CA1083526A - Sputter-coating of glass sheets or other substrates - Google Patents

Abstract

ABSTRACT
A cathode for use in the sputter-coating of thin films of a selected coating material on glass sheets and other substrates, and means for cooling the same. The cathode is of rectangular construction including a top wall, a bottom; wall and side and end walls defining a closed chamber therein. The cathode is internally cooled by circulating a cooling medium, such as oil, under a constant head pressure, through a closed system in which the cathode is interposed, and means for con-tinuously withdrawing air and any other gases from the system such that as the oil circulates through the cathode chamber it will exert a pressure, less than atmospheric pressure, upon the walls of said cathode and thereby reduce the pressure differential across the cathode walls.

Description

5;26 SPEC IFICATION

me present inventien relates ~o impro~remellks in the coating o~ glass sheet~ or other substra~e~ with ~hin :Eilms o:E
a ~elected coating materiai and more particularly to the coat-ing of ~uch substrates by the cath~de sp~lt~ering process.
~ he proces~ of ~pu~ter-coating in~rolves ~n bombard-ing a target o~ the coating ma~erial in an ionized gas atmos-phere in a chamber in which a c~ntrolle~ vacuum i9 mai~ltain0d ~o cau~e atomic particles o~ the coa~ing ma~erial t~ be dis-lodged and deposi~;ed on the substra~es t~G be coated. One 10 ~ype ~ appara~us employed for carrying out ~he proces~
embodies a plurali~y of aligned , ind~pendently con~rolled: ;
contiguous chamber~ including a~ entry chamber~ a c~a~i~g chamber and an exit: chamber, ~putter-coa~ing means in ~he ~orm cf a sub~qtaDk~ally rec~angular ¢a~lhode mounted h~r~o~t~lly in the upper portion of~ the coati~g chamber and ha~ ig ~ sheet : or layer Or a selected coatlng material carr~ed by the bottQm surface ther~of and con~eyor mearl~ for movin~ khe subskra~es . . . - . . . . .

1~35;26 (~lass sheets) in a horizontally disposed po~ition through the successive chambers and beneath the ~pukter-coating means such that a continuous film of the selected coating material will be deposited on the upper surfa¢es o~ the substrates. The cathode comprises a housing including a top wall, a bottom ~all and side and end walls which define a clo~ed chamber therein. The walls o~ the cathode are pre~erably formed of aluminum of the desired thickness and.are welded together along their meetin~ edges, In such a process, the thin films desposited on the substrates are usually of a metal such as, for example, nickel, gold, chromium1 copper, molybdenum or t~tanium, or allo~s Or these metals, Typical sputtering conditio~s are 5,000 volts potential on khe ~arget (coa~ing m~terial~ and a resulting current dansity o~ 0~1 to 1.0 ma/cm2 for a t-ime period o~ 0.2 to several minutes depending on the thickness of coating.desired It wlll be appreciated that thi~ pote~tial on the tar~et in the ionized gas atmosphere of th~ coating chamber will gsnerate a very h~gh temperature whichi~ends to heat the me~al cathode to an undesirable degree, On the other hand, it i9 desirable tha~ the cathode be operated as hot as possible without damage to the m~terlals of which it.i~:con-~tructed since the heat aids in keepin~ the oathod~.in a clean and operable condition~ :
~. In order to maintain acceptable working conditions~ it is essential that the cathode~ be maintained at a tempera~ure ..
compatible with the materials of cDnstruction and to this end di~ferent methods ha~e been propo~sd for effe~ting ~he cooling thereo~, However, the cooling procedure~ heratofore u~illzed ~.
30 have not proven wholly sati~ackory in meeting khe requirem2nts of continuou~ commercial operation. - -A typical cooling procedure heretofore utilized ha~ been ~3~
.~
. .
. . . . .

83~i26 ~o circulate ordinary tap water directly from the water main through the cathode chamber at a pressure of such magnitude that it will exert a pressure o~ a~out 3 lb~. p,s.i. on th~
walls of the cathode. However, this pressure together with the atmospheric pressure of about 14.7 lbs. p.s.i. on the wat~r supply-results in a total pressure of abou~ 17~7 lbs.
p~s.i~ bein~ imposed on the walls o~ ~he cathode. On the other hand, in the operation of a continuous sput-ter-coatin~ apparatus of the character re~erred to above~ the coating chamber is pumped down from atmosphere to a pressure usually in the range of 2 to 6x10-2 torr and preferably of about 4xlO-2 torr, which pr~ssure is maintained constan~ The ou~ward pressure exerted by the tap water on the walls o~ the cathode coupled with the vacuum created within the coating chamber places an undue stress on the walls of the cathode and more par~icularly on the welded joints securing ~he walls ~iogether. The result-ing s~eady rate o~ stress, commonly referred to as creep, causes a gradual weakening and eventual rupture o~.the..weIded joints between the walls of the ca~hode resulting ln leaks which necessitates removal of the ca~hode for repair and ~ep~acement~ This is, of cour3e, highly objectionali:not only ~rom the standpoint of increased maintenance costs~.bu~ also because of the loss of produc~ion timeO
The present invention comprehends a:new a~d~lmproved procedure for internally ~ooling the cathodes emplo~ed in the sputter-coating o~ thin ~ilms of a ma~erial on glass shee~ or other substrates.
Another object of the inven~ion is the provision o~ an improved method and apparatus which involves the internal cooling i 3 of the cathode b~ circulaking a cooling medium, suah as oil, therethrough und~r a cons~an~ head pres~ure in ~uch a.manner a~

.- :
. . ~ .

~3~5~ 6 to reduce the pre~sure di~ferential acrosq the cathode walls and thereby minimize the stresses and resulting ~krains therein.
A further object of the :invention is the provision o~ a method and apparatus in which air and other gases are continuou~ly withdrawn from ~he cooling system as the oil circulates through the cathode such that the pressure of the oil upon the walls o~ the cathode is less khan atmospheric pressure.
With reference to the accompanying drawings. -Fig. 1 is a vertical longitudinal sec~ional v~ew through one form of continuous spu~ter-coating apparatus with which the present inven~ion may be employed, Fig. 2 is a diagramatic ~iew showing ~he cooling ~y~em ~or the ca~hode, Fig. 3 is a vertical kransverse section ~aken substan-tially along line 3--3 of Fig 1, a~d Fig~ 4 is a ver~ical section through the cathode taken substant ially along line 1~ --4 of Fig . 3 .
The ~putter-coating appara~u~ illu~tra~ed in Fig. 1, with which the pre~ent invention may be empl~ed, co~prises ~our succ~ssive, contiguo~s 0nclo~ure~ ~hich define ~our indep-endently con~rol~ed chambers - an entry chamber lO, a heating and cleaning chamber 11, a coating chamber 12 and an ex~t chamber 13. The chambers are rectangular in shape and the dimen~
sions thereof, especlally the heigh~j are kept ~o a mininum in order to minimize the in~ernal ~olume and ~hereb~ ~he vacuum pumping re~uired, Each o~ ~he chamber~ i~ subsl;antially closed e~c~pt for aii~ elongatcd entrance opening and an elongated exit opening.
The.~outer ~all 14 o~ the entry chamber 10 i~ provided with an entrance opening 15, while ~he ou~er end wall 16 of exit chamber 13 is pro~ided with a discharge ope~lng 17. The 1~8`35~6 chambers are al90 separa~ed by parkition walls 1~, 19 and 20 Provided with similar openings 217 22 and 23 respectively.
All o~ the openings are positioned a~ ~he same heigh~ to allow for ingress and egress of the glass sheets or other ~ubstrates a~ they are moved into9 through and out of the successive chambers. Pre~erably, qulck-opening and clo~ing vacuum-ti~ht closllres are provided ov~r at least some of the elong-a~ed openings to reduce the vacuum pumping requiremen~s.
These closures are open when a substrate is moved through the opening and closed when no substra~e is in the opening~
Each of the chambers is provided with at least one outlet tube 2~, preferably lo¢ated at the bottom of the chamber.
Each tube communicates with a vacuum pump (not shown) and a valve 25 is provided on each tube to independently control the pressure within the respecti~ chamber. Inlet ~ubes 2~ extend through the top o~ ~he c`oating chamber and eommuni¢a~e with a source of inert gas, preferably argon. A valve 27 i9 provided on each tube 26 to control ~he flow of gas into the.coQting cha~ber~ -Conveyor mean~ indicated generally by ~he numeral 2 are located in the low~r portion o~ the chambers ~o.tran3por~
the substrates 29 to be coated through the sequence ~ chamber~.
l'hè ~ubstra~e3 are preferably carried upon rigid.metal platens ~0, The conveyor.means illustrated in Fig. !3' compr~ses a plural~ty o~ ho~20ntally ali~ned transversa sha~ts 31 mounted at opposite ends in bearings 3~ and 33 supported upon the base 34 of the apparatus, Keyed to each sha~k ~ djacen~ th~
op~osite end~ thereof, are gears 35 and 36 and ~rained abou~
these gears are endle~ chains 37 and 3B respectivel~ which convey the platens and substrates through successive chambers.
The endlesq chains are drlven by suitable drive means, no~
sho~n.

--6_ .

.

1~83S26 Heatin~ means 39 (Fig 1) co~prising elongated, tubular radiation heaters ~0, are mounted in the upper portion of the chamber 11. These heaters are preferably hig~-intensity radiation heaters and a reflector ~1, moun~ed above the heaters, is used to cohc~n~rate the heat on the passing sub~trates 29 The substrakes are heated prior to coating to promote out-gassing and thereby attain additional surfa~e cleaning and improved adherence of the coating~ A ~low-discharge cleaning electrode 42, which may be in the form of a closed loop, i~
located at the top of chamber 11. The elec~rode is supported b~ a rod 43 and vol~age is supplied to the elec~rode by the high-voltage D.C. power source 44. One side of the source is ~rounded and the other side thereof connected to ~he rod 43.
$hields ~5 may be position2d below the elec~rode tha~ are ~ust large enough to preven~ the substrates frq~ "seeing" the electrode as they pass through the chamber. The electrode may be operated either as an ordinary spu~tering electrode with the shields which prevent the electrode ma~erial ~rom being deposited on the substrate~ or at power levels below ~hat required for spu~tering without the shields, The ionized ion~
of the gas will bombard khe surfaces of the substrate~ ~o clean ~hem bu~ no sput~ersd material is deposi~ed in ei~her case.
Sputter-coating ca~hodes 46 and ~7 (to be more f~lly hereinaPter de~cr~bed) are mounted in ~he upper portion o~ the coatin~ chamber 12~ The cathodes are u~ed ~o deposit a. thin film of a metal on the substra~e5 and voltage is applied to these cathodes by hi~h-voltage D.C power sources 4~ and 49 respectiYely. All power ~ources are pre~erably ground~d ~o khe apparatus ~uch that the apparatus wlll act a~ the anode for ~0 the cleaning and sputtering op~ra~ions.
~ In practice, one or moro cathod~s may be u~ed in the coating chamber~ Ssveral ca~hode~ o~ di~ferent materials may be applie~ consecutively as) for example5 making cakhode 46 of .
. .

1~83~2~;

one metal and cathode 47 o~ a di~ferent metal. Or the cathode 47 ma~ be used to deposit a ~hin protective layer of a silic-eous material, such as Pyrex glass on a previously deposited film of metal. Also the coating chamber can be increased in len~th and a greater numb~r of cathodes of the ~ame material used to increase ~he deposition rate and therefore the product-ion rate.
In operation, the glass sheet substrates to be coated are Pirst cleaned by a conventional washing opera~ion and are then passed into the entry chamber 10, with the smooth contin-UOU3 sur~ace to be coated fac ing upward . The vacuum pumping in the entry chamber removes most of the air, moiskure, and other contaminates which may leak in through the entrance opening. The substrate~ 29, carried by the platens 30, are moved by the conveyor means 2~ into the he~ting and cleaning chamber 11 where they are heated by the heaters 40 and then cleaned by the cleaning electrode 42. The ~ubstrates then move at a controlled speed into the coa~ng chamber 12 where a continuous film of the selected coating material or materials is spu~tered on the clean upper surfa¢es thereo~ After belng coated, the substrates move into ~he exit chamber 13 where they ~re cooled before being removed from the apparatus ~hrough the opening 17~
- As brought out above, under typical operating condit-io~s, ~,OOO volts potential may be applied on the target, (coating material) and ~his high potential generates an exce~s amount of heat that must be rap~d~ removed in order ~o pro-duce a commerciall~ satis~ac~ory coating on the substrates without damage ~o the apparatus or the glass substrates. Ths 30 present inven~ion is particularly concerned with ~he provision of a new and improved method and means ~or ef~ecting a more controlled func~ioning of the cathode.

; . _~_ , ,.,. ' . . . . . .. ,- . - . - . - .
. ~ , . . . . ,, - . .
... i . . . . . . . . .. ..

3~zfi Each of ~he cathodes 46 and 47, as illustrated in Figs. ~ and 4, is o:~ substantially box-like form comprising a hou~ing includin~ a top wall 50, a bottom wall 517 side walls 52 and ~3 and end walls 54 and ~5 which define within the housing a closed chamber 56. The slde and end wall~ are - sealed to the top and bo~tom walls preferably by welding.
The cathodes extend transversely within the coating chamber 12 and are located in ~he upper portion thereo~ by support lmits 57, 5~ and 59 mounted on the top wall 60 o~ the coat-10 ing chamber 12.
Each of these support units includes a metal ring 61 ~ertically aligned wi~h an opening 62 in the top wall of the coatin~ chamber. An annular insulating member 63 having a depending collar 64 is disposed above the ring 61, with a cover plate 65, having a central aperture therein, positioned above said insulating member The ring has tapped holes for receiving bolts 66 passing through openings in the insulati~g ~ember 63 and ~ov~r pla~e 65. An 0-ring 67 i9 located between the ring 61 and insula~ing member 63 to provide a vacuum-tight aèal, while an 0-ring 6~ between ~he insula~ing member 63 and cover plate 65 serves the same purpo~e.
Secured to the top wall 50 of tha cathode housing, as by welding, is an annular ~leeve 69 which is received in concentr~c rela~ion within the collar 64 depending from insulating member 63. This sleeve is provided at its upper ; end with a centrally disposed aper~ure in an inw~rdly ~urned rim~70 formed with tapped hole~ to receive bo.lts 71 passing through the cover plate 65. An 0-ring 72 is located around the bolts to a~ord an additional vacuum-tight seal.
: The coatin~ material ~target) is carried by the under surface of the bottom wall 51 o~ ~he cathode.hous!ing and consists of a sheet or layer 73 of ~he seleaked me~al or me~al allQy which is to be. deposited upon the upper ~urrace - . . . , ~, .
.

of the substrates as they pass therebeneath. The coating material may be applied to a support plate 74 by electro_ platin~, brazing or in some other ~uitable manner.
A thin foil sheet 75 of a ~oft, thermally conduct-ive material, such as aluminum or indium~ is pre~erably positioned between the bo~tom wall 51 of ~he'catho~è housing and said support plate. The support plate is secured to the cathode housing by bolts 76~
The required electrical power for the cathodes 46 and ~7 can be supplied there~o ~rom the respec~ive po~er ~ources 4~ and ~9 through power lines 77 and 7~ connected to conductor rods 79 a3sociated with the suppor~ unit~ 5~.
Grounded shielding pla~e~ ~0 are seoured bo the ~op wall of the coating chamber a short dis~ance from the edges o~ the cathodes to prs~ent reverse spu~tering of the mater~al on the edges of the cathodes~
To pro~ide for the ¢ontinuous circulation of the cooling medium through ~he cathodes ~6 and 471 each cathode is~provided wi~h an inlet pipe ~1 adjacent one end thereo~
and an outlet pipe ~2 adjacent the opposi~e end. Ea~h pipe passes downwardly through bhe aligned aper~ures in the cover plate 65 and ~leeve 69 o~ the re3pec~ive suppor~ uni~ 57 and 59 and communicates with the cathode chamber 56 throu~h an opening ~3 in the top wall 50 o~ ~he cathode housing.
The improved means contemplated by the present inve~bion for internally cooling the cathode~ i~ illustrated diagramaticall~ in Fig. 2. Such means com:~ises a reservoir which may be in the form of an elongated crlindrical ~ank containing a upply o~ the oil used for cooling ~he cathode~
Connected to the bottom of the tank ~4 is a pipe ~5 leading to a coolin~ unit ~6, while connec~ed to the bottom o~ ~he cooling unit i3 one end o~ khe pipe ~1, the opposite end o~
, .
-10;

,. - ,. . . .. . ., , .: , .

~8352~

which communicates with the cathode chamber. The outlet pipe ~2 conducts the cooling medium ~rom the cathode chamber to a pump ~7 w~lich returns the oil through a line ~3~ back to the tank ~Is, It will thus be seen that the oil is con-tinuou~ly recirculated through a closed system under a constant head pressure from the reservoir to and through the ca~hode and9 upon exitlng from the cathode, is pumped baGk to the reservoir.
The amount of oil contained in the closed sys~em is such ~hat tha tank ~ is maintained about hal~ full, the level of the oil being indica~ed a~ ~9~ Connected ~o the top of ~he tank ~4 and communicating with ~he space above khe oil suppl~ is one end of a pipe 90 which leads to a vacuum pump 91. The vacuum pump i5 continuously opera~ed to with-draw any air and other gases from.~he cooling system. As a result, the pressure o~ the atmospharic air i9 substracted from the head pre~sure of the oil on the walls of the cathode so that the pressure exerted on the walls o~ the cathode is . less than atmospheri¢ pre~sure, While the pressure exerted on the walls o~ the cathode housing may vary as operating 20 conditlons dictate it is usually in the range o~ 2 to ~ lb~. .
p.s.i., and preferably about 3 14s. p.s.i.
The continued mainkenance of the vacuum in the upper part of the tank ~4 will effect ths withdrawal o~ air ~hat may lea~ into the system a~ well as any gasas tha~ may be released ~ro~m the oil. The oil can be of any typ~ ordin-arily recommended ~or heat transfer applica~ions.
; It will thus be apparent ~hat the oll cooling ~
system of the present in~ention overcomes the objec~ional features present in prior water cooling systems in that the pressure of ~he oil on the walls o~ ~h~ cathode will be less than atmospheric pres3ure. This will, of course, result in reducing the pressure differential acro~s the walls o~ the cathode housing with the ~onsequenk reduc~ion of the ~tresses .

1~83~Z6 and resulting strains kherein. This greatly le~sens the - liabili-ty o.~ leaks ocCUrring in the welded joints between the walls of the cathode housing resultin~ in much les~
maintenance costs as well as in reduced !'down time" in the operation of the coating apparatusO Another advantage in the use o* oil as the cooling medium is that it also aliminates corrosion in the system due to salts in ~he tap water here-tofore used.
~hile this lnvention is not limited to use with any part icular type of cathode, it is of ~pec ial ut ility whan employed in the internal cooling of ~he type of cathode des-cribed above in a continuous sputtering process.
It ls to be understood ~hat the words used herein to describe the invention are words of description rather than of lim~tation and that ~he scope o~ the invention is ~o be limited only inso~ar as s~t forth in the appended claim~

. -12

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In the method of sputter-coating glass sheets and other substrates with a thin film of a selected coating material applied by transport from a surface of a sputtering cathode provided with a chamber through which a cooling medium is circulated, the improvement which comprises circulating an oil under a constant head pressure through a closed system in which the cathode is interposed, and continuously withdrawing air and other gases from said system to reduce the pressure differential across the walls of the cathode as the oil circulates through the cathode chamber at less than atmospheric pressure.

2. The improvement of claim 1, wherein the oil is recirculated through the cathode chamber.

3. The improvement of claim 2, wherein the oil is cooled before being returned to the cathode.

4. The improvement of any one of claims 1, 2 or 3, wherein the air and other gases are withdrawn from the system by suction.

5. The improvement of any one of claims 1, 2 or 3, wherein the supply of oil is contained in a reservoir forming a part of said system, and the air and other gases are with-drawn from said system by creating a vacuum in said reservoir above the supply of oil therein.

6. In apparatus for sputter-coating glass sheets and other substrates with a thin film of a selected coating material, a cathode which includes a housing having a chamber therein, said housing adapted to have a sheet of the coating material applied to a surface thereof, means for internally cooling said cathode comprising a closed cooling system in which the cathode is interposed, said system including means for circulating an oil under constant head pressure through the chamber in said cathode, and means for continuously withdrawing air and other gases from said system such that the pressure differential across the walls of the cathode chamber is less than atmospheric pressure.

7. Apparatus as claimed in claim 6, in which said cooling system includes a reservoir for the oil, means for conveying the oil from the reservoir to the cathode under a constant head pressure, and means for receiving the oil from the cathode and returning it to said reservoir.

8. Apparatus as claimed in claim 7, in which said cooling system includes means for cooling the oil before it is returned to the cathode.

9. Apparatus as claimed in claim 6, in which said cooling system includes a reservoir for the oil, and in which the means for withdrawing air and other gases from the system comprises means connected with said reservoir.

10. Apparatus as claimed in claim 9, in which said last-named means comprises means for creating a vacuum in said reservoir above the level of the oil therein.

11. Apparatus as claimed in claim 7, in which said cooling system includes means for cooling the oil before it is returned to the cathode, in which the means for receiving the oil from the cathode, and returning it to the reservoir comprises a pump, and in which the means for withdrawing the air and other gases from said cooling system comprises a vacuum pump connected to the reservoir above the level of the oil contained therein.