Treatment to reduce shunting of an MTJ device

Abstract

Methods for etching an MTJ structure, including: Provision of a stack of MTJ layers (14) on a lower electrode (12); provision of an upper electrode (16) on the stack of MTJ layers (14); structuring of the upper electrode (16); then oxidizing or nitriding the entire stack of MTJ layers (14) using the structured upper electrode (16) as a mask, thereby converting the entire stack of MTJ layers (14) not covered by the structured upper electrode (16) into oxide or nitride; then structuring the stack of MTJ layers (14) using the structured upper electrode (16) as a mask to form an MTJ device, wherein each sidewall deposition (22) formed on sidewalls of the MTJ device is non-conductive, where oxidation or nitration is carried out by applying an oxygen-containing water or solvent or a nitrogen-containing water or solvent, respectively.

Description

TECHNICAL AREA

[0001] This application relates to the general field of magnetic tunneling connections (MTJ) and more specifically to etching methods for forming MTJ structures. GENERAL STATE OF THE ART

[0002] A typical MTJ etched using a chemical etching process exhibits sidewall damage, possibly caused by oxygen or other chemicals released after the etching process. Purely physical etching processes, such as ion beam etching (IBE), can minimize sidewall damage. However, a drawback of physical etching is the re-deposition of material from the bottom electrode to the sidewall and of MTJ material to the MTJ sidewalls. This re-deposition of the bottom electrode creates a shunting path around the MTJ sidewall, resulting in a low yield for the MRAM chip.

[0003] Several patents teach methods for reducing shunting. These include US patents US 9,257,638 B2 (Tan et al.), US 7,043,823 B2 (Childress et al.), US 8,981,507 B2 (Takahashi et al.), US 6,798,626 B2 (Hayashi et al.), US 8,045,299 B2 (Fontana Jr. et al.), US 8,673,654 B2 (Hong et al.), and US patent application US 2016 / 0079308 A1 (Ito). US patent US 8,045,299 B2 (Fontana Jr. et al. - HGST) teaches etching and then oxidizing the MTJ stack or adding ozone or water to the etching process to oxidize the re-deposition material. From US 2014 / 0 295 579 A1, it is known that an MTJ stack can be structured prior to oxidation or nitration. US 2013 / 0 288 393 A1 discloses a method for structuring an MTJ stack using ion implantation. US 2005 / 0 277 206 A1 also discloses a method for structuring an MTJ stack. BRIEF SUMMARY OF THE INVENTION

[0004] One goal of this revelation is to provide an improved etching process for the formation of MTJ structures.

[0005] Another objective of the present disclosure is to provide an etching process that reduces the shunting of MTJ devices.

[0006] In accordance with the objectives of this disclosure, a method for etching a magnetic tunnel junction (MTJ) structure is achieved. A stack of MTJ layers is provided on a lower electrode. An upper electrode is provided on top of the MTJ stack. The upper electrode is structured. Subsequently, the portion of the MTJ stack not covered by the structured upper electrode is oxidized or nitrided. Then, the MTJ stack is structured to form an MTJ device, wherein a new sidewall deposition forming on the sidewalls of the MTJ device is non-conductive. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The accompanying drawings, which form a substantial part of this description, show: Fig. 1, Fig. 2, Fig. 3A and Fig. Figure 3B illustrates in cross-section representation steps in a first preferred embodiment of this disclosure. Fig. 1, Fig. 2, Fig. 4A and Fig. Figure 4B illustrates in cross-section representation steps in a second preferred embodiment of this disclosure. DETAILED DESCRIPTION

[0008] For most purely physical etching processes (such as IBE), the sidewall always experiences a severe re-deposition problem because the byproducts of the etched material are non-volatile. To prevent the re-deposition material around the MTJ sidewall from becoming a shunting path for the MTJ, we apply an oxygen surface treatment to change the potential re-deposition material from conductive to non-conductive. This step ensures that any re-deposition is non-conductive and does not lead to shunting of the MTJ devices.

[0009] Now, specifically with reference to… Fig. 1, Fig. 2, Fig. 3 to Fig. 4 the new revelation described in detail. A lower electrode 12 is formed on the substrate 10, as in Fig. Figure 1 shows that layers are now deposited on the lower electrode to form a magnetic tunnel connection.

[0010] Layers 14 comprise the MTJ layers, including one or more seed layers, pinned layers, tunnel barrier layers, and free layers, as is common in the technology. Finally, an upper electrode 16 is deposited on the MTJ layers 14.

[0011] A photoresist mask 25 is formed over the upper electrode. As in Fig. As shown in Figure 2, the upper electrode is structured using the photoresist mask 25.

[0012] Now, a further post-treatment process is added in the middle of the etching process. After defining the upper electrode 16 and before the main physical etching to define an MTJ region, an oxidation treatment 27 is preferably carried out to oxidize the entire exposed MTJ region, whereby the exposed MTJ region not covered by the structured upper electrode 20 is oxidized and thus becomes non-conductive, as shown in Fig. Figure 3A illustrates this. This means that the entire stack not covered by the top electrode hard mask is oxidized, including the cover layer, free layer, pinned layer, seed layer, and so on. This ensures that the entire new deposit remains non-conductive after IBE etching to prevent shunting.

[0013] Oxidation of the newly deposited material after etching is undesirable because the oxygen can damage the MTJ device. Controlling the oxide penetration depth is difficult. Oxidation before etching does not cause this problem because all oxygen is removed after etching.

[0014] Following the treatment process, physical etching is applied to define the MTJ area, as shown in Fig. Figure 3B illustrates this. Further treatment does not eliminate sidewall re-deposition, but we can ensure that the re-deposition material 22 is non-conductive and therefore does not lead to a shunting path across the MTJ barrier. Most of the etched material should be pumped out during the etching process, but even if some re-deposition occurs on the MTJ sidewall, it will not form a shunting path because it is non-conductive.

[0015] Depending on the process integration, the lower electrode could be patterned before the deposition of the MTJ layers. Alternatively, the lower electrode could be patterned after the MTJ fixture has been patterned. We can eliminate the re-deposition hunting problem from the lower electrode by increasing the oxidation power and / or the time required to oxidize the lower electrode portion not covered by the upper electrode hard mask before performing the MTJ etching, as shown in Fig. 4A shown. Then, when we pattern the lower electrode, all new deposition 22 on horizontal surfaces of the lower electrode layer is removed during this etching. Some new deposition may occur on sidewalls of the MTJ stack, but this is non-conductive material 22, as shown in Fig. 4B shown.

[0016] Post-treatment can be applied in a variety of ways. These may include: 1) natural oxidation or nitration by introducing oxygen or nitrogen gas, 2) plasma-assisted or ion-assisted oxidation or nitration, or 3) treatment with a liquid such as water or a solvent, as required. It may be necessary to apply the treatment multiple times to ensure that all metallic material in the MTJ stack is converted to oxide or nitride, rendering it non-conductive.

[0017] In Option 1, oxygen or nitrogen is introduced into a chamber containing the wafer prior to MTJ etching. If the MTJ stack is not very thick, natural oxidation or nitration may be sufficient to convert the entire MTJ stack, covered by the top electrode hard mask, into non-conductive material.

[0018] Option 2 can utilize plasma oxidation or nitration using pure O2, pure N2, or a mixture of O2 and N2. Optionally, plasma oxidation, nitration, or mixed O2 / N2 can be performed with a noble gas such as Ar, Xe, or similar. O2 or N2 implantation could be performed to convert the material. Alternatively, O2 or N2 ion beam irradiation can perform oxidation or nitration of the exposed layer.

[0019] In Option 3, water or a solvent containing, for example, -OH or -NH, converts the exposed layers into oxides or nitrides.

[0020] Since the MTJ layers are oxidized or nitrided before the main physical etching takes place, no residual oxygen or nitrogen gas should remain in the area when the MTJ etching is complete. This reduces damage from oxygen or nitrogen to the MTJ sidewalls.

[0021] Although the preferred embodiment of this disclosure has been illustrated and this form has been described in detail, it is easy for a person skilled in the art to see that various modifications to it are possible without departing from the spirit of the disclosure or from the scope of the accompanying claims.

Claims

[1] Method for etching an MTJ structure, comprising: Provision of a stack of MTJ layers (14) on a lower electrode (12); provision of an upper electrode (16) on the stack of MTJ layers (14); structuring of the upper electrode (16); then oxidizing or nitriding the entire stack of MTJ layers (14) using the structured upper electrode (16) as a mask, thereby converting the entire stack of MTJ layers (14) not covered by the structured upper electrode (16) into oxide or nitride; then structuring the stack of MTJ layers (14) using the structured upper electrode (16) as a mask to form an MTJ device, wherein each sidewall deposition (22) formed on sidewalls of the MTJ device is non-conductive, where oxidation or nitration is carried out by applying an oxygen-containing water or solvent or a nitrogen-containing water or solvent, respectively. [2] Method according to claim 1, wherein the stack of MTJ layers (14) is structured using a physical etching process. [3] Method according to claim 1 or 2, wherein the oxidizing or nitriding is repeated until the metal in the stack of MTJ layers (14) that is not covered by the structured upper electrode (16) is completely converted to oxide or nitride. [4] Method according to any one of claims 1 to 3, further comprising oxidizing or nitriding the lower electrode (12) which is not covered by the structured upper electrode (16). [5] Method for etching an MTJ structure, comprising: Providing a stack of MTJ layers (14) on a lower electrode (12); Providing an upper electrode (16) on the stack of MTJ layers (14); Structuring the upper electrode (16); then oxidizing or nitriding the entire stack of MTJ layers (14) and the lower electrode (12) using the structured upper electrode (16) as a mask, thereby converting the entire stack of MTJ layers (14) and the lower electrode (12) not covered by the structured upper electrode (16) into oxide or nitride; then structuring the stack of MTJ layers (14) using the structured upper electrode (16) as a mask to form an MTJ device, wherein each sidewall re-deposition (22) formed on sidewalls of the MTJ device is non-conductive; and then structuring the lower electrode (12) using the structured upper electrode (16) as a mask, wherein each sidewall re-deposition (22) on sidewalls of the MTJ device is non-conductive, where oxidation or nitration is carried out by applying an oxygen-containing water or solvent or a nitrogen-containing water or solvent, respectively. [6] Method according to claim 5, wherein the stack of MTJ layers (14) is structured using a physical etching process. [7] Method according to claim 5 or 6, wherein the oxidizing or nitriding is repeated until the metal in the stack of MTJ layers (14) and the lower electrode (12) not covered by the structured upper electrode (16) is completely converted to oxide or nitride.

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