JP2013237908A - Sputtering target for forming thin film and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Sn-Nb sputtering target in which the frequency of generation of abnormal discharge is reduced during sputtering, and which has a high strength and an improved crack resistance of the target, and to provide a manufacturing method thereof.SOLUTION: A sputtering target for forming a thin film is produced such that Nb crushed powder and Sn powder are mixed to make a mixture at a weight ratio where the amount of the Sn powder is equal to or more than that of the Nb crushed powder, and the mixture is pressurized and baked at a temperature less than the melting point of Sn to make a sintered body. The Nb forms a dispersed phase in the Sn matrix of the sintered body, and a shape derived from the crushed powder is kept.

Description

  The present invention relates to a sputtering target for forming a thin film excellent in cracking resistance and suitable for forming a recording layer of an optical disc, in particular, a recording layer (Sn—Nb) of a phase change optical disc, and a method for producing the same.

  In recent years, production of thin films using a sputtering method has been actively performed. For example, a sputtering method is used to form a thin film such as a protective layer and a recording layer in an optical disc such as a DVD or a BD that records information using a light beam. In order to improve the performance and value of these thin films, a composite target composed of two or more components is required as the sputtering target.

  Conventionally, as a method for producing a sputtering target, a melting method, a hot press method, an atmospheric pressure sintering method, or the like is used. However, when trying to fabricate a composite target of a high melting point material such as a high melting point metal or ceramic and a low melting point material, the conventional sputtering method may cause phase separation due to the density difference of each component or the melting point of each component. Due to problems such as composition changes due to differences and outflow due to melting of low melting point metals, a uniform and high density target could not be produced.

For example, there is a method in which a mixture of a powder of a high melting point material and a powder of a low melting point metal is pressed at room temperature, but in order to produce a high-density sputtering target by this method, an additive of 1000 to 3500 kgf / cm ² is used. Pressure or higher pressure molding is required, and if an attempt is made to produce a high-density sputtering target, the apparatus becomes very large, leading to a significant increase in manufacturing cost due to the cost of the apparatus.

  Furthermore, since the sputtering target produced by this method is molded at a high pressure at room temperature, residual stress is generated inside the target, and the target length depends on the bonding of the target and the thermal history during sputtering film formation. However, there was a problem that irreversible elongation of 0.5 to 2% was generated and the dimensional stability of the target could not be obtained, and there were problems such as cracking and dropping off of the target during sputtering.

  In order to solve these problems, Patent Document 1 proposes a sputtering target manufacturing method for forming a thin film composed of a plurality of components by sputtering. In this manufacturing method, when the heat treatment temperature at the time of performing heat treatment in a pressurized state is Tm, which is the lowest melting point component among a plurality of types of components, (Tm × 0.70) ° C. or (Tm × 0.85) A composite target is obtained by setting the temperature range from ° C to Tm.

Further, according to Patent Document 2, a sputtering target manufacturing method for manufacturing a composite thin film of a high melting point substance and a low melting point metal has been proposed. In this production method, a simple substance or a compound powder of at least one element selected from the group consisting of Zr, Ti, Ta, Hf, Mo, W, Nb, La, Si, Ni, C, B, and Cr; A mixture of a powder of a low melting point metal containing at least one metal selected from the group consisting of In, Sn, Zn, and Al with a temperature that is 50 ° C. lower than the melting point of the low melting point metal and lower than the melting point of the low melting point metal The sputtering target is obtained by heating and molding at a pressure of 500 kgf / cm ² or less.

JP 63-128141 A Japanese Patent No. 3827725

  On the other hand, as a recording layer in a rewritable large-capacity phase change optical disc, it is expected to form a thin film composed of two components of Sn and Nb. In forming this thin film, two layers of Sn and Nb are expected. It is necessary to produce a sputtering target containing components. However, Patent Documents 1 and 2 do not disclose the production of a sputtering target containing two components of Sn and Nb.

  The melting point of the component Sn in this Sn—Nb sputtering target is 231.93 ° C., the melting point of the component Nb is 2415 ° C., and there is an extreme difference between the melting points of both components. Therefore, when this Sn—Nb sputtering target was produced by the above-described manufacturing method, not only a high-density and high-strength target could be obtained, but also when sputtering film formation using the sputtering target was performed, The frequency of discharge was high, and many target cracks occurred.

  Therefore, the present invention has been made in view of the above-described problems, and is suitable for forming a recording layer (Sn—Nb) of a phase change optical disc, and the occurrence frequency of abnormal discharge during sputtering is reduced. An object of the present invention is to provide a high-density and high-strength Sn—Nb sputtering target with improved crack resistance of the target and a method for producing the same.

  According to the conventional manufacturing method, a mixture obtained by mixing a plurality of types of components at a predetermined ratio is subjected to pressure treatment while heat-treating at a temperature lower than the melting point of the lowest melting component among the components, and the target. It is shaped into a shape. In this pressure molding, only the component with the lowest melting point becomes a very active state by heat treatment at a temperature lower than the melting point and plays a role as a binder with other components. Is based on the principle that the binding force with each component is increased. Therefore, the manufactured sputtering target has mechanical strength as a target and has a low heat treatment temperature, so that the charged composition before the heat treatment is maintained as it is even after the heat treatment, and the film is formed even during the sputtering film formation. In addition, the composition of the thin film is very close to the charged composition.

  The inventors of the present invention manufactured an even higher density and high strength Sn—Nb sputtering target using the above-described principle, even when using two components of Sn and Nb, and produced abnormal discharge during sputtering. Research was conducted to reduce the frequency of occurrence and to improve the crack resistance of the target. In this research, a crushed powder was used for Nb, and when a sputtering target composed of two components of Sn and Nb set to a specific composition ratio and a specific average particle size ratio was produced, a higher density and higher strength were obtained. An Sn—Nb sputtering target was obtained, and it was found that the frequency of occurrence of abnormal discharge can be reduced and cracking of the target does not occur even during sputtering using this target.

Therefore, the inventors mixed 55 wt% of Sn powder with an average particle diameter of 50 μm and 45 wt% of Nb crushed powder with an average particle diameter of 45 μm, and mixed them in a vacuum atmosphere at a temperature of 190 ° C. and 550 kgf / cm. ^The Sn-Nb sputtering target was manufactured by performing pressure sintering for 2 hours under the condition of 2. The composition component in the manufactured sputtering target was analyzed. The analysis result is shown in FIG.

The photograph in FIG. 1 is an element distribution image obtained by EPMA (Field Emission Electron Beam Probe) for the manufactured sputtering target. From the photograph in the figure, the composition distribution of each element of Sn and Nb Can be observed.
Note that the element distribution image by EPMA is originally a color image, but in the photograph of FIG. 1, it is converted into a black and white image. Therefore, the whiter in the photograph, the higher the concentration of the element. ing. Specifically, in the distribution image related to Sn, it appears white and is distributed continuously, and in the distribution image related to Nb, the Nb element exists in an indefinite white island shape. From these, it can be seen that island-like Nb is dispersed in the target substrate, and Sn exists so as to surround the island-like Nb. This sputtering target has a structure in which Nb pulverized powder is dispersed and distributed in an Sn substrate that is softened by low-temperature heating and pressure firing to form a continuous phase, that is, Nb forms a continuous phase. In the Sn substrate, it was confirmed that a dispersed phase was formed and a shape derived from crushed powder was maintained.

  On the other hand, when the line analysis by X-ray diffraction (XRD) was performed on the Sn and Nb bonding portion in the Sn—Nb sputtering target manufactured as described above, only the Sn peak appeared in the Sn portion, and Nb In the portion, only Nb peaks appear, and it can be seen that each exists as a crystal phase. However, the SnNb alloy phase was not confirmed at the boundary between Sn and Nb. It was confirmed that Nb formed a dispersed phase in the Sn substrate. If it is Sn simple substance, since it is excellent in ductility, it will become difficult to crack, but if SnNb alloy phase is formed, it will become easy to crack.

  Moreover, when the bulk density, density ratio, and maximum stress were investigated about this manufactured Sn-Nb sputtering target, it was confirmed that the result of sufficient high density and high intensity was obtained. Moreover, when sputtering film formation was performed using this sputtering target, the abnormal discharge generated was small and the target itself was not cracked.

Therefore, the present invention has been obtained from the above findings, and the following configuration has been adopted in order to solve the above problems.
(1) The sputtering target for forming a thin film of the present invention is a sintered body mainly composed of Sn and Nb, and Nb forms a dispersed phase in the Sn substrate of the sintered body, and crushed powder. It is characterized by having a shape derived from.
(2) The sputtering target for forming a thin film according to (1) is characterized in that Nb forming the dispersed phase has an average particle diameter of 70 μm or less.

(3) Moreover, the manufacturing method of the sputtering target for thin film formation of this invention mix | blends Nb pulverized powder and Sn powder by mix | blending and mixing Sn powder with Nb pulverized powder by equality or more with respect to weight ratio. A body is prepared, and the mixture is subjected to pressure firing at a temperature lower than the melting point of Sn.
(4) The manufacturing method of (3) is characterized in that the Sn powder has an average particle size of 0.2 to 5 times the average particle size of the Nb crushed powder.
(5) The production method of (3) or (4) is characterized by pressure baking at a pressure of 500 kgf / cm ² or more.

  In the production of the Sn—Nb sputtering target for forming an optical disk recording layer according to the present invention, as described above, only the component having the lowest melting point is brought into a very active state by the heat treatment at a temperature lower than the melting point. Considering the fact that it plays the role of a binder between the two and further uses the principle that a pressurizing effect is added to this to increase the bonding force with each component, the sintering temperature should be optimized. However, this is important for increasing the density and increasing the strength, whereby the cracking resistance of the sputtering target can be improved, and as a result, abnormal discharge during sputtering can be suppressed.

  Therefore, first, as one of the measures for improving the crack resistance, crushed powder is used for Nb. This is because each of the crushed powder has an irregular shape, so that its surface area is increased, and separation due to the difference in specific gravity between raw material powders is suppressed when mixing with Sn powder, thereby increasing the strength of the target. . Sn can be a powder of any shape, but is selected so as to obtain a uniform mixture when mixed with Nb crushed powder. Therefore, the Sn powder and the Nb crushed powder are most preferably those having the same average particle diameter. However, when the Nb crushed powder has an average particle diameter of 10 to 70 μm, the Sn powder has an average particle diameter of Nb. The average particle size can be 0.2 to 5 times the average particle size of the crushed powder.

If the average particle size of the Nb crushed powder exceeds 70 μm, abnormal discharge is caused, which is not preferable. In addition, since mixing may become inhomogeneous due to aggregation of the Nb crushed powder, the average particle size of the Nb crushed powder is more preferably 10 μm or more.
As the optical disk recording layer, the composition of Nb: 30 to 70 wt% and the balance: Sn is generally known, and the same composition is required for the sputtering target.

Next, as one of the measures for improving the crack resistance, optimization of molding pressure when molding a mixture of Sn powder and Nb crushed powder can be mentioned. In the production of the Sn—Nb sputtering target of the present invention, Nb crushed powder is used, and therefore, it is unavoidable to press with a high pressure due to the bulk density at the time of molding. By the way, if the molding pressure is increased, the firing temperature can be lowered, and conversely, if the firing temperature is set higher in the range below the melting point of Sn, the molding pressure can be lowered. Therefore, in the present invention, 500 kgf / cm ² or more, more preferably, to a firing under pressure at 550 kgf / cm ² or more.

When the pressure is 500 kgf / cm ² or more, a target having higher density and excellent crack resistance can be obtained. In addition, in order to prevent a high addition from being applied to the apparatus, the pressure is preferably 2000 kgf / cm ² or less.
On the other hand, since the melting point of Sn is 231 ° C., the firing temperature is 180 ° C. or higher and lower than the melting point of Sn.
When the firing temperature is less than 180 ° C., high density cannot be obtained and crack resistance is inferior. When the firing temperature is higher than the melting point of Sn, the Sn raw material is melted and a target having the intended composition cannot be obtained.
When the average particle size of the Sn powder is less than 0.2 times the average particle size of the Nb crushed powder, the Sn powder is agglomerated due to the aggregation of the Sn powder, and when it exceeds 5 times, abnormal discharge is caused. Therefore, it is not preferable.
The firing time is preferably 2 hours or more in order to make the temperature distribution uniform and prevent uneven density, and is preferably 3 hours or less in order to prevent energy loss.

  According to the present invention, it is suitable for forming a recording layer (Sn—Nb) of a phase change optical disc, and the occurrence frequency of abnormal discharge during sputtering is reduced, and the cracking resistance of the sputtering target is improved. It is possible to provide an Sn—Nb sputtering target having high density and high strength and a method for manufacturing the same.

It is the element distribution image of Sn-Nb measured by EPMA about one specific example of the Sn-Nb sputtering target which concerns on this invention.

  Next, the Sn—Nb sputtering target for forming a thin film and the method for producing the same of the present invention will be specifically described below with reference to examples.

〔Example〕
Manufacture of the Example of this invention was performed on condition of the following.
First, Nb powder (purity 3N) and Sn powder (purity 3N) were weighed so as to have the composition shown in Table 1 below, and these were dry-mixed for 30 minutes with a rocking mixer, and the mixture was Produced. The shape of Nb powder, the particle diameter, and the particle diameter of Sn powder are as shown in Table 1.

<Nb powder>
Among the Nb powders described above, the crushed powder was prepared by pulverizing an Nb ingot using a vibration mill. On the other hand, the spherical powder used what was adjusted by the gas atomization method.

Next, the obtained mixture was dried and then vacuum hot pressed at a temperature of 190 ° C. for 2 hours under the pressure shown in Table 2 to obtain a sintered body.
The sintered body thus hot-pressed was machined into a target shape (diameter 125 mm, thickness 10 mm), and the processed one was bonded to a backing plate made of oxygen-free copper. A sputtering target of Comparative Example 1 was produced.
In addition, the comparative example 1 has shown the case where Nb spherical powder is used.

  Next, for the sputtering targets of Examples 1 to 11 and Comparative Example 1 shown in Tables 1 and 2, the bulk density, the density ratio, and the maximum stress are measured as follows, and further, the sputtering target is measured. Abnormal discharge was observed and the presence or absence of cracks in the target was confirmed.

<Density measurement>
It was measured by an automatic specific gravity measuring device “Archimedes (drive unit SA301, data processing unit SA601)” manufactured by Chow Balance.

<Density ratio measurement>
The theoretical density was calculated by the following method.
In an alloy composed of the element A and the element B, the content of the element A is Wa (wt%), the density is Da (g / cm ³ ), the content of the element B is Wb (wt%), and the density is Db ( g / cm ³ ), the density Dab (g / cm ³ ) of the binary alloy composed of the element A and the element B is calculated by the following calculation formula.
Dab = 100 / [(Wa / Da) + (Wb / Db)]
From the theoretical density Dab obtained here and the measured density of the target, the ratio (target density / theoretical density × 100%) was defined as the density ratio.

<Maximum stress measurement>
Using Shimadzu Autograph: AG-X, the stress curve was measured by a three-point bending test with an indentation speed of 0.5 mm / min, and the maximum stress in the elastic region was measured.

<Others>
Furthermore, the structure of the sputtering target was observed with EPMA, and Sn and Nb, which are metal components in the target, were quantitatively analyzed by the ICP method (high frequency inductively coupled plasma method).
The structure of the sputtering target was observed by filling the debris of the sintered sputtering target with a resin, wet polishing so as to be a flat surface, and then using EPMA (electron beam microanalyzer: JXA-8500F manufactured by JEOL) with Sn, Nb. The surface distribution (MAPPING) of each element was measured. The observation conditions were an acceleration voltage of 15 kV, an irradiation current of 50 nA, a scan type: one direction, a pixel (X, Y): (240, 180), a spot size (X, Y): (1 μm, 1 μm), and a measurement time of 10 ms. . In addition, the observation magnification was 2000 times, and the element distribution (mapping) was measured by dividing the 240 × 180 μm range into several times. According to the obtained mapping image, all of the targets of the examples have a structure in which Sn surrounds Nb, that is, a dispersed phase is formed in a substrate where Nb is Sn, and a shape derived from crushed powder is maintained. It was confirmed that it has a certain organization.
Moreover, it was confirmed by the quantitative analysis by the ICP method that there is no difference between the blend composition and the target composition.

<Number of abnormal discharge>
After attaching the soldered target to a normal magnetron sputtering apparatus and exhausting to 1 × 10 ⁻⁴ Pa, sputtering is performed under the conditions of Ar gas pressure: 0.5 Pa, input power: DC 300 W, and distance between target substrates: 60 mm. Went. The number of abnormal discharges during sputtering was determined by measuring the number of abnormal discharges for 30 minutes from the start of discharge using the arc generation counting function in a DC power source (model number: RPDG-50A) manufactured by MKS Instruments.

<Confirmation of target cracking>
After the above sputtering, whether or not a crack was generated in the sputtering target was visually observed.
The above results are shown in Table 2 below.

As described above, in any of the sputtering targets of Examples 1 to 11, the average particle size of Nb crushed powder is 70 μm or less, the Sn / Nb particle size ratio is 0.2 to 7, and Sn powder and Nb crushed powder are used. As for the blending ratio (wt%), the mixture obtained by mixing and mixing the Sn powder with the Nb crushed powder at a weight ratio equal to or higher than that is mixed with pressure to obtain a sintered body. As a result, in the sintered body, a structure in which a dispersed phase of Nb was formed in the Sn continuous phase and a shape derived from crushed powder was maintained.
And according to Table 1 and Table 2, it is confirmed that the density ratio and the maximum stress are improved for any of the sputtering targets of Examples 1 to 11, and the frequency of occurrence of abnormal discharge during sputtering is reduced. In addition, no target cracking was observed.

  On the other hand, in the sputtering target of Comparative Example 1, except that the Nb powder is a spherical powder, it is the same as the conditions of the example, but in the obtained sintered body, the spherical powder shape is maintained. As a result, the density ratio and the maximum stress were not improved, and many abnormal discharges were generated, causing target cracks.

As described above, according to the sputtering targets of Examples 1 to 11, high-density and high-strength Sn—Nb sputtering in which the frequency of occurrence of abnormal discharge during sputtering is reduced and the crack resistance of the sputtering target is improved. Since a target and a method for manufacturing the target can be provided, it is suitable for forming a thin film such as a protective layer and a recording layer in an optical disk such as a DVD or a BD, for example, forming a recording layer in a phase change optical disk.

Claims (5)

A sintered body mainly composed of Sn and Nb,
A sputtering target for forming a thin film, wherein Nb forms a dispersed phase in the Sn substrate of the sintered body and maintains a shape derived from crushed powder.   2. The sputtering target for forming a thin film according to claim 1, wherein Nb forming the dispersed phase has an average particle diameter of 70 [mu] m or less. Nb crushed powder and Sn powder are mixed in a weight ratio so that Sn powder is equal to or more than Nb crushed powder and mixed to produce a mixture,
A method for producing a sputtering target for forming a thin film, wherein the mixture is subjected to pressure firing at a temperature lower than the melting point of Sn.   The said Sn powder has an average particle diameter of 0.2-5 times with respect to the average particle diameter of the said Nb crushing powder, The manufacturing method of the sputtering target for thin film formation of Claim 3 characterized by the above-mentioned. The method for producing a sputtering target for forming a thin film according to claim 3 or 4, wherein pressure firing is performed at a pressure of 500 kgf / cm ² or more.