JPH08232061A - Forging method of high-purity titanium material - Google Patents

Abstract

(57) [Summary] [Objective] To provide a method for forging a high-purity titanium material for producing a titanium target excellent in the uniformity of the sputtered film thickness. [Structure] Primary forging is performed by combining forging and upsetting so that the wrought forming ratio becomes 5 or more at a temperature equal to or higher than the transformation point. After that, secondary forging processing is performed by combining forging and upsetting so that the wrought forming ratio becomes 5 or more at a temperature below the transformation point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forging a high-purity titanium material used for producing a titanium target for sputtering.

[0002]

2. Description of the Related Art In the manufacture of semiconductor devices, in order to form wiring materials and barrier metals on semiconductor elements,
A thin film forming technique of high-purity titanium by sputtering is used. The high-purity titanium target used for this sputtering is usually manufactured through the processes of casting, forging, rolling, and heat treatment.

By the way, in such a titanium target for sputtering, in order to make the sputtering film thickness uniform, it is necessary to make the crystal grains fine. For this reason, the shape is adjusted by forging and rolling, and rolling is performed. Also, the crystal grain size is controlled by recrystallization by heat treatment.

Here, forging has heretofore been carried out mainly for shaping a cast material, and in the production of a titanium target for sputtering, it has been carried out mainly for adjusting the shape of the cast material to a shape suitable for rolling. Was also used in the destruction of the casting structure. For example, in JP-A-62-286639, although it is not for producing a sputtering target, in the forging of a titanium alloy, a wrought forming ratio of 5 is obtained at a temperature above the transformation point due to repeated forging and upsetting.
It is shown that the crystal grains are refined when the forging of 8 to 8 is performed and the forging of 3 to 4 is performed at the temperature below the transformation point.

[0005]

Forging by repeating such forging and upsetting is effective for breaking the cast structure even in the case of high-purity titanium. However, even if the forged material of high-purity titanium is rolled and heat-treated to be used as a sputtering target, the effect on the uniformity of the sputtered film thickness is small and an effective effect cannot be obtained.

An object of the present invention is to provide a method of forging high-purity titanium for producing a titanium target for sputtering which has a high effect of making the film thickness uniform.

[0007]

In order to manufacture a titanium target for sputtering having a high film thickness uniforming effect, the present inventors have paid attention to the forging process and repeated the experiment. As a result, forging by repeating forging and upsetting, particularly forging at a temperature below the transformation point is important in the production of a titanium target for sputtering.
The reason why the repeated forging shown in Japanese Patent Laid-Open No. 2-280639 does not sufficiently function when manufacturing a sputtering target is that forging at a temperature below the transformation point is insufficient, and forging at a temperature below the transformation point. It was revealed that the sputtering target manufactured from the forged material exhibits a high film thickness uniformizing effect by making the processing equal to or greater than the forging at a temperature equal to or higher than the transformation point.

The present invention has been made on the basis of such knowledge, and in a forging process of a high-purity titanium material for producing a titanium target for sputtering, forging is performed so that the wrought forming ratio becomes 5 or more at a temperature of a transformation point or higher. After performing the primary forging process that combines elongation and upsetting once or more, perform the secondary forging process that combines forging and upsetting so that the wrought forming ratio becomes 5 or more at the temperature below the transformation point. The gist is a method of forging a high-purity titanium material, which is characterized by performing the above.

[0009]

[Function] With the forging method of the present invention, high-purity titanium is 4N5
(99.995%) or higher. Further, the wrought forming ratio is a value obtained by summing the respective cross-sectional area ratios in forging and upsetting as shown in FIG. Then, in the forging method of the present invention, the primary forging process and the secondary forging process with the forging ratio of 5 or more are performed.

The primary forging process aims to destroy the cast structure. Therefore, this processing is performed at a temperature equal to or higher than the transformation point at which the workability is good. However, an excessively high forging temperature accelerates the oxidation of the material surface. Desirable forging temperature is 900-9
50 ° C. The wrought forming ratio in the primary forging process is set to 5 or more because if it is less than this, the fracture of the cast structure is insufficient. However, in this processing, the degree of processing is not so significant as in the secondary forging processing described later, and a large degree of processing causes worse economic efficiency. Therefore, the upper limit of the molding ratio is preferably 10 or less, and the number of times of processing is One time is enough.

The secondary forging process aims to accumulate working strain. In the primary forging process, since the process is performed at a temperature equal to or higher than the transformation point with good workability, the cast structure can be destroyed but the process strain cannot be accumulated. Accumulation of processing strain in the secondary forging process promotes recrystallization in the subsequent rolling and heat treatment steps, and the crystal grains are made finer, so that the sputtering target has excellent film thickness uniformity. Will be things. In order to accumulate the working strain, the casting temperature in the secondary forging is carried out at a temperature below the transformation point where workability is poor. However, if the forging temperature is too low, cracking may occur during processing, so the lower limit of the forging temperature in the secondary forging is preferably 500 ° C. or higher. As the workability, a minimum wrought forming ratio of 5 or more is required, 10 or more is desirable, and 20 or more is more desirable. However, considering economy, 10 to 20 is desirable, and 15 to 20 is particularly desirable. The number of times of processing is preferably 2 or more, and particularly preferably 3 times.

The use of a combination of forging and upsetting in the primary forging process and the secondary forging process is that in the primary forging process, the casting structure is destroyed by increasing the wrought forming ratio to make the macrostructure uniform. This is because in the secondary forging process, the work strain is accumulated by increasing the wrought forming ratio, and the crystal grains in the subsequent rolling and heat treatment steps are refined.

[0013]

EXAMPLES Examples of the present invention will be shown below, and the effects of the present invention will be clarified by comparison with Comparative Examples.

Impurities shown in Table 1 are 99.995% (4N
The high-purity titanium ingot of 5) was forged under the conditions shown in Table 2. With respect to the forged material under each condition, macrostructure determination of cross sections perpendicular to the forging and upsetting directions was performed. The acceptance criterion for macrostructure determination was 5 mm or less in terms of the maximum length of crystal grains.

[0015]

[Table 1]

[0016]

[Table 2]

The forged material under each condition was rolled at a heating temperature of 300 ° C. and a rolling reduction of 50%, and then heat-treated at 500 ° C. to obtain a sputtering target. The crystal grain size of the target was measured by the cutting method. Moreover, sputtering was performed using each target and the film thickness distribution was measured. The average film thickness of the thin film formed by sputtering was about 500 Å, and the film thickness distribution was represented by (maximum film thickness-minimum film thickness) / (average film thickness × 2) × 100 (%).

In No. 1, since the combination of forging and upsetting was not adopted in the primary forging process and the secondary forging process was not performed, the macrostructure of the forged material was rejected and subjected to rolling and heat treatment. Unrecrystallized grains remained on the target, and the sputtering film thickness distribution was 12%. Even if secondary forging is performed as in Nos. 2 and 3, the sputtered film thickness is not so uniform.

In Nos. 4 and 5, since forging and upsetting were combined in the primary forging process, the macrostructure of the forged material passed, but unrecrystallized grains remained on the target,
The distribution of sputtered film thickness was the same as that of No. 1. N
Even if the secondary forging is carried out as shown in o.6, if it is insufficient, the sputtered film thickness is not so uniform even if the degree of processing in the primary forging is increased.

On the other hand, in Nos. 7 to 12, since forging and upsetting were combined in the primary forging process and the secondary forging process, and sufficient processing was performed in the secondary forging process, the forging material was The macrostructure of No. 2 was acceptable, and fine crystal grains free of unrecrystallized grains were obtained even in the target.

[0021]

As described above, the method of forging a high-purity titanium material according to the present invention comprises the steps of primary forging above the transformation point, followed by sufficient secondary forging below the transformation point.
It is possible to provide a high-quality titanium target for sputtering with excellent uniformity of the sputtering film thickness, which contributes to high integration of semiconductor devices.

[Brief description of drawings]

FIG. 1 is a diagram showing a combined processing of forging and upsetting and a wrought forming ratio in the processing.

Claims (1)

[Claims] 1. In a forging process of a high-purity titanium material for producing a titanium target for sputtering, a primary process in which forging and upsetting are combined so that a wrought forming ratio becomes 5 or more at a temperature equal to or higher than a transformation point. After performing the forging process once or more, the secondary forging process combining the forging and upsetting is performed once or more so that the wrought forming ratio becomes 5 or more at the temperature of the transformation point or lower. Method of forging titanium material.