Semiconductor memory device and method of manufacturing the same while avoiding process damage to a variable resistance film

This application is based on and claims the benefit of priority from prior US prior provisional Patent Application No. 62/168,496, filed on May 29, 2015, the entire contents of which are incorporated herein by reference.

Embodiments described herein relate generally to a semiconductor memory device and a method of manufacturing the semiconductor memory device.

Recently, in association with highly integrated semiconductor memory devices, LSI devices constituting the semiconductor memory devices have been increasingly minute. For miniaturization of this LSI device, it is requested to improve dimensional accuracy and position accuracy of a circuit pattern in addition to simply thinning a line width. As a technique to overcome such problem, there has been proposed a Resistive RAM (ReRAM) that uses variable resistive elements, which reversibly change a resistance value, as a memory. This ReRAM includes the variable resistive element between a sidewall of a word line extending parallel to a substrate and a sidewall of a bit line extending perpendicular to the substrate. This structure ensures further highly integrated memory cell array.

In the ReRAM having the bit lines extending perpendicular to the substrate, a resistance change film constituting the variable resistive element is formed at the sidewall of the bit line. However, forming this resistance change film without causing a process damage is not easy.

FIG. 1 is an exemplary block diagram of a semiconductor memory device according to a first embodiment;

FIG. 2 is an exemplary circuit diagram of a memory cell array 11 according to the first embodiment;

FIG. 3 is an exemplary perspective view illustrating a laminated structure of the memory cell array 11 according to the first embodiment;

FIG. 4 is a drawing when FIG. 3 is viewed from an X direction;

FIG. 5 is a top view of FIG. 3 ;

FIG. 6 to FIG. 16 are exemplary perspective views illustrating a method of manufacturing the memory cell array 11 according to the first embodiment;

FIG. 17 and FIG. 18 are exemplary perspective views illustrating a method of manufacturing the memory cell array 11 according to a second embodiment; and

FIG. 19 is an exemplary perspective view illustrating a laminated structure of the memory cell array 11 according to a third embodiment.

A semiconductor memory device according to the following embodiments includes first conducting layers, a memory layer, and second conducting layers. The first conducting layers are laminated at predetermined pitches in a first direction perpendicular to a substrate. The first conducting layers extend in a second direction parallel to the substrate. The second conducting layer extends in the first direction. A memory layer surrounds a circumference of the second conductive layer. The first conductive layers is in contact with a side surface of the second conductive layer via the memory layer. The memory cells are provided at intersections of the first conducting layers and the second conducting layer.

Next, the following describes a semiconductor memory device and a method of manufacturing the semiconductor memory device according to embodiments in detail with reference to the accompanying drawings. The respective drawings of the semiconductor memory devices used in the following embodiments are schematically illustrated. The thickness, the width, the ratio, and a similar parameter of the layer are not necessarily identical to actual parameters.

First Embodiment

First, the following describes an overall configuration of a semiconductor memory device according to the first embodiment. FIG. 1 is an exemplary block diagram of the semiconductor memory device according to the first embodiment. As illustrated in FIG. 1 , the semiconductor memory device includes a memory cell array 11 , a row decoder 12 , a column decoder 13 , a higher-level block 14 , a power supply 15 , and a control circuit 16 .

The memory cell array 11 includes a plurality of word lines WL and bit lines BL, which intersect with one another, and memory cells MC, which are disposed in the respective intersecting portions of these lines. The row decoder 12 selects the word line WL for access (data erasing/writing/reading). The column decoder 13 includes a driver that selects the bit line BL for access to control an access operation.

The higher-level block 14 selects the memory cell MC in the memory cell array 11 to be accessed. The higher-level block 14 gives a row address and a column address to the row decoder 12 and the column decoder 13 , respectively. The power supply 15 generates combinations of predetermined voltages corresponding to the respective operations of data erasing/writing/reading and supplies the combinations to the row decoder 12 and the column decoder 13 . The control circuit 16 performs a control such as transmission of an address to the higher-level block 14 in response to an external command and controls the power supply 15 .

The following describes the memory cell array 11 according to the first embodiment in detail with reference to FIG. 2 and FIG. 3 . FIG. 2 is an exemplary circuit diagram of the memory cell array 11 . FIG. 3 is an exemplary perspective view illustrating the laminated structure of the memory cell array 11 . In FIG. 2 , the X direction, the Y direction, and the Z direction are mutually orthogonal. The X direction is a direction the perpendicular to the paper. The structures illustrated in FIG. 2 are continuously disposed in the X direction. In FIG. 3 , an interlayer insulating film is actually formed between the respective wirings. However, for simplification of the drawing, FIG. 3 omits the illustration of the interlayer insulating film.

As illustrated in FIG. 2 , the memory cell array 11 includes selection transistors STr, global bit lines GBL, and selection gate lines SG in addition to the above-described word lines WL, bit lines BL, and memory cells MC.

As illustrated in FIG. 2 and FIG. 3 , word lines WL 1 to WL 4 are disposed at predetermined pitches in the Z direction. The word lines WL 1 to WL 4 are formed so as to extend in the X direction as its longitudinal direction. The bit lines BL are disposed in a matrix in the X direction and the Y direction. The bit lines BL are formed so as to extend in the Z direction as its longitudinal direction. The memory cells MC are disposed at portions where these word lines WL and bit lines BL intersect. Accordingly, the memory cells MC are disposed in a three-dimensional matrix, the X direction, the Y direction, and the Z direction in the memory cell array 11 . In various operations, an identical voltage is applicable to the selected word line WL among the word lines WL 1 to WL 4 , regardless of the position in the Z direction. An identical voltage is applicable to the non-selected word line WL among the word lines WL 1 to WL 4 , regardless of the position in the Z direction.

As illustrated in FIG. 2 , the memory cell MC includes a variable resistive element VR. The memory cell MC including the variable resistive element VR is electrically rewritable. The memory cell MC stores data in a non-volatile manner based on the resistance value given to the variable resistive element VR. The variable resistive element VR changes from the high resistance state (a reset state) to the low resistance state (a setting state) by a setting operation. The setting operation applies a voltage at a certain magnitude or more to both ends of the variable resistive element VR. The variable resistive element VR changes from the low resistance state (the setting state) to the high resistance state (the reset state) by a reset operation. The reset operation applies a voltage at a certain magnitude or more to both ends of the variable resistive element VR.

Immediately after the manufacture, the variable resistive element VR is in a state of not easily changing its resistance state and in the high resistance state. Therefore, a forming operation, which applies a high voltage equal to or more than the setting operation and the reset operation to both ends of the variable resistive element VR, is performed. This forming operation forms a region where a current is likely to locally flow in the variable resistive element VR (a filament path). This allows the variable resistive element VR to easily change the resistance state, being an operable state as a storage element.

As illustrated in FIG. 2 , the selection transistor STr is disposed between the one end of the bit line BL and the global bit line GBL. The global bit lines GBL are disposed at predetermined pitches in the X direction. The global bit lines GBL are formed so as to extend in the Y direction as its longitudinal direction. The one global bit line GBL is connected to the one end portion of the plurality of selection transistors STr, which are disposed in a line in the Y direction, in common. A gate electrode of the two selection transistors STr, which are adjacently disposed in the Y direction, is connected in common.

The selection gate lines SG are disposed at predetermined pitches in the Y direction. The selection gate lines SG are formed so as to extend in the X direction as its longitudinal direction. The one selection gate line SG is connected to the gates of the plurality of selection transistors STr, which are disposed in a line in the X direction, in common. The gate electrode of the two selection transistors STr, which are adjacently disposed in the Y direction, can be separated. Thus, the two selection transistors STr each can be independently operated.

The following describes the laminated structure of the memory cell array 11 according to the first embodiment with reference to FIG. 3 , FIG. 4 , and FIG. 5 . FIG. 4 is a drawing when the F 4 -F 4 plane in FIG. 3 is viewed from the X direction (Z-Y plane). FIG. 5 is a top view of FIG. 3 . FIG. 3 and FIG. 5 omit an interlayer insulating layer.

The memory cell array 11 , as illustrated in FIG. 3 and FIG. 4 , includes a selection transistor layer 30 and a memory layer 40 laminated over a substrate 20 . The selection transistor layer 30 functions as the selection transistor STr. The memory layer 40 functions as the memory cell MC.

As illustrated in FIG. 3 and FIG. 4 , the selection transistor layer 30 includes conducting layers 31 , interlayer insulating layers 32 , conducting layers 33 , and interlayer insulating layers 34 . These conducting layers 31 , interlayer insulating layers 32 , conducting layers 33 , and interlayer insulating layers 34 are laminated in the Z direction, which is perpendicular to the substrate 20 . The conducting layer 31 functions as the global bit line GBL while the conducting layer 33 functions as the gate of the selection gate line SG and the selection transistor STr.

The conducting layers 31 are disposed at predetermined pitches in the X direction, which is parallel to the substrate 20 . The conducting layers 31 are formed so as to extend in the Y direction as its longitudinal direction (see FIG. 4 ). The interlayer insulating layers 32 cover the top surfaces of the conducting layers 31 . The conducting layers 33 are disposed at predetermined pitches in the Y direction. The conducting layers are formed so as to extend in the X direction as its longitudinal direction (see FIG. 4 ). The interlayer insulating layers 34 cover the lateral faces and the top surface of the conducting layer 33 . The conducting layers 31 and 33 can be made of, for example, polysilicon. The interlayer insulating layers 32 and 34 can be made of silicon oxide (SiO 2 ).

As illustrated in FIG. 3 and FIG. 4 , the selection transistor layer 30 includes columnar semiconductor layers 35 and gate insulating layers 36 . The columnar semiconductor layer 35 functions as a body (a channel) of the selection transistor STr. The gate insulating layer 36 functions as the gate insulating film of the selection transistor STr.

The columnar semiconductor layers 35 are disposed in a matrix in the X and Y directions. The columnar semiconductor layer 35 has a columnar shape and extends in the Z direction as its longitudinal direction. The columnar semiconductor layer 35 is in contact with the top surfaces of the conducting layers 31 . The columnar semiconductor layer 35 is in contact with the lateral face of the conducting layer 33 in the Y direction via the gate insulating layer 36 . The columnar semiconductor layer 35 includes an N+ type semiconductor layer 35 a , a P+ type semiconductor layer 35 b , and an N+ type semiconductor layer 35 c , which are laminated.

As illustrated in FIG. 3 and FIG. 4 , the lateral face of the N+ type semiconductor layer 35 a in the Y direction is in contact with the interlayer insulating layer 32 . The lateral face of the P+ type semiconductor layer 35 b in the Y direction is in contact with the lateral face of the conducting layer 33 . The lateral face of the N+ type semiconductor layer 35 c in the Y direction is in contact with the interlayer insulating layer 34 . The N+ type semiconductor layers 35 a and 35 c can be made of polysilicon into which N+ type impurities are injected. The P+ type semiconductor layer 35 b can be made of polysilicon into which P+ type impurities are injected. The gate insulating layer 36 can be made of, for example, silicon oxide (SiO 2 ).

FIG. 3 and FIG. 4 illustrate the example where the selection transistor layer 30 is formed under the memory layer 40 . However, instead of this, the selection transistor layer 30 may be disposed on the memory layer 40 . That is, the selection transistor STr may be connected to the upper end side of a columnar conducting layer 43 .

As illustrated in FIG. 3 and FIG. 4 , the memory layer 40 includes interlayer insulating layers 41 a to 41 d and conducting layers 42 a to 42 d laminated in alternation in the Z direction. The conducting layers 42 a to 42 d each functions as the word lines WL 1 to WL 4 . Viewed from the Z direction, the conducting layers 42 a to 42 d have a pair of comb shape each opposed in the X direction (see FIG. 5 ). The interlayer insulating layers 41 a to 41 d are made of, for example, silicon oxide (SiO 2 ). The conducting layers 42 a to 42 d are made of, for example, polysilicon or titanium nitride (TiN).

As illustrated in FIG. 3 and FIG. 4 , the memory layer 40 includes columnar conducting layers 43 and variable resistance layers 44 . The columnar conducting layer 43 functions as the bit line BL. The variable resistance layer 44 functions as the variable resistive element VR.

The columnar conducting layers 43 are disposed in a matrix in the X and Y directions. The lower end of the columnar conducting layer 43 is in contact with the top surface of the columnar semiconductor layer 35 . The columnar conducting layer 43 extends in a columnar manner in the Z direction. The variable resistance layer 44 is formed into a closed loop shape over a whole circumference of the columnar conducting layer 43 . That is, as illustrated in FIG. 4 , the variable resistance layers 44 are disposed along both lateral faces of the columnar conducting layer 43 in the Y direction. As illustrated in FIG. 5 , the variable resistance layers 44 are also disposed along both lateral faces of the columnar conducting layer 43 in the X direction (that is, the variable resistance layers 44 are positioned between the columnar conducting layers 43 and interlayer insulating films 51 ). The variable resistance layer 44 is formed into the closed loop shape over the whole circumference of the columnar conducting layer 43 .

However, the variable resistance layer 44 is at least partially removed at a position between the bottom surface of the columnar conducting layer 43 and the columnar semiconductor layer 35 . Accordingly, the columnar conducting layer 43 and the columnar semiconductor layer 35 have a part at which the columnar conducting layer 43 and the columnar semiconductor layer 35 are directly connected without the variable resistance layer 44 therebetween. The variable resistance layer 44 is formed into the closed loop shape so as to cover the lateral faces of the columnar conducting layer 43 over the whole circumference thereof. However, as illustrated in FIG. 3 and FIG. 5 , the variable resistance layer 44 is not formed at the position between the interlayer insulating film 51 and the conducting layers 42 a to 42 d . The variable resistance layer 44 is disconnected at the position of this interlayer insulating film 51 . The variable resistance layer 44 thus shaped can be obtained by a manufacturing method, which will be described later.

With such shape and manufacturing method of the variable resistance layer 44 , the variable resistance layer 44 can be formed without causing the process damage, ensuring improving a yield. The columnar conducting layer 43 is made of a conductive material such as polysilicon, tungsten nitride (WN), tungsten (W), ruthenium (Ru), and titanium nitride (TiN); or a laminated body of a plurality of kinds of these materials. The variable resistance layer 44 can made of, for example, metal oxide (for example, HfO x , Al 2 O x , TiO x , ZrO, AlO, SiOx, NiO x , WO x , and Ta 2 O x ) and the laminated body of these materials.

[Manufacturing Method]

Next, the following describes a method of manufacturing the semiconductor memory device according to the first embodiment with reference to FIG. 6 to FIG. 15 . FIG. 6 to FIG. 15 are exemplary perspective views illustrating the method of manufacturing the memory cell array 11 .

First, the structure of the selection transistor layer 30 is formed on the semiconductor substrate 20 . Although specific illustrations are omitted in FIG. 6 and the subsequent drawings, an interlayer insulating film is formed on the semiconductor substrate 20 . A metal wiring layer, which will be the global bit line GBL, is deposited on the layer. This metal wiring layer is separated by an isolation insulating film having its longitudinal direction in the Y direction. This forms a plurality of the global bit lines GBL (the conducting layers 31 ). Then, on the conducting layers 31 , the interlayer insulating layers 32 , and the conducting layers 33 and the interlayer insulating layers 34 , which are formed having its longitudinal direction in the X direction, are deposited. After that, trenches reaching the conducting layers 31 are formed at predetermined intervals in the X-Y direction. The gate insulating layers 36 and the columnar semiconductor layer 35 are embedded into this trench. This completes the selection transistor layer 30 with the structure illustrated in FIG. 4 .

Next, as illustrated in FIG. 6 , the silicon oxide (SiO 2 ) and the polysilicon (Si) are laminated in alternation on the top surface of the selection transistor layer 30 . Thus, a laminated body of interlayer insulating layers 41 a ′ to 41 d ′ and conducting layers 42 a ′ to 42 d ′ expanding in the X direction and the Y direction are formed. A protecting layer 52 ′ is formed on the conducting layer 42 d′.

Next, as illustrated in FIG. 7 , trenches T 1 are formed. The trenches T 1 divide the laminated body of the interlayer insulating layers 41 a ′ to 41 d ′, the conducting layers 42 a ′ to 42 d ′, and the protecting layer 52 ′ into a plurality of stripe-shaped laminated bodies. The trenches T 1 are disposed at predetermined pitches in the Y direction and extend in the X direction as its longitudinal direction. These trenches T 1 divide the laminated body of the interlayer insulating layers 41 a ′ to 41 d ′, the conducting layers 42 a ′ to 42 d ′, and the protecting layer 52 ′ into the stripe-shaped laminated bodies of the interlayer insulating layers 41 a to 41 d , the conducting layers 42 a to 42 d , and the protecting layer 52 ′ extending in the X direction and disposed at predetermined pitches in the Y direction.

The above-described conventional method forms the state illustrated in FIG. 7 , and then performs a process to sequentially embed a variable resistance layer, which will be a memory film, and a conducting layer, which will be the bit line BL, into the trench T 1 . However, to minimize damage to the variable resistance layer, this embodiment does not form the variable resistance layer at this phase. Instead of this, this embodiment forms the variable resistance layer and the conducting layer in the procedure as follows.

First, as illustrated in FIG. 8 , after the process in FIG. 7 , semiconductor layers 43 S are formed so as to embed the trenches T 1 . The semiconductor layers 43 S are formed so as to embed the stripe-shaped trenches T 1 . As described later, the semiconductor layer 43 S is a sacrificial film removed by etching in a fabrication process. As a result, the semiconductor layer 43 S is made of a material whose etching rate is higher compared with the conducting layers 42 a to 42 d . As one example, in the case where the conducting layers 42 a to 42 d are made of the material of titanium nitride, the semiconductor layer 43 S can be made of the material of polysilicon.

In the case where the conducting layers 42 a to 42 d are made of the material of polysilicon to which impurities are doped, the semiconductor layer 43 S can be made of polysilicon whose content of impurities differs from that of the conducting layers 42 a to 42 d (for example, non-doped polysilicon not containing impurities). After embedding the semiconductor layers 43 S, the semiconductor layers 43 S deposited outside the trenches T 1 are removed by a CMP method for flattening.

Next, as illustrated in FIG. 9 , CMP stopper films M 1 having its longitudinal direction in the Y direction are formed at predetermined pitches in the X direction. These CMP stopper films M 1 are made of a material of, for example, a silicon nitride film.

Subsequently, using these CMP stopper films M 1 as masks, the semiconductor layers 43 S at positions not covered with the CMP stopper films M 1 are selectively etched by an RIE method. For example, when the semiconductor layers 43 S are made of the material of the non-doped polysilicon, the use of etching gas such as CHF 3 allows selectively removing the semiconductor layers 43 S by etching.

Then, as illustrated in FIG. 10 , interlayer insulating films 51 ′ are deposited so as to embed void portions generated by removing the semiconductor layers 43 S. At this time, the interlayer insulating films 51 ′ deposited outside the void portions are removed by the CMP method. In view of this, as illustrated in FIG. 10 , the heights of the surfaces of the interlayer insulating films 51 ′ and the surfaces of the masks M 1 approximately match.

Further, as illustrated in FIG. 11 , the CMP method is performed to remove CMP stopper films M 1 and the interlayer insulating films 51 ′, exposing the surfaces of the semiconductor layers 43 S. As illustrated in FIG. 12 , wet etching is performed to remove the semiconductor layers 43 S.

Next, as illustrated in FIG. 13 , the variable resistance layers 44 are deposited on the entire memory area (including the part on the surface of the selection transistor layer 30 ) that includes the inner walls (the lateral faces and the bottom surfaces) of void portions T 2 , which are generated after the removal of the semiconductor layers 43 S, by, for example, an atomic layer deposition (ALD). The variable resistance layer 44 can be made of, for example, the above-described metal oxides as the materials.

Further, as illustrated in FIG. 14 , a polysilicon film 43 ′ with a film thickness of, for example, approximately 5 to 10 nm is deposited by the CVD method or a similar method so as to cover the formed variable resistance layers 44 . This polysilicon film 43 ′ functions as the process protective film of the variable resistance layers 44 .

Subsequently, as illustrated in FIG. 15 , the variable resistance layers 44 and the polysilicon films 43 ′ deposited outside the void portions T 2 and the bottom surfaces of the void portions T 2 are removed by an RIE method to expose the surface of the selection transistor layer 30 (specifically, the columnar semiconductor layers 35 of the selection transistor layer 30 ). This is performed for better electrical connection between the columnar conducting layer 43 and the columnar semiconductor layer 35 . However, even if the variable resistance layer 44 remains, as long as the electrical connection between both is properly maintained, the process of FIG. 15 can also be omitted.

Subsequently, the polysilicon film 43 ′ as the process protective film is removed by etching. After that, polysilicon films are embedded into the void portions T 2 by the CVD method or a similar method. This forms the above-described columnar conducting layers 43 . Afterwards, a contact and a wiring layer are formed by the well-known method, thus completing the structure of the memory cell array 11 .

As long as the polysilicon film 43 ′ can be directly used as the columnar conducting layer 43 , the process of removing the polysilicon film 43 ′ by etching can also be omitted. That is, the columnar conducting layer 43 is constituted of the polysilicon film 43 ′ and the additional polysilicon film. The additional polysilicon film is deposited to the inner wall of the polysilicon film 43 ′ so as to embed the void portion T 2 .

According to the manufacturing method described in FIG. 6 to FIG. 16 , the variable resistance layer 44 does not receive the process damage by the etching. With the above-described conventional method, the variable resistance layer 44 is formed at the process after the process of FIG. 7 . Thereafter, the variable resistance layer 44 is exposed to the etching gas in the etching for embedding the interlayer insulating film, thus receiving the process damage.

However, with the manufacturing method of this embodiment, the variable resistance layers 44 are formed at the entire memory area including the inner walls of the void portions T 2 at the process of FIG. 13 . After that, the polysilicon films 43 ′ as the process protective films protect the variable resistance layers 44 . Afterwards, the etching removal process of the polysilicon film 43 ′ (can be omitted) and the etching removal process of the polysilicon film 43 ′ and the variable resistance layer 44 at the bottom surface of the void portion T 2 are only performed. Accordingly, the process damage to the variable resistance layer 44 is reduced to the minimum. Thus, according to the embodiment, the process damage to the variable resistance layer 44 can be minimized, ensuring improving the yield.

When using this manufacturing method, the variable resistance layer 44 is formed so as to cover the lateral faces of the columnar conducting layer 43 over the whole circumference. Meanwhile, the variable resistance layers 44 are not formed at the positions sandwiched between the interlayer insulating films 51 and the conducting layers 42 a to 42 d.

Second Embodiment

The following describes a semiconductor memory device according to the second embodiment with reference to FIG. 17 and FIG. 18 . The structure of the semiconductor memory device of this second embodiment is similar to that of the first embodiment; therefore, the description is omitted. However, the semiconductor memory device of this second embodiment differs from the first embodiment in the manufacturing method.

The following describes the method of manufacturing the semiconductor memory device of the second embodiment with reference to FIG. 17 and FIG. 18 . First, the processes described in FIG. 6 and FIG. 7 are performed to obtain the structure of FIG. 7 . Next, as illustrated in FIG. 17 , the interlayer insulating films 51 ′ are embedded into the trenches T 1 with the structure of FIG. 7 by the CVD method or a similar method. In this respect, the second embodiment differs from the first embodiment, which embeds the semiconductor layers 43 S that will be the sacrificial films into the trenches T 1 . The embedded interlayer insulating films 51 ′ are flattened by the CMP method so as to match the top surfaces of an interlayer insulating films 52 .

Next, as illustrated in FIG. 18 , the CMP stopper films M 1 ′ having its longitudinal direction in the Y direction are formed at predetermined pitches in the X direction. These CMP stopper films M 1 are made of a material of, for example, a silicon nitride film. Using these CMP stopper films M 1 ′ as masks, the interlayer insulating films 51 ′ at positions not covered with the CMP stopper films M 1 ′ are selectively etched by the RIE method. This obtains the structure approximately identical to the structure of FIG. 12 of the first embodiment.

Although the illustration is omitted, thereafter, the execution of the processes illustrated in FIG. 13 to FIG. 16 obtains the structure identical to the structure of the first embodiment.

By the manufacturing method of the second embodiment as well, the variable resistance layers 44 are formed at the entire memory area including the inner walls of the void portions T 2 . After that, the polysilicon films 43 ′ as the process protective films protect the variable resistance layers 44 . Thus, according to the second embodiment as well, the process damage to the variable resistance layer 44 can be minimized, ensuring improving the yield similar to the first embodiment.

This manufacturing method of the second embodiment eliminates the need for forming the sacrificial film. This allows reducing a count of processes compared with the first embodiment.

Third Embodiment

The following describes a semiconductor memory device according to the third embodiment with reference to FIG. 19 . The basic constitution of this third embodiment is similar to the above-described embodiment ( FIG. 1 and FIG. 2 ). However, this third embodiment differs from the above-described embodiments in the shapes of the columnar conducting layer 43 (the bit line BL) and the variable resistance layer 44 .

FIG. 19 is a schematic perspective view of the semiconductor memory device according to the third embodiment and corresponds to FIG. 3 . Like reference numerals designate identical configurations to FIG. 3 , and therefore such configurations will not be further elaborated or will be briefly described here.

With the semiconductor memory device of this third embodiment, the columnar conducting layer 43 is formed into an oval shape or a elliptical shape having its longitudinal direction in the X direction. The outline of the variable resistance layer 44 is similarly formed into the oval shape or the elliptical shape so as to cover the peripheral area of the columnar conducting layer 43 . For example, instead of the stripe-shaped masks M 1 , which are illustrated in FIG. 9 , such shape can be formed by using the mask having the oval-shaped or the elliptical-shaped opening.

This third embodiment can also provide the effect similar to the above-described embodiments.

[Others]

While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.