U.S. patent application number 09/136881 was filed with the patent office on 2001-07-26 for in-situ method of cleaning a metal-organic chemical vapor deposition chamber.
Invention is credited to CHARNESKI, LAWRENCE J., NGUYEN, TUE.
Application Number | 20010009154 09/136881 |
Document ID | / |
Family ID | 22474807 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009154 |
Kind Code |
A1 |
NGUYEN, TUE ; et
al. |
July 26, 2001 |
IN-SITU METHOD OF CLEANING A METAL-ORGANIC CHEMICAL VAPOR
DEPOSITION CHAMBER
Abstract
A method is provided to clean the interior surfaces, and
especially the wafer chuck, of a metal vapor deposition chamber.
The method takes advantage of the fact that the chamber controls
the introduction and removal of chemical atmospheres, and the
temperature inside the chamber. The method first oxidizes the
surface to be cleaned with an oxygen plasma, and then removes the
oxide products as a vapor with the use of Hhfac. The oxidization is
controlled through the use of oxygen atmosphere, temperature, and
radio frequency power levels. In this manner, the wafer chuck is
cleaned of deposition byproducts without disassembly of the
chamber.
Inventors: |
NGUYEN, TUE; (VANCOUVER,
WA) ; CHARNESKI, LAWRENCE J.; (VANCOUVER,
WA) |
Correspondence
Address: |
GERALD MALISZEWSKI
SHARP MICROELECTRONICS TECHNOLOGY INC
5700 NW PACIFIC RIM BLVD
CAMAS
WA
98607
|
Family ID: |
22474807 |
Appl. No.: |
09/136881 |
Filed: |
August 19, 1998 |
Current U.S.
Class: |
134/1 ; 216/67;
438/711 |
Current CPC
Class: |
C23C 16/4405 20130101;
C23F 1/12 20130101; Y10S 438/905 20130101 |
Class at
Publication: |
134/1 ; 216/67;
438/711 |
International
Class: |
B08B 003/12; B08B
006/00; B08B 007/00; B08B 007/02 |
Claims
What is claimed is:
1. In an environmental chamber for metal-organic chemical vapor
deposition (MOCVD) on Integrated Circuit (IC) surfaces, a method
for in-situ cleaning of metal deposition byproducts from surfaces
in the chamber comprising the steps of: a) oxidizing the metal
deposition byproducts on the surface to be cleaned; b) introducing
hydrolyzed hexafluoroacetylacetonate (Hhfac) vapor into the chamber
to volatilize the metal deposition byproducts oxidized in Step a);
and c) removing the metal deposition byproducts volatilized in Step
b), whereby chamber surfaces are cleaned without disassembly of the
chamber.
2. A method as in claim 1 including further steps, preceding Step
a), of: introducing an atmosphere including oxygen into the
chamber; and heating the chamber surface to be cleaned, whereby the
oxidation process of Step a) is furthered.
3. A method as in claim 2 in which the step of heating the chamber
surface includes heating the surface to be cleaned to a temperature
in the range between 100 and 500 degrees Celsius.
4. A method as in claim 2 including a further step, preceding Step
a), of: using RF energy to generate a high flux field, creating an
oxygen plasma to further the oxidation process of Step a).
5. A method gas in claim 1 including a further step, following Step
a), of: b.sub.1) establishing a vacuum to remove the oxygen
atmosphere from the chamber.
6. A method as in claim 1 in which Step c) includes creating a
vacuum to remove the volatilized byproducts from the chamber.
7. A method as in claim 1 wherein the chamber surface to be cleaned
is a wafer chuck.
8. A method as in claim 7 wherein the metal film to be removed is
selected from the group consisting of tantalum, tungsten, titanium,
and copper.
9. A method has in claim 1 including the a further step, preceding
Step a) of: introducing water to the chamber surface to be cleaned,
whereby the oxidation process of Step a) is enhanced.
10. A method as in claim 1 in which Step a) includes oxidizing the
surface to be cleaned to a thickness of at least approximately
1,000 Angstroms.
11. In an environmental chamber for metal-organic chemical vapor
deposition (MOCVD) on Integrated Circuit (IC) surfaces, a method
for in-situ cleaning of metal deposition byproducts from a wafer
chuck surface, the method comprising the steps of: a) introducing
an atmosphere including oxygen into the chamber to oxidize the
metal deposition byproducts on the heated surface; b) establishing
a vacuum in the chamber to remove the oxygen atmosphere introduced
in Step a); c) introducing hydrolyzed hexafluoroacetylacetonate
(Hhfac) vapor into the chamber to volatilize the metal deposition
byproducts oxidized in Step a); and d) establishing a vacuum in the
chamber to remove the metal deposition byproducts volatilized in
Step a), whereby wafer chuck surfaces are cleaned without
disassembly of the chamber.
12. A method fans in claim 11 including a further step, preceding
Step a), of: heating the wafer chuck surface to a temperature in
the range between 100 and 500 degrees Celsius, whereby the
oxidation process of Step a) is furthered.
13. A method as in claim 11 wherein the metal deposition byproducts
to be removed are selected from the group consisting of tantalum,
tungsten, titanium, and copper.
14. A method as in claim 11 including the a further step, preceding
Step a), of: introducing water to the chamber surface to be
cleaned, whereby the oxidation of process of Step a) is
enhanced.
15. A method as in claim 11 in which Step a) includes oxidizing the
wafer chuck surface to be cleaned to a thickness of at least
approximately 1,000 Angstroms.
16. A method as in claim 11 in which Step a) including using energy
at a radio frequency to generate oxygen ions impinging the chuck
surface to further the oxidation of the chuck surface.
17. A method for cleaning a thin metal film from a surface
comprising the steps of: a) generating a high flux density of
oxygen ions impinging and oxidizing the thin metal film from the
surface to be cleaned; and b) volatilize the oxidized thin film
byproducts created in Step a), whereby the thin metal film is
oxidized and, then, removed as a vapor.
18. A method as in claim 17 wherein an environmental chamber is
provided to enclose the surface to be cleaned, in which Step a)
includes providing an oxygen atmosphere to further the oxidation
process, and in which Step b) includes providing a hydrolyzed
hexafluoroacetylacetonate (Hhfac) atmosphere to volatilize the
oxidized thin film.
19. A method as in claim 18 wherein the surface to be cleaned is a
heated chuck inside the environmental chamber, and in which Step a)
includes heating the surface to be cleaned to further the oxidation
process.
20. A method as in claim 19 in which Step a) includes heating the
surface to a temperature in the range between 100 and 500 degrees
Celsius.
21. A method as in claim 16 wherein an environmental chamber is
provided to enclose the surface to be cleaned, in which Step a)
includes providing a RF frequency of 13.56 megahertz and a power
level in the range from 200 to 2000 watts per 8 inch diameter
surface to generate an oxygen plasma which oxidizes the thin metal
film.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
[0001] This invention relates generally to integrated circuit (IC)
processes and fabrication and, more particularly, to a method of
maintaining the vessels used in the chemical vapor deposition of
metals in forming metal levels and interconnection structures
between metal levels in an IC substrate.
[0002] The demand for progressively smaller, less expensive, and
more powerful electronic products, in turn, fuels the need for
smaller geometry integrated circuits, and large substrates. It also
creates a demand for a denser packaging of circuits onto IC
substrates. The desire for smaller geometry IC circuits requires
that the interconnections between components and dielectric layers
be as small as possible. Therefore, research continues into
reducing the width of via interconnects and connecting lines. The
conductivity of the interconnects is reduced as the surface area of
the interconnect is reduced, and the resulting increase in
interconnect resistivity has become an obstacle in IC design.
Conductors having high resistivity create conduction paths with
high impedance and large propagation delays. These problems result
in unreliable signal timing, unreliable voltage levels, and lengthy
signal delays between components in the IC. Propagation
discontinuities also result from intersecting conduction surfaces
that are poorly connected, or from the joining of conductors having
highly different impedance characteristics.
[0003] There is a need for interconnects and vias to have both low
resistivity, and the ability to withstand volatile process
environments. Aluminum and tungsten metals are often used in the
production of integrated circuits for making interconnections, or
vias, between electrically active areas. These metals are popular
because they are easy to use in a production environment, unlike
copper which requires special handling.
[0004] Copper (Cu) is a natural choice to replace aluminum in the
effort to reduce the size of lines and vias in an electrical
circuit. The conductivity of copper is approximately twice that of
aluminum, and over three times that of tungsten. As a result, the
same current can be carried through a copper line having half the
width of an aluminum line.
[0005] The electromigration characteristics of copper are also much
superior to those of aluminum. Aluminum is approximately ten times
more susceptible than copper to degradation and breakage through
electromigration. As a result, a copper line, even one having a
much smaller cross-section than an aluminum line, is better able to
maintain electrical integrity.
[0006] Metal cannot be deposited onto substrates, or into vias,
using conventional metal deposition processes, such as sputtering,
when the geometries of the selected IC features are small. It is
impractical to sputter metal, either aluminum or copper, to fill
small diameter vias, since the gap filling capability is poor. To
deposit copper, various chemical vapor deposition (CVD) techniques
are under development in the industry.
[0007] In a typical CVD process, the metal copper is combined with
an organic ligand to make a volatile copper compound or
metal-organic chemical vapor deposition (MOCVD) precursor. That is,
copper is incorporated into a compound that is easily vaporized
into a gas. Selected surfaces of an integrated circuit, such as
diffusion barrier material, are exposed to the copper containing
gas in an elevated temperature environment. When the volatile
copper gas compound decomposes, copper is left behind on the heated
selected surface. Several copper compounds are available for use
with the CVD process. It is generally accepted that the molecular
structure of the copper compound, at least partially, affects the
conductivity of the copper film residue on the selected
surface.
[0008] The metal-organic precursor used to deposit metal metals is
typically introduced into an environmental chamber containing the
target IC substrate surface. Control over the metal-organic vapor
is a major process concern, with care taken to control the flow
rates and precursor temperature. Some processes atomize the
precursor, others vaporize the precursor, and the precursor is
often mixed with a carrier gas. The IC substrate is mounted to a
heated wafer chuck, and it is intended that the precursor vapor
react with the heated substrate to decompose, leaving a solid metal
film over the substrate. Unfortunately, the precursor may cover the
chamber walls as a result of incomplete vaporization and, at least
partially, decompose on these surfaces. One major problem in
maintaining deposition chambers is that the precursors decompose on
the heated chuck around the heated wafer substrate.
[0009] Tolerance differences between wafer substrates, and in the
positioning of the wafers on the chuck sometimes makes it difficult
to center a wafer, which in turn results in an uneven transfer of
heat to the wafer and, ultimately, unequal metal deposition. A
build-up of metal around the wafer can also result in bridging of
deposition material around the wafer, and the wafer edges. Further,
metal build-up on the chuck may cause a wafer to stick to the chuck
after the deposition process. If the build-up flakes, the flaking
material can lodge between the chuck and wafer, or can attach
itself to the wafer surface.
[0010] Therefore, the wafer chuck, and other chamber surfaces, must
be periodically cleaned of deposition byproducts and metal film
build-up. A determination is made of the time it takes for a
critical buildup to occur. A critical build-up, depending on the
process, may be in the range from 10 to 1000 microns. Depending on
the cycle, it may be necessary to clean a chamber on a weekly,
daily, or even on a shift basis. Typically, a chamber is cleaned by
disassembling the parts, such as the wafer chuck, and etching the
parts with acid. A 2-4% maintenance budget against the overall time
of use in IC processes is significant, and the cleaning process can
take as long as an entire shift.
[0011] A co-pending application, Ser. No. 08/717,267, filed Sep.
20, 1996, entitled, "Oxidized Diffusion Barrier Surface for the
Adherence of Copper and Method for Same", invented by Nguyen et
al., Attorney Docket No. SMT 123, which is assigned to the same
Assignees as the instant patent, discloses a method for oxidizing
the diffusion barrier surface to improve the adherence of copper to
a diffusion barrier. However, no disclosure is made for the removal
of the oxidized surfaces, or the treatment of large scale
surfaces.
[0012] Another co-pending application, Ser. No. 08/729,567, filed
Oct. 11, 1996, entitled, "Chemical Vapor Deposition of Copper on an
ION Prepared Conductive Surface and Method for Same," invented by
Nguyen and Maa, Attorney Docket No. 114, which is assigned to the
same Assignees as the instant patent, discloses a method of
preparing a conductive surface, such as a barrier layer, with an
exposure to the ions of an inert gas and a reactive oxygen species
to improve electrical conductivity between a conductive surface and
a subsequent deposition of copper. However, the primary purpose of
this invention is to prepare a conductive IC surface, not clean a
MOCVD chamber surface.
[0013] George et al., in "Reaction of
1,1,1,5,5,5-Hexafluoro-2,4-pentanedi- one (H.sup.+hfac) with CuO,
Cu.sub.2O, and Cu Films", in J. Electrochem. Soc., Vol. 142, No. 3,
March 1995, generally discuss the use of Hhfac to etch copper.
However, no explicit process to clean copper coated surfaces in an
environmental chamber is disclosed.
[0014] It would be advantageous to employ a method of simplifying
the cleaning of equipment used in MOCVD processes. It would
likewise be advantageous if the cleaning time required could be
reduced.
[0015] It would be advantageous to clean an MOCVD chamber of vapor
deposited metal using gaseous atmospheres and processes similar to
those used in the standard operation of the MOCVD chamber. It would
be advantageous if the cleaning process could be adapted to
pre-existing automated techniques.
[0016] It would be advantageous to remove vapor deposited metals
from a MOCVD chamber without disassembly of the chamber or the
dismantling and removing of the parts to be cleaned. It would be
advantageous if the cleaning process could be carried out quickly,
in small time gaps between other chamber processes.
[0017] Accordingly, a method is provided for removing a thin metal
film from a surface. The method comprises the steps of:
[0018] a) oxidizing a thin metal film from the surface to be
cleaned; and
[0019] b) volatilizing the oxidized thin metal film created in Step
a). That is, the thin metal film is oxidized, and then removed as a
vapor. This process can be repeated for further removal of metal
film on a surface.
[0020] In one aspect of the invention, a metal deposition chamber
is provided to enclose the surface to be cleaned. Then, Step a)
includes providing an oxygen atmosphere to further the oxidation
process. Step b) includes providing a hydrolyzed
hexafluoroacetylacetonate (Hhfac) atmosphere to volatilize the
oxidized thin film. Step a) also includes heating the surface to be
cleaned to further the oxidation process. In some aspect of the
invention, the surface is heated to a temperature in the range
between 100 and 500 degrees Celsius.
[0021] Oxidation is dependent upon a number factors such as the
temperature or of the surface to be oxidized, the amount of oxygen
in the atmosphere, and the specific type of oxygen bonding. These
factors all influence the diffusion of oxygen molecules into the
thin metal film to be oxidized. Typically, it is desirable to
oxidize at least a thickness of 1,000 Angstroms from the metal film
surface. However, in some process the oxygen levels in the
atmosphere, or the time permitted for the oxidation process are
varied to produce either thicker or thinner oxidation layers.
[0022] An oxygen plasma is provided to oxidize the thin metal film.
That is, a radio frequency (RF) energy field is applied to create
ions which impinge into the surface to be cleaned. The oxygen
atmosphere and RF energy promote the oxidation process. Then, the
ability of oxygen ions to diffuse into the thin metal surface makes
the temperature of the surface to be cleaned and the amount of
oxygen in the ambient air less critical.
[0023] Typically, the environmental chamber is designed for
metal-organic chemical vapor deposition (MOCVD). During the vapor
deposition processes, thin metal films tend to form on both
intended and unintended surfaces, especially heated surfaces. Since
the wafer chuck is used to heat the substrate upon which metal is
being deposited, metal is also deposited on the wafer chuck. The
present invention takes advantage of the control over the
atmosphere and temperature on the chamber surfaces that are
necessarily present in a typical vapor deposition chamber. That is,
the environmental chamber is already designed to control the
atmosphere introduced into the chemical vapor deposition chamber,
and to control the temperature of the wafer chuck and other
internal chamber surfaces. The present invention allows the wafer
chuck to be cleaned of metal film accumulations through control of
the atmosphere and temperature in the chamber. Therefore, the wafer
chuck can be cleaned in the chamber; it need not be removed for
cleaning.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 illustrates an exemplary metal-organic chemical vapor
deposition (MOCVD) system (prior art).
[0025] FIG. 2 is a flowchart illustrating the method for in-situ
cleaning of metal deposition byproducts from surfaces.
[0026] FIG. 3 is a flowchart illustrating a method for cleaning a
surface.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0027] FIG. 1 illustrates an exemplary metal-organic chemical vapor
deposition (MOCVD) system 10 (prior art). System 10 includes a
chamber 12 to maintain and control the gaseous environment. Chamber
12 includes an inlet port 14 to introduce gases and atmospheres to
chamber 12. In some aspects of the invention, a showerhead 16 is
used to deliver the gases to the wafer surface. Showerhead 16 often
has small outlet holes 18 to spray the input gases in a wider, more
uniform distribution pattern. Chamber 12 also includes an outlet
port 20 to exhaust and vent a gaseous atmosphere from chamber 12.
An exhaust pump 24, operatively connected to outlet port 20, aids
in the venting and removal of exhaust gases from chamber 12.
[0028] A wafer chuck 24 is typically included in system 10.
Integrated circuits substrates 26 are mounted on wafer chuck 24,
and thin films of metal are deposited on the substrates through a
chemical deposition process. Wafer chuck 24 is heated to maintain
the optimal temperature at IC substrate 26 for the deposition of
metal on substrate 26.
[0029] Metal-organic vapor can penetrate between the surface of the
wafer chuck and the IC substrate. Over repeated deposition
processes, a thin film of metal 28 forms over the surface of wafer
chuck 24. Thin film of metal 22 can interfere with the transfer
heat from wafer chuck 20 to the IC substrate. Also, metal film 22
interferes with the mechanic placement of an IC substrate on wafer
chuck 20. For this reason, wafer chuck 20 must be periodically
cleaned. The present invention provides away of cleaned wafer chuck
20 without removing it from chamber 12.
[0030] A metal film can also build up on the chamber walls 24, even
though the wall temperature is below optimal deposition
temperatures. Further, the vaporization of metal deposition
precursors is not always efficient. That is, some of the precursor
may enter input port 14 as a liquid, and coat chamber walls 24 with
a film of thin metal.
[0031] It is not uncommon for chamber 12 to be equipped with an
electrical biasing system 30 operating at a radio frequency (RF),
which breaks the bonds of molecules in the chamber atmosphere.
Breaking the bonds typically creates a high flux density of charged
particles, or plasma ions which are attracted to, and impinge into
oppositely charged chuck surfaces 20. These ions often react
chemically with a material mounted on wafer chuck 20. Alternately,
the ions impart kinetic energy to the wafer mounted material.
Regardless, metal bonds in the material are broken and the metal
combines with oxygen molecules.
[0032] In one exemplary process, the RF frequency is 13.56
megahertz, at a power level in the range from 200 to 2000 watts for
an eight inch diameter wafer chuck surface. The power is
proportionally scaled for different sized chuck surfaces. Pure
oxygen is used at a flow rate of 250 to 1000 cubic centimeters per
minute, when cleaning an eight inch diameter surfaces. The flow
rate is scaled proportional for different sized surfaces to be
cleaned. In some aspects of the invention, water vapor, generated
with a bubbler, is added to the oxygen. The chamber pressure is in
the range from 1 milliTorr to 1 Torr.
[0033] FIG. 2 is a flowchart illustrating the method for in-situ
cleaning of metal deposition byproducts from surfaces. These
byproducts include metal unintentionally deposited on process
equipment surfaces. Step 100 provides an environmental chamber for
metal-organic chemical vapor deposition on integrated circuit
surfaces. Step 102 oxidizes the metal deposition byproducts on the
surface to be cleaned. Step 104 introduces hydrolyzed
hexafluoroacetylacetonate (Hhfac) vapor into the chamber to
volatilize the metal deposition byproducts oxidized in Step
102.
[0034] A metal such as copper is forms one of two oxides, CuO and
Cu.sub.2O. When Hhfac reacts with CuO, the following chemical
reaction occurs:
2H+hfac+CuO.fwdarw.Cu(hfac).sub.2+H.sub.2O.
[0035] When Hhfac reacts with Cu.sub.2O, the following chemical
reaction occurs:
2H+hfac+Cu.sub.2O.fwdarw.Cu+Cu(hfac).sub.2+H.sub.2O.
[0036] Step 106 removes the metal deposition byproducts volatilized
in Step 104. Step 108 is a product, where chamber surfaces are
cleaned without disassembly or removal from the chamber.
[0037] In some aspects of the invention, further steps precede Step
102. Step 100a introduces an atmosphere including oxygen into the
chamber. Step 100b (not shown) heats the chamber surface to be
cleaned. The chamber surface is heated to a temperature in the
range between 100 and 500 degrees Celsius. In this manner, the
oxidation process of Step 102 is furthered. Typically, a further
step follows Step 102, and proceeds Step 104. Step 102a establishes
a vacuum to remove the oxygen atmosphere from the chamber. Step 106
includes creating a vacuum to remove the volatilized byproducts
from the chamber.
[0038] In some aspects of the invention, other steps precede Step
102. Step 100c uses a RF energy to generate a high flux field,
creating an oxygen plasma to further the oxidation process of Step
102.
[0039] Typically, the most important chamber surface to be cleaned
is the wafer chuck upon which the IC substrates are mounted for
vapor deposition. The metal film and metal film deposition
byproducts to be removed from the wafer chuck surface are selected
from the group consisting of tantalum, tungsten, titanium, and
copper. Step 102 typically includes oxidizing the surface to be
cleaned to a thickness of at least approximately 1,000 Angstroms.
At increased temperatures and prolonged oxidation times, the
thickness of the oxidation layer is increased, in some aspects of
the invention. Alternately, temperatures and oxidation times are
reduced to generate thinner oxidation thicknesses. The practical
limit for depth of oxidation is approximately 1,000 Angstroms. When
the metal film to be removed is thicker 1000 .ANG., it is often
more cost effective to remove the material in steps, rather than
oxidize for prolonged periods of time, higher chuck temperatures,
or higher RF power levels. Then, Steps 102 through 104 are repeated
a plurality of cycles until the proper thickness of material is
removed.
[0040] In one aspect of the invention, a dry oxygen atmosphere is
introduced into the chamber to promote oxidation of the surfaces to
be cleaned. The dry oxygen atmosphere is relatively easy to vent
and remove from the chamber. However, the addition of water, or
water vapor to the oxygen atmosphere in the chamber to enhance the
oxidation process. Therefore, in some aspects of the invention
water is introduced to the chamber surface to be cleaned to further
the oxidation process of step 102.
[0041] FIG. 3 is a flowchart illustrating a method for cleaning a
surface. Step 200 provides a surface with an overlying thin metal
film. Step 202 generates a high flux density of oxygen ions
impinging and oxidizing the thin metal film from the surface to be
claimed. Step 204 volatilizes the oxidized thin film byproducts
created in Step 202. Step 206 is a product where the thin film is
oxidized and then removed as a vapor. As described above, a metal
vapor deposition chamber is typically provided to enclose the
surface to be cleaned, and Step 202 includes providing oxygen
atmosphere to further the oxidation process. In some aspects of the
invention, the surface to be cleaned is a heated chuck surface in
an environmental chamber. Step 202 includes heating the surface to
a temperature in the range between 100 and 500 degrees Celsius.
[0042] Step 204 includes providing an Hhfac atmosphere to
volatilize the oxidize then film. Step 202 provides an RF frequency
of approximately 13.56 megahertz and a power level in the range
from 200 to 2000 watts per 8 inch diameter surface to generate an
oxygen plasma which oxidizes the thin metal film.
[0043] A method has been provided to clean the interior surfaces,
and especially the wafer chuck, of a metal vapor deposition
chamber. The method takes advantage of the fact that the chamber
inherently has control over the introduction and removal of
chemical atmospheres and the temperature inside the chamber. The
method first oxidizes the surface to be cleaned, and then removes
the oxide products as a vapor with the use of Hhfac. Other
variations and embodiments of the inventions will occur to those
skilled in the art.
* * * * *