TW201919173A - Contact hole structure mrthod for fabricting the same and applications thereof - Google Patents

Abstract

A contact hole structure includes a substrate, an interlayer dielectric (ILD), a contact layer and an insulating capping layer. The ILD is disposed on the substrate and has a first opening. The contact layer is disposed in the ILD and aligns the first opening. The insulating capping layer has a spacer disposed on a first sidewall of the first opening, wherein the spacer contacts to the conductive layer and defines a second opening in the first opening, so as to expose a portion of the conductive layer.

Description

Contact opening structure and manufacturing method and application thereof

The disclosure is related to an integrated circuit structure and a manufacturing method and application thereof. In particular, it relates to a contact opening structure and a manufacturing method and application thereof.

As the complexity of the integrated circuit and the feature size continue to shrink, it becomes more and more difficult to form an interlayer contact structure (pattern) with high dimensional accuracy and reliability. How to meet the requirements of the ultra-large-scale integration circuit for the dimensional accuracy and operational reliability of the interlayer contact structure (pattern) has become a major challenge in the industry. The contact opening structure and its fabrication method are the key to making interlayer contact structures (patterns) with high dimensional accuracy and reliability.

Therefore, there is a need to provide an advanced contact opening structure and fabrication method and its application to solve the problems faced by the prior art.

An embodiment of the present specification discloses a contact opening structure including: a substrate, an interlayer dielectric layer, a conductive layer, and an insulating cover layer. An interlayer dielectric layer is over the substrate and has a first opening. The conductive layer is in the interlayer dielectric layer and is aligned with the first opening. The insulating cover layer has a spacer on the first sidewall of the first opening, wherein the spacer contacts the conductive layer and defines a second opening in the first opening to expose a portion of the conductive layer.

Another embodiment of the present specification discloses a method of fabricating a contact opening structure, the method comprising the steps of first providing a substrate and then forming an interlayer dielectric layer on the substrate. And forming a conductive layer in the interlayer dielectric layer such that at least a portion of the conductive layer is exposed to the outside through a first opening in the interlayer dielectric layer. Thereafter, an insulating cover layer is formed on the interlayer dielectric layer and extends into the first opening. A metal containing buffer layer is formed to cover the insulating cover layer. After removing a portion of the metal-containing buffer layer above the interlayer dielectric layer, removing a portion of the insulating cap layer in the first opening such that the remaining insulating cap layer forms a gap on the first sidewall of the first opening The wall is in contact with the conductive layer to define a second opening in the first opening to expose at least a portion of the conductive layer.

Another embodiment of the present disclosure discloses a resistive random access memory (ReRAM) device including: a substrate, an interlayer dielectric layer, a bottom electrode layer, and an insulating layer. A cover layer, a Transition Metal Oxides (TMO) layer, and an upper electrode layer. The interlayer dielectric layer is over the substrate and has a first opening. The bottom electrode layer is in the interlayer dielectric layer and is aligned with the first opening. The insulating cover layer has a spacer on the first side wall of the first opening, wherein the spacer wall is in contact with the bottom electrode layer and defines a second opening in the first opening. A transition metal oxide layer is located in the second opening and is in contact with the bottom electrode layer. The upper electrode layer is located in the second opening and is in contact with the transition metal oxide layer.

According to the above embodiment, the present specification provides a contact opening structure, a manufacturing method thereof, and a resistive random access memory cell fabricated by using the contact opening structure. It is first formed in the interlayer dielectric layer to expose it to the outside through the first opening. An insulating cover layer is further formed to partially fill the first opening, and a metal-containing buffer layer is covered on the insulating cover layer. After removing a portion of the metal-containing buffer layer overlying the interlayer dielectric layer, a portion of the metal-containing buffer layer remains in the first opening to cover a portion of the insulating cap layer on the sidewall of the first opening. Thereafter, a portion of the insulating cover layer at the bottom of the first opening is removed, thereby defining a second opening in the first opening to expose at least a portion of the conductive layer.

By protecting the metal-containing buffer layer, a portion of the insulating coating remaining on the sidewall of the first opening is not damaged by the subsequent etching process, and the width dimension of the second opening can be accurately controlled to be in the interlayer dielectric layer. A contact opening having a smaller width dimension is formed in the middle. The structural dimensions of the subsequently formed elements or interconnects in the contact openings can be further reduced, thereby increasing the component density of the overall circuit.

The present specification provides a contact opening structure and a manufacturing method thereof, and a resistive random access memory unit fabricated by using the contact opening structure, which can be formed into a component or an interconnect structure in a contact opening, thereby improving the overall The component density of the circuit. The above described embodiments and other objects, features and advantages of the present invention will become more apparent and understood.

However, it must be noted that these specific embodiments and methods are not intended to limit the invention. The invention may be practiced with other features, elements, methods and parameters. The preferred embodiments are merely illustrative of the technical features of the present invention and are not intended to limit the scope of the invention. Equivalent modifications and variations will be made without departing from the spirit and scope of the invention. In the different embodiments and the drawings, the same elements will be denoted by the same reference numerals.

Referring to FIGS. 1A through 1E, FIGS. 1A through 1E are cross-sectional views showing a series of process structures for fabricating the contact opening structure 100 in accordance with an embodiment of the present specification. The method of fabricating the contact opening structure 100 includes the steps of first providing a substrate 101 and forming an interlayer dielectric (ILD) 104 on the surface 101a of the substrate 101 to have a conductive layer 102 via the interlayer. A first opening 105 of the dielectric layer 104 is exposed to the outside.

For example, the substrate 101 can be a tantalum substrate. The substrate 101 further includes a Metal-Oxide-Semiconductor Filed Effect Transistor (MOSFET) unit 103. An interlayer dielectric layer 104 includes a first portion of the interlayer dielectric layer 104A stacked over the surface 101a of the substrate 101, and a second portion of the interlayer dielectric layer 104B stacked over the first portion of the interlayer dielectric layer 104A. The conductive layer 102 is in contact with the source/drain 103a of the transistor unit 103, and is used as a metal plug electrically connected to other components (not shown). . The second portion of the interlayer dielectric layer 104B overlies the conductive layer 102 and has a first opening 105 for exposing at least a portion of the conductive layer 102 (as depicted in FIG. 1A).

In some embodiments of the present specification, the material constituting the first partial interlayer dielectric layer 104A and the second partial interlayer dielectric layer 104B may be made of tantalum oxide (SiOx), tantalum nitride (SiNx), and nitrogen. At least one of cerium oxide (SiON) or other suitable dielectric material. The materials constituting the first partial interlayer dielectric layer 104A and the second partial interlayer dielectric layer 104B may be the same or different. The material constituting the conductive layer 102 may include a metal.

In this embodiment, a first portion of the interlayer dielectric material of the material ceria is formed on the surface 101a of the substrate 101 by a deposition process (for example, an Atomic Layer Deposition (ALD) process). Layer 104A. A dry etching process (such as a reactive ion etching (RIE) process) is used to remove a portion of the first portion of the interlayer dielectric layer 104A, and the through hole 111 is formed to expose a portion of the surface 101a of the substrate 101. . Thereafter, the through hole 111 is filled with a conductive material, and then planarized, for example, by a chemical-mechanical polishing (CMP) process to form the conductive layer 102. Subsequently forming a second portion of the interlayer dielectric layer 104B over the first portion of the interlayer dielectric layer 104A and the conductive layer 102, and then removing a portion of the second portion of the interlayer dielectric layer 104B by an etching process to form the first opening 105. At least a portion of the conductive layer 102 is exposed to the outside. Wherein, the width of the first opening 105 ranges substantially between 50 nm and 150 nm.

An insulating cap layer 106 is then formed over the dielectric layer 104 and extends into the first opening 105 to cover a portion of the conductive layer 102 that is exposed (as depicted in FIG. 1B). In some embodiments of the present specification, the material constituting the insulating cover layer 106 may be tantalum oxide, tantalum nitride, or a combination of both. In this embodiment, the insulating cap layer 106 may be formed on the interlayer dielectric layer 104 and the conductive layer 102 by a deposition process (for example, atomic layer deposition), and the thickness is substantially between 100 angstroms (Åstroms) and 1500 degrees. A layer of erbium dioxide. The insulating cover layer 106 includes a first partial insulating cover layer 106A overlying the second partial interlayer dielectric layer 104B, and a second partial insulating cover layer overlying the first sidewall 105a and the bottom portion 105b of the first opening 105. 106B. And the insulating cover layer 106 does not completely fill the first opening 105.

Next, a metal-containing buffer layer 107 is formed overlying the insulating cap layer 106 (as depicted in FIG. 1C). In some embodiments of the present specification, the material constituting the metal-containing buffer layer 107 may be titanium (Ti), tantalum (Ta), titanium nitride (TiN), tantalum nitride (TaN), or any combination thereof. In the present embodiment, the insulating cap layer 106 may be a titanium nitride film formed by a deposition process (for example, atomic layer deposition) having a thickness substantially between 10 angstroms and 200 angstroms.

Subsequently, a portion of the metal containing buffer layer 107 overlying the first portion of the insulating cap layer 106A (overlying the second portion of the interlayer dielectric layer 104B) is removed. In some embodiments of the present specification, the step of removing a portion of the metal-containing buffer layer 107 may be performed by using a first portion of the insulating cap layer 106A as an etch stop layer for dry plasma etching without using any mask. Except for a portion of the metal containing buffer layer 107.

Depending on the nature of the deposition process, generally the thickness of the deposited layer (e.g., metal-containing buffer layer 107) formed in the opening (e.g., first opening 105) will be substantially less than that deposited on the plane (e.g., the top surface of the first portion of insulating coating 106A). The thickness on the). Therefore, in the present embodiment, when a portion of the metal-containing buffer layer 107 located above the first portion of the insulating cover 106A is removed, a portion of the metal-containing buffer layer 107 on the bottom portion 105b of the first opening 105 is removed. While a portion of the second portion of the insulating cap layer 106B is exposed, only a portion of the metal buffer layer 107 remains, covering another portion of the second portion of the insulating cap layer 106B of the first sidewall 105a of the first opening 105. Wherein, a portion of the remaining metal buffer layer 107 may have an L-shaped cross-sectional shape (as shown in FIG. 1D). However, in other embodiments of the present specification, all of the metal containing the first sidewall 105a and the bottom 105b of the first opening 105 are removed when a portion of the metal containing buffer layer 107 above the first portion of the insulating cap layer 106A is removed. The buffer layer 107 may be removed together.

Then, using the conductive layer 102 as an etch stop layer, another etching process is performed to remove a portion of the second partial insulating cover layer 106B on the bottom portion 105b of the first opening 105, so that the remaining second portion of the insulating cover layer 106B is first. A spacer 108 is formed on the first sidewall 105a of the opening 105 to be in contact with the conductive layer 102, and a second opening 109 is defined in the first opening 105, thereby electrically conducting a portion of the bottom portion 105b of the first opening 105. The layer 102 is exposed to form a contact opening structure 100 as depicted in FIG. 1E. The remaining metal-containing buffer layer 107 is located on the spacers 108 and is separated from the exposed conductive layer 104 by a distance H1.

In the present embodiment, the first portion of the insulating cover layer 106A is not completely removed when the second opening 109 is formed. The remaining first portion of the insulating cover layer 106A has a thickness of substantially between 10 angstroms and 300 angstroms. However, in some embodiments of the present specification, the first portion of the insulating cover layer 106A in the contact opening structure 100' will be completely removed when the second opening 109 is formed. That is, the remaining first portion of the insulating cap layer 106A has a thickness of 0, the second portion of the interlayer dielectric layer 104B may be exposed, and the remaining second portion of the interlayer dielectric layer 104B and the second portion of the insulating cap layer Between the two, a stepped structure 110 having a high step is formed (as shown in FIG. 1E'). In other embodiments of the present specification, when the second opening 109 is formed, not only the remaining first partial insulating cover layer 106A is removed, but also a portion of the second partial interlayer dielectric layer 104B is removed. The thickness of the second portion of the interlayer dielectric layer 104B is reduced by between 10 angstroms and 300 angstroms.

By the protection of the metal-containing buffer layer 107, the first sidewall 105a of the first opening 105 can be left over, and a part of the insulating cover layer 106 for forming the spacers 108 is not damaged by the etching process, and can be accurately controlled. The width dimension of the second opening 109 is formed by miniaturizing the component or interconnect structure formed in the second opening 109, thereby increasing the component density of the overall circuit.

Referring to FIGS. 2A-2E, FIGS. 2A-2E are cross-sectional views showing a series of process structures for fabricating the contact opening structure 200 according to still another embodiment of the present specification. The method of fabricating the contact opening structure 200 includes the steps of first providing a substrate 201 and forming an interlayer dielectric layer 204 on the surface of the substrate 201 to have a conductive layer 202 via a layer of the interlayer dielectric layer 204. An opening 205 is exposed to the outside.

For example, substrate 201 can be a tantalum substrate. Also included in the substrate 201 is a metal-oxide-semiconductor field effect transistor unit 203. The interlayer dielectric layer 204 is stacked over the surface 201a of the substrate 201. The conductive layer 202 penetrates the interlayer dielectric layer 204, is in contact with the source/drain 203a of the transistor unit 203, serves as a metal plug of the transistor unit 203, and is exposed through the first opening 205 in the interlayer dielectric layer 204. Outside (as shown in Figure 2A). In some embodiments of the present specification, the material constituting the interlayer dielectric layer 204 may be at least one of tantalum oxide, tantalum nitride, and hafnium oxynitride or other suitable dielectric material. Conductive layer 202 can include a metal.

In this embodiment, the interlayer dielectric layer 204 made of cerium oxide may be formed on the surface 201a of the substrate 201 by a deposition process (for example, an atomic layer deposition process). A dry etching process (for example, a reactive ion etching process) is used to remove a portion of the interlayer dielectric layer 204, and a through hole 211 is formed to expose a portion of the surface 201a of the substrate 201. Thereafter, the through hole 211 is filled with a conductive material, and then planarized to form a conductive layer 202 extending downward from the surface 201a of the substrate 201 and in contact with the source/drain 203a of the transistor unit 203.

Thereafter, the conductive layer 202 is etched back, and a portion of the conductive layer 202 is removed, so that the top portion 202a of the conductive layer 202 is substantially lower than the surface 201a of the substrate 201 to define the first opening 205 (as shown in FIG. 2A). ). In some embodiments of the present invention, the depth D2 of the first opening 205 is calculated from the surface 201a of the substrate 201 to the top portion 202a of the conductive layer 202, substantially between 500 angstroms and 2000 angstroms. In the present embodiment, the depth of the through opening 211 after etch back is substantially between 1000 Å and 1500 Å.

An insulating cap layer 206 is then formed overlying the interlayer dielectric layer 204 and extending into the first opening 205 (as depicted in FIG. 2B). In some embodiments of the present specification, the insulating cap layer 206 may be a ceria layer formed on the interlayer dielectric layer 204 by a deposition process (eg, atomic layer deposition) having a thickness substantially between 50 Å and 2500 Å. . In the present embodiment, the thickness of the insulating cover layer 206 is substantially between 100 angstroms and 2000 angstroms. The insulating cover layer 206 includes a first partial insulating cover layer 206A overlying the interlayer dielectric layer 204 (not overlapping the first opening 205), and extending into the first opening 205 but not completely filling the first opening 205. The second portion of the insulating cover layer 206B.

Next, a metal containing buffer layer 207 is formed overlying the insulating cap layer 206 (as depicted in FIG. 2C). In some embodiments of the present specification, the insulating cap layer 206 may be a titanium nitride film formed by a deposition process (eg, atomic layer deposition) having a thickness substantially between 5 angstroms and 200 angstroms. In the present embodiment, the thickness of the insulating cover layer 206 is substantially between 10 angstroms and 100 angstroms.

Subsequently, a portion of the metal-containing buffer layer 207 above the first portion of the insulating cap layer 206A (and the interlayer dielectric layer 204) is removed. In some embodiments of the present specification, the step of removing a portion of the metal-containing buffer layer 207 may employ a first portion of the insulating cap layer 206A as an etch stop layer for dry plasma etching without using any mask. A portion of the metal containing buffer layer 207 is removed directly.

Depending on the nature of the deposition process, generally the thickness of the deposited layer (eg, metal-containing buffer layer 207) formed in the opening (eg, first opening 205) will be substantially less than deposited on the plane (eg, at the top of the first portion of insulating cover 206A) The thickness on the top. Therefore, in this embodiment, when a portion of the metal-containing buffer layer 207 located above the first portion of the insulating cover 206A is removed, a portion of the metal-containing buffer layer 207 located on the bottom portion 205b of the first opening 205 is removed. While a portion of the second portion of the insulating cap layer 206B is exposed, only a portion of the metal buffer layer 207 remains, covering another portion of the second portion of the insulating cap layer 206B that is located on the first sidewall 205a of the first opening 205. Wherein, a portion of the remaining metal buffer layer 107 may have an L-shaped cross-sectional shape (as shown in FIG. 2D). However, in other embodiments of the present specification, all of the metal-containing buffers 207 on the sidewalls 205a and 205b of the first opening 205 are removed when a portion of the metal-containing buffer layer 207 located above the first portion of the insulating cap layer 206A is removed. May be removed together.

Then, the conductive layer 202 is used as an etch stop layer, and another etching process is performed to remove a portion of the second partial insulating cover layer 206B located at the bottom 205a of the first opening 205, so that the remaining second portion of the insulating cover layer 206B is in the first opening. A spacer 208 is formed on the sidewall 205a of the 205, and is in contact with the conductive layer 202, and a second opening 209 is defined in the first opening 205, thereby exposing a portion of the conductive layer 202 to the outside, forming a pattern as shown in FIG. The contact opening structure 200 is illustrated. The remaining metal-containing buffer layer 107 is located on the spacer 208 and spaced apart from the exposed conductive layer 104 by a distance H2.

In the present embodiment, when the second opening 209 is formed, the first partial insulating cover layer 206A is not completely removed. The remaining first portion of the insulating cover layer 206A has a thickness substantially between 50 angstroms and 1000 angstroms. However, in some embodiments of the present specification, the first portion of the insulating cover layer 206A of the contact opening structure 200' will be removed when the second opening 209 is formed. That is, the remaining first portion of the insulating cap layer 206A has a thickness of zero, and the interlayer dielectric layer 204 can be exposed to the outside (as shown in FIG. 2E').

By the protection of the metal-containing buffer layer 207, the first sidewall 205a of the first opening 205 can be left on the first sidewall 205a of the first opening 205, and a portion of the insulating coating 206 for forming the spacer 208 is not damaged by the etching process, and can be accurately controlled. The width dimension of the second opening 209 is used to reduce the component or interconnect structure formed in the second opening 209, thereby increasing the component density of the overall circuit.

Referring to FIGS. 3A to 3C, FIGS. 3A to 3C are cross-sectional views showing a process structure for fabricating the resistive random access memory cell 300 by applying the contact opening structure 200 of FIG. 2E. The manufacturing method of the resistive random access memory cell 300 includes the following steps: First, a transition metal oxides (TMO) layer 301 is formed to cover a portion of the conductive layer 202 exposed through the second opening 209. The transition metal oxide layer 301 is brought into contact with the conductive layer 202. In some embodiments of the present specification, the material constituting the transition metal oxide layer 301 may be a metal oxide such as (TaOx) tantalum oxide, tungsten oxide (WOx), tantalum oxide (HfOx) or the like. combination. In the present embodiment, the transition metal oxide layer 301 does not completely fill the second opening 209 (as shown in FIG. 3A).

Thereafter, an upper electrode layer 302 is formed overlying the transition metal oxide layer 301, and a metal material layer 303 is formed on the upper electrode layer 302 (as shown in FIG. 3B). In some embodiments of the present specification, the material constituting the upper electrode layer 302 may include tantalum nitride. The metal material layer 303 may include tungsten (W).

Then, the first portion of the insulating cover layer 206A is used as a stop layer, and the metal material layer 303, the upper electrode layer 302, and the transition metal oxide layer 301 are planarized, for example, a chemical mechanical polishing process to complete the resistive random access memory. Fabrication of body unit 300 (as depicted in Figure 3C). In the present embodiment, the conductive layer 204 in the contact opening structure 200 can serve as the lower electrode layer of the resistive random access memory cell 300.

As previously mentioned, the contact opening structure 200 can precisely control the width dimension range of the second opening 209. For example, in the present embodiment, the second opening 209 may have a bottom width BW substantially between 5 nanometers (nm) and 50 nanometers, and an opening width OW substantially between 10 nanometers and 100 nanometers. Therefore, the size of the resistive random access memory cell 300 formed in the second opening 209 can be reduced to the size range of the second opening 209, which greatly increases the storage density of the memory element.

Referring to Fig. 4, Fig. 4 is a cross-sectional view showing the structure of a resistive random access memory cell 400 fabricated by applying the contact opening structure 200' of Fig. 2E'. The structure and fabrication of the resistive random access memory cell 400 is substantially similar to that of the resistive random access memory cell 300. The only difference is that the resistive random access memory cell 400 does not have the first partial insulating cap layer 206A. When the metal material layer 303, the upper electrode layer 302, and the transition metal oxide layer 301 are planarized, the interlayer dielectric layer 204 is used as a stop layer. Since other process steps for fabricating the resistive random access memory cell 400 are detailed above, they are not described again.

According to the above embodiment, the present specification is to provide a contact opening structure and a manufacturing method thereof, and a resistive random access memory unit fabricated by using the contact opening structure. It is formed by first forming a conductive layer in the dielectric layer to be exposed to the outside through the first opening. An insulating cover layer is further formed to partially fill the first opening, and a metal-containing buffer layer is covered on the insulating cover layer. After removing a portion of the metal-containing buffer layer overlying the interlayer dielectric layer, a portion of the metal-containing buffer layer remains in the first opening to cover a portion of the insulating cap layer on the sidewall of the first opening. Thereafter, a portion of the insulating cover layer at the bottom of the first opening is removed, thereby defining a second opening in the first opening to expose the conductive layer.

By protecting the metal-containing buffer layer, a portion of the insulating coating remaining on the sidewall of the first opening is not damaged by the subsequent etching process, and the width dimension of the second opening can be accurately controlled to be in the interlayer dielectric layer. A contact opening having a smaller width dimension is formed in the middle. The size of the component or interconnect structure that is subsequently formed in the contact opening can be further miniaturized, thereby increasing the component density of the overall circuit.

While the invention has been described above by way of a preferred embodiment, it is not intended to limit the invention, and it is to be understood by those skilled in the art without departing from the spirit and scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

100, 100', 200, 200'‧‧‧ contact opening structure

101, 201‧‧‧ substrate

101a, 201a‧‧‧ substrate surface

102, 202‧‧‧ conductive layer

103, 203‧‧‧Optocell unit

103a, 203a‧‧‧Source/drain of the crystal unit

104, 204‧‧‧ Interlayer dielectric layer

104A‧‧‧The first part of the interlayer dielectric layer

104B‧‧‧Second part interlayer dielectric layer

105, 205‧‧‧ first opening

105a, 205a‧‧‧ first side wall of the first opening

105b, 205b‧‧‧ bottom of the first opening

106, 206‧‧ ‧ insulating cover

106A, 206B‧‧‧ first part insulation cover

106B, 206B‧‧‧Second part insulating cover

107, 207‧‧‧ metal buffer layer

108, 208‧‧‧ spacers

109, 209‧‧‧ second opening

110‧‧‧step structure

111, 211‧‧‧through holes

202a‧‧‧Top of the conductive layer

300‧‧‧Resistive random access memory unit

301‧‧‧Transition metal oxide layer

302‧‧‧Upper electrode layer

303‧‧‧Metal material layer

H1, H2‧‧‧ distance

OW‧‧‧ opening width

BW‧‧‧ bottom width

D2‧‧‧Deep depth of the first opening

In order to better understand the above and other aspects of the present specification, the following specific embodiments are described in detail below with reference to the accompanying drawings: FIGS. 1A through 1E are diagrams showing contact openings according to an embodiment of the present specification. A series of process structure cross-sectional views of the structure; FIG. 1E' is a schematic cross-sectional view of the contact opening structure according to another embodiment of the present specification; FIGS. 2A to 2E are diagrams according to still another embodiment of the present specification, FIG. 2E′ is a cross-sectional view showing a structure of a contact opening according to still another embodiment of the present specification; FIGS. 3A to 3C are diagrams showing an application. FIG. 4 is a cross-sectional view showing a process structure of the resistive random access memory cell 300; and FIG. 4 is a resistive random access memory fabricated by using the contact opening structure of FIG. 2E respectively. A structural section view of the unit.

no.

Claims (10)

A contact hole structure comprising: a substrate; an interlayer dielectric layer on the substrate and having a first opening; a conductive layer located in the interlayer dielectric layer and aligned The first opening; and an insulating cover layer having a spacer on a first sidewall of the first opening, wherein the spacer contacts the conductive layer and defines a second in the first opening Opening to expose a portion of the conductive layer to the outside. The contact opening structure of claim 1, further comprising a metal-containing buffer layer on a second sidewall of the second opening and spaced apart from the conductive layer, wherein the metal-containing buffer layer comprises At least one of titanium nitride (TiN), tantalum nitride (TaN), titanium metal, and base metal. A method for fabricating a contact opening structure, comprising: providing a substrate; forming an interlayer dielectric layer on the substrate; forming a conductive layer in the interlayer dielectric layer; and allowing at least a portion of the conductive layer to pass through the layer a first opening in the interlayer dielectric layer is exposed to the outside; and an insulating coating layer is formed on the interlayer dielectric layer and extends into the first opening; forming a metal-containing buffer layer to cover the insulating cover Removing a portion of the metal-containing buffer layer over the interlayer dielectric layer; and removing a portion of the insulating cover layer in the first opening such that the remaining insulating cover layer is in the first opening A spacer is formed on a first sidewall to contact the conductive layer, thereby defining a second opening in the first opening to expose at least a portion of the conductive layer to the outside. The method of fabricating the contact opening structure of claim 3, wherein the interlayer dielectric layer comprises a first partial interlayer dielectric layer and a second partial interlayer dielectric layer, and the first opening is formed The step of forming: forming the first partial interlayer dielectric layer on the substrate; forming the conductive layer in the first partial interlayer dielectric layer; forming the second partial interlayer dielectric layer, covering the a first portion of the interlayer dielectric layer and the conductive layer; and removing a portion of the second portion of the interlayer dielectric layer over the conductive layer. The method for fabricating the contact opening structure according to claim 3, wherein the forming the first opening comprises: forming the interlayer dielectric layer on the substrate; forming the conductive layer in the interlayer dielectric layer And etch back the conductive layer. The method of fabricating the contact opening structure of claim 3, wherein the portion of the insulating cover layer located in the first opening is removed while completely removing the cover layer on the interlayer dielectric layer A portion of the insulating cover. The method of fabricating the contact opening structure of claim 3, wherein the portion of the insulating cover layer located in the first opening is removed, and only partially removed over the interlayer dielectric layer The other part of the insulating cover. The method for fabricating a contact opening structure according to claim 3, wherein the portion of the metal-containing buffer layer located above the interlayer dielectric layer is removed, including a portion of the metal-containing buffer layer remaining And partially covering the second side wall of one of the second openings. A Resistance. Random Access Memory (ReRAM) unit includes: a substrate; an interlayer dielectric layer on the substrate and having a first opening; a bottom electrode layer located at The interlayer dielectric layer is aligned with the first opening; an insulating cover layer having a spacer on a first sidewall of the first opening, wherein the spacer is in contact with the bottom electrode layer, and a second opening is defined in the first opening; a transition metal oxides (TMO) layer is disposed in the second opening and is in contact with the bottom electrode layer; and an upper electrode layer is located in the first opening In the two openings, and in contact with the transition metal oxide layer. The resistive random access memory unit of claim 9, further comprising: a metal-containing buffer layer on a second sidewall of the second opening and spaced apart from the conductive layer, wherein The metal-containing buffer layer comprises at least one of titanium nitride, tantalum nitride, titanium metal and tantalum metal; and a Metal-Oxide-Semiconductor Filed Effect Transistor (MOSFET) unit is located The substrate has a source/drain structure in contact with the bottom electrode layer.