JP2010118407A - Thin-film transistor having etching resistance, and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide: a high-performance thin-film transistor having PAN resistance, having high mobility, a low off-current value, a low threshold voltage and a low S value in a normally-off operation, and exhibiting high operation stability; and to provide a production method thereof. <P>SOLUTION: This thin-film transistor includes an oxide sintered body composed of an oxide semiconductor in which the atomic ratio of each element of an indium element (In), a gallium element (Ga), a zinc element (Zn) and a tin element (Sn) relative to the total (In+Ga+Zn+Sn) satisfies the relationships: 0.18<In/(In+Ga+Zn+Sn)<0.79; 0.00010<Ga/(In+Ga+Zn+Sn)<0.27; 0.060<Zn/(In+Ga+Zn+Sn)<0.49; and 0.12<Sn/(In+Ga+Zn+Sn)<0.40. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an oxide sintered body, a thin film transistor, and a method for manufacturing the same.

Although known amorphous IGZO is known to exhibit good characteristics as a thin film transistor, it is generally used as a mixed solution of phosphoric acid, acetic acid, nitric acid and water (hereinafter referred to as a PAN solution) used as an Al etching solution. There was no resistance, and the display manufacturing process could be difficult.
Patent Document 1 discloses an IGZO + Sn thin film transistor. However, in all regions, there is a possibility that a thin film transistor having a high On / Off ratio, a high mobility, a low threshold voltage, and a low S value may not be obtained.
JP 2007-123699 A

  An object of the present invention is to provide a high-performance thin film transistor having PAN resistance, normally-off, high mobility, low off-current value, low threshold voltage, low S value and high operational stability, and its manufacture A method is provided.

  In order to achieve the above-mentioned object, the present inventors have conducted intensive research and found that each element with respect to the sum of indium element (In), gallium element (Ga), zinc element (Zn), and tin element (Sn) (In + Ga + Zn + Sn). The present inventors have found that a thin film transistor manufactured using an oxide sintered body made of an oxide semiconductor having an atomic ratio satisfying a predetermined relationship as a sputtering target can achieve the above object, and has completed the present invention.

That is, this invention provides the manufacturing method of the following oxide sintered compact, sputtering target, a thin-film transistor, and a thin-film transistor.
1. Oxide sintering made of an oxide semiconductor in which the atomic ratio of each element satisfies the following relationship with respect to the sum (In + Ga + Zn + Sn) of indium element (In), gallium element (Ga), zinc element (Zn), and tin element (Sn) body.
0.18 <In / (In + Ga + Zn + Sn) <0.79
0.00010 <Ga / (In + Ga + Zn + Sn) <0.27
0.060 <Zn / (In + Ga + Zn + Sn) <0.49
0.12 <Sn / (In + Ga + Zn + Sn) <0.40
2. 2. The oxide sintered body according to 1, wherein the atomic ratio of each element is an oxide semiconductor satisfying the following relationship.
0.18 <In / (In + Ga + Zn + Sn) <0.62
0.00010 <Ga / (In + Ga + Zn + Sn) <0.27
0.090 <Zn / (In + Ga + Zn + Sn) <0.49
0.12 <Sn / (In + Ga + Zn + Sn) <0.40
3.1 A sputtering target comprising the oxide sintered body according to 1 or 2.
4). A thin film transistor made of an oxide semiconductor in which the atomic ratio of each element satisfies the following relationship with respect to the sum (In + Ga + Zn + Sn) of indium element (In), gallium element (Ga), zinc element (Zn), and tin element (Sn).
0.18 <In / (In + Ga + Zn + Sn) <0.79
0.00010 <Ga / (In + Ga + Zn + Sn) <0.27
0.060 <Zn / (In + Ga + Zn + Sn) <0.49
0.12 <Sn / (In + Ga + Zn + Sn) <0.40
5). 5. The thin film transistor according to 4, wherein the atomic ratio of each element is made of an oxide semiconductor that satisfies the following relationship.
0.18 <In / (In + Ga + Zn + Sn) <0.62
0.0001 <Ga / (In + Ga + Zn + Sn) <0.27
0.090 <Zn / (In + Ga + Zn + Sn) <0.49
0.12 <Sn / (In + Ga + Zn + Sn) <0.40
6). The film forming step is performed by sputtering using the target comprising the oxide sintered body according to claim 1, and the oxide semiconductor film is formed by setting the oxygen concentration during sputtering to 2 to 20% by volume. 6. A method for producing a thin film transistor according to 5.
7). 7. The method for producing a thin film transistor according to 6, wherein the oxide semiconductor film is heat-treated at 150 to 450 ° C. for 0.1 to 1200 minutes in the presence of oxygen.
8). 8. The method for producing a thin film transistor according to 6 or 7, which is a method for producing a channel etch type thin film transistor.
9. 8. The method for producing a thin film transistor according to 6 or 7, which is a method for producing an etch stopper type thin film transistor.

  According to the present invention, an oxide that provides a high-performance thin film transistor having PAN resistance, normally-off, high mobility, low off-current value, low threshold voltage, and low S value and high operational stability. A sintered body, a thin film transistor, and a manufacturing method thereof are provided.

I. Oxide Sintered Body The oxide sintered body of the present invention has an atomic ratio of each element to the total of the indium element (In), gallium element (Ga), zinc element (Zn) and tin element (Sn) (In + Ga + Zn + Sn). Is made of an oxide semiconductor satisfying the following relationship.
0.18 <In / (In + Ga + Zn + Sn) <0.79
0.00010 <Ga / (In + Ga + Zn + Sn) <0.27
0.060 <Zn / (In + Ga + Zn + Sn) <0.49
0.12 <Sn / (In + Ga + Zn + Sn) <0.40

Preferably, it consists of an oxide semiconductor in which the atomic ratio of each element satisfies the following relationship.
0.18 <In / (In + Ga + Zn + Sn) <0.62
0.00010 <Ga / (In + Ga + Zn + Sn) <0.27
0.090 <Zn / (In + Ga + Zn + Sn) <0.49
0.12 <Sn / (In + Ga + Zn + Sn) <0.40

More preferably, it consists of an oxide semiconductor in which the atomic ratio of each element satisfies the following relationship.
0.18 <In / (In + Ga + Zn + Sn) <0.60
0.03 <Ga / (In + Ga + Zn + Sn) <0.27
0.090 <Zn / (In + Ga + Zn + Sn) <0.46
0.12 <Sn / (In + Ga + Zn + Sn) <0.40

Particularly preferably, it is made of an oxide semiconductor in which the atomic ratio of each element satisfies the following relationship.
0.25 <In / (In + Ga + Zn + Sn) <0.60
0.030 <Ga / (In + Ga + Zn + Sn) <0.22
0.10 <Zn / (In + Ga + Zn + Sn) <0.38
0.13 <Sn / (In + Ga + Zn + Sn) <0.40
If an oxide sintered body having an atomic ratio of each element in the above range is used as a sputtering target, a thin film transistor having a high field effect mobility, a low S value, a high on / off ratio and excellent operational stability can be obtained. It is done.

In addition, when an oxide sintered body made of an oxide semiconductor in which the atomic ratio of each element satisfies the following relationship is used as a sputtering target, a thin film transistor exhibiting particularly high mobility tends to be obtained.
0.33 <In / (In + Ga + Zn + Sn) <0.79
0.0001 <Ga / (In + Ga + Zn + Sn) <0.27
0.06 <Zn / (In + Ga + Zn + Sn) <0.27
0.13 <Sn / (In + Ga + Zn + Sn) <0.40

The oxide sintered body of the present invention includes indium element (In), gallium element (Ga), zinc element (Zn), and tin element (Sn), and the following conditions (1) to (3) are satisfied. It is preferable to satisfy.
(1) A compound represented by Ga ₂ In ₆ Sn ₂ O ₁₆ and / or (Ga, In) ₂ O ₃ is included.
(2) A compound represented by Ga ₂ In ₆ Sn ₂ O ₁₆ and a compound represented by In ₂ O ₃ are included.
(3) A compound represented by Ga _2.4 In _5.6 Sn ₂ O ₁₆ and a compound represented by In ₂ O ₃ are included as main components.

When the oxide sintered body of the present invention satisfies any of the above conditions (1) to (3), the occurrence of abnormal discharge during sputtering can be reduced, and the PAN resistance of the resulting oxide semiconductor film can be reduced. Will improve.
The oxide semiconductor film of the present invention can be suitably used for a thin film transistor, a display drive circuit, a resistance change memory, an RFID tag, and the like.

The oxide sintered body of the present invention can be produced, for example, by mixing indium oxide, gallium oxide, zinc oxide and tin oxide powders, and pulverizing and sintering the mixture.
For the raw material powder, the specific surface area of the indium oxide powder ^{8~10m 2 / g, 5~10m 2 /} g specific surface area of the gallium oxide powder, the specific surface area of 2 to 4 m ² / g of zinc oxide powder, tin oxide powder The specific surface area is preferably 8 to 10 m ² / g. Alternatively, the median diameter of indium oxide powder is 1 to 2 μm, the median diameter of gallium oxide powder is 1 to 2 μm, the median diameter of zinc oxide powder is 0.8 to 1.6 μm, and the median diameter of tin oxide powder is 1 to 2 μm. It is preferable to do.
In addition, it is preferable to use the powder whose specific surface area of an indium oxide powder and the specific surface area of a gallium oxide powder are substantially the same. Thereby, it can pulverize and mix more efficiently. Specifically, the difference in specific surface area is preferably 5 m ² / g or less. If the specific surface area is too different, efficient pulverization and mixing cannot be performed, and gallium oxide particles may remain in the sintered body.

In the raw material powder, the mixing ratio of indium oxide powder, gallium oxide powder, zinc oxide powder and tin oxide powder (indium oxide powder: gallium oxide powder: zinc oxide powder: tin oxide powder) is the ratio in which the atomic ratio of each element is described above. For example, it is preferable to weigh so that the weight ratio is 57: 5: 19: 19.
In addition, as long as the mixed powder containing indium oxide powder, gallium oxide powder, zinc oxide powder, and tin oxide powder is used, other components that improve the characteristics of the sintered body may be added.

The mixed powder is mixed and ground using, for example, a wet medium stirring mill. At this time, pulverization is performed so that the specific surface area after pulverization is 1.5 to 2.5 m ² / g higher than the specific surface area of the raw material mixed powder, or the average median diameter after pulverization is 0.6 to 1 μm. It is preferable to do. By using the raw material powder thus adjusted, a high-density oxide sintered body can be obtained without requiring a calcination step at all. Moreover, a reduction process is also unnecessary.
In addition, if the increase in the specific surface area of the raw material mixed powder is less than 1.0 m ² / g or the average median diameter of the raw material mixed powder after pulverization exceeds 1 μm, the sintered density may not be sufficiently increased. On the other hand, if the increase in the specific surface area of the raw material mixed powder exceeds 3.0 m ² / g or the average median diameter after pulverization becomes less than 0.6 μm, contamination (impurity contamination amount) from the pulverizer machine during pulverization ) May increase.

  Here, the specific surface area of each powder is a value measured by the BET method. The median diameter of the particle size distribution of each powder is a value measured with a particle size distribution meter. These values can be adjusted by pulverizing the powder by a dry pulverization method, a wet pulverization method or the like.

  The raw material after the pulverization step is dried with a spray dryer or the like and then molded. For forming, a known method such as pressure forming or cold isostatic pressing can be employed.

Next, the obtained molded product is sintered to obtain a sintered body. Sintering is preferably carried out at 1400-1600 ° C. for 2-20 hours. As a result, a sintered body having a density of 6.0 g / cm ³ or more can be obtained. When the temperature is lower than 1400 ° C., the density does not improve. When the temperature exceeds 1600 ° C., zinc evaporates, the composition of the sintered body changes, or voids (voids) are generated in the sintered body due to evaporation. There is.
Sintering is preferably carried out in an oxygen atmosphere by circulating oxygen, or under pressure. Thereby, transpiration of zinc can be suppressed, and a sintered body free from voids (voids) can be obtained.
Since the sintered body manufactured in this way has a high density of 6.0 g / cm ³ or more, the generation of nodules and particles at the time of use is small, and thus an oxide semiconductor film having excellent film characteristics is manufactured. Can do.
Ga ₂ In ₆ Sn ₂ O ₁₆ is mainly produced in the obtained sintered body.

The oxide sintered body of the present invention becomes a target for physical film formation by performing processing such as polishing. Specifically, the sintered body is ground by, for example, a surface grinder so that the surface roughness Ra is 5 μm or less. Further, the sputter surface of the target may be mirror-finished so that the average surface roughness Ra is 1000 angstroms or less. For this mirror finishing (polishing), a known polishing technique such as mechanical polishing, chemical polishing, mechanochemical polishing (a combination of mechanical polishing and chemical polishing) can be used. For example, polishing to # 2000 or more with a fixed abrasive polisher (polishing liquid: water) or lapping with loose abrasive lapping (abrasive: SiC paste, etc.), and then lapping by changing the abrasive to diamond paste Can be obtained by: Such a polishing method is not particularly limited.
By bonding the obtained target for physical film formation to a backing plate, it can be used by being mounted on various apparatuses. Examples of the physical film forming method include a sputtering method, a PLD (pulse laser deposition) method, a vacuum deposition method, and an ion plating method.

In addition, air blow, running water washing | cleaning, etc. can be used for the cleaning process of the target for physical film-forming. When removing foreign matter by air blow, it is possible to remove the foreign matter more effectively by suctioning with a dust collector from the opposite side of the nozzle.
In addition to air blow and running water cleaning, ultrasonic cleaning and the like can also be performed. In ultrasonic cleaning, a method of performing multiple oscillations at a frequency of 25 to 300 KHz is effective. For example, it is preferable to perform ultrasonic cleaning by causing multiple oscillations of 12 types of frequencies at intervals of 25 KHz between frequencies of 25 to 300 KHz.

When the physical film formation target is used as a sputtering target, the bulk resistance of the target is preferably less than 20 mΩcm, more preferably less than 10 mΩcm, still more preferably less than 5 mΩcm, and particularly preferably less than 2 mΩcm. In the case of 20 mΩcm or more, when DC sputtering is continued for a long time, a spark is generated due to abnormal discharge, the target is cracked, particles ejected by the spark adhere to the deposition substrate, and the performance as an oxide semiconductor film is degraded. There is a case to let you.
The bulk resistance is a value measured by a four-probe method using a resistivity meter.

II. Thin Film Transistor The thin film transistor of the present invention is an oxide in which the atomic ratio of each element with respect to the sum of the indium element (In), gallium element (Ga), zinc element (Zn), and tin element (Sn) (In + Ga + Zn + Sn) satisfies the following relationship: It is characterized by comprising a semiconductor.
0.18 <In / (In + Ga + Zn + Sn) <0.79
0.00010 <Ga / (In + Ga + Zn + Sn) <0.27
0.060 <Zn / (In + Ga + Zn + Sn) <0.49
0.12 <Sn / (In + Ga + Zn + Sn) <0.40

Preferably, it consists of an oxide semiconductor in which the atomic ratio of each element satisfies the following relationship.
0.18 <In / (In + Ga + Zn + Sn) <0.62
0.0001 <Ga / (In + Ga + Zn + Sn) <0.27
0.090 <Zn / (In + Ga + Zn + Sn) <0.49
0.12 <Sn / (In + Ga + Zn + Sn) <0.40

More preferably, it consists of an oxide semiconductor in which the atomic ratio of each element satisfies the following relationship.
0.18 <In / (In + Ga + Zn + Sn) <0.60
0.03 <Ga / (In + Ga + Zn + Sn) <0.27
0.090 <Zn / (In + Ga + Zn + Sn) <0.46
0.12 <Sn / (In + Ga + Zn + Sn) <0.40

Particularly preferably, it is made of an oxide semiconductor in which the atomic ratio of each element satisfies the following relationship.
0.25 <In / (In + Ga + Zn + Sn) <0.60
0.030 <Ga / (In + Ga + Zn + Sn) <0.22
0.10 <Zn / (In + Ga + Zn + Sn) <0.38
0.13 <Sn / (In + Ga + Zn + Sn) <0.40
When the atomic ratio of each element is in the above range, a thin film transistor having a high field effect mobility, a low S value, a high on / off ratio, and excellent operational stability can be obtained.

In addition, when an oxide sintered body made of an oxide semiconductor in which the atomic ratio of each element satisfies the following relationship is used as a sputtering target, a thin film transistor exhibiting particularly high mobility tends to be obtained.
0.33 <In / (In + Ga + Zn + Sn) <0.79
0.0001 <Ga / (In + Ga + Zn + Sn) <0.27
0.06 <Zn / (In + Ga + Zn + Sn) <0.27
0.13 <Sn / (In + Ga + Zn + Sn) <0.40

III. Method for Producing Thin Film Transistor In the method for producing a thin film transistor of the present invention, the film forming step is carried out by sputtering using a target comprising the oxide sintered body of the present invention, and the oxygen concentration during sputtering is set to 2 to 20% by volume. A physical semiconductor film is formed.
The obtained oxide semiconductor film is preferably heat-treated at 150 to 450 ° C. for 0.1 to 1200 minutes in the presence of oxygen. This is because the defect level in the semiconductor film is reduced by heat treatment, the off-current value is reduced, and the operational stability is further improved. Further, the damage generated in the insulating film during the sputtering of the semiconductor film is recovered.
For the heat treatment of the semiconductor film, an electric heating furnace, a lamp annealing device, a laser annealing device, a hot air heating device, a contact heating device, or the like can be used in the presence of oxygen.
If the temperature is lower than 150 ° C., the defect density in the semiconductor film and the damage to the insulating film may not be sufficiently reduced. If the temperature exceeds 450 ° C., the substrate and the semiconductor film may be damaged. The heat treatment temperature is more preferably 180 ° C to 350 ° C, and particularly preferably 200 ° C to 300 ° C.
Also, if the heat treatment time is less than 0.1 minutes, the heat treatment time is too short and the defect density of the film and the damage to the insulating film may not be reduced sufficiently. If it exceeds 1200 minutes, it takes too much time and is not productive. The heat treatment time is more preferably 1 minute to 600 minutes, and particularly preferably 5 minutes to 60 minutes.
The crystallization and / or oxidation treatment of the semiconductor film may be performed immediately after the formation of the semiconductor film, or may be performed after the formation of other components such as source / drain electrodes.

Hereinafter, a method for manufacturing a thin film transistor including an oxide semiconductor film will be described.
By performing a film formation method such as sputtering using a target for physical film formation, an oxide semiconductor film mainly containing oxides of In, Ga, Zn, and Sn can be formed on an object such as a substrate. it can. This oxide semiconductor film is amorphous and exhibits stable semiconductor characteristics and good PAN resistance. Therefore, it is suitable as a material constituting the semiconductor layer (active layer) of the thin film transistor (TFT). By using the oxide semiconductor film of the present invention, the selection of an etchant is widened, so that the structure of the TFT and the degree of freedom of the manufacturing process can be increased.
Note that the thin film transistor of the present invention only needs to include the above-described oxide semiconductor film as an active layer, and other members (for example, insulating films, electrodes, etc.) and structures are known members and structures in the TFT field. Can be adopted.

  In the thin film transistor of the present invention, the thickness of the active layer is usually 0.5 to 500 nm, preferably 1 to 150 nm, more preferably 3 to 80 nm, and particularly preferably 10 to 60 nm. This is because if it is thinner than 0.5 nm, it is difficult to form an industrially uniform film. On the other hand, if it is thicker than 500 nm, the film formation time becomes long and cannot be adopted industrially. Moreover, when it exists in the range of 3-80 nm, TFT characteristics, such as field effect mobility and an on-off ratio, are especially favorable.

  The ratio W / L of the channel width W to the channel length L of the thin film transistor is usually 0.1 to 100, preferably 1 to 20, and particularly preferably 2 to 8. This is because if W / L exceeds 100, the leakage current may increase or the on-off ratio may decrease. On the other hand, if it is less than 0.1, the field effect mobility may be lowered, or pinch-off may be unclear.

  The channel length L is usually 0.1 to 1000 μm, preferably 1 to 100 μm, and more preferably 2 to 10 μm. This is because, when the thickness is 0.1 μm or less, it is difficult to manufacture industrially, and there is a possibility that a short channel effect may appear or a leakage current may increase. Further, when the thickness is 1000 μm or more, it is not preferable because the element becomes too large or the driving voltage becomes large.

The material of the gate insulating film of the thin film transistor is not particularly limited, and any commonly used material can be selected as long as the effects of the present invention are not lost. For _{example, SiO 2, SiNx, Al 2} O 3, 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 Oxides such as ₂ O ₃ , Hf ₂ O ₃ , CaHfO ₃ , PbTi ₃ , BaTa ₂ O ₆ , SrTiO ₃ , AlN, and SiON can be used. Among _{these, SiO 2, SiNx, Al 2} O 3, Y 2 O 3, Hf 2 O 3, it is preferable to use CaHfO _3, more preferably _{SiO 2, SiNx, Y 2 O} 3, Hf 2 O 3 , CaHfO ₃ , particularly preferably Y ₂ O ₃ . The number of oxygen in these oxides does not necessarily match the stoichiometric ratio (for example, it may be SiO ₂ or SiO x).
Such a gate insulating film may have a structure in which two or more different insulating films are stacked. The gate insulating film may be crystalline, polycrystalline, or amorphous, but is preferably polycrystalline or amorphous that is easy to manufacture industrially.

  The material for the source electrode and the drain electrode is not particularly limited, and a metal, an alloy thereof, an oxide conductor material, or the like that is generally used can be arbitrarily selected as long as the effects of the present invention are not lost.

When forming the active layer, sputtering methods include DC sputtering method, DC magnetron sputtering method, AC sputtering method, AC magnetron sputtering method, RF sputtering method, RF magnetron sputtering method, counter target sputtering method, cylindrical target sputtering method, An ECR sputtering method or the like can be used. As the vacuum deposition method, a resistance heating method, an electron beam heating method, a pulse laser deposition (PLD) method, or the like can be used. Furthermore, as the ion plating method, an ARE method or an HDPE method can be used. As the CVD method, a thermal CVD method or a plasma CVD method can be used.
Among these, the DC magnetron sputtering method or the AC magnetron sputtering method, which is stable in discharge, inexpensive and easy to increase in size, is preferable industrially, and the DC magnetron sputtering method is particularly preferable. Further, co-sputtering, reactive sputtering, or DC / RF superimposed sputtering may be used.

When the sputtering method is used, the ultimate pressure of the back pressure is usually 5 × 10 ⁻² Pa or less. This is because if it exceeds 5 × 10 ⁻² Pa, the field-effect mobility may be lowered due to impurities in the atmospheric gas.
In order to avoid such problems more effectively, the ultimate pressure is preferably 5 × 10 ⁻³ Pa or less, more preferably 5 × 10 ⁻⁴ Pa or less, and even more preferably 1 × 10 ⁻⁴ Pa or less. It is particularly preferably 5 × 10 ⁻⁵ Pa or less.
After the back pressure reaches the ultimate pressure, it is preferable that the mixed gas of Ar and oxygen is an atmosphere gas and the oxygen concentration at that time is 2 to 20% by volume. If the oxygen partial pressure is less than 2% by volume, the resistance is low and a semiconductor film may not be obtained. On the other hand, if it is higher than 20% by volume, the field effect mobility may be lowered or the carrier concentration may be unstable. Moreover, there is a possibility that a residue is generated during wet etching.
The sputtering pressure (total pressure) is preferably 1 × 10 ^{−1 to 3} Pa, and the input power is preferably 50 to 150 W, more preferably 100 W. A preferable film formation time is 15 to 35 minutes, and more preferably 25 minutes. The ST distance is preferably 50 to 140 nm, and more preferably 100 mm.

  Further, 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. This is because if the ST distance is short, the substrate is exposed to plasma during sputtering, so that activation of oxygen can be expected. On the other hand, if the length is longer than 150 mm, the film formation rate becomes slow and may not be suitable for industrialization.

  Usually, physical film formation is performed at a substrate temperature of 250 ° C. or lower. When the substrate temperature is higher than 250 ° C., the effect of post-treatment is not sufficiently exhibited, and it may be difficult to control the carrier concentration and mobility at a low level. In order to avoid such a problem more effectively, the substrate temperature is preferably 200 ° C. or lower, more preferably 150 ° C. or lower, still more preferably 100 ° C. or lower, and particularly preferably 50 ° C. or lower.

The method of manufacturing a thin film transistor of the present invention is suitable for manufacturing a channel etch type thin film transistor or an etch stopper type thin film transistor, and particularly suitable for manufacturing a channel etch type thin film transistor.
Since the semiconductor film manufactured using the sputtering target of the present invention has PAN resistance, it is not only an etch stopper type (a structure in which a semiconductor layer is protected so as not to be directly in contact with an etching solution) but also a channel etch type (semiconductor layer). A thin film transistor can be suitably manufactured even in a configuration in which is exposed to an etching solution.

FIG. 1 is a schematic cross-sectional view showing an embodiment of a thin film transistor of the present invention.
The thin film transistor 1 has a gate electrode 20 sandwiched between a substrate 10 and a gate insulating film 30, and a semiconductor film 40 is stacked on the gate insulating film 30 as an active layer. Further, a source electrode 50 and a drain electrode 52 are provided so as to cover the vicinity of the end of the semiconductor film 40. A channel portion 60 is formed in a portion surrounded by the semiconductor film 40, the source electrode 50 and the drain electrode 52.
1 is a so-called channel etch type thin film transistor. The thin film transistor of the present invention is not limited to a channel etch type thin film transistor, and an element configuration known in this technical field can be adopted.

FIG. 2 is a schematic cross-sectional view showing another embodiment of the thin film transistor of the present invention. In addition, the same number is attached | subjected to the same structural member as the thin-film transistor 1 mentioned above, and the description is abbreviate | omitted.
The thin film transistor 2 is an etch stopper type thin film transistor. The thin film transistor 2 has the same configuration as the thin film transistor 1 described above except that an etch stopper 70 is formed so as to cover the channel portion 60. A source electrode 50 and a drain electrode 52 are provided so as to cover the vicinity of the end of the semiconductor film 40 and the vicinity of the end of the etch stopper 70.

  In the present invention, a semiconductor thin film made of the oxide sintered body of the present invention, which is made of indium oxide, gallium oxide, zinc oxide, and indium tin oxide, is used as the semiconductor film 40. The trap density at the film interface can be reduced. As a result, the S value can be reduced.

  Subsequently, the present invention will be described while comparing Examples and Comparative Examples. In addition, a present Example shows the suitable example of this invention, and this invention is not restrict | limited to an Example. Therefore, the present invention includes modifications based on the technical idea or other embodiments.

Example 1
(1) and the oxide sintered body raw material powder as a specific surface area of 6 m 2 ^{/ g} and is indium powder and the specific surface area oxidation gallium oxide powder and the specific surface area is 6m 2 ^{/ g} 3m 2 ^{/ g} zinc oxide powder The tin oxide powder having a specific surface area of 6 m ² / g is 57: 5: 19: 19 (atomic ratio of metal atoms: 49.9: 6.6: 28.8: 15.3) by weight. And mixed and ground using a wet medium stirring mill. As the medium, 1 mmφ zirconia beads were used.
The specific surface area after pulverization was increased by 2 m ² / g from the specific surface area of the raw material mixed powder, and then dried with a spray dryer.
The mixed powder was filled into a mold, pressure-molded with a cold press machine, and further sintered for 8 hours in an oxygen atmosphere at a high temperature of 1450 ° C. while circulating oxygen.

Thus, an oxide sintered body having a density of 6.23 g / cm ³ was obtained without performing the calcination step. The density of the sintered body was calculated from the weight and outer dimensions of the sintered body cut into a certain size.
When this sintered body was analyzed by X-ray diffraction, it was confirmed that a compound represented by Ga ₂ In ₆ Sn ₂ O ₁₆ was a main component and a compound represented by InGaZnO ₄ and In ₂ O ₃ was present. did it.
In addition, the measurement conditions of the X-ray diffraction measurement (XRD) of the target were as follows.
・ Device: Ultimate-III manufactured by Rigaku Corporation
-X-ray: Cu-Kα ray (wavelength 1.5406mm, monochromatized with graphite monochromator)
・ 2θ-θ reflection method, continuous scan (1.0 ° / min)
・ Sampling interval: 0.02 °
・ Slit DS, SS: 2/3 °, RS: 0.6 mm
The bulk resistance of the sintered body was measured by a four-probe method using a resistivity meter (manufactured by Mitsubishi Oil Chemical Co., Ltd., Loresta) and found to be 0.95 mΩcm.

(2) Sputtering target A sputtering target was produced by subjecting the sintered body produced in (1) to processing such as polishing.

(3) Oxide semiconductor film The target prepared in (2) is mounted on an RF magnetron sputtering film forming apparatus (made by Shinko Seiki Co., Ltd.), which is one of the sputtering methods, and placed on a glass substrate (Corning 1737). An oxide semiconductor film was formed.
Sputtering conditions are: substrate temperature: 25 ° C. (room temperature), ultimate pressure: 5 × 10 ⁻⁴ Pa, atmospheric gas: Ar 98 vol%, oxygen 2 vol%, sputtering pressure (total pressure); 1 × 10 ⁻¹ Pa, The input power was 100 W, the film formation time was 25 minutes, and the ST distance was 100 mm.

  After film formation, the obtained thin film was heat-treated in an electric heating furnace at 300 ° C. for 1 hour.

As a result, a transparent conductive glass in which a transparent conductive oxide semiconductor film having a thickness of 50 nm was formed on a glass substrate was obtained.
Note that almost no abnormal discharge occurred during the formation of the oxide semiconductor film. Although the reason is not clear, it is thought that Ga ₂ In ₆ Sn ₂ O ₁₆ suppressed the abnormal growth of InGaZnO ₄ .

The PAN resistance of the oxide semiconductor film was evaluated. Specifically, etching was performed with a PAN etching solution (phosphoric acid of about 91.4 wt%, nitric acid of about 3.3 wt%, and acetic acid of about 5.3 wt%) at about 30 ° C., and the etching rate at that time was evaluated.
The case where the etching rate was 10 nm / min or less was evaluated as having PAN resistance (◯), and the case where the etching rate exceeded 10 nm / min was evaluated as having no PAN resistance (×).

Moreover, the electron carrier density measured by AC Hall measuring machine (made by Toyo Technica Co., Ltd.) was 2.9 × 10 ¹⁷ cm ⁻³ , and the hole mobility was 16 cm ² / Vs.

(4) Thin Film Transistor A channel etch type thin film transistor shown in FIG. 3 was manufactured.
A conductive silicon substrate 10 with a thermal oxide film (SiO ₂ film) having a thickness of 100 nm was used. The thermal oxide film functions as the gate insulating film 30 and the conductive silicon portion functions as the gate electrode 20.
A 50 nm semiconductor film 40 was formed on the gate insulating film 30 by sputtering. Sputtering was performed by evacuating the back pressure to 5 × 10 ⁻⁴ Pa, then adjusting the pressure to 0.2 Pa while flowing argon 9.0 sccm and oxygen 1.0 sccm, and the T-S distance was 10 cm. The substrate temperature was set to room temperature and the sputtering power was 100 W.

A metal mask is placed on the semiconductor film 40, and in the vicinity of both ends of the channel part 60, a channel part 60 having a gap (L) between the source and drain electrodes of 100 μm and a width (W) of 1000 μm is formed. Gold was deposited to form the source electrode 50 and the drain electrode 52.
Then, it heat-processed in the air at 300 degreeC for 1 hour in the hot-air heating furnace, and produced the thin-film transistor.
Table 1 shows the atomic percent of the metal element of the oxide sintered body, the PAN resistance, and the performance of the thin film transistor.

  The performance of the thin film transistor was evaluated by the following method for field effect mobility, On / Off ratio, threshold voltage, and S value.

  The field effect mobility was obtained from the slope of the tangent and the capacitance of the insulating film in the transfer curve (Vd-Id curve) of the thin film transistor.

  The On / Off ratio is defined as the ratio between the maximum value and the minimum value of the current in the transfer curve.

  Various methods are used for determining the threshold voltage. In the present invention, the threshold voltage is obtained from the X-intercept of the graph of the transfer curve (Id-Vg). In the present invention, normally-off is defined as a case where the threshold voltage value is negative.

  The S value (V / dec) is defined as the reciprocal of the slope of the rising portion of the transfer curve (Id-Vd Log curve). The steeper the slope, the smaller the S value, indicating better switching characteristics.

Examples 2, 3 and Comparative Examples 1-3
An oxide sintered body was prepared in the same manner as in Example 1 except that the atomic ratio (atomic%) of metal atoms and the conditions were changed as shown in Table 1, a target was prepared, and an oxide semiconductor film was prepared. A thin film transistor was manufactured. Table 1 shows the results of evaluating the PAN resistance of the oxide semiconductor film and the performance of the thin film transistor.

Example 4
An etch stopper type thin film transistor shown in FIG. 5 was manufactured by a photoresist method.
On the conductive silicon substrate 10 with the thermal oxide film (SiO ₂ film), the composition of indium oxide, gallium oxide, zinc oxide, and tin oxide was 57: 5: 19: by weight in the same manner as in Example 1. A 19 nm semiconductor film 40 was formed by sputtering using 19 targets.
Thereafter, as a layer to be an etch stopper, SiO ₂ was deposited by RF sputtering at 300 nm under the conditions of an oxygen partial pressure of 15% and an argon of 85%.
A resist was applied on the semiconductor film with SiO ₂ and prebaked at 80 ° C. for 15 minutes. Thereafter, the resist film was irradiated with UV light (light intensity: 300 mJ / cm ² ) through a mask, and then developed with 3 wt% tetramethylammonium hydroxide (TMAH). After cleaning with pure water, the resist film was post-baked at 130 ° C. for 15 minutes, and SiO ₂ was etched by dry etching using CF 4 to form an etch stopper 70 having a desired shape.
Thereafter, a molybdenum metal film having a thickness of 300 nm was formed on the semiconductor film 40, the gate insulating film (thermal oxide film) 30, and the etch stopper 70.

A resist was applied to the molybdenum metal film, and prebaked at 80 ° C. for 15 minutes. Thereafter, the resist film was irradiated with UV light (light intensity: 300 mJ / cm ² ) through a mask, and then developed with 3 wt% tetramethylammonium hydroxide (TMAH). After washing with pure water, the resist film was post-baked at 130 ° C. for 15 minutes to form a resist pattern having a desired source / drain electrode shape.

The substrate with a resist pattern was treated with a mixed acid of phosphoric acid / acetic acid / nitric acid to etch the molybdenum metal film, thereby forming the source electrode 50 and the drain electrode 52. At the same time, the portion of the semiconductor film 40 in contact with the gate insulating film 30 was also etched. Thereafter, the resist was peeled off, washed with pure water, dried by air blowing, and a thin film transistor (a gap (L) between the source and drain electrodes of the channel portion 60 was 1000 μm and a width (W) was 200 μm) was produced.
Thereafter, this thin film transistor was heat-treated in air at 300 ° C. for 1 hour in a hot air heating furnace.

Table 1 shows the results of evaluating the PAN resistance of the oxide semiconductor film manufactured in Example 4 and the performance of the thin film transistor.
For the thin film transistor manufactured in Example 4, the threshold voltage shift amount (V) (Vg = 20 V, 100 min) was measured by the following method. The results are shown in Table 1. The shift amount of the threshold voltage was defined as a shift voltage (Vth) after a 20 V voltage was applied to the gate electrode for 100 minutes.

Further, FIG. 4 shows a transfer curve of the thin film transistor manufactured in Example 4.
The transfer curve shows the relationship between the gate voltage (Vgs) and the drain current (Ids). FIG. 4 shows the drain current when the gate voltage is changed from -10V to 20V.

The thin film transistor of the present invention can be suitably used for sensors such as a display panel, an RFID tag, an X-ray detector panel, a fingerprint sensor, and a photosensor.
The method for manufacturing a thin film transistor of the present invention is particularly suitable for manufacturing a channel etch type thin film transistor.

It is a schematic sectional drawing which shows embodiment of the channel etch type thin-film transistor of this invention. It is a schematic sectional drawing which shows embodiment of the etch stopper type thin-film transistor of this invention. It is a schematic sectional drawing of the channel etch type thin-film transistor produced in Examples 1-3 and Comparative Examples 1-3. 6 is a diagram showing a transfer curve of a thin film transistor manufactured in Example 4. FIG. 6 is a schematic cross-sectional view of an etch stopper type thin film transistor fabricated in Example 4. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 20 Gate electrode 30 Gate insulating film 40 Semiconductor film 50 Source electrode 52 Drain electrode 60 Channel part 70 Etch stopper

Claims (9)

Oxide sintering made of an oxide semiconductor in which the atomic ratio of each element satisfies the following relationship with respect to the sum (In + Ga + Zn + Sn) of indium element (In), gallium element (Ga), zinc element (Zn), and tin element (Sn) body.
0.18 <In / (In + Ga + Zn + Sn) <0.79
0.00010 <Ga / (In + Ga + Zn + Sn) <0.27
0.060 <Zn / (In + Ga + Zn + Sn) <0.49
0.12 <Sn / (In + Ga + Zn + Sn) <0.40 The oxide sintered body according to claim 1, comprising an oxide semiconductor in which an atomic ratio of each element satisfies the following relationship.
0.18 <In / (In + Ga + Zn + Sn) <0.62
0.00010 <Ga / (In + Ga + Zn + Sn) <0.27
0.090 <Zn / (In + Ga + Zn + Sn) <0.49
0.12 <Sn / (In + Ga + Zn + Sn) <0.40   A sputtering target comprising the oxide sintered body according to claim 1. A thin film transistor made of an oxide semiconductor in which the atomic ratio of each element satisfies the following relationship with respect to the sum (In + Ga + Zn + Sn) of indium element (In), gallium element (Ga), zinc element (Zn), and tin element (Sn).
0.18 <In / (In + Ga + Zn + Sn) <0.79
0.00010 <Ga / (In + Ga + Zn + Sn) <0.27
0.060 <Zn / (In + Ga + Zn + Sn) <0.49
0.12 <Sn / (In + Ga + Zn + Sn) <0.40 The thin film transistor according to claim 4, comprising an oxide semiconductor in which an atomic ratio of each element satisfies the following relationship.
0.18 <In / (In + Ga + Zn + Sn) <0.62
0.0001 <Ga / (In + Ga + Zn + Sn) <0.27
0.090 <Zn / (In + Ga + Zn + Sn) <0.49
0.12 <Sn / (In + Ga + Zn + Sn) <0.40   The film forming step is performed by sputtering using the target made of the oxide sintered body according to claim 1 or 2, and the oxide semiconductor film is formed by setting the oxygen concentration during sputtering to 2 to 20% by volume. 6. A method for producing a thin film transistor according to 4 or 5.   The method for manufacturing a thin film transistor according to claim 6, wherein the oxide semiconductor film is heat-treated at 150 to 450 ° C. for 0.1 to 1200 minutes in the presence of oxygen.   The method for manufacturing a thin film transistor according to claim 6 or 7, which is a method for manufacturing a channel etch type thin film transistor.   The method of manufacturing a thin film transistor according to claim 6 or 7, which is a method of manufacturing an etch stopper type thin film transistor.

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