JP2001244482A - Semiconductor element and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily obtain satisfactory interface in SrTiO3 whose concentration of a carrier is comparatively high and which is made into semiconductor, and to realize a semiconductor element superior in Schottky connection and interface control by an oxide semiconductor. SOLUTION: An oxide semiconductor is annealed in oxygen at 1000 deg.C and it is cleaned by using acid in a nitrogen atmosphere. Thus, a substance causing an interface level is removed and an electrically clean surface is obtained.

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 semiconductor device such as a Schottky diode, a ferroelectric device, a MOS semiconductor device and the like which are used as a switching device, a memory device, and the like. It relates to a manufacturing method.

[0002]

2. Description of the Related Art In the manufacture of an oxide semiconductor device, if impurities adhere to an interface or the surface is disordered,
An interface state occurs, destabilizing the electronic state of the interface and deteriorating the performance of the semiconductor. Conventionally, the following method has been proposed as a method for removing such impurities at the interface and planarizing the interface to control the electronic state of the interface, for example, the interface electronic state of SrTiO ₃ which is one kind of oxide semiconductor. I have.

That is, the surface of SrTiO ₃ , which is a kind of oxide semiconductor, is etched with an acid such as hydrofluoric acid, and then annealed at about 1000 ° C. in oxygen to flatten the crystal surface. Thereafter, the surface of SrTiO ₃ is subjected to ozone treatment in a high vacuum. According to this method, for example, in the production of a Schottky diode, good Schottky connection between an oxide semiconductor and gold is proved from its current-voltage characteristics.

In the manufacture of a ferroelectric capacitor used as a semiconductor nonvolatile memory device, it is not possible to deposit a ferroelectric substance on a lower electrode, clean the surface of the ferroelectric substance and remove impurities, and then manufacture the ferroelectric substance. I haven't done anything.

[0005]

However, regarding the manufacture of an oxide semiconductor device, the above-mentioned conventional method has the following problems.
The effect has been confirmed only for SrTiO ₃ having a low donor impurity concentration, and is not always a simple method such as requiring an ozone generator. Further, it is not suitable for mass processing of a large-area oxide semiconductor substrate.

An object of the present invention is to solve the above-mentioned conventional problems in an oxide semiconductor device and realize an oxide semiconductor having a good interface with a small interface level without performing ozone treatment or the like. It is an object to realize a method for mass-producing such an oxide semiconductor. And, even in an oxide semiconductor such as SrTiO ₃ having a relatively high carrier density,
It is an object of the present invention to easily realize an electronic element that easily controls an interface such as a Schottky connection with a small reverse current.

[0007] Regarding the manufacture of ferroelectric capacitors, if impurities are attached to the interface of the ferroelectric or the surface is disturbed, the ferroelectric is in the same manner as in the case of the oxide semiconductor. In addition, an interface state is generated, which makes the electronic state of the interface unstable and causes deterioration of characteristics of the ferroelectric capacitor.

Therefore, an object of the present invention is to solve the above-mentioned conventional problems in a ferroelectric capacitor,
As with the oxide semiconductor, a ferroelectric capacitor is intended to realize a ferroelectric having a good interface with a small number of interface states and to prevent deterioration of the capacitor characteristics.

[0009]

According to the present invention, there is provided a semiconductor device using an oxide semiconductor, wherein the oxide semiconductor is annealed at 1000 ° C. in oxygen. Thereafter, by performing a cleaning treatment using an acid in a gas atmosphere containing no inert gas or carbide, a substance causing an interface state is removed, and an electrically clean surface is obtained. A semiconductor device is provided.

The present invention is directed to a semiconductor device having a ferroelectric capacitor, wherein the ferroelectric capacitor comprises a lower electrode, a ferroelectric formed on the lower electrode, and a semiconductor device. Consisting of an upper electrode formed on a ferroelectric substance, the ferroelectric substance causes an interface state by being etched using an acid in an inert gas or a gas atmosphere containing no carbide. Provided is a semiconductor element characterized in that a causative substance has been removed and an electrically clean surface has been obtained.

As a semiconductor device having the above ferroelectric capacitor, there is a nonvolatile memory device using the above ferroelectric capacitor.

In order to solve the above-mentioned problems, the present invention provides a step of annealing an oxide semiconductor at 1000 ° C. in oxygen, and a step of removing the annealed oxide semiconductor from an inert gas or carbide. Performing a cleaning process using an acid in a gas atmosphere to remove a substance causing an interface state and obtain an electrically clean surface. Provide a way.

According to the present invention, there is provided a method of manufacturing a semiconductor device having a ferroelectric capacitor, wherein the ferroelectric capacitor comprises first forming a ferroelectric substance on a lower electrode by vapor deposition. And then the surface of the ferroelectric,
In an atmosphere of an inert gas or a carbide-free gas, an etching treatment is performed using an acid to remove a causative substance that causes an interface state, and to provide an electrically clean surface. A method of manufacturing a semiconductor device, wherein the method includes manufacturing an upper electrode by vapor deposition.

The inert gas or carbide-free gas atmosphere employed in the semiconductor device and the method of manufacturing the same according to the present invention is a nitrogen gas atmosphere.

In the semiconductor device and the method of manufacturing the same according to the present invention, for example, a first metal is deposited on one surface of the electrically cleaned oxide semiconductor to form a Schottky-connected first metal electrode. There is a semiconductor device in which a second metal is deposited on the other surface opposite to the one surface to form an ohmic-connected second metal electrode, and a method of manufacturing the same.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a semiconductor device and a method for manufacturing the same according to the present invention will be described with reference to the accompanying drawings. First Embodiment As a first embodiment of the present invention, a Schottky diode and a method of manufacturing the same will be described below.

A Schottky diode as an embodiment of the semiconductor device according to the present invention is manufactured as follows. First, La carbonate is used as a dopant in the raw material of SrTiO ₃
A single crystal is grown by a pulling method (CZ method, Czochralski method) or the like in addition to 3.75 wt%. And
The prepared single crystal is cut out into a plate having a thickness of 1 mm from the (100) plane, and the surface is polished to a mirror surface. As a result, SrTiO ₃ (SrTiO ₃ substrate) turned into a semiconductor is formed.

The semiconductor formed as described above
SrTiO ₃ is treated as follows by the process which is the most characteristic feature of the present invention and is shown in FIG. That is, the SrTiO ₃ made into a semiconductor is annealed at about 1000 ° C. in oxygen (a step of performing an annealing process). The annealing time is preferably one hour, but may be shorter or longer as long as the surface flatness is ensured. Also, the annealing temperature is preferably about 1000 ° C., but may be lower.
For example, about 900 ° C may be used.

Next, a cleaning treatment (nitric acid treatment) is performed by dipping in nitric acid at room temperature in a nitrogen atmosphere (cleaning step). The time of the cleaning process is, for example, about 5 minutes. As the cleaning liquid, may be an acid other than nitric acid, it may be used a mixture of H ₂ 0 _2. After the cleaning treatment with nitric acid, ultrasonic cleaning is performed with pure water for about 1 minute. This results in a TiO surface.

Here, when producing a Schottky connection, the semiconductor-converted SrTiO ₃ washed by the above-described cleaning method is used.
A first metal is vapor-deposited on one surface of the substrate by a method described below so as not to be exposed to the air as much as possible to form a first metal electrode (Schottky electrode). In this embodiment, Au (gold) is used as the first metal, which is deposited by about 3000 ° using an electron beam evaporation apparatus. As the first metal, other A
There are metals such as g, Ni, Cu, Pt, Ge, and W.

As a specific operation, semiconductor-converted SrTi
After performing the above-described cleaning in a glow box in a nitrogen atmosphere, O ₃ is transported into an electron beam evaporation apparatus, for example, in a sealed container, and is taken out there, and the semiconductor-converted SrTiO ₃ is removed.
A first metal is vapor-deposited on one surface of the first electrode by electron beam to form a first metal electrode of Schottky connection. This allows
The first metal electrode can be deposited while preventing exposure to the air as much as possible, while preventing adhesion of dust and the like.

Further, a second metal is deposited on the other surface of the semiconductor-converted SrTiO ₃ opposite to the one surface to form an ohmic-connected second metal electrode (ohmic electrode). In this embodiment, Al (aluminum) is deposited as the second metal. As the second metal, other A
There are metals such as l, Mg, Na and Nb.

As a result, as shown in FIG. 2, the semiconductor device according to the present embodiment has a first Schottky connection in which Au is vapor-deposited on one surface of the semiconductor device so as to sandwich SrTiO ₃ 1 made into a semiconductor. A Schottky diode 4 is obtained in which the metal electrode 2 and the second metal electrode 3 of ohmic connection in which Al is deposited on the other surface are formed. The Schottky diode 4 has characteristics shown in FIG. 3 described later, and exhibits a switching function.

The diode characteristics of the Schottky diode 4 according to the present embodiment manufactured by the above steps will be described. FIG. 3 shows the Schottky diode 4 shown in FIG.
FIG. 4 is a characteristic diagram showing a hysteresis curve obtained by applying a bias voltage between the first metal electrode 2 and the ohmic-connected second metal electrode 3 and measuring a change in current of the Schottky diode 4. The vertical axis in FIG. 3 indicates the absolute value of the current (the same applies to FIGS. 4 and 5 described later).

Referring to FIG. 3, in the Schottky diode 4 according to the present invention, the impurities and / or the SrO layer (surface) (the impurities and / or the SrO layer (surface)) adhered to the interface by performing the cleaning treatment with nitric acid. Is referred to as “causing substance” in the present specification), so that a good interface can be obtained by removing or reducing the interface state. As a result, when a voltage is applied between the first metal electrode 2 and the second metal electrode 3 of the Schottky diode 4 in the positive direction and the voltage is reduced, the linearity is excellent in the vicinity of 0.5 to 1.5 V, and an extremely stable shot is obtained. Key operation becomes possible. Note that when the voltage is about 0.5 V or less, the value is lower than the measurement limit due to the convenience of the measuring device, and the constant portion is a value observed as noise of the measuring device.

On the other hand, FIG. 4 shows an example in which SrTiO _3, which has been converted into a semiconductor by injecting La3.73%, is annealed at 1000 ° C., but is not cleaned with nitric acid. FIG. 4 is a characteristic diagram showing a hysteresis curve when a voltage is applied to a semiconductor element formed with a first metal electrode 2 and a second metal electrode as in FIG.

According to FIG. 4, when the bias voltage is gradually increased from 0 V in the positive direction and further decreased, the increase or decrease of the current is inferior in linearity. Also, when the bias voltage is changed in the negative direction, a large leak current is generated in the Schottky diode where almost no current should flow. In short, the semiconductor device according to FIG. 4 has unstable characteristics as a Schottky diode. this is,
This is probably because the surface of the semiconductor is not sufficiently cleaned, so that impurities adhere to the interface and an interface state exists.

Further, FIG. 5 shows that SrTiO ₃ , which was made into a semiconductor by injecting La3.73%, was subjected to the above-described cleaning treatment with nitric acid but not subjected to annealing treatment.
FIG. 4 is a characteristic diagram showing a hysteresis curve when a voltage is applied to a semiconductor element formed with a first metal electrode and a second metal electrode as in FIG. 3.

The hysteresis curve of FIG. 5 is similar to that of FIG. 4, and the semiconductor element has unstable characteristics as a Schottky diode. This indicates that unless the surface is flattened by annealing at 1000 ° C., stable characteristics cannot be obtained even with a subsequent cleaning treatment with an acid. In short, it is shown that a desired effect as a Schottky diode, in which a stable hysteresis as shown in FIG. 3 can be obtained only after an annealing process and a subsequent cleaning process with an acid as in the present invention, can be obtained. Is what it is.

Next, as a second embodiment of the present invention, a semiconductor nonvolatile memory device will be described with reference to FIGS. As shown in FIG. 6, the semiconductor nonvolatile memory element
It is generally known that a capacitance portion of a RAM is replaced with a ferroelectric capacitor. The ferroelectric capacitor 5 includes a ferroelectric and upper and lower electrodes sandwiching the ferroelectric as described later.

The invention according to the second embodiment has the following features of the ferroelectric capacitor 5. As shown in FIG. 7, the ferroelectric capacitor 5 has a lower electrode 7 made of a mixture of SrTiO ₃ and La (La weight 3.73 wt% based on the total weight), and Bi ₄ Ti ₃ formed on the lower electrode 7. It comprises a ferroelectric 8 made of O ₁₂ and an upper electrode 9 made of Al formed on the ferroelectric 8. The material of the lower electrode 7 may be Pt, IrO ₂ or the like. The material of the ferroelectric 8 may be SrBi ₂ Ta ₂ O ₉ or Pb (ZrTi) O ₃ .

The manufacturing process of the ferroelectric capacitor 5 is as follows. First, a ferroelectric material 8 is formed on the lower electrode 7 by vapor deposition. Next, the surface (upper surface) of the ferroelectric material 8 is etched using nitric acid in an atmosphere of an inert gas such as a nitrogen gas or a gas atmosphere containing no carbide to remove a causative substance that causes an interface state. Remove, leaving an electrically clean surface. Next, an upper electrode 9 is formed on the ferroelectric 8 by vapor deposition. For the etching treatment, an acid other than nitric acid may be used as long as the acid has a strong oxidizing property.

The characteristics of the ferroelectric capacitor 5 according to the second embodiment manufactured by the above steps will be described. FIG. 8 is a characteristic diagram (bias voltage-capacitance) obtained by applying a bias voltage between the upper electrode 9 and the lower electrode 7 of the ferroelectric capacitor 5 shown in FIG. 7 and measuring the capacitance. . FIG. 9 is a characteristic diagram of the ferroelectric capacitor 5 which has the same structure as the ferroelectric capacitor 5 shown in FIG. 7, but does not perform any processing on the surface of the ferroelectric 8 as in the present invention.

In a conventional ferroelectric capacitor 5 in which no treatment is performed on the surface of the ferroelectric 8, as shown in FIG.
The history appears and indicates uncontrollable characteristics. This is because
It is considered that not the hysteresis characteristic of the ferroelectric itself, but the impurity adhering to the interface of the ferroelectric and the presence of an interface state, the charge is accumulated and a leak current occurs, and as a result, the capacitance characteristic is not stabilized. .

However, in the ferroelectric capacitor 5 according to the second embodiment of the present invention, as shown in FIG. 8, the removal of hysteresis was realized, and a capacitance characteristic with good controllability was obtained. That is, the surface (upper surface) of the ferroelectric 8
Is etched with a strong acidic acid, etc. to remove the substances that cause the interface order, thereby reducing the charge accumulation caused by the interface order and reducing the current leakage. Possible electric characteristics can be obtained, and a uniform dielectric thin film can be obtained in a wide range.

Although the embodiments of the present invention have been described based on the embodiments, the semiconductor device and the method of manufacturing the same according to the present invention are not limited to the switching of the Schottky diode or the ferroelectric device as in the above embodiments. The present invention is not only used as an element or a memory element, but also applied to a semiconductor element such as a MOS semiconductor element.

[0037]

According to the semiconductor device and the method of manufacturing the same according to the present invention having the above-described structure, an oxide semiconductor having a low interface state can be obtained without using an ozone generator or the like which has been conventionally required. An interface can be easily obtained.

In particular, a favorable interface can be easily obtained even in an oxide semiconductor having a relatively high carrier concentration. This makes it possible to easily and mass-produce a semiconductor element having excellent characteristics in interface control, such as a Schottky diode that can extremely reduce a reverse current, by using an oxide semiconductor.

Further, according to the present invention, the ferroelectric capacitor is also subjected to an etching treatment with an acid or the like to remove a substance which causes an interface order, by using a ferroelectric capacitor.
The accumulation of electric charge due to the interface order is reduced to reduce the current leakage. As a result, controllable electric characteristics can be obtained, and a uniform dielectric thin film can be obtained in a wide range.

[Brief description of the drawings]

FIG. 1 is a view for explaining Example 1 according to the present invention, and is a flow chart of a surface treatment step of SrTiO ₃ made into a semiconductor.

FIG. 2 is a view showing a Schottky diode which is an embodiment of the semiconductor device and the manufacturing method according to the present invention.

FIG. 3 is a diagram showing voltage-current characteristics of the Schottky diode according to the present invention shown in FIG.

FIG. 4 is a diagram showing characteristics of an Au / SrTiO ₃ Schottky diode prepared using a SrTiO ₃ substrate before nitric acid treatment (not subjected to nitric acid treatment).

FIG. 5: SrTi treated with nitric acid but not annealed
FIG. ₃ is a view showing characteristics of an Au / SrTiO ₃ Schottky diode formed using an O ₃ substrate.

FIG. 6 is a diagram illustrating a second embodiment of the present invention, and is a diagram illustrating a semiconductor nonvolatile memory element having a ferroelectric capacitor.

FIG. 7 is a diagram illustrating a ferroelectric capacitor according to a second embodiment of the present invention.

FIG. 8 is a diagram showing voltage-current characteristics of the ferroelectric capacitor according to the second embodiment of the present invention.

FIG. 9 is a diagram showing voltage-current characteristics of a ferroelectric capacitor which is not etched with nitric acid.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 semiconductor-converted SrTiO ₃ (SrTiO ₃ substrate) 2 first metal electrode (Schottky electrode) 3 second metal electrode (ohmic electrode) 4 Schottky diode 5 ferroelectric capacitor 6 diode 7 lower electrode 8 ferroelectric Body 9 Upper electrode

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H01L 21/8242 H01L 27/10 651 29/48 F F-term (Reference) 4M104 AA10 BB02 BB04 BB05 BB06 BB08 BB09 BB18 BB36 CC01 CC03 DD22 DD26 GG03 HH17 HH20 5F043 AA40 BB30 DD02 DD10 GG10 5F083 AD21 GA06 JA14 JA15 JA17 JA36 JA38 JA43 PR05

Claims (9)

[Claims] 1. A semiconductor element using an oxide semiconductor, wherein the oxide semiconductor is subjected to an annealing treatment in oxygen at 1000 ° C., and thereafter, in an inert gas or a gas atmosphere containing no carbide. A semiconductor element having an electrically clean surface by removing a causative substance causing an interface state by performing a cleaning treatment using an acid. 2. A first metal is deposited on one surface of the electrically cleaned oxide semiconductor to form a first metal electrode of Schottky connection, and a first metal electrode is formed on another surface opposite to the one surface. 2. The semiconductor device according to claim 1, wherein a second metal electrode is formed by vapor-depositing the second metal, and a second metal electrode in ohmic connection is formed. 3. A semiconductor device having a ferroelectric capacitor, wherein the ferroelectric capacitor includes a lower electrode, a ferroelectric formed on the lower electrode, and an upper electrode formed on the ferroelectric. The ferroelectric substance is subjected to an etching treatment using an acid in a gas atmosphere containing no inert gas or carbide, thereby removing a causative substance causing an interface state,
A semiconductor element having an electrically clean surface. 4. The semiconductor device according to claim 3, wherein the semiconductor device is a nonvolatile memory device configured by connecting the ferroelectric capacitor and a pn junction diode in series. 5. The semiconductor device according to claim 1, wherein the gas atmosphere containing no inert gas or carbide is a nitrogen gas atmosphere. 6. A step of annealing an oxide semiconductor in oxygen at 1000 ° C., and a step of cleaning the annealed oxide semiconductor using an acid in an inert gas or carbide-free gas atmosphere. Performing a cleaning step of removing a causative substance causing an interface state to obtain an electrically clean surface. 7. A first metal electrode is formed by depositing a first metal on one surface of the electrically cleaned oxide semiconductor to form a Schottky-connected first metal electrode, and a first metal electrode is formed on the other surface opposite to the one surface. 7. The method for manufacturing a semiconductor device according to claim 6, wherein a second metal electrode of ohmic connection is formed by depositing a second metal. 8. A method of manufacturing a semiconductor device having a ferroelectric capacitor, comprising: forming a ferroelectric substance on a lower electrode by vapor deposition; , An etching treatment using an acid in an atmosphere of an inert gas or a carbide-free gas to remove a causative substance causing an interface state, and to obtain an electrically clean surface. A method for manufacturing a semiconductor device, comprising: manufacturing an upper electrode by vapor deposition. 9. The method for manufacturing a semiconductor device according to claim 6, wherein the gas atmosphere containing no inert gas or carbide is a nitrogen gas atmosphere.