An etching method for an MRAM magnetic tunnel junction

Abstract

The present invention discloses an etching method for an MRAM magnetic tunnel junction, comprising: Step 1, a main etching step with an etching amount of t1 is carried out by using ion beam etching and / or reactive ion etching: the direction angle of the ion beam is 10° to 60°, and the bias voltage of the reactive ion etching is 400 - 1000 V; Step 2, a cleaning step with an etching amount of t2: the bias voltage of the reactive ion etching used is 50 V - 400 V, and the pulse duty ratio is 5% - 50%. t1:t2 ≥ 0.5. After the cleaning step is completed, the etching morphology on the bottom electrode or the bottom dielectric layer is a square groove; Step 3, in-situ protection: a film is deposited for in-situ protection. The present invention combines RIE and IBE etching. Through the arrangement of the etching sequence and the selection of the etching parameters, while significantly improving the etching effect of small-size dense magnetic tunnel junctions, it is also applicable to the etching of non-dense magnetic tunnel junctions. Thus, the problems of low selectivity and low steepness during the etching of dense patterns are solved. Further, the square etching groove can greatly improve the TMR and service life of the MTJ junction and eliminate bottom deposition.

Description

Technical Field

[0001] The present invention relates to the field of magnetic random access memories, and particularly to an etching method for an MRAM magnetic tunnel junction. Background Art

[0002] Currently, the widely used memory types are mainly SRAM (Static Random Access Memory), DRAM (Dynamic Random Access Memory), and Flash (Flash Memory), etc. SRAM can store the data inside it without a refresh circuit, and has high performance, but low integration. DRAM has high integration and low power consumption, but requires a refresh circuit to continuously store data. MRAM (Magnetic Random Access Memory) has the high-speed read / write ability of SRAM and the high integration of DRAM, and can basically be written repeatedly an infinite number of times. It can be used in systems that require both fast and large-scale data storage, and also require data to be retained after power-off and can be quickly restored. In terms of the "non-volatile" feature, currently only MRAM and FLASH have this function, while Flash lacks the "random access" function. This means that MRAM has broad prospects and can play an important role especially in the fields of automotive, industrial, military, and space.

[0003] MRAM is different from traditional memories. It stores data in the form of magnetic polarization rather than in the form of charge. The basic structure of the MRAM storage unit, the MTJ junction, is as Figure 1 shown. The top layer is the free layer with a variable magnetic polarization direction, the middle layer is the tunnel barrier layer, and the bottom layer is the fixed layer with a fixed magnetic field direction. Together, they are called the MTJ junction (Magnetic Tunnel Junctions). When the magnetic field directions of the free layer and the fixed layer are parallel, the storage unit presents a low resistance; when the magnetic field directions are opposite, it presents a high resistance. MRAM determines whether the stored data is 0 or 1 by detecting the high or low resistance of the storage unit.

[0004] In the MRAM manufacturing process, MTJ etching is an extremely critical step. The main etching equipment is reactive ion etching RIE (Reactive Ion Etching) and ion beam etching IBE (Ion Beam Etching). RIE is a method of etching using chemical reactions and physical ion bombardment. IBE is to etch the surface of the material by bombarding it with an ion beam with a certain energy, and has strong directionality. Currently, RIE and IBE etching are the mainstream methods for MTJ etching. Whether using IBE etching or RIE etching, the following requirements must be met:

[0005] 1. During etching, a high steepness (Profile) of the MTJ junction needs to be maintained, which is beneficial to improving the TMR (Tunnel Magnetoresistance Resistance) performance and lifespan.

[0006] 2. There should be no sidewall contamination (Re-dep) in the magnesium oxide layer of the MTJ, otherwise it will cause short-circuit failure.

[0007] 3. There is more remaining mask (HM) and less deposition contamination (Residue), which is beneficial to subsequent process steps and improves the device survival rate.

[0008] As Figure 2 shown, traditional IBE etching has high selectivity, but causes greater damage to the magnesium oxide layer and more deposition contamination. Traditional RIE etching has too low a selectivity ratio and poor steepness. Thus, it is difficult to simultaneously meet the above three etching requirements.

[0009] In addition, as the volume of the magnetic memory layer shrinks, the spin-polarized current required for writing or switching operations is also smaller. Therefore, it is desired to fabricate smaller and denser MTJ junction patterns to reduce the damage and shortening of the lifespan of MTJ memory devices caused by control. However, for smaller and denser MTJ junctions, it is more difficult to meet the above three etching requirements using conventional IBE etching or RIE etching. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide an etching method for an MRAM magnetic tunnel junction in view of the deficiencies of the above-mentioned prior art. This etching method for the MRAM magnetic tunnel junction combines traditional RIE and IBE etching, and through the layout of the etching sequence and the careful selection of various etching parameters, it can significantly improve the etching effect of small-sized dense magnetic tunnel junctions while also being applicable to the etching of non-dense magnetic tunnel junctions.

[0011] To solve the above technical problem, the technical solution adopted by the present invention is:

[0012] An etching method for an MRAM magnetic tunnel junction, comprising the following steps.

[0013] Step 1, main etching step of the magnetic tunnel junction: Use ion beam etching and / or reactive ion etching to perform main etching step etching with an etching amount of t1 on the magnetic tunnel junction. Among them, the direction angle of the ion beam is 10 - 60°, and the bias voltage of the reactive ion etching is 400 - 1000V.

[0014] Step 2, Magnetic Tunnel Junction Cleaning Step: For the magnetic tunnel junction that has completed the main etching step, perform a cleaning step etching with an etching amount of t2. Among them, t1:t2≥0.5. The cleaning step etching includes reactive ion etching, and the mode of reactive ion etching is continuous mode or pulse mode. The bias voltage of the reactive ion etching is 50V - 400V, and the pulse duty cycle is 5% - 50%. After the cleaning step etching is completed, the etched morphology on the bottom electrode or bottom dielectric layer is a square groove.

[0015] In Step 2, the cleaning step etching uses a combination of ion beam etching and reactive ion etching. Among them, the beam voltage of the ion beam etching is 50V - 200V.

[0016] It further includes Step 3, In-situ Protection of the Magnetic Tunnel Junction: Using chemical vapor deposition, grow a dielectric film layer around the magnetic tunnel junction after the cleaning step etching is completed for in-situ protection.

[0017] The etching amount t2 of the cleaning step etching is 5 - 100nm.

[0018] In Step 1, the ion beam etching includes large-angle ion beam etching and small-angle ion beam etching.

[0019] Large-angle ion beam etching means that the direction angle of the ion beam is 30 - 60°, and small-angle ion beam etching means that the direction angle of the ion beam is 10 - 30°. Assuming the time period of large-angle ion beam etching is T1 and the time period of small-angle ion beam etching is T2, then T1≥1.5T2.

[0020] In the main etching step and the cleaning step, when using ion beam etching, the gas used in the ion beam chamber is one or any combination of inert gas, nitrogen, oxygen, fluorine-based gas, amino gas, carbon monoxide, carbon dioxide, and alcohols.

[0021] In the main etching step and the cleaning step, when using reactive ion etching, the ion source power in the reactive ion chamber is 50 - 1000W, the chamber pressure is 0.5 - 10mT, the gas flow rate is 10 - 500sccm, and the gas is one or any combination of inert gas, nitrogen, oxygen, fluorine-based gas, amino gas, carbon monoxide, carbon dioxide, and alcohols.

[0022] The length of the lower bottom side of the square groove is L1, the length of the upper bottom side of the square groove is L2, the height of the square groove is H1, and the angle between the lower bottom side and the side of the square groove is α. Then: L1:L2 = 0.3~1.0, H1:L2 = 0.1~2.0, α = 90 - 130°.

[0023] An etching method for an MRAM magnetic tunnel junction includes the following steps.

[0024] Step 1, Main Etching Step of Magnetic Tunnel Junction: Using ion beam etching, perform a main etching step with an etching amount of t1 = 35 nm on the magnetic tunnel junction. The ion beam etching method is as follows: Transfer the magnetic tunnel junction sample into the ion beam etching chamber, select the direction angle of the ion beam as 25°, the energy as 600 V, and the protective gas as argon. Among them, the magnetic tunnel junction sample includes a mask layer, a cap layer, an MTJ junction, a bottom electrode metal layer, and a bottom dielectric layer from top to bottom. Metal lower electrodes equal in number to the masks in the mask layer are nested at equal intervals in the bottom dielectric layer, and the positions of the metal lower electrodes correspond to those of the masks. The ion beam etching stops when 5 nm of the bottom electrode metal layer remains. At this time, the ion beam etching amount is 35 nm.

[0025] Step 2, Cleaning Step of Magnetic Tunnel Junction: For the magnetic tunnel junction that has completed the main etching step, use reactive ion etching to perform a cleaning step etching with an etching amount of t2 = 30 nm. The reactive ion etching method is as follows: Through the vacuum chamber, transfer the magnetic tunnel junction sample that has completed ion beam etching in Step 1 from the ion beam etching chamber to the reactive ion etching chamber for reactive ion etching. The parameters of the reactive ion etching are: The reactive ion pulse is selected as 20%, the ion source power is 700 W, the bias voltage is 400 V, the chamber pressure is 5 mT, the argon gas flow rate is 100 sccm, and the reactive ion etching amount is 30 nm. After the cleaning step etching is completed, the etched morphology on the bottom dielectric layer is a square groove.

[0026] Step 3, In-situ Protection of Magnetic Tunnel Junction: Through the vacuum transfer chamber, transfer the magnetic tunnel junction sample after the cleaning step etching into the plasma enhanced chemical vapor deposition chamber, and deposit a 35 nm SiN thin film for in-situ protection.

[0027] An etching method for an MRAM magnetic tunnel junction includes the following steps.

[0028] Step 1, Main Etching Step of Magnetic Tunnel Junction: Using reactive ion etching, perform a main etching step with an etching amount of t1 = 20 nm on the magnetic tunnel junction. The reactive ion etching method is as follows: Transfer the magnetic tunnel junction sample into the reactive ion etching chamber, with the reactive ion etching ion source power of 600 W, the bias voltage of 600 V, the chamber pressure of 10 mT, and the argon gas flow rate of 150 sccm. Among them, the magnetic tunnel junction sample to be etched includes a mask layer, a cap layer, an MTJ junction, a bottom electrode layer, and a bottom dielectric layer from top to bottom. The reactive ion etching stops when 3 nm of the bottom electrode layer is consumed. At this time, the reactive ion etching amount is 20 nm.

[0029] Step 2, Magnetic Tunnel Junction Cleaning Step: For the magnetic tunnel junction that has completed the main etching step, reactive ion etching is used to perform an etching with an etching amount of t2 = 15 nm for the cleaning step etching. The etching parameters of the reactive ion etching are as follows: the reactive ion pulse is selected at 30%, the ion source power is 300 W, the bias voltage is 600 V, the chamber pressure is 1.5 mT, the argon gas flow rate is 200 sccm, and the reactive ion etching amount t2 = 15 nm. After the cleaning step etching is completed, the etched morphology on the bottom dielectric layer is a square groove.

[0030] Step 2A, Ion Beam Cleaning: Through the vacuum chamber, the magnetic tunnel junction sample that has completed the cleaning step etching is transferred to the ion beam etching chamber. The ion beam angle is selected to be 45°, the ion beam energy is 100 V, argon gas etching is used, and the etching depth is 3 nm, still remaining on the bottom electrode layer.

[0031] Step 3, In-situ Protection of the Magnetic Tunnel Junction: Through the vacuum transfer chamber, the magnetic tunnel junction sample after the ion beam cleaning is introduced into the plasma enhanced chemical vapor deposition chamber to deposit a 10 nm SiN thin film for in-situ protection.

[0032] The present invention has the following beneficial effects: The present invention combines traditional RIE and IBE etching. By arranging the etching sequence and carefully selecting each etching parameter, while significantly improving the etching effect on small-size dense magnetic tunnel junctions, it is also applicable to the etching of non-dense magnetic tunnel junctions. Thus, the problems of low selectivity and low steepness during the etching of dense patterns are solved. Further, the biggest feature of the present invention is that it can form square etching grooves at the bottom, thereby greatly improving the TMR and service life of the MTJ junction and eliminating bottom deposition. Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the MTJ structure.

[0034] Figure 2 It is a comparison of the etching effect of the present invention with that of traditional RIE etching or IBE etching, and the etching stops on the dielectric SiO.

[0035] Figure 3 It is a schematic diagram of the film layer morphology of the sample after etching of the present invention.

[0036] Figure 4 It is a comparison of the etching effect of the present invention with that of traditional RIE etching or IBE etching, and the etching stops on the bottom electrode metal. Detailed Embodiment

[0037] The present invention will be further described in detail below in conjunction with the drawings and specific preferred embodiments.

[0038] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by terms such as "left side", "right side", "upper part", "lower part", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. "First", "second", etc. do not represent the importance of components, so they cannot be understood as limitations on the present invention. The specific dimensions adopted in this embodiment are only for illustrating the technical solution by way of example, and do not limit the protection scope of the present invention.

[0039] As Figure 1 shown, an etching method for an MRAM magnetic tunnel junction includes the following steps.

[0040] Step 1, main etching step: reactive ion etching (RIE) or ion beam etching (IBE).

[0041] Transfer the wafer into the corresponding reaction chamber and perform a first etching on the magnetic tunnel junction sample to be etched.

[0042] As Figure 2 shown, the magnetic tunnel junction sample to be etched sequentially includes a mask layer, a metal layer (also called a cap layer or a covering layer), an MTJ junction, a metal layer (also called a seed layer), and a bottom dielectric layer from top to bottom.

[0043] Among them, the mask layer includes a plurality of masks evenly distributed on the cap layer at equal intervals. A bottom electrode equal in number to the masks is nested at equal intervals in the bottom dielectric layer, and the position of the bottom electrode corresponds to that of the mask. Further, the bottom dielectric layer is preferably silicon oxide or the like.

[0044] As Figure 4 shown, the magnetic tunnel junction sample to be etched sequentially includes a mask layer, a metal layer (also called a cap layer or a covering layer), an MTJ junction, a metal layer (also called a seed layer), a bottom electrode, and a bottom dielectric layer from top to bottom. The setting of the masks in the mask layer is the same as Figure 2 , and the bottom dielectric layer is preferably silicon oxide or the like.

[0045] The process conditions of the ion beam etching (IBE) are preferably as follows: the direction angle of the ion beam is preferably 10 - 60° (the angle between the ion beam and the wafer normal), the energy is preferably 200 - 1000 V, and the protective gas is preferably one or a different combination of inert gases, nitrogen, oxygen, fluorine-based gases, amino gases, carbon monoxide, carbon dioxide, alcohols, etc., and further preferably inert gases such as argon, krypton, xenon, etc.

[0046] The process conditions of reactive ion etching (RIE) are preferably as follows: the ion source power is 50 - 1000 W, the chamber pressure is 0.5 - 30 mT, the gas flow rate is 10 - 500 sccm, and the gas is one or any combination of inert gas, nitrogen, oxygen, fluorine-based gas, amino gas, carbon monoxide, carbon dioxide, and alcohols.

[0047] In this step 1, the etching amount of the main etching step is t1.

[0048] In this step 1, ion beam etching (IBE) or reactive ion etching (RIE) is adopted, and the preferred beneficial effects are as follows:

[0049] 1. The selection of the direction angle of the ion beam can effectively ensure the steepness of the primary etching and reduce the consumption of CD (the size of the magnesium oxide layer in the MTJ junction). The main RIE etching can quickly achieve the etching of the metal layer with less damage to the sidewalls of the magnesium oxide layer.

[0050] During the IBE etching process of the present embodiment, the ion beam preferably adopts a variable direction angle. The IBE etching includes large-angle IBE etching and small-angle IBE etching. Among them, large-angle IBE etching generally refers to the direction angle of the ion beam being 30 - 60°; small-angle IBE etching generally refers to the direction angle of the ion beam being 10 - 30°. Assuming the time period of large-angle IBE etching is T1 and the time period of small-angle IBE etching is T2, then preferably T1 ≥ 1.5T2.

[0051] 2. Using inert gas etching can obtain a higher steepness and clean sidewalls.

[0052] 3. By increasing the proportion of the etching amount t1 of the main etching step, the recess amount is increased and the steepness is improved.

[0053] Step 2, cleaning step: The magnetic tunnel junction sample that has completed the main etching step in step 1 is transferred to the corresponding cleaning step chamber through the vacuum chamber, and in the cleaning step chamber, the secondary etching of the cleaning step is carried out.

[0054] The cleaning step etching has the following two preferred embodiments.

[0055] The first embodiment: the continuous mode or pulse mode of reactive ion etching.

[0056] The second embodiment: the continuous mode or pulse mode of reactive ion etching, and low-energy ion beam etching.

[0057] The process conditions for reactive ion etching (RIE) are preferably as follows: the reactive ion pulsing is preferably 5% - 50%, the ion source power is 50 - 1000 W, the bias voltage is 10 - 1000 V, the chamber pressure is 0.5 - 10 mT, the gas flow rate is 10 - 500 sccm, and one or any combination of inert gases, nitrogen, oxygen, fluorine-based gases, amino gases, carbon monoxide, carbon dioxide, alcohols, etc. is used. Further preferably, an inert gas such as argon or an oxygen-containing gas is used.

[0058] The process conditions for ion beam etching (IBE) are preferably as follows: the directional angle is preferably 30 - 60° (the angle between the ion beam and the wafer normal), the energy is preferably 50 - 200 V, and the protective gas is preferably one or different combinations of inert gases, nitrogen, oxygen, fluorine-based gases, amino gases, carbon monoxide, carbon dioxide, alcohols, etc. Further preferably, an inert gas such as argon, krypton, xenon, etc. is used.

[0059] In step 2, the etching amount of the cleaning step is t2, and the value of t2 is preferably 5 - 40 nm, and t1:t2 ≥ 0.5. The etching amount ratio of the two etching steps is preferably: t1:t2 = 1.5 - 4.0.

[0060] After the second etching is completed, the etching morphology on the bottom electrode and / or the bottom dielectric layer is as Figure 3 and Figure 4 shown square grooves.

[0061] A square etching groove of a bottom MRAM magnetic tunnel junction, the square groove is the etching morphology on the bottom electrode or the bottom dielectric layer, and the shape is quasi-square. As Figure 2 shown, the square groove is on the bottom dielectric layer. As Figure 4 shown, the directional groove is in the bottom electrode. As an alternative, the square groove can also be located in Figure 4 the bottom electrode and / or the bottom dielectric layer at the same time.

[0062] The length of the lower bottom side of the square groove (corresponding to Figure 3 Square trench length in Figure 3 is L1, the length of the upper bottom side of the square groove (corresponding to Figure 3 Space in

[0063] is L2, the height of the square groove (corresponding to Figure 3 Recess in

[0063] is H1, and the angle between the lower bottom side and the side of the square groove is α; then: α = 90 - 130°, that is, approximately L-shaped, so a quasi-square is formed. Preferably: L1:L2 = 0.3 - 1.0, H1:L2 = 0.1 - 2.0.Due to factors such as charge accumulation effect and selectivity ratio, it is more difficult to form square etching grooves for small-sized dense patterns than for conventional patterns. After adopting the present invention, even when the pattern density reaches a pitch of 80-100 nm, obvious square groove features can still be etched.

[0064] In this step 2, a continuous mode or a pulse mode of low-energy ion beam etching or reactive ion etching is adopted, and preferably, it has the following beneficial effects:

[0065] 1. The low-energy and low-pressure conditions can improve the ability to remove deposition contamination, and in a suitable process window, sidewall contamination can be ensured not to occur.

[0066] 2. The low energy can reduce the sidewall damage of the magnesium oxide layer.

[0067] 3. Using an inert gas such as argon for etching can also obtain a high steepness and a clean sidewall. If an oxygen-containing gas is used for etching, it can have an oxidation effect on the sidewall. Using a reactive gas for etching can increase the selectivity ratio.

[0068] 4. Retain the steepness of the main etching step, and the final steepness is 75-90°. Even when the center-to-center distance Pitch of two units ≤100 nm, it can reach more than 85°.

[0069] 5. Compared with the traditional single etching method, the selectivity ratio is greatly improved.

[0070] 6. A square etching groove can be formed at the bottom. The bottom of the square groove is flat, without deposition contamination or only containing less deposition contamination. The square etching groove can be formed in the dielectric layer or in the lower electrode layer. The bottom corner of the square groove can be in an "L" shape. After the coating is etched, the film layer still has an obvious "L" shape morphology.

[0071] 7. The angle of the obtained square groove is 90-130°, and the length L1 of the lower bottom side of the square groove is 0.5-1.0 times the length L2 of the upper bottom side of the square groove. A better square groove morphology can be achieved when Recess : Space is 0.5-2 and the aspect ratio (total height : Space) is 1.0-5.0.

[0072] Step 3, coating: Coating the etched magnetic tunnel junction sample. The coated film layer is silicon nitride or silicon oxide or a combination of the two, the coating thickness is 10-100 nm, and the coating temperature is 150-350 °C. This in-situ protective film layer can prevent the metal stack of the MTJ from being corroded by water vapor in the air, etc., resulting in device conduction short circuit.

[0073] For the present invention, the following two specific preferred embodiments are adopted for further detailed description.

[0074] Embodiment 1

[0075] Step 1, perform the main etching step using reactive ion etching: Transfer the magnetic tunnel junction sample as shown in Figure 2 to the RIE chamber for main etching. The energy for the main etching step is a source power of 500 W, a bias power of 600 W, a chamber pressure of 20 mTorr, and the etching gas is Kr.

[0076] The reactive ion etching stops at a depth where 10 nm of the bottommost metal layer remains to the bottom dielectric layer of 40 nm. In the first embodiment, the first etching preferably stops when 5 nm of the bottommost metal layer remains, and the etching amount t1 is preferably 35 nm.

[0077] Step 2, perform the cleaning step using a combination of reactive ion etching RIE + ion beam etching IBE

[0078] Step 21, reactive ion etching RIE: Through the vacuum chamber, the magnetic tunnel junction sample completed in the main etching step of Step 1 is subjected to a second reactive ion etching. The parameters for the second reactive ion etching are: an ion source power of 700 W, a bias voltage of 400 V, a chamber pressure of 5 mT, and an argon gas flow rate of 100 sccm.

[0079] Step 22, ion beam etching: Through the vacuum chamber, the magnetic tunnel junction sample completed in the second reactive ion etching of Step 21 is transferred from the RIE to the IBE for ion beam etching. The process conditions for ion beam etching are preferably: BMV 100 V, an incident angle of 60°, and the etching gas is Ar. The etching depth, that is, the ion beam etching amount t2 = 30 nm. After the second etching, the etched morphology on the bottom dielectric layer is a square groove.

[0080] Step 3, coating: Transfer the sample after ion beam etching into the plasma enhanced chemical vapor deposition chamber through the vacuum transfer chamber, and deposit a 30 nm SiN thin film for in-situ protection.

[0081] In this embodiment, the length of the lower bottom side of the obtained square groove (corresponding to Figure 3 Square trench length) is L1, the length of the upper bottom side of the square groove (corresponding to Figure 3 Space) is L2, the height of the square groove (corresponding to Figure 3 Recess) is H1, and the angle between the lower bottom side and the side of the square groove is α; then: α = 120°, that is, approximately L-shaped, so a quasi-square is formed, and L1:L2 = 0.5, H1:L2 = 0.5.

[0082] Embodiment 2

[0083] Step 1, perform the main etching step using reactive ion etching: Transfer the magnetic tunnel junction sample as shown in Figure 4The shown magnetic tunnel junction sample is introduced into the reactive ion chamber. The power of the reactive ion etching ion source is 600 W, the bias voltage is 600 V, the chamber pressure is 10 mT, and the argon gas flow rate is 150 sccm. Among them, the magnetic tunnel junction sample to be etched includes a mask layer, a cap layer, an MTJ junction, a bottom electrode layer, and a bottom dielectric layer from top to bottom in sequence. The reactive ion etching stops when the bottom electrode layer is consumed by 3 nm. At this time, the reactive ion etching amount is 20 nm.

[0084] Step 2, perform a cleaning step using reactive ion etching: The preferred process conditions for the secondary etching are as follows: The reactive ion pulsing is selected as 5%, the reactive ion source power is 300 W, the bias voltage is 600 V, the chamber pressure is 1.5 mT, and the argon gas flow rate is 200 sccm. Etch to the seed layer for 30 nm, that is, the reactive ion etching amount t2 = 15 nm. After the secondary etching is completed, the etched morphology on the bottom electrode is a square groove.

[0085] Step 2A, ion beam cleaning: Transmit the secondary etched sample to the IBE chamber through the vacuum chamber. The ion beam angle is selected as 45°, the ion beam energy is 100 V, and argon etching is used. The etching depth is 3 nm, and it still stays on the bottom electrode. The morphology comparison is as Figure 4 .

[0086] Step 3, in-situ protection of the magnetic tunnel junction: Through the vacuum transfer chamber, transmit the magnetic tunnel junction sample after ion beam cleaning into the plasma enhanced chemical vapor deposition chamber, and deposit a 10-nm SiN thin film for in-situ protection.

[0087] The length of the lower bottom side of the square groove of the sample obtained in this embodiment (corresponding to Figure 3 Square trench length) is L1, the length of the upper bottom side of the square groove (corresponding to Figure 3 Space) is L2, the height of the square groove (corresponding to Figure 3 Recess) is H1, and the angle between the lower bottom side and the side of the square groove is α; then: α = 110°, that is, approximately L-shaped, so a quasi-square is formed, L1:L2 = 0.6, H1:L2 = 0.8.

[0088] Example Three

[0089] Step 1, perform the main etching step using ion beam etching: Transmit the magnetic tunnel junction sample into the ion beam etching chamber. The direction angle of the ion beam is selected as 25°, the energy is 600 V, and the protective gas is selected as argon etching. Among them, the magnetic tunnel junction sample includes a mask layer, a cap layer, an MTJ junction, a bottom electrode metal layer, and a bottom dielectric layer from top to bottom in sequence. Metal lower electrodes equal in number to the number of masks in the mask layer are nested at equal intervals in the bottom dielectric layer, and the positions of the metal lower electrodes correspond to those of the masks. The ion beam etching stops when 5 nm of the bottommost metal layer remains, that is, the ion beam etching amount t1 is 35 nm.

[0090] Step 2: Perform a cleaning step using reactive ion etching: Through the vacuum chamber, transfer the magnetic tunnel junction sample that has completed ion beam etching in Step 1 from the ion beam etching chamber to the reactive ion etching chamber for secondary etching. The secondary etching parameters are as follows: The reactive ion pulse is selected at 20%, the ion source power is 700 W, the bias voltage is 400 V, the chamber pressure is 5 mT, the argon gas flow rate is 100 sccm, and the reactive ion etching amount t2 = 30 nm. After completing the secondary etching, the etched morphology on the bottom dielectric layer is a square groove.

[0091] Step 3: Coating: Transfer the sample after secondary etching into the plasma enhanced chemical vapor deposition chamber through the vacuum transfer chamber to deposit a 35-nm SiN thin film for in-situ protection.

[0092] The length of the lower bottom side of the square groove of the sample obtained in this embodiment (corresponding to Figure 3 Square trench length in Figure 3 is L1, the length of the upper bottom side of the square groove (corresponding to Figure 3 Space in

[0093] Example 4

[0094] Step 1: Perform the main etching step using reactive ion etching: Transfer the magnetic tunnel junction sample as shown in Figure 2 into the RIE chamber for main etching. The main etching step energy is a source power of 700 W, a bias power of 400 W, a chamber pressure of 15 mTorr, a chamber pressure of 10 mTorr, and the etching gas is ethanol.

[0095] The reactive ion etching stops at a depth where 5 nm of the bottommost metal layer remains to 40 nm of the bottom dielectric layer. In this embodiment, the primary etching preferably stops at the interface between the metal and the dielectric, and the etching amount t1 is preferably 20 nm.

[0096] Step 2: Perform a cleaning step using reactive ion etching: Continue with secondary etching in the reactive ion etching chamber. The preferred process conditions for the secondary etching are as follows: The reactive ion pulse Pulsing is selected at 30%, the reactive ion source power Source is 300 W, the bias voltage is 100 V, the chamber pressure is 5 mT, the argon gas flow rate is 200 sccm, and etch 30 nm to the seed layer, that is, the etching amount t2 = 15 nm. After completing the secondary etching, the etched morphology on the bottom electrode is a square groove.

[0097] Step 3, Coating: Transfer the sample after secondary etching into the plasma enhanced chemical vapor deposition chamber through a vacuum transfer chamber, and deposit a 25-nm SiN thin film for in-situ protection.

[0098] The length of the lower bottom edge of the square trench of the sample obtained in this embodiment (corresponding to Figure 3 Square trench length in Figure 3 is L1, the length of the upper bottom edge of the square trench (corresponding to Figure 3 Space in

[0099] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the protection scope of the present invention.

Claims

1. An etching method for an MRAM magnetic tunnel junction, characterized in that: It includes the following steps: Step 1, the main etching step of the magnetic tunnel junction: Using ion beam etching and / or reactive ion etching, perform main etching step etching on the magnetic tunnel junction with an etching amount of t1; wherein, the direction angle of the ion beam is 10~60°, and the bias voltage of the reactive ion etching is 400 - 1000V; Step 2, the cleaning step of the magnetic tunnel junction: Perform cleaning step etching with an etching amount of t2 on the magnetic tunnel junction that has completed the main etching step; wherein, t1:t2≥0.5; the cleaning step etching includes reactive ion etching, and the mode of the reactive ion etching is a pulse mode; the bias voltage of the reactive ion etching is 50V - 400V, and the pulse duty cycle is 5% - 50%; after the cleaning step etching is completed, the etched morphology on the bottom electrode or the bottom dielectric layer is a quasi-square groove; when the center pitch Pitch of two adjacent units in the magnetic tunnel junction ≤ 100nm, the final steepness of the quasi-square groove can reach more than 85°.

2. The etching method of the MRAM magnetic tunnel junction according to claim 1, characterized in that: In Step 2, the cleaning step etching adopts a combination of ion beam etching and reactive ion etching; wherein, the beam voltage of the ion beam etching is 50V - 200V.

3. The etching method of the MRAM magnetic tunnel junction according to claim 1, characterized in that: It also includes Step 3, in-situ protection of the magnetic tunnel junction: Using chemical vapor deposition, grow a dielectric film layer around the magnetic tunnel junction that has completed the cleaning step etching for in-situ protection.

4. The etching method of the MRAM magnetic tunnel junction according to claim 1, characterized in that: The etching amount t2 of the cleaning step etching is 5 - 100nm.

5. The etching method of the MRAM magnetic tunnel junction according to claim 1, characterized in that: In Step 1, the ion beam etching includes large-angle ion beam etching and small-angle ion beam etching.

6. The etching method of the MRAM magnetic tunnel junction according to claim 5, characterized in that: Large-angle ion beam etching means that the direction angle of the ion beam is 30 - 60°, and small-angle ion beam etching means that the direction angle of the ion beam is 10 - 30°; assuming the time period of the large-angle ion beam etching is T1, and the time period of the small-angle ion beam etching is T2, then T1≥1.5T2.

7. The etching method of the MRAM magnetic tunnel junction according to claim 1 or 2, characterized in that: In the main etching step and the cleaning step, when using ion beam etching, the gas used in the ion beam chamber is one or any combination of inert gas, nitrogen, oxygen, fluorine-based gas, amino gas, carbon monoxide, carbon dioxide, and alcohols.

8. The etching method of the MRAM magnetic tunnel junction according to claim 1 or 2, characterized in that: In the main etching step and the cleaning step, when using reactive ion etching, the ion source power in the reactive ion chamber is 50 - 1000W, the chamber pressure is 0.5 - 10mT, the gas flow rate is 10 - 500sccm, and the gas is one or any combination of inert gas, nitrogen, oxygen, fluorine-based gas, amino gas, carbon monoxide, carbon dioxide, and alcohols.

9. The etching method of the MRAM magnetic tunnel junction according to claim 1, characterized in that: The length of the lower bottom side of the quasi-square groove is L1, the length of the upper bottom side of the quasi-square groove is L2, the height of the quasi-square groove is H1, and the angle between the lower bottom side and the side of the quasi-square groove is α, then: L1:L2 = 0.3~1.0, H1:L2 = 0.1~2.0, α = 90 - 130°.

10. The etching method of the MRAM magnetic tunnel junction according to claim 1, characterized in that: It includes the following steps: Step 1, Main Etching Step of Magnetic Tunnel Junction: Using ion beam etching, perform a main etching step on the magnetic tunnel junction with an etching amount of t1 = 35 nm; the ion beam etching method is: transfer the magnetic tunnel junction sample into the ion beam etching chamber, select the direction angle of the ion beam as 25°, the energy as 600 V, and the protective gas as argon; among them, the magnetic tunnel junction sample includes a mask layer, a cap layer, an MTJ junction, a bottom electrode metal layer, and a bottom dielectric layer from top to bottom in sequence; metal lower electrodes equal in number to the masks in the mask layer are nested at equal intervals in the bottom dielectric layer, and the positions of the metal lower electrodes correspond to those of the masks; the ion beam etching stops when 5 nm of the bottom electrode metal layer remains; at this time, the ion beam etching amount is 35 nm; Step 2, Cleaning Step of Magnetic Tunnel Junction: For the magnetic tunnel junction that has completed the main etching step, use reactive ion etching to perform a cleaning step etching with an etching amount of t2 = 30 nm; the reactive ion etching method is: through the vacuum chamber, transfer the magnetic tunnel junction sample that has completed ion beam etching in Step 1 from the ion beam etching chamber to the reactive ion etching chamber for reactive ion etching; the parameters of the reactive ion etching are: the reactive ion pulse is selected as 20%, the ion source power is 700 W, the bias voltage is 400 V, the chamber pressure is 5 mT, the argon gas flow rate is 100 sccm, and the reactive ion etching amount is 30 nm; after the cleaning step etching is completed, the etching morphology on the bottom dielectric layer is a square-like groove; Step 3, In-situ Protection of Magnetic Tunnel Junction: Through the vacuum transfer chamber, transfer the magnetic tunnel junction sample after the cleaning step etching into the plasma enhanced chemical vapor deposition chamber and deposit a 35 nm SiN thin film for in-situ protection.

11. The etching method of the MRAM magnetic tunnel junction according to claim 1, characterized in that: The steps include the following: Step 1, Main Etching Step of Magnetic Tunnel Junction: Using reactive ion etching, perform a main etching step on the magnetic tunnel junction with an etching amount of t1 = 20 nm; the reactive ion etching method is: transfer the magnetic tunnel junction sample into the reactive ion etching chamber, the reactive ion etching ion source power is 600 W, the bias voltage is 400 V, the chamber pressure is 3 mT, and the argon gas flow rate is 150 sccm; among them, the magnetic tunnel junction sample to be etched includes a mask layer, a cap layer, an MTJ junction, a bottom electrode layer, and a bottom dielectric layer from top to bottom in sequence; the reactive ion etching stops when 3 nm of the bottom electrode layer is consumed; at this time, the reactive ion etching amount is 20 nm; Step 2, Cleaning Step of Magnetic Tunnel Junction: For the magnetic tunnel junction that has completed the main etching step, use reactive ion etching to perform a cleaning step etching with an etching amount of t2 = 15 nm; the etching parameters of the reactive ion etching are: the reactive ion pulse is selected as 5%, the anti-ion source power is 300 W, the bias voltage is 600 V, the chamber pressure is 1.5 mT, the argon gas flow rate is 200 sccm, and the reactive ion etching amount t2 = 15 nm; after the cleaning step etching is completed, the etching morphology on the bottom dielectric layer is a square-like groove; Step 2A, Ion Beam Cleaning: Through the vacuum chamber, transfer the magnetic tunnel junction sample after the cleaning step etching to the ion beam etching chamber, select the ion beam angle as 45°, the ion beam energy as 100 V, use argon for etching, and the etching depth is 3 nm, still staying on the bottom electrode layer; Step 3, in-situ protection of the magnetic tunnel junction: Through the vacuum transfer chamber, the magnetic tunnel junction sample after ion beam cleaning is introduced into the plasma enhanced chemical vapor deposition chamber, and a 10-nm SiN thin film is deposited for in-situ protection.

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