JP2007179794A - Thin-film dielectric and thin-film capacitor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin-film dielectric with high specific dielectric constant even under high-temperature environment, with excellent leak characteristics, and easy to manufacture with due consideration that there is long since a strong need for a thin-film capacitor element with sufficient leak characteristics without degradation of leak characteristics even at high ambient temperature. <P>SOLUTION: The thin-film dielectric contains strontium titanate calcium expressed in a composite formula: (Sr<SB>1-x</SB>Ca<SB>x</SB>)<SB>y</SB>TiO<SB>3</SB>. In the formula, x, y satisfy: 0.2≤x≤0.6 and 0.97≤y≤1.10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thin film dielectric and a thin film capacitor element. In particular, the present invention relates to a thin film dielectric capable of realizing a high relative dielectric constant and a low leakage current, and a thin film capacitor element using the thin film dielectric.

  In recent years, along with the downsizing and high performance of electronic devices, the density and integration of electronic circuits have increased, and capacitor elements, which are circuit elements that perform important functions in various electronic circuits, are expected to be further downsized. It is rare.

  On the other hand, as the operating frequency of the integrated circuit increases, the rise time of the clock becomes shorter. Furthermore, lowering the voltage of the power source has been promoted with the aim of reducing the power consumption of the device. Under such conditions, when the load on the integrated circuit fluctuates rapidly, the driving voltage of the integrated circuit tends to become unstable. In order to operate the integrated circuit normally, it is necessary to stabilize the drive voltage.

  For this purpose, a decoupling capacitor is disposed between the voltage power supply line and the ground line of the integrated circuit to stabilize the drive voltage. In order for the decoupling capacitor to function effectively, it is necessary to reduce the equivalent series inductance between the integrated circuit and the decoupling capacitor and to increase the capacity of the decoupling capacitor itself.

  To reduce the equivalent series inductance between the integrated circuit and the decoupling capacitor, place the decoupling capacitor as close to the integrated circuit as possible, and place it between the integrated circuit and the decoupling capacitor. It is effective to reduce the inductance of the wiring.

  For this purpose, an interposer is arranged between the mounting substrate and the semiconductor chip mounted on the mounting substrate, and a through via electrode (through-hole electrode) is provided on the interposer, and decoupling is performed on the surface. A semiconductor device in which a capacitor is formed is disclosed (for example, see Patent Document 1). In this semiconductor device, silicon or glass is used as an insulator used for an interposer, and a thin film capacitor element is formed on a silicon or glass substrate using thin film technology.

Thin film capacitor elements using thin film dielectrics have been widely used in integrated circuits and the like as decoupling capacitors that satisfy the above requirements from the viewpoint of design freedom and the like. Conventionally, materials such as SiO ₂ and Si ₃ N ₄ have been used as materials used for thin film capacitor elements, but these materials cannot provide a large relative dielectric constant. Examples of the material having a relatively high dielectric constant include perovskite oxides such as (Ba, Sr) TiO ₃ , BaTiO ₃ , and SrTiO ₃ . In order to obtain a large capacity with a thin film capacitor element, it is also possible to make the dielectric thin, in addition to using a material having a high relative dielectric constant. However, when the dielectric is thinned, the leak characteristics are deteriorated.

A thin film capacitor element comprising a thin film dielectric layer for accumulating charges and a pair of electrodes formed opposite to each other through the thin film dielectric layer in order to improve leakage characteristics using a material having a high relative dielectric constant The dielectric has a perovskite structure represented by the general formula ABO ₃ (A is at least one of strontium, barium, and calcium, B is at least one of titanium and zirconium), and vanadium, A thin film capacitor element in which at least one of niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodymium, neodymium, gadolinium, or holmium is contained at 0.05 atomic% or more and less than 0.3 atomic% has been proposed ( For example, see Patent Document 2.) In the examples of Patent Document 2, as materials for the dielectric layer, 0.1 atomic% of niobium is added to SrTiO ₃ , 0.3 atomic% of lanthanum is added to BaTiO ₃ , and vanadium is added to SrTiO _3. Examples include 0.05 atomic%, and a leak characteristic of about 10 ⁻⁸ A / cm ² is obtained.
JP 2001-326305 A Japanese Patent Laid-Open No. 6-112082

  However, when a thin film capacitor element is used as a decoupling capacitor, it is inevitably formed in the vicinity of a heat generating element such as an LSI, so that the temperature of the thin film capacitor element becomes higher than room temperature due to the heat generated by the LSI or the like. . Further, when the thin film capacitor element is used for a vehicle, the temperature of the thin film capacitor element may be as high as 100 ° C. or more due to the influence of heat generated by mechanical parts such as an engine. Therefore, there is a demand for a thin film capacitor element that does not deteriorate the leak characteristics even when the ambient temperature becomes high and has sufficient leak characteristics even in a high temperature environment of 100 ° C. or higher.

  Accordingly, an object of the present invention is to provide a thin film dielectric having a high relative dielectric constant, good leakage characteristics, and stable characteristics even in a high temperature environment. Another object of the present invention is to provide a thin film capacitor element having a high capacity and high reliability by using this thin film dielectric.

In order to solve the above problems, the inventors focused attention on the atomic ratio in strontium calcium titanate whose composition formula is represented by (Sr _1-x Ca _x ) _y TiO ₃ . As a result of extensive development, the inventors have found an atomic ratio that can achieve good leakage characteristics even in a high temperature environment, and have completed the present invention. Specifically, the thin film dielectric according to the present invention is a thin film dielectric containing strontium calcium titanate whose composition formula is represented by (Sr _1-x Ca _x ) _y TiO ₃ , The number ratio x is 0.2 ≦ x ≦ 0.6, and the atomic number ratio y is 0.97 ≦ y ≦ 1.10. By setting the atomic number ratios x and y to the above values, a thin film dielectric containing strontium calcium titanate can be a thin film dielectric having a high relative dielectric constant and good leakage characteristics even in a high temperature environment.

In the thin film dielectric, the thin film dielectric further contains a Mn element, and the composition formula of the strontium calcium titanate is represented by (Sr _1-x Ca _x ) _y (Ti _1−z Mn _z ) O ₃ . It is desirable that the atomic number ratio z is 0 <z ≦ 0.05. By adding Mn element to the thin film dielectric containing strontium calcium titanate, the thin film dielectric containing strontium calcium titanate can be provided with reduction resistance and the sintering density can be increased. Further, by setting z to 0 <z ≦ 0.05, the effect of reducing the leakage current density of the thin film dielectric containing strontium calcium titanate can be increased.

  In the thin film dielectric, it is desirable that the thickness of the thin film dielectric is 30 nm to 1000 nm. By setting the film thickness to 30 nm to 1000 nm, both reduction in leakage current density and increase in capacitor capacity can be achieved.

  The thin film dielectric includes a case where the thin film dielectric has a relative dielectric constant of 100 or more at 25 ° C. The thin film dielectric includes a case where the relative dielectric constant is 100 or more under the condition of 125 ° C. When the relative dielectric constant is 100 or more, a thin film dielectric containing strontium calcium titanate can be a highly reliable thin film dielectric. Furthermore, when the relative dielectric constant is 100 or more under the condition of 125 ° C., the thin film dielectric containing strontium calcium titanate can be a highly reliable thin film dielectric even in a high temperature environment.

In the thin film dielectric, the thin film dielectric includes a case where the leakage current density is 10 ⁻⁶ A / cm ² or less under the condition of an applied voltage of 50 kV / cm at 25 ° C. The thin film dielectric includes a case where the leakage current density is 10 ⁻⁶ A / cm ² or less at 125 ° C. under an applied voltage of 50 kV / cm. When the leakage current density is 10 ⁻⁶ A / cm ² or less, a thin film dielectric containing strontium calcium titanate can be a highly reliable thin film dielectric. Furthermore, when the leakage current density is 10 ⁻⁶ A / cm ² or less under the condition of 125 ° C., a thin film dielectric containing strontium calcium titanate can be made a highly reliable thin film dielectric even in a high temperature environment. .

  The thin film capacitor element according to the present invention includes a layer made of the thin film dielectric and a pair of electrodes that sandwich the layer made of the thin film dielectric. Such a thin film capacitor element can increase the capacity even in a high temperature environment. Further, the leakage current can be reduced even in a high temperature environment.

  As described above, according to the present invention, it is possible to provide a thin film dielectric having a stable characteristic with a high relative dielectric constant and good leakage characteristics even under a high temperature environment. In addition, a thin film capacitor element having a high capacity and high reliability can be provided even under a high temperature environment.

  Hereinafter, a thin film capacitor element having a single layer of a thin film dielectric will be described with reference to FIG. FIG. 1 shows a schematic cross-sectional view of a thin film capacitor element according to the present invention. A thin film capacitor element 30 shown in FIG. 1 (4) includes a Si substrate 12 as a substrate, a thermal oxide film 14, a lower electrode 16 which is one of a pair of electrodes, a layer 18 made of a thin film dielectric, and a pair of And an upper electrode 20 which is the other of the electrodes.

As the substrate, a silicon single crystal substrate, or alumina _{(Al 2 O} 3), Magushia (MgO), forsterite (2MgO · _SiO 2), steatite (MgO · _SiO 2), mullite _{(3Al 2} O 3 · 2SiO ₂ ), Beryllia (BeO), zirconia (ZrO ₂ ), aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ), ceramic polycrystalline substrate such as silicon carbide (SiC) magnesia, or obtained by firing at 1000 ° C. or lower. Glass ceramic substrate (LTCC substrate) made of alumina (crystal phase) and silicon oxide (glass phase), glass substrate such as quartz glass, single crystal substrate such as sapphire, MgO, SrTiO ₃ , or Fe-Ni alloy A metal substrate such as is exemplified. The substrate may be any material as long as it is chemically and thermally stable, generates little stress, and can maintain surface smoothness. What is necessary is just to select suitably based on the target dielectric constant and baking temperature. Among the substrates, it is preferable to use a silicon single crystal substrate (hereinafter referred to as an Si substrate) having a smooth substrate surface. In FIG. 1, a Si substrate 12 is used. When the Si substrate 12 is used, it is preferable to form a thermal oxide film (SiO ₂ film) 14 on the surface in order to ensure insulation (FIG. 1 (1)). The thermal oxide film 14 raises the temperature of the Si substrate 12 and forms an oxide film on the surface of the Si substrate 12 in an oxidizing atmosphere. The thickness of the Si substrate 12 is not particularly limited and is, for example, about 100 to 1000 μm.

  Further, via electrodes may be formed on the Si substrate 12 as necessary.

Next, the lower electrode 16 is formed on the Si substrate 12 (FIG. 1 (2)). The material of the lower electrode 16 is not particularly limited as long as it has conductivity. For example, metals such as Au, Pt, Ag, Ir, Ru, Co, Ni, Fe, Cu, Al or alloys thereof, semiconductors such as Si, GaAs, GaP, InP, SiC, ITO, ZnO, SnO _2, etc. Conductive metal oxides can be used.

  The lower electrode 16 is formed by a normal thin film forming method, and for example, a physical vapor deposition method such as a physical vapor deposition method (PVD method) or a pulse laser vapor deposition method (PLD method) can be used. . PVD methods include resistance vapor deposition, vacuum deposition methods such as electron beam heating vapor deposition, DC sputtering, high frequency sputtering, magnetron sputtering, various sputtering methods such as ECR sputtering, ion beam sputtering, high frequency ion plating, activated vapor deposition, or arc. Various ion plating methods such as ion plating, molecular beam epitaxy method, laser ablation method, ionized cluster beam evaporation method, ion beam evaporation method and the like can be used. Although the thickness of the lower electrode 16 is not specifically limited, Preferably it is 10-1000 nm, More preferably, it is about 50-200 nm.

In order to improve the adhesion between the Si substrate 12 and the lower electrode 16, an adhesion layer may be formed prior to the formation of the lower electrode 16 (not shown). Since the affinity with the thin film dielectric increases over the entire surface, the adhesion can be improved. For the adhesion layer, oxides or nitrides such as Ti, Ta, Co, Ni, Hf, Mo, and W can be used. Further, the adhesion layer is formed by vapor deposition using a PVD method or a chemical vapor deposition method (CVD method). These vapor deposition methods are appropriately selected depending on the vapor deposition material. For example to form a TiO ₂ layer by sputtering of TiO ₂ as a target.

Next, a layer 18 made of a thin film dielectric is formed on the lower electrode 16 (FIG. 1C). As described above, the thin film dielectric includes strontium calcium titanate whose composition formula is represented by (Sr _1-x Ca _x ) _y TiO ₃ , and the atomic ratio x in the composition formula is 0.2 ≦ x It is a thin film dielectric in which ≦ 0.6 and the atomic ratio y is 0.97 ≦ y ≦ 1.10. By setting the atomic ratio x to 0.2 ≦ x ≦ 0.6 and the atomic ratio y to 0.97 ≦ y ≦ 1.10, the thin film dielectric containing strontium calcium titanate can be compared even in a high temperature environment. A thin film dielectric having a high dielectric constant and good leakage characteristics can be obtained. Here, if the atomic ratio x is too small (less than 0.2), the dielectric constant tends to decrease and the leakage current density tends to increase. On the other hand, if the atomic ratio x is too large (exceeding 0.6), the leakage current density tends to increase. More preferably, the atomic ratio x is 0.3 ≦ x ≦ 0.5. On the other hand, if the atomic ratio y is too small (less than 0.97), the dielectric constant tends to decrease and the leakage current density tends to increase. On the other hand, if the atomic ratio y is too large (exceeding 1.10), the leakage current density tends to increase. More desirably, 0.98 ≦ y ≦ 1.05.

  The film thickness of the thin film dielectric is desirably 30 nm to 1000 nm. More preferably, it is 100 nm to 1000 nm. If the thickness of the layer 18 made of a thin film dielectric is less than 30 nm, the capacity of the thin film capacitor element 30 increases, but the leakage current increases. If the thickness of the layer 18 made of a thin film dielectric is greater than 1000 nm, it is difficult to form a uniform layer, and cracks tend to occur when fired.

  It is desirable to further add Mn element to the thin film dielectric. By adding Mn element to the thin film dielectric containing strontium calcium titanate, the thin film dielectric containing strontium calcium titanate can be provided with reduction resistance and the sintering density can be increased.

The addition amount of Mn element, 0 atomic ratio z when the notation formula strontium titanate calcium _{(Sr 1-x Ca x)} y (Ti 1-z Mn z) O 3 <z ≦ 0. 05 is desirable. By setting z to 0 <z ≦ 0.05, the Mn element works as an acceptor when a predetermined amount of Mn is added, so that the effect of reducing the leakage current density of the thin film dielectric containing strontium calcium titanate can be increased. . When the added amount of Mn element is larger than 0.05 in terms of the atomic ratio z, the leakage characteristics deteriorate.

  The thin film dielectric according to the present embodiment can use a normal thin film forming method. For example, it can be formed using a vacuum deposition method, a high frequency sputtering method, a pulse laser deposition method (PLD), a MOCVD (Metal Organic Chemical Deposition) method, a MOD (Metalorganic Deposition) method, a sol-gel method, or the like.

  Among the above film formation methods, the sol-gel method and the MOD method are capable of homogeneous mixing at the atomic level, easy composition control and excellent reproducibility, large area at normal pressure without the need for special vacuum equipment It is widely used because of its advantages such as that it can be formed and industrially low cost.

Hereinafter, a method of forming a thin film dielectric by the MOD method will be described in detail. First, a raw material solution for forming the layer 18 made of a thin film dielectric is prepared. When the thin film dielectric is represented by, for example, a composition formula (Sr _0.8 Ca _0.2 ) TiO ₃ , a solution of 2-ethylhexanoic acid Sr in 2-ethylhexanoic acid and 2-ethylhexanoic acid Ca A 2-ethylhexanoic acid solution and a toluene solution of Ti 2-ethylhexanoate are prepared. That is, these three kinds of solutions were mixed so that 2-ethylhexanoic acid Sr was 0.8 mol, 2-ethylhexanoic acid Ca was 0.2 mol, and 2-ethylhexanoic acid Ti was 1 mol. The raw material solution can be obtained by diluting with toluene.

  In addition, when adding Mn element to the thin film dielectric having the above composition, Mn 2-ethylhexanoate is further prepared and added to the mixed solution in a predetermined amount.

  Next, this raw material solution is applied on the lower electrode 16 shown in FIG. The coating method is not particularly limited, and methods such as spin coating, dip coating, and spraying can be used. For example, the conditions for using the spin coating method are not particularly limited, and a desired number of rotations can be appropriately set. A coating film of about 5 to 600 nm can be formed by one application. After coating, the film is dried to evaporate the solvent in the coating film. The drying conditions are, for example, room temperature to 400 ° C. and about 1 minute to 60 minutes.

  Next, the dried coating film is calcined in an oxygen atmosphere. The calcining temperature may be a temperature at which the organic component in the film can be thermally decomposed and removed. For example, the calcining temperature is about 200 to 400 ° C. or about 200 to 700 ° C. for about 5 minutes to 2 hours. If the calcining temperature is too high, there are problems that the unevenness of the film surface increases due to grain growth and compositional deviation occurs. On the other hand, if the calcining temperature is too low, there is a problem that organic substances remain in the film. On the other hand, if the calcining time is too short, the organic matter is not sufficiently decomposed and remains in the film to deteriorate the leak characteristics. If the calcining time is too long, there is no problem in the film characteristics, but the time required for the process becomes long.

  Next, the process from application to calcination is further repeated once or more on the coating film after the calcination. By repeating the process, a thin film dielectric having a desired film thickness can be formed. It should be noted that if the coating thickness is increased by increasing the coating amount at one time, it is possible to reduce the number of repeating steps, but if the coating thickness is increased once, there is a problem such as generation of cracks, so at least the above range, That is, it is preferable to apply so that it may be 600 nm or less.

  Thereafter, the coating film is baked. The temperature during the main baking is performed under a temperature condition that the coating film crystallizes, and is preferably about 500 to 1000 ° C. and about 5 minutes to 2 hours. The atmosphere during the main firing is not particularly limited and may be any of an oxidizing atmosphere, a reducing atmosphere, and a neutral atmosphere. However, when a metal such as Cu or Ni is used as an electrode formed on the lower surface of the thin film dielectric. Needs to be fired at least in a non-oxidizing atmosphere.

  In the main baking, it is preferable that the film thickness after one main baking is set to 200 nm or less, preferably 10 to 200 nm. If the thickness of the coating film before firing is too thick, it tends to be difficult to obtain a well-crystallized thin film dielectric after firing. On the other hand, if it is too thin, in order to obtain a thin film dielectric having a desired film thickness, it is necessary to repeat the main firing many times, which is not economical. By repeating the steps from coating to main firing at least once, a thin film dielectric having a final film thickness of about 30 to 1000 nm can be obtained.

  The thickness of the layer 18 made of a thin film dielectric is 100 nm or more and 1000 nm or less. If the thickness of the layer 18 made of a thin film dielectric is less than 100 nm, the capacity of the thin film capacitor element increases, but the leakage current increases. If the thickness of the thin film dielectric layer is greater than 1000 nm, it is difficult to form a uniform layer, and cracks tend to occur when fired.

In the present embodiment, the layer 18 made of a thin film dielectric is formed by the MOD method, but may be formed by the sputtering method as described above. When forming a layer 18 made of a thin-film dielectric by sputtering, for example, a sintered body having a composition formula is expressed by _{(Sr 1-x Ca x)} y (Ti 1-z Mn z) O 3 as a target . The thin film dielectric can be formed by setting the substrate temperature to 600 ° C., the high frequency input power to the target to 1.7 W / cm ² , and the film forming pressure to 1.6 Pa. At this time, the composition of the target and the composition of the thin film may not exactly match. In such a case, when forming the thin film dielectric represented by the target composition formula, the composition of the sintered body to be the target and the film formation conditions are adjusted as appropriate.

  An upper electrode 20 is formed on the layer 18 made of a thin film dielectric by sputtering or the like (FIG. 1 (4)). The material of the upper electrode 20 is not particularly limited as long as it has conductivity like the material of the lower electrode 16, and the conductive material can be used. The material of the upper electrode 20 is preferably the same as that used for the lower electrode 16. The lower electrode 16 and the upper electrode 20 constitute a pair of electrodes that sandwich the layer 18 made of a thin film dielectric.

  A thin film capacitor element is formed by including a layer 18 made of a thin film dielectric and a pair of electrodes sandwiching the layer 18 made of the thin film dielectric.

  Further, a thin film capacitor element may be formed by providing a multilayer structure in which a plurality of layers made of a thin film dielectric are provided and an internal electrode is provided between the layers made of the thin film dielectric.

An annealing process may be performed after the upper electrode 20 is formed. The annealing treatment may be performed at a temperature of PO ₂ = 20 to 100% and 400 to 1000 ° C. By performing the annealing treatment, the thin film dielectric can be surely made to have a perovskite structure.

Further, a passivation layer (protective layer) is formed as necessary (not shown). As a material for the passivation layer, an inorganic material such as SiO ₂ or Al ₂ O ₃ , or an organic material such as an epoxy resin or a polyimide resin can be used.

  In addition, when forming each said layer, you may perform predetermined patterning using a photolithographic technique each time.

In FIG. 1, the electrode terminal of the lower electrode 16 and the electrode terminal of the upper electrode 20 are arranged in the directions on both sides of the drawing, but each electrode terminal may be arranged in a different direction or arranged in the same direction. Also good. Furthermore, via holes may be provided in the Si substrate 12 so that the lower electrode 16 is connected in the direction opposite to the substrate.
(Example)

Next, the present invention will be described in more detail with reference to specific examples. In addition, this invention is not limited to a following example.
(Coating solution adjustment)

First, a raw material solution for forming a thin film dielectric was prepared. In this example, when expressed by the composition formula (Sr _1-x Ca _x ) _y (Ti _1-z Mn _z ) O ₃ , the thin film dielectric was formed by changing a plurality of combinations of (x, y). FIG. 2 shows a combination of (x, y). In FIG. 2, the horizontal axis represents the atomic ratio x. The vertical axis represents the atomic ratio y. As shown in FIG. 2, in this example, the raw material solutions were prepared for a total of 10 combinations. In the combinations shown in FIG. 2, the atomic ratio z is all set to z = 0. Further, in this example, for the combination of (x, y) = (0.4, 0.99), z is changed to 0, 0.02, 0.04, 0.06 to change the thin film dielectric. Formed. Tables 1, 2 and 3 show combinations of (x, y, z). Table 1 is a table showing combinations of atomic ratios shown in FIG. Table 2 is a table showing combinations in which the atomic ratio x is fixed to 0.4 and y is changed. Table 3 is a table showing combinations in which the atomic ratio (x, y) is fixed at (0.4, 0.99) and z is changed.

Specifically, a 2-ethylhexanoic acid solution of 2-ethylhexanoic acid Sr, a 2-ethylhexanoic acid solution of 2-ethylhexanoic acid Ca, a toluene solution of 2-ethylhexanoic acid Ti, and 2-ethylhexane A toluene solution of acid Mn was prepared, these solutions were mixed so as to have predetermined compositions shown in Table 1, Table 2, and Table 3, and diluted with toluene to obtain a raw material solution. Each of these raw material solutions was filtered into a glass container that had been cleaned in the clean room with a PTFE syringe filter having a pore diameter of 0.2 μm in the clean room.
(substrate)

A substrate for forming a thin film dielectric was prepared. As the substrate, a silicon substrate having an oxide film (insulating layer) formed on the surface by thermal oxidation treatment was used. The thickness of the insulating layer was 0.5 μm. A Pt thin film having a thickness of 0.1 μm was formed as a lower electrode on the surface of the insulating layer by sputtering. The thickness of the substrate was 1 mm, and the area was 5 mm × 10 mm.
(Coating, drying)

  Next, the raw material solution prepared as described above was applied on the lower electrode. A spin coating method was used as the coating method. Specifically, the substrate is set on a spin coater, about 10 μl of each raw material solution is added to the surface of the lower electrode on the substrate, spin-coated under the conditions of 4000 rpm and 20 seconds, and the surface of the lower electrode 6 is applied. A coating film was formed.

Then, in order to evaporate the solvent of a coating film, it was made to dry for 10 minutes at 150 degreeC in air | atmosphere.
(Calcination)

  Next, in order to calcine the coating film, each substrate was placed in a tubular furnace. In this tubular furnace, oxygen is flowed at a rate of 0.3 liter / min, the temperature is increased to 400 ° C. at a temperature increase rate of 10 ° C./min, held at 400 ° C. for 10 minutes, and then the temperature is decreased at a temperature decrease rate of 10 ° C./min. Decreased. Note that the calcination was performed under temperature conditions that do not cause the coating film to crystallize.

  After that, the above-described steps from spin coating to calcination were repeated 5 times using the same kind of raw material solution again on the calcined coating film.

  Next, each substrate was placed in a tubular furnace in order to main-fire the calcined film. In this tubular furnace, oxygen is flowed at 5 ml / min, the temperature is increased to 850 ° C. at a temperature increase rate of 80 ° C./min, held at 850 ° C. for 30 minutes, and then the temperature is decreased at a temperature decrease rate of 80 ° C./min. Part of the thin film dielectric was obtained. The film thickness of a part of the thin film dielectric after the main firing was about 20 nm.

Thereafter, coating, drying, calcining, coating, drying, calcining, and main firing are repeated again on a part of the thin film dielectric after the main firing under the above-described conditions. A 250 nm thin film dielectric was obtained.
(Annealing)

Next, in order to grow particles of the thin film dielectric formed on the lower electrode, the substrate on which the thin film dielectric is formed may be annealed. The annealing temperature exceeds 600 ° C. and is 1000 ° C. or less, preferably 800 ° C. or more and 1000 ° C. or less. In order to prevent oxygen depletion from the thin film dielectric, it is desirable to perform the annealing in an oxidizing atmosphere. In addition, it confirmed that the composition of the formed strontium calcium titanate became a desired chemical composition by XRF (X-ray fluorescence analysis). Further, from the analysis by XRD (X-ray diffraction), it was confirmed that the structure of the formed strontium calcium titanate was a single phase with a perovskite structure.
(Formation of the upper electrode)

With the above formation method, a thin film dielectric is formed for each of the above compositions, and a 0.1 mmφ upper electrode made of Pt is formed on the surface of each thin film dielectric by sputtering to produce a plurality of types of thin film capacitor element samples. did.
(Annealing)

An annealing treatment may be performed after the upper electrode is formed. The annealing process may be performed at a temperature of pO ₂ = 20 to 100% and 400 to 1000 ° C. Further, a passivation layer (not shown) is formed as necessary.

  The electrical characteristics (relative permittivity, leakage current) of the obtained capacitor samples were evaluated.

The relative dielectric constant (no unit) is the capacitance measured for the capacitor sample using an impedance analyzer (YHP4194A) at a room temperature of 25 ° C. and a measurement frequency of 100 kHz (AC 20 mV). It calculated from the distance between electrodes. Tan δ was measured as 1 kHz using a YHP4194A impedance analyzer. The leakage current density was measured using a semiconductor parameter analyzer Agilent 4156C under conditions of room temperature of 25 ° C. and electric field strength of 50 kV / cm ² . For Examples 1, 2, and 3 in Table 1, the relative dielectric constant and the leakage current density were measured even under the conditions of 125 ° C. and electric field strength of 50 kV / cm.

Table 4, Table 5, and Table 6 show the measurement results for the combinations of atomic ratios shown in Table 1, Table 2, and Table 3, respectively. Table 7 shows the measurement results under the conditions of 125 ° C. and electric field strength of 50 kV / cm.

  FIG. 3 is a graph showing the relationship between the atomic ratio x and the leakage current density based on Table 4. In FIG. 3, the horizontal axis represents the atomic ratio x. The vertical axis represents the leakage current density. FIG. 4 is a graph showing the relationship between the atomic ratio y and the leakage current density based on Table 5. In FIG. 4, the horizontal axis indicates the atomic ratio y. The vertical axis represents the leakage current density. FIG. 5 is a graph showing the relationship between the atomic ratio z and the leakage current density based on Table 6. In FIG. 5, the horizontal axis represents the atomic ratio z. The vertical axis represents the leakage current density.

  First, from Table 4, for Examples 1, 2, 3, 4, 5, and 6, the relative dielectric constant was 100 or more, and the atomic ratio x, y was 0.2 ≦ x ≦ 0.6 and 0.97. It can be seen that a high dielectric constant can be obtained by setting ≦ y ≦ 1.10.

FIG. 3 also shows that the leakage current density tends to decrease as the atomic ratio x increases from 0 regardless of whether the annealing temperature is 750 ° C. or 800 ° C. The leakage current density is the smallest when the atomic ratio x is x = 0.4, which is 10 ⁻⁶ (A / cm ² ) or less. Further, FIG. 3 shows that when the atomic ratio x is 0.2 ≦ x ≦ 0.6, the leakage characteristics are good.

Further, from FIG. 4, when the atomic ratio y is increased from 0 and the atomic ratio y is set to y = 0.99, the leakage current density becomes the smallest, 6.7 × 10 ⁻⁸ (A / cm ² ). As the atomic ratio y is further increased, the leakage current density also increases. Therefore, from FIG. 4, when the atomic ratio y is 0.97 ≦ y ≦ 1.10, it is preferable that the leak characteristic is good and y is 0.98 ≦ y ≦ 1.05. Recognize.

Further, from FIG. 5, when the atomic ratio z is decreased from z = 0.06, the leakage current density is 1.2 × 10 ⁻⁸ (A / cm ² ) at the minimum when z = 0.02. Become. Therefore, it can be seen that when the atomic ratio z is 0 <z ≦ 0.05, the leakage characteristics are good, and it is more desirable that z is 0 <z ≦ 0.02.

Further, from Table 7, it is possible to set the relative dielectric constant to 100 or more and the leakage current density to 10 ⁻⁶ (A / cm ² ) or less for Examples 1, 2, and 3 even under a high temperature environment of 125 ° C. By setting the number ratios x and y to 0.2 ≦ x ≦ 0.6 and 0.97 ≦ y ≦ 1.10, the dielectric constant is high, the leakage characteristics are good, and the characteristics are stable even in a high temperature environment. It can be seen that a thin film dielectric can be obtained.

  The thin film dielectric and the thin film capacitor according to the present invention can be used in an electronic circuit such as an integrated circuit together with an active element such as a transistor.

It is a schematic sectional drawing of the thin film capacitor element based on this invention. It is the figure which showed the combination of (x, y). FIG. 5 is a graph showing the relationship between the atomic ratio x and the leakage current density based on Table 4. 6 is a graph showing the relationship between the atomic ratio y and the leakage current density based on Table 5. FIG. FIG. 7 is a graph showing the relationship between the atomic ratio z and the leakage current density based on Table 6.

Explanation of symbols

12 Si substrate 14 Thermal oxide film 16 Lower electrode 18 Layer made of thin film dielectric 20 Upper electrode

Claims (8)

A thin film dielectric containing strontium calcium titanate represented by a composition formula (Sr _1-x Ca _x ) _y TiO ₃ ,
A thin film dielectric characterized in that the atomic ratio x in the composition formula is 0.2 ≦ x ≦ 0.6 and the atomic ratio y is 0.97 ≦ y ≦ 1.10. The thin film dielectric, further a composition formula of the strontium titanate calcium contain a Mn element _{(Sr 1-x Ca x)} y (Ti 1-z Mn z) atomic ratio z of when expressed in _{O 3} The thin film dielectric according to claim 1, wherein 0 <z ≦ 0.05.   The thin film dielectric according to claim 1 or 2, wherein the thickness of the thin film dielectric is 30 nm to 1000 nm.   4. The thin film dielectric according to claim 1, wherein the thin film dielectric has a relative dielectric constant of 100 or more under a condition of 25 ° C. 5.   5. The thin film dielectric according to claim 1, wherein the thin film dielectric has a relative dielectric constant of 100 or more under a condition of 125 ° C. 6. 6. The thin film dielectric according to claim 1, wherein the thin film dielectric has a leakage current density of 10 ⁻⁶ A / cm ² or less at 25 ° C. under an applied voltage of 50 kV / cm. Thin film dielectric. 7. The thin film dielectric according to claim 1, wherein the thin film dielectric has a leakage current density of 10 ⁻⁶ A / cm ² or less at 125 ° C. under an applied voltage of 50 kV / cm. The thin film dielectric described. A thin film capacitor comprising: a layer made of the thin film dielectric according to claim 1, and a pair of electrodes sandwiching the layer made of the thin film dielectric. element.

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