Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1997-10-10
2001-03-06
McDonald, Rodney (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192200, C204S298040, C204S298110, C204S192130, C204S298030
Reexamination Certificate
active
06197164
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the fabrication of thin films by ion beam sputter deposition and, more particularly, to the fabrication of multilayered thin film structures such as magnetoresistive sensors wherein the thickness uniformity of multiple layers deposited on a substrate are controlled by controlling the atom flux deposited on the substrate.
2. Description of Related Art
It is well-known in the prior art to utilize RF or DC magnetron sputter-deposition apparatus for fabrication of thin film devices such as magnetic recording sensors and storage media. Such sputter devices are characterized by crossed electric and magnetic fields in an evacuated chamber into which an inert, ionizable gas, such as argon, is introduced. The gas is ionized by electrons accelerated by the electric field, which forms a plasma in proximity to a target structure. The crossed electric and magnetic fields confine the electrons in a zone between the target and substrate structures. The gas ions strike the target structure, causing ejection of atoms that are incident on a workpiece, typically a substrate on which it is desired to deposit one or more layers of selected target materials.
In the prior art conventional sputtering devices relatively high operating pressures are utilized in order to obtain films having low internal stress which results in non-directional sputtering flux at the substrate. However, this non-directional flux introduces manufacturing process difficulties as device dimensions become increasingly smaller.
It is known in the prior art to utilize ion beam sputter deposition in certain applications to overcome some of the difficulties encountered with conventional RF/DC sputter techniques. Several aspects of ion beam sputter deposition differ from conventional sputter processes and provide significant advantages. For example, (1) the use of low background pressure results in less scattering of sputtered particles during the transit from the target to the substrate; (2) control of the ion beam directionality provides both a variable angle of incidence of the beam at the target and a controllable angle of deposition at the substrate; (3) a nearly monoenergetic beam having a narrow energy distribution provides control of the sputter yield and deposition process as a function of ion energy and enables accurate beam focusing and scanning; and (4) the ion beam is independent of target and substrate processes which allows changes in target and substrate materials and geometry while maintaining constant beam characteristics and allowing independent control of the beam energy and current density.
Apparatus and methods for producing a thin film deposit on a substrate utilizing ion beam sputtering are described, for example, in U.S. Pat. No. 4,923,585 ('585) to Krauss et al. and in U.S. Pat. No. 5,942,605 to Pinarbasi ('605), the contents of which are incorporated herein by reference. Krauss et al discloses the use of a computer controlled, single ion beam with a quartz crystal monitor to produce deposited films of arbitrary composition as well as layered structures of arbitrary thickness from multiple targets of elemental components of the desired films and layered structures. Pinarbasi discloses matching the ion beam gas atomic mass to the target material atomic mass to provide thin films having densities and physical properties very close to their bulk property values. Both the mass of the ion beam sputtering gas and the energy of the ion beam is controlled as a function of the target material to provide single-layered and multilayered structures wherein selected properties of each layer are optimized to provide specific function for each layer in the resulting structure. While the '585 and '605 patents disclose methods for depositing multilayer films and controlling the physical properties, the problems of controlling and improving the thickness uniformity across the wafer of each individual layer deposited are not addressed.
Ion beam sputter deposition systems have been utilized to deposit individual layers of anisotropic magnetoresistive (AMR) sensors and giant magnetoresistive (GMR) sensors for use in magnetic recording devices. In the GMR sensors, for example, the resistance of the magnetoresistive (MR) sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between the ferromagnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the ferromagnetic and non-magnetic layers and within the ferromagnetic layers. GMR sensors using only two layers of ferromagnetic material (e.g., NiFe or Co or NiFe/Co) separated by a layer of GMR promoting non-magnetic metallic material (e.g., copper) are generally referred to as spin valve (SV) sensors.
Magnetoresistive (MR) sensors (AMR or GMR) are very small devices that are generally fabricated by sputtering depositions on large wafer substrates which are generally larger than
5
inches in diameter to form thousands of sensors that will be subsequently separated (diced) to form individual magnetic read transducers for use in magnetic storage devices.
One of the critical issues in the fabrication process of MR sensors is the thickness uniformity of each and every deposited layer over the entire utilized area of the wafer in order to control the uniformity of operating characteristics (for example, resistance and magnetoresistance) of the entire batch of the MR sensors fabricated on the wafer substrate.
In an experiment by the present applicant, an ion beam sputtering system (
FIG. 1
) having a non-movable flux regulator was developed and used to build SV sensors
200
(
FIG. 2
) on a 5 inch diameter wafer substrate (
FIG. 3
) in order to measure the uniformity of physical properties of the various sputtered layers (therefore, uniform thickness).
Referring to
FIG. 1
, there is shown a simplified diagram illustrating the ion beam sputter deposition system
120
developed and used by the Applicant. The ion beam sputter deposition system
120
includes a vacuum chamber
122
in which an ion beam source
121
is mounted. The ion beam system
120
further comprises a target
123
and a workpiece (also referred to as a deposition substrate or wafer substrate)
131
. An ion beam
133
provided by the ion source
121
is directed at the target
123
where the impacting ions cause sputtering of the target material. System
120
further included selectable multiple targets
123
on a rotary target support
125
. The sputtered atoms
126
emitted from the target material is directed onto a deposition substrate
131
on which is formed a layer of the target material.
A thickness monitor
137
positioned closely adjacent to the substrate
131
provides real-time, in-situ monitoring of the thickness of the growing film during deposition. A non-movable flux regulator
150
fixed in front of the deposition substrate
131
partially blocks the sputtered atom flux and is used in conjunction with rotation of the deposition substrate
131
to improve thickness uniformity of the deposited layer. Applicant's non-movable flux regulator refers to a flux regulator that its positioned was fixed prior to the ion beam sputtering deposition of one or more deposited layers and never changed during the deposition of said one or more deposited layers. The substrate or other workpiece
131
is mounted on a movable pedestal or support member
141
which is retrieved into a loading port
139
via a gate valve
138
for changing the workpiece
131
. A magnetic field may also be applied at the workpiece
131
if required for the particular structure being deposited. The pedestal
141
may also be rotated, using a rotary/linear motor, during deposition to rotate the deposition substrate
131
. During operation of the ion beam sputter deposition system, the vacuum chamber
122
is maintained at suitable low pressure by a vacuum pump (not shown) via port
135
.
FIG. 2
shows th
Altera Law Group LLC
International Business Machines - Corporation
McDonald Rodney
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