JP2017109916A - Ceramic material consisting of lanthanum oxide, manufacturing method therefor, target using the same and semiconductor device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic material consisting of lanthanum oxide having high hygroscopic resistance, a manufacturing method thereof, a target using the same and a semiconductor device using the same.SOLUTION: The ceramic material consists of lanthanum oxide to which alkali earth metal fluoride is dissolved in a range of more than 0.01 mol% and 5 mol% or less. Such ceramic material includes a step of mixing lanthanum oxide power and alkali earth metal fluoride powder in a range of more than 0.01 mol% and 5 mol% or less based on the lanthanum oxide power and a step of burning the mixture at a temperature of a temperature range of 1100°C or higher to 1500°C or lower in inert gas atmosphere.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a ceramic material made of lanthanum oxide, a manufacturing method thereof, a target using the same, and a semiconductor device using the same.

In recent compound semiconductor devices, a substance that absorbs moisture in the atmosphere and destabilizes is used, and its stability becomes a problem in device application. For example, lanthanum oxide (La ₂ O ₃ ) has a relative dielectric constant of 27, and although it is a candidate for a high-k material, it has been considered difficult to fabricate devices using it because of its hygroscopic property. .

When lanthanum oxide powder is used as a main component of synthesis or a minor additive, it is necessary to consider the influence of moisture during weighing, which causes a synthesis error. Here, the mechanism by which lanthanum oxide absorbs moisture will be described. Lanthanum oxide is easily transformed into lanthanum hydroxide according to the following formula.
La ₂ O ₃ + H ₂ O → 2LaO (OH)
2LaO (OH) + 2H ₂ O → 2La (OH) ₃

For this reason, not only lanthanum oxide powder but also sintered bodies are difficult to manage in the atmosphere, and it is difficult to maintain the state even with a general desiccator or vacuum desiccator. A sintered body of lanthanum oxide is used as a target for manufacturing a thin film. However, even under a high vacuum with a vacuum degree of 1 × 10 ⁻⁸ torr, moisture remaining in the vacuum container is absorbed and the surface state of the target changes. As a result, there may be a problem in reproducibility of thin film manufacturing.

  In addition, lanthanum oxide has a melting point of 2315 degrees and is poor in atmospheric stability, so that it is usually difficult to obtain a dense sintered body. Referring to the above reaction, when sintering additive-free lanthanum oxide, it is recovered without sintering due to the generation and evaporation of moisture at high temperatures. The particles inside such a sintered body are only clogged in a rough state, and moisture in the atmosphere easily enters the voids, causing the above reaction. As a result, the shape of the sintered body cannot be maintained.

  In response to such a problem, a lanthanum oxide sintered body having improved moisture absorption resistance has been developed (Patent Document 1). According to Patent Document 1, a sintered body containing lanthanum oxide as a basic component, containing one or more of titanium oxide, zirconium oxide, and hafnium oxide, and the remainder being lanthanum oxide and inevitable impurities. Features. According to Patent Document 1, titanium oxide, zirconium oxide, and hafnium oxide to be added are preferably 10 mol% or more, and not only the synthesis is difficult, but the original characteristics of lanthanum oxide may not be obtained.

A semiconductor device using a lanthanum oxide mixed film with improved moisture absorption resistance has been developed (Patent Document 2). According to Patent Document 2, the thin film made of lanthanum oxide is (La _1-x M _x ) ₂ O ₃ (0 <x ≦ 0.3, M is Sc, Y, Hf, Ti, Ta, Al, Nb. 1 or 2 or more metals selected from the group). According to Patent Document 2, a ternary composition spread method is adopted for forming a mixed film. However, the surface state of the lanthanum oxide target used for this change even under high vacuum as described above. In some cases, problems may arise in the reproducibility of thin film production.

  On the other hand, it is known that calcium fluoride and yttrium fluoride are used as sintering aids in the production of polycrystalline transparent yttrium / aluminum / garnet / ceramics or aluminum nitride sintered body (Patent Documents 3 and 4). ). According to Patent Documents 3 and 4, a high-density sintered body can be obtained by adding a sintering aid.

International Publication No. 2010/004861 JP 2003-133523 A JP-A-5-294724 JP-A-8-259328

  As described above, an object of the present invention is to provide a ceramic material made of lanthanum oxide having high moisture absorption resistance, a manufacturing method thereof, a target using the same, and a semiconductor device using the same.

The ceramic material according to the present invention comprises lanthanum oxide in which alkaline earth metal fluoride is dissolved in a range of more than 0.01 mol% and not more than 5 mol%, thereby solving the above problems.
The alkaline earth metal fluoride may be dissolved in a range of 0.25 mol% to 4 mol%.
The alkaline earth metal fluoride may be dissolved in the range of 0.4 mol% to 1.5 mol%.
The alkaline earth metal fluoride may be dissolved in the range of 0.6 mol% to 1.0 mol%.
The alkaline earth metal fluoride may be selected from the group consisting of magnesium fluoride (MgF ₂ ), calcium fluoride (CaF ₂ ), and strontium fluoride (SrF ₂ ).
In the lanthanum oxide, a Q element (here, the Q element is In and / or Ga) may be further dissolved.
The Q element may be dissolved in the range of more than 0 mol% and 15 mol% or less.
The Q element may be dissolved in the range of 4 mol% to 12 mol%.
F (fluorine) for ¹⁶ O (oxygen) when the lanthanum oxide is analyzed by secondary ion mass spectrometry using O ⁻ as primary ions and positive ions flying from the lanthanum oxide as secondary ions. The ionic strength ratio (F / ¹⁶ O) and the ionic strength ratio (M / La) of the alkaline earth element M to La (lanthanum) are respectively
0.0013 <F / ¹⁶ O ≦ 0.15, and
0.0012 <M / La ≦ 6
May be satisfied.
The lanthanum oxide is represented by the general formula _{(La 1-x-z M} x Q z) 2 (O 1-y F y) 3 ( wherein, La is lanthanum, M is an alkaline earth element, Q is , In and / or Ga, O is oxygen and F is fluorine), and the parameters x, y and z are respectively
0.0001 <x ≦ 0.05,
0.0002 <y ≦ 0.1, and
0 ≦ z ≦ 0.15
May be satisfied.
The parameters x and y are respectively
0.0025 ≦ x ≦ 0.04, and
0.005 ≦ y ≦ 0.08,
May be satisfied.
The parameters x and y are respectively
0.004 ≦ x ≦ 0.015, and
0.008 ≦ y ≦ 0.03
May be satisfied.
According to the present invention, a method for producing a ceramic material made of lanthanum oxide in which alkaline earth metal fluoride is solid-solved in a range of more than 0.01 mol% and not more than 5 mol% includes lanthanum oxide powder, alkaline earth metal fluoride, and A step of mixing the powder, wherein the alkaline earth metal fluoride powder is mixed in a range of more than 0.01 mol% and less than 5 mol% with respect to the lanthanum oxide powder, and the mixing step And firing the mixture obtained in step 1 at a temperature in the temperature range of 1100 ° C. or more and 1500 ° C. or less, thereby solving the above-mentioned problem.
The mixing step may further include a material containing a Q element (where the Q element is In and / or Ga).
The material containing the Q element may be selected from the group consisting of the metal, oxide and fluoride of the Q.
The material containing the Q element may be mixed in a range of more than 0 mol% and not more than 15 mol% with respect to the lanthanum oxide powder and the alkaline earth metal fluoride powder.
The target according to the present invention is made of a sintered body used in physical vapor deposition, and the sintered body is made of any of the ceramic materials described above, thereby solving the above-mentioned problems.
The physical vapor deposition method may be selected from the group consisting of sputtering, pulsed laser deposition, and vapor deposition.
A semiconductor device according to the present invention includes a first conductive layer, a second conductive layer opposite to the first conductive layer, and a dielectric positioned between the first conductive layer and the second conductive layer. The dielectric thin film is made of any one of the ceramic materials described above, thereby solving the above-described problems.
The first conductive layer is made of a semiconductor substrate having source / drain regions formed on the surface so as to be spaced apart from each other, and the dielectric thin film is located on the semiconductor substrate between the source / drain regions. The second conductive layer may be a gate electrode, and the semiconductor device may be selected from the group consisting of MOSFET, MFISFET, MFMISFET, MIFIMSFET, MFIMISFET, and MIFMISFET.

  The ceramic material according to the present invention is made of lanthanum oxide in which an alkaline earth metal fluoride is dissolved in a range of more than 0.01 mol% and not more than 5 mol%. When a predetermined amount of alkaline earth element is dissolved in the lanthanum oxide lanthanum site and a predetermined amount of fluorine is dissolved in the oxygen site for charge compensation, electrons are generated and oxygen vacancies are reduced. Thereby, oxygen vacancies that react with water and take in hydrogen are reduced, so that the moisture absorption resistance can be improved. Furthermore, since hydrogen suppresses the solid solution of lanthanum oxide inside the lattice by the generated electrons, the moisture absorption resistance can be improved.

  In the method for producing a ceramic material according to the present invention, the melting point of lanthanum oxide is lowered by including a predetermined amount of alkaline earth metal fluoride powder in the starting material for firing, and the temperature range is from 1100 ° C. to 1500 ° C. Since the above-mentioned ceramic material can be obtained only by firing at a temperature of 1, it is only necessary to use an existing heating furnace or the like, and it is advantageous because a skilled technique is unnecessary.

  Since the semiconductor device according to the present invention uses a thin film made of the above-mentioned ceramic material, it not only exhibits the inherent high dielectric constant of lanthanum oxide, but also has excellent moisture absorption resistance and enables stable operation over a long period of time. To do.

Step flow showing a process of manufacturing a ceramic material according to the first embodiment Schematic diagram of a semiconductor device according to the second embodiment Schematic diagram of another semiconductor device according to the second embodiment The figure which shows the mode of a time-dependent change of the sintered compact by Example 1 / comparative example 2 The figure which shows the sintering temperature dependence of the density of the sintered compact by Example 1 The figure which shows the XRD pattern of the sintered compact by Example 1. The figure which shows the mode of a time-dependent change of the sintered compact by Example 3 / comparative example 5 Shows the dependence of concentration of added CaF ₂ in the density of Example 3 / Comparative Example 5 according to the sintered body It shows the dependence of the addition concentration of Example 3 / F of Comparative Example 5 in the sintered body / O and ⁴⁴ Ca / La of CaF ₂ in the ion intensity ratio The figure which shows the mode of the time-dependent change of the thin film by Example 6 and Comparative Example 7 The figure which shows the influence which it has on the XRD diffraction pattern of the time-dependent change of the thin film by Example 6 and Comparative Example 7 The figure which shows the indium density | concentration dependence of the dielectric constant of capacitor 9-2'-9-6 'by Example 9

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same number is attached | subjected to the same element and the description is abbreviate | omitted.

(Embodiment 1)
In Embodiment 1, the ceramic material of the present invention and the manufacturing method thereof will be described.

  The inventors of the present application have focused on reducing oxygen vacancies in lanthanum oxide in order to improve moisture absorption resistance, and have recalled a ceramic material made of lanthanum oxide in which an alkaline earth metal fluoride is dissolved.

  The mechanism for improving moisture absorption resistance will be described.

The inventors of the present application consider that oxygen vacancies in lanthanum oxide serve as active seats for taking in water and hydrogen, as shown in formula (i), and reducing oxygen vacancies is effective in improving moisture absorption resistance. I found out.
H ₂ O + V _O ^× → 2H + O 2 _O (i)
Here, V 2 _O ^x is oxygen vacancies in the lanthanum oxide, and O 2 _O is oxygen dissolved in the oxygen vacancies. The oxygen vacancies react with water to produce hydrogen, which can diffuse into the lanthanum oxide.

On the other hand, the reaction formula in which MF ₂ (M is an alkaline earth metal element) as an alkaline earth metal fluoride is dissolved in lanthanum oxide (La ₂ O ₃ ) is as shown in formula (ii).
^{_{2MF 2 + V O × → 2M}} La '+ 4F O ● + 2e - ··· (ii)
Here, V _O ^x is oxygen vacancies in lanthanum oxide, M _La ^′ is an alkaline earth metal element dissolved in lanthanum sites, and F 2 _O ^● is a fluorine element dissolved in oxygen vacancies. .

  As shown in the formula (ii), in the alkaline earth metal fluoride dissolved in lanthanum oxide, the alkaline earth metal element dissolves in the lanthanum site, and the fluorine element dissolves in the oxygen vacancies. Furthermore, electrons are generated in the lattice by charge compensation. That is, it can be seen that oxygen vacancies are reduced by the solid solution of alkaline earth metal fluoride. Since lanthanum oxide has a band gap of 6.14 eV, the generated electrons are localized in the vicinity of fluorine and become an insulator.

  Since oxygen vacancies are reduced according to the formula (ii), the formula (i) does not advance and the moisture absorption resistance can be improved. Furthermore, even if the formula (i) occurs, it is only on the surface of lanthanum oxide, so that the generated hydrogen cannot be dissolved into the lattice of lanthanum oxide, and the generation of lanthanum hydroxide can be said to be only in the surface layer.

  Here, the difference between the calcium fluoride or yttrium fluoride used as the sintering aid shown in Patent Documents 3 and 4 and the alkaline earth metal fluoride of the present invention will be described. A sintering aid is an additive added to promote or stabilize sintering, but it does not aim to react with a substance that is originally desired and become a different substance. After firing, segregates into the glassy phase of the grain boundary. However, it is noted that the alkaline earth metal fluoride in the present invention is not segregated in the glass phase at the grain boundary, but is dissolved in each site of lanthanum oxide to control the characteristics of lanthanum oxide. I want. Such a difference can be easily determined by observing the grain boundary glass phase by an electron microscope, elemental analysis using an electron beam, or the like.

  Thus, by dissolving an alkaline earth metal fluoride in lanthanum oxide, oxygen vacancies are reduced, so that not only reaction with water is less likely to occur, but also the generation of electrons causes lanthanum oxide to enter the inside. Hydrogen diffusion can be suppressed.

  The inventors of the present application consider that the moisture absorption resistance of lanthanum oxide can be improved by controlling oxygen vacancies in lanthanum oxide, and further examine the solid solution amount of alkaline earth metal fluoride that exhibits the above-mentioned effects. In addition, we have developed ceramic materials that can improve moisture absorption resistance.

  The ceramic material of the present invention is made of lanthanum oxide in which alkaline earth metal fluoride is dissolved in a range of more than 0.01 mol% and not more than 5 mol%. When the amount of the alkaline earth metal element is 0.01 mol% or less, the amount of solid solution is not sufficient, so that oxygen vacancies may not be reduced. When the alkaline earth metal element exceeds 5 mol%, the crystal structure of lanthanum oxide can be unstable because there is too much alkaline earth metal element.

  The ceramic material of the present invention is preferably made of lanthanum oxide in which an alkaline earth metal fluoride is dissolved in a range of 0.25 mol% to 4 mol%. If it is the amount of solid solution of this range, alkaline-earth metal fluoride will dissolve and moisture absorption resistance can be improved.

  The ceramic material of the present invention is more preferably composed of lanthanum oxide in which alkaline earth metal fluoride is dissolved in the range of 0.4 mol% to 1.5 mol%. If it is the amount of solid solution of this range, an alkaline-earth metal fluoride will carry out solid solution reliably, and it can improve moisture absorption resistance.

  The ceramic material of the present invention is more preferably made of lanthanum oxide in which an alkaline earth metal fluoride is dissolved in the range of 0.6 mol% to 1.0 mol%. When the solid solution amount is within this range, for example, when the ceramic material is a sintered body, a high-strength sintered body with improved moisture absorption resistance can be obtained. In addition, when the amount of solid solution is within this range, for example, when the ceramic material is a thin film, the moisture absorption resistance is particularly improved, and the thin film material can withstand long-term use.

  More preferably, the ceramic material of the present invention is made of lanthanum oxide in which a Q element (wherein the Q element is In and / or Ga) is further dissolved. When the Q element is dissolved in the lanthanum site, the relative dielectric constant of the lanthanum oxide can be improved.

  The solid solution amount of the Q element is preferably in the range of more than 0 mol% and not more than 15 mol%. An improvement in the dielectric constant of lanthanum oxide can be seen by even a slight dissolution. If the solid solution exceeds 15 mol%, the crystal structure of lanthanum oxide may not be maintained.

  More preferably, the solid solution amount of the element Q is in the range of 4 mol% to 12 mol%. If the amount is in this range, the relative dielectric constant of lanthanum oxide can be improved reliably. The solid solution amount of the Q element may be in the range of 4 mol% to 8 mol%. The same effect can be obtained even with less Q element.

Ceramic material of the present invention have the general formula _{(La 1-x-z M} x Q z) 2 (O 1-y F y) 3 ( wherein, La is lanthanum, M is an alkaline earth element, Q is In and / or Ga, O is oxygen, and F is fluorine. Where the parameters x and y are respectively
0.0001 <x ≦ 0.05,
0.0002 <y ≦ 0.1, and
0 ≦ z ≦ 0.15
Meet. When x is 0.0001 or less, since the amount of solid solution is not sufficient, there is a possibility that oxygen vacancies are not reduced. When x exceeds 0.05, the alkaline earth metal element is too much, so that the crystal structure of lanthanum oxide can be unstable. If y is in this range, oxygen vacancies can be filled. If z exceeds 0.15, the crystal structure of lanthanum oxide may become unstable because of too much In and / or Ga. The parameter z may be 0, but if it exceeds 0, the dielectric constant of lanthanum oxide can be improved, and preferably satisfies 0.04 ≦ z ≦ 0.12. Thereby, the relative dielectric constant of lanthanum oxide can be improved reliably.

In the ceramic material of the present invention, the parameters x and y in the general formula are preferably
0.0025 ≦ x ≦ 0.04, and
0.005 ≦ y ≦ 0.08
Meet. If x and y satisfy this range, oxygen vacancies can be reduced and moisture absorption resistance can be improved by the solid solution of the alkaline earth metal element and the solid solution of the fluorine element.

In the ceramic material of the present invention, the parameters x and y in the general formula are preferably
0.004 ≦ x ≦ 0.015, and
0.008 ≦ y ≦ 0.03
Meet. When x and y satisfy this range, oxygen vacancies can be reduced and moisture absorption resistance can be improved by the reliable solid solution of the alkaline earth metal element and the solid solution of the fluorine element.

In the ceramic material of the present invention, the parameters x and y in the general formula are preferably
0.006 ≦ x ≦ 0.01, and
0.012 ≦ y ≦ 0.02
Meet. If x and y satisfy this range, for example, when the ceramic material is a sintered body, a high-strength sintered body with improved moisture absorption resistance can be obtained. For example, when the ceramic material is a thin film, the moisture absorption resistance is particularly improved, and the thin film material can withstand long-term use.

  When oxygen vacancies are completely removed, preferably y = 2x, but any effect can be achieved as long as x and y are within the above ranges. As will be described later, when a fluoride of Q element is used as a raw material containing the Q element, the fluoride of Q element together with the alkaline earth metal fluoride contains fluorine to the oxygen site of lanthanum oxide. Contributes to solid solution. However, even in this case, the fluorine due to the fluoride of the element Q functions to assist the portion of the fluorine due to the alkaline earth metal fluoride not dissolved in the oxygen site. The amount of fluorine to be used may be considered based on the amount of fluorine by the alkaline earth metal fluoride.

The ceramic material of the present invention uses lanthanum oxide in which alkaline earth metal fluoride is solid-solved (simply lanthanum oxide) as a secondary ion by using O- as a primary ion by secondary ion mass spectrometry. When measuring and analyzing positive ions, the ionic strength ratio of F (fluorine) to ¹⁶ O (oxygen) (F / ¹⁶ O) and M to La (lanthanum) (M is an alkaline earth element, For example, when M is calcium, the ionic strength ratio (M / La) of ⁴⁴ Ca calcium isotope is preferably
0.0013 <F / ¹⁶ O ≦ 0.15, and
0.0012 <M / La ≦ 6
Meet. If the ionic strength ratio of F / ¹⁶ O and M / La is within this range, the oxygen vacancies can be filled.

More preferably, in the ceramic material of the present invention, the ionic strength ratio (F / ¹⁶ O) and the ionic strength ratio (M / La) are respectively
0.01 ≦ F / ¹⁶ O ≦ 0.091, and
0.13 ≦ M / La ≦ 4.6
Meet. If the ionic strength ratio of F / ¹⁶ O and M / La is within this range, oxygen vacancies are reduced by the solid solution of alkaline earth metal element and the solid solution of fluorine element, so that the moisture absorption resistance can be improved. .

More preferably, in the ceramic material of the present invention, the ionic strength ratio (F / ¹⁶ O) and the ionic strength ratio (M / La) are respectively
0.016 ≦ F / ¹⁶ O ≦ 0.042, and
0.25 ≦ M / La ≦ 1.5
Meet. If the ionic strength ratio of F / ¹⁶ O and M / La is within this range, oxygen vacancies are reduced due to reliable solid solution of alkaline earth metal elements and solid solution of fluorine elements. Can be improved.

More preferably, in the ceramic material of the present invention, the ionic strength ratio (F / ¹⁶ O) and the ionic strength ratio (M / La) are respectively
0.024 ≦ F / ¹⁶ O ≦ 0.031, and
0.4 ≦ M / La ≦ 0.75
Meet. When the ionic strength ratio of F / ¹⁶ O and M / La satisfies this range, for example, when the ceramic material is a sintered body, a high-strength sintered body with improved moisture absorption resistance can be obtained. For example, when the ceramic material is a thin film, the moisture absorption resistance is particularly improved, and the thin film material can withstand long-term use.

Alkaline earth metal fluorides are from beryllium fluoride (BeF ₂ ), magnesium fluoride (MgF ₂ ), calcium fluoride (CaF ₂ ), strontium fluoride (SrF ₂ ), and barium fluoride (BaF ₂ ). A fluoride selected from the group consisting of magnesium fluoride (MgF ₂ ), calcium fluoride (CaF ₂ ), and strontium fluoride (SrF ₂ ) is particularly preferable. If these fluorides are used, they can be produced with good yield.

More preferably, the alkaline earth metal fluoride is calcium fluoride (CaF ₂ ). In the case of calcium fluoride, calcium is surely dissolved in the La site and fluorine is surely dissolved in oxygen, so that a ceramic material made of lanthanum oxide having improved moisture absorption resistance can be obtained.

  The form of the ceramic material of the present invention is not particularly limited, but may be a powder, a sintered body, or a thin film. When the ceramic material of the present invention is a powder, the moisture absorption resistance is improved. Therefore, the ceramic material is effective as a raw material powder not affected by moisture at the time of weighing, reducing errors at the time of weighing, and a desired final product. Can be obtained.

  When the ceramic material of the present invention is a sintered body, it can be used as a target for manufacturing a thin film used in physical vapor deposition. The physical vapor deposition method is not particularly limited as long as it is a method using a target. Specifically, the physical vapor deposition method is selected from the group consisting of sputtering, pulse laser deposition, and vapor deposition. Also in this case, since the moisture absorption resistance is improved, moisture remaining in the chamber is not absorbed even under a high vacuum, and the surface state of the target does not change, so that a thin film can be manufactured with good reproducibility. . In addition, special processing such as storing the target in a desiccator or vacuum desiccator is not necessary, which is advantageous in reducing maintenance costs.

  When the ceramic material of the present invention is a thin film, the moisture absorption resistance is improved. Therefore, the insulating film or the dielectric thin film used in the semiconductor device can exhibit the insulating properties and high dielectric constant, which are inherent characteristics of lanthanum oxide. Function as. Further, since the characteristics do not change due to the influence of moisture, the semiconductor device using the ceramic material which is the thin film of the present invention enables a stable operation in the air for a long period of time.

  Next, with reference to FIG. 1, the manufacturing method of the ceramic material which consists of a lanthanum oxide in which alkaline-earth metal fluoride is dissolved in the range of at least 0.01 mol% or more and 5 mol% or less of the present invention will be described.

  FIG. 1 is a step flow showing a process for producing a ceramic material according to the first embodiment.

  Step S110: Mixing lanthanum oxide powder and alkaline earth metal fluoride powder. Here, the alkaline earth metal fluoride powder is mixed in a range of 0.01 mol% to 5 mol% with respect to the lanthanum oxide powder. As a result, a ceramic material made of lanthanum oxide in which alkaline earth metal fluoride is dissolved in a range of more than 0.01 mol% and not more than 5 mol% can be obtained.

  Preferably, the alkaline earth metal fluoride powder is mixed in a range of 0.25 mol% to 4 mol% with respect to the lanthanum oxide powder. Thereby, the ceramic material which consists of a lanthanum oxide in which alkaline earth metal fluoride is solid-solved in the range of 0.25 mol% or more and 4 mol% or less is obtained, and moisture absorption resistance can be improved.

  More preferably, the alkaline earth metal fluoride powder is mixed in a range of 0.4 mol% to 1.5 mol% with respect to the lanthanum oxide powder. As a result, a ceramic material made of lanthanum oxide in which alkaline earth metal fluoride is dissolved in the range of 0.4 mol% or more and 1.5 mol% or less is obtained, and the moisture absorption resistance can be reliably improved.

  More preferably, the alkaline earth metal fluoride powder is mixed in the range of 0.6 mol% to 1.0 mol% with respect to the lanthanum oxide powder. As a result, a ceramic material made of lanthanum oxide in which alkaline earth metal fluoride is dissolved in the range of 0.6 mol% or more and 1.0 mol% or less is obtained, and is particularly high when the ceramic material is a sintered body. It can be strength.

The alkaline earth metal fluoride powder is selected from the group consisting of beryllium fluoride, magnesium fluoride, calcium fluoride, strontium fluoride and barium fluoride. From the viewpoint of ease of production, magnesium fluoride (MgF ₂ ), calcium fluoride (CaF ₂ ) and strontium fluoride (SrF ₂ ) are preferred.

  The lanthanum oxide powder and alkaline earth metal fluoride powder used here may both be commercially available. Since commercially available lanthanum oxide powders are hygroscopic, the powders are preferably weighed and mixed in a glove box filled with an inert gas atmosphere. The inert gas atmosphere can be a rare gas element typified by helium, neon, argon, krypton, or nitrogen gas. Alternatively, lanthanum oxide powder may be heat-treated before weighing to remove moisture. Although there is no restriction | limiting in particular in heat processing conditions, For example, 1 hour may be sufficient at 1000 degreeC.

  The weighed powder may be mixed wet or dry, and may be manually pulverized and mixed using a mortar, or mechanically using a pulverizer such as a ball mill. If a ball mill is used, uniform mixing is possible.

  The mixture obtained in step S110 may be dried by a nitrogen flow or the like. Thereby, when a solvent such as ethanol is used in wet mixing, the solvent can be removed.

  In step S110, in addition to the lanthanum oxide powder and the alkaline earth metal fluoride powder, a material containing a Q element (where Q element is In and / or Ga) may be further mixed. . Thereby, a ceramic material made of lanthanum oxide in which the Q element is further dissolved is obtained, and such a ceramic material has a high relative dielectric constant.

  As the material containing the Q element, a material selected from the group consisting of metals, oxides and fluorides of the Q element can be used. For example, an oxide of Q element (indium oxide, gallium oxide) is advantageous because it is easily available. For example, fluorides of element Q (indium fluoride, gallium fluoride), together with alkaline earth metal fluorides, contribute to the reduction of oxygen vacancies in lanthanum oxide and are advantageous in improving moisture absorption resistance.

  Preferably, the raw material containing element Q is mixed in a range of more than 0 mol% and not more than 15 mol% with respect to the lanthanum oxide powder and the alkaline earth metal fluoride. Thereby, the Q element can be dissolved in the lanthanum site, and the relative dielectric constant of the lanthanum oxide can be improved. More preferably, the raw material containing element Q is mixed in a range of 4 mol% or more and 12 mol% or less with respect to the lanthanum oxide powder and the alkaline earth metal fluoride. As a result, the Q element is dissolved in the lanthanum site, and the relative dielectric constant of the lanthanum oxide can be reliably improved. More preferably, the raw material containing element Q is mixed in the range of 4 mol% or more and 8 mol% or less with respect to the lanthanum oxide powder and the alkaline earth metal fluoride. Thereby, the relative dielectric constant of lanthanum oxide can be reliably improved even with a raw material containing a small amount of Q element.

  Step S120: The mixture obtained in Step S110 is fired at a temperature in the temperature range of 1100 ° C. or higher and 1500 ° C. or lower. It should be noted that although the firing temperature is significantly lower than the melting point of lanthanum oxide (2315 ° C.), firing is possible. This is due to the alkaline earth metal fluoride powder mixed in step S110. Alkaline earth metal fluoride acts on the moisture contained in the lanthanum oxide of the raw powder, and becomes an alkaline earth metal fluoride containing partially molten moisture, which acts on the lanthanum oxide, and finally In addition, the firing temperature can be dramatically reduced. The heating furnace used for firing is not particularly limited as long as the firing temperature can achieve the above-described range, but an electric furnace or the like is illustratively used. The method of the present invention is highly versatile because it does not require a special high-temperature furnace.

  For example, when the alkaline earth metal fluoride powder is calcium fluoride powder, the firing temperature is preferably in the range of 1340 ° C. or higher and 1440 ° C. or lower. When the firing temperature is within this range, a sintered body having a high density can be obtained. In particular, when the firing temperature exceeds 1440 ° C., calcium fluoride is vaporized, and the effect of calcium fluoride may not be sufficiently obtained.

  For example, when the alkaline earth metal fluoride powder is calcium fluoride powder, the firing temperature is more preferably in the range of 1355 ° C. to 1418 ° C. When the firing temperature is within the above range, the obtained sintered body becomes sufficiently dense (high density), and calcium fluoride is reliably dissolved in lanthanum oxide. The upper limit is set to 1418 ° C. because it is the melting point of calcium fluoride.

  That is, even if calcium fluoride other than calcium fluoride is used as the alkaline earth metal fluoride powder, the preferable upper limit of the firing temperature may be the melting point of the alkaline earth metal fluoride used. If the lower limit is 70 ° C. lower than the melting point, there is no problem in firing.

  In step S110, when the raw material containing the Q element is further mixed, the firing temperature is preferably in the range of 1100 ° C. or higher and 1350 ° C. or lower. By using the raw material containing the Q element, the firing temperature can be lowered. For example, when the raw material containing the element Q is mixed in the range of 4 mol% to 12 mol%, the sintered body can be sufficiently densified even if the firing temperature is set to a temperature range of 1120 ° C. to 1300 ° C. .

  There is no particular limitation on the firing atmosphere, and firing can be performed in the air or in an inert gas atmosphere. For example, when a raw material containing Q element is not used, firing is preferably performed in an inert gas atmosphere. Thereby, evaporation of the alkaline earth fluoride is suppressed, and the alkaline earth fluoride is effectively dissolved in the lanthanum oxide, so that it can be densified. For example, when a raw material containing Q element is used, it is preferably fired in the air. The thin film formed by using the sintered body thus obtained as a target can have a higher relative dielectric constant.

  The inert gas atmosphere can be a rare gas element typified by helium, neon, argon, krypton, or nitrogen gas. Thereby, the solid solution of alkaline earth metal fluoride in lanthanum oxide is promoted. The firing time is not particularly limited but is 0.5 hours or more and 10 hours or less. When the firing time is shorter than 0.5 hour, the alkaline earth metal fluoride may not be sufficiently dissolved in lanthanum oxide. Even if the firing time exceeds 10 hours, the solid solution may not change any more. More preferably, the firing time is in the range of 1 hour to 5 hours. Thereby, the alkaline earth metal fluoride is efficiently dissolved in lanthanum oxide.

  By such steps S110 to S120, a powdered ceramic material made of lanthanum oxide in which alkaline earth metal fluoride is dissolved in the range of at least 0.01 mol% to 5 mol% of the present invention is obtained.

  Prior to step S120, the mixture may be compacted. For compacting, for example, a normal apparatus such as cold isostatic pressing (CIP) or uniaxial pressing is employed. For example, when the ceramic material is a sintered body such as a target or a pellet, since the powders are in close contact with each other by compacting in the firing in step S120, the alkaline earth metal fluoride is dissolved in lanthanum oxide. Is promoted to obtain a dense sintered body.

  Alternatively, in step S120, hot isostatic pressing (HIP) or hot press may be used. Thereby, since it can calcinate in the state where powders adhered more closely, solid solution to alkaline-earth metal fluoride in lanthanum oxide is promoted, and a denser sintered body is obtained.

  When the ceramic material of the present invention is a thin film, following the above-described steps, the ceramic material, which is the sintered body of the present invention, is used as a target, and a physical atmosphere represented by sputtering, pulse laser deposition, and vapor deposition is used. A thin film can be obtained on a predetermined substrate by the phase growth method. The predetermined substrate is not particularly limited as long as it has a surface on which a thin film can be formed. For example, a glass substrate, a semiconductor substrate such as single crystal silicon, single crystal germanium, or a metal electrode is provided to them. And the like.

  As described above, according to the production method of the present invention, by using a predetermined amount of alkaline earth metal fluoride, the melting point of lanthanum oxide is drastically lowered, and the temperature in the temperature range of 1100 ° C. or higher and 1500 ° C. or lower. Since the above-mentioned ceramic material can be obtained simply by firing, the skill and special equipment are not required, and the versatility is high.

So far, attention has been focused on lanthanum oxide, but the present invention can also be applied to rare earth oxides other than lanthanum oxide. For example, holmium oxide (Ho ₂ O ₃ ), erbium oxide (Er ₂ O ₃ ), europium oxide (Er ₂ O ₃ ), lutetium oxide (Lu ₂ O ₃ ), scandium oxide (Sc ₂ O ₃ ), thulium oxide ( Tm ₂ O ₃ ), ytterbium oxide (Yb ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), etc. are also hygroscopic, and, like lanthanum oxide, alkaline earth metal fluorides are dissolved in them. If it is made, moisture absorption resistance can be improved.

  In addition, rare earth oxides other than lanthanum oxide also have a high melting point, making it difficult to produce a sintered body. Therefore, if a rare earth oxide other than lanthanum oxide is also baked with an alkaline earth metal fluoride, the melting point of the rare earth oxide can be lowered, so that a high-quality sintered body can be obtained.

(Embodiment 2)
In the second embodiment, the application of the ceramic material described in the first embodiment will be described. As described in the first embodiment, when the ceramic material is a powder, it can be used as a raw material powder for a solid phase reaction, and when the ceramic material is a sintered body, physical vapor deposition is possible. It can be used as a target in law. In the second embodiment, an application when the ceramic material is a thin film will be described.

  FIG. 2 is a schematic diagram of a semiconductor device according to the second embodiment.

  The semiconductor device 200 is a capacitor. The semiconductor device 200 includes a first conductive layer 210, a second conductive layer 220 facing the first conductive layer 210, and a dielectric positioned between the first conductive layer 210 and the second conductive layer 220. Body thin film (insulator thin film) 230.

  The first conductive layer 210 and the second conductive layer 220 are existing metal electrodes such as platinum (Pt), gold (Au), platinum iridium (Pt-Ir), or semiconductors such as silicon and polysilicon. obtain. Here, both the first conductive layer 210 and the second conductive layer 220 are metal electrodes.

The dielectric thin film 230 is made of the ceramic material described in the first embodiment. Since the dielectric thin film 230 exhibits the relative dielectric constant of lanthanum oxide without being affected by moisture, the film thickness can be increased, for example, in the range of 2 nm to 4 nm. For example, the equivalent equivalent film thickness (EOT) of SiO ₂ (relative dielectric constant: 3.8), which is well-known as an existing dielectric material, is 0.5 nm. You can see that it can be thicker.

  Such a structure is known as a metal / insulator / metal MIM structure or a metal / insulator / semiconductor MIS structure (also referred to as a MOS capacitor), and includes a first conductive layer 210 and a second conductive layer 220. It is connected to the circuit through a terminal connected to.

  A method for manufacturing the semiconductor device 200 will be described. The semiconductor device 200 is manufactured by a physical vapor deposition method.

  First, a metal thin film is formed as the first conductive layer 210 on a substrate having a smooth surface. Next, a thin-film ceramic material is formed as the dielectric thin film 230 on the first conductive layer 210 using the ceramic material that is the sintered body obtained in Embodiment 1 as a target. Note that when the dielectric thin film 230 has a desired shape, a metal mask may be used on the first conductive layer 210. Next, a metal thin film is formed as the second conductive layer 220 on the dielectric thin film 230.

  FIG. 3 is a schematic diagram of another semiconductor device according to the second embodiment.

  The semiconductor device 300 has a metal / oxide / semiconductor (MOS) type transistor (MOSFET) structure. In the semiconductor device 200 described with reference to FIG. 2, the first conductive layer 210 is made of silicon or the like. This is the case of a semiconductor.

  The semiconductor device 300 includes a first conductive layer made of a semiconductor substrate 330 having a source region 310 / drain region 320 formed at a distance from the surface thereof, a second conductive layer 340 facing the first conductive layer, A dielectric thin film (insulator thin film) 350 is provided between the first conductive layer and the second conductive layer 340. The semiconductor substrate 330 is not limited as long as it is an existing semiconductor substrate, but single crystal silicon, single crystal germanium, or the like is preferable from the viewpoint of consistency with a dielectric thin film formed thereon.

  The semiconductor substrate 330 has a first conductivity type (for example, p-type), and the source region 310 / drain region 320 has a second conductivity type (for example, n-type). Further, for example, a p-type impurity is implanted into the channel region between the source region 310 and the drain region 320, and can be controlled to have a desired threshold voltage. The conductivity type may be reversed.

  Dielectric thin film 350 is made of the ceramic material described in the first embodiment. Since the dielectric thin film 350 exhibits the relative dielectric constant of lanthanum oxide without being affected by moisture, the film thickness can be increased, for example, in the range of 2 nm to 4 nm. The dielectric thin film 350 is located at least on the semiconductor substrate 330 between the source region 310 and the drain region 320. The dielectric thin film 350 may be part of the source region 310 / drain region 320.

  The second conductive layer 340 is an existing metal electrode such as platinum (Pt), gold (Au), platinum iridium (Pt—Ir), and functions as a gate electrode.

  An exemplary method for manufacturing the semiconductor device 300 will be described. Although a case where the semiconductor substrate 330 is p-type silicon and the source region 310 / drain region 320 is formed after the second conductive layer 340 (gate electrode) is described here, this is not restrictive.

  An element isolation insulating film is formed on the semiconductor substrate 330 by local oxide film technology (LOCOS) or shallow trench isolation (STI), and an element region and an element isolation region are formed. The element region is subjected to hydrofluoric acid treatment, and the surface of the semiconductor substrate 330 is terminated with hydrogen. Note that a p-type impurity may be implanted to form a channel region so that a desired threshold voltage can be obtained.

  A thin-film ceramic material is formed as the dielectric thin film 350 on the semiconductor substrate 330 by a physical vapor deposition method using the ceramic material, which is the sintered body obtained in the first embodiment, as a target. A metal thin film is formed as the second conductive layer 340 on the dielectric thin film 350.

  The second conductive layer 340 and the dielectric thin film 350 are sequentially patterned using a known lithography technique or etching technique. Thereafter, an n-type impurity is implanted to form the source region 310 / drain region 320.

Although FIG. 3 shows a metal / oxide (insulator) / semiconductor transistor (MOSFET) structure, the present invention is not limited to this. As long as the thin film made of the ceramic material described in Embodiment 1 is used as the oxide (insulator), metal / ferroelectric / insulator / semiconductor transistor (MFISFET), metal / ferroelectric / metal / insulator / Semiconductor transistor (MFMISFET), metal / insulator / ferroelectric / insulator / metal / semiconductor transistor (MIFIMISFET), metal / ferroelectric / insulator / metal / insulator / semiconductor transistor (MFIMSIS) and metal / insulator / Ferroelectric / metal / insulator / semiconductor transistor (MIFMISFET). The ferroelectric material used here is a known ferroelectric material. From the viewpoint of consistency with the ceramic material of the present invention, for example, lead zirconate titanate (Pb (Zr, Ti) O) ₃ ), bismuth strontium tantalate (SrBi ₂ Ta ₂ O ₉ ) and the like are preferable.

  When the ceramic material of the present invention is used for at least one oxide or insulator of the above-described transistor, it is not affected by moisture in the atmosphere, so that a semiconductor device that operates stably over a long period of time can be provided.

  The present invention will now be described in detail using specific examples, but it should be noted that the present invention is not limited to these examples.

  First, in Examples / Comparative Examples 1 to 5, ceramic materials that were sintered bodies were examined.

[Example 1]
In Example 1, a ceramic material, which is a sintered body, made of lanthanum oxide in which 1.5 mol% of calcium fluoride (CaF ₂ ) was dissolved as an alkaline earth metal fluoride was manufactured. Here, the general formula of the obtained lanthanum oxide sintered body is (La _0.985 Ca _0.015 Q _z ) ₂ (O _1-y F _y ) ₃ (0.008 ≦ y ≦ 0.03, z = 0).

  Lanthanum oxide powder (rare metallic, purity 99.99%) and calcium fluoride powder (Wako Pure Chemicals, purity 99.9%) were mixed (step S110 in FIG. 1). Here, it mixed so that calcium fluoride powder might be 1.5 mol% with respect to lanthanum oxide powder. In addition, the lanthanum oxide powder heat-processed at 1000 degreeC for 1 hour was used for weighing. These raw material powders were pulverized and mixed for 10 hours by a ball mill using zirconia balls (ball diameter: 3 mm). The mixing was wet mixing using ethanol as a solvent. After grinding and mixing, the mixture was dried under nitrogen flow.

  Next, the mixture was compacted by uniaxial pressure molding (40 MPa). The molded shape was a pellet with a diameter of 10 mm and a thickness of 2.0 mm.

  Next, the mixture (molded body) after compacting was fired in a temperature range of 1100 ° C. or higher and 1500 ° C. or lower (step S120 in FIG. 1). Specifically, the pellet-like mixture is placed on a zirconia setter and is fired at 1280 ° C, 1325 ° C, 1340 ° C, 1360 ° C, 1380 ° C, 1400 ° C, 1425 ° C, and 1440 ° C in a siliconit furnace, Sintering was performed for 2 hours while flowing nitrogen gas as an inert gas atmosphere. The rate of temperature increase and the rate of temperature decrease was 220 ° C./hour.

  The state of temporal change in the atmosphere of the sintered body thus obtained was examined. The results are shown in FIG. The density was calculated from the weight and shape of the sintered body. The results are shown in FIG. Each sintered body was mirror-finished using a 9 μm diamond slurry. The size of the obtained sintered body was 6.95 mm in diameter and 1.6 mm in thickness. Powder X-ray diffraction was performed on the sintered body. The results are shown in FIG.

[Comparative Example 2]
In Comparative Example 2, a sintered ceramic material made of lanthanum oxide, in which the alkaline earth metal fluoride was not dissolved, was produced. The firing conditions of Comparative Example 2 were the same as those of Example 1 except that the firing temperature was 1360 ° C. The state of temporal change in the atmosphere of the sintered body of Comparative Example 2 was examined. The results are shown in FIG.

[Example 3]
In Example 3, a ceramic material which is a sintered body made of lanthanum oxide in which calcium fluoride (CaF ₂ ) as an alkaline earth metal fluoride is solid-dissolved in 0.25 mol%, 1 mol%, 1.5 mol% and 4 mol%. Manufactured. The firing conditions of Example 3 were the same as those of Example 1 except that the firing temperatures were 1400 ° C. and 1440 ° C.

Formula lanthanum oxide sintered body obtained _{here, (La 1-x-z} Ca x Q z) 2 (O 1-y F y) 3 (x = 0.0025,0.01,0.015 0.04, 0.005 ≦ y ≦ 0.08, z = 0). Moreover, the sintered body of x = 0.015 (same as the sintered body in which the solid solution amount of CaF ₂ is 1.5 mol%) was the same as the sample of Example 1.

  About the obtained sintered compact, the mode of a time-dependent change was investigated similarly to Example 1, and the density was measured. The results are shown in FIG. 7 and FIG.

As in Example 1, each sintered body was mirror-finished using a 9 μm diamond slurry. Powder X-ray diffraction was performed on the obtained sintered body. Furthermore, a 30 nm thick gold thin film was deposited on the surface of the sintered body. Using this sample, a secondary ion mass spectrometer (SIMS, device name) using oxygen, fluorine was measured calcium isotope ⁽⁴⁴ Ca) and lanthanum. Specifically, using O ⁻ as primary ions, positive ions flying from the surface of the sintered body as secondary ions are measured, and the ionic strength ratio (F / ¹⁶ O) and ionic strength ratio ( ⁴⁴ Ca / La) are determined. Asked. The results are shown in Table 2 and FIG.

[Example 4]
In Example 4, a ceramic material, which is a sintered body, made of lanthanum oxide in which 1.0 mol% of calcium fluoride (CaF ₂ ) was dissolved as an alkaline earth metal fluoride was manufactured. The firing conditions of Example 4 were the same as those of Example 3 except that the firing atmosphere was air and the firing temperature was 1400 ° C. The sintered body of Example 4 was compared with that of Example 3. The results will be described later.

[Comparative Example 5]
In Comparative Example 5, a ceramic material, which was a sintered body, was made of lanthanum oxide in which 0.01 mol% of calcium fluoride (CaF ₂ ) was dissolved as an alkaline earth metal fluoride. The firing conditions of Comparative Example 5 were the same as those of Example 3. As in Example 3, the state of change with time was examined, and SIMS measurement was performed. The results are shown in Table 2 and FIGS.

  For the sake of simplicity, a list of firing conditions for the above Examples / Comparative Examples 1 to 5 is shown in Table 1 and the results will be described.

  FIG. 4 is a diagram illustrating a change with time of a sintered body according to Example 1 / Comparative Example 2. FIG.

  4 shows lanthanum oxide fired at 1380 ° C. as a sintered body according to Example 1. FIG. FIG. 4A shows a state immediately after firing, and FIG. 4B shows a state of being left in the atmosphere for one day.

  According to Fig.4 (a), the sintered compact by Example 1 immediately after baking was hard and easy to handle. On the other hand, the sintered body of Comparative Example 2 immediately after firing was brittle and it was difficult to measure the shape. According to FIG. 4B, the sintered body of Example 1 did not change in shape even when left in the atmosphere for 1 day, and was stable in the atmosphere. On the other hand, when the sintered body of Comparative Example 2 was left in the atmosphere for 1 day, it completely disintegrated and became powder. Although not shown, the sintered body fired at other temperatures according to Example 1 was also stable in the air.

  From this, it was shown that the hygroscopic resistance is improved by solid solution of alkaline earth metal fluoride in lanthanum oxide.

  FIG. 5 is a diagram showing the sintering temperature dependence of the density of the sintered body according to Example 1.

According to FIG. 5, in the temperature range of 1100 ° C. or more and 1500 ° C. or less, the mixture of lanthanum oxide and alkaline earth metal fluoride is sintered, and a sintered body having a density of 5.3 g / cm ³ or more and I found out that In particular, when the alkaline earth metal fluoride is calcium fluoride, a sintered body having a relatively high density can be obtained at a firing temperature in the range of 1340 ° C. to 1440 ° C., and 1355 ° C. to 1418 ° C. It was confirmed that a denser sintered body with a higher density was obtained at a firing temperature in the following temperature range. The density of the sintered body fired at a temperature of 1420 ° C. or higher was remarkably reduced because the firing temperature exceeded the melting point of calcium fluoride (1418 ° C.) and evaporation due to melting of calcium fluoride occurred. From this, it can be said that the upper limit of the firing temperature is desirably the melting point of the alkaline earth metal fluoride.

  6 is a diagram showing an XRD pattern of the sintered body according to Example 1. FIG.

In FIG. 6, the XRD pattern of the lanthanum oxide baked at 1380 degreeC as a sintered compact of Example 1 is shown. According to FIG. 6, all the diffraction peaks corresponded to the diffraction peak (JCPDS # 05-0602) of lanthanum oxide (La ₂ O ₃ ). Further, there was no diffraction peak indicating impurities (for example, undissolved calcium fluoride). Although not shown, the XRD pattern of the sintered body fired at other temperatures was the same. From this, it was found that the ceramic material obtained by the production method shown in FIG. 1 is composed of lanthanum oxide in which calcium fluoride is dissolved as an alkaline earth metal fluoride. Further, it is suggested that the alkaline earth metal fluoride functions as a sintering aid and does not segregate in the glass phase at the grain boundary but is dissolved in the lanthanum oxide site.

  FIG. 7 is a diagram showing a change over time of the sintered bodies according to Example 3 / Comparative Example 5. FIG.

  FIG. 7 shows the change over time of the sintered body fired at 1400 ° C. FIG. 7A shows a state immediately after firing only the sintered body of Comparative Example 5, and shows a state in which all of the sintered body of Example 3 were left in the atmosphere for 1 day. FIG. 7B shows a state in which only the sintered body of Comparative Example 5 is left in the atmosphere for 1 day, and all the sintered bodies in Example 3 are left in the atmosphere for 2 days or more.

  According to FIGS. 7 (a) and 7 (b), the sintered body of Comparative Example 5 was hard and easy to handle immediately after firing, but when left in the atmosphere for one day, it collapsed into a powder. On the other hand, the sintered body of Example 3 did not change in shape even after being left in the atmosphere for 2 days or more, and was stable against changes with time in the atmosphere.

  From this, it was shown that the hygroscopic resistance is improved when more than 0.01 mol% of the alkaline earth metal fluoride is dissolved in lanthanum oxide.

FIG. 8 is a graph showing the dependency of the density of the sintered body according to Example 3 / Comparative Example 5 on the concentration of CaF ₂ added.

According to FIG. 8, the density tends to decrease as the amount of CaF ₂ added increases. From this, it was found that when the solid solution amount of the alkaline earth metal fluoride exceeds 5 mol%, the density is low, which is not preferable as a sintered body.

The appearances of the sintered body obtained in Example 3 (fired in a nitrogen atmosphere) and the sintered body obtained in Example 4 (fired in air) were compared. The sintered body obtained in Example 3 was a dense sintered body as shown in FIG. Similarly, the sintered body obtained in Example 4 was also a dense sintered body. In addition, the sintered body obtained in Example 4 did not change in shape even when left in the atmosphere for 1 day or longer, and was stable in the atmosphere. However, when comparing the density, the density of the sintered body of Example 4 (5.337g / cm ³⁾ was slightly smaller than that (5.456g / cm ³⁾ of the sintered body of Example 3. This is because calcium fluoride evaporated by firing in the atmosphere, and the effect of densification by solid solution was not sufficiently obtained.

  From this, it was shown that the lanthanum oxide in which the alkaline earth metal fluoride is dissolved can be obtained in the air or in the inert gas atmosphere, but in order to obtain a dense lanthanum oxide. It was shown that the firing atmosphere is preferably an inert gas atmosphere.

FIG. 9 is a graph showing the dependency of the CaF ₂ addition concentration on the ionic strength ratio of F / O and ⁴⁴ Ca / La in the sintered body according to Example 3 / Comparative Example 5.

According to FIG. 9, it was found that the secondary ionic strength ratio of F / O and ⁴⁴ Ca / La both increased linearly with the increase of the CaF ₂ addition concentration. From this, it was shown that in the lanthanum oxide in which CaF ₂ was dissolved, Ca was dissolved in the La site and F was dissolved in the O site.

According to Table 2, the ionic strength ratio of F (fluorine) to ¹⁶ O (oxygen) (F / ¹⁶ O) and the ionic strength ratio of ⁴⁴ Ca (calcium isotope) to La (lanthanum) (M / La) Respectively
0.0013 <F / ¹⁶ O ≦ 0.15, and
0.0012 < ⁴⁴ Ca / La ≦ 6
I found out that From the viewpoint of density, preferably,
0.01 ≦ F / ¹⁶ O ≦ 0.091, and
0.13 ≦ ⁴⁴ Ca / La ≦ 4.6
From the viewpoint of moisture absorption resistance as well as density, preferably,
0.016 ≦ F / ¹⁶ O ≦ 0.042, and
0.25 ≦ ⁴⁴ Ca / La ≦ 1.5
And more preferably
0.024 ≦ F / ¹⁶ O ≦ 0.031, and
0.4 ≦ ⁴⁴ Ca / La ≦ 0.75
It turns out that it satisfies.

  Next, in Examples / Comparative Examples 6 to 8, ceramic materials that are thin films were studied.

[Example 6]
In Example 6, a sintered body (diameter: 16.5 mm, thickness: 2.3 mm) obtained by the same method as in Example 3 (firing temperature: 1400 ° C.) by pulse laser deposition (PLD) is used as a target. A ceramic material, which is a thin film made of lanthanum oxide in which calcium fluoride (CaF ₂ ) is dissolved as an alkaline earth metal fluoride on a glass substrate, was manufactured.

For ablation of PLD, KrF excimer laser 248 nm and repetition frequency 5 Hz were used. The film forming conditions were a target-substrate distance of 5 cm, a substrate temperature of 700 ° C., and an oxygen partial pressure of 1 × 10 ⁻⁵ Torr. The film formation time was 60 minutes. The film thickness of the obtained thin film was measured by the X-ray reflectivity method.

  The time course of the obtained thin film was examined. The state of the surface immediately after film formation and one day after film formation was observed with an optical microscope, and an X-ray diffraction pattern was measured. Here, the thin film was stored in a desiccator for 3 days or more. The results are shown in FIG. 10 and FIG.

[Comparative Example 7]
In Comparative Example 7, a sintered body (diameter: 17.0 mm, thickness: 2.1 mm) obtained by PLD in the same manner as in Comparative Example 5 (firing temperature: 1400 ° C.) was used as a target on a glass substrate. A ceramic material, which is a thin film made of lanthanum oxide in which calcium fluoride (CaF ₂ ) as a solid earth metal fluoride was dissolved, was manufactured. The film forming conditions were the same as in Example 6. About the obtained thin film, the surface was observed with the optical microscope similarly to Example 6, and the XRD diffraction pattern was measured. The results are shown in FIG. 10 and FIG.

[Example 8]
In Example 8, a capacitor having an MIM structure, which is a ceramic material / metal, which is a thin film made of lanthanum oxide in which calcium fluoride (CaF ₂ ) is dissolved as a metal / alkaline earth metal fluoride, was manufactured.

Calcium fluoride (CaF ₂ ) was used in the same procedure as in Example 6 except that a silicon substrate on which platinum (the first conductive layer 210 in FIG. 2) was deposited was used and the film formation time was 120 minutes. A ceramic material, which is a thin film made of lanthanum oxide in a solid solution, was formed. Gold (second conductive layer 220 in FIG. 2) was vacuum-deposited on the surface of the obtained thin film. Thus, an MIM structure capacitor using a thin film made of the ceramic material of the present invention was manufactured. In this example, a sufficiently thick film was obtained in order to accurately measure the dielectric characteristics. However, in an actual semiconductor device, the film formation time is appropriately controlled according to desired dielectric characteristics and insulation characteristics. It should be understood that the thickness is 2 nm or more and 4 nm or less.

  The dielectric properties of the obtained capacitor were measured. The measurement conditions were a measurement frequency of 100 kHz and a measurement signal level of 0.5V. The results will be described later.

  For the sake of simplicity, Table 3 shows a list of film forming conditions in the above Examples / Comparative Examples 6-8.

  FIG. 10 is a diagram showing the change over time of the thin films according to Example 6 and Comparative Example 7.

FIG. 10 shows lanthanum oxide in which 1 mol% of CaF ₂ is dissolved as the thin film of Example 6. FIGS. 10A and 10C show the state immediately after the thin film formation of Comparative Example 7 and after one day have passed, respectively. FIGS. 10B and 10D show the state immediately after the formation of the thin film of Example 6 and after 3 days, respectively.

According to FIGS. 10A and 10B, the surfaces of the thin films of Comparative Example 7 and Example 6 were both smooth. In the figure, it is shown by grayscale shading, but since there is no difference in shading, it can be seen that it is smooth. According to FIG.10 (c), when the surface of the thin film of the comparative example 7 passed for 1 day, it was rough with the water | moisture content in air | atmosphere, and light and shade appeared clearly. On the other hand, as shown in FIG. 10 (d), the surface of the thin film of Example 6 is smooth and stable to the atmosphere even after 3 days, as in FIG. 10 (b). It was confirmed that the moisture absorption resistance was improved. Although not shown, the same results were obtained for other thin films of CaF _{2 in} Example 6.

  FIG. 11 is a diagram showing the influence of the temporal change of the thin film according to Example 6 and Comparative Example 7 on the XRD diffraction pattern.

FIG. 11 shows lanthanum oxide in which 1 mol% of CaF ₂ is dissolved as the thin film of Example 6. 11A and 11B show the XRD patterns of the thin films of Comparative Example 7 and Example 6, respectively. According to FIG. 11 (a), the thin film immediately after film formation of Comparative Example 7 showed diffraction peaks of (002) and (100) indicating lanthanum oxide, but these diffraction peaks disappeared after one day. . On the other hand, according to FIG. 11 (b), the thin film of Example 6 showed a sharp diffraction peak of (002) indicating lanthanum oxide both after film formation and after the lapse of 3 days. Did not show. Although not shown, the same results were obtained for other thin films of CaF _{2 in} Example 6.

  From the above, a ceramic material that is a sintered body made of lanthanum oxide in which alkaline earth metal fluoride is dissolved is effective as a target, and even in a thin film, it is resistant to solid solution by dissolution of alkaline earth metal fluoride in lanthanum oxide. It has been shown that the hygroscopicity is improved and the solid solution amount of the alkaline earth metal fluoride is preferably more than 0.01 mol%.

According to the dielectric measurement of the capacitor having the MIM structure according to the example 8, from the obtained capacitance, the solid solution amount (0.25, 1, 1.5 and 4 omole%) of any CaF ₂ was determined as an insulator (dielectric). The relative dielectric constant of a ceramic material made of lanthanum oxide in which CaF _{2 as a} thin film is a solid solution has a value exceeding 20 and is comparable to the relative dielectric constant (27) known as the eigenvalue of lanthanum oxide. It was.

  This indicates that a ceramic material made of lanthanum oxide in which an alkaline earth metal fluoride is dissolved can function as an insulator thin film of a semiconductor device or a dielectric thin film having a high dielectric constant.

[Example 9]
In Example 9, a capacitor having a MIM structure as a ceramic material / metal, which is a thin film made of calcium fluoride (CaF ₂ ) as a metal / alkaline earth metal fluoride and lanthanum oxide in which In as a Q element was dissolved, was manufactured. .

Prior to manufacturing the capacitor, sintered bodies 9-1 to 9-6 were manufactured as ceramic materials made of lanthanum oxide in which CaF ₂ and In were dissolved. Here, the general formula of the obtained sintered body is (La _1−x−z Ca _x Q _z ) ₂ (O _1−y F _y ) ₃ (Q is In, x = 0.0025, 0. 0002 <y ≦ 0.005, z = 0.01, 0.03, 0.06, 0.1). The same procedure as in Example 1 was performed except that indium oxide (manufactured by Wako Pure Chemicals, purity 99.9%) was used as a raw material. Table 4 shows the firing conditions of the sintered body.

All sintered bodies were stable without being changed in shape even after being baked for 1 day in the air. Moreover, when powder X-ray diffraction was performed on the obtained sintered body, the diffraction peak of any sintered body coincided with the diffraction peak of lanthanum oxide, and a diffraction peak indicating calcium fluoride or indium oxide was observed. There wasn't. From this, it was found that the obtained sintered body was composed of lanthanum oxide in which calcium fluoride as alkaline earth metal fluoride and In (indium) as Q element were dissolved. Moreover, the density of the obtained sintered compact, for example, the sintered compact 9-4, was 6.249 g / cm ³ , and it was confirmed that the relative density was improved to 96%.

Next, using the obtained sintered bodies 9-1 to 9-6 as targets, a ceramic material / metal which is a thin film made of lanthanum oxide in which CaF ₂ and In are dissolved in the same procedure as in Example 8. Capacitors 9-1 ′ to 9-6 ′ having a certain MIM structure were manufactured. Table 5 shows the film forming conditions. In the same manner as in Example 8, the dielectric characteristics of the obtained capacitor were measured. The results are shown in Table 6 and FIG.

  FIG. 12 is a graph showing the indium concentration dependency of the relative permittivity of the capacitors 9-2 'to 9-6' according to the ninth embodiment.

12 and Table 6 also show values of relative dielectric constants of the capacitor of Example 8 (CaF ₂ addition concentration is 0.25 mol%). According to FIG. 12, the relative permittivity tends to increase by dissolving In as the Q element. Specifically, the relative dielectric constant is improved when In is in the range of more than 0 mol% and not more than 15 mol%. In particular, referring to Table 6, since a large relative dielectric constant exceeding 30 was obtained when the solid solution amount of In was 6 mol% and 10 mol%, the solid solution amount of In was 4 mol if the error was taken into consideration. % To 12 mol% is preferable, and it was confirmed that a large relative dielectric constant can be obtained even with a small solid solution amount of 4 mol% to 8 mol%.

  Further, when 9-3 ′ and 9-5 ′ of Example 9 are compared with 9-4 ′ and 9-6 ′, a higher relative dielectric constant can be obtained by using a sintered body fired in the atmosphere as a target. It was found that a thin film made of a ceramic material having

[Example 10]
In Example 10, a capacitor having a MIM structure as a ceramic material / metal, which is a thin film made of calcium fluoride (CaF ₂ ) as a metal / alkaline earth metal fluoride and lanthanum oxide in which Ga as a Q element was dissolved, was manufactured. . Raw gallium oxide (manufactured by Wako Pure Chemical Industries, Ltd., purity 99.9%) using the general formula _{(La 1-x-z Ca} x Q z) 2 (O 1-y F y) 3 (Q is Ga, except that the sintered body represented by x = 0.005, 0.0002 <y ≦ 0.005, z = 0.06) was fired and used for capacitor production (film formation time was 120 minutes). Was the same procedure as in Example 9. When the dielectric properties were measured in the same manner as in Example 9, a relative dielectric constant exceeding the theoretical value (27) of lanthanum oxide was obtained.

  From the above Example 9 and Example 10, the ceramic material, which is a sintered body made of lanthanum oxide in which the Q element (Q is In and / or Ga) in addition to the alkaline earth metal fluoride, is obtained. In addition to moisture absorption resistance, the relative dielectric constant has been improved, and the thin film obtained using this sintered body as a target also has moisture absorption resistance and high relative dielectric constant, making it an excellent semiconductor device. It was shown that it can be provided.

  Since the ceramic material made of lanthanum oxide in which alkaline earth metal fluoride is solid-solved in the range of more than 0.01 mol% and less than 5 mol% of the present invention is excellent in moisture absorption resistance, the raw material powder, the sintered compact target, It is advantageous for thin films. Semiconductor devices using such ceramic materials, such as MOS capacitors, MOSFETs, MFISFETs, MFMISFETs, MFIMISFETs, MFIMISFETs, and MIFMISFETs, have excellent moisture absorption resistance, operate stably over a long period of time, and have an inherently high ratio of lanthanum oxide. Dielectric constant can be demonstrated.

200, 300 Semiconductor device 210 First conductive layer 220, 340 Second conductive layer 230, 350 Dielectric thin film / insulator thin film 310 Source region 320 Drain region 330 Semiconductor substrate

Claims (20)

  A ceramic material comprising lanthanum oxide in which an alkaline earth metal fluoride is solid-solved in a range from 0.01 mol% to 5 mol%.   The ceramic material according to claim 1, wherein the alkaline earth metal fluoride is solid-solved in a range of 0.25 mol% to 4 mol%.   The ceramic material according to claim 1, wherein the alkaline earth metal fluoride is solid-solved in a range of 0.4 mol% to 1.5 mol%.   The ceramic material according to claim 1, wherein the alkaline earth metal fluoride is solid-solved in a range of 0.6 mol% to 1.0 mol%. The ceramic according to claim 1, wherein the alkaline earth metal fluoride is selected from the group consisting of magnesium fluoride (MgF ₂ ), calcium fluoride (CaF ₂ ), and strontium fluoride (SrF ₂ ). material.   2. The ceramic material according to claim 1, wherein the lanthanum oxide further contains a Q element (wherein the Q element is In and / or Ga).   The ceramic material according to claim 6, wherein the Q element is solid-solved in a range of more than 0 mol% and not more than 15 mol%.   The ceramic material according to claim 7, wherein the Q element is in a solid solution in a range of 4 mol% to 12 mol%. F (fluorine) for ¹⁶ O (oxygen) when the lanthanum oxide is analyzed by secondary ion mass spectrometry using O ⁻ as primary ions and positive ions flying from the lanthanum oxide as secondary ions. The ionic strength ratio (F / ¹⁶ O) and the ionic strength ratio (M / La) of the alkaline earth element M to La (lanthanum) are respectively
0.0013 <F / ¹⁶ O ≦ 0.15, and
0.0012 <M / La ≦ 6
The ceramic material according to claim 1, wherein: The lanthanum oxide is represented by the general formula _{(La 1-x-z M} x Q z) 2 (O 1-y F y) 3 ( wherein, La is lanthanum, M is an alkaline earth element, Q is , In and / or Ga, O is oxygen and F is fluorine), and the parameters x, y and z are respectively
0.0001 <x ≦ 0.05,
0.0002 <y ≦ 0.1, and
0 ≦ z ≦ 0.15
The ceramic material according to claim 1, wherein: The parameters x and y are respectively
0.0025 ≦ x ≦ 0.04, and
0.005 ≦ y ≦ 0.08,
The ceramic material according to claim 10, wherein: The parameters x and y are respectively
0.004 ≦ x ≦ 0.015, and
0.008 ≦ y ≦ 0.03
The ceramic material according to claim 11, wherein: A method for producing a ceramic material comprising lanthanum oxide in which an alkaline earth metal fluoride is dissolved in a range of 0.01 mol% to 5 mol%,
A step of mixing lanthanum oxide powder and alkaline earth metal fluoride powder, wherein the alkaline earth metal fluoride powder is more than 0.01 mol% and less than 5 mol% with respect to the lanthanum oxide powder. Mixed, steps, and
Calcining the mixture obtained in the mixing step at a temperature in the temperature range of 1100 ° C. or higher and 1500 ° C. or lower.   The method according to claim 13, wherein the mixing step further includes a material containing a Q element (wherein the Q element is In and / or Ga).   15. The method of claim 14, wherein the material containing the Q element is selected from the group consisting of the Q metal, oxide and fluoride.   The method according to claim 14, wherein the material containing the Q element is mixed in a range of more than 0 mol% and not more than 15 mol% with respect to the lanthanum oxide powder and the alkaline earth metal fluoride powder. A target comprising a sintered body used in physical vapor deposition,
The said sintered compact is a target which consists of a ceramic material in any one of Claims 1-12.   The target according to claim 17, wherein the physical vapor deposition method is selected from the group consisting of sputtering, pulsed laser deposition, and vapor deposition. A semiconductor comprising: a first conductive layer; a second conductive layer facing the first conductive layer; and a dielectric thin film positioned between the first conductive layer and the second conductive layer A device,
The said dielectric thin film is a semiconductor device which consists of a ceramic material in any one of Claims 1-12. The first conductive layer is made of a semiconductor substrate having source / drain regions formed on the surface so as to be spaced apart from each other.
The dielectric thin film is located on the semiconductor substrate between the source / drain regions;
The second conductive layer is a gate electrode;
The semiconductor device according to claim 19, wherein the semiconductor device is selected from the group consisting of MOSFET, MFISFET, MFMISFET, MIFIMSFET, MFIMISFET, and MIFMISFET.