RESISTIVE MEMORY DEVICE AND PRODUCTION METHOD

Abstract

A method for producing a resistive memory cell from a stack of layers having a metal-oxide layer interleaved between first and second electrodes includes forming, within one from among the first and second electrodes, an interlayer material-based electrode interlayer having a selectivity to etching greater than or equal to 2:1 relative to materials of the electrodes. During an etching of the stack, overetching is performed configured to laterally consume, in a horizontal direction, the interlayer material such that the electrode interlayer has a lateral recess greater than or equal to 10 nm.

Claims

1. A method for producing a resistive memory device comprising at least one first electrode and one second electrode based on electrode materials, and a metal-oxide layer interleaved between said first and second electrodes in a vertical direction, said device having at least one width L greater than or equal to 30 nm in a horizontal direction of a plane perpendicular to the vertical direction (z), the method comprising: forming at least one from among the first and second electrodes so as to comprise an electrode interlayer based on an interlayer material having a selectivity to etching greater than or equal to 2:1 vis-à-vis the electrode materials, the electrode materials being transition metal-based, and the interlayer material being aluminium alloy-based and of said transition metal or of another transition metal, and after formation of said at least one from among the first and second electrodes comprising the electrode interlayer, performing an overetching configured to laterally consume, in the horizontal direction, the interlayer material such that the electrode interlayer has a lateral recess strictly greater than 5 nm vis-à-vis the at least one width L, said lateral recess being less than or equal to ⅙*L.

2. The method according to claim 1, wherein forming the at least one from among the first and second electrodes comprising the electrode interlayer such that the electrode interlayer is directly in contact with the metal-oxide layer.

3. The method according to claim 1, wherein the overetching is performed using chlorinated chemistry-based plasma.

4. The method according to claim 1, wherein the overetching is isotropic, such that the lateral recess is formed over a whole perimeter of the electrode interlayer projecting into the plane.

5. The method according to claim 1, wherein the electrode interlayer has a thickness between 5 nm and 50 nm.

6. The method according to claim 1, wherein the metal-oxide layer is HfO.sub.2-based, the electrode materials are Ti- or TiN-based, and the interlayer material is Ti.sub.xAl.sub.y-based, with x, y>0.

7. A resistive memory device comprising: at least one first electrode and one second electrode based on electrode materials, and a metal-oxide layer disposed between said first and second electrodes in a vertical direction, said device having at least one width L greater than or equal to 30 nm in a horizontal direction of a plane perpendicular to the vertical direction, wherein at least one from among the first and second electrodes comprises an electrode interlayer based on an interlayer material having a selectivity to etching greater than or equal to 2:1, vis-à-vis the electrode materials, the electrode materials being transition metal-based, and the interlayer material being aluminium alloy-based and of said transition metal or of another transition metal, and the electrode interlayer has a lateral recess strictly greater than 5 nm vis-à-vis the at least one direction in width L, said lateral recess being less than or equal to ⅙*L.

8. The device according to claim 7, wherein the lateral recess extends over a whole perimeter of the electrode interlayer, such that said electrode interlayer is substantially centred vis-à-vis the device, projecting into the plane.

9. The device according to claim 7, wherein the electrode interlayer is directly in contact with the metal-oxide layer.

10. The device according to claim of 7, wherein the metal-oxide layer extends projecting with respect to the electrode interlayer in a direction of the plane.

11. The device according to claim 7, wherein the second electrode comprises a Ti-based oxygen trapping layer.

12. The device according to claim 7, wherein the electrode materials are TiN-based, the metal-oxide layer is HfO.sub.2-based, the interlayer material is Ti.sub.xAl.sub.y-based, with x, y>0.

13. The device according to claim 7, wherein the at least one electrode from among the first and second electrodes is only constituted of the electrode interlayer.

14. The device according to claim 7, wherein the interlayer material has an aluminium percentage greater than or equal to 25 at. %.

15. The device according to claim 7, wherein the selectivity to etching is greater than or equal to 3:1.

16. The device according to claim 7, wherein the electrode interlayer has a lateral recess strictly greater than 10 nm.

17. The method according to claim 1, wherein the selectivity to etching is greater than or equal to 3:1.

18. The method according to claim 1, comprising performing the overetching to laterally consume, in the horizontal direction, the interlayer material such that the electrode interlayer has a lateral recess strictly greater than 10 nm.

19. The method according to claim 1, wherein the electrode interlayer has a thickness between 5 nm and 15 nm.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0027] The aims, objective, as well as the features and advantages of the invention, will emerge best from the detailed description of embodiments of the latter which are illustrated by the following accompanying drawings, wherein:

[0028] FIGS. 1 to 5 schematically illustrate steps of producing a resistive memory device, according to an embodiment of the present invention.

[0029] FIG. 6 is an enlargement of the device undergoing manufacture illustrated in FIG. 5.

[0030] FIGS. 7 and 8 schematically illustrate steps of producing a resistive memory device, according to an embodiment of the present invention.

[0031] FIG. 9 illustrates a device according to another embodiment of the present invention.

[0032] FIG. 10 illustrates a device according to another embodiment of the present invention.

[0033] The drawings are given as examples and are not limiting of the invention. They constitute principle schematic representations intended to facilitate the understanding of the invention and are not necessarily to the scale of practical applications. In particular, on the principle diagrams, the thicknesses of the different layers and portions, and the dimensions of the patterns are not representative of reality.

DETAILED DESCRIPTION

[0034] Before starting a detailed review of embodiments of the invention, below are stated optional features which can possibly be used in association or alternatively:

[0035] According to an example, the formation of said at least one from among the first and second electrodes comprising the electrode interlayer is configured such that the electrode interlayer is directly in contact with the metal-oxide layer.

[0036] According to an example, the electrode interlayer is formed directly in contact with the metal-oxide layer. Alternatively, the electrode which comprises the electrode interlayer also comprises an electrode portion located between the interlayer and the metal-oxide layer. Thus, the electrode interlayer is not in direct contact with the metal-oxide layer.

[0037] According to an example, the etching of the stack and/or the overetching are done by chlorinated chemistry-based plasma. According to another example, the plasma can be fluorinated chemistry-based, or brominated, or iodinated.

[0038] According to an example, during the etching of the stack, at least the first electrode, the second electrode and the metal-oxide layer are etched, preferably on all their respective thicknesses.

[0039] According to an example, the overetching is done in continuity of the etching of the stack, by extending a duration of said etching.

[0040] According to an example, the first electrode and the second electrode are with the basis, even are made, of the same material. According to another example, the first electrode and the second electrode are with the basis, even are made of, different materials.

[0041] The electrode materials are transition metal-based, and the interlayer material is aluminium alloy-based and of said transition metal or of another transition metal. For example, the electrode materials are made of TaN or TiN. According to an example, the transition metal is taken from among Ti, Zr, Hf, Ta, W. The interlayer material is made of TixAly, or ZrxAly, or HfxAly, or TaxAly, or WxAly, with x, y>0.

[0042] According to an example, the interlayer material has an Aluminium percentage greater than or equal to 25 at. % (atomic percentage).

[0043] According to an example, only the electrode which comprises the electrode interlayer is transition metal-based. The other electrode can be made of another electrically conductive material. “The electrode comprises the interlayer” can mean that the electrode is in contact with the interlayer or that the electrode is constituted, possibly only, of the interlayer. According to an example, the electrode material is TiN-based and the interlayer is ZrAl-based.

[0044] According to an example, the overetching is isotropic, such that the lateral recess is formed over a whole perimeter of the electrode interlayer, said electrode interlayer being preferably substantially centred vis-à-vis the device or the stack, projecting into the plane xy.

[0045] According to an example, the electrode interlayer has a thickness of between 5 nm and 50 nm, preferably between 5 nm and 30 nm, preferably between 5 nm and 15 nm.

[0046] According to an example, the metal-oxide layer is HfO2-based, the electrode materials are Ti- or TiN-based, the interlayer material is TixAly-based, with x, y>0.

[0047] According to an example, the electrode interlayer is directly in contact with the metal-oxide layer.

[0048] According to an example, the metal-oxide layer forms an overhang or a step with the electrode interlayer.

[0049] According to an example, the second electrode comprises a Ti-based oxygen trapping layer. According to an example, the oxygen trapping layer is Hf-based.

[0050] According to an example, the electrode interlayer itself forms the at least one electrode from among the first and second electrodes.

[0051] According to an example, the at least one electrode from among the first and second electrodes is only constituted of the electrode interlayer.

[0052] Except for incompatibility, it is understood that all of the optional features above can be combined so as to form an embodiment which is not necessarily illustrated or described. Such an embodiment is clearly not excluded from the invention.

[0053] It is specified that, in the scope of the present invention, the terms “on”, “surmounts”, “covers”, “underlying”, “vis-à-vis” and their equivalents do not necessarily mean “in contact with”. Thus, for example, the deposition of a first layer on a second layer, does not mean compulsorily that the two layers are directly in contact with one another, but means that the first layer covers at least partially the second layer by being either directly in contact with it, or by being separated by it by at least one other layer or at least one other element.

[0054] A layer can moreover be composed of several underlayers of one same material or of different materials.

[0055] By a substrate, a stack, a layer “based on a material A or “A-based”, this means a substrate, a stack, a layer comprising this material A only or this material A and possibly other materials, for example alloy elements and/or doping elements. Thus, a silicon-based layer means, for example, an Si, n-doped Si, p-doped Si, SiGe layer. A germanium-based layer means, for example, a Ge, n-doped Ge, p-doped Ge, SiGe layer.

[0056] By “selective etching vis-a-vis” or “etching having a selectivity vis-à-vis”, this means an etching configured to remove a material A or a layer A vis-à-vis a material B or a layer B, and having an etching speed of the material A greater than the etching speed of the material B. The selectivity is the ratio between the etching speed of the material A and the etching speed of the material B.

[0057] Several embodiments of the invention implementing successive steps of the manufacturing method are described below. Except mentioned otherwise, the adjective “successive” does not necessarily imply, even if this is generally preferred, that the steps follow one another immediately, intermediate steps being able to separate them.

[0058] Moreover, the term “step” means the embodiment of a part of the method, and can mean a set of sub-steps.

[0059] Moreover, the term “step” does not compulsorily mean that the actions carried out during a step are simultaneous or immediately successive. Certain actions of a first step can, in particular, be followed by actions linked to a different step, and other actions of the first step can then be resumed. Thus, the term step does not necessarily extend from single and inseparable actions over time and in the sequence of phases of the method.

[0060] A preferably orthonormal marker, comprising the axes x, y, z is represented in the appended figures. When one single marker is represented on one same set of figures, this marker applies to all figures of this set.

[0061] In the present patent application, the thickness of a layer is taken in a direction normal to the main extension plane of the layer. Thus, a layer typically has a thickness along z. The relative terms “on”, “surmounts”, “under”, “underlying”, “interleaved” refer to positions taken in the direction z.

[0062] The terms “vertical”, “vertically” refer to a direction along z. The terms “horizontal”, “horizontally”, “lateral”, “laterally” refer to a direction in the plane xy. Unless explicitly mentioned otherwise, the thickness, the height and the depth are measured along z.

[0063] An element located “in vertical alignment with” or “in line with” another element means that these two elements are both located on one same line perpendicular to a plane wherein mainly extends a lower or upper face of a substrate, i.e. on one same line oriented vertically in the figures.

[0064] In the scope of the present invention, by horizontal recess or lateral recess, this means a remove of material from a face substantially perpendicular to the plane xy, in a direction normal to this face. The lateral recess of a layer typically forms a step or an overhang vis-à-vis other layers below or above, respectively. The lateral recess can be formed on only one part of the perimeter of the electrode interlayer. The lateral recess can be formed over the whole perimeter of the electrode interlayer. In this latter case, along a transverse cross-section, a lateral recess of each side of the electrode interlayer is observed, that is two lateral recess (which are, in reality, two parts of the same lateral recess). Each lateral recess is thus strictly greater than 5 nm, such that the sum of the lateral recess which can be seen as a transverse cross-section is strictly greater than 10 nm. The lateral recess value is taken locally at the level of said lateral recess. This value does not correspond to the total value of the visible lateral recess, but to each of the visible lateral recess.

[0065] FIGS. 1 to 8 illustrate an embodiment of the method for manufacturing the resistive memory device according to the invention. In the illustrated examples, the resistive memory device takes the form of a memory point of width L. This memory point can be likened to a vertical cylinder comprising the first and second electrodes and the metal-oxide layer. It is typically formed from a stack of layers, by deposition, lithography, etching steps. These different steps are detailed below. Other forms of memory point or of resistive memory device can be fully considered, for example a cube or a parallelepiped. According to a principle of the invention, an interlayer material-based electrode interlayer is inserted in the stack of the memory point, above or below the metal-oxide layer. The electrode, metal-oxide and interlayer materials are preferably chosen such that, under given etching conditions, the etching speed of the interlayer material is greater than the etching speed of the electrode materials, and the etching speed of the electrode materials is greater than the etching speed of metal-oxide. This makes it possible to obtain a narrowing of the memory point at the electrode interlayer.

[0066] The resistive memory device is typically formed during so-called BEOL end-of-line technological steps. Thus, as illustrated in FIG. 1, a substrate supporting different metal and via levels is provided. In FIG. 1 of illustration, only the last metal and via levels are represented. The metal level 100 typically comprises metal lines 102 insulated against one another by a dielectric material 101, typically SiO2. The interconnection level 200 typically comprises through vias 202 insulated from one another by a dielectric material 201, typically SiN. The vias 202 typically have a dimension in width Lv along x. The width Lv of the vias 202 is typically between a few tens of nanometres and a few hundred nanometres, for example between 5 and 1000 nanometres, preferably between 10 and 500 nm. A face 210 of the last level 200 is exposed.

[0067] As illustrated in FIG. 2, a stack of layers is formed on the exposed face 210. In this example, a first electrode 10, also called lower electrode, is deposited directly in contact with the face 210. This electrode 10 is here fully formed by the electrode interlayer 40. It is preferably TixAly-based, with x, y>0, for example TiAl.sub.0.3. The Aluminium percentage of the interlayer 40 can vary, for example between 1% and 99%. Advantageously, the Aluminium percentage of the interlayer is greater than or equal to 25%. This makes it possible to ensure an auto-passivation of this interlayer. The oxygen absorption at the core of the interlayer is thus avoided. This makes it possible to obtain a low and homogenous electrical resistivity for the interlayer. The HRS and/or LRS variability is thus reduced. Zr, Hf, Ta, W can be used in replacement of Ti in the aluminium alloy of the interlayer 40. A metal-oxide layer 30, generally called TMO (Transition Metal Oxide), is then deposited above the electrode interlayer 40. This metal-oxide layer 30 is preferably HfO2-based. A second electrode 20, also called upper electrode, is then formed on the metal-oxide layer 30. This second electrode 20 typically comprises an oxygen trapping layer 21, for example titanium-based, and an electrode layer 22, for example TiN- or TaN-based. The oxygen trapping layer 21 can be directly in contact with the metal-oxide layer 30, as illustrated in FIG. 2. The thickness of the TixAly layer 40 is preferably between 5 nm and 50 nm. The thickness of the HfO2-based metal-oxide layer 30 is preferably between 5 and 15 nm. The thickness of the Ti-based oxygen trapping layer 21 is preferably between 5 and 15 nm. The thickness of the TiN-based electrode layer 22 is preferably between 20 nm and 100 nm.

[0068] According to a possibility, the electrode interlayer 40 is formed by a Ti/TixAly or TixAly/Ti bilayer, the total thickness of the two layers being between 5 nm and 15 nm.

[0069] FIG. 3 illustrates a lithography step carried out prior to the etching of the stack of electrode and metal-oxide layers. A resin pattern 60 is formed in vertical alignment with the via 202, for example such that said pattern 60 is centred vis-à-vis the via 202, projecting into the plane xy. This pattern 60 defines the shape and the dimensions, projecting into the plane xy, from the desired memory point. It typically has a dimension in width L. A hard mask layer 50, for example SiN- or SiO2-based, can be deposited on the upper electrode 20 before formation of the pattern 60. In a known manner, such an optional layer 50 makes it possible to transfer more faithfully the shape and the dimensions of the pattern 60 in the stack of underlying layers 10, 20, 30, during the following etching. This layer 50 also makes it possible to protect the stack during certain steps, during the resin recess step, commonly referenced by “stripping”.

[0070] FIG. 4 illustrates the etching of the stack of layers 20, 30, 10, respectively. In this example, the hard mask 50 of width L is represented. Conventionally, the layer 50 is first etched anisotropically along z. The resin pattern 60 is thus removed. Then, all of the stack of the layers 20, 30, 10 is etched anisotropically along z.

[0071] This latter etching is done, preferably by chlorinated chemistry plasma. This makes it possible to obtain a stack of width L, comprising, from the face 210, a TixAly-based electrode interlayer 40 forming the lower electrode 10, an HfO2-based metal-oxide layer 30, a Ti-based oxygen trapping layer 21, a TiN-based upper electrode layer 22. Stopping the etching is done, preferably on the exposed via 202, at the face 210.

[0072] FIG. 5 illustrates an overetching step making it possible to reduce in width the electrode interlayer 40 only, by preserving the dimension L for the other layers 30, 21, 22 of the stack. During the overetching, the TixAly-based electrode interlayer 40 is etched laterally, along x as a cross-section in FIG. 5, until obtaining a layer 40 of dimension Lc. The overetching is done, typically on either side of the flanks of the stack, such that the layer 40 remains roughly centred vis-à-vis the other layers 30, 21, 22 of the stack. During the subsequent operation of the device, the conductive filament will be formed in a central zone of the metal-oxide layer 30. The reproducibility of formation of the filament during the operation of the device is thus improved. The endurance of the device will thus be improved.

[0073] A lateral recess is thus obtained on each side of the layer 40. The overetching is configured such that this lateral recess reaches at least 10 nm along x, on each side of the layer 40. With such a lateral recess, the presence of roughness on the flanks of the upper electrode 20 will no longer be problematic during the creation of the conductive filament. The duration of the overetching can, in particular, be adjusted according to the desired lateral recess. According to an example, the parameters of the overetching are substantially the same as those of the etching. According to another possibility, the parameters of the overetching are modified, for example such that the isotropy of the overetching is increased.

[0074] FIG. 6 schematically illustrates the memory point 1 obtained from the overetching. In this example, the lateral recess 41 each have a dimension L.sub.R≤10 nm along x. The dimension Lc of the interlayer 40 is equal to L−2.L.sub.R. The layer 30 here forms an overhang above the lateral recess 41. During subsequent steps of packaging and of operating the device 1, the conductive filament will be formed in the central zone S of the layer 30. The conductive filament can be formed anywhere in the central zone S of the layer 30, for example on an edge of this central zone S.

[0075] This strategy therefore makes it possible to reduce the dimensions which appear or which are useful from the memory point, without imposing an additional dimensional limitation for making contact on the memory point, of dimension L.

[0076] As illustrated in FIG. 7, the memory point is then encapsulated by one or more dielectric layers, for example by a first SiN layer 301, then by a second SiO2 layer 302. The first SiN layer 301 has, for example, a thickness of 30 nm. It is deposited in a conform manner on the memory point. The SiO2 layer 302 can have a thickness of 300 nm. These layers 301, 302 form a dielectric encapsulation layer 300 around the memory point. According to an alternative possibility, this dielectric encapsulation level 300 can be formed by one single layer, for example by an SiO2-based layer.

[0077] After deposition of the dielectric layer(s) 301, 302, a planarisation step, for example by mechanical-chemical polishing, is carried out so as to expose an upper face 220 of the upper electrode 20.

[0078] As illustrated in FIG. 8, levels of via 400 and of metal 500 are then formed after the planarisation step. This makes it possible to form a metal contact on the memory point 1. The interconnection level 400 typically comprises through vias 402 insulated from one another by a dielectric material 401, typically of SiN. The via(s) 402 is/are preferably centred vis-à-vis the upper electrode 20 of the memory point 1. The metal level 500 typically comprises metal lines 502 insulated from one another by a dielectric material 501, typically of SiO2.

[0079] The device 1 illustrated in FIG. 8 is thus fully operational. The top contact formed by the via 402 and the metal line 502, and the bottom contact formed by the via 202 and the metal line 102, can be formed conventionally, without particular dimensional limitations. The device 1 can thus be carried out by standard technological microelectronic steps. The introduction of an interlayer within an electrode of the memory point, coupled with the production of a selective overetching of this interlayer, makes it possible to reduce the apparent dimensions of the memory point in vertical alignment with a central zone of the metal-oxide layer of the memory point. Thus, in operation, the conductive filament will be advantageously formed in a localised and reproducible manner at this central zone.

[0080] Other embodiments of the device and of the method according to the invention can be considered.

[0081] FIG. 9 illustrates a possibility wherein the interlayer 40 is formed within the upper electrode 20, for example within the TiN-based electrode layer 22. The TixAly-based interlayer 40 can thus be located between an upper portion 22a and a lower portion 22b of the upper electrode 22. In this example, the interlayer 40 is not in direct contact with the metal-oxide layer 30.

[0082] When the interlayer 40 is located within the upper electrode 20, the metal-oxide layer 30 and/or the lower electrode 10 of the stack do not necessarily have the same dimension in width L as the upper electrode 20.

[0083] According to an example of an embodiment illustrated in FIG. 10, the lower electrode 10 is directly formed by the TIN via 202. The metal-oxide layer 30 is therefore deposited directly on the via 202. The etching of the stack is limited to the upper electrode 20. The metal-oxide layer 30 is therefore not reduced in dimensions in the plane xy. In this example, the interlayer 40 is formed within the upper electrode, directly in contact with the metal-oxide layer 30. It is substituted, for example, for the oxygen trapping layer 21 of the upper electrode 20.

[0084] Numerous stack configurations including an interlayer 40 forming a narrowing in one and/or the other of the lower 10 and upper 20 electrodes of the resistive memory device 1 are possible. These variants are not necessarily illustrated, but can be easily deduced by combination of the features of the embodiments described.

[0085] In any case, such a narrowing formed in the stack makes it possible to localise, in a controlled manner, the formation of the conductive filament in the metal-oxide layer. In particular, the conductive filament is formed in a central zone of the metal-oxide layer located in vertical alignment with the centre of the lower electrode and/or of the upper electrode. This makes it possible to avoid the impact of the edges of the electrodes of the memory point, on the formation of the conductive filament. The variability on the formation voltage of the conductive filament is thus reduced. The reliability of the memory point is advantageously improved. Furthermore, the memory point can have an apparent dimension Lc of a few tens of nanometres, while enabling a facilitated making of contact.

[0086] The invention is not limited to the embodiments described above.