JPH1032189A - Dry etching method of iii nitride semiconductor and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an etching process which is capable of improving reliability in a protective film or a metal film. SOLUTION: A photoresist film 40 is applied onto a GaN layer 30 and subjected to proximity exposure. The parts A-B and E-F of the photoresist film 40 are completely exposed to light, but the part C-D is not at all exposed to light. The parts B-C and D-E are gradually decreased in exposure from a point B or E to a point C or D, due to a light diffraction phenomenon. As a result, the exposed part of the photoresist film 40 is represented by a region shaded with oblique lines, and the photoresist film 40 can be formed with peripheral part to be thinner as the edge is approached, in a taper when it is developed. The GaN layer 30 is dry-etched using a mask 42. The etched side wall of the GaN layer 30 is inclined at an angle smaller than 90 deg.. As a result, a protective film of SiO2 or the like can be continuously formed uniformly in thickness on a non-etched surface, a side wall surface and an etched surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a dry etching method for a group III nitride semiconductor, and more particularly to a method for forming a protective film or a metal film continuously on a non-etched surface and an etched surface via a step. To an etching method.

[0002]

2. Description of the Related Art Conventionally, a blue light emitting device using a group III nitride semiconductor has been known. In this light-emitting element, an n-layer, a light-emitting layer, and a p-layer are mainly formed on a sapphire substrate, and a part of the n-layer is exposed to form an electrode for the n-layer. The exposure of the n-layer is performed by dry etching.

[0003]

However, in the case of dry etching, the etching proceeds perpendicularly to the mask due to anisotropic etching, and the side wall surface between the non-etched surface and the etched surface is etched. (Step wall) is formed vertically. For this reason, when a protective film is formed on the non-etched surface and the etched surface via the side wall surface, the thickness of the protective film becomes extremely thin on the side wall surface because the side wall surface is vertical. The strength becomes extremely weak. As a result, there is a problem that the function of the protective film cannot be sufficiently performed on the side wall surface.

Also, when a metal film is formed continuously on the non-etched surface and the etched surface, the metal film becomes extremely thin on the side wall surface, and its strength becomes extremely weak. As a result, the metal film has a problem that disconnection easily occurs on the side wall surface.

The present invention has been made to solve the above problems, and an object of the present invention is to develop an etching method for forming a protective film and a metal film satisfactorily.

[0006]

According to the present invention, a tapered inclined mask is formed on the surface of a group III nitride semiconductor to be dry-etched such that the peripheral portion becomes thinner toward the edge. Was formed, and the group III nitride semiconductor was dry-etched using the mask, so that the etching side wall surface could be inclined at an angle of 90 ° or less, preferably in the range of 70 ° to 30 °. This allows
Even if a protective film or a metal film is continuously formed on the non-etched surface and the etched surface, since the side wall surface is inclined in a tapered shape, a sufficient thickness of the protective film or the metal film is formed even on the side wall surface. Therefore, occurrence of protection failure or disconnection failure is prevented.

A mask whose thickness is tapered in the peripheral portion can be formed as follows. That is,
The photoresist is uniformly deposited on the surface of the group III nitride semiconductor.
After the application, the photoresist is exposed and developed at the boundary between the portion left as the mask and the portion to be removed so that the exposure amount gradually increases from the remaining portion to the portion to be removed.

When a dry etching mask of a group III nitride semiconductor is made of a metal, the metal may be formed so as to have a tapered thickness at the peripheral portion. This metal mask can be formed by forming a metal film having a uniform thickness, forming a resist mask having a tapered shape in the peripheral portion, and dry-etching the metal film using the mask. it can.

As a group III nitride semiconductor, (In _x Ga _{1 -x} ) _y Al
_{In the case of 1-yN} (0 ≦ x ≦ 1,0 ≦ y ≦ 1), the electrode surface for the n-layer of the blue and green light-emitting diodes and the subsequent dry layer for forming the protective film are formed. The present invention can be used for etching.

Further, according to the invention of claim 4, from the surface of the uppermost layer to the exposed surface of the current supply layer, 90
Since the element has a side wall surface inclined in a tapered shape at an angle of less than degree and provided with a protective film covering at least a part of the surface of the uppermost layer, the side wall surface and at least a part of the exposed surface of the current supply layer. Since the protective film is formed with a sufficient thickness on the side wall surface, the protective function can be sufficiently exhibited. The side wall surface is formed by the above-described dry etching method.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on specific embodiments. The present invention is not limited to the following examples. As shown in FIG. 1A, the GaN layer 30
A photoresist 40 is uniformly applied to a thickness of 1.5 μm on the substrate. Next, as shown in FIG. 1B, proximity exposure is performed in which the distance between the mask 42 (mask pattern film) and the photoresist 40 is 10 to 20 μm. Thus, the photoresist 40 is completely exposed during AB and EF, and is not exposed at all during CD. However, between BC and DE, due to the diffraction phenomenon of light, B
Alternatively, the exposure amount gradually decreases from E to C or D. As a result, the exposed portion of the photoresist 40 is
(B) is a shaded portion, and the exposed photoresist 4
When 0 is developed, as shown in FIG.
It can be inclined in a tapered shape with a smaller thickness toward the edge. After development, the exposed photoresist 40 is rinsed for a predetermined time, and post-baked for a predetermined time.

Next, the GaN layer 30 is dry-etched using a photoresist mask 43 shaped into the shape shown in FIG. For this dry etching, reactive ion beam etching (RIBE) was used. Degree of vacuum
GaN was etched by supplying BCl ₃ gas at a rate of 10 ml / min at 0.04 Torr and high frequency power of 0.44 W / cm ² . in this way,
Due to the anisotropic etching, the angle θ of the etched side wall surface W of the GaN layer 30 with respect to the horizontal plane is smaller than 90 degrees, and the side wall surface W becomes a surface inclined in a tapered shape. As a result, FIG.
As shown in (c), the protective film 44 made of SiO ₂ or the like
Can be continuously formed on the non-etched surface X, the side wall surface W, and the etched surface Y with a uniform thickness. As a result, the protective film 4
4 can secure a sufficient thickness on the side wall surface W, and there is no decrease in strength at that portion, and the protective performance of the protective film 44 can be sufficiently achieved. Similarly, a metal film 4 of Au or Al
5 can also be formed, the thickness of the metal film 45 on the side wall surface W can be sufficiently ensured, and the occurrence of disconnection at that portion is prevented.

Next, an embodiment in which the dry etching is applied to the manufacture of a light emitting device will be described. The light emitting device 100 having the structure shown in FIG.
(PE). The gases used were ammonia (NH ₃ ), carrier gas (H ₂ ), trimethylgallium (Ga (CH ₃ ) ₃ ) (hereinafter referred to as “TMG”), and trimethylaluminum (Al (CH ₃ ) ₃ ) (Written as `` TMA '')
, Trimethylindium (In (CH ₃ ) ₃ ) (hereinafter referred to as “TMI”), silane (SiH ₄ ), diethylzinc (Zn (C ₂ H ₅ ) ₂ ) (hereinafter referred to as “DEZ”) and cyclopentane Dienyl magnesium (Mg (C ₅ H ₅ ) ₂ ) (hereinafter referred to as “CP ₂ Mg”).

First, a single-crystal sapphire substrate 1 is mounted on a susceptor placed in a reaction chamber of an M0VPE apparatus, with the a-plane cleaned by organic cleaning and heat treatment as a main surface. Next, the sapphire substrate 1 was baked at a temperature of 1100 ° C. while flowing H ₂ into the reaction chamber at a flow rate of 2 liter / min at normal pressure for about 30 minutes.

Next, by lowering the temperature to 400 ° C., and H ₂
20 liter / min, NH ₃ 10 liter / min, TMA 1.8 × 10 ^-5
The AlN buffer layer 2 was supplied at about 0.1 mol / min for about 90 seconds.
It was formed to a thickness of 05 μm. Next, the temperature of the sapphire substrate 1 was maintained at 1150 ° C., H ₂ was 20 liter / min, and NH ₃ was 10 lite.
r / min, TMG 1.7 × 10 ^-4 mol / min, 0.86p by H ₂ gas
Silane diluted at 20 × 10 ⁻⁸ mol / min was introduced for 40 minutes at a film thickness of about 4.0 μm, an electron concentration of 1 × 10 ¹⁸ / cm ³ , and a silicon concentration of 4 × 10 ¹⁸ / cm ³ (Si). 3.) A high carrier concentration n ⁺ layer 3 made of doped GaN was formed.

After forming the high carrier concentration n ⁺ layer 3, the temperature is maintained at 1100 ° C. and H ₂ is reduced to 20 liter / hour.
Min, NH ₃ at 10 liter / min, TMG at 1.12 × 10 ^-4 mol / min
Min, silane to 10 × 10 diluted to 0.86ppm with H ₂ gas
Introduced at ^-9 mol / min for 30 minutes, film thickness about 5.0 μm, electron concentration 5
× 10 ¹⁷ / cm ³ , silicon (Si) with a silicon concentration of 1 × 10 ¹⁸ / cm ³
An n layer 4 made of doped GaN was formed.

Subsequently, the temperature is maintained at 800 ° C. and N ₂ or H ₂
20 liter / min, NH ₃ 10 liter / min, TMG 0.2 × 10
^-4 mol / min, TMI 1.6 × 10 ^-4 mol / min, by H ₂ gas
Silane diluted to 0.86 ppm at 10 × 10 ^-8 mol / min, DEZ
Was supplied at a ^rate of 2 × 10 ⁻⁴ mol / min for 30 minutes, and silicon and zinc having a thickness of 100 nm were doped to 5 × 10 ¹⁸ / cm ³ , respectively.
The light emitting layer 5 made of In _0.20 Ga _0.80 N was formed.

Subsequently, the temperature is raised to 1100 ° C. and N ₂ or H ₂
20 liter / min, NH ₃ 10 liter / min, TMG 1.12 × 10
^-4 mol / min, 0.47 × 10 ^-4 mol / min of TMA and CP ₂ Mg
Was introduced at 2 × 10 ⁻⁵ mol / min for 6 minutes to form a cladding layer 6 made of magnesium (Mg) -doped Al _0.08 Ga _0.92 N and having a thickness of about 100 nm. The magnesium concentration of the cladding layer 6 is 5 × 10 ¹⁹ / cm ³ . In this state, the cladding layer 6
Is an insulator having a resistivity of 10 ⁸ Ωcm or more.

Next, the temperature was maintained at 1100 ° C. and N ₂ or H ₂ was added.
20 liter / min, NH ₃ is 10 liter / min, TMG is 1.12 × 10 ^-4
Mole / minute and CP ₂ Mg at a rate of 2 × 10 ⁻⁵ mole / minute for 1 minute, and a magnesium (Mg) -doped GaN film with a thickness of about 200 nm.
The first contact layer 71 made of was formed. The magnesium concentration of the first contact layer 71 is 5 × 10 ¹⁹ / cm ³ .
In this state, the first contact layer 71 still has the resistivity
It is an insulator of 10 ⁸ Ωcm or more.

Next, the temperature is maintained at 1100 ° C. and N ₂ or H ₂ is added.
20 liter / min, NH ₃ is 10 liter / min, TMG is 1.12 × 10 ^-4
Mol / min and CP ₂ Mg were introduced at 4 × 10 ⁻⁵ mol / min for 3 minutes to form a p ⁺ second contact layer 72 of magnesium (Mg) -doped GaN having a thickness of about 50 nm. The magnesium concentration of the second contact layer 72 is 1 × 10 ²⁰ / cm ³ . In this state, the second contact layer 72 is still an insulator having a resistivity of 10 ⁸ Ωcm or more.

Next, the second contact layer 72, the first contact layer 71, and the cladding layer 6 were uniformly irradiated with an electron beam using an electron beam irradiation apparatus. Electron beam irradiation conditions are: acceleration voltage about 10KV, data current 1μA, beam moving speed 0.2m
m / sec, beam diameter 60 μmφ, vacuum degree 5.0 × 10 ⁻⁵ Torr. By the irradiation of the electron beam, the second contact layer 72,
The first contact layer 71 and the cladding layer 6 have a hole concentration of 6 × 10 ¹⁷ / cm ³ , 3 × 10 ¹⁷ / cm ³ , 2 × 10 ¹⁷ / cm ³ and a resistivity of 2 Ωcm, 1 Ωcm and 0.7 Ωcm, respectively. It became a conduction type semiconductor.
Thus, a wafer having a multilayer structure was obtained.

Subsequently, in order to form the electrode pad 10 of the n ⁺ layer 3, the second contact layer 72, the first contact layer 71, the clad layer 6, the light emitting layer 5, and a part of the n layer 4 are etched. Removed. The etching by the method described above was used for the etching here. That is, a photoresist is uniformly applied on the second contact layer 72, and the photoresist is exposed as shown in FIG. A photoresist mask 43 having the shape shown in FIG. This photoresist mask 4
3, the second contact layer 72, the first contact layer 71, the cladding layer 6, the light emitting layer 5, and the n layer 4 are formed by reactive ion beam etching (RIBE) using Cl ₂ gas plasma.
Was partially etched. Etching conditions are vacuum degree 1m
Torr, high frequency power 300W, 5ml / min. By this anisotropic etching, as shown in FIG. 3, the angle θ of the etched side wall surface W with respect to the horizontal plane becomes 60 to 45 degrees, and the side wall surface W becomes a surface inclined in a tapered shape.

Next, at a high vacuum of about 10 ^-7 Torr, Ni is uniformly deposited to a thickness of 25 °, followed by Au to a thickness of 60 °, applying a photoresist, and performing a photolithography process. After the etching process, the first electrode layer 81 and the second electrode layer 82 were formed on the second contact layer 72. As a result, a transparent electrode layer 8 of Ni / Au was formed. And
Except for the region for forming the electrode pads 9 by coating a resist on the uppermost layer of the entire surface at a high vacuum of about 10 ^-7 Torr, Ni, A
u and Al were sequentially evaporated to a thickness of 1000 °, 1.5 μm, and 300 °. Thereafter, the first metal layer 91, the second metal layer 92, and the third metal layer 93 were formed at necessary places by lifting off the resist. Thus, the electrode pad 9 having a three-layer structure was formed. On the other hand, the electrode pad 10 was formed on the n ⁺ layer 3 by depositing Al.

Next, the substrate 1 was placed in a heating furnace, and the substrate 1 was heated for several seconds to 10 minutes while the ambient temperature was set at a temperature in the range of 400 ° C. to 700 ° C. Next, on the uppermost layer of the substrate 1 formed as described above, a 5000 mm thick
An SiO ₂ film was formed by sputtering. Thereafter, through a photoresist coating, a photolithography step, and an etching step, windows 9A and windows 10A were formed by dry etching on the electrode pads 9 and portions of the SiO ₂ film corresponding to the wire bonding regions of the electrode pads 10. Thus, the protective film 11 made of SiO ₂ was formed.

Since the side wall surface W of this protective film 11 is tapered at an angle of less than 90 degrees with respect to the horizontal plane, a thickness of 5000 ° can be obtained on the side wall surface W. Fully functions as a protective film.

The material of the semiconductor layer to be etched to form the tapered sidewall W is, in addition to GaN, a general formula: (In _x Ga _{1 -x} ) _y Al _{1 -y} N (0 ≤x ≤1,0 ≤y ≤1)
Can be used. Further, the thickness of the protective film 11 is
A thickness of 300 mm to 3 μm is desirable. If it is thinner than 300 mm, its function as a protective film to prevent moisture intrusion and scratching will decrease,
If the thickness is more than 3 μm, transparency is undesirably lost. In the above embodiment, the diode is described as the light emitting element. However, the present invention can be applied to a laser diode.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a dry etching method according to a specific embodiment of the present invention.

FIG. 2 is an explanatory view showing a dry etching method according to a specific example of the present invention.

FIG. 3 is a configuration diagram showing a configuration of a light emitting element manufactured by applying the etching method.

FIG. 4 is an explanatory view showing a method for etching a light emitting element.

[Explanation of symbols]

REFERENCE SIGNS LIST 100 light-emitting element 1 sapphire substrate 2 buffer layer 3 high carrier concentration n ⁺ layer 4 n-layer 5 light-emitting layer 6 cladding layer 9, 10 electrode pad 11 protective film 71 first contact layer 72 Second contact layer 81: first electrode layer 82: second electrode layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shiro Yamazaki, 1 Ochiai Nagahata, Kasuga-cho, Nishi-Kasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. Inside Toyoda Gosei Co., Ltd. (72) Inventor Masayoshi Koike 1 Ogataai Nagahata, Kasuga-machi, Nishi-Kasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. 72) Inventor Hiroshi Amano 2-104 Yamanote, Nagoya-shi, Nagoya, Aichi

Claims (4)

[Claims] In the method of dry-etching a group III nitride semiconductor, a peripheral portion of the surface of the group III nitride semiconductor to be dry-etched is tapered in such a manner that its thickness is reduced toward the edge. Forming a mask, and dry-etching the group III nitride semiconductor using the mask, wherein an etching side wall surface of the group III nitride semiconductor is inclined at an angle of 90 degrees or less. Dry etching method for group nitride semiconductor. 2. The mask comprises a photoresist,
After uniform application on the surface of the group III nitride semiconductor, at the boundary between the portion to be left as a mask and the portion to be removed, the photo-exposure is gradually increased from the remaining portion to the portion to be removed. The dry etching method for a group III nitride semiconductor according to claim 1, wherein the resist is exposed and then developed to form the mask inclined in a tapered shape in a peripheral portion. 3. The group III nitride semiconductor is (In _x Ga _1-x ) _y Al
3. The dry etching method for a group III nitride semiconductor according to claim _{1, wherein 1-yN} (0 ≦ x ≦ 1,0 ≦ y ≦ 1). 4. A method according to claim 1, wherein at least a p-layer and an n-layer made of a group III nitride semiconductor are laminated, a part of the upper layer is removed, a part of the lower current supply layer is exposed, and the uppermost layer and the current supply are removed. A light emitting element having an electrode formed on an exposed surface of the layer, wherein a sidewall surface extending from the surface of the uppermost layer to the exposed surface of the current supply layer and tapered at an angle of less than 90 degrees with respect to a horizontal plane; A group III nitride semiconductor device, comprising: a protective film covering at least a part of the surface of the substrate, the side wall surface, and at least a part of the exposed surface of the current supply layer.