JP5029966B2 - Deposition equipment - Google Patents

Description

  The present invention relates to a film forming apparatus for growing a semiconductor crystal by a MOCVD (Metal Organic Chemical Vapor Deposition) method, and a method for manufacturing a semiconductor element by the MOCVD method.

  Since the ZnO-based compound semiconductor material has a large band gap (Eg = 3.37 eV) like the gallium nitride (hereinafter referred to as GaN) -based compound semiconductor, it can emit light from near ultraviolet to visible light. In addition, ZnO-based material (n = 2.0) has a higher refractive index than GaN (n = 2.5), and thus has high light extraction efficiency and high exciton binding energy (60 meV). It has the potential to realize an element with higher luminous efficiency than the system (24 meV).

  Currently, methods for producing ZnO-based semiconductor crystals include molecular beam epitaxy (hereinafter referred to as MBE) method, vacuum deposition method, sputtering method, metalorganic vapor phase epitaxy (hereinafter referred to as MOVPE) method, and liquid source CVD method. It is being considered. In the liquid source CVD method, as described in Patent Documents 1 to 5, a material solution obtained by dissolving a material having a high vapor pressure in a solvent is pumped to a vaporizer, atomized and / or vaporized, and supplied to a reactor. This is a method of growing a crystal to form a film. However, the liquid source CVD method tends to make the atomization and vaporization of the material solution unstable, and it is required to solve this problem.

  In the technique described in Patent Document 1, when a β-diketone-based organometallic compound having sublimability is used as a material, if this material is heated by a vaporizer alone and sublimated, the tube is formed before reaching the substrate to be deposited. In order to deposit on a wall or the like, it is proposed to evaporate with a vaporizer while being mixed with an organic solvent and to oxidize the substrate surface. As a result, it is considered that the organic solvent molecules are attached so as to surround the β-diketone organic metal, and it is difficult to deposit on the tube wall or the like before reaching the substrate, and it reacts with oxygen gas on the substrate to form a high-quality metal oxide film. It is said that the film can be formed efficiently.

  Patent Document 2 aims to suppress the phenomenon that a solid material is deposited when a material solution obtained by dissolving the solid material in a solvent such as tetrahydrofuran is vaporized by a vaporizer, and a part of the solid material becomes particles and is mixed into the film. It is said. In the technique of Patent Document 2, it is considered that the cause of precipitation of the solid material in the vaporizer is that the difference in boiling point between tetrahydrofuran and the solid material is large, and tetrahydrofuran is vaporized at once in the vaporizer and the solid material is precipitated. A method is proposed in which a solvent having a boiling point higher than that of tetrahydrofuran is mixed before the vaporizer. Thereby, vaporization is stabilized, precipitation of solid material is reduced, and the problem of film quality deterioration and film thickness nonuniformity is solved.

  In the technique of Patent Document 3, when a material solution in which a solid material is dissolved in an organic solvent is supplied to a vaporizer with a liquid supply pipe, the organic solvent is vaporized in the liquid supply pipe to precipitate a solid material, The purpose is to solve the problem that the material solution cannot be stably supplied to the vaporizer due to sudden boiling. For this reason, in the technique of Patent Document 3, the tip of the tube is formed into a tapered nozzle shape (liquid pressure adjusting means) so that the liquid pressure in the tube is higher than the vaporizer internal pressure, and gasification of the organic solvent in the tube is performed. Propose to suppress.

  In the technique described in Patent Document 4, when a material solution in which an organic metal material solid is dissolved in an organic solvent is vaporized with a vaporizer, the deterioration caused by receiving heat for a long time, or only the organic solvent is vaporized first. The purpose is to solve problems caused by concentration changes such as precipitation and polymerization of organometallic materials. Patent Document 4 proposes to provide a vaporizer with a first region for maintaining the material solution in liquid and a second region for vaporizing the liquid, and maintaining the pressure in the first region higher than the pressure in the second region. ing.

  In Patent Document 5, in order to provide a vaporizer that can be used for a long time without causing clogging, the pressure of the carrier gas and the raw material solution is higher than the vapor pressure of the raw material solution in the region where the material solution and the carrier gas are in contact with each other. To control. It has been proposed to set the pressure in the reaction section (reaction vessel, reactor) lower than the pressure in the vaporizer.

JP 2003-147529 A JP 2004-260023 A Japanese Unexamined Patent Publication No. 7-94497 Japanese Patent No. 36337763 JP 2003-268552 A

  In the conventional liquid source CVD method, (1) the solid material re-precipitates easily at the parts such as the liquid feed pipe and the atomizing nozzle, and clogging is likely to occur. (2) The solid material re-deposits and deposits in the vaporizer. As a result, the supply amount of the organometallic material gas to the reaction chamber 115 becomes unstable (increase or decrease from the set value). (3) The re-deposited solid material flows into the reaction vessel as particles and adheres to the substrate. Thus, there are problems related to the operational stability of the apparatus, such as abnormal growth, and problems of deteriorating the film quality of the growing crystal.

  In the above-mentioned Patent Documents 1 to 5, various proposals are made to solve the above problem, but they have not been sufficiently solved.

  An object of the present invention is to provide a film forming apparatus capable of completely vaporizing a material solution and stably supplying it to a substrate.

  In order to achieve the above object, according to the first aspect of the present invention, a reaction vessel provided with a substrate holding part for holding a substrate therein, a material solution which is liquid at room temperature, and a gas for atomization support There is provided a film forming apparatus having an atomizing unit that atomizes a material solution by ejecting and a vaporizing unit that vaporizes the atomized material solution and supplies the atomized material solution to a reaction vessel. The vaporizer includes a container having an internal space, and a heating unit that heats the space in the container and vaporizes the mist-like material solution. One end of the container is provided with an atomizing section, and the material solution and the atomization assisting gas are ejected toward the internal space, and the other end of the container is provided with a delivery outlet for delivering the vaporized material solution toward the reaction container. It has been. The heating unit includes one or more fins arranged in a space between the atomization unit and the opening, and a heater that heats the fins. By setting it as such a structure, the atomized material solution can be efficiently heated with a fin, and complete vaporization can be implement | achieved.

  For example, in order to rectify the atomized material solution ejected from the atomizing section, it is desirable that a rectifying space having a predetermined distance be provided between the fin and the atomizing section.

  For example, it is desirable that a space of a predetermined distance is provided between the fin and the delivery port.

  Further, for example, it is possible to have a control unit that controls the heater and maintains the surface temperature of the fin at a temperature lower than the thermal decomposition temperature of the organometallic material contained in the material solution.

  It is possible to make it the structure which has a pressure adjustment part which maintains the internal space of a container at a predetermined pressure.

  An atomization part can be set as the structure provided with the jet nozzle which ejects a material solution, and the jet nozzle which jets the said heating atomization assistance gas from the circumference | surroundings, for example.

  The atomizing unit is configured to spray the material solution at an angle of 30 ° to 60 ° with respect to the central axis.

  As the atomizing section, for example, a material solution that forms droplets having a particle size of 60 μm or less is desirably used.

  It is desirable that the main plane of the fin be oriented parallel to the axis connecting the atomizing section and the delivery port.

  When a plurality of fins are provided, the main plane of the fins can be configured to be arranged radially around the axis.

  It is also possible to adopt a configuration in which a plurality of fins are divided into a plurality of stages in the axial direction, and the directions of the fins are alternately arranged for each stage.

The distance L of the rectifying space is
0.7 <(L · tan θ) /r≦1.0
(However, θ: angle of spraying of the atomizing section (angle from the central axis), r: radius of the fin)
It is preferable to set to.

Distance L ₂ to the fin and the delivery port is preferably a fin diameter equal to or greater than. This is because the drift can be prevented.

  The heating unit may include an external heater that heats the internal space from the outside of the container.

  An embodiment of the present invention will be described with reference to the drawings.

  In order to grow a high-quality metal oxide crystal, for example, a ZnO crystal, on a substrate by a liquid source MOCVD method, the present invention always supplies a completely vaporized organometallic material to the substrate at a stable flow rate and concentration. The configuration.

  First, the liquid source MOCVD apparatus of the present invention will be described. As shown in FIG. 1, the liquid source MOCVD apparatus of the present invention includes a container 417 for containing a material solution 416, a container 415 for containing a solvent 414, a vaporizer 409 for vaporizing the material solution, and a component. It has a reaction vessel 420 in which a substrate 421 to be deposited is disposed, a material gas heater 411 for heating the material gas, and an atomization support gas heater 407 for heating the atomization support gas. The material solution 416 here is a solution in which a solute (organometallic compound) serving as a film forming material is dissolved in a solvent at a predetermined concentration. In the present embodiment, a material that is liquid at room temperature, for example, a β-diketone metal complex, is used as the solute. The material gas is a film forming material that is gaseous at room temperature. The atomization assisting gas is a gas used to assist atomization (misting) of the material solution.

  Inserted into the material solution container 417 and the solvent container 415 are tips of liquid feeding pipes 419 to which flow rate adjusting devices 418a and 418b are attached, respectively. The two liquid supply pipes 419 are joined on the way to form one liquid supply pipe 419 and connected to the vaporizer 409. The material solution container 417 and the solvent container 415 are connected to a pressurizing inert gas pipe 413 that supplies an inert gas for pressurizing each liquid surface. An inert gas supply source 11 is connected to the pressurizing inert gas pipe 413. By pressurizing the liquid surfaces of the material solution container 417 and the solvent container 415 with an inert gas, the material solution 416 and the solvent 414 are pumped through the liquid feeding pipe 419.

  The material solution 416 and the solvent 414 are pumped to the vaporizer 409 after the flow rate is adjusted by the flow rate adjusting devices 418a and 418b, respectively. Thus, the material solution 416 can be supplied to the vaporizer 409 during film formation. Further, during maintenance, the solvent 414 can be supplied to wash the liquid feeding tube 419 and the like. Note that the solvent dissolving the solute of the material solution 416 and the solvent 414 of the solvent container 415 may be the same solvent or different solvents, but here, the same solvent is used.

  In this embodiment, helium gas is used as the pressurizing gas. Since helium gas has a low solubility in liquid, it is difficult to dissolve in the material solution 416 and the solvent 414 even if the pumping pressure is increased, and even if the pressure is reduced after the liquid flow control devices 418a and 418b, bubbles are generated in the liquid feeding pipe 419. It is hard to generate.

  An atomization support gas air supply pipe 406 that supplies atomization support gas (inert gas) is connected to the vaporizer 409. The atomization assisting gas is used to assist atomization (misting) of the material solution 416 in the atomizing nozzle 408. A gas flow rate adjusting device 405 a that adjusts the flow rate of the atomization support gas and the inert gas supply source 12 is connected to the atomization support gas supply pipe 406.

  An atomization assistance gas heater 407 for heating the atomization assistance gas to a predetermined temperature is connected to the atomization assistance gas supply pipe 406. The atomization assistance gas heater 407 includes a pipe through which the atomization assistance gas passes and a heater disposed around the pipe. Thereby, the atomization support gas can be heated and supplied to the vaporizer 409, and the complete vaporization of the material solution in the vaporizer 409 can be realized. Note that the temperature controller 18 is connected to the atomization assist gas heater 407 to adjust the temperature.

  The gas of the material solution vaporized by the vaporizer 409 is introduced into the reaction vessel 420 through the material solution gas introduction pipe 14. The material solution gas introduction pipe 14 is provided with a heater (not shown) for maintaining the temperature of the material solution gas flowing in the pipe. In the middle of the introduction pipe 14, there is connected a material gas guide pipe 412 for joining a material gas, which is a gaseous material at room temperature, with a gas of the material solution. An introduction valve 426 is disposed in the material solution gas introduction pipe 14.

  A material gas heater 411 for heating the material gas is connected to the material gas induction tube 412. The material gas heater 411 is connected to the material gas supply source 13 and the material gas flow rate adjusting device 405d via the material gas supply pipe 410, and the material gas at a predetermined flow rate (for example, the material gas induction tube 412). To the same temperature as the gas of the material solution flowing through the gas, and can be combined with the gas of the material solution. Thereby, it can mix with material gas, without lowering | hanging the temperature of the gas of a material solution, and can be supplied to the reaction container 420 with material gas, maintaining the complete vaporization state of material solution. Even when the material gas flow rate is increased or decreased by connecting the material gas introduction pipe 412 to the latter stage of the vaporizer 409, that is, the material solution gas introduction pipe 14 between the vaporizer 409 and the reaction vessel 420, the vaporizer 409 Does not affect the flow rate and temperature of gas flowing through the. As a result, the material gas flow rate can be increased or decreased while maintaining the temperature and pressure conditions for realizing complete vaporization of the material solution 416 in the vaporizer 409.

  An inert gas pipe 402 for mixing an inert gas as a carrier gas into the material gas is connected to the material gas supply pipe 410. The inert gas supply source 12 is connected to the inert gas pipe 402 via a flow rate adjusting device 405b.

  In addition, the material gas pipe 404 is joined to the atomization support gas supply pipe 406 on the way. The material gas pipe 404 is connected to the material gas supply source 13 via the flow rate adjusting device 405c. Thereby, it is possible to mix the material gas of predetermined flow volume into the atomization assistance gas. When the material gas is oxygen, it is possible to oxidize the material solution 416 and the solvent 414 in the vaporizer 409 to reduce the molecular weight, or to cause cracking that cuts a part of the bond of the solvent molecules. Depending on the type of solute, the solute organic metal and oxygen can be easily combined on the substrate 421.

  The exhaust device 15 is connected to the reaction container 420 via a buffer tank 429, a collection device 423, and a pressure adjustment valve 424. The buffer tank 429 serves as a pressure buffering device, and has a pressure sensor 17 attached thereto. The collection device 423 collects a material solution gas that has not been used for film formation on the substrate 421.

  A drain pipe 425 provided with an exhaust valve 427 is connected to the introduction pipe 14, and the drain pipe 425 is connected to the exhaust apparatus 15 via a buffer tank 429, a collection device 423, and a pressure adjustment valve 424. When the introduction valve 426 provided in the introduction pipe 14 or the exhaust valve 427 provided in the drain pipe 425 is open, the pressure in the reaction vessel 420 is equal to the pressure in the vaporizer 409 and the pressure in the buffer tank 429. By detecting the pressure in the buffer tank 429 by the pressure sensor 17, the pressure in the reaction vessel 420 and the vaporizer 409 can be detected.

  A pressure regulator 21 is attached to the pressure regulating valve 424. The central controller 16 is connected to the pressure regulator 21 and controls the operation of the pressure regulator 21. The central control device 16 takes in the pressure data detected by the pressure sensor 17 of the buffer tank 429 and controls the pressure adjustment valve 424 via the pressure regulator 21 so as to obtain a predetermined pressure. Thereby, the vaporization of the material solution 416 in the vaporizer 409 can be realized by controlling the vapor pressure of the material solution 416 in the vaporizer 409 so as not to reach the saturated vapor pressure.

  Next, the configuration of the vaporizer 409 will be described with reference to FIGS. 2 (a) and 2 (b), FIG. 3, FIG. 4, and FIG.

  As shown in FIGS. 2A and 2B, the vaporizer 409 includes a main body 900 having a cylindrical inner space, an atomizing nozzle 408 fixed to the upper portion of the main body 900, and a predetermined position in the inner space. And heat exchange fins 907 arranged on the surface. An opening 60 is provided in the lower part of the internal space of the main body 900.

  The atomizing nozzle 408 has a double tube structure in which two tubes having different diameters are arranged concentrically as shown in FIG. The above-described liquid feeding pipe 419 is connected to the inner pipe 31, and the atomization assist gas heater 407 is connected to the outer pipe 32. Therefore, the liquid mixture of the material solution 416 and the solvent 414 is ejected from the tip of the inner tube 31, and the atomization assisting gas heated to a predetermined temperature is supplied from the tip of the outer tube 32 to a predetermined air pressure. Is ejected at.

  The diameters and tip shapes of the tubes 31 and 32 of the atomizing nozzle 408 are such that the atomization assisting gas ejected from the tube 32 at a predetermined spread angle θ as shown in FIG. 2A, FIG. 3 and FIG. The material solution ejected from the tube 31 is entrained and subdivided to form a material solution mist (material solution droplet) 51 having a predetermined particle size distribution.

The space between the atomizing nozzle 408 and the heat exchange fins 907 is a mist rectifying space 55 in which the atomization assisting gas and the material solution mist spread as shown in FIGS. The length L of the mist rectifying space 55, the flow of mist spreads in spread angle theta, set to expand to a slightly smaller diameter 2r _m than the diameter 2r of the heat exchange fins 907. Thereby, the area which the material solution mist 51 contacts with the heat exchange fin 907 can be increased, and it becomes possible to heat efficiently. For example, the diameter 2r _m extent of material solution mist 51, when the 0.7-fold to 1.0 times the diameter 2r of the heat exchange fins 907, 0.7 <(L · tanθ) / r <1 The length L of the mist rectification space 55 is set so as to satisfy 0.0.

  The spread angle θ is desirably 30 ° or more and 60 ° or less. By setting in this way, the length L of the mist rectification space 55 can be made compact. Further, the mists are not too close to each other, and the solvent is easily vaporized. Furthermore, it is because there exists an advantage that it is hard to adhere to the inner wall face of the vaporizer | carburetor 409 by making (theta) 60 degrees or less.

  The periphery of the main body 900 is covered with an external heater 905, and the temperature of the external heater 905 is adjusted by a temperature controller 906. The external heater 905 heats the entire internal space of the main body 900.

  The heat exchange fins 907 include four fins arranged every 90 degrees as shown in the perspective view and the top view in FIG. An internal heater 908 is built in each of the four fins (see FIGS. 2A and 2B). A temperature controller 909 is connected to the internal heater 908 to adjust the fin temperature. The mist of the material solution that passes through the space (heat exchange area 56) where the heat exchange fins 907 are arranged together with the heating from the external heater 905 by heating the four fins to a predetermined temperature by the internal heater 908. 51 is heated. When the solvent of the mist 51 is vaporized and heated to the boiling point, vaporization is promoted. As shown in FIG. 4, the solvent evaporates from the material solution mist 51 and is separated into a solute mist 52 and a solvent gas 53. The solute mist 52 is further heated, the vapor pressure of the solute is increased, and the vaporization of the solute is promoted to become a solute gas 54. Therefore, the material solution mist 51 is completely vaporized by passing through the heat exchange area 56 in which the heat exchange fins 907 are arranged, and becomes a mixed gas of the solvent gas 53 and the solute gas 54.

  The four fins 907 are desirable because the main plane is installed so as to be parallel to the flow of mist and gas, so that the gas flow is not hindered and adhesion of the material and mist to the fin can be prevented. Here, four fins 907 are arranged in parallel to the axis connecting the atomizing nozzle 408 and the opening 60.

The space between the heat exchange fin 907 and the bottom of the vaporizer 900 is provided with a space having a predetermined length L ₂ as the drift prevention space 57. Anti-flow distortion space 57, by increasing the distance between the opening 60 of the heat exchange area 56 and the bottom portion L ₂ or more, the solution mist 51 that passes through the heat exchange area 56, the solute mist 52, the solvent gas 53 and solute gas 54 is opened The heat exchange area 56 flows in a radial direction without being biased toward a radially narrow space at the center of 60. Thereby, the contact area of the heat exchange fin 907 and the solution mist 51 etc. can be increased, and heating efficiency can be improved. The length L ₂ of the drift prevention space 57 is set to be equal to or larger than the diameter of the heat exchange area 56 (that is, the diameter 2r of the heat exchange fin 907) (L ₂ ≧ 2r).

  The material solution gas introduction pipe 14 is connected to the opening 60 at the bottom of the vaporizer 409. The material solution gas introduction pipe 14 sends a mixed gas of the solvent gas 53 and the solute gas 54 to the reaction vessel 420.

  In the middle of the material solution gas introduction pipe 14, a material gas induction pipe 412 is connected. The material gas guide pipe 412 joins the material gas to the mixed gas of the solvent gas 53 and the solute gas 54 flowing through the material solution gas introduction pipe 14. Since the material gas is heated by the material gas heater 411 to a temperature equal to or higher than the temperature of the mixed gas of the solvent gas 53 and the solute gas 54, the completely vaporized state of the material solution is maintained without lowering the temperature of the mixed gas. It is mixed and supplied to the reaction vessel 420.

  Further, as the shape of the heat exchange fin 907, as shown in FIG. 5B, the fin may be divided into multiple stages in the axial direction, and the fins may be alternately arranged in odd and even stages. . In this shape, since the fins are arranged so as to cut the flow of the solute mist 52 and the like, the temperature distribution generated in the flow of the solute mist 52 and the like can be reduced and can be efficiently vaporized.

  As another heat exchange fin 907 shape, as shown in FIG. 5 (c), the fins are arranged in a triangular tube shape with three internal heaters as vertices, and two pieces are projected so as to project outward from each vertices. It is also possible to have a shape with each fin. The heat exchange fin 907 in FIG. 5C heats and vaporizes the solution mist 51 not only outside the triangular tube but also in the internal space, so that the effective surface area of the fin is large and the vaporization efficiency can be increased. it can.

  Next, the operation of the central controller 16 will be described with reference to FIG. Various kinds of predetermined set values (values derived from experimental results and experience values) are input to the central processing unit 16 by the operator (step 601). The central control device 16 accepts this input (step 602) and sets a set value for each control device (step 603). As a result, the following control operation is performed.

  The central control device 16 delivers a signal for setting the flow rate input by the operator to the liquid flow rate adjustment devices 418a and 418b in order to control the pumping amount of the material solution 416 and the solvent 414 (step 603-1). . Receiving the signal from the central controller 16, the liquid flow rate adjusters 418a and 418b measure the material solution 416 and the solvent 414, respectively, and send them to the atomizing nozzle 408 (step 604).

  The central control device 16 controls the supply amount and temperature of the atomization support gas. First, the central control device 16 sends a signal for setting the flow rate received from the operator to the gas flow rate adjustment devices 405a and 405c (step 603-2). The gas flow control devices 405a and 405c receiving this signal measure the atomization support gas and send it to the atomization support gas heater 407 (step 605). The central control device 16 sends a signal for setting the temperature received from the operator to the temperature adjuster 18 attached to the atomization assist gas heater 407 (step 603-3). The atomization assistance gas heater 407 heats the atomization assistance gas to the set temperature (step 606). The temperature controller 18 feedback-controls the temperature of the heater 606 to a predetermined set temperature (for example, 300 ° C.) (steps 607 and 608). Thereby, the atomization assistance gas heated to the predetermined temperature can be sent to the atomization nozzle 408.

  By the above steps 604, 605, 606, and 607, the flow rate of the material solution 416 supplied to the atomization nozzle 408 and the temperature and flow rate of the atomization support gas are controlled. The material solution 416 is discharged from the atomization nozzle 408 and is misted by the atomization support gas (for example, the material solution mist particle size is 60 μm). For complete vaporization of the material solution in the vaporizer 409, the central controller 16 sends the set temperature received from the operator to the temperature controller 906 of the external heater 905 and the temperature controller 909 of the internal heater 908 of the vaporizer 409. For example, 300 ° C. is set (step 603-6). The temperature controllers 906 and 909 feedback control the temperature of the internal space of the vaporizer 409 to the set temperature (steps 613 and 614). The external and internal heaters 905 and 907 of the vaporizer 409 completely evaporate the material solution mist 51 as described with reference to FIG. 4 by heating the internal space of the vaporizer 409 to the set temperature, and the solvent gas 53 and the solute gas. The mixed gas is changed to 54 (step 615).

  On the other hand, in order to control the flow rate and temperature of the material gas (oxygen gas), the central control device 16 sets the set flow rate received from the operator in the gas flow rate adjustment devices 405b and 405d (step 603-4). . The gas flow control devices 405b and 405d measure the material gas and send it to the material gas heater 411 (step 609). Moreover, the central control apparatus 16 sets the preset temperature received from the operator to the temperature regulator 19 connected to the material gas heater 411 (step 603-5). The material gas heater 411 heats the material gas (step 610). At this time. The temperature of the material gas heater 411 is feedback-controlled by the temperature controller 19 to a predetermined set temperature (for example, 300 ° C.) (steps 611 and 612). The set temperature is equal to or higher than the temperature of the gas of the material solution vaporized by the vaporizer 409.

  The central controller 16 sets the set temperature received from the operator in the temperature controller 20 of the substrate heater 422 in the reaction vessel 420 (step 603-8). The temperature controller 20 feedback-controls the temperature of the substrate heater 422 to the set temperature (steps 619 and 620).

  Further, the central control device 16 includes each space (reaction vessel 420, vaporizer 409, atomization support gas heater 407, material gas heater 411, and the space between them from the reaction vessel 420 to the subsequent stage of the gas flow rate adjustment devices 405a to 405d. Feedback control of piping pressure. That is, since the pressure in each of these spaces is equal to the pressure in the buffer tank 429, the pressure in the reaction container 420 is detected by the pressure sensor 17 (step 616). The central controller 16 sets the set pressure received from the operator in the pressure regulator 21 (step 603-7). The pressure regulator 21 feedback-controls the pressure regulating valve 424 so that the pressure detected by the pressure sensor 17 becomes the set pressure (steps 617 and 618). Thereby, the pressure of the space of the reaction vessel 420, the vaporizer 409, the atomization assist gas heater 407, the material gas heater 411, and the like can be controlled to a predetermined pressure.

  The central controller 16 keeps the temperature of the material solution gas flowing through the material solution gas introduction pipe 14 by feedback control of the temperature of the material solution gas to a predetermined temperature.

  Next, a method for forming a film using the liquid source MOCVD apparatus of this embodiment will be described. Here, as an example, a method of forming a ZnO crystal film will be described.

As an example of the material solution 416, 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. Is used. In addition, ethylcyclohexane (hereinafter, ECH) is used as a solvent for the material solution 416. The concentration of the material solution 416 is, for example, 0.2 mol / L. The solvent in the solvent container 415 also uses ECH.

  Since this organometallic material is liquid at room temperature, no solid is precipitated by evaporation of the solvent. Moreover, since it mixes with a solvent whole area, it can adjust to a required density | concentration. Further, when the material solution container 417 is replaced, the liquid flow rate adjusting device 418a is replaced, the liquid feeding pipe 419 is maintained, the atomizing nozzle 408 is cleaned, the remaining material solution 416 is easily supplied with the solvent 414. Can be removed by washing.

Examples of other solutes include Mt (THD) _n (THD: tetramethylheptanedionate, Mt: metal, Ba, Pb, Sr, La, Zn), Mt (METHD) _n (METHD) of the same β-diketone type. : Methoxyethoxytetramethylheptanedionate, Mt: metal, Ba, Pb, Sr, Ru, Zr), Mt (OD) _n (OD: octadionato, Mt: metal, Zn, Ru), and Mt (EDMDD) _n ( EMDDD: ethyldimethyldecanedionate, Mt: metal, Cu, Zn, Mg, La, Pr, Nd, Tm, Dy, Er, Ho, Tb, Yb, Ga) and the like can be selected.

Moreover, it is possible to use a solid material including Zn (DPM) ₂ (DPM: dipivaloylmethanato) as a solute. Although materials other than those described above are possible, it is necessary to consider such a combination with a solvent that does not react with the solvent and does not separate or precipitate.

Ethylcyclohexane (ECH) used as a solvent for the material solution is a nonpolar cyclic saturated hydrocarbon solvent and does not interact with the 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 for the operation for stabilizing the atomization / vaporization of the material solution of the present invention. As a similar solvent, butyl acetate, i-butyl alcohol, toluene and the like can be preferably used. Further, as a material having a higher vapor pressure, tetrahydrofuran (hereinafter referred to as THF), hexane, or the like can be used. These can be appropriately selected in consideration of the film forming conditions.

  As the material solution pressurizing gas supplied to the material solution container 417, helium (hereinafter referred to as He) gas can be used. For example, the liquid surface of the material solution 416 is pressurized at 200 kPa, the flow rate is adjusted to 1.0 sccm by the liquid flow rate adjusting device 418 a, and sent to the atomizing nozzle 408 through the liquid feeding tube 419.

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 in the case of 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 therefore the material solution 416 even under reduced pressure after the liquid flow rate control device 418a. Since no bubbles are generated in the inside, it can be used without any problem.

  In the present embodiment, the material solution container 417 and the liquid feeding pipe 419 are not heated between the material solution container 417 and the atomization nozzle 408. However, when the concentration of the material solution 416 is high and the viscosity of the material solution is high, stable supply can be achieved by heating to lower the viscosity. However, the temperature is set so that the solvent does not vaporize or bump in the pipe.

  On the other hand, before the atomization support gas is supplied to the atomization nozzle 408, the flow rate is adjusted by the gas flow rate adjusting device 405a. Further, it is sent to the atomization support gas heater 407 through the atomization support gas air supply pipe 406, heated to an appropriate temperature, and then supplied to the atomization nozzle 408.

  As the atomization support gas, for example, nitrogen gas is used, and the flow rate is adjusted to 250 sccm by the gas flow rate adjusting device 405a. The temperature setting of the atomization assist gas heater 407 is set so that, for example, the ejection temperature from the atomization nozzle 408 is 250 ° C. at a pressure of 2.0 kPa in the vaporizer 409.

  The atomization assisting gas has its gas temperature lowered by adiabatic expansion after passing through the gas flow control device 405a. In addition, when the material solution 416 is atomized in the vaporizer 409, the temperature of the mist and gas is reduced by the heat of vaporization. Therefore, in order to compensate for the temperature decrease due to adiabatic expansion and to warm to a temperature that promotes vaporization in the vaporizer 409, the atomization support gas heater 407 is heated to a predetermined temperature in advance. By heating the atomization support gas in this manner, the material solution mist 51 is heated immediately after being sprayed from the atomization nozzle 408 to the vaporizer 409, and the vaporization of the solvent is promoted. And the production | generation of the solute mist 52 becomes quick, and vaporization of the solute mist 52 is also accelerated | stimulated, and vaporization of the material solution in a short time is attained. Therefore, vaporization efficiency can be improved.

However, the temperature of the atomization assisting gas needs to be set so that the temperature in the vaporizer 409 is always lower than the thermal decomposition temperature of the solute (for example, Zn (EDMDD) ₂ ). The temperature in the vaporizer 409 is controlled not only by the temperature of the atomization assist gas but also by the relationship with the set temperatures of the external and internal heaters 905 and 908, and thus is controlled by the central controller 16.

  By setting a predetermined flow rate in the gas flow rate adjusting device 405c, it is also possible to mix oxygen gas, which is a material gas, with the atomization support gas. Some organic metal compound materials and organic solvents that are material solutions are oxidized or oxidized to cause molecular weight reduction or cracking. For this reason, it is because it may become easy to combine Zn element and oxygen on the substrate 421 by previously mixing oxygen gas with the atomization assist gas. The term “cracking” as used herein means that the molecular weight is reduced by an oxidation reaction, and radicals or intermediates generated by the reaction collide with solvent molecules to cut off some of the solvent molecule bonds.

As the atomization assisting gas, an inert gas such as nitrogen (N ₂ ), argon (Ar), helium (He), hydrogen (H ₂ ), or the like can be preferably used. A gas in which two or more of these are mixed may be used.

As the material gas, a gas containing oxygen such as oxygen (O ₂ ), water vapor (H ₂ O), nitrous oxide (N ₂ O), and nitrous acid gas (NO ₂ ) can be preferably used. A gas in which two or more of these are mixed may be used.

  As described with reference to FIG. 4, the material solution is made into fine particle droplets (mist) by the atomizing nozzle. Since the shape of the atomizing nozzle 408 is the structure of FIG. 3 described above, the material solution that has been pumped joins the heated atomization assisting gas at the tip of the atomizing nozzle. When the atomization assisting gas is ejected by the action of the shape of the nozzle 408, it becomes a swirling current swirling while spreading at an angle θ. By being entrained in this, the material solution 416 becomes fine and uniform droplets (mist) and is sprayed into the vaporizer 409.

  The atomization nozzle 408 has, for example, 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 409 pressure). Under the condition of 20 kPa, a material having a capability of generating mist having a liquid particle size of 60 μm or less is used. When the secondary pressure is 0.1 kPa, the atomization support gas is 15-20 ml / min (standard state), 1 kPa, 150-200 ml / min (standard state), 10 kPa. , 1500-2000 ml / min (standard state) is required. Note that when the secondary pressure is 20 kPa or more, the liquid particle size increases, and accordingly, the vaporizer volume may be increased accordingly.

  In addition, the liquid particle diameter (mist diameter) after atomization varies depending on the liquid flow rate, liquid viscosity, atomization assisting gas flow rate, secondary pressure, temperature, etc. If these conditions are constant, the particle diameter is also constant. .

  The atomizing nozzle 408 having the structure shown in FIG. 3 has a structure in which the material solution 416 is discharged from the central portion, and the atomization assisting gas is ejected from the outer peripheral portion to be misted. Since the tip of the atomizing nozzle is always cleaned by this structure, no solute component is deposited or deposited. It is also possible to eject the atomization assisting gas from the central portion of the atomizing nozzle 408 and discharge the material solution 416 from the outer peripheral portion. However, the material solution 416 accumulates at the tip of the nozzle, and solute components are deposited and deposited. there's a possibility that.

  As described with reference to FIG. 4, the mist 51 of the material solution 416 in the vaporizer 409 is preferentially vaporized from the surface of the mist 51 (high vapor pressure) by being heated in the vaporizer 409. Thus, the solvent gas 53 becomes a mist (solute mist 52) having a smaller particle diameter in which the material solute components are concentrated. Further, the organic metal material component is vaporized from the surface of the finely divided solute mist 52 to become a solute gas 54, whereby the solute mist 52 disappears. Thereby, all the material solution 416 is gasified.

  In the vaporizer 409, the solvent component having a high vapor pressure is preferentially vaporized from the material solution mist 51. Therefore, as the material solution mist 51 moves from the upper part of the vaporizer 409 to the lower part, the material solution mist 51 changes to a solute mist 52 having a high concentration of solute components and a small particle diameter. By this action, the specific surface area (= surface area / volume) of the solute mist 52 is larger than that of the material solution mist 51, so that the vaporization of the solute (zinc organometallic material) is promoted.

If the particle diameter of the material solution mist 51 is, for example, 60 μm at the maximum, the surface area, volume, and specific surface area are as shown in Table 1. The solute mist 52 can also be estimated as shown in Table 1. The liquid viscosity at 25 ° C. of the material solution 416 having concentrations of 0.01 mol / L, 0.2 mol / L, and 1.2 mol / L is about 0.8 cP, 1.0 cP, and 8.0 cP, respectively. The atomization nozzle 408 of the embodiment can be sprayed and atomized. In the present invention, the material solution mist 51 having a particle diameter of 60 μm can be vaporized. At this time, after changing from the vaporization of the solvent to the solute mist 52, it is a two-stage vaporization to vaporize the solute, and the specific surface area of the solute mist 52 is about twice or more the specific surface area of the material solution mist 51, This is preferable because vaporization of the solute mist 52 proceeds effectively.

  Through the above process, the material solution 416 (material solution gas) gasified in the vaporizer 409 is supplied to the reaction vessel 420 together with the atomization assist gas. Note that it is desirable to heat the section from the vaporizer 409 to the reaction vessel 420 so that the vaporized material solution 416 does not re-aggregate (precipitate).

  In addition, by making the particle diameter of the material solution mist 51 small and uniform, the solvent evaporation area becomes wide and the solvent can be vaporized quickly. Further, the vaporization time (distance in the vaporizer 409) can be made constant. The same applies to solute vaporization after solvent vaporization. Therefore, it is desirable to set the atomization nozzle 408 and the supply conditions of the material solution and the atomization assisting gas so that the diameter of the material solution mist 51 becomes small.

  The vaporizer 409 has a structure with a diameter of 10 cm and a length of 65 cm, an internal vaporization heater 908, a fin 907, and an external heater 905 for heat insulation. The heaters 908 and 905 are set by the central controller 16 so that the temperature of the gas contact part is 300 ° C., and the gas temperature when the vaporized material solution gas and the atomization assist gas pass through the opening 60 is 250 ° C. did. Thereby, the temperature of the mist and gas in the vaporizer 409 can be made equal to or lower than the thermal decomposition temperature of the organometallic material (solute), so that thermal alteration of the material can be prevented.

  The internal pressure of the vaporizer 409 needs to be set to be lower than the solvent vapor pressure at the temperature in the vaporizer 409 in order to vaporize the solvent.

At the same time, the space in the vaporizer 409 includes the material solution supply amount and the atomization assist gas flow rate, and the vaporizer inside the vaporizer so that the vapor (solvent gas 53 and solute gas 54) of the material solution 416 does not reach the saturated vapor pressure. It is desirable to set the pressure and vaporizer temperature. For example, when the material solution 416 is supplied at 1.0 sccm, the molar flow rate of the solute Zn (EDMDD) ₂ is 2 × 10 ⁻⁴ mol / min. In this state, when the atomization assist gas supply amount is set to 250 sccm, the vaporizer pressure 2.0 kPa, and the temperature 250 ° C., the flow rate in the vaporizer 409 is about 24.3 L / min. Therefore, the material concentration is 8.2 × 10 ⁻⁶ mol / L, and the theoretical solubility (hereinafter, dissolved concentration) of Zn (EDMDD) ₂ at 250 ° C. is 4.9 × 10 ⁻⁴ mol / L. Is 0.017 (1.7%), which is smaller than 1. By maintaining the saturation rate at 1 or less, the material solution 416 can be maintained in a state where it is easily vaporized. A method for calculating the saturation rate will be described in detail later.

  The material gas is supplied to the material gas heater 411 through the material gas supply pipe 410 after the flow rate is adjusted by the gas flow rate adjusting device 405d. Since the material gas is adiabatically expanded after the gas flow rate adjusting device 405d, the temperature is lowered. Further, it is desirable to keep the temperature of the material solution 416 at the same temperature in order to lower the temperature of the material solution 416 when it is mixed with the gas of the material solution 416 supplied from the vaporizer 409 and to prevent reaggregation. In this embodiment, the same temperature as the gas of the material solution 416 can be obtained by heating with the material gas heater 411. The heated material gas is combined with the gas mixture of the material solution 416 and the atomization assist gas through the material gas induction pipe 412 and before the reaction vessel 420, and is supplied to the reaction vessel 420.

  For example, when oxygen gas is used as the material gas, the flow rate is set to 2.0 SLM. The temperature of the ejection part of the material gas heater 411 is set to the same temperature as the atomization support gas and material solution gas sent from the vaporizer 409, for example, 250 ° C.

  In the present embodiment, since the material gas is configured to merge with the gas of the material solution 416 and the atomization support gas closer to the reaction vessel 420 than the vaporizer 409, the vaporizer 409 is disposed even when the flow rate of the material gas is increased or decreased. The flowing gas flow and temperature can be kept constant. Therefore, the vapor pressure in the vaporizer 409 can be easily maintained below the saturated vapor pressure regardless of the increase or decrease in the material gas, so that complete vaporization in the vaporizer 409 can be maintained.

The material gas can be mixed with an inert gas such as nitrogen gas. The flow rate of the inert gas is set by the gas flow rate adjusting device 405b. Thereby, the gas flow rate flowing into the reaction vessel 420 can be made constant. In this case, the flow rate of the inert gas flowing through the reaction vessel 420 is
Inert gas flow rate = (gas flow rate flowing into reaction vessel 420)-(atomization support gas flow rate + material solution gas flow rate + material gas flow rate)
Set to. Further, when it is desired to increase or decrease the flow rate of gas flowing into the reaction vessel 420, it can be realized without increasing or decreasing the amount of material gas by increasing or decreasing the inert gas flow rate.

  The material gas can be introduced from the front stage of the vaporizer 409 or can be introduced from both the front stage and the rear stage of the vaporizer 409. When oxygen gas (or other gas used as an oxidizing agent) is used as the material gas, the material solution is of a type that does not cause deterioration due to oxidation, and the temperature of the vaporizer 409 is deteriorated due to oxidation of the material solution. It is desirable to consider in advance that the temperature does not occur.

A substrate 421 is set on the susceptor 428 of the reaction vessel 420. For example, a C-plane sapphire substrate is used as the substrate 421. Thereafter, the substrate 421 is heated by the substrate heater 422 as necessary. For example, nitrogen gas at a predetermined flow rate is supplied from the gas flow rate adjustment device 405a as the atomization support gas, and an ECH solution of Zn (EDMDD) ₂ , for example, as the material solution 416 is supplied from the liquid flow rate adjustment device 418a at a predetermined flow rate and atomized by the vaporizer 409. After that, it is completely vaporized and supplied to the reaction vessel 420. A material gas (for example, oxygen) having a predetermined flow rate and temperature is mixed with the gas of the material solution 416 before the reaction vessel 420. Thereby, the crystal is grown on the substrate 421 for a predetermined time, for example, 60 minutes, and a ZnO single crystal having a thickness of 1.0 μm can be obtained.

  In this embodiment, since the material solution can be completely vaporized in the vaporizer 409 and stably supplied to the reaction vessel 420, a uniform ZnO single crystal film that is uniform and homogeneous and does not take in impurities can be obtained.

  Further, in the present embodiment, bubbles can be supplied without “entering” or “not generating” bubbles in the liquid feeding pipe 419 from the material solution container 417 to the tip of the atomizing nozzle 408. When bubbles are present in the liquid feeding pipe 419, the atomization / vaporization in the vaporizer 409 becomes unstable, the supply of the material solution gas to the substrate becomes intermittent, and the concentration of the material solution gas fluctuates. The particle size distribution becomes wider (mixed with mist having a large particle size that cannot be vaporized), which causes problems such as mixing of mist into the vaporized gas, but this embodiment can prevent this.

In the present embodiment, the pressure in the liquid supply pipe 419 is set to a predetermined value in order to “not generate” bubbles in the liquid supply pipe 419. That is, by maintaining the relationship of the following (formula 1) in which the pressure in the liquid feeding pipe 419 is set to be larger than the vapor pressure of the solvent, the material solution 416 is prevented from evaporating and gasifying into bubbles. Specifically, since the pressure in the liquid supply pipe 419 is equal to the pressure in the vaporizer 420, the pressure can be set by the central controller 16 controlling the pressure adjustment valve 424 via the pressure regulator 21. . However, the suction effect at the tip of the atomizing nozzle 408 can be ignored.
(Vapor pressure P of solvent) <(pressure in liquid feeding pipe) (Equation 1)
P (mmHg) = 10 ^ [AB / (T + C)] (Formula 2: Antoine formula)
P (mmHg): Pressure T (° C.): Liquid temperature A: Material-specific constant B: Material-specific constant C: Material-specific constant However, in Formula 2, the increase in molar boiling point due to the solute is negligible. It is assumed that the vapor pressure is determined by the solvent type and temperature.

  Further, in the present embodiment, the material solution 416 is made into a material solution mist having a fine and constant particle size by continuously ejecting from the atomizing nozzle 408 without “bubbles” in the material solution 416, It makes it possible to spray the vaporizer continuously. The configuration of the atomizing nozzle 408 of the present embodiment is as described above with reference to FIG. 3. The material solution 416 is discharged from the hole at the center of the nozzle, and the fog is formed from the hole provided around the hole so as to surround the hole. The gas for gasification is swirled and released. The material solution 416 becomes liquid particles (material solution mist 51 (see FIG. 4)) having a fine particle diameter by the vortex of the support gas.

  As described above, by using the atomizing nozzle 408 having the structure shown in FIG. 3, the material solution 416 is not mixed with bubbles and can be fed to the tip of the nozzle. Furthermore, it is possible to prevent the atomization assisting gas from flowing around the material solution discharge port and liquid from being formed around the discharge port.

  Here, the atomizing nozzle of FIG. 7 will be described as a comparative example of the atomizing nozzle. The atomization nozzle of FIG. 7 has a structure in which the material solution and the atomization assisting gas are merged before jetting. In this structure, the material solution becomes liquid fine particles by the supply pressure of the atomization assisting gas. In this type of atomizing nozzle, since the bubbles of the atomization assisting gas are mixed in the material solution, spraying from the nozzle tip becomes intermittent, and the atomized particle size distribution becomes wide. Furthermore, the material solution component adheres at the nozzle tip and the liquid can easily be accumulated. The generation of the liquid reservoir causes a deviation of the supply amount of the material solution, and at the same time, the liquid droplet of the liquid reservoir suddenly enters the mist, causing a deviation of the supply flow rate. Furthermore, the liquid reservoir causes residual mist. When the particle size distribution of the material solution mist is large, not all the material solution mists can be vaporized in the vaporizer, so that the mists are scattered and adhered onto the substrate, causing abnormal growth and defects.

  Here, the calculation method of the vapor saturation rate of the material solution 416 in the vaporizer 409 will be further described. In order for the liquid to vaporize, a space (volume) corresponding to the amount of liquid is required, and the amount of vapor (concentration or partial pressure) that can exist (dissolve) in the space is determined by the temperature of the system. That is, in order to completely vaporize the material solution, the flow rate (volume) of the atomization support gas simply needs to exceed the space necessary for vaporizing the material solution. In short, the saturation rate of the material solution needs to be 1.0 or less.

The saturation rate of the organometallic material that is a solute can be easily calculated in the following manner. First, the molar concentration is determined, with or without the supply mass being vaporizable. The pressure and temperature of the atomization support gas in the vaporizer are determined by the following formulas 3 and 4 assuming that the pressure and temperature are the same as those in the vaporizer.
(P _st · F _st ) / T _st = (P _vp · F _vp ) / T _vp (Equation 3)
_Fvp = ( _Pst * _Fst / _Tst ) * ( _Tvp / _Pvp ) (Formula 4)
P _st (atm): Unit pressure of the gas flow controller F _st (L / min): Unit flow of the gas flow controller T _st (K): Unit pressure of the gas flow controller P _vp (atm): Inside the vaporizer The pressure of the atomization support gas _Fvp (L / min): The flow rate of the atomization support gas in the vaporizer _Tvp (K): The temperature of the atomization support gas in the vaporizer

Next, the molar flow rate of the solute can be obtained by the following equation 5.
M _sv = C _sv · F _mix (Formula 5)
M _sv (mol / min): Molar flow rate of solute C _sv (mol / L): Molar concentration of solute F _mix (L / min): Flow rate of solution At this time, the solute is in the atomization assisting gas in the vaporizer 409. Therefore, the molar concentration C _sv is expressed by the following equation (6).
C _sv = M _sv / F _vp (Expression 6)
C _sv (mol / L): Molar concentration of solute vapor

Next, the saturation concentration of the solute is determined. First, the partial pressure P of the solute is obtained from Equation 2 (Antoine equation) for calculating the vapor pressure of the liquid.
P (mmHg) = 10 ^ [AB / (T + C)] (Formula 2)
P (mmHg): Pressure T (° C.): Liquid temperature A: Constant B: Constant C: Constant

From the equation of state of gas and the relationship of n / V = C, the saturated solute molar concentration that can be dissolved in the atomization support gas is obtained from Equation 7.
C _sat = P / (R · T _vp ) (Expression 7)
C _sat (mol / L): solute saturation molar concentration R (l · atm / K · mol): gas constant = 0.820205784
Finally, the solute vapor molar concentration C _sv is divided by the solute saturated molar concentration C _sat to derive the saturation rate as shown in Equation 8.
_{S v = (C sv / C} sat) ··· ( Equation 8)
S _v : Saturation rate of solute

Incidentally, saturation S _v of the solute is, if 1.0, although theoretically solutes can be completely vaporized, the solute realistic because the evaporation speed, etc. is slowed near the saturated vapor pressure saturated It is desirable that the rate _Sv be about 0.3 or less. Miniaturization of such vaporizer 409, saturation S _v solute Given the followability when changing the setting gas concentration is more preferably 0.1 or less.

  As described above, in this embodiment, the material solution is supplied onto the substrate by the stable supply to the nozzle, the complete vaporization of the material solution mist by the vaporizer, and the effect of introducing the heated material gas from the subsequent stage of the vaporizer. Residual mist is eliminated in the material solution gas, the concentration of the material solution gas is stabilized, the linear velocity of the gas material, the supply gas temperature, etc. can be accurately controlled, and high-quality crystal growth is possible.

  The apparatus of this embodiment is particularly suitable for the growth of zinc oxide (ZnO) -based compound semiconductor crystals.

  Here, a semiconductor light-emitting element using the zinc oxide-based compound semiconductor film which is crystal-grown in this embodiment will be described with reference to FIG.

  The structure of the semiconductor light emitting element is a structure in which a buffer layer 201, an n-type oxide semiconductor layer 202, and a p-type oxide semiconductor layer 203 are stacked on a substrate 421 as shown in FIG. A p-side electrode (translucent electrode) 204 is disposed on the p-type oxide semiconductor layer 203, and a p-type electrode pad 205 is disposed thereon. An n-side electrode 206 and an n-side electrode bonding member 207 are stacked on the lower surface of the substrate 421.

  As the substrate 421, zinc oxide, sapphire, or the like can be used. The buffer layer 21 is a zinc oxide crystal reconstruction layer. The n-type oxide semiconductor layer 202 and the p-type oxide semiconductor layer 203 are layers obtained by crystal growth of zinc oxide to which n-type and p-type impurities are added, respectively.

  The buffer layer 201, the n-type oxide semiconductor layer 202, and the p-type oxide semiconductor layer 203 can be formed using the liquid source MOCVD apparatus of this embodiment.

As the material solution 416, the above-described solute Zn (EDMDD) ₂ dissolved in the solvent ECH can be used.

Although the ZnO crystal is n-type even in an undoped state, it is possible to further enhance the n-type characteristics by adjusting the residual carrier density in the n-type semiconductor film by changing the growth temperature. If a dopant is used, for example, when Ga is used as an n-type impurity, a dopant solution in which Ga (EDMDD) ₃ is dissolved in ECH may be added and grown.

Further, for example, nitrogen is doped as a p-type impurity, but ammonia (hereinafter, NH ₃ ) gas may be supplied as a dopant gas.

Further, considering the adjustment of the band gap engineering, for example, when an Mg mixed crystal type oxide semiconductor is used for the p-type oxide semiconductor layer, for example, Mg (EDMDD) ₂ is used as a solvent ECH as a Mg material solution. What was melt | dissolved in can be used. In addition, you may use the cocktail material solution which mixed various amounts of impurities beforehand.

  By using the liquid source MOCVD apparatus of this embodiment, the n-type oxide semiconductor layer 202 and the p-type oxide semiconductor layer 203 having excellent crystallinity can be formed.

  The film forming process and the element dividing process of the p-side electrode (translucent electrode) 204, the p-side electrode pad 205, the n-side electrode 206, and the n-side electrode connecting member 207 are performed by known methods.

  Since the semiconductor light emitting element manufactured by the manufacturing method of this embodiment has excellent crystallinity of the n-type oxide semiconductor layer 202 and the p-type oxide semiconductor layer 203, light emission efficiency can be improved as compared with the conventional case. it can.

  When an oxide semiconductor light emitting element is manufactured by the same growth method using the above-described liquid material and gas material as in the present invention, the buffer layer 201 may not be provided.

  Note that a light-emitting layer including a quantum well structure may be formed between the n-type oxide semiconductor layer 202 and the p-type oxide semiconductor layer 203.

  In the embodiment described above, the pressure regulating valve 424 is disposed on the exhaust side of the reaction vessel 420 as shown in FIG. 1, but the present invention is not limited to this configuration. For example, as shown in FIG. 9, a pressure regulating valve 424 may be disposed between the vaporizer 409 and the reaction vessel 420, and the vaporizer 409 may include the pressure sensor 17. Under the control of the central controller 16, the pressure regulator 21 performs feedback control so that the pressure in the vaporizer 409 detected by the pressure sensor 17 becomes a predetermined pressure. The temperature of the vaporizer 409 is feedback controlled by the temperature regulator 18 as in the above-described embodiment. In the configuration of FIG. 9, since the pressure in the vaporizer 409 can be set to a pressure different from the pressure in the reaction vessel 420 by the pressure regulating valve 424, the vaporizer temperature and / or pressure can be set by the vaporizer 409 alone. By adjusting, it becomes possible to control the conditions so that the material solution is completely vaporized (the saturation rate of the solute vapor is 1 or less). However, if the pressure difference is large, the temperature of the vaporized gas decreases after passing through the pressure regulating valve 424 due to adiabatic expansion of the gas, and the material solution gas reaggregates. Accordingly, the difference between the pressure in the vaporizer 409 and the pressure in the reaction vessel 420 is preferably 100 kPa or less, desirably 50 kPa or less, and more desirably 30 kPa or less. Alternatively, the temperature difference is such that the saturation rate of the solution vapor can be maintained at 1 or less.

Examples of the present invention will be described below.
In this example, a ZnO film was formed using the liquid source MOCVD apparatus shown in FIG. Since the apparatus configuration has been described in the embodiment, the description thereof is omitted here.

As the material solution 416, a solution in which the solute Zn (EDMDD) ₂ was dissolved in the solvent ECH was used. The concentration of the material solution 416 was 0.2 mol / L. As the liquid material pressurizing gas 11, helium gas was used.

  The operator sets the C-plane sapphire substrate 421 on the susceptor 428. The operator sets various setting values in the central controller 16. In response to this, the central control device 16 controls the gas flow rate adjusting devices 405b and 405d, and the reaction vessel at a flow rate of 0.25 SLM for nitrogen gas from the gas flow rate adjusting device 405d and 0.5 SLM for oxygen gas from the gas flow rate adjusting device 405d. Supplied to. Further, the temperature of the material gas heater 411 was controlled by the central controller 16 via the temperature controller 19 so that the temperature of the supplied gas was 250 ° C. At the same time, the pressure control valve 424 was controlled by the central control device 16 via the pressure control device 21 so that the inside of the reaction vessel 420 became 2.0 kPa. Thereafter, the substrate heater 422 was feedback controlled by the temperature controller 20, heated to a substrate temperature of 900 ° C., and heat-treated for 10 minutes.

  Next, the substrate heater 422 was controlled, and the substrate temperature was lowered to 750 ° C. and held. In this state, the gas flow rate adjusting device 405a was controlled by the central control device 16, and nitrogen gas was supplied to the atomization assist gas heater 407 at 0.25 SLM as the atomization assist gas. Further, helium gas was used as the material solution pressurizing gas 11, and the liquid surface of the material solution 416 in the material solution container 417 was pressurized at 200 kPa. The liquid flow rate adjusting device 418a was controlled by the central control device 16, and the material solution 416 was supplied to the vaporizer 409 at 1.0 sccm. Thereby, the atomization support gas and the material solution were supplied to the vaporizer 409 at a predetermined flow rate, completely vaporized by the vaporizer 409, and supplied to the reaction vessel 420. The temperature of the liquid feeding tube 419 was controlled so as to be 25 ° C. or lower.

  At this time, the heating temperature of the atomization assisting gas heater 407 is such that the temperature of the atomization assisting gas becomes 250 ° C. at the time of ejection from the atomizing nozzle 408 of the vaporizer 409 (pressure in the vaporizer 409 is 2.0 kPa). Then, the temperature was controlled by the central controller 16 through the temperature controller 18. Further, the external heaters 905 and 908 of the vaporizer 409 are centrally controlled so that the temperature of the material solution 416 vaporized from the vaporizer 409 is 250 ° C. when the gas flows into the material solution gas introduction pipe 14 (spout time). Controlled by device 16. When the temperature of the gas contact surface of the heat exchange fin 907 was 300 ° C., the temperature of the material solution gas was 250 ° C.

  Further, the set flow rate to the gas flow rate adjusting device 405d was changed, and oxygen as the material gas was supplied to the reaction vessel 420 via the material gas heater 411 at a flow rate of 2.0 SLM. The heating temperature of the material gas heater 411 was set so that the temperature of the material gas was 250 ° C. at the point where the material gas induction tube 412 joined the material solution gas introduction tube 14.

Under this condition, a material solution (Zn (EDMDD) ₂ / ECH) 416 gas and a material gas (oxygen gas) are supplied onto the substrate 421 for 60 minutes to grow crystals, whereby a thickness of 1.0 μm is formed on the sapphire substrate. ZnO single crystal was obtained.

The film formation condition is the relationship of Formula 1 which is a condition for preventing bubbles from being generated in the material solution 416 in the liquid supply tube 419:
(Vapor pressure P of solvent) <(pressure in liquid feeding pipe) (Equation 1)
Meet. That is, when the vapor pressure P of the solvent is specifically calculated based on the above equation 2, the vapor pressure P of the solvent is 1.7 kPa as described below, and the pressure in the liquid feeding pipe, that is, the pressure 2. It is smaller than 0 kPa and satisfies Equation 1. Therefore, the material solution is sprayed from the atomizing nozzle into the vaporizer without generating bubbles in the liquid feeding pipe and inside the atomizing nozzle.
P (mmHg) = 10 ^ [AB / (T + C)] (Formula 2)
= 10 ^ [6.9999-1465.203 / (25 + 224.044)] = 13.1 (mmHg)
= 1.7 (kPa)
However,
P (mmHg): ECH vapor pressure T (° C.): 25
A: 6.99949
B: 1465.203
C: 224.044

  Next, it is confirmed that the vapor saturation rate of the material solution in the space in the vaporizer 409 is 1.0 or less under the growth conditions of this example.

The flow rate of the atomization support gas in the vaporizer 409 in the embodiment is expressed by the following equation 4.
_Fvp = ( _Pst * _Fst / _Tst ) * ( _Tvp / _Pvp ) (Formula 4)
= {(1.0 × 0.25) /273.15} × (523.15 / 0.0197) = 24.3 (L / min)
The solute molar flow rate is calculated from Equation 5,
M _sv = C _sv · F _mix (Formula 5)
= 0.2 × 1.0 × 10 ⁻³
= 0.2 × 10 ⁻³ (mol / min)
Solute vapor molarity C _sv is given by equation 6
C _sv = M _sv / F _vp (Expression 6)
= (0.2 × 10 ⁻³ ) /24.3
= 8.24 × 10 ⁻⁶ (mol / L)

Next, the saturation concentration of the solute is determined. First, the partial pressure P of the solute is obtained from Equation 2 ′ for calculating the vapor pressure of the liquid material (Zn (EDMDD) ₂ ).
P (mmHg) = 10 ^ [AB / T] (Formula 2 ′)
T (K): 523.15 (= 250 ° C.)
A: 11.540
B: 5408
∴ P = 15.94 (mmHg) = 0.021 (atm)

The saturated solute molar concentration that can be dissolved in the atomization assisting gas is from Equation 7,
C _sat = P / (R · T _vp ) (Expression 7)
= 0.021 / (0.0820205784 × 523.15)
= 4.89 × 10 ⁻⁴ (mol / L)

By dividing the solute vapor molar concentration C _sv by the saturated solute molar concentration C _sat and deriving the saturation rate S _v by Equation 8, the saturation rate is 0.017.
_{S v = (C sv / C} sat) ··· ( Equation 8)
= (8.24 × 10 ⁻⁶ ) / (4.89 × 10 ⁻⁴ )
= 0.017

  Therefore, under the conditions of this example, since the saturation rate Sv of the solute in the space in the vaporizer 409 is 1.0 or less, it was confirmed that complete vaporization in the vaporizer 409 is possible. Moreover, since the saturation rate (0.017) is 0.3 or less, the evaporation rate is high, and complete vaporization can be realized quickly.

In the conditions of the example, when the gas contact surface temperature of the heat exchange fin 907 in the vaporizer 409 is 300 ° C., the material solution gas ejection temperature is 250 ° C. %.
Heat exchange rate = (material solution gas temperature after vaporization / vaporizer internal temperature) × 100) (Equation 6)

  In addition, since the temperature of the gas contact surface of the heat exchange fin 907 is 300 ° C., the gas temperature can be made equal to or lower than the pyrolysis temperature of the organometallic material, and thermal alteration of the material can be prevented before reaching the substrate surface.

(Comparative example)
As a comparative example, a ZnO film was similarly grown using the liquid source MOCVD apparatus of FIG.

  Unlike the liquid source MOCVD apparatus of FIG. 1 of the present invention, the apparatus of FIG. 10 does not include the atomization assist gas heater 407 and the material gas heater 411. Further, the vaporizer 316 uses the atomizing nozzle of FIG. 7 described as a comparative example of the above embodiment as the atomizing nozzle 315 as shown in FIG. Further, the vaporizer 316 does not include fins and an internal heater. Moreover, the control which maintains the vapor | steam of the material solution in the vaporizer 316 below a saturated vapor pressure is not performed.

  The film forming conditions of the comparative example were set as follows. The solute / solvent / concentration and flow rate of the material solution 416, the material solution pressurized gas type and its pressure, the substrate 421 material and its heat treatment / growth temperature were set to be the same as in the example. Prior to crystal growth, the vaporizer 316 and the reaction vessel 420 were heated to 250 ° C. to prevent the material solution from adhering to the tube wall as much as possible.

  Nitrogen gas and oxygen gas are used as the material gas that also serves as the atomization support gas, and the flow rate is adjusted to 250 sccm by the gas flow rate adjustment device 405a and 2.0 SLM by the gas flow rate adjustment device 405c. 315 was supplied to the nozzle.

  As shown in FIG. 7, the atomizing nozzle 315 joins the two tubes before the jet outlet to mix the material solution and the atomization assisting gas. It moves in the pipe with the atomization support gas sandwiched between them, and is ejected from the nozzle tip by the momentum of the gas. For this reason, the ejection of the material solution becomes intermittent, and the size of the formed solution mist 51 is not uniform and the particle size distribution becomes large. The solution mist 51 having a large particle size takes time to vaporize the solvent and solute in the vaporizer 316, and the solute mist 52 remains even when reaching the outlet of the vaporizer 316. For this reason, it is difficult to completely vaporize the material solution in the vaporizer 316, and the gas of the material solution is sent out to the reaction vessel 420 with the solute mist 52 remaining.

  The pressure in the vaporizer 316 and the reaction vessel 420 was adjusted to 600 Pa by the pressure adjustment valve 424.

  A mixed gas of a material solution vaporized by the vaporizer 316 and a material gas also serving as an atomization assisting gas was introduced into the reaction vessel 420 and sprayed onto the substrate 421 to grow ZnO for 60 minutes. The grown ZnO crystal film was cooled by gradually lowering the substrate temperature.

Since this comparative example uses Zn (EDMDD) ₂ which is a liquid material as the solute as in the example, the solute does not precipitate in the pipe or the atomizing nozzle due to the vaporization of the solvent. However, high quality crystal growth was not realized.

(Evaluation)
Observation images of the ZnO crystals grown in Examples and Comparative Examples using differential interference microscope and scanning electron microscope were obtained. The differential interference microscope image was observed using an Olympus industrial inspection microscope MX51. The scanning electron microscope image was obtained by microscopic observation of the growth film surface using a scanning electron microscope S-2600N manufactured by Hitachi, Ltd.

  In addition, ZnO crystals of Examples and Comparative Examples were analyzed by secondary ion mass spectrometry (SIMS) method.

  Furthermore, the film thickness and unevenness | corrugation of the ZnO crystal of an Example and a comparative example were measured with the palpation type surface shape measuring apparatus (Corporation | KK ULVAC make DEKTAK).

(Evaluation results)
The differential interference microscope observation images are shown in FIGS. It was confirmed that the sample surface of the ZnO crystal of the example of FIG. 12B was a smooth surface without hillrock. On the other hand, as shown in FIG. 12A, the ZnO crystal sample of the comparative example had irregularities with dense hillrocks.

  Scanning electron microscope images are shown in FIGS. When observation was performed at a magnification of 5000 as shown in FIG. 12D, it was confirmed that the sample of the example was a dense film. On the other hand, the sample of the comparative example was a film in which 3-5 μm hillocks were further formed on the ZnO crystal film as shown in FIG.

The SIMS observation results are shown in FIGS. 13 (a) and 13 (b). From FIG. 13 (b), it was confirmed that the concentration of carbon and hydrogen as impurities was the lower limit of analysis in the sample film of the ZnO crystal of the example. On the other hand, it is confirmed that the carbon and hydrogen concentrations as impurities in the ZnO crystal film of the comparative sample are included around 1 × 10 ²¹ and about 1 × 10 ²⁰ as shown in FIG. did.

  Moreover, it was confirmed by film thickness measurement that the sample of the ZnO crystal film of the example had a thickness of 1.0 μm and the sample of the comparative example had a thickness of 0.8 μm. From this, it is considered that the film forming apparatus of the example could use the material for film formation more efficiently than the film forming apparatus of the comparative example.

  From the above results, it is clear that a good ZnO single crystal film that is uniform and homogeneous and does not take in impurities can be obtained by the present invention that stabilizes the supply of the material solution gas and further completely gasifies the material solution.

1 is a block diagram showing an overall configuration of a liquid source MOCVD apparatus according to an embodiment. (A) Sectional drawing of the vaporizer | carburetor of the apparatus of FIG. 1, (b) AB sectional drawing of a figure (a). Sectional drawing of the atomization nozzle of embodiment. Explanatory drawing which shows the process in which the solution mist in the vaporizer | carburetor of embodiment is vaporized. The perspective view and top view of the heat exchange fin of embodiment. The perspective view and top view of the heat exchange fin of another embodiment. The perspective view and top view of the heat exchange fin of another embodiment. The flowchart which shows control of each part of the apparatus by the central control apparatus of embodiment. Sectional drawing of the atomization nozzle of a comparative example. (A) Top view of the light emitting element manufactured by the manufacturing method of this embodiment, (b) Cross-sectional view. The block diagram which shows the structure which has arrange | positioned the pressure regulating valve 424 between the vaporizer | carburetor 409 and the reaction container 420 in the liquid source MOCVD apparatus of embodiment. The block diagram which shows the whole structure of the liquid source MOCVD apparatus of a comparative example. Explanatory drawing which shows the vaporization process of the solution mist in the vaporizer | carburetor of a comparative example. (A) Differential interference microscope image of the ZnO film manufactured in the comparative example, (b) Differential interference microscope image of the ZnO film manufactured in the example, (c) Scanning electron microscope image of the ZnO film manufactured in the comparative example, ( d) Scanning electron microscope image of the ZnO film produced in the example. (A) The graph which shows the SIMS analysis result of the ZnO film | membrane manufactured by the comparative example, (b) The graph which shows the SIMS analysis result of the ZnO film | membrane manufactured by the Example.

Explanation of symbols

  402 ... Inert gas piping, 404 ... Material gas piping, 405 ... Gas flow rate adjusting device, 406 ... Atomization support gas feed pipe, 407 ... Atomization support gas heater, 408 ... Atomization nozzle, 409 ... Vaporizer, 410 ... Material gas air supply pipe, 411 ... Material gas heater, 412 ... Material gas induction pipe, 413 ... Inert gas pipe for pressurizing liquid material, 414 ... Solvent, 415 ... Solvent container, 416 ... Material solution (solvent + solute), 417 ... Material solution container, 418 ... Liquid flow rate control device, 419 ... Liquid feed pipe, 420 ... Reaction vessel, 421 ... Substrate, 422 ... Substrate heater, 423 ... Collection device, 424 ... Pressure adjustment valve, 425 ... Drain piping 426 ... introduction valve, 427 ... exhaust valve, 428 ... susceptor.

Claims (13)

A reaction vessel having a substrate holding unit for holding a substrate therein, an atomizing unit for atomizing the material solution by ejecting a liquid material solution and a gas for atomization support at room temperature, and a mist A vaporization unit that vaporizes the material solution in a shape and supplies the vaporized material solution to the reaction vessel,
The vaporizer includes a container having an internal space, and a heating unit that heats the space in the container and vaporizes the mist-like material solution,
One end of the container is provided with the atomizing section, the material solution and the atomization assisting gas are ejected toward the internal space, and the vaporized material solution is directed to the reaction container at the other end of the container. A delivery outlet is provided,
The heating unit includes one or more fins disposed in a space between the atomization unit and the delivery port, and a heater that heats the fins .
The main surface of the said fin is orientated in parallel with the axis | shaft which connects the said atomization part and the said delivery port, The film-forming apparatus characterized by the above-mentioned .   2. The film forming apparatus according to claim 1, wherein a rectifying space having a predetermined distance is provided between the fin and the atomizing unit to rectify the mist-like material solution ejected from the atomizing unit. Is provided.   2. The film forming apparatus according to claim 1, wherein a space of a predetermined distance is provided between the fin and the delivery port.   4. The film forming apparatus according to claim 1, wherein the heater is controlled to maintain a surface temperature of the fin at a temperature lower than a thermal decomposition temperature of the organometallic material contained in the material solution. A film forming apparatus having a control unit.   5. The film forming apparatus according to claim 1, further comprising a pressure adjusting unit that maintains an internal space of the container at a predetermined pressure. 6.   6. The film forming apparatus according to claim 1, wherein the atomizing unit is configured to eject the material solution from an ejection port, and the ejection port from which the heated atomization assisting gas is ejected. And a film forming apparatus.   The film forming apparatus according to claim 1, wherein the atomizing unit sprays the material solution at an angle of 30 ° to 60 ° with respect to a central axis. Membrane device.   8. The film forming apparatus according to claim 1, wherein the atomizing unit forms the material solution into droplets having a particle size of 60 μm or less. 9.   2. The film forming apparatus according to claim 1, wherein a plurality of the fins are provided, and a main plane of the fins is arranged radially about the axis.   10. The film forming apparatus according to claim 9, wherein the plurality of fins are divided into a plurality of stages in the axial direction, and the directions of the fins are alternately arranged for each stage. 3. The film forming apparatus according to claim 2, wherein the distance L of the rectifying space is
0.7 <(L · tan θ) /r≦1.0
(However, θ: angle of spraying of the atomizing section (angle from the central axis), r: radius of the fin)
A film forming apparatus characterized by the above. A film forming apparatus according to claim 3, the distance L ₂ to the fin and the delivery port, the film forming apparatus wherein said at fin diameter equal to or greater than.   13. The film forming apparatus according to claim 1, wherein the heating unit includes an external heater for heating the internal space from the outside of the container.