JP3555419B2 - Gallium nitride based compound semiconductor electrode forming method and device manufacturing method - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for forming an electrode having improved bonding strength and surface smoothness to a p-type gallium nitride-based compound semiconductor, and a method for manufacturing an element having the electrode.
[0002]
[Prior art]
Conventionally, as disclosed in Japanese Patent Application Laid-Open No. 9-64337, as a p-type gallium nitride electrode, Ni is used for a first layer and Au is used for a second layer. It is known that Ni and Au are inverted. With this configuration, the ohmic properties of the metal electrode are improved.
[0003]
[Problems to be solved by the invention]
However, the electrode having the above structure has a problem that the bonding strength is weak because Au is a bonding metal, and the electrode is easily peeled. In addition, there is a problem that the light emitting pattern is not uniform when the electrode has a poor surface smoothness and is used as a translucent electrode for extracting light from the light emitting diode. Furthermore, the manufacturing process is complicated because the electrodes have a two-layer structure. Since it has a two-layer structure of thin layers, it is difficult to control the thickness, and it is difficult to make the thickness of the electrodes of the product element uniform.
[0004]
Then, an object of the present invention is to obtain an electrode which has a strong bonding strength to a p-type gallium nitride-based compound semiconductor, has a smooth surface, and can be formed by a simple process.
[0005]
[Means for Solving the Problems]
A first invention is a method of forming an electrode of a p-type gallium nitride-based compound semiconductor, wherein platinum (Pt) is formed on a gallium nitride-based compound semiconductor to which a p-type impurity is added, and at least a partial pressure of 100 Pa or more. Heat treatment is performed in a gas containing oxygen.
According to a third aspect of the present invention, there is provided a method of manufacturing a device having a p-type gallium nitride-based compound semiconductor layer and an electrode, wherein the gallium nitride-based compound semiconductor layer doped with a p-type impurity is formed. An electrode made of platinum (Pt) is formed on the layer, and the gallium nitride-based compound semiconductor layer on which the electrode is formed is heat-treated in a gas containing oxygen at a partial pressure of at least 100 Pa or more .
Further, a fifth invention provides a method of manufacturing a device having a p-type gallium nitride-based compound semiconductor layer, an n-type gallium nitride-based compound semiconductor layer, and an electrode for each of the layers. After forming a first electrode made of platinum (Pt) on the compound semiconductor layer and forming a second electrode on the n-type gallium nitride-based compound semiconductor layer, heat treatment is performed in a gas containing at least a partial pressure of 100 Pa or more of oxygen. It is characterized by the following.
Second, fourth, sixth invention is the "gas containing at least a partial pressure 100Pa or more oxygen" are replaced with "0.01 to 100% of the gas containing oxygen."
The gallium nitride-based compound semiconductor is a compound in which part of Ga is replaced with a group 3 element such as In or Al based on GaN. As an example, it can be represented by a quaternary gallium nitride-based compound semiconductor represented by the general formula (Al _x Ga _1-x ) _y In _1-y N (0 ≦ x ≦ 1,0 ≦ y ≦ 1).
[0006]
In all of the above inventions, the oxygen-containing gas includes at least one of O ₂ , O ₃ , CO, CO ₂ , NO, N ₂ O, NO ₂ , H ₂ O, or a mixed gas thereof. Can be used. Or a mixed gas of at least one of O ₂ , O ₃ , CO, CO ₂ , NO, N ₂ O, NO ₂ , or H ₂ O and an inert gas, or O ₂ , O ₃ , CO, A mixed gas of CO ₂ , NO, N ₂ O, NO ₂ , or a mixed gas of H ₂ O and an inert gas can be used. In short, a gas containing oxygen means an oxygen atom or a gas of a molecule having an oxygen atom.
[0007]
The pressure of the atmosphere during the heat treatment may be at least the pressure at which the gallium nitride-based compound semiconductor does not thermally decompose at the heat treatment temperature. The gas containing oxygen may be introduced at a pressure equal to or higher than the decomposition pressure of the gallium nitride-based compound semiconductor when only O ₂ gas is used, and when used in a state of being mixed with another inert gas, It suffices that all gases have a pressure equal to or higher than the decomposition pressure of the gallium nitride-based compound semiconductor, and that the O ₂ gas has a ratio of about 10 ⁻⁶ or more to all gases. In short, it is sufficient for the gas containing oxygen to be present in a very small amount. The upper limit of the amount of the gas containing oxygen is not particularly limited from the characteristics of p-type resistance reduction, electrode alloying, and bonding strength. However, the presence of an extremely small amount is indispensable for the characteristics of strong bonding strength and flattening of a plane. In short, as long as oxygen can be dissociated by using a hydrogen atom bonded to a p-type impurity as a catalyst, it can be used in a very small range where production is possible.
[0008]
As for the heat treatment, the temperature is most desirably 500 to 600 ° C. As described later, at a temperature of 500 ° C. or higher, a low-resistance p-type gallium nitride-based compound semiconductor whose resistivity is completely saturated can be obtained. Further, at a temperature of 600 ° C. or less, the alloying treatment of the electrode can be favorably performed.
Desirable temperature ranges are 450 to 650 ° C, 400 to 600 ° C, and 400 to 700 ° C. As the temperature is lower, the p-type resistivity is higher, and as the temperature is higher, the characteristics of the electrode are deteriorated, and there is a possibility that thermal deterioration of the crystal and deterioration during operation may occur.
[0009]
The thickness of the Pt electrode can be formed in an arbitrary range. If the Pt electrode is formed to be thin and translucent, it can be used as a light extraction electrode of a light emitting diode. In addition, a flip-chip type electrode can be formed thickly. The thickness of the Pt electrode is desirably 5 nm to 10 μm, and a sufficient bonding strength is obtained in this range.
[0010]
The second electrode for the n-type gallium nitride-based compound semiconductor layer is preferably made of aluminum (Al) or an aluminum alloy. This was selected from the viewpoint of the contact resistance to the n-type gallium nitride-based compound semiconductor and the ohmic property.
[0011]
Function and effect of the present invention
In the above invention, the electrode material of the gallium nitride-based compound semiconductor to which the p-type impurity is added is platinum (Pt), and oxygen having a partial pressure of 100 Pa or more or 0.01 to 100 % is supplied to the atmosphere gas for the heat treatment . As a result of using the gas containing, the bonding strength of the electrode was improved, and the surface smoothness was able to be improved. Further, since the thickness range of the electrode having good characteristics is wide, it can be used from a light-transmitting electrode to a flip-chip type bump electrode. In addition, since only one layer is required and the thickness can be easily controlled, an electrode having a uniform thickness can be formed between the elements. Further, platinum is not easily oxidized, and the translucency of the electrode is not deteriorated after the production, and it is possible to prevent the luminescence pattern from changing over time.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on specific examples. The present invention is not limited to the following examples.
FIG. 1 shows a structure of a light emitting device using the platinum electrode of the present invention. In FIG. 1, a light emitting element 100 made of a GaN-based compound semiconductor is formed on a sapphire substrate 1. A buffer layer 12 made of AlN is provided on a sapphire substrate 10, and a high carrier concentration n ⁺ layer 13 made of silicon (Si) doped GaN is formed thereon. On this high carrier concentration n ⁺ layer 13, a cladding layer 14 made of silicon (Si) doped n-type GaN is formed.
[0013]
Then, light emission of a multiple quantum well structure (MQW) composed of a barrier layer 151 made of GaN having a thickness of 35 ° and a well layer 152 made of Ga _0.80 In _0.20 N having a thickness of 35 ° is formed on the cladding layer. Layer 5 is formed. The barrier layer 151 has six layers, and the well layer 152 has five layers. On the light emitting layer 15, a clad layer 16 made of p-type Al _0.15 Ga _0.95 N is formed. Further, a contact layer 17 made of p-type GaN is formed on the cladding layer 16.
[0014]
A translucent electrode 18A made of metal is formed on the contact layer 17, and an electrode 18B is formed on the n ⁺ layer 3. The translucent electrode 18A is made of 500 ° thick platinum (Pt). The electrode 18B is made of vanadium (V) having a thickness of 200 ° and aluminum (Al) or an aluminum alloy having a thickness of 1.8 μm. An electrode pad 20 for wire bonding is formed on a part of the electrode 18A.
[0015]
Next, a method for manufacturing the light emitting device 100 will be described.
The light emitting device 100 was manufactured by vapor phase growth using metal organic chemical vapor deposition (hereinafter, MOVPE).
The gases used were ammonia (NH ₃ ), carrier gas (H ₂ , N ₂ ), trimethylgallium (Ga (CH ₃ ) ₃ ) (hereinafter referred to as “TMG”), and trimethylaluminum (Al (CH ₃ ) ₃ ). ) (Hereinafter referred to as “TMA”), trimethylindium (In (CH ₃ ) ₃ ) (hereinafter referred to as “TMI”), silane (SiH ₄ ), and cyclopentadienyl magnesium (Mg (C ₅ H ₅ ) ₂ ) ) (Hereinafter referred to as “CP ₂ Mg”).
[0016]
First, a single-crystal sapphire substrate 10 having an a-plane as a main surface cleaned by organic cleaning and heat treatment is mounted on a susceptor placed in a reaction chamber of a MOVPE apparatus. Next, the sapphire substrate 10 was baked at a temperature of 1100 ° C. while flowing H ₂ at normal pressure at a flow rate of ₂ liter / min for about 30 minutes.
[0017]
Next, the temperature was lowered to 400 ° C., H ₂ was supplied at 20 liter / min, NH ₃ was supplied at 10 liter / min, and TMA was supplied at 1.8 × 10 ⁻⁵ mol / min for about 1 minute to supply the AlN buffer layer 12. Was formed to a thickness of about 25 nm.
Next, the temperature of the sapphire substrate 10 was maintained at 1150 ° C., H ₂ was 20 liter / min, NH ₃ was 10 liter / min, TMG was 1.7 × 10 ⁻⁴ mol / min, and H ₂ gas was 0.86 ppm. The diluted silane was supplied at 20 × 10 ⁻⁸ mol / min for 40 minutes, and a high GaN layer having a thickness of about 4.0 μm, an electron concentration of 2 × 10 ¹⁸ / cm ³ and a silicon concentration of 4 × 10 ¹⁸ / cm ³ was used. A carrier concentration n ⁺ layer 13 was formed.
[0018]
Next, the temperature of the sapphire substrate 10 was maintained at 1150 ° C., N ₂ or H ₂ was 10 liter / min, NH ₃ was 10 liter / min, TMG was 1.12 × 10 ⁻⁴ mol / min, and TMA was 0.47. × ^{10 -4} mol / min, supplying 60 minutes silane diluted to 0.86ppm with _{H 2} gas at 5 × ^{10 -9} mol / min, a film thickness of about 0.5 [mu] m, an electron concentration 1 × ^{10 18} / A cladding layer 14 made of GaN having a cm ³ and a silicon concentration of 2 × 10 ¹⁸ / cm ³ was formed.
[0019]
After the formation of the cladding layer 14, N ₂ or H ₂ was supplied at 20 liter / min, NH ₃ was supplied at 10 liter / min, and TMG was supplied at 2.0 × 10 ⁻⁴ mol / min for 1 minute to form a film. A barrier layer 151 made of GaN having a thickness of about 35 ° was formed. Next, TMG was supplied at a rate of 7.2 × 10 ⁻⁵ mol / min and TMI was supplied at a rate of 0.19 × 10 ⁻⁴ mol / min for 1 minute while the supply amounts of N _2, H ₂ and NH ₃ were kept constant. A well layer 152 of Ga _0.80 In _0.20 N with a thickness of about 35 ° was formed. Further, a barrier layer 151 and a well layer 152 were formed under the same conditions for five periods, and a barrier layer 151 made of GaN was formed thereon. Thus, the light emitting layer 15 having the MQW structure having five periods was formed.
[0020]
Next, the temperature of the sapphire substrate 10 was maintained at 1100 ° C., N ₂ or H ₂ was 10 liter / min, NH ₃ was 10 liter / min, TMG was 1.0 × 10 ⁻⁴ mol / min, and TMA was 1.0 liter. Magnesium (Mg) having a thickness of about 50 nm and a magnesium (Mg) concentration of 5 × 10 ¹⁹ / cm ^{3 was} supplied by supplying × 10 ⁻⁴ mol / min and CP ₂ Mg at 2 × 10 ⁻⁵ mol / min for 3 minutes. A cladding layer 16 made of doped p-type Al _0.15 Ga _0.85 N was formed.
[0021]
Next, the temperature of the sapphire substrate 10 is maintained at 1100 ° C., N ₂ or H ₂ is 20 liter / min, NH ₃ is 10 liter / min, TMG is 1.12 × 10 ⁻⁴ mol / min, and CP ₂ Mg is 2 A contact layer 17 made of p-type GaN doped with magnesium (Mg) having a thickness of about 100 nm and a magnesium (Mg) concentration of 5 × 10 ¹⁹ / cm ^{3 was} supplied at a ^{rate of} × 10 ⁻⁵ mol / min for 30 seconds. .
[0022]
Next, an etching mask made of SiO ₂ is formed on the contact layer 17, the mask in a predetermined region is removed, and portions of the contact layer 17, the cladding layer 16, the light emitting layer 15, and the cladding layer which are not covered with the mask are removed. 14. A part of the n ⁺ layer 13 was etched by reactive ion etching using a gas containing chlorine to expose the surface of the n ⁺ layer 13. Next, an electrode (second electrode) 18B for the n ⁺ layer 13 and a translucent electrode (first electrode) 18A for the contact layer 17 were formed in the following procedure.
[0023]
(1) With the SiO ₂ mask left, a window is formed in a predetermined area by applying a photoresist and photolithography, and vanadium (V) having a thickness of 200 ° and a thickness of 200 ° C. is applied under a high vacuum of the order of 10 ⁻⁶ Torr or less. Aluminum (Al) having a thickness of 1.8 μm was deposited. Next, the photoresist and the SiO ₂ mask are removed.
(2) Next, a photoresist 19 is uniformly applied on the surface, and the photoresist 19 in an electrode forming portion on the contact layer 17 is removed by photolithography. Form 19A.
(3) After evacuation was performed to a high vacuum of the order of 10 ⁻⁶ Torr or less on the exposed contact layer 17 using a vapor deposition apparatus, a metal layer 81 made of platinum (Pt) was formed to a thickness of 500 °.
(4) Next, the sample is taken out of the vapor deposition apparatus, Pt deposited on the photoresist 19 is removed by a lift-off method, and a translucent electrode 18A for the contact layer 17 is formed.
(5) Next, in order to form an electrode pad 20 for bonding on a part of the light-transmitting electrode 18A, a photoresist is uniformly applied, and a window is formed on the photoresist at a portion where the electrode pad is formed. Open. Next, platinum (pt), cobalt (Co), nickel (Ni), gold (Au), aluminum (Al), or an alloy thereof is deposited to a thickness of about 1.5 μm by vapor deposition. Similarly to step 4), the electrode pad 20 is formed by removing the film made of Co or Ni and Au, Al, or an alloy thereof deposited on the photoresist by vapor deposition by the lift-off method.
(7) Thereafter, the sample atmosphere is evacuated by a vacuum pump, and O ₂ gas is supplied to a pressure of 100 Pa. In this state, the atmosphere temperature is set to about 500 ° C., and the heating is performed for about 3 minutes. The resistance of the contact layer 17 and the electrode 18A were alloyed, and the electrode 18B and the n ⁺ layer 13 were alloyed.
[0024]
This heat treatment is most desirably in the range of 500 to 600 ° C. Within this temperature range, the p-type layer is in a sufficiently low saturation region of the resistance value, and the above-mentioned electrodes 18A and 18B are alloyed with the highest quality, the bonding strength is extremely high, and the surface is extremely high. Becomes smooth. Further, the oxidation of the light-transmitting electrode 18A is prevented, the light emitting pattern is not uneven, and the light emitting pattern can be prevented from aging. In the heat treatment, if the heat treatment is performed at a temperature lower than 400 ° C., the resistance of the p-type layer does not decrease, and the electrode does not show ohmic characteristics. Although the value is shown, the contact resistance of the electrode is increased, the surface morphology is deteriorated, and this causes a wire bonding failure in a later process. Therefore, it is desirable to perform the heat treatment within the range of 400 ° C. to 700 ° C.
[0025]
Although a heat treatment was performed in an atmosphere in which 1% of O ₂ gas was contained with respect to N ₂ gas and the partial pressure of the O ₂ gas was 100 Pa, the same effect was obtained. In addition to pure oxygen gas, a gas obtained by adding one or more of N ₂ , He, Ne, Ar, and Kr to O ₂ can be used. The proportion of O ₂ may be very small, for example, about 10 ⁻⁴ % or more. In particular, an electrode having extremely strong bonding properties and a smooth surface is obtained in the range of 0.01 to 100%.
[0026]
When a current of 20 mA was applied to the light emitting element 100 formed in this way, a driving voltage of 3.5 V was obtained, and it was confirmed that the contact resistance was sufficiently small. Further, the translucent electrode 18A was formed uniformly on the entire surface of the contact layer 17, and a very smooth surface having a high bonding strength was obtained. For this reason, the yield of the product could be improved, and the emission pattern could be made uniform and uniform. Also, the contact resistance was sufficiently low, and good ohmic characteristics were obtained.
[0027]
The p-type impurity magnesium (Mg) added to the contact layer 17 and the cladding layer 16 may be replaced with beryllium (Be), calcium (Ca), strontium (Sr), barium (Ba). , Zinc (Zn), cadmium (Cd) and the like. Further, the light emitting layer 15 of the light emitting element 100 has the MQW structure, but may be a single layer made of SQW, Ga _0.80 In _0.20 N, or any other mixed crystal quaternary or ternary AlInGaN. good.
[0028]
Although the above embodiment has described a light emitting diode having a translucent electrode, the present invention relates to a laser diode (LD), a light receiving element, and other high temperature devices and power devices expected to develop gallium nitride based compound semiconductor devices. Also applicable to electronic devices.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of a light emitting device according to a manufacturing method of the present invention.
FIG. 2 is a cross-sectional view illustrating a method for forming an electrode of a light-emitting element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Sapphire substrate 12 ... Buffer layer 13 ... n ⁺ layer 14 ... Cladding layer 15 ... Light emitting layer 16 ... Cladding layer 17 ... Contact layers 18A and 18B ... Electrode 19A ... Window part 81 ... Metal layer 100 ... Light emitting element

Claims (8)

In a method for forming an electrode of a p-type gallium nitride-based compound semiconductor,
An electrode of a gallium nitride-based compound semiconductor, wherein platinum (Pt) is formed on a gallium nitride-based compound semiconductor to which a p-type impurity is added, and heat treatment is performed in a gas containing oxygen at least at a partial pressure of 100 Pa or more. Forming method. In a method for forming an electrode of a p-type gallium nitride-based compound semiconductor,
platinum (Pt) is formed on the added gallium nitride compound semiconductor of p-type impurity, 0. In gas containing 01 to 100 percent of oxygen, characterized that the gallium nitride compound semiconductor to a heat treatment Electrode formation method. In a method for manufacturing a device having a p-type gallium nitride-based compound semiconductor layer and an electrode,
forming a gallium nitride-based compound semiconductor layer to which a p-type impurity is added;
An electrode made of platinum (Pt) is formed on the gallium nitride-based compound semiconductor layer,
A method for manufacturing a gallium nitride-based compound semiconductor device, comprising: performing a heat treatment on the gallium nitride-based compound semiconductor layer on which the electrode is formed, in a gas containing at least a partial pressure of 100 Pa or more of oxygen. In a method for manufacturing a device having a p-type gallium nitride-based compound semiconductor layer and an electrode,
forming a gallium nitride-based compound semiconductor layer to which a p-type impurity is added;
An electrode made of platinum (Pt) is formed on the gallium nitride-based compound semiconductor layer,
In 0. Gas containing 01 to 100 percent of the oxygen of gallium nitride-based compound semiconductor layer formed of the electrode, heat treatment method for producing a gallium nitride-based compound semiconductor device which is characterized in that. In a method for manufacturing a device having a p-type gallium nitride-based compound semiconductor layer, an n-type gallium nitride-based compound semiconductor layer, and an electrode for each layer,
Forming a first electrode made of platinum (Pt) on the gallium nitride-based compound semiconductor layer to which the p-type impurity is added, and forming a second electrode on the n-type gallium nitride-based compound semiconductor layer;
A method for manufacturing a gallium nitride-based compound semiconductor device, comprising performing heat treatment in a gas containing oxygen having a partial pressure of at least 100 Pa or more . In a method for manufacturing a device having a p-type gallium nitride-based compound semiconductor layer, an n-type gallium nitride-based compound semiconductor layer, and an electrode for each layer,
Forming a first electrode made of platinum (Pt) on the gallium nitride-based compound semiconductor layer to which the p-type impurity is added, and forming a second electrode on the n-type gallium nitride-based compound semiconductor layer;
0. In gas containing 01-100% oxygen, the manufacturing method of a gallium nitride-based compound semiconductor device characterized by a heat treatment. The oxygen-containing gas is at least one of O ₂ , O ₃ , CO, CO ₂ , NO, N ₂ O, NO ₂ , or H ₂ O or a mixed gas thereof, or a mixture of these gases and an inert gas. The method according to any one of claims 1 to 6, wherein the gas is a mixed gas of The method according to claim 1, wherein the heat treatment is performed at a temperature of 400 ° C. or higher.

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