WO2021051969A1

WO2021051969A1 - Method for manufacturing magnetic tunnel junction

Info

Publication number: WO2021051969A1
Application number: PCT/CN2020/101088
Authority: WO
Inventors: 李辉辉
Original assignee: 浙江驰拓科技有限公司
Priority date: 2019-09-18
Filing date: 2020-07-09
Publication date: 2021-03-25
Also published as: CN112531106A

Abstract

The present invention provides a method for manufacturing a magnetic tunnel junction (MTJ). The method comprises: providing a substrate, and successively depositing a bottom electrode material layer, an MTJ material layer, a metal hard mask layer, and a dielectric hard mask layer on the substrate, wherein the MTJ material layer comprises a first magnetic thin film layer, an insulating thin film layer located on the first magnetic thin film layer, and a second magnetic thin film layer located on the insulating thin film layer; photoetching to obtain a mask shape, and etching the dielectric hard mask layer and the metal hard mask layer; further etching the MTJ material layer, and enabling an etching endpoint to stay at an interface of the insulating thin film layer and the first magnetic thin film layer; forming a first protective layer and etching the first protective layer, and only retaining a vertical portion of the first protective layer; and etching the first magnetic thin film layer by taking the etched metal hard mask layer as a hard mask so as to form an MTJ bit. The present invention can reduce the metal deposition produced in the MTJ etching process.

Description

Preparation method of magnetic tunnel junction

Technical field

The present invention relates to the technical field of magnetic memory, in particular to a method for preparing a magnetic tunnel junction.

Background technique

MRAM (Magnetic Random Access Memory) is considered to be the future solid-state non-volatile memory, with excellent properties such as fast reading and writing, non-volatile, and radiation resistance. MRAM uses MTJ (Magnetic Tunnel Junction) as the basic storage unit. The core part of MTJ consists of two ferromagnetic layers (ferromagnetic metal materials, with a typical thickness of 1～2.5nm) sandwiching a tunnel barrier layer. (Insulating material, the typical thickness is 1 ~ 1.5nm) It forms a nano multilayer film similar to a sandwich structure. One of the ferromagnetic layers is called the reference layer or pinned layer, and its magnetization is fixed along the easy axis of magnetization. The other ferromagnetic layer is called the free layer, and its magnetization has two stable orientations, parallel or anti-parallel to the reference layer.

In the MRAM manufacturing process, the patterning process of the magnetic tunnel junction has become one of the most challenging processes. The traditional MTJ patterning process uses ion beam etching, reactive ion etching and other technologies. In the etching process, etching by-products, such as bottom electrode materials, are inevitably produced. These by-products are easy to adhere to the sidewalls of the MTJ. Cause metal deposition pollution, thereby affecting device performance.

Summary of the invention

In order to solve the above problems, the present invention provides a method for preparing a magnetic tunnel junction, which can reduce the metal deposition sputtered on the sidewall of the MTJ.

The present invention provides a method for preparing a magnetic tunnel junction, including:

A substrate is provided, and a bottom electrode material layer, an MTJ material layer, a metal hard mask layer, and a dielectric hard mask layer are sequentially deposited on the substrate, wherein the MTJ material layer includes: located on the bottom electrode material layer A first magnetic film layer, an insulating film layer on the first magnetic film layer, and a second magnetic film layer on the insulating film layer;

Lithographically etch the shape of the first mask, and etch the dielectric hard mask layer and the metal hard mask layer;

Using the etched dielectric hard mask layer and the etched metal hard mask layer as hard masks, the MTJ material layer is etched, and the etching end point remains at the insulating film layer and the insulating film layer. The interface of the first magnetic thin film layer to obtain a pre-etched device;

Forming a first protective layer on the surface of the pre-etched device;

Etching the first protective layer, after the etching is completed, the horizontal part of the first protective layer is completely removed while the vertical part is retained;

Using the etched metal hard mask layer as a hard mask, the first magnetic thin film layer is etched to form MTJ bits.

Optionally, the first protective layer is formed by plasma-enhanced atomic layer deposition or plasma-enhanced chemical vapor deposition.

Optionally, the material of the first protective layer _{is any one of SiO 2} , SiN, SiC, SiON and SiCN.

Optionally, the thickness of the first protective layer is 5-50 nm.

Optionally, dry etching is used to etch the first protective layer.

Optionally, the method further includes:

Forming a second protective layer on the surface of the formed MTJ bit;

Backfill the dielectric material and perform flattening treatment;

The second mask shape is photo-etched, and the MTJ bottom electrode is etched.

Optionally, the second protective layer has the same material as the first protective layer.

Optionally, the photoetching of the first mask shape and etching the dielectric hard mask layer and the metal hard mask layer includes:

A photoresist laminate structure is spin-coated on the dielectric hard mask layer, and the photoresist laminate structure includes an organic carbon-rich spin coating, a low-temperature oxide film, an anti-reflection layer, and a photoresist stacked sequentially from bottom to top Floor;

Exposing and cleaning the photoresist laminated structure, and etches down by layer-by-layer transfer, leaving only the etched organic carbon-rich spin coating;

Using the etched organic carbon-rich spin coating as a mask, the dielectric hard mask layer and the metal hard mask layer are sequentially etched.

Optionally, the material of the metal hard mask layer is one of Ta, TaN, Ti and TiN.

Optionally, the material of the dielectric hard mask layer is SiOx or SiNx.

In the preparation method of the magnetic tunnel junction provided by the present invention, in the etching process of forming the MTJ bit, the etching of the MTJ material layer is divided into two steps. When the MTJ material layer is etched for the first time, only the insulating film layer and the insulating film layer are etched. The interface of the first magnetic thin film layer, and then the first protective layer is deposited, and then the first magnetic thin film layer of the MTJ material layer is etched a second time, which can prevent the metal material of the first magnetic thin film layer from sputtering to the sidewall of the insulating thin film layer , Reduce the pollution of metal deposition, and also avoid the short circuit of the formed MTJ bit.

Description of the drawings

FIG. 1 is a schematic flowchart of a method for preparing a magnetic tunnel junction according to an embodiment of the present invention;

2 to 12 are schematic diagrams of the cross-sectional structure of each process step of a method for fabricating a magnetic tunnel junction according to an embodiment of the present invention.

detailed description

In order to make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments It is only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

An embodiment of the present invention provides a method for preparing a magnetic tunnel junction. As shown in FIG. 1, the method includes:

S101. A substrate is provided, and a bottom electrode material layer, an MTJ material layer, a metal hard mask layer, and a dielectric hard mask layer are sequentially deposited on the substrate, wherein the MTJ material layer includes: the bottom electrode material A first magnetic film layer on the layer, an insulating film layer on the first magnetic film layer, and a second magnetic film layer on the insulating film layer;

S102, photoetching a first mask shape, and etching the dielectric hard mask layer and the metal hard mask layer;

S103. Using the etched dielectric hard mask layer and the etched metal hard mask layer as a hard mask, etch the MTJ material layer, and leave the etching end point at the insulating thin film layer Obtaining a pre-etched device at the interface with the first magnetic thin film layer;

S104, forming a first protective layer on the surface of the pre-etched device;

S105, etching the first protective layer, and after the etching is completed, the horizontal part of the first protective layer is completely removed while the vertical part is retained;

S106: Using the etched metal hard mask layer as a hard mask, etch the first magnetic thin film layer to form MTJ bits.

Specifically, in step S101, as shown in FIG. 2, a bottom electrode material layer 102, an MTJ material layer 103, a metal hard mask layer 104, and a dielectric hard mask layer 105 are sequentially deposited on the substrate 101, wherein the MTJ material The layer 103 includes: a first magnetic film layer 1031 on the bottom electrode material layer 1031, an insulating film layer 1032 on the first magnetic film layer 1031, and a second magnetic film layer on the insulating film layer 1032 1033; The MTJ material layer 103, the metal hard mask layer 104 and the dielectric hard mask layer 105 can be prepared by physical vapor deposition or chemical vapor deposition.

Wherein, the material of the metal hard mask layer 104 may be one of Ta, TaN, Ti, and TiN. The material of the dielectric hard mask layer 105 is SiOx or SiNx.

In step S102, as shown in FIG. 3, a photoresist laminate structure is spin-coated on the dielectric hard mask layer 105. The photoresist laminate structure can be different according to the thickness of the hard mask layer and the light source of the lithography machine. Structure, generally, there are PR/ARC/LTO/SOC and PR/ARC structures. The photoresist laminate structure of PR/ARC/LTO/SOC structure includes organic carbon-rich spin coating (SOC), low temperature oxide film (LTO), anti-reflective layer (ARC) and photolithography stacked sequentially from bottom to top Resin layer (PR): The photoresist laminate structure of the PR/ARC structure, that is, only includes the anti-reflective layer and the photoresist layer. After spin-coating the photoresist laminate structure, the photoresist laminate structure is exposed and cleaned, and the photoresist laminate structure is etched in a layer-by-layer transfer method, namely, PR engraving ARC, ARC engraving LTO, LTO engraving SOC, and finally only leaving SOC, the first mask shape is lithographically formed. Referring to Figure 4-5, using the SOC as a mask, the dielectric hard mask layer 105 and the metal hard mask layer 104 are etched in sequence, and the etched dielectric hard mask layer and metal hard mask layer are denoted as 105a respectively. 104a.

In step S103, the etched dielectric hard mask layer 105a and the etched metal hard mask layer 104a are used as hard masks to etch the MTJ material layer 103. The etching methods include reactive ion etching and ion beam etching. Etching, etc., the end point of the etching is within the range of 5 nm above and below the insulating film layer 1032, that is, the end point of the etching is controlled to be 5 nm above the interface between the insulating film layer 1032 and the second magnetic film layer 1033 to the insulating film layer 1032 and the first magnetic film layer 1031 Within the range of 5nm below the interface, in this embodiment, the etching end point stays at the interface between the insulating film layer 1032 and the first magnetic film layer 1031 to obtain a pre-etched device. The cross-sectional structure of the pre-etched device As shown in FIG. 6, during the etching process, the dielectric hard mask layer 105a is removed;

In step S104, a first protective layer 106 is formed on the surface of the obtained pre-etched device. The first protective layer 106 is non-conductive and non-magnetic, and can be any one of SiO ₂ , SiN, SiC, SiON and SiCN. The first protective layer 106 is formed by plasma enhanced atomic layer deposition or plasma enhanced chemical vapor deposition, and has a thickness of 5-50 nm. The structure after forming the first protective layer 106 is shown in FIG. 7, the horizontal portion of the first protective layer 106 covers the surface of the first magnetic thin film layer 1031 and the etched metal hard mask layer 104a The vertical portion of the first protective layer 106 covers the sidewalls of the etched metal hard mask layer 104a, the etched second magnetic thin film layer 1033a, and the etched insulating thin film layer 1032a.

In step S105, as shown in FIG. 8, the first protective layer 106 is etched. In this embodiment, the first protective layer 106 is dry-etched using reactive ion etching and self-alignment methods. Good directionality, the etching rate of the plane is greater than the etching rate of the sidewall, that is, after the etching is completed, the horizontal part of the first protective layer is completely removed, exposing the first magnetic thin film layer 1031 and the metal hard mask Layer 104a, while the sidewalls still have vertical portions 106a, wherein the insulating film layer 1032a is located or substantially located inside the vertical portions 106a of the first protective layer.

In step S106, a self-aligned method is used to further etch the first magnetic thin film layer 1031 of the MTJ material layer with the etched metal hard mask layer 104a and the vertical portion 106a of the first protective layer as a mask, and the etching end point Located at the interface between the first magnetic thin film layer 1031 and the bottom electrode material layer 102. As shown in FIG. 9, after the etching, only a small amount of the vertical portion 106a of the first protective layer remains, and MTJ bits can be formed so far. However, it should be noted that the vertical portion 106a of the first protective layer may also be completely depleted after etching, which will not have any influence on subsequent processes.

It can be seen from the above that in the method for preparing the magnetic tunnel junction of the embodiment of the present invention, during the etching process of forming the MTJ bit, the etching of the MTJ material layer is divided into two steps. The first time the MTJ material layer is etched, only the MTJ material layer is etched. To the interface between the insulating film layer and the first magnetic film layer, and then deposit the first protective layer, and then etch the first magnetic film layer of the MTJ material layer a second time, which can prevent the metal material of the first magnetic film layer from sputtering to the insulation The sidewall of the thin film layer reduces the pollution of metal deposition, and at the same time avoids the short circuit of the formed MTJ bit.

Further, after the MTJ bit is formed, the following steps are further included:

S107. Based on the MTJ bit shown in FIG. 9, as shown in FIG. 10, a second protective layer 107 is formed on the surface of the formed MTJ bit. The second protective layer 107 is non-conductive and non-magnetic, and is performed by physical vapor deposition or chemical vapor deposition. Formed by deposition, the material used can be the same as the material of the first protective layer 106, silicon oxide, silicon nitride, silicon carbide, or a compound thereof;

S108. As shown in Figure 11, the dielectric material is backfilled to fill the space between the MTJ bits. The dielectric material can be silicon oxide, silicon nitride, silicon carbide, low K material, etc., and CMP is used for planarization, and the polishing stay position can be Above the MTJ, it can also be just on the MTJ;

S109, photoetching the shape of the second mask, and etching the bottom electrode of the MTJ.

The lithography and etching here are mainly for opening the MTJ bottom electrode material layer 102. The lithography pattern is aligned with the MTJ bit, and its size should generally be larger than that of the MTJ bit. The end of the etching is located below the bottom electrode material layer 102. .

In addition, after the MTJ bottom electrode is etched, the subsequent processes are continued, including insulating dielectric filling, CMP polishing, and preparation of the MTJ top electrode. The latter processes are all implemented by conventional means, and will not be repeated here.

The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited to this. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. All should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

A method for preparing a magnetic tunnel junction, which is characterized in that it comprises:

A substrate is provided, and a bottom electrode material layer, an MTJ material layer, a metal hard mask layer, and a dielectric hard mask layer are sequentially deposited on the substrate, wherein the MTJ material layer includes: located on the bottom electrode material layer A first magnetic film layer, an insulating film layer on the first magnetic film layer, and a second magnetic film layer on the insulating film layer;

Lithographically etch the shape of the first mask, and etch the dielectric hard mask layer and the metal hard mask layer;

Using the etched dielectric hard mask layer and the etched metal hard mask layer as hard masks, the MTJ material layer is etched, and the etching end point remains at the insulating film layer and the insulating film layer. The interface of the first magnetic thin film layer to obtain a pre-etched device;

Forming a first protective layer on the surface of the pre-etched device;

Etching the first protective layer, after the etching is completed, the horizontal part of the first protective layer is completely removed while the vertical part is retained;

Using the etched metal hard mask layer as a hard mask, the first magnetic thin film layer is etched to form MTJ bits.
The method according to claim 1, wherein the first protective layer is formed by plasma-enhanced atomic layer deposition or plasma-enhanced chemical vapor deposition.
The method according to claim 1, wherein the material of the first protective layer is any one of SiO 2 , SiN, SiC, SiON and SiCN.
The method according to claim 1, wherein the thickness of the first protective layer is 5-50 nm.
The method according to claim 1, wherein the etching of the first protective layer uses dry etching.
The method according to claim 1, wherein the method further comprises:

Forming a second protective layer on the surface of the formed MTJ bit;

Backfill the dielectric material and perform flattening treatment;

The second mask shape is photo-etched, and the MTJ bottom electrode is etched.
The method according to claim 6, wherein the material of the second protective layer is the same as that of the first protective layer.
The method according to claim 1, wherein the photoetching the first mask shape and etching the dielectric hard mask layer and the metal hard mask layer comprises:

A photoresist laminate structure is spin-coated on the dielectric hard mask layer, and the photoresist laminate structure includes an organic carbon-rich spin coating, a low-temperature oxide film, an anti-reflection layer, and a photoresist stacked sequentially from bottom to top Floor;

Exposing and cleaning the photoresist laminated structure, and etches down by layer-by-layer transfer, leaving only the etched organic carbon-rich spin coating;

Using the etched organic carbon-rich spin coating as a mask, the dielectric hard mask layer and the metal hard mask layer are sequentially etched.
The method according to claim 1, wherein the material of the metal hard mask layer is one of Ta, TaN, Ti and TiN.
The method according to claim 1, wherein the material of the dielectric hard mask layer is SiOx or SiNx.