JP5051467B2 - Method for manufacturing light emitting device - Google Patents

Description

  The present invention relates to a method for manufacturing a light emitting device.

JP 2001-57441 A JP 2002-334816 A WO2008 / 091010

The light-emitting layer portion is formed of (Al _x Ga _1-x ) _y In _1-y P mixed crystal (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1; hereinafter also referred to as AlGaInP mixed crystal or simply AlGaInP). The light emitting device has a high brightness by adopting a double hetero structure in which a thin AlGaInP active layer is sandwiched between an n-type AlGaInP cladding layer and a p-type AlGaInP cladding layer having a larger band gap. An element can be realized.

  In the case of an AlGaInP light emitting device, a GaAs substrate is used as a growth substrate for the light emitting layer portion. However, GaAs absorbs a large amount of light in the emission wavelength region of the AlGaInP light emitting layer portion. Therefore, Patent Document 1 and Patent Document 2 disclose a method in which a GaAs substrate is once peeled and a GaP substrate that is a transparent conductive semiconductor substrate is newly bonded (hereinafter, manufactured by such a method). The light-emitting element is referred to as a “direct junction light-emitting element”).

  In the direct junction type light emitting element as described above, a natural oxide film having a thickness of about 1.5 to 2 nm is generally formed on the surface of a transparent conductive semiconductor substrate such as a GaP substrate to be used. This is a factor that increases the electrical resistance (hereinafter referred to as interface resistance) at the bonding interface between the transparent conductive semiconductor substrate and the transparent conductive semiconductor substrate. Therefore, reducing the interfacial resistance is one of the important issues related to the production of the direct junction type light emitting device. For example, Patent Documents 1 and 2 describe a method of reducing the interfacial resistance by performing a heat treatment after joining. Technology is disclosed. However, from the viewpoint of maintaining the doping profile of the light emitting layer portion, the heat treatment temperature cannot be increased so much, and there is a certain limit in reducing the interface resistance caused by the natural oxide film.

  In addition, cleaning of the transparent conductive semiconductor substrate before bonding is also important from the viewpoint of reducing interface resistance. Patent Document 2 discloses a technique for rotating and drying a transparent conductive semiconductor substrate after cleaning with a spin dryer. However, when the transparent conductive semiconductor substrate is thin or warped, There is a problem that cracks and the like are likely to occur when the substrate is rotationally dried.

  Furthermore, it has been found that not only the series resistance of the light-emitting element obtained by bonding increases, but also the series resistance tends to gradually decrease with time as the energization continues, and lacks stability. When the series resistance is not reduced to a stable level in a short time, there is a problem that the switching response is greatly affected when the light emitting element is dimmed and driven by high-speed switching (PWM control or the like).

  Therefore, Patent Document 3 sufficiently reduces the interface resistance between the light emitting layer portion and the transparent conductive semiconductor substrate by interposing a trace concentration of alkali metal atoms at the bonding interface of the direct junction type light emitting element. A light emitting device with improved switching response and a method for manufacturing the same are disclosed. As a specific method of interposing an alkali metal atom at the bonding interface, a method of immersing a bonding surface of a transparent conductive semiconductor substrate from which a natural oxide film has been removed in an organic solvent containing an alkali component of a specified concentration is disclosed. Has been.

  Specifically, the interfacial resistance of the light-emitting element can be reduced by interposing alkali metal atoms at the bonding interface in the above concentration range. In addition, the bonded light emitting element as described above has a relatively remarkable transient characteristic in which the forward voltage during light emission driving is considered to be derived from a parasitic capacitance component at the bonded interface. Specifically, when the forward voltage immediately after the start of energization is set to the initial value Vf0, the forward voltage gradually decreases as the energization continues and settles to a certain stable value Vf. When the reduction amount of the forward voltage up to the stable value Vf with respect to the initial value Vf0 is defined as a stabilized drop voltage ΔVf (that is, ΔVf≡Vf0−Vf), an alkali metal atom is interposed at the bonding interface in the concentration range. By doing so, the stabilized drop voltage ΔVf can be significantly reduced. A light-emitting element having a small stabilization drop voltage ΔVf has an advantage that the switching response can be greatly improved even in applications where dimming driving is performed by high-speed switching. In addition, since the forward voltage across the element stabilizes in a short time after the start of energization, the linearity and stability of the light emission luminance characteristics according to the drive duty ratio when the light source is driven with a constant drive power supply voltage. Can be increased.

However, in the light-emitting element of Patent Document 3, the concentration of alkali metal added to the bonding interface is about 1 × 10 ¹⁴ atoms / cm ² to 2 × 10 ¹⁵ atoms / cm ² , and secondary ion mass spectrometry ( When the alkali metal concentration analysis at the bonding interface is performed by Secondary Ion Mass Spectrometry (SIMS) etc., it is added to the bonding interface depending on the product even though the alkali metal concentration of the organic solvent used is almost constant. It was found that the alkali metal concentration is one order of magnitude lower than the average level. As a result, a sudden increase in the stabilization voltage drop ΔVf is likely to occur unexpectedly in response to variations in the alkali metal concentration at the bonding interface within the product lot or between lots of light emitting elements during mass production. .

In addition, in anticipation of variation in the interface addition concentration, as a countermeasure for adding an alkali metal at a desired concentration or higher to the bonding interface, the alkali metal in the organic solvent is at a certain level (for example, potassium hydroxide or sodium hydroxide is added). When using the added isopropyl alcohol, it is effective to increase it to about 3 × 10 ⁻⁴ mol / L). However, when the concentration of the alkali metal added to the interface is biased toward the high concentration side, There is a problem in that a bonding failure between the substrate and the transparent conductive semiconductor substrate is likely to occur. For example, when the transparent conductive semiconductor substrate is overlaid on the substrate on the light emitting layer side during the preparatory work for bonding, if the substrate surface on the bonding side is mirrored, initially through a thin air layer The board is floating. However, when a small impact is applied to this, the attractive force acting between high-precision surfaces with small roughness (for example, van der Waals force, hydrogen bonding interaction of adsorbed molecules, or Coulomb force due to surface polarization, etc.) As a result of various factors), an area where the air escapes and the substrates are in close contact with each other occurs.

  Since the attractive force acting between the mirror surfaces of the substrate tends to increase rapidly in inverse proportion to the power of the distance as the distance between the surfaces decreases, once the contact area is generated by impact, the area absorbs the air in the surrounding area. While expelling, it spreads to the surroundings in a shogi-style manner (this is sometimes called a bond wave). Since the adhesion strength between the substrates in the region tends to increase as the alkali metal concentration at the bonding interface increases, if the alkali metal interface addition concentration varies greatly in the plane, the adhesion strength between the substrates also affects the adhesion strength. Unevenness tends to occur inside. In particular, the substrates tend to float in the vicinity of the strongly adhered region, and the bonding state is likely to deteriorate. As a result, the bonding state of the bonded interface after the heat treatment becomes non-uniform, and eventually, it becomes impossible to eliminate variations in the interface resistance, the forward voltage, or the stabilized drop voltage.

  An object of the present invention is to provide a light emitting device capable of achieving a uniform interface alkali metal concentration between the light emitting layer portion and the transparent conductive semiconductor substrate, and thus sufficiently reducing the resistance at the bonding interface and improving the switching response. Is to provide a more stable method with a high yield.

Means for Solving the Problems and Effects of the Invention

In order to solve the above problems, a method for manufacturing a light-emitting device according to the present invention includes directly attaching a transparent conductive semiconductor substrate to one main surface of a main compound semiconductor layer made of a III-V group compound semiconductor having a light-emitting layer portion. A method of manufacturing a light emitting device having a combined structure,
A main compound semiconductor layer growth step of epitaxially growing the main compound semiconductor layer on the first main surface of the growth substrate;
Removing the growth substrate from the main compound semiconductor layer;
A natural oxide film removing step for removing the natural oxide film formed on the bonding surface of the transparent conductive semiconductor substrate to the main compound semiconductor layer;
An organic solvent contact step of contacting the alkali-containing organic solvent while applying ultrasonic waves to the bonding surface of the transparent conductive semiconductor substrate from which the natural oxide film has been removed;
A bonding step of superposing and bonding the bonding surface of the transparent conductive semiconductor substrate on which the organic solvent contact step has been completed to the bonding surface of the main compound semiconductor layer.

  Prior to bonding the transparent conductive semiconductor substrate to the main compound semiconductor layer including the light emitting layer portion, it is necessary to remove the natural oxide film formed on the surface of the transparent conductive semiconductor substrate (herein referred to as “natural oxidation”). “Removal of the film” means that at least part of the natural oxide film is removed to reduce the thickness, and does not necessarily mean that the film is completely removed). However, if the transparent conductive semiconductor substrate after removal of the natural oxide film is left in the atmosphere, the natural oxide film will re-grow in a relatively short time as it is, and the interface resistance reduction effect will be immediately lost. Therefore, an organic solvent contact step is performed in which an organic solvent is brought into contact with the surface of the transparent conductive semiconductor substrate after the natural oxide film is removed. Thereby, the regrowth of the natural oxide film is suppressed, which contributes to the reduction of the interface resistance and the stabilization voltage drop ΔVf. Then, by setting the organic solvent as an alkali-containing organic solvent, the alkali metal component derived from the alkali-containing organic solvent remains on the bonding surface, and the effect of reducing the interface resistance and the stabilization voltage drop ΔVf becomes more remarkable. .

  The concentration distribution of the alkali metal component remaining on the surface of the transparent conductive semiconductor substrate by applying ultrasonic waves when the alkali-containing organic solvent is brought into contact with the surface of the transparent conductive semiconductor substrate after removing the natural oxide film Can be made more uniform. As a result, there is a sudden occurrence of an extremely low stabilization drop voltage ΔVf corresponding to variations in the alkali metal concentration at the bonding interface within a lot or between lots of light emitting elements during mass production. Defects can be greatly reduced. In addition, even if the alkali-containing concentration in the alkali-containing organic solvent is not increased so much, the alkali concentration necessary for reducing the interface resistance or the stabilized drop voltage ΔVf can be ensured uniformly. As a result, in the state where the main compound semiconductor layer and the transparent conductive semiconductor substrate are overlapped for bonding, the above-mentioned bond wave is generated with a slight impact starting from the region where the alkali concentration is extremely high. It is possible to effectively prevent problems that occur.

The alkali metal atom concentration at the bonding interface is preferably adjusted to 1 × 10 ¹⁴ atoms / cm ² or more and 2 × 10 ¹⁵ atoms / cm ² or less. When the alkali metal atom concentration at the bonding interface between the main compound semiconductor layer and the transparent conductive semiconductor substrate is less than 1 × 10 ¹⁴ atoms / cm ² , the effect of reducing the interfacial resistance of the light emitting element and the reduction of the stabilized drop voltage ΔVf are achieved. The effect becomes inconspicuous, and the variation between batches and in the wafer surface increases, leading to a decrease in yield. Moreover, in order to make the alkali metal atom concentration at the bonding interface exceed 3 × 10 ¹⁵ atoms / cm ² , it is necessary to extremely increase the alkali-containing concentration in the alkali-containing organic solvent. However, a region where alkali remains at a high concentration is likely to occur at the bonding interface, and the yield is reduced due to the generation of the bond wave. The alkali metal atom concentration at the bonding interface is more desirably 3 × 10 ¹⁴ atoms / cm ² or more and 1.5 × 10 ¹⁵ atoms / cm ² or less (more desirable from the viewpoint of suppressing bonding failure due to the above-described bond wave or the like). Is preferably 1.0 atoms / cm ² or less.

  In the method for manufacturing a light emitting device of the present invention, the natural oxide film removing step can be an alkali cleaning step, and after the alkali cleaning step, the transparent conductive semiconductor substrate is washed with water, and the organic solvent contact step is performed. Then, after completion of the water washing step, the bonded surface of the transparent conductive semiconductor substrate is immersed in an alkali-containing organic solvent, or vapor of the alkali-containing organic solvent is brought into contact with the bonded surface, and then dried. can do.

  That is, the natural oxide film removal step can be quickly removed by performing an alkali cleaning step using an alkaline etching solution such as an aqueous potassium hydroxide solution or an aqueous sodium hydroxide solution. In this case, the alkali metal atom imparted to the bonding interface is a potassium atom in the former case and a sodium atom in the latter case. The total thickness of the oxide films formed on the main compound semiconductor layer side and the transparent conductive semiconductor substrate side at the bonding interface after the natural oxide film removing step is 1.3 nm or less, more preferably It should be 0.8 nm or less.

  If the natural oxide film is removed by wet etching as described above, a water washing step and a drying step after etching are naturally necessary. In this case, immediately after washing with water, the organic solvent contact step is performed to replace the water with the organic solvent, and drying is performed. As a result, the growth rate of the natural oxide film after drying is greatly reduced, which contributes to reduction in interface resistance. . In addition, after the natural oxide film is removed, the storage interval until the transparent conductive semiconductor substrate is bonded to the main compound semiconductor layer can be secured for a relatively long time, which contributes to an improvement in manufacturing efficiency of the direct junction type light emitting device.

  In this case, use an alkali-containing organic solvent containing an alkali component having a higher concentration than the concentration brought in from the washing liquid through the water washing step per washing step (that is, more than the amount brought in from the washing step). It is more desirable to use an alkali-containing organic solvent to which an alkali component is positively added in order to increase the alkali metal atom concentration at the bonding interface to the above range.

  As the organic solvent used in the organic solvent contact step, it is desirable to use an organic solvent that is freely mixed with water so that replacement of water droplets remaining on the bonding surface after washing with water can easily proceed (for example, alcohol and ketones). In order to efficiently evaporate water together with the organic solvent by azeotropy, it is more preferable to use an organic solvent that is freely mixed with water and has a vapor pressure difference with water at 20 ° C. of 100 hPa or less. desirable. As such an organic solvent, specifically, isopropanol (boiling point: 82.4 ° C., vapor pressure difference with water at 20 ° C .: 20 hPa), or ethanol (boiling point: 78.3 ° C., with water at 20 ° C.) Alcohols such as vapor pressure difference: 36 hPa) can be preferably used. The alcohol is also useful from the viewpoint of easily dissolving the alkali metal hydroxide and easily preparing the alkali-containing organic solvent (that is, the alkali-containing organic solvent may be an alcohol in which the alkali metal hydroxide is dissolved). it can).

  In this case, it is more desirable that the alkali-containing organic solvent contains water together with the alkali metal hydroxide in order to increase the alkali metal atom concentration at the bonding interface to the above range.

  As the alcohol to be used, isopropanol is particularly effective in the present invention because it has a great effect of suppressing regrowth of natural oxide film after drying. Moreover, it is desirable to use potassium hydroxide or sodium hydroxide as the alkali metal hydroxide added to the alkali-containing organic solvent.

In this case, the alkali-containing organic solvent is potassium hydroxide or sodium hydroxide (a combination of both may be added, in which case the total) is 5 × 10 ⁻⁶ mol / L or more and 3 × 10 ⁻⁴ mol / L. It is desirable to use those contained in the following ranges. When the alkali content is less than 5 × 10 ⁻⁶ mol / L, the effect of reducing the interface resistance is insufficient, and when it exceeds 3 × 10 ⁻⁴ mol / L, even if an ultrasonic wave is applied, the interface is highly bonded. A region where alkali remains in the concentration is likely to occur, and the above-described bond wave is likely to occur. The alkali content is more preferably 1 × 10 ⁻⁵ mol / L or more and 3 × 10 ⁻⁴ mol / L or less (more preferably 1 × 10 ⁻⁴ mol from the viewpoint of suppressing poor bonding). / L or less). The alkali-containing organic solvent preferably contains moisture in the range of 1 × 10 ⁻⁴ mol / L to 5 mol / L. When the water content is less than 1 × 10 ⁻⁴ mol / L, it is difficult to increase the alkali metal atom concentration at the bonding interface to the above range. On the other hand, if it exceeds 5 mol / L, moisture tends to remain on the bonding surface, and the natural oxide film re-grows, leading to a decrease in the interface resistance reduction effect or the stabilization drop voltage ΔVf. The water content range is more preferably 0.05 mol / L or more and 5 mol / L or less.

  The organic solvent contact step (or the natural oxide film removal step and the water washing step by alkali cleaning, and the subsequent organic solvent contact step) can be similarly performed on the bonding surface of the main compound semiconductor layer. This further contributes to the reduction of the resistance or the stabilized drop voltage ΔVf.

  Hereinafter, an embodiment of a method for manufacturing a light emitting device according to the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram of a light emitting element to which the present invention is applied. The light-emitting element 100 includes a GaP substrate 70 as a transparent conductive semiconductor substrate (in this embodiment, n-type, but p-type when the stacking order of each layer of the main compound semiconductor layer 50 is reversed p / n above. Yes: Other transparent conductive semiconductor substrates such as GaAsP and AlGaAs can also be used), and the light emitting layer portion 24 is directly bonded to the first main surface. In the present embodiment, the main surfaces of the layers and the substrate, as shown in FIG. 1, are defined as a state where the light extraction surface PF of the light emitting element 100 is on the upper side, and a surface appearing on the upper side of the drawing in the normal state is a first main surface. The surface, the surface appearing on the lower side, is uniformly described as the second main surface. Therefore, for convenience of description of the process, when the drawing is performed in a transposed state that is upside down with respect to the normal state, the vertical relationship between the first main surface and the second main surface in the drawing is also reversed.

The light emitting layer portion 24 is an active layer 5 made of a non-doped (Al _x Ga _1-x ) _y In _1-y P (where 0 ≦ x ≦ 0.55, 0.45 ≦ y ≦ 0.55) mixed crystal. the, the p-type _{(Al z} Ga _1-z) and p-type cladding layer 6 made of _{y In 1-y} P (except x <z ≦ 1), n-type _{(Al z Ga 1-z)} y In 1-y Depending on the composition of the active layer 5, the emission wavelength is changed from green to red region (emission wavelength (peak emission wavelength)). 550 nm to 670 nm). The light emitting layer section 24 _may be configured by _{In x Ga y Al 1-x} -y N (0 ≦ x ≦ 1,0 ≦ y ≦ 1, x + y ≦ 1).

  A GaP current diffusion layer 20 is formed on the first main surface of the light emitting layer portion 24, and constitutes the main compound semiconductor layer 50 together with the light emitting layer portion 24. A light extraction surface side electrode 9 (for example, an Au electrode) for applying a light emission driving voltage to the light emitting layer portion 24 is formed substantially at the center of the first main surface of the current diffusion layer 20. Between the light extraction surface side electrode 9 and the GaP current diffusion layer 20, an AuBe bonding alloyed layer 9a (for example, Be: 2% by mass) as a light extraction side bonding alloyed layer is disposed. A region around the light extraction surface side electrode 9 on the first main surface of the current diffusion layer 20 forms a light extraction region PF from the light emitting layer portion 24. Further, in the present embodiment, the p-type cladding layer 6 is a laminated form in which it is located on the light extraction surface side, but it may be a laminated form in which the n-type cladding layer 4 is located on the light extraction surface side (in this case, current diffusion) The layer 20 must be n-type, and the bonded alloying layer 9a is made of AuGeNi or the like).

The thicknesses of the n-type cladding layer 4 and the p-cladding layer 6 are, for example, 0.8 μm or more and 4 μm, respectively.
The thickness of the active layer 5 is, for example, not less than 0.4 μm and not more than 2 μm (desirably not less than 0.4 μm and not more than 1 μm). The total thickness of the light emitting layer portion 24 is, for example, 2 μm to 10 μm (desirably 2 μm to 5 μm). Furthermore, the thickness of the GaP current diffusion layer 20 is, for example, 5 μm to 28 μm (desirably 8 μm to 15 μm). Therefore, the thickness of the main compound semiconductor layer 50 is, for example, 7 μm or more and 38 μm or less (desirably 10 μm or more and 20 μm or less).

  The GaP substrate 70 is manufactured by slicing and polishing a GaP single crystal ingot, and has a thickness of, for example, 50 μm or more and 500 μm or less. As a GaP substrate, a GaP or InGaP single crystal layer was epitaxially grown on the main surface of the single crystal substrate manufactured by slicing and polishing a GaP single crystal ingot on the bonding surface side with the main compound semiconductor layer 50. A GaP epitaxial wafer may be used (in this case, when using a substrate on which an InGaP layer is epitaxially grown, if the InGaP layer is thinner than the thickness of the GaP single crystal substrate, the epitaxial wafer is broadly defined as a GaP substrate). Considered to belong to the concept). An AuGeNi bonding alloyed layer 16 (for example, Ge: 15% by mass, Ni: 10% by mass) is dispersedly formed on the back surface of the GaP substrate 70 as a substrate side bonding alloyed layer. The bonding alloying layer 16 is bonded to a metal stage (not shown) by, for example, an Ag paste layer.

The interface between the GaP substrate 70 and the main compound semiconductor layer 50 is a bonded interface, and the alkali metal atom concentration at the bonded interface is 1 × 10 ¹⁴ atoms / cm ² or more and 2 × 10 ¹⁵ atoms / cm ² or less ( Desirably, it is adjusted to 3 × 10 ¹⁴ atoms / cm ² or more and 1.5 × 10 ¹⁵ atoms / cm ² or less (more desirably 1.0 × 10 ¹⁵ atoms / cm ² or less). The alkali metal atom is a potassium atom in the present embodiment, but may be a sodium atom or a mixture of potassium and sodium atoms.

  The “concentration of alkali metal atom at the interface” can be measured as follows. That is, the GaP substrate 70 is subjected to SIMS analysis in the depth direction (x) from the first main surface side or the second main surface side, and as shown in FIG. 4, alkali metal atoms per unit volume at each depth position. A depth direction density profile C (x) indicating the density is measured. The SIMS analysis in the depth direction can be performed by D-SIMS (Dynamic SIMS) in which secondary ion mass spectrometry is performed while using the irradiated primary ion beam as a depth direction etching beam on the sample surface. A value obtained by integrating the depth direction concentration profile C (x) by the depth direction distance x in a section including the alkali metal atom concentration peak position corresponding to the interface is adopted as the interface alkali metal atom concentration. The depth direction concentration profile C (x) rapidly decreases as the distance from the interface position (concentration peak position) increases, and forms a baseline indicating the background alkali metal atom concentration. The rise position of the peak from this baseline may be determined as the boundary of the integration interval, but the alkali metal atom concentration at the baseline is usually several orders of magnitude lower than the alkali metal atom concentration at the peak position. The integration interval may be set broadly so that it protrudes outside the peak from the rising position, and this has little influence on the calculated value of the interfacial alkali metal atom concentration.

  Returning to FIG. 1, an oxide film 70 j is formed at the bonding interface between the GaP substrate 70 and the main compound semiconductor layer 50. The oxide film 70j is derived from a natural oxide film formed on each bonding surface of the GaP substrate 70 and the main compound semiconductor layer 50 at the bonding stage, and has a thickness of 1.3 nm or less ( Desirably, it is 0.8 nm or less. The thickness of the oxide film 70j can be measured using, for example, spectroscopic ellipsometry.

Hereinafter, a specific example of the method for manufacturing the light emitting device 100 will be described.
First, as shown in Step 1 of FIG. 2, an n-type GaAs buffer layer 2 is 0.5 μm, for example, and a release layer 3 made of AlAs is 0.5 μm, for example, on the main surface of a GaAs single crystal substrate 1 constituting a GaAs substrate. Epitaxial growth is performed in this order. Thereafter, as the light emitting layer portion 24, an n-type cladding layer 4 (thickness: for example 1 μm), an AlGaInP active layer (non-doped) 5 (thickness: for example 0.6 μm), and a p-type cladding layer 6 (thickness: for example 1 μm). ) In this order. The total thickness of the light emitting layer portion 24 is 2.6 μm. Further, a current diffusion layer 20 made of p-type GaP is epitaxially grown by 17 μm, for example. The epitaxial growth of each of the above layers can be performed by a known MOVPE method. Thus, the main compound semiconductor layer 50 including the light emitting layer portion 24 and the GaP current diffusion layer 20 is formed on the GaAs single crystal substrate 1.

  Next, as shown in Step 2, an adhesive layer 23 made of wax or the like is formed on the first main surface of the main compound semiconductor layer 50, and as shown in Step 3, a temporary support substrate 110 made of Si substrate or the like is formed. The temporary support bonded body 120 is made by bonding. Then, as shown in Step 4 of FIG. 3, the GaAs single crystal substrate 1 as the GaAs substrate attached to the temporary support bonded body 120 is removed. For this removal, for example, the temporary support bonded body 120 (see step 3) is immersed in an etching solution (for example, a 10% aqueous hydrofluoric acid solution) together with the GaAs single crystal substrate 1 and formed between the buffer layer 2 and the light emitting layer portion 24. The GaAs single crystal substrate 1 can be peeled from the temporary support bonded body 120 by selectively etching the AlAs release layer 3 thus formed. It should be noted that an etch stop layer made of AlInP is formed in place of the AlAs release layer 3, and a GaAs single crystal is used by using a first etching solution (for example, ammonia / hydrogen peroxide mixed solution) having selective etching properties with respect to GaAs. Etch and remove the substrate 1 together with the GaAs buffer layer 2 and then etch stop using a second etchant that has selective etching properties with respect to AlInP (for example, hydrochloric acid: hydrofluoric acid may be added to remove the Al oxide layer) A step of etching away the layer can also be employed.

  Next, as shown in Step 5, the first main surface (bonding surface) of the n-type GaP substrate 70 prepared separately is washed with an alkali etching solution made of an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide, and n-type. The natural oxide film 70 i formed on the first main surface of the GaP substrate 70 is removed. Specifically, the thickness of the natural oxide film formed to about 1.5 to 2 nm is greatly reduced (for example, less than 1 nm) by this cleaning. Then, after cleaning, the first main surface of n-type GaP substrate 70 is further washed with water.

Next, as shown in Step 6, the first main surface is immersed in the alkali-containing organic solvent 82 to replace water droplets (organic solvent contact treatment), and then dried. Specifically, the alkali-containing organic solvent to be used is one that specifically uses isopropanol as the organic solvent, and may be potassium hydroxide or sodium hydroxide (a combination of both may be added. 5 × 10 ⁻⁶ mol / L to 3 × 10 ⁻⁴ mol / L (desirably 1 × 10 ⁻⁵ mol / L to 3 × 10 ⁻⁴ mol / L (more desirably 1 × 10 ^-4 mol / L or less)), and containing water in the range of 1 × 10 ^-4 mol / L to 5 mol / L (desirably 0.05 mol / L to 5 mol / L). The alkali-containing organic solvent is an aqueous solution prepared by dissolving potassium hydroxide or sodium hydroxide in water in the range of 1% by mass to 30% by mass with respect to isopropanol, 0.01% by volume to 0.8% by volume. It can be prepared by adding in the range.

  During immersion in the alkali-containing organic solvent 82, ultrasonic waves are applied to the first main surface of the n-type GaP substrate 70. Specifically, an ultrasonic wave is output from an ultrasonic wave generator 81 provided in a tank containing the alkali-containing organic solvent 82 so as to have a frequency of 10 kHz to 500 Hz. The intensity of the ultrasonic wave is adjusted to such an extent that foaming (cavitation) accompanying the generation of ultrasonic waves is recognized and mechanical generation on the substrate surface does not occur. The ultrasonic wave application time is, for example, about 1 to 5 minutes.

  In addition, said natural oxide film removal, water washing, an organic solvent contact process (and application of an ultrasonic wave), and drying also apply to the second main surface (bonding surface) of the main compound semiconductor layer 50 exposed by the implementation of step 4. It is desirable to do exactly the same.

  Then, as shown in Step 7, in the state of the temporary support bonded body 120, the n-type GaP substrate 70 prepared separately on the second main surface of the main compound semiconductor layer 50 exposed by removing the GaAs single crystal substrate 1 is used. One main surface is overlapped and pressed, and further heated to 400 ° C. or higher and 700 ° C. or lower to perform a bonding heat treatment.

  As described above, the first main surface of the n-type GaP substrate 70 (or the second main surface of the main compound semiconductor layer 50) from which the natural oxide film has been removed by alkali cleaning is washed with water and then subjected to alkali-containing organic solvent contact treatment. By performing the drying, the natural oxide film 70i once removed becomes difficult to re-grow, and the thickness of the oxide film 70j at the interface after bonding can be kept within the above-mentioned range. Furthermore, a trace amount of the alkali metal component derived from the alkali-containing organic solvent remains in the concentration range on the bonded surface. Moreover, since the thickness of the natural oxide film can be kept small even if the storage time after removal of the natural oxide film becomes long, the flexibility of the process schedule is increased, which contributes to the improvement of productivity. Since the bonding interface resistance of the light emitting element obtained by bonding can be kept low, the forward voltage Vf can be reduced. In addition, the series resistance change margin after the start of energization, that is, the stabilized drop voltage ΔVf is small and stable. For example, the switching responsiveness is greatly improved even in applications where the light emitting element is dimming driven by high-speed switching. be able to.

  In addition, the concentration distribution of the alkali metal component remaining on the surface of the transparent conductive semiconductor substrate by applying ultrasonic waves when the alkali-containing organic solvent is brought into contact with the surface of the transparent conductive semiconductor substrate after removing the natural oxide film Can be made more uniform. As a result, there is a sudden occurrence of an extremely high stabilization voltage drop ΔVf corresponding to variations in the alkali metal concentration at the bonding interface within the product lot or between lots of light emitting elements during mass production. Defects can be greatly reduced. That is, compared with the case where no ultrasonic wave is applied, the statistical generation ratio of the light emitting elements in which ΔVf becomes an abnormal value can be greatly reduced. In addition, even if the alkali-containing concentration in the alkali-containing organic solvent is not increased so much, the alkali concentration necessary for reducing the interface resistance or the stabilized drop voltage ΔVf can be ensured uniformly. As a result, it is possible to prevent deterioration and non-uniformity of the bonded state.

  When the bonding heat treatment is completed, as shown in Step 8, the adhesive layer 23 is dissolved with an organic solvent or the like, and the temporary support substrate 110 is separated. Next, as shown in Step 9, a part of the first main surface of the main compound semiconductor layer 50 exposed by the separation / removal of the temporary support substrate 110, that is, the first main surface of the GaP current diffusion layer 20 is partially applied. An AuBe light extraction side bonding metal layer is formed so as to be covered, and further subjected to alloying heat treatment at a temperature of 300 ° C. or higher and 500 ° C. or lower to form an AuBe bonding alloyed layer (light extraction side bonding alloyed layer) 9a. . And the light extraction side electrode 9 which consists of Au etc. is formed so that the AuBe joining alloying layer 9a may be covered. Further, an AuGeNi bonded metal layer is dispersedly formed on the second main surface of the GaP substrate 70 by vapor deposition, and further subjected to an alloying heat treatment at a temperature of 300 ° C. or higher and 500 ° C. or lower, whereby an AuGeNi bonded alloyed layer (substrate side) is formed. Bonding alloyed layer) 16.

  In the above, for the purpose of facilitating understanding, the process has been described in the form of a single element stack, but in practice, a bonded wafer in which a plurality of element chips are collectively formed in a matrix form. Is produced. Then, the bonded wafer is diced by an ordinary method to form an element chip, which is fixed to a support and subjected to wire bonding of a lead wire, etc., and then sealed with a resin to obtain a final light emitting element. can get.

  The interface between the GaP current diffusion layer 20 and the light emitting layer portion 24 can be formed as a bonded interface that satisfies the above-described conditions.

  In order to confirm the effect of the present invention, the following experiment was conducted. That is, an aqueous solution in which 22% by mass of potassium hydroxide was dissolved in water was prepared, and this was added to isopropanol so that the potassium hydroxide concentration became various concentrations shown in FIG. Next, as shown in FIG. 3, after removing the natural oxide film and washing with water, the n-type GaP substrate 70 was dipped in the alkali-containing organic solvent and pulled up, and then naturally dried. And the K density | concentration of the bonding interface of the light emitting element sample obtained by performing the bonding process with the main compound semiconductor layer 50 after the drying was measured by the above-mentioned method using SIMS, respectively. The application conditions of ultrasonic waves during immersion in the alkali-containing organic solvent were a frequency of 46 kHz and an application time of 2 minutes. The results are shown in FIG.

  Referring to the results shown in FIG. 5, samples of light-emitting elements with various adjustments of the K concentration at the bonding interface were prepared. The forward voltage Vf immediately after the start of energization by 20 mA energization and the initial value as the initial value were then continued. Then, a reduction margin of the forward voltage Vf until the stable value of Vf gradually decreasing, that is, a stabilization voltage drop ΔVf was measured (each sample number was 5). The above results are shown in FIG. 6 (ΔVf) and FIG. 7 (Vf) in the form of a graph plotted against the K concentration at the bonding interface.

According to the result, when the K concentration at the bonding interface is 1 × 10 ¹⁴ atoms / cm ² or more (particularly, 3 × 10 ¹⁴ atoms / cm ² or more), the values of Vf and ΔVf are remarkably small. It can be seen that good results are obtained. On the other hand, it can be seen that when the K concentration at the bonding interface is less than 1 × 10 ¹⁴ atoms / cm ² , both Vf and ΔVf rapidly increase and the variation becomes large.

For example, an aqueous solution in which 22% by mass of potassium hydroxide is dissolved in water is prepared, and this is further diluted 750 times with water, and then the potassium hydroxide concentration is 1.486 × 10 ⁻⁴ mol / L with respect to isopropanol. When an alkali-containing organic solvent that was added and adjusted to have a concentration was used, the K concentration at the bonding interface was 6.24 × 10 ¹⁴ / cm ² . And when Vf and (DELTA) Vf were measured, the very favorable Vf / (DELTA) Vf characteristic with 1.98-1.99V and 20-50mV, respectively was obtained. Further, when an alkali-containing organic solvent adjusted so that the potassium hydroxide concentration is 2.983 × 10 ⁻⁴ mol / L with respect to isopropanol is used, the K concentration at the bonding interface is 9.90 ×. It was 10 ¹⁴ / cm ² . When Vf and ΔVf were measured, they were 1.92 to 1.93 V and 0 (measurement lower limit) to 10 mV, respectively, and very good Vf / ΔVf characteristics were obtained.

On the other hand, when an alkali-containing organic solvent adjusted to have a potassium hydroxide concentration of 3 × 10 ⁻⁶ mol / L with respect to isopropanol is used as a comparative example, the K concentration at the bonding interface is 7. It was 16 × 10 ¹³ / cm ² . And when Vf and (DELTA) Vf were measured, only 2.05V and 180-220mV and the inadequate value were obtained, respectively. In addition, it was confirmed by SIMS measurement that interfacial metals such as K do not move even when high-temperature and long-time heat treatment was performed, and it was also confirmed that there was no effect of addition on properties other than Vf and ΔVf even after prolonged energization. .

Next, in order to confirm the effect of applying ultrasonic waves in step 6 of FIG. 3, the following experiment was performed. That is, an aqueous solution in which 22% by mass of potassium hydroxide was dissolved in water was prepared, and this was further diluted 750 times with water, and then the concentration of potassium hydroxide was 4 × 10 ⁻⁵ mol / L with respect to isopropanol. This was added to prepare an alkali-containing organic solvent. Next, after removing the natural oxide film and rinsing with water, the n-type GaP substrate 70 was immersed in the alkali-containing organic solvent under the same conditions as described above, pulled up, and then naturally dried. Then, after the drying, a bonding process with the main compound semiconductor layer 50 was performed to produce a wafer (production number: 470). Then, chips were cut out from a plurality of in-plane locations (maximum of 9) from each wafer to prepare light emitting element samples (Examples). In addition, the ultrasonic wave was not applied during the immersion of the n-type GaP substrate 70 in the alkali-containing organic solvent, and the rocking operation was applied 20 times to the n-type GaP substrate 70 in the bath. The same number of light emitting device samples were prepared (comparative example).

  With respect to these light emitting element samples, the stabilization voltage drop ΔVf was measured when energization was started by energization with 20 mA. For the sample to which ultrasonic waves were applied, the average value of ΔVf was 43.24 mV, the standard deviation was 28.97 mV, and the generation ratio of light-emitting element samples in which ΔVf exceeded the reference value (160 mV) was 0.72%. . On the other hand, in the case where no ultrasonic wave was applied, the average value of ΔVf was 50.07 mV, the standard deviation was 37.63, and the generation ratio of light emitting element samples in which ΔVf exceeded the reference value was 2.87%. there were.

  In addition, FIG. 8 shows the actual measurement results of the distribution state of the maximum value, the minimum value, and the average value of ΔVf in the wafer for each of the example and the comparative example in a graph (numbers on the horizontal axis are individual numbers). To identify the wafer). In the example, it is clear that the value of ΔVf is very small and the values are equal for more than half of the wafers.

Next, an aqueous solution in which 22% by mass of potassium hydroxide was dissolved in water was prepared, and this was further diluted 750 times with water, and then the potassium hydroxide concentration was 4.7 × 10 ⁻⁵ mol / L with respect to isopropanol. The alkali-containing organic solvent was prepared by adding various concentrations of ˜1.6 × 10 ⁻⁴ mol / L. Next, after removing the natural oxide film and rinsing with water, the n-type GaP substrate 70 was immersed in the alkali-containing organic solvent under the same conditions as described above, pulled up, and then naturally dried. Then, after the drying, a bonding process with the main compound semiconductor layer 50 was performed to produce wafers (production number: 100 each). Then, the presence or absence of defective bonding of the wafer is confirmed by visual inspection, and the defect occurrence rate is less than 0.5% excellent (◎), 0.5% to less than 1% is good (○), 1% or more Those with less than 3% were evaluated as acceptable (Δ), and those with 3% or more were evaluated as impossible (x). The results are shown in Table 1.

It can be seen that poor bonding can be remarkably reduced by adjusting the potassium hydroxide concentration in the alkali-containing organic solvent to 1 × 10 ⁻⁴ mol / L or less.

The schematic diagram which shows an example of the light emitting element used as the application object of this invention. Process explanatory drawing which shows an example of the manufacturing method of the light emitting element which concerns on this invention. Process explanatory drawing following FIG. Explanatory drawing which concerns on the calculation method of interface alkali atom concentration. The graph which shows the relationship between K density | concentration in an alkali containing organic solvent, and K density | concentration of a bonding interface. The graph which shows the relationship between K density | concentration of a bonding interface, and (DELTA) Vf. The graph which shows the relationship between K density | concentration of a bonding interface, and Vf. The graph which compares and shows the measurement result of the distribution condition of the maximum value of the (DELTA) Vf in a wafer, the minimum value, and an average value about each of an Example and a comparative example.

Explanation of symbols

24 Light emitting layer part 50 Main compound semiconductor layer 70 GaP substrate (transparent conductive semiconductor substrate)
100 light emitting device

Claims (12)

A method of manufacturing a light emitting device having a structure in which a transparent conductive semiconductor substrate is directly bonded to one main surface of a main compound semiconductor layer made of a III-V group compound semiconductor having a light emitting layer portion,
A main compound semiconductor layer growth step of epitaxially growing the main compound semiconductor layer on the first main surface of the growth substrate;
Removing the growth substrate from the main compound semiconductor layer;
A natural oxide film removing step of removing a natural oxide film formed on the bonding surface of the transparent conductive semiconductor substrate to the main compound semiconductor layer;
An organic solvent contact step in which an alkali-containing organic solvent is contacted while applying an ultrasonic wave to the bonding surface of the transparent conductive semiconductor substrate from which the natural oxide film has been removed;
A bonding step of laminating and bonding the bonding surface of the transparent conductive semiconductor substrate on which the organic solvent contact step has been completed to the bonding surface of the main compound semiconductor layer;
A method for manufacturing a light emitting element comprising: The method for manufacturing a light-emitting element according to claim 1, wherein the alkali metal atom concentration at the bonding interface is adjusted to 1 × 10 ¹⁴ atoms / cm ² or more and 2 × 10 ¹⁵ atoms / cm ² or less.   The method for manufacturing a light-emitting element according to claim 2, wherein a thickness of the oxide film formed at the bonding interface is 1.3 nm or less.   The natural oxide film removing step is an alkali cleaning step, and after the alkali cleaning step, the transparent conductive semiconductor substrate is washed with water, and the organic solvent contact step is performed after the water washing step. The method for manufacturing a light-emitting element according to any one of claims 1 to 3, wherein the bonded surface of the substrate is immersed in the alkali-containing organic solvent while applying ultrasonic waves, and then dried. .   The method for producing a light-emitting element according to claim 4, wherein the alkali-containing organic solvent contains an alkali component having a higher concentration than the concentration brought from the cleaning liquid through the water washing step per cleaning step.   The method for manufacturing a light-emitting element according to claim 3, wherein the alkali-containing organic solvent is an alcohol in which an alkali metal hydroxide is dissolved.   The method for producing a light-emitting element according to claim 6, wherein the alkali-containing organic solvent contains water together with the alkali metal hydroxide.   The method for manufacturing a light-emitting element according to claim 6, wherein isopropanol is used as the alcohol.   The method for manufacturing a light-emitting element according to any one of claims 6 to 8, wherein potassium hydroxide or sodium hydroxide is used as the alkali metal hydroxide. The method for producing a light-emitting element according to claim 9, wherein the alkali-containing organic solvent contains potassium hydroxide or sodium hydroxide in a range of 5 × 10 ⁻⁶ mol / L to 3 × 10 ⁻⁴ mol / L. The said alkali containing organic solvent is a manufacturing method of the light emitting element of Claim 9 or Claim 10 which contains a water | moisture content in the range of 1 * 10 < ^-4 > mol / L or more and 5 mol / L or less.   The method for manufacturing a light-emitting element according to claim 3, wherein the organic solvent contact step is also performed on a bonding surface of the main compound semiconductor layer.

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