JP2005340860A - Semiconductor light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting element that has improved ohmic characteristics and has improved reliability, and to provide a method for manufacturing the semiconductor light-emitting element. <P>SOLUTION: As a contact metal that comes into contact with a p-type contact layer, silver or a mixture of silver and gold is used, thus greatly improving the ohmic contact with the p-type contact layer. By forming a tungsten layer on an n-side contact metal layer at the n-side of an element, a barrier effect is maintained, and ohmic contact can be improved. Further, by performing heat treatment in a reducing atmosphere after forming a p-side contact electrode layer, the ohmic contact can be improved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor light emitting device and a method for manufacturing the same. More specifically, the present invention relates to a light-emitting device in which a nitride-based semiconductor layer such as GaN, InGaN, or GaAlN is stacked on a substrate, the semiconductor light-emitting device having an electrode with low contact resistance and good reliability, and It relates to the manufacturing method.

  By using a nitride-based semiconductor typified by gallium nitride, light emitting elements in the wavelength band from ultraviolet light to blue and green are being put into practical use.

In the present application, “nitride-based semiconductor” refers to a group III-V of B _x In _y Al _z Ga _(1-xyz) N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1). In addition to a compound semiconductor, the group V element includes a mixed crystal containing phosphorus (P), arsenic (As), and the like in addition to N.

  By forming a light emitting element such as a light emitting diode (LED) or a semiconductor laser using a nitride-based semiconductor, it is possible to emit ultraviolet light, blue light, green light, etc. with high light emission intensity, which has been difficult until now. is there. Nitride-based semiconductors are also expected to be applied to electronic devices because they have a high crystal growth temperature and are stable at high temperatures.

  Hereinafter, a light-emitting element will be described as an example of a semiconductor element using a nitride-based semiconductor.

  FIG. 8 is a schematic sectional view showing the structure of a conventional light emitting diode using a nitride semiconductor. A GaN buffer layer (not shown), an n-type GaN layer 102 and a p-type GaN layer 106 are crystal-grown on the sapphire substrate 101, and a part of the p-type GaN layer 106 is etched away to form an n-type GaN layer 102. Is exposed. A p-side transparent electrode (Au) 121 is formed on the p-type GaN layer 6, a current blocking insulating film 113 is formed below the p-side bonding electrode, and a p-side bonding electrode connected to the p-side transparent electrode 121 thereon. 123 (Ti / Au) is formed, and an n-side electrode 122 (Al / Au) is further formed on the n-type GaN layer.

  In the light emitting diode of FIG. 8, the current flowed from the p-side electrode is spread in the in-plane direction by the transparent electrode 121 having good conductivity, and the current is injected from the p-type GaN layer 106 to the n-type GaN layer 102 to emit light. The light passes through the transparent electrode 121 and is extracted outside the chip.

  However, the conventional nitride semiconductor as illustrated in FIG. 8 has a problem that it is difficult to ensure ohmic contact with the electrode. That is, since a nitride-based semiconductor has a wide band gap, it is difficult to make ohmic contact with the electrode. Furthermore, the nitride-based semiconductor has a problem that it is difficult to form a layer having a high carrier concentration in both p-type and n-type, and it is difficult to form an ohmic contact from this point.

  In addition, nitride-based semiconductors are difficult to perform chemical wet etching, so it is difficult to perform surface treatment before electrode formation, and the ohmic characteristics greatly depend on the surface state of the electrode and semiconductor layer interface. There was also a problem.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a semiconductor light-emitting device having good ohmic characteristics and improved reliability, and a method for manufacturing the same.

  To achieve the above object, a semiconductor light emitting device according to the first aspect of the present invention includes a first layer made of a p-type nitride-based semiconductor, a second layer made of an n-type nitride-based semiconductor, A p-side electrode provided in contact with the first layer; and an n-side electrode provided in contact with the second layer, wherein the p-side electrode is in contact with the first layer. And having a contact layer containing silver (Ag) and a layer made of tungsten (W) provided on the contact layer, ensuring excellent ohmic contact on the p side can do.

  Here, by providing a light-transmitting conductive film made of a metal oxide on the layer made of tungsten (W), current can be spread in a plane to obtain uniform light emission.

Furthermore, an overcoat layer provided on the translucent conductive film is further provided,
The overcoat layer has a layer made of nickel (Ni) provided in contact with the translucent conductive film, whereby adhesion strength between the translucent conductive film and the overcoat layer can be improved. .

  Alternatively, the semiconductor light emitting device according to the second aspect of the present invention includes a first layer made of a p-type nitride-based semiconductor, a second layer made of an n-type nitride-based semiconductor, and the first layer. A p-side electrode provided in contact with and an n-side electrode provided in contact with the second layer, the n-side electrode provided in contact with the second layer, A contact layer made of hafnium (Hf), aluminum (Al), titanium (Ti) or an alloy containing at least one of these elements, and tungsten (W) provided on the contact layer. It has a barrier layer and a bonding pad layer made of gold (Au) provided on the barrier layer, and ensures good ohmic contact on the n side and the barrier layer functions effectively. Ensure reliability. Can.

  As a preferred embodiment of the present invention, the first layer is composed of a plurality of layers containing a p-type dopant and having a layer thickness of 100 nm or less, and the plurality of layers are nitrided with compositions different from each other in adjacent layers. It is characterized by comprising a physical semiconductor and can further improve ohmic contact.

  Here, the second layer is composed of a plurality of layers containing an n-type dopant and having a thickness of 100 nm or less, and the plurality of layers are composed of nitride-based semiconductors having adjacent compositions different from each other. Is desirable.

  Further, if at least one of the first layer and the second layer is provided with unevenness on the surface that contacts the electrode, the contact area with the electrode is expanded to reduce the contact resistance. The adhesion strength of the electrode can be improved.

  Alternatively, the semiconductor light-emitting device according to the third aspect of the present invention includes a light-emitting layer made of a semiconductor and a light-transmitting conductive film made of a metal oxide and having a light-transmitting property with respect to light emitted from the light-emitting layer. And a layer made of nickel (Ni) provided in contact with the translucent conductive film, and is not limited to nitride-based semiconductors, but various material systems such as InGaAlP-based and InP-based materials In the semiconductor light emitting device using the transparent conductive film, the adhesion strength between the transparent conductive film and the metal layer can be improved.

  On the other hand, in the method for manufacturing a semiconductor light emitting device according to the fourth aspect of the present invention, a stacked body having an n-type layer made of an n-type nitride-based semiconductor and a p-type layer made of a p-type nitride-based semiconductor is formed. A step of forming a p-side contact electrode layer on the surface of the p-type layer of the laminate, and a step of heat-treating in an atmosphere containing a reducing gas. Good ohmic contact can be obtained.

Alternatively, in the method for manufacturing a semiconductor light emitting device according to the fifth aspect of the present invention, a stacked body including an n-type layer made of an n-type nitride semiconductor and a p-type layer made of a p-type nitride semiconductor is formed. A step of forming an n-side contact electrode layer on the surface of the n-type layer of the laminate, a step of heat-treating at a first temperature, and a p-side contact on the surface of the p-type layer of the laminate. A step of forming an electrode layer, and a step of heat-treating at a second temperature lower than the first temperature in an atmosphere containing a reducing gas,
Good ohmic contact can be obtained.

  Here, as a preferred embodiment of the present invention, if the n-side contact electrode layer is made of any one of hafnium (Hf), aluminum (Al), and titanium (Ti), a good n-side ohmic contact is obtained. Is obtained.

  If the p-side contact electrode layer is made of either a metal containing silver (Ag) or nickel (Ni), a good p-side ohmic can be obtained.

  The method further includes the step of forming a light-transmitting conductive film made of a metal oxide on the p-side contact electrode layer and the step of heat-treating the light-transmitting conductive film in an oxygen-containing atmosphere. The sheet resistance of the translucent conductive film can be reduced and the adhesion strength can be increased.

  Alternatively, in the method for manufacturing a semiconductor light emitting device according to the sixth aspect of the present invention, a step of forming a semiconductor stacked body including a light emitting layer and a light-transmitting conductive film made of a metal oxide are formed on the semiconductor stacked body. And a step of heat-treating the translucent conductive film in an oxygen-containing atmosphere, using not only nitride-based semiconductors but also various semiconductors such as InGaAlP-based and InP-based semiconductors In addition, in a semiconductor light-emitting element having a light-transmitting conductive film, the sheet resistance of the light-transmitting conductive film can be reduced and the adhesion strength can be increased.

  ADVANTAGE OF THE INVENTION According to this invention, the ohmic contact can be improved compared with the past, and the light emitting element by which reliability and the adhesion strength of the electrode were improved simultaneously can be provided, and an industrial merit is great.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic cross-sectional view showing a semiconductor light emitting device according to a first embodiment of the present invention. The semiconductor light emitting device of the present invention includes a GaN buffer layer (not shown), an n-type GaN layer 2, an n-type AlGaN contact layer 3, an n-type GaN contact layer 4, an n-type GaN layer 5, and a p on a sapphire substrate 1. The p-type GaN layer 6, the p-type AlGaN contact layer 7, the p-type InGaN contact layer 8, and the p-type GaN contact layer 9 are sequentially stacked.

The p-side electrode includes a translucent electrode and a bonding pad portion. That is, the block layer 13 made of SiO ₂ or the like is selectively formed on the p-type GaN contact layer 9, and the first metal layer 10 / second metal layer 11 are formed on the remaining surface, for example. A translucent electrode in which the / tungsten (W) layer 12 is laminated is formed.

  The block layer 13 has a role of blocking current so that excessive light emission does not occur under the bonding pad. Further, the thickness of each layer of the translucent electrode is extremely thin so that light emitted from the light emitting element is transmitted without being absorbed so much.

  As the first metal layer 10, it is desirable to use silver (Ag). Further, it is desirable to use gold (Au) as the second metal layer 11. Alternatively, a mixture of silver and gold may be used as the first metal layer 10 and the second metal layer may be omitted. Alternatively, as will be described later in detail, when hydrogen annealing unique to the present invention is performed, nickel (Ni) may be used as the first metal layer 10 and the second metal layer may be omitted.

  A bonding layer in which a titanium (Ti) layer 18, a tungsten (W) layer 19, and a gold (Au) layer 20 are deposited in this order on the block layer 13 while being partially connected to the light-transmitting electrode layer. A pad is formed. Here, the titanium (Ti) layer 18 functions as an adhesive layer, the tungsten (W) layer 19 functions as a barrier layer, and the gold (Au) layer 20 functions as a bonding layer.

  On the other hand, an n-side electrode is formed on the n-type contact layer 4. That is, a hafnium (Hf) layer 14 / aluminum (Al) layer 15 / hafnium (Hf) layer 16 / gold (Au) layer 17 are deposited in this order, and a titanium (Ti) layer 18 and tungsten are further formed thereon. A bonding pad portion in which the (W) layer 19 and the gold (Au) layer 20 are deposited in this order is formed.

  Here, the intermediate gold (Au) layer 17 functions as a cap layer for protecting the hafnium (Hf) layer 16. In order to prevent excessive penetration of gold (Au) into the semiconductor, it is desirable that the gold (Au) layer 17 be formed to be relatively thin or omitted.

  The titanium layer 18 acts as an adhesive layer. The tungsten layer 19 acts as a barrier layer. Further, the gold layer 20 functions as a layer for bonding wires or the like.

  The illustrated structure of the n-side electrode layer is merely an example. In the present invention, the metal layer that contacts the n-type contact layer 4 is either hafnium (Hf), titanium (Ti), or aluminum (Al), and a barrier layer made of tungsten (W) is provided thereon. In addition, a bonding pad layer made of gold (Au) is provided thereon.

The surface of the light emitting element is covered with a protective film 22 made of SiO ₂ .

  The light emitting device of the present invention has the following operations with the configuration described above.

  That is, according to the present invention, by using either silver or a mixture of silver and gold as a contact metal in contact with the p-type contact layer 9, first, ohmic contact with the p-type contact layer 9 is achieved. It can be greatly improved. As a result of independent studies, the present inventor has come to know that contact resistance can be particularly reduced when these metals are brought into contact with the semiconductor layer. This is considered to be because it becomes easy to react with the p-type contact layer 9 by adding silver.

  Further, according to the present invention, the ohmic contact can be improved while maintaining the barrier effect by providing the tungsten layer 19 as the barrier layer on the n-side contact metal layer on the n-side of the element. That is, the barrier layer functions to prevent mutual diffusion between the n-side contact metal and the bonding pad and maintain reliability. Conventionally, platinum (Pt) has often been used as the barrier layer of the n-side electrode. However, platinum acts as a p-type dopant when it enters the nitride-based semiconductor. Therefore, platinum is diffused into the n-type contact layer during the temperature rising process such as heat treatment, solder mounting or wire bonding after the bonding pad is formed, and the ohmic contact is deteriorated.

  On the other hand, the present inventor has discovered that long-term reliability can be secured without deteriorating ohmic contact by using a tungsten layer as the barrier layer of the n-side electrode. Further, when the tungsten layer is used as the barrier layer in this way, particularly good results are obtained when any of the above-described hafnium (Hf), titanium (Ti), or aluminum (Al) is used as the contact metal. It turns out that it is obtained.

Furthermore, according to the present invention, the ohmic contact can be further improved by forming these new structures by a new process different from the conventional one. Next, the manufacturing method of the light emitting element of this invention is demonstrated.
FIG. 2 is a flowchart showing the main part of the method for manufacturing a light emitting device of the present invention.
First, as shown in step S <b> 1, the semiconductor layers 2 to 9 are successively grown on the sapphire substrate 1. Crystal growth of each layer can be performed by a method such as MOCVD (metal-organic chemical vapor deposition), hydride CVD, MBE (molecular beam deposition), or the like.

  Next, as shown in step S2, the p-type layer is etched. That is, the p-type semiconductor layers 6 to 9 are selectively etched to expose the n-type GaN layer 4. Specifically, for example, patterning is performed by a PEP (photo-engraving process) method, and etching is performed by an etching method such as RIE (reactive ion etching).

  Next, as shown in step S3, a contact portion of the n-side electrode is formed. Specifically, a hafnium layer 14 / aluminum layer 15 / hafnium layer 16 / gold layer 17 and the like are deposited on the GaN contact layer 4 by a vacuum evaporation method, a sputtering method, or the like, and patterned by a lift-off method.

  Next, as shown in step S4, the contact portion of the n-side electrode is sintered. Specifically, for example, heat treatment is performed at 800 ° C. or higher for about 20 seconds in a nitrogen gas atmosphere.

  Next, as shown in step S5 or S8, a translucent electrode layer of the p-side electrode is formed. Specifically, a first metal layer 10 / second metal layer 11 / tungsten (W) layer 12 and the like are sequentially deposited on the p-type contact layer 9 by vacuum vapor deposition or sputtering. Here, as described above, the first metal layer 10 is either silver, a mixture of silver and gold, or nickel. In the case of silver, the thickness is preferably about 0.5 to 10 nm. Moreover, when setting it as the mixture of silver and gold | metal | money, it is desirable that the ratio of silver shall be about 1-20 atomic%, and the thickness of the mixture layer shall be about 0.5-10 nm. In the case of nickel, the thickness is preferably 0.5 to 5 nm.

The subsequent steps are slightly different depending on the material of the p-side electrode.
That is, as shown in step S5, when nickel is used as the contact metal, annealing is performed in an atmosphere containing a reducing gas in step S6. Hydrogen gas can be used as the reducing gas. The atmosphere can be a mixed gas of hydrogen and nitrogen, and the volume content of hydrogen is desirably in the range of about 0.1% to 5%. The annealing temperature is desirably 500 ° C. or lower.

  Next, as shown in step S7, a bonding pad portion is formed. Specifically, a titanium (Ti) layer 18, a tungsten (W) layer 19, and a gold (Au) layer 20 are deposited in this order by a vacuum evaporation method, a sputtering method, or the like.

  On the other hand, as shown in step S8, when silver or a mixture of silver and gold is used as the contact metal, sintering is performed once in step S9. Specifically, heat treatment is performed at a temperature of 600 ° C. to 800 ° C. in a nitrogen atmosphere. The heat treatment can be performed at 750 ° C. for about 20 seconds, for example.

  Next, as shown in step S10, annealing is performed in an atmosphere containing hydrogen as a reducing gas. This atmosphere and annealing temperature are as described above for step S6.

  Next, as shown in step S11, a bonding pad portion is formed. Specifically, a titanium (Ti) layer 18, a tungsten (W) layer 19, and a gold (Au) layer 20 are deposited in this order by a vacuum evaporation method, a sputtering method, or the like.

  The semiconductor light emitting device of the present invention is completed through the above steps.

  In the manufacturing method of the present invention, a good ohmic contact can be obtained by first forming and sintering an n-side electrode prior to the formation of the p-side electrode. This is because the optimum sintering temperature for the contact metal of the n-side electrode used in the present invention is higher than the optimum heat treatment temperature for the p-side electrode. That is, the sintering temperature of the n-side electrode in step S4 is 800 ° C. or higher, whereas the heat treatment temperatures in steps S6, S9, and S10 are all 800 ° C. or lower. Therefore, as shown in FIG. 2, by performing the formation and sintering of the n-side electrode first, an excessive heat treatment is not applied to the p-side electrode.

  In addition, according to the manufacturing method of the present invention, the p-side ohmic contact and adhesion strength can be further improved by performing annealing in a reducing atmosphere in steps S6 and S10 after the p-side electrode is deposited. it can. This is contrary to the facts that have been reported so far regarding nitride-based semiconductors, and is an experimental fact that the present inventor has independently known. That is, conventionally, it has been reported that when a p-type nitride semiconductor is heat-treated in a hydrogen atmosphere, p-type dopants such as magnesium (Mg) contained in the semiconductor are inactivated by the action of hydrogen. It was. When such inactivation occurs, the acceptor concentration of the p-type semiconductor decreases, and the ohmic contact should have deteriorated.

  On the other hand, when the present inventor first deposits a p-side electrode layer on a p-type nitride semiconductor and then heat-treats it in an atmosphere containing hydrogen, ohmic contact and adhesion strength are obtained. I found a significant improvement. Qualitatively, the p-type semiconductor layer is covered with an electrode layer, thereby interposing between the semiconductor layer and the electrode layer while suppressing inactivation of the p-type dopant in the p-type semiconductor layer. This is presumably because oxides and the like can be reduced and removed.

  FIG. 3 is a graph showing the current-voltage characteristics on the p-side electrode side of the light-emitting element prototyped by the inventors. Here, the p-side electrodes had a width of 100 μm and an interval of 20 μm. In FIG. 3, “present invention A” is an element using silver (Ag) as a p-side contact metal and annealed at 500 ° C. for 10 minutes in a nitrogen gas atmosphere containing hydrogen. In addition, what is expressed as “Invention B” is an element that uses silver as a p-side contact metal and is not annealed in an atmosphere containing hydrogen. Also, what is expressed as “conventional example” is an element that uses gold (Au) as a p-side contact metal and is not annealed in an atmosphere containing hydrogen.

  From FIG. 3, it can be seen that using silver as the p-side contact metal lowers the contact resistance than before, and further lowers the contact resistance by annealing in an atmosphere containing hydrogen. Similar improvements were obtained when using a mixture of silver and gold or nickel as the contact metal.

  On the other hand, FIG. 4 is a graph showing the current-voltage characteristics on the n-side electrode side of the light-emitting element prototyped by the present inventors. Here, the interval between the n-side electrodes was 350 μm. In FIG. 4, “present invention” is an element using hafnium (Hf) as an n-side electrode layer and tungsten (W) as a barrier layer. In addition, what is expressed as “conventional example” is an element using aluminum (Al) as a p-side contact metal and platinum (Pt) as a barrier layer.

  From FIG. 4, it can be seen that according to the present invention, the contact resistance is significantly reduced as compared with the prior art. Similar effects were obtained when aluminum (Al) or titanium (Ti) was used for the contact layer.

  The structure of the layer in the vicinity of the contact on the p side or the n side is, for example, a structure in which InAlGaN layers and AlGaN layers are alternately stacked as shown in the enlarged view of the main part in FIG. It is good also as a structure which laminated | stacked alternately.

  InGaN and AlGaN produce strains in opposite directions with respect to GaN, so that such a laminated structure can compensate for the strains.

  In addition, in the nitride-based semiconductor layer having a thickness of 100 nm or less, it is easy to form a high carrier concentration layer, and when a plurality of layers are formed, the vicinity of the interface (particularly between the layer containing In or Al and the GaN layer). Therefore, high-concentration magnesium (Mg) as a p-type impurity or high-concentration silicon (Si) as an n-type impurity tends to concentrate. When a predetermined heat treatment is performed after depositing the p-side electrode and n-side electrode, the electrode metal reacts with the plurality of nitride-based semiconductor layers, and high-concentration magnesium near the interface between these layers (p-side) In addition, silicon (n-side) and the electrode metal also cause a good reaction, and an electrode contact with good ohmic characteristics can be formed.

  At this time, as will be described later with reference to the second embodiment, if there is an unevenness that penetrates a plurality of nitride-based semiconductor layers, the reaction between the electrode metal and the semiconductor layer can be further promoted efficiently. .

  Next, a second embodiment of the present invention will be described.

  FIG. 5 is a conceptual diagram showing a cross-sectional structure of a light emitting device according to the second embodiment of the present invention. About the same figure, about the structure same as FIG. 1, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted. In the present embodiment, at the p-side and n-side electrode contact portions, the surface portion of the semiconductor is partially etched away and processed into an uneven shape. The p-side and n-side electrode layers are formed on the surface of the uneven semiconductor. When the surface of the semiconductor of the contact portion is processed to be uneven as described above, the contact area with the electrode increases, and the contact resistance can be further reduced. Also, the peel strength of the electrode increases. Furthermore, the unevenness formed on the p side improves the extraction efficiency of the light emitted from the light emitting portion to the outside. That is, the nitride-based semiconductor has a very high refractive index of about 2.67. Therefore, of the light emitted from the light emitting layer, the light that reaches the surface of the p-type contact layer is totally reflected except for light that is incident at an angle close to vertical. On the other hand, according to the present embodiment, by forming irregularities on the surface portion of the p-type contact layer, it is possible to increase the components that are scattered several times and finally taken out.

Next, a third embodiment of the present invention will be described.
FIG. 6 is a conceptual diagram illustrating a cross-sectional configuration of a light emitting device according to a third embodiment of the present invention. Also in this figure, the same parts as those described above with reference to FIG.

  The light emitting element of this embodiment has a configuration for extracting light to the outside through the substrate 1.

  In this embodiment, since both the p-side electrode and the N-side electrode are formed up to the bonding gold (Au) layer at a time, the titanium (Ti) layer 18 as the adhesive layer of the overcoat electrode layer is formed. It has no composition.

  Further, since light is not extracted through the p-side electrode, the p-side electrode does not necessarily have translucency and can be formed thick.

  Next, a fourth embodiment of the present invention will be described.

  FIG. 7 is a conceptual diagram showing a cross-sectional configuration of a light emitting device according to a fourth embodiment of the present invention. Also in this figure, the same parts as those described above with reference to FIG. In this embodiment, a translucent electrode 23 made of ITO (indium tin oxide) is laminated on the surface of the p-side electrode. The p-side overcoat electrode, that is, the bonding electrode, is formed of a nickel (Ni) layer 18 ′ and a gold (Au) layer 20.

  According to the present embodiment, by laminating ITO, the current supplied to the bonding electrode is spread in the in-plane direction within the layer of the transparent electrode 23 made of ITO, and injected through the p-side electrode, Light emission having a uniform intensity distribution can be obtained.

  This effect is particularly effective when the p-side electrode metal is formed in an island shape instead of a layer shape, and a current from the bonding electrode can be efficiently passed in the in-plane direction.

  The nickel layer 18 ′ has good adhesion strength to the transparent electrode 23 made of ITO, and can solve the problem that the overcoat layer on the ITO transparent electrode 23, that is, the bonding electrode is peeled off.

  In the present embodiment, since the transparent electrode 23 acts as a barrier against gold (Au), the tungsten (W) layer is not necessarily required. As shown in the figure, the nickel (Ni) layer 18 ′ and the gold (Au) Only layer 20 is sufficient. Alternatively, only gold (Au) 20 may be used. However, if a barrier layer is provided according to the film thickness and film quality of the transparent electrode 23, the diffusion of gold (Au) can be prevented and the reliability can be further improved. According to the study of the present inventor, it was found that tungsten (W) or platinum (Pt) is particularly suitable as the barrier layer in this case. That is, when a tungsten (W) layer or a platinum (Pt) layer is provided between the nickel layer 18 ′ and the gold layer 20, it is possible to effectively prevent gold diffusion and further improve the reliability of the light emitting element. it can. In addition to these, it has been found that good results can be obtained even when any one of molybdenum (Mo), titanium (Ti), and tantalum (Ta) is used as the barrier layer.

  As a result of repeating trial manufacture examination about the formation process of the ITO transparent electrode 23 in this embodiment, this inventor discovered the process from which a very favorable result is obtained. That is, the light emitting element of this embodiment can be obtained by forming the p-side contact electrodes 10 to 12 and performing the hydrogen annealing, and then forming the transparent electrode 23.

Referring to FIG. 2 described above, first, after hydrogen annealing treatment S6 or S10, ITO is deposited by sputtering or the like. Next, annealing is performed in an atmosphere containing oxygen. This annealing has been found to significantly improve the adhesion strength between the ITO layer and the metal electrode layer. Furthermore, the sheet resistance of ITO can be reduced by this annealing. In order to reliably obtain an improvement in adhesion strength and a decrease in sheet resistance, in an atmosphere containing 5 to 70% oxygen by weight percentage in an inert gas such as nitrogen (N ₂ ) or argon (Ar), It is desirable to anneal at a temperature in the range of 300 to 600 ° C., more preferably 300 to 500 ° C. At the same time, it is desirable that the annealing temperature of the ITO layer be lower than the processing temperature of the hydrogen annealing process S6 or S10 so as not to affect the previous process.

  After this annealing step, as shown in FIG. 2, the light emitting device of this embodiment is completed by executing step S7 or step S11 of forming an overcoat layer, that is, a bonding electrode.

  The configuration relating to the ITO transparent electrode 23 and the manufacturing method thereof in the present embodiment are not necessarily limited to light-emitting elements made of nitride-based semiconductors, and can be similarly applied to other various application examples. For example, the present invention can be similarly applied to a light emitting element using an InGaAlP-based or AlGaAs-based material formed on a GaAs substrate or a semiconductor element using an InP-based or InGaAs-based material formed on an InP substrate. That is, by using nickel as the metal layer to be brought into contact with the ITO electrode, the adhesion strength between the two can be improved and the reliability of the element can be improved.

  In addition, by performing annealing in an atmosphere containing oxygen, the sheet resistance of ITO can be reduced, and the adhesion strength with the metal layer or semiconductor layer can be further improved.

  For example, in an InGaAlP-based or InP-based light-emitting element, it is often necessary to perform an n-side sintering process after forming a transparent electrode on the p-side. In such a case, according to the configuration and the manufacturing method of the present invention, it is possible to prevent the increase of the sheet resistance of ITO, and rather to reduce the sheet resistance and improve the adhesion strength. .

  On the other hand, as the translucent electrode 23 of the present embodiment, various metal oxides such as indium, tin, and titanium can be similarly used in addition to ITO.

  The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples.

  For example, the structure of the n-side electrode is not limited to the specific example shown in the drawing, and any one of hafnium (Hf), titanium (Ti), and aluminum (Al) may be formed on the n-type contact layer. Alternatively, the same effect can be obtained with any structure in which a contact layer made of these alloys is provided, a barrier layer made of tungsten is provided thereon, and a bonding pad made of gold (Au) is provided thereon. .

  Further, the structure of the light emitting element may be, for example, a so-called “double hetero structure” in which an active layer is sandwiched between clad layers, or a superlattice may be used for an active layer, a clad layer, or the like. Furthermore, the same effect can be obtained by similarly applying not only to the light emitting diode but also to various semiconductor lasers.

Also, the substrate used is not limited to sapphire, and other examples include insulating substrates such as spinel, MgO, ScAlMgO ₄ , LaSrGaO ₄ , (LaSr) (AlTa) O ₃ , SiC, GaN, Si Each effect can be obtained by using a conductive substrate such as GaAs in the same manner. In particular, for GaN, for example, a GaN layer that has been grown thick on a sapphire substrate by a hydride vapor phase growth method or the like can be peeled off from the substrate and used as a GaN substrate.

In the case of a ScAlMgO ₄ substrate, it is desirable to use the (0001) plane, and in the case of a (LaSr) (AlTa) O ₃ substrate, the (111) plane is used.

  Furthermore, the present invention can be similarly applied to a semiconductor element having at least one of a p-side electrode and an n-side electrode to obtain the same effect. For example, the present invention is not necessarily limited to a light-emitting element, and can be similarly applied to various electronic elements such as FET (field effect transistor).

  The present invention is implemented in the form as described above, and has the effects described below.

  First, according to an embodiment of the present invention, as a contact metal in contact with a p-type contact layer, either ohmic contact with the p-type contact layer is achieved by using either silver or a mixture of silver and gold. It can be greatly improved.

  According to one embodiment of the present invention, by providing a tungsten layer on the n-side contact metal layer on the n-side of the element, ohmic contact can be improved while maintaining the barrier effect. That is, unlike platinum (Pt) conventionally used as a barrier layer, it effectively acts as a barrier layer without deteriorating ohmic contact, and long-term reliability is ensured.

  According to an embodiment of the present invention, when the tungsten layer is used as the barrier layer, any one of the above-described hafnium (Hf), titanium (Ti), or aluminum (Al) is used as the contact metal. Particularly good results are obtained when used.

  Moreover, according to the manufacturing method of one embodiment of the present invention, good ohmic contact can be obtained by forming and sintering the n-side electrode prior to the formation of the p-side electrode. This is because the optimum sintering temperature for the contact metal of the n-side electrode used in the present invention is higher than the optimum heat treatment temperature for the p-side electrode. That is, by performing the formation and sintering of the n-side electrode first, an excessive heat treatment is not applied to the p-side electrode.

  In addition, according to the manufacturing method of one embodiment of the present invention, the p-side ohmic contact and adhesion strength can be further improved by annealing in a reducing atmosphere after depositing the p-side electrode. . This is contrary to the facts that have been reported so far regarding nitride-based semiconductors, and is an experimental fact that the present inventor has independently known. Thus, when annealing is performed in a reducing atmosphere, even when nickel (Ni) is used as the p-side contact metal, much better ohmic contact than before can be obtained.

  Further, according to one embodiment of the present invention, on the p-side or n-side, when a structure in which InAlGaN layers and AlGaN layers are alternately stacked, or a structure in which InGaN layers and AlGaN layers are alternately stacked, InGaN and Since AlGaN produces strains in opposite directions to GaN, such a laminated structure can compensate for the strains. In addition, in the nitride-based semiconductor layer having a thickness of 0.1 μm or less, it is easy to form a high carrier concentration layer. When a plurality of layers are formed, the vicinity of the interface between them (particularly between the layer containing In or Al and the GaN layer). In the meantime, high-concentration magnesium (Mg) as a p-type impurity or high-concentration silicon (Si) as an n-type impurity tends to concentrate. When a predetermined heat treatment is performed after depositing the p-side electrode and n-side electrode, the electrode metal reacts with the plurality of nitride-based semiconductor layers, and high-concentration magnesium near the interface between these layers (p-side) In addition, silicon (n-side) and the electrode metal also cause a good reaction, and an electrode contact with good ohmic characteristics can be formed.

  At this time, as will be described later with reference to the second embodiment, if there is an unevenness that penetrates a plurality of nitride-based semiconductor layers, the reaction between the electrode metal and the semiconductor layer can be further promoted efficiently. .

  Further, according to one embodiment of the present invention, when the semiconductor surface of the contact portion is processed to be uneven, the contact area with the electrode increases and the contact resistance can be further reduced. Also, the peel strength of the electrode increases. Furthermore, the unevenness formed on the p side improves the extraction efficiency of the light emitted from the light emitting portion to the outside.

  Furthermore, according to one embodiment of the present invention, by using nickel as the metal layer to be brought into contact with the ITO electrode, the adhesion strength between the two can be improved and the reliability of the element can be improved.

  Further, by providing a barrier layer made of tungsten or platinum between such a nickel layer and a gold layer, the diffusion of gold can be reliably prevented.

  In addition, according to an embodiment of the present invention, after depositing ITO, annealing is performed in an atmosphere containing oxygen, thereby reducing the sheet resistance of ITO and further increasing the adhesion strength with a metal layer or a semiconductor layer. It can also be improved.

  As described above in detail, according to each embodiment of the present invention, it is possible to provide a light emitting device that has improved ohmic contact as compared with the related art, and at the same time, improved reliability and adhesion strength of electrodes. The benefits are tremendous.

It is a schematic sectional drawing showing the semiconductor light-emitting device concerning the 1st Embodiment of this invention. It is a flowchart showing the principal part of the manufacturing method of the light emitting element of this invention. It is a graph showing the current-voltage characteristics on the p-side electrode side of the light-emitting element made by the present inventor. It is a graph showing the current-voltage characteristics on the n-side electrode side of the light-emitting element made by the present inventor. It is a conceptual diagram showing the cross-sectional structure of the light emitting element concerning the 2nd Embodiment of this invention. It is a conceptual diagram showing the cross-sectional structure of the light emitting element concerning the 3rd Embodiment of this invention. It is a conceptual diagram showing the cross-sectional structure of the light emitting element concerning the 4th Embodiment of this invention. It is a schematic sectional drawing showing the structure of the conventional light emitting diode using a nitride-type semiconductor.

Explanation of symbols

1 Sapphire substrate 2 n-type GaN layer 3 n-type AlGaN contact layer 4 n-type GaN contact layer 5 n-type GaN layer 6 p-type GaN layer 7 p-type AlGaN contact layer 8 p-type InGaN contact layer 9 p-type GaN contact layer 10 1 metal layer 11 second metal layer 12 tungsten (W) layer 13 block layer 14 hafnium (Hf) layer 15 aluminum (Al) layer 16 hafnium (Hf) layer 17 gold (Au) layer 18 titanium (Ti) layer 19 Tungsten (W) layer 20 Gold (Au) layer 22 Protective film 101 Sapphire substrate 102 n-type GaN layer 106 p-type GaN layer 113 Insulating layer 121 Transparent electrode 122 n-side electrode 123 Bonding pad

Claims (8)

a first layer made of a p-type nitride-based semiconductor;
a second layer made of an n-type nitride-based semiconductor;
A p-side electrode provided in contact with the first layer;
An n-side electrode provided in contact with the second layer;
With
The p-side electrode has a contact layer provided in contact with the first layer and containing silver (Ag), and a layer made of tungsten (W) provided on the contact layer. A semiconductor light emitting device characterized.   2. The semiconductor light emitting element according to claim 1, wherein a translucent conductive film made of a metal oxide is provided on the tungsten (W) layer. An overcoat layer provided on the translucent conductive film;
The overcoat layer is
The semiconductor light emitting element according to claim 1, further comprising a layer made of nickel (Ni) provided in contact with the translucent conductive film. a first layer made of a p-type nitride-based semiconductor;
a second layer made of an n-type nitride-based semiconductor;
A p-side electrode provided in contact with the first layer;
An n-side electrode provided in contact with the second layer;
With
The n-side electrode is provided in contact with the second layer, and is a contact layer made of one of hafnium (Hf), aluminum (Al), and titanium (Ti) or an alloy containing at least one of these elements. And a barrier layer made of tungsten (W) provided on the contact layer, and a bonding pad layer made of gold (Au) provided on the barrier layer. Light emitting element. The first layer includes a plurality of layers containing a p-type dopant and having a layer thickness of 100 nm or less,
5. The semiconductor light-emitting element according to claim 1, wherein each of the plurality of layers is made of a nitride-based semiconductor having a composition different from that of an adjacent layer. The second layer is composed of a plurality of layers containing an n-type dopant and having a layer thickness of 100 nm or less.
6. The semiconductor light emitting element according to claim 1, wherein each of the plurality of layers is made of a nitride semiconductor having a composition different from that of an adjacent layer.   The semiconductor light emitting element according to any one of claims 1 to 6, wherein at least one of the first layer and the second layer is provided with irregularities on a surface in contact with the electrode. . A light emitting layer made of a semiconductor;
A translucent conductive film made of a metal oxide and having translucency with respect to light emitted from the light emitting layer;
A layer made of nickel (Ni) provided in contact with the translucent conductive film;
A semiconductor light emitting device comprising:

Images