JP2020012200A - Manufacturing method of sputtering target - Google Patents

Abstract

To provide a sputtering target manufacturing method capable of suppressing initial particle generation during sputtering, and shortening a burn-in time.SOLUTION: In a manufacturing method of a sputtering target, concerning finishing of the sputtering target, a heat treatment of a target processing surface by a local heating source is performed in vacuum within a temperature range at a degasification initiation temperature or higher and below a melting point, hereby a processing affected layer (cutting strain) of a target surface layer is mitigated sufficiently, and hydrogen adhering onto the target surface can be removed effectively.SELECTED DRAWING: None

Description

The present invention relates to a method for manufacturing a sputtering target capable of suppressing generation of initial particles during sputtering and reducing a burn-in time.

2. Description of the Related Art Sputtering for forming a coating of a metal or ceramic material is used in many fields such as electronics, corrosion-resistant materials and decorations, catalysts, production of cutting / polishing materials and wear-resistant materials. Sputtering itself is a well-known method in the above field, but recently, particularly in the field of electronics, a sputtering target suitable for forming a film having a complicated shape, forming a circuit, and the like has been required.

Generally, a sputtering target is produced by forging, annealing (heat treatment), rolling, and finishing (mechanical, polishing, etc.) an ingot or billet obtained by melting and casting a metal, alloy, or the like as a raw material. When sputtering is performed using the target manufactured in this manner, it is possible to form a film having stable characteristics while minimizing generation of arcing and particles while performing uniform film formation. It has been demanded.

By the way, in the finish processing of the target, when the surface of the target is cut, a processing-altered strain (cutting strain) is introduced into the surface layer. If such a cutting strain exists in the surface layer of the target, the sputtering rate may become unstable or the film thickness may become non-uniform at the beginning of sputtering. Therefore, polishing (wet polishing) is usually performed after cutting the surface of the target in order to remove cutting distortion.

However, metals or their alloys, such as tantalum, that easily absorb hydrogen, when cutting or polishing, expose an active new surface and react with moisture in the air or polishing liquid to absorb a large amount of hydrogen. There is a problem of embrittlement. The present applicant has previously proposed a technique for reducing the amount of hydrogen adsorbed on the surface by heating the surface of the target before installing it in a sputtering apparatus (Patent Document 1).

Further, Patent Literature 2 discloses a technique for reducing the hydrogen content on the surface of a target by performing dehydrogenation treatment after performing surface smoothing by cutting, polishing, and chemical etching. Although all of the techniques provide effective solutions to the respective problems, they did not effectively solve both the problem of hydrogen storage and the problem of the affected layer.

International Publication WO2012 / 014921 JP-A-11-1766

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sputtering target capable of suppressing the generation of initial particles during sputtering and reducing the burn-in time. . In particular, it is an object of the present invention to provide a method for manufacturing a sputtering target capable of sufficiently reducing a work-affected layer (cutting strain) on a target surface layer and effectively removing hydrogen adsorbed on a target surface.

When the surface of the sputtering target is locally heated in a vacuum after being cut or the like, the work-affected layer (cutting strain) on the surface of the target can be alleviated, and the hydrogen adsorbed on the target surface is removed. I got the knowledge that I can do it. Based on this finding, the present application provides the following invention.
1) A method for manufacturing a sputtering target, comprising performing a heat treatment by a local heating source in a vacuum on a target processing surface in finishing processing of the sputtering target.
2) The method for manufacturing a sputtering target according to the above 1), wherein, in the finishing processing of the sputtering target, a heat treatment is performed on the target processing surface by an electron beam in a vacuum.
3) The method for producing a sputtering target according to the above 1) or 2), wherein the heat treatment is performed within a temperature range from a degassing start temperature to a temperature lower than a melting point.
4) A sputtering target, wherein the hydrogen content of the target is 100 μL / cm ² or less, and the full width at half maximum (FWHM) of the X-ray diffraction peak is 0.35 or less.
5) The sputtering target according to 4) above, wherein the sputtering target is made of at least one metal selected from the group consisting of Cu, Ti, Ta, Al, Ni, Co, W, Si, Pt, and Mn.

ADVANTAGE OF THE INVENTION The manufacturing method of this invention can fully reduce the process-affected layer (cutting distortion) of the target surface layer, and can remove the hydrogen adsorbed or occluded on the target surface. The target in which the work-affected layer is alleviated and the hydrogen adsorption is reduced can suppress the initial generation of particles during sputtering and shorten the burn-in time.

  The sputtering target in the present invention can be manufactured by the following steps. In an example using tantalum, for example, high-purity 4N (99.99% or more) tantalum can be used as a target material. This is melted and refined by electron beam melting or the like to increase the purity, and then cast to produce an ingot or billet. It is not necessary to limit to electron beam melting, and other melting methods can be used.

Next, the ingot or billet is subjected to a series of processes such as forging, rolling, and annealing. By forging or rolling, the cast structure is destroyed, and pores and segregation can be diffused or eliminated. In addition, recrystallization can be performed by annealing. The order and number of forging, rolling, and annealing can be appropriately adjusted. The structure can be densified and refined by forging, rolling, and annealing, but it is also possible to manufacture directly from a cast product.

Usually, the target material before finishing is manufactured by the above manufacturing process, but this manufacturing process is an example, and the present invention is characterized by performing a local heat treatment after cutting or polishing. Therefore, it is not intended that the manufacturing process such as melting casting, forging, rolling, annealing and the like be invented, so that it is naturally possible to manufacture by other processes, and the present invention includes all of them. is there.

  The target material thus obtained is finished into a final sputtering target by finishing (cutting, polishing, etc.). After turning the target material with a lathe, the target surface is cut using a processing tool such as a cutting tool, and adjusted to have a desired surface roughness. The cutting method and conditions are not particularly limited, and other known cutting methods and conditions can be used.

By the way, after cutting the surface of the target, the surface layer (crystal) of the target undergoes distortion due to residual stress, and this becomes a work-affected layer. In addition, an active new surface of the target appears on the outermost surface of the target, which reacts with moisture in the atmosphere to adsorb or occlude a gas such as hydrogen. Such a deteriorated layer on the surface of the target and gas adsorption adversely affect the sputtering (particularly at the initial stage).

  Further, after cutting the target surface, removal of the work-affected layer and adjustment of the surface roughness can be performed by known polishing means such as wet polishing or chemical polishing. Since the new surface is exposed, it reacts with the moisture in the polishing liquid and adsorbs a large amount of gas such as hydrogen. As described above, polishing can remove a deteriorated layer, but causes a new problem of gas adsorption or occlusion.

What is important in the present invention is that after the surface of the target is cut, or after cutting and polishing, a local heating radiation source is applied to the processed surface in a vacuum (vacuum degree: 1 × 10 ^-1 Pa or less). Heat treatment. An example of the heat treatment using the local heating radiation source includes electron beam irradiation. Thereby, processing distortion and gas (especially hydrogen) adsorption can be extremely effectively reduced. The reason for selecting local heating as a heating method is to effectively heat only the surface layer of the material to be heated by rapid overheating and rapid cooling of the irradiated part, while minimizing the thermal effect on the backing plate material. is there.

In some sputtering targets, brass (Cu-Zn alloy) with relatively high resistance is used as the backing plate material, which has both high strength and high cooling performance, and can suppress the factors that hinder magnet rotation due to eddy current. Used. However, when the bonded body with the backing plate is heated by resistance heating or the like in a vacuum to perform degassing, Zn (zinc) is evaporated and the backing plate is deteriorated to function as a cooling plate. May lower. By employing local heating, such deterioration of the material of the cooling plate can be prevented.

The heat treatment by local heating can be performed by, for example, electron beam irradiation. The electron beam irradiation is performed in a vacuum chamber provided with an electron gun vacuum exhaust device and a work rotating mechanism. Generally, an electron gun has an output of several kW to several hundreds of kW, but an output of several kW to several tens of kW is sufficient because the present invention does not aim to melt the beam irradiation surface. Next, a target (work) is set on the turntable, the vacuum chamber is closed, and evacuation is performed. Then, when the internal pressure reaches a degree of vacuum of about 1 × 10 ⁻² Pa, an electron beam is generated to focus on the work surface and heat the irradiated part.

The electron beam is rotated at a beam moving speed of 1000 mm / min or less while being spirally rotated. When the speed is 1000 mm / min or less, the target surface temperature becomes about 400 ° C. or more, which is effective for desorbing gas components such as hydrogen adsorbed or occluded on the target surface. Further, when the speed is set at 600 mm / min or less, the surface temperature becomes about 700 ° C. or more, so that gas components adsorbed or occluded on the target surface can be desorbed and cutting strain can be reduced.

On the other hand, if the moving speed of the beam is too slow, the surface temperature becomes higher than the melting point, and the target material is locally melted. Therefore, it is necessary to individually confirm the speed at which the melting point is not exceeded, depending on the material. In the case of a tantalum material, degassing starts at about 400 ° C. in a vacuum, and at about 750 ° C., changes such as recrystallization in the surface properties and internal structure begin to occur. Therefore, it is necessary to appropriately determine and execute the heat source irradiation input value, the rotation speed, and the like so as to control the heating temperature so as not to deteriorate the structure such as the melting point or the recrystallization or the like on the surface. In the case of a tantalum material, the speed is preferably higher than 500 mm / min.

The sputtering target manufactured by the above manufacturing method can have a hydrogen content of 100 μL / cm ² or less and a half-width (FWHM) of an X-ray diffraction peak of 0.35 or less. The measurement of the half width was carried out by an X-ray diffractometer (XRD) manufactured by X-Ray Diffraction Co., Ltd., under the following measurement conditions: X-ray source: Cu, tube voltage: 40 kV, tube current: 30 mA, horizontal goniometer, scan speed: 10 ° / min, scan step: 0.02 °, scan axis 2θ / θ, measurement angle: 30 ° to 60 °, and calculate the half width of the (200) plane peak. The sputtering target to be used in the present invention is preferably made of at least one metal selected from the group consisting of Cu, Ti, Ta, Al, Ni, Co, W, Si, Pt, and Mn. This is because these metals easily occlude hydrogen, often involve precise surface processing, and have many opportunities to occlude hydrogen. In addition, they are often used in the electronics field, particularly as materials for semiconductor integrated circuits.

  Hereinafter, description will be made based on embodiments. The present embodiment is merely an example for facilitating understanding, and is not limited by this example. That is, the present invention is limited only by the claims, and includes various modifications other than the embodiment described in the present invention.

(About measurement of hydrogen content)
In Examples and Comparative Examples, the hydrogen content of the target is measured as follows. A central portion of the target is cut out by a dry method to prepare a sample of 20 mm × 10 mm × 8 mmt. After introducing this sample into the mass spectrometer, it is heated to 800 ° C. and the hydrogen gas released from the surface is measured. A thermal desorption gas mass spectrometer (AGS-7000, manufactured by Anelva) is used as the mass spectrometer. Specifically, the sample is placed in a quartz tube for vacuum heating (thermal desorption gas mass spectrometer), preliminarily evacuated by a rotary pump for 5 minutes, and then evacuated under high vacuum for 10 minutes to remove adsorbed water. After confirming that the ionic strength of the background has decreased, the temperature is raised from room temperature to 800 ° C. at a rate of 20 ° C./min. Thereafter, the temperature is maintained at 800 ° C. for 5 minutes, and then the hydrogen gas generated when the mixture is left to cool for 5 minutes is measured. At this time, a fixed amount of hydrogen is injected and quantified.

(Example 1)
A tantalum raw material having a purity of 99.997% was melted by an electron beam and cast to obtain an ingot having a thickness of 200 mm and a diameter of 200 mmφ. Next, after forging this ingot at room temperature, recrystallization annealing was performed at a temperature of 1227 ° C. to obtain a material having a thickness of 100 mm and a diameter of 100 mmφ. Next, this was cold forged and upset forged, recrystallized and annealed at a temperature of 1173K, then cold rolled, and then annealed at 900 ° C. Then, after performing the cutting finish processing with a lathe, the surface was wet-polished and used as a sputtering target.

  The target thus obtained was introduced into a vacuum chamber, and was irradiated with an electron beam in a spiral at a speed of 600 mm / min. The temperature of the target at this time was 750 ° C. when measured using a thermocouple. Then, the surface of the heat-treated target was analyzed for a surface altered layer (processing strain) using an X-ray diffractometer. The processing strain was evaluated based on the half-width (FWHM) of the measured X-ray diffraction peak. The diffraction peak used for the calculation of the half-value width was a peak of the (200) plane, which had a high intensity and was stable. As a result, FWHM was 0.31.

Also, the amount of hydrogen gas separately measured by the above method could be reduced to 50 μL / cm ² . Next, this target was sputtered using a DC sputtering apparatus (Endura 5500, manufactured by Applied Materials). The burn-in time (time during which the number of particles is less than 10) was 35 kW, and the number of particles at 75 kW was 4, which was a good result.

(Examples 2-3 and Comparative Examples 1-2)
The target obtained in the same manner as in Example 1 was introduced into a vacuum chamber, and irradiated with an electron beam while changing the speed as shown in Table 1. When the temperature of the target at this time was measured using a thermocouple, Examples 2 to 3 were 600 ° C and 400 ° C, respectively, and Comparative Examples 1 and 2 were 1200 ° C and 200 ° C, respectively. . Thereafter, the surface of the heat-treated target was analyzed for a surface-altered layer (process strain) in the same manner as in Example 1. As a result, the FWHM was 0.34 (Example 2), 0.35 (Example 3), 0.28 (Comparative Example 1), and 0.45 (Comparative Example 2). In Comparative Example 1, grain growth occurred, and in Comparative Example 2, processing strain could not be sufficiently removed.

Separately, the amount of hydrogen gas measured by the above method was 80 μL / cm ² (Example 2), 100 μL / cm ² (Example 3), 30 μL / cm ² (Comparative Example 1), 200 μL / cm ² ( Comparative Example 2). In Comparative Example 2, the hydrogen content was large. Next, sputtering was performed on this target under the same conditions as in Example 1. The burn-in time was 45 kW (Example 2), 50 kW (Example 3), 40 kW (Comparative Example 1), and 85 kW (Comparative Example 2). In Comparative Example 2, the burn-in time was longer. The number of particles was 6 (Example 2), 7 (Example 3), 4 (Comparative Example 1), and 12 (Comparative Example 2). In Comparative Example 2, the number of particles increased. . In Comparative Example 1, the film uniformity was poor until 75 kW due to grain growth.

Table 1 shows the above results.

  ADVANTAGE OF THE INVENTION The manufacturing method of this invention can fully reduce the cutting distortion of a material surface layer, and can remove the hydrogen adsorbed on the surface. A target made of such a material has an excellent effect of suppressing initial particles during sputtering and shortening a burn-in time. INDUSTRIAL APPLICABILITY The present invention is useful as a target suitable for the field of electro-optics, particularly for forming a film having a complicated shape or forming a circuit.

Claims (5)

A method for manufacturing a sputtering target, comprising: performing a heat treatment with a local heating radiation source on a target processing surface in a vacuum in a finishing process of the sputtering target. 2. The method for manufacturing a sputtering target according to claim 1, wherein in the finishing of the sputtering target, a heat treatment is performed on the target processing surface by an electron beam in a vacuum. The method for manufacturing a sputtering target according to claim 1, wherein the heat treatment is performed within a temperature range equal to or higher than a degassing start temperature and lower than a melting point. A sputtering target, wherein the hydrogen content of the target is 100 μL / cm ² or less, and the full width at half maximum (FWHM) of the X-ray diffraction peak is 0.35 or less. The sputtering target according to claim 4, comprising one or more metals selected from the group consisting of Cu, Ti, Ta, Al, Ni, Co, W, Si, Pt, and Mn.