CA2523264A1 - Coil having parallel paths having about the same electrical length - Google Patents
Coil having parallel paths having about the same electrical length Download PDFInfo
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- CA2523264A1 CA2523264A1 CA002523264A CA2523264A CA2523264A1 CA 2523264 A1 CA2523264 A1 CA 2523264A1 CA 002523264 A CA002523264 A CA 002523264A CA 2523264 A CA2523264 A CA 2523264A CA 2523264 A1 CA2523264 A1 CA 2523264A1
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Abstract
A plasma processor for large workpieces includes a vacuum chamber having plural individually supported dielectric windows for coupling an r.f. field originating outside of the chamber into the chamber to excite the plasma. A planar coil for inductively deriving the field has plural segments with the same electrical length, each including an element connected in parallel with an element of another segment.
Description
wo 9sris~os' FCTlUS95I15733 ' .
z PhASMA PROC SSOR FOR L G~ WORKPIECES
Field of Invention The present invention .relates generally ,to processors for treating workpieces in a vacuum chamber with'a plasma and more particularly tn~such a proGessQr.
S having plural individually supported dielectric windows . for.eaupliag an r.f: field originating outside of the chamber into the chamber to excite the plasma, and/or a coil for inductively d~riviag the field, wherein the coil has plural segments . with the same electrical. ' length, each 1D ~includizlg an element connected in parallel with an element of another segment.
Ha kid Art Various structures have been daveloped~to supply r.f. ~.ields from devices outside of a vacuum chataber to.
15 excite a gas in the chamber to a plasma state. The r.f_ fields have been derived from electric field sources including capacitive electrodes, electromagnetic field sources including electron ~cyclotran resonators and induction.,.i_e. maguetic,;field sources including coils.
20 The excited plasma interacts with the workpiece to etch the workpiece or deposit materials on it. Typically, the workpiece is. a semiconductor wafer having a , ~larlar circular surface.
A processor for treating workpieces with an 25 inductively coupled planar plasma (ICP)~is disclosed, inter a.Iia, by O~x~.e, U.S. Patent x,948,458, commonly assigned with the present invent3on_ The magnetic field - WO 961,820$. . PGT/US951J.5753 is derived from a plazxar coil positioned ,on or adjacent 1a single planar dielectric window that extends in 'a direction 'generally parallel to the workpiece planar ,surface. Tn commercial devices the window is' usually - , ' S quartz because this material has low impurity content and provides optimum results for r.f, field coupling. The coil is connected to be responsive to an r.f_ source having a ' frequency in the x~aage of 1 to 100 MHz and Coupled to the coil by an impedance matching network including a circuit resonant to the frequency of the . source. The coil. is disclosed as a planar spiral. having.
external - and internal' terminals connected to be responsive to the r.f. source. The circular spiral coil disclosed by Ogle has been modified to include linear, I5 , elongated elements generally in a spiral configuration, to process woxl~pieces having square and rectangwlar shapes.. Caultas et al., U.s. Patent 5,304,279 discloses a similar device employing permanent magnets in combination with the planar spiral coil.
Cuomo et al.,' V:S. Patent 5,280,154 and Ogle, U.S.
Patent 5,77,751 disclose a variation. of the aforementioned processor wherein the lihear spiral coil is replaced by a solenoidal coil. The solenoidal coil is wound on a dielectric mandrel or the like and includes plural helical-like turris, a portion of which extend along the dielectric w~.nr~ow surface. The remainder of tire coil extends above the dielectric window, Opposite .
ends of the solenoidal coil are. connected to an r.f. .
eXClt~tiOn sQCIX'Ce.
None of the prior art plasma processing with whzch we are familiar is well adapted to excite plasmas far processing very Large substxat~s,.for example, substrates used in forming rectangular fJ.at pane. displays having sides in the range of 30,100 cm. Excitation of plasmas ~5 for treating, i.e.y processing, such large substrates requires coils ,having correspondingly large surface areas in contact with or adjacent a dielectric window structure having a large surface area, c4mmensurate with the areas of the workpieces to he treated. It these prior art structures are used for exciting plasmas for treating .
~5 Large workplaces, numerous problems which apparently have not been pxevious,iy considered or resolved axisc.
A problem common to all of the prior art processor designs is that xhe windows must lie increased to a substantial. thickness as . the area thereof irxareases .
Otherwise, the windows would not withstand the differential .pressure between the atmospheric pressure ~~
outside of the chamber and the vacuum in the chamber; .
e.g. to prdtess v;rorkpieces having rectangular treatmexit surfaces of about 75 cm x 80 cm, a single quartz window 1.5 having a surface df approximately 80 cm x 65 cm must have a thickness in excess of 5 cm_ Quartz windows~of the stated area and thickness are also very expensive and fragile so use thereof considerably increases the cast of the processor. In addition, we have found that .the r.f. .
2o . . fields -derived from excitation so~xrces using prier art processor designs are not usually capable of effecti~rely exciting the, plasma in a vacuum chamber with a large area, thick window. This is because the r.f. fields do .
nod have sufficient flux density. after penetrating the 25 thick window, to provide the required excitation. For' . example, the magnetic flux density penetrating a 5 ~ crri 'thick dielectric window from a coil has a much smaller number of effective' magnetic Lanes of. flux than the magnetzc field penetrating a 2.5 cm thick window of a 3D prior art device for treating circular wafers having a 2D
Gm diameter. It is not feasible to simply increase magnetic fiJ.ux density by increasing current from an r. f .
svu.rce .driving the coil because the increased current can cause ea~cessive . heat~.ng of the coil as well as other 35 compozxents and because of the difficulty in obtaining . suitable high power r.f. sources.
wo ~s~zszos pcr~nsgsns~ss A problem peculiar to the use of prior art induction coils for exciting a plasma having a large surface area is non-uniform excitation of the plasma, resulting in non-uniform plasma density and uneven workpiece processing. ' We . have. realized this non-uniform distribution occurs in part because the prior. art coils function as transmission lines likely to (nave lengths, when laid over a 3.arge surface window, approaching or exceeding one-eighth wavelength of the r_f. driving.
~D sources. Because of the coil. length thexe are significant voltage and current variations along the coil, resulting in appreciable magnetic flux density variations in tkze plasma. If the coil has' a length in excess of one-eighth raavelength of the r_~, source there is an RMS voltage null in a coil driven by a current having an RMS peak value because of the substantial mismatch between the source and,the load driven thereby.
The mismatch causes the,coil voltage~and current to be .
phase. displaced by close to 90 ° , resulting in the voltage.
nuJ.l. 'these magnetic flux density variations cause the non-uniform gas excitation and uneven ~workpiece .
proees8zzlg. .
We have realized that the length of the coil between ' terminals thereof connected to the r. f . source must be considerably less than one-ezghth~of a.wavelength of the r . f . source output and that such a result can ha achieved by providing a coil with plural parallel branch elements or segments. While .Hamamoto et al., iT_S. Patent 5,262,962 discloses a planar plasma excitation coil having plural parallel branch segments connected zn a ladder canfiguratian.to a pair of physically opposed terminals connected to the same ends of leads connected to the branch segments,.the structure in Hamamoto et,al:
i.s not suitab7.e for use over a large surface area window.
~If I3amamoto et al. were used on large area windows there would be a tendency fox uneven flux distributa.on and non l 'NO 96118208 FGTIU893115753 uniform plasma density because the different branches are included ~ in r. f . transmission lixies with different lengths across the opposed terminals.. Hence, the branch segment physically closest to the terminals is in the 5 shortest ~.engt~z line, while the branch segment physically farthest from the, terminals is in the longest length l~.ne. The different length lines draw vdifferent currents fram the source so the portion of the plasma adj acent 'the Shortest length line is excited tc~ a considerably greater degree than the plasma portion adjacent the longest length line. This causes non-uniform plasma excitation in processors for treating large surface area~workpieees.
It is, accordingly, an object of the present invention tv , provide a new and iiitproved r, f . field excited plasma processor particularly adapted for ' treating 'large workpieees .. ~ .
~. A further, obj ect of the invention is to provide a 'new and improved r.f_ field excited plasma processor for large workpiec~s wherein the plasma is uniformly distributed over the v~iorkpiece.
Another object of the invention is tw provide a new and improved r.f. field excited. plasma processor vacuum chamber arrangement particularly adapted for relatively.
large workpieces wherein dielectric coupling windows are arranged to taithstand the differential pressure between the chamber interior and exterior while being thin. enough to couple r.f. fields with sufficient density to effectively excite the plasma.
Ann additional object ref the inventyon is to provide a new and improved r.f_ .field excited plasma wori~piece processor wherein a plasma is inductively excited in an efficient manner to provide relativeJ.y uniform plasma distribution for large workpieces.
An added object is to provide a new and improved r. f _ field e~ccited plasma processor ~ having plural VVO 96118208 PC~yI7&95115?'S3 electricalJ.y paral.le~ coil segment bxanches arranged to supply about the same excitation flux to the plasma.
Yet a fuxther object is to provide a new and, improved r.f. field excited plasma processor having plural electrically parallel coil segment branches having about the same electrical and physical lengths. to provide unifox~n flux distribution to the plasma and simplify design, of the coil.
The Invent~.on Inaccordance with one aspect of the present invention, some of the foregoing abjects_are attairxed by providing a pz~oeessor for treating a large workpiece with .
a plasma comprising a vacuum chamber in which the workpiece is adapted to be mounted. A gas which carp be converted into the plasma far treating the workpzece is supplied to the chamber. The,gas is excited into the plasma state _ by an r. f , e~.ectric source outside of the vacuum. The r._ source derives a field~that is coupled to .the p3.asma via plural individually, supported.
dielectric windows on a wall. of the .chamber. ~eca.use there are Plural individually supported windows, rather than a single J.arge window, each window caz}. be thin enough, e.g. 2.5 cm, to provide effective aaupling of the r.f. field to the plasma.
~5 In accordance with another aspect of .the inyrention, other objects of the invention axe attained by providing a processor fox treating a woxkpiece with a plasma comprising a vacuum chamber in which the workpiece is adapted to be mounted,. fhe chamber has introduced into it a gas which can,be converted ~.nto the plasma or treating the workpzece_ A means for converting the gas .. into the plasma includes a coil positioned to couple an r.f. magnetic field to the gas via a dielectric window structure on a wall of the chamber to excite the gas to produce and maintain the plasma. The coil includes first.
WO 96!18208 PL'flilS95i15753 snd second terminals adapted to be connected to an r.f_ source that causes t~ze r. f . magnetic field to be derived, .
as weal as plural wxx~ding segments electrically connected between the first and second terminals so they have about.
the same electric length. Each'segment includes an element that is electrically in parallel with elements of the other segments . Thereby, the R1MS amplitude of tha AC
current flowing in the different coil. elements is about the same to'provide a relatively uniform magnetic flux .
i0 distribution in the plasma. .
In certain preferred embodiments,, first and second tern~inals. of the coil and the co'~.l segments, are .positioned and arranged so the electrical and phys~.cal.
lengths of GUrrent paths are approximately the sane ~ between the first and second ~ ter~oni.nals via at least two, and in same embodiments all , ' of the coil segments . A
particularly advantageous arrangement including this feature comprises plural physically and electrically parallel branch ~cdnduetor elements connected to leads 20~ extending at right angles to the elements, wherein the first ,and second terminals are at diagonally opposite.
ends ~ of the leads . The like electric length lines can also be attained by. proper design of the cross sect.iQn geQmetzy of conductors in the lines to provide lines with Z5 different inductive values and/or by inserting capacitors .
having appropziate values in series with. the~para11e1 .
coil elements. ~. ' The above and still further objects, features and advantages of the present invention will become apparent 30 upozi consideration of the following detailed descriptions pf specific embodiments thereof, especially wrhen taken in conjuncti4n with the accompanying drawings.
WO 9G/18208 PG~YIr59S/I5753 Hrief Descrint~n__of the Drawing ' Fiq. 1 is a~ side seetionaJ, view of a plasma processor in accordance with one embodiment of the present invention; . ' .
,~ Fig. la is a side sectional view, at right anqles to-the view of Fig. 1 of a portion of the pl~.sma processor illustrated zn 'Fig. 1;
Fig. 2 is top view of a coil employing plural paral7.el linear conductor segments ox elexaents, wherein all of the currents flow 'in the same, directinr~ through the segments;
. Fi.g. 2a is a 'tvp view of a portion , of a ~ modified version of F.ig. 2; .
Fig. 3 is a top view of a coil including paxallel.
segments having currents flowing through them in the same direction. whereizi the segments are in paths having equa3.
physical and electrical lengths between diagonally opposite first and second terminals cannected~to, be responsive to an r.f. excitation source;
ZO Fig. 4 is a top view of a further coil configuration wherein ail of the currents flow in .para7ae3. branches in the same. direction between first and second adjacent terminals connected to an AC excitation source;
Fig. 5 is a top view of a coil arrangement including multiple paral3e~. coil segments including adjacent..
elements having cnrre~nt flowing through them in opposite _.' directions, wherein the segments are in paths having ~ .
equal physical and electrical lengths between first and second terminals at opposite ends of adjacent lead lines;
3d - Fig. 6 is a top view of a col,l including parallel.
e~.ements arranged in a woven pattern so current flows in opposite directions in adjacent elements; , Fig. 7 is a modification of the woven pattern ' structure illustrated i.n Fig. 5;
fig. 8 is a top view of a coil canfigurativn having WO 9611820$ ' ~GTlLTS95115753 plural ca~.I portigns, each occupying a mutually, eXClusi.ve area on a different individually supported window and ~~
connected in parallel to an excitation source; .
Fig. 9 is a topwiew of a coil including plural parallel linear segments having differing lengths;
F~.g.. 10 is a top view of a coil .iricluding plural linear elements connected in series between external terminals connected to be responsive to an r.f.- source;
Fig. 1i .is a side view. of magnetic flux lines produced as a result of excitation of the coil configurations'of Figs. 2-4 and 9; . . .
Fig.. 12 is a side aectianal view of magnetic flux lines resulting from excitation of the ~coi~3.
configurations of Figs. 5-8 and 10; and . Figs: 13a-13c are top views of alternate W ndovs configurations .
Descrit~tion of the Preferred Embodiments Ref erence is now made to Figs . 1 and 1 ( a ) of the drawing, wherein a woz~kpiece processor is illustrated as including vacuum camber 10, shaped as a right -parallelepiped having electriGa~.ly grounded, sealed . ' exterior surfaces formed by rectangular metal, preferably anodized aluminum, sidevralls 12 and 14 that extend parallel to each -other and at right angles to rectangular metal- sidewalls 13 and. 15. vacuum, chamber ~-~10 also includes rectangular metal, preferably anodized aluminum, bottom end plate I6 and rectangular top end plate structure 1B, including tour individually supported dielectric, rectangular windows 19 having substantially ' the same size. ' Sealing of these exterior surfaces of . ' chamber l0 is -provided by conventional gaskets (not shown).
Windows 19, preferably made, of quartz, are individually supported by one-piece, rigid frame 23, made of a nax~-magnetic .metal, such as anodized aluminum.
wo 9si~szds . pcTius9s~xs7~
to Frame 23 includes p~:xipheral, mutually perpendicular legs 25 and znterior mutually perpendicular rails 21, connected to the centers of the legs.. Rails 21 and legs 25 include notches 27, which individuall~i support each of.
'S windows 19 since the side walls of the windows and~the bottom portions of the windows adjacent the side wails ~it~ in and rest on gaskets (not shown) on the bottoms and side walls of the notches. Legs 25 of frame 21 are bonded to side walls ~12~15 of chamber 10. Because IO windows 19 are individually supported by rails 21 and legs 25,, the thickness of windows .I9 can be less than about 2~.5 cm and W tkistand the pxessure differential between the atmospheric air on the exterior of chamber 1.0 and the vacuum inside the chamber, whzch is typically in.
ZS the 0.~5-5, mil~,iTorz range. If wi.z~dvws 19 were not individually supported and a single wir~dow were emplpyed, . such a singl~ .window would have to have a thic3cness of at least, S cm to be able to withstand the differential pressure. Such a thick window would sigxiificantly reduce 20 the amount of r.f. field energy that could be coupled through the windows and would be very expensive. To one configuration of chamber 10 for processing large workp~.eces, e_g.,television receiver active matrix liquid crystal displays having a planar ~ractangular 25 configuration with sides as large as 75 am x 85 cm, each of windows 19 3~as an area of about 40 cm. x 43 cm.
Sidewall 12 includes port 20, connected to a conduit (oat shown) leading to a vacuum pump (not shown.) wh~.ch maintains the intez~~.or of chamber 10 at a pressure on the . 30 order of 0.5--5 milliToxr: A gas which can be excited to a plasma, of a type well known in the prior art, is intzoduced from' a suitable source toot shown) into chamber 20 via port 22 an sidewall 1~.
Workpiece 2~,., e.g. a: large semiconductor substrate ~35 wafer having a rectangular share as specified supra, is mounted on metah chuck 26 ~in a p7.ane .parallel to the wo asnszo$ ' rcrms~srxs~sa m planes of bottom end plate l6 and windows 19,.and close to plate 16: An electric field, typically having 'a frequency of about 3o MHz, is applied to woricpiece 24 by . r.f, source 28 via impedance matching networ3c 30 and chuck 26. ~ Chuck ~6 is electrically i3nsulated from,the ' retraining metal parts of chamber 10 because it rests on electric insulator pad 29. Dielectric end plate structure 18 carries planar coil 34, connected to,r.f.
excitation device 33 including impedance matching networ7~
l0 36 and r.f. source 38, having a frequency different from r.~_ source 28, and preferably equal to approximately 13.3 MHz. Both~terminals of source 38 can float or one of them.can .be grounded to the metal walls of chamber- 10. .
Matching network 36 includes circuitry tuned, to the f5 frequency of source 38 to form a resonant cr~upling circuit. Coil 34 ~.s positioned and~responds to source 38 to supply r.f. magnetic lines of flux to the gas coupled.
through port 22, to excite the gas to a.plasma state.
The plasma treats workpiece ~4 to etch the substrate or 20 to deposit molecules thereon.
Planarcoil 34 can have many different conf~.gurations, as illustrated, for example,, in Figs. 2-10. Each of these coil configurations includes multiple linear electrically conducting, metal (preferably silver 25 coated copper) stripe elements ox segments for inductively supplying magnetic lines a~ flux to the gas in chamber 10 to sustain and generate a planar plasma that processes workpieces 24 in chamber lo~_ The linear , elements of coil 34 preferably have a rectangular cross 30 section with a braced 'side fixedly positioned ' on die~.ectx~ic end face structure 18,' although the ri,arrow ' sides of the elements could be fixedly mounted on window 1.9. Coil 34 is basically an, r.t. transmission line including distr~.buted series inductances resulting from 35 the self inductance of the metal elements and shunt capaCitances between the metal elements. and the grounded WO 9G/18208 pGTIUS951I5753 chamber exterior walls. To excite and maizitain the plasma for these purposes, source 3o supplies up~to 3A
amperes to coil 34. ' ' _ To confine and concentrate .magnetic field Wines ~ resulting from current flowing through the linear canductors of coil 34,~ magnetic shield _ cover '40, preferably made of aluminum in whzeh x.f. eddy currents are induced by the r.,f. magnetic flux lines, surrounds the sides and top of the coil. Cover 40,has a roof 42 10~ and feur sidewalk 44, that are fixedly attached to vacuum chamber 10.
According to one embodiment, illustrated i,~ci Fig. 2, coil 34, that extends over all four of windows 19, has a..
configuration including eight elongated, straight, liziear, metal conducting elements 5x-58 having apposite ends connected to elongated straight, fetal (preferably .
si7.ver coated copper) leads 59 anal 60 which extend parallel t4 each other and at right angles to elements . S1-58. The bottom faces of elements 51-58 and leads 59,, ' 60 .are bonded to windows 19, except the portions of elements 51-58 which span gaps 31 across rail 21, between, interior edges of the windows, as illustrated in,Fig. la.
Conducting elements SI~58 are, approximately equidistant from each other '(except for the spacir~g between central y elements 54 and 55 which is somewhat different because of center rail 21?. have about the same length and extend parallel to each other. Leads.5s and,6o include centxal v terminals 62 and 64, located midway between central conductors. 54 and S5. Terminals 62 and 64 are 3~ respectively connected to terminal 66 of r.f. source 38 by cable &s and to output terminal 70 of matching network 36 by cable 72.. Matching netwoxk 36 zs connected to output terminal 74 of r.f. source 3B,.
Tn response to the output of r.~. source 38, current flows through each of conducting, elemezits 51-54 generally zn the same direction at any 7.x~,stant to produce w. f .
wo ~sns~os ~ . ~crms~s~zs~s3 magnetic flux lines 124, x.28, 130 and I32, Fig. 1.l.
wBecause the lengths Qf each,of conducting~elemants 51-58 . is a re3.atively small fraction, e..g. about 1/I6th, of a wavelength (a) of 'the frequdncy derived from r_ f _ source 38, the instantaneous. current arid voltage variations across each of the conducting elements is net substantial. Because central conducting elements 54 and .
55 have.the same I~ngth, same cross sectional geometry and are equispaced from terminals 62 and 64, the lengths 14 of the current paths formed by the transmission lines . from tez~minal 62 to terminal 64 through conducting .
elements 54 and 55 axe the same, whereby the t~c~agnetic flux densities resultizig from the substazitially equal. RMS
.amplitude r.f. curre'rlts flowing through conducting, I5. elements 54 and 55 are approximately the same.
Similarly, slightly off -center conducting elements 53 and 56 have equfl hength transmission lines and eurx~ent paths between terminals 62 ' arid 6-4 , so the magnetic flux densities resulting. from' the substantially equal RMS
20 amplitude currents Flowing through them are about equal.
Because the lengths of the transmission lines and current paths through conducting elements 53 and 55 are somewhat greater than those through elements 54 and 55, there is a tendency far. the RMS values of the r,f.
25 currents flowing through elements 53 and. 55. to be somewhat ~.ess than those through elements 54 .and 55, whereby the magnetic flux densities derived from eJ~emer~ts 53 and 56 tend to'be less than those from elements 54 and 55. Hy the same reasoning, magnetic flux densitie s 30 resulting from r:f. excitation of conducting elements 52 and 57 are approximately the same and tend to , be less than those resulting fz-om current flowing through conducti~zg elements S3 and 56; the same is true for conducting elements 51 and 5s.~
3,5 . As a result of the differential lengths of the transmission. lines a.nd the resulting differences 'in .
Wo 9sixs2o8 pcrrusssns~s3 current, path lengths frbm terminals 62 and 64 through different ones of elements 51-S8 there are differences in the excitation and distribution of. the plasma in chamber z0_ this is iikely.to lead to uneven plasma processing of the Large surface area workpiece because there is greater plasma density in,the workpiece central region (beneath elements 54 and 5S) thari the workpiece periphery . (beneath elements 51 and 58).
According to -one, aspect of the invention, the to lengths of the transmission lines iz~cluding elements 51 58 are approximately eleatrieally equalized by proWding the different 'lines with reactances having different values. Since the self inductance of a single electric lixie is inversely proportional ' to the line .doss seGtior~al area and the inductance of a line increases as the ~.ine length inczeases, the lines closest to terminals 5~ and 64 ean~be made electrically longer by decreasing the cross sectional. areas thereof relative to~the cross sectional areas of the lines farther from the terminals.
zt is also desirable to maintain the electrical length of each of elements 51-56 the same so the RMS voltage and current variations across them are equalized to provide the same plasma .distribution below these elements. .
To these ends, the cross seCtior~a~. areas of leads S'9 and 50 progressively increase between adjacent pairs of ' segments 55-58 and 51.54 while~the crass sectional areas of segments S1-58 are the 'same. Hence, 7.eads 59 and 60 have re~.atively small cross sectional areas between 'segments 55 and 56 as well as between segments 53 and 54 3o and relatively large. cross sectional areas between segmez~ts 57 and 58 as well as between segments 5I and 52.
Alternatively, capacitors 81-88 are connected in series with elements 57.-58 to equalize tl~e lengths of the ltransrnissic~n lines. As illustrated in fig. 2a, capacitors 8~.-88 are connected in series with elements 51-58 arid lead 59, at the end of each, element adjacent WO 96118108 ~ ~ PGT/US95115753 the lead. These locations for capacitors 81-88 do not affect the effecti~re physical lengths of elements 51-58 because of the relatively small physical size Qf the capacitors.
5 To enable the phase. of the currents in each of elements 51-58 to be generally the same (either leading or lagging the voltage across the element? the geometry of elements 51-58 and.the values of capacitors 41-88 are y selected so the net impedance at the frequency of source 10 . 3B of each of the -branches ~.ncluding e3~ements 51-5B is of the same reactar~ce type , i . a ., either - inductive or capacztive. If the inductive impedance of elements 51-58 . ~is dominant, each of series capacitors 81-88 has a .
relatively large value, to provide a relatively small, 15 capacitive impedance in series with each element_ Hence, capaaitars 84 and 85 in series with elements' S4 and 55 have smaller values than capacitors 83 and 86 in series with elements 53 and 56, capacitors 83 and 8~ in series with elements 53 . and 56 have smaller values than 28 Capacitors B2 and 87 in series with elements~52 and 57, etc.. so that capacitors 81 and 88 in sex~.es. with elements .51 and 58 have the largest val-ues or may be eliminated.
.It, however, the dominant impedance in the branches ' including elemezzts.51-58 is capacitive, the values of , capacitors 81-68 are. relatively small to provide high capacitive impedances; the values of pairs of capacitors 84, 85, 83,_86, 82, 87, 81, 88 progressively decrease in the order.named.
Reference is now made to fig. 3 of the drawing, wherein coil 34 is illustrated -as including. linear conducting elements 51-5B, arranged and.constructed the ' same as conducting elements 51-S8 ref Fig. 2. Tn Fig. 3 conducti2~g elements 51-58 have opposite ends. connected td straight elongated metal leads 9o az~,d, 92 that extend paraJ.lel to each other and at right angles to conducting elements 51-5B. Leads 90 and ~~ have large cxoss WU 96!18208 . PGTI(JS95115153 sectional areas resulting in small inductarxces that do not introduce,appreciable transmission line lengths ox phase shifts ~.n the. paths leading to and from elements 51-5B_ Lead 9D includes a portion which ends at terminal 94 and extends slightly beyond caaductor 51; similarly, lead 92 includes a portion which ends at terminal 95 and extends slightly beyond lead 50 . Terminals 94 and 96 axe connected to the same leads and circuitry as terminals 62 .
and 64. respectively. ~ w 1o An advantage of the structure illustrated in fig. 3 _ is that the current path through each of conducting elements 5~.-58 between terminals 94 and 95 has the same physical and electr~.cal length. , xhereby, the, RMS
amplitude of the AC current flowing in each of cor~.r3.uct~.ng ~.5~ elemexxts 51-58 isvirtually the same. Because the RM5 amplitude of the AC current ~~~.owing in each of conducting elements 51-58 is about the same, the magnetic f~.ux .
densities resulting from excitation of these conduct~.ng elements by the r . f . source 3 8 i, s about the same 20 ~ .The magnetic ~lux lines resulting from x.f.
excitation of conducting elements 57.-58 produce r.f.
. ,'. magnetic flux lines 124, 1.28, 130 and 132 (k'ig.' 13? in the gas introduced into chamber la, to excite the gas to a plasma having equal numbers of positive and negative 25 charged tarriers_ Because, of the resulting molecular flux in the plasma, the plasma functions as a single turn secondary winding ~of a trans~ormex including, as its . primary windings, conducting elements 51-58. The . .
conducting properties of the plasma cause r.f. magnetic 3a flux lines 1.24, 128, ~3o and 132 to .lie asymmetrical, i.e., the magnetic flux l~.nes extend above windows I9 into the atmosphere to a considerably greater extent than blow- the windows ' into vacuum chamber to . The charged .
carriers disperse through the,gas to cause the volume of 35 gas to 7oe a pzasma for treating substrate or workpiece 24.
'W096I1820S . PGT/DS95/IS7~3 Reference is now made to Fig_ 4 of the drawing,~a further configuzation of coil 34, including elongated straight leads 134 az~d 135, that extend parallel to each other and include end terminals 138 and 14 D , respectivexy cdnnected~to r.f. exciting device 33 via cables 72 and 68. Extending ~ betv~reen leads . 134 and 136 .are linear, paraJ.lel elongated conducting elements 51-&e ~ which are identical tb the corresponding elements of Figs. 2 and 3.
Elements 51-58 are driven by r.f. exciting device 33 so that at any instant of time, r:f. parallel currents generally flow through them in the'same direction. Leads 134 and 136'and elements 51-58 of Fig. 4 are arranged so end terminals 138 and 140 are at the same ends of the leads relative to the conducting elements and the 15, terminals are spaced from each other by the lengths of the conducting elements. To enable the coil configuration of fig. 4 to include equal electrical length transmzss~.on lines 'through elements 51-58 from tez~ninals 138 and 140 via leads 134 and 236, the cross section geometry of different parts of the leads can d~ffex, as discussed in connection with Fig. 2, and/or -capacitors can be connected in series with elements 51-58 as discussed in connection with Fig. 2a.
a result. of the currents flowing in like direetioz~s through conducting elements 51!59 in each of Figs. 2-4, there is at least one,magnetic~flux line 124 (Fig_ 11) surrounding each of the conducting elements and thexe is a cumulative effect caused by the interact~.on of magnetid fluxes resulting from.the currents flowing in elements 51-58. Thereby,' a highly concentrated, evenly distributed, magneta.c ~.geld is provuded in the plasma beneath windows 1~. Fox example, the like directed currents flowing through conducting elements 52 and 53 or thxough elements 56 and 57 cause these two pairs of.
conducting elements to be surrounded by magnetic flux lines 128 and X29, respectively. The interaetior~ between we 961i$xoa fCTICtS951I5753 the magnetic fluxes resulting from currents fla~aing in a lake direction in conducting eZemezits 5S-58 causes these conducting elements to be surrounded by magnetic flux lines 130. ~An interaction between the magnetic fluxes resulting from currents flo~saing in a like direction , ' through all of conducting elements 51-5~9 causes elements 5Z-58 to be surrounded by magnetic flux lines 132. The - concentrated magnetic flux lines resulting from the excitation patterns of conducting elements 51-58 provide 1~ a relatively uniform distributvon of. plasma in chamber ZO . -beneath top end plate structure l8 so there is an even distribution of~ etchant or deposited molecules on workpiece 24.
According to further embodiments of the invention, 15, illustrated iii figs . 5--7, the' conducting elements of tail 34 are arra~ngeci so current . generally f lows in adj scent .
linear conducting elements of the co~.l in spatially opposite directions at any instant of time. The structure - of Fig . 5 has the advantage of providing 20 current paths with equal physical,azid electrical lengths through each of the~condnctors between opposite terminals of r.f. excitatzon device 33. While the magnetic fluxes coupled to the plasma lay the structures of. Figs. 5-7 have.
lower density than those of Figs. 2-4,- in some instances 25 xt may be.desirable to tailor the flux density to certa~,n regions of the plasma as can- be more easily provided with the structures of Figs. 5-~7 thar~ those of Figs . ~ 2,~
'fhe stru~t~,re of fig. ~5 includes spatially adjacent and parallel, elongated stxaight~ leads lOD and 102, 30 respectively having. terminals lD4 and X06 at spatially oppasit_e ends thereof, connected to opposite terminals 56 and 72 of r.f. excitation device 33.~ Coil 34 of Fig. 5 includes four segments n13., 112., 113 and 214, each including a pair~of elongated; linear straight parallel .
35 conducting elements, having opposite end terminals respectively connected to leads 10p~ and 1D2. heads 10p WO 961I8~08 ~CT/US95115753 and 102 are generally positioned to one side of segments ~.1~.-114 so the conducting elements extend in the same direction to the side of interior lead 102. The coil segments arid conducting elements are arranged so coil segment 111 includes conducting elements 115 and 117, coil segment W2 includes conducting elements 118 and 119, cflil segment 213 includes conducting elements 12.0 and 121 and coil segment 11~ .includes conducting elements 122 anrl 123. The,parallel conducting elements of coil segments 111-114 are connected. to each other by conducting elements 125 that extend parallel to leads 'loo and 102. Conducting, elements 11G-123. are generally equispaced from each other so that, for example, conducting element 117 of coil segment 111 is spaced the same distance from conducting element 118 of coil segment 11.2 as it is spaced from conducting element 116 of coil , segment .111. Each of the transmission lines including coil segments 111-114 has the same physical and electrical length between apposite terminals ~.0~ and 106 because (1) of the geometry of the layout of coil segments 117.-ll~~ and leads 100 and. 102, (2) each of . .
segments 111-11~ has the same cross sectional and longitudinal geometry and (3) leads 100 and 102 have the same cross sectional and vlongitud~.nal geometries.
A further configuration for providing spatially parallel conducting elemer~ts that are electrically cdnnected 'in parallel and have adjacent conducting elements. with currents flowing generally in. apposite.
directions is illustrated in Fig. 6 as a woven pattern 3D including straight elongated linear leads 150, 151, 15~..
and 1,53, in combination with straight elongated linear canducting~ elements 151-158. .Leads 15n-1$3 extend spatially paralldl to each other, and at right angles to conducting elements 161-168 that are gez~erally equisnaced from each other and spatially extend parallel to each other. L~eacis 15b, 151 are on one side of elements 7.61-W'O 961182p8 . ~ - ~~ T1U595115753 z68 while leads 152 and 153 are nn the other side of these elements. . Leads 151 and 153 aze respectively connected by cables 154 and 1S5 tt~ a first terminal 156 of r.f. excitation device ~33 while leads l5fl and 152 are 5 respectively connected by cables 1S7 azid 158 to a second, opposite t$rmina1~159 of the device 33. Alternate equal.
length conducting elements 161, 163, 165 and 157 are electrically connected between leads 150 and 153, whi~Ie the remaining, equal length conductixzg elements x.62, 3.6~,.
~,D ~66~ and 1Ge are electrically connected iii parallel between leads 15l and 152._ $ecause elements 161, z63, 16S and 167 are connected to.exterior leads 1S0 and 153 and .elements 162, 164, 166 and 168 are connected. to interior leads 151 and zS2, the former elements are 15 _ longer than the latter_ Thereby, at any instant of time, currents~generally flow in the same direction through conducting elements 161, 153, I56 and 167, which ~.s opposite from the i3irection cuxrents general~,y flow through, conducting ~.lements 162, 164, 166 and 168.
20 Magnetic flux paths similar to those provided ~by the structure illustrated in Fig. 5 are thus established by the~coil arrangement of Fig. 6. Because the physical distance between terminals 156 and 159 via the transmission lines snc7.uding e3.ements 161-158 differ, it ' is praferable.to change the crass sectional geometry of Zeads~150-153 in a manner sirttilar t4 that described for Fig, 2 or to connect capacitors in series with elements 161-169 as described for Fig. 2a.
The woven coil arrangement of Fig. 6 can be - modified, , as illustrated in F~.g. 7, so .each of~ the conducting elements ha~.the same Length. To these ends, the woven coil structure of. Fig. 7 .includes elongated, parallel straight leads 170, 171, 172 and 173, in ' combination with elongated, parallel straight conducting elements x.81-188. Leads 170-173 extend at right angles to equispaced conducting elements 18z-n88_ Exterior WO 9411$Z08 _ P~YU59S/I5753 leads 170 and 173 are connected to terminal 190 of r.f..
.excitation device 33 by cables 19~ and 192, respectively_ anterior leads 171 and 172 are cQrnn,ected to terminal 193 of r.f_ excitation device 33 by cables 194 and '195, respectively.~.Conductir~g elements 181, 183, 185 and 1s7 ' , are electrically connected in parallel across leads~l7p and 192; while conducting~elements 182, 184, 18G and 18s are electrically connected in parallel across leads 17p and 172. Thereby, generally oppositely directed currents 0 flow through adjacent.pairs of leads' 181-188 so that, for example,. when current is f3.owing through conducting eleutent 182 from lead 170. to lead 172, current is flowing through conduct~.z~g elements 7.81 and 3.83 from lead 173 to lead 1'71. Hence, current f~,ows in apposite directions in ~~ adjacent cc~nduct~ing elements in a similar.manner in the embodiments of Figs. 6 and 7. , ..
In response to.excitation o~ the coils illustrated in Figs. 5-7 by r. f _ excitation device 33, magnetic lines of flux, as illustrated in Fig_ IZ are produced. In Fig_ 12; magnetic flux, ~ lines 38'1=388 are respectively associated with the equal ~.ength conducting elements 3.81-188 of Fig. 7;'3t is to be understood that~s,imilax flux line patterns are obtained for conducting elemerats 1Z6-123 of Fig. 5 and conducting_elements 16z-168. ~ecaus.e current floras in opposite directions in adjacent ones of ~e~.ements .181-188, the magnetic flux lines resulting from these.currents buck each oth~x~ so there is no interaction of flux patterns 381-388 and there is flux null between adjacent. conducting elements. - Since there is no 3D conducting element or magnetic member on the. exterior sides of conducting elements x.87. and 188, magnetic flux lines 381 and 388 bu~.ge away from the center 'of coil 34.
Hecause conducting elements. 18~ and 185 are spaced farther apart than other pairs of the conducting elements 35~- (due to rail 21), magnetic flux lines 384 and 3s5 bulge i toward center dielectric rail 21. The interior WO 96/I8208 ~CTIt159a/15753 22 .
equispaced positions of cbnducting elements x.82, 183, 186. .
ahd 18~ cause ~lux lines 382, 383, 386 and 387 to have ' about the same density and ~spatzai configurat~.on.
The coil structures illustrated in figs. 2-7 are , designed to extend over all four windows 19 of top_end plate structure 18: In certain instances,, howe_ ver, it is desirable to provide individual coils on eaeh.of windows ~.9. To this erid, any of the coil structures described in connection with Figs. 2-7 can be ,connected in parallel and separately overlay each of~windows 19, as illustrated in Fig. 8. In the particular embodiment of Fig. 8, each of windows 19 is overlaid by separate.coil segments 2~1, ~D2, 203 and 204, each constructed generally in the .
manner described irx connection with Fig. 4. Adjacent ' int~rzor leads 205 and 206 of coil segments 201 and 202 are connected tQ terminal 20'7, connected by cable 208 to termiizal ~p9 of r.t.~ excitation device 33. .Terminal 209 is also connected by cable 211 to terminal 212,Iinrturri connected tQ.interior adjacent leads 213 and 214 of coil segments 203 and 204. Exterior leads 21,5 and 215 at coil segments 201.and 202 are connected by cable.217 to the ' other terminal 218 of r.f. excitation device 33.
Terminal 218 is also connected by cable 219 to eXterior leads 220 and 221 of coil segments 203 axi~d 204. Thereby,, segments 20I-204 of coil 34, as illustrated in ~'ig. 8,.
are driven in parallel by device 33.~ Each o~ the ccih segments~has electrically parallel conducting elements with relatively short lengths (rzo more than 1/~.6th of a wavelength of the wave derived by device 33) to minimize ' the like3.ihood of voltage~and/or current nulls therein.
Eecause the four coil segments 201-204 are relatively short transmission lines it may not be necessary in certain ~.nstaz~ces for all of the indivzc~ual transmission lines on the individual windows ~Z9 to have the same length.
WO 961XSx08 PCTl0595I15T53 In each Qf tk~e embodiments of Figs. 2--s, the conducting elements of the various planar coils have equal physical lengths. It is not necessary, however, for the condz~cting elements to have equal physical lengths, and in some instances it may be desirable fdr the physical lengths ~ thereof to differ. ' In the embodiment Qf Fig. 9, the structure of k'ig_ 2 i.s modified to include arcuate leads 226 and 229 between which extend spatially parallel elongated straight cpzzdueting elements 231-23B having differing physical lengths. Midpoints of arcuate leads 226 and 228 include terminals 240 and 241, respectively connected to opposite polarity terminals of r.f. excitation device 33. Currents flow in parallel in generally the same direction through conducting elements 35 231-238. The structure of Fig. 9 is employed to.enable the- plasma in chamber 1o to have certain special spatial canfigurations~for treating substrates having appropriate surfaces_ While it is desirable to pro~ride elements 231-238 with different physical lengths, the electx~.cal lengths of the, transmission lines including these elements are preferably the same, a result which can, be achieved by use of the structures described in connection with Fig.
2 or 2a. Even though elements 23Z-238 are illustrated as being approximately equispaced'from each other, this. is not necessarily the case- for the configux~a~tions of any of Figs. 2=9.
A magnetic flux pattern similar fo that of Fig. 12 can be pxovided by forming coil: 34 as plural series , conduct~.ng elements, as illustrated in Fig. 10. The coil of Fig. 10 includes conducting elements 241-248 that extend spatially in parallel to ,eack~ other, have approximately equal lez~gtk~s and have adj acent ends connected together by conducting elements 249 and 250.
' Conducting elemerits ~2d1 and 248 are connected to end terminals 252 and 254, in. turn connected by appropriate WQ 96!18208 ' PG~Y(J595I15753 cables to opposite end termiz~als of r,f_ excitation w device 33. Current thus flows generally iri opposite directions in~ad~acent conducting elements 241-248, as ~ , result of the sinuous or serpentine relationship of these conducting elements.. The structure of Fig. .10 has a substantial disadvantage relative to the' structures o~
Figs. 2-~ because of its long physical and electrical length, whereby there is a tendencyWar voltage and current nuJ,ls along the length of the coil formed by elements 241-248.' These nulls cause uneven distribution v of magnetic f~.ux acting on the gas ire chamber 10. This , problem is obviated by the parallel structures of Figs.
' Z-9,-all of which have conducting elements in parallel , with each other across the terminals Qf r.f. excitation device 33 and lengths that are about 1/l6th wavelength of the wave derived by device 33. The structures of~all of Figs . 2-ld have the advantage of being. planar coi,l.s having exterior terminals, outside of the conducting elements for ease of.cor~nection so problems. associated with.spiral planar coils having oz~e interior texzninal are avoided. All of'these planar coils, as well as spiral planar coils, can be used as four individual coils, connected in parallel, on the four wzndows~ 19 of end ' plate structure 28, as described in connection with Fig.
8. .
While ez~d plate structure .18 preferably includes four rectangular dielectric~wzndows having the same size and positioned in the guadrants~of a rectangular frame, other individually supported dielectric window ~ Configurations, e.g.. as schematically illustrated ire ~ .
Figs. 13 (a) , Z3 (b) and L3 (c) , can be ect~ployed.
Individually supported dielectric windows 302-310, fig.
13 (a) , in frame. 31.7, have different sizes and shapes such that, rectangular per~.pheral ~wzndows 302-308 have different lengths, extend. at mutually right angles and surround .interior .square window 3~,0. In Fig. 13(b) wo 9snszos ~crmsssms»s is diamond shaped, centrally located dielectric window 312 and triangle shaped.exterinr dielectric c~indows 314 are individually supported in frame 315 , frame, 318 , P'ig .
13(c), individually supports three rectangular windows 320, each.having the same size and parallel Zong sides-.
Planar coils, as illustrated in Figs. 2-10, axe laid an the windows of Figs. 13(a), 13(b) and 23(c). .
While there have been described and illustrated specific embodiments of the invention, it will be clear that variations in the details of the embodimez~ts specifically illustxated and described may be made . without departing from the true spirit and scope of the invention as defined i,n the appended claims. ,
z PhASMA PROC SSOR FOR L G~ WORKPIECES
Field of Invention The present invention .relates generally ,to processors for treating workpieces in a vacuum chamber with'a plasma and more particularly tn~such a proGessQr.
S having plural individually supported dielectric windows . for.eaupliag an r.f: field originating outside of the chamber into the chamber to excite the plasma, and/or a coil for inductively d~riviag the field, wherein the coil has plural segments . with the same electrical. ' length, each 1D ~includizlg an element connected in parallel with an element of another segment.
Ha kid Art Various structures have been daveloped~to supply r.f. ~.ields from devices outside of a vacuum chataber to.
15 excite a gas in the chamber to a plasma state. The r.f_ fields have been derived from electric field sources including capacitive electrodes, electromagnetic field sources including electron ~cyclotran resonators and induction.,.i_e. maguetic,;field sources including coils.
20 The excited plasma interacts with the workpiece to etch the workpiece or deposit materials on it. Typically, the workpiece is. a semiconductor wafer having a , ~larlar circular surface.
A processor for treating workpieces with an 25 inductively coupled planar plasma (ICP)~is disclosed, inter a.Iia, by O~x~.e, U.S. Patent x,948,458, commonly assigned with the present invent3on_ The magnetic field - WO 961,820$. . PGT/US951J.5753 is derived from a plazxar coil positioned ,on or adjacent 1a single planar dielectric window that extends in 'a direction 'generally parallel to the workpiece planar ,surface. Tn commercial devices the window is' usually - , ' S quartz because this material has low impurity content and provides optimum results for r.f, field coupling. The coil is connected to be responsive to an r.f_ source having a ' frequency in the x~aage of 1 to 100 MHz and Coupled to the coil by an impedance matching network including a circuit resonant to the frequency of the . source. The coil. is disclosed as a planar spiral. having.
external - and internal' terminals connected to be responsive to the r.f. source. The circular spiral coil disclosed by Ogle has been modified to include linear, I5 , elongated elements generally in a spiral configuration, to process woxl~pieces having square and rectangwlar shapes.. Caultas et al., U.s. Patent 5,304,279 discloses a similar device employing permanent magnets in combination with the planar spiral coil.
Cuomo et al.,' V:S. Patent 5,280,154 and Ogle, U.S.
Patent 5,77,751 disclose a variation. of the aforementioned processor wherein the lihear spiral coil is replaced by a solenoidal coil. The solenoidal coil is wound on a dielectric mandrel or the like and includes plural helical-like turris, a portion of which extend along the dielectric w~.nr~ow surface. The remainder of tire coil extends above the dielectric window, Opposite .
ends of the solenoidal coil are. connected to an r.f. .
eXClt~tiOn sQCIX'Ce.
None of the prior art plasma processing with whzch we are familiar is well adapted to excite plasmas far processing very Large substxat~s,.for example, substrates used in forming rectangular fJ.at pane. displays having sides in the range of 30,100 cm. Excitation of plasmas ~5 for treating, i.e.y processing, such large substrates requires coils ,having correspondingly large surface areas in contact with or adjacent a dielectric window structure having a large surface area, c4mmensurate with the areas of the workpieces to he treated. It these prior art structures are used for exciting plasmas for treating .
~5 Large workplaces, numerous problems which apparently have not been pxevious,iy considered or resolved axisc.
A problem common to all of the prior art processor designs is that xhe windows must lie increased to a substantial. thickness as . the area thereof irxareases .
Otherwise, the windows would not withstand the differential .pressure between the atmospheric pressure ~~
outside of the chamber and the vacuum in the chamber; .
e.g. to prdtess v;rorkpieces having rectangular treatmexit surfaces of about 75 cm x 80 cm, a single quartz window 1.5 having a surface df approximately 80 cm x 65 cm must have a thickness in excess of 5 cm_ Quartz windows~of the stated area and thickness are also very expensive and fragile so use thereof considerably increases the cast of the processor. In addition, we have found that .the r.f. .
2o . . fields -derived from excitation so~xrces using prier art processor designs are not usually capable of effecti~rely exciting the, plasma in a vacuum chamber with a large area, thick window. This is because the r.f. fields do .
nod have sufficient flux density. after penetrating the 25 thick window, to provide the required excitation. For' . example, the magnetic flux density penetrating a 5 ~ crri 'thick dielectric window from a coil has a much smaller number of effective' magnetic Lanes of. flux than the magnetzc field penetrating a 2.5 cm thick window of a 3D prior art device for treating circular wafers having a 2D
Gm diameter. It is not feasible to simply increase magnetic fiJ.ux density by increasing current from an r. f .
svu.rce .driving the coil because the increased current can cause ea~cessive . heat~.ng of the coil as well as other 35 compozxents and because of the difficulty in obtaining . suitable high power r.f. sources.
wo ~s~zszos pcr~nsgsns~ss A problem peculiar to the use of prior art induction coils for exciting a plasma having a large surface area is non-uniform excitation of the plasma, resulting in non-uniform plasma density and uneven workpiece processing. ' We . have. realized this non-uniform distribution occurs in part because the prior. art coils function as transmission lines likely to (nave lengths, when laid over a 3.arge surface window, approaching or exceeding one-eighth wavelength of the r_f. driving.
~D sources. Because of the coil. length thexe are significant voltage and current variations along the coil, resulting in appreciable magnetic flux density variations in tkze plasma. If the coil has' a length in excess of one-eighth raavelength of the r_~, source there is an RMS voltage null in a coil driven by a current having an RMS peak value because of the substantial mismatch between the source and,the load driven thereby.
The mismatch causes the,coil voltage~and current to be .
phase. displaced by close to 90 ° , resulting in the voltage.
nuJ.l. 'these magnetic flux density variations cause the non-uniform gas excitation and uneven ~workpiece .
proees8zzlg. .
We have realized that the length of the coil between ' terminals thereof connected to the r. f . source must be considerably less than one-ezghth~of a.wavelength of the r . f . source output and that such a result can ha achieved by providing a coil with plural parallel branch elements or segments. While .Hamamoto et al., iT_S. Patent 5,262,962 discloses a planar plasma excitation coil having plural parallel branch segments connected zn a ladder canfiguratian.to a pair of physically opposed terminals connected to the same ends of leads connected to the branch segments,.the structure in Hamamoto et,al:
i.s not suitab7.e for use over a large surface area window.
~If I3amamoto et al. were used on large area windows there would be a tendency fox uneven flux distributa.on and non l 'NO 96118208 FGTIU893115753 uniform plasma density because the different branches are included ~ in r. f . transmission lixies with different lengths across the opposed terminals.. Hence, the branch segment physically closest to the terminals is in the 5 shortest ~.engt~z line, while the branch segment physically farthest from the, terminals is in the longest length l~.ne. The different length lines draw vdifferent currents fram the source so the portion of the plasma adj acent 'the Shortest length line is excited tc~ a considerably greater degree than the plasma portion adjacent the longest length line. This causes non-uniform plasma excitation in processors for treating large surface area~workpieees.
It is, accordingly, an object of the present invention tv , provide a new and iiitproved r, f . field excited plasma processor particularly adapted for ' treating 'large workpieees .. ~ .
~. A further, obj ect of the invention is to provide a 'new and improved r.f_ field excited plasma processor for large workpiec~s wherein the plasma is uniformly distributed over the v~iorkpiece.
Another object of the invention is tw provide a new and improved r.f. field excited. plasma processor vacuum chamber arrangement particularly adapted for relatively.
large workpieces wherein dielectric coupling windows are arranged to taithstand the differential pressure between the chamber interior and exterior while being thin. enough to couple r.f. fields with sufficient density to effectively excite the plasma.
Ann additional object ref the inventyon is to provide a new and improved r.f_ .field excited plasma wori~piece processor wherein a plasma is inductively excited in an efficient manner to provide relativeJ.y uniform plasma distribution for large workpieces.
An added object is to provide a new and improved r. f _ field e~ccited plasma processor ~ having plural VVO 96118208 PC~yI7&95115?'S3 electricalJ.y paral.le~ coil segment bxanches arranged to supply about the same excitation flux to the plasma.
Yet a fuxther object is to provide a new and, improved r.f. field excited plasma processor having plural electrically parallel coil segment branches having about the same electrical and physical lengths. to provide unifox~n flux distribution to the plasma and simplify design, of the coil.
The Invent~.on Inaccordance with one aspect of the present invention, some of the foregoing abjects_are attairxed by providing a pz~oeessor for treating a large workpiece with .
a plasma comprising a vacuum chamber in which the workpiece is adapted to be mounted. A gas which carp be converted into the plasma far treating the workpzece is supplied to the chamber. The,gas is excited into the plasma state _ by an r. f , e~.ectric source outside of the vacuum. The r._ source derives a field~that is coupled to .the p3.asma via plural individually, supported.
dielectric windows on a wall. of the .chamber. ~eca.use there are Plural individually supported windows, rather than a single J.arge window, each window caz}. be thin enough, e.g. 2.5 cm, to provide effective aaupling of the r.f. field to the plasma.
~5 In accordance with another aspect of .the inyrention, other objects of the invention axe attained by providing a processor fox treating a woxkpiece with a plasma comprising a vacuum chamber in which the workpiece is adapted to be mounted,. fhe chamber has introduced into it a gas which can,be converted ~.nto the plasma or treating the workpzece_ A means for converting the gas .. into the plasma includes a coil positioned to couple an r.f. magnetic field to the gas via a dielectric window structure on a wall of the chamber to excite the gas to produce and maintain the plasma. The coil includes first.
WO 96!18208 PL'flilS95i15753 snd second terminals adapted to be connected to an r.f_ source that causes t~ze r. f . magnetic field to be derived, .
as weal as plural wxx~ding segments electrically connected between the first and second terminals so they have about.
the same electric length. Each'segment includes an element that is electrically in parallel with elements of the other segments . Thereby, the R1MS amplitude of tha AC
current flowing in the different coil. elements is about the same to'provide a relatively uniform magnetic flux .
i0 distribution in the plasma. .
In certain preferred embodiments,, first and second tern~inals. of the coil and the co'~.l segments, are .positioned and arranged so the electrical and phys~.cal.
lengths of GUrrent paths are approximately the sane ~ between the first and second ~ ter~oni.nals via at least two, and in same embodiments all , ' of the coil segments . A
particularly advantageous arrangement including this feature comprises plural physically and electrically parallel branch ~cdnduetor elements connected to leads 20~ extending at right angles to the elements, wherein the first ,and second terminals are at diagonally opposite.
ends ~ of the leads . The like electric length lines can also be attained by. proper design of the cross sect.iQn geQmetzy of conductors in the lines to provide lines with Z5 different inductive values and/or by inserting capacitors .
having appropziate values in series with. the~para11e1 .
coil elements. ~. ' The above and still further objects, features and advantages of the present invention will become apparent 30 upozi consideration of the following detailed descriptions pf specific embodiments thereof, especially wrhen taken in conjuncti4n with the accompanying drawings.
WO 9G/18208 PG~YIr59S/I5753 Hrief Descrint~n__of the Drawing ' Fiq. 1 is a~ side seetionaJ, view of a plasma processor in accordance with one embodiment of the present invention; . ' .
,~ Fig. la is a side sectional view, at right anqles to-the view of Fig. 1 of a portion of the pl~.sma processor illustrated zn 'Fig. 1;
Fig. 2 is top view of a coil employing plural paral7.el linear conductor segments ox elexaents, wherein all of the currents flow 'in the same, directinr~ through the segments;
. Fi.g. 2a is a 'tvp view of a portion , of a ~ modified version of F.ig. 2; .
Fig. 3 is a top view of a coil including paxallel.
segments having currents flowing through them in the same direction. whereizi the segments are in paths having equa3.
physical and electrical lengths between diagonally opposite first and second terminals cannected~to, be responsive to an r.f. excitation source;
ZO Fig. 4 is a top view of a further coil configuration wherein ail of the currents flow in .para7ae3. branches in the same. direction between first and second adjacent terminals connected to an AC excitation source;
Fig. 5 is a top view of a coil arrangement including multiple paral3e~. coil segments including adjacent..
elements having cnrre~nt flowing through them in opposite _.' directions, wherein the segments are in paths having ~ .
equal physical and electrical lengths between first and second terminals at opposite ends of adjacent lead lines;
3d - Fig. 6 is a top view of a col,l including parallel.
e~.ements arranged in a woven pattern so current flows in opposite directions in adjacent elements; , Fig. 7 is a modification of the woven pattern ' structure illustrated i.n Fig. 5;
fig. 8 is a top view of a coil canfigurativn having WO 9611820$ ' ~GTlLTS95115753 plural ca~.I portigns, each occupying a mutually, eXClusi.ve area on a different individually supported window and ~~
connected in parallel to an excitation source; .
Fig. 9 is a topwiew of a coil including plural parallel linear segments having differing lengths;
F~.g.. 10 is a top view of a coil .iricluding plural linear elements connected in series between external terminals connected to be responsive to an r.f.- source;
Fig. 1i .is a side view. of magnetic flux lines produced as a result of excitation of the coil configurations'of Figs. 2-4 and 9; . . .
Fig.. 12 is a side aectianal view of magnetic flux lines resulting from excitation of the ~coi~3.
configurations of Figs. 5-8 and 10; and . Figs: 13a-13c are top views of alternate W ndovs configurations .
Descrit~tion of the Preferred Embodiments Ref erence is now made to Figs . 1 and 1 ( a ) of the drawing, wherein a woz~kpiece processor is illustrated as including vacuum camber 10, shaped as a right -parallelepiped having electriGa~.ly grounded, sealed . ' exterior surfaces formed by rectangular metal, preferably anodized aluminum, sidevralls 12 and 14 that extend parallel to each -other and at right angles to rectangular metal- sidewalls 13 and. 15. vacuum, chamber ~-~10 also includes rectangular metal, preferably anodized aluminum, bottom end plate I6 and rectangular top end plate structure 1B, including tour individually supported dielectric, rectangular windows 19 having substantially ' the same size. ' Sealing of these exterior surfaces of . ' chamber l0 is -provided by conventional gaskets (not shown).
Windows 19, preferably made, of quartz, are individually supported by one-piece, rigid frame 23, made of a nax~-magnetic .metal, such as anodized aluminum.
wo 9si~szds . pcTius9s~xs7~
to Frame 23 includes p~:xipheral, mutually perpendicular legs 25 and znterior mutually perpendicular rails 21, connected to the centers of the legs.. Rails 21 and legs 25 include notches 27, which individuall~i support each of.
'S windows 19 since the side walls of the windows and~the bottom portions of the windows adjacent the side wails ~it~ in and rest on gaskets (not shown) on the bottoms and side walls of the notches. Legs 25 of frame 21 are bonded to side walls ~12~15 of chamber 10. Because IO windows 19 are individually supported by rails 21 and legs 25,, the thickness of windows .I9 can be less than about 2~.5 cm and W tkistand the pxessure differential between the atmospheric air on the exterior of chamber 1.0 and the vacuum inside the chamber, whzch is typically in.
ZS the 0.~5-5, mil~,iTorz range. If wi.z~dvws 19 were not individually supported and a single wir~dow were emplpyed, . such a singl~ .window would have to have a thic3cness of at least, S cm to be able to withstand the differential pressure. Such a thick window would sigxiificantly reduce 20 the amount of r.f. field energy that could be coupled through the windows and would be very expensive. To one configuration of chamber 10 for processing large workp~.eces, e_g.,television receiver active matrix liquid crystal displays having a planar ~ractangular 25 configuration with sides as large as 75 am x 85 cm, each of windows 19 3~as an area of about 40 cm. x 43 cm.
Sidewall 12 includes port 20, connected to a conduit (oat shown) leading to a vacuum pump (not shown.) wh~.ch maintains the intez~~.or of chamber 10 at a pressure on the . 30 order of 0.5--5 milliToxr: A gas which can be excited to a plasma, of a type well known in the prior art, is intzoduced from' a suitable source toot shown) into chamber 20 via port 22 an sidewall 1~.
Workpiece 2~,., e.g. a: large semiconductor substrate ~35 wafer having a rectangular share as specified supra, is mounted on metah chuck 26 ~in a p7.ane .parallel to the wo asnszo$ ' rcrms~srxs~sa m planes of bottom end plate l6 and windows 19,.and close to plate 16: An electric field, typically having 'a frequency of about 3o MHz, is applied to woricpiece 24 by . r.f, source 28 via impedance matching networ3c 30 and chuck 26. ~ Chuck ~6 is electrically i3nsulated from,the ' retraining metal parts of chamber 10 because it rests on electric insulator pad 29. Dielectric end plate structure 18 carries planar coil 34, connected to,r.f.
excitation device 33 including impedance matching networ7~
l0 36 and r.f. source 38, having a frequency different from r.~_ source 28, and preferably equal to approximately 13.3 MHz. Both~terminals of source 38 can float or one of them.can .be grounded to the metal walls of chamber- 10. .
Matching network 36 includes circuitry tuned, to the f5 frequency of source 38 to form a resonant cr~upling circuit. Coil 34 ~.s positioned and~responds to source 38 to supply r.f. magnetic lines of flux to the gas coupled.
through port 22, to excite the gas to a.plasma state.
The plasma treats workpiece ~4 to etch the substrate or 20 to deposit molecules thereon.
Planarcoil 34 can have many different conf~.gurations, as illustrated, for example,, in Figs. 2-10. Each of these coil configurations includes multiple linear electrically conducting, metal (preferably silver 25 coated copper) stripe elements ox segments for inductively supplying magnetic lines a~ flux to the gas in chamber 10 to sustain and generate a planar plasma that processes workpieces 24 in chamber lo~_ The linear , elements of coil 34 preferably have a rectangular cross 30 section with a braced 'side fixedly positioned ' on die~.ectx~ic end face structure 18,' although the ri,arrow ' sides of the elements could be fixedly mounted on window 1.9. Coil 34 is basically an, r.t. transmission line including distr~.buted series inductances resulting from 35 the self inductance of the metal elements and shunt capaCitances between the metal elements. and the grounded WO 9G/18208 pGTIUS951I5753 chamber exterior walls. To excite and maizitain the plasma for these purposes, source 3o supplies up~to 3A
amperes to coil 34. ' ' _ To confine and concentrate .magnetic field Wines ~ resulting from current flowing through the linear canductors of coil 34,~ magnetic shield _ cover '40, preferably made of aluminum in whzeh x.f. eddy currents are induced by the r.,f. magnetic flux lines, surrounds the sides and top of the coil. Cover 40,has a roof 42 10~ and feur sidewalk 44, that are fixedly attached to vacuum chamber 10.
According to one embodiment, illustrated i,~ci Fig. 2, coil 34, that extends over all four of windows 19, has a..
configuration including eight elongated, straight, liziear, metal conducting elements 5x-58 having apposite ends connected to elongated straight, fetal (preferably .
si7.ver coated copper) leads 59 anal 60 which extend parallel t4 each other and at right angles to elements . S1-58. The bottom faces of elements 51-58 and leads 59,, ' 60 .are bonded to windows 19, except the portions of elements 51-58 which span gaps 31 across rail 21, between, interior edges of the windows, as illustrated in,Fig. la.
Conducting elements SI~58 are, approximately equidistant from each other '(except for the spacir~g between central y elements 54 and 55 which is somewhat different because of center rail 21?. have about the same length and extend parallel to each other. Leads.5s and,6o include centxal v terminals 62 and 64, located midway between central conductors. 54 and S5. Terminals 62 and 64 are 3~ respectively connected to terminal 66 of r.f. source 38 by cable &s and to output terminal 70 of matching network 36 by cable 72.. Matching netwoxk 36 zs connected to output terminal 74 of r.f. source 3B,.
Tn response to the output of r.~. source 38, current flows through each of conducting, elemezits 51-54 generally zn the same direction at any 7.x~,stant to produce w. f .
wo ~sns~os ~ . ~crms~s~zs~s3 magnetic flux lines 124, x.28, 130 and I32, Fig. 1.l.
wBecause the lengths Qf each,of conducting~elemants 51-58 . is a re3.atively small fraction, e..g. about 1/I6th, of a wavelength (a) of 'the frequdncy derived from r_ f _ source 38, the instantaneous. current arid voltage variations across each of the conducting elements is net substantial. Because central conducting elements 54 and .
55 have.the same I~ngth, same cross sectional geometry and are equispaced from terminals 62 and 64, the lengths 14 of the current paths formed by the transmission lines . from tez~minal 62 to terminal 64 through conducting .
elements 54 and 55 axe the same, whereby the t~c~agnetic flux densities resultizig from the substazitially equal. RMS
.amplitude r.f. curre'rlts flowing through conducting, I5. elements 54 and 55 are approximately the same.
Similarly, slightly off -center conducting elements 53 and 56 have equfl hength transmission lines and eurx~ent paths between terminals 62 ' arid 6-4 , so the magnetic flux densities resulting. from' the substantially equal RMS
20 amplitude currents Flowing through them are about equal.
Because the lengths of the transmission lines and current paths through conducting elements 53 and 55 are somewhat greater than those through elements 54 and 55, there is a tendency far. the RMS values of the r,f.
25 currents flowing through elements 53 and. 55. to be somewhat ~.ess than those through elements 54 .and 55, whereby the magnetic flux densities derived from eJ~emer~ts 53 and 56 tend to'be less than those from elements 54 and 55. Hy the same reasoning, magnetic flux densitie s 30 resulting from r:f. excitation of conducting elements 52 and 57 are approximately the same and tend to , be less than those resulting fz-om current flowing through conducti~zg elements S3 and 56; the same is true for conducting elements 51 and 5s.~
3,5 . As a result of the differential lengths of the transmission. lines a.nd the resulting differences 'in .
Wo 9sixs2o8 pcrrusssns~s3 current, path lengths frbm terminals 62 and 64 through different ones of elements 51-S8 there are differences in the excitation and distribution of. the plasma in chamber z0_ this is iikely.to lead to uneven plasma processing of the Large surface area workpiece because there is greater plasma density in,the workpiece central region (beneath elements 54 and 5S) thari the workpiece periphery . (beneath elements 51 and 58).
According to -one, aspect of the invention, the to lengths of the transmission lines iz~cluding elements 51 58 are approximately eleatrieally equalized by proWding the different 'lines with reactances having different values. Since the self inductance of a single electric lixie is inversely proportional ' to the line .doss seGtior~al area and the inductance of a line increases as the ~.ine length inczeases, the lines closest to terminals 5~ and 64 ean~be made electrically longer by decreasing the cross sectional. areas thereof relative to~the cross sectional areas of the lines farther from the terminals.
zt is also desirable to maintain the electrical length of each of elements 51-56 the same so the RMS voltage and current variations across them are equalized to provide the same plasma .distribution below these elements. .
To these ends, the cross seCtior~a~. areas of leads S'9 and 50 progressively increase between adjacent pairs of ' segments 55-58 and 51.54 while~the crass sectional areas of segments S1-58 are the 'same. Hence, 7.eads 59 and 60 have re~.atively small cross sectional areas between 'segments 55 and 56 as well as between segments 53 and 54 3o and relatively large. cross sectional areas between segmez~ts 57 and 58 as well as between segments 5I and 52.
Alternatively, capacitors 81-88 are connected in series with elements 57.-58 to equalize tl~e lengths of the ltransrnissic~n lines. As illustrated in fig. 2a, capacitors 8~.-88 are connected in series with elements 51-58 arid lead 59, at the end of each, element adjacent WO 96118108 ~ ~ PGT/US95115753 the lead. These locations for capacitors 81-88 do not affect the effecti~re physical lengths of elements 51-58 because of the relatively small physical size Qf the capacitors.
5 To enable the phase. of the currents in each of elements 51-58 to be generally the same (either leading or lagging the voltage across the element? the geometry of elements 51-58 and.the values of capacitors 41-88 are y selected so the net impedance at the frequency of source 10 . 3B of each of the -branches ~.ncluding e3~ements 51-5B is of the same reactar~ce type , i . a ., either - inductive or capacztive. If the inductive impedance of elements 51-58 . ~is dominant, each of series capacitors 81-88 has a .
relatively large value, to provide a relatively small, 15 capacitive impedance in series with each element_ Hence, capaaitars 84 and 85 in series with elements' S4 and 55 have smaller values than capacitors 83 and 86 in series with elements 53 and 56, capacitors 83 and 8~ in series with elements 53 . and 56 have smaller values than 28 Capacitors B2 and 87 in series with elements~52 and 57, etc.. so that capacitors 81 and 88 in sex~.es. with elements .51 and 58 have the largest val-ues or may be eliminated.
.It, however, the dominant impedance in the branches ' including elemezzts.51-58 is capacitive, the values of , capacitors 81-68 are. relatively small to provide high capacitive impedances; the values of pairs of capacitors 84, 85, 83,_86, 82, 87, 81, 88 progressively decrease in the order.named.
Reference is now made to fig. 3 of the drawing, wherein coil 34 is illustrated -as including. linear conducting elements 51-5B, arranged and.constructed the ' same as conducting elements 51-S8 ref Fig. 2. Tn Fig. 3 conducti2~g elements 51-58 have opposite ends. connected td straight elongated metal leads 9o az~,d, 92 that extend paraJ.lel to each other and at right angles to conducting elements 51-5B. Leads 90 and ~~ have large cxoss WU 96!18208 . PGTI(JS95115153 sectional areas resulting in small inductarxces that do not introduce,appreciable transmission line lengths ox phase shifts ~.n the. paths leading to and from elements 51-5B_ Lead 9D includes a portion which ends at terminal 94 and extends slightly beyond caaductor 51; similarly, lead 92 includes a portion which ends at terminal 95 and extends slightly beyond lead 50 . Terminals 94 and 96 axe connected to the same leads and circuitry as terminals 62 .
and 64. respectively. ~ w 1o An advantage of the structure illustrated in fig. 3 _ is that the current path through each of conducting elements 5~.-58 between terminals 94 and 95 has the same physical and electr~.cal length. , xhereby, the, RMS
amplitude of the AC current flowing in each of cor~.r3.uct~.ng ~.5~ elemexxts 51-58 isvirtually the same. Because the RM5 amplitude of the AC current ~~~.owing in each of conducting elements 51-58 is about the same, the magnetic f~.ux .
densities resulting from excitation of these conduct~.ng elements by the r . f . source 3 8 i, s about the same 20 ~ .The magnetic ~lux lines resulting from x.f.
excitation of conducting elements 57.-58 produce r.f.
. ,'. magnetic flux lines 124, 1.28, 130 and 132 (k'ig.' 13? in the gas introduced into chamber la, to excite the gas to a plasma having equal numbers of positive and negative 25 charged tarriers_ Because, of the resulting molecular flux in the plasma, the plasma functions as a single turn secondary winding ~of a trans~ormex including, as its . primary windings, conducting elements 51-58. The . .
conducting properties of the plasma cause r.f. magnetic 3a flux lines 1.24, 128, ~3o and 132 to .lie asymmetrical, i.e., the magnetic flux l~.nes extend above windows I9 into the atmosphere to a considerably greater extent than blow- the windows ' into vacuum chamber to . The charged .
carriers disperse through the,gas to cause the volume of 35 gas to 7oe a pzasma for treating substrate or workpiece 24.
'W096I1820S . PGT/DS95/IS7~3 Reference is now made to Fig_ 4 of the drawing,~a further configuzation of coil 34, including elongated straight leads 134 az~d 135, that extend parallel to each other and include end terminals 138 and 14 D , respectivexy cdnnected~to r.f. exciting device 33 via cables 72 and 68. Extending ~ betv~reen leads . 134 and 136 .are linear, paraJ.lel elongated conducting elements 51-&e ~ which are identical tb the corresponding elements of Figs. 2 and 3.
Elements 51-58 are driven by r.f. exciting device 33 so that at any instant of time, r:f. parallel currents generally flow through them in the'same direction. Leads 134 and 136'and elements 51-58 of Fig. 4 are arranged so end terminals 138 and 140 are at the same ends of the leads relative to the conducting elements and the 15, terminals are spaced from each other by the lengths of the conducting elements. To enable the coil configuration of fig. 4 to include equal electrical length transmzss~.on lines 'through elements 51-58 from tez~ninals 138 and 140 via leads 134 and 236, the cross section geometry of different parts of the leads can d~ffex, as discussed in connection with Fig. 2, and/or -capacitors can be connected in series with elements 51-58 as discussed in connection with Fig. 2a.
a result. of the currents flowing in like direetioz~s through conducting elements 51!59 in each of Figs. 2-4, there is at least one,magnetic~flux line 124 (Fig_ 11) surrounding each of the conducting elements and thexe is a cumulative effect caused by the interact~.on of magnetid fluxes resulting from.the currents flowing in elements 51-58. Thereby,' a highly concentrated, evenly distributed, magneta.c ~.geld is provuded in the plasma beneath windows 1~. Fox example, the like directed currents flowing through conducting elements 52 and 53 or thxough elements 56 and 57 cause these two pairs of.
conducting elements to be surrounded by magnetic flux lines 128 and X29, respectively. The interaetior~ between we 961i$xoa fCTICtS951I5753 the magnetic fluxes resulting from currents fla~aing in a lake direction in conducting eZemezits 5S-58 causes these conducting elements to be surrounded by magnetic flux lines 130. ~An interaction between the magnetic fluxes resulting from currents flo~saing in a like direction , ' through all of conducting elements 51-5~9 causes elements 5Z-58 to be surrounded by magnetic flux lines 132. The - concentrated magnetic flux lines resulting from the excitation patterns of conducting elements 51-58 provide 1~ a relatively uniform distributvon of. plasma in chamber ZO . -beneath top end plate structure l8 so there is an even distribution of~ etchant or deposited molecules on workpiece 24.
According to further embodiments of the invention, 15, illustrated iii figs . 5--7, the' conducting elements of tail 34 are arra~ngeci so current . generally f lows in adj scent .
linear conducting elements of the co~.l in spatially opposite directions at any instant of time. The structure - of Fig . 5 has the advantage of providing 20 current paths with equal physical,azid electrical lengths through each of the~condnctors between opposite terminals of r.f. excitatzon device 33. While the magnetic fluxes coupled to the plasma lay the structures of. Figs. 5-7 have.
lower density than those of Figs. 2-4,- in some instances 25 xt may be.desirable to tailor the flux density to certa~,n regions of the plasma as can- be more easily provided with the structures of Figs. 5-~7 thar~ those of Figs . ~ 2,~
'fhe stru~t~,re of fig. ~5 includes spatially adjacent and parallel, elongated stxaight~ leads lOD and 102, 30 respectively having. terminals lD4 and X06 at spatially oppasit_e ends thereof, connected to opposite terminals 56 and 72 of r.f. excitation device 33.~ Coil 34 of Fig. 5 includes four segments n13., 112., 113 and 214, each including a pair~of elongated; linear straight parallel .
35 conducting elements, having opposite end terminals respectively connected to leads 10p~ and 1D2. heads 10p WO 961I8~08 ~CT/US95115753 and 102 are generally positioned to one side of segments ~.1~.-114 so the conducting elements extend in the same direction to the side of interior lead 102. The coil segments arid conducting elements are arranged so coil segment 111 includes conducting elements 115 and 117, coil segment W2 includes conducting elements 118 and 119, cflil segment 213 includes conducting elements 12.0 and 121 and coil segment 11~ .includes conducting elements 122 anrl 123. The,parallel conducting elements of coil segments 111-114 are connected. to each other by conducting elements 125 that extend parallel to leads 'loo and 102. Conducting, elements 11G-123. are generally equispaced from each other so that, for example, conducting element 117 of coil segment 111 is spaced the same distance from conducting element 118 of coil segment 11.2 as it is spaced from conducting element 116 of coil , segment .111. Each of the transmission lines including coil segments 111-114 has the same physical and electrical length between apposite terminals ~.0~ and 106 because (1) of the geometry of the layout of coil segments 117.-ll~~ and leads 100 and. 102, (2) each of . .
segments 111-11~ has the same cross sectional and longitudinal geometry and (3) leads 100 and 102 have the same cross sectional and vlongitud~.nal geometries.
A further configuration for providing spatially parallel conducting elemer~ts that are electrically cdnnected 'in parallel and have adjacent conducting elements. with currents flowing generally in. apposite.
directions is illustrated in Fig. 6 as a woven pattern 3D including straight elongated linear leads 150, 151, 15~..
and 1,53, in combination with straight elongated linear canducting~ elements 151-158. .Leads 15n-1$3 extend spatially paralldl to each other, and at right angles to conducting elements 161-168 that are gez~erally equisnaced from each other and spatially extend parallel to each other. L~eacis 15b, 151 are on one side of elements 7.61-W'O 961182p8 . ~ - ~~ T1U595115753 z68 while leads 152 and 153 are nn the other side of these elements. . Leads 151 and 153 aze respectively connected by cables 154 and 1S5 tt~ a first terminal 156 of r.f. excitation device ~33 while leads l5fl and 152 are 5 respectively connected by cables 1S7 azid 158 to a second, opposite t$rmina1~159 of the device 33. Alternate equal.
length conducting elements 161, 163, 165 and 157 are electrically connected between leads 150 and 153, whi~Ie the remaining, equal length conductixzg elements x.62, 3.6~,.
~,D ~66~ and 1Ge are electrically connected iii parallel between leads 15l and 152._ $ecause elements 161, z63, 16S and 167 are connected to.exterior leads 1S0 and 153 and .elements 162, 164, 166 and 168 are connected. to interior leads 151 and zS2, the former elements are 15 _ longer than the latter_ Thereby, at any instant of time, currents~generally flow in the same direction through conducting elements 161, 153, I56 and 167, which ~.s opposite from the i3irection cuxrents general~,y flow through, conducting ~.lements 162, 164, 166 and 168.
20 Magnetic flux paths similar to those provided ~by the structure illustrated in Fig. 5 are thus established by the~coil arrangement of Fig. 6. Because the physical distance between terminals 156 and 159 via the transmission lines snc7.uding e3.ements 161-158 differ, it ' is praferable.to change the crass sectional geometry of Zeads~150-153 in a manner sirttilar t4 that described for Fig, 2 or to connect capacitors in series with elements 161-169 as described for Fig. 2a.
The woven coil arrangement of Fig. 6 can be - modified, , as illustrated in F~.g. 7, so .each of~ the conducting elements ha~.the same Length. To these ends, the woven coil structure of. Fig. 7 .includes elongated, parallel straight leads 170, 171, 172 and 173, in ' combination with elongated, parallel straight conducting elements x.81-188. Leads 170-173 extend at right angles to equispaced conducting elements 18z-n88_ Exterior WO 9411$Z08 _ P~YU59S/I5753 leads 170 and 173 are connected to terminal 190 of r.f..
.excitation device 33 by cables 19~ and 192, respectively_ anterior leads 171 and 172 are cQrnn,ected to terminal 193 of r.f_ excitation device 33 by cables 194 and '195, respectively.~.Conductir~g elements 181, 183, 185 and 1s7 ' , are electrically connected in parallel across leads~l7p and 192; while conducting~elements 182, 184, 18G and 18s are electrically connected in parallel across leads 17p and 172. Thereby, generally oppositely directed currents 0 flow through adjacent.pairs of leads' 181-188 so that, for example,. when current is f3.owing through conducting eleutent 182 from lead 170. to lead 172, current is flowing through conduct~.z~g elements 7.81 and 3.83 from lead 173 to lead 1'71. Hence, current f~,ows in apposite directions in ~~ adjacent cc~nduct~ing elements in a similar.manner in the embodiments of Figs. 6 and 7. , ..
In response to.excitation o~ the coils illustrated in Figs. 5-7 by r. f _ excitation device 33, magnetic lines of flux, as illustrated in Fig_ IZ are produced. In Fig_ 12; magnetic flux, ~ lines 38'1=388 are respectively associated with the equal ~.ength conducting elements 3.81-188 of Fig. 7;'3t is to be understood that~s,imilax flux line patterns are obtained for conducting elemerats 1Z6-123 of Fig. 5 and conducting_elements 16z-168. ~ecaus.e current floras in opposite directions in adjacent ones of ~e~.ements .181-188, the magnetic flux lines resulting from these.currents buck each oth~x~ so there is no interaction of flux patterns 381-388 and there is flux null between adjacent. conducting elements. - Since there is no 3D conducting element or magnetic member on the. exterior sides of conducting elements x.87. and 188, magnetic flux lines 381 and 388 bu~.ge away from the center 'of coil 34.
Hecause conducting elements. 18~ and 185 are spaced farther apart than other pairs of the conducting elements 35~- (due to rail 21), magnetic flux lines 384 and 3s5 bulge i toward center dielectric rail 21. The interior WO 96/I8208 ~CTIt159a/15753 22 .
equispaced positions of cbnducting elements x.82, 183, 186. .
ahd 18~ cause ~lux lines 382, 383, 386 and 387 to have ' about the same density and ~spatzai configurat~.on.
The coil structures illustrated in figs. 2-7 are , designed to extend over all four windows 19 of top_end plate structure 18: In certain instances,, howe_ ver, it is desirable to provide individual coils on eaeh.of windows ~.9. To this erid, any of the coil structures described in connection with Figs. 2-7 can be ,connected in parallel and separately overlay each of~windows 19, as illustrated in Fig. 8. In the particular embodiment of Fig. 8, each of windows 19 is overlaid by separate.coil segments 2~1, ~D2, 203 and 204, each constructed generally in the .
manner described irx connection with Fig. 4. Adjacent ' int~rzor leads 205 and 206 of coil segments 201 and 202 are connected tQ terminal 20'7, connected by cable 208 to termiizal ~p9 of r.t.~ excitation device 33. .Terminal 209 is also connected by cable 211 to terminal 212,Iinrturri connected tQ.interior adjacent leads 213 and 214 of coil segments 203 and 204. Exterior leads 21,5 and 215 at coil segments 201.and 202 are connected by cable.217 to the ' other terminal 218 of r.f. excitation device 33.
Terminal 218 is also connected by cable 219 to eXterior leads 220 and 221 of coil segments 203 axi~d 204. Thereby,, segments 20I-204 of coil 34, as illustrated in ~'ig. 8,.
are driven in parallel by device 33.~ Each o~ the ccih segments~has electrically parallel conducting elements with relatively short lengths (rzo more than 1/~.6th of a wavelength of the wave derived by device 33) to minimize ' the like3.ihood of voltage~and/or current nulls therein.
Eecause the four coil segments 201-204 are relatively short transmission lines it may not be necessary in certain ~.nstaz~ces for all of the indivzc~ual transmission lines on the individual windows ~Z9 to have the same length.
WO 961XSx08 PCTl0595I15T53 In each Qf tk~e embodiments of Figs. 2--s, the conducting elements of the various planar coils have equal physical lengths. It is not necessary, however, for the condz~cting elements to have equal physical lengths, and in some instances it may be desirable fdr the physical lengths ~ thereof to differ. ' In the embodiment Qf Fig. 9, the structure of k'ig_ 2 i.s modified to include arcuate leads 226 and 229 between which extend spatially parallel elongated straight cpzzdueting elements 231-23B having differing physical lengths. Midpoints of arcuate leads 226 and 228 include terminals 240 and 241, respectively connected to opposite polarity terminals of r.f. excitation device 33. Currents flow in parallel in generally the same direction through conducting elements 35 231-238. The structure of Fig. 9 is employed to.enable the- plasma in chamber 1o to have certain special spatial canfigurations~for treating substrates having appropriate surfaces_ While it is desirable to pro~ride elements 231-238 with different physical lengths, the electx~.cal lengths of the, transmission lines including these elements are preferably the same, a result which can, be achieved by use of the structures described in connection with Fig.
2 or 2a. Even though elements 23Z-238 are illustrated as being approximately equispaced'from each other, this. is not necessarily the case- for the configux~a~tions of any of Figs. 2=9.
A magnetic flux pattern similar fo that of Fig. 12 can be pxovided by forming coil: 34 as plural series , conduct~.ng elements, as illustrated in Fig. 10. The coil of Fig. 10 includes conducting elements 241-248 that extend spatially in parallel to ,eack~ other, have approximately equal lez~gtk~s and have adj acent ends connected together by conducting elements 249 and 250.
' Conducting elemerits ~2d1 and 248 are connected to end terminals 252 and 254, in. turn connected by appropriate WQ 96!18208 ' PG~Y(J595I15753 cables to opposite end termiz~als of r,f_ excitation w device 33. Current thus flows generally iri opposite directions in~ad~acent conducting elements 241-248, as ~ , result of the sinuous or serpentine relationship of these conducting elements.. The structure of Fig. .10 has a substantial disadvantage relative to the' structures o~
Figs. 2-~ because of its long physical and electrical length, whereby there is a tendencyWar voltage and current nuJ,ls along the length of the coil formed by elements 241-248.' These nulls cause uneven distribution v of magnetic f~.ux acting on the gas ire chamber 10. This , problem is obviated by the parallel structures of Figs.
' Z-9,-all of which have conducting elements in parallel , with each other across the terminals Qf r.f. excitation device 33 and lengths that are about 1/l6th wavelength of the wave derived by device 33. The structures of~all of Figs . 2-ld have the advantage of being. planar coi,l.s having exterior terminals, outside of the conducting elements for ease of.cor~nection so problems. associated with.spiral planar coils having oz~e interior texzninal are avoided. All of'these planar coils, as well as spiral planar coils, can be used as four individual coils, connected in parallel, on the four wzndows~ 19 of end ' plate structure 28, as described in connection with Fig.
8. .
While ez~d plate structure .18 preferably includes four rectangular dielectric~wzndows having the same size and positioned in the guadrants~of a rectangular frame, other individually supported dielectric window ~ Configurations, e.g.. as schematically illustrated ire ~ .
Figs. 13 (a) , Z3 (b) and L3 (c) , can be ect~ployed.
Individually supported dielectric windows 302-310, fig.
13 (a) , in frame. 31.7, have different sizes and shapes such that, rectangular per~.pheral ~wzndows 302-308 have different lengths, extend. at mutually right angles and surround .interior .square window 3~,0. In Fig. 13(b) wo 9snszos ~crmsssms»s is diamond shaped, centrally located dielectric window 312 and triangle shaped.exterinr dielectric c~indows 314 are individually supported in frame 315 , frame, 318 , P'ig .
13(c), individually supports three rectangular windows 320, each.having the same size and parallel Zong sides-.
Planar coils, as illustrated in Figs. 2-10, axe laid an the windows of Figs. 13(a), 13(b) and 23(c). .
While there have been described and illustrated specific embodiments of the invention, it will be clear that variations in the details of the embodimez~ts specifically illustxated and described may be made . without departing from the true spirit and scope of the invention as defined i,n the appended claims. ,
Claims (36)
1. A device for treating a workpiece with a plasma comprising a vacuum chamber in which the workpiece is adapted to be mounted, means for introducing into the chamber a gas which can be converted into the plasma for treating the workpiece, means for converting the gas into the plasma including an electric source for producing an r.f. field originating outside of the chamber, plural individually supported dielectric windows on an exterior surface of the chamber positioned to couple the r.f.
field to the gas so the field coupled through the windows excites the plasma.
field to the gas so the field coupled through the windows excites the plasma.
2. The device of claim 1 wherein the electric source includes a single excitation device for producing the r.f. field that is coupled through the plural windows.
3. The device of claim 2 wherein the excitation device includes a single coil array that extends over the plural windows, the r.f, field being a magnetic field derived from the array.
4. The device of claim 3 wherein the coil array includes a planar coil that extends over the plural windows.
5. The device of claim 3 wherein the coil array has a pair of terminals connected to several parallel segments via a pair of leads, the electrical length for current flow from the terminals through each of the segments being about the same.
6. The device of claim 3 wherein the coil has pair of terminals connected to several parallel segments via a pair of leads, the electrical and physical lengths for current flow from the terminals through each of the segments being about the same.
7. The device of claim 1 wherein the electric source includes plural excitation devices, one for and associated with each window, each excitation device being positioned to produce the r.f, field that is coupled through the associated window.
8. The device of claim 7 wherein each of the excitation devices includes a coil array positioned adjacent the window associated with the excitation device, the r.f. field including magnetic lines of flux derived from the coil arrays associated with the plural windows.
9. The device of claim 8 wherein each coil array includes a substantially planar coil that is positioned adjacent a particular window.
10. The device of claim a wherein the coil arrays are electrically connected in parallel.
11. The device of claim 10 wherein each of the coil arrays has about the same electrical length.
12. The device of claim 11 wherein each coil array has a pair of terminals connected to several parallel segments via a pair of leads, the electrical length for current flow from the terminals through each of the segments being about the same.
13. The device of claim 11 wherein each coil array has a pair of terminals connected to several parallel segments via a pair of leads, the electrical and physical lengths for current flow from the terminals through each of the segments being about the same.
14. The device of claim 1 wherein the surface includes a frame having plural openings, each with a separate window support structure, one of the windows being located in each of the openings and being carried by the support structure of the associated opening.
15. The device of claim 1 wherein the surface includes a frame having four openings arranged in quadrants, each opening including a separate window support structure, one of the windows being located in each of the openings and being carried by the support structure of the associated opening.
16. A device for treating a workpiece with a plasma comprising a vacuum chamber in which the workpiece is adapted to be mounted, means for introducing into the chamber a gas which can be converted into the plasma for treating the workpiece, means. for converting the gas into the plasma including a dielectric window on an exterior surface of the chamber, a coil positioned to couple an r.f. magnetic field to the gas via the window for exciting the gas to a plasma state, the coil including first and second terminals adapted to be connected to an r.f. source that causes the r.f. magnetic field to be derived and plural winding segments connected in parallel between the first and second terminals, at least two of the winding segments being in paths having about the same electric length between the first and second terminals.
17. The device of claim 15 wherein a plurality of dielectric windows are included, the coil extending over said plural dielectric windows.
18. The device of claim 16 wherein a plurality of dielectric windows are included, a separate one of said coils being adjacent each of said windows.
19. The device of claim 18 wherein said separate.
coils are connected in parallel with each other to said r.f. source.
coils are connected in parallel with each other to said r.f. source.
20. The device of claim is wherein the paths have about the same physical lengths between the first and second terminals.
21. The device of claim 20 wherein there are several of said winding segments and an equal number of said paths having about the same electric length between the first and second terminals.
22. The device of claim 21 wherein said several paths and winding segments are arranged so current from the r.f. source generally flows in the same direction through all of the segments at a particular time.
23. The device of claim 22 wherein the coil includes first and second elongated spatially parallel leads having the same cross section geometry, the first and second terminals being at opposite ends of the first and second leads, respectively, each of the several segments including an elongated element extending between the leads and having opposite ends connected to the leads, each of the elements having the same length and cross section geometry.
24. The device of claim 23 wherein each element has a length of no greater than about a 1/16 of a wavelength of a wave applied by the r.f. source to the coil.
25. The device of claim 21 wherein each segment includes at least one element, the paths, segments and elements being arranged so the elements extend generally parallel to each other and being arranged so the elements extend generally parallel to each other and current from the r.f. source generally flows in opposite directions in the elements that are next to each other.
26. The device of claim 25 wherein the coil includes first and second elongated spatially parallel leads having the same cross section geometry, the first and second terminals being at opposite ends of the first and second leads, respectively, each of the several segments including a pair of series connected elongated elements, the leads, elements and segments being arranged so the leads are adjacent each other generally to one side of the elements.
27. The device of claim 20 wherein the two paths having about the same physical and electrical lengths include: (a) first and second generally parallel elongated leads respectively connected to the first and second terminals, and (b) first and second coil elements that extend between the first and second leads, the terminals being connected to the leads at locations between the two coil segments.
28. The device of claim 15 wherein at least some of the paths having about the same electrical lengths have substantially different physical lengths across the terminals, the paths having substantially different physical lengths and about the same electrical lengths having reactances with different values causing the electrical lengths to be about the same.
29. The device of claim 28 wherein each of the paths has the same type of dominant reactive impedance value at the frequency of the current applied by the r.f.
source to the coil.
source to the coil.
30. The device of claim 29 wherein each of the paths includes an element connected between a pair of leads connected to the first and second terminals, each element having about the same physical and electrical length.
31. The device of claim 34 wherein each element has a length of no greater than about a 1/16 of a wavelength of a wave applied by the r.f. source to the coil.
32. The device of claim 29 wherein at least one of said leads has differing values of inductance between connections with adjacent pairs of said elements.
33. The device of claim 32 wherein the differing values of inductance are attained by providing the leads faith different cross sectional areas between connections with adjacent pairs of said elements.
34. The device of claim 29 wherein at least some of the paths include a series capacitor having a reactive impedance valve at the frequency of the current applied by the r.f. source to the coil, the series capacitors causing the paths to have about the same lengths.
35. The device of claim 34 wherein the series capacitors have values causing each path to have a dominant capacitive impedance value at the frequency of the current applied by the r.f. source to the coil.
36. The device of claim 34 wherein the series capacitors have values causing each path to have a dominant inductive impedance value at the frequency of the current applied by the r.f. source to the coil.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/354,122 US5589737A (en) | 1994-12-06 | 1994-12-06 | Plasma processor for large workpieces |
| US08/354,122 | 1994-12-06 | ||
| CA002206679A CA2206679C (en) | 1994-12-06 | 1995-12-05 | Plasma processor for large workpieces |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002206679A Division CA2206679C (en) | 1994-12-06 | 1995-12-05 | Plasma processor for large workpieces |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2523264A1 true CA2523264A1 (en) | 1996-06-13 |
Family
ID=35645538
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002523264A Abandoned CA2523264A1 (en) | 1994-12-06 | 1995-12-05 | Coil having parallel paths having about the same electrical length |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2523264A1 (en) |
-
1995
- 1995-12-05 CA CA002523264A patent/CA2523264A1/en not_active Abandoned
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| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Dead |