MAGNETRON SPUTTERING TARGET FOR MAGNETIC MATERIALS

Abstract

A target for physical-vapor deposition (PVD) and methods for depositing magnetic materials are described. Radio frequency (RF) or direct current (DC) power is introduced into the chamber through the target to produce plasma. The planar magnetron system is chosen for its high deposition rates. Since the permanent magnets are behind the target in the traditional system, a magnetic target interferes with the required magnetic fields on the target. To eliminate this problem permanent magnets are arranged on the surface and a magnetic target is used as a part of the magnetic circuit. Strong magnetic fields on the target can now be maintained for high deposition rates. The permanent magnets may be covered by a relatively thin, suitable protective-film or by a film of the same material as the target.

Description

FEDERALLLY SPONSORED RESEARCH

[0001] Not Applicable

SEQUENCE LISTING OR PROGRAM

[0002] Not Applicable

BACKGROUND—FIELD OF INVENTION

[0003] This invention relates to physical-vapor deposition (PVD) and methods for depositing magnetic materials with planar magnetron sputtering system

SPUTTERING DEPOSION OF PRIOR ART

[0004] Sputtering is a method of physical-vapor deposition (PVD) that involves the removal of material from a solid cathode by bombarding it with positive ions from the discharge of a rare gas such as argon (Ar). The cathode can be made of a metal or an insulator and in contrast to thermal evaporation, complex compounds such as high-temperature superconductor (HTS) materials can be sputtered with less chemical-composition change. Sputtering is often done in the presence of a reactive gas, such as oxygen or nitrogen, to control or modify the properties of the deposited film. The following are some of the advantages of the sputtering method:

[0005] Environmentally benign process systems compared with chemical processes

[0006] Choice of a wide range of deposition rates for the best growth conditions

[0007] Control of a wide range of oxygen or nitrogen levels in the dielectric films

[0008] Use of oxide or non-oxide targets (reactive sputtering deposition)

[0009] Use of single or multi co-sputtering processes

[0010] Growth of c-axis oriented layers on amorphous substrates

[0011] Growth of not only c-axis but also a-axis oriented layers on a single-crystalline substrate

[0012] The sputtering deposition system provides high-density nucleation, which has not only a c-axis but also an a-axis orientation on single-crystalline substrates. This process is ideal for the first, or nucleation step; however, it fails to make a single crystal because of the difficulty to maintain thermal-equilibrium growth-conditions at higher temperatures necessary to grow a single crystal. Ref (1)

BACKGROUND OF THE INVENTION

[0013] The planar magnetron system is simple and provides high deposition rates from a simple flat target. The conventional system has permanent magnets behind the target that provide strong magnetic fields on the target. The magnetic fields confine high-density plasma to the target. The plasma on the target enhances the deposition rate dramatically. If it is a magnetic target, however, magnetic properties bypass the magnetic fields. Hence magnetic fields on the target will be greatly reduced. Magnetic materials cannot be deposited effectively with a conventional planar magnetron system.

[0014] Magnetron systems are very good for Physical Vapor Deposition (PVD) systems as a material source to be deposited because deposition rates are high and excess electron bombardment of the substrate is reduced. Ref (2) The planar magnetron generates magnetic fields through the target. The strong magnetic field on the target confines the high-density plasma causing target erosion. The conventional target will become thinner as erosion advances and magnetic fields on the eroded areas become stronger. The erosion profiles become deeper narrow rings. The stronger magnetic field accelerates erosion. It creates a narrow, deeper channel. This effect leads to a shorter target life and affects the uniformity of the deposited film on the substrate. The target utilization rate is also lower. To partially solve this problem, costly rotating magnets are required. The rotating magnets act as a magnetic break. This requires a significantly high power motor and excess heat generated on the target becomes a problem.

[0015] In the conventional system, magnetic fields are introduced through the target so that very large, strong magnets are required to provide sufficiently strong magnetic fields on the target. Although a thicker target results in a longer life, even stronger magnets are then required to provide adequate magnetic fields on the target.

SUMMARY OF THE INVENTION

[0016] 1. The new magnetron-sputtering target has the magnets on the substrate-facing surface of the magnetic target rather than behind the target so that strong magnetic fields can be applied to the target surface with smaller magnets.

[0017] 2. Magnets to be exposed in the plasma may be coated with proper magnetic and/or non-magnetic materials by plating them on the magnet surfaces. This practice is already in use with the conventional magnetron systems to prevent corrosion.

[0018] 3. The required magnets are very small and provide stronger magnetic flux on the target. Magnetic circuits can be designed more precisely for these front-mounted magnets than for those on the back of the target.

[0019] 4. Better magnetic circuit design eliminates the need for rotated magnetic fields and provides a more uniform deposit.

[0020] The permanent magnets will be placed on the magnetic target rather than behind the target. The major erosion area is between the opposite polarities permanent magnets that are on the magnetic target. The permanent magnets erode very little, but they may be coated with suitable materials to prevent cross contamination. In this configuration, permanent magnet strips or rings form magnetic fields directly on the target, where as the conventional planar magnetron generates magnetic fields through the target. My innovative magnetic circuit design does not limit the thickness of the target and magnetic distribution is far better than that of the conventional design. The required permanent magnets are smaller and much less inexpensive.

[0021] FIG. 1 shows a typical planar magnetron in a vacuum chamber incorporating this new target design. All permanent magnets have a polarization from top to bottom and the target provides a common base for the magnetic circuits set up by the permanent magnets. Strong magnetic fields between opposite permanent-magnet polarities trap and confine the high-density plasma. This high-density plasma on the target enhances target erosion and as erosion advances, the magnetic fields tend to be weaker. This results in wider erosion profiles. Since the magnetic circuits are directly exposed rather than through the thick target, smaller permanent magnets can be used. The smaller magnets make it possible to achieve more efficient erosion patterns. This leads to a more uniform sputtering source without rotating magnets or magnetic fields. Although the rotating magnetic assembly improves deposition uniformity, the rotation reduces the magnetic field on the target, generates more heat due to magnetic break effect, hinders ideal electrical feeding system, and triggers plasma instability, including abnormal arc discharges.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a schematic view of a sputtering system having a vacuum chamber 10 within which a target 15, a substrate 12 and a magnet 16 of a magnetron array are set up according to my invention.

DRAWINGS

Drawings Figures

[0023] In the drawings, closely related figures have the same number but different alphabetic suffixes.

[0024] FIG. 1 schematic diagram of sputtering system

[0025] FIG. 2 prior art target assembly

[0026] FIG. 3 simple target concept diagram of new invention

[0027] FIG. 4 coated permanent magnet, section

[0028] FIG. 5 section diagram of invention, concept 1

[0029] FIG. 6 section diagram of invention, concept 2

[0030] FIG. 7 section diagram of invention, concept 3

[0031] FIG. 8 more realistic magnet arrays, see from substrate side

[0032] Reference Numerals in Drawings

10  vacuum chamber
11  to vacuum pump
12  substrate
13  cooling water in-out lets
14  water jacket
15  magnetic target
16  permanent magnet
16A permanent magnet, large ring
16B permanent magnet, small ring
16N permanent magnet, north pole faces substrate
16S permanent magnet, south pole faces substrate
17  plasma
18  gas inlet
19  insulator-vacuum seal
20  magnetic base plate
21  prior art target
23  surface coat
26  major erosion area

DETAILED DESCRIPTION

[0033] The sputtering system in which my magnetron array is mounted is shown in FIG. 1. The sputtering process occurs in a vacuum chamber 10 containing a target 15 of material to be sputtered onto a substrate 12 which receives a thin film coating of the material deposited from the target. Sputtering is a method of physical vapor deposition that involves the removal of material from a solid cathode or target 15 by bombarding it with positive ions from the discharge of a rare gas such as argon (Ar) supplied from the gas inlet 18. The cathode can be made of a metal or an insulator and is heated by ion bombardment or discharge energy. The excess heat build-up must be removed by a water jacket 14 with continually circulating water through in/outlet 13. The target assembly is built into the chamber by means of an insulating ring and a vacuum seal 19. The substrate 12 is often a wafer on which magnetic components are fabricated, but it can also be a microelectronic wafer, optical element or other structure having a surface to be coated.

[0034] The conventional planar magnetron sputtering assembly is shown in FIG. 2 (PRIOR ART). The magnetic field is provided by permanent magnets 16 mounted on the magnetic base plate 20 behind the target. The field on the target confines the high-density plasma 17. The plasma on the target enhances the deposition rate dramatically. If it is a magnetic target, magnetic properties bypass magnetic fields. Magnetic materials cannot be deposited effectively with a conventional planar magnetron system

[0035] My invention involves the location of the magnetic array, the preferred configuration of which is shown in FIG. 3. The target portion of the sputtering system consists of an array of permanent magnets fastened to the target surface facing the substrates at an appropriate distance from the substrates.

[0036] The magnet 16A and 16B to be exposed in the plasma may be coated with suitable magnetic and/or non-magnetic materials 23 by plating these materials on the magnets as shown in FIG. 4. This practice is already used in the conventional magnetron system to prevent corrosion.

[0037] Three variations of target assemblies are shown in FIG. 5, FIG. 6 and FIG. 7. The simplest application of all is that of two rings of magnets attached to the magnetic target by their own magnetic forces as shown in FIG. 5. The back of the target is bonded to a water jacket 14 for cooling purposes. FIG. 6 shows the magnets partially embedded in a magnetic target. Non-magnetic materials may be sputtered by fastening the target to a magnetic base plate. The surface of the target may be modified according to magnetic properties of the target 15, permanent magnets, gas composition and pressure, operating power, and the spacing between the north 16B and south 16A magnets mounted on the surface of the target. FIG. 7 shows a magnetic target with a machined surface, which, when exposed to the plasma, enhances the thin film uniformity as the target erodes more uniformly leading to longer target life.

[0038] Using a micro-pattered magnetic circuit as shown in FIG. 8 will maximize performance of the new target assembly. The small magnets are embedded or in the guiding trenches and form micro-patterns of magnetic field between north 16N and south 16S poles on the magnetic target 15. The plasma is confined in the magnetic field and micro-erosion patterns 26 will be formed. The erosion patterns are uniformly distributed so that material supply will be uniform. The substrate can be closer to the target. Multiple benefits include high deposition rate, minimum chamber contamination, and better deposition uniformity. The semi-direct exposure of the permanent magnets provides the best uniformity of magnetic field over the whole target area.

Claims

1. The permanent magnets in this magnetron sputtering system are fastened to the magnetic target surface facing the substrates at an appropriate distance from the substrates.

2. The magnets may be coated with suitable materials such as the target material or a non-contaminating material with the deposited film. Since the surface of the magnets erode little and may be coated, no-contaminating materials are deposited on the substrate.

3. Since the permanent magnet circuit is located on the surface of the target and is directly exposed to the plasma rather than through the thick target, the required permanent magnets are smaller and less expensive than those mounted on the back of the target.

4. The smaller magnets make it possible to design suitable erosion patterns. The magnetic circuit design is simpler with surface-mounted permanent magnets.

5. The erosion profiles become wider, rather than deeper rings, so that the utilization of the target is enhanced and the life of the target is increased.

6. The permanent magnets are held on target by their own magnetic force, or they can be bonded on the target. They can also be held on mechanically or by a combination of methods.

7. My innovative target assembly does not limit the thickness of the target and it provides better target-cooling capability.

8. A non-planar, machined surface of the target (FIG. 7) may be used for a variety of applications.

9. The small erosion areas produced are ideal for very small targets.

10. Electrical connections are easier and an ideal power feeding system can be designed.

11. During deposition, the large amount of heat associated with the plasma driving power can be removed effectively with the new invention. There is no limitation on the thickness of the target assembly, including the water jacket since the thickness does not hinder the magnetic field strength on the target.

12. Better magnetic circuit design provides better deposition uniformity and better erosion profile of the target without the need for rotating magnets. The stationary magnetic source provides a stable plasma with no abnormal arc discharge.

13. The rotated magnets in the conventional target work as a magnetic break which requires a high power motor causing target heating. Without the rotating magnets, plasma power feeding and target cooling design can be idealized. Better cooling design makes it easier to remove heat from the target.

14. Fine erosion patterns can be achieved with small magnets so that the uniformity of the deposited film and utilization of the target are greatly improved. The precisely aligned magnets provide uniform magnetic flux over the entire erosion area, as opposed to the magnetic pole pieces. These pole pieces can be effectively used only with the simplest erosion patterns are acceptable. These pole pieces with the complex patterns distribute the magnetic flux unevenly. The fine patterned erosion areas in my innovative design make it possible to reduce the distance between the target and the substrate. This leads to a higher deposition rate with more material deposited on the substrate and less on the chamber walls.

15. A non-magnetic target may be used by laminating it to a magnetic backing plate.