JP2007042944A - Method of manufacturing nitride semiconductor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the method of manufacturing a nitride semiconductor element, small in a contact resistance between a p-type layer and an electrode, and capable of increasing the carrier concentration in the p-type layer, by omitting a process for annealing wherein impurities are readily adhered and keeping crean the surface of the p-type layer. <P>SOLUTION: An epitaxial growth layer 6 including the p-type layer 5 at least on the surface is formed by the vapor phase epitaxial growth of the nitride semiconductor layer on a substrate 1 to grow the most front surface layer 5 of the epitaxial growth layer 6. Thereafter, a protective layer 7 consisting of In<SB>x</SB>Ga<SB>1-x</SB>N (0<x≤1) is grown by using organic nitrogen material gas and nitrogen carrier gas succeedingly in the same growth device (a). Then, at least part of the protective layer 7 is removed through wet etching by dipping it into etchant 12 before forming the electrode by connecting to the p-type layer 5 (b). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a semiconductor device using a p-type nitride semiconductor crystal layer, such as a light emitting diode (LED), a laser diode, a photodetector, or the like using a nitride semiconductor, and a high voltage diode. More specifically, the surface of the p-type nitride semiconductor layer during the manufacturing process is kept clean, the contact resistance with the electrode provided on the surface side is reduced, and the carrier concentration of the p-type nitride semiconductor layer itself The present invention relates to a method for manufacturing a nitride semiconductor device that can be increased.

  In recent years, nitride semiconductor light emitting devices such as blue light emitting diodes (LEDs) and laser diodes (LDs) using nitride semiconductors have been put into practical use. A semiconductor light emitting device that emits blue light using a nitride semiconductor is formed on a sapphire substrate by, for example, MOCVD, a low-temperature buffer layer made of GaN, an n-type layer made of GaN, and the band gap energy is n. A material that determines the emission wavelength smaller than that of the shape layer, for example, an InGaN-based (meaning that the ratio of In and Ga can be changed variously, the same applies hereinafter), an MQW active layer (light-emitting layer) made of a compound semiconductor, GaN, etc. A p-type layer is sequentially stacked, and a p-side electrode (pad electrode) is provided on the surface via a light-transmitting conductive layer (translucent electrode), and a part of the stacked semiconductor stacked portion is etched. An n-side electrode is provided on the surface of the exposed n-type layer. Note that the n-type layer and the p-type layer improve the carrier confinement effect, and therefore further increase the band gap energy such as an AlGaN-based compound (meaning that the ratio of Al and Ga can be variously changed, the same applies hereinafter) on the active layer side. A large semiconductor layer may be used.

When this nitride semiconductor layer is stacked by, for example, the MOCVD method, there is a hydrogen of NH ₃ that is a nitrogen source gas, a carrier gas is hydrogen, and so on, so that Mg introduced as an acceptor of the p-type layer is present. Since it is easily bonded to H, it is combined with hydrogen and taken into the nitride semiconductor layer in the form of Mg—H. Thus, when Mg and H are combined and exist in the nitride semiconductor layer, Mg is deactivated and does not function as an acceptor. For this reason, conventionally, annealing in an atmosphere containing no hydrogen at 400 ° C. or higher is generally performed, and the bond between Mg and H is cut off by temperature, H is released from the nitride semiconductor layer, and the acceptor Mg is activated. (For example, refer to Patent Document 1). Also, during this annealing, a cap layer such as a GaN layer or Si ₃ N ₄ or SiO ₂ is provided on the surface of the semiconductor laminated portion and removed after annealing, thereby preventing decomposition of the GaN-based compound and the cap after annealing. It is also disclosed to remove the layer.
JP-A-5-183189

As described above, when a device using a nitride semiconductor layer is formed, an annealing process is performed to increase the carrier concentration of the p-type layer. However, if the annealing process is performed without providing a protective film on the surface of the semiconductor laminate, the nitride semiconductor layer is likely to decompose during the annealing process, and the carrier concentration cannot be sufficiently increased, and a cap layer is provided. If, for example, Si ₃ N ₄ or SiO ₂ is provided, the film forming operation must be performed by an apparatus different from the semiconductor growth apparatus. In particular, when the temperature is lowered to room temperature after epitaxially growing the semiconductor layer, residual impurities such as C Is easily attached to the surface of the p-type layer, and contaminants are easily attached in the subsequent cap layer formation process. If a GaN layer is provided, it can be formed continuously with the growth of the semiconductor layer. Otherwise, it cannot be removed (see paragraph 0029 of Cited Document 1). When dry etching is performed, the surface of the p-type layer becomes rough and ohmic contacts are formed. There is a problem in that the resistance value of the p-type layer itself increases as it cannot be removed.

  Furthermore, not only in the annealing process, for example, in the case of manufacturing the above-described light emitting diode, when the nitride semiconductor layer is epitaxially grown and then cooled to room temperature, the difference in thermal expansion coefficient between the substrate and the nitride semiconductor layer is large. Therefore, it is necessary to suppress thermal stress to suppress the occurrence of dislocations, cracks, etc., and it is necessary to make the temperature lowering process a very slow process, and cooling for a long time is required. Therefore, residual impurities are deposited on the surface of the epitaxial growth layer during this cooling, and some of the impurities also penetrate into the p-type layer to lower the carrier concentration of the p-type layer or contact resistance with the electrode material formed on the surface. Or make it bigger. Further, there is a case where a mask is formed and dry etching is performed to expose the n-type layer before the p-side electrode (translucent electrode or pad electrode) connected to the p-type layer is formed. In these steps, if the surface of the p-type layer is exposed, impurities are likely to adhere to the exposed surface, and not only the surface but also the inside of the p-type layer is likely to increase the resistance of the p-type layer. In particular, when impurities or the like adhere to the surface of the p-type nitride semiconductor layer, it becomes difficult to make ohmic contact with the electrode formed thereon, and there is a problem that the series resistance between the pair of electrodes cannot be reduced.

  The present invention has been made to solve such problems, and omits an annealing process in which impurities are likely to adhere, and at the step before the electrode formation after the necessary semiconductor layer growth is completed, p. An object of the present invention is to provide a method of manufacturing a nitride semiconductor device that can reduce the contact resistance between a p-type layer and an electrode and increase the carrier concentration of the p-type layer by keeping the shape layer surface clean. And

A method of manufacturing a nitride semiconductor device according to the present invention is a method of manufacturing a nitride semiconductor device having an epitaxial growth layer including a p-type layer at least on the surface side by vapor phase growth of a nitride semiconductor layer on a substrate, wherein the epitaxial growth layer Then, a protective layer made of In _x Ga _1-x N (0 <x ≦ 1) is grown using the organic nitrogen source gas and the nitrogen carrier gas in the same growth apparatus, and the substrate is grown. After the temperature is lowered to room temperature and before forming an electrode on the p-type layer, at least a part of the protective layer is removed by wet etching. The outermost surface layer of the epitaxial growth layer means the last layer of the essential epitaxial growth layer constituting the semiconductor element. The protective layer also becomes the epitaxial growth layer, but means the epitaxial growth layer before forming the protective layer.

  Here, the nitride semiconductor means a compound in which a group III element Ga and a group V element N or a part or all of a group III element Ga is replaced with another group III element such as Al, In and / or Alternatively, it refers to a semiconductor made of a compound (nitride) in which a part of N of the group V element is substituted with another group V element such as P or As.

By removing the protective layer by wet etching while irradiating light having a wavelength corresponding to or shorter than the band gap energy of the protective layer, the In _x Ga _1-x N layer is excited and wet etching is performed. Can also be etched easily. In this case, if the protective layer made of In _x Ga _1-x N is formed of a material having a band gap energy smaller than the band gap energy of the outermost p-type layer by 50 meV or more, In _x Ga _{1 The -x} N layer can be etched with good selectivity to the p-type layer, and can be etched without damaging the p-type layer.

  Specifically, an epitaxial growth layer made of the nitride semiconductor is laminated on the substrate in this order so as to form a light emitting layer, an n-type layer, an active layer, and a p-type layer, and then the protective layer is grown. Then, the protective layer is removed and a p-type electrode is directly formed on the exposed p-type layer surface on the exposed p-type layer surface, or a light-emitting element such as an LED or LD A nitride semiconductor light-emitting device can be obtained by forming.

The protective layer made of In _x Ga _1-x N may be formed as a p-type layer, and at least a part of the protective layer may be left below the p-side pad electrode.

According to the present invention, after the nitride semiconductor layer constituting the device is laminated, the same apparatus is used on the outermost surface of the semiconductor laminated portion, for example, triallylamine (TAN: (C ₂ H ₅ ) ₃ N) or ethyl azide. Since a protective layer made of an In _x Ga _1-x N layer is grown using an organic nitrogen gas such as (EtN ₃ ) and a nitrogen carrier gas, it has the following effects. First, it is not necessary to perform an annealing step later, and a very clean state can be maintained without causing contamination due to the adhesion of contamination to the p-type layer. Second, since the protective layer is continuously formed by the same apparatus after the epitaxial growth of the nitride semiconductor layer, even if contamination adheres in the process of lowering the substrate temperature to room temperature, the protective layer can be removed later. Therefore, the p-type layer can be kept clean. Thirdly, by forming the protective layer until the electrode is formed, the p-type layer can be kept clean even during the production process. Fourth, since the protective layer is removed by wet etching, the damage due to dry etching does not reach the p-type layer at all. As a result, the contact resistance between the p-type layer and the electrode can be made extremely small, and the carrier concentration of the p-type layer itself can be greatly improved.

More specifically, for example, even if a nitride semiconductor layer is grown using NH ₃ as an N source gas by MOCVD, NH ₃ gas is not used as the N source gas when forming the last protective layer. Therefore, almost no activated H is released. For this reason, the bonding between the p-type dopant Mg and the like and H is greatly suppressed, and H that has already been bonded to Mg is also released during the growth of the protective layer, so that the p can be sufficiently produced without any additional annealing step. Activation of the shape dopant can be achieved. As a result, it is not necessary to perform an annealing process after laminating the semiconductor layers, and contamination of the p-type layer surface due to the formation and removal of the protective layer for the annealing process can be prevented.

Furthermore, by leaving the protective layer made of In _x Ga _1-x N on the surface until the process before the electrode formation, impurities adhere to the p-type layer surface in the process before the electrode formation, and p There is almost no risk of contamination adhering to the shape layer. On the other hand, the In _x Ga _1-x N layer can be wet-etched with KOH or the like if certain conditions such as an increase in the composition of In are satisfied, but the wavelength corresponding to the band gap energy or a wavelength shorter than that. Can be easily corroded with an etching solution such as KOH. As a result, it can be removed without dry etching, that is, without damaging the underlying p-type layer. In this case, the etching selectivity between the p-type layer and the protective layer can be sufficiently increased by using an In _x Ga _1-x N layer having a band gap energy of 50 meV or more smaller than the band gap energy of the p-type layer. The protective layer can be removed without affecting the p-type layer.

As described above, the protective layer made of In _x Ga _1-x N preferably has a small band gap energy and is used as an LED in order to increase the etching selectivity with the p-type layer. In such a case, the light generated in the active layer may be absorbed. However, the contact layer may be left as it is if it does not transmit light, for example, below the pad electrode. Further, if the composition is such that there is no such problem of light absorption, or in a semiconductor element not related to light absorption such as an edge-emitting light emitting element such as a semiconductor laser (LD), for example, the surface If a part of the layer is cleaned by the aforementioned wet etching, the remaining layer can be left as it is.

Next, a method for manufacturing the nitride semiconductor device of the present invention will be described with reference to the drawings. The method for manufacturing a nitride semiconductor device according to the present invention is an example of a nitride semiconductor device according to the present invention. As shown in FIG. A nitride semiconductor layer is vapor-phased to form an epitaxial growth layer 6 including a p-type layer 5 at least on the surface side. After growing the outermost surface layer 5 of the epitaxial growth layer 6, organic nitrogen source gas and A protective layer 7 made of In _x Ga _1-x N (0 <x ≦ 1) is grown using a nitrogen carrier gas (FIG. 1A). Then, as shown in FIG. 1B, after the temperature of the substrate 1 is lowered to room temperature and before the electrode connected to the p-type layer 5 is formed, the substrate 1 is immersed in an etching solution 12 such as an aqueous KOH solution. Thereby, at least a part of the protective layer 7 is removed by wet etching. Thereafter, as shown in FIG. 1 (c), a translucent electrode 8 made of, for example, Au—Ni alloy, ITO, ZnO or the like is formed on the surface of the p-type layer 5 as in the normal manufacturing process. Thereafter, a part of the epitaxial growth layer 6 is etched by dry etching to expose the n-type layer 3. A p-side electrode (pad electrode) 9 is formed on a part of the surface of the translucent electrode 8, and the exposed n-type layer 3 is exposed. An n-side electrode 10 is formed on the exposed surface, and an LED chip made of a nitride semiconductor is manufactured by chipping from a wafer.

The protective layer 7 made of In _x Ga _1-x N (0 <x ≦ 1) is provided in order to prevent the p-type layer 5 during the manufacturing process from being contaminated by adhesion of residual impurities and the like. Therefore, the protective layer 7 is continuously provided after the epitaxial growth layer 6 is grown without growing the growth temperature to room temperature after the epitaxial growth layer 6 is grown. The protective layer 7 made of In _x Ga _1-x N needs to be grown at a low temperature because In is easy to escape when the growth temperature is high. In particular, the growth temperature is lower as the In composition is larger. There is a need to. For example, when growing InN, it is preferable to grow at a temperature of about 550 ° C., and when growing In _0.03 Ga _0.97 N at about 800 ° C. Therefore, if Ga is mixed somewhat, it can grow at about 600 to 800 ° C. The larger the composition of In, the easier it is to etch when performing wet etching for removal. On the other hand, the band gap energy is small, and in the case of making an LED, it becomes easier to absorb emitted light. If it is completely removed, there is no problem, but if it is left, its composition is determined in consideration of light absorption. In the case of complete removal, the conductivity type may be p-type, n-type, undoped, or p-type if any part of the contact layer to be described later is left.

The protective layer 7 is grown by, for example, a growth apparatus for growing the epitaxial growth layer 6 as it is. However, the carrier gas is changed from hydrogen to nitrogen, and NH ₃ gas is stopped as a source gas of N. Instead, organic nitrogen source gas is used. This is because activated H is not generated and combined with Mg or the like of the p-type dopant. The organic nitrogen gas contains H, but is contained as a methyl group, an ethyl group, or the like, and hardly forms a single H. Therefore, it is hardly combined with a p-type dopant to be inactivated. Examples of the organic nitrogen gas include triallylamine (TAN), ethyl azide (EtN ₃ ), acetonitrile (acetonitrile), azoisobutane, tertialybutildimethylamine, triethylamine, trimethyllamine, trimethyllamine, Normal propylamine (trinormalpropylamine), triphenylamine (triphenylamine), etc. can be used.

In order to remove the protective layer 7, wet etching can be performed as it is if the In composition is large like InN, but it takes time, and if the In composition decreases, etching becomes more difficult. As shown in FIG. 1 (b), it is possible to perform etching in a short time when immersed in an etching solution such as KOH while irradiating light. For example, the protective layer 7 having a thickness of about 0.02 μm is formed. It can be completely removed by immersing in a 20 wt% KOH aqueous solution for about 10 minutes. Irradiation light is easily excited by light when irradiated with light having a wavelength equal to or less than the band gap energy of In _x Ga _1-x N, which is the protective layer 7, and thus is easily etched. However, when light having a short wavelength is irradiated, not only the protective layer 7 but also the p-type layer 5 is excited, and therefore light having a wavelength longer than the wavelength corresponding to the band gap energy of the p-type layer 5 may be used. preferable. Therefore, there is no problem if light in the vicinity of the wavelength corresponding to the band gap energy of the protective layer is irradiated.

  From these viewpoints, the protective layer 7 is made of a material having an energy difference of 50 meV or more than the band gap energy of the p-type layer 5 (the band gap energy of the protective layer 7 is small). It is preferable to selectively etch only. For example, since the band gap energy of InN is about 0.8 eV and the band gap energy of GaN is about 3.8 eV, the band gap energy can be greatly reduced by a slight increase of In.

As described above, the In _x Ga _1-x N layer has a smaller band gap energy as the In composition increases, but the carrier concentration can be increased, and the ohmic contact with the p-type layer and the electrode pad can be increased. Contact is also easier to obtain. Therefore, it can be left only under the electrode pad as a p-type layer, and can also be left on the entire surface in an element that emits edge light, such as a stripe type semiconductor laser. In this case, as described above, since it is used as a protective layer during the manufacturing process, it is preferable to remove at least part of its surface by wet etching.

Next, the method for producing the nitride semiconductor light emitting device of the present invention will be described in more detail with reference to FIG. As the substrate 1, for example, various substrates made of sapphire, SiC, GaN-based compounds (meaning nitride semiconductors), ZnO-based compounds (meaning oxides containing Zn), Si, GaAs, or the like can be used. . For example, a substrate 1 made of sapphire having a (0001) plane as a main surface is placed on a susceptor of an MOCVD apparatus, and the substrate 1 is thermally cleaned by raising the temperature to about 1070 ° C. while flowing hydrogen gas. Thereafter, the temperature is lowered to about 400 to 600 ° C., and a low temperature buffer layer 2a made of GaN, for example, is formed to about 0.005 to 0.1 μm, and then the temperature is raised to a high temperature of about 600 to 1200 ° C., for example, about 1000 ° C. Then, an undoped high-temperature buffer layer 2b made of GaN is laminated to about 1 μm, and then an n-type layer 3 made of Si-doped GaN is laminated to about 1 to 10 μm, for example, about 4 μm. Next, the growth temperature is lowered to a low temperature of about 700 to 850 ° C., and an undoped InGaN-based compound / GaN-MQW (for example, a well layer made of ₁ to 3 nm of In _0.17 Ga _0.83 N and 5 to 20 nm of In _z Ga _{1 -z N (0 ≦ z ≦ 0.05} ) and a barrier layer made of the laminated about 0.05~0.3μm the active layer 4 having a multiple quantum well structure) is 3-8 pairs stacked. Next, the temperature in the growth apparatus is raised to about 900 to 1100 ° C., for example, about 1000 ° C., and the p-type layer 5 made of GaN doped with Mg is grown to about 0.01 to 0.5 μm.

When growing each of the semiconductor layers described above, the reaction gas such as trimethylethylene gallium (TMG), ammonia (NH ₃ ), trimethylaluminum (TMA), trimethylindium (TMIn) and the like and n-type are used together with the carrier gas H _2. When supplying a necessary gas such as SiH ₄ as a dopant gas and cyclopentadienylmagnesium (Cp ₂ Mg) as a dopant gas when forming a p-type, a desired composition and a desired conductivity type are supplied. The semiconductor layer can be formed to a desired thickness.

Thereafter, the supply of TMG and Cp ₂ Mg is interrupted, and the substrate temperature is lowered to about 800 ° C. Then, after changing the NH _{3 of the} nitrogen source gas to an organic nitrogen gas such as TAA and switching the hydrogen of the carrier gas to nitrogen, the substrate temperature is lowered to 550 ° C. and the supply of TMI is started. The protective layer 7 can be grown, and is grown to about 3 to 200 nm, for example, about 10 nm. At this time, for example, by supplying a Cp ₂ Mg dopant gas to form a p-type layer, even when there is a residue of the InN layer when the InN layer is removed, a surface having a high hole concentration can be easily left. It can also be used as an electrode contact layer. After the growth of the protective layer 7 made of InN, the supply of TMI is interrupted, and the temperature is lowered to room temperature while supplying TAA, whereby the surface of the p-type layer 5 can be cooled to room temperature while completely protecting it.

  Thereafter, SOG is formed to about 500 nm on the surface of the substrate on which the crystal has grown, and then a transparent electrode pattern is formed with a resist. At this point, the protective layer 7 made of InN in the transparent electrode forming portion is exposed. In this state, as shown in a conceptual diagram in FIG. 1B, the wafer is immersed in a container 11 filled with a KOH aqueous solution 12 (concentration 20 wt%) at about 30 ° C., and light is emitted from the light source 13. Thus, the p-type layer 5 can be exposed by etching the portion of the protective layer 7 made of InN exposed in about 10 minutes. Since the protective layer 7 made of InN has a band gap energy of about 0.8 eV, it can be easily excited by visible light or near-ultraviolet light. By irradiating excitation light while being immersed in a KOH aqueous solution, The p-type layer 5 can be selectively etched without being excited. In this case, by using light having a wavelength longer than the wavelength corresponding to the band gap energy of the lower p-type layer 5 as excitation light, highly selective etching is possible, and the uppermost InN layer (protective layer 7) ) Can be removed, and a clean and undamaged surface can be formed.

  Thereafter, as shown in FIG. 1 (c), for example, Ni and Au are laminated and alloyed to form a Ni—Au alloy layer of about 2 to 100 nm, thereby forming a translucent conductive layer. The electrode 8 is formed. Note that the light-transmitting conductive layer attached to unnecessary portions is also removed by removing the SOG as a mask by etching. The translucent electrode 7 can be formed of ZnO, ITO, or the like without depending on this example, or only the pad electrode (p-side electrode) can be formed. According to the material of ZnO or ITO, even if it is thick, it has translucency, and can be provided in a thickness of about 0.01 to 5 μm. After that, a resist film is applied and patterned, and a part of the epitaxial growth layer 6 is etched by dry etching to expose the n-type layer 3, and Ti and Au are formed on a part on the translucent electrode 7 by a lift-off method or the like. And a p-side electrode 8 as a pad electrode, and an n-side electrode 9 for ohmic contact is formed on the exposed n-type layer 3 using a Ti—Al alloy or the like. Then, by dividing into chips, an LED chip as shown in FIG. 1C is obtained. In the above example, the translucent electrode 7 is formed before the n-type layer 3 is exposed. However, after the n-type layer 3 is exposed, the protective layer 7 is removed by etching to form the translucent electrode 8. It can also be formed. Note that the structures and materials of the p-side electrode 9 and the n-side electrode 10 are not limited to this example.

  In the above example, the p-type layer 5 is a single layer of GaN. However, for example, a layer having a large band gap such as an AlGaN-based compound can be formed on the active layer side. Moreover, the n-type layer 3 can also be made into two or more kinds of such multiple layers. Further, in this example, the active layer 4 is sandwiched between the n-type layer 3 and the p-type layer 5, but the pn junction in which the n-type layer and the p-type layer are directly homojunction or heterojunction is used. A structure may be used. Further, in the above-described example, the example of the LED is used. However, even in an LD that forms a stripe-shaped light emitting region by embedding a mesa-shaped dry etching or current confinement layer, an epitaxial growth layer is formed as a normal LD. By laminating and forming the above-mentioned protective layer on the outermost surface layer, the contact resistance between the upper surface electrode and the p-type layer can be reduced, and the carrier concentration of the p-type layer can be improved. .

FIG. 2 is a perspective explanatory view showing the manufacturing process of the ridge type LD. First, as shown in FIG. 2A, an n-type buffer layer 22 made of n-type GaN doped with, for example, Si at an impurity concentration of about 3 × 10 ¹⁸ cm ⁻³ on an n-type GaN substrate 21, for example. N-type cladding layer 23 made of n-type Al _0.08 Ga _0.92 N doped with Si to about 3 × 10 ¹⁷ cm ⁻³ , for example, about 1 μm, for example Si with about 1 × 10 ¹⁷ cm ⁻³ The n-type guide layer 24 made of the n-type GaN has an n-type GaN layer (about 9 nm) having an impurity concentration of about 3 × 10 ¹⁸ cm ⁻³ and an undoped In _0.1 Ga _0.9 N layer (about 3 nm). ) The active layer 25 having a multiple quantum well (MQW) structure in which about 3 pairs of n-type GaN layers (about 12 nm) of about 3 × 10 ¹⁸ cm ⁻³ are stacked is about 54 nm, for example, Mg is 5 × 10 ^19. the dough to about cm ^-3 It has been p-type Al _0.2 Ga 25 nm about the blocking layer 26 made of _0.8 N, for example Mg is 5 × 10 ¹⁹ cm p-type guide layer 27 0.1μm approximately of doped GaN of about ^-3, for example, Mg is A p-type cladding layer 28 made of Al _0.08 Ga _0.92 N doped to about 5 × 10 ¹⁹ cm ⁻³ is applied to a p-type made of GaN doped with about 0.4 μm, eg, Mg of about 1 × 10 ²⁰ cm ^−3. The contact layer 29 is sequentially laminated to a thickness of about 0.1 μm to form an epitaxial growth layer 30.

As in the above example, the growth temperature of each layer is lowered by lowering the growth temperature of the active layer containing In, and epitaxial growth is performed by introducing the necessary gas according to the composition to be grown. After the growth of the epitaxial growth layer 30, the supply of TMG and Cp ₂ Mg is interrupted, and the substrate temperature is lowered to about 800 ° C. Then, as in the previous example, the NH ₃ source gas is changed to organic nitrogen gas such as TAA, the carrier gas hydrogen is changed to nitrogen, the substrate temperature is lowered to 550 ° C., and TMI is supplied. Then, the protective layer 31 made of InN is grown to about 3 to 200 nm, for example, about 10 nm. At this time, as described above, for example, by supplying a dopant gas of Cp ₂ Mg to form a p-type layer, it is possible to leave a part of the thickness without completely removing the protective layer 31 made of InN. it can. After the growth of the protective layer, the supply of TMI is interrupted and cooled to room temperature while supplying TAA.

Thereafter, as shown in FIG. 2B, a mask material such as SiO ₂ is provided on the surface of the protective layer 31, and is patterned so as to remain in a stripe shape forming a light emitting region, thereby forming a mask 38. . Then, the protective layer 31 and the semiconductor stacked portion 30 exposed from the mask 38 are etched to the front of the p-type guide layer 27 by dry etching to form a mesa shape. After that, the insulating layer 32 made of, for example, ZrO _{2 is} formed by, for example, sputtering while leaving the mask 38 as it is, and then the mask 38 is removed, so that the side walls other than the mesa-shaped upper surface and the mesa-shaped bottom surface are formed. An insulating layer 32 is formed on the surface, and the surface of the protective layer 31 is exposed.

  Thereafter, similarly to the example shown in FIG. 1B, the p-type contact layer 29 is exposed by immersing the entire wafer in a KOH etching solution and etching the protective layer 31 while irradiating visible light or the like. Then, as shown in FIG. 2D, the metal film 33a for the p-side contact electrode is formed by providing, for example, Ni / Au or the like on the entire surface by vacuum deposition or the like. Thereafter, a resist film or the like is formed and patterned, so that the p-side contact electrode 33 is formed only in the vicinity of the striped mesa region as shown in FIG.

  Then, as shown in FIG. 2F, the p-side pad electrode 34 is formed on almost the entire surface excluding the peripheral portion of the chip by a lift-off method, for example, with a stacked structure of Ni and Au. Thereafter, the back surface of the substrate 21 is polished so that the thickness of the substrate 21 is about 100 μm, and Ti and Al films are formed by vacuum deposition or the like, and are sintered to form an n-side electrode made of Ti—Al alloy or the like. 35 is formed. Thereafter, dicing is performed in the direction parallel to the stripes, and the direction perpendicular to the stripes is cleaved and divided into chips, thereby obtaining an LD chip as shown in FIG.

  The structures and materials of the p-side contact electrode 33, the p-side pad electrode 34, and the n-side electrode 35 are not limited to this example. When the substrate is made of an insulating substrate such as a sapphire substrate, the n-side electrode is an n-type layer (n-type buffer layer) exposed by etching a part of the protective layer 31 and the semiconductor stacked portion 30. Formed on the exposed surface. Further, as described above, if the protective layer 31 is not completely removed by etching and only the surface is etched to be cleaned, most of the others can be left. In particular, in an edge emitting LD, no light is emitted from the surface, and in the case of such edge emitting, there is no problem even if it remains. Furthermore, the stacked structure of the semiconductors constituting the LD is not limited to the above example, and various stacked structures can be formed.

According to the present invention, since the surface is covered with the protective layer made of In _x Ga _1-x N after the semiconductor layer constituting the element is epitaxially grown, even when the substrate temperature is lowered to room temperature after the epitaxial growth of the semiconductor layer. Since the residual impurities do not directly adhere to the p-type layer and the like, and the protective layer can be easily removed by wet etching, the surface of the p-type layer is very clean without damaging the p-type layer. Can be obtained. As a result, the contact resistance between the electrode (transparent electrode or pad electrode) provided in connection with the p-type layer and the p-type layer can be greatly reduced, and a nitride semiconductor device having a low series resistance and a low driving voltage can be obtained. can get.

It is sectional explanatory drawing which shows the manufacturing process of the light emitting element which is one Embodiment of the manufacturing method of the nitride semiconductor element by this invention. It is sectional explanatory drawing of an example of LD formed by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Low-temperature buffer layer 3 N-type layer 4 Active layer 5 P-type layer 6 Epitaxial growth layer 7 Protective layer 8 Translucent electrode 9 P-side electrode (pad electrode)
10 n-side electrode

Claims (5)

A method for manufacturing a nitride semiconductor device having an epitaxial growth layer including a p-type layer on at least the surface side by vapor-phase growth of a nitride semiconductor layer on a substrate, wherein the same is continued after growing the outermost surface layer of the epitaxial growth layer After growing a protective layer made of In _x Ga _1-x N (0 <x ≦ 1) using an organic nitrogen source gas and a nitrogen carrier gas in a growth apparatus and lowering the temperature of the substrate to room temperature, Before forming an electrode on a p-type layer, at least a part of the protective layer is removed by wet etching.   The method for producing a nitride semiconductor device according to claim 1, wherein the protective layer is removed by wet etching while irradiating light having a wavelength corresponding to or shorter than the band gap energy of the protective layer.   3. The method for manufacturing a nitride semiconductor device according to claim 1, wherein the protective layer is made of a material having a band gap energy that is smaller than the band gap energy of the outermost p-type layer by 50 meV or more.   The epitaxially grown layer made of the nitride semiconductor is laminated on the substrate in this order so as to form a light emitting layer, an n-type layer, an active layer, and a p-type layer, and subsequently the protective layer is grown, and then the protective layer 3. The nitriding device according to claim 1, wherein the light-emitting element is formed by forming a p-side electrode directly on the exposed p-type layer surface through a translucent electrode or on the exposed p-type layer surface. Manufacturing method for semiconductor devices. 5. The method for producing a nitride semiconductor device according to claim 4, wherein the protective layer made of In _x Ga _1-x N is formed as a p-type layer, and at least a part of the protective layer is left below the p-side pad electrode. .

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