Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
2000-07-10
2001-05-29
Diamond, Alan (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S192110, C204S298110, C204S298120, C204S298130, C204S298150, C204S298230, C204S298270, C204S298280, C204S298290, C204S192150, C204S192200, C204S192210
Reexamination Certificate
active
06238531
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 by ion beam sputter deposition wherein the properties of multiple layers deposited on a substrate are controlled by controlling the angle at which atoms are deposited on the substrate.
2. Description of Related Art
It is well-known in the art to utilize radio frequency (RF) or direct current (DC) magnetron sputter-deposition system for fabrication of thin film devices such as magnetic recording sensors (e.g., magnetoresistive sensors) and storage media. Such sputter-deposition systems 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 wafer substrate on which it is desired to deposit one or more layers of selected target materials.
In the conventional sputtering deposition systems 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 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 systems differ from conventional sputter deposition systems 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 wafer substrate; (2) control of the ion beam directionality provides a variable angle of incidence of the beam at the target; (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 depositing a thin layer of material on a substrate utilizing ion beam sputtering deposition systems 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. The '585 patent 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 different materials. The '605 patent discloses matching the ion beam gas atomic mass to the target material atomic mass to produce thin films having densities and physical properties very close to their bulk property values. While the '585 and '605 patents disclose methods for depositing multilayer films, the problems of controlling the amount of flux deposited at the junction between the layers deposited adjacent to each other is 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 disk drives. 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. U.S. Pat. No. 5,206,590 to Dieny et al. ('590), the content of which is incorporated herein by reference, discloses an MR sensor operating on the principle of GMR.
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. The wafer is subsequently diced to form individual magnetic read transducers for use in magnetic storage devices.
One of the major issues in the fabrication process of MR sensors is to precisely control the physical, electrical and magnetic properties of the junction formed between the layers deposited adjacent to each other. An example of such a junction is the contiguous junction formed between the MR layer and the longitudinal biasing layer in an MR sensor.
Another critical issue in the fabrication process of MR sensors is the thickness uniformity of each and every deposited layer over the entire utilized area of a given 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 said given wafer.
In an experiment by the present applicant, an ion beam sputtering system
120
(
FIG. 1
) was developed and used to determine the properties of the junction formed between the layers deposited adjacent to each other and thickness uniformity of various layers deposited in the end region
206
and
204
of the SV sensor
200
(
FIG. 2A
) formed on a 5 inch diameter wafer substrate (FIG.
3
).
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 selectable multiple targets
123
, formed or mounted, on a rotary target support
125
. An ion beam
133
provided by the ion beam source
121
is directed at one of the targets on the selectable multiple targets
123
where the impacting ions cause sputtering of the selected target material. The sputtered atoms
126
emitted from the selected target material is directed at a near-normal angle (85 to 95 degrees) onto a workpiece (wafer substrate, wafer, deposition substrate)
131
on which is formed a layer of the selected target material. The sputtered atoms
126
hit (bombard) the workpiece
131
at a near-normal angle (85 to 95 degrees). The workpiece
131
is placed securely, via clamps or vacuum suction (not shown) on a substrate stage (workpiece stage)
141
. The substrate stage
141
is retrievable into a loading port
139
via a gate valve
138
for changing the workpiece
131
.
A thickness monitor
137
, positioned closely adjacent to the workpiece
131
, provides real-time, in-situ monitoring of the thickness of the growing film during deposition over the entire utilized area of the workpiece
131
. A non-movable flux regulator
150
fixed in front of the workpiece
131
partially blocks the sputtered atom flux and is used in conjunction with rotation of the workpiece
131
to improve thickness uniformity of the deposited layer during the deposition process. The non-movable flux regulator refers to a flux regulator that its position is fixed prior to the ion beam sputtering deposition of one or more deposited layers and remains
Diamond Alan
Gill William D.
International Business Machines - Corporation
Saber Paik
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