# Patent

## Title
Semiconductor memory device having local etch stopper and method of manufacturing the same

## Abstract

A semiconductor memory device includes a semiconductor substrate in which a cell region and a core and peripheral region are defined. The device further comprises isolation layers formed in the semiconductor substrate to define active regions, a first gate electrode structure formed in the cell region and a second gate electrode structure formed in the core and peripheral region. Source and drain regions formed in the active regions on respective sides of each of the gate electrode structures and self-aligned contact pads are formed in the cell region in contact with the source and drain regions. An insulating interlayer is formed on the semiconductor substrate between the self-aligned contact pads, and etch stoppers are formed on the insulating interlayer between the self-aligned contact pads in the cell region.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This is a divisional of application Ser. No. 11/354,175 filed on Feb. 15, 2006, which is incorporated herein by reference in its entirety.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a semiconductor memory device and a method of manufacturing the same. More particularly, the invention relates to a semiconductor memory device having an etch stopper formed in a cell region and a method of manufacturing the semiconductor memory device.
A claim of priority is made to Korean Patent Application No. 10-2005-0015371, filed on Feb. 24, 2005, the disclosure of which is hereby incorporated by reference in its entirety.
2. Description of Related Art
As the integration density of semiconductor memory devices increases, contact holes formed in the semiconductor devices become increasingly narrow. As a result, the aspect ratio of the contact holes tends to increase, and therefore contact holes and associated contacts are often required to be formed using multi-step processes.
The integration density of dynamic random access memory (DRAM) devices is typically very high. Because of this, active regions between adjacent gate electrodes in DRAMs are generally so narrow that it is difficult to form contacts connected to the active regions. One approach to forming contacts in narrow regions is to form a hard mask layer and spacers over and around the gate electrodes before forming self aligned contact pads between the gate electrodes. Then, bitline contacts or storage node contacts are formed over the self-aligned contact pads. This approach is often referred to as “self aligned contact technology.”
Typically, the self-aligned contacts have a larger diameter than the bitline contacts or the storage node contacts. However, as the integration density of DRAM devices continues to increase, the diameter of the self-aligned contact pads reduces and approaches the diameter of the bitline and storage node contacts. As a result, slight misalignments between the bitline or storage node contacts and node can cause serious problems in the manufacture of DRAM devices. Illustrations of some common problems are described below in relation to FIG. 1.
Referring to FIG. 1, a conventional semiconductor memory device comprises a semiconductor substrate 10 in which a cell region “A” and a core and peripheral region “B” are defined. A plurality of isolation layers 15 defining active regions 10a are formed in semiconductor substrate 10, and junction regions 25a and 25b are formed between isolation layers 15 in respective cell and core and peripheral regions “A” and “B”.
A first insulating interlayer 30 is formed over semiconductor substrate 10 and a second insulating interlayer 40 is formed over first insulating interlayer 30.
In cell region “A”, a plurality of self-aligned contact pads 35 are formed in first insulating interlayer 30 over junction regions 25a, and a plurality of bitline contact holes 45 are formed in second insulating interlayer 40 to expose self-aligned contact pads 35.
In core and peripheral region “B”, a gate electrode structure 20 is formed in first insulating layer 30 on side junction region 25b and an interconnection contact hole 50 is formed in first and second insulating interlayer 30 and 40 to expose side junction region 25b. Each gate electrode structure 20 comprises a gate insulating layer 16 formed on semiconductor substrate 10, a gate electrode material 17 formed on gate insulating layer 16, a hard mask layer 18 formed over gate electrode material 17, and spacers 19 formed on the sidewall of gate insulating layer 16, gate electrode material 17, and hard mask layer 18.
Typically, the respective diameters of self-aligned contact pads 35 and bitline contact holes 45 are slightly different from each other, or they are slightly misaligned with each other. As a result, portions of first insulating interlayer 30 adjacent to self-aligned contact pads 35 may be removed when bitline contact holes 45 are formed. Due to the partial loss of first insulating interlayer 30, active regions 10a may also be partially removed, causing leakage current in the semiconductor memory device.
Storage node contact holes (not shown) are typically formed after bitlines are formed in bitline contact holes 45. The storage node contact holes are generally formed between the bitlines to contact self-aligned contact pads 35. However, the storage node contact holes are almost inevitably misaligned with the self-aligned contact pads. As a result, the first insulating interlayer 30 is almost inevitably etched when the storage node contact holes are formed, causing further damage to active regions 10a. 
Interconnection contact hole 50 is typically formed in core and peripheral region “B” at the same time when bit line contact holes 45 are formed in cell region “A”. Unfortunately, however, as the integration density of core and peripheral region “B” increases, interconnection contact hole 50 tends to expose more than just junction region 25b. For instance, interconnection contact hole 50 may expose parts of gate electrode structure 20.
Consequently, spacers 19 and hard mask layer 18 may be partially lost during the formation of interconnection contact hole 50. As a result, gate electrode material 17 may be exposed and may be short-circuited by a conductive material formed later in interconnection contact hole 50.
To solve these problems, some conventional memory devices interpose etch stoppers between first insulating layer 30 and second insulating interlayer 40 to prevent first insulating interlayer 30 from being etched when bitline contact holes 45 are formed. A conventional memory device employing this technique is disclosed, for example, in U.S. Pat. No. 6,787,906 (the '906 patent).
In the '906 patent, etch stoppers are formed on first insulating layer 30. Accordingly, bitline contact holes 45 and storage node contact holes can be formed without further etching first insulating layer 30. However, the etch stoppers are also formed in core and peripheral region “B”, making it difficult to form interconnection contact hole 50. Since interconnection contact hole 50 penetrates first and second insulating layers 30 and 40, if the etch stoppers are interposed between first and second insulating interlayers 30 and 40, it is difficult to expose junction region 25b. 
SUMMARY OF THE INVENTION
According to one embodiment of the invention, a semiconductor memory device comprises a semiconductor substrate in which a cell region and a core and peripheral region are defined, isolation layers formed in the semiconductor substrate to define active regions therein, and a first gate electrode structure formed in the cell region and a second gate electrode structure formed in the core and peripheral region. The semiconductor memory device further comprises source and drain regions formed in the active regions on respective sides of each of the gate electrode structures, self-aligned contact pads contacting the source and drain regions in the cell region, an insulating interlayer formed on the semiconductor substrate between the self-aligned contact pads, and etch stoppers formed on the insulating interlayer in the cell region between the self-aligned contact pads. Typically, the memory device further comprises top spacers formed on upper sidewalls of the second gate electrode structure.
According to another embodiment of the invention, a method of manufacturing a semiconductor memory device comprises forming an insulating interlayer on a semiconductor substrate having conductive regions, forming contact pads in the insulating interlayer so that the contact pads contact the conductive regions, removing a predetermined thickness of the insulating interlayer to partially expose sidewalls of the contact pads, and forming etch stoppers in spaces created by the removal of the predetermined thickness of the insulating interlayer.
According to still another embodiment of the present invention, method of manufacturing a semiconductor memory device comprises forming gate electrode structures in a semiconductor substrate in which a cell region and a core and peripheral region are defined and isolation layers are formed to define active regions, and forming source and drain regions in the active regions on respective sides of each of the gate electrode structures. The method further comprises forming an insulating interlayer on the semiconductor substrate over the source and drain regions, etching the insulating interlayer to expose source and drain regions in the cell region, forming self-aligned contact pads in the insulating interlayer so that the self-aligned contact pads contact the exposed source and drain regions, removing a predetermined thickness of the insulating interlayer, forming etch stoppers in spaces created by removing the predetermined thickness of the insulating interlayer in the cell region, and forming top spacers on upper sidewalls of the gate electrode structure in the core and peripheral region.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described below in relation to several embodiments illustrated in the accompanying drawings. Throughout the drawings, like reference numbers indicate like exemplary elements, components, or steps, and the dimensions of layers and elements may be exaggerated for clarity. In the drawings:
FIG. 1 is a cross-sectional view of a conventional semiconductor memory device;
FIGS. 2A through 2E are cross-sectional views illustrating a method of manufacturing a semiconductor memory device according to an embodiment of the present invention;
FIG. 3 is a plan view of a cell region of a dynamic random access memory (DRAM) device according to an embodiment of the present invention; and
FIGS. 4A through 4E are cross-sectional views illustrating a method of manufacturing a semiconductor memory device according to another embodiment of the present invention.



DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of the invention are described below with reference to the corresponding drawings. These embodiments are presented as teaching examples. The actual scope of the invention is defined by the claims that follow.
FIGS. 2A through 2E are cross-sectional views illustrating a method of manufacturing a semiconductor memory device according to an embodiment of the present invention.
Referring to FIG. 2A, isolation layers 110 are formed in predetermined portions of a semiconductor substrate 100 to define active regions 105. Isolation layers 110 are typically formed by shallow trench isolation (STI). A conductive region 120 is formed in each active region 105 between isolation layers 110. Conductive regions 120 are typically formed by implanting impurities in semiconductor substrate 100. A first insulating interlayer 130 comprising silicon oxide is formed on semiconductor substrate 100. First insulating interlayer 130 is then etched to form contact holes 135 exposing conductive regions 120. A conductive layer such as a doped polysilicon layer, is then deposited on first insulating interlayer 130 to fill first contact holes 135. The conductive layer is planarized by a chemical mechanical polishing (CMP) process or an etch-back process to expose a surface of first insulating interlayer 130, thereby forming contact pads 140.
Referring to FIG. 2B, a predetermined thickness of first insulating interlayer 130 is removed to partially expose sidewalls of contact pads 140. The predetermined thickness of first insulating interlayer 130 is typically removed using a wet etch-back process, and the thickness of first insulating interlayer 130 is generally reduced thereby by between 1/10 and 1⁄2 of its original thickness.
Referring to FIG. 2C, an etch stopper 145 is deposited on first insulating interlayer 130 and contact pads 140. Etch stopper 145 is deposited to substantially fill spaces generated between contact pads 140 when first insulating interlayer 130 is removed. Etch stopper 145 has an etch selectivity relative to first insulating interlayer 130 and typically comprises a silicon nitride (SiN) layer or a silicon nitroxide (SiON) layer. Alternatively, etch stopper 145 could comprise any insulating layer having an etch selectivity relative to first insulating interlayer 130 (silicon oxide) and contact pads 140.
Referring to FIG. 2D, etch stopper 145 is planarized by etch back or CMP until contact pads 140 are opened, thereby forming etch stoppers 145a between contact pads 140.
Referring to FIG. 2E, a second insulating interlayer 150 is formed on contact pads 140 and etch stoppers 145a. Second insulating interlayer 150 typically comprises a silicon oxide layer like first insulating interlayer 130. Second insulating interlayer 150 is selectively etched to form second contact holes 155 exposing contact pads 140. Second contact holes 155 are shown to be misaligned with contact pads 140. However, since etch stoppers 145a are formed between second insulating interlayer 150 and first insulating interlayer 130, first insulating interlayer 130 is not further etched, and active regions 105 are undamaged.
FIG. 3 is a plan view of a cell region “A” in a DRAM device according to an embodiment of the present invention and FIGS. 4A through 4E are cross-sectional views taken along a line IV-IV′ in FIG. 3. In contrast to FIG. 3, FIGS. 4A through 4E also illustrate a core and peripheral region “B” of the DRAM device. FIGS. 4A through 4E illustrate a method of manufacturing a semiconductor memory device according to another embodiment of the present invention.
Referring to FIGS. 3 and 4A, isolation layers 210 are formed in a semiconductor substrate 200 where cell region “A” and core and peripheral region “B” are defined. Isolation layers 210 define active regions 205. A gate oxide layer 212, a conductive layer 214 for a gate electrode, and a hard mask layer 216 are then sequentially stacked on semiconductor substrate 200, and then stacked layers 212, 214, and 216 are partially patterned. Gate spacers 225 are formed on sidewalls of patterned hard mask layer 216 and conductive layer 214 using a well-known method, thereby forming gate electrode structures 220 and 222. Gate spacers 225 typically comprise silicon nitride layers like hard mask layer 216. Gate electrode structure 220 in cell region “A” typically acts as a word line structure.
Impurities are implanted into active regions 205 outside gate electrode structures 220 and 222 to form source/drain regions 230a and 230b and 232a and 232b. A first insulating interlayer 235 is then formed to a predetermined thickness on semiconductor substrate 200. Next, first insulating interlayer 235 is etched to expose source and drain regions 230a and 230b in cell region “A”. Here, source and drain regions 230a and 230b are formed in a self-aligned manner by gate electrode structure 220 surrounded by hard mask layer 216 and gate spacers 225. Next, a conductive layer, such as a doped polysilicon layer, is deposited on first insulating interlayer 235 to contact source/drain regions 230a and 230b. The conductive layer is then planarized by an etch back process or a CMP process to form self-aligned contact pads 240a and 240b. Self-aligned contact pads 240a will contact later formed bitline contact pads and self-aligned contact pads 240b will contact later storage node contact pads.
Referring to FIG. 4B, a predetermined thickness of the first insulating interlayer 235 is removed. The thickness of first insulating interlayer 235 is typically reduced by a range of between 1/10 and 1⁄2 of its original thickness. As first insulating interlayer 235 is partially removed, sidewalls of the self-aligned contact pads 240a and 240b are partially exposed. In addition, as first insulating interlayer 235 is partially removed, a top surface of gate electrode structure 222 and sidewalls of gate spacers 225 in core and peripheral region “B” are partially exposed.
Referring to FIG. 4C, an insulating layer 245 for an etch stopper is deposited on semiconductor substrate 200 to fill spaces between self-aligned contact pads 240a and 240b. Insulating layer 245 typically comprises a silicon nitride layer having an etch selectivity relative to first insulating interlayer 235. When an 80 nm design rule is used, a distance between self-aligned contact pads 240a and 240b is approximately 50 nm. The spaces between self-aligned contact pads 240a and 240b can be filled by depositing insulating layer 245 to a thickness of about 300 Å.
Referring to FIG. 4D, insulating layer 245 is anisotropically etched to form etch stoppers 245a between self-aligned contact pads 240a and 240b in cell region “A”. Top spacers 245b are formed on upper sidewalls of exposed portions of gate spacers 225 in core and peripheral region “B”. Accordingly, etch stoppers 245a can be selectively formed only in cell region “A” without an additional photolithography process.
Referring to FIG. 4E, a second insulating interlayer 250 is deposited on the semiconductor substrate 200 over etch stoppers 245a and top spacers 245b. Next, second insulating interlayer 250 is etched to expose self-aligned contact pads 240a in cell region “A” and source/drain region 232b in core and peripheral region “B”, thereby forming bitline contact holes 255a and an interconnection contact hole 255b in second insulating interlayer 250.
Even though misalignment occurs when bitline contact holes 255a are formed, since etch stoppers 245a are formed on both sides of self-aligned contact pads 240a, first insulating interlayer 235 and active regions 205 are prevented from being etched. In addition, since top spacers 245b are formed outside gate spacers 225 in core and peripheral region “B”, the total loss of gate spacers 225 and hard mask layer 216 is prevented when interconnection contact hole 255b is formed.
Subsequently, a barrier metal layer 260 is formed on inner surfaces of bitline contact holes 255a, an inner surface of interconnection contact hole 255b, and a top surface of second insulating interlayer 250. Thereafter, a conductive layer such as a tungsten layer is deposited on barrier metal layer 260 to fill bitline contact holes 255a and interconnection contact hole 255b. Next, the conductive layer and barrier metal layer 260 are planarized by CMP process or an etch back process to expose a surface of second insulating interlayer 250, thereby forming bitline contact pads 265a and an interconnection contact pad 265b. 
A conductive layer 272 for a bitline and a hard mask layer 273 are deposited on the second insulating interlayer 250 where bitline contact pads 265a and interconnection contact pad 265b are formed. Next, hard mask layer 273 and conductive layer 272 are patterned to contact bitline contact pads 265a and interconnection contact pad 265b, and alternate with gate electrode structure 220 in cell region “A”. Bitline spacers 274 are formed on sidewalls of patterned hard mask layer 273 and conductive layer 272, thereby forming bitline structures 270.
A third insulating interlayer 275 is deposited on semiconductor substrate 200 over bitline structures 270. Subsequently, third insulating interlayer 275 and second insulating interlayer 250 are etched to expose self-aligned contact pads 240b, thereby forming storage node contact holes 280. Storage node contact holes 280 formed between bitline structures 270 are typically separated from bitline structures 270 by a predetermined distance for insulation purposes. Since self-aligned contact pads 240b have a diameter similar to that of storage node contact holes 280, misalignment occurs inevitably. However, since etch stoppers 245a are formed between self-aligned contact pads 240a and 240b, first insulating interlayer 235 is prevented from being lost even though the misalignment occurs. Although not shown, a conductive layer is formed in storage node contact holes 280 to form storage node contact pads (not shown).
As described above, after self-aligned contact pads 240b are formed in cell region “A”, etch stoppers 245a are selectively buried on both sides of self-aligned contact pads 240b to form bitline contact holes 255a and storage node contact holes 280. Consequently, the loss of the insulating interlayer due to misalignment during the formation of the contact holes is prevented, thereby preventing damage to the active regions.
Further, since the etch stoppers are only formed in the cell region without a separate photolithography process, a difficult etching process due to the forming of the interconnection contact hole in the core and peripheral region is avoided.
Furthermore, since the top spacers are formed on the sidewalls of the gate electrode in the core and peripheral region when the etch stoppers are selectively formed, gate electrode material is prevented from being exposed when the interconnection contact hole is formed.
The foregoing preferred embodiments are teaching examples. Those of ordinary skill in the art will understand that various changes in form and details may be made to the exemplary embodiments without departing from the scope of the present invention as defined by the following claims.

## Claims

1. A method of manufacturing a semiconductor memory device, the method comprising:
forming a first insulating interlayer on a semiconductor substrate having conductive regions;
forming contact pads extending through the first insulating interlayer to respectively contact the conductive regions;
removing a predetermined thickness of the first insulating interlayer to partially expose sidewalls of the contact pads; and
forming an etch stopper from a second insulating interlayer completely covering the respective exposed sidewalls of the contact pads and respective upper surfaces of the contact pads, and completely filling respective spaces between adjacent contact pads, wherein the second insulating interlayer has an etch selectivity relative to the first insulating interlayer.

2. The method of claim 1, wherein the predetermined thickness of the first insulating interlayer is removed by applying a wet etching process.

3. The method of claim 1, wherein the predetermined thickness of the first insulating interlayer comprises 1/10 to 1⁄2 of its original thickness.

4. The method of claim 1, further comprising:
planarizing an upper surface of the second insulating interlayer to expose the upper surfaces of the contact pads through the etch stopper.

5. The method of claim 4, further comprising:
forming an upper insulating interlayer on the planarized upper surface of the second insulating interlayer; and
patterning the upper insulating interlayer to form contact holes, each contact hole exposing at least a portion of an upper surface of a corresponding contact pad.

6. The method of claim 5, wherein the contact holes are respectively misaligned with the contact pads, such that only a portion of the upper surface of each contact pad is exposed through each contact hole.

7. The method of claim 1, wherein the second insulating interlayer is a silicon nitride layer.

8. A method of manufacturing a semiconductor memory device, the method comprising:
forming gate electrode structures in a semiconductor substrate in which a cell region and a core and peripheral region are defined and isolation layers are formed to define active regions;
forming source and drain regions in the active regions on respective sides of each of the gate electrode structures;
forming an insulating interlayer on the semiconductor substrate over the source and drain regions;
etching the insulating interlayer to expose source and drain regions in the cell region;
forming self-aligned contact pads in the insulating interlayer so that the self- aligned contact pads contact the exposed source and drain regions;
removing a predetermined thickness of the insulating interlayer;
forming etch stoppers in spaces created by removing the predetermined thickness of the insulating interlayer in the cell region; and
forming top spacers on upper sidewalls of the gate electrode structure in the core and peripheral region.

9. The method of claim 8, wherein forming the gate electrode structures comprises:
forming a gate insulting layer on the semiconductor substrate;
forming a conductive layer for a gate electrode on the gate insulating layer;
forming a hard mask layer on the conductive layer;
patterning the conductive layer and the hard mask layer; and
forming gate spacers on sidewalls of the patterned conductive layer and the hard mask layer.

10. The method of claim 8, wherein the predetermined thickness of the insulating interlayer is removed by wet etching.

11. The method of claim 10, wherein the predetermined thickness of the insulating interlayer comprises 1/10 to 1⁄2 of its original thickness.

12. The method of claim 8, wherein forming the etch stoppers and the top spacers comprises:
forming an insulating layer on the semiconductor substrate to fill the spaces created by removing the predetermined thickness of the insulating interlayer; and
anisotropically etching the insulating layer to form the etch stoppers and the top spacers.

13. The method of claim 12, wherein the insulating layer comprises a silicon nitride layer.