U.S. patent application number 09/738116 was filed with the patent office on 2001-10-11 for in-situ post epitaxial treatment process.
Invention is credited to Dietze, Gerald R..
Application Number | 20010027744 09/738116 |
Document ID | / |
Family ID | 26805536 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010027744 |
Kind Code |
A1 |
Dietze, Gerald R. |
October 11, 2001 |
In-situ post epitaxial treatment process
Abstract
A process for forming an epitaxial layer on a semiconductor
wafer substrate is provided. The process comprises providing a
semiconductor wafer substrate and an area for forming an epitaxial
layer on said semiconductor wafer substrate. The formation area
consists essentially of an epitaxial layer process chamber. The
semiconductor wafer substrate is introduced into the epitaxial
layer process chamber and an epitaxial layer is formed on at least
one surface of the semiconductor wafer substrate. At least one
epitaxial layer surface is substantially hydrophobic. Then, a
chemical reagent is introduced into said epitaxial layer process
chamber. The chemical reagent reacts with the epitaxial layer
surface in situ to form an outer layer.
Inventors: |
Dietze, Gerald R.;
(Portland, OR) |
Correspondence
Address: |
Douglas G. Anderson
SEH America, Inc.
4111 NE 112th Avenue
Vancouver
WA
98682
US
|
Family ID: |
26805536 |
Appl. No.: |
09/738116 |
Filed: |
December 15, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09738116 |
Dec 15, 2000 |
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09108112 |
Jun 30, 1998 |
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Current U.S.
Class: |
117/89 ; 117/105;
117/84; 257/E21.102; 257/E21.285; 257/E21.293 |
Current CPC
Class: |
C30B 33/00 20130101;
H01L 21/0262 20130101; C30B 25/02 20130101; H01L 21/02532 20130101;
C30B 29/06 20130101; H01L 21/02238 20130101; H01L 21/31662
20130101; H01L 21/02255 20130101; H01L 21/02576 20130101; H01L
21/3185 20130101 |
Class at
Publication: |
117/89 ; 117/84;
117/105 |
International
Class: |
C30B 025/00; C30B
023/00; C30B 028/12; C30B 028/14 |
Claims
I claim:
1. A process for forming a protective layer on an epitaxial surface
of a semiconductor wafer, comprising the steps of: providing an
epitaxial layer process chamber; introducing a semiconductor wafer
substrate into said epitaxial layer process chamber; forming an
epitaxial layer on at least one surface of said semiconductor wafer
substrate, said epitaxial layer surface being substantially
hydrophobic; introducing a chemical reagent into said epitaxial
layer process chamber; and reacting said chemical reagent with said
epitaxial layer in-situ to form a protective layer on the surface
of said epitaxial layer.
2. The process of claim 1, further including the step of
introducing said chemical reagent into said epitaxial layer process
chamber immediately after said epitaxial layer is formed.
3. The process of claim 1, wherein the step of forming said
protective layer is a hydrophilic layer.
4. The process of claim 3, wherein the forming of said hydrophilic
layer is an in-situ oxidation step.
5. The process of claim 3, wherein the forming of said hydrophilic
layer is an in-situ nitridation step.
6. The process of claim 1, wherein the step of forming said
protective layer comprises the steps of: raising the operational
temperature of said epitaxial layer process chamber to a deposition
temperature; maintaining the operational temperature of said
epitaxial layer process chamber at said deposition temperature
during the formation of an epitaxial layer on at least one surface
of said semiconductor wafer substrate; reducing the operational
temperature from said deposition temperature to an unload
temperature; and reacting said chemical reagent and said epitaxial
layer while reducing operational temperature from said deposition
temperature to said unload temperature to form said protective
layer.
7. The process of claim 6, wherein the step of forming said
protective layer forms an oxide protective layer.
8. The process of claim 6, wherein the step of forming said
protective layer forms a nitride protective layer.
9. The process of claim 1, wherein the step of forming said
protective layer comprises the steps of: raising the operational
temperature of said epitaxial layer process chamber to a deposition
temperature; maintaining the operational temperature of said
epitaxial layer process chamber at said deposition temperature
during the formation of an epitaxial layer on at least one surface
of said semiconductor wafer substrate; reacting said chemical
reagent and said epitaxial layer to form said protective layer; and
reducing the operational temperature from said deposition
temperature to an unload temperature.
10. The process of claim 9, wherein the step of forming said
protective layer forms an oxide protective layer.
11. The process of claim 9, wherein the step of forming said
protective layer forms a nitride protective layer.
12. A process for forming a protective layer on an epitaxial
surface of a semiconductor wafer, comprising the steps of:
providing an epitaxial layer process chamber, said process chamber
containing at least one deposition reactor area, at least one
protective layer processing area, and a transfer chamber;
introducing a semiconductor wafer substrate into said deposition
reactor area; forming an epitaxial layer on at least one surface of
said semiconductor wafer substrate, said epitaxial layer being
substantially hydrophobic; introducing said semiconductor wafer
substrate containing said epitaxial layer into said protective
layer processing area; introducing a chemical reagent into said
protective layer processing area; and reacting said chemical
reagent with said epitaxial layer in-situ to form a protective
layer on the surface of said epitaxial layer.
13. The process of claim 12, wherein the step of forming said
protective layer is a hydrophilic layer.
14. The process of claim 13, wherein said protective layer is an
oxide layer.
15. The process of claim 13, wherein said protective layer is a
nitride layer.
16. A process for producing a semiconductor wafer substrate having
an epitaxial layer formed thereon, comprising the steps of; (a)
providing an epitaxial layer process chamber; (b) introducing a
semiconductor wafer substrate into said epitaxial layer process
chamber; (c) raising the operational temperature of said epitaxial
layer process chamber to a deposition temperature; (d) maintaining
the operational temperature of said epitaxial layer process chamber
at said deposition temperature during the formation of an epitaxial
layer on at least one surface of said semiconductor wafer
substrate; (e) reducing the operational temperature from said
deposition temperature to an unload temperature; and (f)
introducing a chemical reagent into said epitaxial layer formation
chamber while reducing the operational temperature from said
deposition temperature to said unload temperature, and reacting
said chemical reagent with said epitaxial layer to form a
protective layer on the surface of said epitaxial layer.
17. The process of claim 16, wherein the step of forming said
protective layer is a hydrophilic layer.
18. The process of claim 17, wherein the forming of said
hydrophilic layer is an in-situ oxidation step.
19. The process of claim 17, wherein the forming of said
hydrophilic layer is an in-situ nitridation step.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S.
application Ser. No. 09/108,112 filed Jun. 30, 1998.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a process for forming a protective
oxide film in-situ after deposition of an epitaxial silicon layer
on a silicon substrate wafer.
[0003] Epitaxial deposition is a film grown over a crystalline
substrate in such a way that the atomic arrangement of the film
bears a defined crystallographic relationship to the atomic
arrangement of the substrate wafer. In the case of a
monocrystalline substrate wafer, the crystallographic orientation
of the epitaxial layer will replicate that of the substrate wafer
wherein the substrate wafer provides the crystallographic seed for
epitaxial growth.
[0004] Commonly, growth of an epitaxial layer is accomplished by
chemical vapor deposition (CVD) at temperatures well below the
melting point of either the substrate wafer or the film being
deposited. In the CVD technique, the substrate wafer is heated in a
chamber into which reactive and carrier gases are introduced. For
silicon deposition, reactive gases include Silane (SiH.sub.4),
Dichlorosilane (SiH.sub.2Cl.sub.2), Trichlorosilane (SiHCl.sub.3),
and Silicon Tetrachloride (SiCl.sub.4), with dopant gases that
include Arsine (AsH.sub.3), Phosphine (PH.sub.3), and Diborane
(B.sub.2H.sub.6), and a carrier gas of hydrogen.
[0005] Epitaxial reactors are generally available in three basic
designs. The first design involves placing the substrate wafers on
holders, called susceptors, in a horizontal position. Reactive and
carrier gases are then introduced into the growth chamber at one
side, passed over the substrate wafers, and exhausted out the other
side. The second design employs a vertical system wherein the
substrate wafers are placed horizontally on a rotating susceptor,
and the gases are introduced into the chamber at the top, passed
over the wafers, and exhausted out of the chamber at the bottom.
Finally, the third design places the wafers near vertically on a
barrel-type rotatable susceptor, with the gases introduced in the
top of the chamber, passed over the wafers, and exhausted out the
bottom of the chamber. Older technology produced multiple wafers
simultaneously, and utilized each of these three designs. Newer
technology, however, typically processes wafers individually, and
employs the first general design wherein the wafer is placed
horizontally on a rotating susceptor, and the gases are introduced
at one side of the chamber, passed over the wafer, and exhausted
out the other side.
[0006] In each design, the susceptor is made of a nonreactive
material capable of enduring extreme temperature and pressure
variations, such as graphite, and typically silicon carbide coated
graphite. Heat is typically supplied by radio frequency (RF),
ultraviolet (UV), infrared radiation (IR), or electrical resistance
heaters, with processing temperatures ranging from about
900.degree. C. to 1200.degree. C.
[0007] In general, epitaxial deposition begins by loading the
substrate wafer(s) onto the susceptor, and purging the ambient air
out of the reaction chamber by supplying non-reactive gases such as
helium, argon, or nitrogen, into the chamber. The temperature is
then ramped up to the desired level, and a mixture of the carrier
gas and the reactive gases (including any desired dopant gas) is
introduced into the chamber. When the desired epitaxial layer
thickness is achieved, non-reactive gases are reintroduced into the
chamber, and the temperature is ramped down. The wafer is then
unloaded from the chamber.
[0008] If desired, an etching agent such as anhydrous hydrogen
chloride (HCl) can be introduced before carrier and reactive gases
are introduced. This etching agent will remove a thin layer off the
surface of the substrate wafer, as well as any contaminants adhered
thereto. After such an etch, a contaminant free substrate surface
with strong crystallographic structure is provided for epitaxial
deposition, and generally results in a higher quality epitaxial
layer. This etching step can also be employed without the substrate
wafer present, as a means of controlling epitaxial deposition on
the susceptor or other surfaces in the growth chamber.
Additionally, prior to epitaxial deposition, a hydrogen bake can be
used to remove any native oxide growth on the surface of the wafer,
by chemical reduction. This will provide a clean silicon surface on
the substrate for epitaxial deposition.
[0009] In the case of a silicon epitaxial layer deposited on a
silicon substrate wafer, the surface of the epitaxial layer is
hydrophobic. Such a hydrophobic layer is very reactive, and prone
to attract contaminants. As such, it is common in the industry to
employ a wafer cleaning and oxidizing step after the epitaxial
deposition is complete. This cleaning and oxidizing is done to
remove any contaminants that might have adhered to the epitaxial
surface upon being removed from the deposition chamber, and to put
a protective oxide layer, such as silicon dioxide (SiO.sub.2) on
the surface of the epitaxial layer. An oxide layer surface is
hydrophilic, which is much less reactive than a hydrophobic
surface, and therefore does not as readily attract contaminants.
The oxide layer is therefore used to protect the surface of the
wafer from contaminants until the wafer is ready for further
processing, wherein the oxide layer is removed and the silicon
epitaxial layer is exposed and ready for processing.
[0010] This cleaning and oxidizing step adds both processing time
and cost to the production of the wafer and requires additional
equipment and chemical usage. It is well known in the industry to
use a wet chemical bench to clean and oxidize the wafer surface. A
typical cleaning and oxidizing process involving subjecting the
wafer to submersion in two sequential solutions is as follows:
[0011] NH.sub.4OH (29 weight %)+H.sub.2O.sub.2 (30%)+DI H.sub.2O at
70-80.degree. C.; and
[0012] HCl (37 weight %)+H.sub.2O.sub.2 (30%)+DI H.sub.2O at
75-80.degree. C.
[0013] Subjecting wafers so these solutions will slightly etch the
surface of the wafer to remove contaminants, and then generate a
thin oxide layer. This method of oxidizing is relatively
uncontrolled however, and the thickness of the oxide layer is hard
to control and predict.
SUMMARY OF THE INVENTION
[0014] The present invention relates to a process that overcomes
the disadvantages and problems set forth above. More specifically,
a process is provided for growing an outer protective layer on the
outer surface of a semiconductor wafer directly in an epitaxial
reactor chamber immediately after epitaxial deposition. The subject
process involves the growing of protective films in reactors
designed explicitly for the deposition of epitaxial silicon films.
The growth of these protective films is accomplished during
typically an unproductive part of the deposition cycle, namely, the
cool-down phase. In any case, the oxidation occurs before the wafer
is removed from the epitaxial deposition equipment.
[0015] By incorporating the novel process technique of the present
invention into the epitaxial reaction sequence, the elimination of
the costly and time-consuming cleaning and oxidizing step will
result. Further, since the oxidation occurs in the epitaxial
equipment, the process can be much more tightly controlled, and
will result in a higher quality oxide.
[0016] Additionally, by incorporating the process of the present
invention, the application of an outer layer on the epitaxial
silicon is not limited to an oxide, but could also include
nitrides, or other beneficial layers. Nitride layers cannot
currently be achieved through any presently available wet treatment
technique.
[0017] These features are believed to be a novel approach utilizing
existing epitaxial deposition equipment, and applying a new method.
The invention discloses a method that will allow for the
elimination of post-epitaxial wet processing for cleaning and
oxidizing in preparation for wafer storage. More specifically, the
method comprises introducing a monocrystalline substrate wafer into
epitaxial equipment, processing the wafer to form an epitaxial
layer on the surface of the substrate wafer and having the same
crystalline properties as the substrate wafer, and then forming a
protective layer on the surface of the epitaxial layer before
removing the wafer from the epitaxial equipment.
[0018] The semiconductor wafer substrate is introduced into the
epitaxial layer process chamber, and the temperature in the
epitaxial layer process chamber is increased to a predetermined
operating temperature. Typical operating temperature during
epitaxial deposition ranges from about 1025.degree. C. up to about
1150.degree. C., and preferably from about 1050.degree. C. to
1100.degree. C. Typical operating pressure is about 760 Torr for
atmospheric deposition, but can go down to about 1 Torr for low
pressure applicatons. Upon achieving the desired temperature,
appropriate reactive and carrier gases are introduced into the
epitaxial deposition chamber to facilitate layer growth. The
operating temperature is maintained for a time sufficient to
facilitate epitaxial layer growth of a layer up to 15 microns
thick, preferably in the range of 2 to 4 microns thick. Upon
achieving the desired layer thickness, the reactive gas supply is
terminated, and the deposition chamber is purged with non-reactive
gas. As previously described, the epitaxial layer is hydrophobic in
nature, is of uniform thickness, and has the same crystallographic
orientation as that of the substrate wafer.
[0019] The temperature of the deposition chamber is then ramped
down to a desired unload temperature. While ramping down the
temperature, a chemical reagent gas is introduced into the
epitaxial deposition chamber. Preferably, the step of introducing
the reagent gas into the deposition chamber occurs immediately
after purge gas is introduced into the chamber. In another
preferred embodiment, the operating temperature is ramped down to a
predetermined reduced temperature before introduction of the
reagent gas.
[0020] When the reagent gas is introduced into the deposition
chamber, the reagent gas reacts in-situ with the hydrophobic
epitaxial layer surface to form an outer layer that is
substantially hydrophilic. In one preferred step the substantially
hydrophilic outer layer surface is an in-situ oxidation step. In
another preferred step the substantially hydrophilic outer layer
surface is an in-situ nitridation step. The reaction between the
reagent gas and the hydrophobic epitaxial layer is preferably
conducted without any additional heat being added to the deposition
chamber, but rather takes advantage of the heat present from the
epitaxial deposition during the temperature reduction step. Yet
another additional process step preferably includes the step of
subsequently depositing in-situ at least one additional layer onto
the substantially hydrophilic outer layer.
[0021] In any case, it is preferred that the step of reacting the
reagent gas with the hydrophobic epitaxial layer to form the
hydrophilic layer is conducted without requiring substantial
additional process time compared to the epitaxial deposition
process described above.
[0022] In an alternate embodiment, a stabilized heat controlled
process could be added to the epitaxial deposition process
specifically added to support the formation of the protective
hydrophilic layer. In this case, the process time required for
processing in the epitaxial equipment is slightly increased, such
as for an additional 20 seconds of controlled heating. By
controlling the temperature during formation of the hydrophilic
layer, more precise control of the layer thickness and uniformity
can be achieved. Again, the formation of the hydrophilic layer is
accomplished in-situ after deposition of the epitaxial layer, and
before the wafer is removed from the epitaxial equipment.
[0023] The foregoing and other objects, features and advantages of
the invention will become more readily apparent from the following
detailed description of a preferred embodiment that proceeds with
reference to the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic sectional view of a conventional
cylindrical or barrel type-batch epitaxial reactor.
[0025] FIG. 2 is a schematic sectional view of a conventional
single wafer epitaxial process chamber wherein deposition of an
epitaxial layer occurs in deposition equipment know as an "ASM
Reactor".
[0026] FIG. 3 is a top view of the conventional single wafer
epitaxial process chamber of FIG. 2.
[0027] FIG. 4 is a schematic sectional view of a single wafer
epitaxial process chamber wherein deposition of an epitaxial layer
occurs in deposition equipment known as a "Centura Reactor".
[0028] FIG. 5 is a schematic depiction of the process of epitaxial
deposition related to equipment used in FIG. 1.
[0029] FIG. 6 is a schematic depiction of the process of epitaxial
deposition related to equipment used in FIG. 2.
[0030] FIG. 7 is a schematic depiction of the process of epitaxial
deposition related to equipment used in FIG. 3.
[0031] FIG. 8 is a schematic depiction of a "Centura Reactor".
DETAILED DESCRIPTION OF THE INVENTION
[0032] FIG. 1 shows a typical cylindrical or barrel type batch
epitaxial reactor (1), in which a polyhedral susceptor (3) is
inserted within a bell jar (2). The susceptor can be rotated via a
rotational shaft (5). The susceptor (3) contains individual facets
(9) that include recessed pockets (7) which can accommodate
semiconductor wafers (not shown) within each pocket (7). There can
be one pocket (7) or a multitude thereof, depending on the wafer
diameter to be processed. The bell jar (2) is surrounded by a
quartz lamp heater (11) and a reflective heat shield (13) which is
designed to heat the susceptor (3) and the wafers (not shown)
through the wall of the bell jar (2) by reflecting incident energy
back toward the susceptor(3). The entity is hermetically sealed
with a top plate (17) and process gases (10) are introduced into
the reaction chamber via the gas inlets (15).
[0033] Once the process gases (10) have reacted with the wafers,
any remaining process gases (10) and any byproducts (23) which may
be produced, are flushed out through the exhaust opening (19). The
space defined by the heat shield (13) and the outer wall (14)
usually houses a cooling mechanism, such as a cooling gas and/or
water pipes (not shown).
[0034] A typical single wafer epitaxial reactor chamber (30) is
shown in FIG. 2. In this type of epitaxial reactor, a generally
plate-shaped susceptor (53) is mounted on a chuck (51), which is in
turn supported and rotated by a rotary shaft (57). The rotary shaft
(57) extends through a coupling (59), which allows for rotation and
vertical adjustment. The susceptor (53) is enclosed by a top panel
(31), a bottom panel (33), a vertical wall section (35), and a
lower chamber bottom panel (37). Two side panels (not shown)
complete the enclosure of the unit such that the susceptor (53) is
completely enclosed. Top panel (31), bottom panel (33), and the two
side panels (not shown) mate with a gas injector (41) at injector
flange (39), and mate with a gas outlet (49) at outlet flange
(45).
[0035] A wafer (55) is removably positioned onto the susceptor
(53), and vertically adjusted to be in the optimal position for
gases to flow over the wafer (55). The wafer (55) is heated by
quartz lamps (not shown) or a quartz lamp arrangement that is
placed on the top, on the bottom, or on both sides of the reaction
chamber. As shown in FIG. 3, the process gases are introduced with
established gas flow and velocity, as indicated by the arrow (43).
The process gases will flow across the wafer (55), proceed to the
rear portion (47) of the reaction chamber, and exit through the gas
outlet (49). The process gases are similar to those described for
the cylindrical type batch reactor.
[0036] Another type of single wafer epitaxial reactor is shown in
FIG. 8. This type is marketed by Applied Materials Corporation and
is commonly known as the "Centura Reactor". The reactor (110)
contains one or more loading chambers (112) where wafer carriers
(not shown) are placed. An automated wafer handler (1 14), located
within a transfer chamber (116), is used to transport individual
wafers from a loading chamber (112) to a single wafer reactor
(118), then to a cooling chamber (120) before returning the wafer
to the wafer carrier in the loading chamber (112). The reactor
(110) can contain as many as 8 attachable and/or detachable
component loading chambers (112), single wafer reactors (118), and
cooling chambers (120), in any combination desired, with the
stipulation of a maximum of three high temperature single wafer
reactors (118). Each component is serviced by the automated wafer
handler (114). The loading chambers (112) have doors (not shown)
between the ambient area outside the epitaxial equipment and
transfer chamber (116), such that when the door to the ambient area
is open, the door to the transfer chamber (116) is closed with an
airtight seal. Similarly, when the door to the transfer chamber
(116) is open, the door to the ambient area is closed with an
airtight seal. These seals help prevent contamination in the
ambient area from entering the area within the equipment
itself.
[0037] FIG. 4 reveals the single wafer reactor (70) in which layers
of silicon can be deposited onto a wafer (81). The reactor has a
top wall (73), side walls (75) and a bottom wall (78) that encloses
the reaction chamber (68) into which the wafer (81) can be
positioned. The wafer (81) is removably mounted on susceptor (82)
which is then mounted on a pedestal (84) that is rotated by a motor
(86) to provide a homogeneously averaged environment for the wafer
(81). The wafer (81) is heated by a light source from high
intensity lamps (88) and (91). The top wall (73) and the bottom
wall (78) are highly transparent to light energy in order to enable
the energy from lamps (88) and (91) to enter the reaction chamber
(68). An excellent material choice for the top and bottom walls
(73) and (78) is quartz because it is transparent to light at
visible IR (infrared) and UV (ultra violet) frequencies. It also
has a sufficiently high strength to support pressure differences
between the outside and the reaction chamber (68), and it has a low
rate of outgasing and contamination.
[0038] Process gases flow from a gas input port (100) and across
the wafer (81) to an exhaust port (102). The gas input port (100)
is connected to gas manifolds (not shown) that provides one or a
mixture of gases to enter through pipes (not shown) into the input
port (100). Gas concentrations, gas flow rates, substrate rotation
and temperatures are selected in a way so that processing
uniformity is optimized. Rotation of the wafer (81) and thermal
gradients from lamps (88) and (91) can have a significant influence
of gas flow profiles in the reaction chamber (68). The main flow
profile, however, is dominated by the laminar flow from the gas
input port (100), across the wafer (81) to the exhaust port (102).
Pressures are maintained typically between 1 Torr to 760 Torr,
depending on specifications and applications. Since these are
elevated pressures as compared to the LPCVD (low pressure chemical
vapor deposition) process pressures of less than 1 Torr, such a
process is also referred to as high pressure CVD (chemical vapor
deposition) or APCVD (atmospheric pressure chemical vapor
deposition).
[0039] Processing wafers in any of the epitaxial reactors explained
above will provide an epitaxial silicon layer on the surface of the
wafer, with the orientation of the layer being the same as that of
the wafer, and characteristics of the epitaxial layer such as
resistivity controlled by the process gases. It is possible to then
grow an in-situ protective film layer in the same reaction chamber
in which the epitaxial films are grown. As such, subsequent wet
processing to provide such a protective film layer can be omitted.
Therefore, a preferred embodiment of the invention is an oxidation
step immediately after epitaxial deposition to generate a
protective film layer with a hydrophilic surface. The thickness of
the protective film layer of the present invention is expected to
be in the range of 10 .ANG. to 50 .ANG..
[0040] Another preferred embodiment of the proposed invention is an
oxidation step to provide a thin oxide layer of about 10 .ANG. to
50 .ANG. during the cool-down phase of the process without
requiring added process time. It has been determined that the
cool-down temperatures and times are sufficient to achieve such a
thin film formation. In the case of the Centura reactor, this oxide
growth could be facilitated in any area within the equipment.
[0041] Another preferred embodiment encompasses a reduction in wet
processing. An oxidizing bath after epitaxial deposition would not
be required. Any of the thin oxide films formed by the subject
process can easily be removed via a hydrofluoric acid (HF) etch,
should the user need a bare silicon surface during subsequent
semiconductor wafer processing.
[0042] In a further embodiment, one or more reaction chambers can
be added to the AMT Centura reactor described in FIGS. 4 and 5 to
perform any combinations of subsequent processes, including, but
not limited to oxidation, nitridation, CVD backside deposition,
plasma etching, etc. In such a case, the material would receive
epitaxial deposition in one chamber, and be moved to another
chamber to receive the protective film, without leaving the
confines of the environmentally controlled reactor.
[0043] Another embodiment is the possibility of using the thin film
formed, such as the thin oxide film as a seed for subsequent
treatment (such as oxidation or the like) by wafer users. For
example, sandwich structures can be formed such as a nitride film
on top of an oxidation as a first device-processing step.
[0044] Depending on the epitaxial reactor type, and the individual
epitaxial wafer specification, numerous recipes are possible. A
common cycle for each of the previously mentioned reactor types
presently used is shown in FIGS. 5-7. It should be noted that in
all three examples a chemical reagent is introduced into the
epitaxial layer process chamber (after formation of an epitaxial
layer), and the chemical reagent reacts with the epitaxial layer
(which is hydrophobic) in-situ to form an outer layer which is
substantially hydrophilic. More specifically, an oxidation or
nitridation of the epitaxial layer takes place during the cooling
phase of the process without adding time to the process sequence
prior to unloading the wafer(s) from the reactor chamber. FIGS. 5-7
represent the processes in scale to each other for the main three
different types of equipment used for this type of epitaxial
deposition. The Applied Materials batch type barrel reactor is
represented by the recipe of FIG. 5, the ASM single wafer reactor
by the recipe shown in FIG. 6, and the single/multiple single wafer
chamber Applied Materials (Centura) reactor by the recipe depicted
in FIG. 7. All three figures show the process cycle with regard to
the process temperature, indicated on the ordinate in .degree. C.,
and the time t in minutes on the abscissa to which the cycle is
associated. It should be understood that all these process steps
are generalized.
[0045] A typical operation sequence for the conventional barrel
type batch reactor process (200), which is illustrated in FIG. 5,
is as follows:
[0046] (a) Ramp-up (206) at 0.7.degree. C/s to 1150.degree. C. in
an inert H.sub.2 atmosphere.
[0047] (b) Bake/etch (209) for about 5 minutes in H.sub.2 and HCl
at a temperature of 1150.degree. C.
[0048] (c) Ramp-down (212) at 0.5.degree. C/s to a temperature of
1130.degree. C.
[0049] (d) Epitaxial deposition (215) in H.sub.2 employing a
reactive gas for silicon epitaxial deposition such as
Trichlorosilane (SiHCl.sub.3) and a dopant such as Phosphine for
time period of about 9 minutes.
[0050] (e) Ramp-down (218) at 0.5 C/s in O.sub.2 and H.sub.2 for
forming thin oxidation.
[0051] (f) Unload the finished wafer at about 300.degree. C.
[0052] A typical operation sequence for the single-wafer reactor
process (300), which is illustrated in FIG. 6, is as follows:
[0053] (a) Ramp-up (306) at 3.2.degree. C/s to a temperature of
1190.degree. C. in an inert H.sub.2 atmosphere
[0054] (b) Bake/etch (309) for approximately 2.5 minutes in H.sub.2
and HCl at temperature 1190.degree. C.
[0055] (c) Ramp-down (312) at 6.degree. C/s to a temperature
1150.degree. C.
[0056] (d) Epitaxial deposition (315) in H.sub.2, employing a
reactive gas for silicon epitaxial deposition such as
Trichlorosilane (SiHCl.sub.3) and a dopant such as Phosphine.
[0057] (e) Ramp-down (317) at 6.degree. C./s in O.sub.2 and H.sub.2
for forming thin film oxidation.
[0058] (f) Unload the finished wafer at about 900.degree. C.
[0059] A typical operation sequence for the Centura reactor process
(400), which is illustrated in FIG. 7, is as follows:
[0060] (a) Ramp-up (406) at 18.degree. C./s to a temperature of
1130.degree. C. in an inert H.sub.2 atmosphere.
[0061] (b) Bake (409) for approximately 1 min. in H.sub.2 at
1130.degree. C.
[0062] (c) Epitaxial deposition (412) in H.sub.2, employing a
reactive gas for silicon epitaxial deposition such as
Trichlorosilane (SiHCl.sub.3) and a dopant such as Phosphine for
time period from about 15 seconds through 4 minutes, depending on
desired layer thickness.
[0063] (d) Ramp-down (415) at 18.degree. C/s in O.sub.2 and H.sub.2
for forming thin film oxidation.
[0064] (e) Unload the finished wafer at about 700.degree. C.
[0065] Some care has to be taken when dealing with an atmosphere
consisting of oxygen (O.sub.2) and hydrogen (H.sub.2) due to the
possibility of explosive mixture formation. The limit to form a
dangerous mixture of hydrogen and oxygen is reached at about 4.65
volume % of H.sub.2 in pure O.sub.2 at room temperature or,
respectively, a 6.1 volume % of O.sub.2 in pure H.sub.2 under
atmospheric pressure (760 Torr). These ratios will obviously change
under different temperature and pressure conditions.
[0066] Batch epitaxial reactors typically cool down from the
deposition temperature of 1150.degree. C. to about 300.degree. C.
to 400.degree. C. (at 760 Torr) before unloading the wafers.
Reactors with one or more single wafer reaction chambers typically
cool from 1100.degree. C. to about 700.degree. C. to 900.degree. C.
(at 760 Torr). Reactors with single or multiple single wafer
reaction chambers can afford higher chamber unload temperatures
because they typically contain cool down areas or chambers in which
the wafers can cool down to temperatures which are tolerated by the
wafer carriers, and automated wafer handlers can handle elevated
temperatures. These cool down areas are still contained within the
controlled environment of the epitaxial equipment, and therefore do
not expose the wafer to potential contaminants associated with
ambient air.
[0067] An inert gas, such as helium or argon could be mixed into
the oxygen source to modify dangerous levels of hydrogen-oxygen
ratios. The gases would then be fed through mass flow controllers
(MFC), mixed with process gases (hydrogen in this case) and fed
into the deposit manifold. Additional safety valves and leak
detectors coupled with automatic shut-off mechanisms would render
additional safety features. Another possible solution is to elect
the ideal safe gas ratio by taking the lower explosive mixture and
divide it by a safety factor such as 10 to 100.
[0068] Having illustrated and described the principles of my
invention in a preferred embodiment thereof, it should be readily
apparent to those skilled in the art that the invention can be
modified in arrangement and detail without departing from such
principles. I claim all modifications coming within the spirit and
scope of the accompanying claims.
* * * * *