JP2623463B2 - Gallium nitride based compound semiconductor electrode forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a method for forming a gallium nitride-based compound semiconductor electrode with improved ohmic properties and a method for manufacturing a gallium nitride-based light emitting device.

2. Description of the Related Art A gallium nitride-based compound semiconductor is a material that has attracted attention as a blue light emitting diode. In the halide CVD method that has been studied, SiO ₂ and scratches are formed on the sapphire surface, and the low resistance of poly GaN grown on the sapphire surface is used to selectively contact layers (from n-GaN to electrodes). ). However, this growth method has not been practically used due to lack of uniformity of growth and insufficient properties of the film itself. Currently, M is being considered as an alternative to the halide CVD method.
OVPE (Vapor Growth Using Organometallic) is a method in which an AlN layer is inserted between GaN and sapphire to reduce lattice mismatch. I have.

[Problems to be solved by the invention]

However, in the MOVPE method, scratches on Sapphire and S
Poly GaN does not grow on iO ₂ , Al ₂ O ₃ , and SiN _X. Therefore, to make contact from the n-GaN layer, i-GaN
It is necessary to etch the layer and to form an electrode with good ohmic properties on the etched surface. Thus, the present inventors have conducted research and found that gallium nitride-based compound semiconductors include compounds containing carbon, chlorine, and fluorine,
For example, dichlorodifluoromethane (CCl ₂ F ₂ ), tetrachloromethane (CCl ₄ ), tetrafluoromethane (C
F ₄₎ After etching by gas plasma gas, continuously, an inert gas, for example, after etching by plasma gas of argon (Ar) gas, to form an aluminum electrode by vapor deposition, that the ohmic resistance is good Discover
The present invention has been completed. Therefore, an object of the present invention is to form an electrode having good ohmic properties in a gallium nitride-based compound semiconductor.

[Means for Solving the Problems]

According to another aspect of the present invention, there is provided a method of forming an electrode in a compound semiconductor containing at least gallium and nitrogen, wherein a plasma gas of a gas containing chlorine or / and fluorine is formed in an electrode forming portion of the compound semiconductor. And then dry-etching the etched electrode forming portion with an inert gas plasma gas, and thereafter depositing metal on the electrode forming portion. The compound semiconductor containing at least gallium and nitrogen is GaN and GaAlN, and the compound gas containing chlorine and / or fluorine is dichlorodifluoromethane (CCl
₂ F ₂ ), tetrachloromethane (CCl ₄ ), and tetrafluoromethane (CF ₄ ) gas, and the inert gas includes argon (Ar), helium (He), nitrogen (N ₂ ), krypton (Cr ), Xenon (Xe) gas.

[Action and effect]

According to the considerations of the inventors, when dry etching a gallium nitride compound semiconductor with the above-described plasma gas of CCl ₂ F ₂ , CCl ₄ , CF _4, a barrier is formed in the etched portion by adsorption of an etching gas and a reaction product and the like. Therefore, it is considered that the ohmic property of the metal electrode is not good. Therefore, as a result of repeated experiments, the present inventors have found that a good ohmic property can be obtained by performing plasma etching with an inert gas such as argon after the plasma etching and then forming an electrode.

【Example】

Hereinafter, the present invention will be described specifically based on examples. The semiconductor used in the method of the present example was formed into a structure shown in FIG. 2 by vapor phase growth by metalorganic compound vapor phase epitaxy (hereinafter referred to as “MOVPE”). The gases used were NH ₃ , carrier gas H ₂ , trimethylgallium (Ga (CH ₃ ) ₃ ) (hereinafter referred to as “TMG”), and trimethylaluminum (Al (CH ₃ ) ₃ ) (hereinafter referred to as “TMA”). ). First, a single-crystal sapphire substrate 1 whose main surface is a c-plane cleaned by organic cleaning and heat treatment is mounted on a susceptor placed in a reaction chamber of a MOVPE apparatus. Next, the pressure in the reaction chamber was reduced to 5 Torr, and the sapphire substrate 1 was subjected to vapor phase etching at a temperature of 1100 ° C. while flowing H ₂ into the reaction chamber at a flow rate of 0.3 / min. Next, the temperature was lowered to 800 ° C., and H ₂ was flowed at a flow rate of 3 /
, NH ₃ was supplied at a flow rate of 2 / min, and TMA was supplied at a rate of 7 × 10 ⁻⁶ mol / min. By this heat treatment, the AlN buffer layer 2 was formed to a thickness of about 500 °. Next, when one minute has elapsed, the supply of TMA is stopped, the temperature of the sapphire substrate 1 is maintained at 1150 ° C., and H ₂ is reduced to 2.5 /
Then, NH ₃ was supplied at 1.5 / min and TMG was supplied at 1.7 × 10 ⁻⁵ mol / min for 60 minutes to form an n-type GaN layer 3 having a thickness of about 3 μm. Next, a mask 30 made of sapphire is placed on the upper surface of the GaN layer 3 thus formed as shown in FIG. 3 to form a sample 30, and the parallel plate electrode type plasma etching shown in FIG. The exposed GaN layer 3 was etched by the apparatus. Next, the etching apparatus will be described with reference to FIG. In the parallel electrode type electrode device shown in FIG.
On the side wall of the vacuum vessel 10 made of stainless steel, gas introduction tubes 12 and 34 for introducing an etching gas are connected to each other, and the introduction pipes 12 and 34 are respectively mass flow controllers capable of changing a gas flow rate. They are connected via 14 and 36 to cylinders 16 and 38 which store CCl ₂ F ₂ gas and Ar gas.
Then, CCl ₂ F ₂ gas or Ar gas is introduced from the cylinders 16 and 38 into the reaction chamber 20 via the mass flow controllers 14 and 36. The reaction chamber 20 is evacuated by the diffusion pump 19,
The degree of vacuum in the reaction chamber 20 is adjusted by a conductance valve 18 interposed between the reaction chamber 20 and the diffusion pump 19. On the other hand, an electrode 22 and an electrode 24 are disposed in the reaction chamber 20 so as to oppose each other in the vertical direction. Then, the electrode 22 is grounded, and the electrode 24 is supplied with high-frequency power. The high-frequency power is supplied from a high-frequency power supply 28 having a frequency of 13.56 MHz via a matching unit 26. On the electrode 24, the samples 30 and 32 having the structure shown in FIG. In the apparatus having such a configuration, plasma etching is performed as follows. First, sample 30, etc., are acetone, trichloroethylene,
After washing for 10 minutes each in the order of acetone and drying by spraying with nitrogen, 5 minutes with aqua regia (hydrochloric acid: nitric acid = 3: 1).
For 10 minutes, and washed with pure water for 10 minutes, and dried by blowing nitrogen. Thereafter, the substrate was further placed on a hot plate at 200 ° C. for 5 minutes for dehydration baking, and then placed on the electrode 24 using sapphire 4 as a mask. Next, the inside of the reaction chamber 20 is sufficiently evacuated by the diffusion pump 19 to reduce the degree of vacuum in the reaction chamber 20 to 5 × 10 ⁻⁶ Torr or less. Thereafter, the flow rate of the CCl ₂ F ₂ gas is controlled by the mass flow controller 14.
It is introduced into the reaction chamber 20 at a controlled rate of 10 cc / min, and the degree of vacuum in the reaction chamber 20 is set to exactly 0.04 Torr by the conductance valve 18.
Was adjusted to Then, 0.44 W / cm ² between the electrode 24 and the electrode 22
The RF power glow discharge is started between supplied electrodes, introduced CCl ₂ F ₂ gas becomes a plasma state, the sample
30,32 etching has begun. After etching for 8 minutes, the sample 30 was etched into the structure shown in FIG. That is, the portion of the GaN layer 3 covered with the mask 4 is not etched, and the exposed GaN layer 4 is not etched.
Only the etched shape was shown. Next, the supply of CCl ₂ F ₂ gas was stopped, and argon (Ar) was stopped.
Gas was supplied for 10 minutes, and etching was further performed. The final etching depth was 8500Å. The sample 30 thus etched is removed from the etching apparatus, and the sample 30 is washed with acetone, trichloroethylene, and acetone in this order for 10 minutes each.
Dried with nitrogen. Then, using a stainless steel plate with holes of 200 μmφ and 500 μm pitch on the sample as a mask, aluminum was applied to the sample at a substrate temperature of 225 ° C., a vacuum degree of 3 × 10 ⁻⁶ Torr during vapor deposition, and a thickness of 500 μm.
The electrode 6 was formed by vapor deposition at 0 ° as shown in FIG. The voltage-current characteristics (VI characteristics) of the electrode 6 thus formed were measured. The result is shown in FIG. It can be seen that good ohmic characteristics are obtained. Next, the sample 30 on which the electrode 6 was formed was sintered at 550 ° C. for 10 minutes in a nitrogen atmosphere, but there was no change in ohmic properties, and the resistance was only slightly reduced. Also, the etching time of argon (Ar) gas can be reduced from 10 minutes.
Extending to 20 minutes, an aluminum electrode was similarly formed, and its VI characteristics were measured. The result is shown in FIG. 6 (c). It can be seen that the ohmic properties slightly deteriorate. However, it is understood that the sintering of the sample improves the ohmic properties as shown in FIG. 6 (h). Therefore, it can be seen that the etching time of Ar gas is desirably about 10 minutes in order to obtain good ohmic properties without sintering. As a comparative example, the characteristics obtained when etching was performed only with CCl ₂ F ₂ gas and not performed with Ar gas were the sixth.
As shown in FIG. 7A, no ohmic properties were obtained. The characteristics after sintering of this sample were as shown in FIG. 6 (f), and no improvement in characteristics was observed. Further, in the case where an electrode was formed by etching with a mixed gas of CCl ₂ F ₂ and Ar, no ohmic property was obtained as shown in FIG. 6 (d). When the sample was sintered, no improvement in ohmic properties was observed as shown in FIG. 6 (i). Further, as shown in FIG. 6 (e), in the case where the electrode was formed by etching with Ar gas from the beginning, no ohmic property was obtained. Also, as shown in FIG. 6 (j), no improvement in ohmic properties was obtained in the characteristics of the sample after sintering. In addition, the characteristics when an aluminum electrode was directly deposited on a gallium nitride semiconductor that had not been etched with CCl ₂ F ₂ gas were measured. The characteristic results are shown in FIGS. 7 (a)-(e). The characteristics measured after sintering the sample are shown in FIGS. 7 (f)-(j). Before sintering, no ohmic properties were obtained, but it can be seen that ohmic properties were obtained by sintering. However, it can also be seen that the ohmic properties vary. From the above, it is understood that when a gallium nitride semiconductor is etched with a CCl ₂ F ₂ gas and an aluminum electrode is formed on the etched portion, the VI characteristics of the power show non-ohmic properties that cannot be improved even by a sinter. Is done. However, it was found that when etching was performed with the CCl ₂ F ₂ gas and then continuously performed with the Ar gas to form an electrode, a good ohmic property was obtained from the beginning without sintering. According to the present inventors' consideration, the above-described continuous etching with Ar gas is performed in advance of CCl ₂ F ₂ gas or CCl ₄ gas or CF.
It is considered that the barrier formed by the adsorption of the etching gas and the reaction product generated by the etching of the _four gases is removed. Therefore, another inert gas which is expected to have the same effect as the Ar gas can be used as the gas used for the etching for removing the barrier thereafter. Next, a method for manufacturing a gallium nitride-based light emitting device using the electrode forming method of the present invention will be described. As shown in FIG. 8, a buffer layer 2 made of AlN is formed on the sapphire substrate 1 to a thickness of 500.degree.
-The GaN layer 3 was formed to a thickness of 3 µm. And that n
-An i-GaN layer 40 is grown on the GaN layer 3 at a growth temperature of 900 ° C. and a thickness of 2500.
Å was formed. Next, as shown in FIG. 9, an SiO ₂ layer 41 was formed on the i-GaN layer 40 to a thickness of 2000 ° by sputtering. Next, a photoresist 42 was applied on the SiO ₂ layer 41, and was formed by photolithography into a pattern in which the photoresist at the electrode formation site for the n-GaN layer 3 was removed. Next, as shown in FIG. 10, the SiO ₂ layer 41 not covered with the photoresist 42 was removed with a hydrofluoric acid-based etchant. Next, as shown in FIG.
The part of the i-GaN layer 40 that is not covered by the O ₂ layer 41 and a part of the n-GaN layer 3 thereunder are subjected to CCl ₂ F under the conditions described above.
After etching at ₂ , dry etching was performed with Ar. Next, as shown in FIG. 12, the SiO ₂ layer 41 remaining on the i-GaN layer 40 was removed with hydrofluoric acid. Next, as shown in FIG. 13, an Al layer 43 was formed on the entire upper surface of the sample by vapor deposition under the conditions described above. Then, a photoresist 44 was applied on the Al layer 43, and a pattern was formed by photolithography into a predetermined shape so that the electrode portions for the n-GaN layer 3 and the i-GaN layer 40 remained. Next, as shown in FIG. 14, the exposed portion of the lower Al layer 43 is etched with a nitric acid-based etchant using the photoresist 44 as a mask, and the photoresist 44 is removed with acetone.
An electrode 45 of the GaN layer 3 and an electrode 46 of the i-GaN layer 40 were formed. In this way, the MIS (Metal-Insulater-Semicondu
A gallium nitride-based light emitting device having a ctor) structure can be manufactured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an apparatus for realizing an etching method according to a specific embodiment of the present invention. FIG. 2 is a sectional view showing a configuration of an etching sample. FIG. 3 is a sectional view showing a relationship between an etching sample and a mask. FIG. 4 is a cross-sectional view of the sample after etching. FIG. 5 is a cross-sectional view of a sample in which an electrode is formed on an etched portion. FIG. 6 is a measurement diagram of VI characteristics of an electrode formed on a gallium nitride semiconductor etched under various conditions. FIG. 7 is a measurement diagram of VI characteristics of an electrode formed on a non-etched gallium nitride semiconductor. 8 to FIG.
FIG. 14 is a cross-sectional view showing the steps of manufacturing a gallium nitride-based light emitting device using the electrode forming method of the present invention. DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate, 2 ... Buffer layer 3 ... GaN layer, 4 ... Mask, 5 ... Electrode formation part 6 ... Electrode, 10 ... Vacuum container 12,34 ... Introduction tube 14,36 ... Mass flow controllers 16, 38 Tanks 19 Diffusion pumps 18 Conductance valves 22, 24 Electrodes 28 High frequency power supply 40 i-GaN layer 41 SiO ₂ layer 42 Photoresist Layer, 43 ... Al layer 45,46 ... electrode

Continuing from the front page (72) Inventor Masahiro Kotaki 1 Ochiai Nagahata, Kasuga-mura, Nishi-Kasugai-gun, Aichi Prefecture Within Toyoda Gosei Co., Ltd. Inside the company (72) Inventor Masafumi Hashimoto 41-cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Institute, Inc. (56) References JP-A-1-204425 (JP, A) JP-A-61- 56474 (JP, A) JP-A-56-51580 (JP, A) JP-A-59-130425 (JP, A)

Claims (1)

(57) [Claims] 1. A method for forming an electrode in a compound semiconductor containing at least gallium and nitrogen, the method comprising dry-etching an electrode-forming portion of the compound semiconductor with a plasma gas containing chlorine or / and fluorine. And dry etching the etched electrode forming portion with an inert gas plasma gas, and thereafter depositing a metal on the electrode forming portion.