JP2005350297A - Method of growing zinc oxide material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ZnO production method for growing a high quality ZnO material with remarkably lessened dislocation and extremely low defective density. <P>SOLUTION: The high quality ZnO single crystal thin film/bulk crystal can be obtained by growing from a solution in which ZnCl<SB>2</SB>as a Zn source is mixed into a flux containing a specific chloride. In this case, an alkali metal chloride or alkaline earth metal chloride is preferably used as the specific chloride, and an alkali metal oxide or alkali metal carbonate is desirably used as an O-source. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zinc oxide (ZnO) film having a wide gap, a ZnO material such as a bulk, and more particularly to a method for growing a ZnO material, a product including the ZnO material, and a semiconductor device.

  In general, zinc oxide (ZnO) is expected as a material having a wide range of uses such as a light emitting element, a light receiving element, a piezoelectric element, a transparent conductive electrode, and an active element. Further, in the future, application to a GaN substrate, a single crystal thin film for a SAW (Surface Acoustic Wave) filter, an LED substrate, or the like is also considered. In addition, ZnO has a wide band gap of 3 eV or more, like GaN. Therefore, the use and application to semiconductors for light emitting devices that emit light of a short wavelength from blue to ultraviolet light are attracting particular attention. . Furthermore, in response to these demands, various products that take advantage of the characteristics of ZnO materials will be proposed and developed in the future. For this reason, it is extremely important to establish a method for producing zinc oxide with excellent quality.

  Conventionally, a method of growing ZnO, particularly a single crystal of ZnO, has been proposed in Japanese Patent Application Laid-Open No. 2004-131301 (Patent Document 1). Here, in order to obtain a large zinc oxide single crystal, a method for growing a zinc oxide single crystal by a chemical vapor transport method using zinc oxide and a carrier gas and a growth furnace therefor are disclosed.

  Japanese Patent Application Laid-Open No. 2004-84001 (Patent Document 2) uses an organic metal vapor phase growth method among methods for growing zinc oxide by MBE (molecular beam epitaxy method) and MOCVD (organic metal vapor phase growth method). A method for growing zinc oxide is disclosed. Specifically, Patent Document 2 discloses that a zinc oxide buffer layer and a zinc oxide crystal film are formed on a sapphire substrate using a metal organic vapor phase growth method in order to grow the zinc oxide crystal film easily and at low cost. Propose to form. In this case, the zinc oxide buffer layer is formed under zinc-rich conditions using only an organometallic compound gas containing zinc and oxygen, and subsequently, the zinc oxide crystal film is composed of an organometallic compound gas containing zinc and oxygen and an oxygen gas. Both are used and grown on a zinc oxide buffer layer under the condition that zinc is completely oxidized.

  Furthermore, Japanese Patent Laid-Open No. 2002-289918 (Patent Document 3) proposes a method and a light-emitting device for manufacturing a wide gap zinc oxide (ZnO) -based p-type semiconductor crystal. Patent Document 3 discloses a method of intermittently supplying donor impurities when a p-type semiconductor crystal is manufactured by simultaneously doping a semiconductor crystal with donor / acceptor impurities.

  JP 2000-199097 A (Patent Document 4) discloses a liquid phase deposition method using an aqueous solution containing zinc oxide and zinc nitrate ions and a water-insoluble liquid in contact with the liquid surface of the aqueous solution. A method of forming a ZnO film by a method is disclosed. Here, the ZnO film is formed by electrodeposition.

JP 2004-131301 A JP 2004-84001 A JP 2002-289918 A JP 2000-199097 A

  As apparent from the above, conventionally, the chemical vapor transport method, the MBE method, the MOCVD method, and the like have been mainly used for the production and growth of ZnO materials, in particular, ZnO single crystals. As shown in FIG. 4, a liquid deposition method by electrodeposition is also used. However, ZnO formed by MBE, MOCVD, or chemical vapor transport has many transitions, defects, etc., and is insufficient in terms of crystal quality, and cannot be applied to various uses of ZnO expected in the future. Is in the situation.

  On the other hand, the liquid phase deposition method has a lower reaction temperature and a mild reaction compared to other thin film manufacturing methods, but as in Patent Document 4, using an aqueous solution containing ZnO and zinc nitrate ions, It is difficult to obtain a high-quality ZnO material that can be applied to other than batteries.

  An object of the present invention is to provide a ZnO manufacturing method for growing a high quality ZnO material with extremely low density of dislocations and defects.

  Another object of the present invention is to provide a growth method for growing a high-quality ZnO material from a solution using liquid phase epitaxial growth (LPE).

  Another object of the present invention is to provide a product, particularly a semiconductor device, such as an element or device containing a high quality ZnO material.

According to one aspect of the present invention, in a growth method for growing a zinc oxide (ZnO) material by liquid phase growth, ZnCl ₂ is prepared as a Zn source, and a flux containing a predetermined chloride is prepared, A growth method characterized by growing the ZnO material in a solution in which ZnCl ₂ and the flux are mixed is obtained.

  According to another aspect of the present invention, there is obtained a growing method characterized in that the solution contains a predetermined oxide or carbonate as an O source.

According to another aspect of the present invention, there is provided a growing method characterized in that the chloride contained in the flux is an alkali metal and / or alkaline earth metal chloride. Speaking concretely, the chloride _{LiCl, NaCl, KCl, RbCl,} CsCl, MgCl 2, CaCl 2, SrCl 2, BaCl 2, and is characterized by including at least one ZnCl _2. In this case, the listed single chloride may be used as a flux, or a mixture containing two or more listed chlorides may be used as a flux.

In any case, the mixed solution containing the flux and ZnCl ₂ was found to form a eutectic or hypoeutectic. By using such a mixed solution, the melting temperature can be reduced to 1000 ° C. or lower, preferably 800 ° C. or lower, and a ZnO material having a low thermal strain, specifically, a single crystal film of ZnO is formed by oxygen. It was possible to grow and form a film at a pressure of atmospheric pressure (101 kPa) in a contained atmosphere.

Furthermore, according to still another aspect of the present invention, there is obtained a growing method characterized in that the oxide or carbonate as the O source is an alkali metal oxide or carbonate. In this case, the alkali metal oxide may be selected from Li ₂ O, Na ₂ O, K ₂ O, and the alkali metal carbonate may be Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO. ₃ and Rb ₂ CO ₃ may be selected.

  According to the present invention, it is possible to grow a high quality ZnO film or a bulk material having a very low transition and defect density at a low temperature of 1000 ° C. or less and at atmospheric pressure. In the ZnO thin film / bulk crystal growth method according to the present invention, the impurity precipitation coefficient k of the thin film / bulk crystal can be controlled to be smaller than 1. In addition, since a thin film / bulk crystal can be grown from a liquid phase at a low pressure in the atmospheric state, wafer materials such as LEDs and solar cells can be formed at low cost in the present invention. Furthermore, the method of the present invention has the advantage that it is easy to handle and the chemicals used are inexpensive and non-toxic. Also, although the ZnO does not dissolve in water, the flux used is very soluble in water, so that the grown thin film / bulk crystal and substrate can be easily cleaned.

  The present invention resides in a method for growing ZnO using a flux capable of growing ZnO bulk crystals or thin film crystals having excellent crystallinity and low impurity concentration from a solution. That is, in the present invention, a specific chloride is used as a flux for forming solute ZnO. As the specific chloride in this case, it has been found that alkali metal and / or alkaline earth metal chloride is preferable.

Specifically, the alkali metal and / or alkaline earth metal chloride to form a flux, LiCl, NaCl, KCl, RbCl , CsCl, MgCl 2, CaCl 2, SrCl 2, BaCl 2, and, among the ZnCl ₂ From this, at least one chloride may be selected. In this case, a single chloride may be selected from the listed alkali metal and / or alkaline earth metal chlorides, or two or more may be selected and used in combination. When two or more chlorides are mixed, it is desirable that these mixed chlorides form a eutectic (eg, NsCl-CsCl), thereby lowering the dissolution temperature to 1000 ° C. or less, more preferably 800 ° C. The dissolution temperature of these mixtures was 260 ° C. or higher.

On the other hand, ZnCl ₂ was used in the present invention as a Zn source for forming solute ZnO. Thus, it has been found that ZnCl ₂ used as a Zn source forms a eutectic or hypoeutectic with the chloride forming the above-described flux.

Furthermore, the embodiment according to the present invention uses an alkali metal oxide or an alkali metal carbonate as the O source of the solute ZnO. The alkali metal oxide that can be used as the O source may be one or more oxides selected from the group consisting of Li ₂ O, Na ₂ O, and K ₂ O, and the alkali metal carbonate is Li _2. One or more carbonates selected from the group of CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , and Rb ₂ CO ₃ may be used.

  Hereinafter, a case where a ZnO thin film is formed on the surface of a ZnO substrate will be described as a method for growing and forming ZnO according to an embodiment of the present invention. Here, a so-called vertical furnace core tube film forming apparatus having a furnace core tube provided with a heater and a crucible disposed in the furnace core tube is used. When a ZnO thin film is formed, the ZnO substrate is supported by a substrate holder, and the substrate holder is attached to the lower end of a support bar that can move up and down in the furnace core tube. With the ZnO substrate supported at the lower end, the support rod is guided from the upper part of the furnace core tube to the crucible inside the furnace core tube, a chemical reaction is performed in the crucible, and a ZnO thin film or ZnO bulk is grown on the ZnO substrate. A film is formed.

In this embodiment, a mixed solution of a flux containing chlorides listed above, ZnCl ₂ as a Zn source, and an oxide (or carbonate) as an O source is accommodated. In this example, it is assumed that the mixed solution in the crucible is kept at 1000 ° C. or lower, preferably 800 ° C. or lower by heating with a heater.

First, the case where ZnCl _{2 is} used as the Zn source and K ₂ O and Na ₂ O are used as the O source will be described. Chemical reactions in this case can be expressed by the equations (1) and (2), respectively.

ZnCl ₂ + K ₂ O → ZnO + 2 KCl (1)
ZnCl ₂ + Na ₂ O → ZnO + 2NaCl (2)
The chemical reaction formulas when Na ₂ CO ₃ or K ₂ CO ₃ is used as the O source can be expressed by the formulas (3) and (4), respectively.

ZnCl ₂ + Na ₂ CO ₃ → ZnO + 2NaCl + CO ₂ (3)
ZnCl ₂ + K ₂ CO ₃ → ZnO + 2KCl + CO ₂ (4)
As is apparent from the right side of the formulas (1) to (4), NaCl or KCl is generated as a byproduct together with the solute ZnO, and these NaCl and KCl slightly change the composition or melting point of the mixed solution. In addition, it can be seen that carbon dioxide is released into the atmosphere in the equations (3) and (4).

In any case, the mixed solution used in the above-described embodiment has a low melting point composition composed of the alkali metal chloride and ZnCl ₂ described above. Specifically, a flux formed by a co-crystal of 35 mol% NaCl and 65 mol% CsCl and having a melting point of 486 ° C., and 30.4 mol% NaCl, 24.4 mol% KCl, 45.2 mol% CsCl, Eutectic flux with a melting point of 480 ° C.

In the above, only the alkali metal chloride is exemplified as the chloride contained in the flux. However, according to the experiments by the present inventors, the alkaline earth metal chloride, specifically, MgCl ₂ , CaCl ₂ , SrCl It has been found that the same effect can be obtained even when ₂ , BaCl ₂ or ZnCl ₂ is used.

  According to the embodiment described above, a ZnO crystal could be crystallized on the ZnO substrate. In this case, bulk crystals were grown by seedless solution growth, while ZnO thin films were grown by liquid phase epitaxy growth.

  In the method according to the present invention, the production conditions, pressure, and the like are extremely simple, and the penetration of impurities into the material can be reduced to a segregation count k of 1 or less.

  According to the method of the present invention, it has been found that when a ZnO thin film is homoepitaxially grown from a solution on a ZnO substrate, a ZnO thin film having extremely high crystallinity can be obtained. This was achieved by the absence of lattice misfit and no difference in thermal expansion coefficient between the ZnO substrate and the ZnO thin film.

Hereinafter, with reference to the drawings, the experimental results in the case where crystals are grown using the seedless flux method will be described. FIG. 1 is an SEM photograph (× 4000) showing a ZnO single crystal obtained as a result of a chemical reaction (formula (1)) between ZnCl ₂ and K ₂ O. As is clear from FIG. 1, plate-like crystals are generated.

  FIG. 2 is an SEM photograph (× 15000) showing a ZnO single crystal obtained by the chemical reaction represented by the formula (3) between ZnCl 2 and Na 2 CO 3, and it can be seen that the crystal is grown in a columnar shape.

FIG. 3 is an SEM photograph (× 19000) showing a ZnO single crystal obtained by the chemical reaction represented by the formula (4) between ZnCl ₂ and K ₂ CO ₃ , in which crystals grown in a columnar shape are observed. it can.

Referring to FIG. 4, it is a diagram showing a measurement result by powder X-ray diffraction (XRD) of a ZnO crystal obtained by the present invention. In FIG. 4, a shows the measurement result of the ZnO crystal obtained by the reaction of ZnCl ₂ and K ₂ O (formula (1)), and b shows the reaction of ZnCl ₂ and Na ₂ CO ₃ shown in formula 3. It is a measurement result of the obtained ZnO crystal. Furthermore, c is the measurement result of the ZnO crystal obtained by the reaction of ZnCl ₂ and K ₂ CO ₃ shown in Formula 4.

Referring to FIG. 5, the result of measuring the X-ray rocking curve (XRC) of the ZnO crystal described above is shown. FIGS. 5A, 5B and 5C show the full width at half maximum with respect to the maximum peak of ZnO obtained using Na ₂ CO ₃ , K ₂ CO ₃ and Na ₂ O as an oxygen source, respectively (Full-Width). -At-Half-Maximum) (FWHM). As is apparent from FIG. 5, it can be seen that the ZnO crystal obtained by the present invention has excellent crystallinity. For the measurement in FIG. 5, a GE (440) 4-crystal monochromator was used.

  The high-quality ZnO obtained in the present invention can be applied to various devices such as single crystal thin films for SAW filters, surface modification of bulk crystals, or ZnO pn junction formation, and LED substrates. It is also applicable to the manufacture of Furthermore, the growing method of the present invention can be applied to products such as high-intensity white solid illumination by combining with ultraviolet LEDs and RGB phosphors. Furthermore, the present invention can also be applied to semiconductor devices such as TFT (Thin Film Transistor) and display devices such as organic EL and liquid crystal display devices using TFT.

Is an SEM photograph showing a ZnO single crystal obtained by the present invention, wherein the result of a chemical reaction between the ZnCl ₂ and _{K 2} O, is a photograph of the obtained ZnO single crystal. Is an SEM photograph showing a ZnO single crystal obtained by the present invention, wherein the result of a chemical reaction between the ZnCl ₂ and _Na 2 CO _3, a photograph of the obtained ZnO single crystal. Is an SEM photograph showing a ZnO single crystal obtained by the present invention, wherein the result of a chemical reaction between the ZnCl ₂ and _K 2 CO _3, a photograph of the obtained ZnO single crystal. It is a figure which shows the measurement result by X-ray diffraction of the ZnO single crystal shown by FIGS. (A), a diagram showing measurement results of X-ray rocking curve in the case of using (b), and, (c) _Na 2 _CO 3, respectively as the oxygen source, K2CO3, Na ₂ O.

Claims (17)

In a growth method for growing a zinc oxide (ZnO) material using a solution, ZnCl ₂ is prepared as a Zn source, a flux containing a predetermined chloride is prepared, and the ZnCl ₂ and the flux are mixed. A growth method comprising growing the ZnO material in a solution.   2. The growing method according to claim 1, wherein the solution contains a predetermined oxide or carbonate as an O source.   3. The growing method according to claim 1, wherein the chloride contained in the flux is an alkali metal and / or alkaline earth metal chloride. According to claim 3, wherein the flux contains _{LiCl, NaCl, KCl, RbCl,} CsCl, MgCl 2, CaCl 2, SrCl 2, BaCl 2, and, at least one chloride selected from the group consisting of ZnCl ₂ A breeding method characterized by that. According to claim 4, wherein the flux, LiCl, NaCl, KCl, RbCl , CsCl, MgCl 2, CaCl 2, SrCl 2, BaCl 2 and, that it is formed by a single chloride selected from ZnCl ₂ A breeding method characterized by It according to claim 4, wherein the flux, LiCl, NaCl, KCl, RbCl , CsCl, MgCl 2, CaCl 2, SrCl 2, BaCl 2, and a mixture containing chloride selected from ZnCl ₂ 2 or more A breeding method characterized by 7. The growing method according to claim 5, wherein the mixed solution containing the flux and ZnCl ₂ forms a eutectic or a hypoeutectic.   The growth method according to claim 7, wherein a melting temperature of the eutectic or hypoeutectic is 1000 ° C. or lower, preferably 800 ° C. or lower.   The growth method according to claim 8, wherein the growth is performed in an oxygen-containing atmosphere at a pressure of atmospheric pressure (101 kPa).   3. The growing method according to claim 2, wherein the oxide or carbonate as the O source is an alkali metal oxide or carbonate. 11. The growth method according to claim 10, wherein the alkali metal oxide is at least one oxide selected from the group consisting of Li ₂ O, Na ₂ O, and K ₂ O. 11. The alkali metal carbonate according to claim 10, wherein the alkali metal carbonate is at least one carbonate selected from the group consisting of Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , and Rb ₂ CO _3. Training method.   A ZnO single crystal thin film / bulk obtained by the growth method according to claim 1.   A product comprising a ZnO single crystal thin film / bulk obtained by the growth method according to claim 1.   A semiconductor device comprising a ZnO single crystal thin film / bulk obtained by the growth method according to claim 1.   A TFT comprising a ZnO single crystal thin film / bulk obtained by the growth method according to claim 1. A display device comprising the TFT according to claim 16.

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