JP2000164928A - Semiconductor light emitting device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve ohmic characteristic by forming, in a p-side electrode, a contact layer which includes silver, in contact with a layer made of p-type nitride semiconductor and forming a layer made of tungsten on the contact layer. SOLUTION: A p-side electrode is constituted of a light transmitting electrode and a bonding pad section. More specifically, a block layer 13 comprising at least SiO2 is selectively formed on a p-type GaN contact layer 9 and then a light transmitting electrode stacked with a first metal layer 10, second metal layer 11, and tungsten layer 12 is formed on the rest of the surface, As the first metal layer 10, silver is preferably used. As the second metal layer 11, gold is preferably used. By using either silver or a mixture of silver and gold for contact metal to be brought into contact with the p-type contact layer 9, an ohmic contact with the p-type contact layer 9 can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 element in which a nitride-based semiconductor layer such as GaN, InGaN, and GaAlN is stacked on a substrate, the semiconductor light-emitting element having an electrode with low contact resistance and high reliability. It relates to the manufacturing method.

[0002]

2. Description of the Related Art Light emitting devices in a wavelength band from ultraviolet light to blue and green have been put to practical use by using a nitride semiconductor represented by gallium nitride.

[0003] Incidentally, the term "nitride semiconductor" in the present _{application, B x In y Al z Ga} (1-xyz) N (0 ≦ x ≦ 1,0 ≦
y ≦ 1, 0 ≦ z ≦ 1) containing a III-V compound semiconductor, and as a V-group element, phosphorus (P) in addition to N
It also includes mixed crystals containing arsenic (As) or arsenic.

By forming a light-emitting device such as a light-emitting diode (LED) or a semiconductor laser using a nitride-based semiconductor, light emission such as ultraviolet light, blue light, green light, etc., having high emission intensity, which has been difficult until now, can be achieved. It is becoming possible. In addition, since nitride-based semiconductors have a high crystal growth temperature and are stable materials even at high temperatures, application to electronic devices is also expected.

Hereinafter, a light emitting device will be described as an example of a semiconductor device using a nitride 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) on the sapphire substrate 101,
The n-type GaN layer 102 and the p-type GaN layer 106 are crystal-grown, a part of the p-type GaN layer 106 is removed by etching, and the n-type GaN layer 102 is exposed. p-type GaN layer 6
Above the p-side transparent electrode (Au) 121, under the p-side bonding electrode, an insulating film 113 for blocking a current,
P-side bonding electrode 1 connected to side transparent electrode 121
23 (Ti / Au) are formed, and an n-side electrode 122 (Al / Au) is formed on the n-type GaN layer.

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

[0008]

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

In addition, since the nitride-based semiconductor is difficult to perform chemical wet etching, it is difficult to perform a surface treatment before forming an electrode, and the ohmic characteristics are greatly affected by the surface condition of the interface between the electrode and the semiconductor layer. There was also a problem in the process.

The present invention has been made in view of the above 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 of manufacturing the same. .

[0011]

To achieve the above object, a semiconductor light emitting device of the present invention comprises a first layer made of a p-type nitride semiconductor and a second layer made of an n-type nitride 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 And a contact layer containing silver (Ag) and a layer made of tungsten (W) provided on the contact layer. Ohmic contact can be ensured.

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

[0013] Further, an overcoat layer is further provided on the translucent conductive film, and the overcoat layer is a layer made of nickel (Ni) provided in contact with the translucent conductive film. , The adhesive strength between the light-transmitting conductive film and the overcoat layer can be improved.

Alternatively, in the semiconductor light emitting device according to the present invention, the first layer made of a p-type nitride semiconductor, the second layer made of an n-type nitride semiconductor, and the first layer are in contact with each other. A p-side electrode provided in contact with the second layer, and an n-side electrode provided in contact with the second layer, wherein the n-side electrode is provided in contact with the first layer; A contact layer made of any one of Hf), aluminum (Al) and titanium (Ti), a barrier layer made of tungsten (W) provided on the contact layer, and provided on the barrier layer And a bonding pad layer made of gold (Au), whereby a good ohmic contact can be ensured on the n-side, and the barrier layer works effectively to ensure reliability.

In a preferred embodiment of the present invention, the first layer contains a p-type dopant and has a thickness of 100 n.
m, and the plurality of layers are characterized in that adjacent layers are made of nitride-based semiconductors having different compositions from each other, and can further improve ohmic contact.

Here, the second layer comprises a plurality of layers containing an n-type dopant and having a thickness of 100 nm or less,
It is preferable that the plurality of layers be made of a nitride-based semiconductor in which adjacent layers have different compositions.

Further, if at least one of the first layer and the second layer is provided with irregularities on the surface in contact with the electrode, the contact area with the electrode is enlarged to increase the contact resistance. And the adhesive strength of the electrode can be improved.

According to another aspect of the present invention, there is provided a semiconductor light-emitting device comprising: a light-emitting layer made of a semiconductor; a light-transmitting conductive film made of a metal oxide and having a property of transmitting light emitted from the light-emitting layer; Nickel (N) provided in contact with the light-transmitting conductive film
i) a semiconductor light-emitting device using not only a nitride-based semiconductor but also various material systems such as InGaAlP-based and InP-based and having a light-transmitting conductive film. The adhesive strength between the light-transmitting conductive film and the metal layer can be improved.

On the other hand, a method of manufacturing a semiconductor light emitting device according to the present invention comprises a step of forming a laminate having an n-type layer made of an n-type nitride semiconductor and a p-type layer made of a p-type nitride semiconductor. Forming a p-side contact electrode layer on the surface of the p-type layer of the laminate, and performing a heat treatment in an atmosphere containing a reducing gas.
Good ohmic contact can be obtained on the side.

Alternatively, in the method of manufacturing a semiconductor light emitting device according to the present invention, a step of forming a stacked body having an n-type layer made of an n-type nitride semiconductor and a p-type layer made of a p-type nitride semiconductor Forming an n-side contact electrode layer on the surface of the n-type layer of the laminate, performing a heat treatment at a first temperature, and forming a p-side contact electrode layer on the surface of the p-type layer of the laminate. And a step of performing a heat treatment at a second temperature lower than the first temperature in an atmosphere containing a reducing gas, whereby a good ohmic contact can be obtained. .

Here, as a preferred embodiment of the present invention, the n-side contact electrode layer is formed of hafnium (H
f), aluminum (Al) and titanium (Ti) can provide a good n-side ohmic.

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.

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

Alternatively, in the method for manufacturing a semiconductor light emitting device according to the present invention, a step of forming a semiconductor laminate including a light emitting layer and a step of forming a translucent conductive film made of a metal oxide on the semiconductor laminate And a step of heat-treating the light-transmitting conductive film in an atmosphere containing oxygen. The method is not limited to nitride-based semiconductors.
In a semiconductor light-emitting element using various semiconductors such as an nP-based semiconductor and having a light-transmitting conductive film, the sheet resistance of the light-transmitting conductive film can be reduced and the adhesive strength can be increased.

[0025]

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

The p-side electrode is connected to a light-transmitting electrode and a bonding electrode.
And a pad section. 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, for example, the first metal layer 10 / the second metal layer 11 is formed on the remaining surface. / Tungsten (W) layer 12 is laminated to form a translucent electrode.

The block layer 13 has a function of blocking a current so as not to generate extra light emission under the bonding pad. The thickness of each layer of the translucent electrode is extremely small, so that light emitted from the light emitting element is transmitted without being absorbed much.

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

On the block layer 13, a titanium (Ti) layer 18, a tungsten (W) layer 19, and a gold (Au) layer 20 are deposited in this order while being partially connected to the translucent electrode layer. Bonding pads are 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, on the n-type contact layer 4, an n-side electrode is formed. That is, hafnium (Hf)
Layer 14 / aluminum (Al) layer 15 / hafnium (H
f) layer 16 / gold (Au) layer 17 are deposited in this order;
Further thereon, a bonding pad portion in which a titanium (Ti) layer 18, a tungsten (W) layer 19, and a 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 intrusion of gold (Au) into the semiconductor, the thickness of the gold (Au) layer 17 is desirably formed relatively thin or may be omitted.

The titanium layer 18 functions 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 and the like.

The illustrated structure of the n-side electrode layer is merely an example. In the present invention, the metal layer in contact with the n-type contact layer 4 is any of 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 operation by the configuration described above.

That is, according to the present invention, first, by using either silver or a mixture of silver and gold as the contact metal contacting the p-type contact layer 9, the contact metal with the p-type contact layer 9 is formed. Ohmic contact can be greatly improved. As a result of an independent study, the present inventor has come to realize that when these metals are brought into contact with the semiconductor layer, particularly the contact resistance can be reduced. This is considered to be because the addition of silver facilitates the reaction with the p-type contact layer 9.

According to the present invention, the ohmic contact is improved while maintaining the barrier effect by providing the tungsten layer 19 as a barrier layer on the n-side contact metal layer on the n-side of the device. Can be. That is, the barrier layer has an effect of preventing mutual diffusion between the n-side contact metal and the bonding pad and maintaining reliability. Conventionally, platinum (Pt) has often been used as the barrier layer of the n-side electrode. However, when platinum enters the nitride semiconductor, it acts as a p-type dopant. Therefore, platinum is diffused into the n-type contact layer during a heat-up process such as heat treatment, solder mounting, or wire bonding after the formation of the bonding pad, thereby deteriorating ohmic contact.

On the other hand, the present inventor has discovered that the use of a tungsten layer as the barrier layer of the n-side electrode ensures long-term reliability without deteriorating ohmic contact. When a tungsten layer is used as the barrier layer, the above-described hafnium (Hf) and titanium (Ti) are used as contact metals.
It was also found that particularly good results were obtained when using either aluminum (Al).

Further, 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, a method for manufacturing the light emitting device of the present invention will be described.
FIG. 2 is a flowchart showing a main part of the method for manufacturing a light emitting device of the present invention. First, as shown in step S1, semiconductor layers 2 to 9 are sequentially grown on the sapphire substrate 1. The crystal growth of each layer is performed, for example, by MOCVD.
(Metal-organic chemical vapor deposition), hydride CVD, MBE (molecular beam depositio)
n) and the like.

Next, as shown in step S2, the p-type layer is etched. That is, the layers 6 to 9 made of the p-type semiconductor are selectively etched to expose the n-type GaN layer 4. Specifically, for example, PEP (photo-engrav
RIE (reacting process)
The etching is performed by an etching method such as ive ion etching.

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

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

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, a second metal layer 11, a tungsten (W) layer 12, and the like are sequentially deposited on the p-type contact layer 9 by a vacuum deposition method, a sputtering method, or the like. Here, as described above, the first metal layer 10
It is either silver, a mixture of silver and gold, or nickel. In the case of silver, its thickness is desirably about 0.5 to 10 nm. When a mixture of silver and gold is used, the ratio of silver is preferably about 1 to 20 atomic%, and the thickness of the mixture layer is preferably about 0.5 to 10 nm. In the case of nickel, its thickness is
It is desirable that the thickness be 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 0.1%.
It is desirable to be in the range of about 5%. Further, the annealing temperature is desirably set to 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, in a nitrogen atmosphere, at least 600 ° C. and 800 ° C.
Heat treatment is performed at the following temperature. The heat treatment is, for example, 750
C. for about 20 seconds.

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

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

Through the above steps, the semiconductor light emitting device of the present invention is completed.

In the manufacturing method of the present invention, a good ohmic contact can be obtained by forming an n-side electrode and sintering first before forming a 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 sinter temperature of the n-side electrode in step S4 is 800 ° C.
In contrast, the heat treatment temperatures in steps S6, S9, and S10 are all 800 ° C. or less. Therefore, by performing the formation and sintering of the n-side electrode first as shown in FIG. 2, an excessive heat treatment is not applied to the p-side electrode.

According to the manufacturing method of the present invention, after the p-side electrode is deposited, annealing is performed in a reducing atmosphere in steps S6 and S10 to further improve the p-side ohmic contact and adhesion strength. can do.
This is contrary to the fact that has been conventionally reported on nitride-based semiconductors, and is an experimental fact that the present inventors independently learned. That is, conventionally, when a p-type nitride-based semiconductor is heat-treated in a hydrogen atmosphere, the action of hydrogen causes
It has been reported that a p-type dopant such as magnesium (Mg) contained in a semiconductor is inactivated. If such passivation occurs, the ohmic contact should deteriorate because the acceptor concentration of the p-type semiconductor decreases.

On the other hand, the present inventor has found that a p-side electrode layer is first deposited on a p-type nitride-based semiconductor and then heat-treated in an atmosphere containing hydrogen to obtain ohmic contact. It has been found that the bond strength is greatly improved. This qualitatively covers the upper surface of the p-type semiconductor layer with the electrode layer, so that the p-type semiconductor layer is interposed between the semiconductor layer and the electrode layer while suppressing the inactivation of the p-type dopant in the p-type semiconductor layer. This is presumed to be because oxides and the like can be reduced and removed.

FIG. 3 is a graph showing the p-values of the light-emitting device prototyped by the present inventors.
FIG. 9 is a graph showing current-voltage characteristics on the side electrode side. Here, the p-side electrode had a width of 100 μm and an interval of 20 μm.
In FIG. 3, a device represented by “Invention A” is a device using silver (Ag) as a p-side contact metal and annealing at 500 ° C. for 10 minutes in a nitrogen gas atmosphere containing hydrogen. Further, the device described as "Invention B" is a device which uses silver as a p-side contact metal and is not annealed in an atmosphere containing hydrogen. Further, what is referred to as “conventional example” is gold (Au) as the p-side contact metal.
Is an element which is not subjected to annealing in an atmosphere containing hydrogen.

FIG. 3 shows that the use of silver as the contact metal on the p-side lowers the contact resistance as compared with the conventional one, and that the contact resistance is further reduced 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 current-voltage characteristics on the n-side electrode side of a light-emitting element prototyped by the present inventors.
Here, the interval between the n-side electrodes was 350 μm. In FIG. 4, what is described as “the present invention” is an element using hafnium (Hf) as the n-side electrode layer and using tungsten (W) as the barrier layer. Further, what is referred to as “conventional example” indicates that aluminum (A) is used as a p-side contact metal.
1) and an element using platinum (Pt) as a barrier layer.

FIG. 4 shows that according to the present invention, the contact resistance is greatly reduced as compared with the prior art. A similar effect is
Aluminum (Al) or titanium (T
It was also obtained when i) was used.

The structure of the layer near the contact on the p-side or n-side may be, for example, a structure in which an InAlGaN layer and an AlGaN layer are alternately laminated as shown in an enlarged view of a main part in FIG. A structure in which AlGaN layers are alternately stacked may be employed.

Since InGaN and AlGaN produce strains in the opposite directions to GaN, strains can be compensated for in such a laminated structure.

In the case of a nitride-based semiconductor layer having a thickness of 100 nm or less, a high carrier concentration layer can be easily formed. ), High-concentration magnesium (Mg) as a p-type impurity or high-concentration silicon (Si) as an n-type impurity is likely to concentrate. p-side electrode or n
When a predetermined heat treatment is performed after the side electrode is deposited, the electrode metal and the plurality of nitride-based semiconductor layers react with each other, and furthermore, a high concentration of magnesium (p-side) or silicon (n-side) near the interface between the layers. ) 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 respect to the second embodiment, if there are irregularities penetrating a plurality of nitride-based semiconductor layers, the reaction between the electrode metal and the semiconductor layers is further efficiently promoted. be able to.

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

FIG. 5 is a conceptual diagram showing a sectional structure of a light emitting device according to a second embodiment of the present invention. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description is omitted. In the present embodiment, the surface portion of the semiconductor is partially etched away at the p-side and n-side electrode contact portions, and is 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 in the contact portion is processed into an uneven shape in this manner, the contact area with the electrode increases, and the contact resistance can be further reduced. Also, the peel strength of the electrode increases. further,
Due to the unevenness formed on the p-side, the efficiency of extracting light emitted from the light emitting portion to the outside is improved. That is,
The nitride-based semiconductor has an extremely high refractive index of about 2.67. Therefore, of the light emitted from the light emitting layer, p
Light arriving at the surface of the mold contact layer is totally reflected except for light 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, light can be scattered several times, and the component finally extracted to the outside can be increased.

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 portions as those described above with reference to FIG. 1 are denoted by the same reference numerals, and detailed description is omitted.

The light emitting device of the present embodiment has a configuration in which light is extracted outside through the substrate 1.

In the present embodiment, the p-side electrode,
Since both the N-side electrode and the gold (Au) layer for bonding are formed at one time, there is no titanium (Ti) layer 18 which is an adhesive layer of the overcoat electrode layer.

In addition, since light is not extracted through the p-side electrode, the p-side electrode does not necessarily need to have a light-transmitting property, and can be formed to have a large thickness.

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

FIG. 7 is a conceptual diagram showing a sectional structure of a light emitting device according to a fourth embodiment of the present invention. Also in this figure, the same portions as those described above with reference to FIG. 1 are denoted by the same reference numerals, and detailed description is omitted. In this embodiment,
Translucent electrode 23 made of ITO (indium tin oxide)
Is laminated on the surface of the p-side electrode. The p-side overcoat electrode or bonding electrode is made of nickel (N
i) It is formed by the layer 18 'and the gold (Au) layer 20.

According to the present embodiment, the current supplied to the bonding electrode is reduced by stacking ITO.
By spreading in the in-plane direction in the layer of the transparent electrode 23 made of and injecting through the p-side electrode, light emission having a uniform intensity distribution in the plane 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 the current from the bonding electrode can flow efficiently in the in-plane direction.

The nickel layer 18 'has a good adhesion strength to the transparent electrode 23 made of ITO.
The problem that the overcoat layer on the transparent electrode 23, that is, the bonding electrode is peeled off can be solved.

In this embodiment, since the transparent electrode 23 acts as a barrier against gold (Au), a tungsten (W) layer is not necessarily required, and as shown in FIG. Only the gold (Au) layer 20 is sufficient. Alternatively, only gold (Au) 20 may be used. However,
When a barrier layer is provided in accordance with the thickness and quality of the transparent electrode 23, diffusion of gold (Au) can be prevented, and the reliability can be further improved. According to the study by the present inventors, the barrier layer in this case is made of tungsten (W) or platinum (P).
t) has proven to be particularly suitable. That is, if a tungsten (W) layer or a platinum (Pt) layer is provided between the nickel layer 18 'and the gold layer 20, the diffusion of gold can be effectively prevented and the reliability of the light emitting element can be further improved. it can. In addition, it was found that good results could be obtained by using any of molybdenum (Mo), titanium (Ti) and tantalum (Ta) as the barrier layer.

The present inventor has repeated trial and study on the process of forming the ITO transparent electrode 23 in the present embodiment, and as a result, has found a process which can obtain extremely good results. That is, to form the light emitting device of the present embodiment,
It is obtained by forming the p-side contact electrodes 10 to 12, performing hydrogen annealing, and then forming the transparent electrode 23.

Referring to FIG. 2 described above, first, after hydrogen annealing S6 or S10, ITO is deposited by sputtering or the like. Next, annealing is performed in an atmosphere containing oxygen. By this annealing,
It was found that the adhesion strength between the ITO layer and the metal electrode layer was significantly improved. Further, the sheet resistance of ITO can be reduced by this annealing. In order to reliably improve the adhesion strength and reduce the sheet resistance, in an atmosphere in which an inert gas such as nitrogen (N ₂ ) or argon (Ar) contains 5 to 70% by weight of oxygen in an atmosphere, 30
It is desirable to anneal at a temperature in the range of 0 to 600C, more preferably 300 to 500C. At the same time, the annealing temperature of the ITO layer is set so as not to affect the previous process.
It is desirable that the temperature be lower than the processing temperature of Step 6 or S10.

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

The configuration of the ITO transparent electrode 23 and the method of manufacturing the same in this embodiment are not necessarily limited to the light emitting device made of a nitride semiconductor, and can be similarly applied to other various applications. For example, G
InGaAlP or AlGa formed on aAs substrate
The same can be applied to a light emitting element using a material such as As or a semiconductor element using a material such as InP or InGaAs 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.

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

As an example, InGaAlP-based or InGaAlP-based
In a P-based light emitting device, it is often necessary to perform an n-side sintering step 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 sheet resistance of the ITO from increasing,
Rather, the effect of reducing the sheet resistance and improving the adhesive strength can be obtained.

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

The embodiment of the invention has been described with reference to 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. In addition, hafnium (Hf), titanium (Ti) or aluminum (Al) may be formed on the n-type contact layer. Or a structure in which a contact layer made of any 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. be able to.

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

The material used as the substrate is not limited to sapphire.
O, ScAlMgO ₄ , LaSrGaO ₄ , (LaSr)
Insulating substrate such as (AlTa) O ₃ , SiC, Ga
Each effect can be obtained by using a conductive substrate such as N, Si, or GaAs in the same manner. In particular, for GaN, for example, a GaN layer that has been grown thick on a sapphire substrate by hydride vapor phase epitaxy or the like can be peeled off from the substrate and used as a GaN substrate.

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

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

[0086]

The present invention is embodied in the form described above, and has the following effects.

First, according to the present invention, the use of either silver or a mixture of silver and gold as the contact metal in contact with the p-type contact layer greatly increases the ohmic contact with the p-type contact layer. Can be improved.

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

According to the present invention, when the tungsten layer is used as the barrier layer, the above-mentioned hafnium (Hf), titanium (T
Particularly good results are obtained when using either i) or aluminum (Al).

Further, according to the manufacturing method of the present invention, a good ohmic contact can be obtained by forming an n-side electrode and sintering it before forming a 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, it is not necessary to apply an excessive heat treatment to the p-side electrode.

According to the manufacturing method of the present invention, the p-side ohmic contact and the adhesion strength can be further improved by performing annealing in a reducing atmosphere after depositing the p-side electrode. This is contrary to the fact that has been conventionally reported on nitride-based semiconductors, and is an experimental fact that the present inventors independently learned. As described above, when annealing is performed in a reducing atmosphere, a much better ohmic contact than in the related art can be obtained even when nickel (Ni) is used as the p-side contact metal.

According to the present invention, when a structure in which an InAlGaN layer and an AlGaN layer are alternately stacked or a structure in which an InGaN layer and an AlGaN layer are alternately stacked is formed on the p-side or the n-side, InGaN and AlGaN Is G
Since strains are generated in the opposite directions with respect to aN, such a laminated structure makes it possible to compensate for the strain. In the case of a nitride-based semiconductor layer having a thickness of 0.1 μm or less, it is easy to form a high carrier concentration layer. During the interval, 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 the p-side electrode or the n-side electrode is deposited, the electrode metal reacts with the plurality of nitride-based semiconductor layers, and furthermore, a high concentration of magnesium (p-side) near the interface between the layers. Also, a favorable reaction occurs between silicon and silicon (n side) and the electrode metal, 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 are irregularities penetrating a plurality of nitride-based semiconductor layers, the reaction between the electrode metal and the semiconductor layers is further efficiently promoted. be able to.

Further, according to the present invention, when the surface of the semiconductor in the contact portion is processed into an uneven shape, the contact area with the electrode increases, and the contact resistance can be further reduced. Also, the peel strength of the electrode increases. Further, the efficiency of extracting light emitted from the light emitting portion to the outside is improved by the unevenness formed on the p-side.

Further, according to 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.

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.

Further, according to the present invention, after depositing ITO, annealing is performed in an atmosphere containing oxygen to reduce the sheet resistance of the ITO and further improve the adhesion strength to the metal layer and the semiconductor layer. You can also.

As described in detail above, according to the present invention, it is possible to provide a light emitting device having improved ohmic contact as compared with the conventional one, and at the same time, improved reliability and electrode adhesion strength. Is enormous.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating a semiconductor light emitting device according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a main part of a method for manufacturing a light emitting device of the present invention.

FIG. 3 is a graph showing current-voltage characteristics on a p-side electrode side of a light-emitting element prototyped by the present inventors.

FIG. 4 is a graph showing current-voltage characteristics on the n-side electrode side of a light-emitting element prototyped by the present inventors.

FIG. 5 is a conceptual diagram illustrating a cross-sectional structure of a light emitting device according to a second embodiment of the present invention.

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.

FIG. 7 is a conceptual diagram illustrating a cross-sectional configuration of a light emitting device according to a fourth embodiment of the present invention.

FIG. 8 is a schematic sectional view illustrating a structure of a conventional light emitting diode using a nitride-based semiconductor.

[Explanation of symbols]

 Reference Signs List 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

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Chiharu Nozaki 1 Komukai Toshiba Town, Saiwai-ku, Kawasaki City, Kanagawa Prefecture Inside Toshiba R & D Center (72) Inventor Chisato Furukawa Kawasaki-ku, Kawasaki City, Kanagawa Prefecture 7 No. 1 Nisshincho Toshiba Electronic Engineering Corporation F-term (reference) 4M104 AA04 BB02 BB05 BB08 BB13 BB14 BB36 CC01 DD34 DD37 DD79 FF17 GG04 HH15 5F041 AA21 CA02 CA03 CA34 CA40 CA46 CA83 CA88 CA92

Claims (14)

[Claims] A first layer made of a p-type nitride-based semiconductor; a second layer made of an n-type nitride-based semiconductor; and 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 provided in contact with the first layer and contains silver (Ag), A layer made of tungsten (W) provided on the contact layer. 2. The semiconductor light-emitting device according to claim 1, wherein a light-transmitting conductive film made of a metal oxide is provided on the layer made of tungsten (W). 3. The light-transmitting conductive film further includes an overcoat layer provided on the light-transmitting conductive film, wherein the overcoat layer includes nickel (N) provided in contact with the light-transmitting conductive film.
3. The semiconductor light-emitting device according to claim 1, comprising a layer comprising i). 4. A first layer made of a p-type nitride semiconductor, a second layer made of an n-type nitride semiconductor, and 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 n-side electrode is provided in contact with the first layer, and comprises hafnium (Hf), aluminum (Al), and A contact layer made of any of titanium (Ti); a barrier layer made of tungsten (W) provided on the contact layer; and a bonding layer made of gold (Au) provided on the barrier layer. And a pad layer. 5. The nitride semiconductor according to claim 1, wherein the first layer includes a plurality of layers containing a p-type dopant and having a thickness of 100 nm or less, and each of the plurality of layers has a different composition from an adjacent layer. 5. The method according to claim 1, wherein
The semiconductor light-emitting device according to any one of the above. 6. The second layer comprises a plurality of layers containing an n-type dopant and having a thickness of 100 nm or less, wherein each of the plurality of layers has a different composition from an adjacent layer. 6. The method according to claim 1, wherein
The semiconductor light emitting device according to any one of the above. 7. The semiconductor device according to claim 1, wherein at least one of the first layer and the second layer has an uneven surface provided in contact with the electrode. 13. The semiconductor light emitting device according to claim 1. 8. A light-emitting layer made of a semiconductor, 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; Nickel (Ni) provided
A semiconductor light-emitting device comprising: a layer comprising: 9. An n-type layer comprising an n-type nitride semiconductor and
Forming a stacked body having a p-type layer made of a nitride semiconductor of a type, forming a p-side contact electrode layer on a surface of the p-type layer of the stacked body, containing a reducing gas. A method of performing a heat treatment in an atmosphere, comprising: 10. A step of forming 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; A step of forming an n-side contact electrode layer on the surface; a step of heat treatment at a first temperature; a step of forming a p-side contact electrode layer on the surface of the p-type layer of the laminate; Performing a heat treatment at a second temperature lower than the first temperature in an atmosphere to be heated. 11. The n-side contact electrode layer is made of hafnium (Hf), aluminum (Al) and titanium (Ti).
The method for manufacturing a semiconductor light emitting device according to claim 10, wherein the method comprises: 12. The p-side contact electrode layer is formed of silver (A
12. The method according to claim 9, wherein the metal comprises nickel (g) or nickel (Ni).
5. A method for manufacturing a semiconductor light emitting device according to any one of the above. 13. The method according to claim 13, further comprising: forming a light-transmitting conductive film made of a metal oxide on the p-side contact electrode layer; and heat-treating the light-transmitting conductive film in an atmosphere containing oxygen. The method for manufacturing a semiconductor light emitting device according to any one of claims 9 to 12, comprising: 14. A step of forming a semiconductor laminate including a light-emitting layer, a step of forming a light-transmitting conductive film made of a metal oxide on the semiconductor laminate, and the step of forming the light-transmitting film in an oxygen-containing atmosphere. And b. Heat treating the conductive conductive film.