JP3018985B2 - Method of forming dielectric thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a dielectric thin film used for manufacturing a semiconductor device or the like.

[0002]

_2. Description of the Related Art Development of a semiconductor device using a ferroelectric or a high dielectric as an insulating film in place of SiO ₂ is urgently required.
The former attracts attention as a non-volatile memory, and the latter attracts attention as a use for covering a shortage of memory capacity of a DRAM or the like due to miniaturization.

[0003] Such a ferroelectric thin film or a high dielectric thin film is formed by a sol-gel method, an organometallic solution deposition method,
There are a laser ablation method, a sputtering method, a chemical vapor deposition method (MOCVD) using an organic metal gas, and the like. Ferroelectric characteristics and high dielectric characteristics can be obtained with a crystalline film, but not with an amorphous film such as SiO ₂ . For this reason, it is necessary to form a ferroelectric or high-dielectric crystal film, but a polycrystalline film has poor surface morphology compared to a single-crystal thin film, tends to vary in characteristics, and has deteriorated current / voltage characteristics. Problem. Therefore, a single crystal film is desired as an insulating film having ferroelectric characteristics and high dielectric characteristics.

[0004] In order to obtain a single crystal ferroelectric thin film, a method of performing heteroepitaxial growth using a substrate having a close lattice constant has been attempted (The 56th Annual Meeting of the Japan Society of Applied Physics, 1995, p399).

[0005]

However, MgO is used as a material having a lattice constant close to that of a ferroelectric or high dielectric.
And the like are used, but the material is deliquescent and unstable.

In general, when a ferroelectric thin film or a high dielectric thin film is used for a semiconductor element as a capacitor,
A capacitor is manufactured by disposing SiO ₂ on a substrate, forming a lower electrode on the SiO ₂ , and then forming a ferroelectric thin film or a high dielectric thin film. However, since SiO ₂ is amorphous, the above metal is crystallized, but the above-mentioned MgO
It is difficult to form a single crystal film such as that described above, and a ferroelectric or high dielectric substrate cannot be expected.

Further, in general, a film formed by heteroepitaxial growth has strains and defects caused by a difference in lattice constant, and good electrical characteristics cannot be obtained in many cases.

That is, there are many difficulties in forming a single crystal ferroelectric thin film or high dielectric thin film by heteroepitaxial growth. Further, even if heteroepitaxial growth is possible, the material such as MgO serving as the substrate has deliquescence and is difficult to apply to a semiconductor device. Further, a film formed by heteroepitaxial growth generally has strains and defects caused by a difference in lattice constant, so that good electrical characteristics cannot be expected.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to form a stable single-crystal dielectric thin film having good electric characteristics with little distortion and defects.

[0010]

Means for Solving the Problems The present inventor has made various studies in order to achieve the above object, and as a result, completed the present invention.

According to a first aspect of the present invention , a concave portion is formed in a surface layer of a laminated thin film on a substrate when a ferroelectric or high dielectric thin film is formed later.
The orientation of the growth nucleus is determined by the restrictions from the base and the side
Sea urchin, to form a recess to expose a portion of the lower layer in the recess, then forming a ferroelectric or high-dielectric thin film on a surface having a recess, graphoepitaxy into the recess
The present invention relates to a method for forming a dielectric thin film, which comprises forming a single crystal ferroelectric or high dielectric thin film by thermal growth .

According to a second aspect of the present invention, a step of forming a metal thin film on a substrate, a step of forming a dielectric thin film on the metal thin film, and a step of forming a ferroelectric or high dielectric thin
The orientation of growth nuclei in the recess during film formation is limited from the base and side
As determined by receiving, exposing a portion of the metal thin film in the recess to form a recess, and forming a ferroelectric or high-dielectric thin film on a surface having a recess, the recess A step of forming a single crystal ferroelectric or high dielectric thin film by grapho-epitaxial growth .

According to a third aspect of the present invention, the step of the concave portion is 10 to 50 n.
m, the method for forming a dielectric thin film according to the first or second invention.

A fourth invention relates to the method for forming a dielectric thin film according to the first, second or third invention, wherein one side of the concave portion in the plane of the laminated thin film is 0.1 to 5 μm.

The fifth invention relates to the method for forming a dielectric thin film according to any one of the first to fourth inventions, wherein a ferroelectric or high dielectric thin film is formed by a chemical vapor deposition method using an organic metal.

According to a sixth aspect, the main component of the dielectric thin film is Si.
O ₂ or a method of forming a dielectric thin film the Si ₃ N ₄ in which the first to fifth invention of any one of.

In the present invention, a crystalline dielectric thin film is formed on irregularities. At this time, since the orientation of the film formed inside the concave portion is restricted not only from the base but also from the side, the orientation is determined, and single crystal growth can be performed by the principle of graphoepitaxy. In addition, since the single crystal growth is not performed by inheriting the lattice constant of the underlayer, good electric characteristics can be obtained without distortion or defects near the interface due to the mismatch.

[0018]

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

First, as shown in FIG. 1A, a first dielectric thin film (2), a metal thin film (3) and a second dielectric thin film (4) are formed on a substrate (1).

Thereafter, as shown in FIG. 1B, the second dielectric thin film is locally removed by lithography means usually used in a semiconductor process. As a result, a concave portion is formed on the surface.

Next, a ferroelectric thin film or a high dielectric thin film is formed by MOCVD. The deposition gas is very difficult to adhere to the metal thin film, but easily adheres to the dielectric film. Therefore, the ferroelectric thin film or the high dielectric thin film is exposed on the surface where the second dielectric film is exposed. Is formed. In particular, when the dielectric thin film is S
When iO ₂ or Si ₃ N ₄ is contained as a main component, the deposition gas is easily adsorbed. Therefore, as shown in FIG. 1 (c), the initial growth nucleus (5) is formed on the second dielectric film (4) and at the side surface position in the concave portion.

The orientation of the growth nucleus of the ferroelectric or high dielectric formed on the side surface in the concave portion is determined because it is restricted from the base simultaneously with the side surface, and the orientation is determined. A high dielectric thin film (6) is formed. on the other hand,
Since there is no such restriction on the main surface of the second dielectric thin film (4) outside the concave portion, a polycrystalline ferroelectric or high dielectric thin film (7) is formed (FIG. 1 (d)). .

The formation of the above ferroelectric or high dielectric thin film requires coverage, selectivity and composition controllability, and MOCVD is desirable as a method satisfying these conditions.

When the size of the concave portion is increased, the volume energy of the crystal in the concave portion is increased, and it becomes difficult to maintain single crystallinity and the reproducibility is reduced. One side in the film surface of the concave portion formed in the film is set to 0.
Desirably, the thickness is 1 to 5 μm. It is desirable that the shape of the concave portion in the film surface be rectangular.

Further, in order to suppress the random generation of crystal nuclei on the side surface inside the concave portion and to suppress the polycrystallization, it is preferable that the step of the concave portion is 10 to 50 nm.

Since the above-mentioned crystal growth does not depend on the lattice constant of the substrate, it goes without saying that there is no restriction on the selection of a substrate material such as a Si substrate or a GaAs substrate.

There is no particular limitation on the metal thin film, and electrodes such as Pt, Pt / Ti, Au, RuO _x , and IrO _x are often used for devices using a ferroelectric capacitor or a high dielectric capacitor. All of the materials are applicable.

The first dielectric thin film is made of SiO ₂ or Si ₃ N
All of the dielectrics commonly used in the semiconductor industry, such as _4, are applicable. Note that the first dielectric thin film is provided as needed.

The second dielectric thin film is preferably a dielectric thin film containing SiO ₂ or Si ₃ N ₄ as a main component, which easily adsorbs an organic metal gas.

As the ferroelectric or high-dielectric, all of those usually used for elements using the ferroelectric or high-dielectric can be applied. For example, BaTiO ₃ , Ba _1-x S
barium-based ferroelectrics such as r _x TiO ₃ , PbTiO ₃ , P
_{bZr 1-x Ti x O 3} , Pb (La 1-y Zr y) 1-x Ti x O 3
And the like, a bismuth-based ferroelectric such as SrBi ₂ Ti ₂ O _{9, and} a strontium-based high dielectric such as SrTiO ₃ .

[0031]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

First, as shown in FIG. 2A, a Pt / Ti thin film (1) is formed on a Si oxide film substrate (11) by a sputtering method.
3) the Pt film thickness 2000 Å, after forming a Ti film thickness 500 Å, the film thickness by CVD SiO ₂ film (14) 40
00 °.

Thereafter, the SiO ₂ thin film was locally removed by a usual lithography technique to form a 3 × 3 μm ² concave portion (the shape in the film surface was rectangular) as shown in FIG. 2B. .

Next, PbZr_xTi_1-xO_ThreeThin film (PZT
A thin film) was formed by the MOCVD method. Pb (C
₁₁H₁₉O_Two)_Two, Zr (C₁₁H₁₉O_Two)_FourAnd Ti (i-O
C_ThreeH ₇)_FourAnd the gas flow rate is 10-50 scc
m, 10-50 sccm, 1-5 sccm, substrate temperature 450-
650 ° C. and the film forming pressure were controlled at 1 to 10 Torr. Deposition gas
Is difficult to adhere to the Pt / Ti thin film,
_TwoSelectively adheres to thin films. Therefore, as shown in FIG.
As shown, the PZT initial growth nucleus (15) is SiO 2_TwoThin film
(14) It is formed on the side surface position in the upper part and in the concave part.

Under the above conditions, PZT was replaced with S
When depositing on the plane of the iO ₂ thin film and the Pt / Ti thin film,
The initial growth nuclei are (100) -oriented. However, in the present invention, the growth nucleus is formed of SiO ₂ at the portion where the Pt / Ti thin film is exposed.
It is formed only at the boundary between the thin film and the Pt / Ti thin film. At that time, the orientation is limited to one from both the base and the side surfaces.
Therefore, a single-crystal PZT thin film (16) is formed on the exposed surface of the Pt / Ti thin film. On the other hand, since there is no restriction on the in-plane rotation at the portion covered with the SiO ₂ thin film (14), a polycrystalline PZT thin film (17) rotated in the (100) plane is formed (FIG. 2D).

[0036]

As is apparent from the above description, according to the present invention, a thin film is formed by grapho-epitaxial growth without bringing in a new substrate for lattice matching as in heteroepitaxial. A Si substrate can be used without any special measures. Therefore, a thin film can be easily formed, and a stable thin film can be formed because there is no need to use a special material.

Further, as compared with a film obtained by heteroepitaxial, distortion and defects at the interface can be suppressed. The reason is that heteroepitaxial growth is performed by utilizing the closeness of the atomic arrangement and lattice constant to the substrate side, so that a small lattice mismatch occurs, thereby causing distortion and defects. This is because the orientation by the interface energy with the side is used, and no distortion or defect due to the minute lattice mismatch as described above occurs. As a result, the IV characteristics are greatly improved, the leakage current is suppressed to about 10 ⁻⁸ A / cm ^{2 at} 5 V, and a film can be formed with higher reproducibility.

[Brief description of the drawings]

FIG. 1 is a process sectional view of a method for forming a dielectric thin film of the present invention.

FIG. 2 is a process sectional view of a method for forming a dielectric thin film of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate 2 First dielectric thin film 3 Metal thin film 4 Second dielectric thin film 5 Initial growth nucleus 6 Single crystal ferroelectric or high dielectric thin film 7 Polycrystalline ferroelectric or high dielectric thin film 11 Si oxidation Film substrate 13 Pt / Ti thin film 14 SiO ₂ thin film 15 PZT initial growth nucleus 16 Single crystal PZT thin film 17 Polycrystalline PZT thin film

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ identification code FI H01L 29/792 (58) Investigated field (Int.Cl. ⁷ , DB name) H01L 27/10 451 H01L 21/8242 H01L 21 / 8247 H01L 27/108 H01L 29/788

Claims (6)

(57) [Claims] The present invention relates to a method in which a surface layer of a laminated thin film on a substrate is later strongly induced.
Distribution of growth nuclei in the recesses when forming dielectric or high dielectric thin films
A concave portion is formed to expose a part of the lower layer in the concave portion so that the direction is determined by the restriction from the base and the side surface, and then a ferroelectric or high dielectric thin film is formed on the surface having the concave portion. Forming a single crystal ferroelectric or high dielectric thin film in the recess by grapho-epitaxial growth . 2. A step of forming a metal thin film on a substrate, a step of forming a dielectric thin film on the metal thin film, and forming a recess in the dielectric thin film when forming a ferroelectric or high dielectric thin film later.
Orientation of growth nuclei is limited by the base and sides
Gurafoe manner, thereby exposing a portion of the metal thin film in the recess to form a recess, and forming a ferroelectric or high-dielectric thin film on a surface having a recess, into the recess
A method for forming a dielectric thin film, comprising the step of forming a single crystal ferroelectric or high dielectric thin film by epitaxial growth . 3. The method for forming a dielectric thin film according to claim 1, wherein the step of the concave portion is 10 to 50 nm. 4. One side of the recess in the plane of the laminated thin film is 0.1 to 5
The method for forming a dielectric thin film according to claim 1, 2 or 3, wherein the thickness is μm. 5. A ferroelectric or high-dielectric thin film is formed by a chemical vapor deposition method using an organic metal.
5. The method for forming a dielectric thin film according to any one of items 4 to 4. 6. The main component of the dielectric thin film is SiO ₂ or S
The method for forming a dielectric thin film according to claim 1, wherein the dielectric thin film is i ₃ N ₄ .