US3198422A - Vacuum sputtering pump - Google Patents

Description

Aug. 3, 1965 a. KIENEL VACUUI SPU'I'TERING PUMP 2 Sheets-Sheet 1 Filed June 4, 1963 Aug. 3, 1965 G. KIENEL VACUUI SPUT'I'ERING PUMP Filed June 4, 1963 I'I'I'I'I);

2 Sheets-Sheet 2 occurs in this method.

4 3,198,422 5- VACUUMSPUHERINGPUMP Gerhard Klenel, Hanan 1W. (L Heraeus G.m.b.HZ., Hemm- (Main), Germany, a

corporation of Germany I Filed June 4 1963, Ser. No. 28S',35= Clauns priority, application Germany, June 8, 1962,

9 Claims.- '(Cl. 230-69) pump.

For the purpose of producingand maintaininga vacuum, vacuum pumps have lately beenemployed in which the gases to be eliminated are either chemically or mechamcally bound instead of being conveyed by the (Main), Germany, or to 'Ihe present inventionrelates to a vacuum sputtering While is getter ion pum'p' was ti e th n of the gctter metal it is:possiblc of; evaporation to bury the rare ten'ng" pump since the'rate of sputtering insuch a pump outer shape or y-Pr v tme y-th a which are-absolutely 'necessary,ie., the anode and the cathode, butafitrther' third p trode is. connected-Ito a'ucha voltage thatio'nsiimpinge p thereon. with a low energy' and th'ercforelonly a pump to the mu mie in the conventional manner.

'.'Ihismaybedoneeitherbyfreezingoutthegases, thatis,

by converting them into a.so lid state orby chemically bmdmg them by means. of agctter materiaL For prouse ducing the getter layer, two methods are especially known; namely, by vacuum'evaporation or by cathode sputtering by means of ages discharge, that-is, by an ion bombardment.

The present invention relates to the last-mentioned method of cathode sputtering and more particularly to the of the so-called memory effect" which Such sputtering pumps are at present very frequently employed, especially because they have two 'very important advantages over the pups which operate. by means of evaporation:

(1) The ionization of the gas molecules occurs a,

discharge and does not require a hot cathode which only lasts for a limited length of time and is oftenchanges merely when a chan'ge inlpressur ez occurs but is otherwisefixcdand cannot be This'tact hassalready been the art 'and' attempts have'thereforobeen made to-reduce the memcathode-rota very particuIartwo electrodes" number of already bound rare out T e- 0 sputtering electrodes-which are symmetrically to structure, while cathode and a. negative andtheauxiliary cathodes. Sincethe gas iousthcnimpinge upon an cathode .with a relatively'lowpncrg'y, um

memory eiicct-becomes less prevalent. y

- However, insofar-m rare gases are .co 'cerned, the ions ."and atoms which are taken up by the cathode are not the cause-of trouble. Such sputtering pumps can therefore alsobe employed for very long periods of time at higher pressures of, for example, 10- mm.'-Hg without any decrease in theirefiiciency.

.(2) Since the gas-discharge ctn'rent and thus also the '40 amount of titanium which is sputtcredwithin a certain unit ot-time is proportional to the pressure in-the pump.

- or in the apparatus which is connected thereto, the spot tering of the titanium adjusts itself automatically tothe amount of gas which is to be pumped ofiwithout requir-g ing any special electronic or mechanical means. However, certain; difliculties occur i trode it-is possibie to cover 'thc getter layet-Iwhich conitains rare gases fromtimeto time with athickerlsyer ot-" the more rapidly sputtered material and thusyto bury the uttering pumps if rare gases and also other gases which do not chemically Q combine with the gettermetal are .to be pumped ofi. when in the condition, the rare gases'are largely taken up by thcgetter material. On-the other hand, itis also possible to bind neutral rare gas atoms by a getter layer it such an amount of getter materialis constantly condensed so that the rare gas atoms will be buried thereby.

v In a sputtering pump, the rare gas ions .are taken up to the largest extent by the cathode. However, since the cathode is subjected-to a constant bombardment of ions, not only titanium is sputteredvbut the gases which have already been taken up by'the cathode are again freed. Therefore, at regular intervals ofa few undesirable pressure increases occur which are due-to'the fact that these gases are again liberated from the cathode. This is called the memory eiiect'lwhichpmeans that the pump "remembers" what it has once before pumped off. This memory efie'ct is of vcry minor importance to'the- -willbecomemore suiiicicntly retained-sinoe the rate of? of the titanium of the auxiliary eleetrodeis toolowandicannot be increased, arbitrarily. YAlthoughF the memory eifectfof this pump is reduced,- itstill the best possible vcauum whichmay as V I constancy thereof.

It isan object of le'astone electrode of a are, for example, silver and'coppcr. With an elecrare gas atoms tinally' so that the layer-will; 'no longer 'ahow amemory eflEect; v

' *The features; and advantages-of the invention from the following lcarly apparent embodiments thereof which detailed description of several is to be read with reference to the'aoeompanying in which:

FIGURES 1 to 3 diagrammatically pumps with two groups'of electrodes; p,

FIGURE 4 shows a sputte ump-with three groups 'j 'if eleetrodeszs hile FIGURE 5 shows a circuitadiag'rani tor operating vfr p ot the type as illustrated in FIGURE 2; a

The sputtering pump asillustiated in FIGURE 1 is contained a housingl which. is connected-by. a-

pipe socket 2 to the container which is to be evacuated- Of course, it possible to the pump's'ystem as illustrated as well'as other necessary parts directly 1 the container which is to be evacuatedin which chemically active gases which are primarily takenup and s occurrence of'rare gases, however, the eiiicicncy ofthe sputtering-pump decreases considerably as the result of its I memory etiect.

case the housing l'may be omitted.

At theinside of housing 1, the electrodes 4, 5,'aud 6 are mounted. I The electrodes-land '6 of-solid metal, while the electrode 5 has a honeycomb The electric lines. '1, 3, and 9 leading toztheseelectrodes are passed through .the wall of housing I by means-of vacuumtight, leadins 1 0, 11, and- 12, reaper tively. The magnetic field which is requiredfor the'opcr- .19 5422: r atam-a a by produin'n'g a high rate.

have

n p by the-setter r f ym n -o the w i condensed getter material, this is not possible in-a spu't-- he= re; y nmb g the cathode locatedjoutlside of I a the three mentioned electrodesand serves,' f,or'e'xample,- as an outer housing. These-auxiliary cathodes-are mounted opposite to theactual potential so that the part-oi the gas ions"which flows through the 'honeycombedauxili'arycathodes .is retarded. by the electric-field which prevails bctwecn'the cathodc'" the present invention to overcome this disadvantage by-employing-in a sputtering pump-at material which-is sputtered con-. siderablymore Such 3 l ation of the pump is produced by the magnet pole pieces plied. The conventional three-electrode pump consists 15 and 16. of an anode of a honeycomb structure, a pair of awe The central electrode 5 which is mounted opposite to iliary cathodes 25A, 258 also of a honeycomb structure the sputtering electrodes 4 and 6 is provided with a posiwhich consist of a getter material, for example, titanium, tive potential and therefore serves as the anode, while 5 and are mounted symmetrically to the anode 5, and a the two other electrodes 4 and 6 have a negative potenpair of mthodes 24A, 258 which are likewise mounted tial and therefore form the cathodes. One of the cathsymmetrically to the anode and are supplied with a higher odes, for example, the left cathode 4, consists of the electric potential than the auxiliary cathodes 25A, 25B. getter metal or is at least provided with a thick Cathodes 24A, 248 may also form the housing of the vention of a material, for example, silver, which is more side of the pump houa'ng, a pair of magnet pole pieces Insily sputtered than the getter material titanium. The and 16 are also provided similarly as shown in FIG- cathode 6 may, however, also consist of a different ma- URES l to 3. According to the invention, this three terial and only be provided with a thick coating of silver. 15 electrode pump is further provided with an additional The operation of the sputtering pump according to pair of electrodes 26A, 2613 which are likewise of a honey- FIGURE 1 isasfollows: comb structure and are molmted symmetricaly to the Due to the potential distribution and the magnetic field anode 5. In the particular embodiment of the invention which is provided, gas discharges occur, each of which as shown in FIGURE 4. these additional electrodes 26A, pames through one of the open cells of the honeycomb 26B are inserted between the anode 5 and the electrode 5. For this purpose, the getter electrode 4 is cathodes A, 248. These electrodes 26A, 26B consist given a higher negative potential than the electrode 6 of a material, for example, silver or copper which is which Consists of the easily sputtered material. As the more easily sputtered than the getter material of the auxresult of this, the ions impinge upon the getter electrode iliary electrodes 25A, 25B. 4 with a considerably greater energy than upon the elec- 25 The operation of the pump according to FIGURE 4 trode 6 and thereby sputter the getter material which is is as follows: ondensed in honeycomb cells of the electrode 5 and In the normal operation, the pair of electrodes 26A, on the inner walls of housing 1 and thereby reacts chem- 26B of the casily sputtered material is supplied with the ically with parts of the gases which are to be pumped same potentialastheanode5,whiletheauxiliarycathodcs off. Even rare gases are then at least partly buried. 30 25A, 25B are supplied with a lower potential than anode occur, the electrode 6 is supplied with the same or a the influence of the electric field between the a xiliary higher negative potential than the electrode 4. Highcathodes 25A, 25B and the anode 5, the ions which are energy ions then impinge upon the electrode 6 which is formed in the pump by the as discharge are accelerated acco dingly snowy sp er d The spu tered material in the direction toward the auxiliary cathodes 25A, 2513. then covers the previous getter layers and thereby also A part of these ions impinges at a high velocity upon the buries the tare-gas atoms which are contained in these auxiliary cathodes 25A, 25B and muses a sputtering of layers. These buried rare-gas atoms can therefore no the getter material which is deposited on the cathodes longeremergeandcauseamemoryefi'ect. Afteracer- 49 24A, 24B and onotherpartsofthepump Theother n kflgth of time which y b6 easily determincd y part of the ions flies through the honeycombed auxiliary ests, the original poten al a es are g in s pp i and cathodes 25A, 25B and after being retarded in the electric the pump is again operated in the normal manner. field between the auxiliary cathodes 25A, 25B and cath- FIGURE 2 illustrates a very simple and advantageous odes 24A, 243, these ions impinge at a reduced velodty modifiqtion of the apparatus according to FIGURE 1. 5 upon the cathodes 24A, 24B and are taken up by the get- In this apparatus, the getter el rode 4 nd he Othcr ter layers thereon. In order to eliminate the mentioned electrodeiareeachdividedintoatleasttwopartswhi h memory elfect which also occtns in this three-electrode Ir is, however, more ad antageous not to apply nega i e the electrodes 26A, 26B are sputtered. The getter layer, potentials of different values simul aneously to both pairs for example, of titanium which is already existing and is 0f elccimdcs 4 and i but to pp y a mgalivc Potential formed continuously is then at least interspersed with, oulycithertothepairofelectrodes4A4Bortothepair andatleastpartlycovered,bytheadditiouallysputtercd 6A, B. 'I'heetfcctatminedisthesameasiustdescribcd metal of the elcctl'odes26A, 268. The gaseswhich are since the mutated material is condensed at all points subtaken up in the getter layer are thereby prevented from stantially uniformly. again escaping from this layer and passing back into the FIGURE 3 illustrates a pump system with two normal pump. m r of es, in the p r of cathodes 20A. FIGURE 5 finally illustrates diacally the man- ZOB of getter material is mounted at the opposite sides 0 'ner of imtallation of an apparatus in which ahigh vacuum 'of the honeycombal anode 5. In addition to those elec is produced or maintained by means of a sputtering pump u'odesapairofauxiliaryelcctrodesmlzllisproaccordingtoFIGURELanditalsoshowsa' vided whichoansists of a more easily sputtered material circuit diagram for controlling the operation of this sputelcctrode 5 of the pump according to FIGURE 3 of an which may be evacuated by a conventional pump unit 37 easily sputtered material and to operate it as an auxthrough a vacuum line 35 and a tightly closin vacuum ilraryeb uode,whilethepairofelectrodes22A,22B valve. 'lhispartoftheapparatusisoperatedinthe FIGURE 4 shows the ele trode system of a vacuum the container 30 for example, to a vaurum of 10'' mm. putteringpumpofthetypewhichisknownasathree- Hg. 'lhereaftenvalveuisclmdandthevacumnisim electrode pump, in which the present invention is apcreased by meansofthesputtering pump, for example, to

the maximum value of 10- mm. Hg which is thereafter substantially maintained. For supervising the pressure, a very sensitive vacuum gauge 38, an ionization vacuum gauge, is connected to the vacuum line 35.

The anode is connected by the line 8 to the positive terminal of a high-tension generator 39 which supplies, for example, 5 kv. The negative terminal of the generator 39 is connected by the line 40 to a switch 41 which disconnects the pump when turned to the position 42. The position 43 of switch 41 is used for the normal opera tion in which a negative potential is supplied by the line 7 to the pair of getter electrodes 4A, 4B of titanium so that these electrodes are sputtered as cathodes. In the position 44 of the switch, the getter electrodes 4A, 4B are dead. The negative potential is then, however, supplied by the line 9 to the pair of electrodes 6A, 6B which consists of a metal, preferably silver, which is much more easily sputtered. This electrode material is then strongly sputtered and thereby buries the rare gas atoms which are contained in the getter layers of the electrodes 4A, 4B.

The selector switch 41 is actuated by the electric or magnetic drive mechanism 50 which, in turn, is controlled by a control unit 51. This control unit may be operated by hand by the handle 52, while in other cases, for example, when the handle 52 is in the position A, the control unit receives its control impulses from the vacuum gauge 38 and maintains the vacuum automatically.

The control unit 51 is for this purpose set to carry out a certain program:

At a very high vacuum of, for example, mm. Hg, switch 41 is turned to the position 42. When the vacuum decreases beyond the required operating pres sure of, for example, 10- mm. Hg, by minor amounts of, for example, 3x10- mm. Hg, the pump is started when the switch is changed to the position 43, and it is again switched oil when the pressure drops below the required operating pressure. If this is not attained when the pump has been normally operated for a greater length of time or if the pressure increases rather frequently and especially up to slightly higher pressures due to the mem ory etfect, the control unit moves the switch, for example, forSto lominutestothepositionflandthenreturnsit again to the position 43 for the normal pump operation.

The sputtering pump according to the invention is developed from the Penning-type pressure gauge. It may therefore also be employed for vacuum measuring, in which event the mrrent flowing through the pump is used for indicau'ng the existing vacuum. This very advantageous property of the conventional sputtering pump is therefore retained despite the various changes which are made therein in accordanm with the invention.

Although my invention has been illustrated and described with reference to the preferred embodiments thereofilwishtohaveitrmderstoodthatitisinnoway limited to the details of such embodiments, but is capable of numerous modifications within the scope of the apclaims.

Having thus fully disclosed my invention, what I claim is:

1. Asputteringpumpofthecharacterdescribedcom- 6 prising a housing, an anode of cellular honeycomb structure mounted within said housing, a normal cathode means of getter material and an auxiliary cathode means of more easily sputtered getter material symmetrically disposed on opposite sides of said anode, a pair of pole pieces by which a magnetic field is produced, means by which a positive electric potential is supplied to said anode and a negative electric potential is supplied to said normal and auxiliary cathodes, said normal cathode being supplied with a higher negative potential than said auxiliary cathode.

2. A sputtering pump as defined by claim 1 in which the getter material of said normal cathode means is titanium, and in which the getter material of said auxiliary cathode means is silver.

3. A sputtering pump of the character descnbed comprising a housing, an anode of cellular honeycomb structure mounted in said housing, a pair of normal cathodes of getter material which are symmetrically disposed on opposite sides of said anode, a pair of auxiliary cathodes of more easily sputtered getter material which are symmetricallydisposedonoppositesidesofsaidanode,apair of pole pieces by which a magnetic field is produced, means by which a positive electric potential is supplied to said anode and a negative electric potential to at least one pair of said cathodes.

4. A sputtering pump as defined by claim 3 in which said negative potential is supplied to said pair of auxiliary cathodes, and a higher negative potential is supplied to said pair of normal cathodes.

5. A sputtering pump as defined by claim 4 in which one of said pair of auxiliary cathodes is interposed between said anode and each of said normal cathodes.

6. A sputtering pump as defined by claim 5 in which said auxiliary cathodes are of cellular honeycomb structure.

7. Asputteringpumpasdefinedbyclaimfiinwhicha pair of electrodes of cellular honeycomb structure are provided, one of which is interposed between said anode and one of said auxiliary cathodes and the other of which is interposed between said anode and the other of said auxiliary cathodes, said electrodes having a negative electric potential supplied thereto.

8.Asputteringpumpasdefinedbyclaim7inwhich said auxiliary cathodes are formed of titanium and said electrodes are formed of silver.

9. A sputtering pump as defined by claim 3 in which a pair of electrodes of cellular honeycomb structure to which a negative electric potential is supplied are symmetrically disposed on opposite sides of said anode.

References Cled by the Examiner UNITED STATES PATENTS 2,988,657 6/61 Klopfer ct al.

IAURENCE V. EFNER, Primary Examiner.

WARREN E. COLEMAN, Examiner.

Claims (1)

1. A SPUTTERING PUMP OF THE CHARACTER DESCRIBED COMPRISING A HOUSING, AN ANODE OF CELLULAR HONEYCOMB STRUCTURE MOUNTED WITHIN SAID HOUSING, A NORMAL CATHODE MEANS OF GETTER MATERIAL AND AN AUXILIARY CATHODE MEANS OF MORE EASILY SPUTTERED GETTER MATERIAL SYMMETRICALLY DISPOSED ON OPPOSITE SIDES OF SAID ANODE, A PAIR OF POLE PIECES BY WHICH A MAGNETIC FIELD IS PRODUCED, MEANS BY WHICH A POSITIVE ELECTRIC POTENTIAL IS SUPPLIED TO SAID ANODE

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