Conformal pure and doped aluminum coatings and a methodology and apparatus for their preparation

The present invention relates to a process and apparatus for the formation of conformal pure aluminum and doped aluminum coatings on a patterned substrate. It is directed to the use of low temperature thermal and plasma-promoted chemical vapor deposition techniques with biased substrate to provide conformal layers and bilayers comprised of pure Al and/or doped Al (e.g., Al with 0.5 at % copper) on semiconductor device substrates with patterned holes, vias, and trenches with aggressive aspect ratios (hole depth/hole width ratios). The use of the plasma-promoted CVD (PPCVD) process, which employs low plasma power densities, allows the growth of aluminum films with the smooth surface morphology and small grain size necessary for ULSI applications, while substrate bias provides superior coverage and complete aluminum fill of features intrinsic in microelectronic device manufacture. Aluminum doping is achieved by in-situ deposition by PPCVD of sequential bilayers of Al and Cu followed by in-situ annealing, or in-situ simultaneous PPCVD deposition of copper-doped aluminum.

FIELD OF THE INVENTION 
The present invention relates to conformal pure aluminum and doped aluminum 
coatings on a patterned substrate and a methodology and apparatus to 
prepare such coated substrate. More particularly, the present invention is 
directed to the use of low temperature thermal and plasma-promoted 
chemical vapor deposition techniques to provide conformal layers and 
bilayers comprised of pure Al and/or doped Al (e.g., Al with 0.5 at % 
copper) on semiconductor device substrates with patterned holes, vias, and 
trenches with aggressive aspect ratios (hole depth/hole width ratios). 
BACKGROUND OF THE INVENTION 
Aluminum, as a metallization material, has been one of the key factors in 
the success of solid-state semiconductor circuits. It readily reduces the 
native oxide on silicon surfaces at low temperatures (&lt;500.degree. C.) and 
thus forms excellent contact with silicon and, for the same reasons, bonds 
very well with silicon dioxide (SiO.sub.2) and SiO.sub.2 -based glasses. 
However, incorporating aluminum in emergency ultra-large scale integration 
(ULSI) computer chip devices has encountered several problems. One is 
material reliability due to aluminum's low melting point. Aluminum reacts 
strongly with silicon and easily migrates through silicon. Another problem 
is process reliability. Present physical vapor deposition (PVD) processes, 
of which sputtering is the most popular, cannot meet the increasingly 
stringent requirements of new multilevel metallization schemes. Sputtering 
produces non-conformal coverage, which leads to thinning at via and trench 
edges and walls, and to keyholes in the via. In addition, the deposits, 
grown at or near room temperature, almost invariably are contaminated with 
trapped-in sputter gas and possess small grain size. Both features are 
detrimental to the reliability of aluminum interconnections. Higher 
temperature deposition solves some of these problems. However, 
thermally-fragile low dielectric constant (.epsilon.&lt;2) polymers, which 
are considered for applications as interlayer and passivating dielectric 
to enhance the performance of integrated circuits, are destroyed during 
high temperature processes. 
In spite of these problems, aluminum's use is expected to continue in ULSI 
and beyond, as documented by the Semiconductor Industry Association (SIA) 
industry wide technology roadmap. See The National Technology Roadmap for 
Semiconductors (SIA, San Jose, Calif., 1994). This expectation is 
contingent upon the development of new aluminum alloys and deposition 
techniques which eliminate the inherent problems encountered in PVD 
processes. 
Chemical vapor deposition (CVD) potentially offers a solution to all these 
problems. CVD deposits a thin solid film synthesized from the gaseous 
phase by a chemical reaction which could be activated thermally or 
electrically and/or catalyzed by the substrate to be coated. It is this 
reactive process which distinguishes CVD from physical deposition 
processes, such as sputtering or evaporation. CVD is used to deposit 
layers of silicon, silicon dioxide and silicon nitride. CVD is not used to 
deposit metals on semiconductor substrates. One of the key advantages of 
CVD is its potential ability to involve the substrate surface in the 
deposition reaction which leads, under the proper conditions, to a 
conformal, planarized blanket, or selective metal growth. This conformed 
feature is an essential requirement to produce three-dimensional 
multilevel structures which contain interconnections in the vertical 
direction through vias and holes in the dielectric layers. Another 
advantage of CVD is that it can deposit layers on substrates of complex 
shape and form the layers at growth rates which are much higher than the 
minimum acceptable in electronic device industry. In addition, it can grow 
metal thin films at reduced temperatures, as low as 150.degree. C., with 
no need for post-deposition annealing. This is necessary to minimize the 
effects of interdiffusion and to allow the growth of abrupt multilayered 
structures. It is relatively simple and controllable, and leads to good 
adherence, high uniformity over a large area, and reduced susceptibility 
to interfacial mixing and cross-contamination effects. 
In recent years, considerable efforts have been devoted to the development 
of CVD processes for depositing aluminum layers on substrates, in 
particular semiconductor substrates. Earlier attempts at aluminum CVD used 
tri-alkyl-type sources, such as trimethyl and triethylaluminum, and 
produced deposits with extensive surface roughness, high resistivity, and 
large amounts of carbon, all of which being detrimental to microelectronic 
applications. See, e.g., C. F. Powell, J. H. Oxley, and J. M. Blocher, 
Jr., Vapor Deposition (Wiley, New York, N.Y. 1966) p. 277; and H. J. 
Cooke, R. A. Heinecke, R. C. Stern, and J. W. C. Maas, Solid State 
Technol. 25 (1982) 62. Also, the pyrophoric nature of the alkyl source 
precursors required extensive precautionary measures. These earlier 
attempts used relatively high temperatures, increased reactor pressure, 
and did not use hydrogen. 
To avoid these problems, attempts were made to grow aluminum through 
hydrogen reduction of aluminum halides, such as AlCl.sub.3 and AlBr.sub.3, 
or through disproportionation of aluminum subchlorides. See, e.g., W. 
Klemm, E. Voss, and K. Geigersberger, Z. Anorg. Allg. Chemie 256 (1948) 
15; and A. S. Russel, K. E. Martin, and C. N. Cochran, Am. Chem. Soc. 73 
(1951) 1466. Precursor transport to the reaction zone required however 
prohibitively high temperatures (&gt;700.degree. C.) and made the process 
impractical. 
More recently, several reports were published on the formation of a 
sensitizing layer on SiO.sub.2 prior to aluminum CVD and on the use of new 
organoaluminum source precursors, such as triisobutylaluminum (TIBA) and 
trimethylamine-alane (TMAAl). See, e.g., R. A. Levy, P. K. Gallagher, R. 
Contolini, and F. Schrey, J. Electrochem. Soc. 132 (1985) 457; B. E. Bent, 
R. G. Nuzzo, and L. H. Dubois, J. Am. Chem. Soc. 111 (1989) 1634, and H. 
O. Pierson, Thin Solid Films, 45 (1977) 257; M. E. Gross, K. P. Cheung, C. 
G. Fleming, J. Kovalchick, and L. A. Heimbrok, J. Vac. Sci. Technolo. A9 
(1991) 1; M. E. Gross, L. H. Dubois, R. G. Nuzzo, and K. P. Cheung, Mat. 
Res. Symp. Proc., Vol 204 (MRS, Pittsburgh, Pa., 1991) p. 383; W. L. 
Gladfelter, D. C. Boyd, and K. F. Jensen, Chemistry of Mater. 57 (1989) 
339; D. B. Beach, S. E. Blum, and F. K. LeGoues, J. Vac. Sci. Technol. A7 
(1989) 3117. In addition, NTT in Japan announced the development of a 
multilayer wiring technique based on a selective Al CVD process. However, 
the process requires high vacuum capabilities of rf plasma pre-cleaning 
for in-situ impurity removal from the inner surface of the via holes. 
In spite of all attempts, only a few of which have been cited here, 
low-temperature (&lt;475.degree. C.) CVD of device-quality aluminum is not 
yet feasible. Some particular problems encountered include prohibitive 
surface roughness, impurity contamination (especially oxygen and carbon 
which bond well to aluminum), high deposition temperature, and the lack of 
sensitized layers that allows precursor decomposition on initial, 
insulating, surfaces. In addition, as discussed below, prior CVD methods 
fail to provide device-quality aluminum and aluminum-copper alloys with 
conformal step coverage for substrates having aggressive holes and 
trenches (i.e., with a diameter of 0.25 .mu.m .mu.m or smaller) and high 
aspect ratios (i.e., the ratio of hole depth to hole width equal to or 
greater than about 4:1). 
So, there is a long felt, critical need for a process and apparatus to 
provide specular and pure aluminum and doped aluminum (aluminum with a few 
percent of other elements, such as copper) films suitable for ULSI 
fabrication. A typical, specular aluminum film has a grain size below a 
few thousand angstroms. Such films must be of ultra high quality, in terms 
of purity, with impurity concentrations well below 1 atomic percent, must 
exhibit excellent electromigration properties, must be highly specular, 
with extremely smooth surface morphology, and must be conformal to the 
complex topography of ULSI circuity to provide complete filling of 
aggressive via and trench structures. The desired process and apparatus 
should readily prepare single films containing either aluminum or copper 
doped aluminum, as well as bilayer films of aluminum and copper, and that 
such technology be amenable to process temperatures below about 
475.degree. C. to prevent thermally induced devices damage during 
processing. 
Copper doping is required to enhance aluminum's resistance to 
electromigration. This could be achieved through sequential deposition of 
aluminum then copper, followed by annealing or rapid thermal processing 
(RTP) to alloy the two films and produce a homogeneous copper-doped 
aluminum phase. However, work was recently published on the CVD formation 
of aluminum films doped with 0.7-1.4 wt % copper through the simultaneous 
decomposition in the same CVD reactor of dimethylaluminum hydride (DMAH) 
and cyclopentadienyl copper triethylphosphine which were employed, 
respectively, as the aluminum and copper sources. See T. Katagiri, E. 
Kondoh, N. Takeyasu, T. Nakano, H. Yamamoto, and T. Ohta, Jpn. J. Appl. 
Phys. 32 (1993)LI078 and J. Electrochem. Soc. 141 (1994) 3494. 
Unfortunately, the copper source used in the work was highly reactive and 
unstable during transport and handling, which makes it undesirable for 
real industrial applications. The references fail to disclose plasma 
assisted CVD and the substrate that receives the copper is not 
electrically biased. Clearly, there is critical need for stable copper 
sources which are free of oxygen, fluorine, and halides, and which are 
compatible with aluminum precursors to prevent any cross-contamination 
effects during film growth. 
It is especially desirable that the process and apparatus allows for the 
preparation of the above-mentioned films in-situ, i.e., without the 
necessity of transferring a substrate coated with a single film (Al or Cu) 
to another reaction chamber to deposit the other film. As is known in the 
art, a process which allows either in-situ deposition of sequential 
bilayers of Al and Cu followed by in-situ annealing, or in-situ 
simultaneous deposition of copper-doped aluminum is desirable in part 
because of the high affinity of aluminum for oxygen. This affinity leads 
typically to contamination of the Al film surface during transfer to a 
second reaction chamber where it is coated with Cu. The oxidized aluminum 
surface interferes with annealing of aluminum and copper. 
SUMMARY OF THE INVENTION 
The invention includes a method and apparatus for the chemical vapor 
deposition of conformal metal layers on substrates. In particular, the 
invention deposits aluminum metalization layers on semiconductor 
substrates such as silicon and gallium arsenide. The invention deposits 
other metal layers, such as copper. The invention deposits of two or more 
metals either simultaneously or sequentially. Thus, the invention, can 
form an alloy of two or more metals simultaneously with the deposition of 
a single alloy layer. As an alternative, one may deposit, in-situ, 
sequential, separate layers of two or more metals. With the invention 
sequentially deposited layers are annealed to form an alloy layer. The 
annealing step takes place in-situ in the reactor without removing the 
substrate therefrom. 
The invention provides a low temperature, heat assisted chemical vapor 
deposition process and apparatus. With the invention, aluminum, or copper, 
or both, are deposited on the substrate. This process is carried out by 
using aluminum and/or copper precursor gases. The precursor gases are 
reacted with hydrogen or other suitable reactant gases. The reaction takes 
place in a reactor under a vacuum and at a temperature less than 
500.degree. centigrade. 
The invention electrically assists chemical vapor deposition. An electrical 
bias is applied to the substrate. The electrical bias may be less than 10 
watts and at a frequency less than 500 kHz. The local electrical field in 
the region of the surface of the substrate likely enhances the chemical 
reaction between the reactant gas and the aluminum or copper precursor gas 
so that the metal is released from the precursor and deposited on the 
substrate. 
The invention is also a plasma assisted chemical vapor deposition process. 
The invention uses plasmas of relatively small power to deposit metal 
films. Substantially any suitable precursor gas and reactant gas can be 
used in order to deposit conformal metal films with plasma assisted 
chemical vapor depositions. A metal precursor gas and a reactant gas are 
mixed in a reactor. The reactor is under a vacuum and may be heated to a 
temperature less than 250.degree. centigrade. A relatively small plasma is 
created by electrodes disposed on either side of the substrate. The plasma 
may be as small as a plasma in the range between 0.005 and 2.5 watts per 
centimeters square. The plasma interacts with reactant gas to form a 
plasma of the reactant gas. The plasma of the reactant gas likely enhances 
the release of metal from the metal precursor gas. Suitable aluminum or 
copper metal precursor will work with any suitable reactant gas, such as 
hydrogen, helium, argon, xenon, nitrogen, or a mixture thereof. 
Two key aspects of the invention are: (a) the use of a low power density 
plasma, which promotes precursor decomposition at lower temperatures than 
thermal CVD without undesirable side effects, and (b) the application of 
substrate bias which serves a dual role. Its first role, it turns out, is 
the actual formation of a "soft" plasma region just above the wafer which 
also promotes decomposition. Its second role is to attract the ionized Al 
species to the various topographical region of the substrate, leading to 
conformal via and trench filling. Accordingly, under appropriate plasma 
and/or substrate bias conditions, all chemical sources are expected to 
work.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention includes CVD-based processes that deposit aluminum and 
copper-doped aluminum films which are suitable as signal conductors (both 
plug and interconnect) in integrated circuit fabrication, and, in 
particular in ULSI fabrication. The invention directs selected precursors 
to a thermal or plasma promoted CVD reactor, under specified reaction 
conditions, to deposit high quality metal films including layers of 
aluminum, copper, and aluminum alloys. 
As used herein, the term "aluminum film" refers to a film made from pure 
aluminum metal. Also, the term "doped aluminum film" is used to refer to a 
film made from blends of aluminum metal and a second metal which is 
selected from Groups Ib, IIb and VIIIb of the Periodic Table, such as 
copper. Also the term "bilayered aluminum film" refers to bilayers formed 
from any of aluminum metal, copper metal and blends thereof, which are 
subsequently annealed to yield an aluminum-copper alloy. 
According to one embodiment of the present invention, aluminum-based films 
form at low temperatures and have smooth surface morphology by using 
plasma promoted chemical vapor deposition (PPCVD). As used herein PPCVD 
refers to a CVD process wherein all reactants are introduced to the CVD 
reactor in gaseous form, and the energy necessary for bond cleavage is 
supplied partially by the high energy electrons formed in glow discharges 
or plasmas with low plasma power densities (below 0.25 W/cm.sup.2). This 
technique takes advantage of the high energy electrons present in glow 
discharges to assist in the dissociation of gaseous molecules, as is the 
case with plasma enhanced CVD (PECVD), thus leading to film formation at 
lower substrate temperatures than in thermal CVD processes. However, in 
contrast to PECVD which uses high plasma power densities, the low power 
densities employed in PPCVD prohibit electron- and ion-induced precursor 
fragmentation and substrate and film damage, thus producing films with 
electronic-grade purity and reduced stress levels. According to the 
preferred method, the plasma is generated through use of radio frequency 
(RF) glow discharges, although plasmas with frequencies ranging from kHz 
to GHz could be employed. See, generally, Hess, D. W. and Graves D. B., 
"Plasma-Assisted Chemical Vapor Deposition", chapter 7 in "Chemical Vapor 
Deposition, Principles and Applications," Hitchman, M. L. and Jensen, K. 
F. eds., Academic Press (1993). 
The PPCVD reactor of the invention has several basic components: a 
precursor delivery system which stores and controls the delivery of the 
source precursor, a vacuum chamber and pumping system that maintains an 
appropriately reduced pressure; one power supply that creates the 
discharge; another power supply to apply a bias to the substrate; a 
temperature control system; and gas or vapor handling capabilities to 
meter and control the flow of reactants and products that result from the 
process. 
FIG. 1 shows the inventive CVD reactor. The aluminum source precursor 10 is 
placed in the reservoir (bubbler/sublimator) 11 which could be heated by a 
combination resistance heating tape and associated power supply 12 to a 
temperature which is high enough to ensure the sublimation or vaporization 
of the aluminum source, but not too high to cause its premature 
decomposition. A mass flow controller 13, which can be isolated from the 
bubbler by a high vacuum valve 14, controls the flow of gas (hydrogen, 
argon, xenon, or nitrogen) into the reservoir through inlet 15. This gas 
from reservoir 11 serves as carrier agent when a conventional pressure or 
temperature based mass flow control type delivery system 11 and 13 is 
employed to control the flow of precursor into the CVD reactor 17. 
Alternatively, the gas serves as a pressurizing agent when a liquid 
delivery system 16, consisting of a combination micropump and vaporizer 
head, such as the MKS Direct Liquid Injection (DLI) system, is used to 
deliver the precursor to the CVD reactor 17. A third possibility is to use 
a hot source mass flow controller 16, such as an MKS Model 1150 MFC, which 
does not require the use of a carrier or pressurizing gas. In any case, 
the precursor delivery system is isolated from the precursor reservoir 11 
by a high vacuum valve 18, and the precursor vapor or (precursor+carrier 
gas) mixture vapors is then transported through a high vacuum isolation 
valve 19 and a cone-shaped shower head 20 into the CVD reactor 17. The 
shower head 20 is employed to ensure proper reactant mixing and uniformity 
in reactant delivery and flow over 8" wafers. In one embodiment, the cone 
was 18" high, and was designed with conflat type top and bottom fittings. 
The bottom opening (towards the reactor) was 7", while the top opening was 
1.3". All transport and delivery lines and high vacuum isolation valves 
18, 19, and 20 are maintained at the precursor sublimation/vaporization 
temperature, using typical combinations of resistance heating tapes and 
associated power supplies 21 and 22, to prevent precursor recondensation. 
The reactor 17 is an 8" wafer, cold wall stainless steel CVD reactor. It is 
equipped with a parallel plate type plasma configuration made of two 
electrodes 26 and 27, with the reactor itself providing electrical 
grounding. The upper plate 26 serves as the active discharge electrode and 
is driven by a plasma generator 28, such as a radio frequency (13.56 MHz) 
power supply. This upper plate is constructed in a "mesh" type pattern to 
allow unconstricted reactant flow to the substrate 29. In all cases, a 
hydrogen plasma is used for in-situ pre-deposition substrate cleaning at 
plasma power densities in the range 0.005 to 2.5 W/cm.sup.2, while a 
plasma consisting of hydrogen, an argon-hydrogen, or nitrogen-hydrogen 
mixture is employed during PPCVD of Al and doped Al film growth. No plasma 
is employed during thermal CVD deposition. A mass flow controller 23, 
which can be isolated from the bubbler by a high vacuum valve 24, is used 
to ensure delivery of additional hydrogen, argon, or nitrogen flow to the 
reactor through the side feedthrough 25. The substrate (wafer) 29 is 
placed on the lower electrode 27, and is heated to processing temperatures 
in the range 70-450.degree. C. by an 8" resistive heater 30. The lower 
plate also serves as the bias electrode and could be driven by a frequency 
generator 31, such as a low frequency (95-450 kHz) power supply, when, 
according to some preferred embodiments, thermal or plasma promoted CVD 
with biased substrate are used. 
To guarantee process cleanliness, the reactor is periodically baked under a 
nitrogen, argon, or hydrogen atmosphere to below 0.3 Torr and then pumped 
down to below 10.sup.-7 Torr for an hour at 150.degree. C. The pumping 
stack 32 consists of two pumping packages, the first cryogenic or 
turbomolecular pump based, and the second roots blower pump based, and is 
isolated from the reactor high conductance pumping lines 33 by the high 
vacuum gate valve 34. The cryogenic pump based package is used to ensure 
high vacuum base pressure in the reactor, while the roots blower based 
package is employed for appropriate handling of the high gas throughput 
during actual CVD runs. A high vacuum load lock system is typically used 
for transport and loading of 8" wafers into the reactor. 
In the case of copper doped aluminum films, the copper source precursor 35 
is placed in the reservoir (bubbler/sublimator) 36 which could be heated 
by a combination resistance heating tape and associated power supply 37 to 
a temperature which is high enough to ensure the sublimation or 
vaporization of the copper source, but not too high to cause its premature 
decomposition. A mass flow controller 38, which can be isolated from the 
bubbler by a high vacuum valve 39, is used to control the flow of gas 
(hydrogen, argon, xenon, or nitrogen) into the reservoir through inlet 40. 
This gas serves as carrier agent when a conventional pressure or 
temperature based mass flow, control type delivery system 36 and 38 is 
employed to control the flow of precursor into the CVD reactor 17. 
Alteratively, the gas serves as a pressurizing agent when a liquid 
delivery system 41, consisting of a combination micropump and vaporizer 
head, such as the MKS Direct Liquid Injection (DLI) system, is applied to 
the delivery of the precursor to the CVD reactor 17. A third possibility 
is to use a hot source mass flow controller 41, such as an MKS Model 1150 
MFC, which does not require the use of a carrier or pressurizing gas. In 
any case, the delivery system is isolated from the precursor reservoir by 
a high vacuum valve 42, and the precursor vapor or (precursor+carrier gas) 
mixture vapors is then transported through a high vacuum isolation valve 
19 and a cone-shaped shower head 20 into the CVD reactor 17. All transport 
and delivery lines and high vacuum isolation valves 39, 40, and 42, are 
maintained at the copper precursor sublimation/vaporization temperature, 
using a typical combination of resistance heating tape and associated 
power supply 43, to prevent precursor recondensation. 
We have discovered that the use of a plasma-promoted CVD (PPCVD) process 
allows the growth of aluminum films with the smooth surface morphology and 
small grain size necessary for ULSI applications. This discovery is in 
agreement with the results observed for plasma enhanced CVD (PECVD) 
processes. See, for example, A. Weber, U. Bringmann, K. Schifftnann, and 
C. P. Klages, Mat. Res. Symp. Proc. 282 (1993) p. 311. However, PECVD 
employs glow discharges or plasmas with high power densities. Such high 
densities cause undesirable gas phase precursor fragmentation, leading to 
significant film contamination with carbon, nitrogen, and other elements 
from the source precursor, and prohibiting use of the resulting film in 
computer chip technologies. In contrast, our PPCVD process employs low 
plasma power densities (between 0.005 and 2.5 W/cm.sup.2). Such low power 
densities prohibit undesirable electron- and ion-induced precursor 
fragmentation and lead to the growth of films with electronic-grade purity 
and reduced stress levels. 
While not wishing to be bound by theory, we offer the following explanation 
for the efficacy of our process. In our method, the plasma provides a high 
concentration of the reactive hydrogen species which play a dual role: 
They act as reducing agent which bonds with the free ligands and various 
hydrocarbon fragments resulting from precursor decomposition, thus 
preventing them from recombining with the aluminum atoms and getting 
incorporated in the growing film. The result is a pure aluminum film which 
is free of any oxygen or carbon impurities from the precursors. 
Additionally, these reactive hydrogen species provide an in-situ means for 
substrate surface pre-deposition treatment. This treatment decreases the 
nucleation barrier. In CVD processing, the substrate surface plays a 
critical role in "catalyzing" the reaction that leads to precursor 
decomposition and film nucleation and growth. When the substrate surface 
is not properly cleaned or "conditioned" prior to deposition, surface 
contaminants may act as nucleation barriers by preventing precursor 
adsorption and decomposition. Another factor that contributes to the 
so-called nucleation barrier is surface defects. A surface treated with 
hydrogen provides a uniform seed layer for aluminum grain formation, thus 
leading to the formation of aluminum films with smooth surface morphology. 
It is important to produce films with a grain size which is not too small 
as to cause poor electrical performance (due to electron scattering at the 
grain boundaries) but which is not too large to lead to poor via and 
trench fill and unacceptable surface roughness. 
We have also discovered that, in contrast to other chemical vapor 
deposition methods, our method provides superior coverage and complete 
aluminum fill of features intrinsic in microelectronic device manufacture. 
This superior coverage is achieved by combining PPCVD with substrate bias. 
Substrate bias significantly enhances the flux of aluminum ions impinging 
on the substrate and a increases in the re-emission probability of such 
atoms inside via and trench structures. These re-emission processes 
improve step coverage in patterned holes, vias, and trenches with 
aggressive aspect ratios (0.25 .mu.m features with 4 to 1 aspect ratios 
and beyond). 
We have also discovered that the aluminum and copper delivery systems can 
be combined to produce copper-doped aluminum films can be prepared by 
PPCVD in-situ, i.e., without the necessity of transferring a substrate 
coated with a single film (Al or Cu) to another reaction chamber to 
deposit the other film. This approach allows either in-situ deposition by 
PPCVD of sequential bilayers of Al and Cu followed by in-situ annealing, 
or in-situ simultaneous PPCVD deposition of copper-doped aluminum. Our 
process can also be applied to coatings for refractive, mechanical, 
optoelectronic, or decorative applications in applications other than 
microelectronic. 
The following examples are set forth as a means of illustrating the present 
invention and are not to be construed as a limitation thereon. All 
chemical vapor deposition studies were conducted in the custom designed 
cold-wall aluminum reactor described above and having a single 8 inch 
wafer, a parallel plate-type plasma configuration, and a load locked wafer 
transport system, as shown diagrammatically in FIG. 1. 
EXAMPLE 1 
Preparation of Al Films by Thermal CVD using DMAH and H.sub.2 
Thermal chemical vapor deposition was carried out with the reactor shown in 
FIG. 1, using dimethyl aluminum hydride (DMAH) as the aluminum source. The 
DMAH precursor 10 was placed in the bubbler/sublimator 11 which was heated 
by a combination constant temperature oil bath and associated power supply 
12 to temperatures between 20 and 40.degree. C., during the CVD process. 
An MKS Model 1150 manufactured by MKS of Andover, Mass. hot source mass 
flow controller 16, which can be isolated from the bubbler by a high 
vacuum valve 18, controlled a flow of 0-10 sccm of the DMAH precursor into 
the CVD reactor. All transport and delivery lines and high vacuum 
isolation valves 18, 19, and 20 were maintained at temperatures in the 
range 30 to 60.degree. C., using a combination heating tape and associated 
power supply 21 and 22, to prevent precursor recondensation. 
The reactor was an 8" wafer, cold wall stainless steel CVD reactor. It was 
equipped with a parallel plate type plasma configuration made of two 
electrodes 26 and 27 with the reactor itself providing electrical 
grounding. The upper plate 26 served as the active electrode and was 
driven by the radio frequency (13.56 MHz) power supply 28. It was 
constructed in a "mesh" type pattern to allow unconstricted reactant flow 
to the substrate. A hydrogen plasma was used for in-situ pre-deposition 
substrate cleaning at plasma power densities in the range 0.05-0.25 
W/cm.sup.2, while no plasma was employed during actual deposition for 
thermal CVD. The substrate (wafer) was placed 0on the lower electrode 27, 
which was not biased in this case, and was heated to processing 
temperatures in the range 150-225.degree. C. by an aluminum-encapsulated 
resistive heater 30. The cone shaped shower head 20 was employed to ensure 
proper reactant mixing and uniformity in reactant delivery and flow over 
8" wafers. 
To guarantee process cleanliness, the reactor was periodically baked under 
a hydrogen atmosphere to below 0.2 Torr and then pumped down to below 
10-.sup.7 Torr for an hour at 150.degree. C. The pumping stack 32 
consisted of two pumping packages, the first is turbomolecular pump based, 
and the second roots blower pump based, and was isolated from the reactor 
by the high vacuum gate valve. The turbomolecular pump based package was 
used to ensure high vacuum base pressure in the reactor, while the roots 
blower based package was employed for appropriate handling of the high gas 
throughput during actual CVD runs. A high vacuum load lock system was used 
for transport and loading of 8" wafers into the reactor. Finally, a side 
line 25 was employed to feed the hydrogen gas into the reactor. The 
H.sub.2 flow of 100 to 1000 sccm was controlled by a mass flow controller 
23 and associated isolation valve 24. 
The Al films thus produced were metallic, continuous, and silver colored. 
Their structural and electrical properties as well as chemical 
composition, were thoroughly analyzed by x-ray diffraction (XRD), Auger 
electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), 
Rutherford backscattering (RBS), four point resistivity probe, and 
cross-sectional SEM (CS-SEM). 
As illustration of the quality of the films, FIG. 2 shows a depth profile 
AES spectrum of an aluminum film grown as detailed above. The sample was 
sputter cleaned before data acquisition, and the results were calibrated 
using a sputtered aluminum sample. In quantitative AES analysis, one needs 
a standard of known composition (for example a pure aluminum thin film 
deposited by sputtering) to use as a baseline in determining the 
concentrations of Al and impurities, if any, which are present in the CVD 
grown sample. In this case, the "standard" (i.e., sputtered sample of 
known composition) is analyzed at the same time as the "unknown" (i.e., 
the CVD sample) under identical conditions and the resulting signal from 
the standard is employed to "quantify" the signal from the unknown. The 
choice of a standard of composition and chemical environment and bonding 
similar to that of the CVD film allowed high accuracy in AES analysis. The 
results are based on the expectation that chemical and structural changes, 
if any, induced during the sputter cleaning process are basically the same 
in the standard and CVD produced films. The AES survey spectrum (FIG. 2) 
indicated that, within the detection limits of AES, the Al films were free 
of oxygen, carbon, and similar light element contaminants. Four point 
resistivity probe measurements yielded a resistivity value of 3.4 
.mu..OMEGA.cm. 
The reactions in thermal Al CVD are quite complex because of the dynamic, 
non-equilibrium environment which characterizes CVD processing. This 
complexity is enhanced by the use of a plasma in the case of PPCVD. 
Accordingly, one can only provide general guidelines or "models" on the 
most likely reactions that might be taking place. For instance, in the 
case of thermal CVD from DMEAA, M. E. Gross et al. (M. E. Gross, K. P. 
Cheung, C. G. Fleming, J. Kovalchick, and L. A. Heimbrok, J. Vac. Sci. 
Tehnolo. A9 (1991) 1), proposed the following model: 
##STR1## 
where the subscripts ads, g, and m correspond to, respectively, absorbed 
(on the substrate surface), gaseous (i.e., in the gas phase), and metallic 
(i.e., actual film). Similar models exist for DMAH. 
The thermal CVD method disclosed above can also be used to deposit layers 
of copper. Alternate layers of copper aluminum are deposited and the 
annealed in-situ to provide a layer of copper doped aluminum. Annealing is 
done for 100 minutes at 450.degree. C. in a hydrogen ambient at a working 
pressure of 50-250 torr. A typical CVD copper deposition is summarized as 
follows: 
______________________________________ 
Source Cu.sup.1 (hfac) (trimethylvinylsilane, "tmvs") 
Delivery Rates (liquid) 
0.05 to 5.0 cc/min 
Working Pressure 
50-5000 mtorr 
Carrier Gas None 
Reactant H.sub.2 (25-2000 sccm) 
Vaporization T. 
20-60.degree. C. 
Substrate T 120-350.degree. C. 
Substrate Bias 0-100 W 
______________________________________ 
Where hfac=hexafluoroacetylacetonate and tmvs=trimethyl vinyl silane 
EXAMPLE 2 
Preparation of Al Films by Thermal CVD using DMEAA and H.sub.2 
According to another preferred embodiment, the CVD reactor shown in FIG. 1 
was again employed for the deposition of Al from the chemical source 
dimethylethylamine alane (DMEAA), instead of DMAH. The runs were performed 
under processing conditions similar to those listed above for DMAH, except 
for the temperature of the bubbler/sublimator which was heated in this 
case to temperatures between 20 and 50.degree. C. during the CVD process. 
Similarly, all transport and delivery lines and high vacuum isolation 
valves were maintained at temperatures in the range 20 to 60.degree. C., 
using a combination heating tape and associated power supply, to prevent 
precursor recondensation. The Al films produced by CVD of DMEAA were again 
metallic, continuous, and silver colored for films with thicknesses below 
2000 .ANG.. Analyses by x-ray diffraction (XRD), x-ray photoelectron 
spectroscopy (XPS), Rutherford backscattering (RBS), four point probe, and 
cross-sectional SEM (CS-SEM), indicated that their structural, chemical, 
and electrical properties are equivalent to those produced by CVD of DMEAA 
except for film resistivities, which were as low as 3.2 .mu..OMEGA.cm in 
this case. AES survey spectrum (FIG. 1) indicated that, within the 
detection limits of AES, the Al films were free of oxygen, carbon, and 
light element contaminants. Typical deposition conditions and film 
properties are summarized in Tables I and II for films produced by thermal 
CVD from, respectively, DMAH and DMEAA with no biased substrate. 
TABLE I 
______________________________________ 
Typical Non-biased Thermal CVD Deposition Conditions for Al films 
Source DMAH DMEAA 
______________________________________ 
Working Pressure 
100-2500 mtorr 
100-2000 mtorr 
Carrier Gas None None 
Reactant H.sub.2 (100-2000 sccm) 
H.sub.2 (100-2000 sccm) 
Vaporization T 
20-70.degree. C. 
20-50.degree. C. 
Substrate T 120-450.degree. C. 
70-450.degree. C. 
Substrate Bias 
0 W 0 W 
Precursor Flow 
1-10 sccm 1-10 sccm 
______________________________________ 
TABLE II 
______________________________________ 
Typical Properties of Non-Biased Thermal CVD Deposited Al films 
Source DMAH DMEAA 
______________________________________ 
Purity &gt;99 at % Al &gt;99 at % Al 
As deposited .rho. 
as low as 3.4 .mu..OMEGA.cm 
as low as 3.2 .mu..OMEGA.cm 
Adherence 
Good on Si, SiO.sub.2 & TiN 
Good on Si, SiO.sub.2 & TiN 
Color Silver Silver 
Structure 
Polycrystalline Polycrystalline 
______________________________________ 
*Film properties are given at optimum flow conditions 
EXAMPLE 3 
Preparation of Al Films by PPCVD with Biased Substrate using DMEAA and 
H.sub.2 
According to yet one preferred embodiment, the CVD reactor shown in FIG. 1 
was employed for the PPCVD with biased substrate deposition of Al from 
dimethylethylamine alane (DMEAA). The DMEAA precursor 10 was placed in the 
bubbler/sublimator 11 which was heated by a combination constant 
temperature oil bath and associated power supply 12 to temperatures 
between 20 and 50.degree. C. during the CVD process. An MKS Model 1150 hot 
source mass flow controller 16, which can be isolated from the bubbler by 
a high vacuum valve 18, controlled a flow of 0-10 sccm of the DMEAA 
precursor into the CVD reactor. All transport and delivery lines and high 
vacuum isolation valves 18, 19, and 20 were maintained at temperatures in 
the range 30 to 60.degree. C., using a combination heating tape and 
associated power supply 21 and 22, to prevent precursor recondensation. 
The reactor was an 8" wafer, cold wall aluminum CVD reactor. It was 
equipped with a parallel plate type plasma configuration made of two 
electrodes 26 and 27 with the reactor itself providing electrical 
grounding. The upper plate 26 served as the active electrode and was 
driven by the radio frequency (13.56 MHz) power supply 28. It was 
constructed in a "mesh" type pattern to allow unconstricted reactant flow 
to the substrate. A hydrogen plasma was used for in-situ pre-deposition 
substrate cleaning at plasma power densities in the range 0.05-0.25 
W/cm.sub.2. Hydrogen plasma densities in the range 0.005 to 0.025 
W/cm.sub.2 were employed during actual deposition. The substrate (wafer) 
was placed on the lower electrode 27 which was biased by a low frequency 
power supply 31 at frequencies in the range 90-450 kHz at powers in the 
range 0.1-10 W. The substrate was heated to processing temperatures in the 
range 70-450.degree. C. by an aluminum-encapsulated resistive heater 30. 
To guarantee process cleanliness, the reactor was periodically baked under 
a hydrogen atmosphere to below 0.2 Torr and then pumped down to below 
10.sup.-7 Torr for an hour at 150.degree. C. The pumping stack 32 
consisted of two pumping packages, the first is turbomolecular pump based, 
and the second roots blower pump based, and was isolated from the reactor 
by the high vacuum gate valve. The turbomolecular pump based package was 
used to ensure high vacuum base pressure in the reactor, while the roots 
blower based package was employed for appropriate handling of the high gas 
throughput during actual CVD runs. A high vacuum load lock system was used 
for transport and loading of 8" wafers into the reactor. Finally, a side 
line 25 was employed to feed the hydrogen gas into the reactor. The 
H.sub.2 flow of 100 to 1000 sccm was controlled by a mass flow controller 
23 and associated isolation valve 24. 
The Al films thus produced were metallic, continuous, and silver colored. 
Their structural and electrical properties as well as chemical 
composition, were thoroughly analyzed by x-ray diffraction (XRD), x-ray 
photoelectron spectroscopy (XPS), four point probe, and cross-sectional 
SEM (CS-SEM). Typical deposition conditions and associated film properties 
are summarized in Tables III and for Al films produced by PPCVD with 
biased substrate from DMEAA. In particular, FIG. 4 exhibits a typical 
x-ray photoelectron spectroscopy (XPS) spectrum of an aluminum film 
produced by PPCVD from DMEAA and hydrogen with biased substrate. XPS 
results indicate a pure Al. 
TABLE III 
______________________________________ 
Typical Deposition Conditions for Al films 
Source DMEAA 
______________________________________ 
Working Pressure 100-2000 mtorr 
Reactant H.sub.2 (100-1000 sccm) 
Vaporization T 20-50.degree. C. 
Substrate T 70-450.degree. C. 
Plasma Power Density 
0.005-0.025 W/cm.sup.2 
Bias Power 0.1-10 W @ 100-450 kHz 
Precursor Flow 1-10 sccm 
______________________________________ 
TABLE IV 
______________________________________ 
Typical Properties of Al films* 
Property As deposited After Annealing** 
______________________________________ 
Source DMEAA DMEAA 
Purity &gt;99% Al &gt;99% Al 
Resistivity 
.about.4.2 .mu..OMEGA.cm 
3.2-3.4 .mu..OMEGA.cm 
Adherence 
Good on Si, SiO.sub.2 & TiN 
Good On Si, SiO.sub.2 & TiN 
Color Metallic Silver Metallic Silver 
Structure 
Polycrystalline Polycrystalline 
______________________________________ 
*Film properties are given at optimum flow conditions. 
**@ 450.degree. C. for 1 hour 40 minutes in a hydrogen atmosphere. 
phase with no light element (e.g., C, O, F, etc.) contamination. Also, FIG. 
5 is a Rutherford backscattering (RBS) spectrum of the same aluminum film. 
RBS results also indicate a pure Al phase with no contamination. The XPS 
and RBS results were confirmed with Auger electron Spectroscopy (AES), as 
shown in the AES spectrum in FIG. 6 of an aluminum film produced by PPCVD 
from DMEAA and hydrogen with biased substrate. AES results also indicate a 
pure Al phase with no light element (e.g., C, O, F, etc.) contamination. 
EXAMPLE 4 
Preparation of Al by Thermal CVD with Biased Substrate using DMEAA and 
H.sub.2 
According to yet one preferred embodiment, the CVD reactor shown in FIG. 1 
was employed for thermal CVD aluminum with biased substrate using 
dimethylethylamine alane (DMEAA) as the aluminum source. The DMEAA 
precursor was placed in the bubbler/sublimator which was heated by a 
combination constant temperature oil bath and associated power supply to 
temperatures between 20 and 40.degree. C. during the CVD process. An MKS 
Model 1150 hot source mass flow controller, which can be isolated from the 
bubbler by a high vacuum valve, controlled a flow of 0-10 sccm of the 
DMEAA precursor into the CVD reactor. All transport and delivery lines and 
high vacuum isolation valves were maintained at temperatures in the range 
30 to 60.degree. C., using a combination heating tape and associated power 
supply, to prevent precursor recondensation. 
The reactor was an 8" wafer, cold wall, aluminum CVD reactor. A parallel 
plate type plasma configuration made of two electrodes was employed with 
the reactor itself providing electrical grounding. The upper plate served 
as the active electrode and was driven by the 13.56 MHz radio frequency 
(rf) power supply. It was constructed in a "mesh" type pattern to allow 
unconstricted reactant flow to the substrate. A hydrogen plasma was used 
for in-situ pre-deposition substrate cleaning at plasma power densities in 
the range 0.05-0.25 W/cm.sup.2, while no rf power was applied to the upper 
plate during actual deposition. The substrate (wafer) was placed on the 
lower electrode, which was biased by a low frequency power supply at 
frequencies in the range 90-450 kHz at powers in the range 0.1-10 W. The 
substrate was heated to processing temperatures in the range 
70-450.degree. C. by an aluminum-encapsulated resistive heater. 
The cone shaped shower head was employed to ensure proper reactant mixing 
and uniformity in reactant delivery and flow over 8" wafers. To guarantee 
process cleanliness, the reactor was periodically baked under a hydrogen 
atmosphere to below 0.2 Torr and then pumped down to below 10.sup.-7 Torr 
for an hour at 150.degree. C. The pumping stack consisted of two pumping 
packages, the first is turbomolecular pump based, and the second roots 
blower pump based, and was isolated from the reactor by the high vacuum 
gate valve. The turbomolecular pump based package was used to ensure high 
vacuum base pressure in the reactor, while the roots blower based package 
was employed for appropriate handling of the high gas throughput during 
actual CVD runs. A high vacuum load lock system was used for transport and 
loading of 8" wafers into the reactor. Finally, a side line was employed 
to feed the hydrogen gas into the reactor. The H.sub.2 flow Of 100 to 1000 
sccm was controlled by a mass flow controller and associated isolation 
valve. 
The Al films thus produced were metallic, continuous, and silver colored. 
Their structural and electrical properties as well as chemical 
composition, were thoroughly analyzed by x-ray diffraction (XRD), Auger 
electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), 
Rutherford backscattering (RBS), four point resistivity probe, and 
cross-sectional SEM (CS-SEM). The results of these analyses are shown in 
Tables V and VI. 
As illustration of the quality of the films, FIG. 7 displays an Auger 
electron spectroscopy (AES) spectrum of an aluminum film produced by 
thermal CVD reaction of dimethylethylamine alane (DMEAA) and hydrogen with 
biased substrate. XPS results indicate a pure Al phase with no light 
element (e.g., C, O, F, etc.) contamination. 
TABLE V 
______________________________________ 
Typical Deposition Conditions for Al films 
Source DMEAA 
______________________________________ 
Working Pressure 100-2500 mtorr 
Reactant H.sub.2 (100-1000 sccm) 
Vaporization T 20-70.degree. C. 
Substrate T 80-175.degree. C. 
Plasma Power Density 
0.0 
Bias Power 0.1-10 W @ 100-450 kHz 
Precursor Flow 1-10 sccm 
______________________________________ 
TABLE VI 
______________________________________ 
Typical Properties of Al film* 
Property As deposited After Annealing** 
______________________________________ 
Source DMEAA DMEAA 
Purity &gt;99% Al &gt;99% Al 
Resistivity 
.about.4.2 .mu..OMEGA.cm 
3.2-3.4 .mu..OMEGA.cm 
Adherence 
Good on Si, SiO.sub.2 & TiN 
Good On Si, SiO.sub.2 & TiN 
Color Metallic Silver Metallic Silver 
Structure 
Polycrystalline Polycrystalline 
______________________________________ 
*Film properties are given at optimum flow conditions. 
**@ 450.degree. C. for 1 hour 40 minutes in a hydrogen atmosphere. 
EXAMPLE 5 
In-situ Sequential Preparation of Al/Cu Bilayers by PPCVD using 
DMEAA/Cu(hfac).sub.2 /H.sub.2 Followed by in-situ Annealing 
According to yet one preferred embodiment, the CVD reactor shown in FIG. 1 
was employed for the in-situ sequential deposition of Al then Cu layers 
from, respectively, DMEAA and Cu.sup.II (hfac).sub.2, where 
hfac=hexafluoroacetylacetonate. The Al layer was first grown by the PPCVD 
as described previously in Example 3. 
This step was immediately followed in-situ with PPCVD copper. The copper 
source precursor Cu.sup.II (hfac).sub.2 35 is placed in the reservoir 
(bubbler/sublimator) 36 in FIG. 1 which could be heated by a combination 
resistance heating tape and associated power supply 37 to a temperature in 
the range 50-100.degree. C. This temperature range was selected to ensure 
the sublimation or vaporization of the copper source, while avoiding its 
premature decomposition. A mass flow controller 38 , which can be isolated 
from the bubbler by a high vacuum valve 39, is used to control the flow of 
hydrogen carrier gas into the reservoir through inlet 40. This gas served 
as carrier agent since a conventional pressure based mass flow control 
type delivery system 41 was employed to control the flow of copper 
precursor into the CVD reactor 17. The copper delivery system could be 
isolated from the precursor reservoir by a high vacuum valve 42. The 
(precursor+carrier gas) mixture vapor is then transported through a high 
vacuum isolation valve 19 and a cone-shaped shower head 20 into the CVD 
reactor 17. All transport and delivery lines and high vacuum isolation 
valves 39, 40, and 42, are maintained at the copper precursor 
sublimation/vaporization temperature (50-100.degree. C.), using a typical 
combination of resistance heating tape and associated power supply 43, to 
prevent precursor recondensation. Ultrathin copper films were grown 
in-situ on the top of the aluminum films at substrate temperature of 
130-200.degree. C., plasma power density of 0.05 to 0.25 W/cm.sup.2, zero 
substrate bias, hydrogen carrier gas flow of 10 to 100 sccm, hydrogen 
reactant flow of 100-1000 sccm, and reactor working pressure of 100-2000 
mtorr. After the copper deposition step was completed, in-situ annealing 
of the Al and Cu bilayer was performed for 100 minutes at 450.degree. C. 
in a hydrogen ambient at a working pressure of 50-250 mtorr. 
The Cu doped Al films thus produced were metallic, continuous, and silver 
colored. Their structural and electrical properties as well as chemical 
composition, were thoroughly analyzed by x-ray diffraction (XRD), Auger 
electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), 
Rutherford backscattering (RBS), four point resistivity probe, and 
cross-sectional SEM (CS-SEM). The resulting films were pure aluminum with 
0.4 to 0.9 at % copper and as-deposited resistivity of 4.7 .mu..OMEGA.cm. 
As illustration of the quality of the films, FIG. 8 displays a Rutherford 
backscattering (RBS) spectrum of a copper-doped aluminum film produced by 
in-situ sequential deposition of Al then Cu layers followed by in-situ 
annealing. RBS indicated a pure aluminum film with 0.5 at % Cu, with the 
copper being uniformly distributed across the aluminum film. 
EXAMPLE 6 
In-situ Simultaneous PPCVD of Al-0.5 at % Cu 
According to yet one preferred embodiment, the CVD reactor shown in FIG. 1 
was employed for the in-situ simultaneous deposition of Cu doped Al using 
DMAH and copper n,n'-dimethyl diketenimidate as sources for, respectively, 
aluminum and copper. The DMEAA precursor 10 was placed in the 
bubbler/sublimator 11 which was heated by a combination constant 
temperature oil bath and associated power supply 12 to temperatures 
between 20 and 40.degree. C. during the CVD process. An MKS Model 1150 hot 
source mass flow controller 16, which can be isolated from the bubbler by 
a high vacuum valve 19, controlled a flow of 0-10 sccm of the DMAH 
precursor into the CVD reactor 17. All transport and delivery lines and 
high vacuum isolation valves 18, 19, and 20 were maintained at 
temperatures in the range 30 to 60.degree. C., using a combination heating 
tape and associated power supply 22, to prevent precursor recondensation. 
The copper source precursor Cu n,n'-dimethyl diketenimidate 35 was placed 
in the reservoir (bubbler/sublimator) 36, which could be heated by a 
combination resistance heating tape and associated power supply 37 to a 
temperature in the range 90-175.degree. C. This temperature range was 
selected to ensure the sublimation or vaporization of the copper source, 
while avoiding its premature decomposition. A mass flow controller 38, 
which can be isolated from the bubbler by a high vacuum valve 39, is used 
to control the flow of hydrogen carrier gas into the reservoir through 
inlet 40. This gas served as carrier agent since a conventional pressure 
based mass flow control type delivery system 41 was employed to control 
the flow of copper precursor into the CVD reactor 17. The copper delivery 
system could be isolated from the precursor reservoir by a high vacuum 
valve 42. The (precursor+carrier gas) mixture vapor is then transported 
through a high vacuum isolation valve 19 and a cone-shaped shower head 20 
into the CVD reactor 17. All transport and delivery lines and high vacuum 
isolation valves 39, 40, and 42, are maintained at the copper precursor 
sublimation/vaporization temperature (100-200.degree. C.), using a typical 
combination of resistance heating tape and associated power supply 43, to 
prevent precursor recondensation. 
In-situ copper doped aluminum films were thus grown in-situ at substrate 
temperature of 130-250.degree. C., plasma power density of 0.05 to 0.25 
W/cm.sup.2, low frequency substrate bias of 90-200 kHz at 0.1-10 W, 
hydrogen carrier gas flow of 10-100 sccm for the copper source, hydrogen 
reactant flow of 100-1000 sccm, and reactor working pressure of 100-2000 
mtorr. 
The Al films thus produced were metallic, continuous, and silver colored. 
Their structural and electrical properties as well as chemical 
composition, were thoroughly analyzed by x-ray diffraction (XRD), Auger 
electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), 
Rutherford backscattering (RBS), four point resistivity probe, and 
cross-sectional SEM (CS-SEM). The results of these analyses are shown in 
Tables V and VI. 
The resulting films were aluminum with 0.5 at % copper. As illustration of 
the quality of the films, FIG. 9 displays a Rutherford backscattering 
(RBS) spectrum of a copper-doped aluminum film produced by in-situ 
sequential deposition of Al then Cu layers followed by in-situ annealing. 
RBS indicated a pure aluminum film with 0.5 at % Cu, with the copper being 
uniformly distributed across the aluminum film. 
In addition to the examples given above, other reactants are compatible 
with the invention. 
The aluminum source precursor employed in the practice of the present 
invention can be any aluminum-containing compound capable of dissociating 
to produce elemental aluminum. Examples of suitable aluminum source 
precursors include aluminum compounds used in conventional CVD processes, 
such as those described in, for example, C. F. Wan and K. E. Spear, in the 
Proceedings of the Seventh International Conference on Chemical Vapor 
Deposition, eds. L. F. Donaghey, P. Rai-Chaudhury, R. N. Tauber, Vol. 
75-77 (The Electrochem. Soc., Pennington, N.J., 1977) p. 47; C. F. Powell, 
J. H. Oxley, J. M. Blocher, Jr., Vapor Deposition (Wiley, New York, N.Y., 
1966) p. 277; H. J. Cooke, R. A. Heinecke, R. C. Stern, and J. W. C. Maas, 
Solid State Technol. 25 (1982) 62; W. Y.-C. Lai, R. Liu, K. P. Cheung, C. 
Case, L. F. Tz. Kwakman, and D. Huibreqtse, in the Proceedings of the 
Workshop on Tungsten and Other Advanced Metals for ULSI Applications 1990, 
eds. G. C. Smith and R. Blumenthal (MRS, Pittsburgh, 1991) p. 169; W. 
Klemm, E. Voss, and K. Geigersberger, Z. Anorg. Allg. Chemie 256 (1948) 
15; A. S. Russel, K. E. Martin, and C. N. Cochran, Am. Chem. Soc. 73 
(1951) 1466; R. A. Levy, P. K. Gallagher, R. Contolini, and F. Schrey, J. 
Electrochem. Soc. 133 (1985) 457; R. A. Levy, M. L. Green, and P. K. 
Gallagher, J. Electrochem. Soc. 131 (1985), 457; V. H. Houlding and D. E. 
Coorn, in the Proceedings of the Workshop on Tungsten and Other Advanced 
Metals for ULSI Applications 1990, eds. G. C. Smith and R. Blumenthal 
(MRS, Pittsburgh, 1991), p. 203; M. D. Gross, K. P. Cheung, C. G. Fleming, 
J. Kovalchick, and L. A. Heimbrok, J. Vac. Sci. Technolo. A9 (1991) 1. 
One suitable aluminum source precursor is trialkyl aluminums or 
dialkylaluminum hydrides having the formula AlR.sup.1 R.sup.2 R.sup.3. In 
this formula, R.sup.1 and R.sup.2 are alkyl and R.sup.3 is either, H or 
alkyl, or aryl. Alkyl groups can be substituted or unsubstituted and can 
be branched or straight. Examples of suitable alkyls include but are not 
limited to methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and 
tert-butyl. Suitable substituted alkyl groups include fluorinated alkyls, 
such as fluoromethyl, difluoromethyl, and perfluoromethyl, perfluoroethyl, 
perfluoroisobutyl, and the like. 
Aryl groups can be substituted or unsubstituted and can be monocyclic or 
polycyclic. Examples of suitable aryls include phenyl and naphthyl. 
Suitable substituted aryl groups include fluorinated aryls, such as 
4-fluorophenyl and perfluorophenyl, alkylated aryls, such ar tolyl, 
4-ethylphenyl, 4-(perfluoroethyl)-phenyl, and the like. 
R.sup.1, R.sup.2, and R.sup.3 can be different , such as where 
dimethylethylaluminum, methylethylaluminnum hydride, 
dimethylphenylaluminum, methylphenylaluminum hydride, 
methylethylispropylaluminum, and methylisobutyl aluminum hydride are used 
as aluminum source precursors. However, because of their commercial 
availability, trialkylaluminum source materials where R.sup.1, R.sup.2, 
and R.sup.3 are the same, such as trimethylaluminum, triethylaluminum, 
tri-n-propylaluminum, tri-isopropylaluminum, tri-n-butylaluminum, 
tri-isobutylaluminum, and tri-tert-butylaluminum, triphenylaluminum, are 
preferred. Where dialkylaluminum hydrides are employed, preferred aluminum 
source precursors are those in which R.sup.1, and R.sup.2, are the same, 
such as dimethylaluminum hydride, diethylaluminum hydride, 
di-n-propylaluminum hydride, di-isopropylaluminum hydride, 
di-n-butylaluminum hydride, di-isobutylaluminum hydride, 
di-tert-butylaluminum hydride, and diphenylaluminum hydride. 
Another class of compounds suitable for use as an aluminum source 
precursors in practicing the methods of the present invention include the 
aluminum halides having the formula AlX.sup.1 X.sup.2 X.sup.3. In this 
formula, X.sup.1, X.sup.2, and X.sup.3 can be the same or different and 
can be F, Cl, Br, or I. Illustrative aluminum halides include aluminum 
trifluoride, aluminum trichloride, aluminum tribromide, aluminum 
triiodide, diflourochloroaluminunum, dichlorofluoroaluminum, 
difluorobromoaluminum, fluorodibromoaluminum, dichlorobromoaluminum, and 
fluorochlorobromoaluminum. 
The aluminum source precursor can also be an aluminum 
tris(.beta.-diketonate), such as those having the formula Al(R.sup.1 
COCHCOR.sup.2).sub.3. R.sup.1 and R.sup.2 are the same or different and 
are selected from the group consisting of alkyl, aryl, halogenated alkyl, 
or halogenated aryl. Alkyl groups can be, for example, methyl, ethyl, or 
branched or straight chain propyl, butyl, pentyl, or hexyl. Aryl groups 
include, for example, phenyl, tolyl, naphthyl, and the like. Halogenated 
alkyls and halogenated aryls include alkyl and aryl groups substituted 
with one or more halogen atoms, such as fluorine, chlorine, bromine, 
iodine, or combinations of these. Suitable R.sup.1 and R.sup.2 include 
CH.sub.3, CF.sub.3, C.sub.2 H.sub.5, C.sub.2 F.sub.5, n-C.sub.3 H.sub.7, 
n-C.sub.3 F.sub.7, iso-C.sub.3 H.sub.7, iso-C.sub.3 F.sub.7, n-C.sub.4 
H.sub.9, n-C.sub.4 F.sub.9, iso-C.sub.4 H.sub.9, iso-C.sub.4 F.sub.9, 
tert-C.sub.4 F.sub.9, tert-C.sub.4 F.sub.9, C.sub.6 H.sub.5, and C.sub.6 
F.sub.5. Although it is preferred (from the standpoint of preparing the 
aluminum source precursors) that all of the three .beta.-diketonate groups 
contain the same R.sup.1 and R.sup.2 combination, the three 
.beta.-diketonate groups need not be the same, such as, for example, where 
the aluminum source precursor is Al(CH.sub.3 COCHCOCF.sub.3).sub.2 
(C.sub.2 H.sub.5 COCHCOCF.sub.3). 
Alkyl amide aluminums having the formula (H.sub.2 Al:NR.sup.1 
R.sup.2).sub.3 can also be used as aluminum source precursors. In this 
formula, R.sup.1 and R.sup.2 are the same or different and are alkyl, such 
as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, and 
the like. 
Trialkylamine alanes, having the formula H.sub.3 Al:NR.sup.1 R.sup.2 
R.sup.3, can also be used as aluminum source precursors in practicing the 
methods of the present invention. In this formula, R.sup.1, R.sup.2, and 
R.sup.3 are either alkyl or aryl. Alkyl groups can be substituted or 
unsubstituted and can be branched or straight. Examples of suitable alkyls 
include but are not limited to methyl, ethyl, n-propyl, isopropyl, 
n-butyl, isobutyl, and tert-butyl. Suitable substituted alkyl groups 
include fluorinated alkyls, such as fluoromethyl, difluoromethyl, 
perfluoromethyl, perfluoroethyl, perfluoroisobutyl, and the like. Aryl 
groups can be substituted or unsubstituted and can be monocyclic or 
polycyclic. Examples of suitable aryls include phenyl and naphthyl. 
Suitable substituted aryl groups include fluorinated aryls, such as 
4-fluorophenyl and perfluorophenyl; alkylated aryls, such ar tolyl, 
4-ethylphenyl, or 4-(perfluoroethyl)-phenyl; and the like. R.sup.1, 
R.sup.2, and R.sup.3 can be different , such as where dimethylethylamine 
alane, methyldiethylamine alane, dimethylisobutylamine alane, 
dimethylphenylamine alane, and methylethylispropylamine alane, are used as 
aluminum source precursors. Alternatively, R.sup.1, R.sup.2, and R.sup.3 
can be the same, such as trimethylamine alane, triethylamine alane, 
tri-n-propylamine alane, tri-isopropylamine alane, tri-n-butylamine alane, 
tri-isobutylamine alane, and tri-tert-butylamine alane, and triphenylamine 
alane. 
One may also substitute other reactant gases for hydrogen, including a gas 
selected from the group consisting of helium, argon, xenon, nitrogen, or a 
mixture thereof. Such selected reactants and aluminum precursors may be 
used with plasma processes selected from the group consisting of radio 
frequency plasma, low frequency plasma, high density plasma, electron 
cyclotron resonance (ECR) plasma, or inductively coupled plasma (ICP). An 
electrical bias is applied to the substrate using direct current (dc), 
low-frequency alternating current (90-45-kHz), or radio frequency (rf) 
bias. 
In connection with the deposition of copper, one may use one of a number of 
techniques including but not limited to reactive ion sputtering, direct 
current (dc) sputtering, collimated sputtering, thermal chemical vapor 
deposition (CVD), plasma-promoted CVD (PPCVD), or PPCVD with bias 
substrate.