Method and system for plating workpieces

A method and a system are provided for plating workpieces as part of an "on-track" in-line or a radially arranged manufacturing system, including "on-site" measurement of at least one plating characteristic for computer controlled process regulation and quality control. Movement of workpieces between various stations is controlled in response to a comparison of the measured value(s) of the plating characteristic(s) and (a) target value(s) or target range(s) of values.

FIELD OF THE INVENTION 
The present invention relates to a method and system for plating 
workpieces, including "on-site" measurement of a selected plating property 
for regulation and quality control of a product manufacturing line. More 
particularly, the invention relates to an improved method and system for 
"back-end" metallization of integrated circuit semiconductor devices which 
provide enhanced quality control, increased manufacturing throughput, with 
full compatibility with existing semiconductor manufacturing process 
technology and methodology. 
BACKGROUND OF THE INVENTION 
Metal films are conventionally utilized in semiconductor manufacturing 
technology to form electrically conductive contacts to active as well as 
passive device regions or components formed in or on a semiconductor wafer 
substrate, as well as for filling via holes, interlevel metallization, and 
interconnection routing patterns for wiring together the components and/or 
regions. Because many large scale integration (LSI), very large scale 
integration (VLSI), and ultra large scale integration (ULSI) devices 
presently manufactured are very complex and require multiple levels of 
metallization for interconnections, it has been common to repeat 
metallization processing multiple times, e.g., to form five or more levels 
of metallization interconnected by conductive vias. Thus, in the course of 
manufacturing such devices, each wafer requires passage through one or 
more metallization systems arranged along a device production line or 
path. 
Metals commonly employed for "back-end" metallization purposes include 
nickel, titanium, tantalum, aluminum, chromium, gold, silver, copper, and 
alloys thereof, which metals may be applied to the semiconductor wafers by 
a variety of techniques, including, but not limited to, electroplating, 
electroless plating, dipping, pasting, spraying, physical vapor deposition 
(e.g., evaporation, sputtering, ion plating, plasma spraying, etc.), and 
chemical vapor deposition (including plasma enhanced chemical vapor 
deposition). Of the enumerated metals and deposition methods, 
metallization by electroplated copper or copper-based alloys is 
particularly attractive for use in LSI, VLSI, and ULSI multilevel 
metallization systems used for "back-end" processing of semiconductor 
wafers. Copper and copper-based alloys have very low resistivities, i.e., 
even lower than that of previously preferred aluminum and aluminum alloys, 
as well as significantly higher resistance to electromigration. Moreover, 
copper and its alloys enjoy a considerable cost advantage over a number of 
the above metals, in particular silver and gold. Lastly, copper and its 
alloys can be readily deposited in layer form by well-known electroplating 
techniques, at deposition rates compatible with the requirements of 
adequate manufacturing throughput. 
A significant drawback associated with electroplating systems employed as 
part of in-line semiconductor manufacturing systems is the inability to 
measure the plated film properties concurrently with electrodeposition, or 
at the least, very shortly after withdrawal of the plated semiconductor 
wafer workpieces from the electroplating bath. Referring to FIG. 1, 
illustratively shown therein in schematic form, is a diagrammatic top view 
of a conventional automated or semi-automated "on-track" system 1 which 
forms a portion of a device manufacturing line, e.g., a manufacturing line 
for processing semiconductor wafer substrates into a plurality of 
integrated circuit device regions, which regions are ultimately formed 
into chips by dicing. On-track automated semiconductor manufacturing 
systems of the type contemplated for use as herein described may, for 
example, be obtained from Semitool, Inc. (Kalispell, MT) under the 
designation LT 210 and suitably adapted for performing electroplating 
processing as necessary for a particular manufacturing process sequence. 
The inventive concept is also well adapted for use with alternative 
arrangements or configurations of process stations and wafer transport 
mechanisms, such as radially configured apparatus (available from Applied 
Materials, Santa Clara, Calif.; Novellus, San Jose, Calif.; Semitool, 
Inc., Kalispell, Mont.; and TEL, Tokyo, Japan) wherein process chambers or 
stations are arranged in a radial fashion around a central pivoting robot. 
Moreover, since modern robots and control systems are capable of moving 
workpieces to or from a number of different locations, the arrangement of 
process chambers or stations in a radial or linear apparatus need not 
necessarily be from left to right, but could be from left to right, and 
then back from right to left, for a number of oscillation cycles. 
As illustrated, electroplating system 1 comprises an enclosure 2, a 
workpiece transport mechanism 3, termed a "track" for transporting 
workpieces such as semiconductor wafers (not shown) contained in 
cassette-type workpiece holders 4, 4', each capable of supplying, storing, 
and receiving a plurality of wafers as they pass through various 
processing stations along the manufacturing line. In the figure, and 
simply for the purpose of disclosing the principle of the present 
invention, workpiece holder 4 on track 3 is shown as transporting into 
enclosure 2 semiconductor wafer workpieces from an upstream portion of the 
manufacturing line comprising stations (not shown) for performing 
antecedent processing, and workpiece holder 4' is illustrated as within 
the processing enclosure having received plated, post-treated wafer 
workpieces for storing therein, and as having exited the enclosure via 
track 3 for supplying the plated, post-treated wafer workpieces to a 
subsequent processing station (not shown). 
Electroplating system 1 comprises from left to right within the enclosure 2 
and in the direction of workpiece transport, a first, electroplating 
station 5 and a second, post-treating station 6 where the just-plated 
workpieces are rinsed and dried prior to exiting the enclosure. It is to 
be understood that both cassette-type workpiece holders 4, 4' as shown in 
the drawing for illustrative purposes only, are identically capable of 
supplying, storing, and receiving wafer workpieces, as necessary, for 
performing sequential processing thereof as described. 
Located exteriorly of the enclosure 2 (i.e., "stand-alone" placement) is a 
third, measuring station 7 for determining at least one film 
characteristic of a representative sample 8 of the just-plated workpieces, 
e.g., electrical resistivity, thickness, and reflectivity, for determining 
whether proper electroplating and rinsing/drying conditions have been 
established in first and second stations 5, 6, respectively, and for 
adequate quality assurance. Specifically, measurement of film resistivity, 
as by use of a 4-point probe or a contactless device comprising third 
station 7, is essential for determining whether electrical connections of 
sufficiently low resistivity have been established as a result of the 
electroplating; adequate film thickness is necessary for ensuring complete 
surface coverage as well as sufficient electrical conductivity. 
Reflectivity is indicative of the overall quality and effectiveness of the 
electroplating, e.g., bright copper plating. 
A number of drawbacks are associated with such conventional manufacturing 
technology as a consequence of the "stand alone" placement of the third, 
measuring station 7. For example, if the workpiece transfer mechanism, 
i.e., track 3, is shut down for removal of the test wafer 8, periodic 
withdrawal and testing of a plated wafer workpiece 8 necessarily entails 
lost productivity. Should the production line continue to run during 
testing (for making the same or a different product), and the testing 
indicates one or more substantial deviations from standard, desired film 
characteristics, there is a significant risk of producing "out-of-spec" 
product. A further drawback of the "stand alone" testing arrangement is 
the inability to rapidly adjust plating conditions in response to film 
measurement. Nor is it possible to conveniently re-cycle out-of-spec 
wafers for an additional pass through the electroplating system 1 to 
increase under-spec film thicknesses and/or decrease over-spec 
resistivities to acceptable levels. 
Thus, there exists a need for an "on-track" process and system which 
overcomes the above-described drawbacks associated with conventional 
high-throughput, automated, track type manufacturing apparatus, 
particularly as employed in the metallization of LSI, VLSI, and ULSI 
semiconductor devices having multiple metallization levels. Moreover, 
there exists a need for an improved "on-track" process and apparatus for 
electroplating and post-treatment of semiconductor wafers for 
metallization thereof, which process and apparatus are fully compatible 
with the balance of conventional semiconductor manufacturing lines. 
DISCLOSURE OF THE INVENTION 
An advantage of the present invention is an improved method for plating 
workpieces in a plating system comprising a plurality of interconnected 
stations. 
A further advantage of the present invention is an improved method for 
metallizing semiconductor wafer workpieces utilizing an in-line, 
automated, on-track manufacturing system. 
A still further advantage of the present invention is an improved method 
for plating workpieces in a system comprising a plurality of 
interconnected stations and which provides for "on-site" monitoring of 
plating characteristics and adaptive process control. 
Yet another advantage of the present invention is an improved plating 
system for use in an in-line, "on-track" or radially arranged 
manufacturing apparatus and comprising "on-site" monitoring means and 
adaptive process control. 
Additional advantages, and other features of the present invention will be 
set forth in the description which follows and in part will become 
apparent to those having ordinary skill in the art upon examination of the 
following or may be learned from the practice of the present invention. 
The advantages may be realized and obtained as particularly pointed out in 
the appended claims. 
According to the present invention, the foregoing and other advantages are 
achieved in part by a method of plating at least one workpiece in a 
plating system comprising three interconnected stations, the method 
comprising the sequential steps of: 
(a) supplying a workpiece from a workpiece holder to a first station of the 
system; 
(b) plating the workpiece in the first station; 
(c) supplying the plated workpiece to a second station of the system; 
(d) post-treating the plated workpiece in the second station; 
(e) supplying the post-treated plated substrate to a third station of the 
system; 
(f) determining the value of at least one selected property of the plating 
in the third station; 
(g) comparing the determined value(s) with (a) target value(s) or target 
range(s) of values; and 
(h) performing one of the following steps based upon the comparison: 
i. transporting the post-treated, plated workpiece from the third station 
to the or a workpiece holder for storing therein if the determined 
value(s) correspond(s) with the target value(s) or is (are) within the 
target range(s) of values; 
ii. transporting the post-treated, plated workpiece from the third station 
back to the first station for additional plating thereon if the determined 
value(s) is (are) below the target value(s) or the target range(s) of 
values; 
iii. removing the post-treated, plated workpiece from the system if the 
determined value(s) indicate(s) that additional plating thereon cannot 
provide (a) determined value(s) corresponding with the target value(s) or 
target range(s) of values; or 
iv. adjusting the plating conditions within the first station to provide a 
later-plated workpiece with (a) determined value(s) which correspond(s) 
with the target value(s) or is (are) within the target range(s) of values. 
In embodiments according to the invention, the workpiece comprises a 
semiconductor wafer substrate for an integrated semiconductor device, the 
workpiece holder comprises a cassette-type device for 
supplying/storing/receiving a single one or a plurality of such 
semiconductor wafer substrates multiply or in seriatim, and the first 
station comprises an apparatus for plating a metal by electroplating, 
electroless plating, dipping, pasting, spraying, physical vapor 
deposition, or chemical vapor deposition. 
In preferred embodiments according to the present invention, the metal 
comprises copper or a copper-based alloy electroplated on the workpieces 
in the first station, the second station comprises a rinsing/drying 
station, the method comprising determining at least one of the electrical 
resistivity, thickness, and reflectivity of the plated metal in the third 
station, and utilizing an electronic computer for performing the 
comparison with (a) target value(s). 
Another aspect of the present invention is a system for plating at least 
one workpiece which system comprises: 
a workpiece holder for supplying/storing receiving at least one such 
workpiece; 
a first station for receiving and plating the at least one workpiece; 
a second station for receiving the at least one plated workpiece from the 
first station, performing post-treatment thereof, and supplying the at 
least one post-treated workpiece to a third station; 
a third station for receiving the at least one post-treated workpiece and 
determining the value of at least one selected property of the plating; 
an apparatus for controllably transporting the at least one workpiece 
between the stations and the workpiece holder; and 
a device for comparing the determined value(s) of the at least one selected 
plating property with (a) target value(s) or range(s) of target values, 
the comparison device adapted to controllably operate the system to 
perform one of the following based upon the comparison: 
i. supplying of the plated, post-treated workpiece to the or a workpiece 
holder for receiving and/or storage therein if the determined value(s)of 
the at least one selected property corresponds with the target value(s) or 
is (are) within the target range(s) of values; 
ii. supplying of the plated, post-treated workpiece back to the first, 
plating station for additional plating treatment if the determined 
value(s) is (are) below the target value(s) or the target range(s) of 
values; 
iii. removal of the plated, post-treated workpiece from the system if the 
determined value of the at least one selected property indicates that 
additional plating treatment cannot result in (a) determined value(s) 
corresponding to the target value(s) or within the target range(s) of 
values; and 
iv. adjustment of the plating conditions within the first station to 
provide a later-plated workpiece with (a) determined value(s) of the at 
least one selected property corresponding with the target value(s) or 
within the target range(s) of values. 
According to embodiments of the invention, the workpiece holder comprises a 
cassette-type device for accomodating therein a plurality of semiconductor 
wafer workpieces and the workpiece transport device comprises a linear 
"on-track" mechanism or a radially arranged mechanism with a centrally 
positioned robotic workpiece handler; the first station comprises an 
apparatus for plating a metal by electroplating, electroless plating, 
dipping, pasting, spraying, physical vapor deposition, or chemical vapor 
deposition and the second station comprises an apparatus for post-treating 
the metal plating. 
In preferred embodiments according to the invention, the first station 
comprises an apparatus for electroplating, preferably copper or 
copper-based electroplating, the second station comprises an apparatus for 
rinsing and drying the metal plating, the third station comprises an 
apparatus for measuring at least one of the electrical resistivity, 
thickness, and reflectivity of the metal plating, and the comparison 
device comprises an electronic computer. 
Additional advantages of the present invention will become readily apparent 
to those skilled in the art from the following detailed description, 
wherein only the preferred embodiments of the present invention are shown 
and described, simply by way of illustration but not limitation. As will 
be realized, the invention is capable of other and different embodiments, 
and its several details are capable of modification in various obvious 
respects, all without departing from the spirit of the present invention. 
Accordingly, the drawings and description are to be regarded as 
illustrative in nature and not as restrictive.

DESCRIPTION OF THE INVENTION 
Referring now to FIG. 2, wherein like reference numerals are used to 
designate previously described features, an "on-track" metallization 
plating system 1' according to a first embodiment comprises an enclosure 
2; a track-type workpiece transport mechanism 3; and, for illustrative 
purposes, entering and exiting cassette-type workpiece holders 4, 4', 
respectively. In serial arrangement therewith, are a first, electroplating 
station 5, a second, post-treatment (e.g., rinsing/washing) station 6, and 
a third, measuring station 7. 
According to this embodiment, the third measuring station 7' is placed 
within the enclosure 2 for performing "on-site" measurement of the value 
of at least one of the aforementioned relevant plated film 
characteristics, e.g., resistivity, thickness, and/or reflectivity, and is 
operatively connected via line 10 to an electronic comparator/controller 
device 9, typically a digital computer. In addition, third station 7' is 
provided, for illustrative purposes, with a first and second auxiliary 
workpiece transport mechanisms 11 and 12, respectively, similar to track 
3, and cassette-type workpiece holder 4", similar to cassettes 4, 4', for 
supplying selected workpieces from the third, measuring station 7' back to 
the first, plating station 5 for additional plating thereon or for exiting 
of selected "off-specification" plated workpieces from the system 
enclosure 2. Finally, the first, plating station is operatively connected 
to comparator/controller 9, via line 13, for adjustment of the 
electroplating conditions therein, based upon the output of the comparator 
as determined by the comparison. Comparator/controller 9 is programmed or 
otherwise inputted with target values or ranges of target values of the 
relevant plating characteristics for comparison with those provided by the 
third, measuring station 7'. 
Although comparator/controller 9 is illustrated as placed exteriorly of the 
enclosure 2, it may be placed within the latter if desired or otherwise 
convenient. 
It is also understood that while the first plating station 5 has been 
described as performing electroplating of the workpieces, the present 
invention is capable of use with a variety of other types of metal or 
non-metal plating stations, including, but not limited to electroless 
plating, dipping, pasting, spraying, physical vapor deposition (e.g., 
evaporation, vacuum evaporation, sputtering, ion plating, cathodic arc 
deposition, etc.), and chemical vapor deposition, including plasma 
enhanced chemical vapor deposition. Moreover, although in the illustrated 
embodiment, copper or copper-based metal plating is performed, the 
principles of the invention are equally applicable to various other metals 
and metallic and non-metallic materials, including, for example, nickel, 
titanium, tungsten, tantalum, aluminum, chromium, gold, silver, and their 
various alloys and compounds. Finally, the second, post-treatment station 
6 is not limited to performing rinsing/drying treatment, but may be 
configured to perform any desired treatment necessitated by the particular 
plating method conducted in the first chamber 5. 
Operation of the system 1' according to the present invention is generally 
similar to that of the conventional system described above, with the 
following notable difference: each workpiece, or alternatively, selected 
workpieces exiting the second, post-treatment station 6 pass(es) to and 
through the "on-site" third, measuring station 7, for determination of one 
or more relevant plating characteristics, typically resistivity, 
thickness, and/or reflectivity. The results of the comparison are then 
supplied via line 10 to comparator/controller 9. 
Depending upon the result of the comparison, comparator/controller 9 
determines which of the following possible outcomes occurs for each 
workpiece or selected workpieces: 
(1) if the measured value(s) of the plating characteristic(s) as determined 
by the third, measuring station 7' correspond(s) with the target value(s) 
or is (are) within the target range(s) of values programmed into the 
comparator/controller 9, the plated, post-treated workpieces are supplied 
from the measuring station 7' to cassette-type workpiece holder 4' via 
on-track mechanism 3 for exiting enclosure 2 of plating system 1 to 
receive further processing downstream of the production line. 
(2) if the measured value(s) of the relevant plating characteristics 
determined by the third measuring station 7' indicate that the plated, 
post-treated workpieces are below the target values or ranges of target 
values stored in the comparator/controller 9, the latter, via line 10 and 
auxiliary workpiece transport mechanism 11, directs the return of such 
workpieces to first, electroplating station 5 for further plating thereon. 
Such "second pass" plating treatment is particularly useful in instances 
where the resistivity and/or thickness of the plating as determined by the 
third station 7' is (are) lower than the target value(s) or target 
range(s) of values. 
(3) if the measured value(s) of the relevant plating characteristic(s) of 
the plated, post-treated workpieces as determined by the third measuring 
station 7' and compared with the corresponding value(s) or range(s) of 
values stored in the comparator/controller 9 indicate that the plated, 
post-treated "off specification" workpieces cannot benefit from additional 
plating in first station 5, comparator/controller 9, via line 10, signals 
the third station 7' to supply such workpieces to, for illustrative 
purposes, auxiliary workpiece cassette 4" for exiting the system enclosure 
2 by means of second auxiliary transport mechanism 12. Such would obtain 
when, e.g., the plating thickness exceeds the target thickness or range of 
thicknesses or low reflectivity indicates unacceptably poor plating 
quality. 
(4) if the measured values of the relevant plating characteristics indicate 
that later-treated workpieces would exhibit measured values closer to the 
target values stored in the comparator/controller 9, or would otherwise 
benefit from adjustment of the electroplating conditions in first station 
5, controller/comparator 9 can perform such adjustment via line 13. Such 
capability is also useful when different types of workpieces are supplied 
or when plating conditions require changing for any reason. 
It is therefore apparent that the inventive method and system represents a 
significant improvement over conventional "in-line" technology for the 
processing of workpieces such as semiconductor wafers. Specifically, the 
inventive method and apparatus provides for automated, continuous 
operation of a metallization system, increased product throughput, 
"on-site" process/product measurement, monitoring, and adaptive control, 
and is fully compatible with the balance of the in-line manufacturing 
technology. 
In the previous descriptions, numerous specific details are set forth, such 
as particular materials and deveices, etc., in order to provide a thorough 
understanding of the present invention. However, it should be recognized 
that the present invention can be practiced without resorting to the 
details specifically set forth. For example, while the invention has been 
illustrated as particularly useful in the manufacture of semiconductor 
integrated circuit devices, the invention is capable of use in 
manufacturing numerous and various other devices or products requiring 
plating. 
Only the preferred embodiments of the present invention are shown and 
described herein. It is to be understood that the present invention is 
capable of changes or modifications within the scope of the inventive 
concept as expressed herein.