JPH10321591A - Method for etching gallium nitride compound semiconductor layer and manufacture of semiconductor light emitting element using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To etch the surface of a semiconductor layer perpendicularly to the surface without causing any such a trouble as mask peeling, etc., by forming an etching mask by forming an Ti film directly on the surface of the semiconductor layer and, after etching is completed, removing the mask by using a hydrofluoric acid solution. SOLUTION: After a semiconductor layer 2 is stacked on a substrate 1, a Ti film 3 is formed on the layer 2 and a photoresist film 4 is formed on the film 3 (a). The part to be etched of the semiconductor layer 2 is exposed by etching the Ti film 3 by the RIE method by using the photoresist film 4 as a mask (b). Then the semiconductor layer 2 is etched by the CAIBE method (c). Thereafter, the photoresist film 4 is removed with O2 plasma or an organic solvent, such as the acetone, etc., and the Ti film 3 is removed with a hydrofluoric acid. Therefore, the perpendicular etching can be performed by preventing the slump of etching shoulders.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of etching a gallium nitride compound semiconductor and a method of manufacturing a semiconductor light emitting device using the same.

[0002]

2. Description of the Related Art Conventionally, in manufacturing a semiconductor light emitting device in which a compound semiconductor such as a light emitting diode (hereinafter, referred to as an LED) or a laser diode is stacked to form a light emitting layer, a part of the stacked compound semiconductor layer is dry etched. In this case, a mask is formed and an opening is provided in the mask, so that the semiconductor layer exposed from the opening is subjected to a reactive ion etching (RIE) method or a CAIBE method (chemical a).
Etching by ssisted ion beam ettiching).

GaAs laminated on a conventional GaAs substrate
Etching of a semiconductor layer made of an s-based compound semiconductor is performed as follows using, for example, a three-layer resist method. That is, as shown in FIG.
A photoresist hard bake layer 22 is formed on the semiconductor layer 21 by one step.
A film of about μm is formed (a photoresist is applied and baked at about 200 ° C.), and a Ti film 23 is formed thereon by about 1000 ° by a sputtering method or the like. Then, a photoresist layer 24 having a thickness of about 1.5 μm is further formed thereon, patterned by a usual photolithography method, and an opening is formed in the photoresist layer 24 where etching is to be performed.

Next, as shown in FIG. 3B, an opening is formed in the Ti film 23 by etching the Ti film 23 by RIE using the photoresist layer 24 as a mask. Thereafter, as shown in FIG. 3C, the exposed portions of the photoresist layer 24 and the photoresist hard bake layer 22 on the surface are removed by oxygen plasma to remove the GaAs semiconductor layer 2.
1. Exposing a place to be etched. Then, FIG.
As shown in (d), the C film is formed using the Ti film 23 as a mask.
The GaAs semiconductor layer 21 is etched by the AIBE method. Thereafter, the photoresist hard bake layer 22 is
By removing with a solvent such as H solution, Ti
The film 23 is also removed and the necessary portions are etched.
As semiconductor layer 21 is obtained.

[0005]

SUMMARY OF THE INVENTION GaAs as described above
In the case of etching by CAIBE, a compound semiconductor composed of the following can increase the selectivity between Ti and GaAs, so that etching can be performed using Ti as a mask. However, when etching a gallium nitride-based compound semiconductor such as GaN, which has recently been developed to manufacture a blue-based semiconductor light emitting device, GaN is GaAs.
As described above, the selectivity with Ti cannot be made large, and the selectivity is only about 1/3 or less of that of GaAs. Therefore, for example, if GaN is to be etched by about 5 μm, it is necessary to provide a Ti film as a mask with a thickness of about 2.5 μm. However, in the case of a Ti film, 0.2 μm
When the film thickness is about or more, the adhesion to the photoresist hard bake layer is reduced, the Ti film is peeled off, and the Ti film cannot be used as a mask for etching a gallium nitride compound semiconductor. is there.

On the other hand, when etching is performed using a photoresist as a mask, the selection ratio of the photoresist is smaller than that of Ti. Therefore, a considerably thick mask must be formed or a resist film must be applied again during the etching, and the thickness must be increased. The resulting resist film has a problem that the perpendicularity of the opening cannot be performed because the perpendicularity of the opening is reduced and the tapered shape is formed together with the etching.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and is intended to form a gallium nitride-based compound semiconductor layer at a time perpendicular to the surface thereof without causing troubles such as mask peeling. It is an object of the present invention to provide a method for etching a gallium nitride-based compound semiconductor layer, which can be efficiently etched by a thin mask using the method described above, and a method for manufacturing a semiconductor light emitting device using the same.

[0008]

Means for Solving the Problems The present inventors have found that even if a Ti film is formed directly on a gallium nitride-based compound semiconductor layer,
By using a hydrofluoric acid solution of an appropriate concentration as a solvent, the Ti film can be removed without damaging the gallium nitride-based compound semiconductor layer at all, and the Ti film can be formed without using a photoresist hard bake layer. As a result, it has been found that even if the thickness is about 2 μm, there is no problem such as peeling, and the present invention using a Ti film as a mask for etching a gallium nitride compound semiconductor has been completed.

In the method of etching a gallium nitride-based compound semiconductor layer according to the present invention, a gallium nitride-based compound semiconductor layer is laminated on a substrate, and an etching mask is formed on the surface of the laminated gallium nitride-based compound semiconductor layer. A method of etching the gallium nitride-based compound semiconductor layer by selectively etching the laminated semiconductor layer through an opening of the etching mask, wherein a Ti film is used as the etching mask. I do.

Here, the gallium nitride compound semiconductor is a compound of Ga of group III element and N of group V element or
Compounds in which part of the group III element Ga is replaced by another group III element such as Al or In and / or compound in which part of the group V element N is replaced by another group V element such as P or As. Semiconductor.

By providing the etching mask directly on the surface of the stacked gallium nitride-based compound semiconductor layer, there is no fear of the mask being peeled off, and the thickness of Ti is sufficiently large to etch the gallium nitride-based compound semiconductor layer. A membrane can be provided.

After the etching is completed, the etching mask made of the Ti film is removed by using a hydrofluoric acid solution to remove only the Ti film without damaging the gallium nitride-based compound semiconductor layer. Can be.

According to a method of manufacturing a semiconductor light emitting device of the present invention, a gallium nitride-based compound semiconductor layer including a first conductivity type layer and a second conductivity type layer and constituting a light emitting layer forming portion is laminated on a substrate;
Forming a Ti film on the surface of the laminated semiconductor layer;
Forming a photoresist film on the film, patterning the photoresist film to open a region to be etched of the laminated semiconductor layer, etching and opening the Ti film exposed by the opening of the photoresist film, Etching the gallium nitride-based compound semiconductor layer exposed through the opening of the Ti film, and thereafter removing the Ti film with a hydrofluoric acid solution,
First and second conductive layers are respectively connected to the first conductive type layer and the second conductive type layer of the stacked semiconductor layers.
Are provided.

[0014]

Next, a method for etching a gallium nitride-based compound semiconductor layer of the present invention and a method for manufacturing a semiconductor light emitting device using the same will be described with reference to the drawings.

First, as shown in FIG. 1A, a first conductivity type (for example, p-type) is formed on a substrate 1 made of sapphire or the like.
Gallium nitride-based compound semiconductor layer 2 including a light-emitting layer forming portion, including a second light-emitting layer and a second conductivity type (for example, n-type) layer.
Are stacked, a Ti film 3 is formed on the surface of the stacked semiconductor layer 2, and a photoresist film 4 is formed on the Ti film 3. The Ti film 3 is provided with a thickness of about 0.5 to 5 μm by, for example, a sputtering method or a vacuum evaporation method.
The photoresist film 4 is used as a normal etching mask.
By solidifying at about 120 ° C., a thickness of about 1 to 2 μm is provided. Then, the photoresist film 4 is patterned to open a portion corresponding to a region to be etched of the laminated semiconductor layer 2.

Next, as shown in FIG. 1B, the Ti film 3 is formed by RIE using the photoresist film 4 as a mask.
Is etched to expose places where the stacked semiconductor layers 2 are to be etched. The etching by the RIE method is performed under a gas atmosphere of Cl ₂ , CF ₄ and N ₂ .
This is performed by plasma discharge.

Thereafter, as shown in FIG. 1C, the photoresist film 4 and the Ti film 3 are used as a mask, Cl ₂ gas is used as an assist gas, and the acceleration voltage of the Ar beam is increased to 6 as shown in FIG.
00V, chemical assist ion beam
The stacked gallium nitride-based compound semiconductor layer 2 is etched by an etching (CAIBE) method.

Thereafter, although not shown, the photoresist film 4 is removed by an asher (O ₂ plasma) or an organic solvent such as acetone. Further, the Ti film 3 is removed with a hydrofluoric acid solution. The removal of the Ti film 3 by hydrofluoric acid is performed by using buffered hydrofluoric acid (BHF, 16 wt.
%), The Ti film was not removed even after immersion for 6 minutes,
As a result of immersion in a t% hydrofluoric acid solution, the Ti film could be peeled off in 5 seconds. The immersion in the hydrofluoric acid solution was continued even after the Ti film was peeled off.
No damage on the surface of the gallium nitride-based compound semiconductor layer was observed even after immersion for 2 seconds. That is, when the concentration is 20 to
When the mask made of the Ti film was removed with a 50 wt% hydrofluoric acid solution, only the Ti film could be removed without damaging the gallium nitride-based compound semiconductor layer at all. As a result, as described above, the Ti film can be provided directly on the gallium nitride-based compound semiconductor layer using the Ti film as a mask.

According to the etching method of the present invention, since the Ti film is directly provided on the surface of the gallium nitride-based compound semiconductor layer as a mask, the problem of peeling off of the Ti film does not occur even if it is formed thick. As a result, even if the film is formed to a thickness of about 2 μm, there is no problem of peeling at all, and a gallium nitride-based compound semiconductor layer having a thickness of about 5 μm can be sufficiently etched. Further, even if a Ti film is provided directly on the gallium nitride-based compound semiconductor layer, the Ti film is removed with hydrofluoric acid, so that the gallium nitride-based compound semiconductor layer is not damaged.

Next, a method of manufacturing a blue semiconductor light emitting device by laminating gallium nitride compound semiconductor layers will be described.

A blue-based semiconductor light emitting device is, for example, shown in FIG.
FIG. 2 shows a cross-sectional explanatory view of an example of the LED chip.
In addition, for example, metal organic chemical vapor deposition (MOCVD)
As a result, a gallium nitride-based compound semiconductor layer is laminated.
That is, sapphire (Al _TwoO_ThreeSingle crystal)
Low temperature buffer layer 12 made of GaN on the surface of substrate 11
Is deposited on the order of 0.01 to 0.2 μm, and then n-type GaN
An n-type layer (cladding layer) 13 made of
And the band gap energy is
Material smaller than that of, for example, InGaN-based
The active layer 14 made of a compound semiconductor layer is formed to a thickness of 0.05 to 0.3 μm.
Degree, p-type AlGaN system (Al / Ga ratio varies
It can change. The same applies hereinafter) Compound semiconductor layer
P-type layer (cladding)
Layers) 15 are sequentially laminated in a thickness of about 0.2 to 1 μm.
You.

Thereafter, in order to expose the n-type layer 13 under the stacked semiconductor layers to form an n-side electrode, the stacked semiconductor layers are not shown but are described in FIG. A Ti film of about 0.5 to 3 μm is formed on the surface by vacuum evaporation. Thereafter, a photoresist film is provided and patterned, and an opening is formed in a portion of the laminated semiconductor layer to be etched. Next, a Ti film is opened by RIE using the photoresist film as a mask, and the stacked semiconductor layers are etched by CAIBE using Cl ₂ gas as an assist gas to expose the n-type layer 13. Then 5
The Ti film is removed with 0 wt% hydrofluoric acid.

Next, Ni and A are formed on the surface of the p-type layer 15.
By depositing and sintering u, a current diffusion layer 17 made of a metal layer is formed in a thickness of about 2 to 100 nm.

Then, on the exposed surface of the n-type layer 13, metal Ti and Al for forming the n-side electrode 19 are formed by vacuum evaporation or the like by about 0.1 μm and about 0.3 μm, respectively. After sintering, a part of a protective film (not shown) such as SiN for the p-side electrode 18 is removed and T
By vacuum-depositing and laminating i and Au, respectively,
A p-side electrode 18 and an n-side electrode 19 are formed. afterwards,
This wafer is cut and separated into each LED chip at its boundary.

It is to be noted that the p-type layer 15 in the above-described example of the laminated structure is G
Although it is a multilayer of aN and an AlGaN-based compound semiconductor, it is preferable to provide a layer containing Al from the viewpoint of the effect of confining carriers, so that only a GaN layer may be used. Also, the n-type layer 13 may be provided with an AlGaN-based compound semiconductor layer to form a multi-layer, and these may be formed of another gallium nitride-based compound semiconductor layer. Furthermore, in this example, the active layer is sandwiched between the n-type layer and the p-type layer, but a double hetero junction structure may be used. However, a pn junction structure in which the n-type layer and the p-type layer are directly bonded may be used.

In the above-described example, an example of etching a blue LED is shown. However, in etching the end face of a blue laser diode, the etching depth and verticality are more strictly required. The method of the invention becomes effective.

[0027]

According to the present invention, since a Ti film can be used as an etching mask for etching a gallium nitride compound semiconductor, a thickness sufficient for etching the gallium nitride compound semiconductor can be obtained. And an etching mask thinner than a photoresist or the like. as a result,
Vertical etching can be performed without dripping the etching shoulder, and efficient and accurate etching can be performed.

[Brief description of the drawings]

FIG. 1 is a process explanatory view illustrating an embodiment of an etching method of the present invention.

FIG. 2 is a cross-sectional view illustrating an example of a blue semiconductor light emitting element chip manufactured by using the etching method of the present invention.

FIG. 3 is a process explanatory view of a conventional example of etching a GaAs-based semiconductor layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 GaN-based compound semiconductor layer 3 Ti film 4 Photoresist film

Claims (4)

[Claims] 1. A gallium nitride-based compound semiconductor layer is laminated on a substrate, an etching mask is formed on a surface of the laminated gallium nitride-based compound semiconductor layer, and the lamination is performed through an opening of the etching mask. A gallium nitride-based compound semiconductor layer that selectively etches the etched semiconductor layer, wherein the etching mask includes Ti
A method for etching a gallium nitride-based compound semiconductor, comprising using a film. 2. The etching method according to claim 1, wherein the etching mask is provided directly on a surface of the stacked gallium nitride compound semiconductor layer. 3. After the etching is completed, the Ti
3. The etching method according to claim 1, wherein the etching mask made of the film is removed using a hydrofluoric acid solution. 4. A gallium nitride-based compound semiconductor layer including a first conductivity type layer and a second conductivity type layer and constituting a light emitting layer forming portion is laminated on a substrate, and a T layer is formed on the surface of the laminated semiconductor layer.
forming an i film, forming a photoresist film on the Ti film,
The photoresist film is patterned to open an area to be etched of the laminated semiconductor layer, the Ti film exposed by the opening of the photoresist film is opened by etching, and the chip exposed by the opening of the Ti film is opened. The gallium arsenide-based compound semiconductor layer is etched, and then the Ti film is removed with a hydrofluoric acid solution, and the first semiconductor layer is electrically connected to the first and second conductivity type layers of the stacked semiconductor layers, respectively. And providing a second electrode.