SPUTTERING CATHODE WITH MAGNETIC SHUNT

Abstract: A sputtering cathode with a target going around an axis and a number of permanent magnets arranged around the axis. The permanent magnets provide tunnel-forming and substantially radially directed magnetic fields adjacent the surface of the target to be sputtered. Also present is an electromagnet with a yoke having a first and a second pole for generating an axially directed magnetic field along the axis. The first pole is situated closer to the axis than the electromagnet and the second pole is situated further from the axis than the electromagnet. A magnetic shunt is arranged in axial direction between the electromagnet and the target and in radial direction between the axis and the second pole.

Description: Title: Sputtering cathode with magnetic shunt. The invention relates to a sputtering cathode with a target going around an axis, as well as with a number of permanent magnets arranged around the axis along at least one path closed in itself for generating at least one magnetic field going around the axis, tunnel-forming adjacent a surface of the target to be sputtered, and directed substantially radially, and with an electromagnet for generating a magnetic field going along the axis, directed substantially axially. Such a sputtering cathode is known from the German patent specification DE-C2-39 08 252. The sputtering cathode described therein has two magnetic fields going around the axis, tunnel-forming adjacent the surface of the target to be sputtered, and directed substantially radially. One magnetic field going around the axis and directed substantially radially, which is located closer to the axis than the other magnetic field going around the axis and directed substantially radially is further influenced by an electromagnet. The magnetic field that is generated by the electromagnet ensures that upon progressive sputtering of the target and groove formation thereby induced in the target, the magnetic field strength adjacent the surface of the target within a groove located closer to the axis remains substantially constant or in each case is held at a desired value depending on the depth of the groove. It has been found that it is difficult to cause the sputtering to take place uniformly across the width of the groove. The object of the invention is to provide an apparatus in which the magnetic field going around the axis and directed substantially radially can be influenced by the electromagnet in such a manner that considerable sputtering also takes place adjacent the edges of the groove. To that end, a sputtering cathode according to the invention is characterized in that a first permanent magnet arranged along a first path, closed in itself, having diametric dimensions greater than diametric dimensions of the target generates a substantially radially directed magnetic field and, viewed from the electromagnet, is located in axial direction beyond the side of the target facing the electromagnet, in that a magnetic yoke has a first pole, viewed in radial direction from the axis, located inside, and a second pole located outside the electromagnet, which poles are directed substantially axially, and in that a magnetic shunt is arranged at a location situated in axial direction between an end of the electromagnet proximal to the target and the target and in radial direction between the axis and the second pole. What has thus been achieved is that the increase of the magnetic field strength with increasing depth of the groove adjacent the bottom of the groove formed by the magnetic field going around the axis and directed substantially radially, is more limited than in the absence of the magnetic shunt, so that the sputtering of the target material adjacent the edges of the grooves is stronger than without magnetic shunt, so that a more uniformly distributed erosion of the target takes place. The invention will now be further elucidated with reference to the accompanying drawings, in which: Fig. 1 is a cross section of a first sputtering cathode according to the invention; Fig. 2 is an enlargement of a portion of Fig. 1; Fig. 3 is a view along the line A-A of Fig. 2; Fig. 4 is a cross section of the magnetic field without magnetic shunt; Fig. 5 is a cross section of the magnetic field with magnetic shunt; Fig. 6 is a cross section of a second sputtering cathode according to the invention. In Fig. 1 reference numeral 1 designates a sputtering cathode. The sputtering cathode 1 comprises a fixed portion 2 and a movable portion 3. The movable part 3 can be moved up and down in the direction of the arrow 4. On the movable part 3, a disc, such as a CD or a DVD, etc., 26 can be fixed, which is to be provided with material to be sputtered from a target 8. In a situation where the movable part 3 has been moved up, a sputtering chamber is formed, which is designated by 5, and bounded by a target 8 which constitutes a cathode, the disc 26 and anodes 27 and 28. In the exemplary embodiment, the fixed part 2 is of circular-symmetrical design around an axis 6. It is to be noted that for the present invention, the circular symmetry around the axis 6 is not of importance. Other shapes are also possible, such as square, rectangular, elliptical, etc. The term 'axis' 6 should therefore be interpreted broadly and can also refer to, for instance, a center plane in a square or rectangular shape of the fixed part 2. Even symmetry around the axis 6 is not requisite within the framework of the present invention. The term axis 6 therefore comprises a line 6 as represented in Fig. 1, or a flat plane or even a curved plane, which may or may not be closed in itself. Adjacent and around the axis 6, different elements and channels are represented which serve for the supply of, for instance, argon gas to the space 5, which elements have jointly been designated by the reference numeral 7. A rear side 28 of the target 8 is in contact with a first wall 10 of a cooling channel 9. The cooling channel 9 is further bounded by a second wall 11. The walls 10 and 11 are preferably made of material having a good thermal conductivity, such as copper. Arranged above the wall 11 is an annular permanent magnet 12. Here, too, it is to be noted that permanent magnet 12 has the general shape of the fixed part 2 and, as already discussed in relation to the axis 6, can have, for instance, a rectangular or square or different shape. In the following, Fig. 1 will be discussed as being the representation of a circular sputtering cathode 1 located around a linear axis 6. It is to be borne in mind here that notwithstanding the terminology based on a circular shape, such as, for instance, -annular, the other shapes mentioned are also understood to be encompassed by the term in question. Permanent magnet 12 has been magnetized, for instance, in the direction indicated with the arrow 29. Permanent magnet 12 is attached in a manner known per se to a ring 13a of magnetic material such as for instance soft iron. Ring 13a of magnetic material is mounted on a flat disc 13b, likewise of magnetic material. Disc 13b is mounted around axis 6 with the aid of an element 13c, likewise of magnetic material. In the space formed by the elements 13a, 13b and 13c, a coil of an electromagnet 24 is arranged. Viewed from the electromagnet 24, in axial direction beyond the side 28 of the target 8 facing the electromagnet 24, an annular permanent magnet 14 is situated. Annular permanent magnet 14 generates a radially directed magnetic field, designated by the arrow 30. If necessary, a ring 15 of magnetic material may be arranged to make the radially directed magnetic field of the permanent magnet 14 more homogeneous. A few field lines of the permanent magnet 14 have been designated by reference numeral 16. Also, with the reference numerals 21, 22 and 23, a few field lines have been indicated of the magnetic field generated by the permanent magnet 12 in combination with the electromagnet 24. At a location which is situated in axial direction between an end of the electromagnet 24 proximal to the target 8 and the target 8, and in radial direction between the axis 6 and the permanent magnet 12, a magnetic shunt 25 is arranged. Magnetic shunt 25 consists of a soft magnetic material, preferably, but not necessarily, soft iron. In Fig. 2, the position of the magnetic shunt 25 is represented in enlarged form. The wall 11 of the cooling channel 9 is provided with a recess 31. In the recess 31, the magnetic shunt 25 is arranged. For instance, the thickness of the magnetic shunt 25 is equal to the depth of the recess 31, but this is not requisite. In the exemplary embodiment according to Figs. 1 and 2, the magnetic shunt 25 is present in the form of a flat disc-shaped ring, of which a sector portion is shown in Fig. 3. In Fig. 3, further, with dotted lines, the reference numerals are linked to the electromagnet 24 and permanent magnet 12 situated, in Fig. 3, behind the wall 11. Adjacent the surface 34 of the target 8, the magnetic fields generated by the permanent magnets 14 and 12 as well as the electromagnet 24 form annular tunnels 32 and 33, known per se. With the apparatus 1 in operation, after some time, a groove is formed in the surface 34 of the target 8 adjacent the tunnels 32 and 33. The depth of the inner groove associated with tunnel 33 is schematically indicated with the respective reference numerals 18, 19 and 20 for different consecutive points in time. A comparable phenomenon occurs at the tunnel 32 and has not been further represented there for the sake of clarity. For obtaining a sufficiently fast, but also sufficiently uniform result of the sputtering on the disc 26, the field lines of the magnetic field in the tunnels 32 and 33 adjacent the surface of the target 8 should run substantially parallel to that surface and further should be directed radially with respect to the axis 6. The electromagnet 24 must provide for sufficient field strength of the magnetic field adjacent the surfaces 18, 19 and 20 as these are formed in the course of time associated with the tunnel 33. The disc-shaped ring 25 sucks, as it were, the magnetic field, designated by the field lines 17 (see also Figs. 4 and 5) towards itself, so that relevant field lines, designated by the reference numerals 21, 22 and 23, are created, representing a different magnetic field strength than if the magnetic shunt 25 had not absorbed the field lines located within the field line 23. As a result of the arrangement of the magnetic shunt 25, the change of the magnetic field strength with the increase of the depth of the groove is smaller than in the absence of the magnetic shunt 25. And as a result thereof, adjacent the edges of the groove more sputtering takes place than in the absence of the magnetic shunt 25. In the present exemplary embodiment according to Fig. 1, the magnetic -shunt 25 is arranged in the wall 11 of the cooling channel 9. It is noted that, viewed in axial direction, the best location of the magnetic shunt 25 is also determined by the locations of the permanent magnets 12 and 14, the thickness of the target 8, the maximum field strength that can be generated with a maximum current through the electromagnet 24, the radial dimensions of the fixed part 2, in particular of the target 8, etc. Depending on all those circumstances, the magnetic shunt 25 can also be arranged in a recess of the wall 10 of the cooling channel 9, in the interior of the wall 10, in the interior of the wall 11, on the side of the electromagnet 24 of the wall 11, with a greater or smaller distance to the axis 6. Fig. 6 represents a cross section of a sputtering cathode 1 in which the same elements as in Fig. 1 are indicated with the same reference numerals. The electromagnet 24 cooperates with a yoke 13, consisting of a ring 13a, a flat disc 13b and an element 13c, all of magnetic material such as, for instance, soft iron. The apparatus according to Fig. 6 differs from the apparatus according to Fig. 1 in that the permanent magnet 12 of the apparatus according to Fig. 1 is not arranged in the apparatus according to Fig. 6. For the rest, the apparatus according to Fig. 6 is identical to the apparatus according to Fig. 1. The absence of the permanent magnet 12 in the apparatus according to Fig. 6 has as a consequence that the magnetic field adjacent the surface of the target 8 to be sputtered is only generated by the permanent magnet 14 and the electromagnet 24 and that the magnetic field lines in the space 5 and the target 8 lead to the formation of one tunnel, instead of two, and hence to one groove from which sputtering proceeds. In this situation too, the presence of the magnetic shunt 25 leads, with increasing depth of the groove, to a smaller change of the magnetic field strength adjacent the bottom of the groove formed by the sputtering than in the absence of the magnetic shunt. After the foregoing, many modifications and embodiments of the invention-will readily occur to those skilled in the art. These are all understood to be part of the invention.

Claims: CLAIMS 1. A sputtering cathode with a target going around an axis, as well as with a number of permanent magnets arranged around the axis along at least one path closed in itself for generating at least one magnetic field going around the axis, tunnel-forming adjacent a surface of the target to be sputtered, and directed substantially radially, and with an electromagnet for generating a magnetic field going along the axis and directed substantially axially, characterized in that a first permanent magnet arranged along a first path, closed in itself, having diametric dimensions greater than diametric dimensions of the target generates a substantially radially directed magnetic field and, viewed from the electromagnet, is located in axial direction beyond the side of the target facing the electromagnet, that a magnetic yoke has a first pole, viewed in radial direction from the axis, located inside, and a second pole located outside the electromagnet, which poles are directed substantially axially, and that a magnetic shunt is arranged at a location situated in axial direction between an end of the electromagnet proximal to the target and the target and in radial direction between the axis and the second pole. 2. A sputtering cathode according to claim 1, characterized in that a cooling channel having a first and, opposite thereto, a second wall is present between the electromagnet and the target, that the first wall of the cooling channel is in contact with the target and that the magnetic shunt is arranged in one of the walls of the cooling channel. 3. A sputtering cathode according to claim 2, characterized in that the second wall of the cooling channel is provided with a recess running around the axis of the target and that the magnetic shunt is arranged in the recess. 4. A sputtering cathode according to claim 2 or 3, characterized in that the magnetic shunt is arranged in the second wall. 5. A sputtering cathode according to any one of the preceding claims, characterized in that the magnetic shunt is arranged in the form of a disc-shaped ring going around the axis of the target. 6. A sputtering cathode according to any one of the preceding claims, characterized in that the magnetic shunt is made of soft iron. 7. A sputtering cathode according to any one of the preceding claims, characterized in that two magnetic fields going around the axis, tunnel- forming adjacent the surface of the target to be sputtered, and directed substantially radially, are present, while one magnetic field going around the axis and directed substantially radially is situated closer to the axis than the other magnetic field going around the axis and directed substantially radially, that a second permanent magnet arranged along a second path, closed in itself, having diametric dimensions smaller than diametric dimensions of the target generates a substantially axially directed magnetic field and is situated on the same side of the target as the electromagnet. 8. A sputtering cathode according to claim 7, characterized in that the second permanent magnet is arranged on the second pole.

Inventors: LANDSBERGEN JEROEN FRANCISCUS, VYSKOCIL JIRI, LANDSBERGEN, JEROEN, FRANCISCUS, MARIA, VYSKOCIL, JIRI
Applicants: LANDSBERGEN JEROEN FRANCISCUS, OTB GROUP BV, VYSKOCIL JIRI, LANDSBERGEN, JEROEN, FRANCISCUS, MARIA, OTB GROUP B.V., VYSKOCIL, JIRI
Application year: 2001
Main classification: H01J37
IPC codes: H01J37