JP4590225B2 - Molecular beam epitaxial growth apparatus and method for producing group III nitride single crystal film on silicon substrate using the same - Google Patents

Description

The present invention relates to a molecular beam epitaxial growth apparatus and a method for producing a group III nitride single crystal film on a silicon substrate using the same .

  In forming a thin film, it is necessary that the crystal structure of the substrate and the crystal structure grown thereon coincide with each other, and ideal is homoepitaxial growth that grows on the same single crystal. Many of the compounds are obtained by heteroepitaxial growth in which a substrate crystal for homoepitaxial growth cannot be obtained but grown on a different single crystal. Currently, compound semiconductors such as gallium nitride and gallium arsenide are manufactured on expensive substrates such as sapphire and silicon carbide. However, it is difficult to increase the area of these, and from the viewpoint of industrial production, a substrate that is inexpensive and capable of increasing the area is desired.

  Therefore, the inventor of the present invention uses a molecular beam epitaxial growth apparatus (hereinafter also referred to as “MBE apparatus”) to first irradiate a silicon substrate with a gas containing carbon atoms such as acetylene to form a cubic silicon carbide layer. A method of forming a single crystal thin film of gallium nitride by irradiating a cubic silicon carbide layer with atomic nitrogen flux excited with gallium supplied from a molecular beam cell on a cubic silicon carbide layer has already been proposed ( For example, refer nonpatent literature 1).

The method does not use an expensive substrate such as silicon carbide, and is stable as a single semiconductor having a low cost and a diamond-type cubic structure in an ultra-high vacuum growth chamber of an MBE apparatus. set the silicon substrate in which a single crystal substrate is available, made of the silicon substrate on the silicon carbide single crystal (cubic or hexagonal) films, so-called, after forming the hetero buffer layer for the group III nitride single crystal, forming a single crystal thin film of gallium nitride hetero buffer layer to said, it is an inexpensive so obtained group III nitride single crystal film of gallium nitride.

In addition, according to the method using the MBE apparatus as described above, compared to a generally used metal organic chemical vapor deposition (MOCVD) gallium nitride production method (for example, see Patent Document 1), The consumption of raw materials is 1 / 100th, which is advantageous in terms of material cost.
However, in the MBE apparatus, in order to increase the growth rate of the cubic single crystal thin film, it is necessary to increase the supply amount of acetylene gas as a carbon source or the supply amount of excited nitrogen as a nitrogen source. When the supply amount and the supply amount of excited nitrogen atoms are increased, the growth chamber cannot be kept in a high vacuum, and a reactive gas such as acetylene adheres to the inner wall and shroud of the growth chamber. Then, since the reaction gas adsorbed on the shroud cooled with liquid nitrogen re-evaporates from there, the degree of vacuum does not recover after the reaction, which hinders the preparation of a gallium nitride thin film low-temperature buffer layer that should be continued. Occurs.

Further, according to the method using the MBE apparatus as described above, since the gas is used as the nitrogen source, it is necessary to increase the exhaust amount of the exhaust system as compared with the conventional MBE apparatus using only the solid raw material. It is necessary to use a molecular turbo pump instead of an ion pump.
However, in the MBE apparatus, in order to increase the growth rate of the group III group nitride single crystal thin film, it is necessary to increase the supply amount of excited nitrogen as a nitrogen source. Cannot be kept in a high vacuum, and it becomes difficult to obtain high quality crystals.
Therefore, in the conventional MBE apparatus, if a crystal thin film is to be formed on a large substrate at a high speed, a vacuum pump having a large capacity corresponding to the supply amount of acetylene gas and the supply amount of excited nitrogen atoms is required, and the apparatus becomes large. There are problems in terms of equipment cost and energy cost.

International School on Crystal Growth, Characterization and Applications 9-13 December 2003 La Pedrera Uruguay Abstract Collection P.42-47 JP-A-5-206520

In view of the above circumstances, the present invention is capable of downsizing the apparatus , and is capable of epitaxially growing a group III nitride single crystal film on a substrate efficiently , inexpensively and accurately, and such a molecular beam epitaxial growth apparatus. It is an object of the present invention to provide a method for producing a group III nitride single crystal film such as gallium nitride on a silicon substrate using a simple molecular beam epitaxial growth apparatus.

In order to achieve the above object, a molecular beam epitaxial growth apparatus of the present invention uses a growth chamber set in a high vacuum state, a substrate fixing member disposed in the growth chamber, and a neutral gas supplied into the discharge chamber as RF. An excited atom cell that can be dissociated by (high frequency) discharge to emit a dissociated particle flux toward the substrate fixed to the substrate fixing member in the growth chamber, and at least one that irradiates the substrate with an atomic beam In the molecular beam epitaxial growth apparatus comprising the above melting cell,
A magnetic field applying means configured to apply a static magnetic field for ECR (electron cyclotron resonance) that changes a magnetic flux density in addition to a high-frequency magnetic field applied to the discharge chamber of the excited atom cell; and a discharge chamber of the excited atom cell. And a partition plate formed with a plurality of orifices having a predetermined aspect ratio, adjusting the magnetic flux density of the static magnetic field for ECR, and setting the number of orifices of the partition plate and the aspect of the orifice By adjusting the ratio, the flow rate of the excited atoms and base atoms of the neutral gas injected into the growth chamber can be adjusted.

Furthermore, the molecular beam epitaxial growth apparatus of the present invention is provided with electric field generation means for suppressing charged particles that generates an electric field that intersects with the charged particle flux emitted from the outlet around the outlet of the discharge chamber of the excited atom cell. The charged particles that are ejected from the discharge chamber of the excited atom cell toward the substrate disposed in the growth chamber are suppressed by the electric field generated by the electric field generating means for suppressing the charged particles .

In the present invention, examples of the magnetic field applying means include a coil, an electromagnet, a permanent magnet, and the like, but the coil and the electromagnet are used because the magnetic flux density can be easily controlled by controlling the current. The direction in which the magnetic field is applied is not particularly limited, but at least crosses the excited particle flux emitted from the discharge chamber .

The magnetic flux density of the magnetic field generated by the magnetic field applying means is adjusted according to the discharge frequency of the high frequency discharge, the type of atom to be excited, etc., and is not particularly limited. For example, the discharge frequency is 13.56 MHz and the nitrogen gas Although it depends on the electron temperature of the discharge plasma, it is preferable to have a magnitude that causes cyclotron resonance of several tens of millitesla (mT) or less, for example, about 0.5 millitesla.

And the inner diameter of the orifice formed in the partition plate attached to the outlet portion of the discharge chamber, the number of orifices is appropriately determined empirically determined by the type of thin film to be grown. Regarding the hole diameter and hole length of these orifices, the directivity of radical atoms formed in the discharge chamber improves as the hole length / hole diameter (aspect ratio) increases. Under efficient atom generation conditions, the mean free path of nitrogen atoms is considered to be several millimeters (mm), so the hole length (partition plate thickness) should be several millimeters (mm) or less . Is preferred. Further, a small hole diameter, because it tends to occur a collision between the inner wall and the atoms of the orifice, to prevent the excitation atoms by collisions with the inner wall in a non-excited state, the aspect ratio and the degree 2-10 It is preferable to do.

The electric field generating means for suppressing (or removing) charged particles is not particularly limited as long as it can form a positive electric field or a negative electric field and prevent the discharge of charged particles from the outlet of the discharge chamber. A method of applying a positive or negative charge to a metal cylindrical body, such as steel, is arranged so that the direction in which the charged particles protrude from the discharge chamber outlet and the central axis thereof are parallel to each other. It is done.
Although the shape of a cylindrical body is not specifically limited, A cylinder is preferable.

The apparatus of the present invention further includes at least one reaction gas cell that discharges a reaction gas into a growth chamber in a high vacuum state, and surrounds a peripheral edge portion of an orifice formed at a nozzle tip of the reaction gas cell, and the growth chamber. And a reaction gas jet discharged from the inside of the reaction gas cell into the growth chamber through the orifice is transferred to the substrate fixing member in the growth chamber through the reaction gas guide tube portion. It is characterized by being configured to irradiate a fixed substrate surface .

The single orifice formed at the nozzle tip of the reaction gas cell is determined and determined empirically depending on the type of thin film to be grown. With respect to the hole diameter and the hole length of this single orifice, the directivity of the reaction gas to the substrate is improved as the hole length / hole diameter (aspect ratio) is larger. Since the mean free path of the reaction gas is considered to be about several millimeters (mm), the length of the hole is preferably about several millimeters (mm) or less. In addition, the formation of the reactive gas jet requires a reduction in the diameter of the orifice, and the aspect ratio is preferably about 2 to 10.
In addition, the longer the guide tube portion is, the more the divergence can be prevented and the directivity is improved. The length of the guide tube determines the reaction gas radiation distribution in consideration of its radius, but if it is too long, the characteristics of the reaction gas jet are lost, so the aspect ratio is about 5 to 20, and the inner diameter of the guide tube is the irradiated sample substrate It may be about 1/100 to 1/10 of the outer diameter.

A method for producing a group III nitride single crystal film on a silicon substrate of the present invention is the molecular beam epitaxial growth apparatus, further using a molecular beam epitaxial growth apparatus provided with at least one or more reactive gas cells ,
The silicon substrate was fixed to a substrate fixing member provided in the growth chamber of the molecular beam epitaxial growth apparatus, S _i C by irradiating a reaction gas containing carbon C from the reaction gas cell on the silicon substrate surface while heating the silicon substrate Forming a single crystal heteroepitaxial buffer layer;
The S _i C single crystal heteroepitaxial buffer layer from dissociated by excitation atomic cell by the high-frequency magnetic field to the nitrogen gas N ₂ supplied to the discharge chamber of the excited atoms cells, excited nitrogen atom N ^* and basal nitrogen atom N flux by irradiating the group III atoms flux from the molten cell irradiates a, is characterized by a step of forming a III nitride single crystal layer on the S _i C heteroepitaxial buffer layer.

Production method of the III nitride single crystal film, the silicon substrate surface NoboriAtsushichu is adapted to be exposed to the reactive gas atmosphere containing carbon atoms, the timing is not particularly limited, relatively It may be started when the temperature is raised to a low temperature, for example, about 300 ° C. Further, the inside of the silicon carbide single crystal film formed in carbonization silicon single-crystal layer forming process in consideration of the time in which the silicon atoms diffuse, to intermittently irradiate the reaction gases high-quality silicon carbide single crystal film It is effective to produce.
In addition, although it does not specifically limit as a reactive gas containing a carbon atom, For example, acetylene gas is mentioned.

Furthermore, the method for producing a group III nitride single crystal film of the present invention includes a dissociated charged particle flux (flux) containing excited nitrogen atoms N ^* and ground nitrogen atoms N emitted from the discharge chamber of the excited atom cell . A detection electrode for detecting the flow rate is provided at a position that does not hinder the dissociated particle flux irradiated from the excited atom cell toward the silicon substrate fixed to the substrate fixing member, and based on the detection value of the dissociated particle flow rate by the detection electrode. It is characterized by controlling the formation process of the group III nitride single crystal layer .

  In the present invention, the group III atom is not particularly limited, and examples thereof include Al (aluminum), Ga (gallium), and In (indium). The cubic single crystal thin film obtained by the production method of the present invention includes these III It may be a mixed crystal of group atoms.

In the apparatus of the present invention, the dissociation of the reaction gas, for example, nitrogen gas, dissociated by the high frequency discharge in the discharge chamber by the ECR static magnetic field applied in addition to the high frequency magnetic field in the discharge chamber of the excited atom cell by the magnetic field applying means. Electrons in the plasma caused by a cycloid curve move, and the dissociation of nitrogen molecules in the discharge chamber is promoted, and excited atoms generated thereby are concentrated and supplied from the outlet of the discharge chamber toward the substrate placed in the growth chamber. Become so. Therefore, the concentration of nitrogen gas supplied to the discharge chamber can be reduced, and the growth chamber can be kept at a high vacuum without using a large vacuum pump. That is, energy saving and resource saving can be achieved with downsizing of the apparatus. In addition, since the magnetic field applying means can change the magnetic flux density, the optimum magnetic flux density can be found by examining the discharge spectrum while changing the magnetic flux density. Then, a more efficient molecular beam epitaxial growth can be performed by applying a magnetic field having the optimum magnetic flux density to the discharge chamber.

In addition, the partition plate attached to the exit of the discharge chamber of the excited atom cell is provided with a plurality of orifices having a predetermined aspect ratio, and the radiation diffusion range of the excited atoms can be controlled by these orifices. I can do it. That is, the excited atoms generated in the discharge chamber are effectively supplied without divergence toward the substrate. Therefore, molecular beam epitaxial growth can be performed more efficiently.

Furthermore, an electric field for blocking the passage of positive charges or an electric field for blocking the passage of negative charges is formed in front of the atomic beam outlet of the discharge chamber of the excited atom cell, and charged particles jump out from the atomic beam outlet toward the substrate. The charged particle suppression electric field generating means for preventing the charged particles is generated by generating an electric field at the exit of the atomic beam by the charged particle suppressing electric field generating means to prevent the movement of positive charges. If an electric field is generated at the exit of the atomic beam that prevents the positive ions of a reactive gas from jumping out from the exit of the atomic beam and prevents the movement of negative charges, the exit of the atomic beam of electrons , which are negatively charged particles, generated in the discharge chamber Can be prevented from jumping out. That is, it is possible to prevent charged particles that inhibit crystal growth, particularly positive ion particles, from impacting the substrate surface .

In the apparatus of the present invention, an orifice having a predetermined hole diameter is provided at the tip of the gas supply nozzle, and the gas supply nozzle is provided according to the pressure difference between the atmospheric pressure in the gas supply nozzle and the high vacuum pressure in the growth chamber. injecting a reaction gas is supplied as a reaction gas jet, so extend beauty toward the growth chamber of the substrate from the orifice, providing the guide tube portion to prevent the divergence of the reaction gas jet is injected through the orifice since the, it is possible to place the ejection port of the reaction gas jets still closer to the substrate, without lowering the degree of vacuum in the growth chamber, can be supplied to the reaction gas efficiently substrate surface. Accordingly, the amount of excess reactive gas is reduced, and the system can be kept at a high vacuum without using a large vacuum pump. That is, energy saving and resource saving can be achieved with downsizing of the apparatus.

Further, in the method for producing a group III nitride single crystal layer on a silicon substrate of the present invention, the reaction gas cell can supply a reaction gas containing carbon atoms with good directivity to the silicon substrate, and the minimum necessary number of carbon atoms can be supplied. A silicon carbide single crystal layer can be efficiently formed on the silicon substrate surface by the reaction gas contained.

Further, in the manufacturing method of the present invention , excited nitrogen atoms can be supplied with good directivity to the surface of the silicon carbide single crystal layer formed on the silicon substrate by the excited atom cell , and a predetermined amount provided at the exit portion of the excited atom cell. III nitride single crystal film of gallium nitride or the like of high quality on the silicon carbide single crystal layer with the excitation nitrogen atom flux Therefore the minimum necessary to a plurality of orifices having an aspect ratio of it efficiently formed.
Furthermore, a detection electrode for detecting the flow rate of dissociated particles is provided at a position where the dissociated particle flow irradiated from the excited atom cell toward the silicon substrate fixed to the substrate fixing member is not hindered, and the amount of excited nitrogen atoms is monitored while Since the crystal thin film is grown, a higher-quality group III nitride single crystal film can be easily obtained.

Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof.
1 to 3 show a first embodiment of a molecular beam epitaxial growth apparatus according to the present invention.

  In FIG. 1, 1a is a molecular beam epitaxial growth apparatus (hereinafter referred to as "MBE apparatus"), 2 is a growth chamber, 3a is an Al molecular beam cell (sometimes referred to as Knudsen cell or K-cell), and 3b is Ga. Molecular beam cell for use, 3c for molecular beam cell for In, 3d for molecular beam cell for silicon, 4a for high frequency discharge excitation atom cell, 5 for reaction gas introduction cell for introducing reaction gas into growth chamber 2, 6 for silicon substrate, 7 is a substrate support, 71 is a heater, 8 is a manipulator, 9 is a Q-mass mass analyzer, 10 is a molecular turbo pump, 11 is a gate valve, 12 is a sample preparation chamber, 13 is a viewport, 14 is liquid nitrogen A shroud cryopump, 15 is a RHEED (high-speed reflected electron diffraction) electron gun, 16 is a RHEED screen, and 17 is an ion gauge for flux monitoring, which is excited by high-frequency discharge. Except 5 child cells 4a and reaction gas introduction cell is adapted to the same as the conventional MBE apparatus.

  The molecular beam cell 3a for aluminum, the molecular beam cell 3b for gallium, the molecular beam cell 3c for indium, and the molecular beam cell 3d for silicon have a crucible 31 made of PBN (boron nitride), a heater 32, and a shutter 33, respectively. Each has the same structure as the conventional one.

As shown in FIGS. 1 and 2, the high-frequency discharge excited atom cell 4 a includes a discharge chamber 41, a water-cooled RF (high-frequency) coil 42, and a large number of partition plates attached to the outlet of the discharge chamber 41. an orifice 43, an outer cylinder 44 which surrounds the discharge chamber 41 and the water cooled RF coil 42, a magnetic field applying coil 45, which acts as a wound magnetic field applying means around the outer tube 44, a gas supply pipe 46, the view port 47, and a shutter 48.

Magnetic field applying coils 45a, although not shown, by a controller provided outside, by changing the supply power, the magnetic flux density of the outlet portion of the discharge chamber 41 is in the freely variable Erareru so.
A liquid nitrogen cylinder (not shown) serving as a nitrogen source is connected to the gas supply pipe 46.

The reaction gas cell Le 5, as shown in FIGS. 1 and 3, has a gas supply nozzle 51 to the inside, a single orifice 52 is provided at the tip of the gas supply nozzle 51, the substrate 6 direction from the orifice 52 together with the guide tube portion 53 is extended beauty toward the shutter 54 is provided in front of the guide cylinder portion 53. The attachment 50 formed an orifice 52 in the bottom of the guide tube portion 53, are attachable to existing gas supply nozzle 51 via a joint 56.

  The gas supply nozzle 51 is connected to a cylinder (not shown) of acetylene as a reaction gas through a needle valve 55 provided at the base end. Although the gas supply nozzle 51 and the guide cylinder part 53 are not particularly limited, a stainless steel pipe of about 1/4 inch is used.

  This MBE apparatus 1a is as described above. For example, a cubic single crystal thin film of gallium nitride which is a group III group nitride can be manufactured as follows.

That is, first, the silicon substrate is chemically etched by an etchant having a mixture ratio of HF (hydrogen fluoride): H 2 O = 5%: 95% ( capacity ), that is, cleaned, and then immediately set on the substrate support portion 7 to obtain a growth chamber. The inside of 2 is brought into an ultrahigh vacuum state of 10 ⁻⁸ Pascal or less. Next , while heating the silicon substrate 6 by the heater 71, acetylene gas is supplied from the gas supply nozzle 51 of the reaction gas introduction cell 5 toward the surface of the silicon substrate 6, and the surface of the silicon substrate 6 is exposed to the acetylene gas. A cubic silicon carbide SiC buffer layer having a thickness of about 5 nm is formed on the surface of the silicon substrate 6 by carbonizing the silicon. At this time, the acetylene gas is injected from the orifice 52 through the orifice 52 formed at the tip of the gas supply nozzle 51 in accordance with the pressure difference between the gas supply nozzle 51 and the growth chamber 2 . That is, a reactive gas (acetylene gas) jet is formed. The acetylene gas jet is injected toward the silicon substrate 6 is guided by the guide tube portion 53. Acetylene gas jets injected from the orifice 52, supplied to the guide tube portion 53 thus divergence is suppressed by directional good silicon substrate 6 surface extending toward the silicon substrate 6 disposed in the growth chamber 2 from the orifice 52 Is done. The supply amount can also be controlled by opening and closing the shutter 54.

In the manner described above, after forming the silicon carbide single-crystal layer on the silicon substrate 6, the supply of acetylene gas from the reaction gas cell 5 is stopped, while the substrate is heated to about 500 ° C., the growth chamber 2 ultrahigh It supplies the nitrogen excited atoms from excited nitrogen atom cells 4a while maintaining the vacuum state, the crucible 31 of gallium for molecular beam cell (molten cell) 3b evaporate gallium metal in the crucible 31 is heated by the heater 32 Then, the shutter 33 is controlled to supply gallium atoms to the surface of the silicon carbide cubic layer to form a low-temperature gallium nitride buffer layer having a thickness of about 2 nm to 20 nm .

Further, a high-frequency electromagnetic field is applied to the nitrogen gas supplied into the discharge chamber 41 of the high-frequency discharge excitation atom cell 4a by the high-frequency coil 42, thereby dissociating the nitrogen gas and causing a current to flow through the magnetic field applying coil 45a. magnetic field by causing electron cyclotron resonance (ECR) to generate excited nitrogen atom by Rukoto over the outer periphery of the outlet portion of the discharge chamber 41 to the high-frequency discharge plasma of the discharge chamber 41, the nitrogen gas containing excited nitrogen atom Excited nitrogen atoms are supplied to the silicon substrate 6 through a large number of orifices 43 provided with dissociated particle flux on the partition plate, and gallium atoms are supplied from the Ga molecular beam cell 3b to the silicon substrate 6 at the same time or at a certain interval. Then, a cubic gallium nitride Ga thin film is formed on the surface of the hetero low temperature buffer layer made of cubic silicon carbide SiC. Yes. In the case where the low-temperature buffer layer on the silicon substrate 6 is a hexagonal silicon carbide SiC is hexagonal gallium nitride GaN film by adjusting the flow ratio of nitrogen atoms and gallium atoms during subsequent epitaxial growth It is also possible to grow.

FIG. 4 shows a second embodiment of the MBE apparatus according to the present invention.
As shown in FIG. 4, the MBE apparatus 1b is the same as the MBE apparatus 1a except that the high-frequency discharge excited atom cell 4b is as follows.

Outside the opening of the excitation Okoshigenshi cell 4b, 2 two coils 45b that constitute the magnetic field applying means, 45b is arranged so as to sandwich the discharge chamber 41 of該Reiki atoms cell 4b from both sides, as shown by the arrow, the discharge Except that a magnetic field orthogonal to the longitudinal axis of the chamber 41 is formed, it is the same as the high frequency discharge excited atom cell 4a.

FIG. 5 shows a third embodiment of the MBE apparatus according to the present invention.
As shown in FIG. 5, the MBE apparatus 1c is the same as the MBE apparatus 1a except that the high frequency discharge excited atom cell 4c is as follows.

The high-frequency discharge excited atoms cell 4c, except that the two magnetic poles 45d of the electromagnet 45c constituting the magnetic field applying means, 45d is provided so as to sandwich the discharge chamber 41 from both sides, and the high frequency discharge excited atoms cells 4a It is set as the same structure .

Incidentally, excited atoms cell 4c, instead of the electromagnets 45 c, as shown in FIG. 6, it is also possible to use a magnetic field applying means 45e using a permanent magnet. That is, in this magnetic field applying means 45 e, the distance between the magnetic plate 45f and the magnetic plate 45f arranged permanent magnet 45g is such that the variable magnetic flux density can be adjusted by changing the position of the permanent magnet 45g is a tip portion of both the magnetic plate 45f is disposed adjacent to the outer wall surface of the discharge chamber 41.

7 to 9 show a fourth embodiment of the MBE apparatus according to the present invention.
As shown in FIG. 7, this MBE apparatus 1d is the same as the MBE apparatus 1a except that it includes an electric field generating means 100 for removing charged particles and an excited atom detection electrode 200.

  That is, the charged particle removing electric field generating means 100 includes an electric field generating electrode 110 and a power feeding device 120 as shown in FIGS.

The electric field generating electrode 110 is formed of stainless steel in a cylindrical shape having a diameter of 25 mm and an axial length of 15 mm, and is fixed inside the electric field generating electrode 110 with an atomic beam outlet portion of the discharge chamber 41 being adjacent.
The power supply device 120 includes a DC power supply 121, a feed line 122 to the field generating electrodes 110, and a changeover switch 123, the to switch between the selector switch 123, the ion particles positive charge into the cylinder of the electric field generating electrode 110 field to prevent electric or electronic negative charge blocking is formed.

As shown in FIGS. 7 and 9, the excited atom detection electrode 200 is formed by coiling a tantalum wire having a diameter of about 0.5 mm, and at a position that does not inhibit excited atoms toward the substrate in the vicinity of the substrate. The detection circuit 210 is connected.
The detection circuit 210 includes a DC power supply 211, a power supply line 212 to the excited atom detection electrode 200, a changeover switch 213, and an ammeter 214. By switching the changeover switch 213, the excitation atom detection electrode 200 is connected to the ground. Therefore, a positive or negative potential can be applied.

The MBE apparatus 1d is adapted to the above, for example, when manufacturing a gallium nitride single crystal film as a substrate a Group III nitride compound, 250V～1000V the field generating electrodes 110 of the charged particle suppression for electric field generating means 100 applying a degree of positive voltage, to form a positive electric field to the outlet front of the excited atoms cell, when the detection electrode 200 negative bias voltage is applied, excited nitrogen atom N ^* collides with the detecting electrode 200, the detection except adapted to form a gallium nitride single crystal film while monitoring current flowing through the circuit 210 by the ammeter 214 is made in the same manner as in the manufacturing method using the MBE apparatus 1a.

Wherein according to the manufacturing method, since suppressing the electric field the flow of positive charge in the atomic beam exit forward of the discharge chamber 41 of the excited atoms cell by an electric field generating electrode 110 is formed, a group-III nitride single crystal nitride film the single-crystal gallium (cubic) membrane nitrogen positive ions N ⁺ is generated in the discharge chamber 41 to adversely affect the growth of, by the repulsive force due to suppressing the electric field of the flow of positive charge from the atomic beam exit into deposition chamber 2 It is locked popped out Shiga阻. Therefore, exclusively excited nitrogen atom effective neutral to the growth of cubic single crystal thin film of gallium nitride (N ^*) and basal atom N are supplied to the substrate surface, a single crystal (cubic) film of high quality gallium nitride It can be obtained stably.
Moreover, since the gallium nitride single crystal (cubic) thin film can be grown while monitoring the current value of the ammeter 214 of the detection circuit 200, it is checked against the calibration curve obtained in advance, which is monitored by the ammeter 214. However, the thickness of the single crystal film can be freely controlled by controlling the amount of nitrogen supplied to the excited atom cell.

In addition, since the MBE apparatus 1d can switch the polarity of the excited atom detection electrode 200 , if a positive bias voltage is applied to the excited atom detection electrode 200 , the electron flow rate that jumps out from the atomic beam outlet into the growth chamber 2 Can be measured. Further, if the excited atom detection electrode 200 is in a state where a negative bias voltage is applied , the amount of N ⁺ ions can be detected by the excited atom detection electrode 200.

FIG. 10 shows a fifth embodiment of the MBE apparatus according to the present invention.
As shown in FIG. 10, this MBE device 1e includes a filter 510 in the high-frequency circuit 400 to the high-frequency coil 42 of the high-frequency discharge excitation atom cell 4a, instead of providing the magnetic field applying coil 45 as in the MBE device 1a. A DC circuit 500 is connected in parallel, and the same as the MBE apparatus 1a except that a high frequency is generated and a magnetic field is generated simultaneously by flowing an alternating current and a direct current through the RF coil. In FIG. 10, reference numeral 420 denotes a matching box.

  This MBE device 1e uses a high-frequency coil 42 with a simple configuration in which a DC circuit 500 including a filter 510 is connected in parallel to the high-frequency circuit 400 without separately providing magnetic field applying means such as the magnetic field applying coil 45. As a result, a magnetic field can be generated at the same time as generating a high frequency, and the cost can be reduced, and the high frequency discharge excited atom cell 4a can be downsized.

The present invention is not limited to the above embodiment. For example, the crucible can be replaced with alumina instead of PBN. Further, in the embodiments, although the excitation Okoshigenshi cell was used as the excitation source of nitrogen can be used as the excitation source of oxygen. That is, the active oxygen atom in an ultra-high vacuum, as engineering utilizing the reaction between the substrate to be utilized and is also applicable to higher oxygen compound prepared Engineering.

In the above embodiment, the electric field generating means for removing charged particles has a cylindrical shape, but may have a rectangular tube shape. Further, if the electric field is well formed, the columnar ones may be intermittently arranged on the same circumference, or may be formed of a wire mesh. Furthermore, the cylindrical opening may be covered with a metal mesh.
The same effect can be obtained even when the electric field generating means for removing charged particles and the excited atom detecting electrode of the present invention are adopted in a conventional MBE apparatus in which no magnetic field generating means is provided.

Example 1
In this example, an MBE apparatus as shown in FIG. 1 was used. This is MBE apparatus, the K cell ports of a conventional GaAs for MBE apparatus (VG Semicon Co. 80H), high-frequency discharge excited atoms cells (Arios Co. IRFS-501RF; 13.56MHz) as the excitation source of nitrogen is attached, the excitation A PBN partition plate having a thickness ( orifice length) of 2 mm, an orifice diameter (diameter) of 0.5 mm, and an orifice number of 185 is mounted at the atomic beam outlet of the discharge chamber of the atomic cell, as shown in FIG. electromagnet 45c is attached. Furthermore, as shown in FIG. 3, the tip of the gas supply nozzle, an inner diameter of 1/4 inch at one end, e Bei the guide tube portion of the length 20 cm, and the other end to the hole diameter 1 mm, the Anacho of 0.5mm single A reaction gas cell equipped with an attachment forming one orifice is mounted.

First, after chemically etching the silicon (001) and (111) substrates with an etchant having a mixture ratio of HF (hydrogen fluoride): H ₂ O = 5%: 95% (Vol.), The MBE apparatus is promptly transferred to the MBE apparatus. Introduced. Thereafter, the growth chamber is set to an ultrahigh vacuum of 10 ⁻⁸ Pa or less, and when the substrate temperature reaches 300 ° C. during the temperature rise, acetylene (99.95%) gas is changed into a molecular beam from the gas supply nozzle. The substrate temperature was raised to 900 ° C. while supplying the surface. The degree of vacuum in the growth chamber at this time was 5.0 to 10.0 × 10 ⁻⁶ Pascal or less. As a result, the silicon substrate surface was carbonized, and an RHEED image of cubic silicon carbide was confirmed. Then, after the low temperature buffer layer is grown by 5 to 10 nm, gallium atoms are excessively supplied from the molecular beam cell for gallium into the growth chamber, and the flow rate of nitrogen gas to the high frequency discharge excited atom cell is 0.3, 0.00. 4, 0.7, and 0.85 sccm, and by changing the magnetic flux density of the magnetic field applied to the discharge chamber by the electromagnet at each flow rate, the N atom spectrum intensity at 747 nm was measured, and the result is shown in FIG. Indicated. The spectrum intensity was measured with an attenuation filter interposed in the optical path when the actual intensity was too high.

(Example 2)
The same measurement as in Example 1 was performed except that the orifice at the outlet of the discharge chamber had a thickness of 0.5 mm, a hole diameter of 2 mm, a hole number of 1 and a different attenuation filter was interposed in the optical path. This is shown in FIG.

(Example 3)
Example 1 except that an orifice having a thickness (hole length) of 2 mm, a hole diameter (diameter) of 0.2 mm, and a hole number of 185 holes was set at the outlet of the atomic beam in the discharge chamber, and a different attenuation filter was interposed in the optical path. Measurements similar to those described above were performed, and the results are shown in FIG.

  From FIG. 11 to FIG. 13, it can be seen that if a magnetic field is applied to the discharge chamber from the outside, the spectrum intensity increases even at the same flow rate, and excited N atoms can be efficiently supplied to the substrate surface. That is, in the orifice of Example 1, as shown in FIG. 11, when the magnetic flux density is 1.0 at a flow rate of 0.3 sccm, the spectral intensity is larger than that at a flow rate of 0.7 sccm without applying a magnetic field.

Moreover, it is well understood from FIGS. 11 to 13 that the efficiency of the excited atom cell changes depending on the shape of the orifice provided at the exit of the excited atom cell .
In other words, if the optimum orifice shape (number of holes, hole length, hole diameter) and the magnetic flux density generated by the magnetic field applying means are set in advance, the ultrahigh vacuum can be maintained efficiently with the minimum flow rate. It can be seen that a group III nitride single crystal film can be manufactured.

Example 4
A cubic silicon carbide layer was formed on the surface of the silicon substrate in the same manner as in Example 1 except that the silicon surface was irradiated with silicon atoms from the molecular beam cell for silicon together with acetylene gas. As a result of observation with an atomic force scanning microscope (also referred to as “AFM”), 1 to 8 pits per 1 m 2 of a micron square disappear when the silicon atom is not irradiated, and the surface roughness is reduced. The roughness shown was reduced to 0.29 nm upon irradiation. Therefore, when forming a cubic silicon carbide layer, it has been found that if a silicon atom is simultaneously irradiated onto a silicon substrate surface together with a reaction gas containing carbon, it is effective for the subsequent group III group nitride single crystal thin film growth.

(Example 5)
Using the same MBE apparatus and sample preparation conditions as in Example 1, the substrate of the low temperature buffer layer was formed on the surface of the cubic silicon carbide layer obtained through the cubic silicon carbide layer forming step following the cubic silicon carbide layer forming step. After the growth at a temperature of 500 ° C., a gallium nitride film was grown at a substrate temperature of 800 ° C., a gallium molecular beam cell temperature of 965 ° C., and a nitrogen flow rate of 0.5 sccm over 3 hours.

And the PL (photoluminescence) measurement result measured at 16K of the obtained gallium nitride film is shown in FIG.
As shown in FIG. 14, under the conditions of Example 5, light emission near the band edges of cubic gallium nitride and hexagonal gallium nitride was observed, and light emission near 2.8 eV was also observed. The light emission in the vicinity of 2.8 eV is considered to be light emission through a deep level formed by defects.

(Example 6)
In the gallium nitride film growth step, a gallium nitride thin film was formed on a silicon substrate in the same manner as in Example 4 except that silicon atoms were simultaneously supplied from a molecular beam cell for silicon at a cell temperature of 1300 ° C. FIG. 15 shows the PL (photoluminescence) measurement result of the gallium nitride film measured at 16K.

As shown in FIG. 15, under the conditions of Example 6, no light emission was observed in the vicinity of 2.8 eV, and light emission in the vicinity of the cubic gallium nitride band was mainly observed.
From the results of Examples 4 and 5, it can be seen that the crystallinity of the cubic gallium nitride single crystal thin film is improved by irradiating silicon simultaneously with gallium.

  In addition, when XRD (X-ray diffraction) measurement was performed on the crystal films of Examples 5 and 6, as in Example 6, when the silicon was irradiated simultaneously with gallium, the half-value width was reduced compared to Example 5, The strength was increasing. This result also shows that the crystallinity of the cubic gallium nitride single crystal thin film is improved by irradiating silicon simultaneously with gallium.

(Example 7)
The charged particle removal electric field generating means 100 and the excited atom detection electrode 200 are attached to the high frequency discharge excited atom cell of the MBE device of Example 1 as in the MBE device 1d shown in FIG. 7, and −100 V is applied to the excited atom detection electrode 200. Then, the high-frequency discharge excited atomic cell is used to excite nitrogen under a nitrogen activation condition with a nitrogen gas flow rate of 0.5 sccm and an RF input power of 500 W, and then inject into the growth chamber and apply to the electric field generating electrode of the electric field generating means for removing charged particles. The applied voltage was changed from −1000 V to 1000 V, and changes in the applied voltage and the current value (charged particle density of nitrogen ions) measured by the excited atom detection electrode 200 were examined. The results are shown in FIG.

From the experimental results shown in FIG. 16, as the applied voltage applied to the electric field generating electrode becomes positive, the current value decreases, and when the applied voltage applied to the electric field generating electrode 110 is more positive than 250 V, it may be in a substantially balanced state. Recognize. That is, when a positive bias voltage of 250 V or more is applied to the electric field generating electrode 110, it is understood that the emission of nitrogen plus ions from the exit of the excited atom cell is completely prevented by the electric field that prevents the flow of the positive charges. .

1 is a cross-sectional view schematically showing a first embodiment of a molecular beam epitaxial growth apparatus according to the present invention. It is a perspective view of the high frequency discharge excitation atom cell part of the molecular epitaxial growth apparatus of FIG. It is principal part sectional drawing of the gas supply nozzle part of the molecular epitaxial growth apparatus of FIG. It is a perspective view showing the high frequency discharge excitation atom cell part of 2nd Embodiment of the molecular beam epitaxial growth apparatus concerning this invention. It is a perspective view showing the high frequency discharge excitation atom cell part of 3rd Embodiment of the molecular beam epitaxial growth apparatus concerning this invention. It is a perspective view showing the other example of the magnetic field provision means used for the high frequency discharge excitation atom cell of the molecular beam epitaxial growth apparatus concerning this invention. It is sectional drawing which represents typically 4th Embodiment of the molecular beam epitaxial growth apparatus concerning this invention. It is a perspective view explaining the attachment state of the electric field generation electrode of the molecular beam epitaxial growth apparatus of FIG. It is explanatory drawing explaining the electric circuit of the electric field generation means for charged particle removal of the molecular beam epitaxial growth apparatus of FIG. 7, and an excited atom detection electrode. It is explanatory drawing explaining the electric circuit of the high frequency coil of 5th Embodiment of the molecular beam epitaxial growth apparatus concerning this invention. 4 is a graph showing the relationship between magnetic flux density and spectral intensity at each gas flow rate obtained in Example 1. FIG. 6 is a graph showing the relationship between magnetic flux density and spectral intensity at each gas flow rate obtained in Example 2. 6 is a graph showing the relationship between magnetic flux density and spectrum intensity at each gas flow rate obtained in Example 3. 6 is a graph showing a PL measurement result of the gallium nitride crystal film obtained in Example 4. 6 is a graph showing a PL measurement result of the gallium nitride crystal film obtained in Example 5. FIG. When the MBE apparatus shown in FIG. 7 obtained in Example 7 is used, the applied voltage applied to the electric field generating electrode of the electric field generating means for removing charged particles is changed from −1000 V to 1000 V, and measured by the applied voltage and the excited atom detecting electrode. It is a graph showing the result of having investigated the change of the electric current value to be performed.

Explanation of symbols

1a, 1b, 1c, 1d, 1e Molecular beam epitaxial growth equipment (MBE equipment)
2 Growth chamber 3a Molecular beam cell for Al 3b Molecular beam cell for Ga 3c Molecular beam cell for In 3d Molecular beam cell for silicon 4a, 4b, 4c High frequency discharge excitation atom cell 41 Discharge chamber 43 Orifice 45a Magnetic field applying coil (magnetic field applying means) )
45b Coil (magnetic field applying means)
45c Electromagnet (magnetic field applying means)
45e Magnetic field applying means 5 Reactive gas introduction cell 51 Gas supply nozzle 52 Orifice 53 Guide cylinder 6 Substrate 100 Electric field generating means 200 for removing charged particles Excited atom detection electrode

Claims (5)

A growth chamber set in a high vacuum state, a substrate fixing member disposed in the growth chamber, and a neutral gas supplied into the discharge chamber are dissociated by RF (radio frequency) discharge to generate dissociated particle flux in the growth chamber. In a molecular beam epitaxial growth apparatus comprising: an excited atom cell that can be emitted toward a substrate fixed to the substrate fixing member; and at least one molten cell that irradiates an atomic beam toward the substrate.
A magnetic field applying unit configured to apply a static magnetic field for ECR (electron cyclotron resonance) that changes a magnetic flux density in addition to a high-frequency electromagnetic field applied to a discharge chamber of the excited atom cell; and discharge of the excited atom cell A partition plate that is attachable to the outlet of the chamber and has a plurality of orifices having a predetermined aspect ratio, adjusts the magnetic flux density of the static magnetic field for ECR, and sets the number of orifices of the partition plate and the orifice A molecular beam epitaxial growth apparatus characterized in that the flow rate of excited atoms and base atoms of the neutral gas injected into the growth chamber can be adjusted by adjusting the aspect ratio. Furthermore, the outlet periphery of the discharge chamber of the excited atoms cell, the charged particles suppressing electric field generating means for generating an electric field intersecting the charged particle flux emitted from the outlet provided by the electric field generating means for charged particle suppression 2. The molecular beam epitaxial growth apparatus according to claim 1, wherein a flow of charged particles ejected from a discharge chamber of the excited atom cell toward a substrate disposed in the growth chamber is suppressed by the generated electric field. .   The reaction gas further includes at least one reaction gas cell that discharges the reaction gas into the growth chamber in a high vacuum state, and surrounds the periphery of a single orifice formed at the nozzle tip of the reaction gas cell and extends into the growth chamber. A substrate provided with a guide cylinder, and a reaction gas jet discharged from the inside of the reaction gas cell through the orifice into the growth chamber is fixed to a substrate fixing member in the growth chamber through the reaction gas guide cylinder The molecular beam epitaxial growth apparatus according to claim 1, wherein the apparatus is configured to irradiate a surface. 4. The molecular beam epitaxial growth apparatus according to claim 3, wherein a silicon substrate is fixed to a substrate fixing member provided in a growth chamber of the molecular beam epitaxial growth apparatus, the silicon substrate is heated, and a reaction gas cell is formed on the surface of the silicon substrate. forming a S _i C single crystal heteroepitaxial buffer layer by irradiating a reaction gas containing carbon C from Subsequently, nitrogen gas N ₂ supplied to the discharge chamber of the excited atoms cells dissociated by high-frequency magnetic field from該Reiki atoms cell to the S _i C single crystal heteroepitaxial buffer layer, by irradiating the group III atoms flux from the molten cell irradiates the excitation nitrogen atom N ^* and basal nitrogen atom N flux, monocrystal silicon, characterized in that it comprises a step of forming a III nitride single crystal layer S _i C heteroepitaxial buffer layer A method for producing a group III nitride single crystal film on a silicon substrate. Furthermore, a detection electrode for detecting the flow rate of dissociated particles containing excited nitrogen atoms N ^* and ground nitrogen atoms N emitted from the discharge chamber of the excited atom cell is directed from the excited atom cell to the silicon substrate fixed to the substrate fixing member. The dissociated particle flux irradiated in this way is disposed at a position where the dissociated particle flux is not hindered, and the growth rate of the group III nitride single crystal layer is controlled based on the detected particle flow rate detected by the detection electrode. Of Group III Nitride Single Crystal Film on Silicon Substrate.

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