JPS63238268A - Production of target for sputtering - Google Patents

Abstract

PURPOSE:To produce a target for forming a magnetic thin film having superior magnetic characteristics by melting a specified alloy in vacuum, solidifying the molten alloy in a casting mold in one direction to make an ingot and forging the ingot from the solidification direction to form a fine isometric crystal structure. CONSTITUTION:A magnetic alloy based on at least one among Fe, Ni and Co as magnetic metals is melted in vacuum or in an inert gaseous atmosphere. The molten alloy is poured into a ceramic casting mold and solidified from the top to the bottom in one direction to make an ingot and the upper and lower edges of the ingot are removed by cutting. The resulting ingot consists of uniform columnar crystals having + or -0.1% variation of compsn. in a plane intersecting the solidification direction. The ingot is then forged by pressing from the solidification direction to convert the columnar crystals into fine isometric crystals. By the forging, the ingot is made flat and a target for forming a superior magnetic thin film by sputtering is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a target suitable for sputtering used in manufacturing a magnetic thin film.

[Conventional technology]

Thin film functional materials are increasingly being used not only as semiconductor thin films but also as conductors, dielectric thin films, magnetic films, superconducting films, and optical functional films in various electronics and devices. In particular, the growth of magnetic thin films has been remarkable in recent years. This is an essential technology for achieving high recording density.

Conventional magnetic heads are made of Ni-Zn ferrite or Mn-
It was made by sintering Zn-based ferrite, then machining it and winding it.

However, there were the following problems. First, since ferrite is used, the magnetic permeability is low in the high frequency range, and a high read voltage cannot be obtained. Furthermore, the cutting and processing limit of ferrite is thought to be 25 to 30 μm, and the track width is determined by this processing limit dimension. Furthermore, the recording wavelength depends on the core thickness and the gap length at the tip, and it is difficult to make it even shorter considering the current processing accuracy.

Improving recording density requires shortening track width and recording wavelength.

In order to compensate for the above-mentioned drawbacks, it is thought that the trend toward thinner magnetic films will increase in the future.

On the other hand, methods for manufacturing these magnetic thin films include sputtering, vapor deposition, and plating, but the sputtering method is superior because of its uniformity of film composition, ease of composition control, and high reliability of film formation.

The required characteristics of a target used for sputtering include uniform composition (±0.1% or less), fine crystal grains, and few impurities. In addition, at the mass production stage, it is desired to reduce manufacturing costs, and as a result, targets as large as possible are required, and currently targets with a diameter of 2
A disk above 0 μm is required.

The above-mentioned sputtering target is generally produced by casting into a mold with a predetermined shape, and finishing the resulting ingot into the predetermined shape by cutting, etc., or by hot working or hot working the ingot. There is a method of cutting and grinding the obtained ingot into a predetermined shape by cold working, or a powder metallurgy method in which the obtained ingot is crushed into powder, press-formed, and then sintered to form a predetermined shape. Kaisho 61-60803
, JP-A-61-91336, JP-A-60-96738
).

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, little consideration was given to the method of melting and processing the target, and there were problems with target segregation and compositional variations between target lots.

In order to manufacture a target with a diameter of 201 mm or more, it is necessary to prepare an ingot of a larger size.

With conventional methods, compositional fluctuations are large due to material segregation.

±0.1 required for sputtering target
It was impossible to keep the composition variation within %.

In addition, the method of pulverizing the melted material and then sintering it can suppress compositional fluctuations, but the oxidation of the pulverized material or oxygen adhering to the surface may mix in as impurities. In addition, the manufacturing process was complicated and had poor productivity, such as sieving the powder and sintering in a reducing atmosphere to remove mixed oxygen.

As described above, magnetic thin films sputtered using sputtering targets manufactured by the conventional method have many variations in magnetic properties, and cannot be used in applications requiring high reliability.

An object of the present invention is to provide a method for producing a sputtering target having a uniform composition, fine crystal grains, and few impurities by adding a casting process to a unidirectional solidification method.

[Means for solving problems]

In the production of large ingots with a diameter of 20 CII+ or more, it is extremely difficult to keep the composition variation range within ±0.1%. It is thought that as the ingot becomes larger, the solidification interface becomes irregular, causing solute convection and heat convection, resulting in segregation.

Therefore, it can be seen that segregation can be suppressed by making the solidification interface horizontal. For this purpose, unidirectional solidification from below is suitable. It is said that the height of the ingot needs to be 50mm or more for unidirectional solidification, but the thickness of the target used as a product is around 10mm, so it is necessary to produce a unidirectionally solidified ingot with a large diameter. is extremely uneconomical. Therefore, it can be seen that it is economically advantageous to manufacture a unidirectionally solidified ingot with a small diameter and a high height, and then cast it into a predetermined shape.

However, as a result of examining the forging direction of a unidirectionally solidified ingot, it became clear that by removing the top and bottom ends of the unidirectionally solidifying ingot and heat-forging it, it could be forged into the desired shape without causing the above cracks. Ta.

The above purpose is to dissolve Fe, N, dissolved in vacuum or inert gas.
A molten alloy based on i, Co is deoxidized in the same crucible, then poured into a heated mold, solidified in one direction from below to produce a one-way solidified ingot, and the upper and lower ends are cut. This is achieved by heat forging after removal.

[Operation] A sputtering target of a predetermined shape is manufactured by the method shown in FIG. Impurities are removed in the first and second steps. The third step is to make the composition uniform, and the fourth step is to form fine equiaxed crystals. The amount of oxygen contained is lowered to 30 ppm by removing impurities in the first and second steps. As shown in FIG. 2, if it exceeds 30 ppm, the coercive force of the film increases significantly, deteriorating the magnetic properties of the film. Therefore, a two-step deoxidation treatment is performed to effectively remove the oxygen contained in the molten metal. This is done by adding elements that easily combine with oxygen, such as C, AQ, Si, and Ca, either singly or in combination of two or more.

This addition causes the oxygen in the molten metal to float to the surface in the form of oxides or gas. The amount of addition is such that the oxygen content reacts with the added element to sufficiently form an oxide or the like. By this method, it is possible to reliably reduce the amount of oxygen in the alloy to 30 ppm or less.

Next, composition uniformity in the third step will be described.

The molten metal whose oxygen content has been reduced to 3 Qppm or less by the above method is forged into a prepared heating mold and unidirectionally solidified. The heating temperature of the mold may be 1200°C or higher, but more than half of the height of the mold is above the liquidus temperature of the alloy, and the upper end of the mold is heated above the liquidus temperature until the end of solidification. This is desirable.

At this time, any method of heating the mold may be used as long as it can be heated above the above temperature, such as an electric resistance furnace, high frequency heating using a susceptor, or an exothermic mold.

Ceramic molds or alumina molds are suitable for the molds used, as they do not react with the molten metal and do not contain oxygen.

Under the above heating conditions, the unidirectional solidification rate is 150 cs/h or less as shown in Figure 3, and the composition fluctuation width can be suppressed to ±0.1% or less without generating cavities. It is possible to obtain directionally solidified ingots.

The produced unidirectionally solidified ingot has columnar crystals and is very uniform in composition, but the crystal grains are very large at 10 nm. If sputtering is performed in a state where crystal grains are large, it is difficult to obtain a uniform film thickness. The reason for this is that each crystal grain has a different plane orientation, so the sputtering rate differs. As a result, if the crystal grains are large, the rate at which they are sputtered differs, making it difficult to achieve a uniform film thickness. Therefore, it is necessary to perform sputtering using a target made into a fine equiaxed product by forging.

The directionally solidified ingot is forged to form fine equiaxed crystals. For forging, after removing both ends and the outer periphery of the ingot, repeated forging is performed above the recrystallization temperature to form fine equiaxed crystals. By raising the temperature above the recrystallization temperature, recrystallization nuclei are generated, and it is possible to make fine equiaxed crystals by repeated processing. The reason why the ingot before forging has columnar crystals is because it is impossible to keep the composition within ±0.1% with equiaxed products, and unidirectional columnar products are essential for uniform composition.

〔Example〕

[Example 1] An example of the present invention is shown in FIG.

A permalloy target with a diameter of 3 Qcm and a thickness of 9 nwn was manufactured by the method described above.

Approximately 7.6 kg of pure Ni and approximately 1.6 lcg of pure Fe were placed in an aluminum crucible and subjected to high frequency melting in a vacuum of 10'' Torr. Immediately after pouring the metal into the deoxidized and heated ceramic mold, the mold was pulled downward at a rate of 20 cm/h.
A directionally solidified ingot was produced. It was then hot forged and finished into a machined target.

The composition variation of the example product was ±0.08. The amount of oxygen at that time was 8 to 10 ppm at less than wt%. The size of the crystal grains was 0.1 to 0.5 m. Table 1 shows a comparison with conventional products.

Table 1 [Example 2] Shows the target surface after sputtering with the developed target. Developed product 1 has very fine crystal grains. In comparison, the target sputtering surface of the conventional product is 5
~10 nm, which is approximately the same size as before sputtering. From this sputtered surface, it is expected that the resulting thin film will be more uniform if the developed target is used as described above.

[Example 3] Applying the developed method to a Co-Ni-Fe alloy, Targera 1~ with a diameter of 30 holes and a thickness of 9 m was manufactured. The manufacturing conditions are the same as in Example 1.

The manufactured target had a uniform oxygen content of 6PPm*composition variation range of ±0.1 wt%, and a uniform crystal grain size of around 0.5 m.

[Example 4] Permalite Gera 1 to Sputter materials produced by the method of the present invention were able to significantly reduce total impurities compared to conventional products, especially in ○・CIS and Co.

Table 2 Unit: ppm [Effects of the Invention] According to the present invention, it is possible to produce a fine equiaxed crystal sputtering target with less impurities and a composition within ±0.1%, which has excellent properties. It becomes possible to create a magnetic film with

[Brief explanation of drawings]

Figure 1 is a diagram showing the manufacturing process of the target, Figure 2 is a graph showing the relationship between the amount of oxygen in the target and the coercive force of the magnetic film manufactured by sputtering using the target, and Figure 3 is the width of composition variation. Graph showing the relationship between and solidification rate, 4th
The figure is a graph showing a comparison of compositional fluctuations between a target manufactured according to the present invention and a conventional target. Oxygen amount (PPm) in Figure 2 - Figure 3 (CTn7h) (Medium; ()

Claims (1)

[Claims] 1. A molten alloy based on one of Fe, Ni, and Co is unidirectionally solidified from the bottom to the top, and the solidification rate is controlled, so that the composition variation in the cross section with respect to the solidification direction is ±0.1.
% or less, and then forging the ingot by applying pressure from the direction of solidification to destroy columnar crystals and make fine equiaxed crystals. Features: A manufacturing method for sputtering targets.