Method of forming thin oxidation layer by cluster ion beam

Details Method of forming thin oxidation layer by cluster ion beam Method of forming thin oxidation layer by cluster ion beam

2003-01-13

2004-10-05

Niebling, John F. (Department: 2812)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

C438S706000, C438S712000

Reexamination Certificate

active

06800565

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a cluster ion beam (CIB) method for forming thin oxidation layers in devices used for data storage and retrieval or any application in which detection of small magnetic fields is the method of operation. For example, the CIB method is applicable for forming specular reflecting layers in spin valve sensors for increasing the giant magnetoresistive ratio of the magnetic element, or for forming tunnel barrier layers in tunnel magnetoresistive devices.
BACKGROUND OF THE INVENTION
Computer systems generally utilize auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Magnetic heads, including read sensors, are then used to read data from the disk surfaces.
In high capacity disk drives, magnetoresistive read sensors (MR sensors) are the prevailing read sensors. An MR sensor detects a magnetic field through the change in resistance of its MR sensing layer (MR element) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
One type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect, and another type is a tunnel magnetoresistance (TMR) sensor manifesting the TMR effect. In GMR sensors, the resistance of the MR element varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a nonmagnetic, conductive layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and nonmagnetic layers and within the magnetic layers. In TMR sensors, the resistance of the MR element varies as a function of the tunneling current allowed to pass between magnetic layers through a nonmagnetic, insulating layer (barrier layer).
GMR sensors using two layers of ferromagnetic material separated by a layer of nonmagnetic electrically conductive material are generally referred to as spin valve (SV) sensors manifesting the GMR effect. In a spin valve sensor, one of the ferromagnetic layers, referred to as the pinned layer, has its magnetization typically pinned by exchange coupling with an antiferromagnetic layer. The magnetization of the other ferromagnetic layer, referred to as the free layer, is not fixed and is free to rotate in response to the field from the recorded magnetic medium. In spin valve sensors, the spin valve effect varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the free layer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium causes a change in the direction of the magnetization in the free layer, which in turn causes a change in resistance of the spin valve sensor and a corresponding change in the sensed current or voltage.
FIG. 1
shows a typical simple spin valve
10
(not drawn to scale) comprising a central region
12
separating end regions
14
formed on a substrate
16
. In central region
12
, a free layer (free ferromagnetic layer)
18
is separated from a pinned layer
20
(pinned ferromagnetic layer) by a nonmagnetic, electrically-conducting spacer layer
22
. The magnetization of the pinned layer
20
is fixed through exchange coupling with an antiferromagnetic (AFM) layer
24
.
FIG. 1
is an air bearing surface (ABS) view, and the arrows indicate that the free layer
18
has a magnetization direction, in the absence of an external magnetic field, parallel to the ABS and the pinned layer
20
has a magnetization direction perpendicular or 90° to the ABS, wherein the ABS is an exposed surface of the sensor that faces the magnetic medium. Hard biased layers
26
are formed in the end regions
14
to provide longitudinal bias for the free layer
18
. Leads
28
are formed over hard biased layers
26
and provide electrical connections for the flow of a sensing current from a current source
30
to the sensor
10
. Sensor device
32
is connected to leads
28
and senses the change in the resistance due to the changes induced in the free layer
18
by the external magnetic field. The construction depicted in
FIG. 1
is the simplest construction for a spin valve sensor, and is well known in the art.
Another type of spin valve sensor is an antiparallel (AP) pinned spin valve sensor. In this type of magnetic element, a laminated AP pinned layer structure is substituted for the single pinned layer in FIG.
1
. The AP pinned layer structure includes a nonmagnetic AP coupling layer (APC layer) between first and second AP pinned layers (AP
1
and AP
2
, respectively). The AP
1
pinned layer is exchange coupled to the antiferromagnetic pinning layer, which pins the magnetic moment (magnetization direction) of the AP
1
pinned layer in the same direction as the magnetic spins of the pinning layer. By exchange coupling between the AP
1
and AP
2
layers, the magnetic moment of the AP
2
pinned layer is pinned antiparallel to the magnetic moment of the AP
1
pinned layer. An advantage of the AP pinned layer structure is that demagnetization fields of the AP
1
and AP
2
pinned layers partially counterbalance one another so that a small demagnetization field is exerted on the free layer for improved biasing of the free layer.
FIG. 2
shows an exemplary AP pinned spin valve sensor
10
′ (not drawn to scale) of the prior art. As with sensor
10
of
FIG. 1
, spin valve sensor
10
′ has a central region
12
separating end regions
14
formed on substrate
16
. AP pinned spin valve sensor
10
′ comprises free layer
18
separated from a laminated AP pinned layer structure
40
by spacer layer
22
. The magnetization of the laminated AP pinned layer structure
40
is fixed by the AFM pinning layer
24
. The laminated AP pinned layer structure
40
includes a first ferromagnetic layer (AP
1
layer)
42
and a second ferromagnetic layer (AP
2
layer)
44
separated from each other by an antiparallel coupling layer (APC layer)
46
. As with sensor
10
in
FIG. 1
, hard bias layers
26
are formed in end regions
14
to provide longitudinal biasing for the free layer
18
, and electrical leads
28
provide electrical current from current source
30
to the spin valve sensor
10
′. Sensor device
32
is connected to leads
28
to sense the change in resistance due to changes induced in the free layer
18
.
Various parameters of a spin valve sensor may be used to evaluate the performance thereof. Examples of such parameters include the structure sheet resistance (R) and the GMR ratio (&Dgr;R/R), also referred to as the GMR coefficient. The GMR ratio is defined as (R
AP
-R
P
)/R
P
, where R
AP
is the antiparallel resistance and R
P
is the parallel resistance. The GMR ratio is an expression of the magnitude of the sensor response, and thus, the operation of a spin valve sensor is maximized by maximizing the GMR ratio. The GMR effect depends on the angle between the magnetizations of the free and pinned layers. In a spin valve sensor, the electron scattering, and therefore the resistance, is maximum when the magnetizations of the pinned and free layers are antiparallel, i.e., a majority of the electrons are scattered as they try to cross the boundary between the MR layers. On the other hand, electron scattering and therefore the resistance is minimum when the magnetizations of the pinned and free layers are parallel, i.e., a majority of electrons are not scattered as they try to cross the boundary between the MR layers. Thus, there is net change in resistance of a spin valve sensor between parallel and antiparallel magnetization orientations of the pinned and free layers. The GMR effect, i.e., the net change in resistance, exhibited by a typical prior art spin valve sensor, such as that shown in
FIG. 2
, is about 6% to 8%.
The disk drive industry has been engaged in an ongoing effort to increase the o

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