Semiconductor memory device and method of manufacturing the same

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-205339, filed on Aug. 8, 2008, the entire contents of which are incorporated herein by reference.

1. Field of the Invention

The present invention relates to a semiconductor memory device, and more particularly to a nonvolatile semiconductor memory device having a stacked structure.

2. Description of the Related Art

Electrically erasable programmable nonvolatile memories include a flash memory as well known in the art, which comprises a memory cell array of NAND-connected or NOR-connected memory cells having a floating gate structure. A ferroelectric memory is also known as a nonvolatile fast random access memory.

On the other hand, technologies of pattering memory cells much finer include a resistive memory, which uses a variable resistive element in a memory cell as proposed. Known examples of the resistive element include a phase change memory element that varies the resistance in accordance with the variation in crystal/amorphous states of a chalcogenide compound; an MRAM element that uses a variation in resistance due to the tunnel magneto-resistance effect; a polymer ferroelectric RAM (PFRAM) memory element including resistors formed of a conductive polymer; and a memory element that causes a variation in resistance on electrical pulse application (Patent Document 1: JP 2006-344349A, paragraph 0021).

The resistive memory may configure a memory cell with a serial circuit of a Schottky diode and a variable resistive element in place of the transistor. Accordingly, it can be stacked easier and three-dimensionally structured to achieve much higher integration advantageously (Patent Document 2: JP 2005-522045A).

Many of the semiconductor memory devices having such the stacked structure include a contact plug for connecting a line in a certain memory layer to a line in a different memory layer. Further, at an end of the line in each memory layer, a contact connector is formed for connection to the contact plug. Therefore, there is a need for providing space for formation of the contact plug and the contact connector, which not only results in an increase in chip area but also, depending on the connection state, causes variations in electrical property among lines in the memory layers as a problem.

In an aspect the present invention provides a semiconductor memory device, comprising: a semiconductor substrate; a cell array block formed on the semiconductor substrate and including plural stacked cell array layers each comprising a plurality of first lines, a plurality of second lines crossing the plurality of first lines, and memory cells connected at intersections of the first and second lines between both lines; and a plurality of contact plugs extending in the stack direction of the cell array layers to connect between the first lines, between the second lines, between the first or second line and the semiconductor substrate, or between the first or second line and another metal line, in the cell array layers. The first or second line in a certain one of the cell array layers has a contact connector making contact with both sides of the contact plug.

In another aspect the present invention provides a semiconductor memory device, comprising: a semiconductor substrate; a cell array block formed on the semiconductor substrate and including plural stacked cell array layers each comprising a plurality of first lines, a plurality of second lines crossing the plurality of first lines, and memory cells connected at intersections of the first and second lines between both lines; and a plurality of contact plugs extending in the stack direction of the cell array layers to connect between the first lines, between the second lines, between the first or second line and the semiconductor substrate, or between the first or second line and another metal line, in the cell array layers. The first or second line in a certain one of the cell array layers has a pair of contact connectors formed sandwiching the side of the contact plug from both sides.

In an aspect the present invention provides a method of manufacturing semiconductor memory devices, comprising: forming on a semiconductor substrate a plurality of multilayered cell array layers each comprising first and second mutually crossing lines and memory cells connected at intersections of the first and second lines between both lines; forming contact connectors in the first and second lines using a mask having two convex shapes with a certain gap; forming penetrated holes through the gaps in the contact connectors formed in the cell array layers; and forming contact plugs extending in the stack direction of the cell array layers by filling the formed penetrated holes with a conductive material to connect the first or second line in the cell array layer with the semiconductor substrate individually.

FIG. 1 is a block diagram of a semiconductor memory device according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing part of a memory cell array in the semiconductor memory device according to the same embodiment.

FIG. 3 is a cross-sectional view of one memory cell taken along I-I′ line and seen from the direction of the arrow in FIG. 2 .

FIG. 4 is a schematic cross-sectional view showing a variable resistive element example in the semiconductor memory device according to the same embodiment.

FIG. 5 is a brief diagram showing connections among word lines, bit lines and contact plugs in the semiconductor memory device according to the same embodiment.

FIG. 6 is a top view of bit lines in the semiconductor memory device according to the same embodiment.

FIG. 7 is a top view of bit lines in the semiconductor memory device according to the same embodiment.

FIG. 8 shows sectioned shapes of a contact connector and a contact plug with a word line used as a surface normal in the semiconductor memory device according to the same embodiment.

FIG. 9 is a perspective view showing a process step of manufacturing the semiconductor memory device according to the same embodiment.

FIG. 10 is a perspective view showing a process step of manufacturing the semiconductor memory device according to the same embodiment.

FIG. 11 is a perspective view showing a process step of manufacturing the semiconductor memory device according to the same embodiment.

FIG. 12 is a perspective view showing a process step of manufacturing the semiconductor memory device according to the same embodiment.

FIG. 13 is a perspective view showing a process step of manufacturing the semiconductor memory device according to the same embodiment.

FIG. 14 is a perspective view showing a process step of manufacturing the semiconductor memory device according to the same embodiment.

FIG. 15 is a perspective view showing a process step of manufacturing the semiconductor memory device according to the same embodiment.

FIG. 16 is a perspective view showing a process step of manufacturing the semiconductor memory device according to the same embodiment.

FIG. 17 is a perspective view showing a process step of manufacturing the semiconductor memory device according to the same embodiment.

FIG. 18 is a perspective view showing a process step of manufacturing the semiconductor memory device according to the same embodiment.

FIG. 19 is a perspective view showing a process step of manufacturing the semiconductor memory device according to the same embodiment.

FIG. 20 is a perspective view showing a process step of manufacturing the semiconductor memory device according to the same embodiment.

FIG. 21 provides a top view of a bit line and a cross-sectional view of a contact plug in a semiconductor memory device according to a second embodiment of the present invention.

FIG. 22 provides a top view of a bit line and a cross-sectional view of a contact plug in another semiconductor memory device according to the same embodiment.

FIG. 23 shows sectioned shapes of a contact connector and a contact plug with a word line used as a surface normal in a semiconductor memory device according to a third embodiment of the present invention.

FIG. 24 shows sectioned shapes of a contact connector and a contact plug with a word line used as a surface normal in another semiconductor memory device according to the same embodiment.

FIG. 25 is a top view of bit lines in a semiconductor memory device of an example in comparison with the first embodiment.

FIG. 26 shows sectioned shapes of a contact connector and a contact plug with a word line used as a surface normal in the same semiconductor memory device.

The embodiments associated with the semiconductor memory device according to the present invention will now be described in detail with reference to the drawings.

[First Embodiment]

FIG. 1 is a block diagram of a semiconductor memory device according to a first embodiment of the present invention.

This semiconductor memory device comprises a cell array block, which includes plural memory cell arrays 1 stacked. Each memory cell array is composed of memory cells arranged in matrix, using a later-described ReRAM (resistive element) or the like. A column control circuit 2 is provided on a position adjacent to the memory cell array 1 in the bit line BL direction. It controls the bit line BL in the memory cell array 1 to erase data from the memory cell, write data in the memory cell, and read data out of the memory cell. A row control circuit 3 is provided on a position adjacent to the memory cell array 1 in the word line WL direction. It selects the word line WL in the memory cell array 1 and applies voltages required to erase data from the memory cell, write data in the memory cell, and read data out of the memory cell.

A data I/O buffer 4 is connected to an external host, not shown, via an I/O line to receive write data, receive erase instructions, provide read data, and receive address data and command data. The data I/O buffer 4 sends received write data to the column control circuit 2 and receives read-out data from the column control circuit 2 and provides it to external. An address fed from external to the data I/O buffer 4 is sent via an address register 5 to the column control circuit 2 and the row control circuit 3 . A command fed from the host to the data I/O buffer 4 is sent to a command interface 6 . The command interface 6 receives an external control signal from the host and decides whether the data fed to the data I/O buffer 4 is write data, a command or an address. If it is a command, then the command interface transfers it as a received command signal to a state machine 7 . The state machine 7 manages the entire semiconductor memory device to receive commands from the host, read, write, erase, and execute data I/O management. The external host can also receive status information managed by the state machine 7 and decide the operation result. The status information is also utilized in control of write and erase.

The state machine 7 controls the pulse generator 8 . Under this control, the pulse generator 8 is allowed to provide a pulse of any voltage at any timing. Specifically, the state machine 7 receives an address fed from external via the address resistor 5 , determines which memory layer is accessed, and uses the parameter corresponding to the memory layer to control the height/width of the pulse from the pulse generator 8 . This parameter is a value, which is obtained by grasping write characteristics and so forth in memory layers and then evening the write characteristics in the memory layers, and stored in memory cells. The pulse formed herein can be transferred to any line selected by the column control circuit 2 and the row control circuit 3 .

Peripheral circuit elements other than the memory cell array 1 can be formed in a silicon substrate immediately beneath the memory cell array 1 . Thus, the chip area of the semiconductor memory device can be made almost equal to the area of the memory cell array 1 .

FIG. 2 is a perspective view of part of the memory cell array 1 , and FIG. 3 is a cross-sectional view of one memory cell taken along I-I′ line and seen in the direction of the arrow in FIG. 2 .

There are plural first lines or bit lines BL( 0 )-BL( 2 ) disposed in parallel, which cross plural second lines or word lines WL( 0 )-WL( 2 ) disposed in parallel. A memory cell MC is arranged at each intersection of both lines as sandwiched therebetween. Desirably, the first and second lines are composed of heat-resistive low-resistance material such as W, WSi, NiSi, CoSi.

The memory cell MC comprises a serial connection circuit of a variable resistive element VR and a non-ohmic element NO as shown in FIG. 3 .

The variable resistive element VR can vary the resistance through current, heat, or chemical energy on voltage application. Arranged on an upper and a lower surface thereof are electrodes EL 2 , EL 1 serving as a barrier metal layer and an adhesive layer. Material of the electrodes may include Pt, Au, Ag, TiAlN, SrRuO, Ru, RuN, Ir, Co, Ti, TiN, TaN, LaNiO, Al, PtIrOx, PtRhOx, Rh/TaAlN. A metal film capable of achieving uniform orientation may also be interposed. A buffer layer, a barrier metal layer and an adhesive layer may further be interposed.

Available examples of the variable resistive element VR include: one that changes the resistance in accordance with a phase change between the crystalline state and the amorphous state, such as a chalcogenide (PCRAM); one that changes the resistance by precipitating metal cations to form a bridge (conducting bridge) between electrodes and ionizing the precipitated metal to destruct the bridge (CBRAM); and one that changes the resistance by applying a voltage or current (ReRAM) (which is roughly divided into two: one that causes a variation in resistance in accordance with the presence/absence of charge trapped in charge traps present in the electrode interface, and one that causes a variation in resistance in accordance with the presence/absence of the conduction path due to an oxygen loss and so forth).

FIG. 4 shows an example of the variable resistive element VR. The variable resistive element VR shown in FIG. 4 includes a recording layer 12 arranged between electrode layers 10 , 11 . The recording layer 12 is composed of a composite compound containing at least two types of cation elements. At least one of the cation elements is a transition element having the d-orbit incompletely filled with electrons, and the shortest distance between adjacent cation elements is 0.32 nm or lower. Specifically, it is represented by a chemical formula A x M y X z (A and M are different elements) and may be formed of material having a crystal structure such as a spinel structure (AM 2 O 4 ), an ilmenite structure (AMO 3 ), a delafossite structure (AMO 2 ), a LiMoN 2 structure (AMN 2 ), a wolframite structure (AMO 4 ), an olivine structure (A 2 MO 4 ), a hollandite structure (A x MO 2 ), a ramsdellite structure (A x MO 2 ), and a perovskite structure (AMO 3 ).

In the example of FIG. 4 , A comprises Zn, M comprises Mn, and X comprises O. In the recording layer 12 , a small white circle represents a diffused ion (Zn), a large white circle represents an anion (O), and a small black circle represents a transition element ion (Mn). The initial state of the recording layer 12 is the high-resistance state. When the electrode layer 10 is kept at a fixed potential and a negative voltage is applied to the electrode layer 11 , part of diffused ions in the recording layer 12 migrate toward the electrode layer 11 to reduce diffused ions in the recording layer 12 relative to anions. The diffused ions arrived at the electrode layer 11 accept electrons from the electrode layer 11 and precipitate as a metal, thereby forming a metal layer 11 . Inside the recording layer 12 , anions become excessive and consequently increase the valence of the transition element ion in the recording layer 12 . As a result, the carrier injection brings the recording layer 12 into electron conduction and thus completes setting. On regeneration, a current may be allowed to flow, of which value is very small so that the material configuring the recording layer 12 causes no resistance variation. The programmed state (low-resistance state) may be reset to the initial state (high-resistance state) by supplying a large current flow in the recording layer 12 for sufficient time, which causes Joule heating to facilitate the oxidation reduction reaction in the recording layer 12 . Application of an electric field in the opposite direction from that at the time of setting may also allow resetting.

Between the electrode EL 2 and the bit line BL, a stopper ST composed of tungsten (W) is provided. This is operative to play a role in stopping the planarization by CMP at a certain position in the stack direction during the process step of manufacturing the semiconductor memory device later described.

FIG. 5 is a brief diagram showing connections among word lines WL, bit lines BL and contact plugs CL in the semiconductor memory device according to the present embodiment.

This semiconductor memory device includes plural bit lines BL 1 , BL 2 arranged between a metal line M 1 in the lowermost layer and a metal line M 2 in the uppermost layer in a stacked structure formed on a semiconductor substrate SB. Between the metal line M 1 and the bit line BL 1 , between the bit lines BL 1 and BL 2 , and between the bit line BL 2 and the metal line M 2 , plural word lines WL 1 , WL 2 , WL 3 crossing the bit lines BL are arranged, respectively. At each intersection of the word line WL 1 and the bit line BL 1 , of the bit line BL 1 and the word line WL 2 , of the word line WL 2 and the bit line BL 2 , and of the bit line BL 2 and the word line WL 3 , a memory cells MCs shown in FIG. 3 are connected, respectively. Thus configured is a four-layer structured memory cell array 1 . The memory cells MC adjoining in the stack direction share a bit line BL or a word line WL.

The certain word lines WL 2 , WL 3 and the metal line M 2 are connected at the ends of the word lines WL 2 , WL 3 with a contact plug CLw 2 extending in the stack direction. The contact plug CLw 2 is shaped in a frustum gradually tapered from the metal line M 2 toward the certain word line WL 2 and has a step formed above the upper surface of the word line WL 3 . Formed at the end of the certain word line WL 3 is a contact connector, which includes two parallel plates portions formed sandwiching both sides of the contact plug CLw 2 immediately beneath the step. This brings the certain word lines WL 2 , WL 3 and the metal line M 2 almost at equipotential. Similarly, the certain word line WL 2 and the metal line M 1 are connected at the ends of the word lines WL 2 , WL 1 with a contact plug CLw 1 extending in the stack direction. The contact plug CLw 1 also has a step formed above the upper surface of the word line WL 1 . Formed at the end of the word line WL 1 is a contact connector, which includes two parallel plates portions formed sandwiching both sides of the contact plug CLw 1 immediately beneath the step.

Another contact plug CLw 3 extending in the stack direction may be formed, if required, to bring the certain word line WL 2 in contact with the semiconductor substrate SB.

On the other hand, there are contact plugs CLb 1 -CLb 4 extending in the stack direction formed between the metal lines M 1 , M 2 and the bit lines BL 1 , BL 2 as well. The figure expresses the contact plugs CLb 1 -CLb 4 for the bit lines BL 1 , BL 2 as formed on the opposite side of the memory cell array 1 from the contact plugs CLw 1 -CLw 4 for the word lines WL 1 -WL 3 though the contact plugs CLb 1 -CLb 4 are actually formed on one side in the direction of the bit lines BL 1 , BL 2 extending. The contact plug CLb 1 connects the certain bit lines BL 2 , BL 1 with the metal line M 1 . Similarly, the contact plugs CLb 2 , CLb 3 , CLb 4 connect the metal line M 2 with the bit line BL 2 , the bit line BL 2 with the metal line M 1 , and the metal line M 2 with the bit line BL 2 , respectively.

(Shapes of Ends of Bit Lines and Word Lines)

The shapes of ends of the bit lines BL and the word lines WL are described next.

FIG. 6 shows the shapes of ends of the bit lines BL (for example, BL 2 in FIG. 5 ) having a contact connector formed therein, through which no contact plug CLb penetrates.

The bit lines BL are formed over a memory cell area AR 1 with the memory cells MC arranged and a peripheral area AR 2 with the contact plugs CLb arranged (in the following description, the direction in parallel with the bit line BL and directing from the peripheral area AR 2 to the memory cell area AR 1 is referred to as the “column direction”, and the direction in parallel with the word line WL and orthogonal to the column direction is referred to as the “row direction”).

Plural bit lines BL are formed with a certain width (for example, 43 nm) and arranged in parallel with each other in the row direction at intervals of a length F.

The k-th (k is an integer) bit line BL(k) counted from a certain position in the row direction extends within the memory cell area AR 1 to the boundary with the peripheral area AR 2 in the column direction.

The (k+1)-th bit line BL(k+1) extends within the memory cell area AR 1 to the boundary with the peripheral area AR 2 in the column direction and then extends in the column direction via a position P 11 at a distance 2 F in the column direction from this position, a position P 12 at a distance 2 F in the column direction and a distance 2 F in the row direction from the position P 11 , a position P 13 at a distance 26 F in the column direction from the position P 12 , and a position P 14 at a distance 2 F in the column direction and a distance 2 F in the row direction from the position P 13 . There is formed a rectangular contact connector Cb 1 having apexes on a position at a distance 7 F in the column direction from the position P 14 , and a position at a distance 4 F in the column direction and a distance 6 . 5 F in the row direction from this position.

The (k+2)-th bit line BL(k+2) extends within the memory cell area AR 1 to the boundary with the peripheral area AR 2 in the column direction.

The (k+3)-th bit line BL(k+3) extends within the memory cell area AR 1 to the boundary with the peripheral area AR 2 in the column direction and then extends in the column direction to a position at a distance 28 F from this position. There is formed a rectangular contact connector Cb 3 having apexes on a position at a distance 14 F in the column direction from the boundary between the areas AR 1 and AR 2 , and a position at a distance 4 F in the column direction and a distance 8 . 5 F in the row direction from this position.

The (k+4)-th bit line BL(k+4) extends within the memory cell area AR 1 to the boundary with the peripheral area AR 2 in the column direction.

The (k+5)-th bit line BL(k+5) extends within the memory cell area AR 1 to the boundary with the peripheral area AR 2 in the column direction and then extends in the column direction via a position P 51 at a distance 2 F in the column direction from this position, and a position P 52 at a distance 6 F in the column direction and a distance 6 F in the row direction from the position P 51 , then to a position at a distance 20 F in the column direction from the position P 52 . There is formed a rectangular contact connector Cb 5 having apexes on a position at a distance 1 F in the column direction and a distance − 8 . 5 F in the row direction from the position P 52 , and a position at a distance 4 F in the column direction and a distance 8 F in the row direction from this position.

The (k+6)-th bit line BL(k+6) extends within the memory cell area AR 1 to the boundary with the peripheral area AR 2 in the column direction.

The (k+7)-th bit line BL(k+7) extends within the memory cell area AR 1 to the boundary with the peripheral area AR 2 in the column direction and then extends in the column direction via a position P 71 at a distance 2 F in the column direction from this position, a position P 72 at a distance 4 F in the column direction and a distance 4 F in the row direction from the position P 71 , a position P 73 at a distance 24 F in the column direction from the position P 72 , and a position P 74 at a distance 4 F in the column direction and a distance − 4 F in the row direction from the position P 73 . There is formed a rectangular contact connector Cb 7 having apexes on a position at a distance − 6 . 5 F in the column direction from the position P 74 , and a position at a distance 4 F in the column direction and a distance 6 . 5 F in the row direction from this position.

There are also formed island-shaped contact connectors Cb 1 ′, Cb 3 ′, Cb 5 ′, Cb 7 ′, which are not connected to any of the bit lines BL(k)-BL(k+7).

The contact connector Cb 1 ′ is a rectangular area having apexes on a position at a distance 15 F in the column direction and a distance 6 . 5 F in the row direction from the position P 74 , and a position at a distance 4 F in the column direction and a distance 5 F in the row direction from this position.

The contact connector Cb 3 ′ is a rectangular area having apexes on a position at a distance 16 F in the column direction and a distance − 8 . 5 F in the row direction from the position P 52 , and a position at a distance 4 F in the row direction and a distance 7 F in the column direction from this position.

The contact connector Cb 5 ′ is a rectangular area having apexes on a position at a distance 11 F in the column direction and a distance − 8 . 5 F in the row direction from the position P 52 , and a position at a distance 4 F in the row direction and a distance 7 F in the column direction from this position.

The contact connector Cb 7 ′ is a rectangular area having apexes on a position at a distance 10 F in the column direction and a distance 6 . 5 F in the row direction from the position P 14 , and a position at a distance 4 F in the column direction and a distance 5 F in the row direction from this position.

These contact connectors Cb 1 ′, Cb 3 ′, Cb 5 ′ and Cb 7 ′ have surfaces not shown, which are connected via the contact plugs CLb to the bit lines BL in the lower layer. On the other hand, the shown surfaces are connected via the contact plugs CLb to the bit lines BL in the upper layer. In a word, the contact connectors Cb 1 ′, Cb 3 ′, Cb 5 ′ and Cb 7 ′ relay the connections between the bit lines BL in the lower and upper layers.

The above-described bit lines BL(k)-BL(k+7) and contact connectors Cb 1 ′, Cb 3 ′, Cb 5 ′ and Cb 7 ′ form a layout pattern, which is repeatedly arranged in the row direction.

FIG. 7 shows the shapes of ends of the bit lines BL (for example, BL 1 in FIG. 5 ) having a contact connector formed therein, through which the contact plug CLb penetrates.

FIG. 7 is similar in layout to FIG. 6 except for the contact connectors Cb.

The contact connector Cb 1 in the bit line BL(k+1) is formed in a rectangular area having apexes on a position at a distance 12 F in the column direction from the position P 14 , and a position at a distance 4 F in the column direction and a distance 6 . 5 F in the row direction from this position.

The contact connector Cb 3 in the bit line BL(k+3) is formed in a rectangular area having apexes on a position at a distance 24 F in the column direction and a distance 0 . 5 F in the row direction from the position of the bit line BL(k+3) intersecting the boundary surface between the memory cell area AR 1 and the peripheral area AR 2 , and a position at a distance 4 F in the column direction and a distance 8 F in the row direction from this position.

The contact connector Cb 5 in the bit line BL(k+5) is formed in a rectangular area having apexes on a position at a distance 11 F in the column direction and a distance − 8 . 5 F in the row direction from the position P 52 , and a position at a distance 4 F in the column direction and a distance 8 F in the row direction from this position.

The contact connector Cb 7 in the bit line BL(k+7) is formed in a rectangular area having apexes on a position at a distance 10 F in the column direction and a distance − 6 . 5 F in the row direction from the position P 74 , and a position at a distance 4 F in the column direction and a distance 6 F in the row direction from this position.

The contact connector Cb shown in FIG. 7 differs in shape from the contact connector Cb shown in FIG. 6 . Specifically, it includes two plate portions projected in the direction orthogonal to the bit line BL. These two plate portions are formed sandwiching both sides of the contact plug CLb and arranged in contact with the step formed on the side of the contact plug CLb. Thus, each bit line BL can be connected, via the contact connector Cb thereof and the contact plug CLb surrounded by the contact connector Cb, to a bit line BL in a different layer.

In FIGS. 6 and 7 the bit lines BL are described while the word lines WL are similarly shaped except that the column direction and the row direction are changed from each other.

The following description is given to the sizes of the contact connector Cb and the contact plug CLb.

FIG. 8 shows shapes of the contact connector Cb and the contact plug CLb in a portion surrounded by a dotted-line in FIG. 5 . The indications of lengths at various locations in the figure are values calculated under the condition for ensuring a contact width, 60 nm or more, between the contact connector Cb in the bit line BL 1 and the contact plug CLb, and a width, wcm 1 =80 nm or more, of the contact plug CLb at the height of the bit line BL 1 . In addition, the height from the metal line M 1 to the bit line BL 1 top is hbm=490 nm, the height from the bit line BL 1 top to the bit line BL 2 bottom is hmt=480 nm, and the thickness of the bit line BL 1 is tlm=50 nm.

At the beginning, the sizes in the column direction are determined.

First, the width wlm of the plate portions formed as sandwiching the contact plug, the interval wcm 1 between two plate portions, and the width wcm 2 of the contact plug at the height of the bit line BL 1 top are determined. On the assumption that wlm has a variation of ±20%, wcl 2 has a variation of ±20%, and the contact connector Cb in the bit line BL 1 and the contact plug CLb have an alignment error of 25 nm, the following equations (1), (2) are established to ensure a margin of 5 nm.

The equations (1), (2) yield wlm≈110 nm, and wcm 2 ≈210 nm. Therefore, when the variation of ±20% in wlm and the variation of ±20% in wcl 2 are taken into account, wlm=110 ±22 nm, wcm 2 =210±42 nm, and wcm 1 =96±16 nm are determined.

Subsequently, the width wct of the bit line BL 2 bottom (the contact plug CLb top) and the width of the contact connector Cb in the bit line BL 2 are determined. If the contact plug herein has a taper angle of 87°, then wct can be derived as wct≈260 nm from the following.

[ Equation ⁢ ⁢ 3 ] wct = hmt tan ⁢ ⁢ 87 ⁢ ° × 2 + wcm ⁢ ⁢ 2 ( 3 )

Therefore, the dimensional variation of 20% in wct is taken into account to determine wct=260±52 nm. In addition, when the dimensional variation of 20% in the contact connector in the bit line BL 2 , the variation of ±0.5% in taper angle, the spec alignment error of 25 nm in the bit line BL 2 direction, and the dimensional variation of 20% in the width wlt itself of the contact connector in the bit line BL 2 are taken into account, the width wlt of the contact connector in the bit line BL 2 is determined as 460±92 nm.

Subsequently, the width wcb of the bit line BL 1 top (the contact plug CLb bottom), and the width wlb of the contact connector in the metal line M 1 are determined. If the contact plug herein has a taper angle of 87°, then wcb can be derived as wcb≈50 nm from the following.

[ Equation ⁢ ⁢ 4 ] wcb = wcm ⁢ ⁢ 1 - 2 × ( hbm - tlm ) tan ⁢ ⁢ 87 ⁢ ° ( 4 )

Therefore, when the dimensional variation of 20% in wcb is taken into account, wcb=50±10 nm is determined. In addition, when the dimensional variation of 20% in the contact connector in the metal line M 1 , the variation of ±0.5% in taper angle, the spec alignment error of 25 nm in the metal line M 1 direction, and the dimensional variation of 20% in the width wlb itself of the contact connector in the metal line M 1 are taken into account, the width wlt of the contact connector in the metal line M 1 is determined as 133±27 nm.

The sizes in the row direction are determined next.

First, the depth dcb of the contact plug CLb bottom is determined. A 43 nm-generation NAND flash memory has an area of 43 nm×43 nm in the contact plug bottom and accordingly a need for ensuring almost the same area results in dcb≈36 nm from the width wcb=50 nm of the contact plug CLb bottom previously obtained. When the dimension variation of 15% in dcb is taken into account, dcb=36±10 nm is determined. If the contact connector in the metal line M 1 has a depth, dlb, and the contact connector in the metal line M 1 has a fringe, dmb, in the word line WL direction, then a need for ensuring a margin of 5 nm establishes the following equations (5), (6).

⁢ [ Equation ⁢ ⁢ 5 ] ⁢ dlb = 2 × dmb + dcb ( 5 ) ⁢ [ Equation ⁢ ⁢ 6 ] dmb - ( 0.15 × dmb 2 ) 2 + ( 0.2 × dcb 2 ) 2 - 25 2 + 25 2 + 25 2 > 5 ( 6 )

The equations (5), (6) yield dmb≈62 nm, and dlb≈160 nm. Therefore, when the dimensional variation of 15% in dlb is taken into account, dlb=160±24 nm is determined.

Subsequently, the depth dcm of the contact plug CLb at the height of the bit line BL 1 top, and the depth dct of the contact plug dlb at the height of the bit line BL 2 bottom are determined. If the contact plug herein has a taper angle of 88.5° in the column direction, then dcm≈62 nm is determined. When the dimensional variation of 15% is taken into account, dcm=62±10 nm is determined. In addition, as for dct≈86 nm, when the dimensional variation of 15% is taken into account, dct=86±13 nm is determined.

For reference purpose, FIG. 26 shows the sizes of a contact connector and a contact plug in a semiconductor device according to a comparison example. This is the case of the contact connector and the contact plug of which contact connector formed at an end of the bit line BL has only a plate portion located on one side of the contact plug. The values in the figure are calculated under the condition for ensuring a contact width, wlc=60 nm or more, between the contact connector top in the bit line BL 1 and the contact plug, and a width, wcm 1 =80 nm or more, of the contact plug at the height of the bit line BL 1 , similar to FIG. 8 .

In this case, there is a deviation of 56 nm on the bit line BL 201 top in the bit line BL direction when alignment errors such as a dimensional variation in the contact plug are considered. Therefore, wlc=117±56 nm, wcm 1 =137±56 nm are determined, which lead to a width, wcm 2 =255±51 nm, on the bit line BL 2 top.

If the contact plug CLb has a taper angle of 87° in the bit line BL direction and the alignment error is considered, the widths wct and wcb of the contact plug CLb at the bit line BL 1 bottom and the metal line Ml top are determined as wcb=85±17 nm and wct=300±60 nm, respectively. Thus, there is a need for ensuring the width wlt of the contact connector in the bit line BL 2 determined as wlt=505±101 nm, for example.

As can be seen from the above, the sizes (widths) of the contact connector and the contact plug in the present embodiment can be made smaller than those in the comparison example shown in FIG. 26 for the following reason. If the contact connector has only a plate portion on one side as is in the comparison example shown in FIG. 26 , the contact plug deviates relative to the contact connector and consequently the contact area increases or decreases in proportion to the deviation. Therefore, in addition to the dimensional variations in the contact plug and the contact connector, there is a need for considering the misalignment of the contact plug relative to the contact connector to ensure the contact area. With this regard, the contact connector has two plate portions on both sides of the contact plug in the present embodiment shown in FIG. 8 . In this case, even if the contact plug deviates relative to the contact connector to decrease the contact area of one plate portion with the contact plug, the contact area of the other plate portion with the contact plug increases. As a result, a large influence can be prevented from exerting on a total contact area of two plate portions with the contact plug. In a word, the present embodiment shown in FIG. 8 has a stronger structure over the misalignment between the contact connector and the contact plug than the comparison example shown in FIG. 25 .

In addition, the contact connector and the contact plug can be downsized and consequently the increase in chip area resulted from ensuring the areas of the contact connector and the contact plug can be suppressed additionally in the present embodiment.

(Process Steps of Manufacturing Semiconductor Memory Device according to Present Embodiment)

FIGS. 9-20 are perspective views showing steps of forming the word line WL 1 and much higher layer portions in order of step. The process of forming the upper layer portions are described with reference to FIGS. 9-20 appropriately. For convenience of description, insulators are omitted in part from the figures.

First, an interlayer insulator is formed, and then layers L 11 -L 17 are deposited thereon in turn. The layers L 11 -L 17 are later turned into the word line WL 1 , the barrier metal BM, the non-ohmic element NO, the electrode EL 1 , the variable resistive element VR, the electrode EL 2 and the stopper ST.

Subsequently, a hard mask of TEOS or the like, not shown, is formed on the upper surface of the above-described stacked structure, and a first anisotropic etching is executed with this mask, thereby forming trenches T 1 extending in the column direction at a certain pitch, through the layers L 11 -L 17 . The layer L 11 is turned into the word line WL 1 . The contact connector at the end of the word line WL 1 is omitted from the figure though the contact connector is formed with a mask of the pattern as shown in FIG. 7 .

Then, an interlayer insulator IL 11 is buried in the trenches T 1 . A suitable material of the interlayer insulator IL 11 has excellent insulation, a low capacity, and an excellent burial property. Subsequently, a process of planarization by CMP or the like is applied to remove extra parts from the interlayer insulator IL 11 and expose the layer L 17 . The layer L 17 (turned into the stopper ST later) plays a role in stopping the planarization by CMP at a certain position in the stack direction.

Subsequently, layers L 21 -L 27 are deposited in turn on the CMP-processed surface. The layers L 21 -L 27 later serve as the bit line BL 1 , the electrode EL 2 , the variable resistive element VR, the electrode EL 1 , the non-ohmic element NO, the barrier metal BM, and the stopper ST. The state up to this step is shown in FIG. 9 .

Then, a hard mask of TEOS or the like, not shown, is formed on the upper surface of the stacked structure shown in FIG. 9 , and a second anisotropic etching is executed with this mask, thereby forming trenches T 2 extending in the row direction at a certain pitch, through the layers L 21 -L 27 and L 12 -L 17 . The layer L 21 is turned into the bit line BL 1 . Also at the end of the bit line BL 1 , a contact connector is formed with a mask of the pattern as shown in FIG. 7 . This step turns the layers L 12 -L 17 into a memory cell MC, which includes the barrier metal BM, the non-ohmic element NO, the electrode EL 1 , the variable resistive element VR, the electrode EL 2 , and the stopper ST.

Subsequently, an interlayer insulator IL 12 is buried in the trenches T 2 . A suitable material of the interlayer insulator IL 12 has excellent insulation, a low capacity, and an excellent burial property. Next, a process of planarization by CMP or the like is applied to remove extra parts from the interlayer insulator IL 12 and expose the layer L 27 . The layer L 27 (turned into the stopper ST later) plays a role in stopping the planarization by CMP at a certain position in the stack direction. A cross-sectional view after the planarization is shown in FIG. 11 . At the step shown in FIG. 11 , a contact plug CLw is formed in the peripheral area through the interlayer insulator IL 12 (not shown). The contact plug CLw is formed in the contact connector formed at the end of word line WL 1 . The contact plug CLw is formed in contact with the lower line M 1 (see FIG. 5 ) located beneath the word line WL.

Subsequently, layers L 31 -L 37 are deposited in turn on the CMP-processed surface shown in FIG. 11 . The layers L 31 -L 37 later serve as the word line WL 2 , the barrier metal BM, the non-ohmic element NO, the electrode EL 1 , the variable resistive element VR, the electrode EL 2 and the stopper ST. The state up to this step is shown in FIG. 12 .

Then, a hard mask of TEOS or the like, not shown, is formed on the upper surface of the stacked structure shown in FIG. 12 , and a third anisotropic etching is executed with this mask, thereby forming trenches T 3 extending in the row direction at a certain pitch, through the layers L 31 -L 37 and L 22 -L 27 . The layer L 31 is turned into the word line WL 2 . The contact connector at the end of the word line WL 2 is formed with a mask of the pattern as shown in FIG. 6 . The upper surface of the contact plug CLw comes in contact with the contact connector in the word line WL 2 . This step turns the layers L 22 -L 27 into a memory MC, which includes the electrode EL 2 , the variable resistive element VR, the electrode EL 1 , the non-ohmic element NO, the barrier metal BM, and the stopper ST. Next, an interlayer insulator IL 13 is buried in the trenches T 3 . A suitable material of the interlayer insulator IL 13 has excellent insulation, a low capacity, and an excellent burial property. Subsequently, a process of planarization by CMP or the like is applied to remove extra parts from the interlayer insulator IL 13 and expose the layer L 37 . The layer L 37 (turned into the stopper ST later) plays a role in stopping the planarization by CMP at a certain position in the stack direction. A cross-sectional view after the planarization is shown in FIG. 13 .

Subsequently, at the step shown in FIG. 14 , a contact plug CLb is formed through the interlayer insulators IL 11 -IL 13 . The contact plug CLb is formed in contact with the contact connector formed at the end of the bit line BL 1 . The contact plug CLb is formed in contact with the lower line M 1 (see FIG. 5 ) located beneath the word line WL.

Then, layers L 41 -L 47 are deposited in turn as shown in FIG. 15 on the CMP-processed surface shown in FIG. 14 . The layers L 41 -L 47 later serve as the bit line BL 2 , the electrode EL 2 , the variable resistive element VR, the electrode EL 1 , the non-ohmic element NO, the barrier metal BM, and the stopper ST.

Subsequently, a hard mask of TEOS or the like, not shown, is formed on the upper surface of the stacked structure shown in FIG. 15 , and a fourth anisotropic etching is executed with this mask, thereby forming trenches T 4 extending in the column direction at a certain pitch, through the layers L 41 -L 47 and L 32 -L 37 . The layer L 41 is turned into the bit line BL 2 . The contact connector at the end of the bit line BL 2 is formed with a mask of the pattern as shown in FIG. 6 . The upper surface of the contact plug CLb comes in contact with the end of the bit line BL 2 . This step turns the layers L 32 -L 37 into a memory MC, which includes the barrier metal BM, the non-ohmic element NO, the electrode EL 1 , the variable resistive element VR, the electrode EL 2 , and the stopper ST.

Next, an interlayer insulator IL 14 is buried in the trenches T 4 . A suitable material of the interlayer insulator IL 14 has excellent insulation, a low capacity, and an excellent burial property. Subsequently, a process of planarization by CMP or the like is applied to remove extra parts from the interlayer insulator IL 14 and expose the layer L 47 . The layer L 47 (turned into the stopper ST later) plays a role in stopping the planarization by CMP at a certain position in the stack direction. A cross-sectional view after the planarization is shown in FIG. 16 .

Then, a layer L 51 is deposited as shown in FIG. 17 on the CMP-processed surface shown in FIG. 16 . The layer L 51 later serves as the word line WL 3 .

Subsequently, a hard mask of TEOS or the like, not shown, is formed on the upper surface of the layer L 51 shown in FIG. 17 , and a fifth anisotropic etching is executed with this mask, thereby forming trenches T 5 extending in the row direction at a certain pitch, through the layers L 51 , L 42 -L 47 . The layer L 51 is turned into the word line WL 3 . The contact connector at the end of the word line WL 3 is formed with a mask of the pattern as shown in FIG. 6 . This step turns the layers L 42 -L 47 into a memory MC, which includes the electrode EL 2 , the variable resistive element VR, the electrode EL 1 , the non-ohmic element NO, the barrier metal BM, and the stopper ST. Next, an interlayer insulator IL 15 is buried in the trenches T 5 . A suitable material of the interlayer insulator IL 15 has excellent insulation, a low capacity, and an excellent burial property. The state up to this step is shown in FIG. 18 .

Then, a different interlayer insulator is deposited on the interlayer insulator IL 15 . Thereafter, a contact plug CLw is formed through the interlayer insulators IL 16 -IL 13 . The contact plug CLw is formed in the contact connector formed at the end of the word line WL 3 . The contact plug CLw is formed in contact with the upper surface of the word line WL 2 at the end. In addition, a contact plug CLb is formed through the interlayer insulators IL 16 -IL 14 . The contact plug CLb is formed in contact with the upper surface of the bit line BL 2 at the end. A cross-sectional view after these processes is shown in FIG. 19 .

An upper line layer M 2 is formed on the upper portion of the interlayer insulator IL 6 (the upper surface of the contact plug CL) to complete the semiconductor memory device shown in FIG. 20 .

The present embodiment makes it possible to reduce the sectional area of the contact plug and the area of the contact connector in each layer in the semiconductor memory device having a stacked structure without any increases in contact resistance caused by interlayer connections.

[Second Embodiment]

FIGS. 21 and 22 show shapes of a contact connector and a contact plug in a semiconductor memory device according to a second embodiment of the present invention, or sectioned shapes with a surface normal in the stack direction of the semiconductor memory device.

The sectioned shape of the contact plug is not limited to a particular sectioned shape. For example, it may be a circular shape as shown in FIG. 21 or an elliptical shape having the major axis in the column direction as shown in FIG. 22 to exert the same effect as the first embodiment. In the case of the elliptical shape, the influence exerted on the contact area of the contact plug with the contact connector due to the deviation of the contact plug in the column direction can be made lower than the circular shape.

[Third Embodiment]

FIGS. 23 and 24 show shapes of a contact connector and a contact plug in a semiconductor memory device according to a third embodiment of the present invention, or sectioned shapes with a surface normal in the stack direction of the semiconductor memory device.

The contact plug CL of FIG. 23 connects among bit lines BL 200 , BL 201 and BL 202 . In this case, a sum of contact areas s 201 a , s 201 b between the contact plug CLb and the bit line BL 201 , and a contact area s 200 between the contact plug CLb and the bit line BL 200 are equated, thereby equating the connection resistances between the contact plug CLb and the bit lines BL 200 , BL 201 .

The contact plug CLb of FIG. 24 connects among bit lines BL 205 -BL 208 . In this case, a sum of contact areas s 207 a , s 207 b between the contact plug CLb and the bit line BL 207 , a sum of contact areas s 206 a , s 206 b between the contact plug CLb and the bit line BL 206 , and a contact area s 205 between the contact plug CLb and the bit line BL 205 are equated. Also in this case, the connection resistances between the contact plug CLb and the bit lines BL 205 -BL 207 are equated, like in the case of FIG. 23 .

The present embodiment not only exerts the same effect as the first embodiment but also can equate the contact areas of the contact plug with the contact connector in the lines to suppress the variations in characteristic among the bit lines.

FIGS. 23 and 24 describe the connections between the bit line BL and the contact plug CLb while the connections between the word line WL and the contact plug CLw may be treated similarly.