KR20220019525A - Method for producing copper target for thin film coating technology by sputtering through hot extusion process - Google Patents

Abstract

Disclosed is a method of manufacturing a copper target for thin film coating technology by sputtering through hot extrusion process. The method of manufacturing the copper target comprises the following steps of: hot extruding a copper ingot into a water tunnel through an extrusion die; cold drawing the copper ingot after the hot extrusion; and stretching the copper ingot after cold drawing.

Description

Method for manufacturing a copper target for thin film coating technology by sputtering through a hot extrusion process

The following examples relate to a method of manufacturing a copper target for thin film coating technology by sputtering through a hot extrusion process.

Currently, most coatings use chemical methods such as electroplating. However, this method has disadvantages in research and development of new coating technologies such as vacuum coating due to low coating quality and environmental problems. Vacuum coating only takes place in a vacuum (vacuum state) and the coating process does not use chemicals that cause environmental problems. It can also be coated very thinly, known as a “thin film”. A “thin film” is a film not exceeding 5 microns in thickness.

Thin film coatings in vacuum are divided into two types, for example thin film coatings by chemical processes and thin film coatings by physical processes.

1. Chemical Vapor Deposition Process (CVD) is a chemical coating of gas and chemical reaction, and it becomes a new coating on the substrate material like plasma CVD and laser CVD methods.

2. Physical Vapor Deposition Process (PVD) is a process in which atoms of the coating are removed from the surface and then diffused or dispersed to the surface of the substrate material. Evaporation and sputtering methods are the same. same.

Sputtering technology is one of the most suitable vacuum film coating technology for research and development of some film products. This process uses a variety of film coatings such as film, metal, alloy glass, ceramic or semiconductor films. The thickness of the film can be precisely controlled, and the properties of the film can be adjusted. Industries such as microelectronics, semiconductors, films, conductors and membrane resistors, hard disk drives, automotive glass, fiber optic buildings, photovoltaic TV screens and mobile screens use sputtering technology.

1 to 4 are views for explaining a sputtering process.

The sputtering process begins with the creation of an atmosphere in the coating room by absorbing air mass from the coating. The pressure is adjusted so that it does not exceed 1×10 ^-6 milligrams, and then an inert gas such as argon is added to the coating at an appropriate pressure. Then, the coating is started by forming ions of argon gas with a magnetic field. Then, an electric field causes ions (ions of argon gas) to collide with the target surface so that coating particles (metal atoms of the target) on the target surface splash onto the surface of the workpiece to form a thin film as desired. .

In the past, the 1958 sputtering process used aluminum (Al) metal as a target material for the surface layer of a semiconductor property (see patent US5598285 liquid crystal display device). Although the resistance of aluminum is not the lowest, because of the limitations of the technology, aluminum was used.

However, with the development of IBM in the 1980s, copper (Cu) and silver (Ag) were used as target metals. This is because the resistance of both metals is much lower than that of aluminum, and the resistance to electromigration is better than that of aluminum (Handbook of Thin Film De location, p. 193-195).

The quality of the thin film depends on the operating conditions of the sputtering machine, such as atmospheric pressure in the chamber, and the number of gas ions that will strike the target material, including the type of gas used. The quality of the thin film also depends on the properties of the target material. The properties of the target material that directly affect the quality (quality of the thin film) during sputtering are:

1. Purification of target substances

2. Dielectric content: oxide (Al ₂ O ₃ for Al target, CuO for Cu target)

3. Porosity due to gas during sputtering, pore volume

4. Particle size of target material

5. Surface roughness of target material

6. Mechanical strength or hardness of the target material

Conventionally, there have been many studies on the properties of the material, the production method, and the production conditions that affect the properties of the target material. Previous studies can be summarized as follows.

(1) Patent US 2000-6139701 (Applied Materials)

A copper target with a hardness greater than 45 Rockwell will produce less splat than a soft copper target or a low hardness target. Testing of high hardness copper targets up to 75 Rockwell has the same effect. The increased hardness results in less splat. For control of hardness, the particle size (copper particle size) should be less than 50 microns (more preferably less than 25 microns). When the grain size becomes smaller by techniques such as forging, rolling and other machining, the hardness will increase. On the other hand, copper sputtering target material with large particle size affects high surface roughness and strength reduction.

(2) Patent US 2004-6746553 (Honeywell International)

The quality of the thin film formed on the substrate by the sputtering method depends on the surface roughness of the target material. Anything protruding from the target surface (eg, protrusion) results in an abnormal electrical discharge during sputtering. Sometimes this is called micro-arcing and causes large particles (macro-particles) to scatter out from the target surface (eg, scatter outward) and deposit on the substrate. Large particles in the film layer can cause a short circuit in the semiconductor device. The large particles deposited are referred to as “Particles” or “splats”. The patent revealed that the surface roughness was related to the particle size of the target. If the particle size of the target is small and slightly changed, it will make the surface smoother (the surface will be smoother). Thus, it is also possible to reduce the particle size in the target to avoid the problem of “particles”. The quality of the thin film produced by a target with a small particle size is better than that with a large particle size. The patent discloses particle size reduction and change when forming a target material using a forgoing process.

(3) Patent JP 2010-065252 (Mitsubishi Material)

The copper target material must be at least 99.99% pure and have a grain size of less than 20 microns by a multi-axial forgoing process.

(4) Patent JP-A 11-158614

The copper target has an average particle size of less than 80 microns, which reduces coarse clusters and abnormal discharge problems. The smaller grain size results from the recrystallization mechanism of the copper target production process.

(5) Patent US 2011/0139615 (Hitachi Cable)

High surface roughness due to large particle size and low surface roughness due to small particle size. Increasing the amount of forming (eg, workability) in the cold rolling process will affect the small grain size. Cold work reduction is between 40-70% in the cold rolling process to obtain a grain size of 30-100 microns. The copper target is heat treated to generate a recrystallization mechanism. The recrystallized grain size increases with the heat treatment temperature. The heat treatment temperature is between 300-400°C (recommended). If the heat treatment temperature is higher than 400 °C, the particle size will be larger. While the heat treatment temperature is less than 300°C, recrystallization cannot be obtained. The copper target production process in this study is as follows.

Casting → Hot Rolling → Cold Rolling → Heat Treatment → Finish Rolling

(6) Patent JP 2012-046771 (Furukawa Electric)

A copper target is produced according to temperature control before hot working. To control the grain size in the range of 50-200 microns, the %reduction in hot rolling and the cooling rate after finish rolling are controlled. The copper target production process in this study is as follows.

Cu=99.99% or more copper slab → hot rolling → cold working → heat treatment.

The copper slab is heated to 700-1,000°C before the hot rolling process. The hot rolling ratio of each pass is set to 5-30%. The rolling ratio of the last pass of final rolling is 10-25%. The copper is cooled at a cooling rate of at least 50° C./sec within 60 seconds after the final hot rolling.

(7) Patent JP 2012-4974197 (Furukawa Electric)

The particle size affects the sputtering properties. In this patent, the particle size is 100-200 microns, preferably 110-190 microns, more preferably 120-180 microns. When the particle is small, the particle boundary increases. The particles or atoms of the boundary layer are perturbed. Atoms of the coating are removed from the copper target during the sputtering process and diffuse randomly (heterogeneously) into the substrate material. Because sputtering of large particle size requires high energy, the result is formation of coarse clusters and non-uniform film coating. In this patent, the copper target is produced by two hot working processes: a hot rolling process and a hot extrusion process. The production process is as follows.

Copper ingot (Cu = 99.99% or more) → heating (temperature = 700-1,050 °C) → hot rolling or hot extrusion → water cooling (cooling rate = 50 °C/sec or more) → cold rolling

For hot rolling process: copper cake (thickness 150 x width 220 mm) → heating to a temperature of approx. 1,000 °C → hot rolling (using multi-pass) → cooling in the last pass of hot rolling (cooling rate = 50 °C/ Within 60 seconds) → Copper plate (thickness 23 x width 220mm) → Processed surface oxide (0.5mm/side) → Copper plate (thickness 22 x width 220mm) → Cold rolling → Copper plate (thickness 20 x width 200mm)

For hot extrusion process: copper ingot (diameter 300 mm x length 800 mm) → heated at a temperature of about 1,000 °C → hot extrusion → water cooling (cooling rate = over 100 °C/sec in 20 sec) → copper plate (thick 22 x width 200 mm) → cold rolled → copper plate (thickness 20 x width 200 mm)

The results showed that both the grain size of hot rolling and hot extrusion can be controlled to the desired dimension. However, the uniformity of the grain size of copper in the extrusion process (head-end position along the length and center-edge position along the width) is smaller than in the hot rolling process.

(8) Patent JP 2012-4974198 (Furukawa Electric)

After researching that patent, I am doing more research on the uniformity of the particles. In that patent, it was found that dynamic recrystallization occurs during processing by hot rolling. When a copper target is cooled in the atmosphere, the problem of irregular grain size occurs across the width and length of the copper target. In that patent, the particle size is controlled by water cooling at a cooling rate of 50° C./sec or higher. Hot rolling process, the copper target is cooled in water within 60 seconds. In the hot extrusion process, the copper target is cooled with water within 10 seconds after being pressed through an extrusion die. Particle sizes at 1/2 and 1/4 of the thickness are 100-200 microns (+/- 10 microns). The production process is as follows.

Casting → hot rolling or hot extrusion → cold rolling → heat treatment (cold rolling and heat treatment can be repeated)

(9) Patent JP 2013-019010 (Furukawa Electric)

In order to reduce abnormal discharge in the sputtering process, the sputtering target material must contain at least 99.99% copper purity, voids and inclusion defects must not exceed 30 microns, and the defects must not exceed 10 pieces/m ² and have a particle size in the range of 50-200 microns and a hardness in the range of 60-100 HV. The production process is as follows.

Copper slab (Cu = 99.99% or more) → Heating at 700-1,000 °C → Hot rolling (total hot working rate = 20% or more, hot working rate in final hot rolling = 10% or more at 400-600 °C) → Water cooling in the last pass of hot rolling (cooling rate = 50°C/sec or more) → oxide surface processing → cold rolling

(10) Patent JP 2013-133491 (Hitachi Cable)

The copper target should contain at least 99.9% copper purity and a particle size in the range of 100-200 microns. The production process is as follows.

OF copper slab (Cu = 99.9% or more) → hot rolled → cold rolled (cold working rate = 5-30 %)

(11) Patent JP 2014-025129 (SH Copper Products (Hitachi))

The copper target should be OF grade copper with a purity of at least 99.9% purity and particle sizes ranging from 70-200 microns and 100-150 microns. The production process is as follows.

OF copper slab (Cu = 99.9 % or more) → heating at 800-900 °C → hot rolling (thickness reduction rate = 85-90 % and temperature after hot rolling process = 600-700 °C)

(12) Patent JP 2015-017299 (SH Copper Products (Hitachi))

The copper target must be OF grade copper with a purity of at least 99.9% and particle sizes ranging from 70-200 microns and 100-150 microns. The production process is as follows.

OF copper slab (Cu = 99.9 % or more) → heating at 800-900 °C → hot rolling (thickness reduction rate = 85-90 %, temperature after hot rolling = 600-650 °C) → cold rolling → heat treatment (cold rolling and Heat treatment can be repeated) → Complete cold rolling (working rate = 5-7%)

According to prior studies, it has been found that most copper target processes are 1) Forging, 2) Hot Rolling, and 3) Hot Extrusion. In general, the forging process produces a small amount of copper target. Therefore, most copper targets are produced by hot rolling or hot extrusion processes because they can produce small or large copper targets. However, currently popular ones are produced by the hot rolling process.

Copper target research by hot extrusion has been conducted in recent years (Furukawa Electric, 2012). Comparing the copper target production of the hot rolling process and the hot extrusion process, it was found that the production process of the copper target by the hot extrusion process was less than the hot rolling process.

Copper target production process by hot rolling process:

1) Copper slab → 2) Heating at 1,000°C → 3) Hot rolling (multi-pass) → 4) Water cooling → 5) Copper plate → 6) Oxide surface processing → 7) Copper plate → 8) Cold rolling → 9) Heat treatment → 10) copper target (Note: steps 8 and 9 can be reproduced to any desired size)

Copper target production process by hot extrusion process:

1) Copper ingot → 2) Heating at 1,000°C → 3) Hot extrusion (single pass only) → 4) Water cooling → 5) Copper plate → 5) Cold rolling or cold drawing → 6) Copper target

In addition, the patents of Furukawa Electric (JP 2012-4974197 and JP 42012-974198) studied the properties of copper targets, especially in terms of particle size comparison between hot rolling and hot extrusion. Studies have shown that the grain size of hot rolling and hot extrusion can be controlled to the desired size. However, the uniformity of copper grain size in the extrusion process (head-end position along the length and center-edge position along the width) is smaller than in the hot rolling process. This means that the hot extrusion process has a more uniform grain size than the hot rolling process.

In addition, various studies have shown that the surface roughness of the target is associated with abnormal discharge during sputtering, resulting in a problem known as “particles” or “splats”. Studies have shown that copper targets have a very small grain size and therefore have a smoother surface. Accordingly, the problem of "particles" may be prevented by reducing the particle size of the copper particles. Therefore, the quality of the thin film produced with the copper target material is better with a small particle size than with a large particle size. However, according to a recent study by Furukawa Electric (JP 2012-4974197 and JP 2012-4974198), the grain size of the hot extrusion process is 100-200 microns for the copper target. Copper targets suitable for thin film applications are produced by a hot extrusion process with a particle size of less than 100 microns.

Embodiments may provide a technique for manufacturing a copper target for thin film coating by a sputtering method using a hot extrusion process.

Embodiments may provide a copper target having a small particle size in the range of 50-100 microns.

However, the technical tasks are not limited to the above-described technical tasks, and other technical tasks may exist.

A copper target for a thin film according to an embodiment includes 99.99% or more of pure copper.

The copper target may further comprise oxygen not exceeding 5 ppm.

The copper target may further include other elements not exceeding 100 ppm.

The particle size of the copper target may not exceed 100 microns.

The hardness of the copper target may not exceed 100 Vickers.

A method of manufacturing a copper target for a thin film according to an embodiment includes hot extruding a copper ingot into a water tunnel through an extrusion die; cold drawing the copper ingot after the hot extrusion; and stretching the cold drawn copper ingot.

The copper ingot may be heated to a temperature between 750 and 850° C. before the hot extrusion.

The copper ingot may be extruded through the extrusion die and rapidly cooled in water at a temperature not exceeding 40° C. without exposure to air.

The extrusion rate may be 5, 10, or 20 mm/sec.

The cold drawing workability may not exceed 35%.

1 to 4 are views for explaining a sputtering process.
5 and 6 are views for explaining a copper target manufacturing process for a thin film according to an embodiment.
7 shows the position of the sample for measuring the particle size along the length of the copper bar.
8 shows the position of the sample for measuring the particle size along the copper bar width.
9 to 35 show the microstructure results of samples prepared with 10-inch diameter copper ingots.
36 to 62 show the microstructure results of samples prepared from 12 inch diameter copper ingots.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, since various changes may be made to the embodiments, the scope of the patent application is not limited or limited by these embodiments. It should be understood that all modifications, equivalents and substitutes for the embodiments are included in the scope of the rights.

The terms used in the examples are used for the purpose of description only, and should not be construed as limiting. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present specification, terms such as "comprise" or "have" are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiment belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

In addition, in the description with reference to the accompanying drawings, the same components are given the same reference numerals regardless of the reference numerals, and the overlapping description thereof will be omitted. In describing the embodiment, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the embodiment, the detailed description thereof will be omitted.

In addition, in describing the components of the embodiment, terms such as first, second, A, B, (a), (b), etc. may be used. These terms are only for distinguishing the elements from other elements, and the essence, order, or order of the elements are not limited by the terms. When it is described that a component is “connected”, “coupled” or “connected” to another component, the component may be directly connected or connected to the other component, but another component is between each component. It will be understood that may also be "connected", "coupled" or "connected".

Components included in one embodiment and components having a common function will be described using the same names in other embodiments. Unless otherwise stated, descriptions described in one embodiment may be applied to other embodiments as well, and detailed descriptions within the overlapping range will be omitted.

In previous studies, it has been confirmed that the quality of thin films produced with small-grain-size copper target materials is better than that of large-grain size. And, the hot extrusion process has a more uniform copper grain size than the hot rolling process (head-end position along length and center-edge position along width).

The embodiments relate to a method of manufacturing a copper target for thin film coating by sputtering using a hot extrusion process. The inventors of the present application (Oriental Copper) have researched and developed copper targets with small particle sizes in the range of 50-100 microns.

Methods for preparing copper targets and grain sizes obtained in the above-mentioned prior studies and examples are summarized in Table 1.

Embodiments can be made by a hot extrusion process to control the copper particle size below 100 microns so that the coating layer or thin film is of good quality.

A copper ingot having at least 99.99% purity of copper and an oxygen content not exceeding 5 ppm is processed by a hot extrusion process, which is the most important process to control the dimension and uniformity of copper grain size. The variables studied and controlled are extrusion ratio, ingot temperature, and extrusion rate.

1. Extrusion ratio in hot extrusion process

The cross-sectional area or diameter of the copper ingot used for hot extrusion, which is extruded through an extrusion die, is variable. In an embodiment, copper ingot diameters were tested at 10 inches and 12 inches.

2. Temperature of copper ingot before hot extrusion process

The temperature of the copper ingot before the hot extrusion process may be in the range of 750 to 850 °C. For example, the copper ingot may be heated at 750, 800 or 850 °C in the range of 750 to 850 °C.

3. Extrusion speed in hot extrusion process (main ram speed)

The extrusion rate, measured by (by) the speed of a hydraulic cylinder used to extrude the copper ingot through an extrusion die (mold). In an embodiment, extrusion rates were tested at speeds of 5, 10, and 20 mm/sec. After copper is extruded through an extrusion die in a hot extrusion process, the copper can be rapidly cooled by exposure to water (extrusion in water). This is an important technique for preventing grain growth of copper as shown in FIG. 5 . This technique is called underwater extrusion and stops the particle growth mechanism.

That is, the control variable is copper cooling. In general, after copper is deformed in a hot extrusion process, the grain size becomes smaller due to a mechanism known as dynamic recrystallization. If copper is normally cooled in the atmosphere after the hot extrusion process, the copper grain size increases.

For another embodiment, the copper is cooled with water after hot copper extrusion through an extrusion die during the hot extrusion process within 10 seconds. In a short time before the copper is cooled, a recrystallization process can proceed to a grain growth process, which results in a larger grain size and non-uniform grain size.

In this embodiment, the copper cooling control differs from other practices in which the copper is cooled immediately after copper extrusion through an extrusion die in a hot extrusion process. The copper moves immediately into a water tunnel (underwater extrusion) behind the extrusion die. The copper is immediately cooled and does not undergo a grain growth process, resulting in a small and uniform grain size.

The optimum conditions for the copper particle size not to exceed 100 microns in the extrusion process are:

1) Extrusion process using a copper ingot with a diameter of 10 inches

1.1) The ingot temperature of copper ingot is 750°C

1.2) Extrusion speed is 5-20 mm/sec

2) Extrusion process using 12 inch diameter copper ingot

2.1) The ingot temperature of copper ingot is 750-800°C

2.2) Extrusion speed is 5-20 mm/sec

After the hot extrusion process, the copper is brought through a cold drawing process so that the dimensions of the target material within specification and hardness are between 50 and 100 Vickers (HV) before manufacturing in the next process.

The copper dimensions after being pressed through the extrusion die are 188 mm wide and 24 mm thick. After that, the dimensions of the copper are reduced in the cold drawing process. To achieve a width of 185 mm and a thickness of 21 mm, the control of the cold working rate does not exceed 30%. The surface hardness of the copper target is 85 HV (not exceeding 100 HV).

Hereinafter, an experiment in which a copper target was manufactured will be described.

Prepare copper ingots (10 inches diameter, 643 mm long and 12 inches diameter, 471 mm long) heated at 750, 800, and 850 °C prior to the hot extrusion process. The hot copper ingot is immediately extruded through an extrusion die into a water tunnel (submerged extrusion). The extrusion rates are 5, 10 and 20 mm/sec as shown in Table 2.

The copper dimensions after being pressed through the extrusion die are 188 mm wide, 24 mm thick and 6,000 mm long. Then, copper is drawn through a drawing die in a cold drawing process. The working rate of the cold drawing process is 14% (not exceeding 30%). The copper dimensions after being drawn through a drawing die are 185 mm wide, 21 mm thick and 7,000 mm long.

As shown in Figure 7, samples for microstructure testing were cut at head, middle and tail positions along the copper rod length. All samples (head, middle and tail) were examined for microstructure at the edge and center of width, quarter thickness and half thickness of the surface as shown in FIG. 8 .

The microstructure results of each position of the 10-inch diameter copper ingot are shown in FIGS. 9-35 and Table 3, and the microstructure results of each position of the 12-inch diameter copper ingot are shown in FIGS. 36-62 and Table 4. there is.

The embodiment is as follows.

1) The copper target contains more than 99.99% pure copper.

2) Copper target does not exceed 5 ppm oxygen.

3) The copper target contains other elements not exceeding 100 ppm.

4) The copper target according to 1) to 3) has the following process:

4.1) Underwater thermal extrusion

4.2) cold drawing

4.3) Stretch

5) Heat the copper ingot to 750-850℃ before hot extrusion.

6) The copper ingot is extruded through an extrusion die and rapidly cooled (quenched) in water at a temperature not exceeding 40°C without exposure to (or touching) air.

7) Extrusion speed is 5, 10 and 20 mm/sec (measured with main ram).

8) Cold drawing workability does not exceed 35%.

9) The copper particle size of the copper target should not exceed 100 microns.

10) The hardness of the copper target does not exceed 100 Vickers.

As described above, although the embodiments have been described with reference to the limited drawings, those skilled in the art may apply various technical modifications and variations based on the above. For example, the described techniques are performed in an order different from the described method, and/or the described components of the system, structure, apparatus, circuit, etc. are combined or combined in a different form than the described method, or other components Or substituted or substituted by equivalents may achieve an appropriate result.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (10)

A copper target comprising:
A copper target containing at least 99.99% pure copper.
The method of claim 1,
A copper target further comprising oxygen not exceeding 5 ppm.
The method of claim 1,
A copper target further comprising other elements not exceeding 100 ppm.
The method of claim 1,
wherein the particle size of the copper target does not exceed 100 microns.
The method of claim 1,
The hardness of the copper target does not exceed 100 Vickers (Vickers), copper target.
11. A method of making the copper target of any one of claims 1 to 10, comprising:
hot extruding the copper ingot through an extrusion die into a water tunnel;
cold drawing the copper ingot after the hot extrusion; and
stretching the cold drawn copper ingot
A method comprising
7. The method of claim 6,
The method of claim 1, wherein the copper ingot is heated to a temperature between 750 and 850° C. prior to the hot extrusion.
7. The method of claim 6,
wherein the copper ingot is extruded through the extrusion die and rapidly cooled in water at a temperature not exceeding 40° C. without exposure to air.
7. The method of claim 6,
The extrusion rate is 5, 10, or 20 mm/sec.
7. The method of claim 6,
The method of claim 1, wherein the cold drawing workability does not exceed 35%.

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