JPH11302837A - High purity iridium material for thin film formation, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high purity Ir material suitably used for a high purity Ir thin film forming material such as sputtering target and reduced in the occurrence of particles at the time of sputtering. SOLUTION: Relating to the high purity Ir material for thin film formation, the content of an alkali metal element is <=1 ppm, and the contents of radioactive elements are <=10 ppb, respectively, and further, the contents of carbon and gas component elements are <=100 ppm. This material can be manufactured by adding a metal which forms an alloy together with Ir and dissolves in acid to an Ir raw material to produce an Ir alloy, leaching the Ir alloy with acid or acid and alkali to remove the components other than Ir by dissolution, and subjecting the resultant Ir residue to degassing treatment and then to electron beam melting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a MOS-ULSI
High-purity Ir material which can be used for forming a thin film such as an upper or lower electrode material of a ferroelectric capacitor and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, in the manufacture of semiconductor memories, a semiconductor device such as silicon has
BaTi composite oxide, SrTi composite oxide, or B
It has been studied to use a ferroelectric thin film such as aSrTi composite oxide as a capacitor. Studies have been made on forming an Ir thin film by sputtering as a material for the upper or lower electrode of such a ferroelectric capacitor thin film. For semiconductor members formed by sputtering, in order to guarantee reliable semiconductor operation performance,
It is important that semiconductor devices contain minimal harmful impurities. That is, it is necessary to remove impurities such as (1) alkali metal elements such as Na and K, (2) radioactive elements such as U and Th, and (3) heavy metal elements such as Fe and Ni. Alkali metal elements such as Na and K easily move in the insulating film, and MOS-ULS
It causes deterioration of I interface characteristics. Radioactive elements such as U and Th cause α-rays emitted from these elements to cause soft errors in the element. In addition, heavy metals such as Fe and Ni also cause troubles at the interface joint.

[0003] In general, as an industrial production method of Ir, for example, a method of purifying Ir, which is made into a solution by an alkali melting method or the like, by a solvent extraction method or the like is used. However, the commercially available Ir powder manufactured by such a method contains a large amount of alkali metals such as Na and K and radioactive elements such as U and Th, and is unsatisfactory as an electrode material for a ferroelectric capacitor. Met. In addition, for example, Japanese Patent Application Laid-Open
No. 41131 describes a method for producing a high-purity Ir sputtering target, which comprises subjecting an Ir raw material to electron beam melting, placing the obtained Ir ingot in a metal container, and performing hot rolling. However, although the above method can reduce the amount of alkali metal elements and heavy metal elements such as Fe, Ni, and Cr, it has a problem that radioactive elements such as U and Th cannot be sufficiently reduced. Furthermore, with the increase in the density of semiconductor thin film wiring, generation of particles when forming a thin film by sputtering has become a major problem. However, particle generation can be reduced with an Ir target obtained by a conventional method. Did not.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an alkali metal such as Na or K, U or Th suitable for use as a material for forming a high-purity Ir thin film such as a sputtering target.
It is an object of the present invention to develop a method of producing high-purity Ir having a low content of radioactive elements such as Ir. Further, it is also an object to reduce the generation of particles at the time of sputtering.

[0005]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, by combining acid leaching treatment, degassing treatment, and electron beam melting, these impurities have been obtained. Has been found to be significantly reduced. Furthermore, the high-purity Ir sputtering target obtained thereby not only has a low content of metal impurity components, which has been a problem in the past, but also has a sufficiently reduced content of gas components. It has been found that the occurrence can also be reduced.

Based on these findings, the present invention provides: A high-purity Ir material for forming a thin film, wherein the content of an alkali metal element is 1 ppm or less, the content of a radioactive element is 10 ppb or less, and the content of carbon and gas component elements is 100 ppm or less.

[0007] 2. 0.1pp for each alkali metal element content
m, a radioactive element content of 1 ppb or less, respectively, and a carbon and gas component content of 10 ppm or less.

[0008] 3. 3. The high-purity Ir material for forming a thin film according to the above item 1 or 2, wherein the content of each of transition metal impurity elements other than the platinum group is 10 ppm or less.

4. A metal that forms an alloy with Ir and dissolves in an acid is added to the Ir raw material to produce an Ir alloy, and the Ir alloy is leached with an acid or an acid and an alkali to obtain an Ir alloy.
A method for producing a high-purity Ir material, comprising dissolving and removing other components, degassing the obtained Ir residue, and then performing electron beam melting.

[0010] 5. Mn, as a metal forming an alloy with Ir,
The above-mentioned item 4, wherein Zn, Ni or Cu is used.
It is intended to provide a method for producing the high-purity Ir material described above.

[0011]

Embodiments of the present invention will be described below in detail. As Ir which is a raw material of the high-purity Ir material of the present invention, a commercially available Ir powder may be used. Alternatively, Ir generated when manufacturing an Ir alloy target
It is also possible to use Ir-containing scraps such as alloy chips.

A metal which forms an alloy with Ir and is dissolved in an acid is added to the Ir raw material to produce an Ir alloy. Where I
r is once made of an Ir alloy because alloying
The purpose is to dissolve impurities contained in r into atoms in the alloy atomically and to melt out only alloy elements and impurities. As a metal that forms an alloy with Ir and dissolves in acid,
Mn, Zn, Ni, Cu, etc. can be raised, but Mn-Ir
When manufacturing an alloy target, the alloy component Mn
It is particularly preferred to use These added metals should be of high purity with as few impurities as possible. The composition range of Ir in the alloy may be 10 to 50 wt%. If Ir is less than 10% by weight, the amount of the additive is large and it is not efficient. If Ir exceeds 50% by weight, the melting point of the alloy increases, which is not preferable.

The alloying is performed, for example, by high frequency melting to 700
What is necessary is just to melt at ~ 1700 degreeC. The obtained low melting point Ir alloy is then subjected to an acid leaching treatment. As the acid, nitric acid,
Aqua regia can be used. Ir and W,
Impurity components other than Mo are dissolved and removed. Next, it is preferable to perform alkali leaching. As the alkali, NaO
H solution or the like may be used. Thereby, W, Mo, etc. can be removed.

The Ir residue powder obtained here is subjected to a degassing treatment. The degassing process is performed in an atmosphere of an inert gas such as Ar or a reducing gas such as hydrogen at a temperature of 800 to 1 ° C.
What is necessary is just to carry out at 500 degreeC. By this degassing process,
Most of the gas components such as O, N and C are removed. The high-purity Ir powder thus obtained can be formed into an ingot by a method such as electron beam melting and processed into a predetermined shape to form a sputtering target. Alternatively, a sputtering target can be obtained by a sintering method such as hot pressing.

The high-purity Ir material for forming a thin film according to the present invention has a content of alkali metal elements such as Na and K of 1 ppm or less, a content of radioactive elements such as U and Th of 10 ppb or less, and further contains carbon and gas components (oxygen and oxygen). (Hydrogen, nitrogen, chlorine) content is 100 ppm or less. Alkali metal elements such as Na and K are particularly easily diffused and easily move in the insulating film, and MOS-LSI
Since it causes deterioration of interface characteristics, the content should be 1 ppm or less, preferably 0.1 ppm or less. U, Th
Since a radioactive element such as emits α-rays and causes a soft error in a semiconductor device, it must be particularly severely restricted, and should be 10 ppb or less, preferably 1 ppb or less, more preferably 0.5 ppb or less. . Since carbon and gas component elements (oxygen, hydrogen, nitrogen, and chlorine) cause generation of particles during sputtering, the content should be 100 ppm or less. More preferably, it should be 10 ppm or less.

Since transition metal elements such as Fe, Ni, Cr, and Co Cu also cause troubles at the interfacial junction, they should be preferably at most 10 ppm, more preferably at most 1 ppm. In addition, Pt group elements (Ru, Rh,
(Pd, Os, Pt) is a homologous element to Ir and is contained to some extent in the Ir raw material.
Although some tens of ppm may be contained in r, the Pt group element exhibits almost the same behavior as Ir and has no particular adverse effect, so that there is no problem even if it is excluded from impurity metal elements to be particularly reduced. . By setting the purity of Ir excluding carbon, gas component elements, and impurity Pt group elements to be as extremely high as 99.99% or more, the specific resistance value can be extremely reduced.

[0017]

Hereinafter, the present invention will be described with reference to Examples.
The content of the present invention is not limited to this embodiment. (Example 1) Commercial iridium powder (purity 99.9%)
, High-purity Mn (purity 99.99%) was added thereto, and high-frequency melting was performed using an alumina crucible. The atmosphere was an Ar atmosphere. Melting temperature: 1500 ° C., holding time 5 minutes. After melting, it was cast in a mold to obtain a Mn-20 wt% Ir alloy. This alloy was dissolved in aqua regia to obtain an Ir residue. Then IOH with NaOH solution
The residue was washed with stirring. The obtained Ir residue was subjected to degassing at 1000 ° C. in a hydrogen atmosphere. Thereafter, it was molded and further subjected to electron beam melting to obtain an Ir ingot. The electron beam melting conditions are shown below. Degree of vacuum: 1-3 × 10 ⁻⁴ Torr Emit Current: 0.2-0.5 A Melting time: 10 minutes The obtained purified Ir lump is molded into a predetermined shape, and the rolling is performed at a temperature of 1 mm.
This was performed at 200 ° C. to obtain a disk-shaped Ir sputtering target having a diameter of 110 mm and a thickness of 5 mm.

Example 2 High-purity Mn (purity 99.99%) was added to cutting powder of an Mn-50 wt% Ir alloy, and high-frequency melting was performed using an alumina crucible. Atmosphere is A
r atmosphere. Melting temperature: 1500 ° C., holding time 2 minutes. After melting, it was cast in a mold to obtain a Mn-20 wt% Ir alloy. This alloy was dissolved with nitric acid (61%) to obtain an Ir residue. I obtained
The degassing process was performed on the r residue at 1500 ° C. in an Ar atmosphere. Thereafter, it was molded and further subjected to electron beam melting to obtain an Ir ingot. The electron beam melting conditions are shown below. Degree of vacuum: 1-3 × 10 ⁻⁴ torr Emit Current: 0.2-0.5 A Melting time: 5 minutes The obtained purified Ir lump is molded into a predetermined shape, and the rolling is performed at a temperature of 1 mm.
This was performed at 500 ° C. to obtain a disk-shaped Ir sputtering target having a diameter of 110 mm and a thickness of 5 mm.

(Comparative Example 1) 1100 g of commercially available Ir powder was molded into a predetermined shape, hot press temperature was 1800 ° C, hot press pressure was 300 kg / cm ² , and hot press time was 2
Hot pressing was performed under the conditions of time to obtain a disk-shaped iridium sputtering target having a diameter of 110 mm and a thickness of 5 mm and a density of 97%. Each Ir sputtering target obtained by the above method is joined to a copper backing plate using In-Sn alloy solder,
An Ir oxide thin film was formed on a 3-inch Si wafer by reactive sputtering in an oxygen atmosphere using a magnetron sputtering apparatus. Ir obtained by the above method
The sputtering target was bonded to a copper backing plate using In-Sn alloy solder, and an Ir oxide thin film was formed on a 3-inch Si wafer by reactive sputtering in an oxygen atmosphere using a magnetron sputtering apparatus.

(Results) Table 1 shows the Ir content of the raw material and the impurity content of the sputtering target.

[0021]

[Table 1]

In addition, the density of the Ir sputtering target, the average particle size of the target, the electric resistance of the thin film formed using the sputtering target, and the
Table 2 also shows the number of particles of 0.3 μm or more on the thin film and the electrode characteristics of the formed thin film.

[0023]

[Table 2]

The high-purity Ir sputtering target of the present invention was of extremely high purity, in which not only alkali metals and radioactive elements but also carbon and gas component elements were reduced. The thin film formed using the high-purity Ir sputtering target of the present invention had good electrode characteristics and generated few particles during sputtering.
In contrast, commercially available Ir powder has a high content of alkali metal elements, alkaline earth metal elements, carbon and gas component elements, transition metal elements and radioactive elements. And a high electrical resistance, and could not withstand use as a semiconductor thin film.

[0025]

According to the present invention, a high-purity Ir target in which not only alkali metals and radioactive elements but also carbon and gas component elements are sufficiently reduced can be manufactured.
This makes it possible to manufacture a high-purity Ir material for forming a thin film in which these impurities are reduced. In addition, the high-purity Ir material for forming a thin film of the present invention has a low resistance, generates less particles during sputtering, has good electrode characteristics of the formed thin film, and is suitable as a material for forming a semiconductor thin film such as an electrode for a dielectric capacitor. Can be used.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI H01L 21/8242

Claims (5)

[Claims] An alkali metal element content of 1 ppm or less,
A high-purity Ir material for forming a thin film, characterized in that the content of each radioactive element is 10 ppb or less and the content of carbon and gas component elements is 100 ppm or less. 2. An alkali metal element content of 0.1 ppm each
A high-purity Ir material for forming a thin film, wherein the content of each radioactive element is 1 ppb or less and the content of carbon and gas components is 10 ppm or less. 3. The high-purity Ir material for forming a thin film according to claim 1, wherein the content of transition metal impurities other than the platinum group is 10 ppm or less. 4. An Ir alloy is prepared by adding a metal which forms an alloy with Ir and dissolves in an acid to an Ir raw material to produce an Ir alloy, and then leaches the Ir alloy with an acid or an acid and an alkali to dissolve and remove components other than Ir. Then, after degassing the obtained Ir residue, it is subjected to electron beam melting to obtain high purity I.
r Manufacturing method of material. 5. Mn, Z as a metal forming an alloy with Ir
4. The method according to claim 3, wherein n, Ni or Cu is used.
A method for producing a high-purity Ir material as described above.