JP5491258B2 - Method for forming oxide semiconductor - Google Patents

Description

  The present invention relates to a method for forming an oxide semiconductor.

Field effect transistors are widely used as unit electronic elements, high frequency signal amplifying elements, liquid crystal driving elements and the like of semiconductor memory integrated circuits, and are the most widely used electronic devices at present.
With the remarkable development of display devices in recent years, not only a liquid crystal display device (LCD) but also various display devices such as an electroluminescence display device (EL) and a field emission display (FED) have a driving voltage applied to the display element. Thin film transistors (TFTs) are frequently used as switching elements for applying a voltage to drive a display device.

A transparent semiconductor thin film made of a metal oxide, in particular, a transparent semiconductor thin film made of a zinc oxide crystal has attracted attention as being more stable than a silicon-based semiconductor thin film.
For example, Patent Document 1 and Patent Document 2 disclose a method of forming a thin film transistor by crystallizing zinc oxide at a high temperature. In Patent Document 3, an attempt is made to use a positive divalent element as a dopant in order to positively control the carrier density to a low concentration, and an example in which the obtained semiconductor film is applied to a thin film transistor is reported. (Patent Document 4). Furthermore, an example has been reported in which, in the step of obtaining a thin film transistor, crystallization is performed after patterning an amorphous oxide film to realize high mobility (Patent Document 5).

A technique (Patent Document 6) for obtaining a high mobility oxide semiconductor by setting the water pressure in the system to 10 ⁻³ Pa or less is disclosed.

However, the zinc oxide semiconductor used in Patent Documents 1 and 2 has a drawback of poor chemical stability.
In addition, the oxide semiconductors in Patent Documents 3 and 4 are oxide semiconductors containing indium oxide as a main component, and are excellent in chemical stability. However, the variation in carrier concentration is large, and a highly reliable transistor can be obtained. It was difficult.

In Patent Document 5, a highly reliable transistor is obtained by performing patterning in an amorphous state and performing crystallization. And in order to obtain an amorphous oxide film, there have been reports of introducing water and hydrogen. However, in Patent Document 5, since the sputtering pressure is not determined, the partial pressure of water or hydrogen is not uniquely determined, and it is difficult to obtain an oxide film having a stable amorphous structure.
Patent Document 6 refers to moisture pressure in order to obtain a high mobility crystalline oxide transistor, but this is the case of RF sputtering, in the case of DC sputtering, or AC sputtering with a frequency of 10 MHz or less. Were not necessarily suitable conditions.

JP 2003-86808 A JP 2004-273614 A JP 7-235219 A WO2007 / 058248 WO2008 / 096768 JP 2008-311342 A

  An object of the present invention is to provide a method for manufacturing an oxide semiconductor with significantly improved transistor characteristics.

  As a result of intensive studies, the inventors have found that transistor characteristics of an oxide semiconductor used by crystallization can be significantly improved by appropriately controlling moisture during DC sputtering.

According to the present invention, the following oxide semiconductor manufacturing method is provided.
1. An oxide semiconductor film forming method in which a film formation body is formed by DC sputtering of a sputtering target at a water pressure of 3 × 10 ^{−4 to} 5 × 10 ⁻² Pa in the system, and the film formation body is crystallized.
2. Formation of a film-forming body by high-frequency sputtering with a water pressure of 3 × 10 ^{−4 to} 5 × 10 ⁻² Pa in the system and a frequency of 10 MHz or less of the sputtering target, and formation of an oxide semiconductor that crystallizes the film-forming body. Membrane method.
3. 3. The oxide semiconductor film forming method according to 1 or 2, wherein the crystallization is performed by annealing.
4). The oxide semiconductor is made of In ₂ O ₃ or an oxide of one or more additional elements having a positive trivalent or lower valence other than In ₂ O ₃ and indium, 4. The oxide semiconductor film forming method according to any one of 1 to 3, wherein the atomic ratio (total added elements) / (In + total added elements) is 0.0001 or more and 0.2 or less.
5. 5. The additive element having a valence of 3 or less is one or more selected from Mg, Al, Ca, Fe, Co, Ni, Cu, Zn, Ga, Sr, Ba and rare earth elements. A method for forming an oxide semiconductor.

  According to the present invention, a method for manufacturing an oxide semiconductor with greatly improved transistor characteristics can be provided.

It is a schematic sectional drawing which concerns on one Embodiment of the thin-film transistor provided with the oxide semiconductor of this invention. It is a schematic sectional drawing which concerns on other embodiment of the thin-film transistor provided with the oxide semiconductor of this invention. It is a figure which shows the relationship between the gate voltage and drain current of a thin-film transistor. It is a figure which shows the relationship between the water pressure at the time of sputtering, and the S value of a thin-film transistor.

In the oxide semiconductor film formation method of the present invention, a film formation body is formed by DC sputtering of a sputtering target at a moisture pressure in the system of 3 × 10 ^{−4 to} 5 × 10 ⁻² Pa. Is crystallized to form an oxide semiconductor.
Further, in the oxide semiconductor film forming method of the present invention, the film formation body is formed by high-frequency sputtering with a water pressure of 3 × 10 ^{−4 to} 5 × 10 ⁻² Pa in the system and a sputtering target having a frequency of 10 MHz or less. Then, the film-forming body is crystallized.

In the film forming method of the present invention, the water pressure in the system during sputtering is set to 3 × 10 ^{−4 to} 5 × 10 ⁻² Pa, preferably 1 × 10 ⁻³ to 1 × 10 ⁻² Pa. By setting the water pressure in the system within this range, the carrier concentration can be effectively reduced in the crystallization treatment.
When the water pressure in the system is less than 3 × 10 ⁻⁴ Pa, since the amount of water taken into the thin film is small, the subsequent crystallization process is hindered by having a structure immediately after film formation, and the carrier is efficiently Concentration may not be reduced. On the other hand, in the case of more than 5 × 10 ⁻² Pa, the mobility is likely to be small because the denseness and adhesion are poor.

Sputtering is performed by DC sputtering with low plasma activity or high-frequency sputtering with a frequency of 10 MHz or less. Sputtering may be pulse sputtering.
DC sputtering, AC sputtering with a frequency of 1 MHz or less, and pulse sputtering can suppress damage to the film formation body because the plasma in the system is difficult to spread. In addition, DC sputtering is preferable from the viewpoint of industrialization because it can form a film over a large area and has a high film formation speed.
In the case of DC sputtering, crystallization is likely to proceed before the crystallization step, but in the present invention, it is possible to obtain a complete amorphous film by positively introducing water.

  In the film forming method of the present invention, RF sputtering can be applied. However, since RF is a film forming method with high activity by nature, it is not necessary to introduce water into the system, or by introducing electrons, Since it becomes extremely small, there is a possibility that the obtained transistor does not drive the FET. In particular, in the case of AC sputtering or RF sputtering with a frequency exceeding 1 MHz, the plasma in the system tends to spread, so that the thin film is likely to be damaged, and an oxide semiconductor with high mobility may not be obtained. In addition, since the film formation rate decreases as the frequency increases, it is preferable in production to introduce water and form a film at a frequency of 10 MHz or less.

The ultimate pressure at the time of sputtering is usually 3 × 10 ⁻⁴ Pa or less, preferably 1 × 10 ⁻⁴ Pa or less.
When the ultimate pressure is more than 3 × 10 ⁻⁴ Pa, the adhesion between the substrate for film formation and the oxide thin film may be deteriorated due to the influence of an impurity element containing carbon other than H ₂ O in the atmospheric gas.

The sputtering pressure at the time of sputtering is not particularly limited as long as the plasma can be stably discharged, but is preferably 0.1 to 5.0 Pa.
The ultimate pressure refers to the degree of vacuum before introducing argon, oxygen, water, or the like, and the sputtering pressure refers to the pressure at the start of sputtering after introducing argon, oxygen, water, or the like.

The oxygen partial pressure in the atmosphere gas of sputtering is usually 40 × 10 ⁻³ Pa or less, preferably 15 × 10 ⁻³ Pa or less, more preferably 7 × 10 ⁻³ Pa or less, and particularly preferably 1 × 10 ⁻³ Pa. Pa or less.
When the oxygen partial pressure in the atmospheric gas is more than 40 × 10 ⁻³ Pa, the mobility of the obtained semiconductor may be lowered or the carrier concentration may become unstable. This is because too much oxygen in the atmosphere gas during film formation causes more oxygen to be taken in between the crystal lattices, which can cause scattering or easily desorb and destabilize oxygen from the film. Presumed.

As the substrate on which the film-formed body is formed, inorganic materials such as alkali glass, non-alkali glass, and quartz glass; plastic sheets such as polycarbonate, polyarylate, polyethersulfone, and polyethernitrile, and films can be used.
Moreover, if it is a substrate of a bottom gate transistor, inorganic substances such as SiO ₂ , SiNx, SiNxOy, Al ₂ O ₃ , Ta ₂ O ₃ , and HfO ₂ ; organic substances such as polyethylene terephthalate, polyvinyl phenol, PMA, and fluorine-based polymer Can be used.

The distance between the substrate and the target during sputtering (ST distance) is usually 150 mm or less, preferably 110 mm, and particularly preferably 80 mm or less. If the ST distance is greater than 150 mm, the film formation rate may be slow, making it unsuitable for industrialization.
The film formation speed can be increased by shortening the ST distance, which is suitable for industrialization. However, if it is too close, the film formation body may be damaged by plasma.

In the present invention, since the film-forming body is formed and then crystallized by post-treatment, the temperature of the substrate on which the film is formed is usually room temperature to 200 ° C., preferably room temperature to 100 ° C.
When the substrate temperature is higher than 200 ° C., a microcrystalline layer is formed immediately after film formation (as-depo), which may hinder crystallization in post-processing.
In the case of forming a large area, it is preferable to take a method such as rotating the folder to which the substrate is fixed or moving the magnet to widen the erosion range in order to have a uniform film quality.

  The target to be used is preferably a sintered target containing indium, one or more elements selected from elements having a valence of less than positive trivalence, and oxygen, or a sintered target made of indium oxide. Alternatively, co-sputtering may be performed using a sintering target containing indium oxide and one or more elements selected from elements having a positive valence of 3 or less and a sintering target containing oxygen.

The sintered target is preferably a target sintered in a reducing atmosphere.
The bulk resistance of the sintered target is preferably 0.001 to 1000 mΩcm, and more preferably 0.01 to 100 mΩcm. When the sintered target contains an element having a positive trivalent or less, the doped element having a positive trivalent or lower can be added in the form of an oxide or a metal powder when the sintered target is manufactured.
The sintered density of the sintered target is usually 70% or more, preferably 85% or more, more preferably 95% or more, and particularly preferably 99% or more.

An oxide semiconductor is manufactured by crystallizing the film-formed body obtained by the above-described sputtering. The carrier concentration of the oxide semiconductor obtained by crystallization treatment can be controlled.
Examples of the crystallization method include heat treatment using a lamp annealing apparatus (LA), a rapid thermal annealing apparatus (RTA), a gold image furnace, or the like. Crystallization is possible with an excimer laser or a YAG laser using a wavelength that can be absorbed by the oxide semiconductor, but annealing is preferred.

When crystallization is performed by annealing, the annealing temperature can be appropriately selected within a range in which the substrate is not deformed or damaged, but is preferably 150 ° C. or higher and 500 ° C. or lower, more preferably 200 ° C. or higher and 400 ° C. or lower.
If the annealing temperature is less than 150 ° C., crystallization may not occur. If the annealing temperature exceeds 500 ° C., the usable substrate may be significantly restricted.
The heat treatment time depends on the annealing temperature, but is preferably within 2 hours. If it exceeds 2 hours, the productivity may decrease.

  Crystallization may be performed by applying ultraviolet rays, plasma or other energy in addition to these heat and electromagnetic waves.

Crystallization can be performed, for example, by a heat treatment at a heat treatment temperature of 150 to 500 ° C. and a heat treatment time of 0.5 to 12000 minutes in the presence or absence of oxygen.
If the temperature of the heat treatment is less than 150 ° C., the treatment effect may not be exhibited or the treatment time may be excessive, and if it exceeds 500 ° C., the substrate may be deformed.
Also, if the heat treatment time is less than 0.5 minutes, the time for transferring heat to the inside may be insufficient, and the treatment may be insufficient. If it exceeds 12000 minutes, the treatment apparatus becomes large and cannot be used industrially. Or the substrate may be damaged or deformed during processing.

  The above method can be applied to any target made of an oxide that can be expected to have high mobility by crystallization, such as zinc oxide, tin oxide, and titanium oxide, but an indium oxide-based target is most suitable.

  The obtained oxide semiconductor preferably contains a bixbyite crystal of indium oxide. When indium oxide has a bixbyite structure, mobility can be increased. This is presumed to be due to the fact that the 5S orbital of indium has a ridge-sharing structure. The inclusion of bixbite type crystals can be confirmed by X-ray diffraction.

Oxide semiconductor obtained by the film forming method of the present invention (hereinafter, simply referred to the oxide semiconductor of the present invention), preferably consists essentially of In ₂ O _3, or In ₂ O ₃ and other indium element And an atomic ratio of the indium element to the additive element (total additive element) / (In + total additive element) of 0.0001 or more and 0.2 or less. It is.
Note that an element having a valence of 3 or less is an element that can have a valence of 3 or less in the ionic state.

  An oxide semiconductor containing indium oxide and an oxide of an additive element can exhibit high mobility by containing indium oxide as a main component (80 at% or more), and is positive trivalent with respect to indium which is a positive trivalent element. By containing the following additive elements, the carrier concentration can be reduced and the carrier concentration can be controlled.

The oxide semiconductor is made of one or more kinds of additive elements having a positive trivalent or lower valence other than In ₂ O ₃ and indium elements, and the atomic ratio of the indium elements and the additive elements in the oxide semiconductor (total added elements) ) / (In + total additive element) is 0.0001 or more and 0.2 or less, (total additive element) / (In + total additive element) is preferably 0.08 to 0.1.
When (total additive element) / (In + total additive element) is less than 0.0001, the number of carriers may not be controlled. On the other hand, if (total additive element) / (In + total additive element) exceeds 0.2, the crystallization temperature becomes high and crystallization becomes difficult, the carrier concentration increases, or the hole mobility decreases. There is a risk. Further, when a transistor including the oxide semiconductor is driven, the threshold voltage may fluctuate or the driving may become unstable.

The additive element having a positive trivalent or less valence other than the indium element is preferably Mg, Al, Ca, Fe, Co, Ni, Cu, Zn, Ga, Sr, Ba or a rare earth element, more preferably Mg. , Al, Ga, Ni, Cu, Zn, Sr or Y.
The oxide semiconductor of the present invention can contain one or more of these additive elements.

  The oxide semiconductor may contain a positive tetravalent element such as Sn or Ce at a ratio of 3% by weight or less in order to reduce the electrical resistance value of the sputtering target. In particular, Sn has a great effect of improving the sintered density and reducing the electric resistance of the target. The content of the element capable of taking positive tetravalence is more preferably 2% by weight or less, and particularly preferably 1% by weight or less. If the content of the positive tetravalent element exceeds 3% by weight, the carrier density may not be controlled to a low concentration.

  The oxide semiconductor of the present invention can be suitably used as a semiconductor thin film of a thin film transistor. The field-effect transistor including an oxide semiconductor of the present invention is a transistor with high field-effect mobility and on-off ratio, normally-off, and clear pinch-off. In addition, since the field-effect transistor including an oxide semiconductor of the present invention can form an oxide semiconductor at a low temperature, the field-effect transistor can be formed over a substrate having a limit of heat resistance such as alkali-free glass.

The oxide semiconductor of the present invention can be applied to various field effect transistors.
For example, although the oxide semiconductor of the present invention is usually used in an n-type region, it is a PN junction transistor in combination with various P-type semiconductors such as a P-type Si-based semiconductor, a P-type oxide semiconductor, and a P-type organic semiconductor. It can utilize for various semiconductor devices. The TFT can also be applied to various integrated circuits such as logic circuits, memory circuits, and differential amplifier circuits. In addition to field effect transistors, it can be applied to electrostatic induction transistors, Schottky barrier transistors, Schottky diodes, and resistance elements.

As the structure of the transistor, known structures such as a bottom gate, a top gate, a bottom contact, and a top contact can be used without limitation. In particular, the bottom gate configuration is advantageous because high performance can be obtained as compared with amorphous silicon or ZnO TFTs. The bottom gate configuration is preferable because it is easy to reduce the number of masks at the time of manufacturing, and it is easy to reduce the manufacturing cost for uses such as a large display.
Here, a TFT having a bottom gate structure is usually a structure in which a semiconductor layer is provided (film formation) after a gate electrode is provided (film formation).

FIG. 1 is a schematic cross-sectional view according to an embodiment of a thin film transistor including the oxide semiconductor of the present invention.
The thin film transistor 1 which is a field effect transistor is a bottom gate type, and a gate electrode 30 is formed on a glass substrate 60 and a gate insulating film 50 is formed thereon. An oxide semiconductor film 40 is formed on the gate insulating film 50, and the drain electrode 10 and the source electrode 20 are further formed on the oxide semiconductor film 40.

There are no particular limitations on the material for forming the drain electrode 10, the source electrode 20, and the gate electrode 30, and any commonly used material can be selected.
For example, a transparent electrode such as ITO, IZO, ZnO, or SnO ₂ , a metal electrode such as Al, Ag, Cu, Cr, Ni, Mo, Au, Ti, or Ta, or a metal electrode made of an alloy containing these may be used. it can.

  Each of the drain electrode 10, the source electrode 20, and the gate electrode 30 may have a multilayer structure in which two or more different conductive layers are stacked. For example, in FIG. The first conductive layers 31, 21, 11 and the second conductive layers 32, 22, 12 are respectively configured. In particular, since the source / drain electrode has a strong demand for low-resistance wiring, a good conductor such as Al or Cu may be sandwiched with a metal having excellent adhesion such as Ti or Mo.

The material for forming the gate insulating film 50 is not particularly limited, and any commonly used material can be selected.
As a material of the gate insulating film 50, for example _{SiO 2, SiNx, Al 2 O3} , Ta 2 O 5, TiO 2, MgO, ZrO 2, CeO 2, K 2 O, Li 2 O, Na 2 O, Rb 2 O , Sc ₂ O ₃ , Y ₂ O ₃ , HfO ₃ , CaHfO ₃ , PbTi ₃ , BaTa ₂ O ₆ , SrTiO ₃ , AlN, and the like can be used. Among these, it is preferably _{SiO 2, SiNx, Al 2 O} 3, Y 2 O3, HfO 3, CaHfO 3, more preferably _{SiO 2, SiNx, Y 2 O} 3, HfO 3, CaHfO 3.
Note that the number of oxygen in the oxide does not necessarily match the stoichiometric ratio (for example, it may be SiO ₂ or SiO x).

  Such a gate insulating film 50 may have a structure in which two or more different insulating films are stacked. The gate insulating film 50 may be crystalline, polycrystalline, or amorphous, but is preferably polycrystalline or amorphous that is easy to manufacture industrially.

The oxide semiconductor 40 is an oxide semiconductor obtained by the film forming method of the present invention, and is preferably a thin film containing indium oxide and an oxide of a positive trivalent element or less.
The oxide semiconductor 40 preferably has a carrier density obtained by Hall measurement of less than 1 × 10 ⁺¹⁹ cm ⁻³ , more preferably less than 5 × 10 ⁺¹⁷ cm ⁻³ , and even more preferably less than 5 × 10 ⁺¹⁶ cm ^−3. It is. When the carrier density is 1 × 10 ⁺¹⁹ cm ⁻³ or more, the leakage current may increase.
Note that the lower limit of the carrier density is preferably 10 ⁺¹⁵ / cm ⁻³ or more, for example, although it depends on the use of the element including the oxide semiconductor 40.

As for the specific resistance of the oxide semiconductor 40, the value obtained by the four probe method is usually 10 ⁻¹ to 10 ⁸ Ωcm, preferably 10 ¹ to 10 ⁷ Ωcm, and more preferably 10 ² to 10 ⁶ Ωcm. is there.
When the specific resistance is less than 10 ⁻¹ Ωcm, electricity may flow easily and may not function as a semiconductor thin film. On the other hand, when the specific resistance exceeds 10 ⁸ Ωcm, there is a possibility that the semiconductor does not function unless a strong electric field is applied.

The film thickness of the oxide semiconductor 40 is appropriately selected in accordance with the specific resistance of the oxide semiconductor 40 itself, but is usually 0.5 to 500 nm, preferably 1 to 150 nm, more preferably It is 3-80 nm, Most preferably, it is 10-60 nm. When the film thickness is in the range of 3 to 80 nm, TFT characteristics such as mobility and on / off ratio are particularly good.
When the film thickness is less than 0.5 nm, it may be difficult to form an industrially uniform film. On the other hand, when the film thickness exceeds 500 nm, the film formation time becomes long and there is a possibility that it cannot be adopted industrially.

The field effect mobility of the thin film transistor 1 is usually 1 cm ² / Vs or more, preferably 5 cm ² / Vs or more, more preferably 18 cm ² / Vs or more, further preferably 30 cm ² / Vs or more, particularly preferably 50 cm ² / V. Vs or higher.
When the field effect mobility is less than 1 cm ² / Vs, the switching speed may be slow.

The on-off ratio of the thin film transistor 1 is usually 10 ³ or more, preferably 10 ⁴ or more, more preferably 10 ⁵ or more, still more preferably 10 ⁶ or more, and particularly preferably 10 ⁷ or more.

The thin film transistor 1 is preferably normally off with a positive threshold voltage (Vth) from the viewpoint of low power consumption. If the threshold voltage (Vth) is negative and normally on, power consumption may increase.
The threshold voltage is usually 0.01 to 5 V, preferably 0.05 to 3 V, more preferably 0.1 to 2 V, and still more preferably 0.2 to 1 V. If it is greater than 5V, the power consumption may increase, and if it is less than 0.01V, there is a risk of being normally on due to fluctuations.

Reference example 1
[Fabrication of thin film transistor and Hall effect measurement element]
A magnetron sputtering apparatus was equipped with a 2 inch In ₂ O ₃ target, a silicon wafer with a thermal oxide film having a thickness of 100 nm as the substrate A1, and a slide glass (# 1737 manufactured by Corning) as the substrate B1. An amorphous film having a thickness of 20 nm was formed on each of the substrate A1 and the substrate B1 by the DC magnetron sputtering method on the substrate A1 and the substrate B1 under the following conditions using a 3 mm square metal mask. The substrate on which the amorphous film was formed was annealed in the atmosphere at 300 ° C. for 1 hour, and the amorphous film was crystallized to form an oxide semiconductor film.

The sputtering conditions are as follows.
Substrate temperature: 25 ° C
Ultimate pressure: 1 × 10 ⁻⁴ Pa
Atmospheric gas: Ar 98%, H ₂ O 2%
Sputtering pressure (total pressure): 6 × 10 ⁻¹ Pa
Moisture pressure: 6.0 × 10 ⁻⁴ Pa
Input power: DC100W
ST distance: 170mm

In the 2-inch cathode magnetron sputtering apparatus, the substrate A1 and the substrate B1 on which the oxide semiconductor film is formed are mounted again, and an Au target is mounted on the cathode. An Au electrode was formed.
An oxide semiconductor element A1 having W / L = 1000/200 μm was obtained from the substrate A1, and a Hall effect measuring element B1 having 10 mm □ was obtained from the substrate B1.

The sputtering conditions are as follows.
Substrate temperature: 25 ° C
Ultimate pressure: 1 × 10 ⁻⁴ Pa
Atmospheric gas: Ar100%
Sputtering pressure (total pressure): 6 × 10 ⁻¹ Pa
Input power: 100W
Deposition time: 4 minutes ST distance: 170 mm

[Evaluation of device]
The oxide semiconductor element A1 was set to Keithley 4200SCS, and the transfer characteristics were evaluated under the conditions of Vds = 10V and Vgs = -20 to 20V. The results are shown in Table 1.
The Hall effect measuring element B1 was set in Toyo Technica's RSITEST 8300, and the Hall effect was evaluated at room temperature. The results are shown in Table 1.

Reference Examples 2, 3, 7, 13, 15, 19, 20, Examples 4-6, 8-12, 14, 16-18, 21 and Comparative Examples 1-6
Thin film transistor and Hall effect in the same manner as in Reference Example 1 except that the target used for forming the oxide semiconductor film, and the sputtering conditions and annealing conditions thereof were changed to the targets and conditions having the compositions shown in Tables 1 to 6. Measurement elements were fabricated and evaluated. The results are shown in Tables 1-6.
In the pulse DC of Example 16, a rectangular wave having a duty ratio of 20% (On state 80%) was set to 800 kHz. In Example 21, two pieces of In ₂ O ₃ : Nd ₂ O ₃ = 93: 7 having a diameter of 4 inches and a thickness of 5 mm were used as targets, mounted on an AC sputtering apparatus, and sputtered at a frequency of 10 MHz.

About the oxide semiconductor element manufactured by the reference examples 1-3 and the comparative examples 1 and 2, a specific gate voltage was applied and the drain current in that case was measured.
FIG. 3 is a drawing in which the vertical axis represents the drain current and the horizontal axis represents the gate voltage, and the characteristics of the transistor of the element can be understood from this drawing.
As can be seen from this figure, in Comparative Example 1, since the amount of water is small, the carrier concentration after crystallization is large, and the Off current is high. In Comparative Example 2, since the amount of moisture was too large, the semiconductor film was inferior in denseness, the On current was small, and the mobility was small. On the other hand, it can be seen that Reference Examples 1 to 3 are appropriate water introduction amounts and exhibit good On-Off characteristics.

FIG. 4 is a drawing in which the horizontal axis represents the water pressure during sputtering, and the vertical axis represents the S value that is a parameter indicating the steepness of the rise from Off to On.
From this figure, it can be seen that the S value is small when the moisture pressure is between 3e-4 Pa and 5e-2 Pa, and the transistor manufactured by setting the moisture pressure within this range is a transistor with a steep rise.

Reference Example 22
[Manufacture of thin film transistors with microfabricated channels]
A magnetron sputtering apparatus was equipped with a target (atomic ratio In ₂ O ₃ : ZnO = 95: 5) made of 2 inches of In ₂ O ₃ and ZnO, and a silicon wafer with a thermal oxide film having a thickness of 100 nm was attached. An amorphous film having a film thickness of 50 nm was formed by DC magnetron sputtering using a 3 mm □ metal mask under the following conditions.

The sputtering conditions are as follows.
Substrate temperature: 25 ° C
Ultimate pressure: 1 × 10 ⁻⁴ Pa
Atmospheric gas: Ar 98%, H ₂ O 2%
Sputtering pressure (total pressure): 6 × 10 ⁻¹ Pa
Moisture pressure: 6.0 × 10 ⁻⁴ Pa
Input power: DC100W
ST distance: 170mm

  A positive resist OFPR-800 manufactured by Tokyo Ohka was spin-coated on the wafer with IZO (without heat treatment) produced above under the conditions of 3000 rpm and 60 s, and then pre-baked in air at 80 ° C. for 3 minutes. Next, it was set in Canon exposure machine PLA-501 and exposed from above the mask. This substrate was immersed in a developer (Tokyo Ohka NMD-3), developed and rinsed, and then post-baked in air at 120 ° C. for 30 minutes. After completion of baking, it was immersed in an etching solution for aluminum (mixed acid of phosphoric acid, acetic acid and nitric acid) manufactured by Kanto Chemical to dissolve unnecessary parts of IZO, and finally was immersed in a resist stripping solution (106 manufactured by Tokyo Ohka Kogyo Co., Ltd.) to strip the resist . Thereafter, heat treatment was performed in air at 300 ° C. for 1 hour.

The Mo target was mounted on a sputtering apparatus, and a Mo thin film was formed on the semiconductor substrate. Then, the source / drain electrodes were patterned in the same manner as described above to obtain a thin film transistor with W / L = 20 / 10μ.
The obtained thin film transistor was evaluated in the same manner as in Reference Example 1. The results are shown in Table 7.

  The oxide semiconductor obtained by the oxide semiconductor manufacturing method of the present invention can be widely used as a semiconductor thin film of a field effect transistor such as a thin film transistor.

DESCRIPTION OF SYMBOLS 1,2 Thin-film transistor 10 Drain electrode 11 1st conductive layer 12 2nd conductive layer 20 Source electrode 21 1st conductive layer 22 2nd conductive layer 30 Gate electrode 31 1st conductive layer 32 2nd conductive layer 40 Oxide semiconductor 50 Insulating film 60 glass substrate

Claims (4)

The sputtering target was DC-sputtered at a moisture pressure of 1 × 10 ^{−3 to} 5 × 10 ⁻² Pa in the system to form a film formation body,
An oxide semiconductor film forming method for crystallizing the film formed body ,
The oxide semiconductor is made of one or more oxides of additive elements having positive or lower valence other than In ₂ O ₃ and indium element, and the atomic ratio of the indium element and the additive element (total additive elements) / (In + all added elements) is 0.08 or more and 0.2 or less,
The oxide semiconductor film-forming method, wherein the additive element having a valence of 3 or less is at least one selected from Al, Fe, Ga, Ba, and rare earth elements. A film-forming body was formed by high-frequency sputtering with a frequency of 10 MHz or less at a water pressure of 1 × 10 ^{−3 to} 5 × 10 ⁻² Pa in the system,
An oxide semiconductor film forming method for crystallizing the film formed body ,
The oxide semiconductor is made of one or more oxides of additive elements having positive or lower valence other than In ₂ O ₃ and indium element, and the atomic ratio of the indium element and the additive element (total additive elements) / (In + all added elements) is 0.08 or more and 0.2 or less,
The oxide semiconductor film-forming method, wherein the additive element having a valence of 3 or less is at least one selected from Al, Fe, Ga, Ba, and rare earth elements.   3. The oxide semiconductor film forming method according to claim 1, wherein the crystallization is performed by annealing.   The oxide semiconductor film forming method according to claim 1, wherein the rare earth element is at least one selected from Y, Sm, and Nd.

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