Process for forming a sputter deposited metal film

A metal deposition process in which a high-purity metal film (46) is sputter deposited within a sputtering system (10) having insitu passivated metal components. A sputtering target (14) is provided having a thin aluminum coating (44) overlying a refractory metal layer (42). During operation, the aluminum coating (44) is sputtered away from the target (14) and onto exposed metal surfaces within the vacuum chamber (20) of the sputter deposition system (10). Subsequently, a semiconductor substrate (38) is placed in the sputter deposition system (10) and a high-purity metal film (46) is deposited onto the semiconductor substrate (38). Because the insitu passivation process avoid the oxidation of the passivating aluminum, refractory metal sputtered away from the target (14) adheres to the passivating aluminum layer, and does not re-deposit onto the surface of the semiconductor substrate (38) during the sputter deposition process.

FIELD OF THE INVENTION 
This invention relates in general to a method for fabricating a 
semiconductor devices, and more particularly to a method for the sputter 
deposition of metal films in a semiconductor fabrication process. 
BACKGROUND OF THE INVENTION 
The trend in semiconductor fabrication is toward faster and more complex 
devices. Increased operating speeds are typically attained through the 
fabrication of devices having small feature sizes, and through the use of 
a variety of electrically conductive metals. A multitude of different 
metals and metal alloys are now in use which increase device operating 
speeds, and in some cases, provide a diffusion barrier to protect the 
devices from contamination. Further, complex metallization structures are 
being used to form electrical interconnection to the various components 
found in an integrated circuit. The need for complex metallization systems 
has occurred, in part, as a result of the need to form many overlying 
layers of conductive interconnects to electrically couple the vast number 
of device components in an integrated circuit. 
The process technology fused to form the metallization structures must have 
the capability to produce metal films of high purity. The deposited metal 
films must not only be highly electrically conductive, but also must 
possess the necessary optical reflectivity characteristics to enable high 
definition photolithographic processing. In order to meet the film quality 
requirements demanded in semiconductor fabrication, sputter deposition has 
become a widely used technique. A metal sputtering process is typically 
carried out in an ultra-high vacuum environment in which processing 
parameters, such as metal film deposition rates and morphological 
characteristics of the metal film, can be carefully controlled. Using a 
state of the art sputtering process, a metal film can be rapidly deposited 
onto the surface of a semiconductor substrate, while controlling the grain 
size and film thickness uniformity with a high degree of precision. 
Additionally, the sputter deposition process is adaptable to the formation 
of metal alloy films, either by using multi-component sputtering targets, 
or by introducing reactive gases into the sputter deposition system. 
Although a sputtering system can be adapted to produce a variety of metals 
and metal alloys, the deposition of certain metals and their alloys can be 
accompanied by high levels of contamination during the sputter deposition 
process. For example, many refractory metals do not adhere well to metal 
surfaces commonly present in a sputter deposition chamber. During a 
sputter deposition process, in addition to depositing a metal layer on the 
semiconductor substrate, the metal being deposited from a sputtering 
target also coats the exposed metal surfaces within the sputter deposition 
chamber. If the sputtered metal does not adhere well to the metal surfaces 
within the deposition chamber, the sputtered metal can continuously peel 
away from the chamber surfaces and contaminate the film deposited on the 
semiconductor substrate. 
One method of preventing film contamination from sputtering system 
components, is to disassemble the components of the chamber and 
individually coat the components with a metal having good adhesion 
properties. The individually coating of metal components requires that the 
vacuum chamber be open to ambient atmosphere, and each individual 
component removed and disassembled. In addition to requiring a large 
amount of time, and associated loss of production capacity, the individual 
component coating method exposes the coated components to oxygen in the 
ambient atmosphere. The coating metal can oxidize during periods prior to 
reinstallation into the sputtering apparatus. Aluminum is a commonly used 
adhesion metal, which readily oxidizes to form aluminum oxide. The 
formation of aluminum oxide is undesirable because aluminum oxide does not 
have the adhesion properties of elemental aluminum. 
Another component passivation approach is to fabricate the internal 
components of the sputtering system from a metal which inherently has good 
adhesive properties. However, the fabrication of internal components from 
an adhesive metal is expensive and can compromise the structural integrity 
of the sputter deposition system. Additionally, whenever the sputtering 
system is open to atmosphere, the internal components can be subject to 
oxidation. Accordingly, further development of sputter deposition 
processes is necessary to provide high-purity sputter deposited metal 
films, while avoiding excessive expense and loss of production time. 
SUMMARY OF THE INVENTION 
In practicing the present invention there is provided a process for a 
sputter depositing a high-purity metal film in a semiconductor device. A 
high-purity metal film is deposited onto a semiconductor substrate within 
a sputtering apparatus having insitu-passivated internal surfaces. In one 
embodiment, a sputtering target is provided having a surface layer of 
aluminum overlying a refractory metal layer. The surface layer of aluminum 
is sputtered away to expose the underlying refractory metal layer. 
Thereafter, refractory metal layers are subsequently deposited onto 
semiconductor substrates by sputter deposition from the sputtering target. 
In the process of the invention exposure of the passivating aluminum to 
ambient atmospheric conditions is avoided. The internal elements of the 
sputter deposition chamber are passivated directly from aluminum which has 
been coated onto the surface of the sputtering target. The 
insitu-passivation process reduces the maintenance time necessary to 
prepare the sputter deposition system for production activity. The process 
of the present invention, in one aspect, provides both high-purity metal 
films, and a highly efficient metal deposition process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the reactive sputter deposition of metal films it often occurs that the 
particular metal being deposited does not adhere well onto internal metal 
surfaces of the deposition system. When poor adhesion occurs, metal 
particles can dislodge from internal metal surfaces and become trapped in 
the metal film, which is being sputter deposited onto a semiconductor 
substrate. The metal particulate contaminates can reduce the electrical 
conductivity of the deposited metal films, and in the case of sputter 
deposition of a multi-component film, can alter the stoichiometry of the 
sputtered film. The present invention provides both a sputtering system 
component and a process which reduces the contamination of deposited films 
caused by metal flaking during the sputter deposition process. 
Shown in FIG. 1 is a schematic diagram of an exemplary sputter deposition 
system 10. Sputtering system 10 is equipped with a substrate stage 12 
aligned parallel to and opposite from a sputtering target 14. Both 
substrate stage 12 and sputtering target 14 are electrically coupled to 
power supplies which can apply either direct current or radio frequency 
power to either electrode. As illustrated, target power supply 16 can be 
adjusted by the user to apply either DC voltage or RF frequency power to 
sputtering target 14. Similarly, stage power supply 18 can supply either 
DC or RF power to stage 12, or alternatively, can supply a ground signal 
to stage 12. Both stage 12 and target 14 are contained within a vacuum 
chamber 20, which can be evacuated to ultra high vacuum by vacuum system 
22. Reactive and inert gases can be introduced to vacuum chamber 20 by gas 
supply system 24. By controlling both the evacuation rate and the gas 
introduction rate, the internal pressure of vacuum chamber 20 can be 
controlled at a desired level during the sputter deposition process. 
Both substrate stage 12 and sputtering target 14 are surrounded by ground 
shields 26 and 28, respectively. Ground shields 26 and 28 function to 
confine the ion bombardment to sputtering target 14 during the sputter 
deposition process,. In the absence of a ground shield, internal target 
support structures, such as a backing plate, mounting clips, and 
mechanical supports, and the like, could also be subjected to ion 
bombardment. The ion bombardment of mechanical structures supporting 
sputtering target 14 can result in film contamination in the metal film 
being deposited on a semiconductor substrate. To function properly, the 
ground shields must be spaced at a carefully defined distance from the 
target and the substrate stage. Typically, the spacing distance is 
extremely small in order to prevent local discharges, known as voltage 
arcs, between the ground shield and the electrode. Ground shields are also 
supplied for the substrate stage to facilitate the operation of the 
sputtering system while applying a bias voltage to the substrate stage. 
Sputtering system 10 is equipped with a shutter 30, which is positioned 
between substrate stage 12 and sputtering target 14. Shutter 30 is 
attached to a rotating arm 32 and can be rotated away from target 14 and 
expose underlying substrate stage 12. Shutter 30 is positioned between 
stage 12 and target 14 during the initial power-up period when the first 
few atomic layers are sputtered away from target 14. During the 
pre-sputtering period, any contaminants present on the surface of target 
14 are sputter deposited onto shutter 30. Once the pre-sputtering period 
is complete, shutter 30 is rotated away from target 14 and the sputter 
deposition process continues onto stage 12. 
Target 14 is equipped with cooling coils 32 which prevent the temperature 
of target 14 from temperature induced damage during the sputter deposition 
process. Excessive target temperatures can lead to damage of the bonding 
between the target and the backing electrode and fields associated with 
the target mounting mechanisms. Similarly, substrate stage 12 can be 
equipped with cooling coil 34 to prevent excessive temperatures of the 
semiconductor substrate during the sputter deposition process. Moreover, 
in certain sputter deposition processes, the formation of a desired alloy 
film can be influenced by the substrate temperature during sputter 
deposition. Further temperature control capability can be provided by 
heating elements 36 positioned internal to substrate stage 12. 
Those skilled in the art will appreciate that the foregoing description of 
sputtering system 10 is a general description of common, commercially 
available sputter deposition systems. Accordingly, not all of the 
previously described features are necessarily present on any particular 
sputter deposition system. Furthermore, a conventional sputter deposition 
system also includes many systems not illustrated in FIG. 1. Additionally, 
the configuration of the various components of sputtering system 10 can 
vary substantially from that shown. For example, ground shields 26 and 28 
can be configured to partially overlap the front surfaces of substrate 
stage 12 and sputtering target 14. 
In operation, a semiconductor substrate 38 is placed on substrate stage 12, 
and vacuum chamber 20 is evacuated to ultra-high vacuum pressure. A 
reactive or inert gas is introduced to vacuum chamber 20 from gas supply 
system 24. Then, either DC or RF power is applied to target 14 and a 
plasma is created in the space between substrate stage 12 and target 14. 
The electric fields induced by the power to target 14 cause ions to 
bombard the surface of target 14, thereby dislodging metal atoms from the 
surface of target 14. After the sputtering process is initiated, shutter 
30 rotates away from target 14 and metal atoms are sputtered from the 
surface of target 14 and deposit on the surface of semiconductor substrate 
38. Successive layers of metal atoms are sequentially deposited onto the 
surface of substrate 38 forming a thin-film on the substrate surface. The 
sputter deposition process is continued for a predetermined period of 
time, pending upon the rate of sputter deposition and the desired 
thickness of the deposited metal film. Upon completion of the sputter 
deposition process, substrate 38 is removed from vacuum chamber 20 and 
continues on to subsequent processing steps, which transform the deposited 
metal film into a patterned layer of metal interconnects. 
The sputter deposition process for a multi-component film, such as a 
refractory-metal alloy, is preferably carried out by introducing a 
reactive gas into vacuum chamber 20, and sputtering a metal component from 
sputtering target 14. During the reactive sputter deposition process, or 
reactive ion sputtering (RIS) process, a gas phase reaction takes place 
between the reactive gas and the metal atoms sputtered from the target. 
For example, a titanium nitride film can be deposited by sputtering 
titanium metal from target 14 in the presence of reactive nitrogen gas. 
Under proper processing conditions, a titanium nitride film is formed on 
the surface of substrate 38. During the sputter deposition process, 
titanium atoms can also deposit on the surfaces of ground shields 26 and 
28. Typically, the internal metal elements and mechanisms of a sputter 
deposition system are constructed from stainless steel. Since titanium 
does not adhere well to stainless steel surfaces, the titanium metal 
eventually flakes off the surface of shields 26 and 28 and can become 
trapped in the growing titanium nitride film on the surface of substrate 
38. 
To prevent metal contamination during the active ion sputtering process, 
the refractory metal in target 14 is coated with a layer of aluminum, as 
illustrated in FIG. 2. Target 14 includes a backing plate 40, which 
supports a refractory metal layer 42. A thin aluminum layer 44 overlies 
the surfaces of refractory metal layer 42. Aluminum layer 44 can be 
incorporated into target 14 using a conventional metallization process. 
For example, aluminum layer 14 can be plated onto refractory metal layer 
42 using a conventional plate bonding process. Additionally, aluminum 
layer 44 can be applied to refractory metal layer 42 by a plasma flame 
spraying process. Further, aluminum layer 44 can be evaporated onto 
refractory metal layer 42. Because aluminum layer 44 is removed from 
refractory metal layer 42 very early in the lifetime of sputtering target 
44, aluminum layer 44 need only be secured to refractory layer 42 such 
that aluminum layer 44 will remain in place until early removal in the 
sputter deposition system. 
The process of the present invention begins by placing target 14 in vacuum 
chamber 20. At the time of placing target 14 in vacuum chamber 20, shields 
26 and 28 are also replaced. Next, a series of test substrates are 
sequentially processed in sputtering system 10. The test substrates are 
used for system burn-in and testing, and do not contain active 
semiconductor devices. As the test substrates are sequentially processed, 
aluminum layer 44 is sputtered from target 14. During the aluminum 
sputtering process, aluminum is deposited onto the test substrates, and 
onto exposed stainless steel surfaces of ground shields 26 and 28. The 
aluminum bonds to the stainless steel surfaces of ground shields 26 and 
28, and completely coats the exposed surfaces of the ground shields with a 
thin layer of aluminum metal. Eventually, all of aluminum layer 44 is 
removed from the surface of refractory metal layer 42. At this point, the 
sputtering of refractory metal layer 42 is initiated. 
Following the removal of aluminum layer 44 from target 14, the processing 
of active semiconductor devices begins. During a sputtering process to 
form, for example, a titanium nitride film on a semiconductor substrate, 
titanium nitride also forms on the aluminum metal surfaces of ground 
shields 26 and 28. Since titanium nitride adheres to aluminum, titanium 
nitride metal does not become dislodged from the surface of ground shields 
26 and 28 during the sputter deposition process. Accordingly, highly pure 
titanium nitride films can be sputter deposited in sputtering system 10. 
Using the process of the present invention, a refractory metal alloy 46 is 
sputter deposited onto semiconductor substrate 38, as illustrated in FIG. 
3. Refractory metal alloy film 46 is substantially free of metal 
contaminants introduced during the sputter deposition process. The highly 
pure condition of refractory metal alloy 46 enables the use of the alloy 
for formation of highly conductive metal leads. Additionally, the absence 
of film contamination enables the photolithographic patterning and etching 
of high definition interconnect features in a semiconductor device. The 
presence of metal contamination in a deposited film can cause 
inconsistencies in the etching process used to define metal interconnects. 
The absence of any such impurities enables refractory metal alloy 46 to be 
uniformly etched over the entire surface of a semiconductor device. 
Refractory metal alloy 46 can be one of a number of different alloys, such 
as titanium nitride, tungsten nitride, titanium tungsten, a copper alloy, 
and the like. Alternatively, the process of the present invention can be 
used to sputter deposit a pure metal layer, such as titanium, molybdenum, 
tungsten, gold, copper, and the like. In the case of sputter depositing a 
pure metal, an inert gas such as argon is introduced into vacuum chamber 
20. 
Those skilled in tile art will recognize that the foregoing process offers 
process efficiency advantages in addition to providing a high-purity 
thin-film. By passivating the internal metal surfaces of a sputter 
deposition system using an insitu aluminum deposition process, the need to 
continuously remove and clean shields within the sputter deposition 
chamber is reduced. Each time the system is opened and exposed to ambient 
atmospheric conditions, oxide layers form on the internal surfaces of the 
sputter deposition system. These oxide layers further reduce the adhesion 
of refractory metal films deposited during the sputter deposition process. 
By passivating internal surfaces using an insitu passivation process, the 
necessity of opening the system and exposing its atmospheric conditions is 
reduced. 
Thus it is apparent that there has been provided, in accordance with the 
invention, a process for forming sputter deposited metal film which fully 
meets the advantages set forth above. Although the invention has been 
described and illustrated with reference to specific illustrative 
embodiments thereof, it is not intended that the invention be limited to 
those illustrative embodiments. Those skilled in the art will recognize 
that variations and modifications can be made without departing from the 
spirit of the invention. For example, other reactive gases such as 
tungsten hexafluoride, and the like, can be used to form a RIS deposited 
titanium tungsten alloy film. It is therefore intended to include within 
the invention all such variations and modifications as fall within the 
scope of the appended claims and equivalents thereof.