Self-aligned MRAM contact and method of fabrication

Details Self-aligned MRAM contact and method of fabrication Self-aligned MRAM contact and method of fabrication

2001-03-15

2004-08-24

Fourson, George (Department: 2823)

Semiconductor device manufacturing: process

Having magnetic or ferroelectric component

C438S238000

Reexamination Certificate

active

06780652

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates MRAM semiconductor structures and, more particularly, to a method of forming self-aligned contacts in MRAM structures.
BACKGROUND OF THE INVENTION
Magnetic random access memories (MRAMs) employ magnetic multilayer films as storage elements. When in use, an MRAM cell stores information as digital bits, which in turn depend on the alternative states of magnetization of thin magnetic multilayer films forming each memory cell. As such, the MRAM cell has two stable magnetic configurations, high resistance representing a logic state 0 and low resistance representing a logic state 1, or vice versa.
A typical multilayer-film MRAM includes a number of bit or digit lines intersected by a number of word lines. At each intersection, a film of a magnetically coercive material is interposed between the corresponding bit line and word line. Thus, this magnetic material and the multilayer films from the digit lines form a magnetic memory cell which stores a bit of information.
The basic memory element of an MRAM is a patterned structure of a multilayer material, which is typically composed of a stack of different materials, such as copper (Cu), tantalum (Ta), permalloy (NiFe) or aluminum oxide (Al
2
O
3
), among others. The stack may contain as many as ten different overlapping material layers and the layer sequence may repeat up to ten times. Fabrication of such stacks requires deposition of the thin magnetic materials layer by layer, according to a predefined order.
FIG. 1
shows an exemplary conventional MRAM structure including MRAM stacks
22
which have three respective associated bit or digit lines
18
. The digit lines
18
, typically formed of copper (Cu), are first formed in an insulating layer
16
formed over underlayers
14
of an integrated circuit (IC) substrate
10
. Underlayers
14
may include, for example, portions of integrated circuitry, such as CMOS circuitry. A pinned layer
20
, typically formed of ferromagnetic materials, is provided over each digit line
18
. A pinned layer is called “pinned” because its magnetization direction does not rotate in the presence of applied magnetic fields.
Many attempts are currently being made to integrate structures of magnetic random access memories, such as the MRAM stack
22
of
FIG. 1
, with semiconductor devices, for example CMOS circuits and/or with circuitry that can be formed over such integrated MRAM/CMOS devices. For this, conventional small contact openings from the pinned layers
20
of
FIG. 1
, for example, to word line conductors (not shown) are typically formed by photolithography techniques.
As known in the art, the photolithography techniques employ a mask that must be previously aligned to define small openings in such MRAM structures. With increased packing density of MRAM cells, however, there is a need for minimizing if not eliminating mask misalignment problems posed by the conventional photolithography techniques when forming small contact openings from MRAM stacks to adjacent circuitry. Accordingly, there is a need for an improved method for fabricating high quality MRAM structures, such as pinned layers and digit lines, which are highly integrated with a CMOS circuit, and which have self-aligned contacts that minimize the misalignment drawbacks of the prior art.
SUMMARY OF THE INVENTION
The present invention provides a method for forming self-aligned MRAM contacts for MRAM structures, such as magnetic layers of an MRAM stack, formed over various underlayers of an integrated circuit substrate. In an exemplary embodiment of the invention, MRAM stacks are formed to include a top layer of a conductive material, such as tungsten nitrogen. An insulating material is formed over the whole substrate including the MRAM stacks. The insulating material is subsequently chemically mechanically polished (CMP) to expose the upper surface of such conductive material and to form a self-aligned MRAM contact on a respective MRAM stack. Subsequent word lines and conductive plugs are formed over the self-aligned MRAM contacts.
These and other features and advantages of the invention will be more apparent from the following detailed description which is provided in connection with the accompanying drawings, which illustrate exemplary embodiments of the invention.


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“Chemical-mechanical polishinig as an enabling technology for giant magnetoresistance devices”, Y.Z. Hu et al., 1997 Elsevier Science SA, vol. 308-309, p. 555-561.

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