Arc source with confined magnetic field

1. An ARC evaporator comprising:

a cathode assembly comprising a cooling plate, a target as cathode element, the target having a thickness in a cross direction, a front surface disposed to be evaporated, and a back surface, the front surface being parallel to the back surface, the front surface and the back surface being separated from each other by a thickness of the target, the cathode assembly having a total height in a transversal direction and borders delimiting a total amplitude in any longitudinal direction,

an electrode arranged for enabling an arc to be established between the electrode and the front surface of the target for causing evaporation of at least part of the front surface of the target, and

a magnetic guidance system placed in front of the back surface of the target comprising means for generating one or more magnetic fields resulting in a total magnetic field comprising magnetic field lines which extend through a cross section of the target and along a space in front of the front surface of the target for guiding a cathode spot that results from contact of an arc to the target, when the arc is established between the electrode and the front surface of the target,

wherein the borders of the cathode assembly comprise a surrounding shield made of ferromagnetic material, wherein the surrounding shield has a total height in the transversal direction, said total height including a component (C) measured in the transversal direction from the cooling plate to an end of the surrounding shield, wherein the end of the surrounding shield exceeds the cooling plate in the transversal direction, wherein the component (C) causes a shielding effect of magnetic field lines extending in any of the longitudinal directions, establishing in this manner the borders of the cathode assembly as a limit of the extension of the magnetic field lines in any longitudinal direction, and wherein the cathode assembly has a symmetrical construction comprising a disc-shaped target with a target diameter (D 1 ) and the cathode assembly has a total diameter (D), wherein the target diameter is in the following range: 100 mm≤D 1 ≤150 mm and the total diameter of the cathode assembly is in the following range: 150 mm≤D≤200 mm, and the component (C) has a value in the following range: D/20≤C≤D/5.

2. An ARC evaporator according to claim 1 , wherein the ferromagnetic material is pure iron or ARMCO pure iron or construction steel or martensitic chromium steel.

3. An ARC evaporator according to claim 2 , wherein the ferromagnetic material is construction steel S355J2.

4. An ARC evaporator according to claim 1 , wherein the magnetic guidance system in the ARC evaporator comprises means placed in a central region for generating at least one magnetic field and means in a peripherical region for generating at least one further magnetic field, wherein the magnetic fields generated in this manner result in a total magnetic field for guiding the arc and controlling the cathode spot path at the front surface of the target.

5. An ARC evaporator according to claim 4 , wherein the means placed in the central region comprises one electromagnetic coil for generating a magnetic field and the means placed in the peripherical region comprises two electromagnetic coils for generating two further magnetic fields.

6. An ARC evaporator according to claim 4 , wherein the means for generating the magnetic fields comprises permanent magnets and only one electromagnetic coil to be used as a control coil for producing variations of the magnetic field characteristics.

7. An ARC evaporator according to claim 1 , wherein the magnetic guidance system comprises ferromagnetic material disposed surrounding the means for generation of the magnetic field, wherein the ferromagnetic material is distributed encircling the means with no ferromagnetic material placed between the magnetic guidance system and the cathode assembly.

8. An ARC evaporator comprising:

a cathode assembly comprising a cooling plate, a target as cathode element, the target having a thickness in a cross direction, a front surface disposed to be evaporated, and a back surface, the front surface being parallel to the back surface, the front surface and the back surface being separated from each other by a thickness of the target, the cathode assembly having a total height in a transversal direction and borders delimiting a total amplitude in any longitudinal direction,

an electrode arranged for enabling an arc to be established between the electrode and the front surface of the target for causing evaporation of at least part of the front surface of the target, and

a magnetic guidance system placed in front of the back surface of the target comprising means for generating one or more magnetic fields resulting in a total magnetic field comprising magnetic field lines which extend through a cross section of the target and along a space in front of the front surface of the target for guiding a cathode spot that results from contact of an arc to the target, when the arc is established between the electrode and the front surface 1 A of the target, wherein the magnetic guidance system comprises means placed in a central region comprising one electromagnetic coil for generating a magnetic field and means in a peripheral region comprising two electromagnetic coils for generating two further magnetic fields, wherein the magnetic fields generated in this manner result in a total magnetic field for guiding the arc and controlling the cathode spot path at the front surface of the target,

wherein the borders of the cathode assembly comprise a surrounding shield made of ferromagnetic material, wherein the surrounding shield has a total height in the transversal direction, said total height including a component (C) for causing a shielding effect of magnetic field lines extending in any of the longitudinal directions, establishing in this manner the borders of the cathode assembly as a limit of the extension of the magnetic field lines in any longitudinal direction, and

wherein the magnetic guidance system comprises ferromagnetic material disposed surrounding the means for generation of the magnetic field, wherein the ferromagnetic material is distributed partially encircling the means but no ferromagnetic material is placed between the magnetic guidance system and the cathode assembly, wherein an upper part with length (S) of the electromagnetic coil placed in the central region as well as an upper part with length S′ of the electromagnetic coil placed in the peripheral region but closest to the electromagnetic coil placed in the central region is not encircled by ferromagnetic material, resulting in a space comprising air, allowing in this manner that the total magnetic field that results from the sum of the generated magnetic fields exhibits more magnetic field lines that are parallel to the front surface of the target in comparison with a similar arc evaporator without having said space comprising air.

9. An ARC evaporator according to claim 8 , wherein the upper length (S) is in the following range: 3 mm≤S≤15 mm, the target diameter (D 1 ) is in the following range: 100 mm≤D 1 ≤150 mm and the total diameter (D) of the cathode assembly is in the following range: 150 mm≤D≤200 mm.