Note: Descriptions are shown in the official language in which they were submitted.
CA 0208964~ 1998-01-0~
METHOD OF ENHANCING THE PERFORMANOE OF A MAGNETRON SPUI~ERING TARGET
The present invention relates to methods for P~tf~nrliny the use of cathode S~)U~Lt;ling targets and more
particularly to methods for controlling the ~ ;iLdtiUII of a cathode sputtering target over the course of its life
to broaden the erosion area of the target and thereby increase the lltili7~tion of target material.
5 B~ c.~ I of the Invention
Sputter coating is a process carried out in a vacuum chamber, filled with a generally rhPmir~llly inert
gas, in which a substrate to be coated is mounted facing a target formed of the coating material. In the
chamber, the target is subjected to an electrical potential negative with respect to the chamber wall or some
other anode within the chamber. The potential gradient adjacent the target surface causes electrons to be
10 emitted from the target. As they are attracted toward the chamber anode, the emitted electrons strike and ionize
some of the atoms of the inert gas by stripping electrons from them. Positive ions of the gas are thereby
formed and attracted toward the negative target which they strike, ~ rr. ~ g ~ -,.. to the target
material, and ejecting particles of the material from the target surface. The substrate to be coated, which is
posilioned in the chamber usually with its surface facing the target so as to intercept the moving particles of
15 coating material sputtered from the target, receives sûme of the ejected particles, which adhere to and coat the
substrate surface.
In magnetron enhanced 'l"~' ~ ;- g processes, a magnetic field is formed over the target surface with
magnetic field lines having collll,ulle~lts extending parallel to the target surface. In many applications, the field
lines arch over the target surface and form a closed magnetic tunnel. The magnetic field causes the electrons
20 moving from the target to curve in spiral paths over regions of the target surface enclosed by the field, thereby
h~lea~illg the electron density in the enclosed space, and resulting in an increase in the rate of electron
collisions with gas atoms over the enclosed regions of the target surface. The increased collision rate in turn
increases the ioni7~til~n of the gas in the enclosed space and thus increases the ~rrl~ ,y of the ;~ ;.,g
process at the ull~llyhl~ target region. There the magnetic field lines equal or exceed a critical field strength
25 over the target surface, a glowing ion cloud or plasma is seen trapped within the field over the region of the
target surface.
~ ~ CA 0208964~ 1998-01-0~
In the collulloilly assigned U.S. Patent No. 4,957,605, entitled "Method and Apparatus for Sputter
Coating Stepped Wafers," a sputter coating apparatus and method are disclosed in which a concave annular
target is provided with a pair of co ~- e-,l, ;r annular ClC~ ulll.~ i with concCllLlic pole pieces behind and at
the rim of the target. The fields produced by these magnets cause the forrn ~ion of a pair of conl c~ltl ic plasma
5 rings overlying CO~ lrl iilg regions on the target surface. The two plasma rings are ~l 'y
energized by ~l Iy supplying current to the magnet coils while the target power is switched between to
controlled power levels in s~ ;luu~liL~tion with the switching 'of the current to the magnetic coils. This causes
the two target regions to be ~' Iy activated so that the ~ Ul~Clillg from the regions is alternately switched
on and off. This provides different controllable rates of ~ llr~ from inner and outer COIICcll~liC regions of
10 the surface of a single piece ~ target.
Separate control of the sputtering from the plural target regions enables the control of the distribution
cllal~t i~ of the sputtered Material deposited on the substrate or wafer being coated. .For example,
varying the relative p~alll. tc~s affecting the ~ ncl~,iLdtion of the two target regions, as for example the "on"
power levels or the duty cycle of the activation of each target region, provides control of coating ullirulllli~y
15 on the substrate surfaces. his control is especially important where dirf. l- l"ly facing surfaces of ~ ' such
as stepped ~ ' Wafers must be ullirullllly coated. The arul~ l~f~lellcf d U S. Patent No. 4,957,605
particularly describes in detail certain effects on the coating, ~r ~~/ caused by target and substrate geometry
and by the electrical p-.~...,. h 1:1 relating to the cllcl~;iLalion of the target and the plasmas. The patent also
discusses the effects of target erosion on sputter coating ullirullll;~y.
By its very nature, the process of cathode sputter coating involves the removal of material from the
S~Ju~t~ ring target and the l~dclJu~ilion of the sputtered material onto the substrate surface. The removal of
material from the cathode ~ g target ~-lli~..-~-. s the target, reducing the thickness of the target until
eventually an erosion groove or area will "punch through" to the back surface of the target. The erosion of the
target surface is usually uneven, being cun~ in areas which underlie the denser regions of ion
CC~n~'f .I~ if)n or plasmas in the space above the target adjacent the target surface. To broaden the area of target
erosion, some prior art devices have caused the plasma to move on the target surface, usually by lll~ U~
made in magnetic fields. This Illu~. lll. lll of the plasma moves the area of erosion about the surface of the target
reducing the tendency of a sharp erosion groove to be formed. Movement of the position of the plasmas,
however,: ~ s, or at least ~~-~" ~ the selective control of the ~l~ullrl ;u~ rate from different target
regions to achieve coating ullirulllli~y.
With lll~,l~lloll ~l~u~ e devices, the plasmas are generally confined to one or more regions of a
target surface, in part due to design lc~luil~ t~ of the magnet structure, and in part due to certdin
pclrullllallct lc~luil~ which -lee~ the location of the plasmas in specific g~Olll~,~liC positions in
relation to the substrate surfaces to achieve a desired coating flictrihutil-n on the substrate. For example, in
U.S. Patent No. 4,957,605 the ~ -e of separate plasmas on a target in specific g_Vlll~ hic relationships
with the substrate surface are employed in order to control the l ~ r ~ ~/ of the coating on a substrate surface,
particularly where the surface of the substrate includes diversely facing surfaces such as steps on
wafers.
CA 0208964~ l998-Ol-0~
In the above-,-,f,-~,nced patent the positions of the plasmas d~ t. .. ~ r the locations from which the
s~ultl,.il~ material is emitted, which d~ t .1l~ 5 the COIl~ Junling distribution of the deposited coating
material on the substrate surface. By controlling the ratios of material emitted from different s~,u~t~,.in~ regions
on a s~,u~ target, the I ~ 1 of the coating is controllable. Acco,.l;"~jly, it is hllL)ul~ that the
5 location of the cl,ul Irl ;u~, regions be located on the target in particular positions selected to provide the desired
coating ullirulll~ly. Thus, the tPrhn:q~lps devised by certain devices of the prior art for moving the plasmas
about the target surface in order to redefine the areas of erosion ll~uu6hvuL the life of the target interfere with
the ability to freely achieve desired coating ullifullllily by precise pla.Cf ~ of the plasma and, cù~ C'
of the erosion region of the target.
Erosion of the target surface by the emission ~f ~ t~ ~ ;uc~ material is ~ . . - .; r. ~ d in the formation of
a plu~ ,ai~.,ly ~ e erosion groove. The form ~tir n of this erosion groove alters the pc.ru~ ce of the
s~uuer;ng target, generally with a declining emission rate from the ~l~ullr~ ;u,~ target region, a rh~
referred to as rate "roll-offn. This rate roll-off is due in part to the fact that the erosion groove is receding
g~ ~.. . ,~1, ;. ~lly from the substrate surface, but more ci~nifir ~ltly, is due to the change in contour of the target
15 surface and the deeply ~t~ ;ug sides of the erosion groove. The ~tf epPnPd sides of the erosion groove tend
to shift the direction of emission of the flux of c~ llr~ , material, causing it to be less ~l~du..l;l~-..lly directed
toward a substrate to be coated. In addition, the redirection of sputtered material tends to cause h"~,i"~ "~""
of the material on the u~ y facing wall of the erosion groove and a ,~,depo~ilion of the material onto the
target surface. Accordingly, while this erosion proceeds, I~,dcpoai~ion of material on the side walls of the
20 erosion groove tends to further narrow the groove. Also, in that ~l~ul~ energy is conc~mPd by emission
of material, rerlP$~cifion of the sputtered material onto the target, rather than onto the substrate, progressively
lessens the err,cif IlUy of the process of ~ ,ly coating the substrate surface. Thus, a decline in the
d~vai~iun rate is r,-ll- ~ ;- ~ed Cc.~ n for the effect of a declining deposition rate is usually achieved
by ~IUgl~ aai~,ly hl~ dail~ the power applied to the target over the course of the useful target life in order to
25 maintain an acceptable or even constant dppocition rate onto the aU~ I ' C
The dc~,~c,lh,g of the steep erosion groove lluuuglluul the life of the target and the cull~ ;uL~
npcf~ d increase in ~ ,lt, . ;.~g power have certain dialld~ ,f S which shorten the life of the target and
inhibit the use of the material of the target ~rr~,h""ly. The ~1r~ n:.~g of the erosion groove tends to progress
toward a rapid punch through of the target in a small area or band on the target surface. When this occurs, the
30 ,-""ai"d~, of the material in the target can no longer be used, as the t~rget's life has ended. In addition, the
continual increase of the power of the target in order to provide an effective deposition rate, in many cases,
will exceed the n~ imnm power which the target can handle and, accu,di,,bly, the target life may be
pl~ ull,ly ended when the target can no longer be (,~ iL~d to operate at an effficient ,l~ullr~ e rate.
Limiting the increased power to a safe power tends to u~lsrc~ l.y slow down the ~ t~ process which
35 may have altered effects on the quality of the substrate coating being applied and in addition render the use of
the e-lllirmPnt i,,c;rrl~,;~,,,l.
The location of the erosion groove is d~ t ~ f d by the pl rl ~- Irl1l, in a ~, ~u" ~ , apparatus,
of magnet structure which includes pole pieces po~ d either behind the side or around portions of the
CA 0208964~ 1998-01-0~
.;ng target. The magnets so formed usually generate magnetic fields which arch over the ~uLt,.;l~g
regions of the target and which confine the ion pl~lu~;;..v plasmas therein. The magnetic field lines which over
the target generally decline in strength with the distance from the magnet. In order for such fields to effectively
confine a plasma, it is nc~ aly that some field line of a pa~ ,ulal minimnm critical strength arch over the
S target surface. The necessary strength for the critical field line is f~ l on several design palcull~,t~ but
may, for example, be in the area of a~ ~ Iy 160 to 180 gauss. When a target is new and its ~ P
surface is farthest from the magnet, it is found that a certain amount of m~n~ticm iS required to produce a
critical field line of a proper size and shape over the desired location on the target surface to effectively confine
a plasma. Where the magnets are ele.,ll~ v and the strengths of the magnetic fields relate to the level of
10 current through the magnet windings, the critical field strength with such a new target can be precisely
established.
As the target erodes, however, the erosion groove is formed and the surface of the target recedes
toward the UllJ~ illt, magnet. If the strength and shape of the magnetic field are constant as the target erodes,
the changing contour of the target surface causes the surface to erode fastest where the magnetic field is
15 strongest and the lines of the strongest field bridge the target surface. Therefore, where the magnetic field at
the center of an erosion zone of a new target may have been in the area of 180-190 gauss, as the erosion groove
is formed, the field strength at the target surface within the erosion groove may increase to, for example, 240
gauss. At this field strength increases at the target surface, the plasma which forms tends to be more tightly
confined and drawn more closely to the target surface. This is found to occur at the center of the erosion
20 groove. This tig~ ~ v and c~ v of the plasma in the presence of the increased field strength is believed
to ~rc~l~ the fnrm~tion of a sharply defined, deep, narrow erosion groove in the target surface. While the
fulllld~ion of the deep steeply walled narrow erosion groove in the target surface may be partially UV~I~;Ullle
with the prior art proposal to move the magnetic field and thus the position of the plasma, in many cases, this
will shift the point of origin of the ~l~unr~ v material so as to u -~rce~ .ly alter the ullirullll;ly of the coating
25 on the substrate surface.
While many schemes for controlling the electrical palcUII t~ of a target have been devised, these
control schemes have focused on satisfying p~ such as substrate coating ullirullllily. The prior art has
not, however, ~rrt~ ,ly produced a method for controlling the operating palalll~,t~ of the ~
apparatus over the course of the life of the ~l-u~t~ g target in such a way as to avoid ~ form~ion
30 of the steep erosion groove without ~7.~ ri- ;uV or limiting the abiliy to otherwise control the sputter coating
process. It is desirable that the formation of the erosion groove be controlled in such a way that the contour
or profile of the target surface most closely conforms to that of the original target ~hIUU~IIUUI the target life,
cmd particularly to be able to do so without moving the ~ e region on the target surface. In this way, the
efforts to control the ullirullll;ly of the ~i~poCition on sul/~ t~,~ is rendered easier to achieve while the use of
35 the target material is made more efficient.
e ~ of the I~
It is a primary objective of the present invention to enhance the pe~ru~llldnce of a ~ r~ g target
having at least one ~ r~ v region thereon in such a manner as to increase the number of ~ull~lldt,i, which
CA 0208964~ 1998-01-0~
may be coated with a ~ rl ;~ target over the course of the life of the target. It is a more particular objective
of the present invention to enhance the p.,.ru~ ance of a ~ullciing target by ,. ~ a broad erosion
profile at the ~uUclill~, region of the target.
It is an q~' ' ' objective of the present invention to enhance the pelrulllla lcc of the sl,u~ g target
5 which presents a plurality of ~I,ultl,ling regions, and more particularly, to enhance the pclrullll~lce of a
c. target formed of a single piece of ~l- -lh ~ ;~, material having thereon a plurality of !~lJullr. ;.~ regions.
U.s.patent4soo4o9describesal~la6l~cLunsputtercoatingdeviceinwhichanelecll~l~llr~;Jlrl;rcoilwith
an alju~Ldl)'~ ene~6iLin& current is employed rather than p~,.llldll.,.l~ magnets. Electrical ;~ e~l~nrt of the
plasma or glow discharge produced by the coil is controlled by controlling the current flow through the coil
10 which allows, for example, operation at desired values of voltage or current A Hall probe located near the
target may be used to monitor the magnetic field intensity to allow an ~c~ c~"~ ,l to be made of the end of
target's useful life.
European Patent Al-pl~ n 0330445 published August 30, 1989 describes a g hun sputter coating
assembly with a concave target, two elc~l,ull ~c,l- I;r coils and a plurality of pole pieces. The target may
15 include a central planar base and an angled outer annulus. The coils and pole pieces are arranged and operated
to control target erosion and, in particular, to cause ~ ~ ;u,~ from both target regions and the transition
region Ll-c~,b.,t~en.
European Patent ArFIir~tirln 0162643 published November 27, 1985 describes a sputter coating source
with two annular targets spaced UUI~TaII1IY from each other around a central axis. Each target has its own
20 magnetic field gen~,.alin& means and separately controllable power supply.
A method of ~ ..1. -n. :-~g the p- r~."~ ~n~e of a ,, ~on ~ rl ;~e t, rget having at least one ;~
region thereon to increase the number of ~ub~lldt.,l coated from the target over the course of the life of the
target, in accu.~ce with the invention, cu~ c providing an ele~,L u~agnet to produce a plasma confining
field having magnetic lines of force extending over the sr~l~rine region of the target, the lines of force having
25 initial positions above the sl,ult~,.i--6 region and through the target and including a critical field line which
1'1 1' 5 the shape of the plasma, ene.6iLi.l6 the target by supplying electric power thereto to cause material
to be sputtered from the ~ult~,.in,~ region thereof and deposited at a ~ d~ t~ -Pd rate onto a substrate that
faces the cr~ltPrine region of the target cllald~ t,fiL~,d in that, as the target erodes, the crlttrrine region thereof
~u6.c~ivcly recedes through different ones of the positions of the magnetic lines of force at which the lines
30 of force plu~ ly flatten and in that the method includes sensing the voltage applied to the target and
producing a control signal in response thereto, ~,-u~,-.,i,si~.,ly ill~ ,dsin~ the power supplied to the target over
SU~ Y the entire useful life of the target as the target erodes and IJ-u~ .si~.,ly reducing the strength of
the field and flattening the critical field line over the :~JU~C.ill~, region Ll--uu~,l.uu~ the useful life of the target
in response to the control signal to maintain the voltage, as the power increases and the target erodes, at or
35 above a ~ d level. Preferably a plurality of magnets is provided which define ~ ;ug regions on
the target surface. Each magnet generates a plasma confining magnetic field over a co..~ unl~ region of
the ~uucling target, each field having a critical field line which ~1~ t ~ ~;n. S the shape of the plasma which
forms over the region. Over the course of the useful life of the target, the critical field lines are ~-u~5-c~ivcly
CA 0208964~ 1998-01-0~
flattened as the target erodes. This flattening is caused to occur plue,l~ .ly over the active or useful life of
the target in accold~lce with the erosion of the target. The ylu6l,~ ., flattening of the critical field lines over
the ~yu~ ing regiûns of the target, may occur either cc,..l;.- ~ ly or i,~ r~ y~ but at frequent enough
intervals so that the plasma does not tend to CullC~lLl at the center of the erosion groove. As such, a broad
5 erosion profile at the syuu~lillg region of the target is thereby l~ I With targets having more than one
erosion zone formed by plural magnets, each g_neldLillr separate fields with separate critical field defining
lines to define the position and shapes of the plasmas over the ~ y~.Liv~ regions, the method may be employed
at ûne or more of the target regions to extend target life and target p~..rul~dllcc. In the preferred application,
the target pr- r~" ,.. - ,,e is enhanced with respect to a multiple plasma, one piece target in which the two plasmas
10 are alternately switched on and offby the switching of the current to the clcuLIulll~ll.,L~ which produce the
l~.i,~li~., magnetic fields that contain them. In multiple plasma ~I~L~ ". the method is particularly useful
when employed with respect to the one region of the target which is l~,~yOlls;l~'~ for the major portion of the
~l~u~ " but may also be employed at the other regions of the target with advallt~_. In an al~yli~ where
power to any given target region is switched on and off, the "life" of the target, or any region of a target, as
15 that term is used herein, includes only that portion of the cycle during which the relevant ~yult~lhlg region is
activated by the e~ iLatiOll of the magnet suyl)ullil4 the plasma to thereby cause the sl)ult~ ;..g to occur from
the target or target region.
In a~,cc,ld~l~,e with the preferred r~ 1 of the present invention, the magnets include a structure
having a design which results in the shape of the critical field lines having a tendency to flatten over the
20 Sy~lt~ ~ ;ug region of the target as the strength of the magnetic field decreases. It has been found that such a
magnet structure includes, but is not ll~cei,~alily limited to, those magnets, particularly clc.,LIu...~gn~tc, which
have pole ~Llu~_~ules which are spaced behind and around the sides of a particular ~y .lt~,;"g region of the
target. Such magnet structure pl-,f~,ldbly surrounds the target material in such a way that, as the target erodes,
the erosion groove recedes down into the target and between the ends of the pole pieces. Many various magnet
25 sLIu~,~ul~,s, however, may be devised having such a tendency.
The field strength of the magnet is reduced, or otherwise changed, over the useful life of the target,
so as-to cause the critical field line over the target region to plu~ iv~,ly flatten as the target erodes. This
reduction of field strength is pl~l~lably achieved by providing an cle~,Llull~ ,L and y~u~"~,s~ ly reducing
the current through the coil of the ele.,ll~ ~, in such a way as to cause the field strength to decline and to
30 cause the critical field line to thereby flatten.
The target is energized with a regulated power supply which is caused to operate at a regulated power
which increases over the useful life of the target in such a way as to maintain the ~yuLL~lhlg deposition rate
from the target region at an dyyl~ ~ 'y constant level. Such power supplies then tend to develop a voltage-
to-current ratio that is lu:,yur~ , to changes in the paldlll~ of the target, including target erosion, so as to
35 supply power at the regulated level. It has been found, for example, that such a power supply seeks a voltage
level necc,~d,y to deliver the regulated power to the target, which, as the target erodes, is found to decline.
It has also been found that reducing the magnetic field strength over the target region tends to increase the
voltage which the power supply must deliver in order to produce the regulated power.
CA 0208964~ 1998-01-0~
By controlling the magnetic field strength of the target magnet in such a way as to reduce the field
strength of magnets, the shape of the plasma confining critical field line changes, changing the erosion of the
target. As that field strength is decreased, 1,roaJ.,.1..4 the erosion zone occurs. By reducing this field strength
in such a way as to maintain the voltage of the target power supply at or above some ~l~d~ ~t~ . d level, and
S so controlling the magnetic field in this way over ~.~h~ lly the entire life of the target, the erosion groove
becomes broader and the use of material from the target surface is Pnhqnrerl particularly so if the field strength
is reduced to maintain the power supply voltage at a constant level IL~uugl-uul the life of the target.
According to the preferred ~mho-limPnt of the invention, the current to the coil of an el~ . l,u,.,~..~l,
having pole pieces that surround the target material, is reduced to reduce the field strength and thereby flatten
10 the magnetic field over the target, particularly the critical plasma co~ g field line over the target region
being sputtered, when the power supply voltage drops below a p".1. ~ ~...;,~- d level to maintain the power
supply voltage at or above a desired level. By doing so, effective enh~ r~ of the p~ lrullll~l, c of a
~I.u~ c target is attained.
As a result of the present invention, it has been found that the width of the erosion groove formed on
15 a ~ ;u~ target region is broadened so as to render the target capable of ~li~flg more ~l~llllr ;"c material
over the life of the target, that is, before the erosion of the target proceeds to punch through to the back of the
target, or the target power exceeds the limit of the target. This b-uader~l~ of the erosion groove can be
obtained without IllUV~ ,.lt. of the effective location of the region on the target surface from which .~ g
is occurring. Ful~h.,l--,u-~;, it has been found that the amount of power needed to sustain a constant d~o~ilion
20 rate on the substrate from a target, in a- cu-ddnce with the plhlCi~)' - of the present invention is reduced over
the life of the target so that the power increase proceeds more slowly, not only delaying the point in time at
which a target can no longer be operated because the power is too high, but in reducing heat, arching, and
other ullJ~ildlJle side effects of high power. As a result, the number of s~ll.ltl s which can be coated with
a given dUI)U~i~iUn thickness has been drastically increased by as much as 30% with targets of proper design.
These and other objectives and ad~ ulL~;. of the present invention will be more readily apparent from
the following detailed description of the drawings in which:
Brief Dc.,~ of the D~
Figure 1 is a cross-sectional view of a l,.uccci,~i"~, Chamber of the sputter coating apparatus embodying
~lin :r1 ~ of the present invention;
Figure 2 is a diagram ~ trqting an electrical circuit .ul~4~ ll1 according to l~lhl.,il~' of the present
invention;
Figure 3 is a graph illustrating the variation of various electrical values of the circuit of Figure 2 as a
function of time over the operative life of the target; and
Figures 4 4A, 4B and 4C are r...~,lll~l.~y cross-sectional diagrams of targets cu--,l,~i"g the field line,
35 plasma and erosion groove shapes with and withcu_ the present invention.
:Detailed De.,.- ;r ~i ~ of DraW~u~
Magnetron s~ g devices of the type to which the present invention relates are described -n the
following U.S. Patents:
- CA 0208964~ 1998-01-0~
U.S. Patent 4853033 for "Cathode Target Design for a Sputter Coating Apparatus";U.S. Patent 4871433 for "Apparatus for I~ u.hl~ the U ~r '~/ of Ion Bu,,,~ d~ ll in a Magnetron
Sp~ttfrin~ System";
U.S. Patents Nos. 4,909,675 and 4,915,564 entitled "Method and Apparatus for Handling and
Plucf ;,~h~g Wafer-Like Materials": and,
U.S Patent No. 4,957,605 entitled "Methûd and Apparatus for Sputter Coating Stepped Wafers."
Fig. 1 illustrates, in cross-section, a sputter coating pluCf ~ lg chamber 10 of a sputter coating
a~)p.ll~lu~ ac~,o,di,~ to ~ ,' of the present invention. The chamber 10 is a portion of the sputter
IJ,U~ c ;~ lg apparatus disclosed in U.S. Patent 4,909,675. The plucc;,~hl~, chamber 10 is a vacuum pluce:~sillg
chamber formed of an isolated section of a main chamber 11. The main chamber 11 is isolated from the
' IC of the machine C~lvilulllll lll 12 by a plenum wall 14. The ~lucejsing chamber 10 is capable of
co---------~:~;~;uc with the main chamber.11 Illluu~lluul opening 15 in the plenum wall 14. The opening 15 is
generally circular. The procfssill~ chamber 10 is capable of being selectively isolated from the main
chamber 11 by the selective IIIVVCIII~,Ill of a ~IIUCf ~sing chamber back plane section 16 against a portion of a
disk shaped rotary wafer transport member 17 clamping the transport member 17 between the bll. ~lallc
section 16 and the plenum wall 14 in a sealing relqtil ' ." thereby enclosing a back plane space 19 within the
)lUCf ~;~illg chamber 10 and isolating the l)lUCf'~sing chamber 10 from the main chamber 11.
Opposite the 1- - klll 'Uf section 16, on the front plane side of the transport member 17, the ~lu~,el~hlg
chamber 10 is isolated from the machine Cllvilu~ull~ t 12 with a cathode assembly module 20 mounted in a
vacuum sealing relqti~mcl~ir against the plenum wall 14 :~llllUUlldill,& the opening 15. The module 20, or
p~uceci,~hlh chamber r,~ ~, section, cooperates with the ba. h~ e section 16 and the transport member 17
to form the sealed isolated l"uc.,j~hl~ chamber which is isolated from both the main chamber 11 and the
machine cllvilolul~,.ll 12. Within the ~lucc~shlg chamber 10 is a wulh~ ~e 21 in the form of a flat silicon
wafer or disk which has the surface ~ upon which a coating is to be deposited in a sputter coating process to
be p. .rulllled within the l,luceJ~h.g chamber 10. The wafer 21 is held by a set of clips or other retaining
devices 24 in a wafer holder 25 resiliently carried by the transport member 17. The transport member 17 is
rotatable within the main chamber to bring the holder 25, and the WUI~ or wafer 21 into qlig~m~nt with
the hole 15 so that the l)ruccssil.g chamber 10 can be formed around the wafer 21 on the holder 25 by
lld l~-vcl~e lllU.~ ul~,l,l of the b~ section 16 to move the member 17 against the plenum wall 14. (The
transport member portion 17 is a llal~v. l~Gly movable ring carried by a rotatable index plate which is not
shown.) In this preferred ~...l ~1;Illr-~1~ the wafer 21 is c~ with and ~u~l~)u~t~d in a plane p~ ,~,~....l;..~lqr
to a central axis 27 of the main chamber 10, which is also cuncG.lllic with the hole 15 in the plenum wall 14.
Sulluull~lhlg the wafer 21 on the holder 25 is a disk 29 which at least partially protects the holder 25 from an
excessive rC~m~llq~ n of coating intended for but which missed, the surface 22 of the wafer 21. Details of
35 the ~ rl i.~ apparatus of which the p,u c~i"~, chamber IO is a part including p uli~ ulduly det. ils of the wafer
transport 17, wafer holder 25, and back plane section 16, are described and illustrated in the U.S. Patents
4,909,675 and 4,915,564
CA 0208964~ 1998-01-0~
The cathode assembly module 20 includes two ass~."l,lics, a removable cathode assembly 30 and a
fixed assembly portion 31. The fixed assembly portion 31 is an annular enclosure rigidly mounted in sealed
rPlq~i- mhir against the plenum wall 14 SUllUUlldill~, the opening 15. It includes a cylindrical metal side wall
33 of the chamber 10 which is electrically grounded to the frame 14 of the plenum, a wafer holder shield 34
S which ~U~UUII Is the opening 15 and a chamber door frame assembly 35.
The cathode assembly 30 is mounted to a hinged door assembly 37 which l~llw~ably but sealably
supports the cathode assembly 30 to the fixed assembly 31. The cathode assembly 30 carries the s~u~L~
target 40, which is an annular concave target having a cfmtinllouc smooth concave ~)uLkiing surface 41. The
assembly 30 supports the target 40 with its axis in qlignm~nt with the axis 27 of the chamber 10 and with its
~ r- il~g surface 41 facing the surface to be coated 22 of the wafer 21.
The target 40 is ~u~J~ulL~d in a target holder or nest 42 having a generally circular back plate 43
collc.",L,ic with the axis 27. The target holder 42-has an outer ~,yli~ ,al wall 44 and an ~ g cylindrical
midwall 45. The outer wall 44 sulluull~l~ the outer rim of the target 40. The target 40 has an outer cooling
surface which, when the target 40 is mounted in holder 42 and expanded to opérating Ltlll~J~,.aLulc;, conforms
to and lies in close cooling contact with the inner surface of the holder 42. An annular groove 47 on the back
of the target 40 lies in partial contact with the midwall 45 of the holder 42. The target holder or nest 42 has
a plurality of annular grooves 48 in its back surface and annular grooves 49 on the outside of its outer wall 44
for the .,;l~,uldLiun of cooling liquid, which is generally water, to remove heat generated in the target 40 during
sputtering by cooling the heat colldu~,Li~, target holder 42. The shapes of the surfaces Of the target 40 are
~,~r~.~ly such that all the target 40 is capable of being formed by turning bloc k of sl.ul~r~ g material on a
lathe. The target holder 40 is made of a heat culllu~ and electrically condu~,Liv~ material, preferably hard
tempered OFHC copper or Alloy 110. The target 40, when operationally heated, expands and ~,~r~,ably
plastically deforms into a shape which conforms tightly to the interior cavity of the holder 42 and thereby
cou~ with the holder 42 to conduct heat thereto. The cooperation or the holder n and the target 40 are
plcr~d)ly as described in U.S. Patent No. 4,871,433.
The target assembly 30 is provided with a magnet assembly 50 which ~l~r .ably includes a pair of
con~ tlic annular magnets 51 and 52, preferably cl~ lu"l~ ,Ls having annular inner and outer Findings 53
and 54, l~,spt~;liv~ly, Iying c-)u~ lly in a plane behind the target holder 42 and centered about and
P~ ~L " ' to the axis 27. A rigid ferrous material, such as 410 annealed stainless steel, forms the structural
support of t. rget assembly 30 and c~ ~ the magnetic pole pieces of the magnets 51 and 52. This ferrous
material includes a circular center plate 56, which forms the planar rear support of the assembly 30 and
sustains the Lla~ , magnetic field between pole pieces of the magnets 51 and 52. A ~;yli,~ical outer pole
piece 57 is welded to the plate 56 at the outer edge thereof to stand upwardly ~h~ fiulll and to surround the
outer wall of the holder 42. A target outer retainer ring 58, is bolted to the upper edge of the outer pole piece
57, so as to rest on an outer annular lip 40a of the target 40 to retain the target 40 in the nest n. The upper
exposed surface of the outer pole piece 57 and ring 58 is shielded by a metal dark space shield 59, which
prevents ~ r~ of the pole piece 57 or retainer ring 58. The dark space shield 59 is rigidly secured to the
chamber wall 33 and thereby electrically grounded.
- CA 0208964~ 1998-01-0~
- 10-
An inner cylindrical pole piece 61, having as its axis the axis 27, projects through the inner rim of the
target 40. This pole piece 61 is threaded through the center of the holder 42 below the target 40, and has
threaded thereon, above the target 40, a center retainer nut 62 which retains the target 40 af its center hole.
The center pole piece 61 has bolted to the bottom end thereof a pole cap assembly 63. The pole cap
S assembly 63 includes a circular inner plate 64, a ~"~lh,J.ical lower middle pole piece 65 welded at its base to
the outer edge of the plate 64, an annular outer plate 66 welded at its inner edge to the outside of the lower
middle pole piece 65, and a lower ~"ylh,J~ical outer pole piece 67 welded at its base to the outer edge of the
annular plate 66. The lower outer pole piece 67 has bolted to its upper edge, base 68 of outer pole piece 57.
The components 64, 65, 66 and 67 of the pole cap 63 have a common axis Iying on the axis 27 of the
10 chamber 10.
The middle cylindrical pole piece 65 underlies the annular groove 47 in the back of the target 40, and
projects either in a continl~o~C annular ring or at spaced intervals through the plate 56 into a recess 69 in the
back surface of the holder 42. A ring 69 of rigid f~ g, ~ material and having ~ lu~illlat~ the same
diameter as that of the middle pole piece lies, and is emhe~ Pd within, the annular groove 47 in the back
15 surface of the target 40. The upper end of the middle pole piece 65 lies in the annular groove through the
surface of the backplate 56 close to the ring 69a. The ferromagnetic ring 69 sulluullJs the midwall 45 of the
holder 42 in the groove 47 in the back of the target 40.
The middle pole piece 65 together with the ring 69a form a pole piece which the inner and outer
magnets 51 and 52 have in common. The ring 69a is ~~-a~;J~ lly coupled to the middle pole piece 65 so as
20 to extend the effective pole piece at the annular groove 47 of the target 40 to very near, but beneath, the surface
41 of the target 40. In that the r~... ,-- .r~" .. I ;r ring 69a is of a rigid ~ material, it is ~ lly
stronger structurally than the soft copper of the holder 40 is made of a material which expands less when
heated. As such, it serves to structurally reinforce the midwall 45 of the target holder 42 against radial
r~ caused by the heating of the target 40, thereby also l~ g the target 40 against radial thermal
25 r ~
Conr~ ly mounted at the top of the center pole piece 61 is a central electrode 70, electrically
insulated from the pole piece 61 by a ceramic washer 71. The center pole piece 61, the target 40, the holder 42
and the entire center plate 56 and pole cap assembly 63 are energized to the same cathode potential.
Accu,J;l,oly, the assembly 30 is insulated from the grounded fixed assembly 31 by a Teflon insulated annular
30 spacer 73.
A center pole cap 76 is fixed to the bottom of the pole cap assembly 63, cu",~.lllic with the axis 27.
The cap assembly 63 supports an outer cooling fluid tube 77 which extends vertically through a bore 78 in the
central pole piece 61 to the electrode 70 with which it makes electrical contact. The tube 77 is electrically
collJu,liv~ and insulated from the cap 76 to provide for the Cl,.,.L~iLi,~6 of the electrode 70 at a potential which
35 is different from the target 40 or the grounded chamber wall 33. Mounted to the bottom of the cap 76 is an
outlet tube assembly 79 for i g cooling fluid from the tube 77. An inlet assembly 80, connected to the
base of the outlet assembly 79 supports an inlet tube 81 which extends through the center of the tube 77 to the
electrode 70 to supply cooling fluid thereto. A water inlet 83 and outlet 84 are provided in the inlet
- CA 0208964~ 1998-01-0~
assembly 80 and outlet assembly 79 ,.,~e~liv~ly. Similarly, cooling passages 85 are provided in the plate 56
for cu~ r~l;ng cooling water from passages 48 and 49 to a cooling water outlet 86 in the plate 56. A
cooling water inlet 87 c~ ~ water through a grinder inlet duct to the passages 48 and 49 in the
holder 42.
S Referring to Fig. 2, the target 40 is shown SU~ulL d in the target or cathode assembly 30 which
includes the magnet core 50 which in turn includes the ~,ylh- hi~ al outer pole 57, the center post or pole
piece 61 and the ~ ylinLi~al int~rmPrliqt~ pole piece 65. The outer pole piece 57 ~ulluu~d~ the outer edge of
the target 10 while the center pole piece 61 projects through the central hole of the target 40. The ~ '
pole piece 65 extends into the annular groove 47 which is formed in the back surface of the target 40.
For purposes of the present invention, the magnets, of which the pole pieces 57, 61 and 65 of the
magnet core 50 form a part, may be capable of producing a field line which can be ~)IU~ Iy flattened over
the life of the target, either lll_ ' 'ly or electrically, and either by making the magnet assembly 50 function
in a variable manner or by the introduction of auxiliary magnets which can cooperate with the structure 50 to
vary the field. Mechanical flattening of the field is less desirable in that it would normally require the
15 lllu~ lll of magnet elements, a technique which is less flexible and complex. Acco,.li~,ly, the use of
elc~l.u...agnets as described herein is preferred.
In the preferred 1 .~.1~1;.~. .~1 illustrated in Fig. 2, the magnets 51, 52 are cl~ u...a~,-.. L~ having inner
and outer magnet windings 53, 54. When energized with current, the magnet windings 53 and 54 generate
magnetic fields, l~ generally by the arched lines 101 and 102, I~,~pe.,lil,~ly, in Fig. 2, over the
~I-ul~r- in~, surface 41 of the target 40, which confines or traps the l~ ,IiVt; plasmas, illustrated generally as
the oval shapes 103 and 104, ~ C~ Li~. Iy, over l-,~.,LiVC; inner and outer ~l.u~lr~ iug regions 105 and 106 on
the target surface 41 in Fig. 2. In addition, the magnet core structure 50 which includes the positions and
shapes of the pole pieces 57, 61, and 65 particularly, in r~ L, around l~ JC~ v~ regions 105 and 106,
e~ ,ly, of the target surface 41, produces change in shape as the current in the coils or windings 53, 54,
and thus the strengths of the fields 101, 102 vary, as described more fully below in relation to Fig. 4.
In the preferred and illustrated embodiment of the invention, the magnets 53, 54 are alternately
switched on and off so as to alternately maintain magnetic fields 101 and 102 at ql-~-nq~ing times over the
)C~liv~ regions 105, 106 of the surface 41 of the target 40 thereby alternately al livaling the regions 105,
106 for ~ c, The fields 101 and 102 are ' alternately to ~' 'y support l~ C~ , plasmas
103 and 104 over the target regions 105, 106. In this embodiment, the "flattening" of the field refers to the
fields which exist only when the ~ ., magnets 51, 52 are energized. Similarly, the "life" of the target
or more ~peçifirqlly of a region of the target refers herein to the times during which a given region is activated
and material is being sputtered ~h~ .~ flulll.
The magnet currents are switched by a switching power supply 110, which supplies current alternately
at desired levels through lines 116 and 118 I, ~c~,Li~,ly, to coils 53 and 54. The magnet power supply 110
switches, in response to a timing signal on a control line 111 from a IL)IU~6l~ '1l1' '1ll~ or gettable control circuit
120. The magnets ql Iy energize to current levels l~ OllaiV~ to a control signal on line 119 from the
- CA 0208964~ 1998-01-0~
controller 120. The switching of the magnets causes a co~ ,o~ ;,.g alternate activation of the plasmas 103
and 104.
A power supply 122 supplies power to the target 40 through a line 121 from the target power supply
l~. This power is switched between two regulated power levels in response to a signal applied through line
123 from the control circuit 120. The switching of the magnet power supply 110 and that of the target power
supply 122 are ~ lrd in ayll ,luulf~i~lll under the control of control 120 by a power timing signal supplied
to the target power supply l~ on line 112 from the controller 120.
The substrate 21 to which the sputter coating is to be applied may, for some applications, also be
subjected to a bias voltage through a substrate bias power supply 1~ i generally by the block 124 in
Fig. 2. The voltage of the substrate 21 may be, in the alternative, ~ d at the same voltage as a system
anode 1~,~l. 1 by the chamber wall 33 which is generally at ground potential. While illustrated in
co~n~- I;n.~ with a switched dual plasma apparatus using a one piece concave annular target, the features of the
present invention are ~ r~ to single plasma, non-planar targets, and to systems which may be magnetron
enhanced either with l,e ~ rl~l or C~ UII~gJ~
Fu~hc;--llu-~, the target power supply l~, which supplies the ~I~u~r~ ;ug energy to the target 40, may
produce a constant power output. Over the life of the target, however, the total power output on line 121 of
the target power supply l~ may be pe.io" lly adjusted, ~)luf~lably by cull~hluuu~ly~ periodically, or
otherwise ~lu~,lu;~ai~,ly illUltia~;.~ the regulated level of power delivered to the target 40 to maintain a constant
~lrpc!~!;tinn rate upon the wafer 21. Such d~ai~iun rate may be, for example, one micron for every 45 seconds
of target ~ 6iLation. This ~ - of constant ~lepu~i~ion rate in the face of the pl ~ known a~s rate
roll-off, which occurs as the target is eroded over the course of its useful life, usually iâ COull ~ ~ by
hlull,a;~ 6 the power output of the target power supply 122 over that life. When, as in the preferred
embodiment, the target regions are al Iy ene.6iL.,d, the power delivered to the target 40 is switched
between two regulated power levels in sy-lcluu~ ... with the magnet current ~wi~ul.i..~,~, one for each region
105, 106 of the target, so that the sr~ttrnng from the different region~s can proceed at a power level a~lul ~
for ~,uuU~,.i-.g from that region. The hl~ ,a~ill6 of the ~ r~ , power, in a system so controlled, will be
carried out by ;i~.L ~ ly i~ ua~ the regulated power levels at different rates cull~ on~ g to the
different rate roll-off of the different ~u~l~lillg regions 105, 106.
The controller 120 is also provided with an input line 130 which is cnnnPct~d to the target power supply
l~ to provide a signal to the controller 120 proportional to the voltage on the power supply output line 121
to the target. The controller 120 contains a ~lirr~.-,.llial amplifier or other filnrtinnqlly equivalent circuit that
compares the voltage reference signal on line 130 with some ~ d~ d reference voltage. The controller
120 develops, from the dirf~ ,nce between the target voltage signal 130 and the reference voltage, an error
signal that controls the current level signal on line 119 to the magnet power supply 110. This control function
operates to reduce l)lugl~ ,ly the el.~,.6iLi-L~ current on the l~ c~ , magnet winding 53 or 54 as the
voltage of the target power supply, when the ~,i"~uli~, winding is activated, drops below the reference level.
Similarly, the current of the activated magnet will increase wl-~ ,. the voltage of the target power supply
rises above the reference voltage. A different reference voltage is provided for each target region. Each region
CA 0208964~ 1998-01-0
- 13-
105, 106 of the target 40 is Scpal Iy controlled by changing the coil current s~ 'y to the magnet windings
53, 54.
In the ~ " line 130 may be connPct~p~ instead of to the power supply 122, to the output of a
target erosion sensor, and the signal on line 130 cu~ ~, d at the controller 120 with some reference criteria.
S In response to the c~ nl~ the controller 130 will generate an error signal which will be logically
~l~ci~ed to control the current of the magnet power supply 110 to reduce the current on a l,,~e~ , one of
the magnet windings 53 or 54 in accul~c with the sensed target erosion at the ~ , target regions 105,
106.
Referring to Fig. 3, curve I l~rcsc,l~ a typical course of variation of activation level of the voltage
10 of the power supply on line 121 to the target 40, for any given region of the target, as the s~uLl~,in6 surface 41
of the target erodes over the life of the target. This voltage generally tends to decline. At the same time, to
maintain a constant ~ppocitil n rate, the power applied to the target 40 frûm the power supply l~ would,
without the invention, typically increase along the curve III of Fig. 3. Thus, without the invention, the life of
the target would be ended in one of two ways. First, the end of the life of the target could occur when the
15 target burns through to its back surface, that is, when the erosion groove p~ the target. This is
1~1~ ' by point A on curve III in Fig. 3. Also, even when the target does not burn through, its useful life
could nn,.~ be i ~ ' when the required power level exceeds a ~ " level that can be tolerated
by the target, as ill ~ by point B on curve III in Fig. 3.
With the present invention, a control signal on line 130 is processed by controller 122 to vary the
20 control signal on line 119 to the magnet power supply 110 to adjust the levels of the currents on the magnet
windings 53, 54, in order to maintain a constant target c.-~l6iLaLioll voltage on line 121 to tdrget 40 to produce
a constant cncl6iLaLion voltage over the useful life of the target as shown by curve II of Fig. 3. It has been
;r~ ed that, with this control of the present invention, the power from the target power supply 122 to the
target 40 need be increased less rapidly than '~ without the invention to maintain a constant d~;~o~ilion
25 rate. A~,~,o-d ~ " the target power supply power on line 121, with the present invention, will conform more
to curve IV in the graph of Fig. 3. Thus, the end of the life of the target has been found to occur at the point
C on curve IV, after ~ Iy 25 to 30% more s~t"t~,s have been plùccsscd than with the prior art
control method that i ~ ' at point B in in graph of Fig. 3. This improved pCI rulllldn~,C iS believed to be
a result of the broadened erosion groove that results from the present invention as described in relation to Figs.
30 4-4C below.
Fig. 4 illustrates the cU~r~ ;on of the field 102 and the shape of the plasma 104 for the outer target
region 106 of a target 40 at the bc6i.ll in~, of a ~ r- ;l~g process when the target 40 is new. Given the
particular current through the winding 54 of the magnet 52, a field will develop over the region 106 having
a strength and shape l~ by the individual field lines 102a-102f. These lines represent fields of
35 Ics~c~ively hl~l~dsing strength varying from, for example, 160 gauss to 260 gauss. Given the particular
conditions of the slm~ e chamber, one of these lines, for example, a 180 gauss field strength line 102b,
,s.,.l~ a critical field line of a minimum strength required to sustain and support a glowing plasma
discharge 104 bounded by line 104a. With such a magnetic field configuration, plasma will tend to be more
CA 0208964~ 1998-01-0
- 14-
dense near the surface 41 of the target 40. This is, in part, because the field at line 102c is of a greater field
strength, for example, 200 gauss. The field lines 102b and 102c emerge above the surface 41 to form a closed
tunnel or magnetic trap over the region 106 of the target surface 40. The stronger field line 102c tends to
contain the more dense area of the plasma 104 as ~ i by the line 104b of Fig. 4. The a~u~L~lhlg of the
target surface 41 at the region 106 will proceed more rapidly in ~ / to the portion of the plasma 104 that
is the densest. Without the present invention, as seen in Fig. 4A, as the target 40 proceeds to erode, an erosion
groove 41a in the surface 41 will develop. Without the present invention, this erosion groove will deepen over
the life of the target until ~ , the groove punches through the target as illustrated by the erosion groove
surface contour 41b. As this occurs, the plasma 134 is drawn deeper into the erosion, as at erosion groove 41a,
10 where it tends to be more dense as illustrated by the portions 134c and 134d, within the weaker portions of the
plasma 134a and 134b. This is believed to be due to the influence of the stronger field lr~ d by lines
102d and 102e. As a c..~ e of a stronger and denser plasma 134, the rate of ion flux bullll,~dlll~ at
the target surface increases, particularly in the deep portion of the erosion groove 41a. This causes a current-
voltage ratio in the power delivered to the target 40 to increase. In addition, particles sputtered from the surface~5 41a tend to impact with i~ s;ng frequency upon other portions of t
he surface 41a, from one side of the
g groove 41a to the opposite side of the erosion groove 41a, thus reducing the a~uU~lill6 ~rr~.;;e" y
and the dr~a;liun rate onto the substrate. This decline in the d~a;lion rate, or rate roll-off, is normally offset
with the hl.;l.,ds;,lg of the power applied to the target 40 until that deposition rate is ...~ d at a constant
level on the substrate, but also hl~ ;ng the ~ osiLion on the sides of the erosion groove 41a. This
20 Ir-lr~-~ of material on the target surface tends to further narrow the erosion groove 40a. When the target
has punched through, as shown by the groove 41b in Fig. 4A, the l- ,ll~.hlJ~, of the material in the target 40
is unusable. In addition, the increase of the power to offset the a~ULI~l ill~6 rate roll-off due to the rl~ ~p~n; ~ g of
the erosion groove may have, in certain instances, exceeded the capability of the target thus ending the useful
life of the target even before punch-through.
Referring to Fig. 4B, the ~)lugl~,~aivr erosion of the target 40 in the system embodying the plill~
of the present invention is illustrated. The structure of the magnet 52 is such that, as the field between the pole
pieces 57 and 65 declines in strength, the field lines between the pole pieces 57 and 65 tend to flatten. The field
lines 202a-e represent fields of strengths of, for example, 160 through 240 gauss, in hl~ a of 20 gauss,
assume less curved shapes at positions closer to and behind the original surface 41 of the target 40.
30 Accoldi.4,1y, the critical plasma defining line 202b of, for example, 180 gauss, defines a plasma 204 of a shape
illustrated by the line 204a. The 200 gauss field line, 202c, confines the denser portion of the plasma 204b
above the eroded target surface 41c. The stronger field lines 202d and 202e will be below and not above the
erosion surface 41c. These field lines 202a-e will have a flattened shape in relation to field lines 102a-e of
Co1,~ 1i-4 strengths as shown in Figs. 4 and 4A. As such, the shape of the plasma 204, as shown with the
35 invention in Fig. 4B, is broader over the surface 41c, causing the surface 41c to erode more broadly, thus
assuming a profile of an erosion groove 41c which is broader and shallower than the groove 41a of Fig. 4A.
Similarly, as seen in Fig. 4C, as the target ~ludclles punch through condition where the target surface 41
assumes a profile 41d, evi~,-~,i..~, an erosion groove nearing the back surface of the target 40, a wide erosion
- CA 0208964~ 1998-01-0~
- 15-
pattern will have d~ ,lv~d and ~ ly more of the target than in Fig. 4A will have been rendered usable.
To approach this ~ ~ ' the strength of the field 302 as shown in Fig. 4C continues to flatten such that the
plasma confining field lines 302a-c are recessed into the erosion groove did, confining the plasma 304,
including both the less and more dense portions 304a, 304b thereof, in a broad flat band near the eroded
5 surface 41d.
While variation of the magnet strength has been described in the illustrated embodiment in c~ nrtion
with magnet pole pieces 57 and 65 that cause the magnetic field to flatten as the magnet current is decreased,
other means such as the ~ Vyll~ t of auxiliary magnets, electrically variable or ' ~ lly movable, may
be employed for this purpose.
