JP5281371B2 - Zinc oxide-based semiconductor growth method and semiconductor device manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for growing a high-quality zinc oxide semiconductor, especially a zinc oxide (ZnO) single crystal with excellent flatness and crystallinity on a substrate, and to provide a semiconductor element having a semiconductor layer, flat and excellent in crystallinity, and exhibiting high performance, high reliability, and excellent mass productivity. <P>SOLUTION: The zinc oxide semiconductor layer is crystal-grown on the substrate by an MOCVD method having a process for supplying material gas formed by vaporizing material solution of ketone compound organic metal material containing zinc and mixture gas of polar oxidation gas and nonpolar oxidation gas. A mixing ratio of the polar oxidation gas to nonpolar oxidation gas in the mixing gas is in a range of 1:4 and 4:1. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for growing a zinc oxide based semiconductor and a method for manufacturing a semiconductor element, and more particularly to a method for growing a zinc oxide based semiconductor layer by MOCVD and a method for manufacturing a semiconductor light emitting element using the same.

  Zinc oxide (ZnO) is a direct transition type semiconductor having a band gap energy of 3.37 eV at room temperature, and is expected as a material for optical elements in the blue or ultraviolet region. In particular, the exciton binding energy is 60 meV and the refractive index n = 2.0, which is very suitable for a semiconductor light emitting device. Further, the present invention can be widely applied not only to light emitting elements and light receiving elements but also to surface acoustic wave (SAW) devices, piezoelectric elements, and the like. In addition, the raw material is inexpensive and harmless to the environment and the human body.

  In general, MOCVD (Metal Organic Chemical Vapor Deposition) method, MBE (Molecular Beam Epitaxy) method, and the like are used as crystal growth methods for zinc oxide compound semiconductors. The MBE method is a crystal growth method under an ultra-high vacuum, and has problems such as expensive equipment and low productivity. On the other hand, the MOCVD method has the advantages that the apparatus is relatively inexpensive, allows large area growth and simultaneous growth of a large number of sheets, has high throughput, and is excellent in mass productivity and cost. .

Various reports have been made on the method of crystal growth of zinc oxide (ZnO) or a zinc oxide based semiconductor on a dissimilar material substrate such as sapphire (Al ₂ O ₃ ) by MOCVD. However, dislocations and defects are likely to occur during growth, resulting in crystals or polycrystals containing many defects. As a result, there has been a problem that it becomes a factor causing an increase in residual carrier density and impurity concentration. In order to achieve high performance and high reliability of semiconductor elements, particularly semiconductor light emitting elements having a large operating current density, it is extremely important to develop a method for growing a flat high quality crystal with few crystal defects.

As a method for growing a ZnO-based crystal by MOCVD, there are a method using an alkyl metal material and a method using a liquid source such as a diketone material (hereinafter referred to as a liquid source MOCVD method). The liquid source MOCVD method is a method for growing a crystal by atomizing and / or vaporizing a liquid material obtained by dissolving a high vapor pressure material in a solvent and supplying the atomized material to a reactor. As a growth method using such a liquid source CVD method, for example, a β-diketone compound and oxygen (O ₂ ) are used as materials, and zinc oxide is crystal-grown on a sapphire substrate. However, when a diketone-based material is used and crystal growth is performed particularly on an A-plane sapphire or C-plane sapphire substrate, a needle-like crystal or a nanocolumn-like crystal tends to be formed. Therefore, crystal growth is performed using an R-plane sapphire substrate to improve flatness (for example, Patent Document 1 and Patent Document 2), but sufficient improvement has not been achieved.
Japanese Patent No. 3826165 Japanese Patent No. 3903209

  The present invention has been made in view of the above points, and its purpose is to grow a high-quality zinc oxide-based semiconductor excellent in flatness and crystallinity on a substrate, particularly a zinc oxide (ZnO) single crystal. It is to provide a method. In addition, to provide a semiconductor element having a flat and excellent crystallinity and having high performance, high reliability, and mass productivity, in particular, a high performance semiconductor light emitting element excellent in luminous efficiency and mass productivity. is there.

The present invention is a method for crystal growth of a zinc oxide based semiconductor layer on a substrate by MOCVD,
Supplying a material gas obtained by vaporizing a material solution of a ketone compound organometallic material containing zinc and a mixed gas of a polar oxidizing gas and a nonpolar oxidizing gas to the substrate,
The mixing ratio of the polar oxidizing gas and the nonpolar oxidizing gas in the mixed gas is in the range of 1: 4 to 4: 1.

Further, the present invention is a method for manufacturing a semiconductor light emitting device by laminating a zinc oxide based semiconductor layer on a substrate by MOCVD method,
While supplying a material gas obtained by vaporizing a material solution of a ketone compound organometallic material containing zinc and a mixed gas of a polar oxidizing gas and a nonpolar oxidizing gas to the substrate, at least the first conductivity type semiconductor layer and the first And sequentially growing a second conductivity type semiconductor layer having a polarity opposite to the conductivity type,
The mixing ratio of the polar oxidizing gas and the nonpolar oxidizing gas in the mixed gas is in the range of 1: 4 to 4: 1.

As one feature of the present invention described above, the polar oxidizing gas includes any one of water vapor (H ₂ O), ozone, methyl alcohol, and ethyl alcohol, and the nonpolar oxidizing gas is oxygen (O ₂ ) gas, Any one of nitrous oxide (N ₂ O) and carbon dioxide (CO ₂ ) is contained.

  Hereinafter, a method for growing a zinc oxide (ZnO) -based semiconductor crystal layer having excellent single crystallinity and flatness on a substrate by MOCVD using a liquid material (hereinafter referred to as liquid source MOCVD) will be described. Details will be described with reference to FIG.

In the liquid source MOCVD method, the present invention exists inside a solute molecule of a material gas which is completely vaporized and has a relatively large molecular weight in order to grow a high-quality and flat ZnO-based semiconductor crystal layer having a c-axis orientation on a substrate. It was examined from the viewpoint that it is important to reliably oxidize Zn atoms to be broken, or to break bonds around Zn, and to oxidatively decompose the solvent components and solute side chains (functional groups). As a result, as an oxygen source, two types of oxygen sources, oxygen (O ₂ ) gas (non-polar oxidant) and water vapor (H ₂ O) (polar oxidant), were mixed at a constant ratio, and the flatness was excellent. A method for growing a high-quality ZnO-based semiconductor single crystal has been found.

  Further, a semiconductor light emitting element (LED: Light Emitting Diode) will be described as an example of the semiconductor element formed by the growth method.

  In the drawings described below, substantially the same or equivalent components or parts are denoted by the same reference numerals.

FIG. 1 schematically shows a configuration of a liquid source MOCVD apparatus 100 used for crystal growth.
[Supply of material solution and material solution]
A material solution 116 made of a solute and a solvent and containing an organic metal material of a ketone compound was used as a zinc material (group II material). Specifically, bis (6-ethyl-2,2-dimethyl-3,5-decanedionato) zinc (hereinafter referred to as Zn (EDMDD) ₂ ) which is a β-diketone metal complex which is an organometallic material as a solute. Using. Further, ethylcyclohexane (hereinafter referred to as ECH) was used as a solvent. The concentration of the material solution 116 was 0.2 mol / L.

  As other β-diketone materials, for example, the following can be used.

  Mt (THD) n: Here, THD is tetramethylheptanedionate, and Mt (metal) is, for example, Ba, Pb, Sr, La, Zn.

  Mt (METHD) n: Here, METHD is methoxyethoxytetramethylheptanedionate, and Mt (metal) is, for example, Ba, Pb, Sr, Ru, Zr.

  Mt (OD) n: Here, OD is octadionato, and Mt (metal) is, for example, Zn or Ru.

  Mt (EDMDD) n: Here, EMDDD is ethyldimethyldecanedionate, and Mt (metal) is, for example, Cu, Zn, Mg, La, Pr, Nd, Tm, Dy, Er, Ho, Tb, Yb. , Ga.

Furthermore, solid materials such as Zn (DPM) ₂ (here, DPM: dipivaloylmethanato) can also be used. In addition, materials other than those described above are possible, but a combination with a solvent that does not react with the solvent and does not separate or precipitate must be considered. However, in view of clogging of equipment piping, maintenance, etc., a liquid organometallic material is preferred.

As described above, ethylcyclohexane (ECH) was used as the solvent for the material solution. ECH is a nonpolar cyclic saturated hydrocarbon solvent and does not interact with solute Zn (EDMDD) ₂ at room temperature. Further, the vapor pressure of ECH is relatively high at about 1.3 kPa at 20 ° C., which is suitable in terms of stabilizing the above-described atomization / vaporization of the material solution. As a similar solvent, butyl acetate, i-butyl alcohol, toluene and the like are suitable. Further, materials having higher vapor pressure include tetrahydrofuran (THF), hexane, and the like, which can be appropriately selected.

  The material solution 116 is stored in the material solution container 117. Helium (He) gas was used as the material solution pressure feeding gas, the material solution container 117 was pressurized to 200 kPa, and the pressure was fed to the liquid flow rate adjusting device 118a. The flow rate of the material solution 116 was adjusted to 0.1 sccm by the liquid flow rate adjusting device 118 a and supplied to the atomizing nozzle 108 through the liquid feeding tube 119.

He gas has an advantage of low solubility in a liquid, and even when the pumping pressure is increased, bubbles are not easily generated during decompression. However, even with nitrogen gas (N ₂ ), argon gas (Ar), etc., if the feed pressure is 400 kPa or less, the amount dissolved in the material solution is small, and bubbles are generated in the material solution even under reduced pressure after the liquid flow control device. There is no problem because there is no issue.
[Atomization of material solution]
Nitrogen (N ₂ ) gas was used as the atomization assist gas. Before the atomization support gas is supplied to the atomization nozzle 108, the flow rate is adjusted by the gas flow rate adjusting device 105 a, and the atomization support gas is sent to the atomization support gas heater 107 through the atomization support gas supply pipe 106 and heated to an appropriate temperature. After that, it was supplied to the atomization nozzle 108. That is, the atomization assisting gas is heated by the atomization assisting gas heater 107 because the gas temperature decreases due to adiabatic expansion after passing through the gas flow rate adjusting device 105a. Moreover, since the gas temperature in the vaporizer is lowered by the heat of vaporization when the material solution is atomized and the vaporization is prevented from being accelerated, the heating of the atomization support gas is effective in improving the vaporization efficiency. Specifically, the gas flow rate adjusting device 105a was adjusted so that the flow rate of the atomization support gas (N ₂ gas) was 1.5 SLM. Further, the atomization support gas heater 107 heated the atomization support gas to 250 ° C. and supplied it to the atomization nozzle 108.

The atomization assisting gas may be a chemically inert gas such as nitrogen (N ₂ ), argon (Ar), helium (He), hydrogen (H ₂ ), and a mixture of two or more thereof. Gas may be used. A material gas (oxidation source) described later is preferably a mixture of a nonpolar oxidation source (for example, oxygen (O ₂ )) and a polar oxidation source (for example, water vapor (H ₂ O)) at a constant ratio. Two or more of each may be mixed.

  The material solution was made into fine particle droplets (mist) by the atomizing nozzle 108. The used atomizing nozzle is configured such that the material solution that has been fed and the atomization assisting gas that has been heated merge at the tip of the atomizing nozzle 108. Therefore, the material solution is atomized into fine and uniform droplets (mist) by the action of the atomization assisting gas (violently swirled) and sprayed into the vaporizer 109.

  The atomization nozzle 108 used in this example has a liquid flow rate of 0.05 to 1.00 ml / min, a liquid viscosity of 10 cP (centipoise) or less, an atomization assist gas volume of 15000 to 20000 ml / min, and a secondary pressure (vaporizer). It has the capability of generating mist having a liquid particle size of 60 μm or less at a pressure of 20 kPa.

  For example, if the secondary pressure is 0.1 kPa, the atomization support gas is 15 to 20 ml / min (standard state). If 1 kPa, the support gas is 150 to 200 ml / min (standard state). 2000 ml / min (standard state) is required. The liquid particle size after atomization varies depending on the liquid flow rate, liquid viscosity, atomization assist gas flow rate, secondary pressure, temperature, and the like. If the above conditions are constant, the particle size is also constant.

As described above, the atomization nozzle 108 used in the present example has a structure in which the material solution is discharged from the central portion, and the atomization assisting gas is ejected from the outer peripheral portion to be misted. With this structure, the tip of the atomizing nozzle is always cleaned and no solute component is deposited or deposited. In the opposite case, the material solution may accumulate at the tip of the atomizing nozzle and the solute component may be deposited and deposited.
[Solvent / solute vaporization and vaporizer]
The material solution mist sprayed from the atomizing nozzle 108 is a mist having a smaller particle diameter (hereinafter referred to as a mist component) in which the solvent having a high vapor pressure is preferentially evaporated from the surface of the mist in the heated vaporizer 109 and the material solute components are concentrated. , Called solute mist). Furthermore, the organometallic material component evaporates from the surface of the finely divided solute mist, the mist disappears, and all the material solution is gasified. The atomization support gas and the gasified material solution (material solution gas) are supplied to the reaction vessel 120 through the above process. The section from the vaporizer 109 to the reaction vessel 120 was also heated so that the vaporized material solution did not re-aggregate.

  Here, by making the material solution mist particle size small and uniform, the solvent evaporation area is widened, the solvent is quickly evaporated, and the evaporation time (distance in the vaporizer) can be made constant. The same applies to solute evaporation after solvent evaporation.

Specifically, the vaporizer 109 used in this example has a diameter of 10 cm and a length of 65 cm, is provided with an internal vaporization heater and has fins for widening the gas contact area, and externally used for heat insulation. The structure was equipped with a heater. Moreover, the temperature of the gas contact part was set to 300 ° C., and the jet part temperature was set to 250 ° C. In addition, it is preferable that the vaporization temperature of a material solution is 200 degreeC or more.
[Material gas]
As the material gas (Group VI gas), oxygen (O ₂ ) gas (nonpolar oxidation source or nonpolar oxidation gas) and water vapor (H ₂ O) (polar oxidation source or polar oxidation gas) were used. Oxygen (O ₂ ) gas was supplied to the material gas heater 111 through the material gas pipe 103 and the material gas supply pipe 110 after the flow rate was adjusted by the gas flow rate adjusting device 105 d. The oxygen gas is adiabatically expanded and cooled at the subsequent stage of the gas flow rate adjusting device 105d, and is heated by the material gas heater 111 because it is necessary to have the same temperature as the gas supplied from the vaporizer 109.

Water vapor (H ₂ O), which is another material gas, heats a water container 131 containing water (ultra-pure water) 130 with a water container side heater 132 and a water container bottom heater 133 to produce heated steam. After adjusting the flow rate with the high-temperature gas flow rate adjusting device 135, the gas was fed to the vaporized gas introduction tube 129 through the water vapor pipe 136. The water was overheated so that the water vapor pressure was equal to or higher than the sum of the internal pressure of the water vapor pipe (reaction vessel pressure) and the operation differential pressure of the high-temperature gas flow rate adjusting device 135. Further, since the water vapor is adiabatically expanded and cooled at the subsequent stage of the flow rate adjusting device 135 like oxygen, the high-temperature gas flow rate adjusting device 135 and the water vapor pipe 136 were heated. The heated oxygen and water vapor were combined with the atomization support gas and the material solution gas before the reaction vessel 120 and supplied to the reaction vessel 120 through the introduction pipe 129.

As described above, in this example, since the ZnO crystal was grown, oxygen gas (nonpolar oxidation source) and water vapor (polar oxidation source) were used as the material gas. The flow rate is adjusted by a gas flow rate adjusting device, the mixing ratio of water vapor (H ₂ O) and oxygen gas is 2 to 3 (H ₂ O: O ₂ = 2: 3), and the total flow rate is 0.5 SLM. did. The ejection temperature of the gas heater was set to 250 ° C., which is the same as that of the atomization support gas and material solution gas fed from the vaporizer.

As for the ZnO crystal growth material gas, in a polar oxidation source, lower alcohol such as ozone, methyl alcohol, or ethyl alcohol may be used instead of water vapor (H ₂ O). In the case of a nonpolar oxidation source, nitrous oxide (N ₂ O), carbon dioxide (CO ₂ ), or the like may be used instead of oxygen (O ₂ ). Moreover, you may use these mixtures.
As described above, by adopting a configuration in which the material gas is merged from the subsequent stage of the vaporizer 109, the gas flow rate and temperature flowing through the vaporizer 109 can be kept constant even when the material gas flow rate is increased or decreased. Moreover, you may supply inert gas, such as nitrogen gas, simultaneously with material gas.

  In addition, what is necessary is just to flow the following flow volume, when you want to make constant the gas flow volume which flows into reaction container.

Inert gas flow rate = Gas flow rate flowing into the reaction vessel-(Atomization support gas flow rate + Material solution gas flow rate + Material gas flow rate)
Further, when it is desired to increase or decrease the flow rate of gas flowing into the reaction vessel, it is sufficient to supply an inert gas that is commensurate.
[Growth of ZnO crystal]
As the substrate 10 for crystal growth, α-sapphire single crystal (Al ₂ O ₃ ) having a corundum structure was used. In this example, the ZnO crystal layer 11 was grown on the sapphire A plane with the sapphire A plane ({11-20} plane) as the crystal growth plane. Hereinafter, a substrate having a sapphire A plane ({11-20} plane) as a main surface (crystal growth plane) is referred to as an A-plane sapphire substrate. Here, the Miller index {} indicates a representative value of an equivalent surface.

  The A-plane sapphire substrate 10 was set on the susceptor 121, and oxygen gas (flow rate 0.5 SLM) was supplied to the reaction vessel 120 from the gas flow rate adjusting device 105d. The temperature of the material gas heater 111 was adjusted so that the temperature of the supplied gas was 250 ° C., and further the pressure in the reaction vessel 120 was adjusted to 10 kPa by the pressure adjusting device 124 at the rear stage of the reaction vessel 120. . Thereafter, the substrate 10 was heated to 900 ° C. by the substrate heater 122 and subjected to a heat treatment for 10 minutes. At this time, the material solution gas introduction valve 126 is closed, the exhaust valve 127 is opened, and nitrogen gas (flow rate: 1.5 SLM) is allowed to flow from the gas flow rate adjusting device 105a to ensure the total amount of gas during growth and to stabilize Turned into.

Next, the substrate temperature was lowered and held, and the growth temperature (Tg) was set to 500 ° C. to grow the ZnO crystal layer 11. Atomization support gas is atomized by supplying 1.5 SLM of nitrogen gas from the gas flow controller 105a and 0.1 sccm of 0.2 mol / L Zn (EDMDD) ₂ / ECH solution as the material solution from the liquid flow controller 118a The vaporized material solution gas was supplied to the reaction vessel 120. The spraying temperature of the atomization assisting gas was 250 ° C., and the spraying temperature of the vaporizer 109 was 250 ° C. Furthermore, the flow rate of oxygen as the material gas was changed, and the total flow rate with water vapor supplied from the high-temperature gas flow rate adjustment device 135 was adjusted to 0.5 SLM (H ₂ O: O ₂ = 2: 3). Crystal growth was performed for 120 minutes to obtain a ZnO single crystal that was two-dimensionally grown with a thickness of 1.0 μm on the A-plane sapphire substrate 10 (growth rate Rg = 0.5 μm / hr).

  In addition, oxygen gas etc. which are material gas may be mixed and introduced into atomization assistance gas. The organometallic compound material and the organic solvent, which are material solutions, may be oxidized by oxygen to cause low molecular weight or cracking. By mixing with the gas of the material solution in advance, the reaction between the Zn element and the oxygen source on the substrate It is because it may make it easy. In addition, cracking is to separate oxygen molecules or atoms from collision with solvent molecules and break some of the bonds of the solvent molecules apart from the reduction of molecular weight by oxidation reaction.

  In this embodiment, an A-plane sapphire substrate is used as the substrate, but the present invention is not limited to this. In the case of a ZnO crystal having c-axis orientation on the substrate surface, the crystal substrate may be such that the substrate surface has lattice matching points at rotationally symmetric positions of 60 °, 120 °, and 180 °. Further, in the case of an a-axis or m-axis oriented ZnO crystal, any crystal substrate in which a lattice matching point exists at a rotationally symmetric position of 180 ° may be used. For example, a crystal substrate such as R-plane sapphire, C-plane sapphire, ZnO, or SiC (silicon carbide) can be used.

Further, the case of growing zinc oxide (ZnO) has been described as an example, but the above growth method can also be applied to the case of growing a zinc oxide based semiconductor (mixed crystal). That is, as described in detail for the material solution 116, various organometallic materials (ketone materials) can also be used. Specifically, the organometallic material may be a material containing gallium (Ga), magnesium (Mg), aluminum (Al), copper (Cu), or a rare earth metal. For example, when growing a Mg mixed crystal type oxide semiconductor (Mg _x Zn _{(1-x) 2} O 3), for example, Mg (EDMDD) ₂ dissolved in an ECH solution can be used.
[Growth layer crystallinity]
FIGS. 2 and 3 show the surface of the ZnO crystal grown by the above method with a growth temperature (Tg) of 500 ° C. and a mixing ratio of water vapor and oxygen gas (H ₂ O: O ₂ ) of 2: 3. A differential interference microscope image and a surface SEM image (magnification 20,000 times) are shown. From these results, it was confirmed that the surface of the ZnO crystal grown by the above process had no irregularities or pits and was a very flat mirror surface microscopically.

  Moreover, FIG. 4 is a figure which shows the analysis result of secondary ion mass spectrometry (SIMS). It was confirmed that the concentrations of carbon (C), hydrogen (H) and nitrogen (N) in the grown ZnO crystal were below the analysis limit. When the thermal decomposition or oxidative decomposition of the material solution gas is not performed well, a part of the functional group in the material solution gas may be taken into the crystal film. It was confirmed that high quality crystals were obtained without taking in impurities such as carbides and hydrogen.

FIG. 5 is a diagram showing an X-ray diffraction (0002) 2θ-ω rocking curve of the ZnO growth layer. From these measurement results, it was confirmed that the ZnO growth layer was a c-axis oriented single crystal.
[Effects of using nonpolar oxygen source (O ₂ ) and polar oxygen source (H ₂ O)]
The reason why a flat and high-quality single crystal can be grown by using oxygen which is a nonpolar oxidation source and water vapor which is a polar oxidation source is considered as follows.

  (A) First, the material solution gas (solvent gas and solute gas) vaporized (completely) by the vaporizer 109 is merged with the heated oxygen and water vapor in the vaporized gas introduction pipe 129, and enters the reaction vessel 120. It is guided and supplied onto the substrate 10.

(B) In the space on the substrate 10 heated by the substrate heater 122, a part of the bond of the material solution gas is cut by thermal decomposition, and, for example, CH ₂ , CH ₃ , H ₂ , C, etc. are generated. .

(C) The cleaved solute component and the remaining functional groups are sequentially oxidized by oxygen to become, for example, CO ₂ , CO, H ₂ O, etc., and exhausted. On the other hand, water which is a polar oxygen source is adsorbed on the substrate, and bonds the Zn material thermally decomposed and oxidized and decomposed by oxygen onto the substrate.

  (D) Since water molecules are polar, the adsorptive power on the substrate is strong. Strong force to adsorb Zn material that has started to react on the substrate. Therefore, the probability of growth on the substrate is improved as compared with the case where the oxidation reaction is performed using only oxygen.

  (E) As described above, oxidation of materials (especially functional groups) with oxygen and adsorption of Zn onto the substrate by water proceed simultaneously, so that carbide and hydrogen are not mixed in the crystal film, and a high-quality plane is obtained. Crystals are obtained.

As described above, a suitable ratio of two types of oxygen sources, a non-polar oxygen source and a polar oxygen source, is used to oxidize and decompose a material (gas) having many functional groups (high molecular weight) and grow a crystal. It is effective to carry out oxidative decomposition and oxidation reaction by mixing with the above. That is, the molecular weight is reduced by oxidative decomposition of the functional group of the material solution gas with a nonpolar oxygen source, the polar oxygen source improves the substrate adsorption efficiency, and metal atoms, for example, Zn atoms are adsorbed on the substrate for growth. It is important to proceed with the reaction. Since the solvent component remaining in the periphery is also oxidized by a non-polar oxygen source that is present in a large amount in the periphery, carbon is exhausted as a gas such as CO ₂ , CO, and hydrogen is H ₂ O. The amount of impurities mixed in can be greatly reduced.

  There is an appropriate range for the mixing ratio of oxygen and water vapor. As described above, the surface adsorption rate to the substrate decreases without water vapor, and the oxidative decomposition reaction of the solute material (that is, the functional group) stagnates without oxygen gas. Can not.

FIG. 6 shows the surface state (scanning electron microscope image) of the grown crystal with respect to the mixing ratio of oxygen and water vapor. From these experimental results, in order to obtain flat crystals, the mixing ratio of polar oxidizing gas (H ₂ O) and nonpolar oxidizing gas (O ₂ ) is in the range of 1: 4 to 4: 1 (H ₂ O: O ₂ = 1: 4 to 4: 1) was confirmed to be good. The mixing ratio is preferably in the range of 1: 2 to 2: 1 (H ₂ O: O ₂ = 1: 2 to 2: 1), and more preferably in the range of 2: 3 to 3: 2 (H ₂ O: O ₂ = 2: 3 to 3: 2) is more preferable.
[Growth temperature]
In this embodiment, by lowering the growth temperature (reaction temperature) of the substrate, excessive thermal decomposition of the material in the space on the substrate is suppressed, and incorporation of impurities into the growth layer is suppressed. Further, water (H ₂ O), which is a polar oxygen source having a high adsorption ability to the substrate, is used together with oxygen gas. Although the decomposition of the solute gas requires a certain temperature, at a high temperature, the adsorption capacity of the board of the water is a polar oxygen source (H 2 _O) is reduced. Therefore, the crystal growth temperature (substrate temperature) (Tg) has an appropriate temperature range, and Tg = 400 ° C. to 600 ° C.

As described above, in this embodiment, the material supply onto the substrate is optimized by adjusting the thermal decomposition and oxidative decomposition of the solute (ketone compound) by low temperature growth. Furthermore, as an oxygen source, a nonpolar oxygen source (O ₂ ) and a polar oxygen source (H ₂ O) are mixed at an optimum ratio, and the nonpolar oxygen source promotes oxidative decomposition of solvent components and solute functional groups, The substrate adsorption efficiency is improved by the polar oxygen source. By this growth method, a high-quality planar (two-dimensional) growth ZnO single crystal film that is flat and does not take in impurities can be obtained.

  The above-described crystal growth method is applied when manufacturing element operation layers of various semiconductor electronic devices, operation layers (light emitting operation layers) such as LEDs (Light Emitting Diodes) and LDs (Laser Diodes), and semiconductor light emitting elements. be able to.

  Note that in this specification, an operation layer or an element operation layer refers to a layer formed of a semiconductor to be included in order for a semiconductor element to perform its function. For example, a simple transistor includes a structural layer formed by a pn junction of an n-type semiconductor, a p-type semiconductor, and an n-type semiconductor (or a p-type semiconductor, an n-type semiconductor, and a p-type semiconductor). Note that a semiconductor layer that includes a p-type semiconductor layer, a light-emitting layer, and an n-type semiconductor layer (or a p-type semiconductor layer and an n-type semiconductor layer) and emits light by recombination of injected carriers, particularly, emits light. The operation layer

  FIG. 7 is an element top view and a cross-sectional view of a semiconductor light emitting element (LED) 200 manufactured by performing crystal growth according to the above-described process. FIG. 7 illustrates the semiconductor light emitting device 200 after the substrate with the LED operation layer on which crystal growth has been performed by the above process is separated by breaking. 7 is a top view of the semiconductor light emitting device 200, and the bottom is a cross-sectional view taken along line AA shown in the top view.

  As shown in FIG. 7, a semiconductor light emitting device 200 includes a zinc oxide buffer layer 201, an n-type zinc oxide semiconductor layer (hereinafter simply referred to as an n-type semiconductor layer) 202, and a p-type zinc oxide semiconductor on a substrate 10. A layer (hereinafter simply referred to as a p-type semiconductor layer) 203 is stacked. A p-side translucent electrode 204 is disposed on the p-type semiconductor layer 203, and a p-side pad electrode 205 is formed on the p-type translucent electrode 204. An n-side electrode 206 and an n-side electrode joint 207 are formed on the lower surface of the substrate 10.

  As the substrate 10, a substrate made of zinc oxide (ZnO) based semiconductor, silicon, SiC, or the like can be used. An insulating substrate such as sapphire can also be used. FIG. 8 is a top view (upper stage) of the semiconductor light emitting element 200 when the insulating substrate 10 is used, and a cross-sectional view (lower stage) along the line AA shown in the top view. More specifically, the semiconductor light emitting device 200 has a structure in which a zinc oxide buffer layer 201, an n-type semiconductor layer 202, a light emitting layer 208, and a p-type semiconductor layer 203 are stacked on the substrate 10. Further, the p-type semiconductor layer 203 and the light emitting layer 208 are partially removed so that a part of the n-type semiconductor layer 202 is exposed. On the exposed n-type semiconductor layer 202, an n-side electrode 206 and an n-side electrode junction 207 are formed. A p-side translucent electrode 204 is disposed on the p-type semiconductor layer 203, and a p-side pad electrode 205 is formed on the p-type translucent electrode 204.

The n-type semiconductor layer 202 and the p-type semiconductor layer 203 are layers to which, for example, zinc oxide is crystal-grown, to which n-type and p-type impurities are added, respectively. A ZnO-based semiconductor is n-type even if it is undoped, but the n-type characteristics can also be changed by changing the growth temperature to adjust the residual carrier density in the n-type semiconductor. Moreover, when using a dopant, for example, when using Ga as an n-type impurity, a dopant solution in which Ga (EDMDD) ₃ is dissolved in ECH may be added to perform crystal growth.

For example, when doping nitrogen as the p-type impurity, ammonia (NH ₃ ) gas may be supplied as the dopant gas.

Furthermore, the band gap of the semiconductor layer can be adjusted by so-called band gap engineering. For example, when an Mg mixed crystal oxide semiconductor is used as the semiconductor layer, for example, a Mg material solution in which Mg (EDMDD) ₂ is dissolved in an ECH solution can be used. A mixed solution in which various mixed crystal materials are mixed in appropriate amounts in advance can also be used.

  By the liquid source MOCVD method of the present invention, the n-type semiconductor layer 202 and the p-type semiconductor layer 203 with excellent crystallinity can be formed.

  The formation process of the p-side translucent electrode 204, the p-side pad electrode 205, the n-side electrode 206, and the n-side electrode bonding portion 207, and the division (dividing into pieces) by breaking are performed by a known general method. It can be carried out.

  Note that the buffer layer 201 is not necessarily provided when a semiconductor layer is grown by using the above-described liquid material, material gas, and growth method to manufacture a semiconductor light emitting element. Further, a light emitting layer may be formed between the n-type semiconductor layer 202 and the p-type semiconductor layer 203. The light emitting layer may have a quantum well structure.

  Therefore, according to the liquid source MOCVD method of the present invention, it is possible to form a flat semiconductor layer having excellent crystallinity, high emission efficiency with suppressed leakage current and current concentration, and high output and high performance semiconductor light emission. An element can be provided. Moreover, it is excellent also in element lifetime. Furthermore, high accuracy is obtained also in the semiconductor process, and the manufacturing yield in cleavage, braking, etc. is high, and the mass productivity is excellent.

It is a figure which shows typically the structure of the liquid source MOCVD apparatus 100 used for crystal growth. 2 is a differential interference microscope image of the surface of a ZnO crystal grown by the crystal growth method of Example 1. FIG. 2 is a surface SEM image (magnification of 20,000 times) of a ZnO crystal grown by the crystal growth method of Example 1. FIG. FIG. 4 is a diagram showing the results of secondary ion mass spectrometry (SIMS) analysis of ZnO crystals grown on a substrate by the crystal growth method of Example 1. It is a figure which shows the X-ray diffraction (0002) 2 (theta) -omega rocking curve of a ZnO growth layer. The surface state (scanning electron microscope image) of the grown crystal with respect to the mixing ratio of oxygen and water vapor is shown. It is the element top view and sectional drawing of the semiconductor light emitting element (LED) manufactured by performing crystal growth by this growth method. It is the element top view and sectional drawing of the semiconductor light emitting element (LED) manufactured by performing crystal growth by this growth method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 107 Atomization assistance gas heater 108 Atomization nozzle 109 Vaporizer 110 Material gas air supply tube 111 Material gas heater 116 Material solution 200 Semiconductor light emitting element 201 Buffer layer 202 N-type semiconductor layer 203 p-type semiconductor layer

Claims (9)

A method for crystal growth of a zinc oxide based semiconductor layer on a substrate by MOCVD,
Supplying a material gas obtained by vaporizing a material solution of a ketone compound organometallic material containing zinc and a mixed gas of a polar oxidizing gas and a nonpolar oxidizing gas to the substrate,
The mixing ratio of the polar oxidizing gas and the nonpolar oxidizing gas in the mixed gas is in the range of 1 to 4 to 4 to 1. The polar oxidizing gas includes any one of water vapor (H ₂ O), ozone, methyl alcohol, and ethyl alcohol, and the nonpolar oxidizing gas is oxygen (O ₂ ) gas, nitrous oxide (N ₂ O), and carbon dioxide. The method of claim 1, comprising any one of carbon (CO ₂ ).   The method according to claim 2, wherein a vaporization temperature of the material solution is 200 ° C. or more.   The method according to claim 2, wherein the ketone compound organometallic material further includes any one of gallium (Ga), magnesium (Mg), aluminum (Al), copper (Cu), and a rare earth metal.   5. The method according to claim 1, wherein the substrate is any one of A-plane sapphire, C-plane sapphire, zinc oxide (ZnO), and silicon carbide (SiC).   The method according to claim 1, wherein a mixing ratio of the polar oxidizing gas and the nonpolar oxidizing gas in the mixed gas is in a range of 1 to 2 to 2 to 1.   The method according to claim 1, wherein a mixing ratio of the polar oxidizing gas and the nonpolar oxidizing gas in the mixed gas is in a range of 2 to 3 to 3 to 2. A method of manufacturing a semiconductor light emitting device by stacking a zinc oxide based semiconductor layer on a substrate by MOCVD,
While supplying a material gas obtained by vaporizing a material solution of a ketone compound organometallic material containing zinc and a mixed gas of a polar oxidizing gas and a nonpolar oxidizing gas to the substrate, at least the first conductivity type semiconductor layer and the first And sequentially growing a second conductivity type semiconductor layer having a polarity opposite to the conductivity type,
The mixing ratio of the polar oxidizing gas and the nonpolar oxidizing gas in the mixed gas is in the range of 1 to 4 to 4 to 1. The polar oxidizing gas includes any one of water vapor (H ₂ O), ozone, methyl alcohol, and ethyl alcohol, and the nonpolar oxidizing gas is oxygen (O ₂ ) gas, nitrous oxide (N ₂ O), and carbon dioxide. the method according to claim 8, characterized in that it comprises any one of the carbon (CO _2).