JPH0822715A - Sputtering target material for forming ferroelectric thin film - Google Patents

Abstract

PURPOSE:To provide a sputtering target material for forming a PZT and PLZT ferroelectric thin film by which dispersion of film thickness is small and the occurrence of soft errors is remarkably reduced. CONSTITUTION:A sputtering target material for forming a PZT and PLZT ferroelectric thin film composed of a sintered body of composite oxide of Pb, Zr and/or Ti or a sintered body of composite oxide of Pb, La, Zr and/or Ti or a sintered body of Pb oxide used together with the sintered bodies as needed, is provided. The content of unavoidable impurity of these sintered bodies is set to be not more than 50ppm, and the content of a radioactive isotope is set to be not more than 50ppb.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric substance of perovskite structure composite oxide (PZT and PLZT) in which the variation of the film thickness is extremely small even if the film thickness is further reduced, and the soft error is not significantly generated in practical use. The present invention relates to a sputtering target material capable of forming a thin film.

[0002]

2. Description of the Related Art Generally, PZT and PLZT ferroelectric thin films having a thickness of 1000 to 5000 angstroms are formed on the surface of a substrate such as single crystal Si or Pt by a sputtering method. Further, the target materials used in the sputtering method are Pb and Zr.
And / or sintered compound oxide of Ti, or Pb
It is also known that it comprises a sintered body of a complex oxide of La and Zr and / or Ti, and, if necessary, a sintered body of a Pb oxide used together with the sintered body as a PbO replenishing source. There is.

[0003]

On the other hand, in recent years, various electro-optical devices have been remarkably improved in performance, reduced in size, and reduced in weight. Along with this, PZT and PLZT ferroelectric thin films constituting them have been further improved. However, when the ferroelectric thin film having a film thickness of 1000 angstroms or less is formed by using the above conventional sputtering target material, it is necessary to avoid the variation in the film thickness from appearing. I can't.

[0004]

Therefore, the present inventors have
From the viewpoints described above, in order to form a PZT and PLZT ferroelectric thin film in which the film thickness does not vary even if the film thickness is reduced by one step, attention is paid particularly to the sputtering target material, and as a result of the research, the above-mentioned conventional sputtering is performed. If the content of unavoidable impurities contained in the target material (usually 200 ppm or more) is reduced to 50 ppm or less, the thickness of the PZT and PLZT ferroelectric thin films formed on the surface of the substrate is reduced to 1000 angstroms or less. In addition, the variation in film thickness is extremely small, and the content (usually 500 ppb or more) of U and Th and the radioactive isotopes (hereinafter referred to as isotopes) mainly composed of these decay nuclides contained in them is 50 ppb or less. Is set, the isotope content of the PZT and PLZT ferroelectric thin films formed ( 50 is usually 500 ppb or more)
ppb or less, and as a result, the ferroelectric thin film has a radioactive α
The number of particles counted was 0.01 cph / cm ² or less, and the research results were obtained that the occurrence of soft errors due to this was significantly suppressed.

The present invention has been made based on the above-mentioned research results, and contains Pb, Zr and / or T.
Sintered body of complex oxide of i, or Pb, La, and Zr
And / or a sintered body of a composite oxide of Ti, and a sintered body of a Pb oxide which is used together with the sintered body if necessary (PZT and P.
LZT) sputtering target material for forming a ferroelectric thin film, the content of inevitable impurities in each of the three types of sintered bodies used as the target material is 50 ppm.
The characteristics are characterized in that the film thickness of the ferroelectric thin film is made uniform and the occurrence of soft error is suppressed by making the content below and the content of the isotope not more than 50 ppb. In the target material of this invention,
The content of the unavoidable impurities is set to 50 ppm or less because the desired film thickness cannot be made uniform if the content exceeds the above, as described above, and the content of the isotope is also set to 50 ppb or less. The reason is that if the content exceeds this range, soft errors due to the formed ferroelectric thin film will rapidly occur frequently.

[0006]

EXAMPLES Next, the target material of the present invention will be specifically described by way of examples. As raw material powders, various highly purified Pb oxides (hereinafter referred to as PbO) having the impurity content, isotope content (total quantitative analysis value of U and Th), and average particle size shown in Tables 1 and 2 respectively. ) Powder, highly purified Zr oxide (hereinafter referred to as ZrO ₂ ) powder, highly purified Ti
Oxide (hereinafter referred to as TiO ₂ ) powder, highly purified La oxide (hereinafter referred to as La ₂ O ₃ ) powder, and various commercially available PbO powder, ZrO ₂ powder, TiO ₂ powder,
And La ₂ O ₃ powder were prepared. The above-mentioned highly purified P
Each of the bO powders has a high purity (5 to 5) obtained by electrolytic refining.
6N) metal Pb is melted in the air, stirred and oxidized to PbO, and further oxidized in the air at a temperature of 600 ° C. for a predetermined time to be formed.
₂ powder and high-purity TiO ₂ powder are high purity (5 to 6 N) metal Zr and metal Ti to ZrCl _{4 respectively.}
And TiCl ₄ are formed, and this is reacted with pure water to form a precipitate, which is heated in the air at a temperature of 600 ° C. to form a precipitate, and the highly purified La ₂ O ₃ powder is High purity (5-6N) obtained by electrolytic refining
The metal La is dissolved in concentrated hydrochloric acid and heated to form a precipitate, which is heated in the air at a temperature of 600 ° C. to form a precipitate.

Next, these raw material powders were blended in the proportions shown in Tables 1 and 2 and mixed in a ball mill for 1 hour, and then heated at atmospheric temperature for 4 hours at 900 ° C. and heated again in a ball mill. In the crushed state, the temperature:
By hot pressing under the conditions of 900 ° C., pressure: 200 kg / cm ² , time: 4 hours, diameter: 100 mm × thickness:
The target materials 1 to 6 of the present invention made of a 5 mm disk-shaped sintered body
And the conventional target materials 1-6 were manufactured, respectively. Then, regarding the various target materials obtained as a result,
Inevitable impurity content and isotope content (U and T
The total quantitative analysis value of h) was measured, and the measurement results are shown in Table 3. In addition, the above-mentioned highly purified PbO powder and commercially available PbO
An auxiliary target material composed of a highly purified PbO sintered body as a PbO replenishing source and a commercially available PbO sintered body was also manufactured by hot pressing each of the powders under the above conditions.

Next, the above-mentioned target materials 1 to 6 of the present invention are used.
Using conventional target materials 1 to 6 and, if necessary, the above auxiliary target materials in a high frequency magnetron sputtering apparatus, substrate: diameter 10 cm, single crystal Si wafer of thickness 0.5 mm, atmosphere gas composition: molar ratio Then, Ar: O ₂ = 9: 1, atmospheric pressure: 1 Pa, substrate surface temperature: 600 ° C., sputter output: 500 W, distance between target material surface and substrate surface: 5 cm, sputtering time: between 1 and 7 minutes Ferroelectric thin films having the target film thicknesses shown in Table 3 were formed on the surface of the substrate by sputtering for a predetermined time. For the ferroelectric thin film formed as a result of this, the change in film thickness at the center of the substrate: 5 mm was measured using a film thickness measuring device, the maximum film thickness and the minimum film thickness were picked up, and further gas flow proportional counting was performed. Using a tube, radioactive α
Particle counts were measured. The results are shown in Table 3.

[0009]

[Table 1]

[0010]

[Table 2]

[0011]

[Table 3]

[0012]

From the results shown in Tables 1 to 3, the ferroelectric thin films formed by using the target materials 1 to 6 of the present invention are
Even if the film thickness is 1000 angstroms or less, the variation in the film thickness is extremely small compared with the conventional target materials 1 to 6, and the count number of radioactive α particles is 0.01 cph / cm ² or less. It is clear that it is relatively significantly lower. As described above, according to the sputtering target material of the present invention, it is possible to form the PZT and PLZT ferroelectric thin films in which the film thickness is uniform and the occurrence of soft errors is significantly suppressed.

Claims (4)

[Claims] 1. A sputtering target material for forming a ferroelectric thin film of a perovskite structure complex oxide comprising a sintered body of Pb and a complex oxide of Zr and / or Ti, the content of inevitable impurities in the sintered body. Is 50 ppm or less, and the contents of U and Th and radioisotopes mainly containing these decay nuclides are 50 ppb or less, and a sputtering target material for forming a ferroelectric thin film. 2. Pb, La, Zr and / or T
In a sputtering target material for forming a ferroelectric thin film of a perovskite structure composite oxide, which comprises a sintered body of a complex oxide of i, the content of unavoidable impurities in the sintered body is 50 ppm or less, and U and Th, and A sputtering target material for forming a ferroelectric thin film, characterized in that the content of a radioisotope mainly composed of the decay nuclide is set to 50 ppb or less. 3. A sputtering method for forming a ferroelectric thin film of a perovskite structure composite oxide, which comprises a sintered body of Pb and a composite oxide of Zr and / or Ti and a sintered body of a Pb oxide used together therewith. In the target material, the content of unavoidable impurities in each of the above sintered bodies is 50 pp.
m or less, and the contents of U and Th, and radioisotopes mainly composed of these decay nuclides are 50
A sputtering target material for forming a ferroelectric thin film, which has a ppb or less. 4. Pb, La, Zr and / or T
In a sputtering target material for forming a ferroelectric thin film of a perovskite structure complex oxide, which comprises a sintered body of a complex oxide of i and a sintered body of a Pb oxide used together with the sintered body, inevitable impurities of both the sintered bodies Content of 50 pp
m or less, and the contents of U and Th, and radioisotopes mainly composed of these decay nuclides are 50
A sputtering target material for forming a ferroelectric thin film, which has a ppb or less.