FERROELECTRIC STORAGE DEVICE AND METHOD FOR MANUFACTURING SUCH A DEVICE

Abstract

The invention relates to a method for manufacturing a ferroelectric storage device (1) comprising steps of: - depositing a first layer (2), - depositing, by a physical vapor deposition method, a layer of ferroelectric material (5), the layer of ferroelectric material (5) comprising a first part (5A) having a first thickness (e1) and a second part (6; 6A) having a second thickness (e2), the first thickness and the second thickness being distinct, and - depositing a second layer (7), the layer of ferroelectric material extending between the first layer and the second layer (7). 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 method of manufacturing a ferroelectric storage device comprising steps of: - provision of a support layer, - forming a cavity in the support layer, the cavity comprising a bottom wall and a side wall, the side wall forming an angle of inclination relative to a direction normal to the bottom wall, - deposit of a first layer in the cavity,

[0019] - deposition, by a physical vapor deposition method, of a layer of ferroelectric material in the cavity, the layer of ferroelectric material comprising a first portion having a first thickness and a second part having a second thickness, the first thickness and the second thickness being distinct, the deposition of the layer of ferroelectric material comprising steps of: a) deposition of the first part of the layer of ferroelectric material in a first direction associated with a first deposition angle formed relative to a direction normal to the bottom wall, b) deposition of the second part of the layer of ferroelectric material in a second direction associated with a second deposition angle formed relative to the direction normal to the bottom wall, then

[0020] - deposition of a second layer in the cavity, the layer of ferroelectric material extending between the first layer and the second layer.

[0021] Thus, according to the manufacturing method according to the invention, the layer of ferroelectric material of the ferroelectric storage device 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 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.

[0022] 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.

[0023] The different thicknesses used are therefore associated with different intermediate polarization states in the ferroelectric storage device.

[0024] 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.

[0025] In addition to the characteristics which have just been mentioned in the preceding paragraphs, the method of manufacturing 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:

[0026] - the deposition of the layer of ferroelectric material is carried out in a manner anisotropic; - the deposition of the ferroelectric material layer is carried out in a non-compliant manner; - the deposition of the ferroelectric material layer is carried out by an ion beam deposition method or by an evaporation deposition method; - the first deposition angle and the second deposition angle are less than 90 degrees; - the deposition of the first part of the layer of ferroelectric material is implemented by orientation of a first unidirectional ion beam in the first direction and the deposition of the second part of the layer of ferroelectric material is implemented by orientation of a second unidirectional ion beam in the second direction; - a modification of the orientation of the first unidirectional ion beam and / or the second unidirectional ion beam is carried out by tilting the support layer; - a modification of the orientation of the first unidirectional ion beam and / or the second unidirectional ion beam is carried out by tilting a target from which the first unidirectional ion beam and / or the second unidirectional ion beam is formed; - the ferroelectric material layer comprises hafnium dioxide or hafnium dioxide doped with a doping element or an HfxZri XO2 alloy, with 0 <x<l ; et

[0027] - an implantation step is provided before the step of depositing the second layer. of a doping element in the layer of ferroelectric material so as to dope the layer of ferroelectric material with the doping element. BRIEF DESCRIPTION OF THE FIGURES

[0028] 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:

[0029] [Fig.l] illustrates the different intermediate polarization states in the case of a FeRAM type ferroelectric memory having several storage levels,

[0030] [Fig.2] represents, in schematic form, an example of a ferroelectric storage device according to the invention,

[0031] [Fig.3] illustrates, in schematic form, the principle of deposition of a layer of ferroelectric material of the ferroelectric storage device according to the invention,

[0032] [Fig.4] represents, in the form of a flowchart, a first example of a method of manufacturing the ferroelectric storage device according to the invention,

[0033] [Fig.5] illustrates step E102 of the manufacturing method shown in [Fig.4],

[0034] [Fig.6] illustrates step E104 of the manufacturing method shown in [Fig.4],

[0035] [Fig.7] illustrates step E106a of the manufacturing method shown in [Fig.4],

[0036] [Fig.8] illustrates step E106b of the manufacturing method shown in [Fig.4],

[0037] [Fig.9] illustrates step E106c of the manufacturing method shown in [Fig.4],

[0038] [Fig. 10] illustrates step E108 of the manufacturing method shown in [Fig.4],

[0039] [Fig. 11] represents, in the form of a flowchart, a second example of a method of manufacturing the ferroelectric storage device according to the invention,

[0040] [Fig. 12] illustrates step E206b of the manufacturing method shown in [Fig. 11],

[0041] [Fig. 13] illustrates step E206c of the manufacturing method shown in [Fig. 11], and

[0042] [Fig. 14] illustrates step E208 of the manufacturing method shown in [Fig. 11].

[0043] For clarity, identical or similar elements are identified by signs identical references on all figures.

[0044] DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT

[0045] 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.

[0046] [Fig. 2] represents a ferroelectric storage device 1 (also referred to as device 1 hereinafter) according to the invention. As can be seen in this figure, the ferroelectric storage device 1 comprises a first layer 2, a second layer 7 and a layer of ferroelectric material 5 which is arranged between the first layer 2 and the second layer 7.

[0047] The ferroelectric storage device 1 is in the form of a stack of layers. The first layer 2, the layer of ferroelectric material 5 and the second layer 7 form the different layers of this stack.

[0048] As will be described in more detail below with the associated manufacturing method, the ferroelectric storage device 1 is formed in a cavity 50 (visible in FIGS. 5 to 10 and FIGS. 12 to 14).

[0049] This cavity 50 is for example formed in a support layer 10. In other words, the cavity 50 forms a part of the support layer which has a generally “U”-shaped profile (as will be seen later, the lateral branches of the “U” shape can here be inclined relative to the base of the “U” shape). Here, the different layers of the ferroelectric storage device 1 have a shape profile similar to the part 50 with a “U”-shaped profile of the support layer 10.

[0050] This support layer 10 is here formed from a dielectric material. For example, the support layer 10 comprises silicon oxide SiO2.

[0051] 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.

[0052] The cavity 50 comprises a bottom wall 52 and a side wall 55. The bottom wall 52 corresponds to the base of the “U” shape and the side wall 55 corresponds to the lateral branches of the “U” shape. The side wall 55 forms an angle of inclination [3 with respect to an axis z, corresponding to a direction normal to the bottom wall 52. Preferably, this angle of inclination a is non-zero. This angle of inclination [3 is for example less than 50 degrees. Preferably, it is for example less than 35 degrees. Alternatively, this angle of inclination may be zero (the side wall is therefore vertical).

[0053] In [Fig. 3], the angle of inclination of the side wall 55 is substantially zero while in Figures 5 to 10 and Figures 12 to 14, this angle of inclination [3 is non-zero.

[0054] The present invention finds a preferred application in the context of ferroelectric storage devices formed in such a support provided with a cavity having a bottom wall and a side wall.

[0055] The stack forming the ferroelectric storage device 1 extends from the bottom wall 52 and the side wall 55. This stack then comprises several parts (one extending from the bottom wall 52 and another extending from the side wall 55). For the part formed on the bottom wall 52, the different layers of the stack extend parallel to each other. The same is true for the part extending from the side wall 55 (the different layers of the stack also extend parallel to each other on this side wall 55).

[0056] Alternatively, the side wall of the cavity may comprise several portions forming distinct angles relative to a direction normal to the bottom wall. In other words, the side wall of the cavity could have a plurality of slope breaks.

[0057] Each of the layers forming the ferroelectric storage device 1 is now described.

[0058] The first layer 2 is formed from an inert conductive material. This first layer 2 comprises, for example, a metallic material.

[0059] 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).

[0060] As can be seen in the example shown in [Fig.2], the first layer 2 is here in the form of a two-layer structure. Here it comprises a first sub-layer 20 and a second sub-layer 22.

[0061] The second sub-layer 22 is arranged on the first sub-layer 20.

[0062] The first sub-layer 20 comprises a metallic conductive material. Preferably, it comprises titanium Ti or tantalum nitride TaN.

[0063] The first sub-layer 20 has a thickness of between 3 and 20 nanometers (nm). Preferably, this thickness is between 5 and 10 nm.

[0064] This first sub-layer 20 plays both the role of a protective layer and the role of a contact layer allowing the device 1 to be electrically connected to its electronic control and reading circuit.

[0065] The second sub-layer 22 is arranged on the first sub-layer 20. It is in direct contact with the layer of ferroelectric material 5. In other words, the second sub-layer 22 extends between the first sub-layer 20 and the layer of ferroelectric material 5.

[0066] The second sub-layer 22 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.

[0067] For example, when the second sub-layer 22 comprises titanium nitride, the first sub-layer 20 is formed from a conductive material such as titanium Ti.

[0068] Alternatively, when the second sub-layer 22 comprises tantalum, the first sub-layer 20 is formed for example from tantalum nitride TaN.

[0069] As a further variant, when the second sub-layer 22 comprises tungsten, the first sub-layer 20 is formed from a conductive titanium Ti material.

[0070] Here, the thickness of the second sub-layer 22 is between 10 and 100 nm. Preferably, this thickness is between 5 and 10 nm.

[0071] Alternatively, the first layer may comprise a semiconductor material. This semiconductor material comprises, for example, silicon.

[0072] The layer of ferroelectric material 5 is arranged on the first layer 2. Alternatively, the layer of ferroelectric material can be deposited on another layer formed, beforehand, on the first layer.

[0073] This layer of ferroelectric material 5 comprises an active material of variable resistance. This layer of ferroelectric material 5 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 comprises more than 50% of hafnium dioxide).

[0074] 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".

[0075] 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.

[0076] Alternatively, other doping elements may be used such as aluminum Al, germanium Ge, gadolinium Gd, yttrium Y, lanthanum La, scandium Sc or nitrogen N.

[0077] 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).

[0078] As can be seen in Figures 2, 8 and 12, the layer of ferroelectric material 5 comprises at least a first part 5A and a second part 6; 6A.

[0079] In the examples visible in Figures 2 and 8, the first part 5A extends at the level of the bottom wall 52 of the cavity 50 while the second part 6 extends at the level of the side wall 55 of the cavity 50.

[0080] In the example shown in [Fig. 12], the first part 5A extends at the level of the bottom wall 52 of the cavity 50 and the second part 6A extends at the level of the side wall 55 of the cavity 50 as well as partly at the level of the bottom wall 52 (here on the first part 5A).

[0081] Advantageously according to the invention, the first part 5A has a first thickness ei and the second part 6; 6A 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.

[0082] Here, the first thickness ei and the second thickness e2 are distinct. In other words, the layer of ferroelectric material 5 has a non-uniform thickness. In other words, the layer of ferroelectric material 5 has a variable thickness.

[0083] The thickness differences form essential characteristics of the ferroelectric storage device to obtain the different polarization states.

[0084] Thus, thanks to the invention, the differences in thickness used for the layer of ferroelectric material introduces a non-uniformity in the ferroelectric 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. 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.

[0085] 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.

[0086] 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.

[0087] The second thickness e2 is for example between 8 and 17 nm. Preferably, this second thickness e2 is of the order of 10 nm.

[0088] Here, the second thickness e2 is therefore greater than the first thickness ep. This then implies that it will be necessary to apply a higher voltage to allow the storage of information in the intermediate polarization state associated with the second thickness e2 (in comparison with the first thickness ei).

[0089] 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.

[0090] Furthermore, in a plane orthogonal to the direction used to define the thickness, a surface of the first part 5A is defined at one of the faces of the layer of ferroelectric material 5. It is also possible to define the total surface of the layer of ferroelectric material 5 as the surface of one of the faces of the layer of ferroelectric material 5. In other words, the surface of the first part 5A corresponds to a part of the total surface of the layer of ferroelectric material 5.

[0091] Advantageously according to the invention, the first part 5A has a surface area of ​​at least 15% of the total surface area of ​​the layer of ferroelectric material 5. In other words, the surface area of ​​the first part 5A represents at least 15% of the total surface area of ​​the layer of ferroelectric material 5.

[0092] Thus, advantageously according to the invention, the non-uniformities (associated with the thickness differences) 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 well-defined polarization states. distinct (and therefore an absence of overlap between my ranges of voltages to be applied to go back to the different states of polarization).

[0093] In the case of the ferroelectric storage device shown in Figures 9 and 13, the layer of ferroelectric material 5 comprises a third part 6B; 6C. This third part 6B: 6C has a third thickness e3, distinct from the first thickness ei and the second thickness e2.

[0094] In the examples shown in Figures 9 and 13, the third part 6B; 6C extends at the level of the side wall 55 of the cavity 50.

[0095] This third thickness makes it possible to add an additional non-uniformity in the ferroelectric properties of the layer of ferroelectric material 5.

[0096] As shown in Figures 2, 10 and 14, the second layer 7 is arranged on the layer of ferroelectric material 5.

[0097] This second layer 7 comprises, for example, a conductive material. This is in particular a metallic material.

[0098] 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. As a further variant, other conductive materials may be used (and in particular, metal nitride more generally).

[0099] As can be seen in Figures 2, 10 and 14, the second layer 7 is here in the form of a two-layer structure. Here it comprises a first sub-layer 70 and a second sub-layer 72.

[0100] The second sub-layer 72 of the second layer 7 is arranged on the associated first sub-layer 70.

[0101] The second sub-layer 72 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.

[0102] The second sub-layer 72 has a thickness of between 10 and 200 nm.

[0103] This second sub-layer 72 plays both the role of a protective layer and the role of a contact layer allowing the device 1 to be electrically connected to its electronic control and reading circuit.

[0104] The first sub-layer 70 is arranged on the layer of ferroelectric material 5. It is in direct contact with the layer of ferroelectric material 5. In other words, the first sub-layer 70 of the second layer 7 extends between the second sub-layer 72 and the layer of ferroelectric material 5.

[0105] The second sub-layer 72 comprises a metallic conductive material. Preferably, it comprises titanium Ti or tantalum Ta.

[0106] For example, when the second sub-layer 72 comprises titanium nitride, the first sub-layer 70 is formed from a conductive material such as titanium Ti.

[0107] Alternatively, when the second sub-layer 72 comprises tantalum nitride, the first sub-layer 70 is formed from a conductive material such as tantalum Ta.

[0108] As a further variant, when the second sub-layer 72 comprises tungsten, the first sub-layer 70 is formed from a conductive material chosen from titanium Ti or tantalum Ta.

[0109] Here, the thickness of the first sub-layer 70 is between 3 and 20 nm.

[0110] In practice, in the case of an OxRAM type memory (for “Oxide Resistive RAM”), when this bilayer structure is used for the second layer 7, the first sub-layer 70 also has the particularity of being a layer which will allow the creation of oxygen vacancies in the layer of ferroelectric material 5 (when this first sub-layer 70 is in contact with the layer of ferroelectric material 5). In this case, the first sub-layer 70 comprises a conductive material chosen from titanium Ti or tantalum Ta and the second sub-layer 72 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.

[0111] 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.

[0112] 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.

[0113] Alternatively, the second layer may comprise a semiconductor material. This semiconductor material comprises, for example, silicon.

[0114] 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.

[0115] 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.

[0116] Alternatively, the layer of ferroelectric material may comprise more than three distinct thicknesses. This may in particular be a continuous variation in thickness.

[0117] The present invention also relates to a method for manufacturing a ferroelectric storage device 1. Figures 4 to 13 relate to this manufacturing method. More particularly, Figures 4 to 10 relate to a first example of this method for manufacturing the ferroelectric storage device 1 according to the invention. Figures 11 to 14 relate to a second example of the method for manufacturing the ferroelectric storage device 1.

[0118] The method for manufacturing the ferroelectric storage device 1 finds a preferred application for ferroelectric storage devices formed in a cavity. The specificity of the manufacturing method here aims to take advantage of the edge of the side wall of the cavity to form different parts of the layer of ferroelectric material with different thicknesses.

[0119] [Fig.4] represents, in the form of a flowchart, a first example of the manufacturing process.

[0120] As can be seen in this figure, the manufacturing method firstly comprises a step E100 of providing a support layer 10 on which the ferroelectric storage device 1 will be formed. In practice, this support layer 10 is provided with at least one logic component associated with a metal interconnection element (not shown) intended to connect the ferroelectric storage device 1 to lower metal levels.

[0121] Then, the manufacturing method continues to step E102, during which the cavity 50 (in which the ferroelectric storage device 1 will be formed) is formed. [Fig.4] illustrates this step E102.

[0122] In practice, this step E102 is implemented by anisotropic etching so as to form the bottom wall 52 and the side wall 55 of the cavity 50. This is, for example, a dry chemical etching.

[0123] As described previously, the side wall 55 of the cavity 50 is made in such a way as to form the angle of inclination [3 with respect to the z axis parallel to a direction normal to the bottom wall 52. The side wall 55 therefore forms an angle of inclination [3 with respect to a z axis, corresponding to a direction normal to the bottom wall 52.

[0124] As can be seen in [Fig.4], the manufacturing process continues, at step E104, with the deposition of the first layer 2. [Fig.6] illustrates this step E104.

[0125] This first layer 2 is deposited in the cavity 50. More particularly, the first layer 2 is deposited along the bottom wall 52 and the side wall 55 of the cavity 50. The first layer 2 therefore lines and matches the shape of the cavity 50.

[0126] The deposition of the first layer 2 is carried out here in a conformal manner. In this description, the term “conformal deposition” means a deposition carried out in such a way that the layer has a substantially constant thickness at all points. In this description, “substantially constant” means a thickness not varying by more than 20%, preferably by more than 10%, and more preferably by more than 5%. For example, the first layer 2 may be formed by an atomic layer deposition method (or ALD for “Atomic Layer Deposition” according to the commonly used acronym of Anglo-Saxon origin).

[0127] As indicated previously, the first layer 2 here comprises a first sub-layer 20 and a second sub-layer 22.

[0128] Step E104 of depositing the first layer 2 therefore here comprises two sub-steps: a first sub-step E104a of depositing the first sub-layer 20 and a second sub-step E104b of depositing the second sub-layer 22.

[0129] The first sub-layer 20 is therefore first of all deposited, in a conformal manner, in the cavity 50 (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.

[0130] Alternatively, the first sub-layer 20 may be formed by cathode sputtering in a vacuum deposition chamber. In the case where the first sub-layer 20 is formed from titanium nitride, it is a reactive cathode sputtering.

[0131] Then, the second sub-layer 22 of the first layer 2 is deposited, in a conformal manner, on the first sub-layer 20 (step E104b). 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.

[0132] In the case where the second sub-layer 22 is formed from titanium nitride, it is a reactive cathode sputtering.

[0133] Then, the method continues at step E106 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.

[0134] The deposition of the ferroelectric material layer 5 is here implemented anisotropically. Furthermore, the deposition of the ferroelectric material layer 5 is here non-conformal.

[0135] In practice, the layer of ferroelectric material 5 is deposited by a physical vapor deposition (or PVD) method.

[0136] Preferably here, the ferroelectric material layer 5 is deposited by an ion beam deposition (or IBD) method. Alternatively, the ferroelectric material layer may be deposited by a vacuum evaporation deposition method. Similar deposition rates can be achieved using a vacuum evaporation deposition method and a vacuum evaporation deposition method. Ion beam deposition. In practice, in the case of a vacuum evaporation deposition method, a crucible contains the material to be deposited. This crucible is heated by the Joule effect. By varying the current intensity, it is then possible to vary the deposition rate.

[0137] The anisotropic character of the deposition is based here on controlling the orientation of a target, from which atoms are torn off, relative to a substrate (here for example the support layer). The atoms torn off from the target then form an ion beam associated with a corresponding deposition direction. Thus, the anisotropic character of the deposition is associated with different deposition directions (using the deposition methods introduced previously).

[0138] [Fig.3] schematically illustrates the principle of this anisotropic deposition of the layer of ferroelectric material according to the invention.

[0139] In this figure, the cavity 50 is shown with a side wall 55 forming a zero angle with respect to the normal direction (parallel to the z axis) to the bottom wall 52. Of course, the principle described below applies in the same way for cavities whose side wall forms a non-zero angle with this normal direction with the bottom wall.

[0140] Here, the different thicknesses of the layer of ferroelectric material are obtained by using several unidirectional ion beam depositions, each oriented in a given direction.

[0141] More particularly, in general, the layer of ferroelectric material is obtained by the deposition of a plurality of parts (at least two) forming, at the end, this layer of ferroelectric material 5. The deposition of each of these parts is carried out according to an associated deposition angle ai, a2, a3. Each deposition angle ai, a2, a3 is defined with respect to a normal direction (parallel to the z axis) to the bottom wall 52 of the cavity 50. Here, each deposition angle ab a2, a3 is for example less than 90 degrees. Preferably, each deposition angle ab a2, a3 is between 5 and 85 degrees.

[0142] Advantageously according to the invention, the ion beam making it possible to deposit each of these parts is arranged relative to the edge of the side wall 55 of the cavity 50. More particularly here, each ion beam is arranged relative to a corner C1 formed at the end of the side wall 55 of the cavity 50. More particularly, the ion beam concerned is directed towards the support layer and is partly cut because it crosses the corner C1 formed at the end of the side wall 55 of the cavity 50. The corner C1 then generates a shadowing effect by cutting the ion beam, thus making it possible to expose only certain areas of the cavity 50 to this ion beam.

[0143] In other words, the side wall 55 of the cavity 50 produces, for certain areas of the cavity, a shading effect, that is to say that certain areas of the cavity 50 are not not reached by the ion beam concerned. In other words, thanks to the configuration of the ion beams used in the invention, each ion beam (at an associated deposition angle) causes the deposition of the ferroelectric material on a specific area of ​​the cavity 50.

[0144] In addition, the characteristics associated with this ion beam make it possible to adjust the thickness of the portion of the deposited ferroelectric material layer 5. In particular, the thickness of each portion of the deposited ferroelectric material layer 5 depends, for example, here on the deposition speed and deposition time to form the ion beam concerned.

[0145] Advantageously, the use of several deposition angles ai, a2, a3 and the adjustment of the parameters of each ion beam then make it possible to carry out depositions in different zones of the cavity 50 but also to vary the thickness of the layer of ferroelectric material 5 in certain zones of the cavity 50.

[0146] This deposition principle is illustrated, schematically, in [Fig. 3]. A deposition of a first part 105A of the ferroelectric material layer 5 is carried out according to a first deposition angle ab As can be seen in [Fig. 3], according to this deposition, the first part 105A is deposited on a part of the bottom wall 52 and a part of the side wall 55 of the cavity 50. This deposition of the first part 105A is carried out with a deposition speed and for a deposition time making it possible to obtain a thickness ex[ for this first part 105A.

[0147] Elsewhere in the cavity 50, as can be seen in [Fig.3], the other zones are not exposed to the ion beam emitted according to the first deposition angle ab; therefore, no layer of ferroelectric material is formed (following this deposition of the first layer 105A) in these zones.

[0148] Then, a deposition of a second part 105B of the layer of ferroelectric material 5 is carried out according to a second deposition angle a2. According to [Fig. 3], this second part 105B is also deposited on a part of the bottom wall 52 and a part of the side wall 55 of the cavity 50. More particularly, as shown in [Fig. 3], the second part 105B is, in part, deposited on the first layer 105 A (which makes it possible for the areas concerned to obtain a greater thickness of ferroelectric material).

[0149] This deposition of the second part 105B is carried out with a deposition speed and for a deposition time making it possible to obtain a thickness ex2 for this second part 105B. Thus, for the zones of the cavity 50 already provided with the first part 105A, at this stage, the layer of ferroelectric material has a thickness of the order of the sum of the thickness exi and the thickness ex2. For the other zones concerned by the deposition of the second part 105B, the layer of ferroelectric material has the thickness ex2.

[0150] Here too, the zones not exposed to the ion beam emitted according to the second deposition angle a2 are therefore devoid of this second part 105B (and for certain zones, which had not been subjected to the ion beam emitted according to the first deposition angle ab they are, at this stage, completely devoid of ferroelectric material).

[0151] As shown in [Fig. 3], the deposition of a third portion 105C of the layer of ferroelectric material 5 is carried out at a third deposition angle a3. This third portion 105C is also deposited on a portion of the bottom wall 52 and a portion of the side wall 55 of the cavity 50. More particularly, as shown in [Fig. 3], the third portion 105C is, in part, deposited on the second layer 105B (which makes it possible for the areas concerned to obtain a greater thickness of ferroelectric material).

[0152] This deposition of the third part 105C is carried out with a deposition speed and for a deposition time making it possible to obtain a thickness ex3 for this third part 105C. Thus, for the areas of the cavity 50 already provided with the first part 105A and the second part 105B, at this stage, the layer of ferroelectric material has a thickness of the order of the sum of the thickness exb of the thickness ex2 and of the thickness ex3. For the areas of the cavity 50 provided with the second part 105B (only), the layer of ferroelectric material has (at this stage) a thickness of the order of the sum of the thickness ex2 and of the thickness ex3. For the other areas concerned by the deposition of the third part 105C, the layer of ferroelectric material has the thickness ex3.

[0153] Here too, the zones not exposed to the ion beam emitted according to the third deposition angle a3 are therefore devoid of this third part 105C (and for certain zones, which had not been subjected to the ion beam emitted according to the first deposition angle oq or emitted according to the second deposition angle a2, they are, at this stage, completely devoid of ferroelectric material).

[0154] The example shown in [Fig. 3] involves the emission of ion beams at three distinct deposition angles. The present invention is of course not limited to three deposition angles. There may be only two or more than three. Moreover, a generalization to a higher number of deposition angles makes it possible to obtain a quasi-continuous variation in the thickness of the layer of ferroelectric material in the cavity.

[0155] In practice, the change in orientation of the ion beam (i.e. the modification of the deposition angle) is implemented by positioning the support layer 10 on a manufacturing support (not shown) and by tilting this manufacturing support so as to obtain the desired deposition angle.

[0156] Furthermore, in order to obtain a circular symmetry of deposition for each part of the layer of ferroelectric material (and therefore for the layer of ferroelectric material itself), the manufacturing support can be rotated around an axis orthogonal to the bottom wall 52 of the cavity 50. This can be implemented regardless of the deposition method considered in the present invention.

[0157] Alternatively, the change in orientation of the ion beam can be implemented by changing the orientation of the target from which the atoms are torn off (and which make it possible to form the ion beam) so as to obtain the different desired deposition angles.

[0158] Based on this principle of anisotropic deposition, the method of manufacturing the ferroelectric storage device 1 then comprises, in step E106, a step E106a of deposition of the first part 5A of the layer of ferroelectric material 5. This step is shown in [Fig.7].

[0159] As described previously, this first part 5A is deposited, in the cavity 50, according to a first deposition angle ab. This step El06a is implemented so as to obtain a thickness ei of ferroelectric material, for the first part 5A, in the cavity 50.

[0160] Here, the first part 5A is deposited at the bottom wall 52 of the cavity 50. This means that, in this first example of implementation of the manufacturing method according to the invention, the first deposition angle ai is substantially zero.

[0161] Step El06 of depositing the layer of ferroelectric material 5 then comprises a step El06b of depositing a second part 6 of the layer of ferroelectric material 5. This step E106b is shown in [Fig.8].

[0162] As described previously, this second part 6 is deposited in the cavity 50, at a second angle a2. This step El06b is implemented so as to obtain a second part 6 with a thickness e2 (in the cavity 50).

[0163] Here, the second part 6 is deposited at the level of the side wall 55 of the cavity 50. The second deposition angle a2 is therefore chosen here as a function of the dimensions of the cavity 50 in order to allow deposition (by ion beam) only on the side wall 55 of the cavity 50.

[0164] Furthermore, in order to ensure circular symmetry of the deposition of this second part 6 of the layer of ferroelectric material 5, step E106b comprises for example the rotation of the manufacturing support (not shown) in order to ensure that the second part 6 is deposited on the entire side wall 55 of the cavity 50. This can be implemented regardless of the deposition method considered in the present invention.

[0165] Alternatively, this circular symmetry of the deposit can be ensured by a change in the orientation of the target from which the atoms are torn off (and which make it possible to form the ion beam).

[0166] Finally, as can be seen in [Fig.4], step E106 of depositing the layer of ferroelectric material 5 here comprises a step El06c of depositing a third part 6B of the layer of ferroelectric material 5. This step El06c is shown in [Fig.9].

[0167] This second part 6 is deposited in the cavity 50 at a third angle a3. This step E106c is implemented so as to obtain a third part 6B with a thickness e3 (in the cavity 50).

[0168] Here, the third part 6B is deposited at the level of the side wall 55 of the cavity 50 (and even here at the level of the end of the side wall 55, opposite the bottom wall 52 of the cavity 50). The third deposition angle a3 is therefore chosen here in order to allow deposition (by ion beam) only on the relevant area of ​​the side wall 55 of the cavity 50.

[0169] Furthermore, in order to ensure, here too, a circular symmetry of the deposition of this third part 6B of the layer of ferroelectric material 5, step E106c comprises for example the rotation of the manufacturing support (not shown) in order to ensure that the third part 6B is deposited on the relevant zone of the side wall 55 of the cavity 50. This can be implemented whatever the deposition method considered in the present invention.

[0170] Alternatively, this circular symmetry of the deposit can be ensured by a change in the orientation of the target from which the atoms are torn off (and which make it possible to form the ion beam).

[0171] Finally, at the end of step E106, the layer of ferroelectric material 5 is formed in the cavity 50. In this first example of the method for manufacturing the device 1 of ferroelectric material, the layer of ferroelectric material 5 here comprises the first part 5A of thickness ei formed on the bottom wall 52 of the cavity 50, the second part 6 of thickness e2 formed on the side wall 55 of the cavity 50 and the third part of thickness e3 formed on a part of the side wall 55 of the cavity 50.

[0172] The thicknesses eb e2, e3 are here distinct. This then implies that it will be necessary to apply different voltages to allow the reading of the information stored in the intermediate polarization state associated with each of the first part 5A, the second part 6 and the third part 6B.

[0173] It should be noted here that step E106c may be omitted if it is desired that the layer of ferroelectric material comprises only two different thicknesses. Of course, step E106 may comprise additional steps corresponding to the deposition of additional parts of the layer of ferroelectric material having other thicknesses (these depositions being carried out according to other deposition angles for example).

[0174] The method then continues, at step E108, with the deposition of the second layer 7. This step E108 is shown in [Fig.10].

[0175] The second layer 7 is formed on the layer of ferroelectric material 5 obtained at the end of step E106.

[0176] The deposition of the second layer 7 is carried out in a compliant manner.

[0177] As indicated previously, the second layer 7 may here comprise a first sub-layer 70 and a second sub-layer 72.

[0178] Step E108 of depositing the second layer 7 therefore comprises two sub-steps here: a first sub-step E108a of depositing the first sub-layer 70 and a second sub-step 108b of depositing the second sub-layer 72.

[0179] The first sub-layer 70 is therefore first deposited, in a conformal manner, on the layer of ferroelectric material 5 (step E108a). 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.

[0180] Alternatively, the first sub-layer may be formed by chemical vapor deposition.

[0181] Then, the second sub-layer 72 of the second layer 107 is deposited, in a conformal manner, on the first sub-layer 70 (step E108b). As can be seen in [Fig. 10], the second sub-layer 72 is formed so as to fill all the remaining space in the cavity 50. This then makes it possible to obtain a ferroelectric storage device 1 completely integrated in the cavity 50 and without any projection or recession formed relative to the surface of the support layer 10. The assembly formed by the support layer 10 in which the ferroelectric storage device 1 is integrated therefore has a uniform surface.

[0182] In practice, 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.

[0183] In the case where the second sub-layer 72 is formed from titanium nitride, it is a reactive cathode sputtering.

[0184] In practice, although this is not visible in the attached figures, it is not excluded that the different layers of the ferroelectric storage device 1 are also deposited on the front face (free surface opposite the bottom wall 52) of the support layer 10. Thus, optionally, in order to ensure the flatness and uniformity of the ferroelectric storage device 1 (and in particular of the free surface of the device 1), 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 acronym of Anglo-Saxon origin commonly used). Any other suitable method can be used (notably masking methods).

[0185] 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.

[0186] Alternatively, an encapsulation step may be provided after this planarization step. Finally, a connection to the second layer 7 may be implemented.

[0187] Thus, at the end of the manufacturing process according to this first example, the ferroelectric storage device 1 obtained comprises a layer of ferroelectric material 5 with variable thickness. Here, this variability of thicknesses is obtained by playing on the difference in uniformity of the deposition between the bottom wall and the side wall of the cavity. More particularly, the differences in thicknesses are obtained by choosing optimal conditions for the deposition of the ferroelectric material by judicious control of the inclination of the flux of atoms used for this deposition.

[0188] As indicated previously, the variability of thicknesses makes it possible to introduce non-uniformities into the ferroelectric properties of the layer of ferroelectric material. This non-uniformity of properties makes it possible in particular to increase the differences between the ranges of voltages to be applied to access the different intermediate polarization states.

[0189] 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 information read.

[0190] In addition, the manufacturing method according to this first example makes it possible to obtain an architecture of the ferroelectric storage device 1 in three dimensions. This makes it possible in particular to increase the surface area of ​​the capacity of the ferroelectric storage device 1.

[0191] According to an alternative implementation of this first example, the manufacturing method may comprise, between step E106 of depositing the layer of ferroelectric material and step E108 of depositing the second layer, a step of implanting a doping element in the first layer of ferroelectric material formed in step E106. This step then makes it possible to dope the layer of ferroelectric material with the doping element.

[0192] 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.

[0193] 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 cm2.

[0194] [Fig. 11] represents, in the form of a flowchart, a second example of the manufacturing method according to the invention.

[0195] This second example of the manufacturing process is similar to the first example described previously. Also, only the differences from this first example are described in detail below.

[0196] As can be seen in [Fig.l 1], the manufacturing method firstly comprises a step E200 (similar to step E100) of providing a support layer 10 on which the ferroelectric storage device 1 will be formed. In practice, this support layer 10 is provided with at least one logic component associated with a metal interconnection element (not shown) intended to connect the ferroelectric storage device 1 to lower metal levels.

[0197] Then, the manufacturing method continues at step E202 (similar to step E102 described previously), during which the cavity 50 (in which the ferroelectric storage device 1 will be formed) is formed.

[0198] In practice, this step E202 is implemented by isotropic etching so as to form the bottom wall 52 and the side wall 55 of the cavity 50. This is, for example, dry chemical etching.

[0199] As described above, the side wall 55 of the cavity 50 is made in such a way as to form the angle of inclination [3 relative to the z axis parallel to a direction normal to the bottom wall 52.

[0200] As can be seen in [Fig.l 1], the manufacturing method according to this second example continues at step E204, by the deposition of the first layer 2. Step E204 is similar to step E104 described for the first example.

[0201] This first layer 2 is deposited in the cavity 50. More particularly, the first layer 2 is deposited along the bottom wall 52 and the side wall 55 of the cavity 50. The first layer 2 therefore lines and matches the shape of the cavity 50.

[0202] As indicated previously, the first layer 2 here comprises a first sub-layer 20 and a second sub-layer 22.

[0203] Step E204 of depositing the first layer 2 therefore here comprises two sub-steps: a first sub-step E204a of depositing the first sub-layer 20 and a second sub-step E204b of depositing the second sub-layer 22.

[0204] The first sub-layer 20 is therefore first deposited, in a conformal manner, in the cavity 50 (step E204a). In practice, the first sub-layer 20 is for example formed by an atomic layer deposition (or ALD) method or by chemical vapor deposition.

[0205] Alternatively, the first sub-layer 20 may be formed by spraying ca thodic in a vacuum deposition chamber. In the case where the first sub-layer 20 is formed from titanium nitride, it is a reactive cathodic sputtering.

[0206] Then, the second sub-layer 22 of the first layer 2 is deposited, in a conformal manner, on the first sub-layer 20 (step E204b). 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.

[0207] In the case where the second sub-layer 22 is formed from titanium nitride, it is a reactive cathode sputtering.

[0208] Then, the method continues at step E206 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.

[0209] The deposition of the ferroelectric material layer 5 is, here too, implemented anisotropically. Furthermore, the deposition of the ferroelectric material layer 5 is here non-conformal.

[0210] In practice, the layer of ferroelectric material 5 is deposited by a physical vapor deposition (or PVD) method.

[0211] Preferably here, the layer of ferroelectric material 5 is deposited by an ion beam deposition (or IBD) method. Alternatively, the layer of ferroelectric material may be deposited by a vacuum evaporation deposition method. It is possible to obtain similar deposition rates using a vacuum evaporation deposition method and an ion beam deposition method. In practice, in the case of a vacuum evaporation deposition method, a crucible comprises the material to be deposited. This crucible is heated by the Joule effect. By varying the intensity of the current, it is then possible to vary the deposition rate.

[0212] The anisotropic character of the deposition is also based here on controlling the orientation of a target, from which atoms are torn off, relative to a substrate (here for example the support layer). The atoms torn off from the target then form an ion beam associated with a corresponding deposition direction. Thus, the anisotropic character of the deposition is associated with different deposition directions (using the deposition methods introduced previously).

[0213] Based on this principle of anisotropic deposition, the method for manufacturing the ferroelectric storage device 1 then comprises, in step E206, a step E206a (similar to step E106a described previously) of deposition of the first part 5A of the layer of ferroelectric material 5.

[0214] As described previously, this first part 5A is deposited, in the cavity 50, according to a first deposition angle ab. This step E206a is implemented so as to obtaining a thickness ei of ferroelectric material, for the first part 5A, in the cavity 50.

[0215] Here, the first part 5A is deposited at the bottom wall 52 of the cavity 50. This means that, in this second example of implementation of the manufacturing method according to the invention, the first deposition angle ai is substantially zero.

[0216] Step E206 of depositing the layer of ferroelectric material 5 then comprises a step E206b of depositing a second part 6A of the layer of ferroelectric material 5. This step E206B is shown in [Fig. 12].

[0217] As described previously, this second part 6A is deposited in the cavity 50, at a second angle a2. This step E206b is implemented so as to obtain a second part 6A having a thickness e2 (in the cavity 50).

[0218] Here, the second part 6A is deposited at the level of the side wall 55 of the cavity 50 and of a part of the bottom wall 52 of the cavity 50. The second deposition angle a2 is therefore chosen here in order to allow deposition (by ion beam) on the side wall 55 and at the level of a part of the bottom wall of the cavity 50.

[0219] Furthermore, in order to ensure circular symmetry of the deposition of this second part 6A of the layer of ferroelectric material 5, step E206b comprises for example the rotation of the manufacturing support (not shown) in order to ensure that the second part 6A is deposited on the whole of the side wall 55 and on the relevant part of the bottom wall 52 of the cavity 50. This can be implemented regardless of the deposition method considered in the present invention.

[0220] Alternatively, this circular symmetry of the deposit can be ensured by a change in the orientation of the target from which the atoms are torn off (and which make it possible to form the ion beam).

[0221] Finally, as can be seen in [Fig. 1 1], step E206 of depositing the layer of ferroelectric material 5 here comprises a step E206c (similar to step El06c described previously) of depositing a third part 6C of the layer of ferroelectric material 5. This step E206c is shown in [Fig. 13].

[0222] This third part 6C is deposited in the cavity 50 at a third angle a3. This step E206c is implemented so as to obtain a third part 6C with a thickness e3 (in the cavity 50).

[0223] Here, the third part 6C is deposited at the level of the side wall 55 of the cavity 50 (and even here at the level of the end of the side wall 55, opposite the bottom wall 52 of the cavity 50). The third deposition angle a3 is therefore chosen here in order to allow deposition (by ion beam) only on the relevant area of ​​the side wall 55 of the cavity 50.

[0224] Furthermore, in order to ensure, here too, a circular symmetry of the deposition of this third part 6C of the layer of ferroelectric material 5, step E206c includes for example rotating the manufacturing support (not shown) in order to ensure that the third part 6C is deposited on the relevant area of ​​the side wall 55 of the cavity 50. This can be implemented regardless of the deposition method considered in the present invention.

[0225] Alternatively, this circular symmetry of the deposit can be ensured by a change in the orientation of the target from which the atoms are torn off (and which make it possible to form the ion beam).

[0226] Finally, at the end of step E206, the layer of ferroelectric material 5 is formed in the cavity 50. In the second example of the method for manufacturing the device 1 of ferroelectric material, the layer of ferroelectric material 5 here comprises the first part 5A of thickness ei formed on the bottom wall 52 of the cavity 50, the second part 6A of thickness e2 formed on the side wall 55 and on a part of the bottom wall of the cavity 50 and the third part 6C of thickness e3 formed on a part of the side wall 55 of the cavity 50.

[0227] The thicknesses eb e2, e3 are here distinct. This then implies that it will be necessary to apply different voltages to allow the reading of the information stored in the intermediate polarization state associated with each of the first part 5A, the second part 6A and the third part 6C.

[0228] It should be noted here that step E206c may be omitted if it is desired that the layer of ferroelectric material comprises only two different thicknesses. Of course, step E206 (as for step E106 described previously) may comprise additional steps corresponding to the deposition of additional parts of the layer of ferroelectric material at other thicknesses (these depositions being carried out according to other deposition angles).

[0229] The method then continues, at step E208, with the deposition of the second layer 7. This step E208 is shown in [Fig. 14]. This step is similar to step El08 described previously for the first example.

[0230] The second layer 7 is formed on the layer of ferroelectric material 5 obtained at the end of step E206.

[0231] The deposition of the second layer 7 is carried out in a compliant manner.

[0232] As indicated previously, the second layer 7 may here comprise a first sub-layer 70 and a second sub-layer 72.

[0233] Step E208 of depositing the second layer 7 therefore here comprises two sub-steps: a first sub-step E208a of depositing the first sub-layer 70 and a second sub-step E208b of depositing the second sub-layer 72.

[0234] The first sub-layer 70 is therefore first of all deposited, in a conformal manner, on the layer of ferroelectric material 5 (step E208a). In practice, the first sub-layer 70 is for example formed by cathode sputtering in a chamber of vacuum deposition. In the case where the first sub-layer 70 is formed from titanium nitride, it is a reactive cathode sputtering.

[0235] Alternatively, the first sub-layer may be formed by chemical vapor deposition.

[0236] Then, the second sub-layer 72 of the second layer 107 is deposited, in a conformal manner, on the first sub-layer 70 (step E208b). As can be seen in [Fig. 14], the second sub-layer 72 is formed so as to fill all the remaining space in the cavity 50. This then makes it possible to obtain a ferroelectric storage device 1 completely integrated in the cavity 50 and without any projection or recession formed relative to the surface of the support layer 10. The assembly formed by the support layer 10 in which the ferroelectric storage device 1 is integrated therefore has a uniform surface.

[0237] In practice, 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.

[0238] In the case where the second sub-layer 72 is formed from titanium nitride, it is a reactive cathode sputtering.

[0239] In practice, although this is not visible in the attached figures, it is not excluded that the different layers of the ferroelectric storage device 1 are also deposited on the front face (free surface opposite the bottom wall 52) of the support layer 10. Thus, optionally, in order to ensure the flatness and uniformity of the ferroelectric storage device 1 (and in particular of the free surface of the device 2), a planarization step may also 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).

[0240] 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.

[0241] Alternatively, an encapsulation step may be provided after this planarization step. Finally, a connection to the second layer 7 may be implemented.

[0242] Thus, at the end of the manufacturing process according to this second example, the ferroelectric storage device 1 obtained comprises a layer of ferroelectric material with variable thickness. Here, this variability of thicknesses is obtained by playing on the difference in uniformity of the deposit between the bottom wall and the side wall of the cavity. More specifically, the thickness differences are obtained by choosing optimal conditions for the deposition of the ferroelectric material by judicious control of the inclination of the flux of atoms used for this deposition.

[0243] As indicated previously, 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 access 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 information read.

[0244] In addition, the manufacturing method according to this second example also makes it possible to obtain a three-dimensional architecture of the ferroelectric storage device 1. This makes it possible in particular to increase the surface area of ​​the capacity of the ferroelectric storage device 1.

[0245] According to an alternative implementation of this second example, the manufacturing method may comprise, between step E206 of depositing the layer of ferroelectric material and step E208 of depositing the second layer, a step of implanting a doping element in the first layer of ferroelectric material formed in step E206. This step then makes it possible to dope the layer of ferroelectric material with the doping element.

[0246] 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.

[0247] 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 cm2.

[0248] Applications

[0249] 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).

[0250] 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 acronym of Anglo-Saxon origin commonly used).

[0251] 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 In this case, an additional layer is added between the ferroelectric material layer and the second layer. This additional layer includes a dielectric material. This dielectric material is, for example, aluminum oxide A12O3.

[0252] 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 method of manufacturing a ferroelectric storage device (1) comprising steps of: - providing a support layer (10), - forming a cavity (50) in the support layer (10), the cavity (50) comprising a bottom wall (52) and a side wall (55), the side wall (55) forming an angle of inclination (|3) relative to a direction normal to the bottom wall (52), - depositing a first layer (2) in the cavity (50), - depositing, by a physical vapor deposition method, a layer of ferroelectric material (5) in the cavity (50), the layer of ferroelectric material (5) comprising a first portion (5A) having a first thickness (ej and a second portion (6;6A) having a second thickness (e2), the first thickness (ej and the second thickness (e2) being distinct, the deposition of the layer of ferroelectric material (5) comprising steps of: a) deposition of the first part (5A) of the layer of ferroelectric material (5) in a first direction associated with a first deposition angle (ai) formed with respect to a direction normal to the bottom wall (52), b) deposition of the second part (6; 6A) of the layer of ferroelectric material (5) in a second direction associated with a second deposition angle (a2) formed with respect to the direction normal to the bottom wall (52), then - deposition of a second layer (7) in the cavity (50), the layer of ferroelectric material (5) extending between the first layer (2) and the second layer (7).;

2. Manufacturing method according to claim 1, wherein the deposition of the layer of ferroelectric material (5) is carried out anisotropically.

3. A manufacturing method according to claim 1 or 2, wherein the deposition of the ferroelectric material layer (5) is carried out in a non-conformal manner.

4. Manufacturing method according to any one of claims 1 to 3, wherein the deposition of the ferroelectric material layer (5) is carried out by an ion beam deposition method or by a evaporative deposition method.

5. A manufacturing method according to any one of claims 1 to 4, wherein the first deposition angle (aj) and the second deposition angle (a2) are less than 90 degrees.

6. Manufacturing method according to any one of claims 1 to 5, wherein the deposition of the first part (5A) of the layer of ferroelectric material (5) is carried out by orientation of a first unidirectional ion beam in the first direction and the deposition of the second part (6; 6A) of the layer of ferroelectric material (5) is carried out by orientation of a second unidirectional ion beam in the second direction.

7. A method according to claim 6, wherein a change in the orientation of the first unidirectional ion beam and / or the second unidirectional ion beam is achieved by tilting the support layer (10).

8. A method according to claim 6 or 7, wherein a change in the orientation of the first unidirectional ion beam and / or the second unidirectional ion beam is achieved by tilting a target from which the first unidirectional ion beam and / or the second unidirectional ion beam are formed.

9. A method according to any one of claims 1 to 8, wherein the layer of ferroelectric material (5) comprises hafnium dioxide or hafnium dioxide doped with a doping element or an alloy Hfx Zri XO2, with 0 <x<l.

10. Method according to any one of claims 1 to 9, in which there is provided, before the step of depositing the second layer (7), a step of implanting a doping element in the layer of ferroelectric material (5) so as to dope the layer of ferroelectric material (5) with the doping element.

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