WO2010128629A1 - Oxide sintered body sputtering target, method for producing the target, gate insulating film formed from oxide, and method for heat-treating the gate insulating film - Google Patents

Abstract

Disclosed is an oxide sintered body sputtering target which is formed from an oxide of lanthanum (La) and aluminum (Al), and characterized in that the oxide has an constituent composition expressed as LaAl(1.01-2)O3. Also disclosed is a method for producing an oxide sintered body sputtering target having a constituent composition of LaAl(1.01-2)O3, which is characterized in that an La2(CO3)3 powder and an Al2O3 powder are used as starting material powders, the powders are blended and mixed at an Al/La molar ratio of 1.01-2, then the powder mixture is heated and synthesized in the atmosphere, then the resulting synthesized material is pulverized into a powder, and then the resulting synthesized material powder is hot-pressed, thereby obtaining a sintered body. The method provides a sintered body sputtering target which is formed from an oxide of lanthanum (La) and aluminum (Al), and is capable of efficiently and stably providing an oxide for a high-k gate insulating film.

Description

Oxide sintered sputtering target, method for manufacturing the target, gate insulating film made of oxide, and heat treatment method for the gate insulating film

The present invention relates to a sintered sputtering target composed of an oxide of lanthanum (La) and aluminum (Al), a method for producing the target, a gate insulating film composed of an oxide of lanthanum (La) and aluminum (Al), and the gate The present invention relates to a heat treatment method for an insulating film.

Lanthanum (La) is contained in rare earth elements, but is contained in the earth's crust as a mixed complex oxide as a mineral resource. Since rare earth elements were separated from relatively rare (rare) minerals, they were named as such, but they are not rare when viewed from the entire crust. Lanthanum is a white metal having an atomic number of 57 and an atomic weight of 138.9, and has a double hexagonal close-packed structure at room temperature. The melting point is 921 ° C., the boiling point is 3500 ° C., and the density is 6.15 g / cm ^{3. The} surface is oxidized in the air and gradually dissolved in water. Soluble in hot water and acid. There is no ductility, but there is slight malleability. The resistivity is 5.70 × 10 ⁻⁶ Ωcm. It burns at 445 ° C or higher to become oxide (La ₂ O ₃ ) (see Physics and Chemistry Dictionary).
As rare earth elements, compounds having an oxidation number of 3 are generally stable, but lanthanum is also trivalent. Recently, lanthanum is a metal that is attracting attention because of research and development as an electronic material such as a metal gate material and a high dielectric constant material (High-k).

Since lanthanum metal has a problem that it is easily oxidized during purification, lanthanum metal is a material that is difficult to be highly purified, and no high-purity product exists. In addition, when lanthanum metal is left in the air, it oxidizes in a short time and turns black, so that there is a problem that handling is not easy.
Recently, thinning is required as a gate insulating film in next-generation MOSFETs, but in SiO ₂ that has been used as a gate insulating film so far, leakage current due to a tunnel effect increases and normal operation has become difficult. .
For this reason, HfO ₂ , ZrO ₂ , Al ₂ O ₃ , La ₂ O ₃ having a high dielectric constant, high thermal stability, and a high energy barrier against holes and electrons in silicon are proposed. Has been. In particular, among these materials, La ₂ O ₃ is highly evaluated, electrical characteristics have been investigated, and research reports as a gate insulating film in next-generation MOSFETs have been made (see Non-Patent Document 1). However, in the case of this patent document, a La ₂ O ₃ film is the subject of research, and the characteristics and behavior of the La element are not particularly mentioned.

Thus, although lanthanum (lanthanum oxide) is still in the research stage, when investigating the characteristics of such lanthanum (lanthanum oxide), if the lanthanum metal itself exists as a sputtering target material, It is possible to form a thin film of lanthanum on the surface, and it is easy to investigate the behavior of the interface with the silicon substrate, and further the characteristics of a high dielectric constant gate insulating film by forming a lanthanum compound. It has a great advantage that the degree of freedom increases.

However, even if a lanthanum sputtering target is produced, it is oxidized in the air in a short time (in about 10 minutes) as described above. When an oxide film is formed on the target, the electrical conductivity is lowered, resulting in poor sputtering. Further, if left in the air for a long time, it reacts with moisture in the air and is covered with a white powder of hydroxide, and there is even a problem that normal sputtering cannot be performed. For this reason, it is necessary to vacuum pack immediately after the production of the target, or to cover it with oil and fats and take an anti-oxidation measure, which is a very complicated operation. Because of these problems, the lanthanum element target material has not yet been put into practical use.

On the other hand, it has been proposed to use lanthanum aluminate (LaAlO ₃ ) instead of lanthanum (lanthanum oxide) as a starting material (see Non-Patent Document 2). This document suggests that the material is superior to HfO ₂ and HfSiO, which are high-k insulating films proposed as the next generation.
In this case, the film forming process is a problem. According to this document, it is considered that high-temperature film formation (film formation at 700 ° C.) has less leakage current than room-temperature film formation, which means that high-temperature film formation eliminates defects in the film. It is explained that the cause is that excess oxygen present in LaAlO ₃ is removed. In this document, the film formation process is not specified, but since there is an explanation of high temperature (700 ° C.) film formation, it is expected that the process uses a reactive gas.
This document is premised on that the film formation process is at a high temperature in order to form a good High-k insulating film, and thus the problem is not solved.

Eisuke Tokumitsu and 2 other authors, “Studies on oxide materials for high-k gate insulating films”, Electrochemical Society of Japan, Vol. 6-13, Page. 37-41, issued on September 21, 2001 2 Masamichi Suzuki "Lantern aluminate direct junction gate insulating film", Toshiba review, Vol. 62, no. 2 (2007) 37-41

The present invention provides a sintered sputtering target made of an oxide of lanthanum (La) and aluminum (Al), and provides a technique capable of providing an oxide for a high-k gate insulating film efficiently and stably. The issue is to provide.

As described in the above prior art, lanthanum is a material that easily binds to oxygen and is difficult to remove oxygen. It is used as a sintered body of aluminate. In this sense, it is similar to the above document 2, but there is no problem as shown in the document. And it utilizes as a sputtering target, and also a component composition is equivalent to a novel substance.

The present invention
1) A sintered sputtering target composed of an oxide of lanthanum (La) and aluminum (Al), wherein the component composition of the oxide is _{LaAl (1.01-2)} O ₃ 2) Oxide sintered sputtering target 2) Oxide sintered sputtering target 3) Relative density 98 according to 1) above, wherein the oxide component composition is _{LaAl (1.05-1.2)} O ₃ The oxide sintered sputtering target according to 1) or 2) above, wherein the oxide sintered body sputtering target is characterized by having a maximum particle size of 10% or more.

The present invention further includes 4) using La ₂ (CO ₃ ) ₃ powder and Al ₂ O ₃ powder as raw material powder, mixing and mixing so that the molar ratio of Al to La is 1.01 to 2, This mixed powder is heated and synthesized in the atmosphere, and then the synthetic material is pulverized to form a powder, and then the synthetic powder is hot-pressed to form a sintered body _{. 01-2)} Manufacturing method of sputtering target of oxide sintered body of O ₃ 5) Using La ₂ (CO ₃ ) ₃ powder and Al ₂ O ₃ powder, the molar ratio of Al to La is 1.05 to 1 The oxide composition sputtering target production method 6 according to the above 4), wherein the component composition is _{LaAl (1.05-1.2)} O ₃ , characterized in that the composition is mixed so as to be 2 and sintered. ) Mixing by wet ball mill, synthesis in the atmosphere The method for producing an oxide sintered body sputtering target according to 4) or 5) above, wherein the heating is carried out at a temperature of 1350 to 1550 ° C. for 5 to 25 hours, and a hot press is performed at 1300 to 1500 ° C. in vacuum. The method for producing an oxide sintered body sputtering target according to any one of 4) to 6) above, wherein the method is performed for 1 to 5 hours.

8) wherein the component composition _{LaAl (1.01-2)} gate insulating film 9 consisting of oxides of lanthanum and aluminum are _{O 3)} component composition is _{LaAl (1.05-1.2) O 3} 8) After forming a gate insulating film made of lanthanum and aluminum oxide whose composition is _{LaAl (1.01-2)} O ₃ , heating at 50 to 300 ° C. 11) A heat treatment method of a gate insulating film characterized in that it is processed. 11) The insulating film is composed of a lanthanum of _{LaAl (1.05-1.2)} O ₃ and an oxide of aluminum. And a heat treatment method for the gate insulating film according to claim 1.

When a conventional lanthanum (lanthanum oxide) sputtering target is left in the air for a long time, it reacts with moisture in the air and is covered with a white powder of hydroxide, and normal sputtering cannot be performed. Although a problem occurs, the target made of an oxide of lanthanum and aluminum of the present invention does not cause such a problem.
In addition, since the amount of Al is excessive as compared with LaAlO ₃ which is the stoichiometric component composition, free oxygen or excess oxygen contained in the oxide of lanthanum and aluminum is thereby reduced by Al having a strong oxidizing power. It has a great effect that it can be prevented that free oxygen moves in the LaAlO ₃ film formed by sputtering and reacts at the interface with Si to form harmful SiO ₂ .

A LaAl _(1.07) external view of the _{O 3} oxide sintered body is showing a target bonded to a backing plate made of Cu (photograph). LaAl _{(1.07) O 3} the result of structure observation of the oxide sintered compact target is a photomicrograph showing the. A LaAl _(1.07) Appearance shows a flooded test result of the end member of _{O 3} in which the oxide sintered body diagram (photograph). A diagram showing a result of measuring the LaAl _{(1.07) O 3} in which the intensity of 2θ by X-ray diffraction of the oxide sintered body end material after immersion test before and immersion tests 24 hours (XRD) (CPS) is there.

The oxide sintered sputtering target of the present invention is a sintered sputtering target composed of an oxide of lanthanum (La) and aluminum (Al), and the component composition of the oxide is _{LaAl (1.01-2) 2} O 3. ₃ , more preferably _{LaAl (1.05-1.2)} O ₃ .
As is apparent from this composition ratio, Al is in excess of the stoichiometric composition ratio. That is, the molar ratio of Al to La is 1.01 to 2. When the molar ratio of Al to La is less than 1.01, oxygen cannot be captured by Al and the effect cannot be achieved. If the molar ratio of Al to La exceeds 2, the characteristics as LaAlO ₃ , particularly the excellent characteristics as an oxide material for a high-k gate insulating film, cannot be maintained. The molar ratio of La was 2. Further recommended conditions are a molar ratio of Al to La of 1.05 to 1.2.

In the production of this oxide sintered compact target, La ₂ (CO ₃ ) ₃ powder and Al ₂ O ₃ powder are used as the raw material powder, and the molar ratio of Al to La is 1.01 to 2 or Al and La. The mixture is blended so that the molar ratio is 1.05 to 1.2, mixed, and then heated and synthesized in the atmosphere. Next, the synthetic material is pulverized into powder, and this synthetic powder is further hot pressed. Can be manufactured by forming a sintered body.
It is recommended that the mixing be performed by a wet ball mill and the synthesis be performed by heating in the atmosphere at 1350 to 1550 ° C. for about 5 to 25 hours. In addition, performing the hot pressing at 1300 to 1500 ° C. in a vacuum for 1 to 5 hours is also a recommended manufacturing condition as a sintering condition. The above are the conditions for efficiently performing synthesis and sintering. Therefore, it should be understood that other conditions and other conditions can be added.

Thereby, an oxide sintered sputtering target having a relative density of 98% or more and a maximum particle size of 10 μm or less can be obtained. Improving the density and reducing the crystal grain size are preferable conditions that can suppress the generation of nodules and particles and can form a uniform film.
Further, in general, rare earth elements contained in lanthanum include Sc, Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, in addition to lanthanum (La). Although there is Lu, it is difficult to separate and purify from La due to similar characteristics. In particular, since Ce approximates La, it is not easy to reduce Ce.

However, since these rare earth elements have similar properties, it will be understood that if the total rare earth elements are less than 1000 wtppm, they are not particularly problematic when used as an electronic component material. Therefore, the use of lanthanum in the present invention is allowed to contain this level of rare earth elements.
In addition to this, there are impurities inevitably mixed. The analytical values are shown in Table 1. In particular, although a large amount (4200 wtppm) of Zr is contained, a gate insulating film made of an oxide of lanthanum and aluminum that is _{LaAl (1.05-1.2)} O ₃ even if such impurities are present. It is effective as However, in order to make use of the characteristics of the lanthanum element, further reduction is a preferable condition. The present invention includes these.

Generally, C, N, O, S, and H exist as gas components. As shown above, oxygen can be fixed as a harmful component, but other gas components are not particularly problematic. These may exist as single elements, but many may exist in the form of compounds (CO, CO ₂ , SO ₂ etc.) or compounds with constituent elements. Since these gas component elements have a small atomic weight and atomic radius, even if they are present as impurities, they do not significantly affect the properties of the material unless they are contained in large amounts. Therefore, the purity of the lanthanum of the present invention is preferably 3N or more excluding rare earth, Zr, and gas components.

By sputtering with the use of the target, from a component composition _{LaAl (1.01-2) O 3,} more oxides of lanthanum and aluminum component composition is _{LaAl (1.05-1.2) O 3} A gate insulating film can be formed. The component composition of the target is directly reflected in the film formation. Further Thus, gate insulating composed of the formed component composition is or component composition in _{LaAl (1.01-2) O 3} oxides of lanthanum and aluminum are _{LaAl (1.05-1.2) O 3} After the film is formed, heat treatment can be performed at 50 to 300 ° C.
This is a condition for additionally fixing free oxygen existing in the film, which is intended to be further fixed. It should be understood that it is not essential. In particular, in the manufacturing conditions for next-generation MOSFETs and the like, the manufacturing conditions that dislike such heating are unnecessary conditions.

Next, examples will be described. In addition, this Example is for understanding easily and does not restrict | limit this invention. That is, other examples and modifications within the scope of the technical idea of the present invention are included in the present invention.

Example 1
La ₂ (CO ₃ ) ₃ powder and Al ₂ O ₃ powder were used as raw material powders, blended so that the molar ratio of Al to La was 1.07, and the mixture was mixed by a wet ball mill. This mixed powder was synthesized by heating in the atmosphere at 1450 ° C. for 20 hours. This synthetic material was wet pulverized with a ball mill for 16 hours to obtain a powder. This synthetic powder was hot pressed in vacuum at 1400 ° C. for 2 hours to obtain a sintered body. The size of the sintered body was φ190 mm, and the press pressure was 300 kg / cm ² .
Thus, the component composition was obtained oxide sintered body as a _{LaAl (1.07) O 3.} This was machined to obtain a sputtering target. The target size after machining was φ164 mm × 6 mmt. The relative density of the target was 98.9% (6.436 g / cm ³ : theoretical density was 6.51 g / cm ³ ).

Further, this was joined to a Cu backing plate in the atmosphere. A target bonded to a Cu backing plate is shown in FIG. Moreover, the result of having observed the structure | tissue of the target is shown in FIG. FIG. 2 shows the results of extracting five locations on the target surface at random. As shown in FIG. 2, the average particle size is 0.885 to 1.64 μm, the maximum particle size is 2.33 to 4.4 μm, the minimum particle size is 0.2 μm, and the pore area ratio is 0.053 to 0.003. It was in the range of 66%, and a dense and fine structure could be confirmed.

FIG. 3 shows the result of the immersion test of the end material of the oxide sintered body in which the component composition thus prepared is LaAl _(1.07) O ₃ . FIG. 3 shows the results before the water immersion test on the left and the results 24 hours after the water immersion test on the right. As shown in FIG. 3, there was no evidence of corrosion due to oxidation or hydroxylation even after the 24-hour immersion test.
Usually, lanthanum (lanthanum oxide) is rapidly corroded by oxidation or hydroxylation even if it is left in the atmosphere for 1 hour. At first, discoloration is seen from white to black, but this LaAl _(1.07) No corrosion was observed on the oxide sintered body of O ₃ .

Furthermore, in order to evaluate this, the 2θ strength (CPS) was measured by X-ray diffraction (XRD) of the end material before the immersion test and 24 hours after the immersion test. The result is shown in FIG. As shown in FIG. 4, the end material before the immersion test and 24 hours after the immersion test did not change. This also confirmed that corrosion due to oxidation or hydroxylation did not progress.
Furthermore, high-frequency sputtering was performed using this target to form a LaAl _(1.07) O ₃ oxide thin film on the Si substrate. As a result, no Si oxide film layer was observed at the interface between Si and the LaAl _(1.07) O ₃ oxide thin film. This indicates that it is useful as a material for the gate insulating film.

(Example 2 to Example 8)
La ₂ (CO ₃ ) ₃ powder and Al ₂ O ₃ powder are used as the raw material powder, and the molar ratio of Al to La is 1.01, 1.02, 1.05, 1.1, 1.2, 1. It mix | blended so that it might become 25 and 2.0, and mixing was mixed with the wet ball mill. The manufacturing conditions were the same as in Example 1. As a result, the same structure and water immersion test results as in Example 1 were obtained.
The molar ratio of Al to La is not particularly affected by corrosion as long as the minimum molar ratio of Al to La is maintained at 1.01, but the inclusion of a large amount of Al has the characteristics of La. Since there is a tendency to lower, the upper limit of the molar ratio of Al to La needs to be 2.0.

(Comparative Example 1)
La ₂ (CO ₃ ) ₃ powder and Al ₂ O ₃ powder were used as raw material powders, blended so that the molar ratio of Al to La was 1.00, and mixed by a wet ball mill. The following steps are the same as in Example 1. That is, this mixed powder was synthesized by heating in the atmosphere at 1450 ° C. for 20 hours. This synthetic material was wet pulverized with a ball mill for 16 hours to obtain a powder.
This synthetic powder was hot pressed in vacuum at 1400 ° C. for 2 hours to obtain a sintered body. The size of the sintered body was φ190 mm, and the press pressure was 300 kg / cm ² . As a result, an oxide sintered body was obtained. Thereafter, using this oxide sintered body, a target was produced by the same process as in Example 1, and a water immersion test was performed using the end material of the oxide sintered body target.

In Comparative Example 1, a La-rich compound was partially produced. As a result, pulverization occurred when the produced target was left in the air, and pulverization occurred in the water immersion test.
From this fact, it is effective to make the amount of Al excessive as compared with LaAlO ₃ which is a stoichiometric component composition, in addition to the effect of capturing free oxygen and excess oxygen, and also to suppress the pulverization phenomenon. I was able to confirm.

When a conventional lanthanum (lanthanum oxide) sputtering target is left in the air for a long time, it reacts with moisture in the air and is covered with a white powder of hydroxide, and normal sputtering cannot be performed. Although a problem occurs, the target made of an oxide of lanthanum and aluminum of the present invention does not cause such a problem.
In addition, since the amount of Al is excessive as compared with LaAlO ₃ which is the stoichiometric component composition, free oxygen or excess oxygen contained in the oxide of lanthanum and aluminum is thereby reduced by Al having a strong oxidizing power. It has a great effect that it can be fixed and free oxygen moves through the LaAlO ₃ film formed by sputtering and reacts at the interface with Si to prevent the formation of harmful SiO ₂ . Therefore, forming a film using this target has a great effect on the formation of a uniform film, and the formed thin film is an electronic material, particularly as an electronic material disposed close to a silicon substrate. It is useful as a material for a gate insulating film without lowering or disturbing the function of

Claims (11)

A sintered sputtering target comprising an oxide of lanthanum (La) and aluminum (Al), wherein the oxide composition is _{LaAl (1.01-2)} O _3. Combined sputtering target. 2. The oxide sintered sputtering target according to claim 1, wherein the component composition of the oxide is _{LaAl (1.05-1.2)} O ₃ . The oxide sintered compact sputtering target according to claim 1 or 2, wherein the relative density is 98% or more and the maximum particle size is 10 µm or less. La ₂ (CO ₃ ) ₃ powder and Al ₂ O ₃ powder were used as raw material powders, mixed and mixed so that the molar ratio of Al to La was 1.01 to 2, and then this mixed powder was The composition composition is _{LaAl (1.01-2)} O ₃ , characterized by heat synthesis, and then pulverizing the synthetic material to form a powder, and then hot-pressing the synthetic powder to form a sintered body. A manufacturing method of a certain oxide sintered compact sputtering target. A component composition characterized by using La ₂ (CO ₃ ) ₃ powder and Al ₂ O ₃ powder, blending so that the molar ratio of Al to La is 1.05 to 1.2, and sintering. The method for producing an oxide sintered sputtering target according to claim 4, wherein the production method is _{LaAl (1.05-1.2)} O ₃ . 6. The method for producing an oxide sintered sputtering target according to claim 4, wherein the mixing is performed by a wet ball mill and the synthesis is performed by heating in the atmosphere at 1350 to 1550 ° C. for 5 to 25 hours. The method for producing an oxide sintered sputtering target according to any one of claims 4 to 6, wherein the hot pressing is performed in a vacuum at 1300 to 1500 ° C for 1 to 5 hours. A gate insulating film made of an oxide of lanthanum and aluminum having a component composition ratio of _{LaAl (1.01-2)} O ₃ . _9. The gate insulating film according to claim 8, wherein the component composition ratio is _{LaAl (1.05-1.2)} O ₃ . Heat treatment at 50 to 300 ° C. after forming a gate insulating film made of an oxide of lanthanum and aluminum whose component composition is _{LaAl (1.01-2)} O ₃ Method. _{11. The} method for heat treatment of a gate insulating film according to claim 10, wherein the insulating film is made of an oxide of lanthanum _{having a} composition of _{LaAl (1.05-1.2)} O ₃ and aluminum.

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