Solid electrolyte switching element, and fabrication method of the solid electrolyte element, and integrated circuit

The switching element of the present invention is of a configuration that includes: a first electrode (14) and a second electrode (15) provided separated by a prescribed distance; a solid electrolyte layer (16) provided in contact with the first electrode (14) and the second electrode (15); a third electrode (18) that can supply metal ions and that is provided in contact with the solid electrolyte layer (16); and a metal diffusion prevention film (17) that covers points of the surface of the solid electrolyte layer (16) that are not in contact with the first electrode (14), the second electrode (15) or the third electrode (18). This configuration prevents the adverse effect of metal ions upon other elements.

TECHNICAL FIELD

The present invention relates to a solid electrolyte switching element that includes an electrode that correspond to a gate that can supply metal ions and electrodes that correspond to a source and a drain, to a fabrication method, and to an integrated circuit.

BACKGROUND ART

U.S. Pat. Nos. 5,761,115 and 6,487,106 disclose cases in which a programmable metallization cell (PMC) is applied as a solid electrolyte switch of the related art. In a PMC, two electrodes are provided with a solid electrolyte interposed, a suitable amount of metal ions being dissolved in the solid electrolyte. In the working examples in the above-described documents, the solid electrolyte is a construction in which silver ions are introduced into a chalcogenide glass containing germanium or selenium. The solid electrolyte switch is an element for controlling the electrical resistance between the two electrodes by applying voltage between these two electrodes to bring about an oxidation-reduction reaction of the metal ions in the solid electrolyte.

To briefly explain the operation of this solid electrolyte switch, a state of high resistance exists between the two electrodes in the initial state, but when voltage is applied across these two electrodes, the metal ions in the solid electrolyte at one of the electrodes (the cathode side) to which a relative negative voltage is applied are reduced and precipitate as metal atoms. The continuation of the reduction reaction causes the precipitated metal to grow toward the other electrode (the anode) until a metal bridge is finally formed between the two electrodes and an electrical low-resistance state is established between the two electrodes.

On the other hand, when a positive voltage is applied to the cathode side in the state in which the metal bridge is formed, the metal bridge oxidizes and dissolves into the solid electrolyte as metal ions. The electrical high resistance state is reestablished between the electrodes when this metal bridge ceases to exist. The high-resistance state and low-resistance state are each maintained when voltage is not applied, and the solid electrolyte switch therefore is a non-volatile switch with an extremely high ON/OFF ratio, and can be expected to be applicable to non-volatile memory. In addition, the anode also serves the role of a supply source of metal ions, and preferably contains metal that is prone to ionization (such as silver) for the purpose of stable operation.

DISCLOSURE OF THE INVENTION

In the above-described two-terminal solid electrolyte switch, when a metal bridge is formed between the two terminals at the time of a transition from the OFF state to the ON state, a low-resistance state is established between the two terminals and a large current flows between the two terminals. When transitioning from the ON state to the OFF state, voltage for bringing about the OFF state between the two terminals is then applied while in the low-resistance state, resulting in the problem of a large flow of current and a high level of power consumption.

One means of solving this problem is a three-terminal solid electrolyte switch that is provided with a terminal for control in addition to the above-described two terminals. In this solid electrolyte switch, the application of voltage across an electrode that corresponds to a gate electrode capable of supplying metal ions and two electrodes that correspond to source and drain electrodes brings about the precipitation or dissolution of metal in the vicinity of the source and drain electrodes to control the electrical resistance between the source and drain electrodes. In this construction, the resistance between the source and drain electrode can be controlled by the voltage that is applied to the gate electrode, and there is consequently no flow of current other than that required when switching between ON and OFF.

However, when integrating this three-terminal solid electrolyte switch, the concern arises that metal ions will leak from the solid electrolyte layer or interconnect layer into surrounding regions and thus adversely affect neighboring elements.

The present invention was realized to solve the above-described problem inherent to the related art and has as its object the provision of: a solid electrolyte switching element that eliminates the influence of metal ions upon other elements, a method of fabricating this solid electrolyte switching element, and an integrated circuit.

The solid electrolyte switching element of the present invention for achieving the above-described object is of a construction that includes: a first electrode and a second electrode provided separated by prescribed distance, a solid electrolyte layer provided in contact with the first electrode and second electrode, a third electrode that is provided in contact with the solid electrolyte layer and that can supply metal ions, and a metal diffusion prevention film that covers points of the surface of the solid electrolyte layer that do not contact any of the first electrode, second electrode, and third electrode.

The integrated circuit of the present invention for achieving the above-described object is equipped with the above-described solid electrolyte switching element of the present invention and multilayered interconnects that include an interconnects and a viaplug, and is of a configuration in which the third electrode is provided in the same layer as the interconnects and the solid electrolyte layer is provided in the same layer as the viaplug.

In addition, the integrated circuit of the present invention is provided with the solid electrolyte switching element of the above-described invention and multilayered interconnects that include interconnects and viaplug, and is of a configuration in which the third electrode is provided on the same layer as the viaplug and the solid electrolyte layer is provided on the same layer as the interconnects.

In addition, the fabrication method of the solid electrolyte switching element of the present invention for achieving the above-described object includes steps of: forming a resist having a first aperture pattern and a second aperture pattern separated by a prescribed distance on an insulating layer; enlarging the area of the apertures of the first aperture pattern and the second aperture pattern by means of a first etching; carrying out a second etching of the insulating layer with the resist as a mask to form a first aperture and a second aperture in the insulating layer; after removing the resist, embedding an interconnect material in the first aperture and second aperture to form a first electrode and a second electrode; forming a solid electrolyte layer that contacts the first electrode and the second electrode; forming a metal diffusion prevention film that covers the solid electrolyte layer; forming a third aperture in the metal diffusion prevention film; and embedding an interconnect material that can supply metal ions in the third aperture to form a third electrode.

Still further, the fabrication method of the solid electrolyte switching element of the present invention includes steps of: forming a resist having a first aperture pattern and a second aperture pattern separated by a prescribed distance on an insulating layer; carrying out first etching on the insulating layer with the resist as a mask to form a first aperture and a second aperture on the insulating layer; carrying out a second etching on the insulating layer to enlarge the areas of the first aperture and second aperture; after removing the resist, embedding an interconnect material in the first aperture and second aperture to form a first electrode and second electrode; forming a solid electrolyte layer that contacts the first electrode and second electrode; forming a metal diffusion prevention film that covers the solid electrolyte layer; forming a third aperture in the metal diffusion prevention film; and embedding an interconnect material that can supply metal ions in the third aperture to form a third electrode.

In the present invention, points on the surface of the solid electrolyte layer that do not contact any of the first electrode, the second electrode, or the third electrode are covered by a metal diffusion prevention film, whereby the leakage and diffusion of metal ions contained in the solid electrolyte layer can be prevented. Thus, when the solid electrolyte switching element is provided in an integrated circuit, metal ions that leak to the surrounding area from the solid electrolyte layer can be prevented from adversely affecting adjacent elements.

EXPLANATION OF REFERENCE NUMBERS

BEST MODE FOR CARRYING OUT THE INVENTION

The solid electrolyte switching element of the present invention is of a configuration provided with a film for preventing the diffusion of metal from a solid electrolyte layer.

First Embodiment

Explanation next regards the configuration of the solid electrolyte switching element of the present embodiment.

FIGS. 1A and 1Bshow an example of the configuration of the solid electrolyte switching element of the first embodiment.FIG. 1Ais a plan view of the element, andFIG. 1Bis a sectional view taken along broken line a-a′ shown inFIG. 1A.

As shown inFIGS. 1A and 1B, solid electrolyte switching element1is provided with: insulating layer11that is formed including first aperture12and second aperture13provided separated by a prescribed distance on substrate10that is covered by a base insulating film; first interconnect14realized by embedding an interconnect material in first aperture12; and second interconnect15realized by embedding an interconnect material in second aperture13. In addition, solid electrolyte layer16is formed on first interconnect14and second interconnect15, and metal diffusion prevention film17for preventing the diffusion of metal is formed on solid electrolyte layer16. Third interconnect18that contacts solid electrolyte layer16through an aperture provided in metal diffusion prevention film17is formed on metal diffusion prevention film17. Third interconnect18contains a material capable of supplying metal ions to solid electrolyte layer16. Insulating layer11not only serves to maintain electrical insulation but also serves as a metal diffusion prevention film.

The side surfaces and points of the upper surface of solid electrolyte layer16that do not contact third interconnect18are covered by metal diffusion prevention film17.

Although third interconnect18is not arranged in the a-a′ portion ofFIG. 1A, for the purpose of explanation, third interconnect18is displayed in the sectional view ofFIG. 1Bprovided with the aperture portion of metal diffusion prevention film17interposed.

In the present invention, the spacing of first interconnect14and second interconnect15is a dimension smaller than the minimum value of the limits of lithography. As a result, the dimension is smaller than in constructions of the related art. In the current actual case, this dimension is formed as a dimension no greater than 30 nm.

The configuration shown inFIGS. 1A and 1Bis only one example. The solid electrolyte switching element of the present invention may be of a construction other than shown inFIGS. 1A and 1Bas long as an arrangement is realized in which first interconnect14and second interconnect15are embedded in first aperture12and second aperture13that are provided separated by a prescribed distance on insulating layer11, solid electrolyte layer16contacts first interconnect14and second interconnect15, and third interconnect18contacts solid electrolyte layer16.

Explanation next regards the operation of solid electrolyte switching element1shown inFIGS. 1A and 1B. Here, first interconnect14is assumed to be the source electrode, second interconnect15is assumed to be the drain electrode, and third interconnect18is assumed to be the gate electrode. The material of solid electrolyte layer16is copper sulfide, the interconnect material of the gate electrode is copper, and the interconnect material of the source electrode and drain electrode is titanium.

When the source electrode is grounded and a positive voltage is applied to the gate electrode, the copper of the gate electrode becomes copper ions and dissolves in solid electrolyte layer16. The copper ions that have dissolved into solid electrolyte layer16become copper and precipitate on the surface of the drain electrode, and the precipitated copper electrically connects the drain electrode and source electrode. The electrical connection of the drain electrode and source electrode causes the solid electrolyte switching element to enter the ON state.

On the other hand, when the source electrode is grounded in the above-described ON state and a negative voltage is applied to the gate electrode, the precipitated copper between the drain electrode and source electrode dissolves in solid electrolyte16, whereby the electrical connection between the drain electrode and source electrode is cut. The electrical disconnection between the drain electrode and source electrode causes the solid electrolyte switching element to enter the OFF state. In addition, from the stage preceding the complete of the electrical disconnection, the electrical properties undergo changes such as an increase in the resistance between the drain electrode and source electrode and variation in the inter-electrode capacitance, following which the electrical connection is cut.

In the solid electrolyte switching element, the distance between the source electrode and drain electrode is set to a dimension smaller than the minimum value of the limits of lithography. The distance between the source electrode and drain electrode can be made sufficiently small compared to the distance between the gate electrode and source electrode and the distance between the gate electrode and the drain electrode. As a result, when switching from the OFF state to the ON state, the metal that precipitates connects the source electrode and drain electrode before a connection is realized between the gate electrode and the drain electrode. The switching from the OFF state to the ON state is therefore more stable than in the related art, and stable switching operations can therefore be repeated.

In addition, points of solid electrolyte layer16that do not contact any of first interconnect14, second interconnect15, and third interconnect18are covered by at least one of metal diffusion prevention film17and insulating layer11that serve as metal diffusion prevention films, whereby metal ions do not diffuse to the surrounding area. As a result, the metal ions can be prevented from exerting an adverse influence on neighboring elements, and the solid electrolyte switching element of the present embodiment can be used together with other elements in an integrated circuit.

Insulating layer11is here assumed to be a metal diffusion prevention film, but insulating layer11may also be of a construction in which a plurality of insulating films are stacked. In such a case, the insulating film of the uppermost layer serves as the metal diffusion prevention film.

Explanation next regards the fabrication method of solid electrolyte switching element1shown inFIGS. 1A and 1B.FIGS. 2A to 2Iare plan views and sectional views showing the fabrication method of the solid electrolyte switching element of the present embodiment. The sectional views show the portion of broken line a-a′ in the plan view.

A semiconductor circuit that includes semiconductor elements such as transistors and resistors is formed on a semiconductor substrate by means of integrated circuit fabrication methods of the related art, and a base insulating film for maintaining insulation between semiconductor elements is formed. A substrate on which a semiconductor circuit and a base insulating film for protecting the semiconductor circuits are thus formed is referred to as simply “substrate10.” This provision of an insulating film for protecting semiconductor circuits serves the purpose of electrically isolating solid electrolyte switching element1and the semiconductor circuits.

The base insulating film may be an insulating material used in integrated circuits of the related art. For example, the base insulating film is preferably a compound of silicon and an oxygen, and is preferably a low-permittivity insulating film to which any amount of hydrogen, fluorine, carbon and nitrogen have been added. The low-permittivity insulating film is an insulating film having a lower dielectric constant than a silicon oxide film. In addition, plugs (not shown) are provided in the portion in which semiconductor circuits and solid electrolyte switching element1electrically connect. The construction and method of fabricating the plugs are the same as in the related art and detailed explanation is therefore here omitted.

As shown inFIG. 2A, insulating layer11of silicon nitride is formed to a film thickness of 20-100 nm on substrate10. This insulating layer11is not limited to silicon nitride and may also be a material in which any amount of carbon has been mixed in silicon nitride. Insulating layer11suppresses the diffusion of metal ions into substrate10.

A resist pattern having apertures is next formed on insulating layer11as next described. After applying a photoresist to insulating layer11, an exposure process is carried out. The exposed photoresist is next subjected to a development process to form photoresist21having first aperture pattern22and second aperture pattern23as shown inFIG. 2B. The spacing between first aperture pattern22and second aperture pattern23is a distance at the minimum limits of lithographic processing. Photoresist21is next subjected to first dry etching having an isotropic etching characteristic to enlarge the area of the apertures of first aperture pattern22and second aperture pattern23(FIG. 2C). The conditions of this first dry etching can be found by using an etching apparatus of the related art to optimize the etching gas.

Insulating layer11is then subjected to a second dry etching from above first aperture pattern22and second aperture pattern23for which the aperture areas have been enlarged, whereby first aperture12and second aperture13are formed in insulating layer11as shown inFIG. 2D. The spacing between first aperture12and second aperture13is formed to a distance that is still smaller than photoresist pattern21ofFIG. 2Bthat was formed at the minimum value of the limits of lithography. The optimization of the etching conditions enabled a decrease of this spacing to 30-15 nm. Next, by removing the photoresist by acidic peeling and ashing processes, first aperture12and second aperture13separated by the above-described micro distance are formed in insulating layer11as shown inFIG. 2E.

Explanation here regards another method for forming first aperture12and second aperture13separated by the above-described micro distance in insulating layer11. Photoresist21having first aperture pattern22and second aperture pattern23is formed on insulating layer11. The spacing between first aperture pattern22and second aperture pattern23is formed to the minimum value of the limits of lithography as in the configuration shown inFIG. 2B. Insulating layer11is then subjected to a first dry etching having anisotropic etching characteristics, to form a first preparatory aperture corresponding to first aperture pattern22and a second preparatory aperture corresponding to second aperture pattern23. A second dry etching having isotropic etching characteristics is next carried out to enlarge the aperture areas of the first preparatory aperture and the second preparatory aperture, whereby first aperture12and second aperture13are formed in insulating layer11. Photoresist21is then removed to complete fabrication of the construction shown inFIG. 2E.

In this method as well, the spacing between first aperture12and second aperture13can be formed to a distance even smaller than the minimum value of the limits of lithography. Optimization of the etching conditions can then further reduce this spacing to the order of 30-15 nm.

After first aperture12and second aperture13have been formed in insulating layer11as shown inFIG. 2E, first interconnect14and second interconnect15are formed as next described. An interconnect material is deposited to bury at least first aperture12and second aperture13, following which interconnect material that has formed at points other than aperture12and aperture13is removed.

As the interconnect material, no particular restrictions apply as long as the material realizes the functions of interconnects and is of the same type as metal used in the interconnects of integrated circuits of the related art. In particular, interconnects that contain at least one of the metals titanium and tantalum exhibited good compatibility with other interconnects. An interconnect realized by a laminated film of at last one of the metals titanium and tantalum and the nitride of that metal also exhibited good compatibility with other interconnects.

A CMP (Chemical and Mechanical Polishing) method used in the interconnect formation steps of integrated circuits of the related art is ideal as the method of removing the interconnect material formed in points other than first aperture12and second aperture13. Using a CMP method to polish the interconnect material until the upper surface of insulating layer11is exposed eliminates the interconnect material that has formed at points other than first aperture12and second aperture13.

In this way, first interconnect14in which the interconnect material is embedded in first aperture12and second interconnect15in which the interconnect material is embedded in second aperture13are formed in insulating layer11as shown inFIG. 2F. First interconnect14and second interconnect15are separated by the above-described micro distance.

Solid electrolyte layer16is next formed in contact with first interconnect14and second interconnect15on insulating layer11. After first forming a solid electrolyte layer by means of a laser deposition method or a sputtering method, unnecessary points are eliminated. The use of these methods keeps the film formation temperature of the solid electrolyte layer to no more than 350° C. The film thickness of solid electrolyte layer16should be on the order of 5-200 nm. The material of solid electrolyte layer16is preferably a compound of a metal or semiconductor and a chalcogen such as oxygen, sulfur, selenium, and tellurium. In particular, a sulfide, oxide, or oxysulfide of a metal such as copper, tungsten, tantalum, molybdenum, chromium, titanium and cobalt is ideal. An oxysulfide may have any sulfur-oxygen ratio.

After forming the solid electrolyte layer on insulating layer11, a photoresist having a desired pattern is formed by a normal lithographic process. Dry etching or wet etching is next carried out to remove the unnecessary points of the solid electrolyte layer and thus form the pattern of solid electrolyte layer16. The photoresist is then eliminated to complete the construction shown inFIG. 2G.

Metal diffusion prevention film17is next formed to cover solid electrolyte layer16, following which metal diffusion prevention film17is patterned by means of a lithographic process and an etching process to form the construction shown inFIG. 2H. Metal diffusion prevention film17is here formed to cover solid electrolyte layer16. Although a lithographic process and etching process are here carried out to pattern metal diffusion prevention film17and remove portions of metal diffusion prevention film that has been formed, metal diffusion prevention film17may be left on first interconnect14and second interconnect15.

A photoresist having a prescribed aperture pattern is further formed by a lithographic process on metal diffusion prevention film17. The aperture pattern is here located over solid electrolyte layer16. Anisotropic etching is then carried out from over the photoresist to form an aperture in metal diffusion prevention film17. After thus forming an aperture in metal diffusion prevention film17to expose a portion of the surface of solid electrolyte layer16, the photoresist is removed.

Third interconnect18that contacts solid electrolyte layer16is next formed as follows. Copper or a metal that contains copper is used as the interconnect material, copper being used in this example. Copper is formed to a film thickness of 5-200 nm on at least solid electrolyte layer16. Next, similar to the method of forming solid electrolyte layer16, a photoresist having a desired pattern is formed on the copper by normal lithographic steps following which dry etching or wet etching is carried out to remove unnecessary points of copper and thus form third interconnect18on solid electrolyte layer16. The photoresist is then removed to produce the construction shown inFIG. 2I. Regarding the distance from third interconnect18to first interconnect14and second interconnect15, control is possible by setting the desired distance when forming the pattern of the photoresist corresponding to third interconnect18by lithographic steps. At this time, the photoresist pattern is set by taking into consideration the etching conversion differential, which is the dimensional differential when transferring the photoresist pattern to the copper.

Solid electrolyte switching element1shown inFIGS. 1A and 1Bis produced by the above-described fabrication method that allows the formation of first interconnect14and second interconnect15separated by a distance smaller than the minimum value of the limits of lithography. In addition, the fabrication method enabled control of the distances from third interconnect18to first interconnect14and second interconnect15in the lithographic steps.

Explanation next regards another example of the configuration of the solid electrolyte switching element of the present embodiment.FIG. 3is a plan view and a sectional view showing another example of the configuration of the solid electrolyte switching element in the present embodiment. In addition, components identical to those of the solid electrolyte switching element shown inFIGS. 1A and 1Bare given the same reference numbers, and detailed explanation of these components is here abbreviated. Although third interconnect18is not arranged in the a-a′ portion ofFIG. 3, third interconnect18is displayed provided by way of the aperture of metal diffusion prevention film17in the sectional view ofFIG. 3for the purpose of explanation as inFIGS. 1A and 1B.

In solid electrolyte switching element shown inFIG. 3, second insulating layer31is formed between insulating layer11and solid electrolyte layer16. Fourth aperture32that is to serve as the aperture for placing solid electrolyte layer16in contact with first interconnect14and second interconnect15is provided on second insulating layer31. Solid electrolyte layer16formed on second insulating layer31contacts first interconnect14and second interconnect15by way of aperture32. In the solid electrolyte switching element shown inFIG. 3, the area in which metal can be precipitated by metal ions supplied from third interconnect18is limited to a solid electrolyte layer in fourth aperture32. This form therefore enables a switching operation from the OFF state to the ON state by the minimum amount of precipitated metal, whereby more stable operation of the solid electrolyte switching element can be achieved.

The following brief explanation relates to the fabrication method of the solid electrolyte switching element shown inFIG. 3. The formation of first interconnect14and second interconnect15as shown inFIG. 2Fis followed by the formation of second insulating layer31, which is a metal diffusion prevention film. A resist pattern having a prescribed aperture is then formed by a lithographic step. At this time, the aperture position is set to overlap with a portion of each of first interconnect14and second interconnect15. Anisotropic etching is then carried out from above the resist pattern to form fourth aperture32in second insulating layer31. The formation of fourth aperture32exposes a portion of the surface of first interconnect14and second interconnect15. The photoresist is then removed to complete the formation of solid electrolyte layer16as shown inFIG. 2G.

Second Embodiment

Explanation next regards the configuration of the solid electrolyte switching element of the present embodiment.FIGS. 4A and 4Bshow an example of the configuration of the solid electrolyte switching element of the present embodiment.FIG. 4Ais a plan view andFIG. 4Bis a sectional view taken along broken line a-a′ shown inFIG. 4A.

As shown inFIGS. 4A and 4B, solid electrolyte switching element101is of a configuration that includes: a third interconnect provided on first interconnect layer103, solid electrolyte layer141provided on first insulating layer104, and first interconnect145and second interconnect146provided on second interconnect layer105. First interconnect layer103, first insulating layer104, and second interconnect layer105are formed successively.

First interconnect layer103is realized by the successive formation of first protective insulating film110, interlayer insulating film111, and stopper insulating film112. The third interconnect, which serves as an anode that supplies metal ions, is of a configuration that includes copper132aand barrier metal131afor preventing the diffusion of copper. The side walls and bottom surface of copper132aare covered by barrier metal131a. In addition, the third interconnect is formed of copper132aand barrier metal131a, but because copper132arealizes the key role in the solid electrolyte switching element, the third interconnect is hereinbelow indicated by reference number132a. As barrier metal131a, a material that contains at least any one of titanium, titanium nitride, tantalum, and tantalum nitride is preferable because these materials prevent the diffusion of copper. Accordingly, barrier metal131anot only serves the function of an interconnect for conducting electrons, but also serves the function of a metal diffusion prevention film.

First insulating layer104is realized by the successive formation of second protective insulating film113, second interlayer insulating film115, and second stopper insulating film116. Solid electrolyte layer141contacts third interconnect132aby way of third aperture140, which is an aperture provided in second protective insulating film113. The side walls of solid electrolyte layer141are covered by cover insulation film114that functions as a metal diffusion prevention film.

Second interconnect layer105is realized by the successive formation of third protective insulating film117that serves the function of a metal diffusion prevention film, third interlayer insulating film118, and third stopper insulating film119. First interconnect145and second interconnect146are formed on third protective insulating film117. First interconnect145and second interconnect146are arranged separated by a prescribed distance, and both interconnects contact solid electrolyte layer141. The distance between first interconnect145and second interconnect146is a dimension smaller than the minimum value of the limits of lithography, as in the first embodiment. More specifically, this distance is on the order of 30-15 nm. Lead-out interconnects are provided on third interlayer insulating film118and third stopper insulating film119to lead out first interconnect145and second interconnect146. The lead-out interconnects are of a construction that includes copper136and barrier metal135for preventing the diffusion of copper. The side walls and bottom surface of copper136are covered by barrier metal135.

The thickness of first interconnect layer104is greater than the distance between first interconnect145and second interconnect146. In addition, points of solid electrolyte layer141that do not contact any of first interconnect145, second interconnect146, and the third interconnect are covered by either one of cover insulation film114and third protective insulating film117.

Solid electrolyte141is embedded in a multilayer insulating film in which second protective insulating film113, second interlayer insulating film115, and second stopper insulating film116are stacked. Third interconnect132ais embedded in a multilayer insulating film in which first protective insulating film110, interlayer insulating film111, and stopper insulating film112are stacked.

The operation of solid electrolyte switching element101of the present embodiment is the same as that of the first embodiment and a detailed explanation of the operation is therefore here omitted.

In solid electrolyte switching element101shown inFIGS. 4A and 4B, first interconnect145that serves as the source electrode and second interconnect146that serves as the drain electrode are separated by the above-described micro distance. This distance is sufficiently smaller than the distance between third interconnect132athat serves as the gate electrode that supplies metal ions and each of first interconnect145and second interconnect146, i.e., the height of via layer104, whereby greater stability is achieved in the operation of the solid electrolyte switching element.

In addition, points of solid electrolyte layer141that do not contact any of first interconnect145, second interconnect146, and the third interconnect are covered by a metal diffusion prevention film constituted by either of cover insulation film114and third protective insulating film117, and metal ions therefore are not diffused to the surroundings. As a result, metal ions can be prevented from adversely affecting neighboring elements, and the solid electrolyte switching element of the present embodiment can be used in circuits that are integrated with other elements.

Explanation next regards a configuration in which solid electrolyte switching element101shown inFIGS. 4A and 4Bis applied to an integrated circuit. A via construction for interconnecting semiconductor circuits is here shown as one part of the integrated circuit.

FIG. 5is a sectional view showing the solid electrolyte switching element and the via construction. Components of the construction that are identical to elements shown inFIGS. 4A and 4Bare given the same reference numerals and detailed explanation of these components is here omitted.

As shown inFIG. 5, the integrated circuit is of a configuration that includes solid electrolyte switching element101and via construction102for connecting together the interconnects. Via construction102includes: first circuit interconnect provided on first interconnect layer103, second circuit interconnect provided on second interconnect layer105, and a viaplug for connecting the first circuit interconnect and the second circuit interconnect. The viaplug is formed on first insulating layer104. The layer in which this viaplug is formed is referred to as the “via layer.”

The first circuit interconnect includes copper132′ and barrier metal131′ for preventing the diffusion of copper. The bottom surface and side walls of copper132′ are covered by barrier metal131′. This copper132′ is of the same material as copper132aof the third interconnect, and barrier metal131′ is of the same material as barrier metal131aof the third interconnect.

The viaplug includes copper134′ and barrier metal133′ for preventing the diffusion of copper. The bottom surface and side walls of copper134′ are covered by barrier metal133′.

Second circuit interconnect includes copper136′ and barrier metal135′ for preventing the diffusion of copper. The bottom surface and side walls of copper136′ are covered by barrier metal135′. This copper136′ is of the same material as copper136of the lead-out interconnect, and barrier metal135′ is of the same material as barrier metal135of the lead-out interconnect.

The integrated circuit shown inFIG. 5is of a construction in which the processing of a portion of the multilayer interconnects can be shared in the fabrication method of solid electrolyte switching element101and via construction102.

In the configuration shown inFIGS. 4A,4B and5, first interconnect layer103and second interconnect layer105are taken as the interconnect layer in an integrated circuit, but these layers may be the via layer as well. In other words, a solid electrolyte switching element may be formed to correspond to a construction made up from two via layers and an interconnect layer between these two layers.

Explanation next regards the fabrication method of the solid electrolyte switching element and via construction shown inFIG. 5.

FIGS. 6A to 6Pare sectional views showing the fabrication method of the solid electrolyte switching element and via construction.

First interconnect layer103is formed as described below.

First protective insulating film110for protecting an interconnect that is formed underneath (not shown), first interlayer insulating film111that is a film having a low dielectric constant, and first stopper insulating film112are deposited successively. The material of first protective insulating film110is preferably a material that suppresses the diffusion of copper into the oxide film, such as silicon nitride or a material in which any amount of carbon is mixed into the film. This first protective insulating film110, in addition to the effect of suppressing the diffusion of copper into an oxide film, also has the effect of maintaining resistance to hydrogen annealing with respect to solid electrolyte layer141, which is to be described hereinbelow. The film thickness may be on the order of 20-100 nm.

First interlayer insulating film111is a compound of silicon and oxygen, and is preferably a low-dielectric constant insulating film to which any amount of any of hydrogen, fluorine, and carbon has been added. A film containing holes is even more preferable. It is known that the dielectric constant of a film is further reduced when the film contains holes. The size of the holes is preferably no greater than 2 nm. The film thickness of first interlayer insulating film111is on the order of 50-250 nm. First stopper insulating film112may be a silicon oxide film, and may have a film thickness on the order of 50-200 nm. First stopper insulating film112serves the purpose of detecting the endpoint of CMP and protecting first interlayer insulating film111during CMP.

Apertures are formed in first protective insulating film110, first interlayer insulating film111, and first stopper insulating film112as described hereinbelow. A photoresist is applied to first stopper insulating film112and an exposure process then carried out. A developing process is carried out upon the exposed photoresist to form a photoresist having openings. Etching is then carried out through this photoresist to form apertures. For example, in 90 nm-generation lithography, the diameter of the aperture is on the order of 80-200 nm.

After the photoresist is removed, the barrier metal and a copper seed layer that is a portion of the copper are formed by a sputtering method in the aperture that has been formed. Barrier metal131aand barrier metal131′ are of the same type of material. Barrier metal131aand131′ are laminated films of tantalum nitride and tantalum and are formed to cover the bottom surface and side walls of the aperture. Barrier metal131aand131′ prevent the diffusion of copper into first interlayer insulating film111. The film thickness of the tantalum nitride and tantalum is on the order of 5-30 nm. The thickness of the copper seed layer is on the order of 20-100 nm.

Copper is next formed on the copper seed layer by a plating method. Copper132aand copper132′ are formed in the same step. The film thickness of the copper is on the order of 300-800 nm. The barrier metal and copper on first stopper insulating film112are next polished by a CMP method to remove the unnecessary barrier metal and copper that are outside the aperture.

In this way, first interconnect layer103is formed in which barrier metal131aand131′ and copper132aand132′ are embedded in apertures provided in first protective insulating film110, first interlayer insulating film111, and first stopper insulating film112. Third interconnect composed of barrier metal131aand copper132ais formed in the solid electrolyte switching element formation region, and first circuit interconnect composed of barrier metal131′ and copper132′ is formed in the via construction formation region. Second protective insulating film113is then formed on first interconnect layer103(FIG. 6A). Second protective insulating film113serves the same role effected by first protective insulating film110and is therefore of the same construction as first protective insulating film110. The film thickness is 20-100 nm.

Second interlayer insulating film115and second stopper insulating film116are next formed successively on second protective insulating film113to form first insulating layer104that is composed of second protective insulating film113, second interlayer insulating film115and second stopper insulating film116. The film thickness of second interlayer insulating film115is on the order of 50-250 nm. Second interlayer insulating film115serves the same role as first interlayer insulating film111and is therefore of the same construction as first interlayer insulating film111. Second stopper insulating film116serves the same role as first stopper insulating film112and is therefore of the same construction as first stopper insulating film112. The film thickness is on the order of 50-200 nm.

Third aperture140is formed as next described. A photoresist is applied to second stopper insulating film116, following which an exposure process is carried out. The exposed photoresist is then subjected to a developing process to form a photoresist having an aperture. Etching is then carried out through the photoresist to form third aperture140in first insulating layer104(FIG. 6B). In 90-nm generation lithographic technology, the diameter of third aperture140is on the order of 80-200 nm.

Cover insulation film114is next deposited to completely cover the side walls and bottom surface of third aperture140(FIG. 6C). Cover insulation film114should be a film that serves the same role as first protective insulating film110and is therefore of the same construction as first protective insulating film110. The film thickness is 10-50 nm.

Etching having high anisotropy is further implemented to remove cover insulation film114that has been formed on second stopper insulating film116and on the bottom surface of third aperture140. A dry etching method such as reactive ion etching is effective as an etching having high anisotropy. Cover insulation film114is thus formed that completely covers only the side walls of third aperture140(FIG. 6D).

Next, as shown inFIG. 6E, solid electrolyte layer141is formed to completely bury third aperture140. The material and formation method of solid electrolyte layer141is the same as in the first embodiment. The film thickness of solid electrolyte layer141that is formed to bury third aperture140is set to at least the total film thickness of first insulating layer104that is made up from second protective insulating film113, second interlayer insulating film115, and second stopper insulating film116. The film thickness of first insulating layer104is on the order of 100-400 nm. The material of solid electrolyte layer141is the same as in the first embodiment. The film formation temperature is no greater than 350° C.

Of solid electrolyte layer141that has been formed, unnecessary solid electrolyte layer141that is outside third aperture140is removed by a CMP method. In this way, solid electrolyte layer141is embedded in cover insulation film114in third aperture140provided in first insulating layer (via layer)104that is made up from second protective insulating film113, second interlayer insulating film115, and second stopper insulating film116(FIG. 6F). As described hereinabove, the height of solid electrolyte layer141is 100-400 nm.

A viaplug is next formed on first insulating layer (via layer)104as described hereinbelow. A photoresist is applied to second stopper insulating film116and then subjected to an exposure process. The exposed photoresist is then subjected to a development process to form a photoresist having an aperture. Etching is then carried out through this photoresist to form aperture142in first insulating layer104as shown inFIG. 6G(FIG. 6G). In 90-nm generation lithographic technology, the diameter of aperture142is on the order of 80-200 nm.

Barrier metal133′ and a copper seed layer that is to be one portion of copper134′ is formed by a sputtering method in aperture142that has been formed. The barrier metal is a laminated construction of tantalum nitride and tantalum and is formed to cover the bottom surface and side walls of aperture142. The barrier metal serves the role of preventing the diffusion of copper into first insulating layer104. The film thickness of tantalum nitride and tantalum is on the order of 5-30 nm. The film thickness of the copper seed layer is on the order of 20-100 nm. Copper plating is then carried out (FIG. 6H). The film thickness of the copper is on the order of 300-800 nm.

Unnecessary barrier metal and copper outside aperture142are next removed by a CMP method, whereby a viaplug composed of barrier metal133′ and copper134′ is formed in first insulating layer104(FIG. 6I).

Third protective insulating film117is then formed on first insulating layer104as shown inFIG. 6J. Third protective insulating film117should be a film that serves the same role as first protective insulating film110and therefore has the same construction as first protective insulating film110. The film thickness is 20-100 nm.

First aperture143and second aperture144are next formed separated by the above-described micro distance on third protective insulating film117as in the first embodiment (FIG. 6K). When first aperture143and second aperture144are formed, a portion of the surface of solid electrolyte141is exposed. The spacing of first aperture143and second aperture144can be made smaller than the minimum value of the limits of lithography and is formed on the order of 30-15 nm by optimizing conditions.

First interconnect145and second interconnect146are formed as described below. Interconnect material is deposited to cover first aperture143, second aperture144, and third protective insulating film117(FIG. 6L). As the interconnect material, no particular restrictions are placed on the type of material as long as the material is a metal of the same type used in interconnects of integrated circuits of the related art and achieves functionality as an interconnect. An interconnect that contains at least one of the metals titanium and tantalum has compatibility with other interconnects. Alternatively, an interconnect realized by a laminated film of at least one of the metals titanium and tantalum and the nitride of that metal has compatibility with other interconnects. Interconnect material that has formed at points other than first aperture143and second aperture144is next removed by a CMP method, whereby first interconnect145and second interconnect146are formed that are arranged separated by the above-described micro distance on third protective insulating film117(FIG. 6M).

Second interconnect layer105is formed as next described. Third interlayer insulating film118and third stopper insulating film119are successively deposited on third protective insulating film117(FIG. 6N). The film thickness of third interlayer insulating film118is on the order of 50-250 nm. Third interlayer insulating film118serves the same role as first interlayer insulating film111and therefore is of the same construction as first interlayer insulating film111. Third stopper insulating film119serves the same role as first stopper insulating film112and therefore is of the same construction as first stopper insulating film112. The film thickness is on the order of 50-200 nm.

A photoresist is then applied to third stopper insulating film119and then subjected to an exposure process. The exposed photoresist is then subjected to a development process to form a photoresist that includes apertures. Etching is then carried out through this photoresist to form apertures in third interlayer insulating film118and third stopper insulating film119on first interconnect145and second interconnect146in the solid electrolyte switching element formation region. An aperture is also formed in third protective insulating film117, third interlayer insulating film118, and third stopper insulating film119in the via construction formation region (FIG. 6O). In 90-nm generation lithography, the diameter of the aperture is on the order of 80-200 nm. When forming the aperture, etching is carried out under the conditions for etching the insulating film, and the reduction of first interconnect145and second interconnect146is therefore suppressed.

After the photoresist has been removed, barrier metal and a copper seed layer that is a portion of the copper are formed by a sputtering method in the apertures that have been formed. Barrier metal135and barrier metal135′ are of the same type of material. Barrier metal135and135′ are laminated films of tantalum nitride and tantalum, and are formed to cover the bottom surfaces and side walls of the apertures. Barrier metal135and135′ prevent the diffusion of copper into third interlayer insulating film118. The film thickness of the tantalum nitride and tantalum is on the order of 5-30 nm. The thickness of the copper seed layer is on the order of 20-100 nm.

Copper is next formed by a plating method on the copper seed layer. Copper136and136′ are formed by the same step. The film thickness of copper is on the order of 300-800 nm. The barrier metal and copper on third stopper insulating film119is next polished by a CMP method to remove unnecessary barrier metal and copper that are outside the apertures. Second interconnect layer105is thus formed with lead-out interconnects composed of barrier metal135and copper136formed in the solid electrolyte switching element formation area and second circuit interconnect composed of barrier metal135′ and copper136′ formed in the via construction formation region (FIG. 6P).

Protective layer106composed of fourth protective insulating film120, fourth interlayer insulating film121, fourth stopper insulating film122, and fifth protective insulating film123is next formed on second interconnect layer105as shown inFIG. 5. Fourth protective insulating film120and fifth protective insulating film123serve the same role as first protective insulating film110and are therefore of the same construction as first protective insulating film110. The film thickness is on the order of 20-100 nm. Fourth interlayer insulating film121serves the same role as first interlayer insulating film111and is therefore of the same construction as first interlayer insulating film111. The film thickness is on the order of 50-250 nm. Fourth stopper insulating film122serves the same role as first stopper insulating film112and is therefore of the same construction as first stopper insulating film112. The film thickness is on the order of 50-200 nm.

Lead-out interconnects were formed on second interconnect layer105in the present embodiment, but the lead-out interconnects may also be formed on the layer of first insulating layer104. Alternatively, lead-out interconnects may be formed on both second interconnect layer105and first insulating layer104.

Solid electrolyte switching element101of the present embodiment was produced by means of the above-described fabrication method. The fabrication method can achieve an interconnect construction in which first interconnect145and second interconnect146are embedded in third protective insulating film117separated by a micro distance that surpasses the limits of lithography. The distance between third interconnect132athat is the gate electrode and first interconnect145that is the source electrode and the distance between third interconnect132athat is the gate electrode and second interconnect146that is the drain electrode are determined by the thickness of via layer104, but these distances are sufficiently greater than the distance between the source electrode and drain electrode.

In the three-terminal solid electrolyte switching element101that employs the interconnect construction formed by the above-described method, the distance between the source electrode and drain electrode is sufficiently smaller than the distance between the gate electrode and source electrode (or the drain electrode), whereby stable switching operations can be repeated. Further, a construction in which a second insulating layer containing a fourth aperture is inserted between solid electrolyte layer141and third protective insulating film117in which first interconnect145and second interconnect146are embedded limits the region in which metal ions can precipitate to within the fourth aperture and is therefore effective for stabilizing switching operations.

Still further, starting with the step of forming third interconnect132a, the large number of steps that can be shared with the multilayer interconnect fabrication steps, the minimization of the number of added masks to just two, the suppression of the diffusion of atoms into insulating films, and the measures taken for resistance to hydrogen annealing all enable the introduction to the production line with minimal additional costs. As has been made clear here, one skilled in the art of forming multilayered interconnects of integrated circuits of the related art would encounter no particular difficulty in carrying out the above-described steps without requiring special steps.

Third Embodiment

Explanation next regards the configuration of the solid electrolyte switching element of the present embodiment.

FIGS. 7A and 7Bshow an example of the configuration of the solid electrolyte switching element of the present embodiment.FIG. 7Ais a plan view, andFIG. 7Bis sectional view taken along broken line a-a′ shown inFIG. 7A.

In the construction shown inFIGS. 7A and 7B, first interconnect layer203, first insulating layer204, second interconnect layer205, and protective layer206are formed successively on a substrate (not shown). The solid electrolyte switching element of the present embodiment is of a configuration that includes: first interconnect245, second interconnect246and solid electrolyte layer241provided on protective layer206, and third interconnect provided on second interconnect layer205.

Protective layer206is of a configuration in which fourth protective insulating film220, fourth interlayer insulating film221, fourth stopper insulating film222, and fifth protective insulating film223are successively formed. First interconnect245and second interconnect246are formed on fourth protective insulating film220. First interconnect245and second interconnect246are arranged separated by a prescribed distance, and both interconnects contact solid electrolyte layer241. As in the first embodiment, the distance between first interconnect245and second interconnect246is a dimension smaller than the minimum value of the limits of lithography. More specifically, this distance is on the order of 30-15 nm.

Solid electrolyte layer241is provided in fourth interlayer insulating film221and fourth stopper insulating film222and contacts first interconnect245and second interconnect246. The side surfaces of solid electrolyte layer241are covered by cover insulation film214, and the upper surface of solid electrolyte layer241is covered by fifth protective insulating film223. In addition, points of the bottom surface of solid electrolyte layer241that do not contact either one of first interconnect245and second interconnect246are covered by fourth protective insulating film220. Fourth protective insulating film220, fifth protective insulating film223, and cover insulation film214serve the function of a metal diffusion prevention film.

Second interconnect layer25is realized by the successive formation of third protective insulating film217, third interlayer insulating film218, and third stopper insulating film219. The lead-out interconnects for leading out first interconnect245and second interconnect246are provided on third interlayer insulating film281and third stopper insulating film219. The lead-out interconnects are of a construction that includes copper236and barrier metal235for preventing the diffusion of copper. The side walls and bottom surface of copper236are covered by barrier metal235. In addition, a third interconnect is provided on third interlayer insulating film218and third stopper insulating film219. The third interconnect is of a construction that includes copper236aand barrier metal235afor preventing the diffusion of copper. The side walls and bottom surface of copper236aare covered by barrier metal235a. Copper236aof the third interconnect contacts solid electrolyte layer241by way of third aperture240provided in fourth protective insulating film220. In addition, the third interconnect is formed by copper236aand barrier metal235a, but because copper236aplays the key role in the solid electrolyte switching element, the third interconnect is indicated hereinbelow by just reference number236a.

The distance from third interconnect236ato first interconnect245and second interconnect256is made greater than the distance between first interconnect245and second interconnect246. The distances between third interconnect236aand first interconnect245and second interconnect246are set in the lithography step when third interconnect236ais patterned.

First interconnect layer203is realized by the successive formation of protective insulating film210, interlayer insulating film211, and stopper insulating film212. First insulating layer204is realized by the successive formation of second protective insulating film213, second interlayer insulating film215, and second stopper insulating film216.

The operation of solid electrolyte switching element201of the present embodiment is the same as the case of the first embodiment, and a detailed explanation of this operation is therefore here omitted.

In solid electrolyte switching element201shown inFIGS. 7A and 7B, first interconnect245that serves as the source electrode and second interconnect246that serves as the drain electrode are separated by the above-described micro distance. This distance is smaller than the distance between third interconnect236athat serves as the gate electrode that supplies metal ions and first interconnect245and second interconnect246, whereby greater stability is achieved in the operation of the solid electrolyte switching element.

In addition, points of solid electrolyte layer241that do not contact any of first interconnect245, second interconnect246, and the third interconnect are covered by any of fourth protective insulating film220, cover insulation film214and fifth protective insulating film223, whereby metal ions do not diffuse to the surrounding areas. As a result, metal ions can be prevented from adversely affecting neighboring elements, and the solid electrolyte switching element of the present embodiment can be used in circuits that are integrated together with other elements.

Explanation next regards a configuration in which solid electrolyte switching element201shown inFIGS. 7A and 7Bis applied to an integrated circuit. A via construction for connecting together semiconductor circuits is here shown as a part of the integrated circuit.

FIG. 8is a sectional view showing a solid electrolyte switching element and a via construction. Components that are the same as components shown inFIGS. 7A and 7Bare given the same reference numbers and detailed explanation of these components is omitted.

As shown inFIG. 8, the integrated circuit is of a configuration that includes solid electrolyte switching element201and via construction202for connecting together interconnects. Via construction202includes a first circuit interconnect provided in first interconnect layer203, a second circuit interconnect provided in second interconnect layer205, and a viaplug for connecting the first circuit interconnect and second circuit interconnect. The viaplug is formed in first insulating layer204. The layer in which this viaplug is formed is referred to as the “via layer.”

The first circuit interconnect includes copper232′ and barrier metal231′ for preventing the diffusion of copper. The bottom surface and side walls of copper232′ are covered by barrier metal231′. The viaplug includes copper234′ and barrier metal233′ for preventing the diffusion of copper. The bottom surface and side walls of copper234′ are covered by barrier metal233′. The second circuit interconnect includes copper236′ and barrier metal235′ for preventing the diffusion of copper. The bottom surface and side walls of copper236′ are covered by barrier metal235′. This copper236′ is of the same material as copper236of the lead-out interconnects and copper236aof the third interconnect, and barrier metal235′ is of the same material as barrier metal235of the lead-out interconnect and barrier metal235aof the third interconnect.

The differences between the solid electrolyte switching element of the present embodiment and that of the second embodiment are the positional relationships in the multilayered interconnects between third interconnect236afor supplying metal ions to solid electrolyte layer241and solid electrolyte layer241that is formed above this third interconnect236aand first interconnect245and second interconnect246embedded in fourth protective insulating film220.

In the second embodiment, the positional relationships are such that third interconnect132afor supplying metal ions to solid electrolyte layer141and solid electrolyte layer141that is formed above this third interconnect132aare in the same vertical axis as first interconnect145and second interconnect146that are embedded in third protective insulating film117. In contrast, in the present embodiment, first interconnect245and second interconnect246that are embedded in fourth protective insulating film220are arranged below solid electrolyte layer241, and further, are arranged at a point that is separated within the plane from third interconnect236athat is similarly arranged below solid electrolyte layer241.

In the present embodiment, the distance from third interconnect236ato first interconnect245and second interconnect246can be set freely by the position of arrangement of third interconnect236a. In contrast, in the second embodiment, the distance from third interconnect132ato first interconnect145and second interconnect146is determined by the thickness of solid electrolyte layer141.

Compared to the second embodiment, the solid electrolyte switching element of the present embodiment facilitates the control of the distances between third interconnect236aand first interconnect245and second interconnect246. Because metal ions supplied from third interconnect236adiffuse over this distance, the switching characteristics can be determined by controlling this distance. The characteristics of a solid electrolyte switching element in an integrated circuit can therefore be controlled. In particular, making the distance between third interconnect236aand first interconnect245and second interconnect246greater than in related art has proven effective for preventing the occurrence of switching from the OFF state to the ON state.

In addition, forming solid electrolyte layer241over first interconnect245, second interconnect246and third interconnect236aeliminates restrictions on the points at which elements can be formed within the interconnect layer and thus increases the degree of freedom of element formation. This increase in design freedom can be fully applied in the interconnect forming steps by dual damascene that has become mainstream in recent years. In particular, it is now possible to form elements after completing multilayer interconnect steps. This potential has led to both a reduction of the risks involved in introducing new materials as well as a reduction of costs.

Explanation next regards the fabrication method of the solid electrolyte switching element and via construction shown inFIG. 8.

FIGS. 9A to 9Dare sectional views showing the fabrication method of the solid electrolyte switching element and via construction. Detailed explanation relating to steps common to the second embodiment is here abbreviated.

First interconnect layer203and first insulating layer204are formed on a substrate (not shown) in which an insulating film is formed on the uppermost layer. At this time, a first circuit interconnect is formed in first interconnect layer203and a viaplug is formed in first insulating layer (via layer)204in the formation region of via construction202, as in the second embodiment.

Second interconnect layer205is next formed similar to the method of forming second interconnect layer105of the second embodiment. At this time, a third interconnect is formed in addition to the lead-out interconnects in the formation region of solid electrolyte switching element201. The method of forming this third interconnect is similar to that of the lead-out interconnects. Fourth protective insulating layer220is next formed over second interconnect layer205(FIG. 9A). Fourth protective insulating film220is formed from silicon nitride or a material in which any amount of carbon is mixed in silicon nitride. Fourth protective insulating film220suppresses the diffusion of copper into the oxide film. The film thickness is 20-100 nm. The third interconnect is formed at a position separated by a prescribed distance from the lead-out interconnects and is therefore shown by broken lines inFIG. 9A.

Next, as shown inFIG. 9B, first interconnect245and second interconnect246are formed on fourth protective insulating film220separated by the above-described micro distance as in the second embodiment.

Fourth interlayer insulating film221and fourth stopper insulating film222are successively formed on fourth protective insulating film220. A photoresist is applied to fourth stopper insulating film222and then subjected to an exposure process. The exposed photoresist is then subjected to a developing process to form a photoresist having an aperture. Etching is then carried out though the photoresist to form third aperture247in fourth interlayer insulating film221and fourth stopper insulating film222. The formation of third aperture247exposes a portion of first interconnect245, second interconnect246, and third interconnect236a. The photoresist is then removed, following which cover insulation film214is formed. Anisotropic etching is then carried out to leave cover insulation film214on the side walls of third aperture247(FIG. 9C).

Next, after forming solid electrolyte layer241to bury third aperture247, unnecessary solid electrolyte layer that formed at points outside third aperture247is removed by a CMP method. Fifth protective insulating film223is then formed on fourth stopper insulating film222(FIG. 9D). Fifth protective insulating film223serves the same role of preventing the diffusion of copper as fourth protective insulating film220and is therefore formed of the same material as fourth protective insulating film220.

Solid electrolyte switching element201of the present embodiment is produced by the above-described fabrication method. The method enables the realization of an interconnect construction in which first interconnect245and second interconnect246are embedded in forth protective insulating film220separated by a micro distance that exceeds the limits of lithography. In addition, compared to the second embodiment, the above-described fabrication method facilitates the free control of the distance between third interconnect236athat serves as the gate electrode and first interconnect245that serves as the source electrode and the distance between third interconnect236athat serves as the gate electrode and second interconnect246that serves as the drain electrode.

In addition, because solid electrolyte layer241is formed above first interconnect245, second interconnect246, and third interconnect236a, the locations at which elements can be formed are no longer limited within the interconnect layer, and the degree of freedom of element formation is improved. In particular, elements can be formed after completion of the multilayer interconnect steps. This increased freedom leads to both a reduction of the risk involved in introducing new materials and a reduction of costs. Three-terminal solid electrolyte switching element200that uses the interconnect construction formed by the above-described method was able to repeat stable switching operations.

Further, beginning with the steps for forming third interconnect236a, the large number of steps that can be shared with multilayer interconnect fabrication steps, the minimization of the number of added masks to just two, the suppression of the diffusion of atoms into insulating films, and the measures taken for hydrogen annealing resistance all enable the introduction of this method to a production line at minimal additional cost. As described hereinabove, in the present embodiment, one expert in the art for forming multilayer interconnects of integrated circuits of the related art could easily carry out the above-described steps without requiring special steps.

Fourth Embodiment

Explanation next regards the configuration of the solid electrolyte switching element of the present embodiment.

FIGS. 10A and 10Bshow an example of the configuration of the solid electrolyte switching element of the present embodiment.FIG. 10Ais a plan view, andFIG. 10Bis a sectional view taken along broken line a-a′ shown inFIG. 1A.

Solid electrolyte switching element301of the present embodiment is of a configuration in which the film thickness of the solid electrolyte layer of the third embodiment has been made thinner than in the third embodiment. In the present embodiment, the film thickness of the solid electrolyte layer can be controlled. In addition, first interconnect layer303corresponds to first interconnect layer203of the third embodiment, first insulating layer304corresponds to first insulating layer204, second interconnect layer305corresponds to second interconnect layer205, and protective layer306corresponds to protective layer206. The material and type of film in each layer is the same as in the third embodiment and detailed explanation of these points is therefore omitted.

In the present embodiment, the top surface and side surfaces of solid electrolyte layer341are covered by cover insulation film314. In addition, the points of the bottom surface of solid electrolyte layer341that do not contact either of first interconnect345and second interconnect346are covered by fourth protective insulating film320. Fourth protective insulating film320and cover insulation film314have the function of a metal diffusion prevention film.

The chief operations of solid electrolyte switching element301of the present embodiment are the same as in the first embodiment, and detailed explanation of these operations is therefore here omitted.

In solid electrolyte switching element301of the present embodiment, points of solid electrolyte layer341that do not contact any of first interconnect345, second interconnect346, and the third interconnect are covered by the metal diffusion prevention film of either of fourth protective insulating film320and cover insulation film314, whereby metal ions do not diffuse to surrounding areas. As a result, metal ions can be prevented from adversely affecting neighboring elements, and the solid electrolyte switching element of the present embodiment can therefore be used in circuits that are integrated together with other elements.

The following brief explanation regards the fabrication method of solid electrolyte switching element301of the present embodiment. The fabrication method is the same as in the third embodiment other than the method of forming solid electrolyte layer341, and detailed explanation is therefore here abbreviated.

Following the step shown inFIG. 9B, a solid electrolyte layer is formed to a desired film thickness on fourth protective insulating film320. The solid electrolyte layer is processed to a desired pattern by lithography steps and etching steps to form solid electrolyte layer341shown inFIG. 10A. Cover insulation film314is then formed, following which fourth interlayer insulating film321, fourth stopper insulating film322, and fifth protective insulating film323are formed. In this way, solid electrolyte switching element301shown inFIG. 10Bis produced.

Explanation next regards a configuration in which solid electrolyte switching element301shown inFIGS. 10A and 10Bis applied to an integrated circuit. A via construction for connecting together semiconductor circuits is here shown as one part of the integrated circuit.

FIG. 11is a sectional view showing a solid electrolyte switching element and a via construction. Components that are the same as components shown inFIGS. 10A and 10Bare given the same reference numbers and detailed explanation of these parts is here omitted.

As shown inFIG. 11, the integrated circuit is a construction that includes solid electrolyte switching element301and via construction302for connecting together interconnects. Via construction302corresponds to via construction202of the third embodiment and detailed explanation of this construction is therefore here abbreviated.

The difference between the solid electrolyte switching element of the present embodiment and the third embodiment is the method of processing solid electrolyte layer341. The third embodiment is a configuration in which solid electrolyte layer241is embedded in third aperture247provided in the three layers of fourth protective insulating layer220, fourth interlayer insulating film221, and fourth stopper insulating film222that are formed on second interconnect layer205. In contrast to this configuration, in the present embodiment, the solid electrolyte layer is deposited so as to contact first interconnect345, second interconnect346, and the third interconnect, following which unnecessary points of the solid electrolyte layer are removed to form solid electrolyte layer341as shown inFIGS. 10A,10B, and11.

Compared to the third embodiment, the solid electrolyte switching element of the present embodiment facilitates the control of the film thickness of solid electrolyte layer341. Controlling the film thickness of solid electrolyte layer341enables control over the amount of metal ions supplied to first interconnect345and second interconnect346and thus enables adjustment of the switching characteristics.

In addition, a CMP method is not used in the processing of solid electrolyte layer341, whereby damage to solid electrolyte layer341is reduced and the reliability of the solid electrolyte switching elements in the integrated circuit is increased. In addition, the present embodiment can increase the choices of solid electrolyte layer341that can be used and can therefore realize a reduction of costs.

Fifth Embodiment

Explanation next regards the configuration of the solid electrolyte switching element of the present embodiment.

FIGS. 12A and 12Bshow an example of the configuration of the solid electrolyte switching element of the present embodiment.FIG. 12Ais a plan view, andFIG. 12Bis a sectional view taken along broken line a-a′ shown inFIG. 12A. In the construction shown inFIGS. 12A and 12B, first interconnect layer403corresponds to first interconnect layer303of the fourth embodiment, first insulating layer404corresponds to first insulating layer304, second interconnect layer405corresponds to second interconnect layer305, and protective layer406corresponds to protective layer306. The type and material of films in each layer are the same as in the fourth embodiment and detailed explanation is therefore here omitted.

In solid electrolyte switching element401of the present embodiment, solid electrolyte layer441, first interconnect445, and second interconnect446are provided on second interconnect layer405. In addition, the third interconnect is provided on first insulating layer404. The lead-out interconnects of first interconnect445, second interconnect446, and the third interconnect are provided on first interconnect layer403. The third interconnect is a configuration that includes copper434aand barrier metal433afor preventing the diffusion of copper. In addition, viaplugs for connecting each of first interconnect445and second interconnect446are provided in first insulating layer404.

In the present embodiment, the upper surface and side surfaces of solid electrolyte layer441are covered by cover insulation film414. In addition, points of the bottom surface of solid electrolyte layer441that do not contact either of first interconnect445and second interconnect446are covered by third protective insulating film417. Third protective insulating film417and cover insulation film414have the function of a metal diffusion prevention film.

The chief operations of solid electrolyte switching element401of the present embodiment are the same as in the first embodiment and detailed explanation of these operations is therefore here abbreviated.

In solid electrolyte switching element401of the present embodiment, points of solid electrolyte layer441that do not contact any of first interconnect445, second interconnect446, and the third interconnect are covered by one of the metal diffusion prevention films of third protective insulating film417and cover insulation film414, and metal ions therefore do not diffuse to surrounding areas. As a result, metal ions can be prevented from adversely affecting neighboring elements, and the solid electrolyte switching element of the present embodiment can be used in circuits that are integrated together with other elements.

Explanation next regards a configuration in which solid electrolyte switching element401shown inFIGS. 12A and 12Bis applied to an integrated circuit. A via construction for connecting together semiconductor circuits is here shown as a part of the integrated circuit.

FIG. 13is a sectional view showing a solid electrolyte switching element and a via construction. Components that are the same as components shown inFIGS. 12A and 12Bare given the same reference numbers, and detailed explanation of these components is here omitted.

As shown inFIG. 13, the integrated circuit is of a configuration that includes solid electrolyte switching element401and via construction402for connecting together interconnects. Via construction402includes: first circuit interconnect provided on first interconnect layer403, second circuit interconnect provided on second interconnect layer405, and a viaplug for connecting first circuit interconnect and second circuit interconnect. The viaplug is formed in first insulating layer404. The layer in which this viaplug is formed is referred to as the “via layer.”

Explanation next regards the points of difference between the solid electrolyte switching element of the present embodiment and that of the fourth embodiment. In the fourth embodiment, third interconnect336afor supplying metal ions to solid electrolyte layer341is provided in second interconnect layer305, but in the present embodiment, third interconnect434afor supplying metal ions to solid electrolyte layer441is provided in first insulating layer (via layer)404.

In the solid electrolyte switching element of the present embodiment, the third interconnect is formed in the via layer, whereby adjustment of the size of the via-hole makes control of the total amount of metal ions that can be supplied to solid electrolyte layer441easier than in the fourth embodiment. The switching characteristics can therefore be more easily adjusted. In addition, the metal that can be supplied is confined in the shape of the viaplug, allowing the possibility of using metals other than copper, which is the multilayer interconnect material, and further facilitating the adjustment of switching characteristics through the selection of the type of metal.

Sixth Embodiment

Explanation next regards the configuration of the solid electrolyte switching element of the present invention.

FIGS. 14A and 14Bshow an example of the configuration of the solid electrolyte switching element of the present invention.FIG. 14Ais a plan view andFIG. 14Bis a sectional view taken along broken line a-a′ shown inFIG. 14A. In the construction shown inFIGS. 14A and 14B, first interconnect layer503corresponds to first interconnect layer303of the fourth embodiment, first insulating layer504corresponds to first insulating layer304, second interconnect layer505corresponds to second interconnect layer305, and protective layer506corresponds to protective layer306. The type and material of films in each layer are the same as in the fourth embodiment, and detailed explanation of these points is therefore here abbreviated.

Solid electrolyte switching element501of the present embodiment is of a configuration that includes first interconnect545and solid electrolyte layer541provided on second protective insulating film513; second interconnect provided on first insulating layer504; and third interconnect provided on first interconnect layer503. The third interconnect is of a configuration that includes copper532aand barrier metal531afor preventing the diffusion of copper. The second interconnect is of a configuration that includes copper534and barrier metal533for preventing the diffusion of copper. In the following description, the second interconnect is indicated by reference number533and the third interconnect is indicated by reference number532a.

In the present embodiment, the upper surface and side surfaces of solid electrolyte layer541are covered by cover insulation film514. In addition, points of the bottom surface of solid electrolyte layer541that do not contact either of first interconnect545and third interconnect532aare covered by second protective insulating film513. Second protective insulating film513and cover insulation film514have the function of metal diffusion prevention films.

The chief operations of solid electrolyte switching element501of the present embodiment are the same as in the first embodiment and detailed explanation of these operations is therefore here omitted.

In solid electrolyte switching element501of the present embodiment, points of solid electrolyte layer541that do not contact any of first interconnect545, second interconnect533, and the third interconnect are covered by the metal diffusion prevention films of one of second protective insulating film513and cover insulation film514, and metal ions therefore do not diffuse to surrounding areas. The metal ions can therefore be prevented from adversely affecting neighboring elements, and the solid electrolyte switching element of the present embodiment can be used in circuits that are integrated together with other elements.

Explanation next regards a configuration in which solid electrolyte switching element501shown inFIGS. 14A and 14Bis applied in an integrated circuit. In this case, a via construction for connecting together semiconductor circuits is shown as one part of the integrated circuit.

FIG. 15is a sectional view showing the solid electrolyte switching element and via construction. Components that are the same as components shown inFIGS. 14A and 14Bare given the same reference numbers and detailed explanation of these components is here omitted.

As shown inFIG. 15, the integrated circuit is of a configuration that includes solid electrolyte switching element501and via construction502for connecting together interconnects. Via construction502includes a first circuit interconnect provided in first interconnect layer503, a second circuit interconnect provided in second interconnect layer505, and a viaplug for connecting the first circuit interconnect and the second circuit interconnect. The viaplug is formed in first insulating layer504. The layer in which this viaplug is formed is referred to as the “via layer.”

Explanation next regards the points of difference between the solid electrolyte switching element of the present embodiment and the first to fifth embodiments. The biggest difference is the method of forming the spacing between the first interconnect and the second interconnect. A comparison will be made with the first embodiment, which is taken as a representative example from among the first to fifth embodiments. In the first embodiment, first interconnect14and second interconnect15are formed on insulating layer11separated by a minute spacing. In the present embodiment, in contrast, first interconnect545and second interconnect533are separated by solid electrolyte layer541. In the present embodiment, first interconnect545is formed on second protective insulating film513, and second interconnect533is formed on the three insulating films of cover insulation film514, second interlayer insulating film515, and second stopper insulating film516. First interconnect545and second interconnect533are formed sandwiching solid electrolyte layer541. In addition, third interconnect532ais formed of a material that can supply metal ions. Thus, when transitioning from the OFF state to the ON state, metal ions diffuse into solid electrolyte layer541from third interconnect532aand precipitate between first interconnect545and second interconnect533, whereby solid electrolyte switching element501switches from the OFF state to the ON state.

Compared with the first to fifth embodiments, the solid electrolyte switching element of the present embodiment allows control of the spacing between first interconnect and second interconnect by the film thickness of solid electrolyte layer541.

The layer interposed between first interconnect545and second interconnect533may also be a spacer layer made up by an insulating film that contains a solid electrolyte. As the functions of the inserted spacer layer, the spacer layer should be able to electrically isolate first interconnect545and second interconnect533, and further, form a precipitate at the point at which first interconnect545and second interconnect533contact the solid electrolyte layer.

The following brief explanation regards the fabrication method of the solid electrolyte switching element of the present embodiment. Detailed explanation regarding steps that are the same as steps in the second embodiment and the third embodiment is here omitted.

Three insulating films that make up first insulating layer503are formed on a substrate (not shown) on which an insulating film has been formed on the uppermost layer. As in the second embodiment, a lead-out interconnect and third interconnect532aare formed in the solid electrolyte switching element formation region, and a first circuit interconnect is formed in the via construction502formation region. The lead-out interconnect includes copper532and barrier metal531, and the third interconnect includes copper532aand barrier metal531a.

Second protective insulating film513is next formed on first interconnect layer503. Second protective insulating film513is formed from silicon nitride or a material in which any amount of carbon is mixed in silicon nitride. Second protective insulating film513suppresses the diffusion of copper into the oxide film. The film thickness is 20-100 nm. First interconnect545that contacts the lead-out interconnect is then formed on second protective insulating film513as in the second embodiment.

An aperture is then provided in second protective insulating film513on third interconnect532aby lithography and etching steps to expose a portion of third interconnect532a, which supplies metal ions to solid electrolyte layer541. After next depositing a solid electrolyte layer, solid electrolyte layer541as shown inFIGS. 14A and 14Bis formed by carrying out lithography and etching steps. Cover insulation film514is then deposited to completely cover solid electrolyte layer541and second protective insulating film513. Cover insulation film514is formed from silicon nitride or a material in which any amount of carbon is mixed with silicon nitride. Cover insulation film514suppresses the diffusion of copper into the oxide film. Second interlayer insulating film515and second stopper insulating film516are then deposited on cover insulation film514.

An aperture is next formed by means of lithography steps and etching steps in cover insulation film514, second interlayer insulating film515, and second stopper insulating film516, and the second interconnect is formed in this aperture as in the second embodiment. The second interconnect is of a configuration that includes copper534and barrier metal533. Barrier metal533covers the bottom surface and side surfaces of copper534. In forming the second interconnect, the second interconnect is arranged at a position to confront first interconnect545with solid electrolyte541interposed. Then, as in the second embodiment, the lead-out interconnect of the second interconnect is formed in the solid electrolyte switching element501formation region, and protective layer506is formed.

Solid electrolyte switching element501of the present embodiment is produced by the above-described fabrication method. Making the film thickness of the solid electrolyte layer thinner than the minimum value of the limits of lithography allows the realization of an interconnect construction in which first interconnect545and second interconnect533are each formed on separate insulating films and are separated by a minute distance that surpasses the limits of lithography. The component that separates first interconnect545and second interconnect533is solid electrolyte layer541. The spacing between the first interconnect and the second interconnect that are separated by a micro spacing can be realized by merely controlling the film thickness of solid electrolyte layer541. The setting of the spacing by film thickness control is easier than control by means of dry etching as in the first embodiment and results in a reduction of variations in fabrication as well as an increase production yield of solid electrolyte switching elements in integrated circuits.

In addition, the present embodiment facilitates the free control of both the distance between third interconnect532a, which is the gate electrode, and first interconnect545, which is the source electrode, and the distance between third interconnect532a, which is the gate electrode, and second interconnect533, which is the drain electrode. Metal ions supplied from third interconnect532adiffuse over this distance, and control of this distance therefore can determine the switching characteristics. The present embodiment thus enables control of the characteristics of the solid electrolyte switching element in an integrated circuit. In particular, making the distance from third interconnect532ato first interconnect545and second interconnect533greater than in the related art is effective for preventing the occurrence of switching from the OFF state to the ON state. As a result, solid electrolyte switching element501can achieve greater stability in repeated switching operations.

Beginning with the formation steps of third interconnect532aand second interconnect533, the great number of steps that can be shared with the multilayer interconnect formation steps, the suppression of the diffusion of atoms into insulating films and the implementation of measures for hydrogen annealing resistance all enable introduction of the present invention to a production line at minimal additional cost. As described hereinabove, one versed in the art of forming multilayer interconnects of integrated circuits of the related art could easily carry out the above-described steps in the present embodiment without requiring special steps.

In addition, although explanation in the above-described first to sixth embodiments regarded cases in which the first interconnect was taken as the source electrode and the second interconnect was taken as the drain electrode, the second interconnect may be taken as the source electrode and the first interconnect may be taken as the drain electrode.

Finally, the present invention is not limited by any of the above-described embodiments and is open to various modifications within the scope of the invention, these modifications obviously being included within the scope of the present invention.