Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-11-15
2003-04-29
Chaudhuri, Olik (Department: 2823)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S659000, C438S003000, C365S066000
Reexamination Certificate
active
06555858
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a magnetic random access memory (MRAM) device and a fabricating method thereof, and more particularly to a MRAM device write line structure
RELATED ART
Magnetic random access memory (MRAM) technology development is currently underway for use as a type of non-volatile memory by the semiconductor industry. MRAM may also prove useful as dynamic random access memory (DRAM) or static random access memory (SRAM) replacements. There are two main types of MRAM: MTJ (magnetic tunnel junction) and GMR (giant magnetoresistive) MRAM.
FIG. 1
shows a portion, or a memory bit, of an MTJ array
10
which includes a write line or a bit line
12
intersected by a number of digit lines
14
. At each intersecting write line and digit line, a magnetic tunnel junction sandwich
16
forms a memory element in which one “bit” of information is stored. The magnetic tunnel junction sandwich
16
is comprised of a non-magnetic material
18
between a magnetic layer of fixed magnetization vector
20
and a magnetic layer in which the magnetization vector can be switched
22
; these will be referred to as a fixed layer
20
and a free or switching layer
22
.
It is advantageous for a variety of reasons to increase the packing density of memory cells in the memory array. A number of factors influence packing density; they include memory element size and the relative dimensions of associated memory cell circuitry, i.e. bit lines and digit lines, and any semiconductor switching or access device within the memory cell. For example, referring to
FIG. 2
, a cross-sectional view of a portion of a prior art MRAM write line structure
100
is shown. (The write line structure
100
can be a bit line structure in an MTJ array or a word line structure in a GMR array.) The write line structure
100
includes a conductive material
104
surrounded by magnetic cladding members
103
and
106
. The magnetic cladding members
103
are formed using high-permeability materials that have magnet domains in the plane of the cross-section shown in
FIG. 2
which are magnetized and demagnetized upon the application and removal of an applied magnetic field. When current is applied through the conductive material
104
, the corresponding magnetic fields associated with the magnetic cladding members
103
and
106
help to enhance the magnitude and more effectively focus the overall magnetic field associated with the write line structure
100
toward its associated memory element (not shown). Additionally, the magnetic cladding members
103
and
106
also help to shield the bit line's magnetic field from memory cells associated with other write lines, thereby protecting their programming state information.
The prior art method for forming the write line structure
100
includes first etching a trench
102
in the dielectric layer
101
. Next, a layer of a high-permeability magnetic material, such as a layer of an alloy of nickel-iron (NiFe), is deposited over the dielectric layer
101
and in the trench
102
. The layer of high-permeability magnetic material is then anisotropically etched to form magnetic cladding sidewall (spacer) members
103
adjacent the trench sidewalls. After forming the magnetic cladding sidewall members
103
, a conductive material
104
, such as copper or aluminum, is deposited overlying the dielectric layer
103
and within the trench opening
102
. Then, portions of the conductive material
104
not contained within the opening
102
are removed using a chemical mechanical polishing (CMP) process. Finally, an overlying layer of high-permeability magnetic material is deposited, patterned, and etched to form the magnetic cladding capping member
106
.
The magnitude of the magnetic field at the location of the memory element is enhanced by the presence of the cladding, thus less current is required in the conductive material
104
. Because the magnetic cladding capping member
106
is formed overlying the trench
102
, it must be patterned and etched having a width dimension Z which is yet greater than the trench
102
width dimension X. Moreover, alignment of the magnetic cladding capping member
106
to the trench
102
can be critical. Failure to properly align the magnetic cladding capping member
106
over the trench
102
can result in less-than-optimal magnetic fields being generated by the bit line or the undesirable exposure of adjacent circuitry to uncontained magnetic fields. Thus, the dimension Z of the magnetic cladding capping member
106
must additionally be upsized to take into account any alignment tolerance error. Therefore, an ability to reduce the dimension Z of the magnetic cladding capping member
106
can correspondingly improve the scalability of the MRAM array packing density.
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DeBear et al., “Spin-etch Planarization for Dual Damascene Interconnect Structures,” Solid State Technology, 5 pgs. (2000).
Barron Carole C.
Jones Robert E.
Luckowski Eric D.
Melnick Bradley M.
Chaudhuri Olik
Motorola Inc.
Pham Thanh
Rodriguez Robert A.
Vo Kim-Marie
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