阅读说明：本技术 用于物理蚀刻制程的减少分流的装置的后处理 (Post-processing of a device for reducing shunting for physical etch processes ) 是由 王郁仁 沈冬娜 维格纳许·桑达 沙希·帕特尔 于 2018-03-08 设计创作，主要内容包括：描述一种蚀刻磁通道接面(MTJ)结构的方法。提供MTJ层在底电极上。提供顶电极在MTJ堆叠上。顶电极被图案化。未被图案化顶电极覆盖的MTJ堆叠被氧化或氮化。之后,图案化MTJ堆叠以形成MTJ装置,其中任何在MTJ装置侧壁上形成的侧壁再沉积为非导电,其中一些介电层保留在底电极的水平表面上。(a method of etching a Magnetic Tunnel Junction (MTJ) structure is described. An MTJ layer is provided on the bottom electrode. A top electrode is provided over the MTJ stack. The top electrode is patterned. The MTJ stack not covered by the patterned top electrode is oxidized or nitrided. Thereafter, the MTJ stack is patterned to form an MTJ device, wherein any sidewalls formed on the MTJ device sidewalls are redeposited as non-conductive, wherein some of the dielectric layer remains on the horizontal surface of the bottom electrode.)

1. A method of etching a Magnetic Tunnel Junction (MTJ) structure, comprising:

providing an MTJ stack on a bottom electrode;

Providing a top electrode over the MTJ stack;

patterning the top electrode;

Thereafter oxidizing or nitriding the MTJ stack not covered by the patterned top electrode;

The MTJ stack is then patterned to form an MTJ device, wherein any sidewalls formed on the sidewalls of the MTJ device are then non-conductive.

2. the method of claim 1, wherein the MTJ stack is patterned by a physical etching process.

3. the method of claim 1, wherein said oxidizing or nitriding is by natural oxidation or natural nitridation.

4. The method of claim 1, wherein said oxidizing or nitriding is by an oxide or nitride plasma or ion beam process comprising pure oxygen, or pure nitrogen, or oxygen or nitrogen mixed with one or more noble gases.

5. The method of claim 1, wherein said oxidizing or nitriding is by coating with water or an oxygen or nitrogen containing solvent.

6. the method of claim 1, wherein said oxidizing or nitridizing is repeated until all metal in said MTJ stack not covered by said patterned top electrode is converted to an oxide or nitride.

7. The method of claim 1, further comprising oxidizing or nitriding said bottom electrode not covered by said patterned top electrode.

8. A method of etching a Magnetic Tunnel Junction (MTJ) structure, comprising:

Providing an MTJ stack on a bottom electrode;

Providing a top electrode over the MTJ stack;

Patterning the top electrode;

Thereafter oxidizing or nitriding the MTJ stack and the bottom electrode not covered by the patterned top electrode;

Patterning the MTJ stack to form an MTJ device, wherein any sidewalls formed on the sidewalls of the MTJ device are non-conductive; and

The bottom electrode is then patterned, wherein any sidewalls on the MTJ device are redeposited as non-conductive.

9. The method of claim 8, wherein the MTJ stack is patterned by a physical etching process.

10. The method of claim 8, wherein said oxidizing or nitriding is by natural oxidation or natural nitridation.

11. The method of claim 8, wherein said oxidizing or nitriding is by an oxide or nitride plasma or ion beam process comprising pure oxygen, or pure nitrogen, or oxygen or nitrogen mixed with one or more noble gases.

12. The method of claim 8, wherein said oxidizing or nitriding is by coating with water or an oxygen or nitrogen containing solvent.

13. The method of claim 8, wherein said oxidizing or nitridizing is repeated until all metal in said MTJ stack not covered by said patterned top electrode is converted to an oxide or nitride.

Technical Field

the present application relates to the field of Magnetic Tunnel Stacks (MTJs), and more particularly, to etching methods for forming MTJ structures.

Background

Typical MTJ etching by chemical etching processes has been found to have sidewall damage, which may be caused by oxygen or other chemicals during the etching process. Purely physical etching processes such as Ion Beam Etching (IBE) can minimize sidewall damage. However, one drawback of the physical etching process is the redeposition of the bottom electrode and the sidewalls of the MTJ material to the MTJ sidewalls. Sidewall redeposition of the bottom electrode will cause path shunting around the MTJ sidewalls, which in turn leads to low yield of the MRAM chip.

Many patents teach methods of reducing the split. These include U.S. patents 9,257,638(Tan et al), U.S. patent 7,043,823(Childress et al), U.S. patent 8,981,507(Takahashi et al), U.S. patent 6,798,626(Hayashi et al), 8,045,299(Fontana, Jr et al), 8,673,654(Hong et al) and U.S. patent Application 2016/0079308 (Ito). U.S. patent 8,045,299(Fontana, Jr et al-HGST) teaches etching and then oxidizing the MTJ stack, or adding ozone or water during the etching process to oxidize the redeposited material.

disclosure of Invention

it is an object of the present disclosure to provide an improved etching process for forming MTJ structures.

It is another object of the present disclosure to provide an etching process that reduces MTJ device shunting.

In accordance with the purpose of the present disclosure, a method for etching an MTJ structure is implemented. An MTJ layer is provided on the bottom electrode. A top electrode is provided over the MTJ stack. The top electrode is patterned. The MTJ stack not covered by the patterned top electrode is oxidized or nitrided. Thereafter, the MTJ stack is patterned to form the MTJ device, wherein any sidewalls formed on the MTJ device sidewalls are redeposited non-conductive.

Drawings

The accompanying drawings, which form an essential part of the specification, are shown in the drawings in which:

Fig. 1, 2, 3A and 4A are cross-sectional views showing representative steps according to a first preferred embodiment of the present disclosure.

Fig. 1, 2, 3B and 4B are sectional views showing representative steps according to a second preferred embodiment of the present disclosure.

Detailed Description

For most purely physical etch processes (e.g., IBE), the sidewalls always suffer from severe redeposition problems because the by-products of the etch material are non-volatile. To prevent redeposited material around the MTJ sidewalls from becoming a shunt path for the MTJ, we perform a surface treatment with oxygen to convert the potential redeposited material from being conductive to non-conductive. This step will ensure that any redeposition is non-conductive and will not result in shunting of the MTJ device.

Referring now in particular to fig. 1 to 4, the novel disclosure will be described in detail. The bottom electrode 12 is formed on the substrate 10 as shown in fig. 1. Now, a film layer is deposited on the bottom electrode to form the magnetic tunnel junction. The layers 14 include MTJ layers including one or more seed layers, pinned layers, tunnel barrier layers, and free layers, as is conventional in the art. Finally, a top electrode 16 is deposited on the MTJ layer 14.

A photoresist mask 25 is formed on the top electrode. As shown in fig. 2, the top electrode is patterned using a photoresist mask 25.

Now, an additional post-treatment process is added in the middle of the etching process. After the top electrode 16 is defined and before the main physical etch to define the MTJ regions, an oxidation process 27 is preferably performed to oxidize the entire exposed MTJ regions, wherein the exposed MTJ regions not covered by the patterned top electrode become oxide 20 and therefore non-conductive, as shown in fig. 3A. That is, the entire stack not covered by the top electrode hard mask is oxidized, including the capping layer, free layer, pinned layer, seed layer, etc. This will ensure that all redeposition remains non-conductive after IBE etching to prevent any closed paths.

Oxidizing the redeposited material after etching is undesirable because oxygen can damage the MTJ device. It is difficult to control the depth of penetration of the oxide. Oxidation before etching does not lead to this problem because all oxygen disappears after etching.

After the processing, a physical etch is applied to define the MTJ region, as shown in FIG. 4A. Additional processing does not eliminate sidewall redeposition, but we can ensure that redeposited material 22 is not conductive, and therefore, it does not cause a shunt path through the MTJ barrier. Most of the etch material should be pumped out during the etch, but even if there is some redeposition on the MTJ sidewalls, it will not be a closed path because it is not conductive.

Depending on process integration, the bottom electrode may be patterned prior to deposition of the MTJ layers. Or the bottom electrode may be patterned after the MTJ device is patterned. As shown in fig. 3B, the redeposition shunting problem from the bottom electrode can be eliminated if the oxidation capability and/or time is increased to oxidize the portion of the bottom electrode not covered by the top electrode hard mask prior to performing the MTJ etch. Then, when we pattern the bottom electrode, any redeposition 22 on the horizontal surfaces of the bottom electrode layer is removed during this etch. Some redeposition may occur on the sidewalls of the MTJ stack, but this will be the non-conductive material 22, as shown in fig. 4B.

Post-processing can be applied in a number of different ways. These may include: (1) natural oxidation or nitridation by introducing oxygen or nitrogen, (2) oxidation or nitridation by plasma assistance or ion beam assistance, or (3) treatment by a liquid such as water or a solvent. Multiple application processes may be required to ensure that all of the metal material in the MTJ stack is converted to an oxide or nitride, thereby rendering it non-conductive.

In option 1, oxygen or nitrogen is introduced into the chamber containing the wafer prior to the MTJ etch. If the MTJ stack is not very thick, the natural oxidation or nitridation may be sufficient to convert all of the MTJ stack not covered by the top electrode hard mask to a non-conductive material.

in the 2 nd option, plasma oxidation or nitridation can use pure oxygen, pure nitrogen or a mixture of oxygen and nitrogen. Plasma oxidation, nitridation or mixed oxygen/nitrogen gas is optionally (optically) performed with some noble gas such as Ar, Xe, etc. An oxygen or nitrogen implant may be performed to convert the material. Alternatively, oxygen or nitrogen ion beam irradiation may perform oxidation or nitridation on the exposed layer.

In option 3, water or a solvent containing, for example, -OH or-NH, may convert the exposed layer to an oxide or nitride.

since the MTJ layer is oxidized or nitrided before the main physical etch is performed, there should be no residual oxygen or nitrogen in this region after the MTJ etch is complete. This will mitigate oxygen or nitrogen damage to the MTJ sidewalls.

While the preferred embodiments of the present disclosure have been illustrated and described, it will be appreciated by those skilled in the art that changes may be made thereto without departing from the spirit and scope of the disclosure as set forth in the appended claims.