FERROELECTRIC STORAGE DEVICE AND METHOD FOR MANUFACTURING SUCH A DEVICE

Abstract

The invention relates to a ferroelectric storage device (1) comprising a first layer (2), a second layer (7) and a layer of ferroelectric material (5) which extends between the first layer (2) and the second layer (7), the layer of ferroelectric material (5) comprising a first part (5A) having a first thickness (e1) and a second part (6) having a second thickness (e2), the first thickness (e1) and the second thickness (e2) being distinct. Figure to be published with the abstract: Fig. 2

Description

Title of the invention: FERROELECTRIC STORAGE DEVICE AND METHOD FOR MANUFACTURING SUCH A DEVICE Technical field

[0001] The present invention relates generally to the field of microelectronics. It relates more particularly to the field of non-volatile memories.

[0002] In particular, the invention relates to a ferroelectric storage device. It also relates to a method of manufacturing such a ferroelectric storage device. STATE OF THE ART

[0003] The main quality of ferroelectric memories of the FeRAM type (for "Ferroelectric Random Access Memory" according to the commonly used acronym of Anglo-Saxon origin) is that they are non-volatile, that is to say, they retain the stored information even when the voltage is cut off. They also have the advantages of consuming little energy and having short writing and reading times compared to other types of non-volatile memories such as FLASH memories.

[0004] FeRAM type ferroelectric memories are generally in the form of a stack in which a layer of ferroelectric material is positioned between two metal electrodes. Ferroelectric memories are capacitive type memories having two remanent polarization states +Pr and -Pr. The operation of these ferroelectric memories is based on the ferroelectric properties of the ferroelectric material placed between two metal electrodes.

[0005] More particularly, concerning the operation of FeRAM type ferroelectric memories, by applying a potential difference between the two electrodes creating an electric field of a value greater than a positive coercive field +Ec, the ferroelectric memory is placed in a state of high remanent polarization +Pr and by applying a potential difference creating an electric field of a value lower than the negative coercive field -Ec, the ferroelectric memory is placed in a state of low remanent polarization -Pr.

[0006] The high remanent polarization state +Pr then corresponds to the binary logic state '0' and the low remanent polarization state -Pr to the binary logic state '1', which allows the storage of information.

[0007] Furthermore, when the application of the potential difference between the two metal electrodes is stopped, the state of remanent polarization remains: this then explains the non-volatile nature of ferroelectric memories.

[0008] For reading, it is assumed that the memory is in a given state and a voltage is applied. This voltage is for example positive, greater than the voltage creating an electric field of a value greater than the positive coercive field +Ec. Thus, if the memory was already in the high remanent polarization state +Pr, this polarization state is unchanged and no current peak is observed (or a very low current peak may be observed). Conversely, if the memory was in the low remanent polarization state -Pr, a much larger current peak is observed.

[0009] The consequence of this reading operation is that it is destructive of the polarization state.

[0010] Ferroelectric tunnel junction (FTJ) memories are also known. FTJ ferroelectric memories are generally in the form of a stack in which a layer of ferroelectric material is positioned between two metal electrodes. FTJ ferroelectric memories are resistive type memories having two opposite polarization states for the layer of ferroelectric material. The operation of these ferroelectric memories is based on the ferroelectric properties of the ferroelectric material placed between two metal electrodes.

[0011] More particularly, concerning the operation of FTJ type ferroelectric memories, the two polarization states correspond respectively to two different resistance levels: a highly resistive level, corresponding for example to a high polarization state +Pr and a weakly resistive level, corresponding to a low polarization state -Pr. By way of example, the weakly resistive level has an electrical resistance approximately a thousand times lower than that of the highly resistive level.

[0012] In the case of FTJ type ferroelectric memories, the reading operation comprises the application of a reading voltage -Vr. The reading voltage -Vr is for example negative and lower in absolute value than a voltage Vc associated with the coercive field. This then makes it possible to carry out a non-destructive reading by means of the measurement of a tunnel current.

[0013] In order to increase memory density, it is known to implement so-called “multi-level” storage. This “multi-level” storage is associated with different polarization states, on which it will be possible to store information.

[0014] The document "Multilevel data storage memory using deterministic polarization control.", by Lee, Daesu et al., in Advanced materials, vol. 24(3), 2012, 402-406, doi: 10.1002 / adma.201103679 describes a ferroelectric memory of the FeRAM type having several storage levels. In this example, as shown in [Fig.l] (representing the evolution of the polarization P as a function of the applied voltage V), the memory can be placed in several intermediate remanent polarization states Pri, Pr2, Pr3, Pr4, Pr5, Pr6, Pr7 (Pr0 corresponding to the low polarization state 0). It will therefore be possible to store the information at different levels. Thanks to this “multi-level” storage, it is therefore possible to code several states per memory (here, in the example, eight states are coded), whereas in a standard cell only two states are accessible (states 0 or 1 only). Thus, the information contained in a memory with “multi-level” storage is equivalent to that contained in several standard type memories.

[0015] In practice, in this example, to implement this storage on the different intermediate levels, each intermediate polarization state Prb Pr2, Pr3, Pr4, Pr5, Pr6, Pr7 is associated with a corresponding current. Thus, when a voltage is applied between the electrodes, an associated ferroelectric current is read. This current then makes it possible to identify the intermediate polarization state Pri, Pr2, Pr3, Pr4, Pr5, Pr6, Pr7 concerned and therefore to go back to the information initially stored in this intermediate polarization state Prh Pr2, Pr3, Pr4, Pr5, Pr6, Pr7 of the ferroelectric memory.

[0016] However, certain drawbacks are observed in such high-density memories. For example, it may be difficult to distinguish two intermediate polarization states that are close. Indeed, an overlap between the different intermediate polarization states may be encountered. In such a case, the application of a voltage (between the electrodes) of this overlap zone does not make it possible to deduce with certainty the associated current, and therefore the intermediate remanent polarization state concerned. Summary of the invention

[0017] The present invention therefore aims to improve high-density ferroelectric storage devices by allowing unambiguous distinction of the different polarization states.

[0018] The invention then relates to a ferroelectric storage device comprising a first layer, a second layer and a layer of ferroelectric material which extends between the first layer and the second layer,

[0019] the layer of ferroelectric material comprising a first portion having a first thickness and a second portion having a second thickness, the first thickness and the second thickness being distinct.

[0020] Thus, the layer of ferroelectric material of the ferroelectric storage device according to the invention has a non-uniform thickness. This variability in thickness results in a non-uniformity in the ferroelectric properties of the ferroelectric storage device. This non-uniformity of properties allows in particular to increase the differences between the voltage ranges to be applied to store the information in the different intermediate polarization states.

[0021] Indeed, the different thicknesses then imply that, for a given (write) voltage, the electric field is greater in the regions of lower thickness. In other words, to write information in an intermediate polarization state associated with a low thickness, a greater voltage must be applied. The differences in thickness therefore lead to differences in voltages to be applied to encode the information in the different intermediate polarization states.

[0022] The different thicknesses used are therefore associated with different intermediate polarization states in the ferroelectric storage device.

[0023] In other words, due to the non-uniformity created in the ferroelectric material layer (due to the variability of thicknesses), the differences between the intermediate polarization states are created.

[0024] In addition to the characteristics which have just been mentioned in the preceding paragraphs, the ferroelectric storage device according to one aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations:

[0025] - a ratio between the second thickness and the first thickness is between 2 and 4; - the first thickness is between 3 and 7 nanometers and the second thickness is between 12 and 17 nanometers; - the first part of the layer of ferroelectric material has a surface area of ​​at least 15% of the total surface area of ​​the layer of ferroelectric material; - the ferroelectric material layer comprises hafnium dioxide or hafnium dioxide doped with a doping element or an HfxZrl-xO2 alloy, with 0 <x<l; - the first layer comprises a metallic material; - the metallic material included in the first layer is chosen from tungsten, titanium nitride, tantalum nitride; - the first layer comprises a first sub-layer and a second sub-layer, the second sub-layer being arranged on the first sub-layer; - the material of the first underlayer is chosen from titanium nitride, tantalum nitride or tungsten; - the first layer comprises a semiconductor material; - the semiconductor material included in the first layer is silicon; - the material of the second sub-layer is chosen from titanium, tantalum or hafnium; - the second layer comprises a metallic material; - the metallic material included in the second layer is chosen from tungsten, titanium nitride, tantalum nitride; - the second layer comprises another first sub-layer and another second sub-layer, the other second sub-layer being arranged on the other first sub-layer; - the material of the other first sub-layer is chosen from titanium, tantalum or hafnium; - the material of the other second sub-layer is chosen from titanium nitride, tantalum nitride or tungsten; - the second layer comprises a semiconductor material; - the semiconductor material included in the second layer is silicon; - a support layer is also provided having a portion with a U-shaped profile, the first layer, the second layer and the layer of ferroelectric material being positioned in the portion with a U-shaped profile of the support layer so that the first layer, the second layer and the layer of ferroelectric material have a shape profile similar to the portion with a U-shaped profile of the support layer; - the part with a U-shaped profile of the support layer comprises a bottom wall and a side wall, the side wall forming a first non-zero inclination angle relative to a direction normal to the bottom wall; - the first angle of inclination is between 13 and 50 degrees, preferably between 15 and 35 degrees; - the second part of the ferroelectric material layer is positioned on the bottom wall of the part with a U-shaped profile of the support layer and the first part of the ferroelectric material layer is positioned on the side wall of the part with a U-shaped profile of the support layer; - the side wall comprises a first portion and a second portion, the first portion forming said first angle of inclination relative to the direction normal to the bottom wall, the second portion forming a second angle of inclination relative to the direction normal to the bottom wall; - the second angle of inclination is greater than said first angle of inclination; - the second angle of inclination is between 15 and 70 degrees, preferably between 20 and 40 degrees; - the layer of ferroelectric material comprises a third portion having a third thickness, the third thickness being distinct from the first thickness and the second thickness, the second portion of the layer of ferroelectric material being positioned on the bottom wall of the portion with a U-shaped profile of the support layer, the first part of the ferroelectric material layer being positioned on the first portion of the sidewall of the part with a U-shaped profile of the support layer and the third part of the ferroelectric material layer being positioned on the second portion of the sidewall of the part with a U-shaped profile of the support layer; - the first layer forms a first electrode, the second layer forms a second electrode and the layer of ferroelectric material forms a memory layer.

[0026] The invention also relates to a method of manufacturing a ferroelectric storage device comprising steps of:

[0027] - depositing a first layer,

[0028] - deposition of a layer of ferroelectric material, the layer of ferro- material electrical comprising a first part having a first thickness and a second part having a second thickness, the first thickness and the second thickness being distinct, and

[0029] - deposition of a second layer, the layer of ferroelectric material extending between the first layer and the second layer.

[0030] In addition to the characteristics which have just been mentioned in the preceding paragraphs, the manufacturing method according to another aspect of the invention may have one or more additional characteristics among the following, considered individually or according to all technically possible combinations:

[0031] - the deposition of the first layer is carried out by cathodic sputtering or by chemical vapor deposition; - the deposition of the second layer is carried out by cathodic sputtering or by chemical vapor deposition; - a step of removing a portion of the layer of ferroelectric material is provided before the step of depositing the second layer, the first part of the layer of ferroelectric material being formed at a remaining portion associated with said removed portion; - the removal step is implemented by photolithography; - the deposition of the ferroelectric material layer is carried out in a compliant manner; - the deposition of the ferroelectric material layer is carried out by an atomic layer deposition method or by chemical vapor deposition; - a step of implanting a doping element in the layer of ferroelectric material is provided before the step of depositing the second layer so as to dope the layer of ferroelectric material with the doping element; - after the step of depositing the second layer, a planarization step is provided so as to standardize the surface of the second layer; - it is planned, before the step of depositing the first layer, steps of:

[0032] a) providing a support layer, and

[0033] b) forming a cavity in the support layer, the cavity comprising a bottom wall and a side wall, the side wall forming a first non-zero angle of inclination relative to a direction normal to the bottom wall,

[0034] the deposition of the first layer, the layer of ferroelectric material and the second layer being carried out in the formed cavity,

[0035] the second part of the layer of ferroelectric material being positioned on the bottom wall of the cavity and the first part of the layer of ferroelectric material being positioned on the side wall of the cavity; - the first angle of inclination is between 13 and 50 degrees, preferably between 15 and 35 degrees; - the formation of the cavity is implemented by isotropic etching; - the formation of the cavity is implemented by wet chemical etching; - the side wall of the cavity comprising a first portion and a second portion, the first portion forming said first angle of inclination relative to the direction normal to the bottom wall, the second portion forming a second angle of inclination relative to the direction normal to the bottom wall, a step of forming the second portion of the cavity is provided,

[0036] the layer of ferroelectric material comprising a third portion having a third thickness, the third thickness being distinct from the first thickness and the second thickness, the first portion of the layer of ferroelectric material being positioned on the bottom wall of the cavity, the second portion of the layer of ferroelectric material being positioned on the first portion of the side wall of the cavity and the third portion of the layer of ferroelectric material being positioned on the second portion of the side wall of the cavity; - the deposition of the ferroelectric material layer is carried out in a non-compliant manner; - the formation of the second portion of the cavity is implemented by wet chemical etching; and - the second angle of inclination is greater than said first angle of inclination. BRIEF DESCRIPTION OF THE FIGURES

[0037] Other characteristics and advantages of the invention will emerge clearly from the description given below, for information purposes only and in no way limiting, with reference to the appended figures, among which:

[0038] [Fig.l] illustrates the different intermediate polarization states in the case of a FeRAM type ferroelectric memory having several storage levels,

[0039] [Fig.2] represents, in schematic form, a first example of a device for ferroelectric storage according to the invention,

[0040] [Fig.3] represents, in the form of a flowchart, an example of the manufacturing process of the ferroelectric storage device of [Fig.2],

[0041] [Fig.4] illustrates step E4 of the manufacturing process shown in [Fig.3],

[0042] [Fig.5] illustrates step E6 of the manufacturing process shown in [Fig.3],

[0043] [Fig.6] illustrates step E8 of the manufacturing process shown in [Fig.3],

[0044] [Fig.7] illustrates step E10 of the manufacturing process shown in [Fig.3],

[0045] [Fig.8] represents, in schematic form, a second example of a device for ferroelectric storage according to the invention,

[0046] [Fig.9] represents, in the form of a flowchart, an example of the manufacturing process of the ferroelectric storage device of [Fig.8],

[0047] [Fig. 10] illustrates step E102 of the manufacturing method shown in [Fig.9],

[0048] [Fig. 11] illustrates step E104 of the manufacturing method shown in [Fig.9],

[0049] [Fig. 12] illustrates step E106 of the manufacturing method shown in [Fig.9],

[0050] [Fig. 13] illustrates step E108 of the manufacturing method shown in [Fig.9],

[0051] [Fig. 14] represents, in schematic form, a third example of a ferroelectric storage device according to the invention,

[0052] [Fig. 15] represents, in the form of a flowchart, an example of the manufacturing process of the ferroelectric storage device of [Fig. 14],

[0053] [Fig. 16] illustrates step E202 of the manufacturing process shown in [Fig. 15],

[0054] [Fig. 17] illustrates step E204 of the manufacturing method shown in [Fig. 15],

[0055] [Fig. 18] illustrates step E206 of the manufacturing method shown in [Fig. 15], and

[0056] [Fig. 19] illustrates step E208 of the manufacturing method shown in [Fig. 15].

[0057] For clarity, identical or similar elements are identified by identical reference signs throughout the figures.

[0058] DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT

[0059] The present invention aims to improve the manufacture of ferroelectric storage devices. In particular, the present invention relates to a high-density storage device in which several polarization states are used to store information. The present invention then aims to improve the definition of the polarization states in order to be able to clearly distinguish them in order to then be able to read the information stored and associated with each of the polarization states.

[0060] Figures 2, 8 and 14 each represent a ferroelectric storage device 1; 100; 200 according to the invention. [Fig.2] represents the ferroelectric storage device 1 according to a first embodiment. [Fig.8] represents the device 100 ferroelectric storage device according to a second embodiment. [Fig. 14] represents the ferroelectric storage device 200 according to a third embodiment.

[0061] Whatever the embodiment, as can be seen in FIGS. 2, 8 and 14, the ferroelectric storage device 1; 100; 200 comprises a first layer 2; 102; 202, a second layer 7; 107; 207 and a layer of ferroelectric material 5; 105; 205 which is arranged between the first layer 2; 102; 202 and the second layer 7; 107; 207.

[0062] As can be seen in Figures 2, 8 and 15, the device 1; 100; 200 is in the form of a stack of layers. The first layer 2; 102; 202, the layer of ferroelectric material 5; 105; 205 and the second layer 7; 107; 207 form the different layers of this stack.

[0063] In the first embodiment visible in [Fig.2], the stack extends along a z axis. The different layers extend parallel to each other (and parallel to a support layer 10 shown in FIGS. 4 to 7). The z axis is here perpendicular to the plane of the different layers of the stack forming the ferroelectric storage device 1 according to the first embodiment.

[0064] As shown in Figures 4 to 7, the support layer 10 comprises for example at least one via 11 intended to connect the ferroelectric storage device 1 to lower metal levels (for example made of copper Cu). The via 11 is for example formed of tungsten W.

[0065] Alternatively, the first layer may be disposed on a substrate not shown or on another layer.

[0066] In the second and third embodiments, as described in more detail below with the associated manufacturing methods, the ferroelectric storage device 100; 200 is formed in a cavity 150; 250. This cavity 150; 250 is for example formed in a support layer 110; 210. In other words, the cavity 150; 250 forms a part of the support layer which has a generally “U”-shaped profile (as will be seen below, the lateral branches of the “U” shape are here inclined relative to the base of the “U” shape). In these embodiments, the different layers of the ferroelectric storage device 100; 200 have a shape profile similar to the part 150; 250 with a “U”-shaped profile of the support layer 110; 210.

[0067] This support layer 110; 210 is for example formed from a dielectric material. The support layer may comprise a plurality of sub-layers. For example, the support layer may comprise another layer of dielectric material formed under the layer comprising silicon oxide SiO2. This other layer comprises for example silicon nitride SiN or silicon carbonitride SiCN.

[0068] The cavity 150; 250 comprises a bottom wall 152; 252 and a side wall 155; 255, 257. The bottom wall 152; 252 corresponds to the base of the “U” shape and the side wall 155; 255, 257 corresponds to the lateral branches of the “U” shape. The side wall 155; 255, 257 forms a first non-zero inclination angle a; [3 with respect to an axis z, corresponding to a direction normal to the bottom wall 152; 252.

[0069] In the second embodiment shown in [Fig.8], the first angle of inclination a is for example between 13 and 50 degrees, preferably between 15 and 35 degrees. Preferably, this first angle of inclination a is of the order of 18 degrees.

[0070] In the third embodiment visible in [Fig. 14], the side wall 255 of the cavity 250 comprises a first portion 255a and a second portion 255b. The first portion 255a forms a first non-zero inclination angle α relative to the z axis. The second portion 255b forms a second non-zero inclination angle [3 relative to the z axis. In other words, in this third embodiment, the side wall 255 of the cavity 250 has a break in slope, with the first inclined portion 255a inclined according to the first inclination angle α and the second portion 255b inclined according to the second inclination angle [3.

[0071] The second inclination angle [3 is greater than the first inclination angle a.

[0072] The second angle of inclination [3 is for example between 15 and 70 degrees, preferably between 20 and 40 degrees. Preferably, this second angle of inclination [3 is of the order of 20 degrees.

[0073] In these second and third embodiments, the stack (forming the storage device 100; 200) extends from the bottom wall 152; 252 and the side wall 155; 255. This stack then comprises several parts (one extending from the bottom wall 152; 252) and another extending from the side wall 155; 255 (in the third embodiment, one part extends from the first portion 255a of the side wall 255 and another part extends from the second portion 255b of the side wall 255). For the part formed on the bottom wall 152; 252, the different layers of the stack extend parallel to each other. The same is true for the part extending from the side wall 155; 255 (the different layers of the stack also extend parallel to each other on this side wall 155; 255).

[0074] Alternatively, the side wall of the cavity could of course comprise a number greater than 2 of portions forming distinct angles relative to a direction normal to the bottom wall. In other words, the side wall of the cavity may have a plurality of slope breaks.

[0075] Each of the layers forming the ferroelectric storage device 1; 100; 200 is now described.

[0076] The first layer 2; 102; 202 is formed from an inert conductive material. This first layer 2; 102; 202 comprises, for example, a metallic material.

[0077] According to a first example (not shown), the first layer comprises a single layer. The conductive material of this single layer comprises, for example, titanium nitride TiN. Alternatively, the conductive material may be tantalum nitride TaN or tungsten W. As a further variant, other conductive materials may be used (and in particular, metal nitride more generally).

[0078] As can be seen in a second example shown in FIGS. 2, 8 and 14, the first layer 2; 102; 202 is here in the form of a two-layer structure. Here it comprises a first sub-layer 20; 120; 220 and a second sub-layer 22; 122; 222.

[0079] The second sub-layer 22; 122; 222 is arranged on the first sub-layer 20; 120; 220.

[0080] The first sub-layer 20; 120; 220 comprises a metallic conductive material. Preferably, it comprises titanium Ti or tantalum nitride TaN.

[0081] The first sub-layer 20; 120; 220 has a thickness of between 3 and 20 nanometers (nm). Preferably, this thickness is between 5 and 10 nm.

[0082] This first sub-layer 20; 120; 220 plays both the role of a protective layer and the role of a contact layer allowing the device 1; 100; 200 to be electrically connected to its electronic control and reading circuit.

[0083] The second sub-layer 22; 122; 222 is arranged on the first sub-layer 20; 120; 220. It is in direct contact with the layer of ferroelectric material 5; 105; 205. In other words, the second sub-layer 22; 122; 22 extends between the first sub-layer 20; 120; 220 and the layer of ferroelectric material 5; 105; 205.

[0084] The second sub-layer 22; 122; 222 is formed from a conductive material comprising a transition metal. This conductive material is for example titanium nitride TiN. Alternatively, it may be other conductive materials such as tantalum Ta or tungsten W.

[0085] For example, when the second sub-layer 22; 122; 222 comprises titanium nitride, the first sub-layer 20; 120; 220 is formed from a conductive material such as titanium Ti.

[0086] Alternatively, when the second sub-layer 22; 122; 222 comprises tantalum, the first sub-layer 20; 120; 220 is formed for example from tantalum nitride TaN.

[0087] As a further variant, when the second sub-layer 22; 122; 222 comprises tungsten, the first sub-layer 20; 120; 220 is formed from a conductive titanium Ti material.

[0088] Here, the thickness of the second sub-layer 22; 122; 222 is between 10 and 100 nm. Preferably, this thickness is between 5 and 10 nm.

[0089] Alternatively, the first layer may comprise a semiconductor material. This semiconductor material comprises, for example, silicon.

[0090] The layer of ferroelectric material 5; 105; 205 is arranged on the first layer 2; 102; 202. Alternatively, the layer of ferroelectric material can be deposited on another layer present, beforehand, on the first layer.

[0091] This layer of ferroelectric material 50; 105; 205 is for example based on hafnium dioxide HfO2. In the present description, the expression “based on” means that the layer concerned comprises more than 50% of the element mentioned after this expression (for example here, this means that the layer of ferroelectric material 5; 105; 205 comprises more than 50% of hafnium dioxide).

[0092] Alternatively, the hafnium dioxide may be doped with a doping element. In the present description, the expression "doping" of a layer corresponds to the introduction into the material of the layer concerned of atoms of another material called "doping element".

[0093] Here, the doping element preferably used is silicon Si. In the case of silicon, the layer of ferroelectric material based on hafnium dioxide is for example exposed to a dose of dopant of between 1.1014 cm 2 and 1.1015 cm 2 in order to obtain a presence of between 0.7 and 7% of silicon atoms in the layer of ferroelectric material. Preferably, the dose of dopant is between 0.3.1015 cm 2 and 1.1015 cm 2.

[0094] Alternatively, other doping elements may be used such as aluminum Al, germanium Ge, gadolinium Gd, yttrium Y, lanthanum La, scandium Sc or nitrogen N.

[0095] As a further variant, the layer of ferroelectric material may comprise an alloy of the form HfxZri XO2, with 0 <x<l. Par exemple, il est possible d’utiliser un alliage ternaire HfZrO2 (par exemple du Hf0.5Zro.502) en tant que matériau ferroélectrique. En variante encore, la couche de matériau ferroélectrique peut être en nitrure d’aluminium scandium (AIScN).

[0096] As can be seen in Figures 2, 8 and 14, the layer of ferroelectric material 5; 105; 205 comprises at least a first part 5A; 105A; 205A and a second part 6; 106; 206. In the case of the ferroelectric storage device 200 according to the third embodiment, the layer of ferroelectric material 205 comprises a third part 205B.

[0097] In the first embodiment of the ferroelectric storage device 1 (visible in [Fig.2]), the second part 6 of the layer of ferroelectric material 5 has at least two sub-portions 6B, 6C framing the first part 5A. In other words, each of the two sub-portions 6B, 6C is arranged on either side of the first part 5A of the ferroelectric material layer 5.

[0098] In the second embodiment of the ferroelectric storage device 100 (shown in [Fig.8]), the first portion 105A extends along the side wall 155 of the cavity 150 while the second portion 106 extends along the bottom wall 152 of the cavity 150.

[0099] In the third embodiment of the ferroelectric storage device 200 (illustrated in [Fig. 14]), the first part 205A extends along a first portion 255a of the side wall 255 of the cavity 250, the second part 206 extends along the bottom wall 252 and the third part 205B of the layer of ferroelectric material extends along the second portion 255b of the side wall 255 of the cavity 250.

[0100] Advantageously according to the invention, the first part 5A; 105A; 205A has a first thickness ei and the second part 6; 106; 206 has a second thickness e2. In the present invention, the thickness of a part of a layer is defined as the distance separating the two faces of the part of the layer concerned. In other words, the thickness corresponds to the characteristic dimension of the layer concerned in a direction parallel to a direction normal to the faces of the part of the layer concerned.

[0101] For example, in the case of [Fig.2], the layer of ferroelectric material 5 has a first face 10A and a second face 10B. Here, the face 10A is in contact with the first layer 2 and the face 10B is in contact with the second layer 7.

[0102] Here, the first thickness ei and the second thickness e2 are distinct. In other words, the layer of ferroelectric material 5; 105; 205 has a non-uniform thickness. In other words, the layer of ferroelectric material 5; 105; 205 has a variable thickness.

[0103] The thickness differences form essential characteristics of the ferroelectric storage device to obtain the different polarization states.

[0104] Thus, thanks to the invention, the differences in thickness used for the layer of ferroelectric material introduce a non-uniformity in the ferroelectric properties of the layer of ferroelectric material. This non-uniformity of the properties makes it possible in particular to increase the differences between the voltage ranges to be applied to encode the information in the different intermediate polarization states. This then makes it possible to avoid overlap between the voltage ranges concerned and therefore to unambiguously identify the intermediate polarization states concerned by the stored information.

[0105] In order to obtain very distinct polarization states (i.e. without overlap between the voltage ranges to be applied to achieve them), the ratio between the second thickness e2 and the first thickness ei is preferably between 2 and 4.

[0106] In practice, the first thickness ei is for example between 3 and 7 nm. Preferably, this first thickness ei is of the order of 4 nm.

[0107] The second thickness e2 is for example between 8 and 17 nm. Preferably, this second thickness e2 is of the order of 10 nm.

[0108] Here, the second thickness e2 is therefore greater than the first thickness eb. This then implies that it will be necessary to apply a higher voltage to allow the encoding of the information stored in the intermediate polarization state associated with the second thickness e2 (in comparison with the first thickness ej.

[0109] The thickness ranges considered in the invention make it possible to accentuate the non-uniformities of the ferroelectric properties of the layer of ferroelectric material, so as to allow the storage of information on different intermediate polarization states and to allow the encoding of this information by distinctly distinguishing these different states.

[0110] Furthermore, in a plane orthogonal to the direction used to define the thickness, a surface of the first part 5A; 105A; 205A is defined at one of the faces of the layer of ferroelectric material 5; 105; 205. It is also possible to define the total surface of the layer of ferroelectric material 5; 105; 205 as the surface of one of the faces of the layer of ferroelectric material 5; 105; 205. In other words, the surface of the first part 5A; 105A; 205A corresponds to a part of the total surface of the layer of ferroelectric material 5; 105; 205.

[0111] Advantageously according to the invention, the first part 5A; 105A; 205A has a surface area of ​​at least 15% of the total surface area of ​​the layer of ferroelectric material 5; 105; 205. In other words, the surface area of ​​the first part 5A; 105A; 205A represents at least 15% of the total surface area of ​​the layer of ferroelectric material 5; 105; 205.

[0112] Thus, advantageously according to the invention, the non-uniformities (associated with the differences in thickness) of the layer of ferroelectric material are not manufacturing artifacts. The fact that the parts associated with the different thicknesses have substantial surfaces makes it possible to ensure very distinct polarization states (and therefore an absence of overlap between the voltage ranges to be applied to access the different polarization states).

[0113] As shown in Figures 2, 8 and 14, the second layer 7; 107; 207 is arranged on the layer of ferroelectric material 5; 105; 205.

[0114] This second layer 7; 107; 207 comprises for example a conductive material. This is in particular a metallic material.

[0115] According to a first example (not shown), the second layer comprises a single layer. The conductive material of this single layer comprises, for example titanium nitride TiN. Alternatively, the conductive material may be tantalum nitride TaN or tungsten W. Alternatively, other conductive materials may be used (and in particular, metal nitride more generally).

[0116] As can be seen in Figures 2, 8 and 14, the second layer 7; 107; 207 is here in the form of a two-layer structure. Here it comprises a first sub-layer 70; 170; 270 and a second sub-layer 72; 172; 272.

[0117] The second sub-layer 72; 172; 272 of the second layer 7; 107; 207 is arranged on the associated first sub-layer 70; 170; 270.

[0118] The second sub-layer 72; 172; 272 is formed from a conductive material comprising a transition metal. This conductive material is for example titanium nitride TiN. Alternatively, it may be other conductive materials such as tantalum nitride TaN or tungsten W.

[0119] The second sub-layer 72; 172; 272 has a thickness of between 10 and 200 nm.

[0120] This second sub-layer 72; 172; 272 plays both the role of a protective layer, and the role of a contact layer allowing the device 1; 100; 200 to be electrically connected to its electronic control and reading circuit.

[0121] The first sub-layer 70; 170; 270 is arranged on the layer of ferroelectric material 5; 105; 205. It is in direct contact with the layer of ferroelectric material 5; 105; 205. In other words, the first sub-layer 70; 170; 270 of the second layer 7; 107; 207 extends between the second sub-layer 72; 172; 272 and the layer of ferroelectric material 5; 105; 205.

[0122] The second sub-layer 72; 172; 272 comprises a metallic conductive material. Preferably, it comprises titanium Ti or tantalum Ta.

[0123] For example, when the second sub-layer 72; 172; 272 comprises titanium nitride, the first sub-layer 70; 170; 270 is formed from a conductive material such as titanium Ti.

[0124] Alternatively, when the second sub-layer 72; 172; 272 comprises tantalum nitride, the first sub-layer 70; 170; 270 is formed from a conductive material such as tantalum Ta.

[0125] As a further variant, when the second sub-layer 72; 172; 272 comprises tungsten, the first sub-layer 70; 170; 270 is formed from a conductive material chosen from titanium Ti or tantalum Ta.

[0126] Here, the thickness of the first sub-layer 70; 170; 270 is between 3 and 20 nm.

[0127] In practice, in the case of an OxRAM (for “Oxide Resistive RAM”) type memory, when this two-layer structure is used for the second layer 7; 107; 207, the first sub-layer 70; 170; 270 also has the particularity of being a layer which will allow the creation of oxygen vacancies in the layer of ferroelectric material 5; 105; 205 (when this first sub-layer 70; 170; 270 is in contact with the layer of ferroelectric material 5; 105; 205). In this case, the first sub-layer 70; 170; 270 comprises a conductive material chosen from titanium Ti or tantalum Ta and the second sub-layer 72; 172; 272 comprises a titanium nitride TiN or a tantalum nitride TaN (so as to form a protective layer). The creation of these oxygen vacancies then makes it possible to improve the performance of the ferroelectric storage device by facilitating the exchange of oxygen with the layer of ferroelectric material.

[0128] In the case of a FeRAM type memory, the second layer 7 comprises for example a metal nitride or a metal which does not oxidize (such as tungsten W or ruthenium Ru.

[0129] In the case of an FTJ type memory, the structure used is that of a FeRAM type memory with the introduction of a layer comprising a dielectric material between the layer of ferroelectric material 5 and the second layer 7. The dielectric material is for example a dielectric oxide such as aluminum oxide A12O3 or silicon dioxide SiO2.

[0130] Alternatively, the second layer may comprise a semiconductor material. This semiconductor material comprises, for example, silicon.

[0131] Advantageously according to the invention, the ferroelectric storage device comprises a layer of ferroelectric material whose thickness is variable. This variability in thickness results in non-uniformity in the ferroelectric properties of the ferroelectric storage device. This non-uniformity of properties makes it possible in particular to increase the differences between the voltage ranges to be applied to encode the information in the different intermediate polarization states.

[0132] In other words, due to the non-uniformity created in the ferroelectric material layer (due to the variability of thicknesses), differences between the intermediate polarization states are created.

[0133] Alternatively, the layer of ferroelectric material may comprise more than three distinct thicknesses. This may in particular be a continuous variation in thickness.

[0134] The present invention also relates to a method of manufacturing a ferroelectric storage device 1; 100; 200

[0135] Figures 3 to 7 relate to a first embodiment of this manufacturing method according to the invention. This first embodiment of the manufacturing method allows the manufacturing of the ferroelectric storage device 1 shown in [Fig.2].

[0136] Figures 9 to 13 relate to a second embodiment of this manufacturing method according to the invention. This second embodiment of the manufacturing method brication allows the fabrication of the ferroelectric storage device 100 shown in [Fig.8].

[0137] Figures 15 to 19 relate to a third embodiment of the manufacturing method according to the invention. This third embodiment of the manufacturing method allows the manufacturing of the ferroelectric storage device 200 shown in [Fig. 15].

[0138] [Fig. 3] represents, in the form of a flowchart, an example of the manufacturing method according to the first embodiment.

[0139] As can be seen in this figure, the manufacturing method firstly comprises a step E0 of providing a support layer 10 on which the ferroelectric storage device 1 will be formed. As indicated previously, this support layer 10 is provided with at least one via 11 intended to connect the ferroelectric storage device 1 to lower metal levels.

[0140] Alternatively, this step may be a step of providing a substrate.

[0141] The manufacturing process then continues with a step E2 of depositing the first layer 2. This step therefore aims to form the first layer 2 on the support layer 10 (or on a substrate not shown).

[0142] This is a conformal deposition of the first layer 2. In this description, the term "conformal deposition" means a deposition implemented in such a way that the layer has a substantially constant thickness at all points. In this description, the term "substantially constant" means a thickness not varying by more than 20%, preferably by more than 10%, and more preferably by more than 5%.

[0143] As indicated previously, the first layer 2 here comprises a first sub-layer 20 and a second sub-layer 22.

[0144] Step E2 of the first layer 2 therefore here comprises two sub-steps: a first sub-step E2a of depositing the first sub-layer 20 and a second sub-step E2b of depositing the second sub-layer 22.

[0145] The first sub-layer 20 is therefore first deposited, in a conformal manner, on the support layer 10 (or on a substrate not shown). In practice, the first sub-layer 20 is for example formed by cathode sputtering in a vacuum deposition chamber. In the case where the first sub-layer 20 is formed from titanium nitride, this is reactive cathode sputtering.

[0146] Alternatively, the first sub-layer may be formed by chemical vapor deposition.

[0147] Then, the second sub-layer 22 of the first layer 2 is deposited, in a conformal manner, on the first sub-layer 20. The second sub-layer 22 is for example formed by cathode sputtering in a vacuum deposition chamber. In practice, the second sub-layer 22 of the first layer 2 is formed in the same deposition chamber as the first sub-layer 20 of the first layer 2.

[0148] In the case where the second sub-layer 22 is formed from titanium nitride, it is a reactive cathode sputtering.

[0149] Alternatively, the first layer 2 can be deposited by an atomic layer deposition method (or ALD for “Atomic Layer Deposition” according to the commonly used acronym of Anglo-Saxon origin).

[0150] Then the method continues at step E4 of depositing the layer of ferroelectric material 5 on the first layer 2. More particularly, the layer of ferroelectric material 5 is deposited on the second sub-layer 22 of the first layer 2. This step E4 is shown in [Fig.4].

[0151] This is a conformal deposition of the layer of ferroelectric material 5 on the first layer 2.

[0152] Here, the deposition step E4 is for example implemented in such a way that the layer of ferroelectric material has a thickness e2.

[0153] In practice, the layer of ferroelectric material 5 is deposited by an atomic layer deposition (or ALD) method.

[0154] Alternatively, the layer of ferroelectric material may be deposited by sputtering. Alternatively, the layer of ferroelectric material may be deposited by a physical vapor deposition (PVD) method. Alternatively, the layer of ferroelectric material may be deposited by an ion beam deposition (IBD) method.

[0155] Then, as shown in [Fig.3], the method continues with a step E6 of removing a portion of the layer of ferroelectric material 5 formed in step E4. This step E6 is shown in [Fig.5].

[0156] This removal step then makes it possible to form the first part 5A and the second part 6 of the layer of ferroelectric material 5. In other words, the removed portion of the layer of ferroelectric material 5 is such that the remaining part (of the layer of ferroelectric material 5) has a thickness eb. This remaining portion then corresponds to the first part 5A of the layer of ferroelectric material 5.

[0157] In practice, this removal step E6 is carried out by lithography then etching. It is for example implemented by photolithography.

[0158] Thus, thanks to this removal step, the layer of ferroelectric material comprises the first part 5A having the first thickness ei and the second part 6 having the second thickness e2. As indicated previously, the first thickness ei and the second thickness e2 are distinct.

[0159] As previously indicated, the second thickness e2 is greater than the first thickness ep. This then implies that it will be necessary to apply a stronger voltage to allow the encoding of the information stored in the intermediate polarization state associated with the second part 6 (in comparison with the first part 5A).

[0160] The process then continues, at step E8, with the deposition of the second layer 7. This step E8 is shown in [Fig.6].

[0161] The second layer 7 is formed on the layer of ferroelectric material 5 obtained at the end of step E6.

[0162] The deposition of the second layer 7 is also implemented in a compliant manner.

[0163] As indicated previously, the second layer 7 here comprises a first underlayer 70 and a second underlayer 72.

[0164] Step E8 of the second layer 7 therefore here comprises two sub-steps: a first sub-step E8a of depositing the first sub-layer 70 and a second sub-step E8b of depositing the second sub-layer 72.

[0165] The first sub-layer 70 is therefore first deposited, in a conformal manner, on the layer of ferroelectric material 5. In practice, the first sub-layer 70 is for example formed by cathode sputtering in a vacuum deposition chamber. In the case where the first sub-layer 70 is formed from titanium nitride, this is reactive cathode sputtering.

[0166] Alternatively, the first sub-layer may be formed by chemical vapor deposition.

[0167] Then, the second sub-layer 72 of the second layer 7 is deposited, in a conformal manner, on the first sub-layer 70. The second sub-layer 72 is for example formed by cathode sputtering in a vacuum deposition chamber. In practice, the second sub-layer 72 of the second layer 7 is formed in the same deposition chamber as the first sub-layer 70 of the second layer 7.

[0168] In the case where the second sub-layer 72 is formed from titanium nitride, it is a reactive cathode sputtering.

[0169] As can be seen in [Fig.6], since the layer of ferroelectric material 5 comprises the first part 5A of thickness ei smaller than the second part 6 of thickness e2, when the second layer 7 is deposited, the latter does not have a flat free surface.

[0170] The manufacturing method then comprises a planarization step E10. This step E10 consists of flattening and uniformizing the surface of the second layer 7. This step E10 is shown in [Fig.7].

[0171] In practice, this step E10 is for example implemented by chemical mechanical polishing (or CMP for “Chemical mechanical polishing” according to the commonly used acronym of Anglo-Saxon origin).

[0172] This planarization step is particularly advantageous because, thanks to the standardization of the surface of the second layer, it makes it possible to improve the electrical performance of the ferroelectric storage device and to guarantee better quality of the interconnections.

[0173] Finally, at the end of the manufacturing method according to this first embodiment, the ferroelectric storage device 1 obtained comprises a layer of ferroelectric material with variable thickness. This variability of thicknesses makes it possible to introduce a non-uniformity into the ferroelectric properties of the layer of ferroelectric material. This non-uniformity of the properties makes it possible in particular to increase the differences between the voltage ranges to be applied to store the information in the different intermediate polarization states. This then makes it possible to avoid overlap between the voltage ranges concerned and therefore to unambiguously identify the intermediate polarization states concerned by the stored information.

[0174] The ferroelectric storage device 1 obtained at the end of the manufacturing process according to this first embodiment has a so-called “planar” architecture, with a stack of layers parallel to each other. This configuration has the advantage of being easy to implement, in particular because the deposition of the different layers can be carried out in a compliant or non-compliant manner.

[0175] According to an alternative implementation of this first embodiment, the method may comprise, between step E4 of depositing the layer of ferroelectric material and step E6 of removing a portion of the first layer, a step of implanting a doping element in the layer of ferroelectric material formed in step E4. This step then makes it possible to dope the layer of ferroelectric material with the doping element.

[0176] In practice, the implantation step is for example implemented in a reactor different from the deposition chamber of the first layer and the layer of ferroelectric material.

[0177] Here, for example, it is a step of ionic implantation of silicon (which is the doping element) in the layer of ferroelectric material. The implantation doses are for example between 1.1014 cm 2 and 1.1015 cm 2. Preferably, the implantation dose is between 0.3. 1014 cm 2 and 1.1015 cm 2.

[0178] [Fig.9] represents, in the form of a flowchart, an example of the fa process construction according to the second embodiment.

[0179] As can be seen in this figure, the manufacturing method firstly comprises a step E100 of providing a support layer 110.

[0180] Then, the manufacturing method continues to step E102, during which the cavity 150 (in which the ferroelectric storage device 100 will be formed) is formed. [Fig. 10] illustrates this step E102.

[0181] This step E102 is implemented by anisotropic etching so as to form the bottom wall 152 and the side wall 155 of the cavity 150. This is for example a dry chemical etching.

[0182] As described previously, the side wall 155 of the cavity 150 is made in such a way as to form the first angle of inclination α relative to the axis z parallel to a direction normal to the bottom wall 152.

[0183] The side wall 155 therefore forms a first non-zero angle of inclination α relative to an axis z, corresponding to a direction normal to the bottom wall 152.

[0184] As can be seen in [Fig.9], the manufacturing process continues, at step E104, with the deposition of the first layer 102. [Fig. 11] illustrates this step E104.

[0185] This first layer 102 is deposited in the cavity 150. More particularly, the first layer 102 is deposited along the bottom wall 152 and the side wall 155 of the cavity 150. The first layer 102 therefore has the shape of the cavity 150.

[0186] The deposition of the first layer 102 is carried out here in a conformal manner. For example, the first layer 102 can be formed by an atomic layer deposition method (or ALD for “Atomic Layer Deposition” according to the commonly used acronym of Anglo-Saxon origin).

[0187] As indicated previously, the first layer 102 here comprises a first sub-layer 120 and a second sub-layer 122.

[0188] Step E104 of depositing the first layer 102 therefore here comprises two sub-steps: a first sub-step E104a of depositing the first sub-layer 120 and a second sub-step E104b of depositing the second sub-layer 122.

[0189] The first sub-layer 120 is therefore first deposited, in a conformal manner, in the cavity 150 (step E104a). In practice, the first sub-layer 20 is for example formed by an atomic layer deposition (or ALD) method or by chemical vapor deposition.

[0190] Alternatively, the first sub-layer 120 may be formed by cathode sputtering in a vacuum deposition chamber. In the case where the first sub-layer 120 is formed from titanium nitride, it is a reactive cathode sputtering.

[0191] Then, the second sub-layer 122 of the first layer 102 is deposited, in a conformal manner, on the first sub-layer 120 (step E104b). The second sub-layer 122 is for example formed by cathode sputtering in a vacuum deposition chamber. In practice, the second sub-layer 122 of the first layer 102 is formed in the same deposition chamber as the first sub-layer 120 of the first layer 102.

[0192] In the case where the second sub-layer 122 is formed from titanium nitride, it is a reactive cathode sputtering.

[0193] Then, the manufacturing process continues at step E106 of depositing the layer of ferroelectric material 105 on the first layer 102. More particularly, the layer of ferroelectric material 105 is deposited on the second sub-layer 122 of the first layer 102. This step E106 is shown in [Fig. 12].

[0194] Advantageously in this second embodiment, the deposition of the layer of ferroelectric material 105 is carried out in a non-conformal manner. This therefore means that the deposition is carried out in such a way that the thickness of the layer of ferroelectric material 105 is variable.

[0195] More particularly here, the deposition is implemented so as to obtain a thickness e2 of the ferroelectric material at the bottom wall 152 (thus forming the second part 106 of the layer of ferroelectric material 105) and to obtain a thickness ei of the ferroelectric material at the side wall 155 (thus forming the first part 105A of the layer of ferroelectric material 105).

[0196] In practice, the (non-compliant) deposition step E106 is for example implemented by a physical vapor deposition (or PVD) method.

[0197] Alternatively, the layer of ferroelectric material may be deposited by sputtering. Alternatively, the layer of ferroelectric material may be deposited by an ion beam deposition (or IBD) method.

[0198] This non-conformal deposition makes it possible to directly form the layer of ferroelectric material 105 with a first part 105A which has the first thickness ei and a second part 106 which has the second thickness e2. As indicated previously, the second thickness e2 is greater than the first thickness eb. This then implies that it will be necessary to apply a higher voltage to allow the encoding of the information stored in the intermediate polarization state associated with the second part 106 (in comparison with the first part 105).

[0199] The method then continues, at step E108, with the deposition of the second layer 107. This step E108 is shown in [Fig.13].

[0200] The second layer 107 is formed on the layer of ferroelectric material 105 obtained at the end of step E106.

[0201] The deposition of the second layer 107 is carried out in a compliant manner.

[0202] As indicated previously, the second layer 107 here comprises a first sub-layer 170 and a second sub-layer 172.

[0203] Step E108 of depositing the second layer 107 therefore here comprises two sub-steps: a first sub-step E108a of depositing the first sub-layer 170 and a second sub-step 108b of depositing the second sub-layer 172.

[0204] The first sub-layer 170 is therefore first of all deposited, in a conformal manner, on the layer of ferroelectric material 105 (step E108a). In practice, the first sub-layer 170 is for example formed by cathode sputtering in a vacuum deposition chamber. In the case where the first sub-layer 170 is formed from titanium nitride, it is a reactive cathode sputtering.

[0205] Alternatively, the first sub-layer may be formed by chemical vapor deposition.

[0206] Then, the second sub-layer 172 of the second layer 107 is deposited, in a conformal manner, on the first sub-layer 170 (step E108b). As can be seen in [Fig. 13], the second sub-layer 172 is formed so as to fill all the remaining space in the cavity 150. This then makes it possible to obtain a ferroelectric storage device 100 completely integrated in the cavity 150 and without any projection or recession formed relative to the surface of the support layer 110. The assembly formed by the support layer 110 in which the ferroelectric storage device 100 is integrated therefore has a uniform surface.

[0207] In practice, the second sub-layer 172 is for example formed by cathode sputtering in a vacuum deposition chamber. In practice, the second sub-layer 172 of the second layer 107 is formed in the same deposition chamber as the first sub-layer 170 of the second layer 107.

[0208] In the case where the second sub-layer 172 is formed from titanium nitride, it is a reactive cathode sputtering.

[0209] In practice, although this is not visible in the attached figures, it is not excluded that the different layers of the ferroelectric storage device 100 are also deposited on the front face (free surface opposite the bottom wall 152) of the support layer. Thus, optionally, in order to ensure the flatness and uniformity of the ferroelectric storage device 100 (and in particular of the free surface of the device 100), a planarization step may be provided, after step E108. This planarization step is for example implemented by chemical mechanical polishing (or CMP for “Chemical mechanical polishing” according to the commonly used acronym of Anglo-Saxon origin). Any other suitable method may be used (in particular masking methods).

[0210] This planarization step is particularly advantageous because, thanks to the standardization of the surface of the device 100, it makes it possible to improve the electrical performance of the ferroelectric storage device and to guarantee better quality of the interconnections.

[0211] Alternatively, an encapsulation step may be provided after this planarization step. Finally, a connection to the second layer may be implemented.

[0212] Thus, at the end of the manufacturing method according to this second embodiment, the ferroelectric storage device 100 obtained comprises a layer of ferroelectric material with variable thickness. As indicated previously, variability of thicknesses makes it possible to introduce non-uniformities in the ferro- properties. electrical properties of the ferroelectric material layer. This non-uniformity of properties makes it possible in particular to increase the differences between the voltage ranges to be applied to encode the information in the different intermediate polarization states.

[0213] This then makes it possible to avoid overlap between the voltage ranges concerned and therefore to unambiguously identify the intermediate polarization states concerned by the encoded information.

[0214] In addition, the manufacturing method according to this second embodiment makes it possible to obtain an architecture of the ferroelectric storage device 100 in three dimensions. This makes it possible in particular to increase the surface area of ​​the capacity of the ferroelectric storage device 100.

[0215] [Fig. 15] represents, in the form of a flowchart, an example of the manufacturing method according to the third embodiment.

[0216] This third embodiment of the manufacturing method is similar to the second embodiment described previously. Also, only the differences with respect to this second embodiment are described in detail below.

[0217] As can be seen in [Fig.15], the manufacturing method firstly comprises a step E200 (similar to step E100) of providing a support layer 210.

[0218] Then, the manufacturing method continues to step E202, during which the cavity 250 (in which the ferroelectric storage device 200 will be formed) is formed. [Fig. 16] illustrates this step E202.

[0219] The specificity of this third embodiment lies in the formation of the cavity 250, and more particularly in the formation of the side wall 255 of the cavity 250. Here, step E202 actually comprises two sub-steps: a first sub-step E202a of forming a first portion 255a of the side wall 255 and a second sub-step E202b of forming a second portion 255b of the side wall 255.

[0220] The first sub-step E202a is implemented by isotropic etching so as to form the bottom wall 252 and the first portion 255a of the side wall 250. This is for example a wet chemical etching.

[0221] The first portion 255a of the side wall 255 of the cavity 250 is formed in such a way as to have the first angle of inclination α relative to the axis z parallel to a direction normal to the bottom wall 252 (as during the step E102 described previously).

[0222] The first portion 255a of the side wall 255 therefore forms a first non-zero angle of inclination α relative to an axis z, corresponding to a direction normal to the bottom wall 252.

[0223] The second sub-step E202b corresponds to an additional isotropic etching step of the cavity 255. More particularly, this second sub-step E202b aims to form the second portion 255b of the side wall 255 of the cavity 250.

[0224] Here, the second portion 255b of the side wall 255 of the cavity 250 is formed, on the side wall 255, at the surface opposite the bottom wall 252. This second portion 255b is produced in such a way that it forms a second angle of inclination [3 relative to the z axis parallel to a direction normal to the bottom wall 252. In other words, the second portion 255b of the side wall 255 therefore forms a second non-zero angle of inclination [3 relative to a z axis, corresponding to a direction normal to the bottom wall 252.

[0225] Thus, at the end of step E202, the side wall 255 of the cavity 250 having a first portion 255a inclined at a first angle α relative to the z axis and a second portion 255b inclined at a second angle [3 relative to the z axis is formed. Here, this side wall 255 of the cavity 250 therefore has a break in slope, with the first inclined portion 255a inclined at the first angle of inclination α and the second portion 255b inclined at the second angle of inclination [3. The side wall 255 has a sort of “Y” shape here.

[0226] As can be seen in [Fig. 15], the manufacturing process continues, at step E204, with the deposition of the first layer 202. [Fig. 17] illustrates this step E204. Step E204 is similar to step E104 described for the second embodiment.

[0227] This first layer 202 is deposited in the cavity 250. More particularly, the first layer 202 is deposited along the bottom wall 252 and the side wall 255 of the cavity 250.

[0228] The deposition of the first layer 202 is carried out here in a compliant manner.

[0229] As indicated previously, the first layer 202 here comprises a first sub-layer 220 and a second sub-layer 222.

[0230] Step E204 of depositing the first layer 202 therefore here comprises two sub-steps: a first sub-step E204a of depositing the first sub-layer 220 and a second sub-step E204b of depositing the second sub-layer 222.

[0231] The first sub-layer 220 is therefore first deposited, in a conformal manner, in the cavity 250 (step E204a). In practice, the first sub-layer 220 is for example formed by cathode sputtering in a vacuum deposition chamber. In the case where the first sub-layer 220 is formed from titanium nitride, this is reactive cathode sputtering.

[0232] Alternatively, the first sub-layer may be formed by chemical vapor deposition.

[0233] Then, the second sub-layer 222 of the first layer 202 is deposited, compliant manner, on the first sub-layer 220 (step E204b). The second sub-layer 222 is for example formed by cathode sputtering in a vacuum deposition chamber. In practice, the second sub-layer 222 of the first layer 202 is formed in the same deposition chamber as the first sub-layer 220 of the first layer 202.

[0234] In the case where the second sub-layer 222 is formed from titanium nitride, it is a reactive cathode sputtering.

[0235] Then, the manufacturing method continues at step E206 of depositing the layer of ferroelectric material 205 on the first layer 202. More particularly, the layer of ferroelectric material 205 is deposited on the second sub-layer 222 of the first layer 202. This step E206 is shown in [Fig. 18]. Step E206 is similar to step E106 described previously for the second embodiment.

[0236] Advantageously in this second embodiment, the deposition of the layer of ferroelectric material 205 is carried out in a non-conformal manner. This therefore means that the deposition is carried out in such a way that the thickness of the layer of ferroelectric material 205 is variable.

[0237] More particularly here, the deposition is implemented so as to obtain a thickness e2 of the ferroelectric material at the bottom wall 252, to obtain a thickness ei of the ferroelectric material at the first portion 255a of the side wall 255 and a thickness e3 at the second portion 255b of the side wall 255 of the cavity 250. Here, the thicknesses verify the following inequality: e2 > e3 > ei.

[0238] In other words, the greatest thickness e2 of ferroelectric material is formed at the bottom wall 252, an intermediate thickness e3 is formed at the second portion 225b of the side wall 255 of the cavity 250 and the smallest thickness ei is formed at the first portion 255a of the side wall 255 of the cavity 250.

[0239] In practice, the (non-compliant) deposition step E206 is for example implemented by a physical vapor deposition (or PVD) method.

[0240] Alternatively, the layer of ferroelectric material may be deposited by sputtering. Alternatively, the layer of ferroelectric material may be deposited by an ion beam deposition (or IBD) method.

[0241] This non-conformal deposition makes it possible to directly form the layer of ferroelectric material 205 with a first part 205A which has the first thickness ei (smallest thickness), a second part 206 which has the second thickness e2 (largest thickness) and a third part 205B which has the third thickness e3.

[0242] These differences in thickness then imply that it will be necessary to apply a higher voltage to enable encoding of information stored in the intermediate polarization state associated with the second part 206, an intermediate voltage to enable encoding of information stored in the intermediate polarization state associated with the third part 205B and finally a lower voltage to enable encoding of information stored in the intermediate polarization state associated with the first part 205A.

[0243] The method then continues, at step E208, with the deposition of the second layer 207. This step E208 is shown in [Fig. 19]. This step is similar to step El08 described previously for the second embodiment.

[0244] The second layer 207 is formed on the layer of ferroelectric material 205 obtained at the end of step E206.

[0245] The deposition of the second layer 207 is carried out in a compliant manner.

[0246] As indicated previously, the second layer 207 may here comprise a first sub-layer 270 and a second sub-layer 272.

[0247] Step E208 of depositing the second layer 207 therefore comprises two sub-steps here: a first sub-step E208a of depositing the first sub-layer 270 and a second sub-step 208b of depositing the second sub-layer 272.

[0248] The first sub-layer 270 is therefore first deposited, in a conformal manner, on the layer of ferroelectric material 205 (step E208a). In practice, the first sub-layer 270 is for example formed by cathode sputtering in a vacuum deposition chamber. In the case where the first sub-layer 270 is formed from titanium nitride, this is reactive cathode sputtering.

[0249] Alternatively, the first sub-layer may be formed by chemical vapor deposition.

[0250] Then, the second sub-layer 272 of the second layer 207 is deposited, in a conformal manner, on the first sub-layer 270 (step E208b). As can be seen in [Fig. 19], the second sub-layer 272 is formed so as to fill all the remaining space in the cavity 250. This then makes it possible to obtain a ferroelectric storage device 200 completely integrated in the cavity 250 and without any projection or recession formed relative to the surface of the support layer 210. The assembly formed by the support layer 210 in which the ferroelectric storage device 200 is integrated therefore has a uniform surface.

[0251] In practice, the second sub-layer 272 is for example formed by cathode sputtering in a vacuum deposition chamber. In practice, the second sub-layer 272 of the second layer 207 is formed in the same deposition chamber as the first sub-layer 270 of the second layer 207.

[0252] In the case where the second sub-layer 272 is formed from titanium nitride, it is a reactive cathode sputtering.

[0253] In practice, although this is not visible in the attached figures, it is not excluded that the different layers of the ferroelectric storage device 200 are also deposited on the front face (free surface opposite the bottom wall 252) of the support layer. Thus, optionally, in order to ensure the flatness and uniformity of the ferroelectric storage device 200 (and in particular of the free surface of the device 200), a planarization step may be provided, after step E208. This planarization step is for example implemented by chemical mechanical polishing (or CMP for “Chemical mechanical polishing” according to the commonly used acronym of Anglo-Saxon origin). Any other suitable method may be used (in particular masking methods).

[0254] This planarization step is particularly advantageous because, thanks to the standardization of the surface of the device 1, it makes it possible to improve the electrical performance of the ferroelectric storage device and to guarantee better quality of the interconnections.

[0255] Alternatively, an encapsulation step may be provided after this planarization step. Finally, a connection to the second layer may be implemented.

[0256] Thus, at the end of the manufacturing method according to this second embodiment, the ferroelectric storage device 200 obtained comprises a layer of ferroelectric material with variable thickness. As indicated previously, the variability of thicknesses makes it possible to introduce a non-uniformity into the ferroelectric properties of the layer of ferroelectric material. This non-uniformity of the properties makes it possible in particular to increase the differences between the voltage ranges to be applied to store the information in the different intermediate polarization states. This then makes it possible to avoid overlap between the voltage ranges concerned and therefore to unambiguously identify the intermediate polarization states concerned by the stored information.

[0257] In addition, the manufacturing method according to this third embodiment makes it possible to obtain an architecture of the ferroelectric storage device 200 in three dimensions. This makes it possible in particular to increase the surface area of ​​the capacity of the ferroelectric storage device 200.

[0258] Applications

[0259] The ferroelectric storage device according to the invention finds a preferred application in the context of resistive memories of the FeRAM type (for “Ferroelectric Random Access Memory” according to the commonly used acronym of Anglo-Saxon origin).

[0260] It also finds a particular application in the context of transistors, for example of the FeMFET type (for “Ferroelectric-metal field effect transistor” according to the commonly used acronym of Anglo-Saxon origin).

[0261] The ferroelectric storage device according to the invention can also be used in the context of ferroelectric tunnel junctions (or FTJ for "Ferroelectric tunnel junction" according to the commonly used acronym of Anglo-Saxon origin). In this case, an additional layer is added between the layer of ferroelectric material and the second layer. This additional layer comprises a dielectric material. This dielectric material is for example an aluminum oxide A12O3.

[0262] In the case of certain applications mentioned (for example FeRAM or FTJ type memories), the first layer forms a first electrode (for example a lower electrode), the second layer forms a second electrode (for example an upper electrode) and the layer of ferroelectric material forms a memory layer.

Claims

Claims

1. A ferroelectric storage device (1; 100; 200) comprising a first layer (2; 102; 202), a second layer (7; 107; 207) and a layer of ferroelectric material (5; 105; 205) which extends between the first layer (2; 102; 202) and the second layer (7; 107; 207), the layer of ferroelectric material (5; 105; 205) comprising a first portion (5A; 105A; 205A) having a first thickness (ei) and a second portion (6; 106; 206) having a second thickness (e2), the first thickness (ei) and the second thickness (e2) being distinct.

2. A ferroelectric storage device (1; 100; 200) according to claim 1, wherein a ratio between the second thickness (e2) and the first thickness (ej) is between 2 and 4.

3. A ferroelectric storage device according to claim 1 or 2, wherein the first thickness (ej) is between 3 and 7 nanometers and the second thickness (e2) is between 12 and 17 nanometers.

4. A ferroelectric storage device (1; 100; 200) according to any one of claims 1 to 3, wherein the first portion (5A; 105A; 205A) of the layer of ferroelectric material (5; 105; 205) has a surface area of ​​at least 15% of the total surface area of ​​the layer of ferroelectric material (5; 105; 205).

5. A ferroelectric storage device (1; 100; 200) according to any one of claims 1 to 4, wherein the layer of ferroelectric material (5; 105; 205) comprises hafnium dioxide or hafnium dioxide doped with a doping element or an HfxZri XO2 alloy, with 0 <x<l.

6. A ferroelectric storage device (100; 200) according to any one of claims 1 to 5, comprising a support layer (110; 210) having a portion (150; 250) with a U-shaped profile, the first layer (102; 202), the second layer (107; 207) and the layer of ferroelectric material (105; 205) being positioned in the portion (150; 250) with a U-shaped profile of the support layer (110; 210) such that the first layer (102; 202), the second layer (107; 207) and the layer of ferroelectric material (105; 205) have a shape profile similar to the portion (150; 250) with a U-shaped profile of the support layer (110; 210).

7. A ferroelectric storage device (100; 200) according to claim 6, wherein the second portion (106; 206) of the ferroelectric material layer (105; 205) is positioned on the bottom wall (152; 252) of the portion (150; 250) with a U-shaped profile of the support layer (110; 210) and the first portion (105A; 205A) of the ferroelectric material layer (105; 205) is positioned on the side wall (155; 255) of the portion (150; 250) with a U-shaped profile of the support layer (110; 210).

8. A ferroelectric storage device (200) according to claim 6 or 7, wherein the portion (150; 250) with a U-shaped profile of the support layer (110; 210) comprises a bottom wall (152; 252) and a side wall (155; 255), the side wall (155; 155) forming a first non-zero inclination angle (a; |3) relative to a direction normal to the bottom wall (152; 252), the side wall (255) comprising a first portion (255a) and a second portion (255b), the first portion (255a) forming said first inclination angle (a) relative to the direction normal to the bottom wall (252), the second portion (255b) forming a second inclination angle (|3) relative to the direction normal to the bottom wall (252), the layer of ferroelectric material (205) comprises a third portion (250B) having a third thickness (e3),the third thickness (e3) being distinct from the first thickness (ej) and the second thickness (e2), the second part (206) of the layer of ferroelectric material (205) being positioned on the bottom wall (252) of the part (250) with a U-shaped profile of the support layer (210), the first part (205A) of the layer of ferroelectric material (205) being positioned on the first portion (255a) of the side wall (255) of the cavity (250) and the third part (250B) of the layer of ferroelectric material (205) being positioned on the second portion (255b) of the side wall (255) of the part (250) with a U-shaped profile of the support layer (210).,

9. A ferroelectric storage device (200) according to claim 8, wherein the second tilt angle (|3) is greater than said first tilt angle (a).

10. A ferroelectric storage device (100; 200) according to any one of claims 1 to 9, wherein the first layer (2; 102; 202) forms a first electrode, the second layer (7; 107; 207) forms a second electrode and the layer of ferroelectric material (5; 105; 205) forms a memory layer.

11. A method of manufacturing a ferroelectric storage device (1; 100; 200) comprising steps of: - depositing a first layer (2; 102; 202), - depositing a layer of ferroelectric material (5; 105; 205), the layer of ferroelectric material (5; 105; 205) comprising a first portion (5A; 105A; 205A) having a first thickness (ei) and a second portion (6; 106; 206) having a second thickness (e2), the first thickness (ej) and the second thickness (e2) being distinct, and - depositing a second layer (7; 107; 207), the layer of ferroelectric material (5; 105; 205) extending between the first layer (2; 102; 202) and the second layer (7; 107; 207).

12. Manufacturing method according to claim 11, wherein there is provided, before the step of depositing the second layer (7), a step of removing a portion of the layer of ferroelectric material (5), the first part (5A) of the layer of ferroelectric material (5) being formed at a remaining portion associated with said removed portion.

13. A manufacturing method according to claim 12, wherein the deposition of the ferroelectric material layer (5) is carried out in a conformal manner.

14. Manufacturing method according to claim 11, wherein there are provided, before the step of depositing the first layer (102; 202), steps of: - providing a support layer (110; 210), and - forming a cavity (150; 250) in the support layer (110; 210), the cavity (150; 250) comprising a bottom wall (152; 252) and a side wall (155; 255), the side wall (155; 255) forming a first non-zero inclination angle (a, |3) relative to a direction normal to the bottom wall (152; 252), the deposition of the first layer (102; 202), the ferroelectric material layer (105; 205) and the second layer (107; 207) being carried out in the cavity (150; 250) formed, the second part (106; 206) of the ferroelectric material layer (105; 205) being positioned on the bottom wall (152; 252) of the cavity (150; 250) and the first part (105A; 205A) of the ferroelectric material layer (105;205) being positioned on the side wall (155; 255) of the cavity (150; 250).

15. A manufacturing method according to claim 14, wherein the deposition of the layer of ferroelectric material (105; 205) is carried out in a non-conformal manner.

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