Patent Application
20230060860
The present invention generally relates to a resistive memory device, and more specifically, a non-volatile resistive memory device and its production method.
OxRRAM (Oxide-Based Resistive Random Access Memories)-type resistive memories are currently developed for non-volatile applications, with the aim of replacing Flash-type memories. They have, in particular, the advantage of being able to be integrated into interconnecting lines at BEOL (Back-End Of Line)-level of CMOS (Complementary Metal-Oxide-Semiconductor) transistor-based technology. OxRRAM resistive memories are devices comprising, in particular, a metal-oxide layer disposed between two electrodes. The electrical resistance of these devices can be modified by writing and deleting operations. These writing and deleting operations make it possible to make the OxRRAM resistive memory device pass from an LRS (Low Resistive State) to an HRS (High Resistive State), and vice versa.
From cycle to cycle, the resistances of low resistive states LRS and high resistive states HRS do not show a very good reproducibility of performances. A variability of the cycle-to-cycle performances is indeed observed. This variability is particularly important for the high resistive state HRS, inducing a decrease in the programming window, even a total loss of the programming window. This variability problem is today an obstacle to industrialisation.
This concern remains, despite numerous efforts made in the fields of methods for producing resistive memory devices and programming methods.
In a conventional configuration of the resistive memory device, the metal-oxide layer is sandwiched between a first electrode, also called lower electrode, and a second electrode, also called upper electrode.
It has been shown that the lateral reduction of the dimensions of this stack makes it possible to reduce the variability of the electrical performances. This makes it possible, in particular, to limit and to localise the passage of the current through a so-called filamentary or filament zone. The conduction through the metal-oxide layer is thus facilitated.
To contain the filament in a determined zone of reduced width of the metal-oxide layer, a solution consists of only reducing the width of one of the lower or upper electrodes of the stack.
Document US2020/0127197 A1 discloses a resistive memory device formation comprising an upper electrode, reduced in width. A disadvantage of this device and of this formation method is that the reduced size of the upper electrode causes problems in making contact on this upper electrode. The implementation of the device is difficult. It thus appears that other complex and expensive steps are necessary to obtain a device architecture which is utilisable in practice.
An aim of the present invention is to overcome at least partially the disadvantages mentioned above.
An aim of the present invention is to propose a resistive memory device having a reduced HRS variability and which is easy to implement.
Another aim of the present invention is to propose a method for manufacturing such a resistive memory device, having a limited number of steps.
Other aims, features and advantages of the present invention will appear upon examining the following description and the accompanying drawings. It is understood that other advantages can be incorporated.
To achieve this aim, according to an embodiment, a method for producing a resistive memory device comprising at least one first electrode and one second electrode material-based electrode is provided, and a metal-oxide layer interleaved between said first and second electrodes in a so-called vertical direction. The device has at least one dimension in width L, preferably greater than or equal to 30 nm in a so-called horizontal direction of a plane perpendicular to the vertical direction.
Advantageously, at least one from among the first and the second electrode is formed so as to comprise an interlayer material-based electrode interlayer having a selectivity S to etching greater than or equal to 2:1, and preferably greater than or equal to 3:1, vis-à-vis electrode materials. 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.
The method further comprises, after formation of said at least one from among the first and the second electrode comprising the electrode interlayer, 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, and preferably greater than or equal to 10 nm, vis-à-vis the at least one direction in width L, said lateral recess being preferably less than or equal to ⅙*L.
The overetching step thus makes it possible to only reduce a dimension in width Lc of the electrode interlayer, without reducing the dimension in width L of the device. Only one part of the electrode is thus reduced in width, which enables both to localise the creation of the conductive filament during the operation of the resistive memory device, while enabling a good making of contact on another part of the electrode, the dimension in width L of which has not been reduced. In particular, the width of the electrode is reduced in a localised manner, at the interlayer, without the electrode being reduced at the top of the device. The localisation effect of the filament is thus obtained without complexifying the making of contact on the device. By localising the filament by lateral recess, the HRS variability is reduced. Moreover, a lateral recess less than or equal to ⅙*L makes it possible to preserve a formation voltage of the filament, called “forming” voltage, not too high, typically less than 3V, even 2.5V.
A good compromise between the localisation of the filament and the forming voltage is thus obtained. This type of compromise is specific to OxRRAM-type resistive memory devices, and cannot be deduced from solutions implemented for other types of memory, in particular PCRAMs (Phase Change Random Access Memories).
The selectivity S to etching corresponds here to the difference in etching speed between the interlayer material and the electrode materials, during overetching. A selectivity S≥2:1 or S≥3:1 makes it possible de facto to obtain a more significant lateral recess at the electrode interlayer during overetching. The parameters of the overetching step are chosen here, in accordance with the selectivity S, so as to enable a lateral recess of the electrode interlayer of at least 10 nm during overetching.
In the scope of development of the present invention, it has been observed that the perimeter of the device, also called memory point, has after etching, typically of numerous singularities subsequently inducing a random creation of the conductive filament. These singularities extend from the edge of the device over around 2 to 5 nm in the horizontal direction. Thus, a slight involuntary lateral recess which could occur during an etching of the memory point is not sufficient to avoid the impact of the singularities at the periphery of the memory point.
On the contrary, the lateral recess according to the invention is voluntarily done over more than 5 nm and preferably over at least 10 nm to divert the electrode interlayer so as to avoid singularities at the periphery of the memory point. This makes it possible to localise in a controlled and reproducible manner, the creation of the conductive filament during later operating phases of the resistive memory device. This makes it possible to limit the variability of the high resistive state HRS. The programming window of the resistive memory device is stabilised.
Moreover, the overetching step makes it possible to limit the number of total steps of the method. It is not, for example, necessary to provide additional lithography steps. The overetching step can be advantageously carried out in extension and in the continuity of an etching making it possible to obtain a width L device.
According to another embodiment, a resistive memory device is provided, comprising at least one first electrode and one second electrode material-based electrode, and a metal-oxide layer interleaved between said first and second electrodes in a so-called vertical direction. The device has at least one dimension in width L, preferably greater than or equal to 30 nm, in a so-called horizontal direction of a plane perpendicular to the vertical direction.
Advantageously, at least one from among the first and second electrodes comprises an interlayer material-based electrode interlayer having a selectivity to etching greater than or equal to 2:1, and preferably greater than or equal to 3:1, vis-à-vis the electrode materials. 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.
Advantageously, the electrode interlayer has a lateral recess strictly greater than 5 nm, preferably greater than or equal to 10 nm, vis-à-vis of the at least one direction in width L of the device, said lateral recess being less than or equal to ⅙*L.
Thus, at least one electrode of the device comprises materials having different etching speeds. This differentiation makes it possible to facilitate the production of the device, and in particular to obtain a lateral recess within the electrode, at the interlayer.
The device has a lateral recess at the electrode interlayer of at least 5 nm even of at least 10 nm. An electrode of the device thus advantageously has at least one dimension in width Lc strictly less than the dimension L, partially defined by the lateral recess. The smallest dimension in width of the electrode thus corresponds to the dimension Lc of the electrode interlayer. This advantageously makes it possible to limit the formation of the conductive filament in a localised zone of the metal-oxide layer during the operation of the resistive memory device. The HRS variability is thus reduced. A lateral recess less than or equal to ⅙*L further makes it possible to preserve a correct forming voltage, typically less than 3V even 2.5V. The greatest dimension in width of at least one of the electrodes corresponds to the dimension L of the device. This advantageously makes it possible to facilitate the making of contact for the later connection of the resistive memory device.
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:
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.
Before starting a detailed review of embodiments of the invention, below are stated optional features which can possibly be used in association or alternatively:
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.
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.
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.
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.
According to an example, the overetching is done in continuity of the etching of the stack, by extending a duration of said etching.
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.
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.
According to an example, the interlayer material has an Aluminium percentage greater than or equal to 25 at. % (atomic percentage).
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.
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.
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.
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.
According to an example, the electrode interlayer is directly in contact with the metal-oxide layer.
According to an example, the metal-oxide layer forms an overhang or a step with the electrode interlayer.
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.
According to an example, the electrode interlayer itself forms the at least one electrode from among the first and second electrodes.
According to an example, the at least one electrode from among the first and second electrodes is only constituted of the electrode interlayer.
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.
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.
A layer can moreover be composed of several underlayers of one same material or of different materials.
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.
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.
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.
Moreover, the term “step” means the embodiment of a part of the method, and can mean a set of sub-steps.
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.
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.
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.
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.
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.
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.
The resistive memory device is typically formed during so-called BEOL end-of-line technological steps. Thus, as illustrated in
As illustrated in
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.
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.
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.
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.
As illustrated in
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.
As illustrated in
The device 1 illustrated in
Other embodiments of the device and of the method according to the invention can be considered.
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.
According to an example of an embodiment illustrated in
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.
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.
The invention is not limited to the embodiments described above.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21 08067 | Aug 2021 | FR | national |
