JP2005085805A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device which is equipped with a magnetoresistive element where data can be written in with a smaller current. <P>SOLUTION: Either line 10 of a word line and a bit line sandwiching a TMR element of MRAM between them is so formed as to make its side closer to the TMR element than its other side wider in line width than the other side, and to be trapezoidal in cross section. By this setup, a uniform magnetic field can be generated by this line more efficiently toward the TMR element than by a conventional line which is rectangular or square in cross section and set equal in current density to the above line, and a writing current can be reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a structure in which a magnetoresistive element is sandwiched between a write word line (digit line) and a bit line.

  In recent years, research and development of a magnetic random access memory (MRAM), which is a magnetic semiconductor memory device, has become very active (see, for example, Patent Document 1). The MRAM is a memory having very excellent potential such as non-volatility, low voltage operation, infinite number of writing / reading, high speed, large capacity, and radiation resistance.

FIG. 10 shows an example of the structure of a conventional MRAM. However, FIG. 10 shows only one memory cell among the plurality of memory cells formed in the MRAM.
10 includes an MRAM module having a write word line 101, a tunnel magnetoresistance (TMR) element 102, and a bit line 103 via a conductive layer 104 and a conductive plug 105, and a complementary metal oxide semiconductor (CMOS). ). In the CMOS, a read word line 108 is formed on a silicon (Si) substrate 107 on which an impurity diffusion layer 106 is formed. The CMOS impurity diffusion layer 106 is connected to the bit line 103 of the MRAM module through the conductive layer 104 and the conductive plug 105. The TMR element 102 of the MRAM module is formed at a position where the bit line 103 intersects the write word line 101, and a magnetic tunnel junction (Magnetic magnetic field) in which a nonmagnetic layer 109 is sandwiched between a magnetic pinned layer 110 and a free layer 111. Tunnel Junction (MTJ) structure.

FIG. 11 is a conceptual diagram illustrating the switching characteristics of the TMR element. However, in FIG. 11, the same elements as those shown in FIG. 10 are denoted by the same reference numerals.
As described above, the TMR element 102 has a laminated structure of magnetic body (pinned layer 110) / nonmagnetic body (nonmagnetic layer 109) / magnetic body (free layer 111). As shown in FIG. When the spins are in the same direction, the resistance is low, and when the spins are in the opposite direction, the resistance is high. Using this property, data is recorded as 1 and 0 according to the level of the resistance, and the data recorded according to the level of the resistance is read out.

FIG. 12 is a conceptual diagram illustrating the switching mechanism of the TMR element. However, in FIG. 12, the same elements as those shown in FIG.
The TMR element 102 is formed between the wiring lines at the intersection of the write word line 101 and the bit line 103 formed in a square section or a rectangular section. When a current flows through both the write word line 101 and the bit line 103, a magnetic field corresponding to the direction of the current is generated around each of the lines. By this magnetic field, the spin of the free layer 111 shown in FIGS. 10 and 11 of the TMR element 102 is reversed, and writing to the MRAM 100 is performed.
JP 2002-520767 A

  As described above, in the MRAM, at the time of writing, current must be passed through the bit line and the writing word line to generate a magnetic field, and the spin of the free layer of the TMR element must be reversed. However, writing to such MRAM usually requires a large writing current of several mA. A magnetic semiconductor memory device that can reverse the spin of the free layer with a smaller current is desired.

  The present invention has been made in view of such a point, and an object thereof is to provide a semiconductor device having a magnetoresistive element in which writing is performed with a smaller current.

  In order to solve the above problem, the present invention provides a semiconductor device having the wiring structure illustrated in FIG. In the semiconductor device according to the present invention, in a memory cell having a structure in which a magnetoresistive element is sandwiched between wirings, at least one of the wirings (wiring 10) sandwiching the magnetoresistive element is on the surface side close to the magnetoresistive element. The line width is formed to be longer than the line width on the surface side far from the magnetoresistive element.

  According to such a semiconductor device, the wiring 10 sandwiching the magnetoresistive element such as the TMR element is formed so that the line width on the surface side close to the TMR element is longer than the line width on the surface side far away. This makes it possible to generate a more efficient and uniform magnetic field on the TMR element side as compared with the case where the current density is the same in the conventional wiring having a rectangular cross section or a square cross section.

  The semiconductor device of the present invention can increase the magnetic field generation efficiency from the wiring sandwiching the magnetoresistive element and can generate a more uniform magnetic field, so that the write current can be reduced. Thereby, the power consumption of the magnetic semiconductor memory device can be reduced, and writing to the adjacent memory cell can be suppressed and the operation margin can be widened.

  The reduction of the write current in the MRAM portion of the semiconductor device has been realized by a wiring structure that generates a uniform magnetic field with high magnetic field generation efficiency. In the following description, the wiring refers to a write word line and / or a bit line of the MRAM.

First, the first wiring structure will be described.
FIG. 1 is a schematic cross-sectional view of the first wiring structure of the MRAM portion.
As shown in FIG. 1, the wiring 10 that is the first wiring structure has a trapezoidal shape with a cross-sectional shape having a long side of 0.15 μm, a short side of 0.05 μm, and a height of 0.1 μm. It is assumed that an MRAM TMR element is formed on the upper side (the long side of the trapezoid) in FIG.

  With respect to the wiring 10 having such a shape, a generated current magnetic field is calculated using a three-dimensional electromagnetic field simulator. However, for comparison, the current magnetic field is also calculated for the wiring shown in FIG. 2 as a conventional wiring structure.

FIG. 2 is a schematic cross-sectional view of a conventional wiring structure of the MRAM portion.
For comparison with the first wiring structure, a wiring 40 having a square cross section as shown in FIG. 2 is used here as a conventional wiring structure. In the calculation of the current magnetic field using the three-dimensional electromagnetic field simulator, it is assumed that the wiring 40 is a square having a cross-sectional shape of 0.1 μm per side and a TMR element is formed in the upper part in FIG. Therefore, the wiring 10 in FIG. 1 and the wiring 40 in FIG. 2 have the same cross-sectional area, and the wiring 10 has a longer line width near the TMR element than the wiring 40 due to its shape. ing. That is, the line 10 has a line width near the TMR element of 0.15 μm and a line width of the far side 0.05 μm, and the line 40 has a line width of both the near side and the far side. It is 0.1 μm.

  In the calculation of the current magnetic field, the magnitude of the current flowing through the wirings 10 and 40 is the same. Also, in this calculation, as shown in FIGS. 1 and 2, the width direction of the wirings 10 and 40 is the X-axis direction, and the direction perpendicular to the X-axis direction is the Y-axis direction. The center in the width direction on the surface to be processed is set to X = 0 μm and Y = 0 μm.

FIG. 3 is a diagram showing the X-axis direction distance dependency of the magnetic field strength when Y = 0.05 μm.
In FIG. 3, the horizontal axis represents the distance (μm) in the X-axis direction, and the vertical axis represents the magnetic field strength (Oe / mA). In FIG. 3, the solid line shows the calculation result for the first wiring structure, and the dotted line shows the calculation result for the conventional wiring structure.

  FIG. 3 shows that the first wiring structure and the conventional wiring structure have the same cross-sectional area and the same current, but the first wiring structure is more conventional when X = 0 μm. The magnetic field strength is 5% to 10% stronger than the wiring structure. The magnetic field strength of the first wiring structure remains strong until X = 0.1 μm. From around X = 0.15 μm, the magnitude relationship of the magnetic field strength is reversed, and the conventional wiring structure has a stronger magnetic field strength.

  As described above, according to the trapezoidal wiring 10 having a long side on the side where the TMR element is formed, the writing efficiency with respect to the TMR element can be increased as compared with the wiring 40 having a square cross section. The influence of the magnetic field on the TMR element can be reduced.

Next, the second wiring structure will be described.
FIG. 4 is a schematic cross-sectional view of the second wiring structure of the MRAM portion.
As shown in FIG. 4, the wiring 20 which is the second wiring structure has a cross-sectional shape in which a rectangle of 0.15 μm × 0.05 μm and a square of 0.05 μm × 0.05 μm are overlapped. It is assumed that a TMR element is formed above 20 (rectangular side) in FIG. When the wiring 20 in FIG. 4 and the conventional wiring 40 in FIG. 2 are compared, both have the same cross-sectional area. From the shape, the wiring 20 is closer to the TMR element than the wiring 40. The line width on the side is long. That is, the wiring 20 has a line width on the surface side close to the TMR element of 0.15 μm, and a line width on the surface side far from the TMR element is 0.05 μm.

  A current magnetic field is calculated for these wirings 20 and 40 using a three-dimensional electromagnetic field simulator. In the calculation of the current magnetic field, the magnitude of the current flowing through the wirings 20 and 40 is the same. In this calculation, as shown in FIG. 4, the width direction of the wiring 20 is defined as the X-axis direction, and the direction perpendicular thereto is defined as the Y-axis direction. = 0 μm, Y = 0 μm.

FIG. 5 is a graph showing the X-axis direction distance dependency of the magnetic field strength when Y = 0.05 μm.
In FIG. 5, the horizontal axis represents the distance (μm) in the X-axis direction, and the vertical axis represents the magnetic field strength (Oe / mA). In FIG. 5, the solid line indicates the calculation result for the second wiring structure, and the dotted line indicates the calculation result for the conventional wiring structure.

  As shown in FIG. 5, the second wiring structure and the conventional wiring structure have almost the same magnetic field strength when X = 0 μm, although they have the same cross-sectional area and the same current, but X = 0. Up to about 15 μm, the second wiring structure has a smaller decrease in magnetic field strength when X increases. For example, at X = 0.05 μm, the magnetic field strength of the second wiring structure is about 10% larger. From this, it can be said that the second wiring structure is more uniform as the magnetic field exerted on the TMR element than the conventional wiring structure. From around X = 0.15 μm, the magnitude relationship of the magnetic field strength is reversed, and the conventional wiring structure has a stronger magnetic field strength.

  As described above, the wiring 20 having a cross-sectional shape formed of a rectangle and a square so that the TMR element side is rectangular can also improve the writing efficiency for the TMR element as compared with the conventional wiring 40 having a square cross-section. The influence of the magnetic field on the TMR element of the adjacent memory cell can be reduced.

Next, a third wiring structure will be described.
FIG. 6 is a schematic cross-sectional view of the third wiring structure of the MRAM portion.
In the third wiring structure shown in FIG. 6, the wiring 30 has a long side of 0.15 μm, a short side of 0.05 μm, and a height of 0, similar to the wiring 10 of the first wiring structure shown in FIG. It is assumed that a trapezoid of 1 μm is formed, and a TMR element is formed above the wiring 30 in FIG. 6 (the long side of the trapezoid). Accordingly, the wiring 30 has a line width on the surface side close to the TMR element of 0.15 μm, and a line width on the surface side far from the TMR element is 0.05 μm.

  Further, in the third wiring structure, a magnetic clad layer 31 having a thickness of 0.01 μm, a relative permeability μ = 1000, and a saturation magnetization of 1T is provided around the wiring 30 except for the surface on the TMR element side. Yes. In this respect, the third wiring structure shown in FIG. 6 is different from the first wiring structure shown in FIG.

  In the calculation of the current magnetic field using the three-dimensional electromagnetic field simulator for such a third wiring structure, the calculation is also performed for the fourth wiring structure as shown in FIG.

FIG. 7 is a schematic cross-sectional view of the fourth wiring structure of the MRAM portion.
In the fourth wiring structure shown in FIG. 7, the wiring 50 is a square having a cross-sectional shape of 0.1 μm per side, like the wiring 40 of the conventional wiring structure shown in FIG. It is assumed that a TMR element is formed in the middle upper part. Accordingly, the wiring 50 has a line width of 0.1 μm on both the surface side close to the TMR element and the surface side far from the TMR element.

  Further, in the fourth wiring structure, as in the third wiring structure, the thickness of 0.01 μm, the relative permeability μ = 1000, and the saturation magnetization 1T are provided around the wiring 50 except for the surface on the TMR element side. A body cladding layer 51 is provided. In this respect, the fourth wiring structure shown in FIG. 7 is different from the conventional wiring structure shown in FIG.

  The wirings 30 and 50 in the third and fourth wiring structures have the same cross-sectional area, and the cross-sectional areas of the wirings 10 and 40 in the first and conventional wiring structures are also equal. In addition, due to the shape of the wirings 30 and 50, the wiring 30 has a longer line width near the TMR element than the wiring 50. When the current magnetic field is calculated by the three-dimensional electromagnetic field simulator, the magnitudes of the currents flowing through the wirings 30 and 50 are the same. Further, as shown in FIGS. 6 and 7, the width direction of the wirings 30 and 50 is the X-axis direction, and the direction orthogonal to the width direction is the Y-axis direction. The direction center is set to X = 0 μm and Y = 0 μm.

FIG. 8 is a graph showing the dependence of the magnetic field strength on the Y-axis direction distance when X = 0 μm.
In FIG. 8, the horizontal axis represents the distance (μm) in the Y-axis direction, and the vertical axis represents the magnetic field strength (Oe / mA). In FIG. 8, the alternate long and short dash line indicates the calculation result for the third wiring structure, and the alternate long and two short dashes line indicates the calculation result for the fourth wiring structure. FIG. 8 also shows the calculation results for the first and second wiring structures, with the solid line indicating the calculation results for the first wiring structure and the dotted line indicating the calculation results for the second wiring structure. Each is shown.

  As shown in FIG. 8, the magnetic field strength generated in the third and fourth wiring structures in which the magnetic cladding layers 31 and 51 are provided is larger than that in the first and conventional wiring structures in which the magnetic cladding layer is not provided. Is getting stronger. This tendency is particularly remarkable in the region where the distance in the Y-axis direction is small, that is, in the region close to the wirings 10, 30, 40, and 50. Further, for the third and fourth wiring structures, the third wiring structure in which the magnetic clad layer 31 is provided in the trapezoidal cross section wiring 30 is provided with the magnetic cladding layer 51 in the wiring 50 having a square cross section. Compared to the fourth wiring structure, a higher magnetic field strength can be obtained.

  Thus, by providing the magnetic clad layers 31 and 51 around the wirings 30 and 50 excluding the surface on the TMR element side, the magnetic field generation efficiency on the TMR element side can be improved as compared with the case where no magnetic clad layer is provided. Can be improved. Furthermore, like the wiring 30, the cross-sectional shape is trapezoidal, and the line width on the surface side close to the TMR element is increased, so that the TMR element side is more efficient than the wiring 50 having a square cross section. It becomes possible to generate a magnetic field.

FIG. 9 is a diagram showing the X-axis direction distance dependency of the magnetic field strength when Y = 0.3 μm.
In FIG. 9, the horizontal axis represents the distance (μm) in the X-axis direction, and the vertical axis represents the magnetic field strength (Oe / mA). In FIG. 9, the alternate long and short dash line indicates the calculation result for the third wiring structure, the alternate long and two short dashes line indicates the calculation result for the fourth wiring structure, the solid line indicates the calculation result for the first wiring structure, and the dotted line indicates the calculation result. The calculation results for the conventional wiring structure are shown.

  From FIG. 9, although all the wirings 10, 30, 50, and 40 in the first, third, fourth, and conventional wiring structures have the same cross-sectional area and the same magnitude of current, X = At 0 μm, the magnetic field strength is about 6 Oe / mA for the first and conventional wiring structures, and the magnetic field strength is about 15 Oe / mA for the fourth wiring structure. In the third wiring structure, the magnetic field strength is about 25 Oe / mA when X = 0 μm, and the generated magnetic field is increased by 60% or more compared to the fourth wiring structure. In the case of the wirings 10 and 40 having the first and conventional wiring structures in which the magnetic clad layer is not provided, the generated magnetic field is increased by about 5% when the trapezoidal cross-sectional shape is larger than the square cross-sectional shape. By providing the clad layer 31, the effect of the wiring shape is further enhanced.

  From FIG. 9, the magnetic field intensity is stronger in the third wiring structure than in the fourth wiring structure from X = 0 μm to X = 0.3 μm, and conversely when X becomes larger than that. The fourth wiring structure has a stronger magnetic field strength. In the MRAM, for example, a wiring of a certain memory cell and a wiring of a memory cell adjacent to the memory cell are formed with a distance of about 0.3 μm. Therefore, according to the third wiring structure, it is possible to increase the writing efficiency to the TMR element by appropriately setting the distance of the TMR element between the adjacent memory cells, and also the adjacent memory cell. The influence of the magnetic field on the TMR element of the cell can be reduced.

The same effect can be obtained even if a magnetic clad layer is formed around the wiring 20 in the second wiring structure except for the surface on the TMR element side.
As described above, the wiring structure formed in the MRAM has a cross-sectional shape that is a trapezoid having a long side on the TMR element side, so that the magnetic field generation efficiency is higher than when the cross-sectional shape is a square with the same cross-sectional area. Can be increased. The wiring structure is the same even if the cross-sectional shape is a structure in which a rectangle and a square are overlapped and the rectangle side is the TMR element side. With such a wiring structure, a write current can be reduced. As a result, the power consumption of the MRAM can be reduced, and writing to the adjacent memory cell is suppressed and the operation margin is increased.

  Furthermore, by providing a structure in which a magnetic clad layer is provided around the periphery of the trapezoidal cross-section wiring or the cross-section wiring combining the rectangle and the square, except for the surface on the TMR element side, It becomes possible to further increase the magnetic field generation efficiency.

  In the case of a wiring structure having a trapezoidal cross section and a magnetic clad layer, first, a magnetic clad layer is formed by sputtering, for example, on a cross section trapezoidal groove formed by etching or the like, and then copper (Cu) or aluminum ( A wiring metal such as Al) is deposited. In this case, since the wall surface of the groove having a trapezoidal cross section is inclined toward the bottom of the groove, the magnetic wall cladding and the bottom of the groove are more uniform than the magnetic clad layer formed on the groove having a square cross section. A body cladding layer can be formed.

  In the above description, the case of a wiring structure having a trapezoidal cross section and a wiring structure having a sectional shape combining a rectangle and a square has been described. However, the wiring sectional shape of the MRAM unit according to the present invention is not limited to this. . For example, the cross-sectional shape of the wiring may be a triangle or another polygon. In the present invention, the line width on the surface side close to the TMR element of the wiring is formed so as to be longer than the line width on the surface side far away, or the magnetic body is formed around the wiring except for the surface on the TMR element side. It suffices if a cladding layer is provided.

  Furthermore, the line width of the wiring described in the above description is set as an example so that the cross-sectional area of each wiring becomes equal in order to study the difference in magnetic field generation efficiency. It is not limited to the illustrated line width, and is designed according to the memory cell integration degree, the memory cell dimension, the TMR element size, and the like. Similarly, the values of the thickness, relative permeability, and saturation magnetization described in the above description are examples for the magnetic clad layer, and the design can be changed as necessary.

  The above wiring structure may be formed on both the write word line and the bit line in the MRAM portion, or may be formed only on either the write word line or the bit line.

  Further, in forming the wiring of the MRAM portion, it is desirable to form the wiring so that the width of the wiring is wider than that of the TMR element. By forming the wiring with such a line width, the magnetic field generated from the wiring in one memory cell can be effectively applied to the TMR element of the memory cell.

  The wiring structure including the magnetoresistive element of the present invention is applied to a semiconductor device in which a logic cell and a memory cell are mixedly mounted. In addition to a TMR element, a magnetism using a giant magnetoresistive (GMR) element is used. It can also be applied to a semiconductor memory device.

It is a cross-sectional schematic diagram of the 1st wiring structure of an MRAM part. It is a cross-sectional schematic diagram of the conventional wiring structure of the MRAM part. It is a figure which shows the X-axis direction distance dependence of the magnetic field intensity in case of Y = 0.05 micrometer. It is a cross-sectional schematic diagram of the 2nd wiring structure of an MRAM part. It is a figure which shows the X-axis direction distance dependence of the magnetic field intensity in case of Y = 0.05 micrometer. It is a cross-sectional schematic diagram of the 3rd wiring structure of an MRAM part. It is a cross-sectional schematic diagram of the 4th wiring structure of an MRAM part. It is a figure which shows the Y-axis direction distance dependence of the magnetic field intensity in case of X = 0 micrometer. It is a figure which shows the X-axis direction distance dependence of the magnetic field intensity in case of Y = 0.3 micrometer. It is a figure which shows one structural example of MRAM. It is a conceptual diagram explaining the switching characteristic of a TMR element. It is a conceptual diagram explaining the switching mechanism of a TMR element.

Explanation of symbols

10, 20, 30, 40, 50 Wiring 31, 51 Magnetic clad layer

Claims (5)

In a semiconductor device including a structure in which a magnetoresistive element is sandwiched between wirings,
At least one of the wirings sandwiching the magnetoresistive element is formed such that the line width on the surface side close to the magnetoresistive element is longer than the line width on the surface side far from the magnetoresistive element. Semiconductor device.   The wiring formed so that the line width on the surface side close to the magnetoresistive element is longer than the line width on the surface side far from the magnetoresistive element is magnetic around the surface except for the surface side close to the magnetoresistive element. 2. The semiconductor device according to claim 1, further comprising a body cladding layer.   The wiring formed so that the line width on the surface side close to the magnetoresistive element is longer than the line width on the surface side far from the magnetoresistive element has a cross-sectional shape with a long side on the side close to the magnetoresistive element. 2. The semiconductor device according to claim 1, wherein the side far from the magnetoresistive element is a trapezoid having a short side.   The wiring formed so that the line width on the surface side close to the magnetoresistive element is longer than the line width on the surface side far from the magnetoresistive element has a cross-sectional shape of a rectangle or a square having a different cross-sectional area, 2. The semiconductor device according to claim 1, wherein the semiconductor device has a shape of being overlapped toward the magnetoresistive element so that a side closer to the magnetoresistive element is longer than a side far from the magnetoresistive element.   The wiring formed so that the line width on the surface side close to the magnetoresistive element is longer than the line width on the surface side far from the magnetoresistive element, the line width on the surface side close to the magnetoresistive element is 2. The semiconductor device according to claim 1, wherein the semiconductor device is formed wider than the magnetoresistive element.

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