JPH09252091A - Dielectric thin film device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a device possessed of a dielectric thin film of perovskite oxide to be effectively enhanced in permittivity, by a method wherein distortions or defects are prevented from occurring in a low-permittivity insulating layer formed at an interface between the dielectric thin film and an electrode layer or the dielectric thin film. SOLUTION: A dielectric thin film device is equipped with an Si electrode 11, a conductive barrier layer 12 formed on the Si electrode 11, and a dielectric thin film 14 of perovskite oxide formed on the conductive barrier layer 12. The dielectric thin film 14 is possessed of a conductive transition region 15 located near its interface with the conductive barrier 12 and so doped with transition metal element or rare earth element as to be gradient in concentration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric thin film element using a dielectric thin film made of a perovskite oxide.

[0002]

2. Description of the Related Art In recent years, research on high-dielectric materials and ferroelectric materials for LSI has been actively conducted for application to large-capacity DRAMs and nonvolatile RAMs. D of 1 Gbit or more
In the memory cell for RAM, it is necessary to secure a necessary amount of accumulated charge in a limited cell area of, for example, 0.3 μm ² or less in order to miniaturize the cell structure accompanying high integration. The accumulated charge amount Q is obtained by the following formula.

Q = CV, C = εS / d (dielectric constant ε = ε _r ε _o , ε _r : relative permittivity, ε _o : vacuum permittivity) Among these parameters, the voltage V is the power consumption and the transistor. From the viewpoint of the reliability of the Therefore,
If the electrostatic capacitance C is not increased, the hold characteristic and soft error resistance cannot be satisfied.

In order to deal with this, the film thickness d of the capacitor insulating layer has been made thinner, and the effective cell area S has been increased by complicating the capacitor structure. SiO ₂ which has been conventionally used as a capacitor material
Therefore, in order to secure the electrostatic capacitance, it is necessary to make the film thickness about 2 to 3 nm, but there is a problem that the leak current increases, and the securing of the electrostatic capacitance by thinning has reached the limit.

Further, in a capacitor for a DRAM of 1 Gbit or less, as a structure for ensuring the capacitance, there are a thick film type, a fin type, a cylindrical type differentiated from a stack structure, and a substrate cell plate type developed from a trench structure. big
Four structures have been developed. On the other hand, similar structures are being studied for DRAMs of 1 Gbit or more, but the cell structure becomes finer, and the complexity of the capacitor structure increases the number of manufacturing process steps and technical difficulty, resulting in cost reduction. The result will be a significant increase. As described above, in the DRAM of 1 Gbit or more, it is becoming difficult to secure the capacity by thinning the material and the complicated structure which have been used conventionally.

Therefore, studies have begun to secure the charge storage amount by using a material having a higher dielectric constant for the capacitor. For example, Si that has been conventionally used
The relative permittivity of O ₂ / Si ₃ N ₄ is 3.9, and Ta ₂
The relative permittivity of O ₅ is 20. On the other hand, perovskite type oxides generally have a high dielectric constant, such as SrTi.
The relative permittivity of O ₃ is 400. Therefore, if a perovskite type oxide having a high dielectric constant is used for the capacitor insulating layer, it is possible to secure a sufficient amount of accumulated charge corresponding to the miniaturization of the cell structure, and without using a complicated capacitor structure. Since the capacity can be secured, it is possible to simplify the process, which is expected to significantly reduce the cost.

When a high dielectric material made of a perovskite type oxide is used for a capacitor for DRAM of 1 Gbit or more, it is necessary to satisfy three electrical characteristics, that is, capacity density, leak current and breakdown voltage. First, cell area 0.3 μm ² , voltage 1.
At 5 V, the required accumulated charge is estimated to be 20 fC or more from the calculation results for soft error tolerance, so the capacitance density is 60
fF · μm ^-2 or more is required. The value of 60 fF · μm ^-2 corresponds to about 0.5 nm in terms of SiO ₂ . Next, the leak current of the film needs to be 10 ⁻⁸ A / cm ² or less in the high temperature operation region when voltage is applied. Regarding resistance, it is required that there be no initial failure at 2.5V and that the life is 100 years or more.

When a dielectric thin film made of a perovskite type oxide is used for a capacitor, the following two new problems occur. First, a large number of defects in the dielectric thin film make the dielectric conductive, which increases the leakage current. In order to cope with this problem, metal electrodes such as Pt having a large work function absorb the carriers generated in the dielectric, and the dielectric thin film is polycrystallized to increase the resistance.
With the improvement of the film quality of the dielectric thin film, this problem is being solved.

The second problem is that, for example, as shown in FIG. 13, the low dielectric constant layer 3 is formed at the interface between the electrode 1 and a dielectric thin film (hereinafter referred to as a perovskite type dielectric thin film) 2 made of a perovskite type oxide. Is formed. The reason why the low dielectric constant layer 3 is formed is that the constituent material of the electrode 1 is oxidized to form a heterogeneous insulating layer, and that defects and strain are generated in the dielectric thin film 2 near the electrode 1. The dielectric constant of the dielectric thin film 2 near the interface of the electrode 1 is lowered. When the perovskite type dielectric thin film 2 is directly formed on the polycrystalline Si which has been used as the electrode 1 from the past,
The Si surface is oxidized during the process and a SiO ₂ layer is generated at the interface. Therefore, the capacitor insulating layer becomes a laminated film of the perovskite type dielectric thin film 2 and the SiO ₂ layer having a low dielectric constant, and the effective dielectric constant lowers.

In order to solve the above problem, for example, as shown in FIG. 14, a conductive barrier layer 4 made of Pt, Ta, TiN or the like is provided between the Si electrode 1 and the perovskite type dielectric thin film 2. It is considered to be formed. The conductive barrier layer 4 prevents the diffusion of Si to prevent the precipitation of Si at the interface with the perovskite type dielectric thin film 2 and also has a low dielectric constant at the interface with the perovskite type dielectric thin film 2. It is required not to generate layers.

However, for example, Pt is used as the conductive barrier layer 4
When used as a material, the diffusion of Si cannot be sufficiently prevented, and the perovskite type dielectric thin film 2 is formed on Pt.
There is a problem in that it is difficult to form satisfactorily.
Further, when Ta or TiN is used as the conductive barrier layer 4, the material of the barrier layer 4 is oxidized and Ta ₂ O ₅ or Ti is added to the interface with the perovskite type dielectric thin film 2, respectively.
The low dielectric constant layer 5 made of O ₂ or the like is generated.

As described above, with the conventional conductive barrier layer 4 material, it is difficult to prevent the formation of a different dielectric layer having a low dielectric constant at the interface with the perovskite type dielectric thin film 2, and at the same time, the conductivity is reduced. Due to the lattice mismatch between the material of the barrier layer 4 and the perovskite type dielectric thin film 2, distortion and defects are likely to occur in the perovskite type dielectric thin film 2, and the effective dielectric constant is lowered by these. Has not been resolved. This problem becomes more remarkable as the film thickness of the perovskite dielectric thin film 2 is reduced. Although the diffusion of Si and the formation of the low dielectric constant layer at the interface also depend on the process conditions, it is very difficult to suppress the generation and form a high dielectric constant film that satisfies the above-mentioned requirements for a capacitor. It was

[0013]

As described above, although the perovskite type oxide has advantages such as a high dielectric constant, it has a low dielectric constant insulating layer formed at the interface with the electrode layer and a conductive layer. It is difficult to effectively obtain a high dielectric constant due to strains and defects in the dielectric thin film caused by the lattice mismatch with the electrode layer such as the barrier layer, which poses a problem for application to capacitors such as DRAM. I have left.

The present invention has been made to solve such a problem, and an insulating layer having a low dielectric constant is generated at the interface with the electrode layer, and a distortion or a defect is generated in the dielectric thin film. By preventing this, it is an object of the present invention to provide a dielectric thin film element that makes it possible to effectively utilize the characteristics of the dielectric thin film made of a perovskite type oxide, such as high dielectric constant.

[0015]

According to a first aspect of the present invention, there is provided a dielectric thin film element comprising a dielectric body comprising an electrode layer and a perovskite type oxide formed on the electrode layer. In a dielectric thin film element comprising a thin film, the dielectric thin film has a transition region doped with a transition metal element in the vicinity of an interface with the electrode layer, and the transition region has a dopant concentration on the electrode layer side. Is characterized by having a concentration gradient such that the concentration becomes high.

Further, the second dielectric thin film element is defined by claim 3.
As described above, in a dielectric thin film element comprising an electrode layer and a dielectric thin film formed of a perovskite type oxide formed on the electrode layer, the dielectric thin film is formed near an interface with the electrode layer. It is characterized in that it has a transition region doped with a rare earth element, and the transition region has a concentration gradient such that the concentration of the dopant becomes high on the electrode layer side.

That is, in the present invention, the A site of the perovskite type oxide (chemical formula: ABO ₃ ) is replaced by La, Pr and N.
By substituting trivalent rare earth element ions such as d, Sm, and Y, or substituting the B site with a transition metal such as Nb and Ru, the perovskite-type oxide has low resistivity and high conductivity. To be Between the perovskite-type oxide having enhanced conductivity and the perovskite-type oxide that functions as a dielectric, formation of a low-dielectric-constant dissimilar insulating layer and reduction of the dielectric constant in the vicinity of the interface do not occur. Therefore,
To make full use of the properties such as high dielectric constant of perovskite oxide by forming the above-mentioned transition region having conductivity in the vicinity of the interface of the dielectric thin film made of perovskite oxide with the electrode layer. Is possible.

The transition region of the dielectric thin film having a concentration gradient of the transition metal element or the rare earth element provided near the interface with the electrode layer is a space generated in the dielectric thin film, as will be described later in detail. The charge region is stopped only near the interface with the electrode layer. This reduces the space charge region loss and makes it possible to suppress the deterioration of the high frequency characteristics of the capacitance.

[0019]

Embodiments of the present invention will be described below.

FIG. 1 is a sectional view showing the structure of the main part of a dielectric thin film element according to an embodiment of the present invention. In the figure, 11 is a semiconductor electrode (hereinafter referred to as Si electrode) made of a Si substrate or the like, and a conductive barrier layer 12 is formed on the Si electrode 11. Here, the conductive barrier layer 12 functions as a part of the electrode layer 13. A dielectric thin film 14 made of a perovskite type oxide is formed on the conductive barrier layer 12. The dielectric thin film 14 made of this perovskite type oxide is the electrode layer 13
A transition region 15 doped with a transition metal ion or a rare earth element ion so as to have a concentration gradient is provided in the vicinity of the interface with.

Here, for example, a typical perovskite type oxide, strontium titanate (chemical formula: SrT
The band structure of iO ₃ (ABO ₃ )) has a band gap of about 3 eV, as schematically shown in FIG.
It is considered that the valence band is composed of the 2p orbit of oxygen (O), the conduction band is composed of the 3d orbit of titanium (Ti), and the Fermi level is located in the gap. Therefore, it is usually an insulator. However, due to the non-stoichiometric composition, the introduction of impurities, the d-electron structure, etc., carriers are generated in the conduction band composed of the 3d orbital of Ti, and the electric conductivity is modified by this.

There are two methods for imparting conductivity to the perovskite type oxide by doping. One is to use an A site element such as Sr as a trivalent rare earth element ion such as La, Pr, Nd, Sm or Y. The replacement method is T, and the other is T
In this method, the B site element such as i is replaced with a transition metal such as Nb or Ru. When the A site is replaced with a trivalent rare earth element ion to form Sr _1-x R _x TiO ₃ (R: trivalent rare earth element, x: 0 <x <1), electrical neutrality is obtained. In order to maintain the Ti, the formal charge of Ti changes from Ti ⁴⁺ to Ti ^{3 + x +} , carriers are generated in the 3d band of Ti, and the resistivity decreases to show conductivity. On the other hand, by substituting the B site with a transition metal ion such as Nb or Ru, SrTi _1-x M _x
O ₃ (M: transition metal element other than basic element of B site,
Even in the case of x: 0 <x <1), a donor level is generated just below the conduction band and electrons are excited in the conduction band, so that the resistivity decreases and the conductivity is exhibited.

As described above, the transition region 15 in which the perovskite type oxide which is originally an insulator is doped with transition metal ions or rare earth element ions so as to have a concentration gradient,
It has lower resistivity and higher conductivity than the original perovskite oxide. That is, the dielectric thin film 14 made of a perovskite type oxide has a conductive transition region (hereinafter referred to as a conductive transition layer) in which an interface side with the conductive barrier layer 12 is doped with a transition metal ion or a rare earth element ion. ) 15. In other words, the conductive transition layer 15 of perovskite type oxide is formed on the conductive barrier layer 12.
Is formed, and a perovskite type oxide layer as the original dielectric layer 16 is formed on the conductive transition layer 15.

For the dielectric thin film 14 made of perovskite type oxide, various perovskite type oxides having a function as a dielectric can be used, for example, BaTi.
Simple perovskite type oxides such as O ₃ , SrTiO ₃ , PbTiO ₃ and PbZrO ₃ , (Ba _1-x Sr _x ) Ti
Examples thereof include solid solution perovskite type oxides such as O ₃ and Pb (Zr _1-x Ti _x ) O ₃ (0 <x <1). These perovskite type oxides are used as the dielectric layer 16, and those doped with transition metal ions or rare earth element ions so as to have a concentration gradient are used as the conductive transition layer 15.

In the dielectric thin film element of the above-described embodiment, the conductive transition layer 15 is formed as a buffer layer between the conductive barrier layer 12 and the dielectric layer 16, and the dielectric layer 16 and the conductive layer 16 are electrically conductive. The heterogeneous insulating layer having a low dielectric constant is not formed between the transition layer 15 and the oxidative transition layer 15. Further, since the lattice mismatch between the conductive barrier layer 12 and the dielectric layer 16 is mitigated by the conductive transition layer 15, the interface or the strain in the dielectric layer 16 is unlikely to occur. By these, the electrode layer 1
Even in the vicinity of the interface with 3, the effective dielectric constant of the dielectric thin film 14 does not decrease, so that it is possible to obtain a high dielectric constant even if the film thickness is very thin. Furthermore, by adjusting the thickness and the doping amount of the conductive transition layer 15,
The height and shape of the Schottky barrier formed at the interface between the electrode layer 13 and the dielectric thin film 14 can be changed.

Further, the above-mentioned conductive transition layer 15 has a structure as shown in FIG.
As shown in (1), since it has a concentration gradient of the transition metal element or the rare earth element, it is possible to reduce the loss due to the generation of the space charge region. That is, at the interface between the metal and the perovskite oxide, as shown in FIG. 4, in order to compensate for the Fermi level difference, electrons move to the metal side, the depletion layer extends to the dielectric side, and the positive space charge is increased. Area is created. The space charge induced in the dielectric causes loss and deteriorates the high frequency characteristics of the capacitance. On the other hand, as shown in FIG. 3, when the interface between the conductive barrier layer 12 and the dielectric layer 16 is highly doped with a transition metal element or a rare earth element, the space charge region becomes the conductive barrier layer 12. Can be stopped only in the vicinity of the interface, and at this time, in the conductive transition layer 15, it is possible to particularly reduce the space charge region loss by providing the doping concentration with a gradient. Further, the band shape of the interface can be adjusted by changing the doping profile. In the present invention, the doping concentration of the transition metal element is in the range of x = 0 to 0.3 when expressed as AB _1-x M _x O ₃ (A: A site element, B: B site element, M: transition metal element). It is preferable to provide a concentration gradient with. This is because when x exceeds 0.3, the conductivity of the perovskite oxide is rather lowered. Also,
There is no particular limitation on the doping concentration of the rare earth element, and when expressed by A _1-x R _x BO ₃ (A: A site element, B: B site element, R: rare earth element), x = 0 to 1 Can be selected with. However, considering the lattice matching with the dielectric layer 16, x = 0 to 0.5 is preferable. Further, the thickness of such a conductive transition layer 15 in the present invention is preferably set to 1 to 20 nm, which is 1 nm.
If it is less than 20 nm, uniform film formation is difficult, and if it exceeds 20 nm, the space charge region expands at the interface with the conductive barrier layer 12.

As described above, by providing the conductive transition layer 15 having the concentration gradient of the transition metal element or the rare earth element in the vicinity of the interface between the conductive barrier layer 12 and the dielectric thin film 14, the film thickness becomes extremely large. A high dielectric constant can be obtained even if it is thin, and the loss due to the generation of the space charge region is reduced, so that a high frequency characteristic with good capacitance can be obtained. As a result, it becomes possible to obtain a dielectric thin film element suitable for, for example, a 1 Gbit or more DRAM capacitor.

Although it is possible to use a conventional barrier layer material for the conductive barrier layer 12, it is preferable to use niobium nitride or ruthenium nitride as shown below. That is, the conductive barrier layer 12 is desired to satisfy the following conditions. First, a low dielectric constant insulating layer is not formed at the interface with the Si electrode 11, Si diffusion can be prevented, and a low dielectric constant dissimilar insulating layer is not formed at the interface with the perovskite oxide. That is.

In order to meet such required characteristics, niobium nitrides such as NbN and ruthenium nitrides such as RuN are essentially excellent in oxidation resistance and stable, and have excellent ability to prevent Si from diffusing. A steep interface is formed with the electrode 11. Moreover, since the dielectric thin film 14 made of a perovskite type oxide is made of an element that imparts conductivity, a heterogeneous layer is not formed by diffusion of the constituent material of the conductive barrier layer 12, and even if an oxide is formed. Even if you do N
Since bO ₂ and RuO ₂ have conductivity, it is possible to prevent the effective reduction of the dielectric constant due to the formation of the different dielectric layer having a low dielectric constant. For the same reason, the transition metal elements doped in the perovskite oxide are Nb and Ru.
Among these, Ru is more preferable because the oxide has higher conductivity.

Even when TiN or the like is used as the conductive barrier layer 12, by selecting a transition metal such as Nb or Ru as an element to be doped in the dielectric thin film 14 made of a perovskite type oxide, TiO ₂ can be obtained. Even if formed, Nb and Ru diffuse into TiO ₂ and become conductive. Therefore, it is possible to avoid an effective decrease in the dielectric constant that accompanies the formation of the different dielectric layer having a low dielectric constant.

[0031]

Next, specific examples of the present invention will be described.

Example 1 First, an example of forming a conductive transition layer by doping a perovskite type oxide with a transition metal element will be described.

That is, an NbN layer is formed as the conductive barrier layer 12 on the Si electrode 11, and SrTiO 3 is formed thereon.
_{When the} dielectric thin film 14 made of ₃ is formed, Nb is doped with a concentration gradient at the beginning to form the conductive transition layer 15, and then the SrT as the high dielectric constant dielectric layer 16 is formed.
to form a iΟ ₃ layers.

Specific film formation was performed by the reactive sputtering method as follows. That is, Nb, SrO
By using Ti and Ti as targets and controlling these three sputtering sources independently, an NbN layer is formed as the conductive barrier layer 12 and SrTi
The composition of _1-x Nb _x O ₃ and SrTiO ₃ was controlled. First, for the NbN layer, the substrate temperature is set to a constant value in the range of 473 to 673 K, N ₂ gas of 5 mTorr and Ar gas of 5 mTorr are introduced, and the input power is dc 50 to 100 W and the film formation rate is 0.5 to 1 nm / s. The film was formed with a film thickness of 100 nm.

Then, SrTi _1-x N was formed on the NbN layer.
A b _x O ₃ layer was deposited. The composition ratio of Ti and Nb is
The electric power applied to the Ti target and Nb target
It was possible to control to a predetermined value in the range of x = 0 to 0.1 by adjusting in the range of 0 to 100W. SrTi
_{The 1-x} Nb _x O ₃ layer is formed at a substrate temperature of 673 K, an oxygen gas of 1 mTorr and an Ar gas of 9 mTorr are introduced, and the film formation rate is 0.1 nm.
A 20 nm film was formed at / s. The Nb doping amount x has a concentration gradient from x = 0.1 to x = 0 over the film thickness of 20 nm from the vicinity of the NbN layer. Then, 5 mTorr of oxygen gas and 5 mTorr of Ar gas were introduced, and SrTi _1-x Nb was formed under the condition of the film forming rate of 0.1 nm / s.
_A 20 nm SrTiO ₃ layer was formed on the _x O ₃ transition layer.

The electrical characteristics of SrTi _1-x Nb _x O ₃ are Nb
It changed depending on the doping amount. FIG. 5 shows changes in the resistivity of SrTi _1-x Nb _x O ₃ depending on the Nb doping amount x. It has been found that this change in resistivity corresponds to a change in carrier density. FIG. 6 schematically shows the band structure of SrTi _1-x Nb _x O ₃ . Nb doped in SrTiO ₃
Is T as a formal charge tetravalent ion or pentavalent ion
Dissolve in the i-site. Nb doped as tetravalent is
Immediately below the conduction band of 3d orbital of Ti, a donor level of Nb4d ¹ orbital is formed. D of this donor level
The electrons do not localize in Nb ⁴⁺ , but are excited in the conduction band consisting of the 3d orbital of Ti and become conductive. When Nb is doped as pentavalent, in order to maintain electrical neutrality,
Ti ⁴⁺ around Nb ⁵⁺ becomes Ti ^{3 + δ +} , and carriers are generated in the conduction band to show conductivity. In any case, the Nb doping amount of SrTi _1-x Nb _x O ₃ is x ≦ 0.3.
Since the number of electrons excited in the conduction band composed of the 3d orbital of Ti increases as the ratio increases within the range of, the resistivity decreases. In reality, since there is a deviation from the stoichiometric composition of oxygen, the valence (3 + δ) of Ti also depends on the redox property of the atmosphere.

Next, by a cross-section TEM and EDX, Si
The interface of / NbN / SrTi _1-x Nb _x O ₃ / SrTiO ₃ was observed. No Si diffusion was observed at the interface between Si and NbΝ, and a steep interface was formed. Also, NbN
NbO ₂ was partially formed at the interface between SrTi _1-x Nb _x O ₃ and SrTi _1-x Nb _x O ₃ , but since this oxide has conductivity,
It did not affect the dielectric properties. SrTi _1-x
At the interface between Nb _x O ₃ and SrTiO ₃ , the disorder of the lattice was small, and the diffusion of Nb into SrTiO ₃ was hardly seen. The relative permittivity of the device having the SrTiO ₃ layer having a film thickness of 20 nm is about 250, and the leakage current when the SrTi _1-x Nb _x O ₃ layer is on the negative electrode side is 1 × 10 ^-8 A when 3 V is applied. /
It was confirmed to have cm ² or less and sufficient characteristics to be used as a capacitor.

Here, when the SrTi _1-x Nb _x O ₃ layer is on the positive electrode side, the leakage current is SrTi _1-x Nb _x O ₃
Larger than when the layer is on the negative electrode side, 1 × with 10 V applied
It was 10 ⁻⁷ A / cm ² . FIG. 7 shows an electrode layer / SrTi _1-x Nb _x O ₃ when the SrTi _1-x Nb _x O ₃ layer is the positive electrode side.
/ Shows the band structure of the bonded interface of SrTiO ₃ / electrode layer schematically. As shown in FIG. 7, it is considered that the cause of the large leak current is that carrier injection from SrTi _1-x Nb _x O ₃ into SrTiO ₃ occurs. Therefore, when the Nb-doped layer is used as the buffer layer,
A method of using the Νb-doped layer side as the negative electrode is suitable.

Similar results were obtained when Ru was used instead of Nb. Although it is slightly inferior to Ru and Nb in terms of oxidation resistance, Re, Os, I
A similar effect can be obtained with a nitride of r and Rh.

Example 2 Next, an example in which a perovskite type oxide is doped with a rare earth element to form a conductive transition layer will be described.

That is, a RuN layer was formed as the conductive barrier layer 12 on the Si electrode 11, and SrTiO 3 was formed thereon.
_{When the} dielectric thin film 14 made of ₃ is formed, La is doped with a concentration gradient at the beginning to form the conductive transition layer 15, and then the SrT as the high dielectric constant dielectric layer 16 is formed.
to form a iΟ ₃ layers.

Specific film formation was carried out by the reactive sputtering method as follows. That is, Ru, Sr
By using O, La ₂ O ₃ and Ti as targets and controlling these four sputtering sources independently, a RuN layer is formed as a conductive barrier layer 12 on a Si substrate, and Sr having a La concentration gradient is further formed. _1-x La _x
Conductive transition layer composed of TiO ₃ (x = 0.3 to 0) layer and Sr
A TiO ₃ layer was deposited. First, the RuN layer has a substrate temperature of 473
Set to a constant value in the range of ~ 673K, N ₂ gas 5mTorr and Ar
Introduced gas 5mTorr, input power 100W, deposition rate 0.5nm / s
A film having a film thickness of 100 nm was formed under the above conditions.

Then, Sr _1-x La _{x is formed} on the RuN layer.
A TiO ₃ film was formed. The composition ratio of Sr and La can be adjusted by adjusting the input power in the range of 0 to 100W.
It was possible to control to a predetermined value in the range of x = 0 to 1. The Sr _1-x La _x TiO ₃ layer is formed at a substrate temperature of 67
At 3 K, oxygen gas of 1 mTorr and Ar gas of 9 mTorr were introduced, and a film thickness of 20 nm was formed at a film formation rate of 0.1 nm / s. The La doping amount x was made to have a concentration gradient from x = 0.3 to x = 0 over a film thickness of 20 nm from the vicinity of the electrode. Next, 5mTorr of Ο ₂ gas and Ar gas
Introducing 5mTorr, Sr _{1-x under} the condition of film formation rate 0.1nm / s
A 20 nm SrTiO ₃ layer was formed on the La _x TiO ₃ layer.

The electrical characteristics of Sr _1-x La _x TiO ₃ are La
It changes depending on the doping amount, and when x is in the range of 0.01 to 0.5,
The resistivity was about 1 × 10 ^-3 Ω · cm at room temperature. Generally, the electrical characteristics of perovskite oxide can be represented by the Hubbard model. FIG. 8 shows changes in electrical characteristics of the perovskite type oxide due to the Ti type charge and the rare earth element doped. The horizontal axis represents the number n of electrons per Ti 1 site, and the vertical axis represents the ratio U / t between the electron transfer integral t to the adjacent site and the Coulomb repulsive force U at the same site. Increasing rare earth doping from x = 0
This corresponds to increasing the number of electrons n from 0. Further, increasing the ionic radius of the rare earth element to be doped increases the 1-electron band width of the conduction band consisting of the 3d orbital of Ti, and corresponds to the increase of t. Therefore, conductivity can be imparted to the perovskite oxide by appropriately adjusting the type of rare earth element and the doping amount according to the perovskite oxide layer to be doped.

Here, as shown in FIG. 8, the valence 3+ of Ti in the perovskite type oxide used in the present invention is 3+.
In the range of δ, the ionic radius of the rare earth element is large and U /
The smaller the value of t, the more convenient it is to impart conductivity to the perovskite type oxide. That is, it is found that La or Nd, which has a large ionic radius and a stable valence of 3, is preferable as the rare earth element to be doped.

Next, by a cross-section TEM and EDX, Si
The interface of / RuN / Sr _1-x La _x TiO ₃ / SrTiO ₃ was observed. No diffusion of Si was observed at the interface between Si and RuN, and a steep interface was formed. Also, RuN
RuO ₂ was partially formed at the interface between Sr _{1 -x} La _x TiO ₃ and Sr _1-x La _x TiO ₃ , but since this oxide has conductivity,
It did not affect the dielectric properties. Sr _1-x La
the interface between the _x TiO ₃ and SrTiomikuron ₃ is less disturbance of the lattice diffusion into the SrTiO ₃ of La was hardly observed. The relative permittivity of the element having the SrTiO ₃ layer having a film thickness of 20 nm is about 250, and the leakage current is 3 V regardless of whether the Sr _1-x La _x TiO ₃ layer is the positive electrode side or the negative electrode side.
It was 1 × 10 ^-8 A / cm ² or less when applied, confirming that it has sufficient characteristics for use as a capacitor.

Unlike the case of SrTi _1-x Nb _x O ₃ ,
Even when the Sr _1-x La _x TiO ₃ layer is on the positive electrode side, the cause of the small leak current is considered to be due to the band structure of Sr _1-x La _x TiO ₃ . Electrode layer / Sr _1-x La
band structure of the bond _x TiO ₃ / SrTiO ₃ / electrode layer is believed to be as shown in Figure 9, in this case S
Carrier injection does not occur even when the r _{1 -x} La _x TiO ₃ layer is on the positive electrode side. Therefore, when a buffer layer doped with a rare earth element such as La is used, excellent characteristics as a capacitor can be obtained regardless of the direction of the applied voltage.

In place of La, Pr, Nd, Sm, Y
Similar results were obtained using other trivalent rare earth elements such as.

Example 3 Next, N epitaxially grown on a Si (100) substrate was used.
An example in which aCl type NbN is used as the conductive barrier layer will be described.

The film formation was carried out in the same manner as in Example 1 by reactive sputtering. The NbN film forming conditions are as follows: the substrate temperature is set in the range of 723 to 873K, and the N ₂ gas pressure is set to 1 to 5 m.
Torr and Ar gas pressures were set in the range of 5 to 9 mTorr, and a film was formed at 50 nm at a film forming rate of 0.1 to 0.5 nm / s. SrTi _1-x Nb _x
The O ₃ layer and the SrTiO ₃ layer were formed under the same conditions as in Example 1 except that the thickness of the SrTiO ₃ layer was 30 nm.

When the in-plane growth orientations of Si and NbN were observed by a planar TEM, as shown in FIG.
The <001> orientation of NbN is aligned with the <001> orientation, and N
It was confirmed that the bN (100) plane was epitaxially grown. NaCl-type NbN has a lattice constant of 0.515 nm and S
The mismatch of i with the lattice constant of 0.543 nm is 5.4%,
The growth surface was flat, resulting in a good single crystal thin film. SrTi grown on this epitaxially grown NbN
_As shown in FIG. 11, _1-x Nb _x O ₃ / SrTiO ₃ has a composition of SrTiO ₃ / Sr with respect to the <011> orientation of NbN.
The Ti _1-x Nb _x O ₃ was grown in the <001> orientation, and the surface flatness was good.

Next, when the interface of the laminated film was observed by the cross-section TEM and EDX, it was confirmed that Si was not diffused at the interface between Si and NbN, and the interface was steep. Although Nbomikuron ₂ were observed partially at the interface between the NbN and _{SrTi 1-x Nb x O 3} , NbO 2 because there is a conductive, did not become a factor inhibiting dielectric properties. Further, SrTi _1-x Nb _x having a concentration gradient of Nb
In the SrTiO ₃ layer on the conductive transition layer composed of O ₃ ,
Almost no defects due to strain at the interface were observed.
It is considered that this is because the SrTi _1-x Nb _x O ₃ layer acts as a buffer layer that relaxes the lattice mismatch with the NbN layer, and thus the defects and strains of the SrTiO ₃ layer grown thereon are reduced. To be The element having the SrTiO ₃ layer having a thickness of 30 nm has a relative permittivity of about 300 and a leak current of 1 × 10 ⁻⁸ A / cm ² or less at the time of applying 3 V, which is sufficient characteristics for use as a capacitor. I was able to.

Thus, in the dielectric thin film element, NaC
By epitaxially growing a conductive barrier layer made of l-type NbN on the Si electrode, the crystallinity of the dielectric thin film is enhanced, and the improvement of the dielectric property can be expected. Similar results were obtained when NaCl-type RuN was used as the conductive barrier layer.

Example 4 Next, an example in which conventionally used TiN is used as a conductive barrier layer will be described. S as a dielectric
r _0.5 Ba _0.5 TiO ₃ was used.

The film formation was performed by reactive spattering.
That is, Ti, SrO, BaO, and Nb are used as targets, and the composition is controlled by controlling each of these sputter sources independently, and the TiN layer and Sr are formed on the Si substrate.
_0.5 Ba _0.5 Ti _1-x Nb _x O ₃ layer, Sr _0.5 Ba _0.5
TiO ₃ layers were sequentially stacked. First, the TiN layer is the substrate temperature
Set a predetermined value in the range of 473 to 673K, introduce N ₂ gas 5mTorr and Ar gas 5mTorr, input power 50 to 100W, film formation rate
A film having a thickness of 100 nm was formed under the condition of 0.5 to 1 nm / s. afterwards,
When forming Sr _0.5 Ba _0.5 TiO ₃ on the TiN layer,
First, Sr _0.5 Ba was doped with Nb to a film thickness of 20 nm.
_A film of _0.5 Ti _1-x Nb _x O ₃ was formed. The composition ratio of Ti and Nb is x = 0 to by adjusting the electric power applied to the Ti target and the Nb target in the range of 0 to 100 W.
It was possible to control to a constant value in the range of 0.1. S
The film formation of r _0.5 Ba _0.5 Ti _1-x Nb _x O ₃ was performed at a substrate temperature of 673 K, 1 mTorr of O ₂ gas and 9 mTorr of Ar gas were introduced, and a film thickness of 20 nm was formed at a film formation rate of 0.1 nm / s. Nb doping amount x
Is from x = 0.1 to x over the thickness of 20 nm from near the electrode.
There was a concentration gradient up to = 0. Next, Ο ₂ oxygen gas 5mTorr
And Ar gas of 5 mTorr were introduced, and Sr _0.5 Ba _0.5 T was formed on the SrTi _1-x Nb _x O ₃ layer under the condition that the film formation rate was 0.1 nm / s.
An iO ₃ layer was formed to a thickness of 20 nm.

Here, Sr _0.5 Ba depending on the Nb doping amount
The change in the electrical characteristics of _0.5 Ti _1-x Nb _x O ₃ is shown in Example 1.
It was almost the same as the case of SrTi _1-x Nb _x O ₃ shown in. Si / TiN / Sr by cross-section TEM and EDX
_0.5 Ba _0.5 Ti _1-x Nb _x O ₃ / Sr _0.5 Ba _0.5 T
Observing the interface of iO ₃ , no diffusion of Si was observed at the interface between Si and TiN, and a sharp interface was formed. In addition, TiN and Sr _0.5 Ba _0.5 Ti _1-x Nb _x O
_A part of TiO ₂ was formed at the interface with ₃ . Normal,
TiO ₂ is an insulator with a relative permittivity of about 80, but here it was found by elemental analysis by ΕDX that Nb was diffused into TiO _2, and N ₁ -doped Ti _1-x Nb
_{Since xO 2} has conductivity, it did not affect the dielectric properties. Furthermore, Sr _0.5 Ba _0.5 Ti _1-x
The interface between Nb _x O ₃ and Sr _0.5 Ba _0.5 TiO ₃ had little lattice disorder, and almost no diffusion of Nb into Sr _0.5 Ba _0.5 TiO ₃ was observed. Sr with this film thickness of 20 nm
The relative permittivity of a device having a _0.5 Ba _0.5 TiO ₃ layer is 300
The leakage current when the Sr _0.5 Ba _0.5 Ti _1-x Nb _x O ₃ layer is on the negative electrode side is 1 × 10 ^-8 A /
Since it was cm ² or less, sufficient characteristics could be obtained for use as a capacitor.

Next, FIG. 12 shows a simple stack type memory cell structure of a DRAM to which the dielectric thin film element of the present invention is applied. Here, since the perovskite-type oxide conductive transition layer 15 that is in direct contact with the Si substrate 21 has a high resistance due to a slight diffusion of Si, the problem of crosstalk between memory cells hardly occurs, and good characteristics are obtained. Can get D
It was confirmed that the application to RAM is possible. In FIG. 12, 22 is a Si plug corresponding to a semiconductor electrode, 23 is an upper electrode, 24 is a lower bit line, 25 is an upper bit line, 26 is a word line, 27 is Al / Cu wiring, and 2 is.
Reference numeral 8 is an ion implantation layer, and the other portions are insulating layers.

[0058]

As described above, according to the dielectric thin film element of the present invention, an insulating layer having a low dielectric constant is formed at the interface between the dielectric thin film made of perovskite type oxide and the electrode layer, Since it is possible to prevent distortion and defects from occurring in the body thin film, it is possible to effectively prevent the effective dielectric constant of the dielectric thin film made of the perovskite type oxide from decreasing. Therefore, it is possible to provide a dielectric thin film element having a high relative dielectric constant and a small leak current.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a main part of a dielectric thin film element according to an embodiment of the present invention.

FIG. 2 is a diagram schematically showing a band structure of SrTiO ₃ .

FIG. 3 is a diagram schematically showing an energy band at an interface when a conductive transition layer is formed according to the present invention.

FIG. 4 is a diagram schematically showing an energy band at an interface between a metal and a perovskite oxide.

FIG. 5 is a diagram showing a change in electrical resistivity depending on a doping amount x of Nb in SrTi _1-x Nb _x O ₃ .

FIG. 6 is a diagram schematically showing a band structure of SrTi _1-x Nb _x O ₃ .

FIG. 7: Electrode layer / SrTi _1-x Nb _x O ₃ / SrTiO ₃ / when the SrTi _1-x Nb _x O ₃ layer is on the positive electrode side
It is a figure which shows the band structure of junction of an electrode layer.

FIG. 8 is a phase diagram of a Hubbard model of a perovskite oxide.

FIG. 9: Electrode layer / Sr _1-x La _x TiO ₃ / SrTi
O ₃ is a diagram showing a band structure of a junction / electrode layer.

FIG. 10 is a diagram showing a relationship between in-plane growth orientations of a Si (100) plane and an NbN (100) plane.

FIG. 11: NbN (100) plane and SrTi _1-x Nb _x O ₃
/ SrTiomikuron is a diagram showing the relationship between the in-plane growth orientation of ₃ (100) plane.

FIG. 12 is a DRA to which the dielectric thin film element of the present invention is applied.
It is a figure which shows the structure of the M simple stack type memory cell.

FIG. 13 is a cross-sectional view showing one structural example of a conventional dielectric thin film element.

FIG. 14 is a cross-sectional view showing another configuration example of a conventional dielectric thin film element.

[Explanation of symbols]

 11 ... Si electrode 12 ... Conductive barrier layer 13 ... Electrode layer 14 ... Dielectric thin film made of perovskite oxide 15 ... Conductive transition layer 16 ... Dielectric layer

Claims (4)

[Claims] 1. A dielectric thin film element comprising an electrode layer and a dielectric thin film made of a perovskite type oxide formed on the electrode layer, wherein the dielectric thin film is provided near an interface with the electrode layer. A dielectric thin film element having a transition region doped with a transition metal element, wherein the transition region has a concentration gradient such that the concentration of the dopant becomes high on the electrode layer side. 2. The dielectric thin film element according to claim 1, wherein the electrode layer has a semiconductor electrode and a conductive barrier layer made of niobium nitride or ruthenium nitride formed on the dielectric thin film side. The dielectric thin film element is characterized in that the transition region of the dielectric thin film is doped with niobium or ruthenium. 3. A dielectric thin film element comprising an electrode layer and a dielectric thin film made of a perovskite type oxide formed on the electrode layer, wherein the dielectric thin film is provided near an interface with the electrode layer. A dielectric thin film element having a transition region doped with a rare earth element, the transition region having a concentration gradient such that the concentration of the dopant is high on the electrode layer side. 4. The dielectric thin film element according to claim 3, wherein the electrode layer has a semiconductor electrode and a conductive barrier layer made of niobium nitride or ruthenium nitride formed on the dielectric thin film side. The dielectric thin film element is characterized in that the transition region of the dielectric thin film is doped with lanthanum or neodymium.