JP3299909B2 - Multilayer structure electrode using oxide conductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-layered electrode using an oxide conductor, and more particularly to various devices using an oxide ferroelectric, such as a ferroelectric nonvolatile memory, a DRAM, and an infrared sensor. The present invention relates to a multilayer structure electrode used as a lower electrode of a ferroelectric thin film in an array or the like.

[0002]

2. Description of the Related Art In recent years,
A ferroelectric memory has been developed as a nonvolatile memory having high integration, high-speed operation, low power consumption, and high reliability comparable to a DRAM. PZT (lead zirconate titanate), S
Crystal thin films of oxide ferroelectrics such as rBi ₂ Ta ₂ O ₉ and Bi ₄ Ti ₃ O ₁₂ are used.

When a crystalline thin film of an oxide ferroelectric is formed, a high-temperature heat treatment at 600 to 800 ° C. is usually required in an atmosphere containing oxygen. Therefore, Pt having a high melting point and excellent oxidation resistance has been often used for the lower electrode formed thereunder. On the other hand, realization of a stack cell (STC) structure is desired for higher integration of memory elements. S
In the TC structure, it is necessary to connect the semiconductor transistor and the ferroelectric memory capacitor with a plug such as polysilicon. However, although the conventional Pt electrode is excellent in oxidation resistance, it has a problem that oxygen is easily transmitted. For this reason, when a Pt electrode is formed on polysilicon, the polysilicon used for the plug when the ferroelectric thin film is formed is oxidized, and the electrical connection cannot be obtained. Occur.

On the other hand, a multi-layer electrode such as Pt / TiN / Ti using TiN as a barrier layer for preventing oxygen permeation and Ti as an adhesive layer between a plug and a lower electrode has been studied. . However, also in this case, the TiN layer is oxidized by oxygen permeated by Pt, and the volume expansion causes a new problem such as separation at the Pt / TiN interface and generation of hillocks (43rd Applied Physics Spring 1996). Proceedings of the Lectures at Academic Alliance Lectures 28p-V-6, 7).

The use of an oxide conductive material as the lower electrode has also been studied, of which IrO ₂ ,
RuO ₂ , YBa ₂ Cu ₃ O _7-x , LaSrCoO _{3, and the} like are promising from the viewpoint of excellent barrier properties and compatibility with oxide ferroelectrics. In particular, it has been reported that IrO ₂ is formed directly on polysilicon. For example, Tokuho 6
Japanese Patent No. 87493 describes that BaTiO ₃ is produced on IrO ₂ / polysilicon to obtain good dielectric properties. Appl.Phys.Lett.vol.65 (1994) p
p.1522-1524, Jpn.J.Appl.Phys.vol.33 (1994) pp.5207-5
210 and JP-A-8-51165, Ir / Ir
It is described that when PZT is formed on O ₂ / polysilicon or Pt / IrO ₂ / polysilicon, the fatigue characteristics thereof are greatly improved.
It is mentioned that the _two films have good barrier properties against ferroelectric constituent elements such as Pb.

However, when IrO ₂ of oxide is formed directly on polysilicon as in these structures, there is a concern that contact failure may occur due to oxidation of the polysilicon surface. Therefore, a study of a multilayer electrode having an IrO ₂ / Ir / TiN / Ti structure in which a barrier metal is inserted between polysilicon and IrO ₂ has been reported (43rd Spring 1996).
Proceedings of the JSCE Lecture Meeting 28p-V-
4). According to this report, I was formed by sputtering.
rO ₂ (100 nm) / Ir (50 nm) / TiN (3
0 nm) / Ti (20 nm) / High dielectric SrTiO ₃ (200 nm) is formed on an electrode having a structure of a Si substrate.
In the capacitor using Pt (50 nm) as the upper electrode, the relative dielectric constant is 216 or less, and the leak current density is 10 ⁻⁷ A / c.
Relatively good electrical properties of less than m ² have been obtained, indicating that this multilayered electrode is promising for STC applications.

However, the oxygen barrier property, reaction prevention property, and the like of this multilayer structure electrode are unknown. That is, S
rTiO ₃ is usually formed at a relatively low temperature of 500 ° C. or lower, but when this multilayer structure electrode is applied to a ferroelectric thin film forming process requiring a film forming temperature of 600 ° C. or higher, It is not self-evident whether its process tolerance is sufficient. For example, when a PZT film is formed on the Pt / TiN / Ti electrode by the sol-gel method,
Hillock generation and peeling do not occur in the pre-firing stage at -450 ° C, but it is known that these problems occur in the main firing at 600 ° C or higher.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and since there is a need to develop an electrode having excellent process resistance applicable to an STC structure, hillocks and peeling do not occur on the electrode itself and the lower polysilicon plug can be connected to the lower polysilicon plug. Without oxygen diffusion
Provide a multi-layer electrode capable of realizing an electrode having process resistance to a heat treatment step in an oxygen atmosphere at 600 ° C. or higher, which ensures the surface flatness and denseness of the electrode and ensures electrical characteristics such as sheet resistance as the electrode. The purpose is to do.

[0009]

According to the present invention, a multi-layered electrode formed on a semiconductor substrate has a lower Ta electrode.
Or a barrier metal containing Hf, Si, and N as constituent elements (hereinafter, referred to as “TaSiN or HfSiN”), and a 36 to 82 nm-thick I
A multilayer structure electrode using an oxide conductor formed by forming an Ir (upper layer / lower layer) laminated electrode of rO ₂ / film thickness of 22 to 66 nm is provided.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A multilayer electrode according to the present invention comprises:
It can be used as a lower electrode of a ferroelectric thin film in a ferroelectric nonvolatile memory, a DRAM, an infrared sensor array, and the like, and is formed on a semiconductor substrate. The semiconductor substrate is not particularly limited as long as it can be used as a substrate of the above-described element.
For example, a silicon substrate, a compound semiconductor substrate of GaAs, InGaAs, or the like can be used. The multilayer structure electrode of the present invention may be formed directly on a semiconductor substrate,
It may be formed via an insulating film such as iN or SiO ₂ ,
A desired element such as a capacitor, a transistor, or a metal wiring may be formed over an interlayer insulating film. For example, when formed through an insulating film, the thickness of the insulating film is preferably about 500 to 2000 nm. When formed through a desired element and an interlayer insulating film, the interlayer insulating film is It is preferable that the film thickness is sufficient to ensure the insulating property with respect to. These insulating films and the like can be formed by a known method such as a CVD method and a spin coating method. The film forming temperature at this time is preferably about 600 ° C. or less.

The multi-layer electrode of the present invention is an electrode using either TaSiN or HfSiN as a barrier metal, and more specifically, a multi-layer electrode of IrO ₂ / Ir / TaSiN or IrO ₂ / Ir / HfSiN. is there. The TaSiN or HfSiN film serving as a barrier metal is formed with a thickness of, for example, about 100 to 500 nm by various methods such as a known method, for example, an RF magnetron sputtering method, a DC magnetron sputtering method, a vacuum evaporation method, and an electron beam evaporation method. be able to. Here, TaSiN or HfS
In order to use an iN film as a barrier metal, an amorphous structure is generally desirable, so that the composition ratio can be freely changed.

Further, the Ir film constituting the laminated electrode formed directly on the barrier metal can be formed by a known method, for example, R
A film thickness sufficient to suppress oxidation of the lower barrier metal when forming an IrO ₂ layer in a later step by various methods such as an F magnetron sputtering method, a DC magnetron sputtering method, a vacuum evaporation method, and an electron beam evaporation method. It is preferable to form with. This film thickness is, for example, 22 nm or more. Further, the Ir layer is preferably formed to be oriented in the (111) plane. Specifically, in the case of the RF magnetron sputtering method, the RF power is about 80 to 200 W,
A method of forming a film by using an inert gas such as Ar or N as a sputtering gas while maintaining the substrate temperature at about 200 to 270 ° C.

The IrO ₂ film formed on the Ir film is sufficiently formed by a known method, for example, the same method as described above, to suppress the oxidation of the lower barrier metal during the high-temperature annealing of the laminated electrode described below. It is preferable to form it with a small thickness. This film thickness is, for example, 36 nm or more. However, the total thickness of the IrO ₂ / Ir film is preferably 150 nm or less, more preferably 60 nm or more.
Further, the IrO ₂ layer is preferably formed to be oriented in the (100) plane. Specifically, in the case of the RF magnetron sputtering method, while maintaining the RF power at about 80 to 200 W and the substrate temperature at about 200 to 270 ° C., an oxygen gas is added to an inert gas such as Ar or N as a sputtering gas at a ratio of 1: 10
A method of forming a film using a gas mixed at a ratio of about 10: 1 is exemplified.

With such a multilayer laminated electrode, a temperature of 600 ° C.
An electrode structure having sufficient resistance to the heat treatment process in the above oxygen atmosphere can be realized. In IrO ₂ , (1
By using a crystal thin film oriented in the (00) plane and the (111) plane, a laminated electrode structure composed of fine crystal grains and having excellent surface flatness can be realized. Such surface flatness, a multilayer laminated electrode of orientation with denseness is not only suitable as a base electrode of a ferroelectric thin film,
Since the sheet resistance of the electrode itself can be controlled, it can be used as an electrode of various elements. less than,
The multi-layered electrode using the oxide conductor of the present invention will be described.

Embodiment 1 As shown in FIG. 1, a multi-layered electrode of the present invention has a 600 nm thick S on a surface of a single crystal Si (100) wafer 1.
iO ₂ film 2, on which TaSiN is used as barrier metal 3
(100 nm), and IrO as an electrode layer 4 thereon.
₂ (230 nm), Ir (130 nm), IrO ₂ (82
nm) / Ir (66 nm). The composition of TaSiN in this example is Ta
₅ SiN ₄ .

The above-mentioned multilayer structure electrode is formed as follows. First, on the surface of the Si wafer 1, SiO
_Two films 2 were formed. Next, TaS is formed on the SiO ₂ film 2.
An iN film was formed by a sputtering method. Furthermore, this Ta
On the SiN film, one of the three types of electrode layers 4 is RF
It was formed by magnetron sputtering. The film formation conditions were as follows: RF power 100 W, substrate temperature 250 ° C., gas pressure 1 Pa, Ir film formation was Ar gas, and IrO ₂ was Ar /
O ₂ = 1/1 mixed gas was used as a sputtering gas. Also, I
The rO ₂ / Ir laminated structure was formed by forming Ir under the above conditions and then forming IrO ₂ . The morphology of each electrode surface was dense and smooth as a result of SEM observation. This is presumably because the film formation temperature was relatively low at 250 ° C., so that grain growth during film formation was suppressed.

Subsequently, in order to examine the resistance to high-temperature heat treatment in oxygen, the above three kinds of electrodes were subjected to 62-hour pressure in 1 atmosphere of oxygen.
Annealing was performed at 5 ° C. for 10 minutes. As a result, IrO
_{In the 2} / TaSiN structure, peeling of IrO ₂ was observed. This is presumably because the TaSiN surface was oxidized by the O ₂ plasma during the IrO ₂ film formation and subsequently by the high-temperature annealing in oxygen, and as a result, separation occurred to release the stress at the interface.

On the other hand, when the O ₂ plasma is not used during film formation,
In the case of the r / TaSiN structure, the surface of the electrode that was flat immediately after film formation became uneven after high-temperature annealing in oxygen, and the surface flatness was impaired. To investigate the cause, the change in the XRD pattern before and after annealing was measured. Immediately after the film formation, the Ir film is (111) -oriented, but the oxide IrO ₂ is generated by the annealing. In addition, Ir (11
1) It was found that the peak intensity of reflection increased by about 40%, and crystallization was promoted. It is considered that as a result of these oxidation and crystallization (grain growth), irregularities on the Ir electrode surface occurred.

As a result, in the IrO ₂ / TaSiN structure and the Ir / TaSiN structure, peeling of the film or unevenness of the electrode surface occurs due to an oxidation reaction or the like in the high-temperature annealing treatment in oxygen after the film is formed. However, it is not suitable as a lower electrode for forming an oxide ferroelectric thin film. Next, looking at the IrO ₂ / Ir / TaSiN structure, as shown in FIG. 2, no peeling or hillocks were observed even after the high-temperature annealing in oxygen, and the flatness of the electrode surface was maintained at the same level as before the annealing. It is a dense and thin film. Also, from the XRD measurement, no change in the diffraction pattern was observed before and after annealing, indicating that an IrO ₂ (100) / Ir (111) alignment film structure was obtained.

These results are obtained by forming an Ir film on TaSiN, and directly forming an IrO ₂ layer on the Ir film.
The aSiN surface does not need to be exposed to oxygen plasma. Further, the Ir surface is slightly oxidized, and the oxide layer IrO ₂ suppresses the oxidation of the TiSiN interface, and the film forming temperature is 250 ° C.
And that the IrO ₂ layer formed on the uppermost portion suppresses the oxidation of the lower Ir / TaSiN due to oxygen diffusion during annealing. Conceivable.

When the sheet resistance of the IrO ₂ / Ir / TaSiN structure was measured, it was found to be about 1.2 Ω immediately after the film formation.
/ □ was obtained, and there was no significant change after annealing. The sheet resistance of the conventionally used Pt (100 nm) / TiN / Ti structure is about 1 Ω / □, and the sheet resistance is almost the same, confirming that the sheet can be sufficiently used as an electrode. .

Similarly, in the IrO ₂ / Ir / HfSiN structure using HfSiN as the barrier metal, a dense electrode having a flat surface without peeling or hillocks can be produced, and it has been confirmed that it has high temperature annealing resistance in oxygen. Was done.

As described above, in the electrode structure formed on the semiconductor substrate, the lower structure is TaSiN, H
The structure is selected from any one of fSiN, and the crystalline (100) -oriented IrO ₂ and (11
1) A multilayer electrode having an IrO ₂ / Ir multilayer structure composed of oriented Ir has an annealing process resistance in an oxygen atmosphere at 600 ° C. or higher. That is, the Ir layer is made of IrO ₂
TaSiN, HfSi which is a lower structure when forming a layer
A film thickness not less than the thickness for suppressing oxidation of N, and
It was shown that an electrode having the above process resistance was obtained when the _two layers had a thickness not less than the thickness for suppressing the oxidation of the barrier metals TaSiN and HfSiN, which are the lower structures by the high-temperature annealing process in oxygen. Further, this electrode has surface flatness and denseness, and has excellent sheet resistance similar to that of the Pt / TiN / Ti structure.

Example 2 Samples having IrO ₂ / Ir / TaSiN structures having different thicknesses were prepared by using the same substrate and the same film forming conditions as in Example 1. However, the thickness of the (100) -oriented IrO ₂ layer was in the range of 36 to 82 nm, and the thickness of the (111) -oriented Ir layer was in the range of 15 to 66 nm. Here, the film thickness was controlled by changing the sputter deposition time. Annealing similar to that of Example 1 was performed for the electrode structures having different thicknesses.

The thickness of the Ir layer is 15 nm, the thinnest IrO
Hillocks were observed after annealing in the ₂ (82 nm) / Ir (15 nm) / TaSiN structure. This is considered to be the same cause as the separation of IrO _{2 in} the IrO ₂ / TaSiN structure shown in the first embodiment. That is, the TaSiN surface is not completely covered because the thickness of the Ir layer is very thin, or TaSiN is oxidized because it is so thin that the oxidation by oxygen plasma during the formation of IrO ₂ cannot be suppressed. It is considered that there was a place where the stress caused hillocks.

No peeling or hillocks were observed in any of the other samples even after annealing, confirming that the samples had annealing resistance. IrO ₂ (36 nm) / Ir (22 nm) with the thinnest film thickness among the fabricated samples
When the cross section of the / TaSiN structure after annealing was observed by SEM, the flatness was maintained even when the film thickness of IrO ₂ / Ir was as thin as about 60 nm, and no reaction or diffusion was observed in the TaSiN portion.

That is, IrO ₂ oriented to (100)
By using the IrO ₂ / Ir laminated electrode structure made of Ir with (111) orientation, the film formation process resistance of the oxide ferroelectric thin film can be realized with a very dense and thin film of about 60 nm. Further, when the sheet resistance of the fabricated sample was measured, as shown in FIG. 3, IrO ₂ / Ir
It was found that the sheet resistance of the entire electrode could be controlled in the range of 1.2 to 2.8 Ω / □ by changing the thickness of the Ir layer and the IrO ₂ layer in the laminated electrode.

In the IrO ₂ / Ir / HfSiN structure using HfSiN as a barrier metal, at least the thickness of the IrO ₂ / Ir electrode is about 60 nm to 150 nm.
Similarly, it was confirmed that a flat and dense electrode structure without peeling and hillocks could be produced in the range of nm, and high-temperature annealing resistance in oxygen could be obtained. As described above, by using the IrO ₂ / Ir electrode structure of the present invention, flatness,
An electrode having excellent denseness can be manufactured. As a result, the thickness of the Ir layer was 22 nm or more, and the thickness of the IrO ₂ layer was 36 nm.
Under the above conditions, the film thickness of the IrO ₂ / Ir electrode is about 60
An electrode excellent in process resistance as thin as 150 nm was produced. Further, the sheet resistance could be controlled from 1.1 to 2.8 Ω / □ by changing the thickness of each layer.

[0029]

According to the present invention, a lower electrode having excellent process resistance, which is indispensable for practical use of a ferroelectric memory or a DRAM using an STC structure, can be formed with good reproducibility. In particular, the IrO ₂ layer and the Ir layer are crystalline thin films,
The rO ₂ layer is oriented in the (100) plane, and the Ir layer is oriented in the (111) plane.
When the electrode is oriented in a plane, the electrode is excellent in flatness and denseness, so that applicability to a fine processing process or the like is also increased.

Further, the thickness of the IrO ₂ / Ir layer is 150
When the thickness is not more than nm, electric characteristics such as sheet resistance can be controlled by changing the film thickness of each layer of the laminated structure electrode. As described above, in the multilayer structure electrode of the present invention, for example, in the process of forming a ferroelectric film, it is possible to prevent a reaction with a lower semiconductor and interdiffusion, and to have high reliability and good characteristics. An element can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an embodiment of a multi-layered electrode using an oxide conductor according to the present invention.

FIG. 2 shows IrO ₂ / Ir / Ta of a multilayer structure electrode of the present invention.
It is a SEM photograph of the surface and cross section of the SiN structure after annealing.

FIG. 3 shows IrO ₂ / Ir / Ta of a multilayer electrode according to the present invention.
4 is a graph showing a sheet resistance of a SiN structure.

[Explanation of symbols]

Single crystal Si substrate 2 SiO ₂ film 3 barrier metal 4 electrode layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI H01L 29/788 29/792 (72) Inventor Hironori Matsunaga 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-8-116032 (JP, A) JP-A-8-236479 (JP, A) JP-A-10-173154 (JP, A) JP-A-10-150155 (JP, A) JP-A-9 -82666 (JP, A) JP-A-9-8253 (JP, A) JP-A-8-330513 (JP, A) JP-A-8-306722 (JP, A) JP-A-8-277196 (JP, A) JP-A-8-264665 (JP, A) JP-A-8-107153 (JP, A) JP-A-8-51165 (JP, A) JP-A-7-302888 (JP, A) 245237 (JP, A) JP-A-7-99290 (JP, A) JP-A-7-74177 (JP, A) JP-A-6-338249 (JP, A) JP-A-6-89355 (JP, A) JP-A-8-260148 (JP, A) JP-A-11-510317 (JP, A) A) Electrodes for Gbit-DRAM, Semiconductor / Integrated Circuit Technology 51st Symposium Proceedings, Electronic Materials Committee of the Institute of Electrical Chemistry, Japan, December 5, 1996, 54-59 Jpn. J. Appl. Phys. , Vol. 33, Part 1, No. 9B, 5207-5210 (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/28 301 H01L 21/822 H01L 21/8247 H01L 27/04 H01L 27/105 H01L 29/788 H01L 29/792

Claims (2)

(57) [Claims] 1. A multilayer electrode formed on a semiconductor substrate, comprising a barrier metal containing Ta or Hf, Si, and N as constituent elements in a lower portion, and a film thickness of 36 to 82 nm on an upper portion of the barrier metal. IrO ₂ / film thickness 22-66n
A multilayered electrode using an oxide conductor, wherein a laminated electrode of m (upper layer / lower layer) is formed. 2. The IrO ₂ layer and the Ir layer are crystalline thin films, the IrO ₂ layer is oriented in the (100) plane, and the Ir layer is (1).
11) The multilayer structure electrode according to claim 1, which is oriented in a plane.