JPS61267313A - Manufacture of magnetic memory element - Google Patents

Abstract

PURPOSE:To obtain the magnetic memory element of ultra-high density by a method wherein a photoresist pattern is baked at the temperature of the photoresist softening point or above, and a garnet is processed into saw-toothed form by performing an ion milling method. CONSTITUTION:A photoresist pattern 2 is formed on a garnet substrate 1, a resist is baked at the temperature of the resist-softening point or above, and then an ion milling is performed with argon-oxygen mixed gas. When the ion milling is continued further, the condition as shown in the diagram (d) is obtained. As a result, the saw tooth shape can be formed in an excellent controllability, and the magnetic garnet film 3 of good quality can be epitaxially grown in liquid phase.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a nonvolatile ultra-high density magnetic memory element.

(Prior art and its problems) With the development of high-density solid-state magnetic storage elements, magnetic bubble elements have been developed such as permalloy devices, continuous injection continuous disk devices, current-driven devices, and so-called hybrid devices that combine these devices. Devices are being actively discussed in various places. It has been said that the limit to the high density of these devices lies in the photolithography technology used to form bubble transfer paths. However, in recent years, the technology has progressed rapidly, and as a result, the question of how much material can be used to increase the density, that is, how small the bubble diameter can be made, has once again become an issue. With the garnet materials currently in use, the minimum attainable bubble diameter is said to be 0.3 μm. Therefore, it is necessary to find a bubble material other than garnet material that can hold bubbles with a diameter of 0.3 μm or more. This is not an easy task, and it is even considered that this is the limit of increasing the bubble density.

As a magnetic memory element that can significantly improve the densification limit based on the characteristics of such a bubble retention layer, we use vertical Bloch lines existing in the Bloch domain walls that form the boundaries of striped domains formed in a ferromagnetic film as a memory unit. A device for use was invented.

(TokuM Sho 57-182346) One of the most important parts of this device is the information storage section (hereinafter referred to as the minor loop).

This magnetic memory element is equipped with an information reading means, an information writing means, and an information storage means, and has a ferromagnetic film (including a ferrimagnetic film) whose easy magnetization direction is perpendicular to the film surface.
Vertical Bloch lines (hereinafter referred to as VBL
It uses pairs (referred to as . . . ) as a storage unit and has means for transferring the vertical Bloch lines within the Bloch domain wall. In such a magnetic memory element, it is essential to stably hold the VBL pairs of striped domain domain walls written as information and to be able to selectively transfer them one bit at a time.

In order to perform these basic operations reliably, it is important to keep the length of the stripe domain domain wall constant. Due to the nature of magnetic domains, it is extremely difficult to keep the length of the 0-stripe domain constant. . For example, if a magnetic field is applied from the outside in a direction perpendicular to the film thickness, the width and length will immediately change. As described above, if the shape of the stripe domain changes, especially the length, the information string written in the domain wall becomes disordered, and the function as a memory element is lost. To overcome this difficulty, it is necessary to provide a potential well in the stripe domain retention layer itself to stabilize the stripe domain tips in a predetermined position.

Conventionally, as shown in Fig. 4, the surface of the stripe domain holding layer is trenched in the area where the stripe domain is desired to be placed, and the stripe domain is stabilized in the thinned area. Domain retention layer, 5
is magnetization, 7 is a stripe domain domain wall, 8 is a substrate, 9 is a stripe domain stable region, and lO is a grooving groove wall. In this stabilization method, the matching between the stripe domain width and the groove width on the surface is very important.The drive along the stripe domain wall of the Ploch line, which is considered in a 0-line element, is performed using a pulsed bias magnetic field perpendicular to the film surface. This is done by dynamically moving the domain wall by applying , and using the gyroscopic force generated at the Ploch line. This gyroscopic force is proportional to the moving speed of the domain wall. The moving speed of the domain wall depends on the magnitude of the effective pulsed bias magnetic field (the algebraic sum of the externally applied pulsed bias magnetic field, the demagnetizing field generated from the stripe domain shape, the demagnetizing field generated from the film thickness step of the surface groove, etc.). Therefore, the Ploch line driving force depends on the magnitude of the externally applied pulse bias magnetic field and the degree of matching between the stripe domain width and the surface groove width. Furthermore, in the Ploch line memory, magnetic bubbles are used for writing and reading information, and Ploch lines within the striped domain domain walls are used for the storage section. Therefore, it is important to make the magnetic bubbles and striped domains coexist, and to match the magnetic bubble transfer bias margin and the Ploch line transfer bias margin area. Considering stability, compared to the conventional in-plane magnetic field drive method,
Uses current drive method. Therefore, the magnetic bubble transfer characteristic can be expressed as a relation between the bias magnetic field and the bubble drive current amplitude. On the other hand, the Ploch line transfer margin is expressed in the relationship between the amplitude of the Ploch line driving pulse bias magnetic field and its pulse width on the premise that the length of the striped domain surrounded by the domain wall where the Ploch line exists is kept constant.

Therefore, the bubble transfer section and the Plochline transfer section must be able to share the bubble stable transfer bias magnetic field region and the stripe domain stable existence bias magnetic field region at the same bias magnetic field level, respectively.

When information is expressed by the presence or absence of magnetic bubbles, it is necessary to apply an appropriate bias magnetic field in the direction perpendicular to the film surface in the region where the bubble transfer section exists. On the other hand, in the striped domain stabilization region, it is better for the effective bias magnetic field to be as small as possible. A method for making such a distinction is to provide means for locally applying a bias magnetic field only to the bubble transfer region. The most accurate method is to place a conductor pattern in the bubble transfer area on the striped domain retention layer, apply a steady current to the conductor, and apply a bias magnetic field locally.However, this method is a feature of this device. It inhibits the non-volatility of some information.

There is also a method of installing a permanent magnet plate, such as a ferrite magnet plate for applying the bias magnetic field of a bubble element, so that a bias magnetic field is effectively applied to the bubble existing area in the direction perpendicular to the film surface. It takes time and effort to accurately define the boundary with the striped domain area.In contrast, we have developed a method that keeps the length of the striped domain, which is a minor loop, constant and automatically provides resilience against deformation. For one thing, it is effective to realize a magnetic garnet film having a cross-sectional structure as shown in FIG.
8 is a garnet substrate whose surface has a periodic sawtooth structure, and 4 is a magnetic garnet film formed on it. 0 When such a structure is realized, in the part where the substrate surface is tilted from the (111) plane, , the easy magnetization direction of the film grown on it is oriented in the direction reflecting the sawtooth surface of the substrate surface.
Figures 5 and 5' show the magnetization in the easy magnetization direction in each part. When an externally applied in-plane magnetic field Hip is added to this as shown in Figure 5, the magnetization direction becomes 5, 5 as shown in Figure 5.
It is fixed in the direction shown by '. When a bias magnetic field of Hz is applied perpendicular to the film surface, the region 6 with magnetization 5 is stabilized to a bias magnetic field value that depends on the inclination angle of the slope of the sawtooth portion of the substrate surface and the material properties of the striped domain retention layer. be done. In other words, the striped domains can be stably maintained up to high bias magnetic fields. Furthermore, the shape of the stripe domain, especially the length, can be kept constant, and when the length changes due to external disturbance, due to the action of Hip,
You will also have the ability to restore the length to its original length.

However, until now, no method has been proposed for effectively realizing a magnetic garnet film having such a cross-sectional structure. Ultra-high-density magnetic field that uses VBL pairs as information units to provide the stripe domain with a restoring force that returns the stripe domain to its original position when the disturbance subsides even if the length changes due to some disturbance. An object of the present invention is to provide a method for manufacturing a memory element.

(Structure of the Invention) According to the present invention, there are a step of forming a photoresist pattern on a garnet substrate, a step of baking at a temperature higher than the softening point of the photoresist, and a step of ionizing the garnet with a mixed gas of argon/oxygen. A method for manufacturing a magnetic memory element is obtained, which comprises the steps of milling and processing the garnet surface into a sawtooth shape, and further forming a magnetic garnet film on the garnet substrate by liquid phase epitaxial growth.

(Detailed Description of the Invention) Figure M1 (al to kl illustrate the manufacturing process according to the present invention. A photoresist pattern 2 is formed on a garnet substrate l (Figure 1 fa)), the softening point of the resist Baking at the above temperature (Figure 1 (b))
Next, ion milling is performed using a mixed gas of argon/oxygen (Fig. 1 (c)) o If ion milling is continued, the state shown in Fig. 1 (d) will be obtained. After this, a magnetic garnet film is grown by liquid phase epitaxial growth. (Figure 1(e)
)3 What is important here are that the sawtooth shape shown in (d) can be formed without control, and in (e) that a high quality magnetic garnet film can be grown by liquid phase epitaxial growth.

To obtain a sawtooth shape, a sawtooth shape is formed on one side of the substrate using a material that is easily etched by ions.As a mask, ion bombardment is applied to the entire surface of the mask from above to form a sawtooth shape on the substrate. However, when I tried to transfer a sawtooth shape onto a garnet substrate using this method, I found that! It was difficult to freely control the angle θ of the serrations because the fine irregularities of the fabric material (for example, photoresist) were not easily transferred to the garnet substrate. As a result of considering a method for forming a good shape, after forming a photoresist mask Bakun, a photoresist O] at a temperature above the softening point, such as A21350J (trade name).

(manufactured by Hoechst, USA), baking at 135°C or higher and ion milling with a mixed gas of argon/oxygen prevents the minute irregularities of the mask material from being transferred to the garnet substrate, and an extremely smooth slope is transferred to the garnet substrate. We have found that the angle of the slope can be arbitrarily controlled by controlling the oxygen partial pressure.

FIG. 2 shows the relationship between the angle θ of the serrations formed on the garnet substrate and the oxygen partial pressure. Here, the horizontal axis is the oxygen partial pressure relative to the total pressure. The acceleration energy during ion milling is 500 eV, and the total pressure of argon/oxygen is 2X10 Torr.
) is a comparison of the shapes obtained in (a) when baking to a temperature higher than the softening point of the photoresist is not performed and (b) when baking is performed. The 8HM observation sphere is shown in a state corresponding to FIG. 1(C), with the etching stopped midway to make it easier to see. It can be seen that a smooth slope can be formed by baking. Another important point is whether high-quality magnetic garnet films can be grown by liquid phase epitaxial growth. There have been no reports of growing a magnetic garnet film on this serrated garnet surface. The inventors have determined that various sawtooth angles θ
When we tried to grow a magnetic garnet film on a garnet substrate with Therefore, in order to grow a uniform film along the garnet substrate, it was necessary to limit the direction of the sawtooth portions to a specific range on the garnet substrate. It has been found that if θ is 30° or less, a uniform film can be grown regardless of the direction of the serrations on the garnet substrate. It was also found that there was no growth defect on the ion beam irradiated surface and that there was no effect of ion beam impact. This is probably
We believe that this is because the garnet substrate surface is remelted in the liquid phase epitaxial melt and the ion bombardment layer is removed.

As described above, it has been found that a magnetic garnet film can be grown on a garnet substrate having a sawtooth structure by the manufacturing process according to the present invention shown in FIG.

(Example) The above-described photoresist AZ1350J pattern having a film thickness of 1.2 μm was formed on a garnet substrate GGG.

The resist pattern width was 4 μm, and the pattern interval was 4 μm. After forming the resist pattern, it was baked at 135°C for 30 minutes.It is important to select the temperature at this time to be above the softening point of the resist, but be careful as if the temperature is too high, the pattern width will fluctuate. The required optimum temperature depends on the type of resist.

Depends on film thickness and pattern width. For A21350J, 135°C was optimal, but as the film thickness and pattern width decreased, the temperature tended to rise slightly above this temperature.The sample was mounted on a rotatable sample stand and heated with a mixed gas of %Ar10H. Ion milled a garnet substrate. Total pressure 2XIO Torr, oxygen partial pressure 0.3X10 Torr
Etching was performed for 27 minutes at an acceleration energy of 500 eV. The machining depth at this time was 0.28 μm, and the inclination angle was 8°. The resist used as a mask has completely disappeared.If the zero machining time is shorter than this value, the machining depth will not be shallow and the resist will remain. On the other hand, when the etching time was longer than this value, the shape transferred to the garnet substrate remained sawtooth-like and the processing latitude was wide.

Next, a magnetic garnet film was grown in liquid phase on the serrated garnet substrate.

The film composition is (Y8mGdLuBica)3(PeGe)5
0+2 was used. Flux components are PbO, Bi2O3
It is. Growth temperature is 883℃, temperature cooling degree is 25℃
The zero characteristic length is 0119 μm, the film thickness is 4 μm, and the growth rate is 0.6 μm/mln. Under these conditions, a high-quality LPE film including the serrations can be obtained, and in the presence of an appropriate bias magnetic field and in-plane magnetic field, the stripe domains are stably maintained in the serrations, and bubbles and A margin for coexistence was secured.

(Effects of the Invention) As described above, according to the present invention, it is possible to obtain a method of manufacturing a magnetic memory element using VBL pairs as information units, which is capable of stably retaining striped domains consisting of minor looseness.

[Brief explanation of the drawing]

FIGS. 1(a) to (e) are diagrams showing an example of the manufacturing method of the present invention, FIG. 2 is a diagram showing the relationship between the oxygen partial pressure ratio and the angle θ of the sawtooth pattern during ion milling, and FIG. Figure (a). (b) is a micrograph showing the case (b) with and without baking the resist at a temperature above its softening point before ion milling the garnet substrate, and Figure 4 shows the conventional structure with grooved surface of the striped domain retention layer. FIG. 5 is a diagram showing a structure in which the substrate surface is selectively tilted in order to stabilize the stripe domain. 1 is a garnet substrate, 2 is a resist pattern, 3 is a magnetic garnet film, 4 is a striped domain retention layer, 5.5
' is magnetization, 6 and 9 are stripe domain stable existence regions,
7 is a striped domain domain wall, 8 is a substrate, and IO is a surface grooving groove wall of a striped domain holding layer. E 1 Figure (b) E 2 Figure Oxygen Partial Pressure Rate Procedural Amendment C-15 Vision 60.9.26 Showa Year Month Day 1, Incident Display 1985 Patent Application No. 1097
No. 27 No. 2, Title of the invention: Method for developing magnetic memory element 3
, Person making the amendment Relationship to the case Applicant: 5-33-1-4 Shiba, Minato-ku, Tokyo, Agent 5, Date of amendment order◆: August 27, 1985 (shipment date) 6, Subject of amendment Brief explanation of the drawings Drawing 7 Contents of amendment 1) In the 15th line of page 15 of the specification, the phrase [Micrograph 4, which is a diagram showing the case where the 2) The drawings attached to this application, Figures 3(a) and 3(b), shall be amended as shown in the attached drawings.

Claims (1)

[Claims] forming a photoresist pattern on a garnet substrate; baking the photoresist pattern at a temperature higher than the softening point of the photoresist material; using the photoresist as a mask, the garnet substrate is exposed to a mixed gas of argon/oxygen. 1. A method for manufacturing a magnetic memory element, comprising: ion milling using a garnet substrate having a serrated surface; and forming a magnetic garnet film by liquid phase epitaxial growth on a garnet substrate whose surface has been processed into a sawtooth shape.