KR102476165B1 - Method for producing copper target for thin film coating technology by sputtering through hot extusion process - Google Patents

Abstract

A method of manufacturing a copper target for thin film coating technology by sputtering through a hot extrusion process is disclosed. A method of manufacturing a copper target includes hot extruding a 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.

Description

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

The examples below 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 the research and development of new coating technologies such as vacuum coating due to low coating quality and environmental problems. Vacuum coating takes place only in a vacuum (vacuum state) and does not use chemicals that cause environmental problems in the coating process. It can also be coated very thinly, known as "thin film". A “thin film” is a film that does not exceed 5 microns in thickness.

Thin film coating in vacuum is divided into two types: thin film coating by chemical process and thin film coating by physical process.

1. The chemical vapor deposition process (Chemical Vapor Deposition Process (CVD)) is a chemical coating of gas and chemical reactions, and 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 the 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 technologies 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 accurately controlled, and the properties of the film can be adjusted. Industries such as microelectronics, semiconductors, membranes, conductors and film resistors, hard disk drives, automotive glass, fiber optic building, 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 at an appropriate pressure to the coating. 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 the 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 a surface layer of semiconductor properties (see patent US5598285 liquid crystal display device). Although aluminum's resistance is not the lowest, aluminum was used because of technology limitations.

However, with IBM's development in the 1980s, copper (Cu) and silver (Ag) were used as target metals. This is because the resistance of the two 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 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 hit the target material, including the type of gas used. The quality of the thin film also depends on the nature of the target material. The properties of the target material that directly affect the quality (thin film quality) during sputtering are:

1. Purification of the target substance

2. Dielectric content: Oxide (Al ₂ O ₃ for Al targets, CuO for Cu targets)

3. Porosity due to gas during sputtering, void volume

4. Particle size of target material

5. Surface roughness of the target material

6. Mechanical strength or hardness of the target material

Conventionally, there have been many studies on the properties of materials, production methods and production conditions that affect the properties of target materials. Prior studies can be summarized as follows.

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

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

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

The quality of a thin film formed on a substrate by the sputtering method depends on the surface roughness of the target material. Anything that protrudes from the target surface (e.g., a protrusion) results in an electrical discharge during sputtering. Sometimes this is called micro-arcing, and causes large particles (macro-particles) to scatter-out (eg, scatter out) from the target surface and deposit on the substrate. Large particles in the film layer may cause a short circuit in the semiconductor device. Large deposited particles are referred to as “particles” or “splats”. The patent found that surface roughness is related to the particle size of the target. When the particle size of the target is small and finely varied, it will make the surface smoother (the surface will become smoother). Therefore, it is also possible to reduce the particle size in the target to avoid the problem of "particles". The quality of thin films produced by targets with small particle sizes is better than that with larger particle sizes. 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 have a purity of at least 99.99% 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 grain size of less than 80 microns, which reduces problems with coarse clusters and abnormal discharge. The smaller grain size result comes from the recrystallization mechanism of the copper target production process.

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

High surface roughness due to large grain size and low surface roughness due to small grain 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 heat treatment temperature. Heat treatment temperature is between 300-400°C (recommended). When the heat treatment temperature is higher than 400°C, the grain size will be larger. Recrystallization cannot be obtained while the heat treatment temperature is less than 300°C. 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. In order 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.

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

The copper slab is heated to 700-1000°C before the hot rolling process. The hot rolling rate of each pass is 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)

Particle size affects sputtering properties. In that patent, the particle size is 100-200 microns, preferably 110-190 microns, more preferably 120-180 microns. When the particles are small, the grain boundaries increase. Particles or atoms in the boundary layer are disturbed. The atoms of the coating are removed from the copper target during the sputtering process and diffuse randomly (heterogeneously) into the substrate material. Since high energy is required for large particle size sputtering, the result is the 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/second or more) → cold rolling

For the hot rolling process: copper cake (thickness 150 x width 220 mm) → heating at a temperature of about 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) → Machining surface oxide (0.5mm/side) → Copper plate (thickness 22 x width 220mm) → Cold rolling → Copper plate (thickness 20 x width 200mm)

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

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

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

After researching the patent, we are working more on particle uniformity. In that patent, it was found that dynamic recrystallization occurs during processing by hot rolling. When the copper target is cooled in the atmosphere, the problem of grain size irregularities across the width and length of the copper target arises. 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. The particle size at 1/2 and 1/4 thickness is 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 should contain copper purity of at least 99.99%, and the voids and inclusion defects should not exceed 30 microns, and the defects should not exceed 10 pieces/m ² and must 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 (sum of 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 machining → cold rolling

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

The copper target should contain greater than 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 rolling → cold rolling (cold working ratio = 5-30 %)

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

The copper target shall be OF grade copper with a purity greater than 99.9% and a grain size in the range of 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 = 85-90% and temperature after hot rolling process = 600-700°C)

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

The copper target should be OF grade copper with a purity of at least 99.9% and a grain size in the range of 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. Generally, the forging process produces a small amount of copper target. Therefore, most of the copper targets are produced by hot rolling or hot extrusion processes because they can produce small or large copper targets. However, the currently popular ones are produced by the hot rolling process.

Research on copper targets 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 that of 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 treatment → 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 grain 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 copper grain size uniformity (head-end location along length and center-edge location along width) of the extrusion process is smaller than that of the hot rolling process. This means that the hot extrusion process has a more uniform particle size than the hot rolling process.

Further, according to various studies, surface roughness of the target is related to abnormal discharge during sputtering, which causes a problem known as "particles" or "splats". Studies have shown that copper targets have a much smaller grain size and a smoother surface. Therefore, the problem of "particles" can be prevented by reducing the particle size of the copper particles. Therefore, the quality of the thin film produced from the copper target material is better with a smaller particle size than with a larger particle size. However, according to recent studies by Furukawa Electric (JP 2012-4974197 and JP 2012-4974198), the particle size of the hot extrusion process is 100-200 microns for copper targets. Copper targets suitable for thin film applications are produced by a hot extrusion process with a grain 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 with a small grain size in the range of 50-100 microns.

However, the technical challenges are not limited to the above-described technical challenges, and other technical challenges 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 contain oxygen not exceeding 5 ppm.

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

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

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 through an extrusion die and immediately sending it to a water tunnel; cold drawing copper after the hot extrusion; and stretching the cold drawn copper.

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 speed 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 manufacturing process of a copper target for a thin film according to an embodiment.
Figure 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 according to the copper bar width.
9 to 35 show microstructure results of samples made of 10 inch diameter copper ingots.
36 to 62 show microstructure results of samples made of 12-inch diameter copper ingots.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, since various changes can 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 changes, equivalents or substitutes to the embodiments are included within the scope of rights.

Terms used in the examples are used only for descriptive purposes and should not be construed as limiting. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person 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 unless explicitly defined in the present application, they should not be interpreted in an ideal or excessively formal meaning. don't

In addition, in the description with reference to the accompanying drawings, the same reference numerals are given to the same components regardless of reference numerals, and overlapping descriptions 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 will be omitted.

In addition, in describing the components of the embodiment, terms such as first, second, A, B, (a), and (b) may be used. These terms are only used to distinguish the component from other components, and the nature, order, or order of the corresponding component is not limited by the term. When an element is described as being “connected,” “coupled to,” or “connected” to another element, that element may be directly connected or connected to the other element, but there may be another element between the elements. It should be understood that may be "connected", "coupled" or "connected".

Components included in one embodiment and components having common functions will be described using the same names in other embodiments. Unless stated to the contrary, descriptions described in one embodiment may be applied to other embodiments, and detailed descriptions will be omitted to the extent of overlap.

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

Embodiments relate to a method of manufacturing a copper target for thin film coating by a sputtering method using a hot extrusion process. The present inventors (Oriental Copper) have developed a copper target with a small particle size in the range of 50-100 microns through research.

Table 1 summarizes the methods for preparing the copper targets and grain sizes obtained in the above-mentioned prior studies and examples.

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

Copper ingots with at least 99.99% purity copper and an oxygen content not exceeding 5 ppm are processed by a hot extrusion process, which is the most important process for controlling the size and uniformity of the copper particle size. 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 in hot extrusion extruded through an extrusion die is variable. In an embodiment, copper ingot diameters of 10 inches and 12 inches were tested.

2. Temperature of copper ingot before hot extrusion process

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

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

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

That is, the controlled variable is copper cooling. Generally, after copper is deformed in the hot extrusion process, the grain size becomes smaller due to a mechanism known as dynamic recrystallization. When the copper is cooled normally in the atmosphere after the hot extrusion process, the grain size of the copper 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 may proceed to a grain growth process, resulting in larger grain sizes and non-uniform grain sizes.

In this embodiment, copper cooling control differs from other implementations in which the copper is cooled immediately after copper extrusion through an extrusion die in a hot extrusion process. The copper immediately moves 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 optimal conditions for the copper particle size not to exceed 100 microns in the extrusion process are as follows.

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) The 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) The extrusion speed is 5-20 mm/sec

After the hot extrusion process, the copper is brought through a cold drawing process to bring the target material dimensions within specification and hardness 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 dimension of the copper is 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 (does not exceed 100 HV).

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

Prepare copper ingots (10 inches in diameter, 643 mm in length and 12 inches in diameter, 471 mm in length) heated at 750, 800, and 850 °C before the hot extrusion process. Hot copper ingots are immediately extruded through an extrusion die into a water tunnel (underwater extrusion). Extrusion speeds 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 processing rate of the cold drawing process is 14% (does not exceed 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 Fig. 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 inspected for microstructure at the edge and center of width, 1/4 thickness and 1/2 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. have.

An embodiment is as follows.

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

2) Copper targets do 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) Stretching

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 exposing (or touching) air.

7) Extrusion speeds are 5, 10 and 20 mm/sec (measured with the 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 limited drawings, those skilled in the art can apply various technical modifications and variations based on the above. For example, the described techniques may be performed in an order different from the method described, and/or components of the described system, structure, device, circuit, etc. may be combined or combined in a different form than the method described, or other components may be used. Or even if it is replaced or substituted by equivalents, appropriate results can be achieved.

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

Claims (10)

A method for producing a copper target containing 99.99% or more of pure copper, wherein the copper target has uniformity in particle size, the method comprising:
hot extruding the copper ingot through an extrusion die and immediately sending it to a water tunnel;
cold drawing copper after the hot extrusion; and
Stages of stretching cold drawn copper
including,
The particle size of the copper of the copper target does not exceed 100 microns;
The uniformity of the particle size means that the standard deviation of the average particle size is 3.76 microns or less,
The method, wherein the method satisfies the following conditions:
i) When using a copper ingot with a diameter of 10 inches,
- The copper ingot is heated to a temperature of 750°C before hot extrusion,
- extrusion speed is 5-20 mm/sec; and
ii) When using a 12 inch diameter copper ingot;
- The copper ingot is heated to a temperature between 750-800°C before hot extrusion,
- Extrusion speed is 5-20 mm/sec.
delete According to claim 1,
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.
According to claim 1,
The extrusion speed is 5, 10, or 20 mm / sec, the method.
According to claim 1,
wherein the cold drawing degree does not exceed 35%.
A copper target having uniform particle size obtained from the method according to any one of claims 1 and 3 to 5,
The particle size of the copper of the copper target does not exceed 100 microns;
The uniformity of the particle size means that the standard deviation of the average particle size is 3.76 microns or less.
7. The copper target of claim 6, further comprising not more than 5 ppm oxygen.
7. The copper target of claim 6 further comprising no more than 100 ppm of other elements.
7. The copper target according to claim 6, wherein the hardness of the copper of the copper target does not exceed 100 Vickers. delete

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