JP5947697B2 - Sputtering target - Google Patents

Description

  The present invention relates to a sputtering target, a semiconductor thin film, a manufacturing method thereof, a thin film transistor using the same, and a display device including the thin film transistor.

  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. Among them, with the development of display devices in recent years, not only liquid crystal display devices (LCD) but also various display devices such as electroluminescence display devices (EL) and field emission displays (FED), drive voltages are applied to display elements. Thin film transistors (TFTs) are frequently used as switching elements that are applied to drive display devices.

  Currently, silicon-based semiconductor thin films are most widely used for TFT drive elements. On the other hand, a transparent semiconductor thin film made of a metal oxide has attracted attention because of its high mobility and excellent surface uniformity.

  As a material for a metal oxide thin film, an IGZO system made of an oxide of indium, gallium and zinc is known. A sputtering target can be used for forming the metal oxide thin film, and an IGZO-based sputtering target has a high relative density and a low resistance, so that industrially useful DC sputtering is possible. However, since gallium is expensive, a metal thin film containing no gallium is required.

A sputtering target made of a metal oxide not containing gallium has been reported.
Non-Patent Document 1 describes a highly reliable TFT manufactured by RF magnetron sputtering using a sputtering target of Hf-indium zinc oxide. However, since the target containing Hf is prone to form aggregates of insulating materials, it is difficult to improve the density, and the resistance value is increased, a semiconductor thin film is formed by DC sputtering or AC sputtering. It was difficult to do.

  On the other hand, as a sputtering target made of a metal oxide not containing gallium and capable of DC sputtering, Patent Document 1 discloses a sputtering target capable of reducing nodules during sputtering. However, the thin film provided by this target is a conductive film and could not be used for the active layer of the TFT.

  As described above, there is a need for a high-density, low-resistance sputtering target that can be manufactured by DC or AC sputtering, which is made of a metal oxide not containing gallium and that exhibits good TFT characteristics. However, detailed target review was insufficient.

JP 2005-307269 A

Appl. Phys. Lett. 96,152102 (2010)

  An object of the present invention is to provide a sputtering target with high density and low resistance.

According to the present invention, the following sputtering target and the like are provided.
1. Containing an oxide comprising indium, zinc and metal M;
A sputtering target including a sintered body containing In ₂ O ₃ , MIn ₂ O ₄ and In ₂ O ₃ (ZnO) _m (1 ≦ m ≦ 20) as a crystal phase and having a relative density of 95% or more. ,
The sintered body includes a structure having a higher In content than the surroundings, a structure having a higher Zn content than the surroundings, and a structure having a higher metal M content than the surroundings.
Sputtering target in which the average diameter of the circle that minimizes the area including the structure with a large amount of In and the average diameter of the circle that includes the structure with a high content of the metal M and that has the minimum area is 25 μm or less. .
2. 2. The sputtering target according to 1, wherein an average diameter of a circle having a minimum area including a structure containing a large amount of In is 10 μm or less.
3. Intensity ratio _I 2 / _{I 1} of the maximum peak intensity _{I 1} of the _MIn 2 _{O 4} in the X-ray diffraction _In 2 _O 3 _(ZnO) maximum peak intensity of the _{m I 2} is located at 0.2 to 2.0 3. The sputtering target according to 1 or 2, comprising a sintered body.
4). The atomic ratio represented by In / (In + Zn + M) is 0.75 or less, the atomic ratio represented by Zn / (In + Zn + M) is 0.70 or less, and the atomic ratio represented by M / (In + Zn + M) is The sputtering target according to any one of 1 to 3, which is 0.01 to 0.30.
5. The sputtering target according to any one of 1 to 4, wherein the metal M is one or more selected from Mg, Ca, Sr, Cu, Ni, Co, Be, and Fe.
6). 6. The sputtering target according to 5, wherein the metal M is Mg.
7). Containing an oxide comprising indium, zinc and metal M;
The atomic ratio represented by In / (In + Zn + M) is 0.75 or less, the atomic ratio represented by Zn / (In + Zn + M) is 0.70 or less, and the atomic ratio represented by M / (In + Zn + M) is 0.01-0.30,
A semiconductor thin film having a hole mobility of 3 cm ² / V · sec or more.
8). 8. The semiconductor thin film according to 7, which is amorphous.
9. The semiconductor thin film according to 7 or 8, wherein the metal M is one or more selected from Mg, Ca, Sr, Cu, Ni, Co, Be, and Fe.
10. 10. The semiconductor thin film according to 9, wherein the metal M is Mg.
11. The semiconductor thin film is formed by sequentially transporting the substrate to a position facing three or more targets arranged in parallel in the vacuum chamber at a predetermined interval, and a negative potential is supplied to each target from an AC power source. When alternately applying a positive potential and at least one of the outputs from the AC power source, the target to which the potential is applied is switched between two or more targets branched and connected. The manufacturing method of the semiconductor thin film in any one of 7-10 performed by the sputtering method which produces | generates a plasma and forms into a film on the substrate surface.
12 12. The method for producing a semiconductor thin film according to 11, wherein the AC power density of the AC power source is 3 W / cm ² or more and 20 W / cm ² or less.
13. The manufacturing method of the semiconductor thin film of 11 or 12 whose frequency of the said AC power supply is 10 kHz-1 MHz.
A thin film transistor using the semiconductor thin film according to any one of 14.7 to 10.
A thin film transistor using a protective film containing at least SiNx on the semiconductor thin film according to any one of 15.7 to 10.
16. A display device comprising the thin film transistor according to 14.14 or 15.

  According to the present invention, a sputtering target having high density and low resistance can be provided.

It is a figure which shows the sputtering device used for one Embodiment of this invention. 2 is an X-ray chart of a sintered body obtained in Example 1. 2 is an EPMA image of the sintered body obtained in Example 1. 6 is an X-ray chart of a sintered body obtained in Comparative Example 4.

The sputtering target of the present invention comprises a sintered body, the sintered body contains an oxide containing indium, zinc and metal _{M, In 2 O 3, MIn} 2 O 4 and _{In 2 O 3 (ZnO) m} ( 1 ≦ m ≦ 20) as a crystal phase.
In addition, the sintered body has a structure in which the In content is higher than that of the surroundings (In rich structure), a structure in which the Zn content is higher than that of the surroundings (Zn rich structure), and a structure in which the content of the metal M is higher than that of the surroundings. (M-rich tissue), the size of the In-rich tissue (the average diameter of the circle that minimizes the area including the In-rich tissue), and the size of the M-rich tissue (the area including the M-rich tissue is the minimum) The average diameter of the circles is 25 μm or less.
The sintered body used in the present invention has a relative density of 95% or more.

The sintered body used in the present invention includes In ₂ O ₃ , MIn ₂ O ₄ and In ₂ O ₃ (ZnO) _m (m is 1 ≦ m ≦ 20) as a crystal phase, and includes an In-rich structure, a Zn-rich structure, and By including the M-rich structure and the In-rich structure and the M-rich structure having a predetermined size, each element can be easily dispersed, the target density can be increased, and the target resistance can be reduced.

It can be confirmed by X-ray diffraction measurement that In ₂ O ₃ , MIn ₂ O ₄ and In ₂ O ₃ (ZnO) _m (m is 1 ≦ m ≦ 20) are included as crystal phases. The crystal structure can be confirmed as follows. Further, the X-ray diffraction measurement can be specifically performed by the method described in the examples.

The crystal structure can be confirmed, for example, because the X-ray diffraction pattern of the target (sintered body) matches the assumed crystal structure X-ray diffraction pattern.
Specifically, it can be confirmed from the coincidence with a crystal structure X-ray diffraction pattern obtained from a JCPDS (Joint Committee of Powder Diffraction Standard) card or an ICSD (The Inorganic Crystal Structure Database).

The crystal phase of In ₂ O ₃ has a bixbite structure.
The bixbite structure can be confirmed by observing the peak of the bixbite structure compound as a result of X-ray diffraction measurement of the sintered body.

Bixbyte is also referred to as rare earth oxide C-type or Mn ₂ O ₃ (I) -type oxide. As disclosed in “Technology of Transparent Conductive Films” (Ohm Publishing Co., Ltd., Japan Society for the Promotion of Science, Transparent Oxide / Optoelectronic Materials 166th Committee, 1999), the stoichiometric ratio is M ₂ X ₃ (M is a cation, X is an anion, usually an oxygen ion), and one unit cell is composed of 16 molecules of M ₂ X ₃ , a total of 80 atoms (M is 32, X is 48) Yes.

The bixbite structure is X-ray diffraction, and the JCPDS database No. A peak pattern of 06-0416 or a similar (shifted) pattern is shown.
The bixbite structure compound also includes a substitutional solid solution in which atoms and ions in the crystal structure are partially substituted with other atoms, and an interstitial solid solution in which other atoms are added to interstitial positions.

Similarly, it can be confirmed by X-ray diffraction measurement that crystals having a composition of MIn ₂ O ₄ are included, but a plurality of crystal phases of MIn ₂ O ₄ may be observed by X-ray diffraction measurement.
For example, the crystal structure having a composition of MgIn ₂ O _4, according to the JCPDS card and _ICSD, In ₂ MgO 4 (JCPDS card: 40-1402) or _{MgIn 2 O 4 (ICSD: ♯24992} ) but such is present , Both are crystals of MgIn ₂ O ₄ composition.

Examples of the crystal phase comprising the composition of MIn ₂ O ₄ include a spinel structure and an inverse spinel structure.
The spinel structure is an ionic crystal having a composition of AB ₂ O ₄ when A is a divalent cation and B is a trivalent cation, and is a tetrahedral gap of a three-dimensional face-centered lattice formed by O ²⁻ . One-eighth is filled with A and half of the octahedral gap is filled with B. The reverse spinel structure is an ionic crystal having a composition of AB ₂ O ₄ like the spinel structure. B is filled in one-eighth of the tetrahedral gap and A and B are filled in one-half of the octahedral gap. Has a structured.

When the sintered body of the present invention includes a crystal phase having a composition of MIn ₂ O ₄ , it is possible to suppress an increase in resistance of the target due to the appearance of the metal M oxide in a single region.

Examples of the crystal phase of In ₂ O ₃ (ZnO) _m (1 ≦ m ≦ 20) include a crystal phase derived from a homologous structure.
A crystal phase derived from a homologous structure is a crystal having a “natural superlattice” structure having a long period in which several crystal layers of different substances are stacked. When the crystal cycle or thickness of each thin film layer is on the order of nanometers, depending on the combination of the chemical composition of these layers and the thickness of the layers, it differs from the properties of a single crystal or a mixed crystal in which each layer is uniformly mixed. May show unique characteristics.

  The crystal structure of the homologous phase can be confirmed, for example, because the X-ray diffraction pattern measured for the target pulverized product or the cut piece matches the crystal structure X-ray diffraction pattern of the homologous phase assumed from the composition ratio. Specifically, it can be confirmed from the coincidence with the crystal structure X-ray diffraction pattern of the homologous phase obtained from the JCPDS card.

M of In ₂ O ₃ (ZnO) _m is preferably 3 to 10, and more preferably 3. When m is 3 to 10, the resistance of the target can be more easily lowered.

The sintered body used in the present invention has a structure with a large In content (In rich structure), a structure with a large Zn content (Zn rich structure), and a structure with a large amount of metal M (M rich structure). It is a mixed state.
By making the Zn-rich structure and the M-rich structure present in the target (sintered body), it is possible to suppress an increase in resistance due to the appearance of zinc oxide and metal M oxide in individual regions. The presence or absence of an In rich structure, a Zn rich structure, or an M rich structure can be confirmed by a dispersion map using EPMA.

  The In-rich structure is a continuous region showing a characteristic X-ray intensity of 70% or more with respect to the strongest characteristic X-ray intensity exhibited by In in the structure. The Zn-rich structure is the strongest exhibited by Zn in the structure. The M-rich structure is a continuous region showing a characteristic X-ray intensity of 70% or more with respect to the characteristic X-ray intensity of 70% or more of the strongest characteristic X-ray intensity exhibited by the metal M in the structure. It is a continuous region showing the characteristic X-ray intensity.

The In-rich structure has a lower oxygen content than the other tissues, and the Zn-rich structure has a higher oxygen content than the other tissues. Therefore, the In-rich structure is In ₂ O ₃ , and the Zn-rich structure is In _2. It can be seen that the O ₃ (ZnO) _m and M rich structures correspond to MIn ₂ O ₄ , respectively.

  In addition, since the In-rich structure and the M-rich structure form a region having a size of 25 μm or less, a target with good dispersibility can be obtained. Preferably, the sizes of the In-rich structure and M-rich structure regions are each 20 μm or less, more preferably 15 μm or less, and still more preferably 10 μm or less. When the size of the region of the In rich structure and the M rich structure is in the above range, nodules are hardly generated.

The In-rich structure and the M-rich structure need only form a region having a size of 25 μm or less, and the size of the Zn-rich structure may be more than 25 μm.
Even if the size of the Zn-rich structure is more than 25 μm, the structure is connected in a network shape, and another structure of 25 μm or less is formed therein, so that a target with good dispersibility can be obtained.

  The size of the region is defined as an average diameter when a circle having a minimum area including a rich tissue is drawn in an EPMA image having a length of 100 μm and a width of 100 μm. However, the number of diameters used when calculating the average is at least five, and when the area of the rich tissue is less than 40% of the area of the circle, it is not used for calculating the average.

The sintered body used in the present invention has a relative density of 95% or more. In particular, when an oxide semiconductor is formed by increasing the sputtering output on a large substrate (1G size or more), the relative density is preferably 95% or more.
The relative density is a density calculated relative to the theoretical density calculated from the weighted average. The density calculated from the weighted average of the density of each raw material is the theoretical density, which is defined as 100%.
If the relative density is 95% or more, a stable sputtering state is maintained. When forming a film with a large substrate and increasing the sputtering output, if the relative density is less than 95%, the target surface may be blackened or abnormal discharge may occur. The relative density is preferably 97% or more, more preferably 98% or more.

Further, the sintered body used in the present invention, preferably, the maximum peak intensity of _MIn 2 _{O 4} in the X-ray diffraction _{I 1} and _In 2 _O 3 _(ZnO) intensity ratio of the maximum peak intensity _{I 2} of _{m I} 2 / I ₁ is 0.2-2.0, More preferably, it is 0.25-1.8, More preferably, it is 0.8-1.7. By setting it as such a range, the dispersibility of the metal M and Zn in a target becomes good, and target resistance becomes easy to fall.
Dispersibility can be confirmed by dispersion MAP of In, Zn, metals M, and O using an electronic probe microanalyzer (EPMA).

The I _{2 /} I ₁ can be determined by from the chart obtained by X-ray diffraction measurement, is calculated from the maximum peak intensity existing in an arbitrary range (e.g., range of 2θ = 15~65 °).

  In the sintered body used in the present invention, the atomic ratio In / (In + Zn + M) is preferably 0.75 or less, more preferably 0.70 or less, further preferably 0.65 or less, and 0.60 or less. Is more preferable. The atomic ratio is preferably 0.20 or more, more preferably 0.25 or more, and further preferably 0.30 or more.

  In the sintered body used in the present invention, the atomic ratio Zn / (In + Zn + M) is preferably 0.70 or less, more preferably 0.60 or less, and further preferably 0.45 or less. The atomic ratio is preferably 0.05 or more, more preferably 0.10 or more, and further preferably 0.20 or more.

  In the sintered body used in the present invention, the atomic ratio M / (In + Zn + M) is preferably 0.01 to 0.30, and more preferably 0.03 to 0.25.

When In / (In + Zn + M) is set to the above value, the target resistance is preferably reduced. When Zn / (In + Zn + M) is set to the above value, it is preferable because the target density is improved. Further, it is preferable to set M / (In + Zn + M) to the above value because the density of the target is improved and generation of nodules during sputtering can be suppressed.
The atomic ratio can be measured by ICP (inductively coupled plasma) emission spectrometry.

  The metal M is preferably 1 or more selected from Mg, Ca, Sr, Cu, Ni, Co, Be, and Fe. The metal M may be only one of these, or two or more.

  The metal M is more preferably Mg. The density of the sputtering target can be further improved by selecting Mg.

  In addition, the sintered compact used for this invention contains the oxide selected from the oxide of indium oxide, zinc oxide, and the metal M, and 2 or more metal complex oxides of indium, zinc, and the metal M.

  In the sintered body used in the present invention, other metal elements (for example, gallium, tin, titanium, silicon, chromium, cadmium, lead, other than In, Zn, and metal M described above, as long as the effects of the present invention are not impaired). (Calcium, zirconium, etc.) may be contained. However, the metal element contained in the sintered body may be substantially only In, Zn and metal M, or only In, Zn and metal M.

In the present invention, “substantially” means that the effect as a sputtering target is caused by the above In, Zn and metal M, or 95 wt% or more and 100 wt% or less (preferably 98 wt% or more of the metal element of the sputtering target). 100% by weight or less) is In, Zn and metal M.
In addition, the metal element contained in the sintered body used in the present invention is composed only of In, Zn, and metal M, and may contain other inevitable impurities as long as the effects of the present invention are not impaired.

  In the sputtering target of the present invention, for example, each powder (raw material powder) (preferably oxide) of an indium compound, a zinc compound and a metal M compound is mixed and pulverized to prepare a mixture, and the mixture is formed into a desired shape. It can be manufactured by forming into a green body and sintering.

  The indium compound powder that is a raw material is not particularly limited, and commercially available products can be used. However, it is preferable that the raw material has a high purity, for example, 4N (0.9999) or more. In addition to oxides, indium salts such as indium chloride, indium nitrate, and indium acetate may be used.

  The zinc compound powder as a raw material is not particularly limited, and those commercially available can be used. However, it is preferable that the zinc compound powder has a high purity, for example, 4N (0.9999) or more. Further, zinc salts such as zinc chloride and zinc nitrate may be used.

Examples of the metal M compound include MgO, CaO, SrO, CuO, NiO, CoO, BeO, FeO, Mg (NO ₃ ) ₂ , Ca (NO ₃ ) ₂ , Sr (NO ₃ ) ₂ , Cu (NO _3). ) ₂ , Ni (NO ₃ ) ₂ , Co (NO ₃ ) ₂ , Be (NO ₃ ) ₂ , Fe (NO ₃ ) _{2 and the} like.

  The mixing and pulverization can be performed using a known device such as a ball mill, a bead mill, a jet mill, or an ultrasonic device. Conditions such as pulverization time may be adjusted as appropriate, but about 6 to 100 hours are preferable.

  The mixing ratio of each raw material is such that the atomic ratio In / (In + Zn + M) is 0.75 or less, the atomic ratio Zn / (In + Zn + M) is 0.70 or less, and the atomic ratio M / (In + Zn + M) is 0.01 to 0.30. Thus, it is preferable to mix each raw material powder. In addition, you may add another component in the range which does not impair the effect of this invention.

The raw material prepared in the above mixing step is molded and sintered to obtain an oxide sintered body.
In the molding step, the mixed powder is pressure-molded to form a molded body. By this step, the product is formed into a product shape (for example, a shape suitable as a target).

Examples of the molding process include mold molding, cast molding, and injection molding. In order to obtain a sintered body (target) having a high sintering density, molding is performed by cold isostatic pressure (CIP) or the like. Is preferred.
In the molding process, molding aids such as polyvinyl alcohol, methylcellulose, polywax, and oleic acid may be used.

A sintering process is a process of baking the molded object obtained at the said formation process.
As sintering conditions, the sintering is usually performed at 1200 to 1550 ° C. for 30 minutes to 360 hours, preferably 8 to 180 hours, and more preferably 12 to 96 hours in an oxygen gas atmosphere or oxygen gas pressurization.

  When the sintering temperature is 1200 ° C. or higher, the target density is likely to increase, and the sintering does not take too long. On the other hand, when the temperature is 1550 ° C. or lower, it is possible to prevent the composition from shifting or the furnace from being damaged due to vaporization of the components.

  When the sintering time is 30 minutes or more, the density of the target is likely to increase, and when it is 360 hours or less, the production time and cost can be in appropriate ranges. In addition, the bulk resistance can be lowered within the above range.

  The heating rate during firing is usually 8 ° C./min or less, preferably 4 ° C./min or less, more preferably 3 ° C./min or less, and further preferably 2 ° C./min or less. If it is 8 ° C./min or less, cracks are unlikely to occur.

The temperature decreasing rate during firing is usually 4 ° C./min or less, preferably 2 ° C./min or less, more preferably 1 ° C./min or less, still more preferably 0.8 ° C./min or less, particularly preferably 0.5 C / min or less. If it is 4 ° C./min or less, cracks are unlikely to occur.
Note that the temperature increase or decrease may be changed step by step.

A sputtering target is obtained by processing the oxide sintered body into a desired shape as necessary.
The processing is performed to cut the oxide sintered body into a shape suitable for mounting on a sputtering apparatus and to attach a mounting jig such as a backing plate. In order to use an oxide sintered body as a sputtering target, 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 sputtering target may be mirror-finished so that the average surface roughness Ra is 1000 angstroms or less. A smaller average surface roughness is preferable because particles generated at the initial stage of sputtering film formation can be reduced.

  The grinding is preferably performed by 0.1 mm or more, more preferably by 0.3 mm or more, further preferably by 0.5 mm or more, and particularly preferably by 1 mm or more. By grinding 0.1 mm or more, it is possible to remove a composition-shifted portion in the vicinity of the surface, which is generated when a component such as zinc is vaporized.

  The obtained sputtering target is bonded to a backing plate. The thickness of the target is usually 2 to 20 mm, preferably 3 to 12 mm, particularly preferably 4 to 10 mm. Further, a plurality of targets may be attached to one backing plate to substantially serve as one target.

The semiconductor thin film of the present invention contains an oxide containing indium, zinc and metal M, has an atomic ratio represented by In / (In + Zn + M) of 0.75 or less, and atoms represented by Zn / (In + Zn + M). The ratio is 0.70 or less, and the atomic ratio represented by M / (In + Zn + M) is 0.01 to 0.30.
By setting the semiconductor thin film to such a composition, good semiconductor characteristics with high mobility and high uniformity can be obtained.

In addition, the semiconductor thin film of the present invention has a hole mobility of 3 cm ² / V · sec or more, preferably 5 cm ² / V · sec or more, more preferably 7 cm ² / V · sec or more.
The hole mobility can be measured by the method described in the examples.

  The semiconductor thin film of the present invention includes an oxide selected from an oxide of indium oxide, zinc oxide and metal M, and a composite oxide of two or more metals of indium, zinc and metal M.

  In the semiconductor thin film of the present invention, the atomic ratio In / (In + Zn + M) is preferably 0.75 or less, more preferably 0.70 or less, further preferably 0.65 or less, and 0.60 or less. And more preferred. The atomic ratio is preferably 0.20 or more, more preferably 0.25 or more, and further preferably 0.30 or more.

  In the semiconductor thin film of the present invention, the atomic ratio Zn / (In + Zn + M) is preferably 0.70 or less, and more preferably 0.60 or less. The atomic ratio is preferably 0.05 or more, more preferably 0.10 or more, and further preferably 0.20 or more.

In the semiconductor thin film of the present invention, the atomic ratio M / (In + Zn + M) is preferably 0.01 to 0.30, and more preferably 0.03 to 0.25.
When In / (In + Zn + M) is set to the above value, it is preferable because mobility increases. When Zn / (In + Zn + M) is set to the above value, it is preferable because a residue hardly remains during wet etching. Further, it is preferable to set M / (In + Zn + M) to the above value because the in-plane variation in TFT characteristics can be reduced.
The atomic ratio can be measured by ICP (inductively coupled plasma) emission spectrometry.

The metal M is preferably 1 or more selected from Mg, Ca, Sr, Cu, Ni, Co, Be, and Fe. The metal M may be only one of these, or two or more.
The metal M is more preferably Mg. When the semiconductor thin film contains Mg, the change of the semiconductor thin film with time (deterioration of the characteristics of the thin film) can be reduced.

  The semiconductor thin film of the present invention is preferably amorphous. Amorphous is preferable because the uniformity of the film surface is good and in-plane variations in TFT characteristics can be reduced. Amorphousness can be confirmed from the fact that a halo pattern is observed by X-ray diffraction measurement and does not show a specific diffraction peak.

  The semiconductor thin film of the present invention may contain a metal element other than In, Zn and metal M described above as long as the effects of the present invention are not impaired. However, the metal element contained in the semiconductor thin film may be substantially only In, Zn and metal M, or only In, Zn and metal M.

In the present invention, “substantially” means that the effect as a semiconductor thin film is attributed to the above In, Zn and metal M, or 95 wt% to 100 wt% (preferably 98 wt% or more of the metal element of the semiconductor thin film). 100% by weight or less) is In, Zn and metal M.
Further, the metal element contained in the semiconductor thin film of the present invention is composed of only In, Zn, and metal M, and may contain other inevitable impurities as long as the effects of the present invention are not impaired.

By sputtering the target such as a substrate using the sputtering target of the present invention, the semiconductor thin film of the present invention can be formed. By using the sputtering target of the present invention, the oxygen concentration during film formation can be suppressed.
For example, the oxygen concentration during sputtering is usually about 1 to 50%, but in the present invention, it can be about 1 to 30%.

The oxide semiconductor thin film may be formed by AC sputtering as follows.
The substrate is sequentially transported to a position facing three or more targets arranged in parallel at a predetermined interval in the vacuum chamber, and negative and positive potentials are alternately applied to each target from an AC power source. Then, plasma is generated on the target to form a film on the substrate surface.
At this time, at least one of the outputs from the AC power supply is performed while switching a target to which a potential is applied between two or more targets that are branched and connected. That is, at least one of the outputs from the AC power supply is branched and connected to two or more targets, and film formation is performed while applying different potentials to adjacent targets.

When the film is formed by AC sputtering, an oxide layer having industrially excellent large area uniformity can be obtained, and improvement in the utilization efficiency of the target can be expected.
Further, when sputtering film formation is performed on a large-area substrate having a side exceeding 1 m, it is preferable to use an AC sputtering apparatus for large-area production as described in, for example, JP-A-2005-290550.

  Specifically, the AC sputtering apparatus described in JP-A-2005-290550 includes a vacuum chamber, a substrate holder disposed inside the vacuum chamber, and a sputtering source disposed at a position facing the substrate holder. . FIG. 1 shows a main part of a sputtering source of an AC sputtering apparatus. The sputter source has a plurality of sputter units, each of which has plate-like targets 31a to 31f, and the surfaces to be sputtered of the targets 31a to 31f are sputter surfaces. It arrange | positions so that it may be located in. Each target 31a to 31f is formed in an elongated shape having a longitudinal direction, each target has the same shape, and the edge portions (side surfaces) in the longitudinal direction of the sputtering surface are arranged in parallel at a predetermined interval. Therefore, the side surfaces of the adjacent targets 31a to 31f are parallel.

  AC power supplies 17a to 17c are arranged outside the vacuum chamber, and one of the two terminals of each AC power supply 17a to 17c is connected to one of the two adjacent electrodes, The other terminal is connected to the other electrode. Two terminals of each of the AC power supplies 17a to 17c output voltages having different polarities, and the targets 31a to 31f are attached in close contact with the electrodes, so that the two adjacent targets 31a to 31f are adjacent to each other. AC voltages having different polarities are applied from the AC power sources 17a to 17c. Accordingly, when one of the targets 31a to 31f adjacent to each other is placed at a positive potential, the other is placed at a negative potential.

  Magnetic field forming means 40a to 40f are arranged on the surface of the electrode opposite to the targets 31a to 31f. Each of the magnetic field forming means 40a to 40f includes an elongated ring-shaped magnet whose outer periphery is substantially equal to the outer periphery of the targets 31a to 31f, and a bar-shaped magnet shorter than the length of the ring-shaped magnet.

  Each ring-shaped magnet is arranged in parallel with the longitudinal direction of the targets 31a to 31f at a position directly behind the corresponding one of the targets 31a to 31f. As described above, since the targets 31a to 31f are arranged in parallel at a predetermined interval, the ring-shaped magnets are also arranged at the same interval as the targets 31a to 31f.

The AC power density when an oxide target is used in AC sputtering is preferably 3 W / cm ² or more and 20 W / cm ² or less. When the power density is 3 W / cm ² or more, the film forming speed is high, which is economical in production. If it is 20 W / cm ² or less, damage to the target can be prevented. More preferred power density is ^{3W / cm 2 ~15W / cm 2} .

  The frequency of AC sputtering is preferably in the range of 10 kHz to 1 MHz. If it is 10 kHz or more, the problem of noise hardly occurs. When the frequency is 1 MHz or less, plasma does not spread too much, and sputtering is performed at a desired target position, so that uniformity is easily maintained. A more preferable frequency of AC sputtering is 20 kHz to 500 kHz.

  The oxide thin film of the present invention can be used for a transparent electrode, a semiconductor layer of a thin film transistor, an oxide thin film layer, and the like. Among these, it can be suitably used as a semiconductor layer of a thin film transistor.

Said oxide thin film can be used for a thin-film transistor (TFT), and can be used especially suitably as a semiconductor layer (channel layer).
If the thin-film transistor of this invention has said oxide thin film, the element structure will not be specifically limited, Various well-known element structures are employable. The thin film transistor of the present invention preferably has the above oxide thin film as a channel layer.

  The film thickness of the channel layer in the thin film transistor of the present invention is usually 10 to 300 nm, preferably 20 to 250 nm, more preferably 30 to 200 nm, still more preferably 35 to 120 nm, and particularly preferably 40 to 80 nm. When the film thickness of the channel layer is 10 nm or more, the film thickness is uniform even when the film is formed in a large area, and the characteristics of the manufactured TFT are easily made uniform in the plane. On the other hand, when the film thickness is 300 nm or less, the film formation time is appropriate and industrially preferable.

  The channel layer in the thin film transistor of the present invention is usually used in an N-type region, but a PN junction transistor or the like 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 be used for various semiconductor devices.

The thin film transistor of the present invention preferably includes a protective film on the channel layer. The protective film in the thin film transistor of the present invention preferably contains at least SiN _x . Since SiN _x can form a dense film as compared with SiO ₂ , it has an advantage of a high TFT deterioration suppressing effect.

In addition to SiN _x , the protective film may be, for example, SiO ₂ , 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, It may contain oxides such as Sc ₂ O ₃ , Y ₂ O ₃ , HfO ₂ , CaHfO ₃ , PbTi ₃ , BaTa ₂ O ₆ , Sm ₂ O ₃ , SrTiO _3, or AlN, but substantially SiN _x. It is preferable that it consists only of. Here, “consisting essentially of SiN _x ” means that 70 wt% or more, preferably 80 wt% or more, more preferably 85 wt% or more of the thin film constituting the protective layer in the thin film transistor of the present invention is SiN _x. Means.

Before forming the protective film, the channel layer is preferably subjected to ozone treatment, oxygen plasma treatment, nitrogen dioxide plasma treatment, or nitrous oxide plasma treatment. Such treatment may be performed at any timing after the channel layer is formed and before the protective film is formed, but is preferably performed immediately before the protective film is formed. By performing such pretreatment, generation of oxygen defects in the channel layer can be suppressed.
Further, when hydrogen in the oxide semiconductor film diffuses during driving of the TFT, a threshold voltage shift may occur and the reliability of the TFT may be reduced. By performing ozone treatment, oxygen plasma treatment, or nitrous oxide plasma treatment on the channel layer, the bond of In—OH is stabilized in the crystal structure, and diffusion of hydrogen in the oxide semiconductor film can be suppressed. it can.

  A thin film transistor usually includes a substrate, a gate electrode, a gate insulating layer, an organic semiconductor layer (channel layer), a source electrode, and a drain electrode. The channel layer is as described above, and a known material can be used for the substrate.

The material for forming the gate insulating film in the thin film transistor of the present invention is not particularly limited, and a commonly used material can be arbitrarily selected. Specifically, for _{example, SiO 2, SiN x, 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, A compound such as Sc ₂ O ₃ , Y ₂ O ₃ , HfO ₂ , CaHfO ₃ , PbTi ₃ , BaTa ₂ O ₆ , SrTiO ₃ , Sm ₂ O ₃ , or AlN can be used. Among them, preferred are _{SiO 2, SiN x, Al 2} O 3, Y 2 O 3, HfO 2, CaHfO 3, more preferably _{SiO 2, SiN x, HfO 2} , Al 2 O 3.

The gate insulating film can be formed by, for example, a plasma CVD (Chemical Vapor Deposition) method.
When a gate insulating film is formed by plasma CVD and a channel layer is formed on the gate insulating film, hydrogen in the gate insulating film may diffuse into the channel layer, leading to deterioration in channel layer quality and TFT reliability. is there. In order to prevent deterioration in channel layer quality and TFT reliability, the gate insulating film may be subjected to ozone treatment, oxygen plasma treatment, nitrogen dioxide plasma treatment or nitrous oxide plasma treatment before forming the channel layer. preferable. By performing such pretreatment, it is possible to prevent deterioration of the channel layer film quality and TFT reliability.
Note that the number of oxygen in the oxide does not necessarily match the stoichiometric ratio, and may be, for example, SiO ₂ or SiO _x .

  The gate insulating film may have a structure in which two or more insulating films made of different materials are stacked. The gate insulating film may be crystalline, polycrystalline, or amorphous, but is preferably polycrystalline or amorphous that can be easily manufactured industrially.

There are no particular limitations on the material for forming each of the drain electrode, the source electrode, and the gate electrode in the thin film transistor of the present invention, and a commonly used material can be arbitrarily 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, the source electrode, and the gate electrode can have a multilayer structure in which two or more different conductive layers are stacked. In particular, since the source / drain electrodes have 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 thin film transistor of the present invention can be applied to various integrated circuits such as a field effect transistor, a logic circuit, a memory circuit, and a differential amplifier circuit. Further, in addition to the field effect transistor, it can be applied to an electrostatic induction transistor, a Schottky barrier transistor, a Schottky diode, and a resistance element.

  As the structure of the thin film transistor of the present invention, known structures such as a bottom gate, a bottom contact, and a top contact can be adopted without limitation.

  In particular, the bottom gate structure is advantageous because high performance can be obtained as compared with thin film transistors of amorphous silicon or ZnO. 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.

  For large-area displays, a channel-etched bottom gate thin film transistor is particularly preferable. A channel-etched bottom gate thin film transistor has a small number of photomasks at the time of a photolithography process, and can produce a display panel at a low cost. Among them, a channel-etched bottom gate structure and a top contact structure thin film transistor are particularly preferable because they have good characteristics such as mobility and are easily industrialized.

  The thin film transistor of the present invention can be suitably used for a display device such as a liquid crystal display or an organic EL display.

Examples 1-8
In ₂ O ₃ powder having an average particle size of 1 μm or less, ZnO powder having an average particle size of 1 μm or less, and MgO powder having an average particle size of 1 μm or less were weighed so as to have the atomic ratio shown in Table 1, and mixed. placed in a resin pot, in addition to water, it was wet ball mill mixing using a hard ZrO ₂ balls. The mixing time was 20 hours.
The obtained mixed slurry was taken out, filtered, dried and granulated. The obtained granulated product was put into a mold and molded by applying a pressure of 3 ton / cm ² with a cold isostatic press to obtain a molded product.

The obtained molded body was sintered as follows. First, the compact was placed in a sintering furnace, and oxygen was introduced at a rate of 5 liters / minute per volume of 0.1 m ³ in the sintering furnace. In this atmosphere, the molded body was sintered at 1400 ° C. for 24 hours.
At this time, the temperature in the sintering furnace was increased at a rate of 0.5 ° C./min up to 800 ° C., and was increased at a rate of 1 ° C./min from 1000 ° C. to 1400 ° C. Then, after sintering for 24 hours at 1400 ° C., the temperature was naturally lowered.

  When the content of each atom in the obtained sintered body was quantitatively analyzed by ICP (inductively coupled plasma) emission spectrometry, the charged composition when mixing the raw material powder was maintained even in the sintered body. It could be confirmed.

Moreover, the X-ray-diffraction measurement was performed about the obtained sintered compact.
The X-ray diffraction chart obtained in Example 1 is shown in FIG. In FIG. 2, the vertical axis represents the intensity of the diffracted X-ray, and the horizontal axis represents the angle of the diffracted X-ray. In the sintered body of Example 1, crystals of In ₂ O ₃ , In ₂ MgO ₄ and In ₂ O ₃ (ZnO) ₃ were confirmed. These crystals were also confirmed in the sintered bodies of Examples 2 to 8. The results are shown in Table 1.

_Further, the maximum peak intensity _{I 1} of an In 2 MgO _4, the ratio of In ₂ O 3 _{(ZnO) 2} of the maximum peak intensity _{I 2 was} I ₂ / I 1 = 1.6. I ₂ / I ₁ was also calculated for the sintered bodies of Examples 2 to 8. The results are shown in Table 1.

X-ray diffraction measurement was performed with the following apparatus and conditions.
Device: Rigaku Ultima-III
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

Further, the sintered body obtained in Example 1 was observed with an electron probe microanalyzer (EPMA), and the state of dispersion of In, Zn, Mg, and O was examined. The obtained EPMA image is shown in FIG.
As a result, an In rich structure, a Zn rich structure, and an Mg rich structure were observed. The size of the In-rich structure was 5 μm or less, and the size of the Mg-rich structure was 9 μm. Furthermore, the Zn-rich structure is connected in a network shape, and since an In-rich structure and an Mg-rich structure of 25 μm or less are present in the inside, it was confirmed that the dispersibility is good.
Also in Examples 2 to 8, it was found that an In-rich structure, a Zn-rich structure, and an Mg-rich structure exist, and the dispersibility is good from the size of each region. Table 1 shows the sizes of the In-rich structure, the Zn-rich structure, and the Mg-rich structure.

  The relative density of the obtained sintered body was measured by the Archimedes method. Moreover, the bulk specific resistance (conductivity) was measured based on the four-probe method (JIS R 1637) using a resistivity meter (manufactured by Mitsubishi Chemical Corporation, Loresta). The results are shown in Table 1.

  Next, the sputtering surface of the sintered body was polished with a cup grindstone, processed to a diameter of 100 mm and a thickness of 5 mm, and a backing plate was bonded using an In-based alloy to produce a sputtering target.

The obtained target was mounted on a DC sputtering apparatus, and a semiconductor thin film having a thickness of 50 nm was formed on a glass slide at room temperature.
In addition, the voltage fluctuation was monitored during the sputter film formation to examine the presence or absence of abnormal discharge, but no abnormal discharge was observed. In addition, the case where voltage fluctuation was 10% or more with respect to the steady voltage was defined as abnormal discharge.
Further, as a result of X-ray diffraction measurement of the deposited semiconductor thin film, it was found that no peak was observed and the semiconductor thin film was amorphous.
ICP analysis also confirmed that the atomic ratio of the sintered body was maintained in the semiconductor thin film.

Gold was vapor-deposited on the obtained thin film, annealed at 300 ° C. for 1 hour, and then the Hall effect was evaluated by a Van der Paw method using a ResiTest 8300 type (manufactured by Toyo Technica Co., Ltd.) at room temperature and atmospheric pressure. As a result, the hole mobility of Example 1 was 23 cm ² / V · sec. It measured similarly about Examples 2-8. The results are shown in Table 1.

Next, a thin film transistor was manufactured using the above target as follows.
Using a target, a DC sputtering film was formed on a conductive silicon substrate with a thermal oxide film having a thickness of 100 nm to produce an amorphous thin film having a thickness of 50 nm. The sputtering conditions are as follows. The oxygen partial pressure during film formation is shown in Table 1.
Substrate temperature: 25 ° C
Ultimate pressure: 8.5 × 10 ⁻⁵ Pa
Atmospheric gas: Ar gas, O ₂ gas Sputtering pressure (total pressure): 0.4 Pa
Input power: DC50W
S (substrate) -T (target) distance: 100 mm

  OFPR # 800 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) was used as a resist, and coating, pre-baking (80 ° C., 5 minutes), and exposure were performed. After development, it was post-baked (120 ° C., 5 minutes), etched with oxalic acid, and patterned into a desired shape. Thereafter, heat treatment (annealing treatment) was performed at 300 ° C. for 60 minutes in a hot air heating furnace.

Thereafter, Mo (100 nm) was deposited by sputtering using a lift-off method, and the source / drain electrodes were patterned into a desired shape. After that, a protective film by forming a SiO _x by plasma CVD (PECVD). A contact hole was opened using hydrofluoric acid to produce a thin film transistor. The channel width and channel length were 20 μm and 10 μm, respectively.

  With respect to the obtained TFT, a field effect mobility and Vth were measured using a semiconductor parameter analyzer (Caseley 4200) in a dry nitrogen atmosphere at atmospheric pressure at room temperature and in a light-shielding environment. The results are shown in Table 1.

Comparative Examples 1-3
Powders were mixed so that the atomic ratios shown in Table 1 were obtained, and sputtering targets, thin films and TFTs were prepared and evaluated under the same conditions as in Examples 1-8. The results are shown in Table 1.
In Comparative Example 1, a conductive film was formed and not driven as a TFT. In Comparative Examples 2 and 3, the mobility was low, and good TFT characteristics were not obtained.

Comparative Examples 4-6
Powders were mixed so that the atomic ratios shown in Table 2 were obtained, sputtering targets were produced under the same conditions as in Examples 1 to 8, and the crystal phase, relative density, and bulk specific resistance were evaluated. The results are shown in Table 2. When these targets were used for DC sputtering, abnormal discharge occurred.
The X-ray diffraction chart obtained in Comparative Example 4 is shown in FIG. The sintered body obtained in Comparative Example 4 did not contain a crystal layer of MIn ₂ O ₄ .

Examples 9-12, Comparative Example 7
It was disclosed in Japanese Patent Application Laid-Open No. 2005-290550 using six targets having a width of 200 mm, a length of 1700 mm, and a thickness of 10 mm, which were produced under the same atomic ratio and conditions as in Examples 1 to 4 and Comparative Example 1. Using a film forming apparatus, AC sputtering is performed under the conditions shown in Table 3 to form an amorphous film, heat treatment is performed, source / drain patterning is performed by dry etching, and annealing temperature and time are shown in Table 3. A thin film transistor was fabricated and evaluated in the same manner as in Examples 1 to 8, except that the conditions were as described. The results are shown in Table 3.

Specifically, AC sputtering was performed using the apparatus shown in FIG.
The six targets 31a to 31f having a width of 200 mm, a length of 1700 mm, and a thickness of 10 mm produced as described above were used, and the targets 31a to 31f were arranged in parallel to the width direction of the substrate so that the distance was 2 mm. The widths of the magnetic field forming means 40a to 40f were 200 mm, which is the same as the targets 31a to 31f.
Ar and O ₂ as sputtering gases were introduced into the system from the gas supply system. The sputtering conditions are as follows.
Substrate temperature: 25 ° C (RT) or 80 ° C
Ultimate pressure: 8.5 × 10 ⁻⁵ Pa
Atmospheric gas: Ar gas, O ₂ gas Sputtering pressure (total pressure): 0.5 Pa

For example, in Example 9, in order to investigate the film formation rate, a film was formed for 10 seconds under the described conditions, and the thickness of the obtained thin film was measured to be 11 nm. The film formation rate is as high as 66 nm / min and is suitable for mass production.
Further, from XRD measurement, it was confirmed that the film was amorphous immediately after deposition of the thin film and was amorphous even after 30 minutes at 350 ° C. in air.

  The sputtering target of this invention can be used for preparation of oxide thin films, such as an oxide semiconductor and a transparent conductive film. The oxide thin film of the present invention can be used for a transparent electrode, a semiconductor layer of a thin film transistor, an oxide thin film layer, and the like.

31a to 31f: Target 40a to 40f: Magnetic field forming means 17a to 17c: AC power source

Claims (14)

Containing indium, zinc, and an oxide containing a metal M that is one or more selected from Mg, Ca, Sr, Cu, Ni, Co, Be and Fe ;
In ₂ O ₃ , MIn ₂ O ₄ and In ₂ O ₃ (ZnO) _m (1 ≦ m ≦ 20) are contained as crystal phases, the relative density is 95% or more, and the atomic ratio In / (In + Zn + M) is A sputtering target including a sintered body satisfying 0.70 or less ,
The structure in which the sintered body has a higher In content than the surroundings that are the In ₂ O ₃ crystal phase, the structure that has a higher Zn content than the surroundings that are the In ₂ O ₃ (ZnO) _m crystal phase, and Including a structure in which the content of the metal M is higher than that of the surrounding, which is the MIn ₂ O ₄ crystal phase ,
Sputtering target in which the average diameter of the circle that minimizes the area including the structure with a large amount of In and the average diameter of the circle that includes the structure with a high content of the metal M and that has the minimum area is 25 μm or less. .   2. The sputtering target according to claim 1, wherein an average diameter of a circle having a minimum area including a structure containing a large amount of In is 10 μm or less. Intensity ratio _I 2 / _{I 1} of the maximum peak intensity _{I 1} of the _MIn 2 _{O 4} in the X-ray diffraction _In 2 _O 3 _(ZnO) maximum peak intensity of the _{m I 2} is located at 0.2 to 2.0 The sputtering target of Claim 1 or 2 containing a sintered compact. The atomic ratio represented by In / (In + Zn + M) is 0.70 or less, the atomic ratio represented by Zn / (In + Zn + M) is 0.70 or less, and the atomic ratio represented by M / (In + Zn + M) is It is 0.01-0.30, The sputtering target in any one of Claims 1-3. The sputtering target according to claim 1 wherein the metal M is Mg. Containing indium, zinc, and an oxide containing a metal M that is one or more selected from Mg, Ca, Sr, Cu, Ni, Co, Be and Fe ;
The atomic ratio represented by In / (In + Zn + M) is 0.70 or less, the atomic ratio represented by Zn / (In + Zn + M) is 0.70 or less, and the atomic ratio represented by M / (In + Zn + M) is 0.01-0.30,
A semiconductor thin film having a hole mobility of 3 cm ² / V · sec or more. The semiconductor thin film according to claim 6 which is amorphous. The semiconductor thin film according to claim 6 or 7 , wherein the metal M is Mg. The semiconductor thin film is formed by sequentially transporting the substrate to a position facing three or more targets arranged in parallel in the vacuum chamber at a predetermined interval, and a negative potential is supplied to each target from an AC power source. When alternately applying a positive potential and at least one of the outputs from the AC power source, the target to which the potential is applied is switched between two or more targets branched and connected. The method for producing a semiconductor thin film according to claim 6 , wherein the method is performed by a sputtering method in which plasma is generated on the substrate surface to form a film. The method for producing a semiconductor thin film according to claim 9 , wherein the AC power density of the AC power supply is 3 W / cm ² or more and 20 W / cm ² or less. The method of manufacturing a semiconductor thin film according to claim 9 or 10 , wherein the frequency of the AC power source is 10 kHz to 1 MHz. A thin film transistor using the semiconductor thin film according to claim 6 . A thin film transistor using a protective film containing at least SiNx on the semiconductor thin film according to claim 6 . Display device having a thin film transistor according to claim 12 or 13.