JP5019160B2 - Method for manufacturing light emitting device - Google Patents

Description

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

JP-A-6-151959 JP 2001-36129 A Japanese Patent No. 3726882 JP-A-2005-116615 Japanese Patent No. 3657270 Japanese Patent Laid-Open No. 10-200196

A light emitting device in which a light emitting layer portion is formed of Al _x Ga _1-x As mixed crystal (where 0 ≦ x ≦ 1; hereinafter also referred to as AlGaAs mixed crystal or simply referred to as AlGaAs) has high directivity and high luminous efficiency. It is put into practical use as a red light emitting element. In such a light emitting device, the area around the metal electrode of the AlGaAs layer is used as the light extraction surface, but the light entering from the inside of the device to the light extraction region is incident on the light extraction region at an angle larger than the critical angle. The incident light (incident angle is an angle formed by the incident direction of the light beam and the region surface normal) returns to the inside of the element by total reflection, and thus not all of it can be extracted. Therefore, in Patent Document 1 to Patent Document 6, the light extraction surface is roughened with an anisotropic etching solution to form fine irregularities (also referred to as frost treatment), and the emitted luminous flux is incident at a large angle. A technique for increasing the light extraction efficiency by reducing the probability is disclosed.

  However, when the surface roughening process is performed by the methods of Patent Document 1 to Patent Document 6, unevenness is likely to occur in the protrusion formation state (protrusion form and protrusion height) due to the surface roughening, and the yield reduction of the element and the appearance inspection process are performed. There is a problem in that it tends to increase the number of steps for removing defective products. In particular, when the thickness of the surface layer that forms from the light extraction surface to the pn junction surface is small, when a deeply cut protrusion is locally formed, a valley-like portion adjacent to the protrusion is formed at the pn junction interface. And the surface layer is interrupted in the surface, the current diffusion state in the surface is deteriorated, and the light extraction efficiency is easily lowered.

  An object of the present invention is to provide a method for manufacturing a light-emitting element in which an AlGaAs light-emitting element can be uniformly roughened on the light extraction surface, and thus hardly causes unevenness in the surface-roughened state.

Means for Solving the Problems and Effects of the Invention

In order to solve the above problems, a method for manufacturing a light-emitting element of the present invention includes:
An n-type AlGaAs layer and a p-type AlGaAs layer each formed of a compound represented by a composition formula (AlxGa1-xAs (where 0 <x <1)) form a pn junction. A light emitting element wafer manufacturing process for manufacturing as a stacked body,
The main surface of the laminate contains acetic acid, hydrofluoric acid, nitric acid, iodine and water so that the total amount is 90% by mass or more, and the total mass content of acetic acid, hydrofluoric acid, nitric acid and iodine is A main light extraction region surface roughening step for forming a protrusion by roughening the surface by anisotropic etching with a surface roughening etchant composed of an aqueous solution higher than the mass content of water;
Are performed in this order ,
A main light extraction region is a pretreatment step in which a main surface used as a light extraction surface of a laminate composed of an n-type AlGaAs layer or a p-type AlGaAs layer is brought into contact with a pretreatment liquid made of a sulfuric acid hydrogen peroxide aqueous solution. Prior to the surface roughening process,
A pretreatment liquid having a mixing ratio of 96% sulfuric acid: 30% hydrogen peroxide water: water of 5: 1: 1 to 20: 1: 1 is used.
Main light extraction area surface roughening process is characterized Rukoto performed before dicing of the light-emitting element wafer.

  According to the above-described method of the present invention, by using the surface roughening etching solution peculiar to the present invention containing acetic acid, hydrofluoric acid, nitric acid and iodine, the first main surface of the laminate made of AlGaAs is particularly masked. Even if the first main surface is not contacted with the first main surface, the formation of irregularities by the anisotropic etching principle proceeds remarkably, and as a result, the first main surface of the laminate is roughened and the protrusion is roughened. Can be formed efficiently and inexpensively. The total of acetic acid, hydrofluoric acid, nitric acid, iodine, and water is 90% by mass or more, and if the content is less than this, the surface is roughened and the protrusions cannot be formed efficiently. Further, even if the total mass content of acetic acid, hydrofluoric acid, nitric acid and iodine is lower than the mass content of water, the surface is similarly roughened and the protrusions cannot be formed efficiently. The balance obtained by subtracting the total of acetic acid, hydrofluoric acid, nitric acid, iodine and water from 100% by mass is within the range where the anisotropic etching effect on AlGaAs is not impaired, and other components (for example, carboxylic acids other than acetic acid) Etc.).

  Note that the projection formation effect (anisotropic etching effect) on AlGaAs using this surface-roughening etching solution is particularly remarkable with respect to the (100) plane of AlGaAs. 100) wafers are desirable.

  Prior to the surface roughening step using the surface roughening etchant, the first main surface (main light extraction region) of the laminate made of AlGaAs is brought into contact with a pretreatment liquid made of a sulfuric acid hydrogen peroxide aqueous solution. Processing can be performed. As a result, it is possible to effectively prevent unevenness in the protrusion formation state of the wafer obtained by surface roughening. As a result, the formation of deep protrusions locally is suppressed, and the inconvenience that the AlGaAs layer on the light extraction surface side is disconnected in-plane by the deep protrusions hardly occurs. And the yield of the element obtained by dicing the wafer can be improved, and the labor of removing defective products in the appearance inspection process can be saved greatly.

This effect is particularly remarkable when the n-type AlGaAs layer and the p-type AlGaAs layer located on the light extraction surface side are formed as thin layers of 10 μm or less (however, in-plane current diffusion is sufficient). Therefore, the thickness of the layer is preferably 1 μm or more).

Specifically, the surface roughening etchant is:
Acetic acid (converted to CH ₃ COOH): 37.4% by mass or more and 94.8% by mass or less,
Hydrofluoric acid (converted to HF): 0.4 mass% or more and 14.8 mass% or less,
Nitric acid (in terms of HNO ₃ ): 1.3% by mass or more and 14.7% by mass or less,
Iodine (I ₂ equivalent): It is desirable to use 0.12% by mass or more and 0.84% by mass or less and a water content of 2.4% by mass or more and 45% by mass or less. . If any component is out of the range of the above composition, the anisotropic etching effect on the (100) plane of the AlGaAs single crystal is insufficient, and the surface roughening protrusion cannot be sufficiently formed on the first main surface of the laminate. More preferably, the surface roughening etchant is
Acetic acid (converted to CH ₃ COOH): 45.8 mass% or more and 94.8 mass% or less,
Hydrofluoric acid (converted to HF): 0.5% by mass or more and 14.8% by mass or less,
Nitric acid (converted to HNO ₃ ): 1.6 mass% or more and 14.7 mass% or less,
Iodine (I ₂ equivalent): It is contained in the range of 0.15% by mass or more and 0.84% by mass or less, and the water content is 2.4% by mass or more and 32.7% by mass or less. Is good. That is, in order to enhance the anisotropic etching effect on the (100) plane of the AlGaAs single crystal, the content of water is particularly limited as described above, and the function of the acid main solvent is not accrued by water but by acetic acid. Can be said to be important.

  It is preferable to use a pretreatment liquid having a mixing ratio of 96% sulfuric acid: 30% hydrogen peroxide solution: water of 5: 1: 1 or more and 20: 1: 1 or less. If the ratio of sulfuric acid is less than 5: 1: 1, the effect of suppressing unevenness in the formation of protrusions by pretreatment becomes insufficient, and if it exceeds 15: 1: 1, the protective resist for etching is decomposed, and electrode pattern defects are likely to occur. When the protective resist is not used, the effect of suppressing the unevenness of the protrusion formation can be sufficiently obtained if it is 20: 1: 1 or less.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a conceptual diagram showing a light emitting device 100 according to an embodiment of the present invention. The light emitting element 100 includes a p-type Al _x Ga _1-x As (where 0 <x <1) layer 20 (hereinafter referred to as a p-type AlGaAs layer 20) that forms a light extraction surface (first main surface), N-type Al _x Ga _1-x As (where 0 <x <1) layer 90 (hereinafter referred to as n-type AlGaAs layer 90) forming the main surface (second main surface) opposite to the p- It is comprised as a laminated body laminated | stacked so that n junction might be formed. The p-type AlGaAs layer 20 has a thickness of 1 μm to 10 μm (for example, 6 μm), and the n-type AlGaAs layer 90 has a thickness of 150 μm to 200 μm (for example, 170 μm). In either case, the p-type AlGaAs layer 20 and the n-type AlGaAs layer 90 are sequentially formed from the n-type AlGaAs layer 90 side on the growth substrate (the main surface is the (100) plane) made of n-type GaAs single crystal, as will be described later. It is formed by homoepitaxial growth.

  In the p-type AlGaAs layer 20, the light extraction region side metal electrode 9 is formed so as to cover a portion (here, the central portion) of the first main surface ((100) plane). One end of an electrode wire 17 is joined to the light extraction region side metal electrode 9. A peripheral region of the light extraction region side metal electrode 9 forms a main light extraction region 20p. Further, the side surface of the laminate formed by dicing (that is, the side surface of the p-type AlGaAs layer 20 and the n-type AlGaAs layer 90) forms a side surface light extraction region 20S. On the other hand, the entire surface of the second main surface of the n-type AlGaAs layer 90 is covered with a back electrode 15 made of an Au electrode or the like. Between the back electrode 15 and the n-type AlGaAs layer 90, a bonding alloyed layer 15c made of an AuGeNi alloy or the like is formed in a dot-like manner to reduce the contact resistance between them. Further, a bonding alloyed layer 9 a made of AuBe alloy or the like is formed between the light extraction region side metal electrode 9 and the p-type AlGaAs layer 20.

  As shown in FIG. 3, surface roughening projections 40f and 50f by chemical etching are formed in both the main light extraction region 20p of the p-type AlGaAs layer 20 and the side surface light extraction region 20S of the stacked body. The surface roughening protrusion 40f is formed by anisotropic etching by bringing a flat (100) crystal main surface into contact with a surface roughening etching solution described later. Further, the side main light extraction region 20S is, for example, a {110} plane, and the surface roughened protrusion 50f is similarly formed by anisotropic etching. By forming the roughened protrusions 40f and 50f, the light extraction efficiency of the light emitting device 100 can be greatly increased, coupled with the increase in the side surface area due to the increase in the thickness of the p-type AlGaAs layer 20. ing.

Hereinafter, a method for manufacturing the light emitting device 100 of FIG. 1 will be described.
First, as shown in step 1 of FIG. 4, an n-type GaAs single crystal substrate 1 is prepared as a growth substrate. Next, as shown in Step 2, an n-type GaAs buffer layer 2 is epitaxially grown on the main surface of the substrate 1, and then an n-type AlGaAs layer 90 (the n-type dopant is Te) is epitaxially grown. Then, as shown in step 3 of FIG. 4, a p-type AlGaAs layer 20 (p-type dopant is Zn or C) is further epitaxially grown thereon. Epitaxial growth of each of the above layers is performed by a known liquid phase epitaxial growth method.

  When the growth of the p-type AlGaAs layer 20 is completed, the process proceeds to step 4 where the GaAs substrate 1 is removed by chemical etching using an etching solution such as an ammonia / hydrogen peroxide mixture. When the above steps are completed, the bonding alloy is formed on the first main surface of the p-type AlGaAs layer 20 and the second main surface of the n-type AlGaAs layer 90 by sputtering or vacuum evaporation as shown in step 5 of FIG. Each of the metal layers for forming the alloying layer is formed, and heat treatment for alloying (so-called sinter treatment) is performed to form the bonded alloyed layers 9a and 15c (see FIG. 1; not shown in FIG. 6). And the light extraction area | region side electrode 9 and the back surface electrode 15 are formed so that these joining alloying layers 9a and 15c may each be covered, and it is set as the light emitting element wafer W. FIG.

  Subsequently, the light emitting element wafer W is immersed in the above-described pretreatment liquid PTA, and the first main surface of the p-type AlGaAs layer 20 exposed around the light extraction region side electrode 9 is pretreated. Subsequently, as shown in step 6, the main light extraction region ((100) main surface) of the p-type AlGaAs layer 20 is anisotropically etched using a surface roughening etchant FEA, A rough projection 40f is formed.

The surface roughening etching solution is an aqueous solution containing acetic acid, hydrofluoric acid, nitric acid, and iodine. Specifically, acetic acid (converted to CH ₃ COOH): 37.4% by mass or more and 94.8% by mass or less,
Hydrofluoric acid (converted to HF): 0.4 mass% or more and 14.8 mass% or less,
Nitric acid (in terms of HNO ₃ ): 1.3% by mass or more and 14.7% by mass or less,
Iodine _{(I 2} equivalent): it contains in the range of 0.12 mass% or more 0.84 wt% or less, and those water content below 45 wt% to 2.4 wt%, more desirably,
Acetic acid (converted to CH ₃ COOH): 45.8 mass% or more and 94.8 mass% or less,
Hydrofluoric acid (converted to HF): 0.5% by mass or more and 14.8% by mass or less,
Nitric acid (converted to HNO ₃ ): 1.6 mass% or more and 14.7 mass% or less,
Iodine (I ₂ conversion): It is contained in the range of 0.15% by mass or more and 0.84% by mass or less, and the water content is 2.4% by mass or more and 32.7% by mass or less. The liquid temperature is suitably 40 ° C. or higher and 60 ° C. or lower. As a specific example, a composition of 81.7% by mass of acetic acid, 5% by mass of hydrofluoric acid, 5% by mass of nitric acid, 0.3% by mass of iodine, and 8% by mass of water can be exemplified (liquid temperature is, for example, 50 ° C.).

  In addition, the pretreatment liquid has a mixing ratio of 96% sulfuric acid: 30% hydrogen peroxide solution: water of 5: 1: 1 or more and 20: 1: 1 or less (for example, 5: 1: 1). used.

  When surface roughening treatment is performed on the first main surface side of the p-type AlGaAs layer 20 of the wafer before dicing without performing the above pretreatment, the state of protrusion formation due to surface roughening, particularly the protrusion form and protrusion height, is obtained. Unevenness is likely to occur. In particular, when the thickness of the surface layer that forms the light extraction surface to the pn junction surface is small as in the present embodiment, as shown in FIG. The valley portion adjacent to the pn junction interface J reaches the pn junction interface J, the surface layer (p-type AlGaAs layer 20) is interrupted in the surface, the current diffusion state in the surface is deteriorated, and the light extraction efficiency is likely to be lowered. Become. For these locally deep protrusions, a hydrofluoric acid-based etching solution, a nitric acid-based etching solution, or a mixed acid-based etching solution in which sulfuric acid and nitric acid are mixed as used in Patent Documents 1 to 6 is used. It was particularly easy to form.

  On the other hand, the etching solution used in the present invention has a very remarkable and sensitive selective etching property with respect to {111}, which is a low energy surface of AlGaAs. It is considered that even a slight rubbing that decreases rapidly and does not normally cause a problem causes roughening and leads to formation of an insufficient region. However, when the surface roughening etchant employed in the present invention is applied to AlGaAs, the progress of etching is gentler than that of the surface roughening etchant employed in the prior art, and the pn junction interface is used. Deep local protrusions reaching J are relatively difficult to form. And, the important point is that by performing pretreatment with the hydrogen peroxide-based pretreatment liquid prior to the etching, deep local protrusion formation as described above can be almost certainly prevented, This significantly contributes to the improvement of the manufacturing yield of the light emitting element chip.

  Returning to FIG. 6, when the formation of the rough surface protrusion 40f in the main light extraction region is completed, the groove DG is formed by the dicing blade from the first main surface side of the wafer W along the two <110> directions. Then, dicing is performed on each chip area. At the time of dicing, as shown in step 7 of FIG. 6, a processing damage layer 20D having a relatively high crystal defect density is formed. Since a large number of crystal defects included in the processing damage layer 20D cause current leakage and scattering during light-emission energization, the processing damage layer 20D is removed from the damage layer removing etching solution DEA as shown in Step 8. It is removed by the chemical etching used. As the damage layer removing etching solution DEA, a sulfuric acid-hydrogen peroxide aqueous solution having a lower sulfuric acid content ratio than the above-mentioned pretreatment solution can be used. As the aqueous solution, for example, a sulfuric acid: hydrogen peroxide: water mass blending ratio of 20: 1: 1 can be used.

  Thereafter, as shown in Step 9, the side surface of the chip from which the processing damage layer 20D has been removed is brought into contact with the surface roughening etching solution FEA, and the side surface of the p-type AlGaAs layer 20 is subjected to anisotropic etching to perform surface roughening. A protrusion 50f is formed. In the present embodiment, the wafer W is attached to the base material 60 via the adhesive sheet 61, and the wafer W is fully diced in that state, and the surface is roughened on the entire side surface of the laminate, and the protrusion 50f is formed. Is done.

  As for the side surfaces, the formation direction of the projections 50f differs from the projections 40f on the light extraction surface side by 90 °, and there is no possibility of dividing the pn junction surface. Accordingly, since the influence of the unevenness of formation of the protrusion 50f (the above-mentioned local deep protrusion) is relatively small, the pretreatment using the pretreatment liquid PTA is omitted. In addition, the surface roughening etching solution FEA is limited to the hydrofluoric acid etching solution, nitric acid etching solution, sulfuric acid and nitric acid as employed in Patent Documents 1 to 6 only on the side surface. It is possible to substitute with a mixed acid type etching solution mixed with.

  If the roughening protrusion 50f is formed on the side surface light extraction region 20S and the etching effect is not desired to affect the main light extraction region 20p on which the roughening protrusion 40f has already been formed, step 7 is performed. The main light extraction region 20p may be masked with an etching resist, as indicated by the alternate long and short dash line in FIG. Further, dicing is first performed before forming the rough surface protrusion 40f to the main light extraction region 20p, and the rough surface protrusions 40f and 50f are collectively formed into the main light extraction region 20p and the side light extraction region 20S. It may be formed. In this case, both the main light extraction region 20p and the side surface light extraction region 20S are pretreated with the pretreatment liquid PTA prior to the surface roughening treatment.

  After the separation, the second main surface side of the light emitting element chip is bonded to a metal stage via an Ag paste layer, and further, as shown in FIG. 1, a bonding wire 17 is connected to the light extraction side electrode 9, and an epoxy is further bonded. If a mold part (not shown) made of resin is formed, a final light emitting element is completed.

The side surface cross-sectional schematic diagram which shows an example of the light emitting element used as the application object of this invention. Similarly, a plan view schematic diagram. The conceptual diagram of the surface roughening projection part formed in the laminated body of FIG. Process explanatory drawing which shows the manufacturing method of the light emitting element of FIG. Process explanatory drawing following FIG. Process explanatory drawing following FIG. The figure explaining the influence of protrusion formation nonuniformity.

Explanation of symbols

20 p-type AlGaAs layer 90 n-type AlGaAs layer 20p main light extraction region 20S side surface light extraction region W light emitting element wafer 40f roughening protrusion 50f roughening protrusion 100 light emitting element PTA pretreatment liquid FEA roughening etching liquid DEA Damage layer removal etchant

Claims (3)

An n-type AlGaAs layer and a p-type AlGaAs layer each formed of a compound represented by a composition formula (AlxGa1-xAs (where 0 <x <1) ) form a pn junction in a light-emitting element wafer. A light emitting element wafer manufacturing process for manufacturing as a laminated body laminated as described above,
The main surface of the laminated body contains acetic acid, hydrofluoric acid, nitric acid, iodine and water so that the sum thereof is 90% by mass or more, and the total mass content of acetic acid, hydrofluoric acid, nitric acid and iodine. A main light extraction region surface roughening step for forming a projection by roughening the surface by anisotropic etching with an etching solution for surface roughening comprising an aqueous solution having a water content higher than the water content;
Are performed in this order ,
A pretreatment step of pretreating a main surface used as a light extraction surface of the laminate composed of the n-type AlGaAs layer or the p-type AlGaAs layer with a pretreatment liquid comprising a hydrogen peroxide aqueous solution; Prior to the light extraction area roughening process,
The pretreatment liquid is 96% sulfuric acid: 30% hydrogen peroxide water: water having a mixing ratio of 5: 1: 1 to 20: 1: 1,
Said main light extraction area surface roughening process, the method of manufacturing the light emitting device characterized Rukoto performed before dicing of the light-emitting element wafer. 2. The method for manufacturing a light-emitting element according to claim 1, wherein the n-type AlGaAs layer and the p-type AlGaAs layer located on the light extraction surface side are formed to have a thickness of 1 μm to 10 μm. The method for manufacturing a light-emitting element according to claim 2, wherein the light extraction surface is formed by the p-type AlGaAs layer.

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