JP3127834B2 - Sputtering target for high dielectric film formation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sputtering target for forming a high dielectric film for forming a thin film for a capacitor such as a semiconductor memory, and more particularly to a sputtering target for forming a high dielectric film with less occurrence of soft errors.

[0002]

2. Description of the Related Art In general, a composite oxide of Ba and Ti (hereinafter referred to as a BaTi composite oxide), Sr and Ti
(Hereinafter, referred to as SrTi composite oxide) and a composite oxide of Ba, Sr, and Ti (hereinafter, BaSr
Sputtering target for forming a high dielectric film having a perovskite structure composed of Ti composite oxide)
It is used for forming a capacitor thin film used for a semiconductor memory or the like.

In order to manufacture these sputtering targets for forming a high dielectric film, first, raw material powders such as BaCO ₃ powder, SrCO ₃ powder and TiO ₂ powder are blended in a predetermined ratio, mixed in a ball mill, and obtained. The mixed powder was put into a MgO crucible and placed in an air atmosphere at a temperature of 1200.
焼 成 1350 ° C., sintering for 3 to 10 hours, and pulverizing with a ball mill to produce a composite oxide powder. The obtained composite oxide powder was repeatedly fired and crushed under the above conditions twice or more, and then subjected to a pressure of 150.
kg / cm ² , temperature: 1200-1350 ° C., 0.5-
Hot pressing is performed for 3 hours to prepare a hot pressed body made of a BaTi composite oxide, a SrTi composite oxide, or a BaSrTi composite oxide. The hot pressed body is machined and finished to a predetermined target shape.

At present, the occurrence of a soft error is radiated from U and Th contained in a high dielectric film having a perovskite structure composed of a BaTi composite oxide, a SrTi composite oxide or a BaSrTi composite oxide obtained by sputtering. It is believed to be due to alpha radiation. Therefore, a sputtering target for forming a high dielectric film in which U and Th are removed from the sputtering target and the total content thereof is limited to 10 ppb or less has been proposed. It is said that no soft error is caused by radiation (see Japanese Patent Application Laid-Open No. 7-70747).

[0005]

However, U and Th are completely removed from the sputtering target to remove U and Th.
Even when the total content of is limited to 10 ppb or less, a soft error due to α-radiation may still occur.

[0006]

Means for Solving the Problems Accordingly, the present inventors have:
As a result of further investigation of this α-radiation source, (a) a large amount of α-radiation is radiated from the BaTi composite oxide high dielectric film containing Ba and the BaSrTi composite oxide high dielectric film. The amount of α-radiation radiated from Ra having a mass number of 226 (hereinafter referred to as ²²⁶ Ra) and radiating from the BaTi composite oxide high dielectric film containing Ba and the BaSrTi composite oxide high dielectric film is set to 0. 01
If it is less than CHP / cm ² , the effect of soft error due to α radiation can be neglected. (C)
The amount of alpha radiation emitted from the high dielectric film is 0.01 CHP
/ Cm ² or less, the BaTi composite oxide and B
The ²²⁶ Ra concentration contained in the sputtering target for forming the high dielectric film made of the aSrTi composite oxide was set to 50 mB.
It has been found that this is achieved by controlling the amount to q / g or less.

The present invention has been made based on these findings. (1) The concentration of ²²⁶ Ra is 50 mBq /
g (preferably 20 mBq / g or less)
And a sputtering target for forming a high dielectric film having a perovskite structure composed of a composite oxide of Ti and
(2) Ba, Sr and Ti having a ²²⁶ Ra concentration of 50 mBq / g or less (preferably 20 mBq / g or less)
Characterized by a sputtering target for forming a high dielectric film having a perovskite structure comprising a composite oxide of the above.

In the present invention, the concentration of ²²⁶ Ra is 50 mBq /
In order to manufacture a sputtering target for forming a high-dielectric film having a perovskite structure composed of a Ba-containing composite oxide having a ²²⁶ Ra concentration of 5 g or less,
Organic Ba salt powder reduced to 0 mBq / g or less, organic Sr
Salt powder and organic Ti salt powder may be used.

[0009] Organic Sr salt powder with a reduced ²²⁶ Ra concentrations below 50 MBq / g can be produced by recrystallizing the organic Sr salt, also, 50MB the ²²⁶ Ra concentration
Although the organic Ti salt powder reduced to q / g or less can be produced by purifying the organic Ti salt by distillation,
There is no way of removing ²²⁶ Ra from organic Ba salt, ²²⁶ R
The a concentration obtained following organic Ba salt powder 50 MBq / g, ²²⁶ the barite screened less Ra, ²²⁶ Ra concentration 50 MBq / g or less of organic Ba salt less barite of ²²⁶ Ra as a starting material ²²⁶ Ra concentration of 50 mB
There is no method other than using an organic Ba salt powder produced using an organic Ba salt of q / g or less as a raw material powder.

The concentration of ²²⁶ Ra thus produced is 5
Organic Ba salt powder reduced to 0 mBq / g or less, organic Sr
The salt powder and the organic Ti salt powder are mixed in a predetermined ratio, dissolved in pure water to form an aqueous solution, the water is evaporated and dried, and then fired in air at 1200 ° C. for 4 hours to produce a composite salt fired body. The obtained composite salt fired body is pulverized into powder, and the powder of the composite salt fired body is used to produce a sputtering target for forming a high dielectric film having a ²²⁶ Ra concentration of 50 mBq / g or less according to the present invention. it can.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

Example α of barite which is a starting material for producing an organic Ba salt
The radiation dose is measured with a gas flow type α-ray
Barite having a linear emission of 0.05 CHP / cm ² or less was selected to obtain barite having a ²²⁶ Ra concentration of 50 mBq / g or less. The barite having a low ²²⁶ Ra concentration is pulverized and mixed with graphite having an α-ray emission of 0.1 CHP / cm ² or less, reduced and roasted, and the obtained roasted product is leached with hot water to produce a Ba sulfide solution. Then, purified carbon dioxide gas was blown into the Ba sulfide solution to precipitate Ba carbonate. The obtained precipitate was taken out by filtration, dried sufficiently, and then heated to 1300 ° C. in the atmosphere to obtain BaO.

Water was applied to this BaO to form BaOH, and acetic acid was further applied to evaporate the water, followed by cooling and crystallization to obtain an acetate. Purification was achieved by repeating the recrystallization of the acetate, and ²²⁶ Ra shown in Table 1 was obtained.
High purity Ba acetate having a content of 50 mBq / g or less, a U content of 1 ppb or less, and a Th content of 1 ppb or less was produced.

Further, high purity Sr acetate was prepared by recrystallizing the Sr acetate acetate, and high purity isopropoxide Ti salt was prepared by distilling and purifying the isopropoxide Ti salt. The high-purity acetic acid Ba thus obtained,
A high-purity acetic acid Sr and a high-purity isopropoxide Ti salt were mixed in a predetermined ratio, then an aqueous solution was formed, and the water was evaporated and dried. Was produced.

This composite oxide is further placed in a ball mill and pulverized to produce a composite oxide powder having an average particle size of 1 to 5 μm, and the obtained composite oxide powder is filled in a graphite mold and heated. Speed: 5 ° C./min, Heating temperature: 1300 ° C., Pressure: 150 ton / cm ² , Holding time: 1 hour, Cooling: Furnace cooling, diameter: 350 m by hot pressing
m, thickness: 6 mm, a hot pressed body made of a high dielectric compound having a composition shown in Table 1 was prepared, and the hot pressed body was machined to obtain a diameter of 300 mm.
mm and thickness: 5 mm of the present invention sputtering targets (hereinafter referred to as the present invention targets) 1 to 5 were produced.

These targets 1 to 5 of the present invention include
^{The 226} Ra concentration was measured by radiochemical analysis and the U and T
h concentration is analyzed by IPC-MS, and α radiation emitted from the targets 1 to 5 of the present invention is further converted to gas flow type α
The measurement was performed with a line measuring instrument, and the results are shown in Table 1.

Comparative Example Ba acetate was prepared by the same method as in the example without sorting barite according to the ²²⁶ Ra concentration, and a comparative sputtering target (hereinafter referred to as comparative example) was prepared in the same manner as in the example except that this acetate was used. (Referred to as targets) 1 to 5 were produced. U contained in these comparative targets 1 to 5,
Th and ²²⁶ Ra concentrations and α-radiation emitted from comparative targets 1 to 5 were measured, and the results are shown in Table 1.

[0017]

[Table 1]

[0018]

From the results shown in Table 1, it can be seen that high purity organic Ba having a ²²⁶ Ra concentration of 50 mBq / g or less was used as a raw material powder.
Salt, and further, high-purity organic Sr salt and organic Ti
Each of the targets 1 to 5 of the present invention prepared using a salt has a ²²⁶ Ra concentration of 50 mBq / g or less and an α radiation dose of 0.01 CPH / cm ² or less, and is prepared using the targets 1 to 5 of the present invention. It can be seen that the occurrence of the soft error due to the high dielectric film is negligible.

However, the comparative targets 1 to 5 whose ²²⁶ Ra concentration exceeds 50 mBq / g have an α radiation dose of 0.01 C
It can be seen that the occurrence of soft errors due to the high dielectric film produced by using this exceeds PH / cm ² cannot be ignored. As described above, the sputtering target for forming a high dielectric film according to the present invention has an extremely small amount of α-radiation, can ignore the occurrence of soft errors, and has excellent industrial effects.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H01L 21/31 H01L 21/31 D 21/8242 27/10 651 27/108 (56) References JP-A-59-199504 (JP) , A) JP-A-7-70747 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 14/00-14/58 C01G 23/00 C01G 25/00-57/00 C04B 35/42-35/51 C01F 11/16 C01B 13/16 H01L 21/203 H01L 21/285 H01L 21/31 H01L 21/8242 H01L 27/108 JICST file (JOIS)

Claims (4)

(57) [Claims] A mass number of Ra of 226 (hereinafter referred to as ²²⁶ Ra)
) Having a perovskite structure comprising a composite oxide of Ba and Ti, wherein the sputtering target has a concentration of 50 mBq / g or less. 2. A sputtering target for forming a high dielectric film having a perovskite structure comprising a composite oxide of Ba, Sr and Ti, wherein the concentration of ²²⁶ Ra is 50 mBq / g or less. 3. The emitted alpha radiation dose is 0.01 CPH.
/ Cm ^Two B according to claim 1, characterized in that:
Perovskite structure composed of composite oxide of a and Ti
A sputtering target for forming a high dielectric film, comprising: 4. The emitted alpha radiation dose is 0.01 CPH.
/ Cm ^Two B according to claim 2, characterized in that:
Perovskite composed of composite oxide of a, Sr and Ti
Target for forming a high dielectric film having a gate structure
To