Sintered non-porous cathode and sputter ion vacuum pump containing the same

Abstract

The present invention relates to cathodes electrodes compositions suitable to provide a pumping mechanism which exhibits an extremely high pumping speed and capacity of noble gas suitable to be used in several vacuum devices as for example sputter ion vacuum pumping systems comprising them as active element.

Claims

1. A cathode comprising: a molded sintered bulk mixture of a powder of a first metal M1; a powder of a second metal M2, which is different from M1; and optionally, a powder of one or more metallic elements, which are different from M1 and M2; wherein the powders M1, M2 and one or more metallic elements different from M1 and M2 are homogeneously distributed in the sintered bulk mixture, the molded sintered bulk mixture is nonporous, a content of the one or more metallic elements is less than 3 atonic %, based on a total number of atoms Q of the sintered bulk mixture, wherein M1 and M2 are each independently selected from a group consisting of titanium (Ti), tantalum (Ta), zirconium (Zr), niobium (Nb), hafnium (Hf), a rare earth metal, nickel (Ni), and molybdenum (Mo), and wherein M1 and M2 have a mean atomic mass W in a range of 80 to 160 amu according to the formula
W=W1*q1+W2*q2 wherein M1 has an atomic mass W1 in an amount q1 expressed as an atomic percent of the total number of atoms Q of the sintered bulk mixture and M2 has atomic mass W2 in an amount q2 expressed as an atomic percent of the total number of atoms Q.

2. The cathode of claim 1, wherein W is in a range of 100 to 160 amu.

3. The cathode of claim 2, wherein M1 and M2 are Ta and Ti respectively and a ratio of Ta/Ti is 50 parts Ta to 50 parts Ti.

4. The cathode of claim 2, wherein M1 and M2 are Ta and Zr respectively and a ratio of Ta/Zr is 35 parts Ta to 65 parts Zr.

5. A sputter-ion pump system comprising as active pumping elements at least two of the non-porous cathodes of claim 4.

6. The cathode of claim 2, wherein M1 and M2 are Ta and Zr respectively and a ratio of Ta/Zr is 50 parts Ta to 50 parts Zr.

7. A sputter-ion pump system comprising as active pumping elements at least two of the non-porous cathodes of claim 2.

8. The cathode of claim 1, wherein the one or more metallic elements, which are each different from M1 and M2, are each independently selected from the group consisting of aluminum, copper, titanium, tantalum, zirconium, niobium, molybdenum, nickel, a rare earth metal, hafnium, iron, cobalt, and vanadium.

9. A sputter-ion pump system comprising as active pumping elements at least two of the non-porous cathodes of claim 8.

10. The cathode of claim 1, wherein M1 and M2 are each independently selected from the group consisting of titanium, tantalum, and zirconium.

11. A sputter-ion pump system comprising as active pumping elements at least two of the non-porous cathodes of claim 10.

12. A sputter-ion pump system comprising as active pumping elements at least two of the non-porous cathodes of claim 1.

13. The cathode of claim 1, wherein M1 and M2 are Ta and Ti respectively and a ratio of Ta/Ti is 35 parts Ta to 65 parts Ti.

14. A sputter-ion pump system comprising as active pumping elements at least two of the non-porous cathodes of claim 13.

15. The cathode of claim 1, wherein M1 and M2 are Ta and Ti respectively and a ratio of Tall is 50 parts Ta to 50 parts Ti.

16. A sputter-ion pump system comprising as active pumping elements at least two of the non-porous cathodes of claim 15.

17. The cathode of claim 1, wherein M1 and M2 are Ta and Zr respectively and a ratio of Ta/Zr is 35 parts Ta to 65 parts Zr.

18. A sputter-ion pump system comprising as active pumping elements at least two of the non-porous cathodes of claim 17.

19. The cathode of claim 1, wherein M1 and M2 are Ta and Zr respectively and a ratio of Ta/Zr is 50 parts Ta to 50 parts Zr.

20. A sputter-ion pump system comprising as active pumping elements at least two of the non-porous cathodes of claim 19.

Description

(1) In order to better understand the invention and appreciate its advantages, a number of non-limiting examples of embodiment are described below with reference to the attached drawings in which:

(2) FIG. 1 shows a schematic layout of an experimental test-bench for the characterization of SIPs;

(3) FIG. 2 shows a schematic layout of the electrodes in a possible embodiment of the invention; and

(4) FIG. 3 is a cross section view of an assembled pump showing the electrodes in the possible embodiment of FIG. 2 therein.

(5) In accordance with a preferred embodiment, the present invention consists in a cathode having mean atomic mass W, said cathode being suitable to be used as electrode in a sputter ion pump and comprising in its chemical composition a sintered bulk mixture of at least two different metal elements M1 having atomic mass W1 in an amount q1 expressed as atomic percent of the total number of atoms Q of the cathode and M2 having atomic mass W2 in an amount q2 expressed as atomic percent of the total number of atoms Q of the cathode, wherein M1 and M2 are both selected among titanium (Ti), tantalum (Ta), zirconium (Zr), niobium (Nb), hafnium (Hf), rare earths, nickel (Ni) or molybdenum (Mo) and q1, q2, W1 and W2 are selected in such a way that the atomic mass of the cathode defined as W=W1*q1+W2*q2 is comprised in the range between 80 and 160 amu.

(6) In a preferred embodiment according to the present invention, the cathode has mean atomic mass W comprised in the range between 80 and 160 amu, preferably between 100 and 160 amu. Said mean atomic mass W is defined as the sum of the atomic masses W1 and W2 respectively of the metallic elemental components M1 and M2 in the cathode chemical composition, each one weighted in function of their atomic percent respect to the overall number of atoms Q of the cathode. In other words, said mean atomic mass of the cathode is defined by the formula W=W1*q1+W2*q2.

(7) According to the present invention the cathode consists in a bulk composite material made of two or more metal elements and at least two of them are selected in the list of titanium, tantalum, zirconium, niobium, hafnium, rare earths, nickel or molybdenum. More preferably said at least two metal elements are two selected among titanium, tantalum and zirconium.

(8) In some specific embodiments according to the present invention the two different metal elements M1 and M2 selected among titanium, tantalum, zirconium, niobium, hafnium, rare earths, nickel or molybdenum can be mixed with one or more additional metallic elements different from M1 and M2, not strictly limited to the previous claimed list of metallic elements, in a cumulative amount lower than the 3% (atomic percentage) of the sintered bulk cathode. This limited amount of additional metallic elements, even if they comprise elements having a high atomic mass, only slightly affects the mean atomic mass W of the cathode that can be still approximated to the sum W1*q1+W2*q2 considering only M1 and M2. In addition to titanium, tantalum, zirconium, niobium, hafnium, rare earths, nickel or molybdenum, said additional elements can be selected among copper, aluminum, iron, cobalt.

(9) Cathodes according to the present invention can be produced by Hot Uniaxial Pressure (HUP) sintering of powders. Alternative techniques suitable to be used to manufacture cathodes with the same advantages of the HUP process are Hot Isostatic Pressure (HIP) sintering and Metal Injection Moulding (MIM). The choice of the HUP, HIP or MIM techniques results in a new way of producing cathodes for SIPs, differently to other solutions proposed in the past. As a matter of fact, the HUP process allows to make couples of cathodes in which two different metals are homogeneously distributed, in contrast with the conventional noble-diode SIP layout, where a pure Ti cathode is opposed to a pure Ta one. If necessary, it also permits to increase the number of elements constituting each cathode, instead of using only two of them each time. Moreover, the atomic percentage of each element in the mixture to be sintered can be easily tuned in.

(10) HUP sintering process, for example, consists in the simultaneous application of uniaxial pressure and heat to a mould containing the metal powders to be sintered. Hot pressing allows to greatly reduce porosity and to obtain bulk density; furthermore, it results in better mechanical properties and in a more uniform microstructure compared to conventional press or sintering processes. Furthermore, the HUP technique is a good way to produce a mixture of different materials with bulk density without using alloys, which instead would result in new compounds with different physical and chemical properties. In order to obtain the sintered non-porous bulk cathodes according to the present invention can be applied temperature comprised between 800 and 1200 C., uniaxial pressure between 40 and 100 bar/cm.sup.2 for time lasting from 1 to 4 hours.

(11) Cathodes according to the present invention and suitable to be used in a sputter ion pump configuration can be sintered and shaped without particular limitations, in function of the requirements related to the design of the final device in which said cathodes have to be included.

(12) In a second aspect the present invention consist in a sputter-ion pump comprising the cathodes according to claim 1 as active pumping elements.

(13) The present invention will be further explained by the following non-limiting examples.

Example 1Cathodes According to the Present Invention

(14) Some Pairs of Cathodes (S1 to S4) according to the present invention have been produced by HUP process selecting processing temperature generally ranged between several hundreds of Celsius degrees, while the applied uniaxial pressure was of the order of several tens of bar.

(15) At the end of the HUP process, each cathode was grinded, if necessary, and carefully cleaned in an ultrasonic bath with an appropriate alkaline detergent (M-Aero-NS, Arm & Hammer). Afterwards, each pair of cathodes underwent an in-vacuo annealing thermal treatment, with the main aim of reducing the degassing rate of H.sub.2. Different combinations of temperature and time length of annealing have been tested.

(16) Table 1 resumes the tested configurations and the corresponding thermal treatments.

(17) TABLE-US-00001 TABLE 1 Mean atomic Sample Pair of Cathodes Temperature Time length mass [amu] S1 Ta.sub.35Ti.sub.65 800 C. 3 h 94.455 S2 Ta.sub.50Ti.sub.50 1100 C. 72 h 114.415 S3 Ta.sub.35Zr.sub.65 1100 C. 72 h 122.628 S4 Ta.sub.50Zr.sub.50 1100 C. 72 h 136.087

(18) In Table 1 the subscript number associated with each element of the pair show the atomic ratio of that pair. For example, in Sample 1 the ratio 35:65 shows the ratio of Tantalum to Titanium.

Example 2Cathodes not According to the Present Invention

(19) A first set of Cathodes not according to the present invention useful to give evidence of the technical effect are commercial electrodes (plate-shaped) made of only Titanium, only Zirconium or only Tantalum.

(20) A second set of sintered cathodes not according to the present invention have been produced by HUP process using powders of a single metal (C2) or a mixture of powders of Zirconium and Titanium having a mean atomic mass outside the claimed range (C4).

(21) Table 2 resumes the considered configurations and the corresponding thermal treatments when cathodes produced by HUP process have been used.

(22) In particular, a standard diode configuration with titanium commercial cathodes (C1) has been considered as well as the same configuration using cathodes made only in titanium by HUP process of powders (C2). Noble diode configurations have been considered pairing commercials cathodes of tantalum and titanium (C5).

(23) TABLE-US-00002 TABLE 2 Time Mean atomic Sample Pair of Cathodes Temperature length mass [amu] C1 TiTi (diode) n.a. n.a. 47.880 C2 TiTi (HUP) 600 C. 3 h 47.880 C3 TaZr (noble diode) n.a. n.a. 136.087 C4 Zr.sub.50Ti.sub.50 (HUP) 1100 C. 40 min 69.552 C5 TaTi (noble-diode) n.a. n.a. 114.415

Example 3Comparison of Noble Gas Sorption Performances

(24) An experimental test-bench having schematic layout of FIG. 1 has been used for the characterization of SIPs. The system is made of a main vacuum vessel 1, with a volume of 26.7 l, where a Pfeiffer Prisma Plus quadrupole mass spectrometer 2 for residual gas analyses and the SIP 3 under test are installed.

(25) The entire system is pumped by an Edwards XDS 10 scroll pump 4 connected in series to a Pfeiffer Vacuum HiPace 300 turbomolecular pump 5, which provides a nominal pumping speed of 260 l/s for N.sub.2. Gas leakage into the system is controlled by automatic valves built in-house 6, 6, 6. Two hot-cathode Bayard-Alpert gauges Granville-Phillips 360/370 Stabil-Ion 7, 7 are placed in proximity of the gas inlet 8 and in the main volume near SIP 3 and QMS 2, respectively. Their working pressure range is 10.sup.2 Torr to 10.sup.10 Torr.

(26) After every venting necessary for the installation of a new SIP to be characterized and prior to make whichever sorption test, the entire vacuum system is baked by means of an ad hoc oven. The injection line and the SIP to be tested, without magnets, are also baked. The adopted procedure includes a 10 h long bake-out at 180 C., which is sufficient to reach base pressures typically in the 10.sup.10-10.sup.9 Torr range.

(27) A schematic layout of the electrodes in the assembled pumps is shown in FIG. 2. It comprises an array of four identical cylindrical anodes 21, 21, 21, 21 made of stainless steel located between two cathode plates 22, 22: the dimensions of the stainless-steel vacuum envelope enclosing the electrodes are 606242 mm. The cross section view of the assembled pumps showing the electrodes embodiment of FIG. 2 therein is shown in FIG. 3. are connected to the vacuum system through a CF35 flange 23 and magnets are placed outside the vacuum envelope 24, in correspondence of the cathodes 22, 22.

(28) TABLE-US-00003 TABLE 3 Sample Cathodes Ar pumping speed l/s Ne pumping speed l/s S1 Ta.sub.35Ti.sub.65 0.91 0.71 S2 Ta.sub.50Ti.sub.50 1.00 0.78 S3 Ta.sub.35Zr.sub.65 1.20 0.87 S4 Ta.sub.50Zr.sub.50 1.14 0.89 C1 TiTi 0.29 0.37 C2 TiTi 0.18 0.25 C3 TaZr 0.94 0.80 C4 Zr.sub.50Ti.sub.50 0.56 0.55 C5 TaTi 0.72 0.71

(29) Experimental results showed in table 3 clearly show that all the samples according to present invention (S1 to S4) have performances higher than the corresponding pairs of cathodes in which each cathode is made of one of the two components of the HUP cathodes (S1 and S2 vs C5, S3 and S4 vs C3). (C1, C3), On the contrary, the use of HUP process with powders of only a single metal (C2) has shown to jeopardize the sorption performance if compared to the configuration with commercial cathodes of the same metal (C1).

(30) Samples according to the invention (S1 to S4) have shown a better performance respect to the use of HUP cathodes made with mixed powders of two metals and having mean atomic mass outside the claimed one (C4): the improvements obtained with the invention allow to achieve noble gas sorption performances comparable or superior to noble diode configuration (C5) but without requiring complex modifications of the structure of the pumping device, i.e. maintaining the simple structure of the diode sputter ion pump.