JP2001115258A - Non-planar, ferromagnetic sputtering target with low magnetic permeability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-planar sputtering target for magnetron cathode sputtering of magnetic thin film, capable of eliminating waste of expensive ferromagnetic material, reducing the frequency of replacement of target, and causing no deposition of foreign particles, by reducing the magnetic permeability of at least part of the ferromagnetic material to a value lower than the intrinsic magnetic permeability of the material. SOLUTION: The reduction in magnetic permeability can be attained by bending the ferromagnetic material in the part of targets 10 and 100 where most of sputtering occurs. By the reduction in magnetic permeability, considerable increases in leakage flux 26 and 126 at the target surface 38 and 138 are brought about and argon pressure reduction necessary to obtain stable plasma takes place. The reduction in magnetic permeability makes possible the increase of target thickness, which results in the prolongation of target life and reduction in the frequency of target replacement. Because of the absence of machining and target gap, waste of material can be eliminated and deposition of foreign particles can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferromagnetic non-planar sputter target having low magnetic permeability and thereby improving target performance, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Sputter targets made of ferromagnetic materials are used for data storage and VLSI (very large scale integrated circuits) /
It is important for thin film deposition in industries such as semiconductors. Magnetron cathode sputtering is one means of sputtering magnetic thin films.

[0003] Cathodic sputtering involves ion bombardment of a target made of a ferromagnetic material. The ferromagnetic target forms part of a cathode assembly in an exhaust chamber containing an inert gas, such as argon. When an electric field is applied between the cathode assembly and the anode in this room, the gas is ionized by collision with electrons emitted from the surface of the cathode,
A plasma is formed between the target surface and the substrate. As the positive gas ions are attracted to the cathode surface, and when they collide with the target, particles of material are knocked out and then across the enclosure onto a support maintained at or near the anodic potential. It is deposited as a thin film on the substrate on which it is located.

[0004] The sputtering method can be performed only by an electric field, but it is possible to considerably increase the deposition rate by magnetron cathode sputtering. In this case, an arc-shaped magnetic field formed in a closed loop on the surface of the target is superimposed on the electric field.
This arcuate closed-loop magnetic field confines electrons in an annular region adjacent to the target surface, thereby increasing collisions between the electrons and gas atoms, resulting in a corresponding increase in the number of ions in that region. This magnetic field is typically created by placing one or more magnets behind the target. This creates a stray magnetic field on the surface of the target so that the plasma concentration increases.

[0005] Erosion of particles from the sputter target surface generally occurs in a relatively narrow ring-shaped region corresponding to the shape of this closed-loop magnetic field. The target must be replaced without consuming only a portion of the total target material in this erosion channel, the so-called "runway" area. As a result, typically only 18-25% of the target material is utilized. Thus, a significant amount of generally expensive material must be wasted or re-used. In addition, a significant amount of deposition equipment "downtime" results from the need for frequent target replacement.

[0006] To overcome these disadvantages of the magnetron sputtering method, various possible solutions have been sought. One possible solution is to increase the thickness of the target. If the target is relatively thick, sputtering can proceed for a long time before this runway area is consumed. However, ferromagnetic materials present difficulties not encountered with non-ferromagnetic materials. For magnetron sputtering, the leakage flux (MLF) at the target sputter surface must be high enough to activate and sustain the plasma. Argon pressure 0.7-1.3P
under normal sputtering conditions, such as a
LF should be about 15 mT, preferably about 20 mT for high speed sputtering. For normal sputtering conditions, a magnet strength of at least about 100 mT is required. The strength of the cathode magnet partially determines the MLF. The higher the magnet strength, the higher the MLF. However, in the case of a ferromagnetic sputter target, the inherently high permeability of the material effectively shields the magnetic field from the magnet behind the target, thereby reducing the MLF on the target surface.

For air and non-ferromagnetic materials, the permeability is very close to 1.0. The ferromagnetic material referred to here is
It is a material having an intrinsic magnetic permeability exceeding 1.0. Permeability describes the reaction (magnetization) of a material in a magnetic field. In the SI unit system, it is defined as: Permeability = {1 + 4π (M / H)} where M is magnetization and H is magnetic field. For currently available sputter targets, the permeability is from near 1.0 to 10
0 or more. This value depends on the particular material and manufacturing method. For example, a machined Co sputter target has a permeability of less than about 10, while a machined NiFe and Fe sputter target has a permeability of less than about 10.
Has a magnetic permeability exceeding

[0008] Because of the high permeability and thus the low MLF, ferromagnetic sputter targets are generally much thinner than non-magnetic sputter targets in order to leak out enough magnetic field to sustain the plasma required for magnetron sputtering. create. Non-ferromagnetic sputter targets are typically 6.4 mm or greater, while ferromagnetic targets are typically less than 6.4 mm. For some ferromagnetic materials, especially high permeability materials, the target must be machined to 1.6 mm or less to achieve a MLF of 15 mT, and very high permeability materials are easily Is 1
Since an MLF of 5 mT cannot be achieved, magnetron sputtering is not possible. Thus, these ferromagnetic targets cannot only be made thicker to reduce equipment downtime, but they must actually be made thicker. In order to increase the thickness, the MLF must somehow be increased.

US Pat. No. 4,401,546 discloses a planar ferromagnetic target which achieves a thickness of 5 mm with a segmented target, wherein the segments are separated by a gap and through the gap. The magnetic field leaks, creating a 20 mT MLF on the surface of the target. This is described as an improvement over conventional ferromagnetic targets that can be machined to 1.4 mm or less, preferably 0.7 mm or less to make a 20 mT MLF.

US Pat. No. 4,412,907 also discloses FIG.
Discloses a segmented planar ferromagnetic target having a thickness of up to 25 mm, wherein the individual segments have ramps to create curved gaps, through which magnetic fields leak, and the surface of the target Make MLF up to 73mT on top. U.S. Pat. No. 5,827,414 discloses a planar ferromagnetic target which claims to achieve a thickness of 4-25 mm, again due to the gap between the targets. The gap in this configuration is a radial gap created by a slot in the target body, perpendicular to the magnetron flux, thereby increasing the sputter plasma concentration so that a more effective and homogeneous leakage field on and in parallel with the target body. make.

[0011] These methods of machining slots in the target body to increase the MLF and assembling the targets from the individual segments allow for thicker targets, but these gaps can be removed from the backing plate, for example. This is undesirable because it allows for the sputtering and deposition of foreign particles. Foreign particles in the thin film sacrifice the integrity of the target. Furthermore, this solution of increasing the thickness of the target does not reduce the waste of the target material.

Another solution to the above problem is
Either eliminating the target portion outside the runway area or changing the design of the target to increase the efficiency of erosion of the runway area. It is known in the art that in some applications, initial sputtering from a perfectly flat target surface tends to be non-uniform due to the effects of an arcuate closed-loop magnetic field. As sputtering progresses,
Erosion valleys form on the target surface in this closed-loop magnetic field region. The deposition of material sputtered from the target tends to be more uniform when the shape of the valley is stable. Thus, uniform sputtering can be obtained from the beginning using a non-planar target which has a notch, groove or bend pre-formed by machining the runway area. The dish or cup-shaped target is particularly useful for a variety of reasons, such as designing it to correspond to a valley with a natural curvature or removing unwanted material in the center of the runway area before sputtering. I know. These non-planar target configurations reduce waste of target material, increase efficiency, and increase the uniformity of the deposited film, but they reduce the target thickness of the ferromagnetic target to reduce the time required for target replacement. Not effective to increase. In addition, these non-planar targets are typically made from a rectangular or circular target blank by machining, such as with a lathe. Machining is simply a material removal process.
It still results in wasting an unnecessary amount of material before magnetron sputtering.

In general, the higher the permeability of a ferromagnetic material, the thinner the sputter target needs to be.
However, such target thickness limitations result in short target life, wasted material, and the need for frequent target replacement. Further, the high permeability and low MLF of the ferromagnetic target can cause problems of high impedance, low deposition rate, narrow erosion grooves, poor film uniformity and poor film performance. Thus, it is desirable to provide a low magnetic permeability, high MLF, non-planar ferromagnetic sputter target that can be made relatively thick without sacrificing film integrity.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a non-planar ferromagnetic sputter target for use in magnetron cathodic sputtering of magnetic thin films, wherein the ferromagnetic material comprises at least a portion of the target. It has a magnetic permeability lower than the intrinsic magnetic permeability of this material.

[0015]

To this end, and in accordance with the principles of the present invention, a non-planar structure is formed from a solid single target blank containing cobalt, nickel, iron or an alloy thereof, at least to a large extent, with a target. Is formed by a deformation method in which a material is essentially bent at a portion where sputtering occurs. This deformation technique reduces the intrinsic permeability of the material, which is at least 1.0, such that an increase in magnetic field leakage occurs at least in the deformed region. The ferromagnetic sputter target can then generate and maintain a magnetron sputtering plasma.

A further feature of the present invention is the ability to increase the thickness of this non-planar target while still achieving a sufficiently high leakage flux to activate and sustain this plasma, Increases target life and reduces target replacement frequency. A ferromagnetic target of any ferromagnetic material, according to the principles of the present invention, has a minimum M of about 15 mT.
It can be made at least about 1.3 mm thick to make LF. The impedance of the target material is also such that a low argon pressure can be used to obtain a stable plasma and can be maintained throughout the sputtering process.
descend.

These and other objects and advantages of the present invention will become more apparent from the accompanying drawings and detailed description of the invention. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description of the invention and the following detailed description, serve to explain the principles of the invention. .

[0018]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a low magnetic permeability, non-planar ferromagnetic sputter target. This low magnetic permeability is achieved by applying a deformation method as described below. The low magnetic permeability of the ferromagnetic material used for the sputter target of the present invention depends on the ML
This results in a significant increase in F and a reduction in the argon pressure required to obtain a stable plasma. The low permeability of the ferromagnetic material also allows for an increase in target thickness, which extends target life and reduces target replacement frequency. This low permeability allows for high deposition rates at comparable or lower magnetic field strengths, which contributes to improved magnetic properties of the film and improves film thickness uniformity. The low permeability target is
Wide sputter erosion grooves or areas, and thus also advanced target utilization, are very important in reducing waste of targets made of expensive materials.

Ferromagnetic materials contemplated by the present invention include, but are not limited to, the following: a. ) Pure Co and CoCr used for magnetic recording media,
CoCrPt, CoCrTa, CoNiCr, CoCr
PtTa, CoCrPtTaNb, CoCrPtTaB
And CoCrPtTaMo, and CoFe, CoNiFe, CoNb, CoNb used in a magnetic recording head
Co-based alloys such as Zr, CoTaZr, CoZrCr; b. B.) Pure Ni and Ni-based alloys such as NiFe and NiFeCo; ) Pure Fe and FeTa, FeCo and FeNi
An Fe-based alloy such as, and d. ) Ni, F having an intrinsic magnetic permeability exceeding 1.0
Other binary, ternary, quaternary and higher dimensional basic alloys, including e, Co and other elements.

In accordance with the principles of the present invention, a ferromagnetic material is formed into a non-planar, solid, single-sputter target structure by a modification as described herein. As used herein, non-planar sputter target is meant to include any sputter target having a non-planar structure, such as a concave dish-shaped structure, where sputtering occurs in a curved or curved area of the target. These non-planar structures have been found to have a number of advantages over planar structures for certain applications.

The ferromagnetic target of the present invention is manufactured by deforming the target blank in its entirety or only in the region where sputtering occurs, thereby increasing the permeability of the ferromagnetic material to its own in the deformed region. Decrease from value. Thus, as used herein, a "low-permeability" ferromagnetic target of the present invention includes a material having an intrinsic magnetic permeability greater than 1.0, wherein the magnetic permeability is greater than 1.0 but less than the intrinsic magnetic permeability of this material. Refers to a sputter target having a deformed area. The curved or curved area of this non-planar target is created by deformation (unlike removal of the material by machining), especially in the runway area. This deformation reduces the permeability of the ferromagnetic material in regions where the stresses and strains introduced into the material, particularly by bending of the material during the deformation process, are deformed. Without being bound by theory, it is believed that the stresses and strains introduced into the material change the magnetic energy of the material, which in turn changes the permeability. Thus, this non-planar target has a low magnetic permeability, at least in the curved or curved portion of the target, which is by design in the runway region where sputtering occurs. Since the high permeability of the ferromagnetic target will block or shield the magnetic field from the magnet, a decrease in the permeability of the target material in the deformed region will cause the magnetic field to leak from this target material and a high MLF on the target surface Yields
This results in maintaining the plasma. If you want
The entire target may be deformed, which will reduce the permeability throughout the target material, not just the sputtering area. This will also result in increased MLF at the surface of the ferromagnetic target.

By way of example, and not limitation, a NiFe target blank machined by a conventional method may be 20.5.
Showed a uniform magnetic permeability. The same NiFe target blank deformed according to the principles of the present invention exhibited a permeability of 19 in the deformed region. 2.8mm thickness, magnet strength 10
At 0 mT and an argon pressure of about 0.7-1.3 Pa, a conventional NiFe sputter target has an MLF of about 30 mT at the sputtering surface, while the two 2.8 mm NiFe targets of the present invention each have a MLF of 38 mT at the sputtering surface. And an MLF of about 35 mT.

The deformation techniques of the present invention include any deformation method that introduces stress, strain, or other microstructural or physical changes in a material to produce a uniform or localized change in magnetic permeability. Bending, compressing, stretching or other deformation effects may affect all or part of the target blank material. By way of example, and without intending to limit the scope of the invention in any way, this deformation technique may include spinning, press forming, roll forming, deep or shallow drawing, deep extrusion, stamping, stamping, dropping. Any of hammer molding and explosive molding may be used. Among these approaches, spinning, press forming, deep extrusion and drop hammer forming are likely to provide the best results and / or the most efficient and economical approach. For deformation approaches to bending the material, preferably a change of about 10 ° or more will introduce enough stress and / or strain to cause a change in permeability.

The spinning process produces a target blank into a seamless hollow cylinder with or without a bottom, or other toroid, by a combination of rotation and force. Typically,
A curved or bent sputter target creates an end-to-bottom. Press molding applies pressure to the press ram and presses the target blank against the press die to create a non-planar target shaped to match the die and ram. During this deformation step, the ram speed and holding pressure can be tightly controlled.

The roll forming method uses three or more rolls to transform a target blank into a non-planar shape with a seam. This roll forming method simply reduces the thickness of the material,
Unlike other rolling methods that use two opposing rolls, it involves bending the material. However, this seam may cause some non-uniformity in the deposited film. Deep and shallow drawing methods use punches and dies (drawing rings) with opposing edges to deform the target blank to make a cup, cone or similar shape. Deep extrusion involves displacement of the ferromagnetic material by plastic flow under non-uniform but steady pressure. The relative movement between the punch and the die causes the ferromagnetic material to flow in the required direction. The ferromagnetic materials work harden when deformed at temperatures below their recrystallization temperature.

The stamping method creates a shallow indentation in the target blank by compression between the punch and the die. Generally, a uniform thickness is maintained in all areas of the target, but some stretching may occur. Stamping is similar to stamping and pressing. During deformation, the shape or contour of the target is controlled by the mating die portion. In the drop hammer molding method, a target blank is deformed by a sudden impact that emits a high rate of deformation energy from the drop hammer. This forged hammer relies on gravity for its force. Explosive molding processes a target blank by the instantaneous high pressure resulting from the explosion of an explosive. This explosion operation may be performed in a sealed system or a non-sealed system.

By reducing the permeability of the ferromagnetic material and thereby increasing the MLF at the surface of the target, the ferromagnetic targets of the present invention can be made thicker than conventional machined ferromagnetic targets. Magnetic fields that are no longer shielded by high permeability can now leak through the thick target material. The target of the present invention is also made as an integral product so that foreign particles are not mixed into the deposited film through the gaps in the target structure.

The particular thickness and shape of the target of the present invention will depend on customer specifications and the particular ferromagnetic material used. In general, any target of any shape and material can be made thick if deformed according to the principles of the present invention. Cobalt and its alloys have inherently lower magnetic permeability than nickel and iron, so that with cobalt-based targets, with or without the variants of the present invention,
Generally thicker than nickel-based and iron-based targets. The present invention is intended to enable nickel- and iron-based targets, or magnets that do not allow magnetron sputtering, to achieve sufficient leakage of the magnetic field, where the permeability of the starting material is as high as 15 mT previously not achievable. It is particularly advantageous for the production of targets that had to be machined to very thin dimensions. These materials can now be formed into relatively thick targets that leak enough magnetic field to activate and sustain the plasma, and even greater amounts to increase deposition rates at the same field strength.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As an example and not by way of limitation, FIG. 1 illustrates a centrally-located central section having a ring-shaped bottom 12, a side wall 14, and a curved region 16 between the bottom and the side wall. An attachable, right-angled dish-shaped target 10 (shown in reverse use position) is depicted in cross section. The target 10 was made from a circular target blank (not shown) by a deformation technique, such as spinning, in which most of the deformation was applied to a portion 18 of the material, including the bent portion 16 and the sidewalls 14. . Thereby, the permeability of the material is most significantly reduced at and near this deformed portion 18 and the decrease in permeability becomes less noticeable in the direction toward the center 22 of the bottom 12. Most of the leakage of the magnetic field from the magnet (not shown) behind the target 10 occurs in the deformation region 18 where the permeability is lowest, as indicated by the magnetic flux lines 26. As indicated by phantom lines, the deformation area 18 includes the area where erosion areas or grooves 30 are created, the so-called runway area of these specially designed targets. A dense plasma 34 is thereby maintained near this runway region, where gas ions constantly strike the sputter surface 38, releasing target particles 42,
Next, they are deposited on the substrate 46 as a magnetic thin film until the target material is completely sputtered.

As a further example, FIG. 2 depicts a cross-section of a curved dish-shaped target 100 (shown in an inverted position) mounted on a supporting backing tray 110, which is an alternative embodiment of the present invention. Is the bottom 112, the side wall 1
14 and a curved area 116 between the bottom and the side walls to form a seamless unitary structure. The deformation eventually results in a portion 1 of the material comprising the curved region 116 and the side wall 114.
18 was applied. Again, most of the magnetic field leakage occurs in the deformation region 118, as indicated by the magnetic flux lines 126. The erosion groove 1 indicated by the phantom line due to the thick plasma 134 is thereby formed.
30 is obtained in the vicinity of the region where
Is constantly expelled from the sputter surface 138 and is deposited on the substrate 146 as a magnetic thin film.

The low permeability target of the present invention enables high deposition rates with magnetron field strengths of equal or less. High speed deposition has been found to be useful in many cases to improve the magnetic properties of the film. A low magnetic permeability target has a more uniform film thickness and a wide sputtering erosion groove, thus improving target utilization. Therefore, the target of the present invention, in addition to providing a uniform, high-purity magnetic thin film,
Reduces target replacement frequency and reduces target material waste.

An additional advantage of the present invention is that the target ML
With increasing F, there is a corresponding decrease in sputtering impedance, which also reduces the minimum argon pressure required to obtain a stable plasma. High impedance creates a plasma arc, which can destabilize the plasma and make it difficult to sputter the target. According to the present invention, a stable plasma can be obtained by lowering the impedance of the target,
A low minimum argon pressure can be maintained throughout this sputtering process.

[0033]

In order to demonstrate the effects of the present invention, two NiFe sputter targets having an ashtray shape and a thickness of 2.8 mm were sputtered by magnetron cathode sputtering under substandard conditions. The cathode contained a standard S gun magnet and trapped the plasma in the corner of the inner ashtray ring.
Standard S gun magnets, such as those available from Sputter Film Company of Santa Barbara, California, have a magnet strength of only about 40 mT and are typically used to sputter non-ferromagnetic materials, such as aluminum. use. This standard S gun magnet produces a much weaker magnetic flux at the corners of the magnet and thus at the target surface. The minimum argon pressure required to obtain a stable plasma and the magnetic flux at the target surface are given in Table 1 for the conventional uniform permeability target and the target of the present invention.

Table 1

As Table 1 shows, for targets of equal thickness and shape, the improved NiFe target of the present invention required only a small argon pressure to obtain a stable plasma. Achieving and maintaining this stable plasma results in significantly higher ML on the surface of the target of the present invention.
F is 65% greater than the surface of a conventional target, especially M
LF has occurred.

To achieve an MLF of at least about 15 mT, the ferromagnetic target should be sputtered under standard conditions. To achieve standard conditions, at least one
A magnet strength of 00 mT is typically required,
It may be small for serving targets in low permeability regions close to 1, or for relatively thin targets. An example of a cathodic magnet having a strength of about 100 mT that can be used in accordance with the principles of the present invention is RMX-3 available from Materials Research, Inc. of Orangeburg, NY, USA.
It is a 4-type magnet. For high MLF readings or thick targets, high strength magnets, such as a 200-300 mT SYM-4B magnet from Sony Corporation of Tokyo, Japan, may be used in accordance with the principles of the present invention. With a high-strength magnet designed for a ferromagnetic target, an argon pressure on the order of 0.7 to 1.3 Pa or less will be required to achieve and maintain a stable plasma.

The invention has been elucidated by the description of its embodiments, and these embodiments have been described in considerable detail, which limit the scope of the appended claims to such details or to limit them in any way. Not intended. Additional advantages and modifications will be readily apparent to those skilled in the art. For example, while the deformation techniques described herein have been described, other techniques may be used in accordance with the principles of the present invention, provided that the techniques are effective in reducing the magnetic permeability of the material in the deformed region of the target. Accordingly, the invention is not limited in its broader aspects to the specific details, representative devices and methods, and the illustrated and described embodiments. Accordingly, departures may be made from such details without departing from the scope or spirit of applicant's general inventive concept.

[Brief description of the drawings]

FIG. 1 is a cross-sectional side view of a non-planar target of the present invention having a right angle shape.

FIG. 2 is a cross-sectional side view of a non-planar target of the present invention having a curved shape.

[Description of Signs] 10 Sputter target 12 Bottom 14 Side wall 16 Curved region 100 Sputter target 112 Bottom 114 Side wall 116 Curved region

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) H01F 41/18 H01F 41/18 (72) Inventor Peter MacDonald United States New York, Suffern, Wilder Road 63 (72) Inventor Hun-Lee Ho United States of America New Jersey, Livingstone, AW, Cedar Street 64

Claims (3)

[Claims] 1. A method of making a low magnetic permeability, non-planar ferromagnetic sputter target for use in magnetron cathode sputtering, comprising: forming a target blank from a ferromagnetic material having an intrinsic magnetic permeability greater than 1.0; Transforming the target blank into a non-planar sputter target, thereby lowering the permeability of the ferromagnetic material from the intrinsic value at least in a portion of the sputter target. 2. A non-planar ferromagnetic sputter target for use in magnetron cathode sputtering.
00), Co, CoCr, CoCrPt, Co
CrTa, CoNiCr, CoCrPtTa, CoCr
PtTaNb, CoCrPtTaB, CoCrPtTa
Mo, CoFe, CoNiFe, CoNb, CoNbZ
r, CoTaZr, CoZrCr, Ni, NiFe, N
a material selected from the group consisting of iFeCo, Fe, FeTa, FeCo, FeNi and alloys thereof, wherein the permeability is lower than the intrinsic permeability of the material, at least in the region where most of the sputtering of the target occurs; The target is at the bottom (12, 112),
It has a dish shape with sidewalls (14, 114) and curved or curved regions (16, 116), wherein the permeability of the ferromagnetic material is at least in the curved or curved regions of the sputter target. Sputter target lower than the intrinsic magnetic permeability of 3. The sputter target according to claim 2, wherein
0, 100), the specific magnetic permeability is greater than 1.0 and the sputter surface (3
8, 138) having a leakage flux of at least 15 mT.