JP2002100763A - Semiconductor device and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device comprising a gate insulating film formed from a single crystal epitaxial film, in which an Si substrate conforms to a lattice constant for an MOS transistor where a gate insulating film of high dielectricity is provided on the Si substrate, and to provide a method for manufacturing a semiconductor device comprising a gate insulating film having no phase transition in a high-temperature thermal process, with a thermally stable interface, few interface defects, high dielectricity, and low leakage. SOLUTION: A single crystal epitaxial film 12 of high dielectricity where an Si substrate 15 conforms with a lattice constant is used as a gate insulating film. The gate insulating film is formed by epitaxially growing, especially, an Ln2O3 rare-earth metal oxide (Ln is lanthanide element) having C-rare earth structure on (001) plane of Si. An Si single-crystal 11 may be epitaxially grown on a high-dielectric constant single-crystal epitaxial growth insulating film 12 for use as a gate electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, to a MOS transistor device using a high dielectric constant metal oxide film as a gate insulating film and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, in this type of semiconductor device having a structure in which an insulating film is sandwiched between a gate electrode and a semiconductor active layer, a metal oxide film material having a high dielectric constant is used for the gate insulating film. By avoiding a direct tunnel current and increasing the effective film thickness when converted to a silicon oxide film, the actual film thickness can be reduced, and required device characteristics can be obtained.

However, the reaction with Si is likely to occur.
Ta_TwoO_FiveAnd (Ba, Sr) TiO _ThreeEtc. for the gate insulating film
When used for Si, a low dielectric constant
A surface layer is formed, and the effective dielectric constant decreases. this
Therefore, the reaction with Si hardly occurs in ZrO_TwoAnd HfO_Two 
(Journal of Material Research Vol. 11 2
757, 1996) or more stable ammo
Rufus Zr_xSi_yO, Hf_xSi_ySilicate such as O
G (Journal of Applied Physics No. 87
Vol. 484, 2000).
ing. Furthermore, SrTiO_ThreeAnd (Ba, Sr) TiO_Three
Attempt to use epitaxially grown films (Physical Review)
View Letters, Vol. 81, page 3014, 1998
Year).

Conventionally, in a field effect transistor using a superconductor as a gate electrode, a proposal has been made to epitaxially grow an insulating film based on a perovskite structure on a Si substrate or an oxide substrate (Japanese Patent Laid-Open No. Hei 2 (1994)). -292876, JP-A-3-149882). This requires lattice matching with an oxide superconductor gate based on a perovskite structure, so that it is close to the lattice constant of both the superconducting gate and the substrate, and
A material having a perovskite structure similar to that of the oxide superconductor was selected.

[0005]

SUMMARY OF THE INVENTION However, ZrO
₂ and HfO ₂ are said to be thermodynamically stable at the interface with Si. However, since oxygen easily passes through the interface, Si is oxidized at the interface during high-temperature heat treatment in the process of manufacturing a semiconductor device, resulting in a low dielectric constant. A phase is formed. In addition, since it is polycrystalline, the interface has many defects and adversely affects device characteristics.

On the other hand, it has been proposed to use a silicate of Zr or Hf in an amorphous state. But,
The first problem is that these silicate films have a somewhat low dielectric constant. The second challenge of these silicate films is that
Because it is not stoichiometric amorphous,
Crystallization and phase separation occur at high temperatures, and it is difficult to stably produce the composition ratio. Therefore, if a single crystal high dielectric constant material can be epitaxially grown, a gate insulating film with stable interface and film composition and few interface defects can be formed. However, the proposed SrTiO ₃ and (Ba, S
r) Since the TiO ₃ epi film does not completely match the lattice constant with Si, a special film forming technique is required at the interface, and interface control is a problem. In addition, since the number of elements is large, it is difficult to control the composition.

Also, the insulating film having a perovskite structure proposed for a superconducting transistor is a ternary or quaternary system, and it is most important that the composition is difficult to control and that the matching with the superconducting gate electrode is the most important. That is the task. A silicon MOS transistor requires a single-crystal epitaxial insulating film in which compatibility with a Si crystal used for both a substrate and a gate electrode is first considered.

An object of the present invention is to provide a semiconductor device having a gate insulating film made of a single crystal epitaxial film having a lattice constant matching that of a Si substrate, and a MOS transistor having a high dielectric constant gate insulating film on a Si substrate. Is to get It is still another object of the present invention to provide a method for manufacturing a semiconductor device having a gate insulating film, which has no phase transition due to high-temperature heat treatment, has a thermally stable interface, has few interface defects, has a high dielectric constant, and has a low leak.

[0009]

According to the present invention, there is provided a semiconductor device comprising:
As a basic structure, a Ln ₂ O ₃ thin film having a C-rare earth structure (Ln is at least one of lanthanide elements, the same applies hereinafter) is used as a gate insulating film. Ln ₂ O ₃ thin film with structure
It is characterized in that a gate insulating film epitaxially grown on a (001) substrate is used, and a silicon single crystal epitaxially grown on the gate insulating film is used as a gate.

Next, a method of manufacturing a semiconductor device according to the present invention
The basic configuration is that an Ln ₂ O ₃ thin film having a C-rare-earth structure having a lattice constant that is within 5% of the lattice constant of Si (001) is equal to twice the lattice constant of Si (001), and is epitaxially grown on a Si substrate. As a typical application form, among the C-rare earth structure Ln ₂ O ₃ , an Eu ₂ O ₃ thin film having a lattice constant completely coincident with a lattice constant twice as large as that of Si (001) is used. The present invention is characterized in that epitaxial growth is performed on a substrate, and further, silicon single crystal is epitaxially grown on a gate insulating film.

By using the semiconductor device and the method of manufacturing the same according to the present invention, it is possible to form a semiconductor device having the following effects.

First, among Ln ₂ O _{3 having} a C-rare earth structure, Eu ₂ O _{3 has} a lattice constant of 1.086 nm and Si has a lattice constant of 1.086 nm.
Is completely equal to twice the lattice constant (1.086 nm). Therefore, when Eu ₂ O ₃ is deposited on Si, the distance between oxygen inserted between Si atoms at the interface matches the oxygen position of Eu ₂ O ₃ , so that a natural epitaxial film without distortion can be formed. And the interface defects can also be controlled. Since the epitaxial film thus formed is a single crystal instead of a polycrystal, a leak current via a grain boundary is also suppressed.

Further, since the lattice constant of the rare earth metal oxide continuously decreases with an increase in the atomic number of the lanthanide element, the lattice constant before and after Eu, ie, Sm ₂ O ₃ (lattice constant 1.
093 nm) and Gd ₂ O ₃ (1.081 nm) are also promising candidates.

Further, these rare earth metal oxides are metal oxide films having a high dielectric constant, and are materials which are unlikely to react with Si. Further, since the melting point of the rare earth oxide exceeds 2000 ° C., it is extremely stable.

[0015]

Next, a first embodiment of the present invention will be described in detail with reference to FIG. The first embodiment shows a basic structure of a MOS transistor element according to the present invention, and FIG. 1 is a schematic sectional view thereof.

In FIG. 1, a C-
A single crystal epitaxial film 12 of a rare earth metal oxide having a rare earth structure is formed as a gate insulating film, and a single crystal epitaxial film 11 of Si is formed thereon as a gate electrode.

In order to form such a structure, it is important that the lattice constant of the gate insulating film completely matches the lattice constant of Si. Further, as properties of such a gate insulating film, it is necessary that the gate insulating film has an insulating property and a high dielectric constant, and that a contact interface with Si is thermodynamically stable. From the viewpoint of composition control, a compound having a small number of elements (preferably a binary system) is desirable. Rare earth metal oxide L
n ₂ O ₃ has a high melting point, low reactivity with Si, and a C-rare earth structure having a lattice constant about twice as large as that of Si. There are 15 lanthanide elements from La of atomic number 57 to Lu of 71, and physical properties such as ionic radius change almost continuously with atomic number, so that process design when used as a gate insulating film is easy. is there.

Next, a specific application of the first embodiment, which is the basic structure of the present invention, will be described as a second embodiment of the present invention with reference to FIG.

The unit cell of the C-rare earth structure is a combination of eight fluorite unit cells lacking anions. Each fluorite structure (octant) has six oxygen atoms and two oxygen vacancies with metal atoms at the center of each ridge and at the center of the unit cell.

In order to lattice match with the (001) plane of Si, it is necessary not only that the lattice constant is equal to or a multiple of an integer, but also that the interval between oxygen atoms is equal to the periodic structure of Si.

FIG. 2A shows the C-rare earth structure, and FIG. 2B shows the (00) of each atomic position in the Si crystal structure.
1) It is a plane projection view. Lanthanide atom of C-rare earth structure 2
The lattice constant (a ₀ ) of 1 is about 2 times the lattice constant (a _Si ) of _Si.
The interval between oxygen atoms in the <110> direction of the C-rare earth structure matches the periodic structure of Si in the <110> direction. FIG.
On the Si surface of (b), oxygen is converted to Si atoms 23 and Si
Although it enters the interstitial position between the atoms 24, filling all the sites causes a large distortion. However, C- in FIG.
In the rare earth structure, the oxygen atoms 22 are not completely packed but have appropriate oxygen vacancies. This allows S
It is a feature of the C-rare earth structure that the strain caused by oxidizing the interface with i can be moderately reduced.

Table 1 shows a rare earth metal acid having a C-rare earth structure.
It is a list of monsters. Ce and Pm among lanthanide elements
Is excluded. The reason is that Ce is CeO_TwoIs stable and L
n_TwoO _ThreeNot have a C-rare earth structure, Pm is a radioactive element
By being elementary.

Also, La ₂ O ₃ , Pr ₂ O ₃ , Nd ₂ O ₃ , G
Since d ₂ O ₃ easily has an A-rare earth structure, it may be difficult to control the crystallinity.

The lattice constant of Eu ₂ O ₃ is completely equal to twice the lattice constant of Si. Since the adjacent Sm ₂ O ₃ and Gd ₂ O ₃ also have a lattice mismatch ratio of less than 1%, there is a high possibility that an epitaxial film having almost no distortion can be formed. Other Ln
_{Since 2} O ₃ also has a mismatch rate of 5% or less, there is a possibility of epitaxial growth.

Therefore, the second embodiment of the present invention is similar to that of FIG.
Single crystal epitaxial film 12 on Si substrate 15 shown in FIG.
Eu ₂ O ₃ , Sm ₂ O ₃ , Gd ₂
O ₃ is used. In addition, CeO ₂ , La ₂
Ln ₂ O ₃ other than O ₃ , Pr ₂ O ₃ , Nd ₂ O ₃ , and Gd ₂ O ₃ can also be used.

[0026]

[Table 1]

Next, a specific application of the first embodiment, which is the basic structure of the present invention, will be described as a third embodiment of the present invention with reference to FIG.

In the third embodiment, as shown in FIG. 3A, a single crystal film 32 which is one of the features of the present invention is used as an insulating film.

FIG. 3B shows a conventional example of the structure of a polycrystalline gate insulating film 33 using polycrystal as an insulating film. A grain boundary 36 exists between crystal grains 34. I do. There are electronic states at the grain boundaries that do not contribute to bonding,
This acts as a trap and generates a leak current.

On the other hand, since there is no grain boundary in the single crystal film 32 of the present embodiment, the bonding state between atoms is perfect, and no trap that causes leakage exists in the film.

Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 4A is a schematic sectional view showing the fourth embodiment, in which the epitaxial film 42, which is one of the features of the present invention, is used as an insulating film.

It is known that interface defects formed at the interface between the gate insulating film and Si have a significant effect on device characteristics.

FIG. 4B is a schematic cross-sectional view showing a conventional example. When a crystal film 43 that does not lattice match with the Si substrate 45 is used, an electronic state that does not contribute to bonding exists at the interface 44. This serves as a trap, resulting in dielectric breakdown and a decrease in long-term reliability. In addition, this may cause the mobility of carriers in the channel region of the substrate 45 to decrease.

On the other hand, in the epitaxial film 42 of this embodiment, the bonding state of the interface 46 is perfect, and there is no interface defect as in the conventional example.

Next, as a fifth embodiment of the present invention, a case will be described in which a stoichiometric binary compound crystal is used as an insulating film.

In controlling the composition of the epitaxial film at the time of film formation and in controlling the stability of the composition of the epitaxial film in the post-heat treatment step, the number of elements is smaller than in the case where a ternary or higher element is used. This is particularly advantageous.

When silicate or the like deviated from stoichiometry is used, the composition may be fluctuated in the post heat treatment step at a high temperature. On the other hand, if the composition of the epitaxial film material is stoichiometry, Is thermodynamically stable.

Further, when amorphous is used as an insulating film as in the conventional case, although the uniformity is superior to that of polycrystal, crystallization occurs in a post-heat treatment step at a high temperature, and a sharp change in characteristics occurs. Can happen. On the other hand, in the present embodiment, such a phase transition does not occur.

Next, as a sixth embodiment of the present invention, S
FIG. 5 is a schematic cross-sectional view of an i-substrate in which the single-crystal epitaxial films described in Embodiments 2 to 5 are formed as a gate insulating film, and a Si single-crystal epitaxial film is further formed thereon as a gate. It will be described with reference to FIG.

FIG. 5A shows that a Si substrate 55 is
FIG. 5 is a diagram in which an insulating film 52 of the present embodiment is lattice-matched with the above, and a silicon single crystal gate 51 is further formed thereon.

FIG. 5B shows a conventional example.
Crystal or amorphous insulating film 53 not lattice-matched with i-crystal
Is used, monocrystalline Si cannot be epitaxially grown thereon, and the polycrystalline Si gate 59 is formed. In this case, the interface 5 between the gate 59 and the gate insulating film 53
7 has an electronic state that does not contribute to the bonding, which serves as a trap, which results in dielectric breakdown and a decrease in long-term reliability. It is obvious that a similar trap exists also at the interface 54 between the gate insulating film 53 and the Si substrate 55.

On the other hand, in the structure of this embodiment,
Since the single crystal epi film 52 lattice-matched to the substrate 55 is used, it is easy to epitaxially grow the Si single crystal 51 lattice-matched thereon. The bonding state of the interface 58 between the insulating film 52 and the gate 51 is perfect, and there is no interface defect as in the conventional example. It is obvious that the bonding state is also complete at the interface 56 between the insulating film 52 and the Si substrate 55 and that there is no interface defect as in the conventional example.

[0043]

According to the semiconductor device and the method of manufacturing the same of the present invention, since a single-crystal epitaxial film of a rare earth metal oxide having a lattice constant matching that of a Si substrate is used as a gate insulating film, there is no phase transition due to high-temperature heat treatment. In addition, it is possible to manufacture a semiconductor device having a gate insulating film, which has a thermally stable interface, few interface defects, high dielectric constant, and low leakage.

The first reason is that, since a single crystal is used, there is no in-film defect such as a grain boundary. Second, Si
This is because there is no interface defect that affects the active layer of the device because the epitaxial film lattice-matched to the substrate is used. Third, since a stoichiometric binary compound is used, the film quality is stable and composition control is easy.
Further, it becomes possible to form an epitaxial film of Si single crystal also for the gate electrode, and it is possible to realize the manufacture of a high-performance MOS transistor element.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a first embodiment of the present invention.

FIG. 2 is a crystal structure diagram for explaining a second embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view for explaining a third embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view for explaining a fourth embodiment of the present invention.

FIG. 5 is a schematic sectional view for explaining a sixth embodiment of the present invention.

[Explanation of symbols]

11,51 Single-crystal Si gate 12,32,42,52 Ln ₂ O ₃ gate insulating film grown by single-crystal epitaxial 13,14 Source and drain electrodes 15,35,45,55 Si substrate 21 Lanthanide (Ln) atom 22 Oxygen atom 23, 24, 25 Si atoms 31, 41 Gate 33 Polycrystalline gate insulating film 34 Crystal grain 36 Grain boundary 43, 53 Gate insulating film 44, 46, 54, 56 Interface between insulating film and Si substrate 57, 58 Interface with gate 59 Polycrystalline Si gate

Claims (6)

[Claims] 1. An Ln ₂ O ₃ thin film having a C-rare earth structure (Ln
Wherein at least one of lanthanide elements is used as a gate insulating film. 2. An Ln ₂ O ₃ thin film having a C-rare earth structure is
(001) A semiconductor device using a gate insulating film epitaxially grown on a substrate. 3. An Ln ₂ O ₃ thin film having a C-rare earth structure is epitaxially grown on a Si (001) substrate, this is used as a gate insulating film, and a silicon single crystal epitaxially grown thereon is used as a gate. Characteristic semiconductor device. 4. An Ln ₂ O ₃ thin film having a C-rare earth structure having a lattice constant that is equal to or less than 5% of a lattice constant of Si (001) within 5% is epitaxially grown on a Si substrate. Manufacturing method of a semiconductor device. 5. Among Ln ₂ O _{3 having} a C-rare earth structure,
A method of manufacturing a semiconductor device, comprising: epitaxially growing an Eu ₂ O ₃ thin film having a lattice constant completely equal to twice the lattice constant of i (001) on a Si substrate. 6. The method of manufacturing a semiconductor device according to claim 4, wherein a Ln ₂ O ₃ thin film having a C-rare earth structure is used as a gate insulating film, and a silicon single crystal is epitaxially grown thereon. Method.