METHOD FOR MANUFACTURING AN ASYMMETRIC SOT-MRAM MEMORY CELL UNIT, MEMORY CELL UNIT OBTAINED BY PERFORMING THE METHOD FOR MANUFACTURING AN ASYMMETRIC SOT-MRAM MEMORY CELL UNIT - Patent application

Abstract

A method (50) for manufacturing an asymmetric SOT-MRAM memory cell unit, the memory cell unit having a conductor track and a pad arranged on the conductor track and having at least one magnetic region that is magnetized free, comprises the steps of creating (100) a stack of multiple extended layers having at least one extended first magnetic layer, depositing (200) a mask on a top surface of the stack, and defining (400, 500) first magnetic regions in the extended first magnetic layer through ion irradiation of the top surface of the stack carrying the mask, where parameters of the ion irradiation are adapted to modify the magnetic properties of the material forming the first magnetic layer.

Description

[Technical field]

[0001] The general field of the invention is that of non-volatile memories of the asymmetric SOT-MRAM type, and more particularly, the invention relates to a method for manufacturing a SOT-MRAM memory point. [Background technology]

[0002] MRAM ("Magnetic Random Access Memory") includes memory points having pads made up of a stack of regions of small thickness, including at least one first magnetic region with free magnetization, a second magnetic region with fixed magnetization and a region forming a tunnel barrier at the interface between the first and second magnetic regions.

[0003] The directions of magnetization in the first and second magnetic regions can be parallel to the plane of these regions or perpendicular to the plane of these regions, and although the case of perpendicular magnetization directions is described in detail herein, the teachings extend equally to the case of parallel magnetization directions.

[0004] Binary information can be stored depending on the magnetization direction of the first magnetic region.

[0005] For STT-MRAM (Spin Transfer Torque MRAM) memory points, binary information is written by injecting a write current through the pads (i.e. perpendicular to the plane of the region) and the stored information is read by injecting a read current also through the pads.

[0006] This technique has several drawbacks, notably a slower write speed linked to rapid aging of the memory due to high write current densities, and the risk of errors during the read and write steps in the STT-MRAM memory point array.

[0007] Therefore, a SOT-MRAM (Spin-Orbit Torque MRAM) memory point is provided, for which a pad is placed in the center of a conductive track and electrodes are attached to the two ends of the track.

[0008] Writing is then performed by injecting a write current through the conductive tracks, i.e. between the two electrodes parallel to the plane of the pad area, while reading is performed on the STT-MRAM memory point by injecting a read current through the pad perpendicular to the plane of the area.

[0009] However, to operate effectively, SOT-MRAM memory points must be subjected to an external magnetic bias field that has a component collinear with the write current injection direction. Yet the means to generate such a field remains the main challenge in integrating SOT-MRAM memories.

[0010] That is why more recently, asymmetric SOT-MRAM memory points have been provided, for example US Pat. No. 6,399,433 which describes various embodiments of asymmetric SOT-MRAM memory points.

[0011] In the above mentioned document, the asymmetry is obtained by shaping the pad so that it is no longer symmetrical about a reference plane that is perpendicular to the plane of the pad area and parallel to the direction of injection of the write current into the conductive track.

[0012] This geometric asymmetry allows for an interruption in the mirror symmetry about the reference plane, which has essentially the same effect as the application of an external magnetic bias field. With asymmetric SOT-MRAM memory points, it is no longer necessary to use an external magnetic field.

[0013] The pads further advantageously have tips which allow the magnetization of the first magnetic region to vary depending on the direction of injection of a current into the conductive track. These tips can be very small, making the industrial production of the pads even more difficult.

[0014] Now that the value of asymmetric SOT-MRAM memory points has been proven, the question arises of producing these non-volatile memory devices on an industrial scale.

[0015] In fact, in laboratories, the methods implemented to fabricate samples with sizes compatible with industrial use, typically less than 100 nm, generally use electron beam lithography.

[0016] These methods make it possible to define asymmetric SOT-MRAM memory pads with the required precision, but are characterized by a slow manufacturing speed, not least due to the need to move the electron beam to irradiate the resin used to define the shape of each memory point. Such methods are therefore not compatible with industrial production, where it is attempted to build billions of memory points as quickly as possible on a semiconductor wafer with a radius of, for example, 300 mm. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] French Patent No. 3031622 Summary of the Invention [Problem to be solved by the invention]

[0018] SUMMARY OF THE PRESENT EMBODIMENT It is therefore an object of the present invention to solve this problem, inter alia, by providing a method for manufacturing SOT-MRAM memory points at the throughput required by the industry. [Means for solving the problem]

[0019] To that end, one object of the present invention is a method for manufacturing an asymmetric SOT-MRAM memory point, comprising a conductive track and a pad arranged on the conductive track and comprising at least one magnetic region that is magnetized free, characterized in that it comprises the steps of fabricating a stack of multiple extended layers including at least one extended first magnetic layer, depositing a mask on the upper surface of the stack, and defining a first magnetic region in the extended first magnetic layer by ion irradiation of the upper surface of the stack carrying the mask, the parameters of the ion irradiation being adapted to modify the magnetic properties of the constituent material of the first magnetic layer.

[0020] According to particular embodiments, the method comprises one or more of the following features, taken separately or in any technically possible combination: The ion irradiation can modify the magnetic properties of areas of the first magnetic layer that are exposed during the ion irradiation while preserving the magnetic properties of areas of the first magnetic layer that are not exposed during the ion irradiation due to the presence of the mask. The step of defining by ion irradiation includes a relative displacement during the irradiation period of the ion source with respect to the upper surface of the stack carrying the mask so as to modify the irradiation direction, the irradiation parameters being adapted to be sufficient to eliminate the magnetic properties of areas exposed throughout the entire irradiation period but insufficient to eliminate the magnetic properties of areas exposed for only a portion of the irradiation period. The step of defining by ion irradiation includes a first irradiation in a first irradiation direction followed by a second irradiation in a second irradiation direction, the parameters of the first and second irradiation being selected to be sufficient to eliminate the magnetic properties of areas exposed during both the first and second irradiation, but insufficient to eliminate the magnetic properties of areas exposed only during the first irradiation or only during the second irradiation. The method includes modifying the mask between the first and second ion bombardments. The ion bombardment is preferably performed with low energy light ions, preferably He, of between 10 keV and 100 keV, more preferably equal to 30 keV. + , 10 14 ions / cm2 and 10 17 ions / cm 2 Between 10 and 20 16 ions / cm 2 is performed with an intensity equal to The method includes, after the step of depositing a mask and before the step of defining by ion irradiation, an etching step consisting in etching the upper layer of the stack around the deposited mask so that the ion current used during the ion irradiation can reach the first magnetic layer. The step of manufacturing a stack of multiple elongated layers consists in superposing a conductive layer, a first magnetic layer, an intermediate layer, a second magnetic layer and an electrode layer on a semiconductor substrate. The method includes, after the step of definition by ion irradiation, a step of finishing the memory point consisting in removing the mask, etching the stack to expose conductive tracks on either side of the pad, and fabricating electrodes on the pad with each of the ends of the conductive layer.

[0021] An object of the invention is also an asymmetric SOT-MRAM memory point obtained by implementing the method described above. [Brief description of the drawings]

[0022] The invention and its advantages will be better understood on reading the following detailed description of particular embodiments, given by way of non-limiting example only, this description being made with reference to the accompanying drawings, in which: [Figure 1] The theoretical representation of the memory point of the perpendicular magnetization type asymmetric SOT-MRAM. [Diagram 2] 2 is a block representation of an embodiment of a manufacturing method according to the invention making it possible to obtain memory points of the type represented in FIG. 1; [Diagram 3] The components obtained at the end of each of the steps of the method of FIG. 2 are shown. [Figure 4] The components obtained at the end of each of the steps of the method of FIG. 2 are shown. [Diagram 5] The components obtained at the end of each of the steps of the method of FIG. 2 are shown. [Figure 6] The components obtained at the end of each of the steps of the method of FIG. 2 are shown. [Figure 7] The components obtained at the end of each of the steps of the method of FIG. 2 are shown. [Figure 8] The components obtained at the end of each of the steps of the method of FIG. 2 are shown. [Figure 9] Figure 3 shows in detail a memory pad obtained by carrying out the method of Figure 2. Figure 4 shows an industrial implementation of the method of Figure 2 for simultaneously manufacturing a large number of memory points on a semiconductor wafer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] 1. Manufactured memory devices An example of a memory point planned for production is displayed in Figure 1. This is an asymmetric SOT-MRAM memory point of the perpendicular magnetization type.

[0024] The memory point 1 comprises a pad 5 above a conductive track 4. The conductive track 4 is preferably formed in a substrate 2.

[0025] For example, the substrate 2 consists of a silicon wafer coated with silicon oxide.

[0026] The conductive track 4 is made of a conductive material, for example a metal such as copper (Cu). The materials available for the region 10 can also be used for the track 4, as described below. Advantageously, the same material is used for both the track 4 and the layer 10. Alternatively, the layer 10 is simply a thickened part of the track 4.

[0027] The conductive tracks 4 are rectilinear along the direction j.

[0028] Near both ends, the conductive track 4 carries electrodes 20 and 21 constituting terminals A and B respectively.

[0029] The pad 5 is arranged substantially in the center of the conductive track 4 .

[0030] The pads 5 comprise superimposed areas of reduced thickness which are stacked along a vertical direction n perpendicular to the plane of the conductive tracks 4.

[0031] The regions may be formed from a single material or from a laminate of several monolayers of different materials.

[0032] Thus, starting from the conductive track 4, the pad 5 comprises in succession along the vertical direction n a conductive contact region 10, a first magnetic region 11, an intermediate region 12, a second magnetic region 13 and an electrode region 14.

[0033] The conductive contact area 10 is made of a conductive material, for example it can be a non-magnetic metal such as Pt (platinum), W (tungsten), Ir (iridium), Ru (ruthenium), Pd (palladium), Cu (copper), Au (gold), Bi (bismuth) or Hf (hafnium), or some alloy of these metals, or a stack of several monolayers of these metals or some alloys of these metals. It can also be a magnetic material, typically an antiferromagnetic material such as PtMn (platinum manganese), IrMn (iridium manganese), FeMn (iron manganese).

[0034] The conductive contact region 10 has a thickness between 0.5 and 200 nm, preferably between 0.5 and 100 nm, more preferably between 0.5 and 3 nm.

[0035] Provided that the conductive track 4 is suitable for the growth of the constituent material of the first magnetic region 11 and allows the occurrence of the spin-orbit torque (SOT) mechanism, the conductive contact region 10 may be omitted. The track 4 then typically consists of the materials listed above for the conductive contact region 10.

[0036] The first and second magnetic regions 11 and 13 are made of magnetic or composite magnetic materials, or several monolayers of magnetic and non-magnetic materials. They can be, for example, alloys with their own perpendicular magnetic anisotropy, such as FePt (iron platinum), FePd (iron palladium), CoPt (cobalt platinum), or rare earth / transition metal alloys, such as GdCo (gadolinium cobalt) or TbFeCo (terbium iron cobalt). They can also be metals or alloys with perpendicular magnetic anisotropy induced by the interface with the neighboring regions, among others Co (cobalt), Fe (iron), CoFe (cobalt iron), CoFeB (cobalt iron boron), FeB (iron boron), Ni (nickel), Py (pyridine), CoNi (copper nickel).

[0037] The first magnetic region 11 has a thickness between 0.7 and 3 nm, more precisely between 0.8 and 1.4 nm.

[0038] The second magnetic region 13 has a thickness which is usually greater than that of the first region 11. In practice it is often made by superposing several monolayers.

[0039] The intermediate region 12 is made of a non-magnetic material. The material of the region 12 is conductive, but preferably insulating, for example MgO (magnesium oxide), SiO (silicon monoxide), AlO (aluminum oxide), TiO (titanium oxide), TaO (tantalum oxide), HfO (hafnium oxide) or dielectric nitrides such as SiN (silicon nitride) or BN (boron nitride).

[0040] It should be noted that the chemical formulas of the materials referred to in this specification are generic in the sense that they do not specify the stoichiometry between their components, especially since this stoichiometry is not realized in the crystals forming the materials under consideration.

[0041] For example, the intermediate region 12 has a thickness between 0.5 nm and 200 nm, preferably between 0.5 nm and 100 nm, and more preferably between 0.5 nm and 3 nm.

[0042] In any event, intermediate region 12, if made of an insulating material, is thin enough to allow electrons to tunnel through it.

[0043] The electrode area 14 is made of a conductive material. The area 14 constitutes an electrical terminal C.

[0044] In the case of a magnetized memory point perpendicular to the plane of the pad area, there is preferably a structural difference between the non-magnetic areas 10 and 12 so as to create an asymmetric system in the perpendicular direction n. This difference may result, inter alia, from differences in the materials, thicknesses or material growth modes of these two areas.

[0045] Also in the case of a memory point with perpendicular magnetization, the magnetic material of the first and second magnetic regions 11 and 13 is formed in such a condition that it has a magnetization oriented in a perpendicular direction n.

[0046] The magnetic material of the second magnetic region 13 is formed under conditions that allow it to retain a permanent magnetization direction (trapped magnetization). For example, the magnetization of the second magnetic region 13 is in the same direction as the perpendicular direction n.

[0047] On the other hand, the magnetic material of the first magnetic region 11 is formed in such a condition that the magnetization direction can be changed (free magnetization). The magnetization of the first magnetic region 11 is therefore either in the same direction as the perpendicular direction n ("up" orientation) or in the opposite direction to the perpendicular direction n ("down" orientation).

[0048] 1 enables the circulation of a write current between terminals A and B through the conductive track 4. The write current circulates in either direction substantially along the direction j in the plane of the conductive track 4.

[0049] “Programming” the memory point 1, i.e. varying the magnetization orientation of the first magnetic region 11 in one direction or the other, is performed by circulating a write current along the direction j, i.e. parallel to the plane of the constituent area of ​​the pad 5.

[0050] The first magnetic region 11 is programmed by selecting an “up” or “down” magnetization direction depending on the circulation direction of the write current in the conductive track 4 (either direction j between terminals A and B, or a direction opposite to direction j between terminals B and A).

[0051] To read the state of memory point 1, a read voltage is applied (by a read circuit not shown in FIG. 1) between terminal C and either terminal A or B. A measurement of the resistance of pad 5 indicates the relative magnetization orientation between the first and second magnetic regions 11 and 13.

[0052] For this effect to be effective even in the absence of an external magnetic bias field, a geometric asymmetry about the reference plane defined by the directions j and n is introduced by pad 5.

[0053] 1, the pads 5 are shaped to have a "V" shape in top view. The pads are positioned on the conductive track 4 such that the reference plane does not coincide with the plane of symmetry of the pads 5 (e.g. a plane along the bisector of the tip of the "V" formed by the pads 5, which is the start of the two lateral arms of the "V" formed by the pads 5).

[0054] 2. Brief information about the manufacturing method according to the present invention Generally speaking, in the manufacturing method according to the present invention, an ion bombardment technique is carried out.

[0055] Ion bombardment is a well-known technique used in the art to modify the structure of materials by etching them or implanting atoms.

[0056] However, it has recently been established that under certain conditions (nature of the ions used, intensity of the ion beam, exposure time, etc.) the properties of magnetic materials can be modified by ion bombardment. By bombarding a magnetic material with a current of ions it is possible, among other things, to reduce the width of the magnetization of this magnetic material, possibly until it is completely eliminated.

[0057] The method according to the invention uses this property to delimit, in an extended magnetic layer made of a magnetic material, a magnetic region whose shape corresponds to that of the first magnetic region of the pad to be manufactured.

[0058] To that end, masking posts are positioned above the extended magnetic layer in such a way that the shadow cast by the masking posts on the extended magnetic layer during ion bombardment at a non-zero angle of incidence prevents modification of the magnetic properties inside the shadowed areas, whereas outside the shadowed areas the magnetic properties of the magnetic material are altered or completely eliminated.

[0059] Advantageously, by performing the irradiation step for various incidence directions (i.e. various incidence planes and / or various incidence angles), it is possible to shift the shadow cast by the masking pillars so as to accurately outline in the extended magnetic layer the first magnetic region of the pad to be produced.

[0060] 3. Detailed description of one embodiment of the method according to the invention for manufacturing the memory point of FIG. 1 More precisely, with reference to FIG. 2, the manufacturing method 50 comprises the following steps.

[0061] In step 100, a laminate is fabricated by stacking a number of stretched layers, the nature of which and the order in which they are stacked, correspond to the memory points being fabricated, in this case, in this embodiment, memory point 1 in FIG.

[0062] As shown in FIG. 3, at the end of step 100, the resulting component 101 includes a substrate 102, a conductive track 104, a conductive contact layer 110, a first magnetic layer 111, an intermediate layer 112, a second magnetic layer 113 and an electrode layer 114.

[0063] At step 200, a primary masking pillar is deposited onto the stretch layered stack.

[0064] It is made of metal materials such as Ta (tantalum), W (tungsten), Ti (titanium) or Pt (platinum), or of resin that can be structured by UV (ultraviolet) light or electron beams, the latter possibility being preferred for industrial applications.

[0065] It has a shape that can be easily manufactured using well known construction techniques, for example a cylinder with a circular base.The primary masking cylinder has a height H0 and a diameter D0.

[0066] The fabrication of the primary masking pillars is for example done by depositing a layer of photoresist. The pillars are then shaped in this thick layer by UV lithography and possibly afterwards by ion etching processes which shape the side of the pillars. As material is consumed during the shaping step, the thickness of the initial layer is chosen such that the required height H0 of the primary masking pillars is obtained at the end of shaping.

[0067] As shown in Figure 4, at the end of step 200 the resulting component 201 has a primary masking post 220 above the stretched layer stack, in vertical alignment with what will become the tip of the "V" shape of the pad 5 to be manufactured.

[0068] In step 300, the stack carrying the primary masking pillars is advantageously etched, for example by performing conventional techniques to remove an extended top layer of the stack around the primary masking pillars until the top surface of the first magnetic layer 111 is exposed.

[0069] It should be noted that the etching step may be performed as a continuation of the shaping step of the primary masking pad.

[0070] In figure 5 the component 301 obtained at the end of step 300 is shown. The upper layer of the stack is now limited to the corresponding area of ​​the pad 5 to be produced, while the lower layer of the stack is not modified by the etching process. Thus the component 301 comprises an intermediate area 312, a second magnetic area 313 and an electrode area 314. These upper areas and the primary masking pillars 220 lying thereon together form a masking pillar 320.

[0071] The masking pillars typically have a height H between 10 and 150 nm, preferably 50 nm, and a diameter D between 5 and 100 nm, preferably between 10 and 30 nm.

[0072] Therefore, the height H0 and diameter D0 of the primary masking pillars are selected depending on the desired height H and diameter D and the thickness of the overlayer.

[0073] Next, a first ion irradiation step 400 is performed.

[0074] The ion flow is oriented in a first incidence direction d1 (FIG. 6). A first incidence plane is defined by the first incidence direction d1 and a normal direction n. In the plane of the conductive track, the first incidence plane forms a first angle a1 with the direction j. In the first incidence plane, the ion flow forms a first incidence angle i1 with the normal direction n.

[0075] During this step, a first shadow 421 is cast on the extending first magnetic layer 411 by the masking pillars 320 .

[0076] The height H and first direction of incidence d1 of the masking pillar 320 are selected such that this first shadow 421 matches the contour of a first arm of the "V" shape desired for the pad.

[0077] The portion of the extended first magnetic layer 411 that is located inside this first shadow 421 and therefore not exposed to the ion current retains its magnetic properties.

[0078] On the other hand, the parts of the magnetic layer 411 that are located outside this projected shadow and are therefore exposed to the ion current will gradually lose their magnetic properties. The parameters of the first ion bombardment are selected such that at the end of step 400 the magnetization width is at least halved.

[0079] This is displayed in FIG. 6, where the component 401 obtained at the end of step 400 comprises a first magnetic layer 411 having a maximum magnetization width M in area 423 and a magnetization width M / 2 in area 422 .

[0080] Then, a second ion irradiation step 500 is performed.

[0081] The ion flow is oriented in a second incidence direction d2. A second incidence plane is defined by the second incidence direction d2 and a normal direction n. In the plane of the conductive tracks, the incidence plane forms a second angle a2 with the direction j. In this second incidence plane, the ion flow forms a second incidence angle i2 with the normal direction n.

[0082] During this step, a second shadow 521 is cast on the extended first magnetic layer by the masking pillars 320 .

[0083] For example, during irradiation, a second shadow cast by masking post 320 defines the contour of a second arm of the "V" shape desired for the pad, with a second angle a2 equal to 180°-a1 and a second angle of incidence i2 equal to i1.

[0084] The portions of the extended first magnetic layer 411 that are located inside the second shadow and therefore not exposed to the ion current retain the magnetic properties they acquired after the first irradiation (step 400).

[0085] On the other hand, the part of the elongated magnetic layer 411 that is located outside this second shadow and is therefore exposed to the ion current will gradually lose its magnetic properties.

[0086] For example, the parameters of the second ion bombardment are chosen to be equal to the parameters of the first bombardment in order to divide the magnetization width M by two.

[0087] At the end of step 500, a component 501 is then obtained having a first magnetic layer 511 comprising: At the intersection of the first and second shadows 421, 521 (and extending under the masking pillar 320) is an area 531 having a magnetization width M, where no magnetic material is exposed. Inside the first shadow 421 and complementary to the area 531 , an area 532 having a magnetization width M / 2, where the magnetic material was exposed during the second ion bombardment 500 . Inside the second shadow 521 and complementary to the area 531 , an area 533 having a magnetization width M / 2, where the magnetic material was exposed during the first ion bombardment 400 . An area 534 outside the first shadow 421 and outside the second shadow 521 having a zero magnetization width, where the magnetic material is exposed during both the first ion bombardment 400 and the second ion bombardment 500 .

[0088] Thus, the shape of the first magnetic region of the pad has been “modeled” with the extended first magnetic layer 511 .

[0089] In a final finishing step 600, the primary masking pillars 220 are removed to expose the electrode areas 14 to form the terminals C. This is necessary when the primary masking pillars are made of plastic. On the other hand, they can be retained when made of a conductive material and therefore allowing the circulation of a read current.

[0090] The extended first magnetic layer 511 is etched to expose the conductive track 4. This etching step is accurate in depth, but not necessarily on the side, since the magnetically active area of ​​the pad is accurately delimited by irradiation. Electrodes 20 and 21 are placed at the ends of the conductive track 4 to form terminals A and B.

[0091] Thus, as represented in Fig. 8, the shape of the memory point 601 obtained by carrying out the method 50 does not exactly correspond to that of the memory point 5. The pad 605 comprises the conductive track 4 on the substrate 2 and the upper layers 12, 13, 14 like the pad 5, but has a different shape from the layers 10 and 11 of the pad 5, being more elongated and having, for example, a rectangular shape, a conductive contact layer 610 and a first magnetic layer 611, in which the magnetically active area, i.e. the first magnetic area of ​​the pad 605, is precisely delimited with the desired geometrical asymmetry. The memory point 601 is in fact of asymmetric SOT-MRAM type, in this case with perpendicular magnetization.

[0092] The fact that the first and second magnetic regions of the pad do not have the same geometric shape is not an issue, since when reading, it is the relative magnetization orientation on each side of the tunnel junction provided by the intermediate region 12 that is determined by measuring the electrical resistance of the pad 605.

[0093] Alternatively, it should be noted that the shape of the top layer corresponds to the footprint of the primary masking cylinder: if the latter has a geometry other than cylindrical, the geometry of the top layer will reflect this.

[0094] Finally, the part of the material of the first magnetic layer located under the side of the pad exposed to the ions, in terms of the penetration length R of the ions, is irradiated and modifies its magnetic properties. A small angle of incidence leads to a large extent of this part. It is therefore necessary to find a compromise between the irradiation parameters in terms of the extent of the cast shadow, which is desired to define the first magnetic region. One solution is, inter alia, to reduce the energy of the ion beam so as to reduce the penetration length R.

[0095] Therefore, the skilled person will realize that the external shape of the memory point obtained as a result of the implementation of the method according to the invention differs from the external shape of a theoretical memory pad, especially in the lower layers of the pad that contain at least the first asymmetric magnetic region (free magnetization), and the external shape of these lower layers is arbitrary (for example symmetrical). The memory point therefore reflects the fabrication method, i.e. the various steps of the method of the invention. In other words, the memory point obtained by implementing the method is specific to this method.

[0096] 4. Industrial production By the method presented above, multiple memory points can be produced simultaneously on a substrate wafer 700, as shown diagrammatically in FIG.

[0097] As shown in FIG. 9, after the growth of the various extending layers, primary masking pillars are deposited according to a matrix pattern.

[0098] A first illumination in a first direction d1 (left side of FIG. 9) makes it possible to model the first arm of the "V" shape desired for all pads.

[0099] A second illumination in a second direction d2 (right side of FIG. 9) makes it possible to model the second arm of the "V" shape desired for all pads.

[0100] At the end of the execution of the method steps, a substrate wafer 700 is obtained carrying a set of pads 605 arranged according to the initial pattern of primary masking pillars.

[0101] Thus, a single iteration of the steps of FIG. 2 results in multiple memory points being fabricated simultaneously.

[0102] Those skilled in the art will therefore appreciate that this method enables the industrialization of the manufacturing of asymmetric SOT-MRAM memory points.

[0103] 5. Ion bombardment parameters Preferably, the ion bombardment is with light ions, preferably He+.

[0104] These ions have low energies between 10 keV and 100 keV, for example 30 keV.

[0105] The intensity of the ion current is characterized by its flux, which is 10 14 ions / cm 2 and 10 17 ions / cm 2 Between 10 and 20 16 ions / cm 2 It is.

[0106] Due to these properties, ion beams induce only atomic displacements of a few angstroms around the equilibrium position of the atoms, without cascade collisions and without physical etching or implantation of atoms. This allows the adjustment of the global magnetization of the magnetic material until it is removed. Low-energy beams therefore make it possible to modify the structure of materials in a controlled manner by irradiation-induced mixing of atoms into the material.

[0107] In industrial applications, it is advantageous for the ion beam to have a wide cross-section so that a large surface, such as that of a semiconductor wafer, can be irradiated at a substantially constant angle of incidence across the cross-section.

[0108] The part of the masking pillar that is not illuminated due to the shadowing effect at its base has a lateral extent d.

[0109] First approximation: d=H×tan(i), where H is the height of the masking pillar and i is the angle of incidence of the ions (0° for a vertical beam, 90° for a horizontal beam).

[0110] Assume masking pillars of height H=50 nm, d=0 for i=0°, d=50 nm for i=45°, and d=280 nm for i=80°.

[0111] Thus, depending on the parameters of the ion beam, the parameters of the masking pillars and the parameters of the shape of the pad to be produced, the angle of incidence ranges from 0° to 90°.

[0112] The penetration length R of an ion in a given material is an important parameter that depends on the energy of the ion and the intensity of the beam. Therefore, the penetration length R is defined as a function of the thickness of the material that is irradiated to reach the first magnetic layer. The above intensities and energies allow the consideration of a wide range of penetration lengths R and, consequently, penetration thicknesses.

[0113] Taking the penetration depth into account, the part that is not irradiated at all due to the shadowing effect has a lateral extent d: tan(i) × [HR × cos(i)], where H is the height of the masking cylinder, i is the ion angle, and R is the ion penetration depth.

[0114] For example, for an energy of 20 keV, the penetration depth R is typically 60 nm. For a masking pillar of height H=50 nm, d=0 for θ=0°, d=8 nm for i=45°, and d=200 nm for i=80°.

[0115] 6. Alternative Manufacturing Methods The method described above can be modified in a variety of ways.

[0116] After etching the masking posts, it is preferable to remove the resin from the primary masking posts using only the top metal layer of the pad as a mask for the irradiation step.

[0117] It is not necessary to carry out an etching step to expose the first magnetic layer, which depends on the penetration length R, taking into account in particular the characteristics of the layers located above the first magnetic layer. If it is possible to modify the magnetization of the first magnetic layer by irradiation without having to remove all or part of the layers located above the first magnetic layer, it is preferable not to do so, if only to facilitate the execution of the method by acceleration.

[0118] Moreover, the order of steps can be modified. For example, it is conceivable to provide a partial stack limited to the lower layer, the exposed extension layer being the first magnetic layer. A primary masking pad is then deposited directly on the first magnetic layer, and regions of the desired geometric shape are defined therein by ion bombardment. The primary masking pad is then removed, and the upper regions, i.e. the intermediate region, the second magnetic region and the electrode region, as components of the pad are deposited.

[0119] Moreover, the method can also be modified when it is intended to manufacture pads consisting of a stack with areas other than those of the pad of Figure 1. For example, the conductive contact areas can in fact be thickened parts of the conductive tracks. In this case, the final step consists in continuing the etching process so as to penetrate into the extended conductive layer.

[0120] Again, for example, the second magnetic layer is preferred but not required: omitting it simplifies the deposition process and reduces the cost of the etching step by making the first magnetic layer more accessible to the ion beam.

[0121] The method can also be modified when it is intended to manufacture pads with another geometric shape. If, instead of manufacturing a "V" shaped pad, it is desired to manufacture, for example, a triangular pad, the two irradiation steps can be replaced by a single step in which the ion source is displaced with a continuous movement relative to the masking cylinder, so that the path of the projected shadow defines in the first magnetic layer a triangular area corresponding to the first magnetic region of the pad. The irradiation parameters are adjusted so that outside the shadowed area the magnetic material loses its magnetization and inside the shadowed area the magnetic material retains all or part of its magnetization.

[0122] Also for example, some geometries may require that the masking pad is produced with a different geometry and / or that the geometry of the mask is modified between the first and second irradiation. For example, it is desirable to produce a pad comprising a central portion that is rectilinear along the direction j and a tip portion at each of its two ends that is arranged at an angle to the central portion. The tip portions are located on the same side of this reference plane defined by the directions j and n. Then, in a first masking step, the masking pad is produced to comprise a parallelepiped bar carrying a first cylinder at one of its two ends. In this way, the first irradiation makes it possible to delimit in the magnetic material a part of the central portion and a first tip portion of the pad to be produced. Then, in a second masking step, the masking pad is modified by removing the first cylinder from the masking pad and a second cylinder is deposited at the other end of the parallelepiped bar. Then, the second irradiation makes it possible to delimit in the magnetic material a part of the central portion and a second tip portion of the pad to be produced. It is advantageous if the second exposure is performed after rotating the source about the vertical direction n while remaining on the same side of the masking pad. The angle of the second exposure is for example equal to 180°-a1, a1 being the angle of the first exposure.

[0123] For example, a different number of exposure steps, especially a single exposure step, can be used. For example, it is desirable to define a simple shape that is nevertheless asymmetric with respect to a reference plane defined by the directions n and j. A single masking step is then used using a cylindrical pad and exposure in a single direction d1 with an angle a1 different from 0° and 90°. The portion delimited in the magnetic material will then have the shape obtained after the first exposure step 400, as previously described, which is displayed in the top view on the left side of FIG. 9. In this case, the exposure parameters are adjusted so as to demagnetize the exposed area in a single exposure. The remaining steps are then identical to those described above, except for step 500, which is omitted.

[0124] Although the method has been described for the case of magnetization perpendicular to the plane of the pad's configuration area, it applies equally to the case of magnetization parallel to the plane of the pad's configuration area.

[0125] 7. Pads with asymmetrical properties due to gradients in magnetic properties and limited examples of this manufacturing method With this method it is possible to obtain asymmetric pads even with a single ion irradiation step, especially in the plane of incidence perpendicular to the reference plane of the memory point.

[0126] Indeed, during ion bombardment, the cast shadow is not delimited absolutely accurately, so that subsequent bombardments result in a gradient in the magnetic properties of the magnetic material in the vicinity of the edges of the cast shadow.

[0127] This applies in particular to the edge of the cast shadow, which corresponds to the upper edge of the mask-forming pillar. In the case where the irradiation is performed with an incidence plane perpendicular to the reference plane, this gradient is then oriented perpendicular to the directions j and n. Nevertheless, this magnetization gradient interrupts the mirror symmetry with respect to the reference plane defined by the directions j and n. As a result, the presence of this magnetization gradient is sufficient to cause an asymmetry in the manufactured pad. It is practically like a first magnetic region consisting of a superposition of elementary magnetic monolayers with the same magnetization, elliptical, nested in each other and eccentric from each other perpendicular to the direction j. Therefore, the asymmetry of the pad can also be said to be a geometric asymmetry. By choosing an incidence angle in the open range 10°, 180°, it is possible to obtain a gradient with a component perpendicular to the reference plane by a single ion irradiation, and therefore to produce an asymmetric SOT-MRAM memory point. [Explanation of symbols]

[0128] 1 memory point 2. Board 4 Conductive Tracks 5 Pad 10 Conductive contact area 11 1st magnetic region 12 Intermediate area 13 Second magnetic region 14 electrode area 20 electrodes 21 electrodes 101 Components 102 Substrate 104 Conductive Track 110 Conductive contact layer 111 First magnetic layer 112 Middle Class 113 Second magnetic layer 114 Electrode layer 201 Components 220 Primary Masking Cylinder 301 Components 312 Intermediate area 313 Second magnetic region 314 Electrode area 320 Masking column 401 Components 411 1st magnetic layer 421 1st shadow 422 area 423 area 501 Components 511 1st magnetic layer 521 2nd shadow 531 area 532 area 534 area 533 area 601 Memory Points 605 Pad 610 Conductive contact layer 611 1st magnetic layer 700 Substrate Wafers A terminal B terminal M maximum magnetization width a1 First angle a2 2nd angle d1 1st irradiation direction d2 Second irradiation direction i1 1st angle of incidence i2 2nd angle of incidence j direction n vertical direction

Claims

1. A method (50) for manufacturing an asymmetric SOT-MRAM memory point, said memory point (1) comprising a conductive track (4) and a pad (5) arranged on said conductive track and including at least one first magnetic region (11) that is magnetized free, A step (100) of fabricating a stack (101) of multiple elongated layers including at least one elongated first magnetic layer (111); Depositing (200) a mask (220) on the top surface of said stack (101); - defining the first magnetic regions (11) in the extended first magnetic layer (111) by ion irradiation of the top surface of the stack carrying the mask, the parameters of the ion irradiation being adapted (400, 500) to modify the magnetic properties of the constituent material of the first magnetic layer (111); The method includes:

2. 2. The method of claim 1, wherein the ion irradiation can modify the magnetic properties of areas of the first magnetic layer (111) that are exposed during the ion irradiation while preserving the magnetic properties of areas of the first magnetic layer (111) that are not exposed during the ion irradiation due to the presence of the mask.

3. 3. The method of claim 1 or claim 2, wherein the step of defining by ion irradiation comprises a relative displacement of an ion source with respect to the top surface of the stack carrying the mask during an irradiation period, and the parameters of the irradiation are adapted to eliminate the magnetic properties in areas that are exposed during the entire irradiation period, but are insufficient to eliminate the magnetic properties in areas that are exposed only for a small portion of the irradiation period.

4. 3. The method according to claim 1 or claim 2, wherein the step of defining by ion irradiation comprises a first irradiation (400) in a first irradiation direction (d1) followed by a second irradiation (500) in a second irradiation direction (d2), the parameters of the first and second irradiation being selected such that they are sufficient to eliminate the magnetic properties of areas exposed during both the first and second irradiation, but are insufficient to eliminate the magnetic properties of areas exposed only during the first irradiation or only during the second irradiation.

5. The method of claim 4 , comprising modifying the mask between the first and second ion bombardment.

6. The ion bombardment is preferably performed with low energy light ions, preferably He, of between 10 keV and 100 keV, even more preferably equal to 30 keV, at 10 １４ ions / cm ２ and 10 １７ ions / cm ２ Between 10 and 20 １６ ions / cm ２ The method of claim 1 or 2, wherein the method is carried out at an intensity equal to

7. 3. The method according to claim 1 or 2, comprising, after the step of depositing the mask (220) and before the step of defining by ion irradiation, an etching step (300) consisting in etching the upper layer of the stack (101) around the deposited mask (220) so that the ion current used during ion irradiation can reach the first magnetic layer (111).

8. 3. The method according to claim 1 or 2, wherein the step (100) of fabricating a stack (101) of multiple stretched layers comprises stacking a conductive layer (104, 110), the first magnetic layer (111), an intermediate layer (112), a second magnetic layer (113) and an electrode layer (114) on a semiconductor substrate (102).

9. 3. A method according to claim 1 or 2, comprising, after the step of definition by ion bombardment, a step of finishing the memory point (600) consisting in removing the mask, etching the stack so as to expose conductive tracks on either side of the pad and fabricating electrodes (A, B, C) on the pads (5) as well as on each of the two ends of the conductive layer (4).

10. An asymmetric SOT-MRAM memory point (601) obtained by carrying out the manufacturing method (50) according to claim 1 or claim 2.

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