U.S. patent application number 09/982954 was filed with the patent office on 2002-04-25 for atomic layer doping apparatus and method.
Invention is credited to Doan, Trung T., Sandhu, Gurtej.
Application Number | 20020046705 09/982954 |
Document ID | / |
Family ID | 24621343 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020046705 |
Kind Code |
A1 |
Sandhu, Gurtej ; et
al. |
April 25, 2002 |
Atomic layer doping apparatus and method
Abstract
An improved atomic layer doping apparatus is disclosed as having
multiple doping regions in which individual monolayer species are
first deposited and then dopant atoms contained therein are
diffused into the substrate. Each doping region is chemically
separated from adjacent doping regions. A loading assembly is
programmed to follow pre-defined transfer sequences for moving
semiconductor substrates into and out of the respective adjacent
doping regions. According to the number of doping regions provided,
a plurality of substrates could be simultaneously processed and run
through the cycle of doping regions until a desired doping profile
is obtained.
Inventors: |
Sandhu, Gurtej; (Boise,
ID) ; Doan, Trung T.; (Boise, ID) |
Correspondence
Address: |
DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP
2101 L STREET NW
WASHINGTON
DC
20037-1526
US
|
Family ID: |
24621343 |
Appl. No.: |
09/982954 |
Filed: |
October 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09982954 |
Oct 22, 2001 |
|
|
|
09653553 |
Aug 31, 2000 |
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Current U.S.
Class: |
118/719 ;
257/E21.148 |
Current CPC
Class: |
H01L 21/2254 20130101;
H01L 21/6719 20130101; H01L 21/67213 20130101; H01L 21/67167
20130101; H01L 21/67207 20130101; H01L 21/67745 20130101 |
Class at
Publication: |
118/719 |
International
Class: |
C23C 016/00 |
Claims
What is claimed as new and desired to be protected by Letters
Patent of the United States is:
1. An atomic layer doping apparatus comprising: a first atomic
layer doping region for depositing a first dopant species on a
first substrate as a monolayer; a second atomic layer doping region
for diffusing said first dopant species in said first substrate,
said first and second doping regions being chemically isolated from
one another; and a loading assembly for moving said first substrate
from said first doping region to said second doping region, thereby
enabling deposition of a first atomic monolayer in said first
doping region, followed by diffusion of said first atomic monolayer
in said second doping region.
2. The doping apparatus of claim 1, wherein said first and second
doping regions are adjacent to one another and chemically
isolated.
3. The doping apparatus of claim 2, wherein said first and second
doping regions are chemically isolated from one another by a gas
curtain.
4. The doping apparatus of claim 3, wherein said gas curtain is
formed of an inert gas.
5. The doping apparatus of claim 2, wherein said first and second
doping regions are chemically isolated from one another by a
physical barrier having a closeable opening through which said
loading assembly can move a substrate.
6. The doping apparatus of claim 1, wherein said loading assembly
is further able to move said substrate from said second doping
region back to said first doping region.
7. The doping apparatus of claim 1 further comprising a plurality
of first and second atomic layer doping regions.
8. The doping apparatus of claim 7, wherein said plurality of first
and second doping regions are grouped in pairs of first and second
doping regions, so that at least said first substrate and a second
substrate can be treated simultaneously in respective pairs of
first and second doping regions.
9. The doping apparatus of claim 8 further comprising a third pair
of first and second atomic layer doping regions for processing a
third substrate in said third pair of first and second atomic layer
doping regions simultaneously with processing of said first and
second substrates.
10. The doping apparatus of claim 7, wherein said loading assembly
is located at the center of said doping regions.
11. The doping apparatus of claim 1 further comprising at least one
third atomic layer doping region.
12. The doping apparatus of claim 11, wherein said first, second,
and third doping regions are adjacent to one another and chemically
isolated.
13. The doping apparatus of claim 12, wherein said first, second,
and third doping regions are chemically isolated from one another
by a gas curtain.
14. The doping apparatus of claim 13, wherein said gas curtain is
formed of an inert gas.
15. The doping apparatus of claim 11, wherein said first, second,
and third doping regions are chemically isolated from one another
by a physical barrier having a closeable opening through which said
loading assembly can move a substrate.
16. The doping apparatus of claim 11, wherein said loading assembly
is further able to move sequentially said first substrate among
said first doping region, said second doping region, and said third
doping region.
17. The doping apparatus of claim 16, wherein said loading assembly
is further able to move sequentially another substrate among said
first doping region, said second doping region, and said third
doping region.
18. A method of operating an atomic layer doping apparatus, said
doping apparatus comprising a first doping region and a second
doping region, said first and second doping regions being
chemically isolated from one another, said method comprising the
steps of: positioning a wafer in said first doping region;
introducing a first dopant species into said first doping region
and depositing said first dopant species on said wafer as a first
atomic monolayer; moving said wafer from said first doping region
to said second doping region; and introducing dopants from said
first atomic monolayer into said wafer in said second doping
region.
19. The method of claim 18 further comprising the act of annealing
said wafer after said act of introducing said dopants into said
wafer.
20. The method of claim 18, wherein said act of introducing said
dopants into said wafer includes diffusion of said dopants.
21. The method of claim 18, wherein said act of introducing said
dopants into said wafer includes contacting said wafer with a
non-reactive plasma.
22. The method of claim 18 further comprising the act of moving
said wafer back and forth between said first and second doping
regions.
23. The method of claim 18 further comprising the act of moving
said wafer back to said first doping region and depositing said
first dopant species as a second atomic monolayer.
24. The method of claim 18, wherein said first and second doping
regions are adjacent to each other.
25. The method of claim 18 further comprising the act of
simultaneously processing at least two wafers among said first and
second doping regions and depositing a respective dopant species in
each of said doping regions.
26. The method of claim 18, wherein said least two wafers are
sequentially moved among said first and second doping regions.
27. A method of conducting atomic layer doping comprising the steps
of: depositing a first atomic monolayer including atoms of a dopant
species on a substrate in a first doping region; moving said
substrate from said first doping region to a second doping region,
which is chemically isolated from said first doping region; and
introducing said atoms of said dopant species into said wafer.
28. The method of claim 27, wherein said act of depositing said
first monolayer species further comprises introducing a first
dopant species into said first doping region.
29. The method of claim 27, wherein said act of introducing said
atoms of said dopant species into said wafer further comprises
introducing a non-reactive plasma into said second doping region
and contacting said non-reactive plasma with said first atomic
monolayer species.
30. The method of claim 27, wherein said act of introducing said
atoms of said dopant species into said wafer further comprises
heating said wafer so that said atoms diffuse into a surface region
of said wafer.
31. The method of claim 27 further comprising the act of annealing
said wafer.
32. The method of claim 27 further comprising the act of moving
said substrate back and forth between said first and second doping
regions.
33. The method of claim 27, wherein a plurality of first and second
doping regions are provided, and said method further comprising
depositing said first monolayer on respective substrates and
introducing atoms from said first monolayers into respective
substrates in respective pairs of first and second doping regions,
said first and second doping regions of each pair being adjacent to
one another.
34. The method of claim 33, wherein a plurality of substrates, each
of said plurality of substrates residing in respective regions, are
moved sequentially from said first doping regions to said second
doping regions.
35. A method of operating an atomic layer doping apparatus, said
doping apparatus comprising a plurality of doping regions, said
doping regions being chemically isolated from one another, said
method comprising the steps of: positioning a plurality of wafers
in respective doping regions; introducing a first dopant species
into some of said plurality of doping regions and depositing said
first dopant species on at least one of said plurality of wafers as
a first atomic monolayer, said first atomic monolayer comprising
dopant atoms of said first dopant species; moving said plurality of
wafers from said some of said plurality of doping regions to other
doping regions; and introducing a second gas species into said
other doping regions and contacting said second gas species on at
least one of said plurality of wafers to introduce said dopant
atoms into said at least one of said plurality of wafers.
36. The method of claim 35 further comprising the act of
sequentially moving said plurality of wafers through at least two
of said plurality of doping regions in accordance with a predefined
pattern.
37. The method of claim 35, wherein said second gas species is a
non-reactive plasma.
38. The method of claim 35 further comprising the act of annealing
said at least one of said plurality of wafers.
39. The method of claim 35 further comprising the act of
sequentially moving said plurality of wafers through all said
doping regions.
40. The method of claim 35 further comprising the act of
sequentially moving said plurality of wafers through predetermined
regions of said doping regions.
41. A method of conducting atomic layer doping comprising the steps
of: depositing a first atomic monolayer including atoms of a first
dopant species on a substrate in a first doping region; moving said
substrate from said first doping region to a second doping region,
which is chemically isolated from said first doping region, for
depositing a second monolayer including atoms of a second dopant
species on said substrate; and moving said substrate from said
second doping regions to a third doping region, which is chemically
isolated from said first and second doping regions, for introducing
said atoms of said first and second dopant species into said
wafer.
42. The method of claim 41, wherein said act of introducing said
atoms of said first and second dopant species into said wafer
further comprises introducing a non-reactive plasma into said third
doping region and contacting said non-reactive plasma with said
first and second atomic monolayer species.
43. The method of claim 41, wherein said act of introducing said
atoms of said first and second dopant species into said wafer
further comprises heating said wafer so that said atoms diffuse
into a surface region of said wafer.
44. The method of claim 41 further comprising the act of annealing
said wafer.
45. The method of claim 41 further comprising the act of
sequentially moving said substrate back and forth between said
first, second and third doping regions.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of semiconductor
integrated circuits and, in particular, to an improved method for
doping wafers.
BACKGROUND OF THE INVENTION
[0002] Incorporation of dopants or chosen impurities into a
semiconductor material, commonly known as doping, is well known in
the art. Thermal diffusion and ion implantation are two methods
currently used to introduce a controlled amount of dopants into
selected regions of a semiconductor material.
[0003] Doping by thermal diffusion is a two-step process. In the
first step, called predeposition, the semiconductor is either
exposed to a gas stream containing excess dopant at low temperature
to obtain a surface region saturated with the dopant, or a dopant
is diffused into a thin surface layer from a solid dopant source
coated onto the semiconductor surface. The predeposition step is
followed by the drive-in step, during which the semiconductor is
heated at high temperatures in an inert atmosphere so that the
dopant in the thin surface layer of the semiconductor is diffused
into the interior of the semiconductor, and thus the predeposited
dopant atoms are redistributed to a desired doping profile.
[0004] Ion implantation is preferred over thermal diffusion because
of the capability of ion implantation to control the number of
implanted dopant atoms, and because of its speed and
reproducibility of the doping process. The ion implantation process
employs ionized-projectile atoms that are introduced into solid
targets, such as a semiconductor substrate, with enough kinetic
energy (3 to 500 KeV) to penetrate beyond the surface regions. A
typical ion implant system uses a gas source of dopant, such as,
BF.sub.3, PF.sub.3, SbF.sub.3, or AsH.sub.3, for example, which is
energized at a high potential to produce an ion plasma containing
dopant atoms. An analyzer magnet selects only the ion species of
interest and rejects the rest of species. The desired ion species
are then injected into an accelerator tube, so that the ions are
accelerated to a high enough velocity to acquire a threshold
momentum to penetrate the wafer surface when they are directed to
the wafers.
[0005] Although ion implantation has many advantages, such as the
ability to offer precise dopant concentrations, for example, for
silicon of about 10.sup.14 to 10.sup.21 atoms/cm.sup.3, there are
various problems associated with this doping method. For example, a
major drawback for ion implantation is the radiation damage, which
occurs because of the bombardment involved with heavy particles and
further affects the electrical properties of the semiconductor. The
most common radiation damage is the vacancy-interstitial defect,
which occurs when an incoming dopant ion knocks substrate atoms
from a lattice site and the newly dislocated atoms rest in a
non-lattice position. Further, most of the doping atoms are not
electrically active right after implantation mainly because the
dopant atoms do not end up on regular, active lattice sites. By a
suitable annealing method, however, the crystal lattice could be
fully restored and the introduced dopant atoms are brought to
electrically active lattice sites by diffusion.
[0006] Ion channeling is another drawback of ion implantation that
could also change the electrical characteristics of a doped
semiconductor. Ion channeling occurs when the major axis of the
crystal wafer contacts the ion beam, and when ions travel down the
channels, reaching a depth as much as ten times the calculated
depth. Thus, a significant amount of additional dopant atoms gather
in the channels of the major axis. Ion channeling can be minimized
by several techniques, such as employing a blocking amorphous
surface layer or misorienting the wafer so that the dopant ions
enter the crystal wafer at angles different than a 90.degree.
angle. For example, misorientation of the wafer 3 to 7.degree. off
the major axis prevents the dopant ions from entering the channels.
However, these methods increase the use of the expensive ionimplant
machine and, thus, could be very costly for batch processing.
[0007] Another disadvantage of the conventional doping methods is
the autodoping. After dopants are incorporated into a crystalline
wafer to form various junctions, they undergo many subsequent
processing steps for device fabrication. Although efforts are made
to use low-temperature processing techniques to minimize
redistribution of incorporated dopant atoms, the dopants still
redistribute during the course of further processing. For example,
this redistribution of dopants becomes extremely important when an
epitaxial film is grown over the top of the doped area,
particularly because of the high temperature required for epitaxial
growth. At high temperatures, the dopant diffuses into the growing
epitaxial film during the epitaxial growth, and this phenomenon is
referred to as autodoping. This phenomenon also leads to
unintentional doping of the film in between the doped regions, or
into the nondiffused substrate. For this, integrated circuit
designers must leave adequate room between adjacent regions to
prevent the laterally diffused regions from touching and
shorting.
[0008] Furthermore, current doping systems today employ a batch
processing, in which wafers are processed in parallel and at the
same time. An inherent disadvantage of batch processing is cross
contamination of the wafers from batch to batch, which further
decreases the process control and repeatability, and eventually the
yield, reliability and net productivity of the doping process.
[0009] Accordingly, there is a need for an improved doping system,
which will permit minimal dopant redistribution, precise control of
the number of implanted dopants, higher commercial productivity and
improved versatility. There is also needed a new and improved
doping system and method that will eliminate the problems posed by
current batch processing technologies, as well as a method and
system that will allow greater uniformity and doping process
control with respect to layer thickness necessary for increasing
density of integration in microelectronics circuits.
SUMMARY OF THE INVENTION
[0010] The present invention provides an improved method and unique
atomic layer doping system and method for wafer processing. The
present invention contemplates an apparatus provided with multiple
doping regions in which individual monolayers of dopant species are
first deposited by atomic layer deposition (ALD) on a wafer and
then the respective dopants are diffused, by thermal reaction, for
example, into the wafer surface. Each doping region of the
apparatus is chemically isolated from the other doping regions, for
example, by an inert gas curtain. A robot is programmed to follow
pre-defined transfer sequences to move wafers into and out of
respective doping regions for processing. Since multiple regions
are provided, a multitude of wafers can be simultaneously processed
in respective regions, each region depositing only one monolayer
dopant species and subsequently diffusing the dopant into the
wafer. Each wafer can be moved through the cycle of regions until a
desired doping concentration and profile is reached.
[0011] The present invention allows for the atomic layer doping of
wafers with higher commercial productivity and improved
versatility. Since each region may be provided with a
pre-determined set of processing conditions tailored to one
particular monolayer dopant species, cross contamination is also
greatly reduced.
[0012] These and other features and advantages of the invention
will be apparent from the following detailed description which is
provided in connection with the accompanying drawings, which
illustrate exemplary embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 illustrates a schematic top view of a
multiple-chamber atomic layer doping apparatus according to the
present invention.
[0014] FIG. 2 is a partial cross-sectional view of the atomic layer
doping apparatus of FIG. 1, taken along line 2-2' and depicting two
adjacent doping regions according to a first embodiment of the
present invention and depicting one wafer transfer sequence.
[0015] FIG. 3 is a partial cross-sectional view of the atomic layer
doping apparatus of FIG. 1, taken along line 2-2' and depicting two
adjacent doping regions according to a second embodiment of the
present invention.
[0016] FIG. 4 is a partial cross-sectional view of the atomic layer
doping apparatus of FIG. 2, depicting a physical barrier between
two adjacent doping chambers.
[0017] FIG. 5 is a schematic top view of a multiple-chamber atomic
layer doping apparatus according to the present invention and
depicting a second wafer transfer sequence.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] In the following detailed description, reference is made to
various exemplary embodiments of the invention. These embodiments
are described with sufficient detail to enable those skilled in the
art to practice the invention, and it is to be understood that
other embodiments may be employed, and that structural and
electrical changes may be made without departing from the spirit or
scope of the present invention.
[0019] The term "substrate" used in the following description may
include any semiconductor-based structure. Structure must be
understood to include silicon, silicon-on insulator (SOI),
silicon-on sapphire (SOS), doped and undoped semiconductors,
epitaxial layers of silicon supported by a base semiconductor
foundation, and other semiconductor structures. The semiconductor
need not be silicon-based. The semiconductor could be
silicon-geranium, germanium, or gallium arsenide. When reference is
made to substrate in the following description, previous process
steps may have been utilized to form regions or junctions in or on
the base semiconductor or foundation.
[0020] The term "dopant" is intended to include not only elemental
dopant atoms, but dopant atoms with other trace elements or in
various combinations with other elements as known in the
semiconductor art, as long as such combinations retain the physical
and chemical properties of the dopant atoms. The term "p-type
dopant" used in the following description may include any p-type
impurity ions, such as zinc (Zn), magnesium (Mg), beryllium (Be),
boron (B), gallium (Ga) or indium (In), among others. The term
"n-type dopant" may include any n-type impurity ions, such as
silicon (Si), sulfur (S), tin (Sn), phosphorus (P), arsenic (As) or
antimony (Sb), among others.
[0021] The present invention provides an atomic layer doping method
and apparatus. As it will be described in more details below, the
apparatus is provided with multiple doping regions in which
individual monolayer dopant species are first deposited on a
substrate and then dopant atoms corresponding to each of the
monolayer species are diffused into respective substrates. Each
doping region is chemically separated from the adjacent doping
regions. A robot is programmed to follow pre-defined transfer
sequences for moving wafers into and out of the respective adjacent
doping regions. According to the number of doping regions provided,
a multitude of substrates could be simultaneously processed and run
through the cycle of different doping regions until a desired
doping concentration of a wafer surface is completed.
[0022] The present invention provides a simple and novel
multi-chamber system for atomic layer doping processing. Although
the present invention will be described below with reference to the
atomic layer deposition of a dopant species Ax and the subsequent
diffusion of its dopant atoms into a wafer, it must be understood
that the present invention has equal applicability for the
formation of any doped material capable of being formed by atomic
layer doping techniques using any number of species, where each
dopant species is deposited in a reaction chamber dedicated
thereto.
[0023] A schematic top view of a multiple-chamber atomic layer
doping apparatus 100 of the present invention is shown in FIG. 1.
According to an exemplary embodiment of the present invention,
doping regions 50a, 50b, 52a, 52b, 54a, and 54b are alternately
positioned around a loading mechanism 60, for example a robot.
These doping regions may be any regions for the atomic layer doping
treatment of substrates. The doping regions may be formed as
cylindrical reactor chambers, 50a, 50b, 52a, 52b, 54a, and 54b, in
which adjacent chambers are chemically isolated from one
another.
[0024] To facilitate wafer movement, and assuming that only one
monolayer of a dopant species Ax is to be deposited per cycle, the
reactor chambers are arranged in pairs 50a, 50b; 52a, 52b; 54a,
54b. One such pair, 50a, 50b is shown in FIG. 2. While one of the
reactor chambers of a pair, for example 50a, deposits one monolayer
of the dopant species Ax, the other reactor chamber of the pair,
for example 50b, facilitates subsequent diffusion of the dopant
atoms of species Ax into the wafer to complete the doping process.
The adjacent reactor chamber pairs are chemically isolated from one
another, for example by a gas curtain, which keeps the monolayer of
dopant species Ax in a respective region, for example 50a, and
which allows wafers treated in one reaction chamber, for example
50a, to be easily transported by the robot 60 to the other reaction
chamber 50b, and vice versa. Simultaneously, the robot can also
move wafers between chambers 52a or 52b, and 54a and 54b.
[0025] In order to chemically isolate the paired reaction chambers
50a, 50b; 52a, 52b; and 54a, 54b, the paired reaction chambers show
a wall through which the wafers may pass, with the gas curtain
acting in effect as a chemical barrier preventing the gas mixture
within one chamber, for example 50a, from entering the paired
adjacent chamber, for example 50b.
[0026] It should be noted that, when a particular doping
concentration and/or profile is required, the robot can simply move
wafers back and forth between the adjacent chambers, for example
50a, 50b, until the desired doping profile and/or concentration of
the wafer is obtained.
[0027] It should also be noted that, while two adjacent chambers
have been illustrated for doping of a substrate using monolayers of
dopant species Ax, one or more additional chambers, for example
50c, 52c, 54c, may also be used for deposition of additional
respective monolayers of dopant species, such as By, for example,
wit h the additional chambers being chemically isolated from the
chambers depositing the Ax monolayer dopant species in the same way
the chambers for depositing the Ax species are chemically
isolated.
[0028] The loading assembly 60 of FIG. 1 may include an elevator
mechanism along with a wafer supply mechanism. As well-known in the
art, the supply mechanism may be further provided with clamps and
pivot arms, so that a wafer 55 can be maneuvered by the robot and
positioned according to the requirements of the atomic layer doping
processing described in more detail below.
[0029] Further referring to FIG. 1, a processing cycle for atomic
layer doping on a wafer 55 begins by selectively moving a first
wafer 55, from the loading assembly 60 to the chamber reactor 50a,
in the direction of arrow A.sub.1 (FIG. 1). Similarly, a second
wafer 55' may be selectively moved by the loading assembly 60 to
the chamber reactor 52a, in the direction of arrow A.sub.2.
Further, a third wafer 55" is also selectively moved by the loading
assembly 60 to the chamber reactor 54a, in the direction A.sub.3.
At this point, each of chambers 50a, 52a, 54a are ready for atomic
layer deposition of a monolayer of a dopant species, for example
Ax.
[0030] FIG. 2 illustrates a cross-sectional view of the apparatus
100 of FIG. 1, taken along line 2-2'. For simplicity, FIG. 2 shows
only a cross-sectional view of adjacent reactor chambers 50a and
50b. In order to deposit an atomic monolayer on the wafer 55, the
wafer 55 is placed inside of the reactor chamber 50a, which may be
provided as a quartz or aluminum container 120. The wafer 55 is
placed by the loading assembly 60 (FIG. 1) onto a suscepter 140a
(FIG. 2), which in turn is situated on a heater assembly 150a.
Mounted on the upper wall of the reactor chamber 50a is a dopant
gas supply inlet 160a, which is further connected to a dopant gas
supply source 162a for a first dopant gas precursor Ax. An exhaust
outlet 180a, connected to an exhaust system 182a, is situated on
the opposite wall from the dopant gas supply inlet 160a.
[0031] The wafer 55 is positioned on top of the suscepter 140a
(FIG. 2) by the loading assembly 60, and then a first dopant gas
precursor Ax is supplied into the reactor chamber 50a through the
dopant gas inlet 160a. The first dopant gas precursor Ax flows at a
right angle onto the wafer 55 and reacts with its top substrate
surface to form a first monolayer 210a of the first dopant species
Ax, by an atomic layer deposition mechanism. Preferred gas sources
of dopants are hydrated forms of dopant atoms such as arsine
(AsH.sub.3) and diborane (B.sub.2H.sub.6). These gases are mixed in
different dilutions in pressurized containers, such as the dopant
gas supply source 162a (FIG. 2), and connected directly to the
dopant gas inlets, such as the dopant gas inlet 160a (FIG. 2). Gas
sources offer the advantage of precise control through pressure
regulators and are favored for deposition on larger wafers.
[0032] Alternatively, a liquid source of dopant such as chlorinated
or brominated compounds of the desired element may be used. When a
liquid source of dopant is used, a boron liquid source, for example
boron tribromide (BBr.sub.3), or a phosphorous liquid source, for
example phosphorous oxychloride (POCl.sub.3), may be held in
temperature-controlled flasks over which an inert gas, such as
nitrogen (N.sub.2), is bubbled through the heated liquid, so that
the gas becomes saturated with dopant atoms. The inert gas carries
the dopant vapors through a gas tube and creates a laminar flow of
dopant atoms. A reaction gas is also required to create the
elemental dopant form in the tube. For BBr.sub.3, for example, the
reaction gas is oxygen, which creates the boron trioxide
(B.sub.2O.sub.3) which further deposits as a monolayer of boron
trioxide on the surface of the wafer.
[0033] In any event, after the deposition of a monolayer of the
first dopant species Ax on the wafer surface 55, the processing
cycle for the wafer 55 continues with the removal of the wafer 55
from the chamber reactor 50a to the chamber reactor 50b, in the
direction of arrow B.sub.1, as also illustrated in FIG. 1. After
the deposition of the first monolayer 210a of the first dopant
species Ax, the wafer 55 is moved from the reactor chamber 50a,
through a gas curtain 300 (FIG. 2), to the reactor chamber 50b, by
the loading assembly 60 (FIG. 1) and in the direction of arrow
B.sub.1 of FIG. 2. It is important to note that the gas curtain 300
provides chemical isolation between adjacent deposition
regions.
[0034] The loading assembly 60 moves the wafer 55 through the gas
curtain 300, onto the suscepter 140b situated in the reactor
chamber 50b, which, in contrast with the reactor chamber 50a,
contains no dopant source and no dopant species. A heater assembly
150b is positioned under the suscepter 140b to facilitate the
diffusion of the dopant atoms from the newly deposited first
monolayer 210a of the first dopant species Ax into the wafer 55.
The heat from the heater assembly 150b drives the dopant atoms into
the wafer 55 and further redistributes the dopant atoms from the
first monolayer 210a deeper into the wafer 55 to form a doped
region 210b of the first dopant species Ax. During this step, the
surface concentration of dopant atoms is reduced and the
distribution of dopant atoms continues, so that a precise and
shallow doping distribution in the doped region 210b of the wafer
55 is obtained. Accordingly, the depth of the doped region 210b of
the wafer 55 is controlled, first, by the repeatability of the
atomic layer deposition for the monolayers of dopant species and,
second, by the degree of diffusion of dopants form the monolayers
of dopant species into the wafers.
[0035] Alternatively, a plasma of a non-reactive gas may be used to
complete the diffusion of the dopant atoms into the doped region
210b of the wafer 55. In this embodiment, a supply inlet 160b (FIG.
2), which is further connected to a non-reactive gas supply source
162b, for the plasma of the non-reactive gas, is mounted on the
upper wall of the reactor chamber 50b. An exhaust inlet 180b,
connected to an exhaust system 182b, is further situated on the
opposite wall to the non-reactive gas supply inlet 160b.
[0036] Next, the non-reactive gas By is supplied into the reactor
chamber 50b through the non-reactive gas inlet 160b, the
non-reactive gas By flowing at a right angle onto the deposited
first monolayer 210a of the first dopant species Ax. This way,
particles of the non-reactive gas By "knock" the dopant atoms from
the first monolayer 210a of the first doping species Ax into the
wafer 55 to form the doped region 210b of the wafer 55.
[0037] Following the formation of the doped region 210b of the
wafer 55, the process continues with the removal of the wafer 55
from the reactor chamber 50b, through the gas curtain 300, and into
the reactor chamber 50a to continue the doping process. This
process is repeated cycle after cycle, with the wafer 55 traveling
back and forth between the reactor chamber 50a, and the reactor
chamber 50b, to acquire the desired doping profile of the region
210b.
[0038] Once the desired doping profile of the wafer 55 has been
achieved, an anneal step in the atomic layer doping process is
required, to restore any crystal damage and to electrically
activate the dopant atoms. As such, annealing can be achieved by a
thermal heating step. However, the anneal temperature must be
preferably below the diffusion temperature to prevent lateral
diffusion of the dopants. Referring to FIG. 2, the anneal step
could take place in the reactor chamber 50b, for example, by
controlling the heat from the heater assembly 150b. Alternatively,
the anneal step may take place into an adjacent reactor chamber,
for example reactor chamber 52a, depending on the processing
requirements and the desired number of wafers to be processed.
[0039] By employing chemically separate reactor chambers for the
deposition process of species Ax dopant and possibly others, the
present invention has the major advantage of allowing different
processing conditions, for example, deposition or diffusion
temperatures, in different reactor chambers. This is important
since the chemisorption and reactivity requirements of the ALD
process have specific temperature requirements, in accordance with
the nature of the precursor gas. Accordingly, the apparatus of the
present invention allows, for example, reactor chamber 50a to be
set to a different temperature than that of the reactor chamber
50b. Further, each reactor chamber may be optimized either for
improved chemisorption, reactivity or dopant conditions.
[0040] The configuration of the atomic layer doping apparatus
illustrated above also improves the overall yield and productivity
of the doping process, since each chamber could run a separate
substrate, and therefore, a plurality of substrates could be run
simultaneously at a given time. In addition, since each reactor
chamber accommodates only one dopant species, cross-contamination
from one wafer to another is greatly reduced. Moreover, the
production time can be decreased since the configuration of the
apparatus of the present invention saves a great amount of purging
and reactor clearing time.
[0041] Of course, although the doping process was explained above
only with reference to the first substrate 55 in the first chamber
reactor 50a and the second chamber reactor 50b, it is to be
understood that same processing steps are carried out
simultaneously on the second and third wafers 55', 55" for their
respective chamber reactors. Further, the second and third wafers
55', 55 ' are moved accordingly, in the directions of arrows
A.sub.2, B.sub.2 (corresponding to chamber reactors 52a, 52b) and
arrows A.sub.3, B.sub.3 (corresponding to chamber reactors 54a,
54b). Moreover, while the doping process was explained above with
reference to only one first substrate 55 for the first and second
reactor chambers 50a, 50b, it must be understood that the first and
second reactor chambers 50a, 50b could also process another first
substrate 55, in a direction opposite to that of processing the
other first substrate. For example, if one first substrate 55
travels in the direction of arrow B.sub.1 (FIG. 2) the other first
substrate 55 could travel in the opposite direction of arrow
B.sub.1, that is from the second reactor chamber 50b to the first
reactor chamber 50a.
[0042] Assuming a specific doping concentration is desired on the
wafer 55, after the diffusion of the dopant atoms from the first
monolayer 210a in the reactor chamber 50b, the wafer 55 is then
moved back by the assembly system 60 to the reactor chamber 50a,
where a second monolayer of the first dopant species Ax is next
deposited over the first monolayer of the first dopant species Ax.
The wafer 55 is further moved to the reactor chamber 50b for the
subsequent diffusion of the dopant atoms from the second monolayer
of the first dopant species Ax. The cycle continues until a desired
doping concentration on the surface of the wafer 55 is achieved,
and, thus, the wafer 55 travels back and forth between reactor
chambers 50a and 50b. As explained above, the same cycle process
applies to the other two wafers 55', 55" that are processed
simultaneously in their respective reactor chambers.
[0043] Although the invention is described with reference to
reactor chambers, any other type of doping regions may be employed,
as long as the wafer 55 is positioned under a flow of dopant
source. The gas curtain 300 provides chemical isolation to all
adjacent deposition regions. Thus, as illustrated in FIGS. 2-3, the
gas curtain 300 is provided between the two adjacent reactor
chambers 50a and 50b so that an inert gas 360, such as nitrogen,
argon, or helium, for example, flows through an inlet 260 connected
to an inert gas supply source 362 to form the gas curtain 300,
which keeps the first dopant gas Ax and the non-reactive gas By
from flowing into adjacent reaction chambers. An exhaust outlet 382
(FIG. 2) is further situated on the opposite wall to the inert gas
inlet 260. It must also be noted that the pressure of the inert gas
360 must be higher than that of the first dopant gas Ax and that of
the non-reactive gas By, so that the two doping gases Ax, By are
constrained by the gas curtain 300 to remain within their
respective reaction chambers.
[0044] FIG. 3 illustrates a cross-sectional view of the apparatus
100 of FIG. 2, with same adjacent reactor chambers 50a and 50b, but
in which the inert gas 360 shares the exhaust outlets 180a and 180b
with the two doping gases Ax and By, respectively. Thus, the atomic
layer doping apparatus 100 may be designed so that the inert gas
360 of the gas curtain 300 could be exhausted through either one or
both of the two exhaust outlets 180a and 180b, instead of being
exhausted through its own exhaust outlet 382, as illustrated in
FIG. 2.
[0045] FIG. 4 shows another alternate embodiment of the apparatus
in which the gas curtain 300 separating adjacent chambers in FIGS.
2-3 is replaced by a physical boundary, such as a wall 170 having a
closeable opening 172. A door 174 (FIG. 4) can be used to open and
close the opening 172 between the adjacent paired chambers 50a,
50b. This way, the wafer 55 can be passed between the adjacent
chambers 50a, 50b through the open opening 172 by the robot 60,
with the door 174 closing the opening 172 during atomic layer
doping processing.
[0046] Although the present invention has been described with
reference to only three semiconductor substrates processed at
relatively the same time in respective pairs of reaction chambers,
it must be understood that the present invention contemplates the
processing of any "n" number of wafers in their corresponding "m"
number of reactor chambers, where n and m are integers. Thus, in
the example shown in FIG. 1, n=3 and m=6, providing an atomic layer
doping apparatus with at least 6 reaction chambers that could
process simultaneously 3 wafers for a repeating two-step atomic
layer doping using Ax as a dopant source and By as a non-reactive
gas for diffusion. It is also possible to have n=2 and m=6 where
two wafers are sequentially transported to and processed in the
reaction chambers for sequential doping with two species, for
example, Ax and a second dopant species Cz, while employing the
non-reactive gas By to facilitate the diffusion of the dopant atoms
Ax and Cz. Other combinations are also possible. Thus, although the
invention has been described with the wafer 55 traveling back and
forth from the reactor chamber 50a to the reactor chamber 50b with
reference to FIG. 2, it must be understood that, when more than two
reactor chambers are used for doping with more than two monolayer
species Ax, Cz, the wafer 55 will be transported by the loading
assembly 60 among all the reaction chambers in a sequence required
to produce a desired doping profile.
[0047] Also, although the present invention has been described with
reference to wafers 55, 55' and 55" being selectively moved by the
loading assembly 60 to their respective reactor chambers 50a and
50b (for wafer 55), 52a and 52b (for wafer 55'), and 54a and 54b
(for wafer 55"), it must be understood that each of the three above
wafers or more wafers could be sequentially transported to, and
processed in, all the reaction chambers of the apparatus 100. This
way, each wafer could be rotated and moved in one direction only.
Such a configuration is illustrated in FIG. 5, according to which a
processing cycle for atomic layer deposition on a plurality of
wafers 55, for example, begins by selectively moving each wafer 55,
from the loading assembly 60 to the chamber reactor 50a, in the
direction of arrow A.sub.1 (FIG. 5), and then further to the
reactor chamber 50b, 52a, 52b, 54a, and 54b. One reaction chamber,
for example 50a, can serve as the initial chamber and another, for
example 54b, as the final chamber. Each wafer 55 is simultaneously
processed in a respective chamber and is moved sequentially through
the chambers by the loading assembly 60, with the cycle continuing
with wafers 55 traveling in one direction to all the remaining
reactors chambers. Although this embodiment has been described with
reference to a respective wafer in each chamber, it must be
understood that the present invention contemplates the processing
of any "n" number of wafers in corresponding "m" number of reactor
chambers, where n and m are integers and n.ltoreq.m. Thus, in the
example shown in FIG. 5, the ALD apparatus with 6 reaction chambers
could process simultaneously up to 6 wafers.
[0048] The above description illustrates preferred embodiments that
achieve the features and advantages of the present invention. It is
not intended that the present invention be limited to the
illustrated embodiments. Modifications and substitutions to
specific process conditions and structures can be made without
departing from the spirit and scope of the present invention.
Accordingly, tie invention is not to be considered as being limited
by the foregoing description and drawings, but is only limited by
the scope of the appended claims.
* * * * *