesive.
[0059] The covering 510 may be a material that is permeable or
impermeable to gases. The covering may be an adhesive or a hard
material applied using an adhesive. Alternately, the covering may
be formed by melt-fusing the edges of the first and second members
502 and 506 with the edge of the energy blocking member 504.
[0060] To avoid refractive effects of the aperture member 500, the
side walls of the opening 508, defined by an interior edge 514 of
the energy blocking member 504, may be tapered, angled, or slanted
to match the propagation direction of photons emerging from the
homogenizer 108.
[0061] FIG. 5B is a side view of an aperture member 520 according
to another embodiment. The aperture member 116 of FIG. 1 may be the
aperture member 520 of FIG. 5B. The aperture member 520 is the same
as the aperture member 500 of FIG. 5A, except that the aperture
member 520 has no central opening 508. The aperture member 520
comprises a transmissive member 522 with the energy blocking member
504 embedded therein. Reducing the number of interfaces between
different media in the aperture member 520 may reduce refractive
effects. The interior edge 514 of the energy blocking member 504 is
shown tapered in the embodiment of FIG. 5B, as described above in
connection with FIG. 5A.
[0062] The aperture member 520 of FIG. 5B may be made by etching or
grinding an annular shelf around a central dais of a first
transmissive member, adhering an annular energy blocking member to
the annular shelf, and then adhering a second transmissive member
to the energy blocking member and the central dais of the first
transmissive member, using an optically inactive adhesive such as
Canada balsam. Alternately, the energy blocking member may be
adhered to a first transmissive member having no central dais, and
the second transmissive member formed by depositing a material over
the energy blocking member and the exposed portion of the first
transmissive member, filling the central opening with transmissive
material. Deposition of transmissive materials is well-known in the
art, and may be practiced using any known deposition or coating
process.
[0063] Aperture members may vary in size. An aperture member having
a smaller aperture may be positioned proximate an aperture member
having a larger aperture to reduce the size of the transmitted
energy field. The smaller aperture member may be removed again to
utilize the larger aperture. Multiple aperture members having
different sizes may be provided to allow changing the size of the
energy field to anneal areas having different sizes. Alternately, a
single aperture member may have a variable aperture size. Two
rectangular channels may be formed in a transparent housing, and
two pairs of opaque or reflective actuated half-plates disposed in
the rectangular channels such that a pair of half-plates meets in a
central portion of the transparent housing. The pairs of
half-plates may be oriented to move along orthogonal axes so that a
rectangular aperture of variable size may be formed by moving each
pair of half-plates closer together or further apart within the
rectangular channels.
[0064] The aperture members 500 and 520 may magnify or reduce the
image of the light passing through the aperture in any desired way.
The aperture members may have magnification factor of 1:1, which is
essentially no magnification, or may reduce the image in size by a
factor of between about 1.1:1 and about 5:1, for example, about 2:1
or about 4:1. Reduction in size may be useful for some embodiments
because the edges of the imaged energy field may be sharpened by
the size reduction. Magnification by a factor between about 1:1.1
and about 1:5, for example about 1:2, may be useful in some
embodiments to improve efficiency and throughput by increasing
coverage area of the imaged energy field.
[0065] Referring again to FIG. 1, an imaging optic 118 receives the
shaped, smoothed, and truncated energy field from the aperture
member 116 and projects it onto a substrate disposed on a work
surface 120 of the substrate support 110. FIG. 6 is a schematic
view of an imaging system 600 according to one embodiment. The
imaging system 118 of FIG. 1 may be the imaging system 600 of FIG.
6. The imaging system 118 has a transmitting module 602 and a
detecting module 616. The transmitting module 602 has a first
transmitting optic 610 and a second transmitting optic 614, with a
sampling optic 612 disposed between the first and second
transmitting optics 610 and 614.
[0066] The sampling optic 612 has a reflective surface 618
optically coupled to the substrate support and to the detecting
module 616. Energy from the aperture member 116 enters the
transmitting optic 602, passing through the first transmitting
optic 610, the sampling optic 612, and the second transmitting
optic 614 to illuminate a substrate disposed on the work surface
120 of the substrate support 110. Energy reflected from the
substrate travels back through the second transmitting optic 614
and reflects from the reflective surface 620 of the sampling optic
612. The reflected energy is directed to the detecting optic
616.
[0067] The detecting optic 616 has a first steering optic 604, a
second steering optic 606, and a detector 608. The first and second
steering optics 604 and 606 are operable to position the energy
field reflected from the substrate in a desired position on the
detector 608. This allows imaging of various parts of the energy
field at the detector 608 with increased precision. The detector
608 may be a photodiode array or a CCD matrix, allowing
visualization of the energy field interacting with the substrate.
Markers on the substrate may be viewed using the imaging system 600
to facilitate alignment of the energy field with desired structures
on the substrate when the substrate is illuminated by the energy
field. Alternately, a constant low-intensity ambient light source
may be provided to facilitate viewing the substrate through the
imaging system 600 when the substrate is not illuminated by the
energy field. Venire adjustments may be made to the x, y, z, and
.theta. positioning of the substrate based on observations using
the imaging system 600 to achieve precise alignment and focus of
the energy and the substrate for processing a first anneal region
of the substrate. Subsequent positioning is then automatically
performed by the substrate support 110 under direction of the
controller 112.
[0068] Diagnostic instruments may be provided to indicate
properties of a substrate during annealing. The imaging module 118
or 600 may have one or more temperature sensors 618 for indicating
intensity of radiation emitted by the substrate as a function of
temperature. A pyrometer may be used for such purposes. The imaging
module 118 or 600 may also have one or more surface absorption
monitor 622 for indicating a change in absorptivity of the
substrate. By measuring an intensity of reflected light in the
wavelengths used to anneal the substrate, the surface absorption
monitor 622 signals a change in state from a more reflective state
to a more absorptive state, and vice versa. A reflectometer may be
used for such purposes. In some embodiments, providing two or more
temperature sensors and two or more surface absorption monitors may
allow comparison of two or more readings for improved accuracy.
[0069] While two diagnostic instruments 618 and 622 are shown in
the imaging module 600 of FIG. 6, any number of diagnostic
instruments may be disposed in a position to monitor condition of
the substrate. In some embodiments, an acoustic detector or a
photoacoustic detector, or both, may be disposed to detect acoustic
effects of annealing energy on a substrate. Acoustic response from
the substrate may be used to indicate a change in state of the
substrate material, such as a phase change. In one embodiment, a
listening device may detect melting of a portion of the
substrate.
[0070] Thermal energy is coupled into a substrate disposed on a
work surface of a substrate support using methods disclosed herein.
The thermal energy is developed by applying electromagnetic energy
at an average intensity between about 0.2 J/cm.sup.2 and about 1.0
J/cm.sup.2 to successive portions of the surface of a substrate in
short pulses of duration between about 1 nsec and about 100 nsec,
such as between about 5 nsec and about 50 nsec, for example about
10 nsec. A plurality of such pulses may be applied to each portion
of the substrate, with a duration between the pulses between about
500 nsec and about 1 msec, such as between about 1 .mu.sec and
about 500 .mu.sec, for example about 100 .mu.sec, to allow complete
dissipation of the thermal energy through the substrate before the
next pulse arrives. The energy field typically covers an area of
between about 0.1 cm.sup.2 and about 10.0 cm.sup.2, for example
about 6 cm.sup.2, resulting in a power delivery of between about
0.2 MW and about 10 GW with each pulse. In most applications, the
power delivered with each pulse will be between about 10 MW and
about 500 MW. The power density delivered is typically between
about 2 MW/cm.sup.2 and about 1 GW/cm.sup.2, such as between about
5 MW/cm.sup.2 and about 100 MW/cm.sup.2, for example about 10
MW/cm.sup.2. The energy field applied in each pulse has spatial
standard deviation of intensity that is no more than about 4%, such
as less than about 3.5%, for example less than about 3.0%, of the
average intensity.
[0071] Delivery of the high power and uniformity energy field
mostly desired for annealing of substrates may be accomplished
using an energy source 102 with a plurality of lasers emitting
radiation readily absorbed by the substrate to be annealed. In one
aspect, laser radiation having a wavelength of about 532 nm is
used, based on a plurality of frequency-doubled Nd:YAG lasers. Four
such lasers having individual power output about 50 MW may be used
together for suitable annealing of a silicon substrate.
[0072] Pulses of energy may be formed by interrupting generation or
propagation of a beam of energy. A beam of energy may be
interrupted by disposing a fast shutter across an optical path of
the beam. The shutter may be an LCD cell capable of changing from
transparent to reflective in 10 nsec or less on application of a
voltage. The shutter may also be a rotating perforated plate
wherein size and spacing of the perforations are coupled with a
selected rate of rotation to transmit energy pulses having a chosen
duration through the openings. Such a device may be attached to the
energy source itself or spaced apart from the energy source. An
active or passive q-switch, or a gain switch may be used. A Pockels
cell may also be positioned proximate to a laser to form pulses by
interrupting a beam of laser light emitted by the laser. Multiple
pulse generators may be coupled to an energy source to form
periodic sequences of pulses having different durations, if
desired. For example, a q-switch may be applied to a laser source
and a rotating shutter having a periodicity similar to that of the
q-switch may be positioned across the optical path of the pulses
generated by the q-switched laser to form a periodic pattern of
pulses having different durations.
[0073] Self-correlation of the pulses is reduced by increasing the
number of spatial and temporal modes of the pulses. Correlation,
either spatial or temporal, is the extent to which different
photons are related in phase. If two photons of the same wavelength
are propagating through space in the same direction and their
electric field vectors point the same direction at the same time,
those photons are temporally correlated, regardless of their
spatial relationship. If the two photons (or their electric field
vectors) are located at the same point in a plane perpendicular to
the direction of propagation, those two photons are spatially
correlated, regardless of any temporal phase relationship.
[0074] Correlation is related to coherence, and the terms are used
almost interchangeably. Correlation of photons gives rise to
interference patterns that reduce uniformity of the energy field.
Coherence length is defined as a distance beyond which coherence or
correlation, spatial or temporal, falls below some threshold
value.
[0075] Photons in pulses can be temporally decorrelated by
splitting a pulse into a number of sub-pulses using a succession of
splitters, and routing each sub-pulse along a different path with a
different optical path length, such that the difference between any
two optical path lengths is greater than a coherence length of the
original pulse. This largely ensures that initially correlated
photons likely have different phase after the different path
lengths due to the natural decline in coherence with distance
travelled. For example, Nd:YAG lasers and Ti:sapphire lasers
typically generate pulses having a coherence length of the order of
a few millimeters. Dividing such pulses and sending parts of each
pulse along paths having length differences more than a few
millimeters will result in temporal decorrelation. Sending
sub-pulses along multi-reflective paths with different lengths is
one technique that may be used. Send sub-pulses along
multi-refractive paths with different effective lengths defined by
different refractive indices is another technique. The pulse
shaping modules described in connection with FIGS. 3A, 3D, and 3G
may be used for temporal decorrelation of pulses.
[0076] Spatial decorrelation may be achieved by creating an energy
field from a pulse and overlapping portions of the energy field.
For example, portions of an energy field may be separately imaged
onto the same area to form a spatially decorrelated image. This
largely ensures that any initially correlated photons are spatially
separated. In one example, a square energy field may be divided
into a checkerboard-style 8.times.8 sampling of square portions,
and each square portion imaged onto a field the same size as the
original energy field such that all the images overlap. A higher
number of overlapping images decorrelates the energy more,
resulting in a more uniform image. The homogenizers 400 and 450 of
FIGS. 4A and 4B may be useful in spatially decorrelating
pulses.
[0077] A laser pulse imaged after the decorrelation operations
described above generally has a cross-section with a uniform energy
intensity. Depending on the exact embodiment, the cross-sectional
energy intensity of a pulsed energy field treated according to the
above processes may have a standard deviation of about 3.0% or
less, such as about 2.7% or less, for example about 2.5%. An edge
region of the energy field will exhibit a decaying energy intensity
that may decay by 1/e along a dimension that is less than about 10%
of a dimension of the energy field, such as less than about 5% of
the dimension of the energy field, for example less than about 1%
of the energy field. The edge region may be truncated using an
aperture, such as the aperture members 500 and 520 of FIGS. 5A and
5B, or may be allowed to illuminate a substrate outside a treatment
zone, for example in a kurf space between device areas on a
substrate.
[0078] If the energy field is truncated, an aperture member is
typically positioned across the optical path of the pulses to trim
the non-uniform edge regions. To achieve clean truncation of the
image, the aperture is located near a focal plane of the energy
field. Refractive effects of the aperture interior edge may be
minimized by tapering the aperture interior edge to match a
direction of propagation of photons in the pulse. Multiple
removable aperture members having different aperture sizes and
shapes may be used to change the size and/or shape of the aperture
by inserting or removing the aperture member having the desired
size and/or shape. Alternately, a variable aperture member may be
used.
[0079] An energy field may be directed toward a portion of a
substrate to anneal the substrate. The energy field may be aligned,
if desired, with structures such as alignment marks on the
substrate surface by viewing the substrate surface along the
optical path of the energy field. Reflected light from the
substrate may be captured and directed toward a viewing device,
such as a camera or CCD matrix. A reflecting surface, such as a
one-way mirror, as in the imaging system 600 of FIG. 6, may be
disposed along the optical path of the energy field to capture the
reflected light.
[0080] Thermal state of the substrate may be monitored by viewing
radiation emitted, reflected, or transmitted by the substrate
during processing. Radiation emitted by the substrate indicates
temperature of the substrate. Radiation reflected or transmitted by
the substrate indicates the absorptivity of the substrate, which in
turn signals a change in the physical structure of the substrate
from a reflective to an absorptive state and vice versa. Accuracy
of the signals from such devices may be improved by comparing the
results using multiple devices.
[0081] A thermal processing apparatus may have a source of
electromagnetic energy operable to produce pulses of
electromagnetic energy, an optical system comprising a pulse
combiner, a pulse shaper, a homogenizer, and an aperture member
positioned to receive pulses of electromagnetic energy from the
source, a substrate support operable to move a substrate with
respect to the optical system, and an imaging system operable to
view the substrate along an optical path of the optical system.
[0082] An apparatus for combining pulses of electromagnetic energy
may have a first energy input, a second energy input, a first optic
for imparting a first property to the first energy, a second optic
for imparting a second property to the second energy, a selecting
surface that reflects or transmits energy based on the first
property and the second property, a steering optic for steering the
first energy to a first location on a first side of the selecting
surface and the second energy to a second location on a second side
of the selecting surface opposite the first side of the selecting
surface, wherein the first location and the second location are
aligned, and a diagnostic module optically coupled to the selecting
surface.
[0083] A thermal processing system may have a plurality of laser
energy sources, each having an active q-switch coupled to an
electronic timer, at least two combiners optically coupled to the
laser energy sources, each combiner having a selecting optic, the
selecting optic having a selecting surface, an optical system to
direct light from the laser energy sources to opposite sides of the
selecting surface, and a homogenizer comprising at least three
microlens arrays.
[0084] A substrate processing system may have a source of
electromagnetic energy, an optical system for focusing the
electromagnetic energy, and an aperture member having a reflective
portion embedded therein, the reflective portion having an opening
through which the electromagnetic energy projects, a surface of the
reflective portion positioned at a focal plane of the
electromagnetic energy.
[0085] A substrate may be processed by directing a field of
electromagnetic energy toward a portion of the substrate, the field
of electromagnetic energy comprising light from a plurality of
lasers that has been combined by passing through two sides of a
selecting surface of a combining optic, temporally decorrelated,
spatially decorrelated, and passed through a reflector optically
coupled to the substrate.
[0086] A substrate may also be processed by directing a field of
electromagnetic energy toward a portion of the substrate, the field
comprising pulsed light from two or more lasers, detecting a
temporal shape of the field using a photodiode, detecting an energy
content of the field using a pyroelectric detector, adjusting a
pulse timing of one or more of the lasers based on the temporal
shape detected by the photodiode, and attenuating one or more of
the lasers based on the energy content of the field detected by the
pyroelectric detector.
[0087] A substrate may also be processed by forming an energy field
having a spatial standard deviation of intensity non-uniformity no
more than about 3% and an energy content of at least about 0.2
J/cm.sup.2 by combining polarized light from two or more lasers and
decorrelating the light temporally and spatially, directing the
energy field toward a first portion of the substrate surface in a
pulse, moving the substrate, and directing the energy field toward
a second portion of the substrate surface.
[0088] A substrate may also be processed by directing a shaped
field of electromagnetic energy toward the substrate through a
reflector optically coupled to the substrate, detecting an
alignment of the substrate and the energy field by viewing light
reflected from the substrate using the reflector, and adjusting the
alignment of the substrate with the energy field.
[0089] 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.
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