JPH0867974A - Sputtering target for forming thin platinum film - Google Patents

Abstract

PURPOSE: To provide a sputtering target uniform in thickness and radiating a small amt. of α-particles. CONSTITUTION: This sputtering target contains 0.5-5ppm, in total, of one or more among Fe, Ni and Co and <=5ppb, in total, of U, Th and radioactive isotopes mainly including decayed nuclides of U and Th in Pt of >=99.999wt.% purity. When this target is used, a thin Pt film not causing a soft error due to α-rays can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sputtering target for forming a Pt thin film as an electrode on the surface of a capacitor thin film such as a semiconductor memory.

[0002]

2. Description of the Related Art Recently, in a semiconductor memory such as 64 MDRM, a BaTi complex oxide thin film having a perovskite structure, a SrTi complex oxide thin film, and a BaSrTi thin film.
Research is underway to use composite oxide thin films as capacitor thin films for semiconductor memories and the like.

BaTi having the perovskite structure
Complex oxide thin film, SrTi complex oxide thin film, BaSrT
When the i-composite oxide thin film is used as a capacitor for semiconductor memory, it is used as a capacitor electrode at 99.99%.
A high purity Pt thin film of ˜99.999% is used. This high-purity Pt thin film is formed by sputtering using a high-purity Pt target.

[0004]

Since Pt is expensive, there is a demand for the Pt thin film to be as thin as possible, and there is a demand for the Pt thin film to have a thickness of 1000 angstroms or less. However, when a Pt thin film having a thickness of 1000 angstroms or less is formed by sputtering using a conventional high-purity Pt target, the film thickness becomes nonuniform, which is not satisfactory as a capacitor electrode.

Further, normal Pt contains 50 ppb of U, Th and radioisotopes mainly composed of these decay nuclides.
If the Pt thin film obtained by this ordinary Pt target is used as the electrode of the capacitor, the α rays emitted from the Pt thin film affect the capacitor, and 64 M or It could not be used in a DRAM of 256M or more.

[0006]

Therefore, the present inventors have
Thickness: Even if a Pt thin film having a thickness of 1000 angstroms or less is formed, research was conducted to develop a Pt target that can obtain a Pt thin film having a uniform film thickness and free of soft error due to α rays. As a result, Fe, Ni, A Pt target containing 0.5 to 5 ppm in total of one or more of Co and 0.5 to 5 ppm in total, and U and Th, and the content of radioisotopes mainly containing these decay nuclides to 5 ppb or less is used. When sputtering, the film thickness is uniform and α
We have found that a Pt thin film can be obtained without soft errors due to lines.

The present invention has been made on the basis of such findings, and is one of Fe, Ni and Co or two of Fe, Ni and Co.
Purity: 99.999 containing 0.5 to 5 ppm in total of 5 or more species and having a radioisotope content of 5 or less and U and Th and mainly these decay nuclides.
It is characterized by a sputtering target for forming a Pt thin film, which is composed of Pt in an amount of at least wt%.

In the sputtering target for forming a Pt thin film of the present invention, the total content of one or more of Fe, Ni and Co is limited to 0.5 to 5 ppm.
If these metals are less than 0.5 ppm, the thickness obtained by sputtering: Pt of 1000 angstroms or less
It is not preferable because the variation in the thickness of the thin film becomes large,
On the other hand, even if the content exceeds 5 ppm, the variation in the thickness of the Pt thin film becomes large, which is not preferable.

Further, the contents of U and Th contained in the sputtering target for forming a Pt thin film of the present invention and the content of radioisotopes mainly containing these decay nuclides are 5 p.
The reason for setting it to pb or less is that if it is 5 ppb or less, the emission amount of α rays becomes 0.001 CPH / cm ² or less, and the soft error due to α rays can be ignored.

[0010]

【Example】

A commercially available Pt plate having a purity of 99.9% by weight and a thickness of 1 mm was cut into a size of length: 5 cm, width: 20 cm, and this was used as an anode electrode under the following conditions: Molten salt composition: NaCl: 24.3% , LiCl: 39.
2%, KCl: 36.5%, molten salt temperature: 500 ° C. ± 10 ° C., voltage: 0.1 V, current: 5 A, molten salt electrolysis was repeated 3 times for purification, and the purity of Pt was shown in Tables 1 to 1. 2, the contents of U and Th, and radioisotopes mainly containing these decay nuclides were reduced to the values shown in Tables 1 and 2.

High purity P containing U and Th, and radioisotopes mainly containing these decay nuclides and having a small content.
After further melting t in vacuum and adding a trace amount of one or more of Fe, Ni and Co, a diameter: 100 mm,
A slab with a thickness of 20 mm was made, and this slab was hot-rolled to a thickness of 6 mm, which was machined to a diameter of 100.
mm, thickness: 6 mm, and finished into a circular plate having a thickness of 6 mm to prepare sputtering targets 1 to 13 for forming a Pt thin film of the present invention (hereinafter referred to as Pt target of the present invention).

On the other hand, for comparison, in Example 1, high-purity Pt which had been zone-melted and refined to reduce the contents of U and Th, and radioisotopes mainly containing these decay nuclides, was used.
One or more of e, Ni, and Co is 0.5 to 5
Sputtering targets for comparative Pt thin film formation (hereinafter referred to as comparative Pt targets) 1 to 6 were prepared with or without addition so as to fall outside the range of ppm, and for conventional Pt thin film formation consisting of ordinary high-purity Pt A sputtering target (hereinafter referred to as a conventional Pt target) was produced.

These Pt targets 1 to 13 of the present invention, comparative Pt targets 1 to 6 and conventional Pt targets were soldered to an oxygen-free copper cooling plate using an In-Sn eutectic solder, and then used in a normal high frequency magnetron sputtering apparatus. Mounting, diameter: 100 mm, thickness: 0.5 mm S
Sputtering was performed on the i plate under the following conditions: atmosphere gas: Ar, atmosphere pressure: 1 pa, Si plate surface temperature: 500 ° C., distance between target and Si plate: 5 cm, and diameter set in high frequency magnetron sputtering device: Table 3 ~ on a 100 mm Si plate
The actual maximum Pt formed on the surface of the central portion of the Si plate by forming a Pt thin film so as to have the target Pt film thickness shown in Table 4
The film thickness and the minimum Pt film thickness were obtained, and the results are shown in Tables 3 to 4.
It was shown to.

Further, by using a gas flow proportional counter, the Pt targets 1 to 13 of the present invention and the comparative Pt targets 1 to 1 are used.
6 and conventional Pt target α-ray particle counts were measured and the results are shown in Tables 3-4.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

[Table 4]

[0019]

From the results shown in Tables 1 to 4, Fe,
One or two or more of Ni and Co in total of 0.5 to
The difference between the highest Pt film thickness and the lowest Pt film thickness formed by the Pt targets 1 to 13 of the present invention containing 5 ppm and U and Th and the content of radioisotopes mainly containing these decay nuclides is 5 ppb or less. In comparison with the difference between the maximum Pt film thickness and the minimum Pt film thickness formed by the conventional Pt target, the amount of α particles emitted by the Pt targets 1 to 13 of the present invention is emitted by the conventional Pt target. Since the amount of radiation of the α particles is extremely small, the thickness of the Pt thin film formed by the Pt targets 1 to 13 of the present invention is more uniform than that of the Pt target formed by the conventional Pt target, and α It can be seen that the radiation dose of the particles is extremely low.

However, if Fe is out of the condition of the present invention,
Comparative Pt targets 1 to 6 (shown with an asterisk in Table 2) containing one or more of Ni and Co in total may have a non-uniform Pt thin film thickness. I understand.

Therefore, when the Pt sputtering target of the present invention is used, a Pt thin film having a more uniform film thickness and less α-ray emission than the conventional Pt sputtering target can be obtained, which is excellent as a capacitor electrode of a semiconductor memory and is soft. This is an industrially excellent effect such that an error-free semiconductor memory can be provided.

Claims (1)

[Claims] 1. A radioisotope content containing 0.5 to 5 ppm in total of one or more of Fe, Ni, and Co, and U and Th, and mainly these decay nuclides. The sputtering target for Pt thin film formation is characterized by comprising Pt in an amount of 99.999% by weight or more with a purity of 5 ppb or less.