JP4400864B2 - Manufacturing method of semiconductor light emitting device - Google Patents

Description

  The present invention relates to a method for manufacturing a semiconductor light emitting device, and more particularly, a short portion of a semiconductor layer or a substrate absorbed when used as a light emitting diode by removing a part of a nitride semiconductor layer epitaxially grown on the substrate and removing the substrate. The present invention relates to a method for manufacturing a semiconductor light emitting device capable of extracting light on the wavelength side.

  Nitride-based semiconductors such as gallium nitride (GaN) are used as blue light-emitting element materials because they have a large forbidden band of 3.4 eV and are directly transitional.

  And according to the light emitting device comprised with such a blue light emitting element material, it is produced by the epitaxial growth with the material.

  By the way, it is desirable to use a bulk crystal of the same material as the epitaxial layer to be grown as the substrate material.

  However, crystals such as gallium nitride (GaN) are extremely difficult to produce bulk crystals due to the high dissociation pressure of nitrogen, which allows epitaxial growth on a GaN single crystal substrate, resulting in a device structure It was difficult to create.

On the other hand, a substrate made of sapphire (Al ₂ O ₃ ), silicon (Si), silicon carbide (SiC), zinc oxide (ZnO) or the like has been used. A light emitting device structure is manufactured by epitaxially growing a nitride semiconductor layer on a substrate having a physical property or chemical property such as a lattice constant or a thermal expansion coefficient different from that of a nitride semiconductor.

  It should also be added here that the substance absorbs light having energy larger than its forbidden band.

  That is, even when a semiconductor light emitting diode or semiconductor laser having a high internal quantum efficiency is produced, if the energy of the required wavelength is larger than the forbidden band of the material constituting the semiconductor, the absorption of the semiconductor causes the external quantum efficiency. There is a problem that dramatic improvement cannot be expected.

  FIG. 1 illustrates an example of a light-emitting element (see Non-Patent Document 1).

  This figure is a schematic cross-sectional view of a conventional nitride-based semiconductor laser, and this nitride-based semiconductor laser structure is fabricated using metal organic chemical vapor deposition (MOVPE).

  Reference numeral 1 denotes a sapphire substrate having a (0001) plane as a surface, and an undoped gallium nitride (GaN) buffer layer 2 having a thickness of 30 nm is formed on the sapphire substrate 1 at a low temperature.

Next, an n-type GaN contact layer 3 having a thickness of 3 μm to which silicon (Si) is added, an n-type In _0.2 Ga _0.8 N layer 4 having a thickness of 0.1 μm to which Si is added, and 0.4 μm to which Si is added. An n-type Al _0.15 Ga _0.85 N cladding layer 5 having a thickness, an n-type GaN optical guide layer 6 having a thickness of 0.1 μm to which Si is added, an undoped In _0.2 Ga _0.8 N quantum well layer having a thickness of 2.5 nm, and An active layer 7 having a multi-quantum well structure composed of an undoped In _0.05 Ga _0.95 N barrier layer having a thickness of 5 nm, a p-type Al _0.2 Ga _0.8 N layer 8 having a thickness of 20 nm to which magnesium (Mg) is added, and Mg P-type GaN optical guide layer 9 having a thickness of 0.1 μm added, p-type Al _0.15 Ga _0.8 N clad layer 10 having a thickness of 0.4 μm to which Mg is added, and 0.5 μm thickness to which Mg is added A p-type GaN contact layer 11 is sequentially formed.

A p-type electrode 12 made of nickel (Ni) -gold (Au) is formed on the p-type GaN contact layer 11, and an n-type electrode 13 made of titanium (Ti) -aluminum (Al) is formed on the n-type GaN contact layer 3. Form.
S. Nakamura. Jan. J. Appl. 35, L74 (1996)

  However, a light emitting device having such a structure is affected by light absorption of a substance constituting the device, particularly when it is desired to extract light generated in a direction perpendicular to the substrate, such as a surface emitting laser or a semiconductor light emitting device. End up.

    An object of the present invention is to remove a part or all of a substrate from a nitride-based semiconductor layer or nitride-based semiconductor element structure grown on the substrate, and to absorb the light emitted from the semiconductor light-emitting layer. It is an object of the present invention to provide a semiconductor light emitting device in which part or all of the above is removed, thereby improving the external quantum efficiency.

The method for producing a semiconductor light emitting device of the present invention is characterized by sequentially performing the following steps (1) to (3).
(1) ··· Zr _{B 2} or Ranaru sequentially forming a nitride-based semiconductor layer and a luminescent layer made of GaN on a single crystal substrate.

( 2 ) ... The single crystal substrate is removed by etching using hydrofluoric acid .

( 3 ) ... A part of the nitride-based semiconductor layer is removed by etching or polishing .

In another method for producing a semiconductor light emitting device of the present invention, the step (3) is characterized in that the light emitting layer is exposed by removing a part of the nitride semiconductor layer by etching or polishing .

According to another method of manufacturing a semiconductor light emitting device of the present invention, in the step ( 3 ) , after removing a part of the nitride semiconductor layer by etching, the surface of the nitride semiconductor layer remaining by etching is removed. It is characterized by flattening .

Further, in the step (2), the temperature of the etchant for the etching is set to 15 ° C. or higher .

In addition, the method for manufacturing a semiconductor light emitting device of the present invention is characterized by sequentially passing through the following steps (1) to (4).
(1) ··· Zr _{B 2} or Ranaru forming a nitride-based semiconductor layer made of GaN on a single crystal substrate.

(2) ... wherein the single crystal substrate, more removed etching grayed using hydrofluoric nitric acid.

  (3) A part of the nitride-based semiconductor layer is removed by etching or polishing.

(4) forming the light-emitting layer over the ... previous SL (3) nitride obtained by the process-based semiconductor layer.

The method for manufacturing a semiconductor light emitting device of the present invention is characterized in that, in the step (2), the temperature of the etching solution for the etching is 15 ° C. or higher .

According to the method for manufacturing a semiconductor light emitting device of the present invention, as shown in the above configuration, a nitride-based semiconductor layer and a light emitting layer are sequentially formed on a single crystal substrate made of XB ₂ (X = Zr, Ti). For absorption of the semiconductor light emitting layer itself by removing part or all of the substrate by (1) step and (2) step of removing the single crystal substrate by etching or polishing. The external quantum efficiency of light on the short wavelength side that could not be used is increased.

  Further, as described above, part or all of the nitride-based semiconductor layer is removed by etching or polishing, thereby removing part or all of the nitride-based semiconductor layer so far. The external quantum efficiency of light on the short wavelength side that could not be used for absorption is increased.

This is a particularly effective technique when using light in the ultraviolet region. For reference, it should be noted that the ZrB ₂ substrate is used, and the lattice constant matching can be _obtained with Al _0.24 Ga _0.76N . However, when the semiconductor light emitting layer is configured with this composition, the emission band is Most of them are in the ultraviolet region, and it is necessary to remove part of the substrate and the nitride semiconductor layer.

  The present invention will be described below with reference to the drawings.

  FIG. 2 is a schematic sectional view showing a layer structure before etching according to the present invention.

  The manufacturing method of the semiconductor light emitting device of the present invention sequentially undergoes the following steps (1) to (3).

(1)... A nitride semiconductor layer and a light emitting layer are sequentially formed on a single crystal substrate made of XB ₂ (X = Zr, Ti).

  (2) The single crystal substrate is removed by etching or polishing.

  (3) A part of the nitride-based semiconductor layer is removed by etching or polishing.

In this example, a nitride-based semiconductor thick film, which is the nitride-based semiconductor layer (this nitride-based semiconductor layer may have a thickness exceeding 10 μm), is epitaxially grown on a ZrB ₂ single crystal substrate. A light emitting layer is formed thereon, and the ZrB ₂ single crystal substrate and the nitride semiconductor thick film are removed by wet etching and mechanical polishing. In such removal, the nitride-based semiconductor light-emitting layer is removed until part or all of it is exposed.

Explaining in more detail, the structure grown nitride semiconductor thick film ZrB ₂ substrate, by etching solution to remove the ZrB ₂ substrate, by chemical mechanical polishing part a nitride semiconductor layer of the light-emitting layer The nitride-based semiconductor thick film substrate is formed by removing it until it is exposed.

(1) Process:
First, a GaN buffer layer 12 having a thickness of about 1 μm is formed on a (0001) -plane ZrB ₂ substrate 11 having a thickness of 300 μm by metal organic chemical vapor deposition (MOVPE).

Next, an SiO ₂ film is formed on the GaN buffer layer 12 and separated into a mask 13 and a growth region 14 by photolithography and wet etching.

  The mask 13 and the growth region 14 are in the form of stripes having a width of 4 μm and 3 μm, respectively.

Subsequently, the growth temperature is set to 1000 ° C. by vapor phase epitaxy (VPE: Vapor Phase Epitaxy) using a chloride transport method using hydrogen chloride (HCl) / gallium (Ga), ammonia (NH ₃ ), and hydrogen (H ₂ ). GaN was grown at an amount of HCl supplied onto Ga of 40 cc / min and NH ₃ gas at 1000 cc / min, and the growth region 14 and the mask 13 were buried. Then, after the growth for 180 minutes, the GaN thick film 15 as the nitride-based semiconductor thick film with a thickness of 250 μm having a flat surface and good crystallinity was obtained on the ZrB ₂ substrate.

  A nitride semiconductor layer as the light emitting layer is stacked on the obtained nitride semiconductor thick film 15.

In the nitride-based semiconductor thick film (GaN film) 15 grown on the ZrB ₂ substrate, the nitride-based semiconductor layer is epitaxially grown on the film 15 to form the structure of the nitride-based semiconductor element, and then the ZrB _{The two} substrates, the nitride-based semiconductor thick film 15, and a part of the nitride-based semiconductor layer are removed.

  In order to stack the light emitting layer in this way, a nitride-based semiconductor layer is formed on the GaN thick film 15 using metal organic chemical vapor deposition (MOVPE).

Specifically, as shown in FIG. 2, the temperature is raised to 1000 ° C., a 1 μm thick n-type GaN layer 16 to which Si is added, and a 0.4 μm thick n-type Al _0.15 Ga _0.85 to which Si is added. N-cladding layer 17, n-type GaN optical guide layer 18 having a thickness of 0.1 μm added with Si, undoped In _0.2 Ga _0.8 N quantum well layer having a thickness of 2.5 nm and undoped In _0.05 Ga _0.95 N barrier having a thickness of 5 nm Active layer 19 having a multi-quantum well structure composed of eight layers, a p-type Al _0.2 Ga _0.8 N layer 20 having a thickness of 20 nm to which magnesium (Mg) is added, and a p-type GaN light guide having a thickness of 0.1 μm to which Mg is added A layer 21, a 0.4 μm thick p-type Al _0.1 Ga _0.9 N cladding layer 22 to which Mg is added, and a 0.5 μm thick p-type GaN contact layer 23 to which Mg is added are sequentially formed.

In this way, the nitride-based semiconductor thick film and the light emitting layer are formed on the ZrB ₂ substrate.

(2) Process:
In this step, the ZrB ₂ substrate is removed by etching or polishing.

ZrB ₂ single crystal substrate is a chemically relatively stable material, but easily dissolves in hydrofluoric acid. This etching rate is very high, and using this means to remove the ZrB ₂ single crystal substrate is a highly productive method.

Next, a mixed solution of hydrofluoric acid and nitric acid in a ratio of 1: 1 is prepared. A nitride-based semiconductor layer including a substrate is immersed in this solution, and the ZrB ₂ substrate is etched. The ZrB ₂ substrate 11 having a thickness of 300 μm is dissolved in about 1 minute at room temperature.

(3) Process:
In this step, after removing the ZrB ₂ substrate as described above, the nitride-based semiconductor layer is removed until part or all of the light emitting layer is exposed. At this time, it is desirable to select abrasive grains or a polishing liquid under conditions of a relatively low polishing rate and perform polishing using a relatively hard surface plate with high flatness.

  Further, it is desirable to use a double-side polishing machine during the polishing. This is because a surface having higher flatness than that of single-side polishing can be obtained and processing with less warpage is possible.

Next, the GaN buffer layer 12, the SiO ₂ mask 13, the nitride-based semiconductor thick film 14, and the nitride-based semiconductor layers 15, 16, 17, and 18 shown in FIG. The semiconductor light emitting device removed by chemical mechanical polishing until it is finished is shown in FIG.

  In the figure, 18 is a light guide layer from which a part has been removed, 19 is a quantum well active layer, 20 is a p-type nitride semiconductor, 21 is a light guide layer, 22 is a p-type cladding layer, and 23 is a p-type contact layer. is there.

For this chemical mechanical polishing, fine powder silica (SiO ₂ ) having a center particle diameter of 50 nm was used as the abrasive grains. Further, an aqueous potassium hydroxide solution adjusted to pH 10 was used as the polishing liquid. Further, as the surface plate, a plate made of cast iron with a Ra CMP pad of about 0.5 nm and a hard CMP pad attached thereto was used.

  In this way, a nitride-based semiconductor layer in which part or all of the light emitting layer is exposed is formed.

  If the nitride-based semiconductor layer is removed by etching, a part of the nitride semiconductor layer may be left by patterning or photolithography.

  Such an example is shown in FIG. Here, a part of the light guide layer 18 is left, but even in such a configuration, a part of the light emitting layer is looked into, so that the light emission efficiency is improved.

  Further, the surface of the nitride semiconductor layer remaining after etching may be polished and planarized.

According to the above embodiment, as a method of removing the substrate from the nitride-based semiconductor layer formed on the ZrB ₂ substrate, because a removal of the substrate with an etchant that dissolves the substrate material, ZrB ₂ substrate by the polishing The ZrB ₂ substrate can be removed without damaging the nitride-based semiconductor layer as compared with the removal.

  As a result, it is possible to improve the external extraction efficiency of light having a wavelength that has not been efficiently extracted so far because the nitride-based semiconductor layer absorbs the light, for example, light having a wavelength near 370 nm.

Further, although a thickness of 300 μm is used for the substrate, a similar effect can be obtained if the ZrB ₂ substrate has a thickness that can prevent cracking due to thermal strain after the formation of the thick GaN film.

Furthermore, regarding this thickness, when a ZrB ₂ substrate is used, the same effect can be obtained even if the thickness is less than 300 μm because the stress of the formed nitride-based semiconductor layer is small.

  In addition, according to the method for manufacturing a semiconductor light emitting device of the present invention, as described above, the light emitting layer was obtained by sequentially performing the steps (1) to (3). Alternatively, it may be performed after etching or polishing of the nitride-based semiconductor layer.

  That is, such a manufacturing method will be described below.

  The following steps (1) to (4) are sequentially performed.

(1)... A nitride-based semiconductor layer is sequentially formed on a single crystal substrate made of XB ₂ (X = Zr, Ti).

  (2) The single crystal substrate is removed by etching or polishing.

  (3) A part of the nitride-based semiconductor layer is removed by etching or polishing.

  (4) ... A light emitting layer is formed on the nitride-based semiconductor layer obtained in the previous step.

  And after forming a light emitting layer in such a (4) process, you may form a protective layer further.

  It should be noted that the present invention is not limited to the above-described embodiment, and various modifications and improvements can be made without departing from the scope of the present invention.

For example, to form a nitride semiconductor thick film ZrB ₂ substrate, after laminating a nitride-based semiconductor layer has been removed ZrB ₂ substrate and the nitride-based semiconductor thick film, the nitride on the ZrB ₂ substrate semiconductor thickness After forming the film, the ZrB ₂ substrate is removed to form a nitride-based semiconductor substrate, and a nitride-based semiconductor layer is stacked on the nitride-based semiconductor substrate, and then the nitride-based semiconductor thick film and the nitride-based film are formed. A part of the semiconductor layer may be removed.

Further, although the main surface of the ZrB ₂ substrate is shown using the (0001) plane, other plane orientations may be used as to whether or not etching is possible. For example, etching can be performed using a low index surface substrate such as {10-10} plane. Furthermore, the same effect can be obtained by using a ZrB ₂ substrate slightly inclined from the (0001) plane.

  Furthermore, although hydrofluoric acid and nitric acid were mixed at 1: 1, the present invention is not limited to this. Further, the temperature during etching is not limited to room temperature. As apparent from FIG. 4, when changing the temperature of the etching solution, it is desirable to set the temperature to 15 ° C. or higher in consideration of productivity.

Moreover, although the example in which the GaN buffer layer 12 and the GaN film 15 are formed on the ZrB ₂ substrate 11 is shown, the present invention is not limited to these, and InxGa1-xN (0 ≦ x ≦ 1), AlxGa1-xN (0 ≦ Similar effects can be obtained with x.ltoreq.1) and Al.sub.xIn.sub.yGa.sub.1-xy N (0.ltoreq.x + y.ltoreq.1) or a layered structure thereof. In addition, the type and concentration of the n-type or p-type impurity do not have a significant effect on the effect of removing part or all of the substrate and the nitride semiconductor layer.

In the embodiment, the nitride-based semiconductor layer is stacked on the nitride-based semiconductor thick film, but, of course, the nitride-based semiconductor layer may be stacked on the ZrB ₂ substrate without using the nitride-based semiconductor thick film. Good.

Furthermore, as described above, the present inventor has the purpose of sequentially performing the following steps (1) to (3), or the purpose of sequentially performing the following steps (1) to (4). ₂ single crystal substrates were used, but it was confirmed that the same effects were obtained even when a TiB ₂ single crystal substrate was used instead.

It is a schematic sectional drawing of the conventional nitride semiconductor laser. It is a section schematic diagram showing the layer composition before the etching concerning the present invention. 1 is a schematic cross-sectional view of a semiconductor light emitting device of the present invention. It is a diagram which shows the melt | dissolution time of a ZrB2 board | substrate.

Explanation of symbols

11 ... ZrB ₂ substrate 12 ... GaN buffer layer 13 ... mask 14 ... growth region 15 ... GaN thick film 16 ... n-type GaN layer 17 ... n-type Al _0.15 Ga _0.85 N-cladding layer 18 ... n-type GaN light guide layer 19 ... active layer 20 with multiple quantum well structure ... p-type Al _0.2 Ga _0.8 N layer 21 ... p-type GaN light guide layer 22 ... p Type Al _0.1 Ga _0.9 N cladding layer 23... P-type GaN contact layer

Claims (6)

A method for manufacturing a semiconductor light emitting device, which sequentially undergoes the following steps (1) to (3).
(1) ··· Zr _{B 2} or Ranaru sequentially forming a nitride-based semiconductor layer and a luminescent layer made of GaN on a single crystal substrate.
(2) The single crystal substrate is removed by etching using hydrofluoric acid.
(3) A part of the nitride-based semiconductor layer is removed by etching or polishing. Wherein (3) The method for manufacturing a semiconductor light-emitting device according to claim 1, characterized in that to expose the more light-emitting layer to be removed by etching or polishing a portion of the nitride-based semiconductor layer. 3. The semiconductor according to claim 2, wherein, in the step (3), a part of the nitride-based semiconductor layer is removed by etching, and then the surface of the nitride semiconductor layer remaining by the etching is planarized. Manufacturing method of light emitting element. The (2) in step, the method for manufacturing a semiconductor light emitting device according to claims 1 to 3, characterized in that the temperature of the etching liquid of the etching and 15 ℃ above. A method for manufacturing a semiconductor light emitting device, which sequentially undergoes the following steps (1) to (4).
(1) ··· Zr _{B 2} or Ranaru forming a nitride-based semiconductor layer made of GaN on a single crystal substrate.
(2) The single crystal substrate is removed by etching using hydrofluoric acid.
(3) A part of the nitride-based semiconductor layer is removed by etching or polishing.
(4) ... A light emitting layer is formed on the nitride-based semiconductor layer obtained in the step (3). 6. The method of manufacturing a semiconductor light emitting element according to claim 5, wherein in the step (2), the temperature of the etching solution for the etching is set to 15 [deg.] C. or higher .

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