JP2008098224A - Film forming method of group iii nitride compound semiconductor laminate structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a group III nitride compound semiconductor layer having stably excellent crystallinity by utilizing a sputtering method as a technique capable of acquiring a crystal film having satisfactory uniformity in a short time in making the group III nitride compound semiconductor layer. <P>SOLUTION: A manufacturing method of the group III nitride compound semiconductor laminate structure includes a step of forming a multi-layer film structure consisting of a group III nitride compound semiconductor on a substrate. In this method, the multi-layer film structure includes at least a buffer layer and a base layer from the substrate side, the buffer layer and the base layer are formed by a sputtering method, and a film-forming temperature of the buffer layer is made to be lower than that of the base layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a group III nitride compound semiconductor with good crystallinity (hereinafter referred to as a group III nitride compound semiconductor represented by InGaAlN), which is used for manufacturing a light emitting diode (LED), a laser diode (LD), and an electronic device. The present invention relates to a method for forming a laminated structure. In particular, the present invention relates to a method for forming a Group III nitride compound semiconductor multilayer structure that can be suitably used for epitaxially growing a Group III nitride compound semiconductor crystal having good crystallinity on a sapphire substrate.

  Group III nitride compound semiconductors have a direct transition type band gap of energy corresponding to the visible light to ultraviolet light region and can emit light with high efficiency, and are thus commercialized as LEDs and LDs. In addition, the electronic device has a potential to obtain characteristics that cannot be obtained by a conventional III-V group compound semiconductor.

In general, a group III nitride compound semiconductor is manufactured by metal organic chemical vapor deposition (MOCVD) using trimethylgallium (TMG), trimethylaluminum (TMA) and ammonia (NH ₃ ) as raw materials. The MOCVD method is a method in which a vapor of a raw material is contained in a carrier gas and conveyed to the substrate surface, and the raw material is decomposed by a reaction with a heated substrate to grow a crystal.

Group III nitride compound semiconductor single crystal wafers are not yet commercially available, and group III nitride compound semiconductors are generally grown on single crystal wafers of different materials. A large lattice mismatch exists between such a heterogeneous substrate and a group III nitride compound semiconductor crystal epitaxially grown thereon. For example, there is a lattice mismatch of 16% between sapphire (Al ₂ O ₃ ) and gallium nitride (GaN) and 6% between SiC and gallium nitride. In general, when such a large lattice mismatch exists, it is difficult to directly epitaxially grow a crystal on a substrate, and a crystal with good crystallinity cannot be obtained even if grown. Therefore, when a group III nitride compound semiconductor crystal is epitaxially grown on a sapphire single crystal substrate or an SiC single crystal substrate by metal organic chemical vapor deposition (MOCVD), Japanese Patent No. 3026087 (Patent Document 1) and As shown in Japanese Patent No. 4-297003 (Patent Document 2), a layer called a low-temperature buffer layer made of aluminum nitride (AlN) or aluminum gallium nitride (AlGaN) is first deposited on a substrate, A method for epitaxially growing a group III nitride compound semiconductor crystal at a high temperature has been generally performed.

  There are also some reports on a technique for forming a layer such as AlN as a buffer layer by a method other than MOCVD and forming the subsequent layers by MOCVD. For example, Japanese Patent Publication No. 5-86646 (Patent Document 3) describes a technique in which crystals having the same composition are grown by MOCVD on a buffer layer formed by high-frequency sputtering. However, among Japanese Patent No. 3440873 (Patent Document 4) and Japanese Patent No. 3700492 (Patent Document 5), only the technique described in Japanese Patent Publication No. 5-86646 (Patent Document 3) is stable. Therefore, it is described that good crystals cannot be obtained. In order to obtain stable and good crystals, in Japanese Patent No. 3440873 (Patent Document 4), annealing is performed in a mixed gas composed of ammonia and hydrogen after the growth of the buffer layer, and in Japanese Patent No. 3700492 (Patent Document 5). ), It is considered important to form the buffer layer by DC sputtering at a temperature of 400 ° C. or higher.

On the other hand, research into producing a group III nitride compound semiconductor crystal by sputtering has also been conducted. For example, in Japanese Patent Application Laid-Open No. 60-39819 (Patent Document 6), a GaN film is directly formed on a sapphire substrate for the purpose of stacking high-resistance GaN. The conditions used are: ultimate vacuum 5 × 10 ⁻⁷ to 10 ⁻⁸ Torr, circulating gas in the chamber is Ar and N ₂ , sputtering gas pressure 3 to 5 × 10 ⁻² Torr, RF voltage 0.7 to 0 0.9 kV (20 to 40 W in power), the distance between the substrate and the target is 20 to 50 mm, the substrate temperature is 150 to 450 ° C., and the like. However, in the intended use, there is no mention of the base layer of the light emitting element, and there is no description of forming a layer on this film.

In the 21st Century Union Symposium Proceedings, Vol 2nd, p295 (2003) (Non-Patent Document 1), GaN on Si (100) and Al ₂ O ₃ (0001) by high-frequency magnetron sputtering using N ₂ gas. It is described that a film was formed. As film formation conditions, the total gas pressure was 2 mTorr, the input power was 100 W, and the substrate temperature was changed from room temperature to 900 ° C. According to the figures listed in the paper, the device used is a target and substrate facing each other.

Further, in Vacuum, Vol 66, P233 (2002) (Non-patent Document 2), a GaN film is formed by an apparatus in which a cathode and a target face each other and a mesh is placed between a substrate and a target. According to this, the film forming conditions are such that the pressure is 0.67 Pa in N ₂ gas, the substrate temperature is 84 to 600 ° C., the input power is 150 W, and the distance between the substrate and the target is 80 mm.

Japanese Patent No. 3026087 Japanese Laid-Open Patent Publication No. 4-297003 Japanese Patent Publication No. 5-86646 Japanese Patent No. 3440873 Japanese Patent No. 3700492 JP 60-39819 A Proceedings of the 21st Century Union Symposium, Vol 2nd, p295 (2003) Vacuum, Vol66, P233 (2002)

  An object of the present invention is to use a sputtering method, which is a technique capable of obtaining a crystal film with good uniformity in a short time, in producing a group III nitride compound semiconductor layer, and to stably provide good crystallinity. It is to obtain a group III nitride compound semiconductor layer.

The present invention provides the following inventions in order to solve the above problems.
(1) In a method of forming a multilayer film structure made of a group III nitride compound semiconductor on a substrate, the multilayer film structure includes at least a buffer layer and an underlayer from the substrate side, and the buffer layer and the underlayer are sputtered. A film forming method of a group III nitride compound semiconductor stacked structure, wherein the film forming temperature of the buffer layer is lower than the film forming temperature of the underlayer;
(2) The method for forming a group III nitride compound semiconductor multilayer structure according to (1), wherein the buffer layer contains Al;
(3) The method for forming a group III nitride compound semiconductor multilayer structure according to (2), wherein the buffer layer is AlN;
(4) The method for forming a group III nitride compound semiconductor multilayer structure according to (2) or (3) above, wherein the buffer layer is an aggregate of columnar crystals;
(5) The method for forming a group III nitride compound semiconductor stacked structure according to any one of (2) to (4), wherein the buffer layer covers at least 60% of the substrate surface;
(6) The method for forming a group III nitride compound semiconductor stacked structure according to any one of (2) to (5) above, wherein the buffer layer has a thickness of 20 to 100 nm;
(7) The method for forming a group III nitride compound semiconductor multilayer structure according to (1), wherein the underlayer contains Ga;
(8) The method for forming a group III nitride compound semiconductor multilayer structure according to the above (7), wherein the underlayer is GaN;
(9) The group III nitride compound semiconductor multilayer structure according to any one of (1) to (3), (7) and (8) above, wherein the buffer layer is AlN and the underlying layer is GaN. Membrane method;
(10) The method for forming a group III nitride compound semiconductor stacked structure according to (1), wherein the film formation temperature of the buffer layer is from room temperature to 800 ° C .;
(11) The method for forming a group III nitride compound semiconductor multilayer structure according to (1), wherein the film formation temperature of the underlayer is 300 to 1500 ° C .; and (12) the film formation temperature of the buffer layer and the underlayer The method for forming a group III nitride compound semiconductor multilayer structure according to (1), wherein the difference in film formation temperature is 100 ° C. or more,
It is.

  According to the method for forming a group III nitride compound semiconductor multilayer structure of the present invention, the base layer that is the thickest and requires good uniformity is formed by a sputtering method with good mass productivity and uniformity. Thus, an element with improved productivity and good characteristics can be formed. That is, the present invention provides a group III nitride compound semiconductor multilayer structure in which a buffer layer laminated at a lower temperature than a base layer is formed by sputtering, and a layer containing Ga is also formed thereon by sputtering. A technique for forming a film can be provided.

  The present invention discloses a technique for forming a group III nitride semiconductor multilayer structure by forming a buffer layer and an underlayer by sputtering, and lowering the film formation temperature of the buffer layer to be lower than the film formation temperature of the underlayer. .

  In general, the sputtering method is suitable for forming a single composition crystal and is excellent in uniformity, productivity, and stability. In addition, there is little contamination in the chamber such as dust. Therefore, there has been a demand for a technique for forming a good crystalline GaN film by sputtering. As a result of extensive research, the present inventor has made the buffer layer deposition temperature lower than the deposition temperature of the underlayer in order to obtain a group III nitride compound semiconductor crystal having good crystallinity by sputtering. Found that is important.

  The substrate temperature at the time of forming the buffer layer is preferably room temperature to 1200 ° C. At a lower temperature, migration on the substrate surface is suppressed, and it is difficult to form a group III nitride compound semiconductor crystal with good crystallinity. On the other hand, group III nitride compound semiconductor crystals cause decomposition at higher temperatures.

  More desirably, the temperature is from room temperature to 800 ° C, and more desirably from 300 to 800 ° C.

  On the other hand, the film formation temperature of the underlayer is preferably 300 ° C. to 1500 ° C., more preferably 500 ° C. to 1000 ° C.

The difference in film formation temperature between the buffer layer and the underlayer is preferably 100 ° C. to 800 ° C., more preferably 400 ° C. to 700 ° C.
<Sputter deposition system>
Sputtering methods include RF sputtering and DC sputtering. Generally, in the case of using reactive sputtering in which a film is formed by reacting metal and nitrogen as in the present invention, DC sputtering in which discharge is continuously performed is so charged that the film forming rate cannot be controlled. For this reason, it is desirable to use pulsed DC sputtering that applies a bias in a pulse manner even in RF sputtering or DC sputtering.

  When RF sputtering is used, it is desirable to move the position of the magnet within the target in order to improve the uniformity of the film thickness. The specific motion method can be selected by the apparatus, and can be swung or rotated.

  When a group III nitride compound semiconductor crystal is formed by sputtering, it is desirable to supply a higher energy reactive species to the substrate during crystal growth. For this reason, as a device, the substrate is positioned in the plasma. Therefore, it is desirable that the target and the substrate face each other. Moreover, it is desirable that the distance between the substrate and the target is 10 mm to 100 mm.

In addition, since it is not desired to leave impurities in the chamber as much as possible, it is desirable that the apparatus used for film formation has an ultimate vacuum of 1.0 × 10 ⁻³ Pa or less.
<Material of buffer layer>
As a material constituting the buffer layer, any material can be used as long as it is a group III nitride compound semiconductor represented by the general formula AlGaInN. Further, As and P may be included as a group V. However, among these, a composition containing Al is desirable. In particular, GaAlN is desirable, and the composition of Al is preferably 50% or more. Since AlN can provide better crystallinity, it is more preferable.

  The buffer layer preferably forms an aggregate of columnar crystals as described below. For this purpose, a good columnar crystal can be obtained by forming a film at a low temperature using a sputtering method, and its density, crystallinity, and coverage can be easily controlled.

  In the present invention, the columnar crystal is separated by forming a crystal grain boundary between adjacent crystal grains, and the columnar crystal itself is a columnar crystal as a longitudinal cross-sectional shape. When a buffer layer made of columnar crystals is formed on a substrate and formed into a film, the group III nitride compound semiconductor formed thereon becomes a crystal film having good crystallinity.

  It is desirable that the buffer layer covers the substrate without any gap. If the buffer layer does not cover the substrate and the surface of the substrate is partially exposed, the group III nitride crystal layer formed on the buffer layer and the group III nitride crystal layer formed directly on the substrate Since the lattice constants of the crystals are different, there is a possibility that the crystals are not uniform. As a result, hillocks and pits are generated.

  For this reason, the buffer layer needs to cover at least 60% of the substrate surface. More desirably, it is 80% or more, and most desirably covers 90% or more.

  The ratio of the buffer layer covering the substrate can be measured from a cross-sectional transmission electron microscope (TEM) photograph. In particular, when the materials of the buffer layer and the group III nitride crystal layer are different, the buffer layer is scanned by scanning the interface between the substrate and the layer in parallel with the substrate surface using an electron beam energy dispersive spectrum (EDS) or the like. It is also possible to estimate the ratio of regions that are not formed. Further, by preparing a sample in which only the buffer layer is formed, it is possible to measure the exposed area of the substrate by a technique such as an atomic force microscope (AFM). In this invention, it measured from the said cross-sectional TEM photograph.

  It is preferable that the buffer layer appropriately controls the grain width of the individual crystals of the columnar crystal. Specifically, it is desirable that the width of each columnar crystal is a value between 0.1 nm and 100 nm. More desirably, the value is between 1 nm and 70 nm.

The width of each columnar crystal can be easily measured by the cross-sectional TEM photograph. That is, the interval between the boundaries of each columnar crystal is the width of each columnar crystal. The width of each columnar crystal cannot be precisely defined and has a certain distribution. Therefore, even if there are about several percent of crystals in which the width of each columnar crystal is out of the above range, the effect of the present invention is not affected. 90% or more is preferably within the above range.
<Buffer layer deposition conditions>
When the buffer layer is formed by sputtering, important parameters are the substrate temperature, nitrogen partial pressure, film formation rate, bias, and power.

  Needless to say, the atmosphere in the chamber must contain nitrogen. Nitrogen is turned into plasma and decomposes to become a raw material for crystal growth. Further, in order to efficiently sputter the target, a heavy and low-reactivity gas is often mixed. For example, argon. The ratio of the nitrogen flow rate to the nitrogen flow rate is preferably 20% to 98% for nitrogen. When the flow rate ratio is smaller than this, the sputtered metal adheres as it is, and when the flow rate ratio is larger than this, the amount of argon is small and the sputtering rate decreases. Particularly desirable is 25% to 90%.

  The film formation rate is desirably 0.001 nm / second to 0.5 nm / second. At a rate higher than this, the film does not become crystalline but becomes amorphous. In addition, when the film forming speed is smaller than this, the process becomes uselessly long, and it is difficult to use it industrially.

Since it is desired to activate migration during crystal growth, it is desirable that the bias applied to the substrate side and the power applied to the target side be large. For example, the bias applied to the substrate during film formation is 1.5 W or more, and the power applied to the target during film formation is between 0.01 W / cm ^{2 and 5} kW / cm ² .
<Underlayer material>
According to the results of experiments by the present inventors, a group III nitride containing Ga is desirable as the material for the underlayer. In order to obtain good crystallinity, it is necessary to loop dislocations by migration, but a material that easily causes dislocation looping is a nitride containing Ga. In particular, AlGaN is desirable and GaN is also suitable.

  The underlayer may have a structure doped with a dopant as necessary, or may have an undoped structure. In the case of using a conductive substrate, it is desirable to have a structure in which electrodes are attached to both sides of a chip by doping a base layer so that a current flows in the layer structure in the vertical direction. When an insulating substrate is used, a chip structure in which electrodes are formed on the same surface of the chip is adopted. Therefore, it is desirable that the layer immediately above the substrate is an undoped crystal with good crystallinity.

  The underlayer is preferably grown using the crystal nuclei generated on the buffer layer as seeds, and flattened while looping dislocations. In order to grow while dislocations are looped, it is necessary to activate migration and bring it closer to facet growth.

For this reason, it is desirable that the substrate temperature when forming the underlayer is higher than that of the buffer layer. By setting the temperature higher than the deposition temperature of the buffer layer, dislocations (columnar crystal interfaces) generated in the buffer layer can be looped. If the base layer is formed at a temperature lower than that of the buffer layer, a crystalline film equivalent to the buffer layer is formed, and a reduction in dislocation density cannot be achieved.
<Underlayer deposition conditions>
Next, parameters for forming the underlayer will be described.

  Needless to say, the atmosphere in the chamber must contain nitrogen. Nitrogen is turned into plasma and decomposes to become a raw material for crystal growth. Further, in order to efficiently sputter the target, a heavy and low-reactivity gas is often mixed. For example, argon. The ratio of the nitrogen flow rate to the nitrogen flow rate is preferably 20% to 100% for nitrogen. When the flow rate ratio is smaller than this, the sputtered metal may adhere to the metal as it is, and it is particularly preferably 50% to 100%.

  The film formation rate is desirably 0.05 nm / second to 5 nm / second. At a rate higher than this, the film does not become crystalline but becomes amorphous. If the deposition rate is smaller than this, the process becomes uselessly long, and it is difficult to use it industrially.

Since the migration during crystal growth is desired to be active, it is better that the bias applied to the substrate side and the power applied to the target side are larger. For example, the bias applied to the substrate during film formation is 1.5 W or more, and the power applied to the target during film formation is between 0.01 W / cm ^{2 and 5} kW / cm ² .
<Other layers>
A layer having an element function can be further laminated on the base layer. For example, in the case of a light emitting layer, a contact layer, a cladding layer, a light emitting layer, and in the case of a laser element, in addition to these, a light confinement layer can be formed. Moreover, if it is an electronic device, an electron transit layer, a confinement layer, etc. can be formed.

These layers are not limited to sputtering, and can be manufactured by any generally known method. For example, the MOCVD method or the molecular beam epitaxy (MBE) method can be used.
<Board>
As a substrate that can be used in the present invention, any material can be used as long as it can generally form a group III nitride compound semiconductor crystal. For example, sapphire, SiC, silicon, zinc oxide, magnesium oxide, manganese oxide, zirconium oxide, manganese zinc iron oxide, magnesium aluminum oxide, zirconium boride, gallium oxide, indium oxide, lithium gallium oxide, lithium aluminum oxide, neodymium gallium oxide Lanthanum strontium oxide aluminum tantalum, strontium titanium oxide, titanium oxide, hafnium, tungsten and molybdenum. In particular, sputtering methods that do not use ammonia can be used as an effective film formation method for oxide substrates and metal substrates that are known to cause chemical modification by contact with ammonia at high temperatures.

  In general, since the sputtering method can keep the temperature of the substrate low, it is possible to form a film on the substrate that decomposes at a high temperature without damaging the substrate.

  The substrate is preferably subjected to wet pretreatment. For example, for a silicon substrate, a well-known RCA cleaning method or the like is performed, and the surface is hydrogen-terminated, so that a stable process is achieved.

On the other hand, after introduction into the reactor, pretreatment can be performed using a method such as reverse sputtering. Specifically, the surface can be prepared by exposure to Ar or N ₂ plasma. For example, by applying plasma such as Ar gas or N ₂ gas to the substrate surface, it is possible to remove organic substances and oxides attached to the surface. In this case, the plasma particles efficiently act on the substrate by applying a voltage between the substrate and the chamber.
<Application>
The device manufactured by the method of the present invention can be packaged and used as a lamp. Further, a technique for changing the emission color by combining with a phosphor is known, and this can be used without any problem. For example, by appropriately selecting a phosphor, light having a longer wavelength than that of the light emitting element can be obtained, and a white package can be obtained by mixing the light emitting wavelength of the light emitting element itself with the wavelength converted by the phosphor. You can also

  Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited only to these examples.

(Example 1)
In this embodiment, an aggregate of columnar crystals of AlN is formed on a c-plane sapphire substrate using RF sputtering as a buffer layer, and a second layer is formed thereon as a second layer in a different chamber and during GaN during RF sputtering. Layers were formed.

  First, a c-plane sapphire substrate that was mirror-polished to such an extent that only one side could be used for epitaxial growth was introduced into a sputtering machine without any wet pretreatment. The sputtering machine to be used has a high-frequency power source and a mechanism that can move the position where the magnetic field is applied by rotating the magnet in the target.

  First, the substrate is heated to 750 ° C. in a sputtering apparatus, nitrogen gas is introduced at a flow rate of 15 sccm, the pressure in the chamber is kept at 0.08 Pa, a high frequency bias of 50 W is applied to the substrate side, The substrate surface was cleaned by exposure to plasma.

Subsequently, after introducing argon and nitrogen gas, the substrate temperature was lowered to 500 ° C. 0.95 W / cm ² of power was applied to the metal Al target side, the pressure in the furnace was maintained at 0.5 Pa, Ar gas was flowed at 15 sccm, and nitrogen gas was flowed at 5 sccm (the ratio of nitrogen to the total gas was 25 %), An AlN film was formed on the sapphire substrate. The growth rate was 0.12 nm / s.

  The magnet in the target was rotated during substrate cleaning and film formation.

  After depositing 50 nm of AlN, the plasma was stopped and the substrate was taken out.

  Subsequently, the substrate was transferred into a different sputtering chamber. A sputtering machine used for GaN film formation has a high-frequency power source and a mechanism capable of moving the position where a magnetic field is applied by sweeping a magnet inside a square Ga target. A pipe for circulating the refrigerant was installed in the Ga target, and the refrigerant cooled to 20 ° C. was circulated in the pipe to prevent melting of Ga due to heat.

Subsequently, after introducing argon and nitrogen gas, the substrate temperature was raised to 1000 ° C. 1.3 W / cm ² power is applied to the metal Ga target side, the pressure in the furnace is kept at 0.5 Pa, Ar gas is flowed at 5 sccm, and nitrogen gas is flowed at 15 sccm (the ratio of nitrogen to the total gas is 75 %), A GaN film was formed on the sapphire substrate. The growth rate was approximately 1 nm / s. After the 6 μm GaN film was formed, the plasma generation was stopped.

Subsequently, a 2 μm Si-doped GaN layer having an electron concentration of 1 × 10 ¹⁹ cm ^{−3 was formed under} the same conditions.

  Each condition was the same as that of the undoped layer, and the Si target placed in the chamber was irradiated with ions emitted from the ion gun to extract Si, and Si was doped.

Through the above steps, a first layer of AlN having a columnar structure is formed on a sapphire substrate, and an undoped GaN layer with a thickness of 6 μm and an electron concentration of 1 × 10 ¹⁹ cm ⁻³ of 2 μm are formed thereon. A group III nitride compound semiconductor multilayer structure of the present invention in which a Si-doped GaN layer was formed was produced. The taken-out substrate exhibited a colorless and transparent mirror shape.

  Next, X-ray rocking curve (XRC) measurement of the undoped GaN layer grown by the above method was performed. The measurement was performed on a (0002) plane which is a symmetric plane and a (10-10) plane which is an asymmetric plane, using a Cuβ ray X-ray generation source as a light source. In general, in the case of a group III nitride compound semiconductor, the XRC spectrum half width of the (0002) plane is an index of crystal flatness (mosaicity), and the XRC spectrum half width of the (10-10) plane is the dislocation density (twist). ). As a result of this measurement, the undoped GaN layer produced by the method of the present invention showed a half width of 80 arcsec in the (0002) plane measurement and a half width of 250 arcsec in the (10-10) plane.

An element structure was formed by MOCVD on the Si-doped GaN layer produced by the above procedure, and finally an epitaxial wafer having a layer structure for a semiconductor light emitting element shown in FIG. 1 was produced. That is, in the epitaxial wafer, an AlN layer 8 (buffer layer) having a columnar structure is formed on a sapphire substrate 9 having a c-plane, and then the 6 μm undoped GaN layer 7 (underlayer), 1 × 2 μm Si-doped GaN layer 6 having an electron concentration of 10 ¹⁹ cm ⁻³ , 20 nm In _0.1 Ga _0.9 N clad layer 5 having an electron concentration of 1 × 10 ¹⁸ cm ⁻³ , starting from the GaN barrier layer and forming a GaN barrier layer Finally, a multi-quantum well structure 20 consisting of six GaN barrier layers 3 with a layer thickness of 16 nm and five non-doped In _0.2 Ga _0.8 N well layers 4 with a layer thickness of 3 nm, doped with 50 Å Mg The Al _0.1 Ga _0.9 N clad layer 2 and the Mg-doped Al _0.02 Ga _0.98 N layer 1 having a thickness of 200 nm are stacked.

  Further, FIG. 2 shows a plan view of the electrode structure of the semiconductor light emitting device manufactured in this example. In the figure, 10 is an n-side electrode, 11 is an exposed surface of the Si-doped GaN layer 6 for forming an n-electrode, 12 is a p-electrode bonding pad, and 13 is a translucent p-electrode.

  The Si-doped GaN wafer produced by sputtering was washed with pure water and dried before entering the MOCVD chamber. The purpose is to remove particles that remain on the surface.

  First, the substrate on which the Si-doped GaN layer was grown was introduced into the MOCVD furnace.

  Thereafter, the temperature of the substrate was raised to 1000 ° C. while the inside of the furnace was replaced with nitrogen, and the dirt adhering to the outermost surface of the Si—GaN layer was sublimated and removed. From the substrate temperature of 830 ° C. or higher, ammonia was circulated in the furnace.

Subsequently, after the substrate temperature is lowered to 740 ° C., the silane (SiH ₄ ) gas and the vapors of trimethylindium (TMI) and triethylgallium (TEG) generated by bubbling are introduced into the furnace while ammonia is allowed to flow as it is. A Si-doped In _0.1 Ga _0.9 N clad layer 5 having a thickness of 18 nm was formed. Thereafter, the valves for TMI, TEG and SiH ₄ were switched, and the supply of these raw materials was stopped.

Next, a multiple quantum well structure 20 composed of a barrier layer 3 made of GaN and a well layer 4 made of In _0.2 Ga _0.8 N was produced. In the production of the multiple quantum well structure, the GaN barrier layer 3 is first formed on the Si-doped In _0.1 Ga _0.9 N cladding layer 5, and the In _0.2 Ga _0.8 N well is formed on the GaN barrier layer. Layer 4 was formed. After repeating this structure five times, a sixth GaN barrier layer was formed on the fifth In _0.2 Ga _0.8 N well layer, and both sides of the multiple quantum well structure 20 were composed of GaN barrier layers 3. The structure.

That is, after the growth of the Si-doped In _0.1 Ga _0.9 N clad layer 5 is completed, the substrate temperature, the pressure in the furnace, the flow rate and type of the carrier gas remain unchanged, and the TEG valve is switched to enter the TEG furnace. The GaN barrier layer was grown. Thereby, the GaN barrier layer 3 having a film thickness of 16 nm was formed.

After the growth of the GaN barrier layer is completed, the TEG and TMI valves are switched to supply the TEG and TMI into the furnace while maintaining the substrate temperature, the pressure in the furnace, the flow rate and type of the carrier gas, and In _0.2 Ga _{0 .8} N well layer was grown. As a result, an In _0.2 Ga _0.8 N well layer 4 having a thickness of 3 nm was formed.

After the growth of the In _0.2 Ga _0.8 N well layer, the GaN barrier layer was grown again. Such a procedure was repeated five times to produce five GaN barrier layers and five In _0.2 Ga _0.8 N well layers. Furthermore, a GaN barrier layer was formed on the final In _0.2 Ga _0.8 N well layer.

On the multiple quantum well structure 20 terminated with the GaN barrier layer, an Al _0.1 Ga _0.9 N clad layer 2 doped with Mg was produced using the MOCVD method.

First, the pressure in the furnace is changed to 200 mbar, the substrate temperature is changed to 1020 ° C., the carrier gas is changed from nitrogen to hydrogen, and the pressure and temperature in the furnace are stabilized, and TEG, TMA, biscyclopentadienyl magnesium ( The Cp ₂ Mg) valve was switched to start supplying these raw materials into the furnace, and an Mg-doped Al _0.1 Ga _0.9 N cladding layer was grown. As a result, an Mg-doped Al _0.1 Ga _0.9 N cladding layer 2 having a thickness of 5 nm was formed.

An Mg-doped Al _0.02 Ga _0.98 N layer 1 was formed on the Mg-doped Al _0.1 Ga _0.9 N cladding layer.

While maintaining the same temperature, pressure, and carrier gas as in the growth of the cladding layer, the supply of TMAl, TMGa, and Cp ₂ Mg into the furnace was started and the growth was performed. The amount of circulating Cp ₂ Mg was examined in advance, and adjusted so that the hole concentration of the Mg-doped Al _0.02 Ga _0.98 N contact layer was 8 × 10 ¹⁷ cm ⁻³ . As a result, an Mg-doped Al _0.02 Ga _0.98 N layer 1 having a thickness of 0.15 μm was formed.

After completing the growth of the Mg-doped Al _0.02 Ga _0.98 N layer, the heater was stopped and the temperature of the substrate was lowered to room temperature over 20 minutes. Immediately after the growth was completed, the NH ₃ flow rate was reduced to 1/50 and the carrier was switched from hydrogen to nitrogen. Thereafter, NH ₃ was completely stopped at 950 ° C.

  After confirming that the substrate temperature was lowered to room temperature, the wafer was taken out into the atmosphere.

By the procedure as described above, an epitaxial wafer having an epitaxial layer structure for a semiconductor light emitting device was produced. Here, the Mg-doped Al _0.02 Ga _0.98 N layer 1 showed p-type even without performing annealing treatment for activating p-type carriers.

Next, a light-emitting diode, which is a kind of semiconductor light-emitting element, was manufactured using an epitaxial wafer in which an epitaxial layer structure was stacked on the sapphire substrate. The wafer prepared on the surface of the Mg-doped Al _0.02 Ga _0.98 N layer by a known photolithography technique, a p-electrode having a transparent p-electrode 13 made of ITO, titanium in this order thereon, a structure in which the aluminum and gold stacked A bonding pad 12 was formed as a p-side electrode. Thereafter, the wafer was dry-etched to expose the portion 11 where the n-side electrode of the Si-doped GaN layer was formed, and an n-side electrode 10 consisting of four layers of Ni, Al, Ti and Au was produced on the exposed portion. Through these operations, an electrode having a shape as shown in FIG. 2 was produced on the wafer.

  For the wafer on which the p-side and n-side electrodes were formed in this way, the back surface of the sapphire substrate was ground and polished to form a mirror-like surface. Thereafter, the wafer was cut into 350 μm square chips, placed on the lead frame so that the electrodes were on top, and connected to the lead frame with gold wires to obtain a light emitting device. When a forward current was passed between the p-side and n-side electrodes of the light-emitting diode produced as described above, the forward voltage at a current of 20 mA was 3.0V. Moreover, when light emission was observed through the p side translucent electrode, the light emission wavelength was 470 nm and the light emission output showed 15 mW. Such characteristics of the light-emitting diode were obtained with no variation for light-emitting diodes manufactured from almost the entire surface of the manufactured wafer.

  The group III nitride compound semiconductor multilayer structure obtained by the method of the present invention comprises a group III nitride compound semiconductor crystal having good crystallinity. Therefore, by forming a group III nitride compound semiconductor crystal layer having further functions on the laminated structure, a semiconductor element such as a light emitting diode, a laser diode, or an electronic device having excellent characteristics is manufactured. can do.

It is a schematic diagram which shows the cross section of the epitaxial wafer which has the epitaxial layer structure for semiconductor light-emitting devices concerning Example 1 of this invention. It is a top view which shows the electrode structure of the semiconductor light-emitting device concerning Example 1 of this invention.

Explanation of symbols

1 Mg-doped Al _0.02 Ga _0.98 N layer 2 Mg-doped Al _0.1 Ga _0.9 N cladding layer 3 GaN barrier layer 4 In _0.2 Ga _0.8 N well layer 5 In _0.1 Ga _0.9 N cladding layer 6 Si-doped n-type GaN layer 7 Undoped GaN Layer (second layer)
8 AlN layer consisting of aggregates of columnar crystals (first layer)
DESCRIPTION OF SYMBOLS 9 Substrate 10 N side electrode 11 Part which forms n side electrode of Si doped GaN layer 12 P electrode bonding pad 13 Translucent p electrode 20 Multiple quantum well structure

Claims (12)

In the method of forming a multilayer film structure made of a group III nitride compound semiconductor on a substrate, the multilayer film structure includes at least a buffer layer and an underlayer from the substrate side,
Laminating a buffer layer and an underlayer by sputtering, and
A film forming method of a group III nitride compound semiconductor stacked structure, wherein a film forming temperature of a buffer layer is lower than a film forming temperature of an underlayer.   The method of forming a group III nitride compound semiconductor multilayer structure according to claim 1, wherein the buffer layer contains Al.   The method of forming a group III nitride compound semiconductor multilayer structure according to claim 2, wherein the buffer layer is AlN.   4. The method for forming a group III nitride compound semiconductor multilayer structure according to claim 2, wherein the buffer layer is an aggregate of columnar crystals.   The method for forming a group III nitride compound semiconductor multilayer structure according to any one of claims 2 to 4, wherein the buffer layer covers at least 60% of the substrate surface.   6. The method for forming a group III nitride compound semiconductor multilayer structure according to claim 2, wherein the buffer layer has a thickness of 20 to 100 nm.   2. The method for forming a group III nitride compound semiconductor multilayer structure according to claim 1, wherein the underlayer contains Ga.   The method for forming a group III nitride compound semiconductor multilayer structure according to claim 7, wherein the underlayer is GaN.   The method for forming a group III nitride compound semiconductor multilayer structure according to any one of claims 1 to 3, 7 and 8, wherein the buffer layer is AlN and the underlayer is GaN.   The method for forming a group III nitride compound semiconductor multilayer structure according to claim 1, wherein the film formation temperature of the buffer layer is from room temperature to 800 ° C.   The method for forming a group III nitride compound semiconductor multilayer structure according to claim 1, wherein the film formation temperature of the underlayer is 300 to 1500 ° C.   The method for forming a group III nitride compound semiconductor multilayer structure according to claim 1, wherein the difference between the film formation temperature of the buffer layer and the film formation temperature of the underlayer is 100 ° C or higher.

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