JPH10135515A - Electrode formation of group-iii nitride semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve bonding strength and ohmic property and reduce contact resistance by forming a nickel(Ni) electrode layer and a gold (Au) electrode layer one by one on a surface of a semiconductor and carrying out heat treatment in the presence of oxygen (O2 ). SOLUTION: Nickel(Ni) is formed to a film in high vacuum on an exposed P<+> -layer 7 by a deposition device and a first metallic layer is formed. Then, an electrode 8A to the p<-> -layer 7 is shaped by removing Ni and Au deposited on a photoresist. Mixture gas of O2 gas and gas containing one or more kinds of N2 , H2 , He, Ne, Ar, Kr is introduced and subjected to heat treatment. Nickel and gold are laminated and are subjected to heat treatment in oxygen atmosphere in this way, an element distribution in a depth direction from a surface of a p-conductivity type group-III nitride semiconductor is made a distribution then, gold permeates deeper than nickel. As a result, ohmic property is improved and contact resistance of an electrode is reduced. Furthermore, junction degree of an electrode layer is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an electrode for a p-type group III nitride semiconductor. In particular, the present invention relates to an electrode having improved junction strength, ohmic properties, and contact resistance of an electrode with respect to a p-type group III nitride semiconductor.

[0002]

2. Description of the Related Art Heretofore, as a p-conductivity type GaN (p-GaN) electrode, one in which gold (Au) is vapor-deposited on a GaN layer surface is known. However, when this gold (Au) is directly deposited on the GaN layer surface, the bonding property is poor, and there is a problem that the alloying of the GaN layer causes the gold electrode to peel off.

Therefore, gold (Au) and GaN
Nickel (Ni) is interposed between the layer surface and gold (Au) G
Improving the adhesion to the aN layer has been performed.
However, even in this case, there is a problem that the ohmic property is not good and the contact resistance of the electrode is large.

Accordingly, an object of the present invention is to provide a method for forming an electrode for a p-type group III nitride semiconductor, which has good adhesive strength, further improved ohmic properties, and reduced contact resistance. It is.

[0004]

According to a first aspect of the present invention, there is provided a method for forming a semiconductor electrode comprising a p-type group III nitride, comprising: a nickel (Ni) electrode layer and a gold (Au) electrode on a surface of the semiconductor; It is characterized in that layers are sequentially formed and heat treatment is performed in the presence of oxygen (O ₂ ).

According to a second aspect of the present invention, the thickness of the gold (Au) electrode layer is reduced.
The thickness of the nickel (Ni) electrode layer is set to 200 mm or less. A fourth aspect of the present invention is that the gold (Au) electrode layer and the nickel (Ni) electrode layer are configured to be translucent.

According to a fifth aspect of the present invention, the heat treatment is performed at 450 ° C. to 65 ° C.
The method according to claim 6, wherein the constituent element of the gold (Au) electrode layer diffuses and penetrates into the p-type group III nitride semiconductor by a heat treatment, so that the nickel (Ni) electrode is relatively formed. The layer is formed on the gold (Au) electrode layer. Furthermore, the invention of claim 7 is characterized in that the heat treatment is performed in a state where the oxygen (O ₂ ) partial pressure in the chamber is 1 Pa or more,
The invention of claim 8 is characterized in that 0.01 to 10% by ratio of oxygen (O ₂₎ nitrogen (N _2).

As described above, the present invention is characterized in that the heat treatment is performed in an oxygen atmosphere so that the element distribution of the electrode is inverted with respect to the distribution at the time of forming the metal layer. That is,
After forming the electrodes, the constituent elements of the upper electrode layer, gold
(Au) is a constituent element of the metal layer formed on the lower side nickel (Ni)
Lower, that is, closer to the group III nitride semiconductor layer, the constituent element nickel (N
The feature is that i) is distributed more above the constituent element gold (Au) of the electrode layer formed on the upper side, that is, farther away from the group III nitride semiconductor layer.

[0008]

[Function and Effect of the Invention] By stacking nickel and gold and heat-treating them in an oxygen atmosphere, the element distribution in the depth direction from the surface of the p-type group III nitride semiconductor is gold (Au) more than nickel (Ni). ) Can be distributed deeply. As a result, the ohmic properties were improved, and the contact resistance of the electrodes could be reduced. In addition, since nickel was first formed on the surface of the p-type conductivity type group III nitride semiconductor, the degree of bonding of the electrode layer was improved.

By setting the thickness of the gold electrode layer to 100 mm or less and the thickness of the nickel electrode layer to 200 mm or less, good translucency and good ohmic properties were obtained. If the thickness of the gold electrode layer is 100 mm or more, oxygen in the atmosphere does not reach the nickel electrode layer, and no inversion of the metal element due to the oxygen element is observed, so that there is no effect. On the other hand, if the thickness of the nickel electrode layer is more than 200 mm, the light transmittance is undesirably reduced. Heat treatment is performed in an oxygen atmosphere at 450
When performed at a temperature in the range of 650 ° C. to 650 ° C., gold could penetrate deeper from the surface of the p-conductivity group III nitride semiconductor, and nickel could be more widely distributed in the surface layer. As a result, the bonding strength of the electrode layer is improved, the ohmic property is improved, and the contact resistance can be reduced.

The above-mentioned improvement in the electrode characteristics was observed by performing the heat treatment at a partial pressure of oxygen (O ₂ ) in the chamber of 1 Pa (7 × 10 ⁻⁷ torr) or more. Furthermore, oxygen
The ratio of (O ₂ ) to nitrogen (N ₂ ) is desirably 0.01% to 100%. If the ratio of oxygen is less than 0.01%, the contact resistance of the electrodes becomes large because the population inversion of nickel and gold does not occur.

A group III nitride semiconductor device having such an electrode has excellent device characteristics such as a reduction in applied voltage, an improvement in reliability, and a decrease in contact resistance. Light emitting diode,
In the laser diode, the luminous efficiency is improved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to specific embodiments. FIG. 1 is a schematic cross-sectional view of a light emitting device 100 formed of a group III nitride semiconductor formed on a sapphire substrate 1. An AlN buffer layer 2 is provided on a sapphire substrate 1, and a Si-doped n-type GaN layer 3 (n
⁺ Layer) is formed. 0.5 μm on this n ⁺ layer 3
A Si doped n-conductivity type Al _0.1 Ga _0.9 N layer 4 (n layer) is formed, and a 0.4 μm thick Al _0.05 Ga _0.95 / In
An active layer 5 having a multiple quantum well structure made of _0.2 Ga _0.8 N is formed, and a magnesium-doped p-type Al _0.1 Ga _0.9 N layer 6 (p layer) is formed on the active layer 5. On the p layer 6, a p-conductivity type doped with high concentration magnesium is doped.
A GaN layer 7 (p ⁺ layer) is formed. An electrode 8A formed by metal deposition is provided on the p ⁺ layer 7, and an electrode 8B is provided on the n ⁺ layer 3.
Are formed. The electrode 8A is composed of nickel bonded to the p ⁺ layer 7 and gold bonded to nickel.
The electrode 8B is made of aluminum or an aluminum alloy.

Next, a method of manufacturing the electrode 8A of the light emitting device 100 will be described. The buffer layer 2 to the p ⁺ layer 7 are formed by MOCVD. Then, a mask is formed on the p ⁺ layer 7 and a predetermined portion of the mask is removed, and the p ⁺ layer 7, the p layer 6, the active layer 5,
The n-layer 4 was etched by reactive ion etching with a gas containing chlorine to expose the surface of the n ⁺ -layer 3.
Thereafter, the mask was removed by an etching process. next,
The electrode 8A was formed in the following procedure.

(1) A photoresist 9 is uniformly applied on the surface, and the photoresist 9 on the electrode forming portion on the p ⁺ layer 7 is removed by photolithography to form a window 9A. (2) On the exposed p ⁺ layer 7, 10 ^-6 To
A first metal layer 81 is formed as shown in FIG. 2A by depositing nickel (Ni) in a high vacuum of about rr or less for 10 to 200 〜. (3) Subsequently, gold (Au) is coated on the first metal layer 81 by 20 to 500 Å.
By forming a film, a second metal layer 82 is formed as shown in FIG. (4) Next, the sample is taken out of the vapor deposition apparatus, and Ni and Au deposited on the photoresist 9 are removed by a lift-off method, and the electrode 8A for the p ⁺ layer 7 is shaped. (5) In the case where an electrode pad is formed on a part of the electrode 8A, a photoresist is uniformly applied, and a window is opened in the photoresist at a portion where the electrode pad is formed. Next, gold (A
u) or aluminum (Al) or an alloy containing them at 1.5 μm
A film is formed by vapor deposition to the extent. Similarly to the step (4), Au or Au deposited on the photoresist by the lift-off method
After removing Al, the electrode pad is shaped. (6) After that, the sample atmosphere is evacuated by a vacuum pump, and then a predetermined gas is introduced.
C. to 650.degree. C. and heat for several seconds to several tens of minutes. However, this heat treatment can be performed under the following conditions. As the atmosphere gas, a mixed gas of O ₂ gas and a gas containing at least one of N ₂ , H ₂ , He, Ne, Ar, and Kr can be used, and the pressure is from 1 mTorr to a pressure exceeding atmospheric pressure. It is optional in the range. Further, N ₂ , H ₂ , He, O ₂ , N
The partial pressure of the e, Ar, or kr gas is 0.01 to 100%, and the gas may be heated in a state sealed with the atmosphere gas or in a state in which the atmosphere gas is refluxed.

As a result of the above heat treatment after the lamination of nickel (Ni) and gold (Au), the gold (Au) of the second metal layer 82 on the first metal layer 81 of nickel (Ni) becomes the first metal. Diffusion or contact into p ⁺ layer 7 through metal layer 81 to form an alloy state with GaN of p ⁺ layer 7. FIG. 2B schematically shows the state after the heat treatment (the pad electrode is not shown). That is,
Before and after the heat treatment, the distribution of Au and Ni in the depth direction is inverted.

The element distribution near the surface of the p ⁺ layer 7 after the heat treatment was examined by Auger electron spectroscopy (AES).
The result is shown in FIG. In the vicinity of the surface of the p ⁺ layer 7 (from the surface to about 3 nm), the nickel concentration is higher than the gold concentration. It can be seen that gold is distributed at a higher concentration than nickel in the p ⁺ layer 7 deeper than about 3 nm from the surface. Therefore,
The gold passes through the first metal layer 81 of nickel and reaches the deep part of the p ⁺ layer 7, where it can be seen that an alloy is formed. In this case, it is understood that the oxygen element is also distributed near the surface of the p ⁺ layer 7 with the same distribution characteristics as nickel (Ni).

Before performing the heat treatment at a predetermined temperature of 450 ° C. or more and 650 ° C. or less, the air is not exhausted to a high vacuum (1 m Torr or less), but is exhausted in a state where air of several torr to several tens of torr remains. Thereafter, it was found that the resistance was reduced by filling the atmosphere with nitrogen (N ₂ ) to atmospheric pressure and then applying heat treatment.
The ratio of oxygen (O ₂ ) to nitrogen (N ₂ ) is preferably in the range of 0.01% to 100% from the viewpoint of reducing the contact resistance of the electrode.

The reason why the population inversion described above occurs is that nickel has a lower ionization potential than gold, so that nickel moves closer to the surface during heat treatment, and as a reaction, gold alloys with the group III nitride semiconductor. It is thought that it penetrates into the semiconductor. As a result, gold having good ohmic properties and a group III nitride semiconductor are alloyed, so that the ohmic properties of this electrode are improved. Further, nickel has higher reactivity than gold and is strongly bonded to the group III nitride semiconductor, so that the bonding strength of the electrode is improved.

In the following, various experiments were conducted on the heat treatment for forming the above-mentioned electrodes on the light emitting device. FIG. 4 shows the driving of the light emitting element when a current of 20 mA flows when the electrode is formed by changing the ratio of oxygen to nitrogen when heat treatment is performed at 600 ° C. by stacking nickel and gold with the above thickness. Voltage V
f is measured. The ratio of O ₂ / N ₂ is 0.05 to 10
At 0%, the driving voltage Vf becomes 3.6 V or less, and the driving voltage Vf formed by heat treatment in the absence of oxygen is 4.V.
Since the voltage is 8 V, it is apparent that the heat treatment in an oxygen atmosphere clearly reduces the contact potential difference between the electrodes.

FIG. 5 is a graph showing the relationship between the heat treatment temperature of 600 ° C., the O ₂ / N ₂ ratio of 1%, and the thickness of the gold layer of 60 °. The drive voltage Vf of the light emitting element when the current of FIG. When the thickness of the nickel layer is in the range of 22Å to 66Å,
The driving voltage Vf became 3.52 V or less. When the thickness of the nickel layer was smaller than 18 °, the driving voltage Vf became 3.88 V or more, and remarkable characteristics were observed with respect to the thickness of the nickel layer.

FIG. 6 shows a nickel layer having a thickness of 44 ° and O ₂ / N
_{2 20} % when the electrode is formed by changing the thickness of the gold layer when the ratio is 1% and the heat treatment temperature is 580 ° C, 600 ° C, and 620 ° C.
The drive voltage Vf of the light emitting element when the current of FIG. It is understood that when the thickness of the gold layer is increased to 110 °, the driving voltage Vf is increased at any heat treatment temperature. This is presumably because the oxygen element in the atmosphere did not reach the nickel layer because the gold layer was thick. Therefore, the thickness of the gold layer is desirably less than 100 mm.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of a light emitting device according to a specific example of the present invention.

FIG. 2 is a cross-sectional view schematically showing a structure of a surface layer of a p ⁺ layer before and after heat treatment of an electrode.

FIG. 3 is a measurement diagram showing the result of Auger electron spectroscopy analysis of the surface layer of the p ⁺ layer.

FIG. 4 is a measurement diagram showing a change in a driving voltage of a light emitting element with respect to an O ₂ / N ₂ ratio.

FIG. 5 is a measurement diagram showing a change in a driving voltage of a light emitting element with respect to a thickness of a nickel electrode layer.

FIG. 6 is a measurement diagram showing a change in a driving voltage of a light emitting element with respect to a thickness of a gold electrode layer.

[Explanation of symbols]

100 GaN-based semiconductor light emitting element 8A, 8B ... electrode 4 ... n layer 5 ... active layer 6 ... p layer 7 ... p ⁺ layer 9A ... window

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiya Uemura 1 Ochiai Nagahata, Kasuga-cho, Nishi-Kasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. Inside Toyoda Gosei Co., Ltd. (72) Inventor Junichi Umezaki 1 Ochiai Ogata, Kasuga-cho, Nishi-Kasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. 1 Toyota Central R & D Laboratories Co., Ltd. (72) Inventor Tomohiko Mori 41-cho, Yokomichi, Oku-cho, Nagakute-cho, Aichi-gun Aichi Prefecture Inside the Toyota Central R & D Laboratories Co., Ltd. 41, Yokomichi, Toyota Central Research Institute, Inc.

Claims (8)

[Claims] 1. A p conductivity type group III method of forming a semiconductor electrode consisting of nitrides, nickel (Ni) electrode layer and a gold (Au) electrode layer are sequentially formed on the semiconductor surface, the oxygen (O ₂ A) a method of forming an electrode of a p-type group III nitride semiconductor, wherein heat treatment is performed in the presence of the electrode. 2. The method according to claim 1, wherein the thickness of the gold (Au) electrode layer is 100 ° or less. 3. The thickness of the nickel (Ni) electrode layer is 200 mm.
2. The method for forming an electrode of a p-type group III nitride semiconductor according to claim 1, wherein: 4. The gold (Au) electrode layer and the nickel (Ni)
The method for forming an electrode of a p-type group III nitride semiconductor according to claim 1, wherein the electrode layer has a light transmitting property. 5. The method according to claim 1, wherein the heat treatment is performed at 450 ° C. to 650 ° C. 6. The heat treatment causes the constituent elements of the gold (Au) electrode layer to diffuse and penetrate into the p-conductivity group III nitride semiconductor, so that the nickel (Ni) electrode layer is relatively
2. The (Au) electrode layer is formed on an electrode layer.
4. The method for forming an electrode of a p-type group III nitride semiconductor according to item 1. 7. The heat treatment is performed using oxygen (O ₂ ) in a heat treatment atmosphere.
2. The method for forming an electrode of a p-type group III nitride semiconductor according to claim 1, wherein the partial pressure is set in the presence of 1 Pa (7 × 10 ⁻⁷ torr) or more. 8. The method according to claim 7, wherein the ratio of the oxygen (O ₂ ) to the nitrogen (N ₂ ) is 0.01 to 100%. .