U.S. patent application number 11/459852 was filed with the patent office on 2007-09-27 for apparatus for thermal processing structures formed on a substrate.
Invention is credited to Dean Jennings, Alexander N. Lerner, Abhilash Mayur, Stephen Moffatt, Timothy N. Thomas.
Application Number | 20070221640 11/459852 |
Document ID | / |
Family ID | 40494875 |
Filed Date | 2007-09-27 |
United States Patent
Application |
20070221640 |
Kind Code |
A1 |
Jennings; Dean ; et
al. |
September 27, 2007 |
APPARATUS FOR THERMAL PROCESSING STRUCTURES FORMED ON A
SUBSTRATE
Abstract
The present invention generally describes one ore more
apparatuses and various methods that are used to perform an
annealing process on desired regions of a substrate. In one
embodiment, an amount of energy is delivered to the surface of the
substrate to preferentially melt certain desired regions of the
substrate to remove unwanted damage created from prior processing
steps (e.g., crystal damage from implant processes), more evenly
distribute dopants in various regions of the substrate, and/or
activate various regions of the substrate. The preferential melting
processes will allow more uniform distribution of the dopants in
the melted region, due to the increased diffusion rate and
solubility of the dopant atoms in the molten region of the
substrate. The creation of a melted region thus allows: 1) the
dopant atoms to redistribute more uniformly, 2) defects created in
prior processing steps to be removed, and 3) regions that have
hyper-abrupt dopant concentrations to be formed.
Inventors: |
Jennings; Dean; (Beverly,
MA) ; Lerner; Alexander N.; (San Jose, CA) ;
Mayur; Abhilash; (Salinas, CA) ; Moffatt;
Stephen; (Jersey, GB) ; Thomas; Timothy N.;
(Portland, OR) |
Correspondence
Address: |
PATTERSON & SHERIDAN, LLP
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Family ID: |
40494875 |
Appl. No.: |
11/459852 |
Filed: |
July 25, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60780745 |
Mar 8, 2006 |
|
|
|
Current U.S.
Class: |
219/121.76 ;
257/E21.347; 257/E21.427 |
Current CPC
Class: |
H01L 21/67115 20130101;
H01L 29/66659 20130101; H01L 21/823418 20130101; H01L 29/6659
20130101; H01L 29/0653 20130101; H01L 21/26506 20130101; H01L
21/324 20130101; H01L 21/268 20130101; H01L 21/26513 20130101 |
Class at
Publication: |
219/121.76 |
International
Class: |
B23K 26/00 20060101
B23K026/00 |
Claims
1. An apparatus for thermally processing a semiconductor substrate,
comprising: a substrate support having a substrate supporting
surface; a heating element that is adapted to heat a substrate
disposed on the substrate support; and an intense light source that
is adapted to deliver an amount of radiation to a region on a
surface of the substrate disposed on the substrate supporting
surface.
2. The apparatus of claim 1, wherein the region on the surface of
the substrate is between about 4 mm.sup.2 and about 1000
mm.sup.2.
3. The apparatus of claim 1, wherein the heating element is adapted
to heat the substrate support to a temperature between about
20.degree. C. and about 600.degree. C.
4. The apparatus of claim 1, further comprising one or more cooling
channels formed within the substrate support that are adapted
receive a heat exchanging fluid that will cool the substrate
support to a temperature between about -240.degree. C. and about
20.degree. C.
5. The apparatus of claim 1, further comprising a stage attached to
the substrate support; wherein the stage is adapted to position the
substrate in at least one direction generally parallel to the
substrate supporting surface.
6. The apparatus of claim 1, wherein the intense light source is
adapted to deliver radiation at a wavelength between about 500 nm
and about 11 micrometers.
7. An apparatus for thermally processing a semiconductor substrate,
comprising: an first intense light source that is adapted to
deliver a first amount of energy to a region on a surface of the
substrate disposed on the substrate supporting surface; and a
second intense light source that is adapted to deliver a second
amount of energy to the region on the surface of the substrate
disposed on the substrate supporting surface; and a controller that
is adapted to monitor the first amount of energy delivered to the
region on the surface of the substrate and control the time between
the delivery of the first amount and second amount of energy and
the magnitude of the second amount of energy to achieve a desired
temperature in the region.
8. The apparatus of claim 7, further comprising: a substrate
support having a substrate supporting surface; and a heating
element that is adapted to heat a substrate disposed on the
substrate support.
9. The apparatus of claim 7, wherein the region on the surface of
the substrate is between about 4 mm.sup.2 and about 1000
mm.sup.2.
10. The apparatus of claim 8, wherein the heating element is
adapted to heat the substrate support to a temperature between
about 20.degree. C. and about 600.degree. C.
11. The apparatus of claim 8, further comprising one or more
cooling channels formed within the substrate support that are
adapted receive a heat exchanging fluid that will cool the
substrate support to a temperature between about -240.degree. C.
and about 20.degree. C.
12. An apparatus for thermally processing a semiconductor
substrate, comprising: a substrate support having a substrate
supporting surface and an aperture formed in the substrate support;
and an intense light source that is adapted to deliver an amount of
radiation to a first area of the substrate through the aperture
formed in the substrate support and a rear surface of the substrate
which is opposite to a front surface of the substrate, wherein the
front surface of the substrate contains one or more semiconductor
devices formed thereon and the amount of radiation is adapted to
melt a region contained within the first area.
13. The apparatus of claim 12, wherein the intense light source is
adapted to deliver radiation at a wavelength greater than about 1
micrometer.
14. The apparatus of claim 12, wherein the intense light source is
adapted to deliver radiation at a wavelength between about 500 nm
and about 11 micrometers.
15. The apparatus of claim 12, wherein the first area is between
about 4 mm.sup.2 and about 1000 mm.sup.2.
16. The apparatus of claim 12, further comprising a stage attached
to the substrate support; wherein the stage is adapted to position
the substrate in at least one direction generally parallel to the
substrate supporting surface.
17. An apparatus for thermally processing a semiconductor
substrate, comprising: a substrate support having a substrate
supporting surface and an aperture formed in the substrate support;
a first source that is adapted to deliver an amount of
electromagnetic radiation to a first area of the substrate through
the aperture formed in the substrate support and a rear surface of
the substrate which is opposite to a front surface of the
substrate, wherein the front surface of the substrate contains one
or more semiconductor devices formed thereon and the amount of
radiation is adapted to melt a region contained within the first
area; and a second source that is adapted to deliver an amount of
electromagnetic radiation to a first area of the substrate at a
desired wavelength.
18. The apparatus of claim 17, wherein the intense light source is
adapted to deliver radiation at a wavelength greater than about 1
micrometer.
19. The apparatus of claim 17, wherein the intense light source is
adapted to deliver radiation at a wavelength between about 500 nm
and about 11 micrometers.
20. The apparatus of claim 17, wherein the first area is between
about 4 mm.sup.2 and about 1000 mm.sup.2.
21. The apparatus of claim 17, further comprising a stage attached
to the substrate support; wherein the stage is adapted to position
the substrate in at least one direction generally parallel to the
substrate supporting surface.
22. The apparatus of claim 17, wherein the second source is adapted
to deliver electromagnetic radiation to the first area at a
wavelength less than about 590 nm.
23. The apparatus of claim 17, wherein the second source is
adjacent to the front surface of the substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. provisional patent
application Ser. No. 60/780,745 [APPM 5635L], filed Mar. 8, 2006,
which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the present invention generally relate to a
method of manufacturing a semiconductor device. More particularly,
the invention is directed to a method of thermally processing a
substrate.
[0004] 2. Description of the Related Art
[0005] The integrated circuit (IC) market is continually demanding
greater memory capacity, faster switching speeds, and smaller
feature sizes. One of the major steps the industry has taken to
address these demands is to change from batch processing silicon
wafers in large furnaces to single wafer processing in a small
chamber.
[0006] During such single wafer processing the wafer is typically
heated to high temperatures so that various chemical and physical
reactions can take place in multiple IC devices defined in the
wafer. Of particular interest, favorable electrical performance of
the IC devices requires implanted regions to be annealed. Annealing
recreates a more crystalline structure from regions of the wafer
that were previously made amorphous, and activates dopants by
incorporating their atoms into the crystalline lattice of the
substrate, or wafer. Thermal processes, such as annealing, require
providing a relatively large amount of thermal energy to the wafer
in a short amount of time, and thereafter rapidly cooling the wafer
to terminate the thermal process. Examples of thermal processes
currently in use include Rapid Thermal Processing (RTP) and impulse
(spike) annealing. While such processes are widely used, current
technology is not ideal. It tends to ramp the temperature of the
wafer too slowly and expose the wafer to elevated temperatures for
too long. These problems become more severe with increasing wafer
sizes, increasing switching speeds, and/or decreasing feature
sizes.
[0007] In general, these thermal processes heat the substrates
under controlled conditions according to a predetermined thermal
recipe. These thermal recipes fundamentally consist of a
temperature that the semiconductor substrate must be heated to the
rate of change of temperature, i.e., the temperature ramp-up and
ramp-down rates and the time that the thermal processing system
remains at a particular temperature. For example, thermal recipes
may require the substrate to be heated from room temperature to
distinct temperatures of 1200.degree. C. or more, for processing
times at each distinct temperature ranging up to 60 seconds, or
more.
[0008] Moreover, to meet certain objectives, such as minimal
inter-diffusion of materials between different regions of a
semiconductor substrate, the amount of time that each semiconductor
substrate is subjected to high temperatures must be restricted. To
accomplish this, the temperature ramp rates, both up and down, are
preferably high. In other words, it is desirable to be able to
adjust the temperature of the substrate from a low to a high
temperature, or visa versa, in as short a time as possible.
[0009] The requirement for high temperature ramp rates led to the
development of Rapid Thermal Processing (RTP), where typical
temperature ramp-up rates range from 200 to 400.degree. C./s, as
compared to 5-15.degree. C./minute for conventional furnaces.
Typical ramp-down rates are in the range of 80-150.degree. C./s. A
drawback of RTP is that it heats the entire wafer even though the
IC devices reside only in the top few microns of the silicon wafer.
This limits how fast one can heat up and cool down the wafer.
Moreover, once the entire wafer is at an elevated temperature, heat
can only dissipate into the surrounding space or structures. As a
result, today's state of the art RTP systems struggle to achieve a
400.degree. C./s ramp-up rate and a 150.degree. C./s ramp-down
rate.
[0010] To resolve some of the problems raised in conventional RTP
type processes various scanning laser anneal techniques have been
used to anneal the surface(s) of the substrate. In general, these
techniques deliver a constant energy flux to a small region on the
surface of the substrate while the substrate is translated, or
scanned, relative to the energy delivered to the small region. Due
to the stringent uniformity requirements and the complexity of
minimizing the overlap of scanned regions across the substrate
surface these types of processes are not effective for thermal
processing contact level devices formed on the surface of the
substrate.
[0011] In view of the above, there is a need for an method for
annealing a semiconductor substrate with high ramp-up and ramp-down
rates. This will offer greater control over the fabrication of
smaller devices leading to increased performance.
SUMMARY OF THE INVENTION
[0012] The present invention generally provide an apparatus for
thermally processing a semiconductor substrate, comprising a
substrate support having a substrate supporting surface, a heating
element that is adapted to heat a substrate disposed on the
substrate support, and an intense light source that is adapted to
deliver an amount of radiation to a region on a surface of the
substrate disposed on the substrate supporting surface.
[0013] Embodiments of the invention further provide an apparatus
for thermally processing a semiconductor substrate, comprising an
first intense light source that is adapted to deliver a first
amount of energy to a region on a surface of the substrate disposed
on the substrate supporting surface, and a second intense light
source that is adapted to deliver a second amount of energy to the
region on the surface of the substrate disposed on the substrate
supporting surface, and a controller that is adapted to monitor the
first amount of energy delivered to the region on the surface of
the substrate and control the time between the delivery of the
first amount and second amount of energy and the magnitude of the
second amount of energy to achieve a desired temperature in the
region.
[0014] Embodiments of the invention further provide an apparatus
for thermally processing a semiconductor substrate, comprising a
substrate support having a substrate supporting surface and an
aperture formed in the substrate support, and an intense light
source that is adapted to deliver an amount of radiation to a first
area of the substrate through the aperture formed in the substrate
support and a rear surface of the substrate which is opposite to a
front surface of the substrate, wherein the front surface of the
substrate contains one or more semiconductor devices formed thereon
and the amount of radiation is adapted to melt a region contained
within the first area.
[0015] Embodiments of the invention further provide an apparatus
for thermally processing a semiconductor substrate, comprising a
substrate support having a substrate supporting surface and an
aperture formed in the substrate support, a first source that is
adapted to deliver an amount of electromagnetic radiation to a
first area of the substrate through the aperture formed in the
substrate support and a rear surface of the substrate which is
opposite to a front surface of the substrate, wherein the front
surface of the substrate contains one or more semiconductor devices
formed thereon and the amount of radiation is adapted to melt a
region contained within the first area, and a second source that is
adapted to deliver an amount of electromagnetic radiation to a
first area of the substrate at a desired wavelength.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] 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.
[0017] FIG. 1 illustrates an isometric view of an energy source
that is adapted to project an amount of energy on a defined region
of the substrate described within an embodiment herein;
[0018] FIGS. 2A-2F illustrate a schematic side view of a region on
a surface of a substrate described within an embodiment herein;
[0019] FIG. 3A illustrate a graph of concentration versus depth
into a region of a substrate illustrated in FIG. 2A that is within
an embodiment herein;
[0020] FIG. 3B illustrate a graph of concentration versus depth
into a region of a substrate illustrated in FIG. 2B that is within
an embodiment herein;
[0021] FIG. 3C illustrate a graph of concentration versus depth
into a region of a substrate illustrated in FIG. 2C that is within
an embodiment herein;
[0022] FIGS. 4A-4G schematic diagrams of electromagnetic energy
pulses described within an embodiment herein;
[0023] FIGS. 5A-5C illustrate a schematic side view of a region on
a surface of a substrate described within an embodiment herein;
[0024] FIG. 6A illustrate methods of forming one or more desired
layers on a surface of the substrate described within an embodiment
contained herein;
[0025] FIGS. 6B-6D illustrate schematic side views of a region of a
substrate described in conjunction with the method illustrated in
FIG. 6A that is within an embodiment described herein;
[0026] FIG. 6E illustrate methods of forming one or more desired
layers on a surface of the substrate described within an embodiment
contained herein;
[0027] FIGS. 6F-6G illustrate schematic side views of a region of a
substrate described in conjunction with the method illustrated in
FIG. 6E that is within an embodiment described herein;
[0028] FIG. 7 illustrates a schematic side view of a region on the
surface of a substrate described within an embodiment herein;
[0029] FIG. 8 illustrates a schematic side view of a region on the
surface of a substrate described within an embodiment herein.
[0030] FIG. 9 illustrates a schematic side view of system that has
an energy source that is adapted to project an amount of energy on
a defined region of the substrate described within an embodiment
herein.
DETAILED DESCRIPTION
[0031] The present invention generally improves the performance of
the implant anneal steps used in the process of manufacturing a
semiconductor devices on a substrate. Generally, the methods of the
present invention may be used to preferentially anneal selected
regions of a substrate by delivering enough energy to the selected
regions to cause them to re-melt and solidify.
[0032] In general the term "substrates" as used herein can be
formed from any material that has some natural electrical
conducting ability or a material that can be modified to provide
the ability to conduct electricity. Typical substrate materials
include, but are not limited to semiconductors, such as silicon
(Si) and germanium (Ge), as well as other compounds that exhibit
semiconducting properties. Such semiconductor compounds generally
include group III-V and group II-VI compounds. Representative group
III-V semiconductor compounds include, but are not limited to,
gallium arsenide (GaAs), gallium phosphide (GaP), and gallium
nitride (GaN). Generally, the term semiconductor substrates include
bulk semiconductor substrates as well as substrates having
deposited layers disposed thereon. To this end, the deposited
layers in some semiconductor substrates processed by the methods of
the present invention are formed by either homoepitaxial (e.g.,
silicon on silicon) or heteroepitaxial (e.g., GaAs on silicon)
growth. For example, the methods of the present invention may be
used with gallium arsenide and gallium nitride substrates formed by
heteroepitaxial methods. Similarly, the invented methods can also
be applied to form integrated devices, such as thin-film
transistors (TFTs), on relatively thin crystalline silicon layers
formed on insulating substrates (e.g., silicon-on-insulator [SOI]
substrates).
[0033] In one embodiment of the invention, an amount of energy is
delivered to the surface of the substrate to preferentially melt
certain desired regions of the substrate to remove unwanted damage
created from prior processing steps (e.g., crystal damage from
implant processes), more evenly distribute dopants in various
regions of the substrate, and/or activate various regions of the
substrate. The preferential melting processes will allow more
uniform distribution of the dopants in the melted region, due to
the increased diffusion rate and solubility of the dopant atoms in
the moltent region of the substrate. The creation of a melted
region thus allows: 1) the dopant atoms to redistribute more
uniformly, 2) defects created in prior processing steps to be
removed, and 3) regions that have hyper-abrupt dopant
concentrations to be formed. The gradient in dopant concentration
in a region that has a hyper-abrupt dopant concentrations is very
large (e.g., <2 nm/decade of concentration) as the concentration
rapidly changes from one region to another in the device.
[0034] Use of the techniques described herein allows junctions to
be formed that contain higher dopant concentrations than
conventional devices, since the common negative attributes of the
formed junctions, such as an increase in the concentration of
defects in the substrate material by the increase in doping level,
can be easily reduced to an acceptable level by use of the
processing techniques described herein. The higher dopant levels
and abrupt changes in the dopant concentration can thus increase
the conductivity of various regions of the substrate, thus
improving device speed without negatively affecting device yield,
while minimizing the diffusion of dopants into various regions of
the substrate. The resultant higher dopant concentration increases
the conductivity of the formed device and improves its performance.
Typically, devices that are formed using an RTP process, will not
use a dopant concentration greater than about 1.times.10.sup.15
atoms/cm.sup.2, since the higher dopant concentrations cannot
readily diffuse into the bulk material of the substrate during
typical RTP processes and will instead result in clusters of dopant
atoms and other types of defects. Using one or more of the
embodiments of the anneal process described herein, much more
dopant (up to 5-10 times more dopant, i.e., 1.times.10.sup.16
atoms/cm.sup.2) may be successfully incorporated into the desired
substrate surface, since regions of the substrate are
preferentially melted so that the dopants will become more evenly
distributed throughout the liquid before the liquefied regions
solidify.
[0035] FIG. 1 illustrates an isometric view of one embodiment of
the invention where an energy source 20 is adapted to project an
amount of energy on a defined region, or a anneal region 12, of the
substrate 10 to preferentially melt certain desired regions within
the anneal region 12. In one example, as shown in FIG. 1, only one
or more defined regions of the substrate, such as anneal region 12,
are exposed to the radiation from the energy source 20 at any given
time. In one aspect of the invention, multiple areas of the
substrate 10 are sequentially exposed to a desired amount of energy
delivered from the energy source 20 to cause the preferential
melting of desired regions of the substrate. In general, the areas
on the surface of the substrate may be sequentially exposed by
translating the substrate relative to the output of the
electromagnetic radiation source (e.g., conventional X/Y stage,
precision stages) and/or translating the output of the radiation
source relative to the substrate. Typically, one or more
conventional electrical actuators 17 (e.g., linear DC servo motor,
lead screw and servo motor), which may be part of a separate
precision stage (not shown), are used to control the movement and
position of substrate 10. Conventional precision stages that may be
used to support and position the substrate 10, and heat exchanging
device 15, may be purchased from Parker Hannifin Corporation, of
Rohnert Park, Calif.
[0036] In one aspect, the anneal region 12 is sized to match the
size of the die 13 (e.g., 40 "die" are shown in FIG. 1), or
semiconductor devices (e.g., memory chip), that are formed on the
surface of the substrate. In one aspect, the boundary of the anneal
region 12 is aligned and sized to fit within the "kurf" or "scribe"
lines 10A that define the boundary of each die 13. In one
embodiment, prior to performing the annealing process the substrate
is aligned to the output of the energy source 20 using alignment
marks typically found on the surface of the substrate and other
conventional techniques so that the anneal region 12 can be
adequately aligned to the die 13. Sequentially placing anneal
regions 12 so that they only overlap in the naturally occurring
unused space/boundaries between die 13, such as the scribe or kurf
lines, reduces the need to overlap the energy in the areas where
the devices are formed on the substrate and thus reduces the
variation in the process results between the overlapping anneal
regions. This technique has advantages over conventional processes
that sweep the laser energy across the surface of the substrate,
since the need to tightly control the overlap between adjacently
scanned regions to assure uniform annealing across the desired
regions of the substrate is not an issue due to the confinement of
the overlap to the unused space between die 13. Confining the
overlap to the unused space/boundary between die 13 also improves
process uniformity results versus conventional scanning anneal type
methods that utilize adjacent overlapping regions that traverse all
areas of the substrate. Therefore, the amount of process variation,
due to the varying amounts of exposure to the energy delivered from
the energy source 20 to process critical regions of the substrate
is minimized, since any overlap of delivered energy between the
sequentially placed anneal regions 12 can be minimized. In one
example, each of the sequentially placed anneal regions 12 are a
rectangular region that is about 22 mm by about 33 mm in size
(e.g., area of 726 square millimeters (mm.sup.2)). In one aspect,
the area of each of the sequentially placed anneal regions 12
formed on the surface of the substrate is between about 4 mm.sup.2
(e.g., 2 mm.times.2 mm) and about 1000 mm.sup.2 (e.g., 25
mm.times.40 mm).
[0037] The energy source 20 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. In one aspect, the
substrate 10 is exposed to a pulse of energy from a laser that
emits radiation at one or more appropriate wavelengths for a
desired period of time. In one aspect, pulse of energy from the
energy source 20 is tailored so that the amount of energy delivered
across the anneal region 12 and/or the amount of energy delivered
over the period of the pulse is optimized to enhance preferential
melting of certain desired areas. In one aspect, the wavelength of
the laser is tuned so that a significant portion of the radiation
is absorbed by a silicon layer disposed on the substrate 10. For
laser anneal process performed on a silicon containing substrate,
the wavelength of the radiation is typically less than about 800
nm, and can be delivered at deep ultraviolet (UV), infrared (IR) or
other desirable wavelengths. In one embodiment, the energy source
20 is an intense light source, such as a laser, that is adapted to
deliver radiation at a wavelength between about 500 nm and about 11
micrometers. In either case, the anneal process generally takes
place on a given region of the substrate for a relatively short
time, such as on the order of about one second or less.
[0038] In one aspect, the amount of energy delivered to the surface
of the substrate is configured so that the melt depth does not
extend beyond the amorphous depth defined by the amorphization
implant step. Deeper melt depths facilitate the diffusion of dopant
from the doped amorphous layers into the undoped molten layers.
Such undesirable diffusion would sharply and deleteriously alter
the electrical characteristics of the circuits on the semiconductor
substrate. In some anneal processes, energy is delivered to the
surface of a substrate for a very short time in order to melt the
surface of the substrate to a sharply defined depth, for example
less than 0.5 micrometers. The exact depth is determined by the
size of the electronic device being manufactured.
Temperature Control of the Substrate During the Anneal Process
[0039] In one embodiment, it may be desirable to control the
temperature of the thermally substrate during thermal processing by
placing a surface of the substrate 10, illustrated in FIG. 1, in
thermal contact with a substrate supporting surface 16 of a heat
exchanging device 15. The heat exchanging device 15 is generally
adapted to heat and/or cool the substrate prior to or during the
annealing process. In this configuration, the heat exchanging
device 15, 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. In general, the substrate 10 is placed within an
enclosed processing environment (not shown) of a processing chamber
(not shown) that contains the heat exchanging device 15. The
processing environment within which the substrate 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.
[0040] 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 and also possibly reduce the defect density in the
resolidified areas of the substrate. In one aspect, the heat
exchanging device 15 contains resistive heating elements 15A and a
temperature controller 15C that are adapted to heat a substrate
disposed on a substrate supporting surface 16. The temperature
controller 15C is in communication with the controller 21
(discussed below). 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 aspect, 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.
[0041] In another embodiment, it may be desirable to cool the
substrate during processing to reduce any interdiffusion due to the
energy added to substrate during the annealing process and/or
increase the regrowth velocity after melting to increase the
amorphization of the various regions during processing, such as
described in conjunction with FIG. 8. In one configuration, the
heat exchanging device 15 contains one or more fluid channels 15B
and a cryogenic chiller 15D that are adapted to cool a substrate
disposed on a substrate supporting surface 16. In one aspect, a
conventional cryogenic chiller 15D, which is in communication with
the controller 21, is adapted to deliver a cooling fluid through
the one or more fluid channels 15B. In one aspect, it may be
desirable to cool the substrate to a temperature between about
-240.degree. C. and about 20.degree. C.
[0042] The controller 21 (FIG. 1) is generally designed to
facilitate the control and automation of the thermal processing
techniques described herein and typically may includes a central
processing unit (CPU) (not shown), memory (not shown), and support
circuits (or I/O) (not shown). The CPU may be one of any form of
computer processors that are used in industrial settings for
controlling various processes and hardware (e.g., conventional
electromagnetic radiation detectors, motors, laser hardware) and
monitor the processes (e.g., substrate temperature, substrate
support temperature, amount of energy from the pulsed laser,
detector signal). The memory (not shown) is connected to the CPU,
and may be one or more of a readily available memory, such as
random access memory (RAM), read only memory (ROM), floppy disk,
hard disk, or any other form of digital storage, local or remote.
Software instructions and data can be coded and stored within the
memory for instructing the CPU. The support circuits (not shown)
are also connected to the CPU for supporting the processor in a
conventional manner. The support circuits may include conventional
cache, power supplies, clock circuits, input/output circuitry,
subsystems, and the like. A program (or computer instructions)
readable by the controller determines which tasks are performable
on a substrate. Preferably, the program is software readable by the
controller and includes code to monitor and control the substrate
position, the amount of energy delivered in each electromagnetic
pulse, the timing of one or more electromagnetic pulses, the
intensity and wavelength as a function of time for each pulse, the
temperature of various regions of the substrate, and any
combination thereof.
Selective Melting
[0043] In an effort to minimize inter-diffusion between various
regions of a formed device, remove defects in the substrate
material, and more evenly distribute dopants in various regions of
the substrate, one or more processing steps are performed on
various regions of the substrate to cause them to preferentially
remelt when exposed to energy delivered from an energy source
during the anneal process. The process of modifying the properties
of a first region of the substrate so that it will preferentially
melt rather than a second region of the substrate, when they are
both exposed to about the same amount energy during the annealing
process, is hereafter described as creating a melting point
contrast between these two regions. In general, the substrate
properties that can be modified to allow preferential melting of
desired regions of the substrate include implanting, driving-in
and/or co-depositing one or more elements within a desired regions
of the substrate, creating physical damage to desired regions of
the substrate, and optimizing the formed device structure to create
the melting point contrast in desired regions of the substrate.
Each of these modification processes will be reviewed in turn.
[0044] FIGS. 2A-2C illustrate cross-sectional views of an
electronic device 200 at different stages of a device fabrication
sequence incorporating one embodiment of the invention. FIG. 2A
illustrates a side view of typical electronic device 200 formed on
a surface 205 of a substrate 10 that has two doped regions 201
(e.g., doped regions 201A-201B), such as a source and drain region
of a MOS device, a gate 215, and a gate oxide layer 216. The doped
regions 201A-201B are generally formed by implanting a desired
dopant material into the surface 205 of the substrate 10. In
general, typical n-type dopants (donor type species) may include
arsenic (As), phosphorus (P), and antimony (Sb), and typical p-type
dopants (acceptor type species) may include boron (B), aluminum
(Al), and indium (In) that are introduced into the semiconductor
substrate 10 to form the doped regions 201A-201B. FIG. 3A
illustrates an example of the concentration of the dopant material
as a function of depth (e.g., curve C.sub.1), from the surface 205
and into the substrate 10 along a path 203 extending through the
doped region 201A. The doped region 201A has a junction depth
D.sub.1 after the implant process, which may be defined as a point
where the dopant concentration drops off to a negligible amount. It
should be noted that FIGS. 2A-2F are only intended to illustrate
some of the various aspects of the invention and is not intended to
be limiting as to the type of device, type of structure, or regions
of a device that may be formed using the various embodiments of the
invention described herein. In one example, the doped regions 201
(e.g., source or drain regions in a MOS device) can be a raised or
lowered relative to the position of the gate 215 (e.g., gate in a
MOS device) without varying from the scope of the invention
described herein. As semiconductor device sizes decrease the
position and geometry of structural elements of the electronic
devices 200 formed on the surface 205 of a substrate 10 may vary to
improve device manufacturability or device performance. It should
also be noted that the modification of only a single doped region
201A, as shown in FIGS. 2A-2E, is not intended to be limiting as to
the scope of the invention described herein and is only meant to
illustrate how embodiments of the invention can be used to
manufacture a semiconductor device.
[0045] FIG. 2B illustrates a side view of the electronic device 200
shown in FIG. 2A during a process step that is adapted to
selectively modify the properties of a discrete region (e.g.,
modified area 210) of the substrate 10, which in this case is a
region containing a single doped region 201A, to create a melting
point contrast. After performing the modification process a melting
point contrast will be created between the modified area 210 and
unmodified areas 211. In one embodiment, the modification process
includes the step(s) of adding a material to a layer as it is being
deposited on the surface of the substrate, where the incorporated
material is adapted to form an alloy with the substrate material to
lower the melting point of a region 202 within the modified area
210. In one aspect, the incorporated material is added to the
deposited layer during an epitaxial layer deposition process.
[0046] In another embodiment, the modification process includes the
step of implanting (see "A" in FIG. 2B) a material that is adapted
to form an alloy with the substrate material to lower the melting
point of a region 202 within the modified area 210. In one aspect,
the modification process is adapted to implant the alloying
material to a depth D.sub.2, as shown in FIG. 2B. FIG. 3B
illustrates an example of the concentration of the dopant material
(e.g., curve C.sub.1) and implanted alloying material (e.g., curve
C.sub.2) as a function of depth, from the surface 205 and through
the substrate 10 along a path 203. In one aspect, where the
substrate 10 is formed from a silicon containing material and the
implanted alloying materials that may be used include, for example,
germanium (Ge), arsenic (As), gallium (Ga), carbon (C), tin (Sn),
and antimony (Sb). In general, the alloying material can be any
material that when heated in the presence of the substrate base
material causes the melting point of the region 202 in the modified
area 210 to be lowered relative to the unmodified areas 211. In one
aspect, a region of a silicon substrate is modified by the addition
of between about 1% and about 20% of germanium to reduce the
melting point between the modified and un-modified area. It is
believed that the addition of germanium in these concentrations
will lower the melting point of the modified areas versus the
un-modified areas by about 300.degree. C. In one aspect, the region
202 formed in a silicon substrate contains germanium (Ge) and
carbon (C), so that a Si.sub.xGe.sub.yC.sub.z alloy will form to
lower the melting point of the region 202 relative to the
unmodified areas 211. In another aspect, a region of a silicon
substrate is modified by the addition of about 1% or less of
arsenic to reduce the melting point between the modified and
un-modified area.
[0047] In another embodiment, the modification process includes the
step of inducing some damage to the substrate 10 material in the
various modified areas (e.g., modified area 210) to damage the
crystal structure of the substrate, and thus make these regions
more amorphous. Inducing damage to the crystal structure of the
substrate, such as damaging a single crystal silicon substrate,
will reduce the melting point of this region relative to an
undamaged region due to the change in the bonding structure of
atoms in the substrate and thus induce thermodynamic property
differences between the two regions. In one aspect, damage to the
modified area 210 in FIG. 2B is performed by bombarding the surface
205 of the substrate 10 (see "A" in FIG. 2B) with a projectile that
can create damage to the surface of the substrate. In one aspect,
the projectile is a silicon (Si) atom that is implanted into a
silicon containing substrate to induce damage to the region 202
within the modified area 210. In another aspect, the damage to the
substrate material is created by bombarding the surface with gas
atoms, such as argon (Ar), krypton (Kr), xenon (Xe) or even
nitrogen (N.sub.2), using an implant process, an ion beam or biased
plasma to induce damage to region 202 of the modified area 210. In
one aspect, the modification process is adapted to create a region
202 that has induced damage to a depth D.sub.2, as shown in FIG.
2B. It is believed that a dislocation or vacancy density of between
about 5.times.10.sup.14 and about 1.times.10.sup.16/cm.sup.2 may be
useful to create the melting point contrast between a modified area
210 versus an unmodified area 211. In one aspect, FIG. 3B
illustrates an example of the concentration of the dopant material
(e.g., curve C.sub.1) and defects density (e.g., curve C.sub.2) as
a function of depth, from the surface 205 and through the substrate
10 along a path 203.
[0048] It should be noted that while FIGS. 2A-2B illustrate a
process sequence in which the modification process is performed
after the doping process, this process sequence is not intended to
be limiting as to the scope of the invention described herein. For
example, in one embodiment, it is desirable to perform the
modification process described in FIG. 2B prior to performing the
doping process described in FIG. 2A.
[0049] FIG. 2C illustrates a side view of the electronic device 200
shown in FIG. 2B that is exposed to radiation "B" emitted from the
an energy source, such as optical radiation from a laser. During
this step the modified area(s) (e.g., modified area 210) and
unmodified areas (e.g., 211) disposed across the substrate 10 are
exposed to an amount of energy which causes the region 202 in the
modified area(s) 210 to selectively melt and resolidify after the
pulse of radiation "B" has been applied, while the unmodified areas
211 remain in a solid state. The amount of energy, the energy
density and the duration that the radiation "B" is applied can be
set to preferentially melt the regions 202 by knowing the desired
depth of the region 202, the materials used to create the region
202, the other materials used to form the electronic device 200,
and the heat transfer characteristics of the components within the
formed electronic device 200. As shown in FIGS. 2C and 3C, upon
exposure to the radiation "B" the remelting and solidification of
the region 202 causes the concentration of the dopant atoms (e.g.,
curve C.sub.1) and alloying atoms (e.g., curve C.sub.2) is more
uniformly redistributed in the region 202. Also, the dopant
concentration between the region 202 and the substrate bulk
material 221 has a sharply defined boundary (i.e., a "hyper-abrupt"
junction) and thus minimizes the unwanted diffusion into the
substrate bulk material 221. In the embodiment, discussed above, in
which damage is induced into the substrate 10 to improve the
melting point contrast the concentration of defects (e.g., curve
C.sub.2) after resolidification will preferably drop to a
negligible level.
Thermal Isolation Techniques
[0050] In another embodiment, the various thermal properties of
different regions of the formed device are tailored to
preferentially cause the melting in one region versus another
region. In one aspect, the melting point contrast is created by
forming different regions of the device with materials that have
different thermal conductivities (k). It should be noted that heat
transferred by conduction is governed by the equation:
Q=kA.DELTA.T/.DELTA.x
in which Q is the time rate of heat flow through a body, k is the
conductivity constant dependent on the nature of the material and
the material temperature, A is the area through which the heat
flows, .DELTA.x is the thickness of the body of matter through
which the heat is passing, and .DELTA.T is the temperature
difference through which the heat is being transferred. Therefore,
since k is a property of the material the selection or modification
of the material in various regions of the substrate can allow one
to control the heat flow into and out-of the different regions of
the substrate to increase the melting point contrast for the
various regions. In other words, where the material in a region of
a substrate has a higher thermal conductivity than the material in
other regions, it will lose more thermal energy via conductive
losses during a laser anneal process, and, hence, will not reach
the same temperatures that another region that has a lower thermal
conductivity will reach. The regions in intimate contact with the
higher thermally conductive regions can be prevented from melting,
while other regions in intimate contact with lower thermal
conductivity regions will reach their melting point during the
laser anneal process. By controlling the thermal conductivity of
the various regions of the electronic device 200 the melting point
contrast can be increased. The creation of regions having varying
thermal conductivities may be performed by performing conventional
deposition, patterning and etching techniques in various underlying
layers of the electronic device 200 to create these regions having
different thermal conductivities. The underlying layers having
differing thermal conductivities may be formed by use of
conventional chemical vapor deposition (CVD) processes, atomic
layer deposition (ALD) processes, implant processes, and epitaxial
deposition techniques.
[0051] FIG. 2D illustrates a side view of the electronic device 200
that is has a buried region 224 that has a lower thermal
conductivity than the substrate bulk material 221. In this case the
radiation "B" emitted from an energy source, is absorbed at the
surface 205 of the substrate and is conducted through the substrate
10, so that the heat flow (Q.sub.1) in the region above (e.g.,
doped region 201A) the buried region 224 is less than the heat flow
(Q.sub.2) from an area that doesn't have the lower conductivity
buried layer. Therefore, since the heat lost from the region above
the buried region 224 is less than the other regions of the
substrate, this area will reach a higher temperature than the other
regions of the device. By controlling the amount of energy
delivered by the energy source 20 the temperature in the regions
above the buried layer can be raised to a level that will cause it
to preferentially melt versus the other regions. In one aspect, the
buried region 224 is made of an insulative material, such as a
silicon dioxide (SiO.sub.2), silicon nitride (SiN), germanium (Ge),
gallium arsenide (GaAs), combinations thereof or derivatives
thereof. So although the actual melting point of the substrate
material in the region that is to be melted is not altered, there
is still a quantifiable and repeatable contrast in thermal behavior
from other regions of the substrate surface that allows it to be
selectively melted. In another embodiment, the buried region 224
may have a higher conductivity than the substrate bulk material
221, which may then allow the areas that do not have the buried
layer to preferentially melt versus the regions above the buried
layer.
Modification of Surface Properties
[0052] In one embodiment, the properties of the surface over the
various regions 202 of the substrate 10 are altered to change the
melting point contrast between one or more desired regions. In one
aspect, the emissivity of the surface of the substrate in a desired
region is altered to change the amount of energy transferred from
the substrate surface during processing. In this case, a region
that has a lower emissivity than another region will achieve a
higher processing temperature due to its inability to reradiate the
absorbed energy received from the energy source 20. When performing
an anneal process that involves the melting of the surface of a
substrate, the processing temperatures achieved at the surface of
the substrate can be quite high (e.g., .about.1414.degree. C. for
silicon), and thus the effect of varying the emissivity can have a
dramatic effect on the melting point contrast, since radiative heat
transfer is the primary heat loss mechanism. Therefore, variations
in the emissivity of different regions of the substrate surface may
have a significant impact on the ultimate temperatures reached by
the various regions of the substrate. Regions with low emissivity
may be elevated above the melting point during the annealing
process, while regions with high emissivity that have absorbed the
same amount of energy may remain substantially below the melting
point. Varying the emissivity of the various surfaces, or
emissivity contrast, may be accomplished via selective deposition
of a low- or high-emissivity coating onto the substrate surface,
and/or modifying the surface of the substrate (e.g., surface
oxidation, surface roughening).
[0053] In one embodiment, the reflectivity of the surface of the
substrate in one or more regions is altered to change the amount of
energy absorbed when the substrate 10 is exposed to energy from the
energy source. By varying the reflectivity of the surface of the
substrate the amount of energy absorbed and thus the maximum
temperature achieved by the substrate in a region at and below the
substrate surface will differ based on the reflectivity. In this
case a surface having a lower reflectivity will more likely melt
than another region that has a higher reflectivity. Varying the
reflectivity of the surface of the substrate may be accomplished
via selective deposition of a low- or high-reflectance coating onto
the substrate surface, and/or modifying the surface of the
substrate (e.g., surface oxidation, surface roughening). A highly
absorbing (non-reflective) coating may be selectively applied to
regions that are intended to be melted during the anneal
process.
[0054] FIG. 2E illustrates one embodiment in which a coating 225 is
selectively deposited, or uniformly deposited and then selectively
removed, to leave a layer that has a different emissivity and/or
reflectivity than the other regions on the surface 205 of the
substrate 10. In this case the heat flow (Q.sub.1) in the doped
region 201A, below the coating 225, can be adjusted based on the
properties of the coating versus the energy absorbed (Q.sub.2) in
other regions of the substrate. In this way the heat loss (Q.sub.3)
or reflected from the coating 225 can be varied versus the heat
lost (Q.sub.4) from the other regions. In one aspect, a carbon
containing coating is deposited on the substrate surface by use of
a CVD deposition process.
[0055] FIG. 2F illustrates one embodiment in which a coating 226
that alters the optical properties of the surface of the substrate
(e.g., emissivity, reflectivity) is deposited over the surface of
the substrate, for example over the device shown in FIG. 2A, and
then an amount of material is removed to create regions that have
differing optical properties. For example, as shown in FIG. 2F, the
coating 226 has been removed from the surface of the gate 215, thus
leaving the surface of the coating 226 and the surface 205 of the
gate exposed to the incident radiation "B." In this case, the
coating 226 and the surface 205 of the gate have different optical
properties, such as a different emissivity and/or a different
reflectivity. The removal process used to expose or create regions
that have differing optical properties may be performed by use of a
conventional material removal process, such as a wet etch or
chemical mechanical polishing (CMP) process. In this case the
absorption and heat flow (Q.sub.1) in the doped regions 201A-201B,
below the coating 226, can be adjusted based on the properties of
the coating versus the absorption and heat flow (Q.sub.2) in gate
215 region of the substrate. In this way the heat loss (Q.sub.3) or
reflected from the coating 226 can be varied versus the heat loss
(Q.sub.4) or reflected from the gate 215 region.
[0056] In one embodiment, the coating 226 contains one or more
deposited layers of a desired thickness that either by themselves
or in combination modify the optical properties (e.g., emissivity,
absorbance, reflectivity) of various regions of the substrate that
are exposed to one or more wavelengths of incident radiation. In
one aspect, the coating 226 contains layers that either by
themselves or in combination preferentially absorb or reflect one
or more wavelengths of the incident radiation "B." In one
embodiment, the coating 226 contains a dielectic material, such as
fluorosilicate glass (FSG), amorphous carbon, silicon dioxide,
silicon carbide, silicon carbon germanium alloys (SiCGe), nitrogen
containing silicon carbide (SiCN), a BLOk.TM. dielectric material
made by a process that is commercially available from Applied
Materials, Inc., of Santa Clara, or a carbon containing coating
that is deposited on the substrate surface by use of a chemical
vapor deposition (CVD) process or atomic layer deposition process
(ALD) process. In one aspect, coating 226 contains a metal, such as
but not limited to titanium (Ti), titanium nitride (TiN), tantalum
(Ta), cobalt (Co), or ruthenium (Ru).
[0057] It should be noted that one or more of the various
embodiments, discussed herein, may be used in conjunction with each
other in order to further increase process window. For example, a
selectively deposited, light absorbing coating may be used in
conjunction with doping of certain defined regions to broaden the
process window of the anneal process.
Tuning the Energy Source Output to Achieve Preferential Melting
[0058] As noted above, the energy source 20 is generally adapted to
deliver electromagnetic energy to preferentially melt certain
desired regions of the substrate 10. Typical sources of
electromagnetic energy include, but are not limited to an optical
radiation source (e.g., laser (UV, IR, etc. wavelengths)), an
electron beam source, an ion beam source, and/or a microwave energy
source. In one embodiment of the invention, the energy source 20 is
adapted to deliver optical radiation, such as a laser, to
selectively heat desired regions of a substrate to the melting
point.
[0059] In one aspect, the substrate 10 is exposed to a pulse of
energy from a laser that emits radiation at one or more appropriate
wavelengths, and the emitted radiation has a desired energy density
(W/cm.sup.2) and/or pulse duration to enhance preferential melting
of certain desired regions. For laser annealing processes performed
on a silicon containing substrate, the wavelength of the radiation
is typically less than about 800 nm. In either case, the anneal
process generally takes place on a given region of the substrate
for a relatively short time, such as on the order of about one
second or less. The desired wavelength and pulse profile used in an
annealing process may be determined based on optical and thermal
modeling of the laser anneal process in light of the material
properties of the substrate.
[0060] FIGS. 4A-4D illustrate various embodiments in which the
various attributes of the pulse of energy delivered from an energy
source 20 to an anneal region 12 (FIG. 1) is adjusted as a function
of time to achieve improved melting point contrast, and improve the
anneal process results. In one embodiment, it is desirable to vary
the shape of a laser pulse as a function of time, and/or vary the
wavelengths of the delivered energy to enhance the heat input into
regions of the substrate intended to be melted and minimize the
heat input into other regions. In one aspect, it may also be
desirable to vary the energy delivered to the substrate.
[0061] FIG. 4A graphically illustrates a plot of delivered energy
versus time of a single pulse of electromagnetic radiation (e.g.,
pulse 401) that may be delivered from the energy source 20 to the
substrate 10 (see FIG. 1). The pulse illustrated in FIG. 4A is
generally a rectangular pulse that delivers a constant amount of
energy (E.sub.1) for the complete pulse duration (t.sub.1).
[0062] In one aspect, the shape of the pulse 401 may be varied as a
function of time as it is delivered to the substrate 10. FIG. 4B
graphically illustrates a plot of two pulses 401A, 401B of
electromagnetic radiation that may be delivered from one energy
source 20 to the substrate 10 that have a different shape. In this
example, each pulse may contain the same total energy output, as
represented by the area under each curve, but the effect of
exposing regions of the substrate 10 to one pulse versus another
pulse may improve the melting point contrast experienced during the
anneal process. Therefore, by tailoring the shape, peak power level
and/or amount of energy delivered in each pulse the anneal process
may be improved. In one aspect, the pulse is gaussian shaped.
[0063] FIG. 4C graphically illustrates a pulse of electromagnetic
radiation (e.g., pulse 401) that is trapezoidal in shape. In this
case, in two different segments (e.g., 402 and 404) of the pulse
401 the energy delivered is varied as a function of time. While
FIG. 4C illustrates a pulse 401 profile, or shape, in which the
energy versus time varies in a linear fashion, this is not intended
to be limiting as to the scope of the invention since the time
variation of the energy delivered in a pulse may, for example, have
a second degree, third degree, or fourth degree shaped curve. In
another aspect, the profile, or shape, of the energy delivered in a
pulse as a function of time may be a second order, a third order,
or exponential-shaped curve. In another embodiment, it may be
advantageous to use a pulse having different shapes (e.g.,
rectangular and triangular modulation pulse, sinusoidal and
rectangular modulation pulse, rectangular, triangular and
sinusoidal modulation pulse, etc.) during processing to achieve the
desired annealing results.
[0064] Depending on the properties of the various regions of the
device the shape of the delivered pulse of electromagnetic
radiation may be tailored to improve the anneal process results.
Referring to FIG. 4B, for example, in some situations in which
various regions of a substrate that are to be melted during the
anneal process are thermally isolated from other regions of the
device by areas that have a low thermal conductivity, use of a
pulse having a shape similar to pulse 401B may be advantageous. A
pulse having a longer duration may be advantageous, since the more
thermally conductive material regions of the substrate will have
more time to dissipate the heat by conduction, while the regions
that are to be melted are more thermally isolated thus allowing the
temperature in the regions that are to be melted to rise to a
melting point temperature. In this case the duration, peak power
level and total energy output of the pulse can be appropriately
selected, so that the areas that are not intended to melt will not
reach their melting point. The process of tailoring the shape of
the pulse may also be advantageous when surfaces of varying
emissivity are used to create a melting point contrast.
[0065] Referring to FIG. 4C, in one embodiment, the slope of the
segment 401, the shape of the segment 401, the shape of the segment
403, the time at a power level (e.g., segment 403 at the energy
level E.sub.1), the slope of the segment 404, and/or the shape of
the segment 404 are adjusted to control the annealing process. It
should be noted that it is generally not desirable to cause the
material within the annealed regions to vaporize during processing
due to particle and process result variability concerns. It is
therefore desirable to adjust the shape of the pulse of energy to
rapidly bring the temperature of the annealed region to it melting
point without superheating the region and causing vaporization of
the material. In one embodiment, as shown FIG. 4G, the shape of the
pulse 401 may adjusted so that it has multiple segments (i.e.,
segments 402, 403A, 403B, 403C, and 404) are used to rapidly bring
the anneal region to its melting point and then hold the material
in a molten state for a desired period of time (e.g., t.sub.1),
while preventing vaporization of material within the annealing
region. The length of time, the shape of the segments and the
duration of each of the pulse segments may vary as the size, melt
depth, and the material contained within the annealing regions is
varied.
[0066] In another aspect, multiple wavelengths of radiant energy
may be combined to improve the energy transfer to the desired
regions of the substrate to achieve an improved melting point
contrast, and/or improve the anneal process results. In one aspect,
the amount of energy delivered by each of the combined wavelengths
is varied to improve the melting point contrast, and improve the
anneal process results. FIG. 4D illustrates one example in which a
pulse 401 contains two wavelengths that may deliver differing
amounts of energy per unit time to a substrate 10 in order to
improve the melting point contrast and/or improve the anneal
process results. In this example, a frequency F1 is applied to the
substrate at a constant level over the period of the pulse and
another frequency F2 is applied to the substrate 10 at a constant
level for most of the period except for a portion that peaks for a
period of time during the period of the pulse.
[0067] FIG. 4E graphically illustrates a plot of a pulse 401 that
has two sequential segments that deliver energy at two different
frequencies F3 and F4. Therefore, since various regions of the
substrate may absorb energy at different rates at different
wavelengths the use of pulse that contains multiple wavelengths
that can deliver variable amounts of energy, as shown in FIGS. 4D
and 4E, may be advantageous to achieve desirable annealing process
results.
[0068] In one embodiment, two or more pulses of electromagnetic
radiation are delivered to a region of the substrates at differing
times so that the temperature of regions on the substrate surface
can be easily controlled. FIG. 4F graphically illustrates a plot of
two pulses 401A and 401B that are delivered a varying distance in
time apart, or period (t), to selectively melt certain regions on
the surface of a substrate. In this configuration, by adjusting the
period (t) between the subsequent pulses, the peak temperature
reached by regions on the substrate surface can be easily
controlled. For example, by reducing the period (t), or frequency,
between pulses the heat delivered in the first pulse 401A has less
time to dissipate the heat before the second pulse 401B is
delivered, which will cause the peak temperature achieved in the
substrate to be higher than when the period between pulses is
increased. In this way by adjusting the period the energy and melt
temperature can be easily controlled. In one aspect, it may
desirable to assure that each pulse by itself does not contain
enough energy to cause the substrate to reach the melt temperature,
but the combination of the pulses causes the regions 202 to reach
the melt temperature. This process of delivering multiple pulses,
such as two or more pulses, will tend to reduce the thermal shock
experienced by the substrate material versus delivering a single
pulse of energy. Thermal shock can lead to damage of the substrate
and generate particles that will create defects in subsequent
processing steps performed on the substrate.
[0069] Referring to FIG. 4F, in one embodiment, two or more energy
sources, such as lasers, are operated in sequence so as to shape
the thermal profile of the surface of a substrate as a function of
time. For example, one laser or an array of lasers may deliver a
pulse 401A that elevates the surface of the substrate to a
temperature T.sub.o for a time t.sub.1. Prior to or at the end of
t.sub.1, a second pulse 402B is delivered from a second laser, or
from multiple lasers operating in tandem, that brings the substrate
temperature to a temperature T.sub.1 for a time t.sub.2. The
thermal profile can thus be shaped by controlling the sequencing
pulses of energy delivered from the multiple lasers. This process
may have thermal processing benefits, such as but not limited to
the application of controlling dopant diffusion and the direction
of the dopant diffusion.
Electromagnetic Radiation Pulses
[0070] For the purpose of delivering sufficient electromagnetic
radiation (light) to the surface of a silicon containing substrate,
or substrate comprised of another material requiring thermal
processing, the following a process controls may be used.
[0071] In one embodiment, two or more electromagnetic energy
sources, such as lasers, are operated in sequence so as to shape
the thermal profile of the surface being thermally processed and
where the lasers are operated in such a manner as to correct for
pulse-to-pulse energy variations. In one aspect, the source 20,
schematically illustrated in FIGS. 1 and 9, contains two or more
electromagnetic energy sources, such as but not limited to an
optical radiation source (e.g., laser), an electron beam source, an
ion beam source, and/or a microwave energy source. The
pulse-to-pulse energy from a device such as a pulsed laser may have
a percent variation of each pulse. The variation in pulse energy
may be unacceptable for the substrate thermal process. To correct
for this pulse variation, one or more laser(s) deliver a pulse that
elevates the substrate temperature. Then an electronic controller
(e.g., controller 21 in FIG. 1), which is adapted to monitor the
pulses delivered and the energy, or rise time, of the pulse that is
in delivery, then is used to calculate the amount of energy
required to "trim" or adjust the thermal profile (e.g., temperature
of a region of the substrate as a function of time) so that it is
within process targets and command a second smaller laser or series
of smaller lasers to deliver the final energy to complete the
thermal processing. The electronic controller generally uses one or
more conventional radiation detectors to monitor the energy and/or
wavelength of pulses delivered to the substrate. The smaller lasers
may also have peak-to-peak variation in pulse output energy, but
because they deliver substantially less energy per pulse than the
initial pulse (or pulses) at the start of the surface treatment
this error will generally be within process limits. The electronic
controller is thus adapted to compensate for the variation in
energy delivered by a pulse, and thus assure that a desired energy
level is delivered during the thermal process.
[0072] In one aspect, the two or more energy sources, discussed
above, may also be implemented using a single color (wavelength) of
laser light with a bandwidth of color frequency, multiple
wavelengths, single or multiple temporal and spatial laser modes,
and polarization states.
[0073] The output of the laser or lasers will likely not have the
correct spatial and temporal energy profile for delivery to the
substrate surface. Therefore, a system using microlenses to shape
the output of the lasers is used to create a uniform spatial energy
distribution at the substrate surface. Selection of glass types and
geometry of the microlenses may compensate for thermal lensing
effects in the optical train necessary for delivering the pulsed
laser energy to the substrate surface.
[0074] High frequency variations in pulse energy at the substrate
surface, known as speckle, is created by neighboring regions of
constructive and destructive phase interference of the incident
energy. Speckle compensation may include the following: a surface
acoustic wave device for rapidly varying the phase at the substrate
such that this rapid variation is substantially faster than the
thermal processing time of the laser pulse or pulses; pulse
addition of laser pulses; alternating polarization of laser pulses
for example, delivery of multiple simultaneous or delayed pulses
that are linearly polarized but have their polarization states
(e-vectors) in a nonparallel condition.
Thermal Stabilizing Structures Formed on a Patterned Substrate
[0075] In one embodiment, as shown in FIGS. 5A-5C, a homogenizing
layer (item 110 in FIG. 5B) is deposited on a surface of the
substrate to reduce the variations in the depth, or volume, of the
silicon region 112 melted when surface of the substrate is exposed
to electromagnetic energy 150 delivered from an electromagnetic
radiation source (not shown). The variation in the depth, or
volume, of the region melted is affected by the variations in the
mass density of the various regions of the patterned substrate, the
absorption coefficient of the material on which the radiant energy
impinges, and the various physical and thermal properties of the
material (e.g., thermal conductivity, heat capacity, thickness of
the material). In general the electromagnetic radiation source is
designed to deliver electromagnetic energy to the surface of
substrate to thermally process or anneal portions of the substrate
surface. Typical electromagnetic radiation sources may include, but
are not limited to optical radiation sources (e.g., lasers),
electron beams, ion beams, or microwave sources.
[0076] The device structure formed on a surface 102 of the
substrate 100 illustrated in FIGS. 5A-5C and 6A-6C are not intended
to be limiting as to the scope of the invention described herein,
since, for example, the silicon region 112 (e.g., source or drain
regions in a MOS device) can be a raised or lowered relative to the
position of the features 101 (e.g., gate in a MOS device) without
varying from the scope of the invention described herein. As
semiconductor device sizes decrease the position and geometry of
structural elements of the devices formed on the surface of a
substrate vary to improve device manufacturability or device
performance.
[0077] FIG. 5A illustrates a cross-sectional view of a substrate
100 that has a plurality of features 101 and silicon regions 112
formed on a surface 102 of the substrate 100. As shown in FIG. 5A
the surface 102 has multiple features 101 that are laterally spaced
a varying distance apart. In one aspect, the features 101 are
"gates" and the silicon regions 112 are "source and drain regions"
used to form a metal oxide semiconductor (MOS) device on the
substrate surface. In the configuration shown in FIG. 5A the
incident electromagnetic energy 150 impinges the surface 102
causing the some regions of the surface 102 of the substrate to
absorb the incident energy and possibly form melt regions 113. The
physical, thermal and optical properties of the various materials
exposed to the incident electromagnetic energy 150 will determine
whether the various areas on the surface 102 will melt upon
exposure to the delivered energy. It is believed that when the
features 101 are polysilicon gates the absorption energy from a
laser, at wavelengths <800 nm, will be significantly less than
the energy absorbed by the silicon regions 112 that contain N-type
or P-type doped silicon, such as found in a source or drain region
of a MOS device. Therefore, it is believed that due to the heat
capacity and thermal mass of the features 101, and their relative
position to the silicon regions 112, the delivered electromagnetic
energy 150 in the areas adjacent to the features 101 will remain
cooler due to the diffusion of heat away from the melt region 113.
The loss of heat to the features 101 will reduce the energy
available to form the melt region 113 and thus affect the depth
and/or volume, of the melt region 113. Therefore, there is a need
for a way to reduce the variation in pattern density on the surface
of the substrate.
[0078] FIG. 5B illustrates a cross-sectional view of a substrate
100 that has a plurality of features 101, silicon regions 112 and a
homogenizing layer 120 formed on a surface 102 of the substrate
100. FIG. 5B is similar to FIG. 5A except the addition of the
homogenizing layer 120. In general the homogenizing layer 120 is
used to make the heat capacity of the surface 102 of the substrate
100 more uniform. In one embodiment, the thickness and material
from which the homogenizing layer 120 is formed is selected to
balance the heat capacity of the surface of the substrate to reduce
the effect of a varying mass density across the substrate surface
and thus reduce the variation in the depth and/or volume of the
melt region 113. In general, the homogenizing layer 120 material is
selected so that it will not melt during the subsequent annealing
process and it can be selectively removed from the surface of the
substrate after the annealing processes have been performed. In one
aspect, the homogenizing layer 120 is a material that is similar in
composition to the material that the features 101 are made from,
such as, for example, a polysilicon containing material. In another
aspect, the homogenizing layer 120 is a silicon carbide containing
material or a metal (e.g., titanium, titanium nitride, tantalum,
tungsten).
[0079] Preferably, the thickness of the homogenizing layer 120
(e.g., d.sub.1) is selected so that the heat capacity of the device
structure is uniform. In one aspect, the thickness, d.sub.1 of the
homogenizing layer 120 is governed by:
d.sub.1=(.alpha..sub.1).sup.0.5.times.[d.sub.2/((.alpha..sub.2).sup.0.5)-
]
where [0080] d.sub.2=Thickness of the features 101 (see FIG. 5B)
[0081] .alpha..sub.1=.kappa..sub.1/(.rho..sub.1C.sub.p1) and [0082]
.alpha..sub.2=.kappa..sub.2/(.rho..sub.2C.sub.p2) where
.kappa..sub.1 equals the thermal conductivity of the material used
to form the homogenizing layer, .rho..sub.1 equals the mass density
of the material used to form the homogenizing layer 120, C.sub.p1
equals heat capacity of the material used to form the homogenizing
layer 120, .kappa..sub.2 equals the thermal conductivity of the
material used to form the features 101, .rho..sub.2 equals the mass
density of the material used to form the features 101, and C.sub.p2
equals the heat capacity of the material used to form the features
101.
[0083] FIG. 6A Illustrates a series of method steps that may be
used to form the homogenizing layer 120 on a surface 102 of the
substrate 100. In step 190, shown in FIGS. 6A and 6B, the
homogenizing layer 120 is deposited over the surface 102 (e.g.,
features 101) of the substrate 100 by use of a conventional
deposition process, such as a chemical vapor deposition (CVD),
plasma enhanced CVD, atomic layer deposition (ALD), plasma enhanced
ALD, or spin coating type deposition process. In step 192, shown in
FIGS. 6A and 6C, the surface 102 of the substrate 100 that contains
the homogenizing layer 120 is planarized using a chemical
mechanical polishing (CMP) process. In step 194, shown in FIGS. 6A
and 6D, the homogenizing layer is then selectively etched using a
selective material removal process, such as a wet etch or dry etch
type process until a desired thickness d.sub.1 is achieved. Next,
an amount of incident electromagnetic energy can be delivered to
the surface of the substrate surface to cause the uniform
annealing/melting of the material contained in the melt regions
113.
Absorption Layer Over Homogenous Layer
[0084] FIG. 5C is a cross-sectional view of a substrate 100 that
contains the device illustrated in FIG. 5B with an added layer 125
deposited thereon to adjust the optical properties of various
regions on the surface of the substrate. In one aspect, the layer
125 is added to improve the absorption of the electromagnetic
energy 150 delivered to various regions of the substrate 100. In
one embodiment, the layer 125 is the same as the coating 225 or the
layer 226 described above. As shown in FIG. 5C the layer 125 is
preferentially formed on the homogenizing layer 120 to improve the
selectivity of energy delivered to the silicon regions 112. The
desired thickness of the layer 125 may vary as the wavelength of
the delivered electromagnetic energy 150 varies.
[0085] Referring to FIGS. 6A-6G, in one embodiment, after
performing steps 190 through 194 the steps 196 and 198 may be used
to form a selectively deposited absorbing layer 125. In step 196,
shown in FIGS. 6E and 6F, the layer 125 is deposited over the
features 101 and the homogenizing layer 120 formed in steps
190-194, discussed above. In step 198, shown in FIGS. 6E and 6G,
the layer 125 is removed from the top surface of the features 101
by performing a material removal step, such as a planarization
process typically completed by use of a chemical mechanical
polishing (CMP) process. In one aspect, the deposited layer 125 is
used to alter the melting point contrast between one or more
desired regions on the substrate surface by allowing a differing
amount of heat to be absorbed and transmitted to the melt regions
103 versus the regions between the melt regions, which are not in
direct contact with the layer 125 and the homogenizing layer
120.
Diffraction Grating
[0086] One issue that arises when features of different sizes,
shapes and distances apart are exposed to electromagnetic radiation
is that depending on the wavelength of the electromagnetic
radiation the amount of energy applied to the features may
experience constructive or destructive interference due to
diffraction effects that undesirably vary the amount of energy, or
energy density (e.g., Watts/m.sup.2), delivered to a desired
region. Referring to FIG. 7, the spacing of the features 101 may
differ such that the wavelength of the incident radiation varies
across the surface causing a variation in energy density delivered
across the surface 102 of the substrate 100.
[0087] In one embodiment, as shown in FIG. 7, a layer 726 is grown
to a thickness that exceeds the height of all of features 101 to
reduce the diffraction effect created by the irregular spacing
between devices (e.g., features 101) formed on the surface of the
substrate. In one aspect, not shown, the surface 720 of the layer
726 is further planarized (e.g., CMP process) to reduce any
inherent topographical variation in the surface 720 of the
substrate 10. In general, it is desirable to reduce the
topographical variation on the surface of the substrate to have a
peak-to-valley variation (see "PV" in FIG. 7) across the surface of
the substrate of less than about a quarter of the wavelength
(<1/4.lamda.) of the energy delivered during the annealing
process. It is also desirable to have the average period between
peaks (see "PP" in FIG. 7) across the surface of the substrate
greater than about five times the wavelength (e.g., >5.lamda.)
of the energy delivered during the annealing process. In one
example, when using an 800 nm wavelength laser source, it is
desirable to reduce the inherent topographical variation in the
surface 720 to an peak-to-valley variation of less than about 200
nm and a period between peak variation greater than about 4000 nm.
In one aspect, the layer 726 is a carbon layer deposited by a CVD
deposition process or a material discussed in conjunction with
layer 125, coating 225, and layer 226 discussed above.
[0088] In one embodiment, the design of the devices formed on the
surface of a substrate that is exposed to incident electromagnetic
radiation is specifically designed and arranged so that a desired
diffraction pattern is created to improve the melting point
contrast between different zones. The physical arrangement of the
various features are thus tailored for a desired wavelength, or
wavelengths, of the incident radiation "B" (FIG. 7) used to anneal
the surface of the substrate.
Forming Amorphous Region in a Substrate
[0089] In one embodiment, one or more processing steps are
performed to selectively form an amorphous region 140 in an
originally single crystal or polycrystalline material to reduce the
amount of damage created during subsequent implantation processing
steps and increase the melting point contrast of the amorphous
region 140 relative to other areas of the substrate. Implanting
dopants in an amorphous region, such as an amorphous silicon layer
will tend to homogenize the implantation depth of the desired
dopant at a fixed ion energy, due to lack of density variation
across the various planes found in crystalline lattice structures
(e.g., single crystal silicon). The implantation in an amorphous
layer will tend to reduce the crystalline damage commonly found in
traditional implantation processes in crystalline structures.
Therefore, when the amorphous region 140 is subsequently re-melted
using an anneal type process, as discussed above, the formed region
can be recrystallized with a more homogenous doping profile and
with reduced number of defects. The re-melting process also removes
any damage created from the implant process. The formation of the
amorphous region 140 will also reduced the melting point of the
affected regions, which can thus improve the melting point contrast
between the amorphous region 140 and the adjacent single crystal
regions 141.
[0090] In one embodiment, a short dose of energy (item "B" in FIG.
8) is delivered to a substrate 10 to selectively modify and form an
amorphous silicon layer in a desired region (e.g., amorphous region
140). In one aspect, a pulse, or dose, of electromagnetic energy is
delivered to the desired region for a sufficiently short period of
time to cause rapid melting and cooling of the affected amorphous
region 140 to produce an amorphous region in the substrate. In this
case the pulse of energy is for such a short duration that it
produce a high regrowth velocity in the heated region to produce an
amorphous region. In one aspect, the re-growth velocity in the
heated region is greater than about 12 m/sec.
[0091] In one aspect, a pulse of energy is delivered to a desired
region of a silicon substrate for period of less than about
10.sup.-8 seconds. In this aspect, the pulse of energy may be
delivered from a laser that delivers a peak power greater than
10.sup.9 W/cm.sup.2, and preferably in a range between about
10.sup.9 and about 10.sup.10 W/cm.sup.2 for a period of less than
about 10.sup.-8 seconds. In one aspect, the power, pulse duration,
shape of the delivered dose to create the amorphous silicon layer
may be varied to achieve an amorphous region 140 of a desired size,
shape and depth. In one aspect, the wavelength of the delivered
dose of energy is selected or varied to achieve a desired melt
profile. In one aspect, the wavelength may be in the UV or IR
wavelengths. In one aspect, the wavelength of the laser may be less
than about 800 nm. In another aspect, the wavelength may be about
532 nm or about 193 nm.
[0092] In one embodiment, a mask is used to preferentially form the
amorphous areas in various regions of the substrate surface.
Electromagnetic Radiation Delivery
[0093] FIG. 9 is a cross-sectional view of a region of a processing
chamber that illustrates one embodiment in which an energy source
20 is adapted to deliver an amount of energy to an anneal region 12
of the substrate 10 from the backside surface 901 to preferentially
melt certain desired regions within the anneal region 12. In one
aspect, one or more defined regions of the substrate, such as
anneal region 12, are exposed to the radiation from the energy
source 20 at any given time. In one aspect, multiple areas of the
substrate 10 are sequentially exposed to a desired amount of energy
delivered through the backside surface 901 from the energy source
20 to cause the preferential melting of desired regions of the
substrate. In one aspect, the anneal region 12 is sized to match
the size of the die (e.g., item # 13 in FIG. 1), or semiconductor
devices, that are formed on the top surface 902 of the substrate
10. In one aspect, the boundary of the anneal region 12 is aligned
and sized to fit within the "kurf" or "scribe" lines that define
the boundary of each die. Therefore, the amount of process
variation, due to the varying amount of exposure to the energy from
the energy source 20 is minimized, since any overlap between the
sequentially placed anneal regions 12 can be minimized. In one
example, the anneal region 12 is a rectangular region that is about
22 mm by about 33 mm in size.
[0094] In one embodiment, the substrate 10 is positioned in a
substrate supporting region 911 formed on a substrate support 910
that has an opening 912 that allows the backside surface 901 of the
substrate 10 to receive energy delivered from the energy source 20.
In this configuration the radiation "B" emitted from the energy
source 20 to heat regions 903 that are adapted to absorb a portion
of the emitted energy. The energy source 20 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. In one aspect, the
substrate 10 is exposed to a pulse of energy from a laser that
emits radiation at one or more appropriate wavelengths for a
desired period of time. In one aspect, pulse of energy from the
energy source 20 is tailored so that the amount of energy delivered
across the anneal region 12 and/or the amount of energy delivered
over the period of the pulse is optimized to enhance preferential
melting of certain desired areas. In one aspect, the wavelength of
the laser is tuned so that a significant portion of the radiation
is absorbed by a silicon layer disposed on the substrate 10. For
laser anneal process performed on a silicon containing substrate,
the wavelength of the radiation is typically less than about 800
nm, and can be delivered at deep ultraviolet (UV), infrared (IR) or
other desirable wavelengths. In either case, the anneal process
generally takes place on a given region of the substrate for a
relatively short time, such as on the order of about one second or
less.
[0095] In one aspect, the wavelength of the emitted radiation from
the energy source 20 is selected so that the bulk material from
which the substrate is formed is more transparent to the incident
radiation than the areas near the top surface 902 that are to be
preferentially melted by the exposure of the incident emitted
radiation. In one aspect, the regions that are to be preferentially
melted contain a material that absorbs an amount of the energy
delivered through the backside of the substrate, such as a dopant
material or ionizing crystal damage (e.g., crystal defects, Frenkel
defects, vacancies) created during the implantation process. In
general the dopant materials may be boron, phosphorous, or other
commonly used dopant material used in semiconductor processing. In
one embodiment, the bulk material from which the substrate is
formed is a silicon containing material and the wavelength of the
emitted radiation is greater than about 1 micrometer. In another
aspect, the energy source 20 contains a CO.sub.2 laser that is
adapted to emit principal wavelength bands centering around 9.4 and
10.6 micrometers. In yet another aspect, the energy source 20 is
adapted to deliver wavelengths in the infrared region, which is
generally between about 750 nm and about 1 mm.
[0096] In one embodiment, an absorbing coating (not shown) is
disposed over the anneal region 12 on the substrate 10 so that the
incident radiation delivered through the back of the substrate can
be absorbed before it passes through the substrate. In one aspect,
the absorbing coating is a metal, such as titanium, titanium
nitride, tantalum, or other suitable metal material. In another
aspect, the absorbing coating is a silicon carbide material,
amorphous carbon material, or other suitable material that is
commonly used in semiconductor device manufacturing.
[0097] In one embodiment, two wavelengths of light are delivered to
the desired regions of the substrate, so that the first wavelength
of light is used to generate free carriers (e.g., electrons or
holes) in the substrate from dopants or other ionizing crystal
damage found in the desired annealing regions, so that the
generated free carriers will absorb the energy delivered through
the back of the substrate at a second wavelength. In one aspect,
the first wavelength is the wavelength of "green light" (e.g.,
about 490 nm to about 570 nm) and/or shorter wavelengths. In one
embodiment, the first wavelength is delivered at a desirable power
density (W/cm.sup.2) to the desired region of the substrate from a
second source 920 that is on the opposite side of the substrate
from the energy source 20, shown in FIG. 9. In another embodiment,
the two wavelengths (e.g., first and second wavelengths) are
delivered through the backside of the substrate from the source 20.
In yet another embodiment, the two wavelengths (e.g., first and
second wavelengths) at desirable power densities (W/cm.sup.2) are
delivered through the backside of the substrate from two separate
sources of electromagnetic energy (not shown).
[0098] 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.
* * * * *