CN114664847A - Semiconductor structure and manufacturing method thereof - Google Patents

Abstract

The invention discloses a semiconductor structure and a manufacturing method thereof, comprising a substrate, a plurality of grooves and active regions, a plurality of bit lines which are arranged on a memory cell region at equal intervals along a first direction and extend towards a second direction orthogonal to the first direction, the bit lines are electrically connected to an active region in the substrate through the grooves, and a dummy bit line which is positioned at the outermost side of the bit lines in the first direction and extends towards the second direction, wherein the width of the dummy bit line in the first direction is larger than that of the bit lines in the first direction, the bottoms of the dummy bit lines are not in the same horizontal plane, and the dummy bit line and the bit lines have the same composition and layer structure.

Description

Semiconductor structure and manufacturing method thereof

Technical Field

The disclosed embodiments relate to a semiconductor structure and a method for fabricating the same, and more particularly, to a semiconductor structure having bit lines with different widths and a method for fabricating the same.

Background

A memory device is an integrated circuit that is typically used in a computer system to store data in one or more arrays of individual memory cells. The memory device can perform writing and reading operations using bit lines (also referred to as digit lines, data lines, or sense lines) that can be electrically connected to the memory cells along columns of the matrix and word lines (also referred to as access lines) that can be electrically connected to the memory cells along rows of the matrix. Each memory cell is individually addressable via a combination of a bit line and a word line.

The memory device may be volatile, semi-volatile, or non-volatile in nature. Non-volatile memory devices can store data for a long period of time without power, volatile memory devices dissipate the stored data and require constant refreshing/rewriting to maintain their data storage. The memory device uses a capacitor or other components to store charges, and reads the charges of the capacitor to determine which memory state the memory cell is in, such as a "0" or "1" memory state, so as to achieve the purpose of data storage and reading. The memory device also has electronic components such as transistors to control the switching of the gate and the storage and release of charge. Peripheral circuit regions exist around a memory cell array region of a memory device, and bit lines and word lines extend from the memory cell array region to the peripheral circuit regions and are electrically connected to external circuits in the peripheral circuit regions through other interconnection structures such as wires and contacts.

In the fabrication of memory devices or other circuits, it is a constant goal of industry to continually shrink, and to make the components more compact, to achieve higher storage capacity per unit area. However, as memory devices continue to shrink, many problems to be overcome, such as micro-loading effect due to different pattern densities or insufficient layout space due to too tight a feature-to-feature structure, are encountered in the fabrication process. The present invention is motivated by overcoming some of the above-mentioned problems encountered in the fabrication of circuits.

Disclosure of Invention

The invention provides a novel semiconductor structure and a manufacturing method thereof, which are characterized in that a dummy bit line positioned at the outermost side has larger width and different partition wall types, and the problem of micro-load effect of a device can be solved.

One aspect of the present invention is to provide a semiconductor structure, which comprises a substrate, the substrate is defined with a memory cell region, and the substrate further has a plurality of grooves, a plurality of bit lines arranged on the memory cell region at equal intervals along a first direction and extending to a second direction orthogonal to the first direction, the bit line is electrically connected to an active region in the substrate through the groove, and a dummy bit line is located at an outermost side of the bit lines in the first direction and extends toward the second direction, wherein the width of the dummy bit line in the first direction is larger than the width of the bit line in the first direction, and the bottom of the dummy bit line is not at the same level, the dummy bit line and the bit lines have the same composition and layer structure, and part of the dummy bit line is positioned in the groove and electrically connected with an active region in the substrate.

Another aspect of the present invention is to provide a method for fabricating a semiconductor structure, which includes providing a substrate defining a memory cell region thereon, the substrate further having a plurality of recesses, forming a bit line material layer on the substrate, forming a plurality of bit line mask patterns on the bit line material layer, wherein the bit line mask patterns are arranged on the memory cell region at regular intervals along a first direction and extend in a second direction orthogonal to the first direction, forming a photoresist on the bit line mask patterns, wherein the photoresist covers a region outside the memory cell region and the bit line mask patterns outermost in the first direction but exposes other bit line mask patterns, and etching the bit line material layer using the photoresist and the bit line mask patterns as an etching mask, thereby forming a plurality of bit lines and dummy bit lines located at the outermost sides of the bit lines in the first direction, the dummy bit lines and the dummy bit lines extend in the second direction, are electrically connected to an active region through a groove, have a width in the first direction greater than the width in the first direction, have the same composition and layer structure, and are partially disposed in the groove and electrically connected to an active region.

These and other objects of the present invention will become more apparent to those skilled in the art after a reading of the following detailed description of the preferred embodiment illustrated in the various figures and drawings.

Drawings

The accompanying drawings are included to provide a further understanding of embodiments of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate some embodiments of the invention and together with the description serve to explain its principles. In these figures:

FIGS. 1A, 2A and 3A are schematic cross-sectional views illustrating a process for fabricating a semiconductor structure according to a preferred embodiment of the present invention;

FIGS. 1B, 2B and 3B are schematic cross-sectional views taken along lines A-A' of FIGS. 1A, 2A and 3A, respectively;

FIG. 4 is a cross-sectional view of a semiconductor structure according to a preferred embodiment of the present invention;

FIG. 5 is a schematic cross-sectional view of a semiconductor structure according to another embodiment of the present invention;

FIG. 6 is a schematic cross-sectional view of a semiconductor structure according to yet another embodiment of the present invention;

FIG. 7 is a schematic cross-sectional view of a semiconductor structure according to yet another embodiment of the present invention;

FIG. 8 is a cross-sectional view of a semiconductor structure according to a preferred embodiment of the present invention;

FIG. 9 is a schematic cross-sectional view of a semiconductor structure according to another embodiment of the present invention;

FIG. 10 is a schematic cross-sectional view of a semiconductor structure according to yet another embodiment of the invention; and

FIG. 11 is a cross-sectional view of a semiconductor structure according to yet another embodiment of the present invention.

It should be noted that all the figures in this specification are schematic in nature, and that various components may be shown exaggerated or reduced in size or in proportion for the sake of clarity and convenience in illustration.

Wherein the reference numerals are as follows:

100 semiconductor substrate

100a memory cell region

100b active region

100c active region

102 device isolation layer

103 groove

104 insulating layer

105 grooves

106 contact layer

108 barrier layer

110 metal layer

112 hard mask layer

114 bit line shield pattern

116 Photoresist

118 bit line spacer

119 bit line spacer

120 spacer wall

122 spacer wall

124 spacer layer

126 spacer layer

128 spacer layer

130 groove

131 contact area

132 polysilicon layer

134 silicide layer

136 Barrier layer

138 metal layer

BL bit line

DBL dummy bit line

D1 first direction

D2 second direction

SC storage node contact structure

W1, W2, W3, W4 widths

Detailed Description

In the drawings, fig. 1A, 2A and 3A are plan views illustrating a manufacturing process of a semiconductor structure according to a preferred embodiment of the present invention, and fig. 1B, 2B and 3B are cross-sectional views along the sectional line a-a' in fig. 1A, 2A and 3A, respectively, illustrating relative positions of components and connections of the semiconductor structure in a direction perpendicular to a substrate.

Please refer to fig. 1A and fig. 1B at the same time. The semiconductor structure of the present invention is fabricated on a semiconductor substrate 100, such as a silicon substrate, a germanium substrate and/or a silicon germanium substrate. The semiconductor substrate 100 defines a memory cell region 100a for arranging memory cells (cells) of the semiconductor memory device, and a plurality of memory cells can be arranged in a number configuration in the memory cell region 100a and can store charges to generate a distinctive memory state, thereby achieving a memory effect. The periphery of the memory cell area 100a may be a peripheral area (not shown) for disposing peripheral circuits of the memory device, such as column decoders, row decoders, sense amplifiers, or I/O control modules. A plurality of active regions 100b are defined in the memory cell region 100a of the semiconductor substrate 100, and each active region 100b is separated and defined by a surrounding device isolation layer 102, such as a Shallow Trench Isolation (STI). In the process, the device isolation layer 102 may be formed by performing a photolithography process on the semiconductor substrate 100 to form respective separated active regions 100b, and filling the trenches between the active regions 100b with an isolation material, such as silicon oxide. An insulating layer 104 is formed on the surface of the semiconductor substrate 100 to isolate the lower active region 100b from the upper components, which can also be used as a gate dielectric layer of the gate device in the peripheral region. The insulating layer 104 may be formed of a single insulating layer or a plurality of insulating layers, such as a silicon nitride layer, and/or a silicon oxynitride layer, and the like. A recess 103 is formed in a portion of the active region 100b, such that the active region 100b is exposed from the insulating layer 104. It should be noted that in practice, the active regions 100b may be stripe-shaped in plan view and have long axes extending in the same direction, and are uniformly arranged in a staggered manner in plan view. Since the active region 100b is not the focus of the present invention, fig. 1A only shows the memory cell region 100a and the bit line mask pattern 114 thereon for the sake of simplicity and clarity and to avoid obscuring the focus of the present invention.

Refer back to fig. 1A and 1B. A contact layer 106, a barrier layer 108, a metal layer 110 and a hard mask layer 112 are sequentially formed on the memory cell region 100a of the semiconductor substrate 100, which may be defined on the memory cell region 100a by an anisotropic photolithography process, which may also simultaneously define the gate members in the peripheral region. Preferably, the material of the contact layer 106 may be doped polysilicon, the material of the barrier layer 108 may be a metal nitride, such as titanium nitride, tantalum nitride and/or tungsten nitride, the material of the metal layer 110 may be a low-resistivity metal, such as tungsten, aluminum, titanium or tantalum, and the material of the hard mask layer 112 may be silicon nitride or silicon oxynitride. A portion of the contact layer 106 is formed in the recess 103 and electrically connected to the exposed active region 100 b. As can be seen from fig. 1A, a plurality of ring-shaped bit line shielding patterns 114 are formed on the semiconductor substrate 100, the ring-shaped bit line shielding patterns 114 are arranged at intervals in the first direction D1, and extend toward the second direction D2 orthogonal to the first direction D1 and cross over the memory cell region 100a, and both ends of the ring-shaped patterns are located outside the memory cell region 100 a. In the cross-sectional view of fig. 1B, the bit line shielding pattern 114 passing through the memory cell region 100a is located on the hard mask layer 112, and is preferably aligned with the lower portion of the recess 103 and the device isolation layer 102. The material of the bit line mask pattern 114 may be a material having an etching selectivity with the underlying hard mask layer 112, such as silicon oxide, which may be formed by a double patterning (double patterning) method. For example, the step of forming the annular patterns may include: (1) forming a plurality of sacrificial patterns on the bit line material layer, the sacrificial patterns being arranged at regular intervals along the first direction D1 on the memory cell region 100a and extending in the second direction D2; (2) forming a spacer on sidewalls of the sacrificial patterns; and (3) removing the sacrificial patterns so that the spacer walls form the circular bit line shielding patterns.

Please refer to fig. 2A and fig. 2B simultaneously. After the layer structure and the bit line mask pattern 114 are formed, a trimming photoresist 116 is formed on the bit line mask pattern 114. As shown in fig. 2A, the photoresist 116 covers the region except the memory cell region 100a, including both ends of the ring-shaped patterns in the second direction D2, and covers the bit line shielding pattern 114 located on the memory cell region 100a and on the outermost side in the first direction D1, but exposes the other bit line shielding pattern 114 located on the memory cell region 100 a. Thus, it can be seen that a part of the layer structure in the memory cell region 100a is also covered by the photoresist 116, and the ring-shaped patterns exposed from the photoresist 116 become a plurality of bit line mask patterns 114 extending in the second direction D2.

Please refer to fig. 3A and fig. 3B simultaneously. After the formation of the photoresist 116, an etching process is performed by using the photoresist 116 and the bit line mask pattern 114 as a mask to remove the exposed layer structure, including the contact layer 106, the barrier layer 108, the metal layer 110 and the hard mask layer 112, thereby forming bit line BL and dummy bit line DBL structures on the memory cell region 100 a. As can be seen from FIG. 3A, the bit lines BL and the dummy bit lines DBL are arranged at equal intervals in the first direction D1 and extend through the memory cell region 100a in the second direction D2, and the two dummy bit lines DBL are located at the outermost side of the 1 st direction D1. As can be seen from fig. 3B, the dummy bit line DBL and the bit line BL have the same composition and layer structure, the formed bit line BL is electrically connected to the underlying active region 100B through the contact layer 106, and the contact layer 106 of the dummy bit line DBL in the recess 103 and the sidewall of the recess 103 form a smaller trench 105. A portion of the dummy bit line DBL located at the outermost side of the memory cell region 100a is located in the recess 103 and electrically connected to the active region 100b below. Due to the trimming process, the width W1 of the dummy bit line DBL in the first direction D1 is greater than the width W2 of the bit line BL in the first direction D1. Forming the dummy bit line DBL having a larger width at the outermost side of the memory cell region 100a helps to improve the problem that the structure of the bit line structure at the outermost side is deformed or easily collapsed due to the micro-loading effect in the prior art. Moreover, the design of simultaneously forming the dummy bit lines DBL on the substrate surface and the groove surface with different levels can make the outermost dummy bit lines DBL more stable and less prone to collapse.

Please refer to fig. 4. After the formation of bit line BL and dummy bit line DBL, bit line spacers 118 are then formed in trenches 105. The bit line spacers 118 may be formed of an insulating material having an etch selectivity with respect to the insulating layer 104, such as silicon oxide, silicon nitride, silicon oxynitride, or a composite structure thereof. After the formation of the bit line spacers 118, spacers 120 and 122 are formed on both sides of the bit line BL and the dummy bit line DBL, which may be formed by a deposition process and an anisotropic etching process. As can be seen from fig. 4, the width W4 of spacer 122 located outside dummy bit line DBL in first direction D1 is greater than the width W3 of spacer 120 inside dummy bit line DBL and spacer 120 on both sides of bit line BL in first direction D1. The spacers 120 located inside the dummy bit line DBL may be located on the bit line spacers 118, and a portion of the deposition layer on the surface of the insulating layer 104 may remain to connect adjacent spacers 120. The material of the spacers 120 and 122 may be silicon oxide, silicon nitride, or a composite structure thereof.

Fig. 5 is a schematic cross-sectional view of a semiconductor structure according to another embodiment of the invention. In addition to the above-described spacer aspects, the present invention may also have other spacer aspects. As shown in fig. 5, in this embodiment, the trench 105 is not filled with the bit line spacer 118, and the spacers 120 located inside the dummy bit line DBL and on both sides of the bit line BL may also be a multi-layer structure including two conformal spacers 124 and 126 distributed along the sidewalls inside the dummy bit line DBL and on both sides of the bit line BL, the trench 105 and the surface of the insulating layer 104. The spacer 122 located outside the dummy bit line DBL has a single-layer structure. In other embodiments, the spacer layer 126 may fill the trench 105. The material of the spacers 124, 126 may be silicon oxide or silicon nitride, respectively. In this embodiment, the spacer 122 on both sides of the dummy bit line DBL is not as high as the bottom surface of the spacers 124 and 126, and the width of the spacer 122 in the first direction D1 is also greater than the width of the spacers 124 and 126.

Fig. 6 is a schematic cross-sectional view of a semiconductor structure according to another embodiment of the invention. In addition to the two aspects described above, the present invention may have other aspects of the spacer walls. In the embodiment of fig. 6, the original trench 105 is not filled with the bit line spacer 118, and a spacer 128 may be formed inside the dummy bit line DBL and on both sides of the bit line BL. The original trench 105 is then etched by an anisotropic etching process to form a trench 130 having a depth greater than the original trench 103. This has the advantage that the isolation between the dummy bit line DBL and the adjacent bit line BL can be further improved.

Fig. 7 is a schematic cross-sectional view of a semiconductor structure according to an embodiment of the invention. After the formation of the bit line spacers 118 and the spacers 120, a storage node contact structure SC may be formed on the active region 100c between the bit lines BL, which may include forming spacer structures (not shown) between the bit lines BL, and then performing an anisotropic etching process using the photoresist, the spacer structures, and the bit lines BL (including the spacers 120 on both sides thereof) as an etching mask to remove the insulating layer 104 between the spacer structures and the bit lines BL, exposing the underlying active region 100c, which is a contact region 131 for the formation of the storage node. This etching step may remove portions of the bit line spacers 118 and the active regions 100c, and it is noted that regions outside the memory cell regions 100a (e.g., regions outside the dummy bit lines DBL) are protected from the photoresist and are not etched. After the contact region 131 is formed, a storage node contact structure SC is formed on the contact region 131, which may include a polysilicon layer 132, a silicide layer 134, a barrier layer 136, and a metal layer 138, in this order, as shown. Polysilicon layer 132 may be doped polysilicon that directly contacts exposed contact regions 131 of the substrate. Silicide layer 134 may include titanium silicide, cobalt silicide, nickel silicide, tungsten silicide, platinum silicide, and/or molybdenum silicide, among others. The metal layer 138 may be tungsten, aluminum, titanium, or tantalum. The barrier layer 136 may include a nitride of a metal material such as tungsten, aluminum, titanium, or tantalum. After the storage node contact structure SC is formed, a contact isolation structure is formed above the storage node contact structure SC and is connected to a charge storage element such as a capacitor.

Fig. 8 is a schematic cross-sectional view of a semiconductor structure according to a preferred embodiment of the invention. The structure of this embodiment is similar to that of fig. 7, except that fig. 8 is a structure that is continuous with fig. 6 to form a storage node contact structure SC in the active area 100c between the bit lines BL, and it can be seen that the depth of the trench 130 inside the dummy bit line DBL is lower than the depth of the recess 103 where the dummy bit line DBL is located and lower than the depth of the trench 105 where the bit line BL is located. Both trenches 130 and 105 have bitline spacers 118, 119 formed therein. It is noted that in this embodiment, the top surface of bitline spacer 118 in trench 130 is lower than the top surface of bitline spacer 119 in trench 105 because trench 130 is lower. The bit line spacers 118 and 119 may be formed of an insulating material having an etch selectivity with respect to the insulating layer 104, such as silicon oxide, silicon nitride, silicon oxynitride, or a composite structure thereof. After the formation of the bit line spacers 118 and 119, another spacer 120 is formed on both sides of the bit line BL and the dummy bit line DBL, and the material thereof may be silicon oxide, silicon nitride, or a composite structure thereof. The bottom surfaces of the spacers 120, 122 on either side of the dummy bit line are not of equal height because the top surface of the bit line spacer 118 is lower. Since the inner sidewall of the dummy bit line DBL and the surface of the trench 130 are further formed with the spacer 128, the spacer 128 and the spacer 120 are integrally formed as a multi-layer spacer structure, and the spacer 122 located outside the dummy bit line DBL is formed as a single-layer structure. Thereafter, a storage node contact structure SC process as described in fig. 7 is performed to form a storage node contact structure SC on the active region 100c between the bit line BL and the dummy bit line DBL. An advantage of this embodiment is that the deeper trench 130 can further improve the isolation between the dummy bit line DBL and the adjacent bit line BL.

Fig. 9 is a schematic cross-sectional view of a semiconductor structure according to another embodiment of the invention. The structure of this embodiment is similar to that of fig. 8, except that in fig. 9, the bitline spacers 118 in the trench 130 do not fill the trench 130, but are formed conformally in the trench 130, with portions of the spacers 120 extending into the bitline spacers 118. Similarly, the uppermost top surface of bitline spacer 118 in trench 130 is lower than the top surface of bitline spacer 119 in trench 105 in this embodiment.

Fig. 10 is a schematic cross-sectional view of a semiconductor structure according to another embodiment of the invention. The structure of this embodiment is similar to that of fig. 8, except that the bit line spacers 118 are not formed in the trenches 130 of fig. 10, and the subsequently formed spacers 120 directly fill the entire trenches 130 along the sidewalls of the dummy bit lines DBL. Bit line spacers 119 are formed in the trenches 105 on both sides of the bit line BL.

Finally, fig. 11 is a schematic cross-sectional view of a semiconductor structure according to another embodiment of the invention. The structure of this embodiment is similar to that of fig. 10, except that in fig. 11, the spacer layer 128 originally formed on the surface of the trench 130 in a co-line manner does not completely cover the surface of the trench 130, and due to the anisotropic etching, a portion of the spacer layer 128 on the bottom surface of the trench 130 is removed, exposing the active region 100 b. As such, the spacer 120 formed subsequently directly fills the entire trench 130 along the sidewalls of the dummy bit line DBL and directly contacts the exposed active region 100 b.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (19)

1. A semiconductor structure, comprising:

a substrate, wherein a memory cell region is defined on the substrate, and the substrate further comprises a plurality of grooves and an active region;

a plurality of bit lines arranged on the memory cell region at equal intervals along a first direction and extending in a second direction orthogonal to the first direction; and

a dummy bit line located at an outermost side of the bit lines in the first direction and extending in the second direction,

wherein the width of the dummy bit line in the first direction is greater than the width of the bit lines in the first direction, and the bottom of the dummy bit line is not in the same horizontal plane;

the bit lines and the dummy bit lines have the same composition and layer structure, and sequentially comprise a contact layer, a conductive layer and a hard mask layer from the substrate to the top, wherein the contact layer of the bit line is positioned in a groove and electrically connected to an active region through the groove and forms a first groove with the side wall of the groove, and the contact layer of the dummy bit line is positioned in the groove and electrically connected to the active region and forms a second groove with the side wall of the groove.

2. The semiconductor structure of claim 1, wherein a depth of the first trench is the same as a depth of the recess, and a depth of the second trench is lower than a depth of the first trench.

3. The semiconductor structure of claim 2, wherein a conformal spacer is formed on sidewalls of both sides of the bit lines, sidewalls of an inner side of the dummy bit line, a surface of the first trench and a surface of the second trench, and further comprising spacers formed on sidewalls of both sides of the bit lines and both sides of the dummy bit line.

4. The semiconductor structure of claim 3, wherein said spacer on said sidewalls inside said dummy bit line directly contacts an underlying said active region of said substrate through said spacer.

5. The semiconductor structure of claim 2, wherein the first trench is filled with a first bit line spacer and the second trench is filled with a second bit line spacer, and further comprising spacers formed on sidewalls on both sides of the bit lines, on sidewalls on both sides of the dummy bit line, on the first bit line spacer and on the second bit line spacer.

6. The semiconductor structure of claim 5, wherein a top surface of the second bit line spacer is lower than a top surface of the first bit line spacer.

7. The semiconductor structure of claim 5, wherein the second bit line spacers are conformally formed on the second trench surfaces, portions of the spacers extending into the second bit line spacers.

8. The semiconductor structure of claim 5, wherein a width of the spacer at an outer side of the dummy bit line in the first direction is greater than a width of the spacer at an inner side of the dummy bit line in the first direction and greater than a width of the spacers of the bit lines in the first direction.

9. The semiconductor structure of claim 5, wherein bottom surfaces of the spacers on both sides of the dummy bit line are not equal in height.

10. The semiconductor structure of claim 5, wherein the spacer outside the dummy bit line is a single-layer spacer and the spacer inside the dummy bit line is a multi-layer spacer.

11. A method of fabricating a semiconductor structure, comprising:

providing a substrate, wherein a memory cell area is defined on the substrate, and the substrate is further provided with a plurality of grooves;

forming a bit line material layer on the substrate;

forming a plurality of bit line shielding patterns on the bit line material layer, wherein the bit line shielding patterns are arranged on the memory cell region at equal intervals along a first direction and extend to a second direction orthogonal to the first direction;

forming a photoresist on the bit line shielding patterns, wherein the photoresist covers the region outside the memory cell region and covers the bit line shielding pattern located on the memory cell region and located on the outermost side in the first direction, but exposes the other bit line shielding patterns; and

etching the bit line material layer using the photoresist and the bit line mask patterns as an etching mask, thereby forming a plurality of bit lines and dummy bit lines located at outermost sides of the bit lines in the first direction,

the dummy bit lines and the dummy bit lines extend in the second direction, are electrically connected to an active region through the grooves, have the same composition and layer structure as the bit lines, and are partially positioned in the grooves and electrically connected to the active region.

12. The method as claimed in claim 11, wherein the bit line shielding patterns are ring patterns extending in the second direction, and the photoresist covers two ends of the ring patterns in the second direction, such that the ring patterns exposed from the photoresist are a plurality of bit line shielding patterns extending in the second direction.

13. The method of claim 12, wherein two ends of the ring-shaped patterns are outside the memory cell region.

14. The method of claim 12, wherein the step of forming the ring-shaped patterns comprises:

forming a plurality of sacrificial patterns on the bit line material layer, wherein the sacrificial patterns are arranged on the memory cell region at equal intervals along the first direction and extend to the second direction;

forming a spacer on sidewalls of the sacrificial patterns; and

the sacrificial patterns are removed, so that the annular patterns are formed on the partition walls.

15. The method as claimed in claim 11, wherein the bit lines and the dummy bit line sequentially comprise a contact layer, a conductive layer and a hard mask layer from the substrate.

16. The method as claimed in claim 11, wherein the substrate further has a plurality of recesses, and the contact layer of the bit line is electrically connected to an active region through one of the recesses.

17. The method as claimed in claim 11, wherein the contact layer of the portion of the dummy bit line is disposed in the recess and electrically connected to an active region.

18. The method of claim 11, wherein forming a layer of bitline material on the substrate further comprises forming an outer spacer on sidewalls of the layer of bitline material.

19. The method of claim 18, further comprising forming spacers on sidewalls of the bit lines and the dummy bit line after forming the bit lines and the dummy bit line, wherein a width of the outer spacers in the first direction is greater than a width of the spacers in the first direction.

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