WO2014076916A1 - スパッタリングターゲット、酸化物半導体薄膜及びそれらの製造方法 - Google Patents
スパッタリングターゲット、酸化物半導体薄膜及びそれらの製造方法 Download PDFInfo
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- WO2014076916A1 WO2014076916A1 PCT/JP2013/006597 JP2013006597W WO2014076916A1 WO 2014076916 A1 WO2014076916 A1 WO 2014076916A1 JP 2013006597 W JP2013006597 W JP 2013006597W WO 2014076916 A1 WO2014076916 A1 WO 2014076916A1
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- Prior art keywords
- thin film
- sputtering
- oxide semiconductor
- oxide
- semiconductor thin
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Definitions
- the present invention relates to a sputtering target, a thin film manufactured using the target, and a thin film transistor including the thin film.
- TFTs thin film transistors
- LCD liquid crystal display devices
- EL electroluminescence display devices
- FED field emission displays
- a driving voltage is applied to the display elements.
- TFTs are often used as switching elements for driving display devices.
- a semiconductor layer channel layer which is a main member of a field effect transistor
- silicon semiconductor compound is most widely used as a material for a semiconductor layer (channel layer) which is a main member of a field effect transistor.
- a silicon single crystal is used for a high-frequency amplifying element or an integrated circuit element that requires high-speed operation.
- an amorphous silicon semiconductor is used for a liquid crystal driving element or the like because of a demand for a large area.
- an amorphous silicon thin film can be formed at a relatively low temperature, its switching speed is slower than that of a crystalline thin film, so when used as a switching element for driving a display device, it may not be able to follow the display of high-speed movies. is there.
- amorphous silicon having a mobility of 0.5 to 1 cm 2 / Vs could be used, but when the resolution is SXGA, UXGA, QXGA or higher, 2 cm 2 / Mobility greater than Vs is required.
- the driving frequency is increased in order to improve the image quality, higher mobility is required.
- the crystalline silicon-based thin film has a high mobility, there are problems such as requiring a large amount of energy and the number of processes for manufacturing, and a problem that it is difficult to increase the area. For example, when annealing a silicon-based thin film, laser annealing using a high temperature of 800 ° C. or higher and expensive equipment is necessary. In addition, since the crystalline silicon-based thin film is normally limited to the top gate configuration of the TFT, the cost reduction such as reduction of the number of masks is difficult.
- an oxide semiconductor thin film is manufactured by sputtering using a target (sputtering target) made of an oxide sintered body.
- a target made of a compound having a homologous crystal structure represented by general formulas In 2 Ga 2 ZnO 7 and InGaZnO 4 is known (Patent Documents 1, 2, and 3).
- Patent Documents 1, 2, and 3 a target made of a compound having a homologous crystal structure represented by general formulas In 2 Ga 2 ZnO 7 and InGaZnO 4 is known (Patent Documents 1, 2, and 3).
- Patent Documents 1, 2, and 3 Patent Documents 1, 2, and 3
- a reduction treatment at a high temperature after sintering is required to reduce the resistance of the target. It was.
- Patent Document 4 a thin film transistor using an amorphous oxide semiconductor film made of indium oxide and zinc oxide without containing gallium has also been proposed (Patent Document 4).
- Patent Document 4 a thin film transistor using an amorphous oxide semiconductor film made of indium oxide and zinc oxide without containing gallium has also been proposed.
- Patent Document 4 a sputtering target for a protective layer of an optical information recording medium in which an additive element such as Ta, Y, or Si is added to an In 2 O 3 —SnO 2 —ZnO-based oxide containing tin oxide as a main component has been studied ( Patent Documents 5 and 6).
- these targets are not for oxide semiconductors, and there are problems that aggregates of insulating materials are easily formed, resistance values are increased, and abnormal discharge is likely to occur.
- JP-A-8-245220 JP 2007-73312 A International Publication No. 2009/084537 Pamphlet International Publication No. 2005/088726 Pamphlet International Publication No. 2005/0778152 Pamphlet International Publication No. 2005/078153 Pamphlet
- An object of the present invention is to provide a sputtering target with high density and low resistance. Another object of the present invention is to provide a thin film transistor having high field effect mobility and high reliability.
- the present inventors have conducted intensive research and are composed of an oxide containing indium element (In), tin element (Sn), zinc element (Zn), and aluminum element (Al), and include InAlO 3. It has been found that a sputtering target containing a homologous structural compound represented by (ZnO) m (m is 0.1 to 10) and a bixbite structural compound represented by In 2 O 3 has a high relative density and a low resistance. It was. Further, the inventors have found that a TFT using a thin film manufactured using this target as a channel layer has high field-effect mobility and high reliability, and completed the present invention.
- the following sputtering target and the like are provided.
- It is made of an oxide containing indium element (In), tin element (Sn), zinc element (Zn), and aluminum element (Al), and the oxide is InAlO 3 (ZnO) m (m is 0.1 to 10).
- the sputtering target according to any one of 1 to 4 which has a bulk specific resistance of 10 m ⁇ cm or less. 6).
- a film is formed by a sputtering method using the sputtering target according to any one of 1 to 6 in an atmosphere of a mixed gas containing one or more selected from water vapor, oxygen gas and nitrous oxide gas and a rare gas; Manufacturing method of oxide semiconductor thin film.
- 9. The method for producing an oxide semiconductor thin film according to 8, wherein the oxide semiconductor thin film is formed in an atmosphere of a mixed gas containing a rare gas and at least water vapor. 10.
- the oxide 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 from each AC power source to each target. In the case of alternately applying a negative potential and a positive potential, at least one of the outputs from the AC power supply is switched between two or more targets that are branched and connected while switching the target to which the potential is applied. 11.
- a high-density and low-resistance sputtering target can be provided.
- a thin film transistor having high field effect mobility and high reliability can be provided.
- FIG. 3 is an X-ray diffraction chart of the sintered body obtained in Example 1.
- FIG. 3 is an X-ray diffraction chart of a sintered body obtained in Example 2.
- FIG. 4 is a diagram showing an X-ray diffraction chart of a sintered body obtained in Example 3.
- FIG. 6 is a diagram showing an X-ray diffraction chart of a sintered body obtained in Example 4.
- FIG. 6 is a diagram showing an X-ray diffraction chart of a sintered body obtained in Example 5.
- FIG. 6 is a diagram showing an X-ray diffraction chart of a sintered body obtained in Example 6.
- the sputtering target of the present invention comprises an oxide containing indium element (In), tin element (Sn), zinc element (Zn), and aluminum element (Al).
- the oxide includes a homologous structure compound represented by InAlO 3 (ZnO) m (m is 0.1 to 10) and a bixbite structure compound represented by In 2 O 3 .
- the target when the target contains the homologous structural compound and the bixbite structural compound, the relative density is high and the bulk resistance is low. Therefore, the occurrence of abnormal discharge can be suppressed when sputtering using the target of the present invention. Further, the target of the present invention can form a high-quality oxide semiconductor thin film efficiently, inexpensively and with a small amount of energy.
- the homologous structural compound represented by InAlO 3 (ZnO) m (m is 0.1 to 10) is obtained by observing the peak of the homologous structural compound as a result of X-ray diffraction measurement of the target (oxide sintered body). I can confirm.
- m is 0.1 to 10, preferably 0.5 to 8, and more preferably 1 to 7. is there.
- M is preferably an integer.
- the homologous structure compound represented by InAlO 3 (ZnO) m (m is 0.1 to 10) is preferably a homologous structure compound represented by InAlZn 4 O 7 , InAlZn 3 O 6 , InAlZn 2 O 5 and InAlZnO 4. One or more selected.
- the homologous crystal structure is a crystal structure composed of a “natural superlattice” structure having a long period in which several crystal layers of different substances are stacked.
- 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 substance or a mixed crystal in which each layer is uniformly mixed. Unique characteristics can be obtained.
- the crystal structure of the homologous phase can be confirmed, for example, because the X-ray diffraction pattern of the powder obtained by pulverizing the target matches the crystal structure X-ray diffraction pattern of the homologous phase assumed from the composition ratio. Specifically, the crystal structure X-ray diffraction pattern of the homologous phase obtained from JCPDS (Joint Committee of Powder Diffraction Standards) card or ICSD (The Inorganic Crystal Structure Database) can be confirmed.
- JCPDS Joint Committee of Powder Diffraction Standards
- ICSD The Inorganic Crystal Structure Database
- RAO 3 (MO) m As an oxide crystal having a homologous crystal structure, an oxide crystal represented by RAO 3 (MO) m can be given.
- R and A are positive trivalent metal elements such as In, Ga, Al, Fe, and B.
- A is a positive trivalent metal element different from R, and examples thereof include Ga, Al, and Fe.
- M is a positive divalent metal element, and examples thereof include Zn and Mg.
- R is In, A is Al, and M is Zn.
- the homologous structure of InAlZnO 4 is X-ray diffraction, and the JCPDS database No. It shows a 40-0258 peak pattern or a similar (shifted) pattern.
- the homologous structure of InAlZn 2 O 5 is No. 1 in the JCPDS database. It shows a 40-0259 peak pattern or a similar (shifted) pattern.
- the homologous structure of InAlZn 3 O 6 is the JCPDS database No. A peak pattern of 40-0260 or a similar (shifted) pattern is shown.
- the homologous structure of InAlZn 4 O 7 can be found in the JCPDS database No. It shows a peak pattern of 40-0261 or a similar (shifted) pattern.
- the bixbite structure compound of In 2 O 3 can be confirmed by observing the peak of the bixbite structure compound as a result of X-ray diffraction measurement of the target.
- the bixbite structure compound of In 2 O 3 is obtained by X-ray diffraction according to No. A peak pattern of 06-0416 or a similar (shifted) pattern is shown.
- Bixbyte is also referred to as rare earth oxide C-type or Mn 2 O 3 (I) -type oxide.
- 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 and a total of 80 atoms (M is 32, X is 48) Yes.
- 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.
- the sputtering target of the present invention preferably does not contain a spinel structure compound represented by Zn 2 SnO 4 .
- the spinel structure compound represented by Zn 2 SnO 4 is X-ray diffraction and has a No. of JCPDS database. It shows a peak pattern of 24-1470 or a similar (shifted) pattern.
- the spinel structure usually refers to a structure of AB 2 X 4 type or A 2 BX 4 type as disclosed in “Crystal chemistry” (Kodansha, Mitsuko Nakahira, 1973) and the like. The compound having this is called a spinel structure compound.
- anions usually oxygen
- cations are present in a part of the tetrahedral gap and octahedral gap.
- a substituted solid solution in which atoms or 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 are also included in the spinel structure compound.
- a spinel structural compound represented by Zn 2 SnO 4 is included.
- the sputter rate differs for each crystal phase, and there is a possibility that uncut portions may be generated.
- the atomic ratio of indium element, tin element, zinc element and aluminum element satisfy the following formulas (1) to (4). 0.10 ⁇ In / (In + Sn + Zn + Al) ⁇ 0.75 (1) 0.01 ⁇ Sn / (In + Sn + Zn + Al) ⁇ 0.30 (2) 0.10 ⁇ Zn / (In + Sn + Zn + Al) ⁇ 0.70 (3) 0.01 ⁇ Al / (In + Sn + Zn + Al) ⁇ 0.40 (4) (In the formula, In, Sn, Zn, and Al each indicate an atomic ratio of each element in the sputtering target.)
- the atomic ratio [In / (In + Sn + Zn + Al)] of the In element is preferably 0.10 to 0.75, more preferably 0.20 to 0.70, and still more preferably 0.25. ⁇ 0.70.
- the atomic ratio of Sn element when the atomic ratio of Sn element is 0.01 or more, the density of the oxide sintered body constituting the target is sufficiently improved, and the bulk resistance value of the target is lowered.
- the atomic ratio of Sn element when the atomic ratio of Sn element is 0.30 or less, SnO 2 that is the cause of abnormal discharge can be suppressed, and abnormal discharge can be prevented.
- the atomic ratio [Sn / (In + Sn + Zn + Al)] of the Sn element is preferably 0.01 to 0.30, more preferably 0.03 to 0.25, and still more preferably 0.05 to 0. .15.
- the atomic ratio of Zn element when the atomic ratio of Zn element is 0.10 or more, a homologous structure compound represented by InAlO 3 (ZnO) m (m is 0.1 to 10) is easily formed. On the other hand, when the atomic ratio of the Zn element is 0.70 or less, ZnO hardly precipitates and abnormal discharge caused by ZnO can be prevented. From the above, the atomic ratio [Zn / (In + Sn + Zn + Al)] of Zn is preferably 0.10 to 0.70, more preferably 0.20 to 0.65, and still more preferably 0.25 to 0. .60.
- the atomic ratio of Al element when the atomic ratio of Al element is 0.01 or more, a homologous structure compound represented by InAlO 3 (ZnO) m (m is 0.1 to 10) is easily formed.
- the atomic ratio of the Al element when the atomic ratio of the Al element is 0.40 or less, generation of Al 2 O 3 that is a cause of abnormal discharge can be suppressed, and abnormal discharge can be prevented.
- the atomic ratio [Al / (In + Sn + Zn + Al)] of Al is preferably 0.01 to 0.40, more preferably 0.02 to 0.30, and still more preferably 0.05 to 0. .25.
- the atomic ratio of each element contained in the sintered body can be obtained by quantitative analysis of the contained elements using an inductively coupled plasma emission spectrometer (ICP-AES). Specifically, when a solution sample is atomized with a nebulizer and introduced into an argon plasma (about 6000 to 8000 ° C.), the elements in the sample are excited by absorbing thermal energy, and orbital electrons are excited from the ground state. Move to the orbit. These orbital electrons move to a lower energy level orbit in about 10 ⁇ 7 to 10 ⁇ 8 seconds. At this time, the energy difference is emitted as light to emit light. Since this light shows a wavelength (spectral line) unique to the element, the presence of the element can be confirmed by the presence or absence of the spectral line (qualitative analysis).
- ICP-AES inductively coupled plasma emission spectrometer
- the sample concentration can be obtained by comparing with a standard solution having a known concentration (quantitative analysis). After identifying the elements contained in the qualitative analysis, the content is obtained by quantitative analysis, and the atomic ratio of each element is obtained from the result.
- the sputtering target of the present invention may contain other metal elements other than the above-described In, Sn, Zn and Al within a range not impairing the effects of the present invention, and substantially includes In, Sn, Zn and It may consist of only Al or only In, Sn, Zn and Al.
- “substantially” means that 95 wt% or more and 100 wt% or less (preferably 98 wt% or more and 100 wt% or less) of the metal element of the sputtering target is In, Sn, Zn, and Al.
- the sputtering target of the present invention may contain inevitable impurities in addition to In, Sn, Zn and Al as long as the effects of the present invention are not impaired.
- the sputtering target of the present invention preferably has a relative density of 98% or more.
- the relative density is preferably 98% 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 98% or more, a stable sputtering state is maintained. In the case of forming a film by increasing the sputtering output on a large substrate, if the relative density is 98% or more, the target surface is hardly blackened and abnormal discharge is not easily generated.
- the relative density is preferably 98.5% or more, more preferably 99% or more.
- the relative density can be measured by the Archimedes method.
- the relative density is preferably 100% or less. When it is 100% or less, metal particles are hardly generated in the sintered body, and the production of lower oxides is suppressed, so that it is not necessary to strictly adjust the oxygen supply amount during film formation.
- the density can be adjusted by performing a post-treatment step such as a heat treatment operation under a reducing atmosphere after sintering.
- a reducing atmosphere an atmosphere of argon, nitrogen, hydrogen, or a mixed gas atmosphere thereof is used.
- the maximum grain size of the crystal in the sputtering target of the present invention is desirably 8 ⁇ m or less.
- crystallization is 8 micrometers or less in particle size.
- the cutting speed varies depending on the direction of the crystal plane, and irregularities are generated on the target surface.
- the size of the unevenness depends on the crystal grain size present in the sintered body. In a target made of a sintered body having a large crystal grain size, the unevenness is increased, and it is considered that nodules are generated from the convex portion.
- the maximum grain size of these sputtering target crystals is the center point (one place) of the circle and the center point and the peripheral part on two center lines orthogonal to the center point.
- the central point (one location) and the intermediate point (4) between the central point and the corner on the diagonal of the quadrangle is measured, and is expressed as an average value of the particle sizes of the maximum particles present in each of these five locations.
- the particle size is measured for the major axis of the crystal grains.
- the crystal grains can be observed with a scanning electron microscope (SEM).
- the bulk resistivity of the sputtering target of the present invention is preferably 10 m ⁇ cm or less, more preferably 8 m ⁇ cm or less, and particularly preferably 5 m ⁇ cm or less. Bulk specific resistance can be measured by the method described in Examples.
- the contents of indium element (In), tin element (Sn), zinc element (Zn), and aluminum element (Al) are within the composition regions (1) to (4) above.
- the relative density of the target can be 98% or more and the bulk resistance can be 10 m ⁇ cm or less.
- the sputtering target of the present invention can be manufactured, for example, by a manufacturing method including the following two steps. (1) Step of mixing raw material compounds and molding to form a molded body (2) Step of sintering the molded body
- Step of mixing raw material compounds and molding to form a molded body The raw material compound is not particularly limited, and is a simple substance or compound of In, Sn, Zn, and Al, and the sintered body has the following formulas (1) to ( It is preferable to use a simple substance or a compound so that it can have the atomic ratio shown in 4).
- the raw material is preferably a powder.
- the raw material is preferably a mixed powder of indium oxide, tin oxide, zinc oxide and aluminum oxide.
- aluminum metal particles are present in the obtained sintered body, and during film formation In some cases, the metal particles on the surface of the target melt and may not be released from the target, and the composition of the obtained film and the composition of the sintered body may differ greatly.
- the average particle size of the raw material powder is preferably 0.1 ⁇ m to 1.2 ⁇ m, more preferably 0.1 ⁇ m to 1.0 ⁇ m.
- the average particle diameter of the raw material powder can be measured with a laser diffraction type particle size distribution apparatus or the like.
- an oxide containing Al 2 O 3 powder having an average particle size of 0.1 ⁇ m to 1.2 ⁇ m is used as a raw material powder, and these are prepared at a ratio satisfying the above formulas (1) to (4).
- the mixing and forming method in step (1) is not particularly limited, and can be performed using a known method.
- an aqueous solvent is blended with a raw material powder containing a mixed powder of oxides containing indium oxide powder, tin oxide, zinc oxide and aluminum oxide powder, and the resulting slurry is mixed for 12 hours or more, followed by solid-liquid separation. ⁇ Dry and granulate, and then put this granulated product into a mold and mold it.
- a wet or dry ball mill, vibration mill, bead mill, or the like can be used.
- a bead mill mixing method is most preferable because the crushing efficiency of the agglomerates is high in a short time and the additive is well dispersed.
- the mixing time by the ball mill is preferably 15 hours or more, more preferably 19 hours or more. If the mixing time by the ball mill is 15 hours or more, a high resistance compound such as Al 2 O 3 is hardly generated in the finally obtained sintered body.
- the pulverization and mixing time by the bead mill varies depending on the size of the apparatus and the amount of slurry to be processed, but is appropriately adjusted so that the particle size distribution in the slurry is all uniform at 1 ⁇ m or less. Further, when mixing, it is preferable to add an arbitrary amount of a binder and mix them at the same time.
- a binder polyvinyl alcohol, vinyl acetate, or the like can be used.
- granulated powder is obtained from the raw material powder slurry.
- rapid drying granulation As an apparatus for rapid drying granulation, a spray dryer is widely used.
- the specific drying conditions are determined by various conditions such as the slurry concentration of the slurry to be dried, the temperature of hot air used for drying, the air volume, etc., and therefore, it is necessary to obtain optimum conditions in advance. If it is quick-drying granulation, uniform granulated powder is obtained. That is, it is possible to prevent the In 2 O 3 powder, the SnO 2 powder, the ZnO powder, and the Al 2 O 3 powder from separating due to the difference in the sedimentation speed due to the difference in specific gravity of the raw material powder.
- the granulated powder is usually molded by a die press or cold isostatic press (CIP) at a pressure of, for example, 1.2 ton / cm 2 or more to obtain a molded body.
- CIP cold isostatic press
- the obtained molded product can be sintered at a sintering temperature of 1200 to 1650 ° C. for 10 to 50 hours to obtain a sintered body.
- the sintering temperature is preferably 1350 to 1600 ° C, more preferably 1400 to 1600 ° C, still more preferably 1450 to 1600 ° C.
- the sintering time is preferably 12 to 40 hours, more preferably 13 to 30 hours.
- a sintering temperature of 1200 ° C. or more and a sintering time of 10 hours or more are preferable because Al 2 O 3 and the like can be prevented from forming inside the target and abnormal discharge can be prevented.
- the firing temperature is 1650 ° C. or less and the firing time is 50 hours or less, an increase in the average crystal grain size due to significant crystal grain growth can be prevented, and the generation of coarse pores can be suppressed. It is preferable because a decrease in body strength and abnormal discharge can be prevented.
- a pressure sintering method such as hot press, oxygen pressurization, hot isostatic pressurization and the like can be employed in addition to the normal pressure sintering method.
- a normal pressure sintering method it is preferable to employ a normal pressure sintering method from the viewpoints of reducing manufacturing costs, possibility of mass production, and easy production of large sintered bodies.
- the compact is sintered in an air atmosphere or an oxidizing gas atmosphere, preferably an oxidizing gas atmosphere.
- the oxidizing gas atmosphere is preferably an oxygen gas atmosphere.
- the oxygen gas atmosphere is preferably an atmosphere having an oxygen concentration of, for example, 10 to 100% by volume.
- the density of the sintered body can be further increased by introducing an oxygen gas atmosphere in the temperature raising process.
- the heating rate during sintering is from 0.1 to 2.5 ° C./min from 800 ° C. to the sintering temperature (1200 to 1650 ° C.).
- the temperature range above 800 ° C. is the range in which sintering proceeds most. .
- a temperature increase rate in this temperature range of 0.1 ° C./min or more is preferable because excessive crystal grain growth can be prevented and high density can be achieved.
- the rate of temperature increase is 2.5 ° C./min or less because Al 2 O 3 and the like can be prevented from being precipitated inside the target.
- the heating rate from 800 ° C. to the sintering temperature is preferably 0.1 to 2.0 ° C./min, more preferably 0.1 to 1.5 ° C./min.
- the temperature lowering rate (cooling rate) during firing is usually 10 ° C./min or less, preferably 9 ° C./min or less, more preferably 8 ° C./min or less, further preferably 7 ° C./min or less, and particularly preferably 5 ° C./min. C / min or less.
- the crystal form of this invention is easy to be obtained as it is 10 degrees C / min or less. In addition, cracks are unlikely to occur when the temperature drops.
- a reduction step may be provided as necessary.
- the reduction method include a method using a reducing gas, vacuum firing, or reduction using an inert gas.
- a reducing gas hydrogen, methane, carbon monoxide, a mixed gas of these gases and oxygen, or the like can be used.
- reduction treatment by firing in an inert gas nitrogen, argon, a mixed gas of these gases and oxygen, or the like can be used.
- the temperature during the reduction treatment is usually 100 to 800 ° C, preferably 200 to 800 ° C.
- the reduction treatment time is usually 0.01 to 10 hours, preferably 0.05 to 5 hours.
- the method for producing a sintered body used in the present invention is, for example, a slurry obtained by blending an aqueous solvent into a raw material powder containing a mixed powder of indium oxide powder, zinc oxide powder and aluminum oxide powder. After mixing for 12 hours or more, solid-liquid separation, drying and granulation are performed, and then this granulated product is put into a mold and molded, and then the obtained molded product is sintered from 800 ° C. in an oxygen atmosphere.
- the sintered body of the present invention can be obtained.
- the sputtering target of the present invention can be obtained by processing the sintered body obtained above. Specifically, the sintered body is cut into a shape suitable for mounting on a sputtering apparatus to obtain a sputtering target (target material). If necessary, the target may be bonded to a backing plate to form a sputtering target.
- a sputtering target target material
- the target may be bonded to a backing plate to form a sputtering target.
- the sintered body is ground with, for example, a surface grinder to obtain a material having a surface roughness Ra of 0.5 ⁇ m or less.
- the sputter surface of the target material may be further mirror-finished so that the average surface roughness Ra may be 1000 angstroms or less.
- Mirror surface processing can be performed using a known polishing technique such as mechanical polishing, chemical polishing, mechanochemical polishing (a combination of mechanical polishing and chemical polishing). 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.
- the surface of the target material is preferably finished with a diamond grindstone of No. 200 to 10,000, and particularly preferably finished with a diamond grindstone of No. 400 to 5,000.
- a diamond grindstone of No. 200 to 10,000 the target material can be prevented from cracking.
- the target material has a surface roughness Ra of 0.5 ⁇ m or less and has a non-directional ground surface. It is preferable that Ra is 0.5 ⁇ m or less and a ground surface having no directionality is provided because abnormal discharge and particles can be prevented.
- Air blow or running water washing can be used for the cleaning treatment.
- This ultrasonic cleaning is effective by performing multiple oscillations at a frequency of 25 to 300 KHz.
- it is preferable to perform ultrasonic cleaning by multiplying twelve frequencies in 25 KHz increments between 25 to 300 KHz.
- the thickness of the target material is usually 2 to 20 mm, preferably 3 to 12 mm, particularly preferably 4 to 6 mm. If necessary, a sputtering target can be obtained by bonding the target material obtained as described above to a backing plate. Further, a plurality of target materials may be attached to one backing plate to substantially serve as one target.
- the oxide semiconductor thin film (oxide thin film) of the present invention is produced by forming a film by the sputtering method using the above sputtering target.
- the oxide semiconductor thin film of the present invention preferably contains indium, tin, zinc, aluminum, and oxygen and satisfies the atomic ratio of the following formulas (1) to (4).
- the target resistance when the atomic ratio of the Sn element is 0.01 or more, the target resistance can be prevented from increasing, so that abnormal discharge is unlikely to occur during sputtering film formation, and film formation is easy to stabilize.
- the atomic ratio of the Sn element when the atomic ratio of the Sn element is 0.30 or less, it is possible to prevent the solubility of the obtained thin film in the wet etchant from being lowered, and wet etching can be performed without any problem.
- the carrier concentration of the oxide semiconductor thin film of the present invention is usually 10 19 / cm 3 or less, preferably 10 13 to 10 18 / cm 3 , more preferably 10 14 to 10 18 / cm 3 , particularly Preferably, it is 10 15 to 10 18 / cm 3 .
- the carrier concentration of the oxide layer is 10 19 cm ⁇ 3 or less, it is possible to prevent leakage current, normally-on and a decrease in on-off ratio when a device such as a thin film transistor is configured, and to have good transistor performance Can be demonstrated.
- the carrier concentration is 10 13 cm ⁇ 3 or more, the TFT is driven without any problem.
- the carrier concentration of the oxide semiconductor thin film can be measured by a Hall effect measurement method. Specifically, it can be measured by the method described in the examples.
- the sputtering target of the present invention has high conductivity, a DC sputtering method having a high deposition rate can be applied as the sputtering method.
- the present invention can be applied to an RF sputtering method, an AC sputtering method, and a pulsed DC sputtering method, and sputtering without abnormal discharge is possible.
- the oxide semiconductor thin film of the present invention can be produced by using the sintered body by a vapor deposition method, an ion plating method, a pulse laser vapor deposition method, or the like, in addition to the sputtering method.
- a mixed gas of a rare gas such as argon and an oxidizing gas can be used.
- the oxidizing gas include O 2 , CO 2 , O 3 , H 2 O, and N 2 O.
- the sputtering gas is preferably a mixed gas containing a rare gas and one or more gases selected from water vapor, oxygen gas and nitrous oxide gas, and more preferably a mixed gas containing a rare gas and at least water vapor.
- the oxygen partial pressure ratio during sputtering film formation is preferably 0% or more and less than 40%.
- the oxygen partial pressure ratio is less than 40%, the carrier concentration of the manufactured thin film is not significantly reduced, and the carrier concentration can be prevented from becoming less than 10 13 cm ⁇ 3, for example.
- the oxygen partial pressure ratio is more preferably 0% to 30%, and particularly preferably 0% to 20%.
- the partial pressure ratio of water vapor contained in the sputtering gas (atmosphere) when depositing the oxide thin film is 0.1. % To 25% is preferable.
- the partial pressure ratio of water in the atmosphere during sputtering is more preferably 0.7 to 13%, particularly preferably 1 to 6%.
- the substrate temperature when forming a film by sputtering is preferably 25 to 120 ° C., more preferably 25 to 100 ° C., and particularly preferably 25 to 90 ° C.
- the substrate temperature at the time of film formation is 120 ° C. or lower, oxygen or the like introduced at the time of film formation can be sufficiently taken in, and an excessive increase in the carrier concentration of the thin film after heating can be prevented.
- the substrate temperature at the time of film formation is 25 ° C. or higher, the film density of the thin film does not decrease and the mobility of the TFT can be prevented from decreasing.
- the oxide thin film obtained by sputtering is further annealed by holding at 150 to 500 ° C. for 15 minutes to 5 hours.
- the annealing temperature after film formation is more preferably 200 ° C. or higher and 450 ° C. or lower, and further preferably 250 ° C. or higher and 350 ° C. or lower. By performing the annealing, semiconductor characteristics can be obtained.
- the atmosphere during heating is not particularly limited, but from the viewpoint of carrier controllability, an air atmosphere or an oxygen circulation atmosphere is preferable.
- a lamp annealing device In the post-treatment annealing step of the oxide thin film, a lamp annealing device, a laser annealing device, a thermal plasma device, a hot air heating device, a contact heating device, or the like can be used in the presence or absence of oxygen.
- the distance between the target and the substrate during sputtering is preferably 1 to 15 cm, more preferably 2 to 8 cm in the direction perpendicular to the film formation surface of the substrate.
- this distance is 1 cm or more, the kinetic energy of the target constituent element particles reaching the substrate does not become too large, and good film characteristics can be obtained. In addition, in-plane distribution of film thickness and electrical characteristics can be prevented.
- the distance between the target and the substrate is 15 cm or less, the kinetic energy of the particles of the target constituent element that reaches the substrate does not become too small, and a dense film can be obtained. In addition, good semiconductor characteristics can be obtained.
- the oxide thin film is preferably formed by sputtering in an atmosphere having a magnetic field strength of 300 to 1500 gauss.
- the magnetic field strength is 300 gauss or more, a decrease in plasma density can be prevented, and sputtering can be performed without any problem even in the case of a high-resistance sputtering target.
- it is 1500 gauss or less, deterioration of controllability of the film thickness and electrical characteristics in the film can be suppressed.
- the pressure in the gas atmosphere is not particularly limited as long as the plasma can be stably discharged, but is preferably 0.1 to 3.0 Pa, more preferably 0.1 to 1.5 Pa. Particularly preferred is 0.1 to 1.0 Pa.
- the sputtering pressure is 3.0 Pa or less, the mean free process of sputtered particles does not become too short, and a decrease in thin film density can be prevented. Further, when the sputtering pressure is 0.1 Pa or more, it is possible to prevent the formation of microcrystals in the film during film formation.
- the sputtering pressure refers to the total pressure in the system at the start of sputtering after introducing a rare gas such as argon, water vapor, oxygen gas or the like.
- the oxide semiconductor thin film may be formed by AC sputtering as described below.
- 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 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.
- an oxide semiconductor thin film is formed by AC sputtering
- sputtering is performed in an atmosphere of a mixed gas containing a rare gas and one or more gases selected from water vapor, oxygen gas, and nitrous oxide gas. It is preferable to perform, and it is particularly preferable to perform sputtering in an atmosphere of a mixed gas containing water vapor.
- 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.
- the AC sputtering apparatus described in Japanese Patent Laid-Open No. 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
- Each target 31a to 31f is formed in an elongated shape having a longitudinal direction, each target has the same shape, and edge portions (side surfaces) in the longitudinal direction of the sputtering surface are arranged in parallel with a predetermined interval therebetween. 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 of positive and negative 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. Therefore, 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 has 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 disposed 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 magnets are also arranged at the same interval as the targets 31a to 31f.
- the AC power density when using an oxide target in AC sputtering is preferably 3 W / cm 2 or more and 20 W / cm 2 or less.
- the power density is 3 W / cm 2 or more, the film formation rate does not become too slow, and production economy can be ensured. If it is 20 W / cm 2 or less, damage to the target can be suppressed.
- a more preferable power density is 3 W / cm 2 to 15 W / cm 2 .
- the frequency of AC sputtering is preferably in the range of 10 kHz to 1 MHz. When the frequency is 10 kHz or more, the problem of noise hardly occurs.
- the frequency is 1 MHz or less, it is possible to prevent the plasma from spreading too much and performing sputtering at a position other than the desired target position, so that uniformity can be maintained.
- a more preferable frequency of AC sputtering is 20 kHz to 500 kHz. What is necessary is just to select suitably the conditions at the time of sputtering other than the above from what was mentioned above.
- the above oxide semiconductor thin film can be used for a thin film transistor (TFT), and particularly preferably used as a channel layer.
- TFT thin film transistor
- its element structure is not particularly limited, and various known element structures can be adopted.
- TFT of the present invention preferably has a field effect mobility of 10 cm 2 / Vs or more, more preferably 13 cm 2 / Vs or more. The field effect mobility can be measured by the method described in the examples.
- the 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.
- the thickness of the channel layer is 10 nm or more, even when the channel layer is formed in a large area, the film thickness is unlikely to be uniform, and the characteristics of the manufactured TFT can be made uniform in the plane.
- the film thickness is 300 nm or less, the film formation time does not become too long.
- 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.
- 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, Sc 2 O 3 , Y 2 O 3 , HfO 2 , CaHfO 3 , PbTiO 3 , BaTa 2 O 6 , Sm 2 O 3 , SrTiO 3, or an oxide such as AlN can be included.
- the oxide thin film containing indium element (In), tin element (Sn), zinc element (Zn), and aluminum element (Al) according to the present invention contains Al, so that the reduction resistance by the CVD process is improved.
- the back channel side is not easily reduced by the process of forming the protective film, and SiN x can be used as 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.
- 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.
- ozone treatment oxygen plasma treatment or nitrous oxide plasma treatment on the channel layer, the In—OH bond is stabilized in the thin film structure, and diffusion of hydrogen in the oxide semiconductor film can be suppressed. .
- 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 , PbTiO 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.
- 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.
- 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.
- 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.
- each of the drain electrode, the source electrode, and the gate electrode in the thin film transistor of the present invention 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.
- 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.
- 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.
- 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.
- the thin film transistor of the present invention can be suitably used for a display device.
- a channel etch type 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.
- 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.
- Example 1-6 [Production of sintered oxide] The following oxide powder was used as a raw material powder.
- the median diameter D50 was employed as the average particle diameter of the following oxide powder, and the average particle diameter was measured with a laser diffraction particle size distribution analyzer SALD-300V (manufactured by Shimadzu Corporation).
- Indium oxide powder Average particle size 0.98 ⁇ m
- Tin oxide powder Average particle size 0.98 ⁇ m
- Zinc oxide powder Average particle size 0.96 ⁇ m
- Aluminum oxide powder Average particle size 0.98 ⁇ m
- the above powder was weighed so as to have the atomic ratio shown in Table 1, and was uniformly pulverized and mixed, and then granulated by adding a molding binder. Next, this raw material mixed powder was uniformly filled into a mold, and pressure-molded with a cold press machine at a press pressure of 140 MPa.
- the green body thus obtained was sintered in a sintering furnace at a temperature increase rate (from 800 ° C. to sintering temperature), a sintering temperature, a sintering time and a temperature decreasing rate shown in Table 1. Manufactured. During the temperature increase, an oxygen atmosphere was used, and the other was in the air (atmosphere).
- Example 1-6 The crystal structure of the obtained sintered body was examined using an X-ray diffraction measurement apparatus (XRD).
- XRD X-ray diffraction measurement apparatus
- Table 2 shows the product compounds (crystal structures of oxides) contained in the sintered body.
- X-ray diffraction measurement The conditions of X-ray diffraction measurement (XRD) are as follows. ⁇ Equipment: Ultimate-III manufactured by Rigaku Corporation -X-ray: Cu-K ⁇ ray (wavelength 1.5406mm, monochromatized with graphite monochromator) ⁇ 2 ⁇ - ⁇ reflection method, continuous scan (1.0 ° / min) ⁇ Sampling interval: 0.02 ° ⁇ Slit DS, SS: 2/3 °, RS: 0.6 mm
- the obtained sputtering target having a diameter of 4 inches was mounted on a DC sputtering apparatus, and a mixed gas in which 2% of H 2 O gas was added to argon gas at a partial pressure ratio was used as the atmosphere, the sputtering pressure was 0.4 Pa, and the substrate temperature was room temperature. Then, 10 kWh continuous sputtering was performed at a DC output of 400 W. Voltage fluctuations during sputtering were accumulated in a data logger, and the presence or absence of abnormal discharge was confirmed. The results are shown in Table 2. In addition, the presence or absence of abnormal discharge was performed by monitoring voltage fluctuation and detecting abnormal discharge.
- the abnormal discharge was determined when the voltage fluctuation generated during the measurement time of 5 minutes was 10% or more of the steady voltage during the sputtering operation.
- the steady-state voltage during sputtering operation varies by ⁇ 10% in 0.1 second, a micro arc, which is an abnormal discharge of the sputter discharge, has occurred, and the device yield may decrease, making it unsuitable for mass production. is there.
- nodules For the nodules, a change in the target surface after sputtering was observed 50 times with a stereomicroscope, and a method of measuring the number average of nodules of 20 ⁇ m or more generated in a visual field of 3 mm 2 was adopted. Table 2 shows the number of nodules generated.
- Comparative Examples 1 and 2 The raw material powders are mixed at the atomic ratios shown in Table 1, and sintering is performed at the heating rate (from 800 ° C. to the sintering temperature), sintering temperature, and sintering time shown in Table 1, and the cooling rate is 15 ° C./min. Otherwise, a sintered body and a sputtering target were produced and evaluated in the same manner as in Example 1. The results are shown in Table 2.
- Examples 7-12 Manufacture of oxide semiconductor thin films
- a 4-inch target having the composition shown in Table 3 or 4 prepared in Examples 1 to 6 was mounted on a magnetron sputtering apparatus, and a slide glass (# 1737 manufactured by Corning) was mounted as a substrate.
- An amorphous film having a thickness of 50 nm was formed on the slide glass by the DC magnetron sputtering method under the following conditions.
- Ar gas, O 2 gas, and H 2 O gas were introduced at a partial pressure ratio (%) shown in Table 3 or Table 4.
- the substrate on which the amorphous film was formed was heated in the atmosphere at 300 ° C. for 60 minutes to form an oxide semiconductor film.
- the sputtering conditions are as follows. Substrate temperature: 80 ° C Ultimate pressure: 8.5 ⁇ 10 ⁇ 5 Pa Atmospheric gas: Ar gas, O 2 gas, H 2 O gas (see Tables 3 and 4 for partial pressure) Sputtering pressure (total pressure): 0.4 Pa Input power: DC100W S (substrate)-T (target) distance: 70mm
- the crystal structure of the thin film formed on the glass substrate was examined with an X-ray diffraction measurement device (Rigaku's Ultimate-III). It was confirmed that the thin films formed in Examples 7 to 12 were amorphous with no diffraction peak observed immediately after deposition of the thin films. In addition, no diffraction peak was observed even after heat treatment (annealing) at 300 ° C. for 60 minutes in the atmosphere, and it was confirmed that the film was amorphous.
- the measurement conditions for the XRD are as follows. Equipment: Ultimate-III manufactured by Rigaku Corporation X-ray: Cu-K ⁇ ray (wavelength 1.5406mm, monochromatized with graphite monochromator) 2 ⁇ - ⁇ reflection method, continuous scan (1.0 ° / min) Sampling interval: 0.02 ° Slit DS, SS: 2/3 °, RS: 0.6 mm
- a conductive silicon substrate with a thermal oxide film having a thickness of 100 nm was used as the substrate.
- the thermal oxide film functions as a gate insulating film
- the conductive silicon portion functions as a gate electrode.
- a sputter film was formed on the gate insulating film under the conditions shown in Table 3 or Table 4 to produce an amorphous thin film having a thickness of 50 nm.
- OFPR # 800 manufactured by Tokyo Ohka Kogyo Co., Ltd.
- pre-baking 80 ° C., 5 minutes
- a SiO x film having a thickness of 100 nm was formed by plasma CVD (PECVD), and a SiN x film having a thickness of 150 nm was formed on the SiO x by plasma CVD (PECVD) to form a protective film.
- PECVD plasma CVD
- a contact hole was opened using dry etching to produce a thin film transistor.
- the thin film transistor was evaluated for field effect mobility ( ⁇ ), threshold voltage (Vth), and S value. These characteristic values were measured using a semiconductor parameter analyzer (4200SCS manufactured by Keithley Instruments Co., Ltd.) at room temperature in a light-shielding environment (in a shield box). The transfer characteristics of the mounted transistors were evaluated with a drain voltage (Vd) of 1 V and a gate voltage (Vg) of ⁇ 15 to 20 V. The results are shown in Table 3 or Table 4. The field effect mobility ( ⁇ ) was calculated from the linear mobility and defined as the maximum value of Vg ⁇ .
- Comparative Examples 3 and 4 Using the 4-inch target prepared in Comparative Examples 1 and 2, the sputtering conditions, heating (annealing) treatment conditions, and protective film formation pretreatment were changed to those shown in Table 4 and were the same as in Examples 7-12 Then, an oxide semiconductor thin film and a thin film transistor were prepared and evaluated. The results are shown in Table 4. As shown in Table 4, the threshold voltage was negative in the elements of Comparative Examples 3 and 4. Further, as a result of the stress test, the threshold voltage fluctuated by 1 V or more, and the characteristic was significantly deteriorated.
- Examples 13-15 Using the film forming apparatus disclosed in JP-A-2005-290550, AC sputtering is performed under the conditions shown in Table 5, an amorphous film is formed under the following conditions, heat treatment is performed, and source / drain patterning is performed. An oxide semiconductor thin film and a thin film transistor were prepared and evaluated in the same manner as in Examples 7 to 12 except that dry etching was performed. The results are shown in Table 5.
- ICP-AES analysis of the oxide semiconductor thin film confirmed that the atomic ratio of each element contained in the oxide thin film was the same as that of the sputtering target.
- AC sputtering was performed as follows 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 manufactured in Example 1, 3 or 4 are used, and the targets 31a to 31f are parallel to the width direction of the substrate and the distance is 2 mm.
- the width of the magnetic field forming means 40a to 40f was 200 mm, which is the same as that of the targets 31a to 31f.
- Ar, H 2 O and / or O 2 as sputtering gases were introduced into the system from the gas supply system.
- the film was formed for 10 seconds under the above conditions, and the thickness of the obtained thin film was measured to be 13 nm.
- the film formation rate is as high as 78 nm / min and is suitable for mass production.
- the glass substrate on which the thin film was formed was placed in an electric furnace, heat-treated in air at 300 ° C. for 60 minutes (in the atmosphere), cut into a size of 1 cm 2 , and hole measurement was performed by the 4-probe method.
- the carrier concentration was 4.83 ⁇ 10 17 cm ⁇ 3 , and it was confirmed that the semiconductor was sufficiently semiconductorized. Further, from XRD measurement, it was confirmed that the film was amorphous immediately after deposition of the thin film and was amorphous even after 60 minutes at 300 ° C. in air.
- the thin film transistor obtained using the sputtering target of the present invention can be used for a display device, particularly for a large area display.
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Abstract
Description
電界効果型トランジスタの主要部材である半導体層(チャンネル層)の材料としては、シリコン半導体化合物が最も広く用いられている。一般に、高速動作が必要な高周波増幅素子や集積回路用素子等には、シリコン単結晶が用いられている。一方、液晶駆動用素子等には、大面積化の要求から非晶質性シリコン半導体(アモルファスシリコン)が用いられている。
一方、結晶性のシリコン系薄膜は、移動度は高いものの、製造に際して多大なエネルギーと工程数を要する等の問題や、大面積化が困難という問題があった。例えば、シリコン系薄膜を結晶化する際に800℃以上の高温や、高価な設備を使用するレーザーアニールが必要である。また、結晶性のシリコン系薄膜は、通常TFTの素子構成がトップゲート構成に限定されるため、マスク枚数の削減等コストダウンが困難であった。
例えば、一般式In2Ga2ZnO7、InGaZnO4で表されるホモロガス結晶構造を示す化合物からなるターゲットが知られている(特許文献1、2及び3)。しかしながら、このターゲットでは焼結密度(相対密度)を上げるために、酸化雰囲気で焼結する必要があるが、その場合、ターゲットの抵抗を下げるため、焼結後に高温での還元処理が必要であった。また、ターゲットを長期間使用していると、得られた膜の特性や成膜速度が大きく変化する、InGaZnO4やIn2Ga2ZnO7の異常成長による異常放電が起きる、成膜時にパーティクルの発生が多い等の問題があった。異常放電が頻繁に起きると、プラズマ放電状態が不安定となり、安定した成膜が行われず、膜特性に悪影響を及ぼす。
また、酸化スズを主成分としたIn2O3-SnO2-ZnO系酸化物に、TaやY、Siといった添加元素を含む光情報記録媒体の保護層用のスパッタリングターゲットが検討されている(特許文献5及び6)。しかしながら、これらターゲットは酸化物半導体用ではなく、また、絶縁性物質の凝集体が形成され易く、抵抗値が高くなってしまうことや異常放電が起こり易いという問題があった。
本発明の他の目的は、高い電界効果移動度及び高い信頼性を有する薄膜トランジスタを提供することである。
1.インジウム元素(In)、スズ元素(Sn)、亜鉛元素(Zn)及びアルミニウム元素(Al)を含有する酸化物からなり、前記酸化物が、InAlO3(ZnO)m(mは0.1~10)で表わされるホモロガス構造化合物と、In2O3で表わされるビックスバイト構造化合物を含む、スパッタリングターゲット。
2.前記ホモロガス構造化合物が、InAlZn4O7、InAlZn3O6、InAlZn2O5及びInAlZnO4で表わされるホモロガス構造化合物から選択される1以上である1に記載のスパッタリングターゲット。
3.前記In、Sn、Zn及びAlの原子比が、下記式(1)~(4)を満たす1又は2に記載のスパッタリングターゲット。
0.10≦In/(In+Sn+Zn+Al)≦0.75 (1)
0.01≦Sn/(In+Sn+Zn+Al)≦0.30 (2)
0.10≦Zn/(In+Sn+Zn+Al)≦0.70 (3)
0.01≦Al/(In+Sn+Zn+Al)≦0.40 (4)
(式中、In、Sn、Zn及びAlはそれぞれ、スパッタリングターゲットにおける各元素の原子比を示す。)
4.相対密度が98%以上である、1~3のいずれかに記載のスパッタリングターゲット。
5.バルク比抵抗が10mΩcm以下である、1~4のいずれかに記載のスパッタリングターゲット。
6.Zn2SnO4で表わされるスピネル構造化合物を含まない、1~5のいずれかに記載のスパッタリングターゲット。
7.上記1~6のいずれかに記載のスパッタリングターゲットを用いて、スパッタリング法により成膜してなる酸化物半導体薄膜。
8.水蒸気、酸素ガス及び亜酸化窒素ガスから選択される1以上と、希ガスを含有する混合気体の雰囲気下において、1~6のいずれかに記載のスパッタリングターゲットを用いてスパッタリング法で成膜する、酸化物半導体薄膜の製造方法。
9.前記酸化物半導体薄膜の成膜を、希ガスと、少なくとも水蒸気とを含有する混合気体の雰囲気下において行う、8に記載の酸化物半導体薄膜の製造方法。
10.前記雰囲気中に含まれる水蒸気の割合が、分圧比で0.1%~25%である、9に記載の酸化物半導体薄膜の製造方法。
11.前記酸化物半導体薄膜の成膜を、真空チャンバー内に所定の間隔を置いて並設された3枚以上のターゲットに対向する位置に、基板を順次搬送し、前記各ターゲットに対して交流電源から負電位及び正電位を交互に印加する場合に、前記交流電源からの出力の少なくとも1つを、分岐して接続した2枚以上のターゲットの間で、電位を印加するターゲットの切替を行いながら、ターゲット上にプラズマを発生させて基板表面に成膜するスパッタリング方法で行う、8~10のいずれかに記載の酸化物半導体薄膜の製造方法。
12.前記交流電源の交流パワー密度を3W/cm2以上、20W/cm2以下とする、11に記載の酸化物半導体薄膜の製造方法。
13.前記交流電源の周波数を10kHz~1MHzとする、11又は12に記載の酸化物半導体薄膜の製造方法。
14.上記8~13のいずれかに記載の方法により成膜された酸化物半導体薄膜をチャネル層として有する薄膜トランジスタ。
15.電界効果移動度が10cm2/Vs以上である、14に記載の薄膜トランジスタ。
本発明によれば、高い電界効果移動度及び高い信頼性を有する薄膜トランジスタが提供できる。
I.スパッタリングターゲット
本発明のスパッタリングターゲットは、インジウム元素(In)、スズ元素(Sn)、亜鉛元素(Zn)及びアルミニウム元素(Al)を含有する酸化物からなる。そして、酸化物がInAlO3(ZnO)m(mは0.1~10)で表わされるホモロガス構造化合物とIn2O3で表わされるビックスバイト構造化合物を含むことを特徴とする。
本発明では、ターゲットが上記ホモロガス構造化合物及びビックスバイト構造化合物を含むことにより、相対密度が高くかつバルク抵抗が低くなる。そのため、本発明のターゲットを用いてスパッタリングする際に、異常放電の発生を抑制することが出来る。また、本発明のターゲットは、高品質の酸化物半導体薄膜を、効率的に、安価に、かつ少ないエネルギーで成膜することが出来る。
InAlO3(ZnO)m(mは0.1~10)で表わされるホモロガス構造化合物において、mは0.1~10であり、好ましくは0.5~8であり、さらに好ましくは1~7である。また、mは好ましくは整数である。
InAlZn2O5のホモロガス構造は、JCPDSデータベースのNo.40-0259のピークパターン、又は類似の(シフトした)パターンを示すものである。
InAlZn3O6のホモロガス構造は、JCPDSデータベースのNo.40-0260のピークパターン、又は類似の(シフトした)パターンを示すものである。
InAlZn4O7のホモロガス構造は、JCPDSデータベースのNo.40-0261のピークパターン、又は類似の(シフトした)パターンを示すものである。
In2O3のビックスバイト構造化合物は、X線回折で、JCPDSデータベースのNo.06-0416のピークパターンか、又は類似の(シフトした)パターンを示す。
また、結晶構造中の原子やイオンが一部他の原子で置換された置換型固溶体、他の原子が格子間位置に加えられた侵入型固溶体もビックスバイト構造化合物に含まれる。
Zn2SnO4で表わされるスピネル構造化合物は、X線回折で、JCPDSデータベースのNo.24-1470のピークパターンか、あるいは類似の(シフトした)パターンを示すものである。
スピネル構造とは、「結晶化学」(講談社、中平光興著、1973)等に開示されている通り、通常AB2X4型あるいはA2BX4型の構造をいい、このような結晶構造を有する化合物をスピネル構造化合物という。
一般にスピネル構造では、陰イオン(通常は酸素)が立方最密充填をしており、その四面体隙間及び八面体隙間の一部に陽イオンが存在している。尚、結晶構造中の原子やイオンが一部他の原子で置換された置換型固溶体、他の原子が格子間位置に加えられた侵入型固溶体もスピネル構造化合物に含まれる。
0.10≦In/(In+Sn+Zn+Al)≦0.75 (1)
0.01≦Sn/(In+Sn+Zn+Al)≦0.30 (2)
0.10≦Zn/(In+Sn+Zn+Al)≦0.70 (3)
0.01≦Al/(In+Sn+Zn+Al)≦0.40 (4)
(式中、In、Sn、Zn及びAlはそれぞれ、スパッタリングターゲットにおける各元素の原子比を示す。)
以上から、In元素の原子比[In/(In+Sn+Zn+Al)]は、0.10~0.75であることが好ましく、より好ましくは0.20~0.70であり、さらに好ましくは、0.25~0.70である。
以上から、Sn元素の原子比[Sn/(In+Sn+Zn+Al)]は0.01~0.30であることが好ましく、より好ましくは0.03~0.25であり、さらに好ましくは0.05~0.15である。
以上からZnの原子比[Zn/(In+Sn+Zn+Al)]は、0.10~0.70であることが好ましく、より好ましくは0.20~0.65であり、さらに好ましくは、0.25~0.60である。
以上からAlの原子比[Al/(In+Sn+Zn+Al)]は、0.01~0.40であることが好ましく、より好ましくは0.02~0.30であり、さらに好ましくは、0.05~0.25である。
具体的に、溶液試料をネブライザーで霧状にして、アルゴンプラズマ(約6000~8000℃)に導入すると、試料中の元素は熱エネルギーを吸収して励起され、軌道電子が基底状態から高いエネルギー準位の軌道に移る。この軌道電子は10-7~10-8秒程度で、より低いエネルギー準位の軌道に移る。この際にエネルギーの差を光として放射し発光する。この光は元素固有の波長(スペクトル線)を示すため、スペクトル線の有無により元素の存在を確認できる(定性分析)。
定性分析で含有されている元素を特定後、定量分析で含有量を求め、その結果から各元素の原子比を求める。
ここで、「実質的」とは、スパッタリングターゲットの金属元素の95重量%以上100重量%以下(好ましくは98重量%以上100重量%以下)がIn、Sn、Zn及びAlであることを意味する。本発明のスパッタリングターゲットは、本発明の効果を損なわない範囲でIn、Sn、Zn及びAlの他に不可避不純物を含んでいてもよい。
相対密度とは、加重平均より算出した理論密度に対して相対的に算出した密度である。各原料の密度の加重平均より算出した密度が理論密度であり、これを100%とする。
相対密度が98%以上であれば、安定したスパッタリング状態が保たれる。大型基板でスパッタ出力を上げて成膜する場合は、相対密度が98%以上であれば、ターゲット表面が黒化しにくく、異常放電が発生しにくい。相対密度は好ましくは98.5%以上、より好ましくは99%以上である。
また、焼結後に、還元性雰囲気下での熱処理操作等の後処理工程等を行って密度を調整することもできる。還元性雰囲気は、アルゴン、窒素、水素等の雰囲気や、それらの混合気体雰囲気が用いられる。
スパッタによってターゲット表面が削られる場合、その削られる速度が結晶面の方向によって異なり、ターゲット表面に凹凸が発生する。この凹凸の大きさは焼結体中に存在する結晶粒径に依存している。大きい結晶粒径を有する焼結体からなるターゲットでは、その凹凸が大きくなり、その凸部分よりノジュールが発生すると考えられる。
これらのスパッタリングターゲットの結晶の最大粒径は、スパッタリングターゲットの形状が円形の場合、円の中心点(1箇所)と、その中心点で直交する2本の中心線上の中心点と周縁部との中間点(4箇所)の合計5箇所において、また、スパッタリングターゲットの形状が四角形の場合には、その中心点(1箇所)と、四角形の対角線上の中心点と角部との中間点(4箇所)の合計5箇所において100μm四方の枠内で観察される最大の粒子についてその最大径を測定し、これらの5箇所の枠内のそれぞれに存在する最大粒子の粒径の平均値で表す。粒径は、結晶粒の長径について測定する。結晶粒は走査型電子顕微鏡(SEM)により観察することができる。
(1)原料化合物を混合し、成形して成形体とする工程
(2)上記成形体を焼結する工程
(1)原料化合物を混合し、成形して成形体とする工程
原料化合物は特に制限されず、In、Sn、Zn及びAlの単体又は化合物であり、焼結体が下記式(1)~(4)に示す原子比を有することができるように単体又は化合物を用いることが好ましい。
0.10≦In/(In+Sn+Zn+Al)≦0.75 (1)
0.01≦Sn/(In+Sn+Zn+Al)≦0.30 (2)
0.10≦Zn/(In+Sn+Zn+Al)≦0.70 (3)
0.01≦Al/(In+Sn+Zn+Al)≦0.40 (4)
(式中、In、Sn、Zn及びAlはそれぞれ、スパッタリングターゲットにおける各元素の原子比を示す。)
原料に単体金属を用いた場合、例えば、酸化インジウム、酸化スズ、酸化亜鉛及びアルミニウム金属の組み合わせを原料粉末として用いた場合、得られる焼結体中にアルミニウムの金属粒が存在し、成膜中にターゲット表面の金属粒が溶融してターゲットから放出されないことがあり、得られる膜の組成と焼結体の組成が大きく異なってしまう場合がある。
原料粉末の平均粒径は、好ましくは0.1μm~1.2μmであり、より好ましくは0.1μm~1.0μmである。原料粉末の平均粒径はレーザー回折式粒度分布装置等で測定することができる。
例えば、平均粒径が0.1μm~1.2μmのIn2O3粉末、平均粒径が0.1μm~1.2μmのSnO2粉末、平均粒径が0.1μm~1.2μmのZnO粉末及び平均粒径が0.1μm~1.2μmのAl2O3粉末を含んだ酸化物を原料粉末とし、これらを、上記式(1)~(4)を満たす割合で調合する。
ボールミルによる混合時間は、好ましくは15時間以上、より好ましくは19時間以上とする。ボールミルによる混合時間が15時間以上であれば、最終的に得られる焼結体中にAl2O3等の高抵抗の化合物が生成しにくい。ビーズミルによる粉砕、混合時間は、装置の大きさ、処理するスラリー量によって異なるが、スラリー中の粒度分布が全て1μm以下と均一になるように適宜調整する。
また、混合する際にはバインダーを任意量だけ添加し、同時に混合を行うと好ましい。バインダーには、ポリビニルアルコール、酢酸ビニル等を用いることができる。
急速乾燥造粒であれば、均一な造粒粉が得られる。即ち、原料粉末の比重差による沈降速度の差によって、In2O3粉末、SnO2粉末、ZnO粉末及びAl2O3粉末が分離することを防ぐことができる。均一な造粒粉から作成した焼結体であれば、Al2O3等の存在によるスパッタリング時の異常放電を防ぐことができる。
造粒粉に対して、通常、金型プレス又は冷間静水圧プレス(CIP)により、例えば1.2ton/cm2以上の圧力で成形を施して成形体を得る。
得られた成形物を1200~1650℃の焼結温度で10~50時間焼結して焼結体を得ることができる。焼結温度は、好ましくは1350~1600℃、より好ましくは1400~1600℃、さらに好ましくは1450~1600℃である。焼結時間は好ましくは12~40時間、より好ましくは13~30時間である。
焼結温度が1200℃以上、焼結時間が10時間以上であると、Al2O3等がターゲット内部に形成することを抑制でき、異常放電を防ぐことができるため好ましい。一方、焼成温度が1650℃以下、焼成時間が50時間以下であると、著しい結晶粒成長による平均結晶粒径の増大を防ぐことができ、また、粗大空孔の発生を抑制できるため、焼結体強度の低下や異常放電を防ぐことができるため好ましい。
常圧焼結法では、成形体を大気雰囲気、又は酸化ガス雰囲気、好ましくは酸化ガス雰囲気にて焼結する。酸化ガス雰囲気とは、好ましくは酸素ガス雰囲気である。酸素ガス雰囲気は、酸素濃度が、例えば10~100体積%の雰囲気であることが好ましい。上記焼結体の製造方法においては、昇温過程にて酸素ガス雰囲気を導入することで、焼結体密度をより高くすることができる。
インジウム元素(In)、スズ元素(Sn)、亜鉛元素(Zn)及びアルミニウム元素(Al)を含有する酸化物のスパッタリングターゲットにおいて800℃から上の温度範囲は、焼結が最も進行する範囲である。この温度範囲での昇温速度が0.1℃/分以上であると、過度の結晶粒成長を防ぐことができ、高密度化を達成できるため好ましい。一方、昇温速度が2.5℃/分以下であると、Al2O3等がターゲット内部に析出することを防ぐことができるため好ましい。
800℃から焼結温度における昇温速度は、好ましくは0.1~2.0℃/分、より好ましくは0.1~1.5℃/分である。
還元方法としては、例えば、還元性ガスによる方法や真空焼成又は不活性ガスによる還元等が挙げられる。
還元性ガスによる還元処理の場合、水素、メタン、一酸化炭素、又はこれらのガスと酸素との混合ガス等を用いることができる。
不活性ガス中での焼成による還元処理の場合、窒素、アルゴン、又はこれらのガスと酸素との混合ガス等を用いることができる。
以上をまとめると、本発明に用いる焼結体の製造方法は、例えば、酸化インジウム粉と酸化亜鉛粉及び酸化アルミニウム粉との混合粉を含む原料粉末に、水系溶媒を配合し、得られたスラリーを12時間以上混合した後、固液分離・乾燥・造粒し、引き続き、この造粒物を型枠に入れて成形し、その後、得られた成形物を酸素雰囲気中、800℃から焼結温度までの昇温速度を0.1~2.5℃/分とし、1200~1650℃で10~50時間焼成し、焼成時の降温速度(冷却速度)を10℃/分以下とすることで本発明の焼結体を得ることができる。
尚、以上のエアーブローや流水洗浄では限界があるので、さらに超音波洗浄等を行なうこともできる。この超音波洗浄は周波数25~300KHzの間で多重発振させて行なう方法が有効である。例えば周波数25~300KHzの間で、25KHz刻みに12種類の周波数を多重発振させて超音波洗浄を行なうのが好ましい。
必要な場合は、上記のようにして得られたターゲット素材をバッキングプレートへボンディングすることによって、スパッタリングターゲットを得ることができる。また、複数のターゲット素材を1つのバッキングプレートに取り付け、実質1つのターゲットとしてもよい。
本発明の酸化物半導体薄膜(酸化物薄膜)は、上記のスパッタリングターゲットを用いて、スパッタリング法により成膜して製造する。
本発明の酸化物半導体薄膜は、インジウム、スズ、亜鉛、アルミニウム、酸素を含み、下記式(1)~(4)の原子比を満たすと好ましい。
0.10≦In/(In+Sn+Zn+Al)≦0.75 (1)
0.01≦Sn/(In+Sn+Zn+Al)≦0.30 (2)
0.10≦Zn/(In+Sn+Zn+Al)≦0.70 (3)
0.01≦Al/(In+Sn+Zn+Al)≦0.40 (4)
(式中、In、Sn、Zn及びAlはそれぞれ、スパッタリングターゲットにおける各元素の原子比を示す。)
酸化物層のキャリア濃度が1019cm-3以下であると、薄膜トランジスタ等の素子を構成した際の漏れ電流、ノーマリーオンや、on-off比の低下を防ぐことができ、良好なトランジスタ性能が発揮できる。キャリア濃度が1013cm-3以上であると、TFTとして問題なく駆動する。
酸化物半導体薄膜のキャリア濃度は、ホール効果測定方法により測定することができる。具体的には実施例に記載の方法で測定できる。
本発明の酸化物半導体薄膜は、上記焼結体を用いて、スパッタリング法の他に、蒸着法、イオンプレーティング法、パルスレーザー蒸着法等により作製することもできる。
酸素分圧比は、より好ましくは0%~30%であり、特に好ましくは0%~20%である。
スパッタリング時の雰囲気中の水の分圧比は0.7~13%がより好ましく、1~6%が特に好ましい。
成膜時の基板温度が120℃以下であると、成膜時に導入する酸素等を十分に取り込むことができ、加熱後の薄膜のキャリア濃度の過度な増加を防ぐことができる。また、成膜時の基板温度が25℃以上であると、薄膜の膜密度が低下せず、TFTの移動度が低下することを防ぐことができる。
また、加熱時の雰囲気は、特に限定されるわけではないが、キャリア制御性の観点から、大気雰囲気、酸素流通雰囲気が好ましい。
酸化物薄膜の後処理アニール工程においては、酸素の存在下又は不存在下でランプアニール装置、レーザーアニール装置、熱プラズマ装置、熱風加熱装置、接触加熱装置等を用いることができる。
この距離が1cm以上であると、基板に到達するターゲット構成元素の粒子の運動エネルギーが大きくなりすぎず、良好な膜特性を得ることができる。また、膜厚及び電気特性の面内分布等を防ぐことができる。
一方、ターゲットと基板との間隔が15cm以下であると、基板に到達するターゲット構成元素の粒子の運動エネルギーが小さくなりすぎず、緻密な膜を得ることができる。また、良好な半導体特性を得ることができる。
尚、スパッタ圧力とは、アルゴン等の希ガス、水蒸気、酸素ガス等を導入した後のスパッタ開始時の系内の全圧をいう。
真空チャンバー内に所定の間隔を置いて並設された3枚以上のターゲットに対向する位置に、基板を順次搬送し、各ターゲットに対して交流電源から負電位及び正電位を交互に印加して、ターゲット上にプラズマを発生させて基板表面上に成膜する。
このとき、交流電源からの出力の少なくとも1つを、分岐して接続された2枚以上のターゲットの間で、電位を印加するターゲットの切替を行いながら行う。即ち、上記交流電源からの出力の少なくとも1つを分岐して2枚以上のターゲットに接続し、隣り合うターゲットに異なる電位を印加しながら成膜を行う。
ACスパッタリングで成膜した場合、工業的に大面積均一性に優れた酸化物層が得られると共に、ターゲットの利用効率の向上が期待できる。
また、1辺が1mを超える大面積基板にスパッタ成膜する場合には、たとえば特開2005-290550号公報記載のような大面積生産用のACスパッタ装置を使用することが好ましい。
各リング状磁石は、対応する1個のターゲット31a~31fの真裏位置で、ターゲット31a~31fの長手方向に対して平行に配置されている。上述したように、ターゲット31a~31fは所定間隔を空けて平行配置されているので、リング状磁石もターゲット31a~31fと同じ間隔を空けて配置されている。
ACスパッタの周波数は10kHz~1MHzの範囲が好ましい。10kHz以上であると、騒音の問題が生じにくい。1MHz以下であると、プラズマが広がりすぎて所望のターゲット位置以外でスパッタが行われることを防ぐことができ、均一性を保てる。より好ましいACスパッタの周波数は20kHz~500kHzである。
上記以外のスパッタリング時の条件等は、上述したものから適宜選択すればよい。
上記の酸化物半導体薄膜は、薄膜トランジスタ(TFT)に使用でき、特にチャネル層として好適に使用できる。
本発明の薄膜トランジスタは、上記の酸化物薄膜をチャネル層として有していれば、その素子構成は特に限定されず、公知の各種の素子構成を採用することができる。
また、上記の酸化物薄膜をTFTのチャネル層に用いることにより、電界効果移動度及び信頼性の高いTFTが得られる。本発明のTFTは、好ましくは電界効果移動度が10cm2/Vs以上、より好ましくは13cm2/Vs以上である。電界効果移動度は、実施例に記載の方法により測定することができる。
本発明の薄膜トランジスタは、上記チャネル層上に保護膜を備えることが好ましい。本発明の薄膜トランジスタにおける保護膜は、少なくともSiNxを含有することが好ましい。SiNxはSiO2と比較して緻密な膜を形成できるため、TFTの劣化抑制効果が高いという利点を有する。
保護膜を形成する前に、チャネル層に対し、オゾン処理、酸素プラズマ処理、二酸化窒素プラズマ処理もしくは亜酸化窒素プラズマ処理を施すことが好ましい。このような処理は、チャネル層を形成した後、保護膜を形成する前であれば、どのタイミングで行ってもよいが、保護膜を形成する直前に行うことが望ましい。このような前処理を行うことによって、チャネル層における酸素欠陥の発生を抑制することができる。
また、TFT駆動中に酸化物半導体膜中の水素が拡散すると、閾値電圧のシフトが起こりTFTの信頼性が低下するおそれがある。チャネル層に対し、オゾン処理、酸素プラズマ処理もしくは亜酸化窒素プラズマ処理を施すことにより、薄膜構造中においてIn-OHの結合が安定化され酸化物半導体膜中の水素の拡散を抑制することができる。
プラズマCVD法によりゲート絶縁膜を形成し、その上にチャネル層を成膜した場合、ゲート絶縁膜中の水素がチャネル層に拡散し、チャネル層の膜質低下やTFTの信頼性低下を招くおそれがある。チャネル層の膜質低下やTFTの信頼性低下を防ぐために、チャネル層を成膜する前にゲート絶縁膜に対してオゾン処理、酸素プラズマ処理、二酸化窒素プラズマ処理もしくは亜酸化窒素プラズマ処理を施すことが好ましい。このような前処理を行うことによって、チャネル層の膜質の低下やTFTの信頼性低下を防ぐことができる。
尚、上記の酸化物の酸素数は、必ずしも化学量論比と一致していなくともよく、例えば、SiO2でもSiOxでもよい。
ドレイン電極、ソース電極及びゲート電極の各電極は、異なる2層以上の導電層を積層した多層構造とすることもできる。特にソース・ドレイン電極は低抵抗配線への要求が強いため、AlやCu等の良導体をTiやMo等の密着性に優れた金属でサンドイッチして使用してもよい。
本発明の薄膜トランジスタの構成は、ボトムゲート、ボトムコンタクト、トップコンタクト等公知の構成を制限なく採用することができる。
特にボトムゲート構成が、アモルファスシリコンやZnOの薄膜トランジスタに比べ高い性能が得られるので有利である。ボトムゲート構成は、製造時のマスク枚数を削減しやすく、大型ディスプレイ等の用途の製造コストを低減しやすいため好ましい。
本発明の薄膜トランジスタは、表示装置に好適に用いることができる。
[酸化物焼結体の製造]
原料粉体として下記の酸化物粉末を使用した。下記酸化物粉末の平均粒径としてメジアン径D50を採用し、当該平均粒径は、レーザー回折式粒度分布測定装置SALD-300V(島津製作所製)で測定した。
酸化インジウム粉 :平均粒径0.98μm
酸化スズ粉 :平均粒径0.98μm
酸化亜鉛粉 :平均粒径0.96μm
酸化アルミニウム粉:平均粒径0.98μm
このようにして得た成形体を、表1に示す昇温速度(800℃から焼結温度)、焼結温度、焼結時間及び降温速度で、焼結炉で焼結して焼結体を製造した。昇温中は酸素雰囲気、その他は大気中(雰囲気)とした。
得られた焼結体の相対密度をアルキメデス法により測定した。実施例1-6の焼結体は相対密度98%以上であることを確認した。
また、得られた焼結体のバルク比抵抗(導電性)を抵抗率計(三菱化学(株)製、ロレスタ)を使用して四探針法(JIS R 1637)に基づき測定した。結果を表1に示す。表1に示すように実施例1-6の焼結体のバルク比抵抗は、10mΩcm以下であった。
得られた焼結体についてICP-AES分析を行い、表1に示す原子比であることを確認した。
また、得られた焼結体についてX線回折測定装置(XRD)により結晶構造を調べた。実施例1-6で得られた焼結体のX線回折チャートをそれぞれ図2-7に示す。
また、焼結体に含まれる生成化合物(酸化物の結晶構造)を表2に示す。
InAlZnO4のホモロガス構造は、JCPDSデータベースのNo.40-0258のピークパターンである。In2O3のビックスバイト構造は、JCPDSデータベースのNo.06-0416のピークパターンである。
実施例2の焼結体には、InAlZn2O5のホモロガス構造及びIn2O3のビックスバイト構造が観測された。InAlZn2O5のホモロガス構造は、JCPDSデータベースのNo.40-0259のピークパターンである。
実施例3の焼結体には、InAlZn2O5のホモロガス構造、InAlZnO4のホモロガス構造及びIn2O3のビックスバイト構造及び観測された。
実施例4の焼結体には、InAlZn2O5のホモロガス構造及びIn2O3のビックスバイト構造が観測された。
実施例5の焼結体には、InAlZn2O5のホモロガス構造、InAlZnO4のホモロガス構造及びIn2O3のビックスバイト構造及び観測された。
実施例6の焼結体には、InAlZn2O5のホモロガス構造及びIn2O3のビックスバイト構造が観測された。
実施例1~6の焼結体には、Zn2SnO4のスピネル構造は観測されなかった。
・装置:(株)リガク製Ultima-III
・X線:Cu-Kα線(波長1.5406Å、グラファイトモノクロメータにて単色化)
・2θ-θ反射法、連続スキャン(1.0°/分)
・サンプリング間隔:0.02°
・スリット DS、SS:2/3°、RS:0.6mm
装置名:日本電子株式会社JXA-8200
加速電圧:15kV
照射電流:50nA
照射時間(1点当りの):50mS
実施例1~6で得られた焼結体の表面を平面研削盤で研削し、側辺をダイヤモンドカッターで切断し、バッキングプレートに貼り合わせ、それぞれ直径4インチのスパッタリングターゲットを作製した。尚、実施例1,3,4については、それぞれ幅200mm、長さ1700mm、厚さ10mmの6枚のターゲットをACスパッタリング成膜用(後述する実施例13-15)に作製した。
得られた直径4インチのスパッタリングターゲットをDCスパッタリング装置に装着し、雰囲気としてアルゴンガスにH2Oガスを分圧比で2%添加した混合ガスを使用し、スパッタ圧0.4Pa、基板温度を室温とし、DC出力400Wにて、10kWh連続スパッタを行った。スパッタ中の電圧変動をデータロガーに蓄積し、異常放電の有無を確認した。結果を表2に示す。
尚、異常放電の有無は、電圧変動をモニターして異常放電を検出することにより行った。具体的には、5分間の測定時間中に発生する電圧変動がスパッタ運転中の定常電圧の10%以上あった場合を異常放電とした。特にスパッタ運転中の定常電圧が0.1秒間に±10%変動する場合は、スパッタ放電の異常放電であるマイクロアークが発生しており、素子の歩留まりが低下し、量産化に適さないおそれがある。
得られた直径4インチのスパッタリングターゲットを用いて、雰囲気としてアルゴンガスに水素ガスを分圧比で3%添加した混合ガスを使用し、40時間連続してスパッタリングを行い、ノジュールの発生の有無を確認した。実施例1~6のスパッタリングターゲット表面において、ノジュールは観測されなかった。
尚、スパッタ条件は、スパッタ圧0.4Pa、DC出力100W、基板温度は室温とした。水素ガスは、ノジュールの発生を促進するために雰囲気ガスに添加した。
ノジュールは、スパッタリング後のターゲット表面の変化を実体顕微鏡により50倍に拡大して観察し、視野3mm2中に発生した20μm以上のノジュールについて数平均を計測する方法を採用した。発生したノジュール数を表2に示す。
表1に示す原子比で原料粉末を混合し、表1に示す昇温速度(800℃から焼結温度)、焼結温度、焼結時間で焼結を行い、降温速度を15℃/分とした他は、実施例1と同様に焼結体及びスパッタリングターゲットを製造し、評価した。結果を表2に示す。
また、比較例1、2のスパッタリングターゲットにおいて、スパッタ時に異常放電が発生し、ターゲット表面にはノジュールが観測された。
比較例1,2の焼結体は、InAlO3(ZnO)m(mは0.1~10)で表わされるホモロガス構造化合物とIn2O3のビックスバイト構造の両方の化合物が形成されないために、焼結体の密度が低下し、バルク抵抗が増大することが分かった。その結果、ノジュールが発生したと考えられる。
[酸化物半導体薄膜の製造]
マグネトロンスパッタリング装置に、実施例1~6で作製した表3又は4に示す組成の4インチターゲットを装着し、基板としてスライドガラス(コーニング社製♯1737)をそれぞれ装着した。DCマグネトロンスパッタリング法により、下記の条件でスライドガラス上に膜厚50nmの非晶質膜を成膜した。成膜時には、表3又は表4に示す分圧比(%)でArガス、O2ガス、及びH2Oガスを導入した。非晶質膜を形成した基板を大気中、300℃で60分加熱して酸化物半導体膜を形成した。
基板温度:80℃
到達圧力:8.5×10-5Pa
雰囲気ガス:Arガス、O2ガス、H2Oガス(分圧は表3,4を参照)
スパッタ圧力(全圧):0.4Pa
投入電力:DC100W
S(基板)-T(ターゲット)距離:70mm
ガラス基板上に成膜した基板を用いてResiTest8300型(東陽テクニカ社製)にセットし、室温でホール効果を評価した。具体的に、キャリア濃度を測定した。結果を表3又は4に示す。
また、ICP-AES分析により、酸化物薄膜に含まれる各元素の原子比がスパッタリングターゲットと同じであることを確認した。
装置:(株)リガク製Ultima-III
X線:Cu-Kα線(波長1.5406Å、グラファイトモノクロメータにて単色化)
2θ-θ反射法、連続スキャン(1.0°/分)
サンプリング間隔:0.02°
スリット DS、SS:2/3°、RS:0.6mm
基板として、膜厚100nmの熱酸化膜付きの導電性シリコン基板を使用した。熱酸化膜がゲート絶縁膜として機能し、導電性シリコン部がゲート電極として機能する。
ゲート絶縁膜上に表3又は表4に示す条件でスパッタ成膜し、膜厚50nmの非晶質薄膜を作製した。レジストとしてOFPR♯800(東京応化工業株式会社製)を使用し、塗布、プレベーク(80℃、5分)、露光した。現像後、ポストベーク(120℃、5分)し、シュウ酸にてエッチングし、所望の形状にパターニングした。その後、熱風加熱炉内にて300℃で60分加熱処理(アニール処理)を行った。
その後、Mo(100nm)をスパッタ成膜により成膜し、リフトオフ法によりソース/ドレイン電極を所望の形状にパターニングした。さらに表3又は表4に示すように保護膜を形成する前段階の処理として、酸化物半導体膜に対し、亜酸化窒素プラズマ処理を施した。その後、プラズマCVD法(PECVD)にてSiOxを100nm成膜し、さらにSiOxの上にプラズマCVD法(PECVD)にてSiNxを150nm成膜し保護膜とした。ドライエッチングを用いてコンタクトホールを開口し、薄膜トランジスタを作製した。
作製した薄膜トランジスタについて、電界効果移動度(μ)、閾値電圧(Vth)及びS値を評価した。これらの特性値は、半導体パラメーターアナライザー(ケースレーインスツルメンツ株式会社製4200SCS)を用い、室温、遮光環境下(シールドボックス内)で測定した。
また、盛装したトランジスタについて、ドレイン電圧(Vd)を1V及びゲート電圧(Vg)を-15~20Vとして伝達特性を評価した。結果を表3又は表4に示す。尚、電界効果移動度(μ)は、線形移動度から算出し、Vg-μの最大値で定義した。
実施例7-12の薄膜トランジスタは、閾値電圧の変動が非常に小さく、DCストレスに対して影響を受けにくいことが分かった。
比較例1、2で作製した4インチターゲットを用いてスパッタ条件、加熱(アニーリング)処理条件及び保護膜形成前処理を、表4に記載のものに変更した他は、実施例7~12と同様にして酸化物半導体薄膜及び薄膜トランジスタを作製し、評価した。結果を表4に示す。
表4に示すように、比較例3、4の素子では閾値電圧がマイナスとなった。また、ストレス試験の結果、閾値電圧が1V以上変動して著しい特性の劣化が生じた。
特開2005-290550号公報に開示された成膜装置を用い、表5に示す条件でACスパッタリングを行い、下記条件で非晶質膜を成膜し、加熱処理を行い、ソース・ドレインパターニングをドライエッチングで行った他は、実施例7~12と同様にして酸化物半導体薄膜及び薄膜トランジスタを作製し、評価した。結果を表5に示す。
ACスパッタリングは、具体的に、図1に示す装置を用いて下記のようにして行った。
実施例1、3又は4で作製した幅200mm、長さ1700mm、厚さ10mmの6枚のターゲット31a~31fを用い、各ターゲット31a~31fを基板の幅方向に平行に、距離が2mmになるように配置した。磁界形成手段40a~40fの幅はターゲット31a~31fと同じ200mmであった。ガス供給系からスパッタガスであるAr、H2O及び/又はO2をそれぞれ系内に導入した。
成膜速度を調べるために、以上の条件で10秒成膜し、得られた薄膜の膜厚を測定すると13nmであった。成膜速度は78nm/分と高速であり、量産に適している。
薄膜が形成されたガラス基板を電気炉に入れ、空気中300℃、60分(大気雰囲気下)の条件で熱処理後、1cm2のサイズに切出し、4探針法によるホール測定を行った。その結果、キャリア濃度が4.83×1017cm-3となり、十分半導体化していることが確認できた。
また、XRD測定から薄膜堆積直後は非晶質であり、空気中300℃、60分後も非晶質であることを確認した。
本願のパリ優先の基礎となる日本出願明細書の内容を全てここに援用する。
Claims (15)
- インジウム元素(In)、スズ元素(Sn)、亜鉛元素(Zn)及びアルミニウム元素(Al)を含有する酸化物からなり、
前記酸化物が、InAlO3(ZnO)m(mは0.1~10)で表わされるホモロガス構造化合物と、In2O3で表わされるビックスバイト構造化合物を含む、スパッタリングターゲット。 - 前記ホモロガス構造化合物が、InAlZn4O7、InAlZn3O6、InAlZn2O5及びInAlZnO4で表わされるホモロガス構造化合物から選択される1以上である請求項1に記載のスパッタリングターゲット。
- 前記In、Sn、Zn及びAlの原子比が、下記式(1)~(4)を満たす請求項1又は2に記載のスパッタリングターゲット。
0.10≦In/(In+Sn+Zn+Al)≦0.75 (1)
0.01≦Sn/(In+Sn+Zn+Al)≦0.30 (2)
0.10≦Zn/(In+Sn+Zn+Al)≦0.70 (3)
0.01≦Al/(In+Sn+Zn+Al)≦0.40 (4)
(式中、In、Sn、Zn及びAlはそれぞれ、スパッタリングターゲットにおける各元素の原子比を示す。) - 相対密度が98%以上である、請求項1~3のいずれかに記載のスパッタリングターゲット。
- バルク比抵抗が10mΩcm以下である、請求項1~4のいずれかに記載のスパッタリングターゲット。
- Zn2SnO4で表わされるスピネル構造化合物を含まない、請求項1~5のいずれかに記載のスパッタリングターゲット。
- 請求項1~6のいずれかに記載のスパッタリングターゲットを用いて、スパッタリング法により成膜してなる酸化物半導体薄膜。
- 水蒸気、酸素ガス及び亜酸化窒素ガスから選択される1以上と、希ガスを含有する混合気体の雰囲気下において、請求項1~6のいずれかに記載のスパッタリングターゲットを用いてスパッタリング法で成膜する、酸化物半導体薄膜の製造方法。
- 前記酸化物半導体薄膜の成膜を、希ガスと、少なくとも水蒸気とを含有する混合気体の雰囲気下において行う、請求項8に記載の酸化物半導体薄膜の製造方法。
- 前記雰囲気中に含まれる水蒸気の割合が、分圧比で0.1%~25%である、請求項9に記載の酸化物半導体薄膜の製造方法。
- 前記酸化物半導体薄膜の成膜を、真空チャンバー内に所定の間隔を置いて並設された3枚以上のターゲットに対向する位置に、基板を順次搬送し、前記各ターゲットに対して交流電源から負電位及び正電位を交互に印加する場合に、前記交流電源からの出力の少なくとも1つを、分岐して接続した2枚以上のターゲットの間で、電位を印加するターゲットの切替を行いながら、ターゲット上にプラズマを発生させて基板表面に成膜するスパッタリング方法で行う、請求項8~10のいずれかに記載の酸化物半導体薄膜の製造方法。
- 前記交流電源の交流パワー密度を3W/cm2以上、20W/cm2以下とする、請求項11に記載の酸化物半導体薄膜の製造方法。
- 前記交流電源の周波数を10kHz~1MHzとする、請求項11又は12に記載の酸化物半導体薄膜の製造方法。
- 請求項8~13のいずれかに記載の方法により成膜された酸化物半導体薄膜をチャネル層として有する薄膜トランジスタ。
- 電界効果移動度が10cm2/Vs以上である、請求項14に記載の薄膜トランジスタ。
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