KR100768402B1 - Method for fabricating semiconductor laser diode - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor laser diode, wherein after forming a ridge structure by a self-aligning method, wet etching a side of the ridge structure and a part of the upper portion of the p-clad layer with a high temperature phosphoric acid solution.

According to the present invention, the damaged region of the side of the ridge structure and the upper surface of the p-clad layer adjacent to the ridge structure can be removed to reduce leakage current and improve the reliability of the device. Since the upper surface of the p-clad layer is formed vertically, the contact resistance is reduced, thereby reducing the operating voltage.

Ridge, Threshold Current, Self Alignment, Wet Etch

Description

Method for fabricating semiconductor laser diode

1 is a cross-sectional view of a conventional nitride-based semiconductor laser diode.

2A to 2C are sectional views showing a process of forming a conventional ridge wave guide structure.

3 is a view showing a transmission electron microscope (TEM) photograph of a ridge structure when the ridge structure is formed by a conventional self-alignment method.

4A to 4H are cross-sectional views showing one embodiment of a method of manufacturing a semiconductor laser diode of the present invention.

5 is a view showing a scanning electron microscope (SEM) photograph of a ridge structure formed according to the method of manufacturing a semiconductor laser diode of the present invention.

6A to 6E are cross-sectional views showing another embodiment of the method for manufacturing a semiconductor laser diode of the present invention.

Explanation of symbols on the main parts of the drawings

100, 300: substrate 110, 310: n-contact layer

120, 320: n-clad layer 130, 330: n-wave guide layer

140, 340: active layer 150, 350: p-wave guide layer

160, 360: p-clad layer 170, 370: p-contact layer

180, 380: p-contact metal layer 190, 390: protective film

200, 400 p-pad electrode 210, 410 n-pad electrode

250, 450: ridge structure

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor laser diode, and in particular, after forming a ridge structure by a self-aligning method, by wet etching with a high temperature phosphoric acid solution, to remove the surface damaged by plasma and to keep the width of the ridge constant A method for manufacturing a semiconductor laser diode that reduces the threshold current.

In recent years, semiconductor laser diodes have been put to practical use in optical communication, multi-communication, space communication, etc. because of the narrow frequency range and sharpness of light. In addition, high-speed laser printing, compact disk player (CDP) and compact disc It is widely used in optical storage devices such as reproduction / recording devices.

In particular, the nitride semiconductor laser diode is a direct transition type having a high probability of laser oscillation, and has a short wavelength of oscillation wavelength from the ultraviolet region to the green region due to the wide band gap energy. I am getting it.

In addition, since the nitride semiconductor laser diode does not use arsenic (As) as a main component, it has a high response in terms of environmental friendliness.

The semiconductor laser diode used for the light source of the optical storage device must satisfy the single mode and high power characteristics. To this end, a ridge waveguide is provided to limit the injected current, thereby lowering the threshold current and gaining only the single mode. To have.

1 is a cross-sectional view of a conventional nitride-based semiconductor laser diode, and shows a semiconductor laser diode having a ridge waveguide to reduce a threshold current value for laser oscillation.

As shown therein, the n-contact layer 11, the n-clad layer 12, the n-wave guide layer 13, the active layer 14, and the p-wave guide layer on the sapphire substrate 10 ( 15) are sequentially stacked,

Mesa is etched from the p-wave guide layer 15 to a portion of the n-contact layer 11 to expose a portion of the n-contact layer 11,

A p-clad layer 16 having a central portion protruding is formed on the p-wave guide layer 15, and a p-contact layer 17 is formed on the protruding p-clad layer 16. Is formed to form a ridge (Ridge) structure,

The p-contact metal layer 18 is formed on the p-contact layer 17, the protective film 19 is formed on the side of the ridge structure and the p-clad layer 16.

A p-pad electrode 20 is formed around the p-contact metal layer 18 and a portion of the passivation layer 18, and the n-pad electrode 21 is disposed on the exposed n-contact layer 11. It is formed.

As described above, the ridge wave guide structure limits the current injected into the active layer 14 to limit the width of the resonance region for laser oscillation in the active layer 14, thereby stabilizing the transverse mode and lowering the operating current.

As a method of forming the ridge wave guide structure, the p-contact metal layer formed on the p-contact layer is patterned, and then the p-contact layer and the p-clad layer are formed using the patterned p-contact metal layer as an etch mask. By dry etching, a Self Align Process that makes a ridge structure is preferred.

2A to 2C are cross-sectional views illustrating a process of forming a conventional ridge wave guide structure. For convenience, only the structure formed on the n-clad layer is shown.

As shown therein, the n-wave guide layer 51, the active layer 52, the p-wave guide layer 53, the p-clad layer 54, and the p-contact layer are formed on the n-clad layer 50. 55, the p-contact metal layer 56 is sequentially stacked (FIG. 2A).

Next, after the photoresist is applied on the p-contact metal layer 56, the photoresist is patterned and the p-contact metal layer 56 is etched using the patterned photoresist as an etch mask (FIG. 2B). .

Thereafter, a portion of the p-contact layer 55 and the p-cladding layer 54 is dry-etched using the remaining p-contact metal layer 56 as an etch mask, thereby removing the p-cladding layer 54. A ridge structure 60 protruding in the center region is formed (FIG. 2C).

Subsequently, a passivation layer 57 is formed on a side surface of the ridge structure 60 and an upper portion of the p-clad layer 54, and the p-contact metal layer 56 and a portion of the passivation layer 57 are wrapped to form p-. The pad electrode 58 is formed (FIG. 2D).

In the case of forming the ridge wave guide structure by such a method, there are the following problems.

First, when the etch structure 60 is formed by dry etching a portion of the p-contact layer 55 and the p-cladding layer 54 using the patterned p-contact metal layer 56 as an etching mask, There is a problem that the effective ridge width is wider than the mask width for forming the ridge width.

That is, when the ridge structure 60 is formed through the dry etching process, the side surface of the ridge structure 60 is not vertically formed and has an inclination of 70 to 80 degrees.

Therefore, the lower width of the ridge structure 60 is formed to be wider than the upper width of the ridge structure 60, which causes a problem in that the contact resistance increases and the threshold current of the semiconductor laser diode increases.

Second, p-clad layer adjacent to ridge structure 60 by dry etching part of p-contact layer 55 and p-clad layer 54 using patterned p-contact metal layer 56 as an etch mask. There is a problem that the surface of the 54 is not flat and the residual depth is nonuniform.

3 is a view showing a transmission electron microscope (TEM) photograph of the ridge structure when the ridge structure is formed by a conventional self-alignment method.

As shown in the drawing, the ridge structure formed by the self-aligning method has an inclined side surface, so that the lower width R2 of the ridge structure is wider than the upper width R1 of the ridge structure, and the width of the ridge structure is increased depending on the etching depth. It's changing.

In addition, it can be seen that the surface of the nitride semiconductor layer adjacent to the ridge structure is not flat and curved.

Third, if the ridge structure is formed through the dry etching process, the side surface of the ridge structure 60 and the top surface of the p-clad layer 54 may be damaged by plasma, causing problems with leakage current and reliability. do.

That is, the dry etching causes plasma damage on the side surface of the ridge structure 60 and the top surface of the p-clad layer 54, which includes many crystallographic defects and leaks when a voltage is applied to the device. It acts as a passage for the current, increasing the operating current of the laser oscillation.

Accordingly, an object of the present invention is to form a ridge structure by the self-aligned method, and then wet etching using a high temperature phosphoric acid solution, thereby removing the surface damaged by plasma and maintaining the width of the ridge to reduce the threshold current The present invention provides a method for manufacturing a laser diode.

According to one embodiment of the method of manufacturing a semiconductor laser diode of the present invention, after n-contact layers, n-clad layers, n-wave guide layers, active layers, and p-wave guide layers are sequentially stacked on the substrate, p Mesa etching from a wave guide layer to a portion of the n-contact layer, and sequentially forming a p-clad layer, a p-contact layer, and a p-contact metal layer on the p-wave guide layer. patterning a p-contact metal layer; dry etching a portion of the p-contact layer and the p-clad layer using the patterned p-contact metal layer as an etch mask to form a ridge structure; Wet etching a side surface of the ridge structure and a portion of the upper portion of the p-clad layer, forming a protective film surrounding the side surface of the ridge structure and the p-clad layer, and forming the protective layer on the p-contact metal layer and the protective film. Some Forming a cheaper p- pad electrode, and is characterized in that the mesa-etching comprises the step of forming a pad electrode on the upper n- n- exposed contact layer.

Another embodiment of the method of manufacturing a semiconductor laser diode of the present invention, an n-contact layer, n- clad layer, n-wave guide layer, active layer, p-wave guide layer, p-clad layer, p-contact on the substrate Sequentially depositing a layer and a p-contact metal layer, and after patterning the p-contact metal layer, the p-contact layer and the p-clad layer using the patterned p-contact metal layer as an etch mask. Forming a ridge structure by dry etching a portion of the etch structure, wet etching a side of the ridge structure and a portion of the upper portion of the p-clad layer, and covering the side surface of the ridge structure and the p-clad layer. And forming a p-pad electrode surrounding a portion of the p-contact metal layer and the passivation layer, and forming an n-pad electrode under the substrate.

Hereinafter, a method of manufacturing the semiconductor laser diode of the present invention will be described in detail with reference to FIGS. 4 to 6. 4A to 4H are cross-sectional views showing one embodiment of a method of manufacturing a semiconductor laser diode of the present invention.

As shown therein, the n-contact layer 110, the n-clad layer 120, the n-wave guide layer 130, the active layer 140, and the p-wave guide layer 150 on the substrate 100. Are sequentially stacked (FIG. 4A).

Here, the substrate 100 is a sapphire (Al ₂ O ₃ ) substrate, silicon carbide (SiC) substrate, silicon (Si) substrate, gallium arsenide (GaAs) substrate, etc. are used, in particular sapphire substrate is typically used This is because there is no commercial substrate in the lattice match that is identical to the crystal structure of the nitride semiconductor material grown on the substrate 100.

The n-contact layer 110 is a GaN-based group III-V nitride compound semiconductor layer, preferably an n-GaN layer, but an AlGaN layer or InGaN containing aluminum (Al) or indium (In) at a predetermined ratio. Layer or InAlGaN layer.

The n-clad layer 120 is composed of In _x Al _y Ga _1-xy N having a predetermined refractive index, where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ x + y ≦ 1. Have

That is, the n-clad layer 110 may be formed of a nitride compound semiconductor such as n-AlGaN, n-InGaN, n-InAlGaN, or the like.

The n-wave guide layer 130 is made of a material having a lower refractive index than the active layer 140 but a higher refractive index than the n-clad layer 110, and is mainly made of n-GaN.

The n-contact layer 110, n-clad layer 120, and n-wave guide layer 130 become the first material layer for lasing used to induce laser oscillation in the active layer 140.

The active layer 140 is a material layer in which lasing occurs by electron-hole recombination, and In _x Al _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1 And a single quantum well structure or a barrier layer consisting of a well layer consisting of a barrier layer consisting of In _x Al _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) The well layer is composed of a multi-quantum well structure formed by sequentially repeating stacking.

Here, by controlling the components of In, Al, and Ga of the active layer 140, a short wavelength laser diode having an energy band gap of AlN (˜6.2 eV) is free from a long wavelength having an energy band gap of InN (˜1.8 eV). I can make it.

The p-wave guide layer 150 is made of a material having a lower refractive index than the active layer 140 while having a higher refractive index than the p-clad layer 160. The p-wave guide layer 150 mainly consists of p-GaN.

Due to the difference in refractive index between the n-wave guide layer 130 and the p-wave guide layer 150 and the active layer 140, the light generated in the active layer 140 does not leave the active layer 140. do.

That is, the n-wave guide layer 130 and the p-wave guide layer 150 serve to trap light generated from the active layer 140 in the active layer 140.

Here, an electron blocking layer (EBL) may be further formed between the active layer 140 and the p-wave guide layer 150.

The electron blocking layer is to prevent the overflow of electrons due to the low hole carrier concentration and mobility of the p-type nitride compound semiconductor, and is made of a thin AlGaN layer having an Al composition of ˜20%.

Next, Mesa is etched from the p-wave guide layer 150 to a portion of the n-contact layer 110 to expose a portion of the n-contact layer 110 from the top (FIG. 4B).

Subsequently, the p-clad layer 160, the p-contact layer 170, and the p-contact metal layer 180 are sequentially formed on the p-wave guide layer 150 (FIG. 4C).

The p-clad layer 160 is formed of the same material layer as the n-clad layer 120 except that the implanted conductive impurities are different.

That is, the p-clad layer 160 may be formed of a nitride compound semiconductor such as p-AlGaN, p-InGaN, or p-InAlGaN according to the n-clad layer 120.

The p-contact layer 170 is formed of the same material layer as the n-contact layer 110 except that the implanted conductive impurities are different, preferably the p-GaN layer, and the p-contact metal layer 180 It has a higher doping concentration than the p-clad layer 160 to lower the contact resistance with.

The p-wave guide layer 150, the p-clad layer 160, and the p-contact layer 170 may have a second material layer for lasing used to induce laser oscillation in the active layer 140. do.

The p-contact metal layer 180 is made of platinum (Pt) or palladium (Pd) having a low contact resistance and suitable for use as a mask.

Thereafter, the p-contact metal layer 180 is patterned (FIG. 4D).

That is, after photoresist is applied on the p-contact metal layer 180, the photoresist is patterned and the p-contact metal layer 180 is etched using the patterned photoresist as an etch mask.

Next, a portion of the p-contact layer 170 and the p-clad layer 160 is etched using the patterned p-contact metal layer 180 as an etching mask to form a ridge structure 250 ( 4e).

Here, the etching uses dry etching such as reactive ion etching (RIE), wherein a chlorine-based gas such as Cl ₂ , CCl ₄ , SiCl _4, or the like is used to etch the nitride semiconductor.

Dry etching the portions of the p-contact layer 170 and the p-cladding layer 160 using the patterned p-contact metal layer 180 as an etch mask, as described above, of the ridge structure 250 The side surface is inclined so that the lower width of the ridge structure 250 becomes wider than the upper width.

In addition, the surface of the p-clad layer 160 adjacent to the ridge structure 250 is not flat, resulting in non-uniform residual depth, and the side surface of the ridge structure 250 and the p-clad layer 160. The top surface is damaged by plasma.

Therefore, in the present invention, the side of the dry-etched ridge structure 250 and a portion of the upper surface of the p-clad layer 160 are wet etched using a high temperature phosphoric acid (H ₃ PO ₄ ) solution in a subsequent process (FIG. 4f).

At this time, the wet etching using the phosphoric acid solution is preferably performed at a temperature of 150 ~ 170 ℃.

When the wet etching process is performed using the hot phosphoric acid solution, the damaged region of the side surface of the ridge structure 250 and the upper surface of the p-clad layer 160 adjacent to the ridge structure 250 is removed.

In addition, the side surface of the ridge structure 250 is etched to have a vertical structure, and the top surface of the p-clad layer 160 is flat to have a uniform residual depth.

As described above, according to the present invention, the side of the ridge structure 250 has a vertical structure, and thus the contact resistance is lowered, thereby reducing the threshold current, and the side of the ridge structure 250 and the side of the ridge structure 250 are adjacent to each other. By removing the damaged region of the upper surface of the p- clad layer 160, there is an effect that the leakage current is reduced and the reliability is improved.

Subsequently, the passivation layer 190 is formed to surround the side surface of the ridge structure 250 and the upper surface of the p-clad layer 160 (FIG. 4G).

That is, first, the passivation layer 190 is deposited to have a constant thickness surrounding the side surface of the ridge structure 250, the upper surface of the p-clad layer 160, and the p-contact metal layer 180.

After the photoresist is coated on the passivation layer 190, the photoresist is etched using O ₂ plasma to expose the passivation layer 190 formed on the p-contact metal layer 180.

Thereafter, after the protective layer 190 formed on the p-contact metal layer 180 is etched by using a dry or wet etching process, the remaining photoresist is removed.

Here, the protective film 190 may be selected from any one of a silicon oxide film (SiO ₂ ), a silicon nitride film (Si ₃ N ₄ ), Al ₂ O ₃ , HfO, TiO ₂ , the protective film 190 It is preferable that the thickness of is 30-300 nm in consideration of the effective refractive index which can exhibit the light shielding effect.

Subsequently, a p-pad electrode 200 is formed on the p-contact metal layer 180 and a portion of the passivation layer 190, and the n-pad electrode 210 is disposed on the exposed n-contact layer 110. ) Is formed (FIG. 4H).

The p-pad electrode 200 and the n-pad electrode 210 may be any one selected from chromium (Cr), nickel (Ni), gold (Au), aluminum (Al), titanium (Ti), and platinum (Pt). Made of a metal or an alloy of the metals.

5 is a view showing a scanning electron microscope (SEM) photograph of a ridge structure formed according to the method of manufacturing a semiconductor laser diode of the present invention.

As shown in the drawing, it can be seen that the side surface of the ridge structure has a vertical structure and the surface of the nitride semiconductor layer adjacent to the ridge structure is flat.

6A to 6E are cross-sectional views showing another embodiment of the method of manufacturing a semiconductor laser diode of the present invention.

As shown in the drawing, first, the n-contact layer 310, the n-clad layer 320, the n-wave guide layer 330, the active layer 340, and the p-wave guide layer 350 on the substrate 300. ), the p-clad layer 360, the p-contact layer 370, and the p-contact metal layer 380 are sequentially stacked (FIG. 6A).

Here, the substrate 100 is a free standing nitride substrate, preferably an n-GaN substrate.

The substrate 100 may be obtained by forming a nitride semiconductor layer on a sapphire substrate to a predetermined thickness, and then separating the sapphire substrate from the nitride semiconductor layer by performing a mechanical lapping process or by irradiating a laser.

Next, after the p-contact metal layer 380 is patterned, a portion of the p-contact layer 370 and the p-cladding layer 360 using the patterned p-contact metal layer 380 as an etching mask. Is etched to form a ridge structure 450 (FIG. 6B).

Subsequently, a portion of the side surface of the ridge structure 450 and an upper portion of the p-clad layer 360 is wet etched using a high temperature phosphoric acid (H ₃ PO ₄ ) solution (FIG. 6C).

Thereafter, the protective layer 390 is formed to surround the side surface of the ridge structure 450 and the upper surface of the p-clad layer 360 (FIG. 6D).

Subsequently, a p-pad electrode 400 is formed around the p-contact metal layer 380 and a portion of the passivation layer 390, and an n-pad electrode 410 is formed below the substrate 300 ( 6e).

Here, before forming the n-pad electrode 410 under the substrate 300, a polishing process of lapping and polishing the lower surface of the substrate 300 to facilitate heat dissipation. Can be further performed.

On the other hand, while the present invention has been shown and described with respect to specific preferred embodiments, various modifications and variations of the present invention without departing from the spirit or field of the invention provided by the claims below It will be readily apparent to one of ordinary skill in the art that it can be used.

According to the present invention, after forming the ridge structure by the self-aligning method, by wet etching using a hot phosphoric acid solution, the damaged region of the side of the ridge structure and the upper surface of the p- clad layer adjacent to the ridge structure is removed There is an effect of reducing the leakage current and improving the reliability of the device.

In addition, since the side surface of the ridge structure is etched to have a vertical structure, the contact resistance is reduced, thereby reducing the operating voltage.

Claims (8)

The n-contact layer, n-clad layer, n-wave guide layer, active layer, and p-wave guide layer are sequentially stacked on the substrate, and mesa etching is performed from the p-wave guide layer to a portion of the n-contact layer. Doing; Sequentially forming a p-clad layer, a p-contact layer, and a p-contact metal layer on the p-wave guide layer, and then patterning the p-contact metal layer; Dry etching the p-contact layer and a portion of the p-clad layer using the patterned p-contact metal layer as an etch mask to form a ridge structure; Wet etching the surface of the ridge structure and a portion of the upper surface of the p-clad layer with a phosphoric acid (H ₃ PO ₄ ) solution; Forming a passivation layer surrounding the side of the ridge structure and the p-clad layer; And And forming a p-pad electrode on the p-contact metal layer and a portion of the passivation layer, and forming an n-pad electrode on the mesa-etched and exposed n-contact layer. And the p-contact metal layer is made of platinum (Pt) or palladium (Pd). The method of claim 1, The substrate is a method of manufacturing a semiconductor laser diode, characterized in that the sapphire substrate. Sequentially depositing an n-contact layer, an n-clad layer, an n-wave guide layer, an active layer, a p-wave guide layer, a p-clad layer, a p-contact layer, and a p-contact metal layer on the substrate; Patterning the p-contact metal layer, followed by dry etching a portion of the p-contact layer and the p-clad layer using the patterned p-contact metal layer as an etch mask to form a ridge structure; Wet etching the surface of the ridge structure and a portion of the upper surface of the p-clad layer with a phosphoric acid (H ₃ PO ₄ ) solution; Forming a passivation layer surrounding the side of the ridge structure and the p-clad layer; And And forming a p-pad electrode around the p-contact metal layer and a portion of the protective layer, and forming an n-pad electrode under the substrate. And the p-contact metal layer is made of platinum (Pt) or palladium (Pd). The method of claim 3, The substrate is a manufacturing method of a semiconductor laser diode, characterized in that the n-GaN substrate. The method according to claim 1 or 3, The wet etching method of manufacturing a semiconductor laser diode, characterized in that performed at a temperature of 150 ~ 170 ℃. The method according to claim 1 or 3, The p-contact layer and the p-clad layer is a semiconductor, characterized in that consisting of p-In _x Al _y Ga _1-xy N (0≤x≤1, 0≤y≤1, 0≤x + y≤1) Method of manufacturing a laser diode. delete The method according to claim 1 or 3, In the wet etching, the side surface of the ridge structure and the upper surface of the p-clad layer is formed vertically.

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