Magnetic random access memory and method of manufacturing same

The present invention relates to a non-volatile memory, particularly a magnetic random access memory.

Magnetic Random Access Memory (MRAM) is a high-density non-volatile memory that can be programmed at high speed. MRAM includes multiple memory cells or memory cell arrays and multiple word and bit lines intersecting each other. Traditional magnetic memory cells include magnetic tunnel junctions (MTJs), separation transistors and intersected word and bit lines. The above-mentioned separation transistor is generally an N-type field effect transistor (FET), and the separation transistor is programmed by generating a magnetic tunnel junction surface, a bit line, and a partial magnetic field by cells connected to each other. Connect to each of the word lines of the MRAM cell.

The MTJ cell mainly contains non-magnetic conductors, the lower electrical contact, the plug-type magnetic layer, the tunnel barrier layer provided on the plug-type magnetic layer, and the free magnetic layer (Free) provided on the tunnel barrier layer. Magnetic Layer) is formed, and upper contacts are provided on the free magnetic layer.

The plug-type magnetic layer has a magnetic vector that is permanently oriented in the same direction, and the magnetic vector of the free magnetic layer is not fixed, but is limited by the physical size of the layer and is one of two directions. Is facing. MTJ cells are used for connectivity in the circuit. Then, a current is vertically passed from one layer to another through this MTJ cell. The MTJ cell may be a resistor corresponding to electrical conductivity, and the magnitude of the resistance value is determined by the direction of the magnetic vector. As those who are familiar with the technology can understand, when the directions of these magnetic vectors are opposite, the resistance value of the MTJ cell is high, and when the directions of the magnetic vectors are the same, the resistance value of the MTJ cell is low. Become.

Basically, the bit line is related to each row of the MTJ cell array, and the word line is related to each column of the MTJ cell array. Bit lines and word lines are used for each cell address in the array to read, program, and store data in the array. Further, by applying a predetermined current to the bit line and the word line of the predetermined cell, programming can be performed for the predetermined cell. In this embodiment, the magnetic field generated by the written current is used in the direction of the modified data layer (or free magnetic layer), so that the data is written immediately when the write current is applied.

Theoretically, the resistance value becomes as small as possible in the low resistance value (parallel vector) state, and the resistance value becomes as large as possible in the high resistance value (anti-parallel vector) state, so the change can be detected very easily in the related electronic circuit. can do. Therefore, in the prior art, an improved high-density MRAM element has been required.

<p> An object of the present invention is to provide a high-density MRAM and a method for producing the same.</p>

<p> In order to achieve the above-mentioned object, the present invention provides MRAM and a method for producing the same. The MRAM of the present invention includes a magnetic tunnel junction surface, a first write line and a second write line. The second write line intersects the first write line at right angles, and at least one of the first write line and the second write line is smaller in width than the width of the magnetic tunnel junction surface.</p>

<p> Since the width of the writing line is smaller than the width of the MTJ cell in the present invention, the area used by the MRAM can be effectively reduced. Also, the magnetic field of the MRAM memory array can be increased by using a surrounding magnetic material or keeper layer. In addition, this improved manufacturing method can reduce the possibility that the CMP surface on which the writing line is not flat causes element defects.</p>

FIG. 1A is a plan view showing the structure of the conventional MRAM cell, and FIG. 1B is a side view showing the structure of the conventional MRAM cell. The write line 102 is provided above the other write line 104, which is separated from the write line 102 by a magnetic tunnel junction (MTJ) cell 106 and intersects at a right angle. The magnetic tunnel junction surface 106 is further connected to the N-type field effect transistor (FET) 110 by a connecting cell 108. In this conventional technique, since writing is performed to the MTJ cell 106 by a uniform magnetic field, the widths of the writing lines 102 and 104 are larger than the width of the MTJ cell 106 as shown in the figure, and the magnetic field current is applied when the writing operation is performed. I was able to convert it appropriately.

However, the size of the write line width is inversely proportional to the cell density and directly proportional to the size of the write current, so the design of the MRAM is very costly. In addition, the decrease in write current density also deteriorated the magnetic flux efficiency, further reducing the function of the MRAM.

FIG. 2A is a plan view showing the structure of the MRAM cell according to a preferred embodiment of the present invention, and FIG. 2B is a side view showing the structure of the MRAM cell according to a preferred embodiment of the present invention. The write line 202 is provided above the other write line 204, which is separated from the write line 202 by a magnetic tunnel junction (MTJ) cell 106 and intersects at a right angle. The magnetic tunnel junction surface 106 is further connected to the N-type field effect transistor (FET) 208 by a connecting cell 206.

The width of the writing lines 202 and 204 of this embodiment is smaller than the width of the MTJ cell 106. It should be noted here that even if the shape of the MTJ is rectangular or square, the width described here indicates the length of any one side. Unlike the conventional MRAM cell, in this embodiment, the cell density can be increased and the current of a specific write line can be reduced only by making the width of at least one write line smaller than one side of the MTJ cell. Further, even if a non-uniform magnetic field is applied, the critical current for switching the MRAM cell does not increase. The writing line may be designed as narrow as the minimum design rule in the technology of the time. However, if the line width is too narrow, a non-uniform magnetic field may be generated and a writing error may occur. Therefore, the width of the writing line according to the present embodiment is set to be larger than half the width of the MTJ cell. In other embodiments, the length of the write line width may be set between half the width of the MTJ cell and the same width as the MTJ cell.

FIG. 3 is a perspective view showing a first improved structure of the MRAM cell according to a preferred embodiment of the present invention. FIG. 3 is a perspective view showing a cross-sectional structure 300 of the writing line, which contains a conductive material 302, which is coupled to a shield layer 304 including a ferromagnetic clad layer and an antiferromagnetic material layer. The conductive material 302 is a copper or aluminum metal, and the ferromagnetic clad layer is made of a material such as iron, cobalt, manganese, nickel or the like. The shield layer 304 acts as a keeper layer, concentrating or strengthening the magnetic field 306 found in MTJ cells. Further, in the present embodiment, the shield layer 304 can be formed by a conventional semiconductor manufacturing process including an oxide etching method, a material deposition method, and a chemical mechanical polishing method. As those who are proficient in the technique will understand, the shield layer 304 made of a magnetic material can improve the magnetic flux efficiency when a current flows through a writing line. Therefore, not only the width of the writing line can be further reduced, but also the writing current can be further reduced.

FIG. 4 is a schematic view showing a magnetic tunnel junction surface formed above the writing line of the prior art. Specifically, in the prior art, the lower conductive wire of the MRAM cell is formed by chemical mechanical polishing (CMP). Section 400 of FIG. 4 shows the pattern and writing lines of the MTJ cell structure, which section structure 400 includes oxide 402, conductor 404 and MTJ cell 406. When the CMP process was completed, pores were well formed on the upper edge of the conductor wire as shown by the two dotted circles 408 in FIG. 4 due to the difference in the removal rate between the conductor 404 and the oxide 402.

To solve the above problems, one preferred embodiment of the invention provides improved process steps, as shown in the structure of the MRAM cell of FIGS. 5A-5D. As shown in FIG. 5A, a trench 502 is formed on a substrate 504 of a dielectric material by mask and plasma etching techniques. Subsequently, as shown in FIG. 5B, the filling material 506 is filled in the trench 502 to cover the opening of the trench to form a writing line.

The filling material 506 is a conductor material such as metal. When a magnetic keeper layer is provided on the writing line, the magnetic material is put into the trench before filling the filling material. Further, an adhesive layer may be formed between the keeper layer and the filling material to improve the connectivity between the keeper layer and the filling material. The material layer 508 is then deposited to cover the trench 502. Before depositing the material layer 508, the surface of the conductive material in the trench and the surface of the substrate are first flattened. It should be noted here that other structural design and manufacturing processes may be used as long as the conductive writing line in the trench 502 and the material layer 508 can be electrically connected, and the filling material 506. And the material of material layer 508 may not necessarily be the same. In this step, since the CMP step is performed on one material, the surface region of the material layer 508 can be further flattened. Then, as shown in FIG. 5C, a plurality of material thin films 510 are deposited to form an MTJ cell structure. Finally, as shown in FIG. 5D, a portion of the material layer 508 and a portion of the plurality of thin films 510 are removed to form the MTJ cell 512.

By providing the material layer 508 between the writing line 506 and the MTJ cell 512 to form a buffer layer, complete electrical contact with the writing line 506 is achieved and flat contact with the MTJ cell 512 is performed. The surface can be obtained. In this way, the CMP process can perform a uniform process, and the pores that affect the function can be prevented from being formed by the CMP process.

Since the width of the writing line is smaller than the width of the MTJ cell, the area used by the MRAM memory can be effectively reduced. In this embodiment, the surrounding magnetic material or keeper layer can be used to increase the magnetic field of the MRAM memory array. In addition, this improved manufacturing method can reduce the possibility of element failure due to the uneven CMP surface of the writing line.

Although suitable embodiments have been disclosed in the present invention as described above, these do not limit the present invention by any means, and anyone who is familiar with the art can use various types within the scope of the gist and domain of the present invention. Can be changed or modified. Therefore, the scope of protection of the present invention is based on the content specified in the claims.

<figref num="1A">It is a top view which shows the structure of the conventional MRAM cell.</figref><figref num="1B">It is a side view which shows the structure of the conventional MRAM cell.</figref><figref num="2A">It is a top view which shows the structure of the MRAM cell by one preferred embodiment of this invention.</figref><figref num="2B">It is a side view which shows the structure of the MRAM cell by one preferred embodiment of this invention.</figref><figref num="3">It is a perspective view which shows the 1st improved structure of the MRAM cell by one preferred embodiment of this invention.</figref><figref num="4">It is sectional drawing which shows the structure of the magnetic tunnel junction surface formed above the writing line of the prior art.</figref><figref num="5A">It is sectional drawing which shows the 2nd improved structure of the MRAM cell by one preferred embodiment of this invention.</figref><figref num="5B">It is sectional drawing which shows the 2nd improved structure of the MRAM cell by one preferred embodiment of this invention.</figref><figref num="5C">It is sectional drawing which shows the 2nd improved structure of the MRAM cell by one preferred embodiment of this invention.</figref><figref num="5D">It is sectional drawing which shows the 2nd improved structure of the MRAM cell by one preferred embodiment of this invention.</figref>

Code description

106 Magnetic Tunnel Junction, 202, 204 Writing Line, 206, 208 Connecting Cell, 300 Cross Section, 302 Conductive Material, 304 Shield Layer, 306 Magnetic Field, 502 Trench, 504 Substrate, 506 Filling Material, 508 Material Layer, 510 Thin Film, 512 MTJ cell