WO2023045049A1

WO2023045049A1 - Method for etching mask of magnetic tunnel junction

Info

Publication number: WO2023045049A1
Application number: PCT/CN2021/129891
Authority: WO
Inventors: 张丛; 刘宏喜; 陈文静; 曹凯华; 王戈飞
Original assignee: 北京超弦存储器研究院
Priority date: 2021-09-27
Filing date: 2021-11-10
Publication date: 2023-03-30
Also published as: CN115884661A

Abstract

Provided in the present invention is a method for etching a mask of a magnetic tunnel junction. The method comprises: etching a dielectric layer step by step, and removing a photoresist and residual organic substances by means of an ashing process prior to the final etching step of the dielectric layer. Before the etching of the dielectric layer, a tunnel junction pattern needs to be patterned onto the dielectric layer by means of a photoresist. During the etching process, the photoresist will form organic residues, and if the organic residues come into contact with a metal film layer beneath the dielectric layer, a metal polymer will form and adhere to the metal film layer, which makes removal more difficult. In the present invention, a treatment via an ashing process is carried out prior to the final etching step of the dielectric layer; and since the dielectric layer still has a certain residual thickness, the organic residues formed by the photoresist are isolated from the metal film layer, such that the difficulty in removing the photoresist is reduced and the risk of an open MRAM circuit is also reduced. The process of the present invention is simple, the process steps are simplified, and the contact of organic residues formed by a photoresist in the process with a metal film layer is avoided, such that the formation of a metal polymer is avoided.

Description

Etching mask method of magnetic tunnel junction

technical field

The invention relates to the technical field of magnetoresistive random access memory DRAM spintronic devices, in particular to an etching mask method for a magnetic tunnel junction.

Background technique

Magnetoresistive Random Access Memory (MRAM) has the advantages of low power consumption, high speed, radiation resistance, etc., and has great advantages in emerging storage technologies. The basic storage unit of MRAM is a magnetic tunnel junction (Magnetic Tunnel Junction: MTJ). The core unit of the magnetic tunnel junction usually includes a three-layer structure free layer, reference layer and tunneling layer. These layers are extremely thin, typically on the order of angstroms. The free layer and the reference layer are generally composed of magnetic materials, and the tunneling layer is generally composed of oxides. MRAM utilizes the magnetic moment directions of the free layer and the reference layer for information storage. When the free layer and the reference layer have the same magnetic moment square, the tunneling resistance of the magnetic tunnel junction is low resistance; when the free layer and the reference layer magnetic moment square are antiparallel, the tunneling resistance of the magnetic tunnel junction is high resistance; MRAM read The circuit judges whether the data state is "0" or "1" by reading the size of the tunnel resistance. The magnetic rectangular shape of the free layer can be changed by the applied current, so the data state of the memory cell can be rewritten to "0" or "1" by the write current.

Traditional MRAM uses spin transfer torque (Spin Transfer Torque, STT) as the most common writing method for MTJ. According to the different directions of magnetic polarization, STT-MRAM is divided into in-plane STT-MRAM and vertical STT-MRAM. The latter has better performance, which can reverse the magnetic memory by providing spin polarization current to the magnetoresistive element. The magnetization direction of the layer. In addition, as the volume of the magnetic memory layer shrinks, the spin-polarized current to be injected becomes smaller.

The latest development uses the spin orbit moment (Spin Orbit Torque, SOT) generated by the current instead of the magnetic field generated by the current to switch the relative magnetization orientation of the pinned layer and the free layer, thereby realizing the SOT MRAM for data writing. Compared with the currently commonly used STT writing method, SOT technology can achieve faster speed and lower power consumption. At the same time, the device structure is not easily damaged under high current density. However, the write current density of this SOT MRAM is still very high, which limits the arrangement density of the memory cell array.

Under the existing technical conditions, the dielectric layer is generally used as a hard mask for forming a tunnel junction, and etching gases such as F-based, F-based/Ar, etc. are usually used when preparing such a hard mask. Before the tunnel junction is etched, the dielectric layer has been completely etched away, and the etching selectivity ratio of the top electrode metal to SiNx (SiO ₂ ) is not high, so metal etching is unavoidable in the process of etching the dielectric hard mask. Etching, resulting in polymer adhesion between the photoresist and the contact with the metal film layer, which is difficult to remove by O ₂ plasma ashing.

Contents of the invention

In order to solve the above-mentioned technical problems, the present invention provides an etching mask method for a magnetic tunnel junction, which includes stepwise etching the dielectric layer, and removing the photolithographic mask by ashing process before completing the last etching step of the dielectric layer. Glue and residual organic matter.

Optionally, during the etching process of the dielectric layer, the etching depth of each sub-step is controlled by controlling the etching time.

Optionally, the etching depth of the last etching step of the dielectric layer is 15-70% of the thickness of the dielectric layer.

Optionally, the etching depth of the last etching step of the dielectric layer is 20-40% of the thickness of the dielectric layer.

Optionally, during the last etching process of the dielectric layer, the etching rate is monitored in real time, and if the etching rate drops significantly, the etching of the dielectric layer is stopped.

Optionally, before etching the dielectric layer, perform the following preparations:

S1: Provide the substrate on which the MTJ film layer has been deposited;

S2: forming a dielectric layer on the substrate;

S3: using a photoresist to pattern the MTJ pattern onto the dielectric layer.

Optionally, the etching of the dielectric layer adopts CF4, CHF3, SF6 or Ar gas reactive ion etching.

Optionally, the ashing process adopts an _O2 ashing process.

Optionally, after the dielectric layer is etched, the MTJ is etched using the dielectric layer as a hard mask.

Optionally, the etching of the MTJ uses plasma etching or reactive ion etching to etch the tunnel junction to complete the patterning of the tunnel junction.

The etching mask method of the magnetic tunnel junction of the present invention adopts the step-by-step etching of the dielectric layer, and adopts the ashing process to remove the photoresist and residual organic matter between the step-by-step etching. The photoresist patterns the tunnel junction pattern to the dielectric layer, and during the etching process, the photoresist will form organic residues. If the organic residues touch the metal film layer under the dielectric layer, they will form metal polymers attached to the metal film. layer, which increases the difficulty of removal. The present invention is used to carry out ashing process before the final etching step of the dielectric layer. Since the dielectric layer still has a certain residual thickness, the organic matter residue formed by the photoresist is isolated from the metal film layer, thereby reducing The difficulty of deglue removal is also reduced, and the risk of MRAM circuit open circuit is also reduced. The process of the present invention is simple, simplifies the process steps, and eliminates the contact between the organic residue formed by the photoresist in the process and the metal film layer, thereby avoiding the formation of metal polymers .

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

The technical solutions of the present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the description, and are used together with the embodiments of the present invention to explain the present invention, and do not constitute a limitation to the present invention. In the attached picture:

1 is a flow chart of an etching mask method for a magnetic tunnel junction in an embodiment of the present invention;

Fig. 2 is the flow chart of the preparatory work before the etching of the dielectric layer in the embodiment of the etching mask method of the magnetic tunnel junction of the present invention;

3 is a flow chart of an application case of the etching mask method of the magnetic tunnel junction of the present invention;

4 is a cross-sectional view of the MTJ pattern transfer dielectric layer before the dielectric layer is etched;

5 is a cross-sectional view after the step-by-step etching of the dielectric layer before the ashing process;

6 is a cross-sectional view of the photoresist after ashing and removal;

7 is a cross-sectional view after the remaining thickness of the dielectric layer is etched after the ashing process;

FIG. 8 is a cross-sectional view after MTJ etching.

Detailed ways

The preferred embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

As shown in Figure 1 and Figure 3-8, an embodiment of the present invention provides an etching mask method for a magnetic tunnel junction, which etches the dielectric layer step by step, including the following steps:

S10 performing the first step of etching the dielectric layer, and the etching depth of the first step of etching is the first depth;

S20 uses ashing process to remove photoresist and residual organic matter;

S30 performing a second etching step on the dielectric layer, the etching depth of the second etching step being the remaining thickness of the dielectric layer.

The working principle of the above-mentioned technical solution is as follows: this solution etches the dielectric layer step by step, which is specifically divided into the first step of etching and the second step of etching, and completes the last step of etching the dielectric layer (ie, the second step of etching). Before the ashing process, the photoresist and residual organic matter are removed by ashing process; of course, the etching of the dielectric layer can also be divided into more steps, that is, before or after the ashing process is used to remove the photoresist and residual organic matter. More than one step of sub-etching can be performed, as long as the ashing process is between the first etching step and the last etching step, and even the ashing process can be performed multiple times.

The beneficial effect of the above-mentioned technical scheme is: this scheme adopts the step-by-step etching of the dielectric layer, and the ashing process is used to remove the photoresist and residual organic matter between the step-by-step etching. Patterning the tunnel junction pattern to the dielectric layer, and during the etching process, the photoresist will form organic residues. If the organic residues touch the metal film layer under the dielectric layer, it will form a metal polymer attached to the metal film layer, increasing In order to reduce the difficulty of removal, this scheme is used to perform ashing process before the last step of etching the dielectric layer. Since the dielectric layer still has a certain residual thickness, the organic matter residue formed by the photoresist is isolated from the metal film layer, thereby reducing the deglue The difficulty also reduces the risk of MRAM circuit open circuit. This solution has a simple process, simplifies the process steps, and eliminates the contact between the organic matter residue formed in the process of the photoresist and the metal film layer, thereby avoiding the formation of metal polymers.

In one embodiment, during the etching process of the dielectric layer, the etching depth of each step is controlled by controlling the etching time.

The working principle and beneficial effects of the above-mentioned technical scheme are as follows: this scheme adopts the method of controlling the etching time to control the etching depth of each sub-step, and takes the total etching time required for etching the dielectric layer as a benchmark, and according to the etching depth of each sub-step The proportion of the etching depth to the total thickness of the dielectric layer is used to allocate the etching time, so as to achieve the precise control of the etching depth of each step and ensure the process requirements of the etching depth of each step.

In one embodiment, the etching depth of the last etching step of the dielectric layer is 15-70% of the thickness of the dielectric layer; it may preferably be 20-40% of the thickness of the dielectric layer. For example, the etching depth of the final etching step of the selective dielectric layer is 20%, 25%, 30%, 35% or 40% of the thickness of the dielectric layer.

The working principle and beneficial effects of the above technical scheme are: this scheme limits the etching depth of the last etching step of the dielectric layer, so as to ensure that the dielectric layer still has sufficient remaining thickness before adopting the ashing process; the scheme It can prevent the dielectric layer from being etched before the last step of etching due to the error of etching control, resulting in the residue formed by the photoresist being in contact with the metal film layer. At this time, the ashing process can no longer achieve the purpose of the invention , Therefore, this solution limits the etching depth of the last etching step to ensure that this unfavorable situation does not occur.

In one embodiment, during the last etching process of the dielectric layer, the etching rate is monitored in real time, and if the etching rate drops significantly, the etching of the dielectric layer is stopped.

The working principle and beneficial effects of the above-mentioned technical scheme are as follows: this scheme monitors the etching rate in real time during the last etching process of the dielectric layer, and stops the etching of the dielectric layer if the etching rate drops significantly; The difference in the material of the metal film layer below, when using the selected working mode of the process equipment for etching, the etching rate of the dielectric layer is higher, and the rate of the metal film layer is lower. Therefore, in the last step of etching the dielectric layer , when the etching rate drops significantly, it indicates that the metal film layer has been etched, and the etching of the dielectric layer has been completely completed. At this time, it should be stopped to prevent the thickness of the metal film layer from being adversely affected by subsequent processes.

In one embodiment, before the dielectric layer is etched, the following preparations are performed:

S1: Provide the substrate on which the MTJ film layer has been deposited;

S2: forming a dielectric layer on the substrate;

S3: using a photoresist to pattern the MTJ pattern onto the dielectric layer.

The working principle and beneficial effects of the above-mentioned technical scheme are as follows: this scheme needs to be prepared before the dielectric layer is etched, and the substrate with the deposited MTJ film layer is provided, and the dielectric layer is formed on the substrate, and then the photoresist is used for patterning From the MTJ pattern to the dielectric layer, after these preparations, the dielectric layer can be etched according to the MTJ pattern. On the one hand, the parts that do not need to be etched are protected, and on the other hand, the etching range can be precisely defined by the MTJ pattern.

In one embodiment, CF4, CHF3, SF6 or Ar gas reactive ion etching is used for etching the dielectric layer.

The working principle and beneficial effects of the above technical scheme are: this scheme uses CF4, CHF3, SF6 or Ar gas reactive ion etching for the etching of the dielectric layer. The reactive ion etching technology is a kind of strong anisotropy and high selectivity. Dry etching technique. It uses molecular gas plasma for etching in a vacuum system, and uses ion-induced chemical reactions to achieve anisotropic etching, that is, uses ion energy to form a damaged layer that is easy to etch on the surface of the etched layer. And to promote chemical reactions, at the same time, ions can also remove surface products to expose a clean etching surface; usually, the entire vacuum wall of the reactive ion etching machine is grounded, as the anode, the cathode is the power electrode, and the ground on the side of the cathode Shields protect the power electrodes from sputtering. The substrate to be etched is placed on the power electrode. The corrosive gas fills the entire reaction chamber according to a certain working pressure and matching ratio. To the corrosive gas in the reaction chamber, a high-frequency electric field greater than the critical value of gas breakdown is added. Under the action of a strong electric field, the stray electrons accelerated by the high-frequency electric field collide randomly with gas molecules or atoms. When the electron energy is large enough To a certain extent, random collisions become inelastic collisions, resulting in secondary electron emission, which further collide with gas molecules and continuously excite or ionize gas molecules. This violent collision causes ionization and recombination. When the production and disappearance of electrons reaches a balance, the discharge can continue to be maintained. The ions, electrons and free radicals (free atoms, molecules or atomic groups) produced by inelastic collisions are also called plasma, which has strong chemical activity and can chemically react with the atoms on the surface of the etched sample to form volatile substances to achieve the purpose of corroding the surface of the sample. At the same time, since the direction of the electric field near the cathode is perpendicular to the surface of the cathode, the high-energy ions shoot vertically to the surface of the sample under a certain working pressure for physical bombardment, which makes reactive ion etching have good anisotropy; for quartz materials, There are many types of gases that can be selected, and the easy availability and cost of gases can be fully considered when choosing, which is conducive to ensuring the progress of process production and reducing production costs.

In one embodiment, the ashing process uses an O ₂ ashing process.

The working principle and beneficial effects of the above-mentioned technical scheme are as follows: this scheme adopts _O2 ashing process for the ashing process, and the ashing method is to use oxygen plasma to carry out low-temperature combustion of organic matter; use oxygen or oxygen ion plasma for ashing, Removing the photoresist pattern can be carried out by introducing plasma into the reaction chamber. In the reaction chamber, the wafer is heated by appropriate heating means under low pressure. Since the ashing rate in the ashing process is proportional to the temperature, the ashing The oxidation process is carried out at high temperature, for example, at 80°C-300°C, the photoresist changes dramatically to the activation energy state in proportion to the increase of temperature, and after the temperature exceeds 300°C, the activation energy decreases to achieve the removal of photoresist and It produces and residual organic matter.

In one embodiment, after the dielectric layer is etched, the MTJ is etched using the dielectric layer as a hard mask.

The working principle and beneficial effects of the above technical solution are as follows: in this solution, after the dielectric layer is etched, the MTJ is etched with the dielectric layer as a hard mask. Due to the adoption of the method of the present invention, the photoetched The glue and its generation and the removal of residual organic matter make the surface of the hard mask clean, avoiding the adverse effects of possible impurities on the MTJ etching process, thereby ensuring the quality of MTJ etching, improving the yield rate, and reducing costs.

In one embodiment, the etching of the MTJ adopts plasma etching or reactive ion etching to etch the tunnel junction to complete the patterning of the tunnel junction.

The working principle and beneficial effects of the above-mentioned technical scheme are as follows: this scheme adopts plasma etching or reactive ion etching to etch the tunnel junction to etch the MTJ, and completes the patterning of the tunnel junction; wherein, the plasma etching machine is also called a plasma etching machine. Etching machine, plasma planar etching machine, plasma etching machine, plasma surface treatment instrument, plasma cleaning system, etc. Plasma etching is the most common form of dry etching. Its principle is that the gas exposed to the electron region forms a plasma, and the resulting ionized gas and gas composed of released high-energy electrons form plasma or ions. When ionized gas atoms are accelerated through an electric field, they release enough force and surface repelling forces to tightly bond materials or etch surfaces. In a way, plasma cleaning is essentially a milder version of plasma etching. The equipment for performing the dry etching process includes a reaction chamber, a power supply, and a vacuum part, and the workpiece is sent into the reaction chamber evacuated by a vacuum pump. The gas is introduced and exchanged with the plasma, which reacts on the surface of the workpiece, and the volatile by-products of the reaction are removed by the vacuum pump. The plasma etching process is actually a reactive plasma process. This method is mature in technology, ensures the stability of the process, and is also conducive to production cost control.

Taking the etching of a certain magnetic tunnel junction hard mask as an example below, the method of the present invention is further described. In the etching of the magnetic tunnel junction hard mask, the etching method of the magnetic tunnel junction hard mask of the present invention is adopted, As shown in Figure 3-8, the specific steps are as follows:

Step S1: providing the substrate 101 on which the tunnel conjunctival layer has been deposited, the thickness of the substrate 101 including the tunnel conjunctival layer 102 is 20-40 nm;

Step S2: forming a dielectric layer 103 on the substrate 101 with a thickness of 50-70 nm;

Step S3: Patterning the tunnel junction pattern on the dielectric layer 103 by using the photoresist 104, the thickness of the photoresist 104 is 90nm-700nm;

Step S4: using CF4, CHF3, SF6, Ar and other gases to etch the dielectric layer 103 in the first step, the etching depth is the first depth 103a, and the tunnel junction pattern is transferred to the remaining thickness 103b of the dielectric layer, the first depth is 103a The specific etching depth is 30-50nm;

Step S5: using an _O2 ashing process to remove the remaining photoresist 104 and the organic matter left by the photoresist due to etching;

Step S6: Etching the dielectric layer in the second step using gas such as reactive ion etching CF4, the etching depth is the remaining thickness 103b of the dielectric layer 103, and measuring the rate during etching. If the rate drops significantly, it means that the dielectric layer is etched Complete contact with the metal film layer, so that the magnetic tunnel junction pattern is transferred to the tunnel conjunctival layer;

Step S7: Using the dielectric layer 103 as a hard mask, the tunnel junction is etched by plasma or reactive ion etching to complete the patterning of the tunnel junction.

The present invention only relates to a dielectric hard mask, which simplifies the process steps and is simple in process. During the etching process of the dielectric hard mask, the photoresist is ashed and removed, and the organic residue formed by the photoresist in the process is eliminated. It is in contact with the metal film layer, thereby avoiding the formation of metal polymers and preventing the formation of polymers attached to the surface of the glue in the subsequent tunnel junction metal etching, thereby reducing the difficulty of glue removal and reducing the risk of MRAM circuit open circuit.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

An etching mask method for a magnetic tunnel junction is characterized in that it includes etching a dielectric layer step by step, and removing photoresist and residual organic matter by using an ashing process before completing the last step of etching the dielectric layer.
The etching mask method of the magnetic tunnel junction according to claim 1, characterized in that, in the etching process of the dielectric layer, the etching depth of each sub-step is controlled by controlling the etching time.
The etching mask method of the magnetic tunnel junction according to claim 1, characterized in that the etching depth of the last etching step of the dielectric layer is 15-70% of the thickness of the dielectric layer.
The etching mask method of the magnetic tunnel junction according to claim 1, characterized in that the etching depth of the last etching step of the dielectric layer is 20-40% of the thickness of the dielectric layer.
The etching mask method of the magnetic tunnel junction according to claim 1, characterized in that, in the last etching process of the dielectric layer, the etching rate monitoring is carried out in real time, and if the etching rate drops significantly, then stop the etching of the dielectric layer etch.
The etching mask method of the magnetic tunnel junction according to claim 1, characterized in that, before the dielectric layer is etched, the following preparations are carried out:

S1: Provide the substrate on which the MTJ film layer has been deposited;

S2: forming a dielectric layer on the substrate;

S3: using a photoresist to pattern the MTJ pattern onto the dielectric layer.
The etching mask method of the magnetic tunnel junction according to claim 1, wherein the etching of the dielectric layer adopts CF4, CHF3, SF6 or Ar gas reactive ion etching.
The method for etching and masking a magnetic tunnel junction according to claim 1, wherein the ashing process adopts an O2 ashing process.
The etching mask method of the magnetic tunnel junction according to claim 1, characterized in that, after the dielectric layer is etched, the MTJ is etched using the dielectric layer as a hard mask.
The etching mask method of the magnetic tunnel junction according to claim 9, characterized in that said etching the MTJ adopts plasma etching or reactive ion etching to etch the tunnel junction to complete the patterning of the tunnel junction.