TWO TERMINAL RESISTIVE SWITCHING DEVICE STRUCTURE AND METHOD OF FABRICATING
A semiconductor device having a memory device includes a semiconductor substrate, a first dielectric layer disposed above the semiconductor substrate, a first adhesion layer disposed upon the first dielectric layer, a bottom wiring metal disposed upon the first adhesion layer, a first barrier layer disposed upon the bottom wiring metal, a resistive switching material disposed in electrical contact with the first barrier layer, wherein the resistive switching material comprises a silicon material having a plurality of defect regions, a conductive metal material disposed upon the resistive switching material, wherein the conductive metal material comprises a plurality of conductive metal particles, a second barrier layer disposed upon the conductive metal material, a top wiring metal disposed upon the second barrier layer, and wherein at least some of the plurality of conductive metal particles are removably disposed in defect regions from the plurality of defect regions in the resistive switching material.
The present application claims priority to and is continuation of U.S. patent application Ser. No. 12/835,704, filed on Jul. 13, 2010 and is incorporated in its entirety for all purposes.
BACKGROUNDThe present invention is in general related to two terminal devices. More particularly, embodiments of the present provide a method and a structure for a two terminal switching device. The two terminal switching device can be used as a non-volatile resistive switching memory with random access and fast switching characteristics.
The success of semiconductor devices has been mainly driven by an intensive transistor down-scaling process. However, as field effect transistors (FET) approach sizes less than 100 nm, problems such as short channel effect start to prevent proper device operation. Moreover, such sub 100 nm device size can lead to sub-threshold slope non-scaling and also increases power dissipation. It is generally believed that transistor based memories such as those commonly known as Flash may approach an end to scaling within a decade. Flash memory is one type of non-volatile memory device.
Other non-volatile random access memory (RAM) devices such as ferroelectric RAM (Fe RAM), magneto-resistive RAM (MRAM), organic RAM (ORAM), and phase change RAM (PCRAM), among others, have been explored as next generation memory devices. These devices often require new materials and device structures to couple with silicon based devices to form a memory cell, which lack one or more key attributes. For example, Fe-RAM and MRAM devices have fast switching characteristics and good programming endurance, but their fabrication is not CMOS compatible and size is usually large. Switching for a PCRAM device uses Joules heating, which inherently has high power consumption. Organic RAM or ORAM is incompatible with large volume silicon based fabrication and device reliability is usually poor.
From the above, an improved semiconductor memory device and techniques are therefore desirable.
BRIEF SUMMARY OF THE PRESENT INVENTIONThe present invention is in general related to two terminal devices. More particularly, embodiments of the present provide a method and a structure for a two terminal switching device. The two terminal switching device has been applied to non-volatile resistive switching memory devices. But it should be recognized that the present invention can have a broader range of applicability.
In a specific embodiment, a method for forming a two terminal switching device is provided. The method includes providing a substrate and forming a first dielectric material overlying a surface region of the substrate. A bottom wiring material is deposited overlying the dielectric material. The method includes depositing a contact material overlying the bottom wiring material and depositing a switching material overlying the bottom wiring material; including the contact material. In certain embodiment, the contact material is optional. The method forms a masking layer overlying the switching material. In a specific embodiment, the method subjects the bottom wiring material, the contact material,-and the switching material to a first etching process using the masking layer to form a first structure. The first structure includes a bottom wiring structure and a switching element. The first structure has a top surface region and a side region. In a specific embodiment, the top surface region including a top region of the switching element. The method includes depositing a second dielectric material overlying at least the first structure including the exposed top region of the switching element and an exposed portion of the first dielectric material. The method includes planarizing the second dielectric material surface overlying at least the first structure while maintaining a portion of the second dielectric material overlying the first structure. An opening region is formed in a portion of the second dielectric layer to expose a portion of the top surface region of the first structure. The method then deposits a conductive material overlying the opening region. The conductive material is in direct contact with the switching element in a specific embodiment. A top wiring material is formed overlying at least the conductive material, and a second etching process is employed to form at least a top wiring structure. In a specific embodiment, the side region of the first structure including a first side region of the switching element is free from a contaminant conductive material from the second etching process.
In an alternative embodiment, a method for forming a two terminal switching device is provided. The method includes providing a substrate and forming a first dielectric material overlying a surface region of the substrate. A bottom wiring material is deposited overlying the dielectric material. The method includes depositing a contact material overlying the bottom wiring material and depositing a switching material overlying the bottom wiring material; including the contact material. In certain embodiment, the contact material is optional. The method forms a masking layer overlying the switching material. In a specific embodiment, the method subjects the bottom wiring material, the contact material,-and the switching material to a first etching process using the masking layer to form a first structure. The first structure includes a bottom wiring structure and a switching element. The first structure has a top surface region and a side region. In a specific embodiment, the top surface region including a top region of the switching element. The method includes depositing a second dielectric material overlying at least the first structure including the exposed top region of the switching element and an exposed portion of the first dielectric material. The method includes planarizing the second dielectric material surface overlying at least the first structure while maintaining a portion of the second dielectric material overlying the first structure. An opening region is formed in a portion of the second dielectric layer to expose a portion of the top surface region of the first structure. The method deposits a conductive material overlying the second dielectric material including the opening region in direct contact with the switching element in a specific embodiment. The method includes depositing a first adhesion layer overlying the conductive material and subjecting the first adhesion layer and the conductive material to a second pattern and etches process. The second pattern and etch process removes a portion of the conductive material and a portion of the first adhesion layer to expose a surface region of the second dielectric material while maintaining at least the conductive material and the adhesion layer at least in the opening region. A top wiring material is formed overlying the first adhesion layer and the exposed portion of the second dielectric layer. In a specific embodiment, the top wiring material is subjected to a second patterning and etching process to form a top wiring structure. In a specific embodiment, the side region of the first structure including the first side region of the switching element is free from a contaminant conductive material from the at least the second pattern and etch process and no short occurs between the top wiring structure and the bottom wiring structure.
Many benefits can be achieved by ways of the present invention. As merely an example, the present method provides a method and a structure for fabricating a switching device using a metal as a top electrode. By not exposing the sidewall of the switching material during etch of the upper electrode, this method provides device structures that are free of defects such as a short between a top electrode and a bottom electrode thereby improving device performance and device yield.
The present invention is in general related to two terminal devices. More particularly, embodiments of the present provide a method and a structure for a two terminal switching device. The two terminal switching device may be used in non-volatile resistive switching memory devices that provide for random access, fast switching, and are scalable to very small sizes. But it should be recognized that the present invention can have a much broader range of applicability.
For switching devices using resistive switching, selected materials are used for each of the electrodes or the wiring structures. For example, a noble metal such as platinum is used for a nickel oxide-based resistive switching device to provide an ohmic contact to the device and to prevent chemical reaction with the switching material. Certain solid electrolyte based (for example, GeSe) switching devices or amorphous silicon based switching devices use silver as at least one of the electrode materials or contact material for an enhanced switching performance. Theses metal materials are not commonly used in current CMOS fabrication. In particular, due to their inert nature, chemical etching of these materials is particularly challenging or impossible, making nano-scale device fabrication difficult.
Accordingly, the present invention provides a method and a structure for forming a switching device, in particular, a resistive switching device using at least a noble metal as one of the wiring structures or both of the wiring structures. But it would be recognized that embodiments according to the present invention can be applied to other devices.
Referring to
As shown in
Referring to
In a specific embodiment, the method forms a switching material 902 overlying the contact material as shown in
Referring to
In a specific embodiment, the method subjects the switching material, the contact material, and the bottom wiring structure material to a first etching process using the masking layer as a mask to form a first structure 1102 as shown in
Referring to
In a specific embodiment, the method employs a planarizing process to form a planarized dielectric surface 1302 as illustrated in
In a specific embodiment, the method deposits a conductive material 1502 overlying the opening region including the exposed top region of the switching element. As shown, the conductive material forms substantially conformal to the opening region and in contact with the switching element in a specific embodiment. In a specific embodiment, for an amorphous silicon switching material, the conductive material can comprise a silver material. The silver material can be deposited using a physical vapor deposition process such as sputtering or evaporation. The silver material may also be formed using a chemical deposition process such as chemical vapor deposition, electrochemical method such as electroplating, or electrodeless deposition or a combination depending on the application. The method deposits a third adhesion layer 1504 overlying the conductive material as shown in
Referring to
In a specific embodiment, the methods includes subjecting the top wiring material together with the barrier layer and the conductive material to a second pattern and etch process to form a top wiring structure for the switching device. In a specific embodiment, the top wiring structure and the bottom wiring structure are spatially arranged in at an angle. In certain embodiment, the first wiring structure and the second wiring structure are spatially arranged in an orthogonal manner. As the first structure including the switching element and the bottom wiring structure is embedded in a dielectric material during etching of the top wiring material, the side region of the first structure is protected from deposited material such as a contaminant conductive material resulting from etching of at least the top wiring material and the conductive material in a specific embodiment. Shorting between the top wiring structure and the bottom wiring structure is thus avoided.
Repeatable resistive switching can be provided by formation or deformation of the filament structure within the switching material. For instance, the repeatable resistive switching can be in response to application, and subsequent variation, of a voltage to the two terminal resistive switching device. As one example, the device can be switching from a high resistance state, e.g., off, to a low resistance state, e.g., on, when the voltage is increased beyond a certain threshold voltage (e.g., a filament formation voltage). The device can be switched from the low resistance state to the high resistance state, e.g., off, when the voltage is decreased lower than a second threshold voltage. In some embodiments, a voltage between the certain threshold voltage and the second threshold voltage can cause a current resistance state of the device to remain unchanged (and utilized, e.g., to read the current resistance state of the device).
In one or more disclosed embodiments, a positive voltage applied to the top wiring structure can generate an electric field(s) causing particles of conductive material 1502 to form within switching material 902. The particles of conductive material 1502 can form a structure (e.g., a filament) extending at least in part across switching material 902. Under suitable circumstances (e.g., application of the positive voltage or the electric field(s)), the filament creates an electrical pathway across switching material 902, resulting in the low resistance state mentioned above. In additional embodiments, a suitable negative voltage applied to the top wiring structure can generate a second electric field(s) that at least in part deforms the filament. Deformation of the filament can interrupt the electrical pathway across switching material 902, resulting in the high resistance state.
In a specific embodiment, the conductive material forms a plurality of conductive material particles including a filament structure in the switching material when a suitable voltage is applied to the top wiring structure or the bottom wiring structure to change a resistance characteristic of the switching material in a specific embodiment. Taking silver material as the conductive material and amorphous silicon as the switching material as an example, upon applying a positive voltage to the top wiring structure, a plurality of silver particles are formed in defect regions of the amorphous silicon material. The plurality of silver particles can include a silver filament structure having a length. The length of the silver filament structure is allowed o changed upon applying a suitable voltage thus changing the resistance of the amorphous silicon material enabling resistive switching o the device. Such a device structure is described in U.S. application Ser. No. 11/875,541, filed on Oct. 19, 2007, commonly assigned, and incorporated by reference in its entirety herein.
Depending on the embodiment, there can be other variations as illustrated in
Referring to
Depending on the embodiment, there can be yet other variations as illustrated in
Again, depending on the application, there can be other variation as shown in
Accordingly, embodiments according to the present invention provide a method to form a switching device free of shorts between the top wiring structure and the bottom wiring structure. The present method has been applied to a device structure having an Ag/amorphous silicon/p+ polysilicon configuration and tungsten material as the top wiring material and the bottom wiring material. It should be recognized the present method can be applied in fabrication of a device that uses an inert metal or a noble metal. Example of such devices can include, a switching device using metal oxide as the switching material, at least one of the top wiring material or the bottom wiring material is inert so as not to chemically react with the metal oxide switching material. Etching of the top inert wiring material is feasible using a physical etch. Redeposition of etched conductor materials from the top wiring materials or the bottom wiring materials, or others, on a side region of the switching element can form shorts between the top electrode and the bottom electrode, affecting device performance and yield.
It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or alternatives in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.
Claims
1. A semiconductor device including a memory device comprising:
- a semiconductor substrate;
- a first dielectric layer disposed above the semiconductor substrate;
- a first adhesion layer disposed upon the first dielectric layer;
- a bottom wiring metal disposed upon the first adhesion layer;
- a first barrier layer disposed upon the bottom wiring metal;
- a resistive switching material disposed in electrical contact with the first barrier layer, wherein the resistive switching material comprises a silicon material having a plurality of defect regions;
- a conductive metal material disposed upon the resistive switching material, wherein the conductive metal material comprises a plurality of conductive metal particles;
- a second barrier layer disposed upon the conductive metal material;
- a top wiring metal disposed upon the second barrier layer; and
- wherein at least some of the plurality of conductive metal particles are removably disposed in defect regions from the plurality of defect regions in the resistive switching material.
2. The semiconductor device of claim 1 wherein the first barrier layer is selected from a group consisting of: titanium, titanium nitride, tantalum, tantalum nitride, tungsten and tungsten nitride.
3. The semiconductor device of claim 1 wherein the bottom wiring metal comprises copper.
4. The semiconductor device of claim 1 wherein the resistive switching material comprises un-doped amorphous silicon.
5. The semiconductor device of claim 1 wherein the conductive metal material is CMOS fabrication compatible.
6. The semiconductor device of claim 1
- wherein the conductive metal material comprises aluminum; and
- wherein a plurality of aluminum particles are disposed within defect regions of the resistive switching material and form a filament structure.
7. The semiconductor device of claim 6 wherein a resistance of the resistive switching material is associated with a filament length of the filament structure.
8. The semiconductor device of claim 1 further comprising a contact material layer disposed between and in contact with the first barrier layer and with the resistive switching material.
9. The semiconductor device of claim 8 wherein the contact material is selected from a group consisting of: a doped polysilicon and a doped semiconductor material.
10. The semiconductor device of claim 1
- wherein the semiconductor substrate comprises a plurality of CMOS devices formed therein;
- wherein the memory device comprises the resistive switching material and the conductive metal material; and
- wherein the memory device is coupled to at least a CMOS device from the plurality of CMOS devices.
11. A semiconductor device including a memory device comprising:
- a semiconductor substrate comprising a plurality of CMOS devices formed therein;
- a first dielectric layer disposed above the semiconductor substrate;
- a bottom wiring structure formed upon the first dielectric layer, comprising:
- a first adhesion layer disposed upon the first dielectric layer;
- a bottom wiring metal disposed upon the first adhesion layer; and
- a second adhesion layer disposed upon the bottom wiring metal;
- the memory device disposed upon the bottom wiring structure, comprising:
- a resistive switching material disposed in electrical contact with the bottom wiring structure, wherein the resistive switching material comprises a silicon material having a plurality of defect regions;
- a conductive metal material disposed upon the resistive switching material, wherein the conductive metal material comprises a plurality of conductive metal particles; and
- wherein at least a group of conductive metal particles from the plurality of conductive metal particles are removably disposed in defect regions from the plurality of defect regions in the resistive switching material, wherein the group of conductive metal particles comprises a filament structure; and
- a top wiring structure formed upon the memory device, comprising:
- a third adhesion layer disposed upon the memory device; and
- a top wiring metal disposed upon the second barrier layer;
- wherein the memory device is coupled to at least a CMOS device from the plurality of CMOS devices.
12. The semiconductor device of claim 11 wherein the first barrier layer is selected from a group consisting of: titanium, titanium nitride, tantalum, tantalum nitride, tungsten and tungsten nitride.
13. The semiconductor device of claim 12 wherein the bottom wiring metal comprises copper.
14. The semiconductor device of claim 11 wherein the resistive switching material comprises un-doped amorphous silicon.
15. The semiconductor device of claim 11 wherein the conductive metal material is CMOS fabrication compatible.
16. The semiconductor device of claim 15 wherein the conductive metal material comprises aluminum.
17. The semiconductor device of claim 11 wherein a resistance of the memory device is associated with a filament length of the filament structure.
18. The semiconductor device of claim 11 wherein the memory device further comprises a contact material layer disposed between and in contact with the bottom wiring structure and with the resistive switching material.
19. The semiconductor device of claim 18 wherein the contact material is selected from a group consisting of: a doped polysilicon and a doped semiconductor material.
20. The semiconductor device of claim 11
- wherein the bottom wiring metal and the top wiring metal each comprise copper;
- wherein the first adhesion layer and the second adhesion layer are each selected from a group consisting of: tungsten nitride, titanium, titanium nitride, tantalum and tantalum nitride; and
- wherein the conductive metal material comprises aluminum.
Type: Application
Filed: Mar 24, 2015
Publication Date: Jul 16, 2015
Inventors: Sung Hyun JO (Sunnyvale, CA), Scott Brad HERNER (San Jose, CA)
Application Number: 14/667,346