KR101660733B1 - nitride semiconductor device and method for fabricating the same - Google Patents

Abstract

A nitride semiconductor device using an m-plane and a method of manufacturing the same, the nitride semiconductor device comprising: a substrate including a first region and a second region having at least one protrusion; a first electrode formed on a second region of the substrate; A semiconductor layer formed on the first region of the semiconductor layer and having a plurality of functional layers stacked thereon, and a second electrode formed on the semiconductor layer.

Description

TECHNICAL FIELD The present invention relates to a nitride semiconductor device and a fabrication method thereof.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly, to a nitride semiconductor device using an m-plane and a manufacturing method thereof.

Generally, laser light of a semiconductor laser device is being put to practical use in places such as optical communication, multiple communication, and space communication.

Such a semiconductor laser device is used as a means for transferring, recording, and reading data in a communication field such as optical communication or an apparatus such as a compact disk player (CDP) or a digital versatile disk player (DVDP) Widely used.

Among them, a nitride semiconductor laser device is of particular interest because of its direct transition type in which the transition method has a high probability of laser oscillation and is capable of blue laser oscillation.

In recent years, the active layer grown by MOCVD using a non-polar, gallium nitride (GaN) substrate has improved efficiency and high performance characteristics. Therefore, it is more improved than the conventional optical device using a polar c- .

The laser device basically has a structure having an active layer made of InGaN of a multi-layered quantum well (MQW) structure between the n-type nitride semiconductor layer and the p-type nitride semiconductor layer, Is increased or decreased.

Such a laser device has a structure in which an n-type nitride semiconductor layer, an active layer and a p-type nitride semiconductor layer are sequentially formed on a sapphire or GaN substrate surface and a ridge stripe is formed in a part of the p-type nitride semiconductor layer Have.

The conditions of the material used for each of the laser devices are such that the energy gap Eg of the semiconductor layer material must be larger than the energy gap of the active layer in order to confine carriers (electrons and holes) in the active layer to obtain an inversion distribution state, In order to confine light in the active layer, the refractive index of the material of the semiconductor layer can be made smaller than the refractive index of the active layer material.

The most widely used N-type semiconductor layer is composed of GaN or AlxGa1-xN doped with Si impurities. The active layer structure includes a quantum well (QW) layer and a quantum barrier (QB) Layer is a multi-quantum well (MQW) layer.

The material composition of the quantum well layer is mainly composed of InxGa1-xN (0 < x < 1) and the quantum barrier layer constituent is composed of InyGa1-yN (0? Y <1, x> y) having a lower In composition than the quantum well layer .

The P-type semiconductor layer is made of GaN or AlxGa1-xN doped with Mg impurities. Each semiconductor layer is composed of a superlattice structure for repeatedly growing GaN and AlxGa1-xN, or a bulk structure of GaN or AlxGa1-xN As shown in Fig.

An object of the present invention is to provide a nitride semiconductor device capable of improving the characteristics of an electrode by forming a fine pattern in which a c-plane or a-plane of a substrate is exposed on a nonpolar m-plane gallium nitride substrate and forming an electrode thereon, And a method of manufacturing the same.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the precise forms disclosed. .

A nitride semiconductor device according to the present invention includes a substrate including a first region and a second region having at least one protrusion; a first electrode formed on the second region of the substrate; and a second electrode formed on the first region of the substrate A semiconductor layer in which a plurality of functional layers are stacked, and a second electrode formed on the semiconductor layer.

Here, the substrate is a non-polar m-plane gallium nitride substrate, the protruding portion of the substrate is formed in a stripe type, the longitudinal direction of the protruding portion is the crystal direction of the substrate a-side, Surface, and the surface between the upper surface of the protrusion and the adjacent protrusion may be an m-plane.

Alternatively, the projecting portion of the substrate is formed in a stripe type, the longitudinal direction of the projecting portion is the crystal direction of the substrate c-plane, the side surface located in the width direction of the projecting portion is the a- May be m-planes.

And, the protrusion of the substrate may have a height of 0.1 - 10 um between the upper surface and the lower surface, and a width of the upper surface of the protrusion may be 0.1 - 5 um.

In addition, the distance between adjacent projections can be 0.2 - 10 um, and the inclination angle between the bottom face and the side faces of the projections can be 10-80 degrees.

Meanwhile, a method of manufacturing a nitride semiconductor device according to the present invention includes the steps of polishing a substrate on which a semiconductor layer is formed, and patterning the polished substrate to form at least one protrusion such that the c- or a- And forming an electrode on the substrate on which the projection is formed.

The step of forming the protrusions may include the steps of forming an oxide film on the polished substrate, forming a photoresist on the oxide film and patterning the oxide film to expose the oxide film in a predetermined region, removing the oxide film exposed by the photoresist as a mask, Exposing the substrate; removing the photoresist and etching the exposed substrate with the oxide film as a mask to a predetermined depth to form at least one protrusion from which the c-plane or the a-plane of the substrate is exposed; .

Other objects, features and advantages of the present invention will become apparent from the detailed description of embodiments with reference to the accompanying drawings.

The nitride semiconductor device and the manufacturing method thereof according to the present invention have the following effects.

A n-type Ohmic electrode of a semiconductor laser diode using a non-polar m-plane gallium nitride substrate is manufactured by forming a fine pattern exposing a c-plane or a-plane of a substrate through dry etching, By implementing an electrode, a low contact resistance can be ensured and heat resistance can be improved.

The present invention can improve the reproducibility, yield and reliability of laser by lowering the threshold voltage and the operation voltage of the nitride semiconductor device.

1 is a view showing a top-top type semiconductor laser device;
2 is a view showing a top-down type semiconductor laser device;
Fig. 3 is a plan view showing a fine pattern formed on the gallium nitride substrate of Figs. 1 and 2. Fig.
Fig. 4 is a cross-sectional view showing a fine pattern formed on the gallium nitride substrate of Figs. 1 and 2
5 is an enlarged view showing a fine pattern in which the c-plane of the gallium nitride substrate is exposed.
6 is a graph showing the resistance values of electrodes formed on the gallium nitride substrate of the c-plane and electrodes formed on the m-plane gallium nitride substrate
7 is a graph showing resistance values of the electrodes before and after the etching of the m-plane gallium nitride substrate

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 shows a top-top type semiconductor laser device. As shown in Fig. 1, an n-type cladding layer 3, an n-type waveguide 3, The p-type cladding layer 11, the p-type contact gallium nitride layer 13, the p-type contact layer 9, A metal layer 15 is sequentially formed on both sides of the ridge and a barrier layer 17 is formed on both sides of the ridge and a p-type electrode 19 is formed on the p-type contact metal layer 15 including the barrier layer 17.

Then, an n-type electrode 21 is formed on the mesa-etched n-type gallium nitride substrate 1.

Since the semiconductor laser device of FIG. 1 is manufactured using an epitaxy grown on a sapphire substrate, the upper layer is mesa etched and the n-type electrode is formed on the mesa etched upper layer as shown in FIG.

In recent years, however, as the fabrication technology of a gallium nitride substrate has been developed, it becomes possible to use a gallium nitride substrate with a low defect number of several hundreds of micrometers.

Therefore, a top-down type semiconductor laser device can be fabricated as shown in FIG.

FIG. 2 is a top-down type semiconductor laser device having almost the same structure as that of the top-top type semiconductor laser device of FIG. 1, as shown in FIG. 2, Is formed under the n-type gallium nitride substrate.

The semiconductor laser device of the type shown in FIG. 2 has many merits such as improvement of the direct degree and simplification of the process. Recently, leading companies have been concentrating on development of nitride semiconductor laser device manufacturing technology of this type.

However, although the semiconductor laser device of the type shown in Fig. 2 has many advantages, the n-type electrode formed under the nitrile nitride substrate is formed after the final step of fabricating the device, i.e., the lapping / polishing step The formation of the ohmic by the heat treatment generally carried out is inevitably limited.

In addition, since the heat resistance of the n-type electrode is low, the driving voltage is increased after the formation of the reflective film or during packaging. In particular, the n-type electrode using the non-polar m- So that an improvement manufacturing technique should be secured.

Accordingly, the present invention provides a method of manufacturing an n-type Ohmic electrode of a semiconductor laser diode using a nonpolar m-plane gallium nitride substrate, which comprises forming a fine pattern through which a c-plane or a-plane of a substrate is exposed through dry etching, By implementing the ohmic contact type ohmic electrode, a low contact resistance can be secured and the heat resistance can be improved.

The present invention can be applied to the top-top type semiconductor laser device shown in Fig. 1 or the top-down type semiconductor laser device shown in Fig.

1 and 2, the m-plane gallium nitride substrate 1 includes a p-type electrode 15 and a first region in which a semiconductor layer is formed and a first region in which an n-type electrode 21 is formed It can be divided into two areas.

The top-top type semiconductor laser device shown in Fig. 1 has the first region and the second region of the gallium nitride substrate 1 arranged side by side, and the top-down type semiconductor laser device shown in Fig. 2 is composed of gallium nitride The first region and the second region of the substrate 1 are arranged to face each other.

Here, the surface of the gallium nitride substrate 1 in the second region where the n-type electrode 21 is formed has a fine pattern having at least one protrusion.

1 and 2, the present invention provides a gallium nitride substrate 1 which is a non-polar m-plane including a first region and a second region having at least one protrusion, and the gallium nitride substrate 1 The n-type electrode 21 is formed on the second region of the n-type electrode.

An n-type cladding layer 3, an n-type waveguide layer 5, an active layer 7, a p-type waveguide layer 9 and a p-type cladding layer 11 are formed on a first region of the gallium nitride substrate 1 ), a p-type contact gallium nitride layer 13, a p-contact metal layer 15, and a barrier layer 17 are formed.

Then, a p-type electrode 19 formed on the semiconductor layer is formed.

Here, the projecting portion of the substrate may be formed in a stripe type.

FIG. 3 is a plan view showing a fine pattern formed on the gallium nitride substrate of FIGS. 1 and 2. FIG. 4 is a sectional view showing a fine pattern formed on the gallium nitride substrate of FIGS.

As shown in FIGS. 3 and 4, the fine pattern formed on the gallium nitride substrate, which is a non-polar m-plane, may be formed in a stripe shape composed of at least one protrusion and arranged in one direction.

Here, the stripe-shaped protrusions are located in the a-plane direction of the gallium nitride substrate in the longitudinal direction, while the side surfaces are exposed in the width direction, and the exposed side becomes the c-plane of the gallium nitride substrate.

In addition, the stripe-shaped protrusions may be formed such that the longitudinal direction is the c-plane direction of the gallium nitride substrate and the widthwise exposed side is the a-plane of the gallium nitride substrate.

That is, as shown in Fig. 3, the a-stripe is the a-plane direction in the longitudinal direction of the protrusion, and the exposed side is the c-plane.

The c-stripe is a c-plane direction in the longitudinal direction of the protrusion, and the exposed side is an a-plane.

Next, the protruding portion of the gallium nitride substrate, which is a non-polar m-plane, may have a height between the upper surface and the lower surface of about 0.1-10 mu m, preferably about 5 mu m, as shown in Fig.

The width of the upper surface of the protrusion (the distance between the exposed both side surfaces) may be about 0.1 - 5 um, preferably about 2 탆 or less.

Further, when a plurality of protrusions are arranged, the distance between adjacent protrusions may be about 0.2-10 mu m, which may vary depending on the height and width of the protrusions.

As described above, the reason for determining the height and the width of the protrusion is that if the width is larger than the above range, the electrode may be short-circuited due to the stepped portion of the protrusion when the electrode is formed. It is not effective to improve the electrode characteristics and the manufacturing process is very difficult.

The projecting portion may be formed in a trapezoidal shape having a larger area of the lower surface than the upper surface, but is not limited thereto.

That is, the protruding portion may be formed not only in a stripe shape but also in another fine uneven structure.

The protrusion of the most preferable structure may have a trapezoidal shape having a larger area of the lower surface than the upper surface. The inclination angle between the lower surface and the side surface of the protrusion may be about 10-80 degrees.

If the inclination angle is larger than the range, the electrode formed on the protrusion can be short-circuited at the side surface of the protrusion. If the inclination angle is smaller than the range, the contact area between the substrate and the electrode is not widened, .

4, the non-polar m-plane gallium nitride substrate is etched by a dry etching process to form a protrusion in a trapezoidal shape having a larger area on the lower surface than the upper surface, as shown in FIG. An SiO 2 silicon oxide film used as a mask remains on the upper surface of the protrusion, and an n-type electrode is formed on the entire surface of the gallium nitride substrate including the protrusion.

A method of forming the projection as shown in FIG. 4 will be described as follows.

First, a gallium nitride substrate on which a semiconductor layer is formed is polished through a lapping and a polishing process.

Then, in the gallium nitride substrate on which the lapping and polishing processes have been completed, a silicon oxide film is formed on the substrate surface on which the n-type electrode is to be formed.

Then, a photoresist is formed on the silicon oxide film, and a photoresist is patterned using a photomask having a stripe opening portion having an open region of about 4 mu m and an open region of about 6 mu m on the photoresist, And the silicon oxide film in a predetermined region is exposed.

Next, using the photoresist of the stripe pattern as a mask, the exposed silicon oxide film is removed to expose the underlying gallium nitride substrate.

Then, the remaining photoresist is removed, and the exposed gallium nitride substrate is etched to a predetermined depth using the silicon oxide film as a mask to form at least one protrusion exposing the c-plane or the a-plane of the gallium nitride substrate.

Here, the etching of the gallium nitride substrate can be performed by a dry etching process and a plasma processing process.

Thus, after the plasma treatment process is performed, an n-type electrode is formed on the gallium nitride substrate having the projecting portion.

Here, the n-type electrode can be formed by sequentially depositing Al / Ti / Au using an electron beam apparatus.

At this time, the surface of the n-type electrode may be formed in a concavo-convex shape along the pattern of the substrate as shown in Fig. 4, or may be formed flat as shown in Figs.

5 is an enlarged view showing a fine pattern in which the c-plane of the gallium nitride substrate is exposed. As shown in FIG. 5, the stripe-shaped protrusions are arranged side by side at regular intervals, and the stripe- Direction, and the exposed side has a c-plane.

As described above, the n-type electrode formed on the fine pattern has a low contact resistance and the heat resistance is improved. Therefore, the threshold voltage and the operation voltage of the nitride semiconductor device are lowered to improve the reproducibility, yield and reliability of the laser .

6 is a graph comparing resistance values of an electrode formed on a gallium nitride substrate with a c-plane and an electrode formed on an m-plane gallium nitride substrate.

6 shows that the electrode area is about 500 * 300 μm and the interval between the electrodes is about 1,000 μm. The temperature is raised at intervals of about 100 ° C. in an N 2 atmosphere using an RTP (rapid thermal process) .

Here, the electrode formed on the c-plane gallium nitride substrate has a stable value within about 2? From about room temperature to about 700 占 On the other hand, the electrode formed on the m-plane gallium nitride substrate has a high resistance of about 200 to 300 占Value is displayed, it can be seen that the value is stable again about 400 degrees.

Generally, since the process is performed at a temperature of about 200 ° C. to 300 ° C. in forming a reflective film or packaging, if the stable value can not be obtained at this temperature, the threshold voltage and the operating voltage of the laser diode, .

For this reason, the present invention provides a method of forming a pattern on a m-plane gallium nitride substrate such that a c-plane or an a-plane other than an m-plane is exposed and forming an electrode on a c- It is possible to obtain characteristics.

As described above, the pattern formation direction and the size of the fine etch-height pattern can be determined so as to obtain the same level of electrode characteristics as the c-plane by exposing other crystal planes other than the m-plane in the m-plane gallium nitride substrate have.

In addition, it is possible to expect the improvement of the deposition contact surface by changing the gradient of the stripe pattern by changing the dry etching condition.

7 is a graph comparing the resistance values of the electrodes before and after the etching of the m-plane gallium nitride substrate.

As shown in FIG. 7, after the stripe pattern is formed by etching the m-plane gallium nitride substrate, the resistance value of the electrode is measured while increasing the temperature. As a result, the resistance value is stable even after about 200 degrees can see.

As described above, according to the present invention, when a nitride semiconductor laser diode is fabricated using an m-plane gallium nitride substrate, when forming an electrode, a dry etching process is performed using a silicon oxide film as a mask to control the formation direction and etching height Thereby making it possible to have different crystal planes on the etched bottom and sides.

Therefore, it is possible to make devices with better electrical properties by exposing the c-plane or the a-plane to form the electrodes thereon than by forming the electrodes only on the m-plane.

In particular, by showing a stable resistance value in a range of about 200 to 300 degrees, threshold voltage and driving voltage are reduced after or after the formation of the reflective film, thereby improving the reproducibility and reliability of the laser diode.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments but should be determined according to the claims.

Claims (12)

A substrate comprising a first region and a second region having a plurality of protrusions;
A first electrode formed on a second region of the substrate;
A semiconductor layer formed on the first region of the substrate and having a plurality of functional layers stacked thereon; And,
And a second electrode formed on the semiconductor layer,
The end face of the protruding portion is formed in a trapezoidal shape having a larger area of the lower surface than the upper surface,
The upper surface of the protrusion is an m-plane, the side surface of the protrusion is a c-plane or an a-plane,
An oxide film is formed in contact with the m-plane, which is the upper surface of the protrusion,
And the first electrode is formed in contact with the c-plane or the a-plane of the protruding portion. The nitride semiconductor device according to claim 1, wherein the substrate is a gallium nitride substrate which is a non-polar m-plane. The nitride semiconductor device according to claim 1, wherein the first region and the second region of the substrate are positioned to face each other. The substrate processing apparatus according to claim 1, wherein the projecting portion of the substrate is formed in a stripe shape, the longitudinal direction of the projecting portion is the a-plane direction of the substrate, the side surface located in the width direction of the projecting portion is the c- And the surface between the upper surface of the projection and the projection adjacent to the projection is an m-plane. The method as claimed in claim 1, wherein the projecting portion of the substrate is formed in a stripe shape, the longitudinal direction of the projecting portion is the c-plane direction of the substrate, the side surface located in the width direction of the projecting portion is the a- And the surface between the upper surface of the projection and the projection adjacent to the projection is an m-plane. The nitride semiconductor device according to claim 1, wherein the protrusion of the substrate has a height of 0.1-10 um between the upper surface and the lower surface, and a width of the upper surface of the protrusion is 0.1-5 um. delete 2. The nitride semiconductor device according to claim 1, wherein a distance between protrusions adjacent to each other among the plurality of protrusions is 0.2 - 10 um. The nitride semiconductor device according to claim 1, wherein an inclination angle between the lower surface and the side surface of the protrusion is 10-80 degrees. Polishing the substrate on which the semiconductor layer is formed;
Patterning the polished substrate to form a plurality of protrusions to expose the c-plane or the a-plane of the substrate; And,
And forming an electrode on the substrate on which the protrusion is formed,
Wherein forming the plurality of protrusions comprises:
Forming an oxide film on the polished substrate;
Forming a photoresist on the oxide film and patterning the exposed oxide film to expose the oxide film in a predetermined region;
Exposing the substrate by removing the exposed oxide film using the photoresist as a mask;
Removing the photoresist and etching the exposed substrate to a predetermined depth using the oxide film as a mask to form a plurality of protrusions exposing the c-plane or the a-plane of the substrate,
The end face of the protruding portion is formed in a trapezoidal shape having a larger area of the lower surface than the upper surface,
The upper surface of the protrusion is an m-plane, the side surface of the protrusion is a c-plane or an a-plane,
An oxide film is formed in contact with the m-plane, which is the upper surface of the protrusion,
And the electrode is formed in contact with the c-plane or the a-plane of the protruding portion. delete 11. The method of claim 10, wherein the etching of the substrate is performed by a dry etching process and a plasma treatment process.

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