JPH06112082A - Thin film capacitive element - Google Patents

Abstract

PURPOSE:To obtain a thin film capacitive element which is small in leakage current, small in surface area, and large in charge storage by a method wherein specific material is added to a crystalline lead-free dielectric body of perovskite structure. CONSTITUTION:A dielectric layer is formed of dielectric material of perovskite structure represented by a general formula ABO3, where A is an element selected from strontium, barium, and calcium, and B denotes either of titanium and zirconium. At least, 0.05 to 0.3at.% of an element selected from vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodymium, samarium, neodymium, gadolinium, or polonium is added to the above dielectric material. As the added element functions as donor, a flow of electron due to diffusion can be ensured, and consequently a thin film capacitive element can be lessened in leakage current even if a thin dielectric layer is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film capacitive element preferably used in a semiconductor integrated circuit such as an LSI memory and its peripheral circuits.

[0002]

2. Description of the Related Art LSI memory, especially dynamic random access memory (DRAM), has been used for about 4 years in the past three years.
High integration is progressing at twice the speed, and it is expected that high integration will continue at the same speed in the future. As such high integration progresses, the ratio of the area occupied by the capacitor in the memory cell will gradually increase as long as silicon oxide or the like is used as the dielectric material. Therefore, for example, in a 4-Mbit DRAM, a stack structure in which an electrode, a dielectric layer, and an electrode are stacked on a semiconductor substrate as a capacitor in a memory cell, or a groove is formed in the substrate, and a thin dielectric layer is inserted in the groove. A three-dimensional structure such as a trench structure in which electrodes are embedded is adopted.
However, further integration is expected in the future, and it is expected that the structure of the memory cell will become more and more complicated and the required capacitor area cannot be secured. From such a viewpoint, silicon oxide (SiO 2) which has been conventionally used as a capacitor material of DRAM is used.
₂ : Simplification of the capacitor structure by using a dielectric material with a large relative permittivity in place of the relative permittivity of about 4) or nitride (Si ₃ N ₄ : about 7) .

Based on the above concept, for example, DRA
As a capacitor material for M, Ta ₂ O ₅ (relative dielectric constant of about 2
5) has been continuously studied as a powerful material, but as a material having a larger relative dielectric constant, a ferroelectric material such as Pb-based lead zirconate titanate (Pb (Zr, T
i) O ₃ ), barium titanate (BaTiO ₃ ), and paraelectric strontium titanate (SrTiO ₃ ).
₃ ), calcium titanate (CaTiO ₃ ) and other crystalline dielectric materials having a perovskite structure are being considered.

That is, up to now, the absolute value of the effective area of the capacitor in the memory cell of the DRAM is too small because a certain capacitance is required to prevent a soft error due to radiation even if the degree of integration increases. is not. However, as described above, it is expected that the capacitor area required for the memory cell cannot be secured as the integration further progresses in the future. This background is the reason why it is necessary to consider using a material having a large relative dielectric constant as a capacitor material. For example, in a 1G DRAM, the value of the plane area that can be used as a capacitor portion is expected to be about 0.1 μm ² , and it is considered difficult to manufacture a trench type three-dimensional structure capacitor. It is obvious that a material having a large relative dielectric constant is required to manufacture a capacitor having a simplified planar area.

[0005]

By the way, the conventional DR
Silicon oxides and silicon nitrides that have been used as capacitor materials for AM are mainly used in an amorphous state, whereas they have the perovskite structure of the Pb-based ferroelectric material or strontium titanate. Dielectric materials use ionic polarization in crystals to obtain a large relative permittivity, and must be used in a crystalline state. For this reason, the leak current in the thin film capacitor tends to be larger than that when an amorphous material is used as the dielectric. Therefore, there is a problem that it cannot be used as a thin film capacitor unless the leak current of the crystalline dielectric is reduced.

When the dielectric material having the perovskite structure is produced, it is usually performed in an oxygen atmosphere.
For this reason, the material corresponding to the lower electrode in the thin film capacitor, that is, the base material for producing the dielectric material having the perovskite structure must be a noble metal or a conductive antioxidative compound. This is because when a base material (lower electrode) is oxidized when a dielectric material having a perovskite structure is produced, a substance having a small relative dielectric constant is formed at the interface between the lower electrode and the dielectric, and a perovskite structure having a large relative dielectric constant is formed. There is no point in using a dielectric material with. However, there is a problem that such materials having oxidation resistance generally do not have good adhesion to the dielectric material having the perovskite structure. Such a problem of adhesion is an important problem not only for the lower electrode but also for the upper electrode.

The present invention has been made to solve such a conventional problem, and a first object thereof is to provide a thin film capacitive element having a small leak current and capable of accumulating a large amount of charges in a small area. Is.

A second object is to provide a thin film capacitive element which is excellent in adhesion and can store a large amount of charges in a small area.

[0009]

In order to achieve the above first object, the first invention of the present application is such that a dielectric layer is generally used in a thin film capacitor used in an integrated circuit (DRAM) or its peripheral circuits. Formed of a dielectric material having a perovskite structure represented by the formula ABO ₃ (A is at least one of strontium, barium, and calcium, B is at least one of titanium and zirconium), and vanadium, niobium, tantalum, antimony , Bismuth, lanthanum, cerium, praseodium, samarium, neodymium, gadolinium, or holmium is contained in an amount of at least 0.05 atomic% and less than 0.3 atomic%.

In order to achieve the second object, according to the second invention of the present application, the dielectric layer is formed of a dielectric material having a perovskite structure represented by the general formula ABO ₃ (A is strontium, barium, calcium). At least one of
At least one of vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodymium, samarium, neodymium, gadolinium, and holmium is 0.3. Atomic% or more, 3
It is configured to contain less than atomic%.

Here, the structure of the thin film capacitor of the present invention is shown in FIG.
Shown in. As shown in the figure, the thin film capacitor of the present invention includes, for example, a lower electrode 2, a dielectric layer 3 and an upper electrode 4 on a substrate 1.
Are sequentially laminated. The dielectric constant material having the perovskite structure used for the dielectric layer 3 includes strontium titanate (SrTiO ₃ ), barium titanate (BaTiO ₃ ), and calcium titanate (CaTi).
O ₃ ), barium zirconate (BaZrO ₃ ), strontium delconate (SrZrO ₃ ), and the like, and mixtures thereof.

[0012]

First, the reduction of the leak current according to the first aspect of the invention will be described. Generally in ceramic (bulk),
As shown in FIG. 2 as an example in which lanthanum is added to barium titanate, vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodymium of 0.05 atom% or more and less than 0.3 atom%, When at least one of samarium, neodymium, gadolinium, and holmium is added to a dielectric material having a perovskite structure, these serve as electron donors, the dielectric becomes a semiconductor, and its electrical resistance is significantly reduced, which in turn causes an increase in leakage current. Becomes

However, the effect of addition of vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodymium, samarium, neodymium, gadolinium, or holmium on the leak current in the thin film is different from that of ceramic (bulk). Typical results obtained by measuring the leak current characteristics of the thin film capacitor having the structure shown in FIG. 1 are shown in FIG. 3. The magnitude of the leak current differs depending on whether the voltage applied to the upper electrode is positive or negative. That is, when a positive voltage is applied to the upper electrode that is in ohmic contact with the dielectric layer, the leak current is small, and conversely, when the upper electrode is negatively applied, the leak current is large. ing. Therefore, by always applying a positive voltage to the upper electrode side for use, it is possible to operate the thin film capacitive element with a small leak current. In order to explain this phenomenon, an energy band configuration diagram corresponding to the structure of the thin film capacitive element and an electron density distribution corresponding thereto are shown in FIG. As can be seen from the energy band configuration diagram of the thin film capacitive element shown in FIG. 4, a Schottky barrier is formed between the lower electrode and the dielectric layer, and a depletion layer is formed in the dielectric layer. This depletion layer is formed on a part of the dielectric layer on the lower electrode side when the dielectric is thick. Therefore, when the upper electrode is applied with a positive voltage, the leakage current of electrons flowing over the Schottky barrier (Schottky current) and diffusion electrons generated in the dielectric layer due to the depletion layer are formed. The value is small because it is only the difference with the flow (diffusion current).
On the other hand, when the upper electrode is negatively applied, the band is pushed upward as the applied voltage increases, and the leak current flowing increases. For this reason, it is possible to explain the magnitude of the leak current due to the positive / negative difference of the upper electrode shown in FIG.

By the way, when the dielectric constant material having the crystalline perovskite structure is used for the thin film capacitive element, it is effective to use a film as thin as possible (500 A or less) from the viewpoint of accumulating a large amount of charges. However, when the film thickness of the dielectric layer becomes thin, a depletion layer is formed over the entire dielectric layer, the flow of electrons due to diffusion to cancel the electrons flowing over the Schottky barrier does not occur, and the leak current is reduced. This will result in an increase.

The present invention has been made in order to improve the above-mentioned inconvenience, and a dielectric constant material having a crystalline perovskite structure can be used in an amount of 0.05 atom% or more and less than 0.3 atom% of vanadium, niobium, tantalum, Antimony, bismuth,
Lantern, cerium, praseodium, samarium,
To increase the concentration of electrons in the dielectric layer by adding at least one of neodymium, gadolinium, or holmium, and to cancel the electrons flowing over the Schottky barrier even when the dielectric layer becomes thin. It aims to secure the flow of electrons due to diffusion. Vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodymium, samarium, neodymium, gadolinium, or holmium is an electron donor by diffusion to act as a donor in the dielectric material having a crystalline perovskite structure. The flow can be secured, and as a result, the leak current can be suppressed even in the thin dielectric layer. Such an effect becomes particularly remarkable when the film thickness is 500 A or less. It should be noted that such an effect does not appear in a dielectric material having a perovskite structure containing lead.

Further, by adding vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodium, samarium, neodymium, gadolinium or holmium, an extremely small amount of compound is formed at the electrode interface and adhesion with the electrode is formed. May improve.

The reason why the addition amount of vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodium, samarium, neodymium, gadolinium, and holmium is 0.05 atom% or more and less than 0.3 atom% is 0. If the amount added is less than 05 atomic%, the effect of reducing the leakage current cannot be obtained. If the amount added is 0.3 atomic% or more, the effect of reducing the leakage current is sufficient especially when the film thickness of the dielectric layer is 500 A or less. This is because it may not be possible to obtain

Next, the improvement of adhesion according to the second invention will be described. The thin film capacitor according to the present invention has a capacity of 0.0
Vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, of 3 at% or more and less than 3 at%
Adhesion between the dielectric layer and the upper and lower electrodes is improved by adding at least one of praseodium, samarium, neodymium, gadolinium, or holmium to a dielectric material having a lead-free crystalline perovskite structure. It is what makes me. It should be noted that the above-described effect is not observed in the dielectric material having a perovskite structure containing lead.

The reason why at least one of vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodium, samarium, neodymium, gadolinium or holmium is added to the dielectric material having a perovskite structure to improve the adhesion is as follows.
Although not completely clarified, the results of SIMS analysis (secondary ion mass spectrometry) show that upper and lower electrodes are Pt and P.
When a noble metal such as d is used, vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodium, samarium, neodymium, gadolinium, or a compound of holmium and a noble metal containing a slight amount of oxygen is formed at the interface. It is thought that it is because it is being done. Also, when a compound having conductivity such as TiN, SnO ₂ or ReO ₂ is used as the upper and lower electrodes, SIMS analysis (secondary ion mass spectrometry) is similarly performed.
From the result, it is considered that a trace amount of an oxide layer containing vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodymium, samarium, neodymium, gadolinium or holmium is formed on the interface.

When the addition amount of such an additional element is within the above range, the electric resistance is remarkably the same as in the example of the ceramic (bulk) in which lanthanum is added to barium titanate as shown in FIG. There is also a side effect of increasing and reducing leakage current through the dielectric.

Vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodium,
The reason why the addition amount of samarium, neodymium, gadolinium, or holmium is limited to 0.3 atom% or more and less than 3 atom% is that the addition amount of less than 0.3 atom% adheres the dielectric layer to the upper and lower electrodes. This is because the improvement of the property is small, and when 3 atomic% or more is added, the relative permittivity of the dielectric constant material having the perovskite structure decreases, and it becomes unsuitable as a dielectric material for a thin film capacitor. Further, within the above composition range, although there are subtle differences depending on the combination of the dielectric material and the additional element, 0.5 atom% or more and less than 1 atom% are particularly desirable.

[0022]

Embodiments of the present invention will now be described in detail with reference to the drawings.

<Embodiment 1> FIG. 5 is a sectional view of an essential part of a thin film capacitor according to the first embodiment. Board 7
Is a MgO (100) single crystal. Pt8 having a film thickness of about 500 A was deposited as a lower electrode on the substrate 7 by RF sputtering at a substrate temperature of 400 ° C. Then, SrTi containing niobium was formed by RF sputtering using a SrTiO ₃ sintered body containing 0.1 atomic% niobium as a target.
The O ₃ dielectric layer 9 was deposited at a substrate temperature of 400 ° C. to a film thickness of about 400A. Further, Ni10 was used as the upper electrode by the same RF sputtering method at a substrate temperature of 350 ° C. to about 500 A.
Deposited to a film thickness of. In order to investigate the electrical characteristics of the thin-film capacitive element manufactured as described above, Ni10 of the upper electrode was etched by a lithographic method to obtain 100 μm × 1.
The size of the electrode was 00 μm. For comparison, a thin-film capacitor element made of a dielectric material containing no niobium was prepared by the same method as described above.

FIG. 6 shows current-voltage characteristics when a positive voltage is applied to the upper electrode of the thin film capacitor according to the present invention, and the same electrical characteristics as those of the comparative example. The leak current 12 of the thin film capacitor manufactured as a comparative example is 10 ⁻⁶ A / cm ² , whereas the leak current 11 of the thin film capacitor according to the present invention is 10 ⁻⁸ A / cm ² . Clearly improved. This result demonstrates the significance of the present invention.

<Embodiment 2> FIG. 7 is a sectional view of an essential part of a thin film capacitor according to the second embodiment. Board 1
3 is a MgO (100) single crystal. P is formed on the substrate as a lower electrode by RF sputtering at a substrate temperature of 400 ° C.
t14 was deposited to a film thickness of about 500A. Subsequently, Ba containing lanthanum was deposited by RF sputtering using a BaTiO ₃ sintered body containing 0.3 atom% of lanthanum as a target.
The TiO ₃ dielectric layer 15 is heated to about 450 at a substrate temperature of 400 ° C.
It was deposited to a film thickness of A. Further, Ni16 was used as the upper electrode by RF sputtering at the substrate temperature of 350 ° C. for about 5 times.
It was deposited to a film thickness of 00A. In order to investigate the electrical characteristics of the thin film capacitive element manufactured as described above, Ni1 of the upper electrode was used.
6 was etched by the lithography method to 100 μ
The size of the electrode was m × 100 μm. For comparison, a thin film capacitive element made of a dielectric material containing no lanthanum was prepared by the same method as described above.

FIG. 8 shows current-voltage characteristics when a positive voltage is applied to the upper electrode of the thin film capacitor according to the present invention, and the same electrical characteristics as the comparative example. The leak current 18 of the thin film capacitor manufactured as a comparative example is 10 ⁻⁶ A / cm ² , whereas the leak current 17 is 10 ⁻⁸ A / cm ² in the thin film capacitor according to the present invention. Clearly improved. This result demonstrates the significance of the present invention.

<Embodiment 3> FIG. 9 is a sectional view of an essential part of a thin film capacitor according to the third embodiment. Board 1
9 is a MgO (100) single crystal. Pt20 having a film thickness of about 500 A was deposited as a lower electrode on the substrate 19 by RF sputtering at a substrate temperature of 400 ° C. Then 0.
A SrTiO ₃ dielectric layer 21 containing tantalum was deposited at a substrate temperature of 400 ° C. to a film thickness of about 450 A by an RF sputtering method using a sintered body of SrTiO ₃ containing 05 atomic% of vanadium as a target. Further, Ni22 is used as the upper electrode by the same RF sputtering method at a substrate temperature of 350.
It was deposited to a film thickness of about 500 A at ° C. In order to investigate the electrical characteristics of the thin film capacitive element produced as described above, Ni22 of the upper electrode was etched by a lithographic method to have an electrode size of 100 μm × 100 μm. For comparison, a thin film capacitive element made of a dielectric material containing no lanthanum was prepared by the same method as described above.

FIG. 10 shows current-voltage characteristics when a positive voltage is applied to the upper electrode of the thin film capacitor according to the present invention, and the same electrical characteristics as those of the comparative example. The leak current 24 of the thin film capacitor manufactured as a comparative example is 10 ⁻⁶ A / cm ^2.
On the other hand, in the thin film capacitor according to the present invention, the leak current 23 is 10 ⁻⁸ A / cm ^2, which is clearly improved. This result demonstrates the significance of the present invention.

<Embodiment 4> FIG. 11 is a sectional view of an essential part of a thin film capacitor according to the fourth embodiment. The substrate 31 is a MgO (100) single crystal. A substrate temperature of 400 is formed on the substrate 31 as a lower electrode by RF sputtering.
Pt32 was deposited to a film thickness of about 500 A at ℃. Then, the SrTiO ₃ dielectric layer 33 containing niobium was applied to the sintered body of SrTiO ₃ containing 0.5 atomic% of niobium as a target by RF sputtering at a substrate temperature of 400 ° C. for about 7 minutes.
It was deposited to a film thickness of 00A. On the other hand, as a comparative example, Pt was deposited on the MgO substrate in the same manner as described above, and then a SrTiO ₃ layer containing no niobium was deposited thereon at about 700 A and 400 ° C.

A test was conducted on both of them to examine the adhesion with Scotch tape.
While no peeling was observed in the TiO ₃ layer,
About 10% Sr in SrTiO ₃ layer containing no niobium
Peeling of the TiO ₃ layer was observed, and the effect of adding niobium was clearly seen.

Further, for both, Ni was used as the upper electrode.
34 was similarly deposited by RF sputtering at a substrate temperature of 350 ° C. to a film thickness of about 500A. In order to examine the electrical characteristics of the thin-film capacitive element manufactured as described above, Ni34 of the upper electrode was etched by a lithographic method.
An electrode having a size of 00 μm × 100 μm was produced.

FIG. 12 shows current-voltage characteristics when a positive voltage is applied to the upper electrode of the thin film capacitor according to this embodiment. The leak current of the thin film capacitor manufactured as a comparative example is 10 ⁻⁸ A / cm ² , whereas the leak current of the thin film capacitor according to the present invention is 10 ⁻⁹ A / cm ² as shown in FIG. It is cm ² , and the secondary effect is clearly shown.

<Fifth Embodiment> FIG. 13 is a sectional view of an essential part of a thin film capacitor according to the fifth embodiment. The substrate 41 is a MgO (100) single crystal. A substrate temperature of 400 is formed on the substrate 41 as a lower electrode by RF sputtering.
Pt42 was deposited to a film thickness of about 500 A at ℃. Then, a SrTiO ₃ dielectric layer 43 containing tantalum was deposited at a substrate temperature of 400 ° C. to a film thickness of about 700 A by RF sputtering using a sintered body of SrTiO ₃ containing 0.5 atomic% of tantalum as a target. On the other hand, as a comparative example, Pt was deposited on the MgO substrate in the same manner as described above, and then a SrTiO ₃ layer containing no tantalum was deposited on the MgO substrate by about 700 A40.
Deposited at 0 ° C.

A test for checking the adhesion with Scotch tape was carried out for both, and S containing tantalum was found.
No peeling was observed in the rTiO ₃ layer, whereas it was about 10% in the SrTiO ₃ layer containing no tantalum.
The peeling of the SrTiO ₃ layer was observed, and the effect of the addition of tantalum was clearly seen.

Further, for both, Ni was used as the upper electrode.
44 was similarly deposited by RF sputtering at a substrate temperature of 350 ° C. to a film thickness of about 500A. In order to investigate the electrical characteristics of the thin-film capacitive element manufactured as described above, Ni44 of the upper electrode was etched by a lithographic method to
An electrode having a size of 00 μm × 100 μm was produced.

The current-voltage characteristics when a positive voltage is applied to the upper electrode of the thin film capacitor according to the present embodiment are as shown in FIG. 12 as in the fourth embodiment. That is, the leak current can be significantly reduced.

[0037]

As described above, according to the first invention of the present application, it becomes possible to reduce the leak current in the thin film capacitor using the dielectric material having the lead-free crystalline perovskite structure. It greatly contributes to high integration of LSI and the like.

Further, according to the second invention of the present application, a thin film capacitor using a dielectric having a lead-free crystalline perovskite structure is excellent in adhesion between the dielectric layer and the upper and lower electrodes. Therefore, it is possible to provide a thin film capacitive element having excellent reliability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structure of a thin film capacitor according to the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the La addition amount and electric resistance when La is added to BaTiO ₃ .

FIG. 3 is a diagram showing a leakage current characteristic of the thin film capacitor according to the present invention.

FIG. 4 is an energy band diagram and an electron density distribution of a thin film capacitor according to the present invention.

5 is a cross-sectional view showing the structure of the thin film capacitive element according to Example 1. FIG.

FIG. 6 is a diagram showing current-voltage characteristics of the thin film capacitive element according to Example 1 and a comparative example.

FIG. 7 is a cross-sectional view showing the structure of a thin film capacitive element according to Example 2.

FIG. 8 is a diagram showing current-voltage characteristics of a thin film capacitive element according to Example 2 and a comparative example.

FIG. 9 is a cross-sectional view showing the structure of the thin film capacitive element according to the third embodiment.

FIG. 10 is a diagram showing current-voltage characteristics of a thin film capacitive element according to Example 3 and a comparative example.

FIG. 11 is a cross-sectional view showing the structure of the thin film capacitive element according to the fourth embodiment.

FIG. 12 is a diagram showing current-voltage characteristics of the thin film capacitive element according to Example 4.

FIG. 13 is a cross-sectional view showing the structure of the thin film capacitive element according to Example 5.

[Explanation of symbols]

 1 substrate 2 lower electrode 3 dielectric layer 4 upper electrode

Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location // H01L 27/108

Claims (2)

[Claims] 1. A thin film capacitive element comprising a dielectric layer for accumulating charges and a pair of electrodes opposed to each other through the dielectric layer, wherein the dielectric layer is represented by the general formula ABO ₃ . A perovskite structure (A is at least one of strontium, barium, and calcium,
B consists of at least one of titanium and zirconium), and at least one of vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodymium, neodymium, gadolinium, or holmium is 0.05 atomic% or more, 0.3 atom%
A thin film capacitive element characterized by being included in less than. 2. A thin film capacitive element comprising a dielectric layer for accumulating charges and a pair of electrodes opposed to each other through the dielectric layer, wherein the dielectric layer is represented by the general formula ABO ₃ . A perovskite structure (A is at least one of strontium, barium, and calcium,
B is made of at least one of titanium and zirconium), and at least one of vanadium, niobium, tantalum, antimony, bismuth, lanthanum, cerium, praseodymium, neodymium, gadolinium, or holmium is 0.3 atom% or more, A thin film capacitive element containing less than 3 atomic%.