Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2003-04-04
2004-11-02
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S295000, C257S421000, C360S324200
Reexamination Certificate
active
06812511
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2002-104388, filed Apr. 5, 2002; and No. 2003-072216, filed Mar. 17, 2003, the entire contents of both of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an information reproduction technique using a ferromagnetic material, and more particularly to a magnetic memory device utilizing a magnetoresistive effect element and a manufacturing method thereof.
2. Description of the Related Art
A magnetic random access memory (which will be abbreviated to an MRAM hereinafter) is a generic designation of solid-state memories which utilize a magnetization direction of a ferromagnetic material as a recording medium for information and are capable of rewriting, holding and reading recorded information at any time.
A memory cell of the MRAM usually has a structure in which a plurality of ferromagnetic materials are superimposed. Information is recorded by parallelizing or anti-parallelizing the relative arrangement of magnetization of a plurality of ferromagnetic materials constituting the memory cell, and associating the parallel or anti-parallel state with binary information “1” or “0”. Recorded information is written by passing a current to write lines arranged in the form of cross strips, and reversing the magnetization direction of the ferromagnetic materials in each cell. It is a non-volatile memory that power consumption when holding recorded information is zero in theory and recorded information is held even if a power supply is turned off. On the other hand, recorded information is read by utilizing a phenomenon that an electrical resistance of the memory cell varies depending on a relative angle between the magnetization direction of the ferromagnetic materials constituting the cell and a sense current or a relative angle of magnetization between a plurality of ferromagnetic layers, which is a so-called magnetoresistive effect.
Comparing functions of the MRAM with functions of a conventional semiconductor memory using a dielectric substance, the MRAM has many advantages. That is, for example, (1) the MRAM is completely non-volatile and rewriting for 10
15
times or more is possible, (2) nondestructive reading is enabled and a refresh operation is not required, thereby shortening a read cycle, and (3) the resistance against radiation rays is strong as compared with a charge storage type memory cell, and others. It is predicted that a degree of integration per unit area and write and read times of the MRAM can be roughly the same as those of a DRAM. Exploiting the great characteristic of non-volatility, therefore, application to an external memory device for a portable device, a use with an LSI and a main storage memory in a personal computer is expected.
At present, the MRAM which has been examined to be put into practical use employs an element which demonstrates a tunneling magnetoresistive effect (which will be abbreviated to a TMR effect hereunder) for the memory cell (for example, see a non-patent cited reference 1). The element demonstrating the TMR effect (which will be referred to as an MTJ (Magnetic Tunneling Junction) element hereinafter) is mainly formed by a three-layer structure consisting of a ferromagnetic layer/an insulating layer/a ferromagnetic layer, and a current flows with the insulating layer being tunneled. A tunnel resistance value varies in proportion to a cosine of a relative angle of magnetizations of the both ferromagnetic metal layers, and takes a local maximum value when the both magnetizations are anti-parallel. At a tunnel junction consisting of, e.g., NiFe/Co/Al
2
O
3
/Co/NiFe, a magnetoresistive change ratio exceeding 25% is found in a low magnetic field not more than 50 Oe (see, e.g., a non-patent cited reference 2). As a structure of the MTJ element, there are known a so-called spin valve structure in which an antiferromagnetic material is arranged in contiguity with one ferromagnetic material and the magnetization directions are fixed for the purpose of improving the field sensitivity (see, e.g., a non-patent cited reference 3), and a structure that a double tunnel barrier is provided in order to improve the bias dependence of a magnetoresistive change rate (see, e.g., a non-patent cited reference 4).
When applying the MTJ element to the MRAM, electrodes at both ends of the MTJ element must be connected to data lines and an external circuit such as a selection transistor or the like. In particular, since the MTJ element has a vertical structure, the element separation must be carried out by using the insulating film when connecting the upper electrode on the MTJ element to an external wiring. As this insulating film, a contact hole for wiring connection is formed. As a method of forming the contact hole, there are mainly used two methods, i.e., (1) a method of using a resist mask and etching the insulating film by reactive chemical etching or the like, and (2) a method of forming the insulating film while leaving a resist used in element processing and then peeling the resist by using a solvent or the like (self-alignment process).
The method (1), however, has a drawback that a mask alignment margin in the above-described process defines a minimum processing dimension and it is difficult to realize minuteness, and other drawbacks. Further, the method (2) has a disadvantage that peeling of the resist is difficult when realization of minuteness advances and a thickness of the photoresist becomes approximately equal to an element dimension. It is to be noted that a patent cited reference 1 discloses a method of depositing an insulating film on the entire surface after processing the element, then performing etch-back to the element surface and opening the contact in the self-alignment manner as a manufacturing method realized by improving the method (2).
Non-patent Cited Reference 1
Roy Scheuerlein, et al., A 10 ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel Junction and FET Switch in each cell, “2000 ISSCC Digest of Technical Papers”, (USA), Febuary, 2000, p. 128-129
Non-patent Cited Reference 2
M Sato, et al., Spin-Valve-Like Properties and Annealing Effect in Ferromagnetic Tunnel Junctions, “IEEE Trans. Mag.”, (USA), 1997, Vol. 33, No. 5, p. 3553-3555
Non-patent Cited Reference 3
M Sato, et al., Spin-Valve-Like Properties of Ferromagnetic Tunnel Junctions, “Jpn. J. Appl. Phys”, 1997, Vol. 36, Part 2, p. 200-201
Non-patent Cited Reference 4
K Inomata, et al., Spin-dependent tunneling between a soft ferromagnetic layer and hard magnetic nano particles, “Jpn. J. Appl. Phys.”, 1997, Vol. 36, Part 2, p. 1380-1383
Patent Cited Reference 1
Specification of U.S. Pat. No. 5,841,692
A concrete example when the MTJ element is applied to the MRAM will now be described with reference to the accompanying drawings.
FIG. 27A
is a plane view showing a magnetic memory device according to a prior art.
FIG. 27B
is a cross-sectional view of the magnetic memory device taken along the line XXVIIB—XXVIIB in FIG.
27
A.
FIGS. 28A and 28B
are cross-sectional views of a magnetic memory device including a memory cell portion (which will be referred to as a cell portion hereinafter) of the magnetic memory device according to the prior art and a peripheral circuit portion (which will be referred to as a core portion hereinafter) of the magnetic memory device. In the cell portion, as shown in
FIG. 28A
, a magnetoresistive effect element
14
a
is arranged on a lower metal layer
13
a
, and the magnetoresistive effect element
14
a
is connected to a selection transistor
3
a
through the lower metal layer
13
a
and a contact
12
. On the other hand, a magnetoresistive effect element and a lower metal layer are not formed in the core portion as shown in FIG.
28
B.
FIGS. 29A and 29B
to
FIGS. 38A and 38B
show a method of manufacturing a cell portion and a core portion of a magnetic memory device illustrated in
FIG
Amano Minoru
Nakajima Kentaro
Kabushiki Kaisha Toshiba
Nelms David
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tran Mai-Huong
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