Method of sputtering and sputter system

Abstract

So as to control the operation of a sputter target during the lifetime of the target and under HIPIMS operation, part of a magnet arrangement associated to the target is retracted from the target whereas a second part II of the magnet arrangement is, if at all, retracted less from the addressed backside during the lifetime of the target. Thereby, part I is closer to the periphery of target than part II, as both are eccentrically rotated about a rotational axis.

Claims

1. A method of sputtering for coating substrates comprising providing a target with a sputtering surface and with a back surface providing along said back surface a magnet arrangement pivoting or rotating said magnet arrangement about a rotational axis which is perpendicular to said back surface wherein said magnet arrangement comprises magnet poles arranged along a pair of closed loops including an outer closed loop and an inner closed loop, the outer closed loop completely surrounding the inner closed loop and being distant from said inner closed loop, the magnet poles facing said back surface and arranged along one of said closed loops of said pair having opposite magnet polarity with respect to the magnet poles facing said back surface and arranged along the other of said closed loops of said pair, wherein said pair of closed loops is subdivided in a first part and in a second part, said outer closed loop of said pair thereby being subdivided in a first outer section in said first part and in a second outer section in said second part and said inner closed loop of said pair being thereby subdivided in a first inner section in said first part and in a second inner section in said second part, said first outer section being more distant from said rotational axis than said second outer section, both considered in radial direction with respect to said rotational axis, said method comprising controllably increasing distances of a majority of magnet poles along at least one of said outer and of said inner first sections to said back surface more than increasing distances to said back surface of a majority of magnet poles of said outer and of said inner second sections, as operation time of said target increases, controlling current pulse peak values supplied by the operation of the target, and performing said controllably increasing said distances of said majority of magnet poles along at least one of said outer and of said inner first sections so as to maintain substantially constant peak current pulse values of said operation over a lifetime of said target.

2. The method of claim 1, wherein said magnet arrangement comprises a single pair of said closed loops.

3. The method of claim 1, wherein said distances to said back surface of said majority of magnet poles of said outer and of said inner second sections are increased by an equal movement considered in direction from said back surface and parallel to said rotational axis.

4. The method of claim 1, wherein said distances to the back surface of said majority of magnet poles of said outer and of said inner second sections are kept constant during operation time of said target.

5. The method of claim 1, wherein the distances of said majority of magnet poles of said outer and of said inner second sections are equal during said operation time of said target.

6. The method of claim 1, wherein controllably increasing said distances of said majority of magnet poles along at least one of said outer and of said inner first sections to the back surface is performed upon magnet poles along said outer and along said inner first sections.

7. The method of claim 1, wherein the distances of said majority of magnet poles along at least one of said outer and of said inner first sections are equally increased.

8. The method of claim 1, wherein said distances to said back surface of said majority of magnet poles of said at least one of said outer and of said inner first sections are increased by an equal movement considered in direction from said back surface and parallel to said rotational axis.

9. The method of claim 1, wherein said distances to said back surface of said majority of magnet poles of said at least one of said outer and of said inner first sections are equal during operation time of said target.

10. The method of claim 1, wherein said distances of magnet poles along said outer and inner first sections are equal during operation time and wherein distances from magnet poles along said outer and said inner second sections are equal as well during operation time of said target.

11. The method of claim 1, wherein an average distance from said rotational axis of magnet poles along said first outer section is larger than an average distance from said rotational axis of magnet poles along said second outer section.

12. The method of claim 1, comprising controllably increasing distances of all magnet poles along at least one of said outer and of said inner first sections to said back surface.

13. The method of claim 1, comprising controllably increasing said distances of said magnet poles along said outer as well as along said inner first sections to the back surface.

14. The method of claim 1, wherein a first locus along said outer first section defines for a maximum distance R.sub.max from said rotational axis and wherein a second locus along the outer second section defines for a minimum distance R.sub.min from said rotational axis and wherein said first part is limited on one side of said first locus by a first limit locus which has a distance R.sub.e1 from said rotation axis which is not less than
R.sub.e1 =(R.sub.max +R.sub.min)/2 and wherein said first part is limited on the other side of said first locus by a second limit locus with a distance R.sub.e2 from said rotation axis which is not less than
R.sub.e2 =(R.sub.max +R.sub.min)/2.

15. The method of claim 1, wherein controllably increasing said distances of said majority of magnet poles along said at least one of said outer and of said inner first sections to the back surface is performed at least one of stepwise and of steadily during said operation time of said target.

16. The method of claim 1, wherein controllably increasing said distances of said majority of magnet poles along at least one of said outer and of said inner first sections is performed in dependency of erosion depth of said sputtering surface adjacent to the periphery of said target.

17. The method of claim 1, wherein controllably increasing said distances of said majority of magnet poles along at least one of said outer and of said inner first sections is controlled by a distance versus time characteristic.

18. The method of claim 1, wherein said magnet poles are magnet poles of magnets arranged with their dipole directions parallel to said rotational axis.

19. The method of claim 1, wherein said controlling current pulse peak values supplied by the operation of the target comprises adjusting voltage, gas pressure, and pulse repetition rate.

20. The method of claim 1, wherein the target comprises ferromagnetic material.

21. The method of claim 1, wherein the voltage is kept constant during the target life.

22. A sputtering system comprising a target arrangement with a sputtering surface and a back surface a magnet arrangement along said back surface a pivoting or rotating drive operationally connected to said magnet arrangement to pivot or rotate said magnet arrangement about a rotational axis perpendicular to said back surface said magnet arrangement comprising magnet poles arranged along a pair of closed loops including an outer closed loop and an inner closed loop, the outer closed loop completely surrounding the inner closed loop and being distant from said inner closed loop the magnet poles facing said back surface and arranged along one of said closed loops of said pair having opposite magnet polarity with respect to the magnet poles facing said back surface and arranged along the other of said closed loops of said pair wherein said magnet arrangement is subdivided in a first part and in a second part, said outer closed loop of said pair thereby being subdivided in a first outer section on said first part and in a second outer section on said second part, and said inner closed loop of said pair being thereby subdivided in a first inner section on said first part and in a second inner section on said second part said first outer section being more distant from said rotational axis than said second outer section, both considered in radial direction with respect to said rotational axis a displacement drive operationally interconnected between said first part and said second part a supply generator operationally connected to said target a displacement control unit operationally connected to said supply generator and to said displacement drive and adapted to control said displacement drive in dependency of operation of said supply generator upon said target so as to move said first part more from said back surface of said target than said second part is moved from said back surface, wherein the system is configured to control current pulse peak values supplied by the operation of said supply generator upon the target by the displacement control unit being configured to control the displacement drive to controllably increasing distances of a majority of magnet poles along at least one of said outer and of said inner first sections so as to maintain substantially constant peak current pulse values of said operation over a lifetime of said target.

23. The sputtering system of claim 22, wherein said pivoting or rotating drive and said displacement drive are both stationarily mounted with respect to said target arrangement.

24. The method of claim 16, wherein controllably increasing said distances of said majority of magnet poles along at least one of said outer and of said inner first sections is selected approximately equal to the erosion depth of said sputtering surface adjacent said periphery of said target.

Description

(1) The invention will now be further exemplified with the help of figures.

(2) The figures show:

(3) FIG. 1: the current rise as a function of applied target voltage for HIPIMS sputter coating and with 100 sec pulses;

(4) FIG. 2: the evolution of current pulses for a HIPIMS sputter coating process with 100 sec pulse length over target life and at constant distance between target backside and magnet arrangement, whereby the pulse voltage is kept constant and the peak current value reaches arc detection limit of approx. 950 A close to target life end;

(5) FIG. 3: a top view on a magnet arrangement as may be exploited for practicing the present invention;

(6) FIG. 4a: most schematically the initial position of the magnet arrangement according to the present invention with respect to the backside of a HIPIMS sputter target;

(7) FIG. 4b: departing from the representation according to FIG. 4a, the positioning of the magnet arrangement according to the present invention as established as a function of increasing operating time of HIPIMS upon the target and further schematically showing the driving and controlling members by means of schematical and simplified functional block/signal flow representation;

(8) FIG. 5: in a simplified cross-sectional representation, a today practiced drive arrangement for the magnet arrangement and according to the present invention;

(9) FIG. 6: over target life of HIPIMS sputter operation, the voltage and current pulses of HIPIMS at 100 s pulsating, as inventively achieved.

(10) A target arrangement as may be exploited in the frame of the present invention, i.e. for properly controlling pulse current peak values of HIPIMS operation, is shown in FIG. 3 in top view. The magnet arrangement comprises magnet poles which are arranged along a pair 1 of closed loops, namely of an outer loop 1.sub.o and an inner loop 1.sub.i. The outer loop 1.sub.o, in fact as a geometric locus, completely surrounds the inner loop 1.sub.i, in fact a geometric locus as well. The two loops of the pair 1 are mutually distant.

(11) The magnet poles which, as will be apparent from the following description, face the backside of a target arrangement and which are arranged along one of the closed loops, let's say loop 1.sub.o of the pair 1, have opposite magnet polarity, as an example S, with respect to the polarity -N- of the magnet poles facing the addressed backside and arranged along the other closed loop, let's say 1.sub.i, of the pair 1.

(12) As schematically shown in FIG. 3 the addressed poles are arranged along the addressed loop 1.sub.i, 1.sub.o in such a way that the respective poles in fact form a continuous pole surface, but may also be mutually separated or spaced, considered along respective loops.

(13) As schematically shown in FIG. 3 the pair 1 of closed loops 1.sub.o and 1.sub.i is subdivided in a first part I and in a second part II as by an annular gap 3. The entire magnet arrangement is further rotatably or pivotably mounted about a rotational axis A, perpendicular to the plane of FIG. 3 and is (not shown in FIG. 3) operationally coupled to a pivoting or rotational drive.

(14) By subdividing the pair 1 of loops 1.sub.o and l.sub.i into two parts I,II the outer loop 1.sub.o is subdivided in a first outer section 1.sub.oI which resides on the first part I and in a second outer section 1.sub.oII which resides on the second part II. In analogy the inner closed loop 1.sub.i is thereby subdivided in a first inner section 1.sub.iI residing on the first part I and in a second inner section 1.sub.iII residing on the second part II.

(15) Each magnet pole or each locus along the first outer section 1.sub.oI as well as along the second outer section 1.sub.oII defines with respect to rotational axis A or is radially distant from rotation axis A, by a distance R. The average of this distance R all along the first outer section 1.sub.oI is larger than the average of that distance R along the second outer section 1.sub.oII. Thus, in fact the outer loop 1.sub.o is eccentric with respect to rotational axis A and so is the overall pair of closed loops 1.

(16) Further, the first outer section 1.sub.oI defines a first locus L.sub.max where R is maximum, R.sub.max.

(17) On the other hand one second locus L.sub.min along the second outer section 1.sub.oII defines for a minimum R, R.sub.min. The delimitation of the first part I from the second part II of the pair 1 of closed loops is selected as follows: On one side of the first locus L.sub.max the first outer section 1.sub.oI propagates up to an end locus Le.sub.1 having a distance R.sub.e1 from the rotational axis A which is not less than
R.sub.e1=(R.sub.max+R.sub.min)/2.

(18) Thus, according to FIG. 3 the left-hand limit L.sub.e1 of part I is at most there, where the addressed relation prevails, but the L.sub.e1 may be closer towards L.sub.max.

(19) The other side limit L.sub.e2 from the first locus L.sub.max is there, where, propagating e.g. to the right-hand and departing from locus L.sub.max, the first outer section 1.sub.oI has a distance R.sub.e2 from the rotational axis A, which is not less than
R.sub.e2=(R.sub.max+R.sub.min)/2.

(20) Here too, the addressed limit is the maximum limit for the right-hand extent of the first outer section 1.sub.oI with respect to the locus L.sub.max. As may be seen from FIG. 3 the right-hand limit locus L.sub.e2 is realized or exploited by the exemplary magnet arrangement, whereas the left-hand limit locus L.sub.e1 is not exploited as the left-hand limit of the first outer section 1.sub.oI is closer to the first locus L.sub.max.

(21) By separating the pair 1 of closed loops 1.sub.o and 1.sub.i in two parts I and II following the addressed limits the magnet arrangement becomes highly suited to perform, in the frame of the present invention, pulse current peak control of HIPIMS operation of the target associated with the addressed magnet arrangement.

(22) Most schematically, FIG. 4a and FIG. 4b show respective cross sections through a target arrangement with associated magnet arrangement as e.g. exemplified with the help of FIG. 3. FIG. 4a shows relative positioning of the magnet arrangement and target backside 7, when the target is new, i.e. not yet sputter eroded, whereas FIG. 4b shows the target eroded by HIPIMS sputter operation and the respective qualitative positioning of the magnet arrangement to cope with the rising current pulse values according to the present invention. Those parts in FIGS. 4a and 4b which accord with the magnet arrangement parts as were presented with the help of FIG. 3 are addressed in FIG. 4 by the same reference numbers.

(23) As may be seen from the FIGS. 4 the magnets 5 which provide for the magnet poles N and S respectively according to FIG. 3 and arranged along the respective closed loops and facing backside 7 of the target arrangement 9 with a sputtering surface 11, are arranged, in a good embodiment, with dipole axes D perpendicular to the backside 7 of target arrangement 9.

(24) When the target 9 is uneroded, i.e. new with a substantially plane sputtering surface 11, part I of the magnet arrangement as was exemplified with the help of FIG. 3, assumes an initial distance d.sub.oI from the backside 7 of the target arrangement 9. The second part II as well assumes an initial distance d.sub.oII from the addressed backside 7 of the target arrangement 9. d.sub.oI is, in a good embodiment, equal to .sub.doll, which nevertheless is not mandatory. As consumption of the target arrangement 9 proceeds and erosion E (see FIG. 4b) increases, part I of the magnet arrangement is retracted from the backside 7 of the target arrangement 9 as denoted in FIG. 4b by d.sub.tI. Thereby, the distance of part II with respect to the backside 7 of the target arrangement 9 may be kept constant, thus at a value of d.sub.oII or may be increased as well (not shown in FIG. 4), but in any case the increase of distance d.sub.tI is larger than the increase of the distance d.sub.tII of part II from the addressed backside 7. Please note that both parts I and II as schematically shown in the FIGS. 4 are in combination rotated about rotational axis A or are pivoted thereabout as schematically addressed by the arrow in FIG. 4b. The representations in FIG. 4a and FIG. 4b are taken at the same angular position of the magnet arrangement with respect to rotational axis A.

(25) In FIG. 4b there is further shown a HIPIMS pulse generator unit 13 which, as schematically shown by line 15, operates the target arrangement 9. As further schematically shown by an output line 17 of HIPIMS pulse generator unit 13 the operation time of target arrangement 9 under HIPIMS operational condition is sensed and registered. A control unit 19 controls a drive 21 operationally connected between the two parts I and II of the magnet arrangement so as to controllably increase the distance d.sub.tI with respect to part II in dependency of the overall HIPIMS operating time of target arrangement 9.

(26) The characteristic of d.sub.tI increase in dependency HIPIMS operating time of target arrangement 9 is in a good embodiment predetermined by experiments and stored in control unit 19. The drive 23 in FIG. 4b addresses the rotational drive for the overall magnet arrangement with parts I and II.

(27) FIG. 5 shows, as an example, a good design of a magnet arrangement drive system so as to control especially the distance d.sub.tI of part I of the magnet arrangement as was exemplified with the help of the FIGS. 3 and 4. A carrier II for part II of the magnet arrangement is connected to the rotational drive 23 according to drive 23 as schematically shown in FIG. 4b. The drive 23, an electric motor, is drivingly connected by a belt 25 to a hollow shaft 27, which is connected by a member 29 to the carrier II.

(28) A carrier I for the part I of the magnet arrangement as was exemplified with the help of the FIGS. 3 and 4 is carried by three spindles 31 upon carrier II. The three spindles 31 are provided with a 120 angular spacing about rotational axis A.

(29) To each of the spindles 31 a gear wheel 33 is mounted.

(30) There is further provided a lift drive 35 in analogy to drive 21, as schematically shown in FIG. 4b e.g. an electric motor. The drive 35 as well as drive 23 are firmly mounted to a stationary frame part 37.

(31) An axle 41 coaxial to rotational axis A is rotationally driven by drive 35 and is provided at its end, pointing towards carrier II with a gear wheel or pinion 43. The pinion 43 meshes with the gear wheels 33. When the carrier I is operated at a constant distance d.sub.tI from the backside 7 of the target arrangement 9 as of FIG. 4a, then the pinion 43 is driven by drive 35 with the same angular velocity as carrier II is driven about rotational axis A by means of drive 23 via belt 25 and hollow shaft 27.

(32) To adjust the distance d.sub.tI of the carrier I and thus of the part I of the magnet arrangement, the pinion 43 is run at a different angular velocity, at a higher one or lower one, which ever direction of movement of carrier I with respect to carrier II with the respective parts of the magnet arrangement, is desired. Associated e.g. with carrier I, e.g. mounted on a jacket 45, there is provided a reflector plate (not shown) so as to monitor the axial position of carrier I by a distance sensor (not shown), e.g. by a laser triangulation sensor.

(33) As noted above the addressed drive system as exemplified by FIG. 5 comprises the two drives for rotational movement about axis A, drive 23 as well as for displacement of carrier I with respect to carrier II, drive 35, whereby both drives are stationary with respect to a frame 37 and thus to the target with the advantage that the electric connections to the addressed drives are stationary.

(34) It is important to avoid any blocking of the four gear wheels 33,43. Thereby, one must consider the rather heavy weight of the magnets of the magnet arrangement residing on the carriers I and II' in view of the eccentricity of the overall magnet arrangement with respect to rotational axis A. The two main reasons for such blocking are: 1. Tilt momentum forces between the magnet loaded carrier I and the housing or frame of the drive system as with respect to frame part 37 or between the two carriers I and II. 2. Sticking forces due to the carrier I running into a stop, defining for a reference distance as of d.sub.oI of FIG. 4a as a reference initialization position of carrier I. Any sticking may require disassembling of the HIPIMS sputtering source and of the magnet drive system as exemplified in FIG. 5. Therefore, the spindles 31, e.g. three of them, are realized by means of ball screw spindles, which as known, provide for low friction, stick-slip-free running and very good repetition accuracy for precise positioning.

(35) The procedure to implement the axial movement characteristic over time of carrier I as of FIG. 5 and thus of part I of the magnet arrangement over HIPIMS target operation time T and thus over target lifetime may be established as follows: 1. Connect a target current sensor, e.g. an oscilloscope, to the power line as of line 15 of FIG. 4b, from the HIPIMS generator unit 13 to the target arrangement 9. 2. Start sputtering with a new target arranged. 3. Adjust the process parameters (voltage, gas pressure, pulse repetition rate) to achieve a desired target current pulse peak value. 4. Run several kWhs sputtering from the target. 5. Measure the current pulse peak values. If these values differ from the value measured in step 3, then apply axial drive so as to increase the distance d.sub.tI of part I of the magnet arrangement (carrier I) so as to re-adjust the current pulse peak value to the set-point (step 3). 6. Repeat this procedure described in step 5 throughout the target life and store the dependency of part I axial position in dependency of running time of HIPIMS target operation, resulting in a control characteristic as exemplified in control unit 19 of FIG. 4b. As a rule of first approximation part I of the magnet arrangement and thus carrier I is to be displaced in axial direction and departing from an initial position by about the same amount as erosion E proceeds adjacent the periphery of the target arrangement 9.

(36) There results over target life of HIPIMS sputter operation a uniform, at least substantially constant current pulse peak value as exemplified in FIG. 6.

(37) By means of the examples as described we have shown an embodiment of the invention as today practiced. Nevertheless, the following is to be considered:

(38) As shown especially in FIG. 4b we have considered that the outer first section 1.sub.oI of the magnet arrangement as well as the inner first section 1.sub.iI are displaced, in axial direction as indicated by d.sub.tI equally and further that the addressed sections have always equal distances to the backside 7 of the target arrangement 9. This may not be mandatory.

(39) Alternatively, the addressed sections may be displaced unequally with respect to the back surface 7 of the target arrangement 9 during HIPIMS operation time , which on one hand would weaken the effect of such displacement and on the other hand would shift the apex of the magnetic field M upon the sputtering surface of target arrangement 9.

(40) Further, the two sections may have an initial distance from the backside 7 of the target arrangement which are different, thereby being further displaced by equal or by different amounts.

(41) Still further, it may be advantageous to displace only a predominant number of magnet poles of section 1.sub.oI and/or of section 1.sub.iI, thereby maintaining the respective distances of the minor number of the addressed poles with respect to the backside of the target arrangement 9 constant or more generically different from the respective distances of the predominant number of the addressed magnet poles. This may be realized e.g. to take in account the varying distances of the magnet poles along the addressed sections from the periphery of the target arrangement 9. Thus, in one area e.g. of the first outer section 1.sub.oI closer to the periphery of the target arrangement all respective magnet poles may be displaced from the backside 7 of target arrangement 9, whereas some few of the magnet poles in areas of the addressed section more distant from the periphery of the target arrangement 9 may be displaced during HIPIMS operation time of the target arrangement 9 by less than the addressed predominant number.

(42) With an eye on part II of the magnet arrangement the examples which have been described show the carrier II and thus part II of the magnet arrangement being axially stationary during HIPIMS operation time of the target arrangement 9. This may not be mandatory.

(43) All or at least a part of the magnet poles upon carrier II may be displaced too from the backside 7 of target arrangement 9 during HIPIMS operation time of the target arrangement 9, but, in any case, less than at least the predominant number of magnet poles along the section 1.sub.oI and/or 1.sub.iI are retracted during the addressed lifetime of the target.

(44) Further, the magnet poles along the second outer section 1.sub.oII and/or along the second inner section 1.sub.iII may have, as described in the example, equal distances with respect to the backside 7 of target arrangement 9 irrespective whether displaced or not displaced during the HIPIMS operation time of the target arrangement 9. A minor number of the addressed magnet poles of part II of the magnet arrangement may be displaced differently from the backside 7 of target arrangement 9 than the predominant number of the addressed poles along the section 1.sub.oII and/or section 1.sub.iII. Within the frame of the invention it is generically essential that the predominant part of magnet poles arranged along the first outer and/or first inner sections 1.sub.oI, 1.sub.iI, are moved by larger amounts from the backside of the target arrangement 9 than at least a predominant number of magnet poles along the second outer section and/or the second inner section 1.sub.iII, 1.sub.oII are moved or displaced from the backside of the target arrangement 9 during HIPIMS operation time of the target arrangement 9, and thus during lifetime of such target.

(45) By the present invention it is achieved that current pulse peak values supplied by HIPIMS operation of the target may be properly controlled during lifetime of the target considered and may especially be controlled to be substantially constant over the addressed lifetime.

OVERVIEW MAGNET ARRANGEMENT-REFERENCES

(46) Part I

(47) Part II

(48) Carrier I

(49) Carrier II

(50) First outer section 1.sub.oI

(51) Second outer section 1.sub.oII

(52) First inner section 1.sub.iI

(53) Second inner section 1.sub.iII

(54) Outer closed loop 1.sub.o

(55) Inner closed loop 1.sub.i

(56) Pair of loops 1