Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
1999-02-22
2001-02-20
Diamond, Alan (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298020, C204S298060, C204S298170, C204S298180, C335S210000, C335S213000, C335S219000, C335S296000, C335S297000, C335S299000, C335S306000
Reexamination Certificate
active
06190517
ABSTRACT:
This invention relates to a magnet array for use in a sputtering apparatus.
Thin film recording heads are an important part of disc drives for use in computers. Current designs of disc drives tend to utilise an inductive “read” head and an inductive “write” head. However, emerging and future generations of high capacity disc drives will incorporate more sensitive “read” heads of a design which is known as a magneto-resistive (MR) head. The technology required to produce such heads is more advanced than that needed to produce inductive “read” and “write” heads.
Building each sensor for reading the magnetic encrypted information from the disc (or sometimes tape) requires the deposition of thin layers, typically from about 1 to about 30 nm thick, of magnetically oriented ferro-magnetic material upon a wafer of ceramic material, such as AlTiC. The deposition conditions to achieve this must be precisely controlled. Such thin layers are normally produced using sputtering techniques.
It is known to deposit the magnetic layers by sputtering under the influence of an orienting magnetic field. Historically this has been achieved by the use of permanent magnet tooling mounted within the vacuum chamber of the sputtering apparatus. More recently it has been proposed to use electro-magnets. It is also common practice to use an oscillating magnetic field applied in a single plane. This last mentioned technique applies the field first in one direction and then reverses the polarity so that the field is applied in the opposite direction at 180° to the first direction, before again reversing the field, and so forth.
New types of very sensitive sensors, known as spin-valves and GMR (giant magneto-resistive) sensors, promise higher performance. These structures require two magnetic layers, i.e. a pinned magnetic layer and a free magnetic layer. The pinned magnetic layer provides a fixed magnetic field, while the free layer is made from a soft magnetic material that has a high magnetic saturation and is readily magnetisable upon exposure to a magnetic field. The free layer has both a hard axis and an easy axis of magnetisation. Examples of suitable soft magnetic materials include Ni/Fe alloys, such as Permalloy™, cobalt alloys, and iron alloys. In a spin-valve MR sensor the pinned and free layers should have their magnetic axes orthogonal, that is to say the magnetic axis of the pinned magnetic layer should be at right angles to the easy axis of magnetisation of the free layer. Ideally the lines of force of the magnetic field in the plane of the film should, for each layer, be parallel across the layer. In practice it is impossible to produce with existing techniques such an ideal arrangement. Hence it is recognised that there is some departure from ideality. This can be expressed by a property known as “skew”. This is the angle, normally expressed in degrees of arc, by which the magnetic field deviates from ideality.
It is difficult to design a form of magnet array to achieve the necessary accuracy of deposition of the free and pinned layers. If two separate sets of electro-magnets are used, the one being used during deposition of the first layer and the other being used during deposition of the second layer, the problem is that the core material of the one set perturbs the magnetic field produced by the other set and vice versa.
The present invention accordingly seeks to provide an improved magnet array for use in a sputtering apparatus for use in depositing magnetically oriented thin layers, particularly successive layers having different orientations of their magnetic axes. It further seeks to provide a magnet array that can produce at different times magnetic fields whose orientation can be precisely and accurately controlled at any given moment. The invention further seeks to provide a form of electro-magnet array which can be used in a sputtering apparatus to effect deposition of successive thin layers of magnetic material whose axes of magnetisation are substantially orthogonal to one another.
In this specification the terms “horizontal” and “vertical” are used for convenience only to designate directions within the magnet array. In use the magnet array of the invention may be mounted in a sputtering apparatus so that the internal “horizontal” direction of the array is not horizontal in a true sense and the internal “vertical” direction of the array is not truly vertical.
According to the present invention there is provided an electro-magnet array for use in a sputtering apparatus comprising:
a magnetisable core member extending substantially horizontally and having magnetisable outward projections arranged as at least two pairs of symmetrically opposed projections projecting outwardly and radially symmetrically from the magnetisable core piece;
a pole piece associated with each projection and vertically displaced with respect thereto;
magnetisable coupling means arranged to couple each pole piece magnetically to its respective projection; and
a magnetising coil around each projection arranged for producing a magnetic field aligned substantially with a horizontal axis of symmetry of its respective projection in dependence upon the direction of flow of electric current through the magnetising coil;
the magnetising coils being arranged so that, upon energisation, the respective magnetic field of one coil of a pair of projections can produce a south pole at an inward side of its respective pole piece while the magnetic field of the coil of the other projection of the pair produces a north pole at an inward side of its respective pole piece and so that, at any moment, at least two inwardly facing south poles are produced on the pole pieces on one side of a vertical plane of symmetry through the array and an equal number of inwardly facing north poles are produced on the pole pieces on the other side of the vertical plane of symmetry, the vertical plane of symmetry passing between adjacent pole pieces.
In a preferred arrangement there are four magnetisable projections on the magnetisable core member arranged in two pairs. However, it is alternatively envisaged that there shall be six magnetisable projections arranged in three pairs or eight magnetisable projections arranged in four pairs. The magnetisable projections typically extend horizontally from the core member.
Preferably the magnetisable core member is formed from a plate and the projections are integral therewith. However, it is possible to attach separate projections to a central core magnetisable member. Other shapes of core member can be used other than a plate member, if desired.
In a preferred embodiment the core member is substantially square in outline and the projections are also substantially square or rectangular in outline so that the core member and its four projections form a cross.
If desired a central aperture can be formed in the magnetisable core member to allow passage of items for connection, for example, to the support for the wafer or other substrate, such as coolant supply lines, electrical connections and the like.
The magnetisable core member and its projections are preferably made from a soft magnetisable material, such as soft iron, mild steel, or a soft magnetic alloy.
The pole pieces are normally identical one to another and displaced by the same vertical distance from the magnetisable core member and its projections. Hence the pole pieces are preferably symmetrically disposed about a vertical axis of the core member.
The magnetisable coupling means preferably comprises a member or members of a soft magnetisable material, for example one of those mentioned above. The pole pieces are similarly made from a soft magnetic material.
Taking for the sake of simplicity a magnet array having a magnetisable member with four projections, it will be apparent that, if the current in one coil of an opposed pair and that in an adjacent coil of the other pair is caused to flow in a direction to produce a south pole at each of the respective radially inner faces of their pole pieces, and if the current in the other coils is
Davis Mervyn Howard
Diver Barry
Diver Joan Mary
Pearson David Ian Charles
Reeves Simon Richard
Diamond Alan
Diver Joan Mary
Nordiko Limited
Senniger Powers Leavitt & Roedel
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