JP2010157574A - Zinc oxide-based semiconductor, and method and device for manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zinc oxide-based semiconductor capable of preventing unintended incorporation of impurities, and sufficiently doping p-type impurities even at high temperature; and a method and device for manufacturing the same. <P>SOLUTION: A reactive gas with a halogenated group II metal gas containing at least zinc and an oxygen-containing gas mixed with each other is introduced onto a substrate 1, and a group V hydrogenated gas is introduced onto the substrate 1 as a p-type impurity material gas. Thus, a zinc oxide-based semiconductor 2 with p-type impurities doped therein is crystal-grown on the substrate 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a zinc oxide (hereinafter referred to as ZnO) -based semiconductor doped with a group V element, a method for manufacturing a zinc oxide-based semiconductor, and a manufacturing apparatus.

  ZnO crystal is a direct transition type semiconductor with a band gap of about 3.37 eV, the exciton binding energy of holes and electrons in solids is as large as 60 meV, and it is stable even at room temperature. The load is small and it is expected as a light emitting device from the blue region to the ultraviolet region.

  ZnO crystals have a wide range of uses other than light-emitting devices, and applications such as light receiving elements, piezoelectric elements, transistors, and transparent electrodes are also expected. For use in these applications, establishment of a high-quality ZnO crystal growth technique excellent in mass productivity is extremely important, and a doping technique for controlling the conductivity of a semiconductor is also important.

  In particular, ZnO p-type has become a major barrier to ZnO device development, and many organizations are still focusing on making ZnO p-type. As a p-type doping material for ZnO-based semiconductors, a method for replacing oxygen atoms with group V elements has been studied by many organizations. N (nitrogen), As (arsenic), P (phosphorus), Sb (antimony), etc. Is a candidate. Among these, N has an ionic radius similar to that of oxygen, and is a promising candidate for a p-type dopant of ZnO.

Usually, the acceptor level in a wide gap semiconductor is often deep, and it is known that the activation rate is low near room temperature. For example, in the case of gallium nitride having a band gap similar to that of ZnO, the activation rate of Mg, which is a p-type dopant, is as low as several percent, and the carrier concentration (1 × 10 ¹⁷ cm ⁻ to achieve the ³ required concentrations above), 10 ¹⁹ or more units of Mg is doped.

  Until now, high doping of ZnO with nitrogen has been considered difficult at high temperatures. For example, in Patent Document 1, a ZnO layer doped with high-concentration N is formed at a low temperature of about 300 ° C., in which a large amount of nitrogen can be doped, and a sequence of annealing and forming a low-concentration N-doped layer at a high temperature of about 800 ° C. is repeated. A method has been proposed. In the present invention, a pulsed laser deposition (PLD) method in which the substrate is heated with a laser is adopted, and the temperature can be rapidly raised and lowered within a short time of several minutes. The step of growing zinc oxide is also included during temperature reduction and temperature reduction, and it is particularly difficult to perform temperature control during temperature reduction, which is natural cooling, with good reproducibility.

  As described above, the doping efficiency of nitrogen strongly depends on the growth temperature. However, if the substrate temperature is lowered, the crystallinity is lowered and nitrogen is not activated, so that it is very difficult to form p-type ZnO.

  In addition to the PLD, there is a molecular beam epitaxy (MBE) apparatus as a high vacuum process apparatus for performing nitrogen doping, but N plasma using a radical cell as an N doping source is often used. . Thus, in an apparatus using a radical cell, when the plasma power is increased in order to increase radical elements, the inner wall of the cell is sputtered and the inner wall material is doped into ZnO.

  When the inner wall material is doped in ZnO, it often becomes a source of contamination, and it is difficult not only to obtain a desired composition and p-type doping but also to make it difficult to control the ion concentration by introducing unintended impurities. There was a problem.

    On the other hand, there is a metal organic chemical vapor deposition (MOCVD) method widely used for crystal growth of III-V semiconductors as a method for producing a ZnO-based semiconductor that does not require high vacuum. However, in the MOCVD method described above, due to the problem of the vapor pressure of zinc, there is a problem that the proportion of zinc that can contribute to the growth of the ZnO-based semiconductor on the growth substrate is small and the efficiency of the material containing zinc is low.

  Further, the reactivity of organic materials such as DMZn (dimethylzinc) and DEZn (diethylzinc) and oxygen materials is high, and in the growth at a pressure of about several hundred Torr, which is adopted in a normal III-V group MOCVD MOCVD, Before the gas reaches the substrate, the organic metal and the oxygen material easily react in the gas phase (premature reaction), which may cause clogging of the raw material outlet and particles.

  Another problem is that it is difficult to grow a ZnO-based semiconductor that does not contain carbon, because carbon is mixed into the ZnO-based semiconductor by a hydrocarbon group generated when an organometallic material gas containing zinc is decomposed.

Therefore, in order to prevent premature reaction in ZnO-based semiconductor crystal growth and to form a high-quality ZnO film with a low impurity concentration without reducing the growth driving force even in a high temperature region, we have halogenated as a Group II material. Japanese Patent Application No. 2008-171610 has already proposed a halide HVPE method in which a halide vapor phase epitaxy (HVPE) method using a group II metal is applied and a halide is used as a Zn source.
JP 2005-223219 A

By the way, since the HVPE method is grown at atmospheric pressure or in a state close to atmospheric pressure, if it is desired to apply nitrogen doping of a group V element as a p-type impurity in the HVPE method, the plasma used in MBE or PLD is used. Cannot be used. Further, when used in the state of N ₂ gas, triple bonds between N are strong and do not work as nitrogen doping gas at a growth temperature of about 1000 ° C. On the other hand, as a nitrogen source, there are gases that can be a nitrogen source even without plasma, such as N ₂ O and NO ₂ gas.

However, in the HVPE method, the premature reaction in which the reaction occurs before the raw material gas arrives on the substrate is prevented by performing growth in a system having a small equilibrium constant using H ₂ O gas and halide. Introducing a gas having oxidizing power, such as N ₂ O or NO ₂ gas, may cause premature reaction and generation of particles and deterioration of raw material efficiency.

  On the other hand, other group V elements, As, P, and Sb, are solid at room temperature, and are not suitable for doping in a vapor phase growth method using a simple substance as a starting material.

  The present invention was devised to solve the above-described problems, and is capable of preventing unintended impurities from being mixed and manufacturing zinc oxide semiconductors and zinc oxide semiconductors that can be sufficiently doped with p-type impurities even at high temperatures. An object is to provide a method and a manufacturing apparatus.

  In order to achieve the above object, the invention described in claim 1 includes the step of introducing a reaction gas obtained by mixing a halogenated group II metal gas containing zinc and an oxygen-containing gas onto a substrate or a semiconductor layer; A step of introducing a group V hydride gas as a p-type impurity source gas on the semiconductor layer, and crystal-growing a zinc oxide based semiconductor layer doped with the p-type impurity on the substrate or the semiconductor layer. A method for producing a zinc oxide based semiconductor.

The invention according to claim 2 is the method for producing a zinc oxide based semiconductor according to claim 1, wherein the group V hydride gas is NH ₃ , AsH ₃ , or PH _3. It is.

The invention according to claim 3 is the method for producing a zinc oxide based semiconductor according to claim 1 or ₂ , wherein the oxygen-containing gas is made of H ₂ O.

  The invention according to claim 4 is the zinc oxide according to any one of claims 1 to 3, wherein the halogenated group II metal gas contains magnesium in addition to zinc. This is a method for manufacturing a semiconductor.

  According to a fifth aspect of the present invention, as the ratio (V / II ratio) between the partial pressure of the Group V hydride gas and the partial pressure of the Group II metal gas containing zinc decreases, The method for producing a zinc oxide semiconductor according to any one of claims 1 to 4, wherein a limit temperature on a high temperature side of a growth temperature range in which the zinc semiconductor layer can be positively grown is increased. It is.

  According to a sixth aspect of the present invention, the zinc oxide based semiconductor layer doped with the p-type impurity is a zinc oxide based semiconductor multilayer film, and each zinc oxide based film constituting the zinc oxide based semiconductor multilayer film The method for producing a zinc oxide based semiconductor according to any one of claims 1 to 4, wherein the growth temperature is changed within a growth temperature range in which positive growth is possible.

  The invention according to claim 7 is a zinc oxide based semiconductor produced by the method for producing a zinc oxide based semiconductor according to any one of claims 1 to 6.

  The invention according to claim 8 provides a raw material zone in which a group II metal material containing zinc metal alone is held, a halogen gas supply means for supplying halogen gas to the raw material zone, and an oxygen material containing oxygen Oxygen material supply means, hydride gas supply means for supplying a Group V hydride gas for adding a p-type impurity, halogen generated from the Group V hydride gas and the Group II metal material A gas supply pipe connected to the hydride gas supply means is arranged to extend into the growth zone, and a gas supply of the gas supply pipe is provided. An apparatus for producing a zinc oxide based semiconductor, characterized in that a mouth is arranged above the substrate or the semiconductor.

  The invention according to claim 9 is the zinc oxide based semiconductor manufacturing apparatus according to claim 8, wherein the gas supply pipe is made of a non-metal.

  A step of introducing a group V hydride gas as a p-type impurity source gas in addition to a step of introducing a reaction gas obtained by mixing a halogenated group II metal gas containing at least zinc and an oxygen-containing gas onto a substrate or a semiconductor layer. Therefore, premature reaction can be prevented and p-type impurities can be sufficiently doped even at a high growth temperature. In addition, the crystal quality of the ZnO-based semiconductor can be improved by increasing the growth temperature. In addition, since no plasma is used, unintended impurities can be prevented from being mixed.

  Next, embodiments of the present invention will be described with reference to the drawings. The drawings are schematic and different from the actual ones. Moreover, the part from which the relationship and ratio of a mutual dimension differ also in between drawings is contained.

  In the following description, “ZnO-based semiconductor” means a Group II oxide semiconductor containing a Group II element Zn.

  A schematic cross-sectional structure showing a step of preparing the substrate 1 is expressed as shown in FIG. A schematic cross-sectional structure showing a step of forming the p-type ZnO-based semiconductor layer 2 by halide vapor phase growth is expressed as shown in FIG.

  First, as shown in FIG. 1A, as the substrate 1, for example, a ZnO substrate having a surface having a + c plane (0001) is prepared. The crystal plane includes a plane in which the c-axis is slightly inclined, for example, by about 0.5 degrees in the m-axis direction <1-100>.

Next, as shown in FIG. 1B, the ZnO substrate 1 was heated to a high temperature of about 700 ° C. to 1000 ° C., and a p-type impurity (acceptor element) was doped on the ZnO substrate 1 by the HVPE method. A ZnO-based semiconductor layer 2 is formed. Specifically, a group V (nitrogen group) hydride gas which introduces a reaction gas in which a halide gas containing zinc and an oxygen-containing gas are mixed on the ZnO substrate 1 and becomes a p-type impurity source gas. Also introduced. In this way, the p-type ZnO-based semiconductor layer 2 is crystal-grown on the ZnO substrate 1. For example, when the p-type impurity is nitrogen, ammonia (NH ₃ ) is used as the p-type impurity source gas. Further, halide vapor phase growth is performed using zinc chloride (ZnCl ₂ ) and water (H ₂ O) as reaction gases. In addition, as the V group hydride gas, AsH ₃ or PH ₃ that becomes a hydride gas such as As or P that is a V group element can be used.

The crystal growth conditions, the partial pressure P _ZnCl2 of ZnCl _2, for example, a halide gas containing a degree of about 1 × 10 -4 ^atm or less, a gas and II-group element containing oxygen is VI element Zn The VI / II ratio, which is the supply ratio (partial pressure ratio), is, for example, about 100 or less, the crystal growth temperature _Tg is, for example, about 1000 ° C., and the crystal growth time is, for example, about 1-6 hours To the extent. Here, for example, when the partial pressure P _ZnCl2 = 1 × ¹⁰ -4 atm of ZnCl _2, when the VI / II ratio is _100, the partial pressure P _H2O = ¹⁰ -2 atm of _H 2 O.

  The value of the VI / II ratio, which is the supply ratio between the group VI element oxygen and the group II element Zn, is preferably about 1 to about 100, for example.

On the other hand, when NH ₃ is used as a group V hydride gas that is a p-type impurity source gas, the NH ₃ gas can be used even if it is not converted to plasma, as it is used for nitride growth in MBE or CVD. It is known to be a good nitrogen source. In the conventional method, for example, when doping a ZnO-based semiconductor with nitrogen as a p-type impurity, N ₂ is converted into plasma and supplied. In the conventional method, the most serious problem is that the nitrogen doping amount strongly depends on the growth temperature, and unless the growth temperature is lowered (about 300 ° C.), a large amount of nitrogen is not doped. When the growth temperature is lowered, the crystallinity of ZnO is lowered and nitrogen is not activated. Therefore, it was very difficult to form p-type ZnO with good crystal quality.

  However, we have found that even if the growth temperature is high, sufficient nitrogen can be doped by using a p-type impurity source gas as a hydride gas of a group V element and reacting with a halide gas containing Zn. Furthermore, it has been confirmed that crystallinity is improved when p-type impurity-doped ZnO is grown by the HVPE method even in a growth temperature region where the crystallinity is lowered by undoped ZnO or the like. This will be described below with reference to the drawings.

  FIG. 4 shows a surface AFM (atomic force microscope) image when an undoped ZnO layer is crystal-grown on a ZnO substrate by the HVPE method at a growth temperature in the range of 800 ° C. to 900 ° C. As shown in FIG. 4, hexagonal pyramid-shaped pits are generated.

On the other hand, FIG. 3 is a representative surface AFM image of the nitrogen-doped ZnO layer sample of the present invention. Specifically, ZnCl ₂ was used as a halide gas on the ZnO substrate 1, H ₂ O was used as an oxygen-containing gas, and NH ₃ was used as a group V hydride gas serving as a p-type impurity source gas. Then, a p-type ZnO-based semiconductor layer 2 was grown on the ZnO substrate 1. 800 ° C. The growth temperature of the halide vapor phase epitaxy, a ZnCl ₂ partial pressure _{^{2.2 × 10 -5 atm, H 2}} O partial pressure 4.4 × ¹⁰ -4 atm, 4.4 × the NH ₃ partial pressure 10 ⁻⁴ atm. As can be seen from FIG. 3, step bunching occurs by flowing NH ₃ and pits disappear. In other words, even at a growth temperature at which pits are generated in the undoped ZnO layer grown on the ZnO substrate, the crystallinity is improved and it can be used by using a nitrogen-doped ZnO layer.

Next, NH ₃ gas is effective as a plasma-less nitrogen source in vapor phase growth. In order to increase the nitrogen doping amount, it is usual to increase the NH ₃ gas flow rate, that is, to increase the NH ₃ partial pressure. It is considered good. However, the following inconvenience occurs. Since NH ₃ gas contains hydrogen, hydrogen generated when a part of NH ₃ is decomposed as in the following equation reduces the growth driving force of ZnO. This is because hydrogen reduces ZnO.
_{NH 3 → (N 2/2} ) + (3H 2/2)

FIG. 5A shows a VI / II ratio which is a partial pressure ratio (supply ratio) between H ₂ O containing Group VI oxygen and a Group II Zn halide gas ZnCl ₂ based on the thermodynamic analysis results. The relationship between the crystal growth driving force and the growth temperature in the case where V is changed is shown. The vertical axis represents the crystal growth driving force (atm), and the horizontal axis represents the growth temperature (° C.). ZnCl ₂ partial pressure was set to 2.2 × ¹⁰ -5 atm. The V / II ratio, which is the partial pressure ratio between NH ₃ , which is a Group V hydride gas, and Group II Zn halide gas, ZnCl ₂ , was 20. The decomposition rate of NH ₃ on the substrate was 3%. As can be seen from FIG. 5A, the growth driving force decreases as the value of VI / II decreases, that is, as the supply amount of H ₂ O decreases. It can also be seen that the growth driving force decreases as the growth temperature increases.

On the other hand, FIG. 5 (b) is obtained by taking out two greatly different curves having a VI / II ratio of 1000 and 10 from FIG. 5 (a) and enlarging them with broken lines. The two curves taken out from FIG. 5 (a) have a V / II ratio of 20, both of which are when the flow rate of NH ₃ is 0 and the V / II ratio is 0. The curve is shown as a solid line with no NH ₃ flow. As can be seen from the solid curve, when there is no NH ₃ flow, the crystal growth driving force does not decrease even if the growth temperature is raised. However, when NH ₃ flow is present, the driving force decreases more quickly when the VI / II ratio is lower, even when the growth temperature is considerably lower. From FIG. 5B, it can be seen that by flowing NH ₃ , a region in which the driving force decreases appears as the growth temperature rises regardless of the VI / II ratio.

As described above, assuming the decomposition rate of NH ₃ , it is possible to determine whether or not growth is possible at a certain growth temperature and raw material partial pressure from thermodynamic analysis. The conditions for growing a nitrogen-doped ZnO layer from FIG. Can be predicted in advance. On the other hand, as shown below, the experimental results also show that when the growth temperature is increased under a constant NH ₃ partial pressure, the growth driving force decreases, and conversely, etching occurs.

FIG. 6 shows how the crystal growth driving force actually changes depending on the partial pressure of NH ₃ gas, which is a group V hydride gas. In halide vapor phase growth, the partial pressure of the halide gas ZnCl ₂ of group II Zn is 2.2 × 10 ⁻⁵ atm, and the partial pressure of H ₂ O containing group VI oxygen is 4.4 × 10 ^{− 4} atm. The NH ₃ partial pressure was changed to 4.4 × 10 ⁻³ atm, 4.4 × 10 ⁻⁴ atm, and 4.4 × 10 ⁻⁵ atm. The growth temperature was changed to 700 ° C., 800 ° C., 900 ° C., and 1000 ° C. The vertical axis in FIG. 6 represents the growth rate (μm / h) of the ZnO crystal, and the horizontal axis represents the growth temperature (° C.).

A range in which the growth rate is greater than 0 (positive range) indicates positive growth, and a range in which the growth rate is less than 0 (negative range) indicates negative growth, that is, etching is performed. It can be seen that as the NH ₃ partial pressure increases, the etching starts earlier from the lower growth temperature.

FIG. 7 summarizes the data of FIG. 6 in an easy-to-understand manner. With respect to the partial pressure curves of the three types of NH ₃ gas in FIG. 6, whether the growth temperature is 700 ° C., 800 ° C., 900 ° C., or 1000 ° C. is positive growth or etching (negative growth). It is shown whether it is. ○ for positive growth and x for negative growth (etching) for easy understanding.

As shown in FIGS. 6 and 7, the growth temperature at the start of etching decreases as the NH ₃ partial pressure increases. However, as disclosed in Patent Document 1, the present inventors have found that there is a phenomenon opposite to the result that the nitrogen concentration decreases as the growth temperature rises. This is shown below.

FIG. 8 shows an HVPE method in which the ZnCl ₂ partial pressure is 2.2 × 10 ⁻⁵ atm, the H ₂ O partial pressure is 4.4 × 10 ⁻⁴ atm, and the NH ₃ partial pressure is 4.4 × 10 ⁻⁵ atm. The nitrogen (N) concentration was measured by secondary ion mass spectrometry (SIMS) measurement of a nitrogen-doped ZnO layer grown on a ZnO substrate by changing the growth temperature between 700 ° C. and 900 ° C. Depth direction analysis results are shown. The horizontal axis indicates the depth (μm) from the surface of the nitrogen-doped ZnO layer, and the vertical axis indicates the N (nitrogen) concentration (cm ⁻³ ).

As can be seen from FIG. 7, when the NH ₃ partial pressure is 4.4 × 10 ⁻⁵ atm, positive growth is performed at a growth temperature of 700 ° C. to 900 ° C. In the state where the positive growth is performed, the N concentration in the nitrogen-doped ZnO layer is highest at 900 ° C. where the growth temperature is the highest, and as the growth temperature decreases to 800 ° C. and 700 ° C., the N concentration also increases in order. It is running low. Thus, when a nitrogen-doped ZnO-based semiconductor is manufactured by the method of the present invention, the nitrogen concentration decreases as the growth temperature rises in the conventional method shown in Patent Document 1, which is a positive opposite to the negative temperature correlation. It can be seen that there is a temperature correlation.

In the method of the present invention, in a state where the NH ₃ partial pressure is constant, high-temperature growth is very preferable for p-type formation because the nitrogen dope concentration becomes higher and activation of nitrogen is facilitated. Further, as seen in FIG. 3, there is an effect of improving the crystallinity by nitrogen doping, but further improvement in crystallinity can be expected by performing high temperature growth.

Moreover, since the higher NH ₃ partial pressure is strong reducing effect on ZnO, reduced effect on ZnO when NH ₃ partial pressure is high it appears at a lower temperature side. However, if the NH ₃ partial pressure is decreased, it can be grown at a higher temperature, and in addition to improving the nitrogen doping concentration, improving the crystallinity, improving the nitrogen activation, etc., reducing the reduction effect on ZnO Is very preferable.

Next, FIG. 9 shows the concentration of N (nitrogen) and H (hydrogen) in the depth direction by secondary ion mass spectrometry (SIMS) measurement of a nitrogen-doped ZnO layer grown on a ZnO substrate. Show. The nitrogen-doped ZnO layer has a growth temperature of 800 ° C., a ZnCl ₂ partial pressure of 2.2 × 10 ⁻⁵ atm, an H ₂ O partial pressure of 4.4 × 10 ⁻⁴ atm, and an NH ₃ partial pressure of HVPE. 4.4 × 10 ⁻⁴ atm. The horizontal axis represents the depth (μm) from the surface of the nitrogen-doped ZnO layer, and the vertical axis represents the concentration (cm ⁻³ ) of N (nitrogen) or H (hydrogen). The ZnO substrate contains background level N, but the nitrogen-doped ZnO layer grown under NH ₃ partial pressure contains N at a concentration exceeding 1 × 10 ²⁰ atms / cm ⁻³ .

Referring to FIG. 7, the limit temperature on the high temperature side of the positive growth with NH ₃ partial pressure of 4.4 × 10 ⁻⁴ atm is 800 ° C. Thus, a high nitrogen concentration can be obtained in the nitrogen-doped ZnO-based semiconductor by setting the limit temperature on the high temperature side of positive growth under a predetermined NH ₃ partial pressure.

  Considering FIGS. 6 to 9, the following tendencies are derived. The nitrogen-doped ZnO-based semiconductor according to the manufacturing method of the present invention is manufactured within the temperature range TW in which positive crystal growth is performed. The limit temperature Th on the high temperature side of the temperature range TW in which positive crystal growth is performed is inversely related to the V / II ratio A. That is, the limit temperature Th decreases as the V / II ratio A increases. Conversely, the limit temperature Th increases as the V / II ratio A decreases. Also, under a constant V / II ratio, the nitrogen doping concentration increases as the growth temperature increases within the temperature range TW in which positive crystal growth is performed.

  Further, when a ZnO-based semiconductor layer doped with a p-type impurity is formed as a multilayered body and it is desired to control the nitrogen concentration in each film differently, the following may be performed. With the V / II ratio kept constant, the growth temperature of the first nitrogen-doped ZnO-based thin film within the temperature range TW for positive growth is T1. Next, let T2 (T1 ≠ T2) be the growth temperature of the second nitrogen-doped ZnO film fabricated within the temperature range TW for positive growth. Thus, if the growth temperature is changed sequentially, multilayer films having different nitrogen concentrations can be formed. Further, depending on whether each growth temperature from the growth temperature T1 of the first nitrogen-doped ZnO-based thin film to the growth temperature TN of the N-th nitrogen-doped ZnO-based thin film is sequentially increased or decreased, p-type impurities A multilayer film having a gradient in concentration (nitrogen) can be formed.

FIG. 2 shows a schematic configuration of a manufacturing apparatus used in the method for manufacturing a ZnO-based semiconductor of the present invention. As shown in FIG. 2, a chlorine gas supply means 17, a moisture gas supply means 11, an ammonia gas supply means 15, a raw material zone 19, and a gas supply pipe 12 are used to form a p-type impurity doped ZnO semiconductor. 16, 18a, 18b, heating means 33, growth zone 30, heating means 31, substrate holding means 32, and the like. As shown in the figure, the moisture gas supply means 11, the chlorine gas supply means 17, and the ammonia gas supply means 15 are mixed with N ₂ (nitrogen gas) as a carrier gas. The raw material zone 19 holds a metal material 20 made of a group II zinc simple substance.

  It is also possible to add other raw material zones to the configuration of the ZnO-based semiconductor manufacturing apparatus. For example, when crystal growth of an MgZnO semiconductor is performed, as shown in the figure, the configuration of a chlorine gas supply means 21, a raw material zone 23, gas supply pipes 22a and 22b, and the like are added. Group II metal material 24 containing a single metal element of magnesium is held in the raw material zone.

Further, in order to produce an n-type ZnO-based semiconductor layer, an n-type impurity source gas supply means 13 can be added as shown in the figure. The n-type impurity source gas supply means 13 can use a halide of Ga or Al, for example, GaCl ₃ as shown in the figure. The n-type impurity source gas supply means 13 is also mixed with N ₂ (nitrogen gas) as a carrier gas (transport gas).

  In the raw material zone 19, zinc disposed inside reacts with chlorine gas supplied from the chlorine gas supply means 17 through the gas supply pipe 18 a to generate zinc chloride gas, and enters the growth zone 30 through the gas supply pipe 18 b. This zone supplies zinc chloride gas.

  The growth zone 30 reacts zinc chloride gas supplied from the raw material zone 19 connected by the gas supply pipe 18b with water (water vapor) supplied from the moisture gas supply means 11 through the gas supply pipe 12 as an oxygen material. In this zone, a ZnO-based semiconductor is grown on the growth substrate 1 held on the substrate holding means 32. Note that what is held on the substrate holding means 32 may be a semiconductor rather than a growth substrate. For example, a stacked body in which an n-type ZnO-based semiconductor layer is formed on a substrate may be held.

In addition, all of the gas supply pipes 12, 14, 16, 18a, 18b, 22a, and 22b that connect each gas supply means, the growth zone 30, and the raw material zones 19 and 23 are made of quartz. In this way, since the non-metal quartz is used for the gas supply pipe and the halide containing Zn is used for the metal material of the ZnO-based semiconductor, the metal acting as a catalyst for decomposition of NH _3, which is a V group hydride, is formed on the substrate. It does not exist around the substrate or semiconductor on the holding means 32.

  The heating means 33 is for heating the raw material zones 19 and 23, the gas supply pipes 12, 14, 16, 18a, 18b, 22a, 22b and the like. The heating means 31 is for heating the growth zone 30. With these heating means 31 and 33, the ZnO-based semiconductor manufacturing apparatus realizes a hot wall system. The heating means 33 may be individually arranged for the raw material zones 19 and 23 and each gas supply path.

  Next, a method for manufacturing a zinc oxide-based semiconductor using the above-described zinc oxide-based semiconductor manufacturing apparatus will be described.

  First, chlorine gas and nitrogen gas are supplied from the chlorine gas supply means 17 to the raw material zone 19 through the gas supply pipe 18a. In the raw material zone 19, a reaction according to the following reaction formula occurs by the group II metal material 20 made of the zinc simple metal and the supplied chlorine gas, and zinc chloride gas is generated.

Zn (s, l) + Cl ₂ (g) ⇔ ZnCl ₂ (g)
Here, the single metal element of zinc held in the raw material zone 20 is preferably highly pure, for example, 99.99999% or more. In the reaction formula, (s), (l), and (g) represent solid, liquid, and gas, respectively.

  In the raw material zone 19, the surface area of the group II metal material 20 made of a single metal of zinc is increased so that the reaction in the above reaction formula can proceed almost to the right side and the flow rate of the zinc chloride gas can be controlled by the supply amount of the chlorine gas. The structure and the appropriate temperature. In addition, as such suitable temperature, about 300 degreeC-about 450 degreeC are desirable. Further, the temperature of the raw material zone 19 is set to about 500 ° C. or less in order to suppress the transport of zinc gas having a very high vapor pressure among the metals to the growth zone 30. And the zinc chloride gas produced | generated by the above-mentioned reaction type is transported to the growth zone 30 via the supply pipe | tube 18b.

  On the other hand, water (water vapor) supplied from the moisture gas supply means 11 is transported through the gas supply pipe 12 to the growth zone 30 as an oxygen material. Further, the ammonia gas supplied from the ammonia gas supply means 15 through the gas supply pipe 16 is transported to the growth zone 30 as a nitrogen material that becomes a p-type impurity.

  In the growth zone 30, a reaction of the following reaction formula proceeds to the right side by the transported zinc chloride gas and water, so that a thin film of ZnO semiconductor grows on the substrate 1.

ZnCl ₂ (g) + H ₂ O (g) Ｚｎ ZnO (s) + 2HCl (g) (1)
At the same time, by reacting with NH ₃ to have been transported to the substrate 1 or semiconductor which is held on the substrate holding means 32, by which part of oxygen atoms of the ZnO is replaced by nitrogen, the nitrogen-doped ZnO A semiconductor layer is formed.

Here, as shown in FIG. 2, the gas supply pipes 12, 14, and 16 are formed up to the inside of the growth zone 30, and the gas supply ports 12a, 14a, and 16a are arranged directly on the substrate 1 or the semiconductor. It is configured to be. By the way, ammonia gas, which is a kind of group V hydride gas, can decompose into nitrogen and hydrogen even at about 400 ° C. from thermodynamic analysis, but when decomposition occurs and becomes N ₂ and H ₂ , p. Does not work as a nitrogen source during doping with type impurities. However, it is known that NH ₃ gas becomes a better N source even if it is not converted to plasma as used for nitride growth in MBE. This is because most gases can be supplied to the substrate surface without being decomposed even at a high temperature of 1000 ° C. in an environment where no catalyst such as metal exists. Incidentally, _{H 2} gas generated from the NH ₃ gas decomposes the ZnO in the following equation.
ZnO (s) + H ₂ (g) ⇔ Zn (g) + H ₂ O (g) (2)
When the H ₂ partial pressure in the growth zone is increased or the growth temperature is increased, the reaction of formula (2) proceeds to the right side, and the growth of ZnO is inhibited.

  In the manufacturing apparatus of the present invention, quartz which is a nonmetal is used as a material of at least the gas supply pipe 16 for transporting ammonia gas, the gas supply pipe 16 crosses the inside of the growth zone 30, and the gas supply port 16 a is directly above the substrate 1. Is provided. For this reason, ammonia gas does not come into contact with the metal until it reaches the substrate 1, so it is not decomposed and can contribute to the reaction immediately above the substrate, so that a sufficient nitrogen dope concentration can be obtained.

  On the other hand, a halide containing Zn is used as the metal material for crystal growth, and the gas supply port 12a of the gas supply pipe 12 for transporting the oxygen-containing gas is provided immediately above the substrate 1. And the oxygen-containing gas react directly on the substrate 1. For this reason, Zn material can be supplied onto a substrate very efficiently.

  Here, the temperature of the growth zone 30 is set to be higher than the temperature of the raw material zones 19 and 23 so that the zinc chloride gas does not precipitate on the way to the growth zone 30. Specifically, the temperature of the growth zone 30 is set to about 700 ° C. to about 1000 ° C.

  In addition, by making the set temperature of the raw material zones 19 and 23 lower than the growth temperature of the growth zone 30, the zinc chloride gas and magnesium chloride gas generated in the raw material zones 19 and 23 are transported to the growth zone 30. Precipitation between them can be suppressed.

  Further, by adopting water instead of simple oxygen as the oxygen material, hydrochloric acid gas is generated instead of chlorine gas on the substrate 1 in the growth zone 30, so that the ZnO thin film is formed in a thermodynamically more stable state. be able to.

As a group V hydride gas, instead of NH _3, for example, it can be any of _AsH 3, PH _3. Further, bromine gas may be employed as the halogen gas instead of chlorine gas. Further, the group II metal material is not limited to two types, and three or more group II metal materials may be used.

In the step of crystal growth of the ZnO based semiconductor layer, the reaction gas may contain a magnesium-containing gas. Further, the partial pressure of the magnesium-containing gas is, for example, about 1 × 10 ⁻⁴ atm or less.

  Zinc and / or magnesium halide does not decompose into zinc and / or magnesium and chlorine gas at a temperature of about 1000 ° C., and direct reaction occurs between zinc and / or magnesium halide and oxygen material on a ZnO substrate. .

  Zinc and / or magnesium halides and oxygen materials do not react as quickly as main organic metals and oxygen materials, so no particles are generated on the ZnO substrate, and the raw material efficiency in the high temperature region is also MOCVD. Higher than the law.

  The molar feed ratio (VI / II ratio) of oxygen source and zinc and / or magnesium halide is an important growth parameter. As described in Japanese Patent Application No. 2008-171610, the VI / II ratio is set to 100 or less, thereby promoting the migration of halide raw material on the substrate surface and at the same time abnormal portions of crystal growth (pits and protrusions). ) And the like. Further, when the VI / II ratio is small, the rate of crystal growth becomes slow, so the VI / II ratio is preferably 1 or more, for example.

For example, when the ZnCl ₂ partial pressure is 2.2 × 10 ⁻⁵ atm and VI / II = 20, a growth rate of about 0.5 μm / h is obtained. This value of about 0.5 μm / h is an acceptable growth rate as the thin film formation rate of the compound semiconductor, and can be used satisfactorily as a method of forming the ZnO-based semiconductor film.

  Next, FIG. 10 shows a schematic cross-sectional structure example of a semiconductor element formed by using the above-described zinc oxide semiconductor manufacturing method and manufacturing apparatus. As shown in FIG. 10, a ZnO substrate 40, an n-type ZnO based semiconductor layer 42 that is disposed on the ZnO substrate 40 and doped with an n-type impurity, and a ZnO based that is disposed on the n-type ZnO based semiconductor layer 42. A semiconductor active layer 44 and a p-type ZnO-based semiconductor layer 46 disposed on the ZnO-based semiconductor active layer 44 and doped with a p-type impurity are provided.

  The n-type ZnO-based semiconductor layer 42, the ZnO-based semiconductor active layer 44, and the p-type ZnO-based semiconductor layer 46 are all manufactured using the above-described zinc oxide-based semiconductor manufacturing apparatus and the above-described manufacturing method using a group II metal halide and an oxygen source. It is formed by.

  A p-side electrode 48 is disposed on the p-type ZnO-based semiconductor layer 46, and an n-side electrode 50 is disposed on the back surface of the conductive ZnO substrate 40. As a material of the p-side electrode 48, for example, a stacked structure of a Ni layer and an Au layer can be adopted. In addition, as a material of the n-side electrode 50, for example, a laminated structure of a Ti layer and an Au layer can be adopted.

  As the n-type impurity, for example, any of B, Ga, Al, In, or Tl can be applied.

  Moreover, as a p-type impurity, a V group element can be used, for example, any of N, P, As etc. is applicable.

The ZnO-based semiconductor active layer 44 is, for example, a multi-quantum well (MQW) in which a barrier layer made of Mg _x Zn _1-x O (0 <x <1) and a well layer made of ZnO are stacked. It has a structure.

The ZnO-based semiconductor active layer 44 may have an MQW structure in which a well layer made of Cd _y Zn _1-y O (0 <y <1) and a barrier layer made of ZnO are stacked.

  The number of quantum well pairs is determined by the distance traveled by electrons and holes. That is, the recombination emission efficiency of electrons and holes is determined by the number of MQW pairs corresponding to a predetermined thickness of the ZnO-based semiconductor active layer 44 that provides the best.

Here, since the band gap energy of MgO is 7.8 eV with respect to the band gap energy of 3.37 eV of ZnO, the composition ratio x of Mg _x Zn _1-x O is adjusted to make Mg _x Zn ₁ a barrier layer made of _-x O, can be well layer made of ZnO to form a laminated MQW structure.

On the other hand, since the band gap energy of CdO is 0.8 eV with respect to the band gap energy of 3.37 eV, the composition ratio y of Cd _y Zn _{1 -y} O is adjusted to obtain Cd _y Zn _{1 -y.} An MQW structure in which a well layer made of O and a barrier layer made of ZnO are stacked can be formed.

  Note that light emission (hν) from the semiconductor device can be extracted from the top surface direction as shown in FIG.

  The p-type ZnO-based semiconductor layer 46 of the ZnO-based semiconductor element of FIG. 10 may be a multilayer film as shown in FIG. 11 instead of a single layer. In FIG. 11, the p-type ZnO-based semiconductor layer 46 includes a p-type ZnO-based semiconductor film 461, a p-type ZnO-based semiconductor film 462,..., A p-type ZnO-based semiconductor film 46 (n-1), and a p-type ZnO. System semiconductor film 46n. Here, n is an integer of 1 or more. The p-type ZnO-based semiconductor film 461 to the p-type ZnO-based semiconductor film 46n may be doped with a group V element that is a p-type impurity at a constant concentration, but may be doped differently.

  As described in the description of FIGS. 6 to 9, the V / II ratio, which is the ratio between the partial pressure of the Group V hydride gas and the partial pressure of the Group II metal gas containing zinc, is made constant, and p If the growth temperature is sequentially changed for each semiconductor film within the positive crystal growth temperature range of the type ZnO-based semiconductor film, multilayer films having different concentrations of group V elements as p-type impurities can be formed. . If the growth temperature is increased or decreased sequentially from the p-type ZnO-based semiconductor film 461, the p-type ZnO-based semiconductor layer 46 having a p-type impurity concentration gradient can be formed.

  The method and apparatus for producing a zinc oxide semiconductor according to the present invention includes a light emitting device such as an LED or a laser diode (LD) from a blue region to an ultraviolet region, a light receiving device, a piezoelectric device, and a HEMT (High Electron Mobility Transistor). It can be applied to a wide range of fields such as HBT (Hetero-junction Bipolar Transistor) and transparent electrodes.

Schematic cross-sectional structure diagram (a) showing a step of preparing a ZnO substrate according to the method for manufacturing a zinc oxide-based semiconductor of the present invention, and a schematic cross-sectional structure diagram showing a step of forming a ZnO-based semiconductor layer by halide vapor phase epitaxy (B). It is a figure which shows the typical structural example of the manufacturing apparatus which applies the manufacturing method of the zinc oxide type semiconductor of this invention. It is a figure which shows the 20 micrometers square AFM image of the nitrogen dope ZnO type semiconductor layer surface formed with the manufacturing method of the zinc oxide type semiconductor of this invention. It is a figure which shows the 20 micrometers square AFM image of the undoped ZnO type semiconductor layer surface formed by HVPE method. It is a figure which shows the comparison with the case where there is no ammonia gas supply, and the relationship between the crystal growth driving force and growth temperature by thermodynamic analysis when changing VI / II ratio. It is a figure which shows the relationship between the growth rate and growth temperature of a nitrogen dope ZnO layer for every ammonia gas partial pressure. It is the figure which classified based on the data of FIG. 6 whether the nitrogen dope ZnO layer was growing or it was etching. It is a figure which shows that the nitrogen concentration of nitrogen dope ZnO changes with growth temperature. The secondary ion mass spectrometry measurement result in the typical example of the nitrogen dope ZnO layer produced with the manufacturing method of the zinc oxide type semiconductor of the present invention is shown. It is a figure which shows the structural example of the ZnO type semiconductor element produced by the manufacturing method of the zinc oxide type semiconductor of this invention. FIG. 11 is a diagram illustrating a configuration example in which the p-type ZnO-based semiconductor layer is a multilayer film in the ZnO-based semiconductor element of FIG. 10.

Explanation of symbols

1 substrate 2 p-type ZnO-based semiconductor layer 11 moisture gas supply means 13 n-type impurity source gas supply means 15 p-type impurity source gas supply means 19 and 23 source zones 20 and 24 Group II metal material 30 growth zones 31 and 33 heating means 32 Substrate holding means 17, 21 Chlorine gas supply means 12, 14, 16 Gas supply pipes 12a, 14a, 16a Gas supply ports 18a, 18b Gas supply pipes 22a, 22b Gas supply pipes

Claims (9)

  Introducing a reaction gas obtained by mixing a halogenated group II metal gas containing zinc and an oxygen-containing gas onto a substrate or a semiconductor layer; and a group V hydride gas as a p-type impurity source gas on the substrate or the semiconductor layer. And a step of crystal growth of a zinc oxide based semiconductor layer doped with a p-type impurity on the substrate or the semiconductor layer. The method for producing a zinc oxide based semiconductor according to claim 1, wherein the group V hydride gas is NH ₃ , AsH ₃ , or PH ₃ . The method for producing a zinc oxide based semiconductor according to claim 1, wherein the oxygen-containing gas is made of H ₂ O.   4. The method for producing a zinc oxide-based semiconductor according to claim 1, wherein the halogenated group II metal gas contains magnesium in addition to zinc. 5.   The growth temperature at which the zinc oxide based semiconductor layer can grow positively as the ratio (V / II ratio) between the partial pressure of the Group V hydride gas and the partial pressure of the Group II metal gas containing zinc decreases. The method for producing a zinc oxide based semiconductor according to any one of claims 1 to 4, wherein a limit temperature on a high temperature side of the range is increased.   The zinc oxide-based semiconductor layer doped with the p-type impurity is a zinc oxide-based semiconductor multilayer film, and each zinc oxide-based film constituting the zinc oxide-based semiconductor multilayer film is within a growth temperature range in which positive growth is possible. The method for producing a zinc oxide-based semiconductor according to any one of claims 1 to 4, wherein the growth temperature is changed.   A zinc oxide-based semiconductor produced by the method for producing a zinc oxide-based semiconductor according to claim 1. A raw material zone in which a group II metal material containing a metal element of zinc is held;
Halogen gas supply means for supplying halogen gas to the raw material zone;
Oxygen material supply means for supplying oxygen material containing oxygen;
a hydride gas supply means for supplying a Group V hydride gas for adding a p-type impurity;
A growth zone in which the Group V hydride gas, the Group II metal material generated from the Group II metal material and the oxygen material react with each other, and
The gas supply pipe connected to the hydride gas supply means is arranged to extend into the growth zone, and the gas supply port of the gas supply pipe is arranged above the substrate or the semiconductor. Zinc-based semiconductor manufacturing equipment.   9. The apparatus for manufacturing a zinc oxide semiconductor according to claim 8, wherein the gas supply pipe is made of a non-metal.