Resistance change memory

According to one embodiment, a resistance change memory includes resistance change elements arrayed with a first space in a first direction and with a second space wider than the first space in a second direction orthogonal to the first direction, second conductive layers disposed on sidewalls of the resistance change elements, each of the second conductive layers having a width greater than or equal to a half of the first space in the first direction and having a width less than a half of the second space in the second direction, the second conductive layers functioning as a first bit line extending in the first direction, a second insulating layer disposed on a sidewall of the first bit line, and not filling the second space, and a third conductive layer functioning as a second bit line extending in the first direction by filling the second space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-135191, filed Jun. 14, 2012, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a resistance change memory.

BACKGROUND

Microfabrication of a memory cell and reduction of a manufacturing cost are required in a resistance change memory including a resistance change element in which a resistance value changes according to a current, a voltage, heat and a magnetic field. However, in the resistance change memory, for example, in order to read and write data, one memory cell includes one resistance change element and one selection transistor, and two bit lines are connected to one memory cell. In this case, a size per memory cell is hardly formed smaller than a constant value, and a lithography process is required to form the bit line and a via.

DETAILED DESCRIPTION

In general, according to one embodiment, a resistance change memory includes: resistance change elements arrayed with a first space in a first direction and with a second space wider than the first space in a second direction orthogonal to the first direction, each of the resistance change elements including a variable resistance layer, a first conductive layer on the variable resistance layer, and a first insulating layer covering a sidewall of at least the variable resistance layer; second conductive layers disposed on sidewalls of the first insulating layer and the first conductive layer of resistance change elements respectively, each of the second conductive layers having a width greater than or equal to a half of the first space in the first direction and having a width less than a half of the second space in the second direction, the second conductive layers functioning as a first bit line extending in the first direction by connecting the resistance change elements arrayed in the first direction; a second insulating layer disposed on a sidewall of the first bit line, and not filling the second space; and a third conductive layer functioning as a second bit line extending in the first direction by filling the second space.

In a process of manufacturing the resistance change memory, generally the via disposed in the same layer as the resistance change element and the bit lines disposed above the via and the resistance change element are formed by the lithography process. However, as described above, in this case, the size per memory cell is hardly formed smaller than the constant value, and the manufacturing cost increases by increasing the number of lithography processes.

Therefore, in the following embodiment, there is proposed a technology in which the microfabrication of the memory cell and the reduction of the manufacturing cost are achieved by forming the bit line in a self-aligned manner with respect to the resistance change element irrespective of the lithography process.

Specifically, using a sidewall process technology, a sidewall conductive layer is formed as the bit line on sidewalls of resistance change elements arrayed with a first pitch in a first direction. In this case, a width in the first direction of the sidewall conductive layer is controlled at a constant value or more in order that the sidewall conductive layer acts as the bit line.

For example, in the case of a 1T1R-type cell structure in which one memory cell includes one resistance change element and one selection transistor, first and second bit lines are connected to the one memory cell. The first bit line is formed in the self-aligned manner with respect to the resistance change element by the sidewall process technology.

The second bit line is formed in a space formed in the self-aligned manner between the first bit lines such that a pitch in a second direction orthogonal to the first direction of the arrayed the resistance change elements is wider than the pitch in the first direction. That is, for example, the second bit line is formed in the self-aligned manner with respect to the first bit line using a burying technology, such as a damascene technology.

As used herein, the resistance change element means an element in which the resistance value changes according to the current, the voltage, the heat, the magnetic field, and the like. The variable resistance memory is a semiconductor memory in which the resistance change element is used as the memory cell. Examples of the variable resistance memory include an MRAM (Magnetic Random Access Memory) in which a magnetoresistive element is used as the memory cell and a ReRAM (Resistive Random Access Memory) in which metal oxide is used as the memory cell.

First Structure Example

FIG. 1illustrates a first structure example of the resistance change memory.FIG. 2is a sectional view along line II-II inFIG. 1, andFIG. 3is a sectional view along line III-III inFIG. 1.

The first structure example relates to structure of a bit line BL1and a bit line BL2, in which the size per memory cell can be reduced than ever before in the case that resistance change elements R are arrayed with a pitch P1in the first direction and arrayed with a pitch P2wider than the pitch P1in a second direction orthogonal to the first direction.

For the first structure example, various modifications can be made in the underlayer structure of the resistance change elements R, for example, a layout of a memory cell array including a switch elements (FET: Field Effect Transistor) connected to the resistance change element R and word lines. Therefore, in the first structure example, only the resistance change element R and bit lines BL1and BL2are described below.

The layout of the memory cell array including the switch element and the word line is described in application examples.

For example, an underlayer10is an insulating layer or a semiconductor layer. When the underlayer10is the insulating layer, a contact plug (a conductive layer) may be provided in the underlayer10immediately below the resistance change element R.

The resistance change elements R are arrayed on the underlayer10.

Each of the resistance change elements R includes a variable resistance layer11, a first conductive layer12on the variable resistance layer11, and a first insulating layer13that covers a sidewall of the variable resistance layer11. For example, the first conductive layer12acts as a hard mask layer when the variable resistance layer11is patterned. For example, the first insulating layer13acts as a protective layer that protects the variable resistance layer11.

When the first insulating layer13acts as the protective layer, it is necessary for the first insulating layer13to cover at least the sidewall of the variable resistance layer11. Therefore, for example, the oxidation of the sidewall of the variable resistance layer11can be prevented.

In the first structure example, an end portion located in a third direction (a direction perpendicular to an upper surface of the underlayer10) orthogonal to the first and second directions of the first insulating layer13exists between a lower surface and an upper surface of the first conductive layer12. Desirably the sidewall of the first conductive layer12is not covered with the first insulating layer13as much as possible. This is because a contact resistance between the first conductive layer12and the second conductive layer14can be decreased with increasing contact area between the two.

The resistance change elements R are disposed in the first direction with a first space SP1, and disposed in the second direction with a second space SP2wider than the first space SP1.

For example, assuming that F is a reference value, the resistance change elements R are disposed in the first direction with a pitch 2F, and disposed in the second direction with a pitch 4F. For example, each of the resistance change elements R has a cylindrical shape having a diameter (a size) of F (the reference value).

F is the reference value that is used to determine the layout of an LSI in design. Although F is not particularly fixed, F means a minimum dimension (a feature size or a half pitch of line and space) that can be formed by photolithography.

In this case, for example, the first space SP1is equal to F, and the second space SP2is equal to 3F.

A second conductive layer14is a sidewall conductive layer, and is disposed on the sidewalls of the first insulating layer13and the first conductive layer12.

Because a width T in the first direction of the second conductive layer14is greater than or equal to a half of the first space SP1(for example, at least F/2), in the second conductive layer14, the resistance change elements R arrayed in the first direction are connected to each other to construct the first bit line BL1extending in the first direction.

The first bit line BL1is constructed by the sidewall conductive layer. Therefore, as is clear fromFIG. 1, a side surface of the first bit line BL1has the layout in which convex curved surfaces is connected.

On the other hand, because the width T in the second direction of the second conductive layer14is less than a half of the second space SP2(for example, less than 3F/2), in the second conductive layer14, the resistance change elements R arrayed in the second direction are not connected to each other.

For example, assuming that second conductive layer14is formed with an even thickness T around the resistance change element R, the width T in the second direction of the second conductive layer14is set to a range of F/2≦T<3F/2.

A second insulating layer15is a sidewall insulating layer, and is disposed on the sidewall of the second conductive layer14. Because the second insulating layer15is provided to electrically insulate the first bit line BL1from the second bit line BL2, it is necessary for the second insulating layer15to have the sufficient thickness.

In the second insulating layer15, because the second bit line BL2is disposed between the first bit lines BL1, it is necessary that the second space SP2be not filled with the second insulating layer15. The second space SP2is filled with a third conductive layer16to construct the second bit line BL2extending in the first direction. That is, the third conductive layer16has a damascene structure.

The second bit line BL2is located in the second space SP2between the first bit lines BL1. Therefore, as is clear fromFIG. 1, the side surface of the second bit line BL2has the layout in which concave curved surfaces is connected.

As can be seen fromFIGS. 1 and 2, the widths in the second direction of the first and second bit lines BL1and BL2vary according to a position. Desirably, in order to equalize wiring resistances of the first and second bit lines BL1and BL2, an average width in the second direction of the second bit line BL2is substantially equal to double (2T) the width T in the second direction of the second conductive layer (the sidewall conductive layer) constructing the first bit line BL1.

According to the first structure example, the first bit line BL1is constructed by the second conductive layer (sidewall conductive layer)14, and the second bit line BL2is constructed by the third conductive layer (damascene structure)16. Therefore, it is not necessary that the first bit line BL1and the second bit line BL2be formed by the lithography process. Additionally, the via is also eliminated, so that the reduction of the manufacturing cost can be achieved. The reduction of the manufacturing cost is described in the manufacturing method.

According to the first structure example, the width and distance of the first and second bit lines BL1, BL2can be set to a value smaller than the reference value F (for example, the minimum dimension that can be formed by the photolithography).

Second Structure Example

FIG. 4illustrates a second structure example of the resistance change memory.FIG. 5is a sectional view along line V-V inFIG. 4, andFIG. 6is a sectional view along line VI-VI inFIG. 4.

The second structure example is a modification of the first structure example.

The second structure example differs from the first structure example in that contact plugs17aand17bdisposed with a constant pitch in the first direction is provided in a second space SP2. Because the second structure example is identical to the first structure example in other points, the detailed description of the second structure example is omitted.

In the second structure example, an underlayer10is the insulating layer.

The contact plugs17aand17bare disposed in the underlayer10. The contact plug17ais disposed immediately below a variable resistance layer11of a resistance change element R, and electrically connected to the variable resistance layer11. The contact plug17bis disposed immediately below a second bit line BL2, and electrically connected to the second bit line BL2.

Like the resistance change element R, for example, the contact plugs17aare disposed in the first direction with the pitch 2F, and disposed in the second direction with the pitch 4F.

For example, the contact plugs17bare disposed in the first direction with the pitch 2F, and disposed in the second direction with the pitch 4F. However, the contact plugs17bare disposed in the second space SP2.

In the second structure example, the width T in the second direction of a second conductive layer14is determined on the condition that the second conductive layer14is not in contact with the contact plug17b.

For example, in the first structure example, the width T is set to the range of F/2≦T<3F/2. On the other hand, in the second structure example, an upper limit of the width T is restricted to the size of the contact plug17b. For example, assuming that F is the size of the contact plug17b, the width T of the second conductive layer14is set to a range of F/2≦T<F.

In the second structure example, like the first structure example, the microfabrication of the memory cell and the reduction of the manufacturing cost can effectively be obtained.

For example, in principle, when the width T of the second conductive layer (sidewall conductive layer)14is set to a minimum value (for example, F/2), the pitch in the second direction of the resistance change elements R is smaller than 4F.

For example, as illustrated inFIG. 7, when the width T of the second conductive layer (sidewall conductive layer)14is set to a minimum value (for example, F/2), the pitch in the second direction of the resistance change elements R can maximally be reduced to a value close to 3F without limit. This means contribution to the microfabrication (the reduction of the size per memory cell) of the memory cell.

However, in the second structure example, it is necessary to insulate the first bit line BL1from the contact plug17band to connect the second bit line BL2with the contact plug17b. Therefore, the pitch in the second direction of the resistance change elements R is greater than 3F, and is set to a range of 4F or less.

Modifications

In the first and second structure examples, the first insulating layer13and the second insulating layer15may include a single layer or layers.

The first conductive layer12, the second conductive layer14, and the third conductive layer16may include the single layer or the plurality of layers.

The planar shape of the resistance change element R is circular. However, the resistance change element R is not limited to the circular shape. The planar shape of the resistance change element R may be square or ellipsoidal. When the planar shape of the resistance change element R is square, for example, the reference value (the size) F is a length of a short side. When the planar shape of the resistance change element R is ellipsoidal, for example, the reference value (the size) F is a length of a short axis.

Material Examples

The first insulating layer13and the second insulating layer15may be made of the same material or different materials.

Desirably the first insulating layer13includes a material having an excellent function of protecting the resistance change element R, for example, a material having an excellent function of preventing the oxidation of the resistance change element R.

For example, the first conductive layer12includes metals, such as tantalum and tungsten, or conductive compounds, such as titanium nitride and tantalum nitride. For example, the second conductive layer14and the third conductive layer16include metals, such as copper and aluminum. The second conductive layer14and the third conductive layer16may be made of the same material or different materials.

For example, the contact plugs17aand17binclude one of tungsten, titanium, titanium nitride, copper, tantalum, and tantalum nitride.

The method for manufacturing the resistance change memory of the first and second structure examples will be described.

Because the first and second structure examples differ from each other in that the contact plug is provided in the underlayer, the method for manufacturing the resistance change memory of the second structure example in which the contact plug is provided in the underlayer will be described below. The method for manufacturing the resistance change memory of the first structure example can easily be obtained when a step of forming the contact plug is eliminated from the following manufacturing method contact plug.

FIGS. 8 to 19illustrate the method for manufacturing the second structure example.

As illustrated inFIGS. 8 to 10, the contact plugs17aand17bare formed in the underlayer10. For example, the contact plugs17aand17bcan be formed by the damascene process. That is, after the holes are made in the underlayer10, the contact plugs17aand17bare formed by filling the holes with the conductive layers by, for example, a CVD method or a CMP method.

The contact plugs17aand17bare collectively disposed with the pitch 2F in the first direction, and collectively disposed with the pitch 2F in the second direction.

Then the resistance change elements R are formed on the contact plug17a.

In the second structure example, each of the resistance change elements R includes the variable resistance layer11, the first conductive layer12on the variable resistance layer11, and the first insulating layer13that covers the sidewall of the resistance change element R. Accordingly, first, the variable resistance layer11and the first conductive layer12are formed on the underlayer10by methods, such as a CVD method, a PVD method, and an ALD method.

After a resist pattern is formed on the first conductive layer12by a lithography process, the first conductive layer12is patterned by RIE with the resist pattern as a mask. The resist pattern is removed, and the variable resistance layer11is patterned by methods, such as IBE and RIE, with the first conductive layer12as a hard mask.

Therefore, the resistance change elements R can be formed.

In the second structure example, the resistance change elements R have the size of the reference value F. The resistance change elements R are arrayed with the pitch 2F in the first direction and with the pitch 4F in the second direction. That is, the resistance change elements R are disposed with the first space SP1in the first direction, and disposed with the second space SP2in the second direction.

For example, the first space SP1is equal to the reference value F, and the second space SP2is equal to triple (3F) the reference value F.

Then the first insulating layer13is formed as the sidewall insulating layer on the sidewall of at least the variable resistance layer11. The first insulating layer13that covers the variable resistance layer11and the first conductive layer12is formed by methods, such as the CVD method, the PVD method, and the ALD method. The first insulating layer13is etched by the RIE to leave the first insulating layer13only on the sidewall of the variable resistance layer11.

At this point, the etching of the first insulating layer13is controlled such that the end portion located in the third direction (the direction perpendicular to the upper surface of the underlayer10) of the first insulating layer13exists between the lower surface and the upper surface of the first conductive layer12after the etching.

Then, as illustrated inFIGS. 11 to 13, the second conductive layer14is formed as the sidewall conductive layer on the sidewalls of the first insulating layer13and the first conductive layer12, whereby the first bit line BL1is formed in the self-aligned manner with respect to the resistance change elements R.

The second conductive layer14that covers the resistance change elements R is formed by methods, such as the CVD method, the PVD method, and the ALD method. The second conductive layer14is etched by the RIE to leave the second conductive layer14only on the sidewall of the resistance change element R.

At this point, for example, the thickness T of the second conductive layer14in the direction (the first and second directions) perpendicular to the sidewall of the resistance change element R is set greater than or equal to a half of the first space SP1and less than a half of the second space SP2. Therefore, the first space SP1is filled with the second conductive layer14, and the second conductive layer14connects the resistance change elements R arrayed in the first direction, and constructs the first bit line BL1extending in the first direction.

Because the second space SP2is not filled with the second conductive layer14, the second space SP2is still ensured between the first bit line BL1. However, for example, assuming that F/2 is the thickness T in the first and second directions of the second conductive layer14, a width SP2′ in the second direction of the second space SP2is reduced to 2F (=3F−F) after the second conductive layer14is formed.

In the second structure example, for example, as illustrated inFIG. 12, a recess is formed on the upper surface of the second conductive layer14on the first space SP1. However, the upper surface of the second conductive layer14can substantially be formed flat on the first space SP1by controlling the thickness T of the second conductive layer14.

Then, as illustrated inFIGS. 14 to 16, the second insulating layer15is formed as the sidewall insulating layer on the sidewall of the second conductive layer14. The second insulating layer15that covers the resistance change element R and the second conductive layer14is formed by methods, such as the CVD method, the PVD method, and the ALD method. The second insulating layer15is etched by the RIE to leave the second insulating layer15as the first bit line BL1only on the sidewall of the second conductive layer14.

At this point, it is necessary that the second insulating layer15be formed such that the second space SP2is not filled with the second insulating layer15. For example, when the second space SP2′ is 2F after the second conductive layer14is formed, the thickness t in the second direction of the second insulating layer15is set less than F. Therefore, the second space SP2(SP2′) is still ensured between the first bit lines BL1.

Then, as illustrated inFIGS. 17 to 19, the second space SP2is filled with the third conductive layer16. Therefore, the second bit line BL2extending in the first direction is formed in the self-aligned manner with respect to the first bit line BL1and the contact plugs17b.

For example, the third conductive layer16can be formed by the damascene process. The third conductive layer16with which the second space SP2is completely filled is deposited by methods, such as the CVD method, the PVD method, and the ALD method. Then the third conductive layer16is left only in the second space SP2by a CMP process or an etching back process.

At this point, the second insulating layer15insulates the second conductive layer14that is of the first bit line BL1from the third conductive layer16that is of the second bit line BL2by exposing the upper surfaces of the first conductive layer12and the second insulating layer15. For example, the upper surface of the third conductive layer16is set to a level lower than the upper surfaces of the first conductive layer12and the second insulating layer15.

In the CMP process or the etching back process, through which the second bit line BL2is formed, there is no trouble even if the material constituting the third conductive layer16remains partially in the recess existing on the upper surface of the second conductive layer14inFIG. 19.

The resistance change memory of the second structure example is completed through the steps.

Application Example

The first and second structure examples and the manufacturing method can be applied to general memories in which the resistance change element is used. An application example in which the first and second structure examples and the manufacturing method are applied to a resistance change memory including a 1T1R-type memory cell array in which one memory cell includes one resistance change element and one selection transistor.

FIG. 20illustrates an equivalent circuit of the 1T1R-type memory cell array. A memory cell array18includes resistance change elements R(1) to R(3), selection transistors (FET) SW(1) to SW(3), first bit lines BL1, second bit lines BL2, and word lines WL1to WL3.

One memory cell MC includes one resistance change element R(i) and one selection transistor SW(i), which are connected in series. Where i is one of 1 to 3.

One end (a side of the resistance change element R(i)) of the memory cell MC is connected to the first bit line BL1, and the other end (a side of the selection transistor SW(i)) of the memory cell MC is connected to the second bit line BL2.

The first bit line BL1extends in the first direction, and one end of the first bit line BL1is connected to a bit line driver/sinker19that is used to read and write the data. The second bit line BL2extends in the first direction, and one end of the second bit line BL2is connected to a bit line driver/sinker & read circuit20.

Alternatively, the first bit line BL1may be connected to the bit line driver/sinker & read circuit20while the second bit line BL2is connected to the bit line driver/sinker19.

The positions of the bit line driver/sinker19and the bit line driver/sinker & read circuit20may be reversed, or the bit line driver/sinker19and the bit line driver/sinker & read circuit20may be disposed in the same position.

For example, a gate electrode of the selection transistor SW(i) extends as the word line WL(i) in the second direction, one end of the gate electrode is connected to a word line driver21that drives the word line WL(i) in reading and writing the data.

FIG. 21illustrates a structure example of the memory cell array inFIG. 20.FIG. 22is a sectional view along line XXII-XXII inFIG. 21.FIG. 23illustrates a layout of the selection transistor including an active area AA in the plan view inFIG. 21.

For example, a semiconductor substrate31is a silicon substrate. For example, an element isolation insulating layer32is a silicon oxide layer having an STI (Shallow Trench Isolation) structure. The active area AA is surrounded by the element isolation insulating layer32. The active area AA extends in a direction (for example, a direction of 45°) oblique to the first and second directions.

In the application example, the active areas AA are arrayed, and an FET is disposed as one selection transistor SW in one active area AA.

The selection transistor SW includes a first source/drain layer33a, a second source/drain layer33b, and a gate electrode34on a channel between the first source/drain layer33aand the second source/drain layer33b. The gate electrode34acts as the word line WL extending in the second direction.

In the application example, the selection transistor SW is formed in a planar manner. However, the selection transistor SW is not limited to the planar manner. For example, the selection transistor SW may be a fin FET in which the upper surface and the side surface of the fin-type active area AA are covered with the gate electrode.

An insulating layer10is formed on the semiconductor substrate31so as to cover the selection transistor SW. The insulating layer10corresponds to the underlayer10of the first and second structure examples. Contact plugs17aand17bare formed in the insulating layer10.

The contact plug17ais connected to a first source/drain layer33aof the selection transistor SW, and the contact plug17bis connected to a second source/drain layer33bof the selection transistor SW.

The resistance change element R is disposed immediately above the contact plug17a. The resistance change element R includes a variable resistance layer11, a first conductive layer12, and a first insulating layer13. A second conductive layer14as the first bit line BL1and a second insulating layer15are disposed on the sidewall of the resistance change element R.

The second bit line BL2is disposed immediately above the contact plug17b.

Because the configurations of the resistance change element R, the second conductive layer14(the first bit line BL1), the third conductive layer16(the second bit line BL2), and the second insulating layer15are identical to those of the first and second structure examples, the detailed description is omitted.

In the case of the 1T1R-type memory cell, as illustrated inFIG. 24, generally the size per memory cell becomes 8F2(=2F×4F).

That is, the resistance change elements R are arrayed with the pitch 2F in the first direction and with the pitch 4F in the second direction.

On the other hand, according to the 1T1R-type memory cell of the application example, the first and second bit lines BL1and BL2are formed in the self-aligned manner, so that the pitch in the second direction of the resistance change elements R is smaller than 4F.

In principle, the pitch in the second direction of the resistance change elements R can be set to a range greater than 3F and less than or equal to 4F. At this point, it is assumed that F is the size of the resistance change element R, that F/2 is the thickness (the first and second directions) T of the second conductive layer14, and that F is the size of the contact plug17b.

In this case, the pitch in the second direction of the resistance change elements R becomes (size of resistance change element=F)+(size of contact plug17b=F)+(double thickness T of second conductive layer14=F)+(thickness of second insulating layer15).

In other words, as shown inFIG. 24, assuming that the space SP1between the resistance change elements in the first direction is F, the space SP2between the resistance change elements in the second direction is greater than 2F, and is equal to or less than 3F.

That is, the pitch in the second direction of the resistance change elements R can be reduced to a value close to 3F without limit. Accordingly, the size per memory cell can be brought close to 6F2(=2F×3F) without limit.

As described above, according to the 1T1R-type memory cell array of the application example, the reduction of the manufacturing cost and the microfabrication of the memory cell can simultaneously be achieved by forming the first and second bit lines BL1and BL2in the self-aligned manner.

The 1T1R-type memory cell array is used in an MRAM (Magnetic Random Access Memory) in which the resistance change element R is an MTJ (Magnetic Tunnel Junction) element, an ReRAM (Resistive Random Access Memory) in which the resistance value varies according to a physical property of the resistance change element R, and an ion memory.

CONCLUSION

According to the embodiment, the microfabrication of the memory cell and the reduction of the manufacturing cost can be achieved in the resistance change memory.