JPH11298040A - Semiconductor light-emitting element and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the sheet resistance, raise the thermal stability and raise the conductivity, even after a high temperature process by forming a higher melting point conductive film on a metal film to contact a nitride semiconductor than this metal and forming a dielectric film on the conductive film to form an ohmic electrode. SOLUTION: An n-electrode 112 is formed on a part of the exposed surface of an n-type GaN layer 103, a resist is coated to pattern it, an Ni or Pd metal film 109 is deposited on the part of a p-type GaN cap layer 108, a high melting point metal Mo conductive film 110 is formed thereon to form a p-electrode, an Au pad layer 111 is formed on a part of the p-electrode, an SiO2 dielectric film 113 is formed by sputtering, and the annealing is made in an inert gas at, e.g. 800 deg.C for 10 min to improve also the ohmic characteristic between a low resistance p-semiconductor of the p-layer of GaAs semiconductor and electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor light emitting device, and more particularly, to an electrode structure thereof and a manufacturing method thereof.

[0002]

2. Description of the Related Art In a conventional gallium nitride-based compound semiconductor light emitting device, an insulating substrate such as sapphire is used. In a light emitting element using this insulating substrate, it is difficult to provide a structure in which electrodes are provided on the back surface side, and a structure in which both pn electrodes are provided on the semiconductor layer side is employed.

FIG. 4 is a schematic diagram of a light emitting diode (LED) based on the prior art. 201 is a sapphire substrate, 202 is n-GaN: Si, 203 is an active layer, 20
4 is p-GaN: Mg, 205 is a Ni / Au translucent electrode formed on p-GaN, and 206 is RIBE (Rea).
An n-type electrode formed on the exposed n-GaN by etching by active ion beam etching, 207 is a bonding electrode pad formed on the Ni / Au translucent electrode, and 208 is SiO ₂
It is a dielectric film. Here, the configuration of the Ni / Au translucent electrode is selected to obtain an ohmic contact between Ni and p-GaN: Mg, and Au is selected to prevent oxidation of Ni. . However, in the case of a structure in which a protective film is provided on an Au electrode, oxidation by oxygen contained in the protective film cannot be prevented. In fixing such a light-emitting element to a base, in a method in which the semiconductor layer side is turned down, it is necessary to devise an energization to each electrode, and productivity is deteriorated. The above method is used. Therefore, as described above, the p-side ohmic electrode is provided so that light generated inside the device can be effectively extracted to the outside.
It is translucent.

[0004]

As described above, the p-side ohmic electrode needs to be formed in a very thin film having a thickness of 50 to 200 ° because of its light transmitting property. The SiO ₂ dielectric film 208 is formed to protect such an extremely thin electrode from damage during a manufacturing process or the like. According to the experimental findings of the present inventor, in a conventional semiconductor device provided with a SiO ₂ dielectric film, Ni is gradually oxidized due to SiO ₂ due to SiO ₂ in a long-term energization or the like, and the electrode portion has a high resistance. There was a problem of doing. Further, in the manufacturing process, when a heat treatment process such as alloying of the electrode and the semiconductor was performed after the formation of the dielectric film, the resistance of the electrode portion was increased.

Further, even in a nitride film containing no oxygen in the composition such as Si ₃ N ₄ , oxidation of the light-transmitting electrode may be caused by a trace amount of oxygen contained during film formation. Do you get it. Due to the increase in the resistance, the sheet resistance increases, and it becomes difficult to reduce the driving voltage.

In view of the above, the present invention provides a light emitting element having a translucent ohmic electrode, low sheet resistance, high thermal stability, and high conductivity even after a high temperature process. Aim.

[0007]

According to the present invention, there is provided a semiconductor light emitting device comprising: an ohmic electrode in contact with a nitride-based semiconductor; and an oxide insulating film covering at least a part of the ohmic electrode. The ohmic electrode is formed on the metal film in contact with the nitride semiconductor, and
It is characterized by comprising a conductive film having a higher melting point than this metal, and further having a dielectric film formed on the conductive film.

The metal film contains Ni or Pd, and the conductive film is made of Pt, W, WN, V, Mo, T
a.

The method for manufacturing a semiconductor light emitting device according to the present invention
Forming a metal film containing Ni or Pd and a conductive film containing any of Pt, W, WN, V, Mo, and Ta on the surface of the type semiconductor nitride semiconductor, and thereafter, on the conductive film, Forming an oxide insulating film; and thereafter, performing a heat treatment at 400 ° C. or more and 1000 ° C. or less.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on specific embodiments. Embodiment 1 FIG. 1 is a schematic structural view of a semiconductor light emitting device according to Embodiment 1 of the present invention. In the figure, 101 is a sapphire substrate, 102 is a GaN buffer layer, 103 is an n-type GaN layer, and 104 is an n-type Al
_0.1 Ga _0.9 N lower cladding layer, 105 is In _0.2 Ga _0.8
N active layer, 106 is a thin p-type Al _0.05 Ga _0.95 N evaporation preventing layer, 107 is a p-type Al _0.1 Ga _0.9 N upper cladding layer,
Reference numeral 108 denotes a p-type electrode GaN cap layer sequentially laminated. Reference numeral 109 denotes a metal film made of Ni or Pd provided on a part of the GaN cap layer 108; 110, a Mo conductive film provided on the metal film 109;
Au electrode pad provided on a part of conductive film 110, 1
Reference numeral 12 denotes an n-electrode provided on a part of the exposed surface of the n-type GaN layer, and 113 denotes a SiO ₂ dielectric film.

Next, a method for manufacturing such a semiconductor light emitting device will be described. First, the sapphire substrate 101 is heated at 1050 ° C. in an H ₂ atmosphere using an MOCVD apparatus to perform a surface treatment of the substrate. After that, the substrate temperature is lowered to 500 ° C., and the GaN buffer layer 102 is formed. At this time, the thickness of the buffer layer is 250 °. Thereafter, the substrate temperature is set to 102
By raising the temperature to 0 ° C., the n-type GaN layer 103 is grown to about 4 μm, and the n-type Al _0.1 Ga _0.9 N lower cladding layer 104 is grown to 1 μm at the same temperature. Next, the substrate temperature is lowered to 800 ° C., and a non-doped or Si-doped In _0.2 Ga _0.8 N active layer 105 is grown to a thickness of about 200 °. Next, at a substrate temperature of about 900 ° C. which is equal to or higher than the growth temperature of the non-doped or Si-doped In _0.2 Ga _0.8 N active layer and equal to or lower than the growth temperature of the p-type Al _0.1 Ga _0.9 N upper cladding layer, the p-type Al _0.05 Ga
_{A 0.95} N evaporation prevention layer 106 is grown. Thereafter, the growth temperature is increased to about 1020 ° C., and the p-type Al _0.1 Ga _0.9 N upper cladding layer 107 is grown to about 1 μm. Next, p-type GaN
The cap layer 108 is grown to about 1 μm. At this time, p-type A
l _0.05 Ga _0.95 N evaporation preventing layer 106 has a substrate temperature of 10
A high quality film is formed during the heating up to 20 ° C.

Thereafter, in order to form an n-type electrode, a resist is applied and patterning is performed by photolithography, and a part of the grown semiconductor layer is removed by dry etching to expose the n-type GaN layer 103. Type G
An n-electrode 112 is formed on a part of the exposed surface of the aN layer 103. Next, a resist is applied and patterned by photolithography to form a p-type GaN cap layer 10.
8, a metal film 109 made of Ni or Pd is deposited in a thickness of 30 to 100 [deg.]
A Mo conductive film 110 was formed to a thickness of 00 ° to form a p-electrode. In the same procedure as when the p-electrode is formed, an Au pad electrode 111 is formed on a part of the p-electrode with a thickness of 4000 °. Finally, a SiO ₂ dielectric film 113 is formed to a thickness of 2000 to 5000 ° by sputtering. Then, in an atmosphere of nitrogen or an inert gas such as Ar
Annealing is performed at 00 ° C. for 10 minutes. This annealing treatment also serves to improve ohmic characteristics between the low-resistance p-type semiconductor of the gallium nitride-based semiconductor p-type layer and the electrode. Here, as the material of the metal film, Pd and Ni capable of obtaining good ohmic contact with p-GaN were used.

In the semiconductor light emitting device of the present embodiment, even if the power is applied for a long period,
Stable characteristics were obtained. This will be described with reference to FIG. FIG. 2 shows that the conductive film on the metal film is made of Au, Ni, Pt,
V, Mo, Ta, W (each metal has a melting point of 1
064 ° C, 1455 ° C, 1772 ° C, 1890 ° C, 26
10 ° C., 2996 ° C., 3387 ° C. ) Shows the deterioration rate of the LED element when formed, and the horizontal axis is plotted with the melting point of each conductive film. Here, the deterioration rate is 3 per 100 LED elements having a conductive film formed of each metal.
This is a ratio of defective elements such as an increase in operating voltage and a stop of lighting after 3000 hours when a current of 0 mA flows. In addition, ● indicates that the metal film under the conductive film is Ni, and Δ indicates P
This is the case for d. When the conductive film is made of Au or Ni, the deterioration rate is as high as 70% or more, and it can be seen that the element is deteriorated by the moderate oxidation with SiO ₂ . On the other hand, when the melting point of the metal of the conductive film is higher than the melting point of the metal film under the conductive film, the deterioration is as extremely low as 30% or less.
(By the way, the melting point of Ni is 1455 ° C and the melting point of Pd is 15
54 ° C. This tendency was the same whether the metal film was Ni or Pd. Further, Ni /
When the SiO ₂ dielectric film is not provided in the Au electrode structure, the deterioration rate is as low as about 20%, which is considered to be because there is no oxidation of the Ni / Au electrode and the SiO ₂ dielectric film. Although not shown in the figure, the deterioration rate of WN is 15% when the metal film is Ni, and 0% when the metal film is Pd. The sheet resistance after annealing at 1000 ° C. for 10 minutes is shown in FIG. The point at 0 ° C. indicates the sheet resistance before annealing. The Ni / Au translucent electrode is formed with a thickness of 70/50 °, the Ni / Mo translucent electrode is formed with a thickness of 70/50 °, and the total film thickness is also the same. In this case, the Ni / Mo translucent electrode has a resistance of 0.2 Ω / c despite the resistance of the Ni / Au electrode having increased to about 100Ω after annealing at 800 ° C.
The sheet resistance was as low as about m ² . M
It can be seen that o effectively prevents the oxidation of Ni by SiO ₂ . By adopting such a two-layer structure, Ni / A
A highly reliable electrode structure having higher thermal stability than the u electrode could be produced.

Further, the dielectric film is not a such oxides SiO _2, it is oxidized by oxygen taken into the film during the formation of the Si ₃ N Si ₃ N ₄ even such nitrides ₄ It was found that the resistance was increased and the resistance of the Ni / Au electrode u electrode was increased. Even in such a case, the Ni / Mo electrode is 0.2
A low sheet resistance of about Ω / cm ² can be maintained, and Ni is generated by oxygen incorporated in the Si ₃ N ₄ film.
It has been found that the oxidation of aluminum is effectively prevented. In addition, Ni /
With respect to the Mo translucent electrode, the contact resistance between the semiconductor and the metal is about the same as the conventional 2 × 10 ⁻² Ω · cm ² , and good ohmic contact is obtained. As shown in FIG. 3, the annealing temperature is 400 ° C. or more and 800
C. or less is preferred. If the temperature is lower than 400 ° C., the hydrogen in the p-GaN layer cannot be completely removed, and the p-layer remains at a high resistance.
If the temperature is higher than 800 ° C., re-evaporation or aggregation of the Ni electrode is caused, which is not preferable. This situation was the same even when any of W, WN, V, Ta, and Pt was used instead of Ni instead of Pd and Mo. If the thickness of the Ni metal film is less than 30 °, a uniform film cannot be formed.
When the angle is 0 ° or more, the light transmittance deteriorates, which is not preferable. Ni
When the thickness of the Mo conductive film on the metal film is less than 10 °, it is difficult to form a uniform film, and when the thickness is more than 90 °, the light transmittance is deteriorated. Preferably, the thickness of Ni is 30 ≦ d ≦ 100
Å, the thickness of the Mo conductive film is between 10 ≦ d <90 °. Considering the light transmission, the total film thickness of the two layers is 200
It is preferable not to exceed Å.

In this embodiment, Mo is used for the conductive film 110, but instead of W, WN, V, T
Similar effects were obtained for a and Pt. Also, instead of SiO ₂ , Al ₂ O ₃ , TiO ₃ , TiO 2
₂ , the same effect was obtained by using other oxide insulators such as Si ₃ N ₄ .

[0016]

In the conventional gallium nitride-based compound semiconductor light emitting device, especially in the LED, Ni has been used as the light-transmitting electrode. Also, due to the nature of the translucent electrode, 50 to 200 mm
It is formed with a very thin film thickness. In addition, a SiO ₂ dielectric film is formed on the translucent electrode to protect the electrode. For this reason, the Ni or Ni / Au translucent electrode is oxidized by SiO ₂ which is a dielectric film when a high-temperature process such as an alloying alloy of the electrode and the semiconductor and further a p-type annealing after forming the electrode is performed. In addition, it has been found that the oxidation progresses slowly even in a long-time energization or the like, and the resistance increases. Due to the increase in the resistance, the sheet resistance increases, and it becomes difficult to reduce the driving voltage. Therefore, a conductive film of Mo, W, WN, V,
By forming Ta and Pt between 10 ° and 300 °, even in a high-temperature process, Ni did not increase in resistance by a dielectric film, and an electrode structure stable to a thermal process could be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a light emitting diode according to a first embodiment of the present invention.

FIG. 2 is a graph showing a deterioration rate of an element when an LED element is made of each conductive film.

FIG. 3 shows the annealing temperature dependence of the sheet resistance of the Ni / Au translucent electrode and the Ni / Mo translucent electrode.

FIG. 4 is a schematic diagram of a conventional light emitting diode.

[Explanation of symbols]

Reference Signs List 101 sapphire substrate 102 GaN buffer layer 103 n-type GaN layer 104 n-type Al _0.1 Ga _0.9 N lower cladding layer 105 In _0.2 Ga _0.8 N active layer 106 p-type Al _0.05 Ga _0.95 N evaporation preventing layer 107 p-type Al _0.1 Ga _0.9 N upper cladding layer 108 p-type GaN cap layer 109 Ni metal film 110 Mo conductive film 111 Au electrode pad 112 n electrode 113 SiO ₂ dielectric film 201 sapphire substrate 202 n-GaN: Si 203 active layer 204 p-GaN: Mg 205 Ni translucent electrode or Ni / Au translucent electrode 206 N-type electrode 207 Bonding electrode pad 208 Dielectric film of SiO ₂

Claims (3)

[Claims] 1. A semiconductor light emitting device comprising: an ohmic electrode in contact with a nitride-based semiconductor; and an oxide insulating film covering at least a part of the ohmic electrode, wherein the ohmic electrode is connected to the nitride semiconductor. A semiconductor light emitting device comprising: a contacting metal film; and a conductive film having a higher melting point than the metal film formed on the metal film, wherein a dielectric film is formed on the conductive film. . 2. The method according to claim 1, wherein the metal film includes Ni or Pd, and the conductive film includes one of Pt, W, WN, V, Mo, and Ta. Semiconductor light emitting device. 3. A step of sequentially forming a metal film containing Ni or Pd and a conductive film containing any of Pt, W, WN, V, Mo and Ta on a p-type nitride semiconductor surface, A method for manufacturing a semiconductor light emitting device, comprising: a step of forming a dielectric film containing oxygen on the conductive film; and a step of subsequently performing a heat treatment at 400 ° C. to 800 ° C.