KR101136239B1 - Method Of Fabricating Laser Diode - Google Patents

Abstract

The present invention relates to a method of manufacturing a laser diode, wherein the electrode is formed by using a high energy deposition method such as ion beam deposition, ion beam assisted deposition, ion beam sputtering, RF / DC sputtering, etc. By depositing, the contact resistance of the lower electrode can be lowered. Since the lower electrode of the laser diode formed through the manufacturing method has the effect that the contact resistance does not increase even in a high temperature environment such as soldering and high temperature heat treatment, As a result, a laser diode having stable electrode characteristics can be realized.

Laser diode, contact resistance, heat, electrode, high energy, deposition method

Description

Laser diode manufacturing method {Method Of Fabricating Laser Diode}

1A and 1B are cross-sectional views schematically illustrating a structure of a general laser diode according to the prior art.

2 is a graph measuring contact resistance values of phase and bottom electrodes changed according to heat treatment temperatures in a conventional laser diode having phase and bottom electrodes including Cr.

3A to 3C are cross-sectional views illustrating a preferred embodiment of the laser diode manufacturing method of the present invention.

4 is a graph measuring contact resistance values of the upper and lower electrodes changed according to the heat treatment temperature in the laser diode of the present invention having the upper and lower electrodes formed to include Ti.

5 is a graph measuring contact resistance values according to temperature during each surface treatment when various surface treatments are performed to ensure thermal stability during heat treatment of the lower electrode.

FIG. 6 is a graph comparing contact resistance values according to heat treatment temperatures of rear electrodes formed by depositing Ti-based metals by E-Beam Evaporation and sputtering deposition according to the present invention. .

<Description of main parts of drawing>

100. Conductive substrate 101. Etch residue

110a. Lower clad layer 110b. Upper cladding layer

120a. Lower waveguide layer 120b. Upper waveguide layer

130. Active layer 140. Electron barrier layer (EBL)

150. Insulation layer 160. Ohmic layer

170a. Lower electrode 170b. Upper electrode

The present invention relates to a method of manufacturing a laser diode, and in particular, can lower the contact resistance of the lower electrode, prevent the increase of the contact resistance of the lower electrode in a high temperature environment, such as soldering (soldering) or high temperature heat treatment process, thermally stable electrode The present invention relates to a method of manufacturing a nitride-based semiconductor laser diode having a vertical electrode structure capable of securing characteristics.

Laser light of semiconductor laser diodes is currently being used in places such as optical communication, multiple communication, and space communication.

In addition, semiconductor lasers are widely used as a means for transferring, recording, and reading data in devices such as a compact disk player (CDP) or a digital versatile disk player (DVDP).

Among them, group 3-5 nitride (Nitrides) semiconductor laser diodes are particularly noticed because of their direct transition type with high laser oscillation probability and the possibility of blue laser oscillation.

Hereinafter, a structure and a problem of a laser diode according to the prior art will be described with reference to the drawings.

1A and 1B are cross-sectional views schematically illustrating a structure of a general laser diode.

1A is a cross-sectional view illustrating a structure of a general horizontal electrode laser diode.

As shown in the figure, the horizontal electrode laser diode is generally a substrate 10, n-GaN (11), n- clad layer (12a), p- clad layer (12b), n-wave guide layer (13a) , p-waveguide layer 13b, active layer 14, electron blocking layer 15, insulating film 16, p-omic layer 17, N-electrode 18a, P-electrode 18b Is done.

In this case, a sapphire (Al ₂ O ₃ ) substrate suitable for growing gallium nitride (GaN) is mainly used as the substrate 10.

An n-GaN 11 is formed on the substrate 10.

In this case, the n-GaN 11 is a gallium nitride (GaN) layer doped with n-type impurities, and some regions are etched, and an N-electrode 18a is formed in the etched region.

N-clad layer 12a, n-wave guide layer 13a, active layer 14, electron blocking layer 15, p-wave guide layer in the remaining regions other than the etched partial region of n-GaN 11 (13b) and the p-clad layer 12a are formed sequentially.

In this case, the p-clad layer 12a has a ridge structure in which a portion of the p-clad layer 12a is protruded, and the p-ohmic layer 17 is formed on the ridge.

An insulating film 16 is formed along the upper surfaces of the p-clad layer 12a and the p-ohmic layer 17, except that the insulating film 16 is formed on the p-ohmic layer 17. It is not.

The P-electrode 18b is formed to be electrically connected to the upper portion of the p-ohmic layer 17.

As such, in order to implement a laser diode, a portion of an epi structure formed by growing on an sapphire (Al ₂ O ₃ ) substrate is mesa-etched, and N is formed on the exposed n-contact layer. The structure in which the electrode was formed was mainly used.

However, with the recent development of gallium nitride (GaN) substrate manufacturing technology, low-defect n-GaN substrates of several hundreds of micrometers in thickness can be used. A laser diode with a top-down structure can be realized.

1B is a cross-sectional view illustrating a structure of a general vertical electrode laser diode.

As shown in the figure, since the vertical electrode laser diode does not require a substrate and has a small area compared to the structure of the horizontal electrode laser diode described above, during the device manufacturing process in units of wafers, the degree of integration is improved and the process is simplified. It has advantages

However, since the substrate lower surface or backside N-electrode 18a of the vertical electrode structure laser diode is formed after a process such as lapping or polishing, which is the final stage of device fabrication, the upper P-electrode 18b is formed. Unlike the formation, technical difficulties are great.

Specifically, the conventional n-ohmic (Ohmic) forming technology for the N-electrode is manufactured in most heating conditions of 500 ℃ or more, since the N-electrode is formed after the upper structure is completed in the laser diode manufacturing process of the vertical electrode structure Inevitably, due to such a high temperature environment, problems such as dielectric film or insulating film destruction including the upper p ohmic contact layer occur.

However, when the lower electrode (N-electrode) is manufactured at a low temperature, it is difficult to stably maintain the electrode characteristics in a high temperature environment such as soldering or high temperature heat treatment. A bottom electrode should be formed.

FIG. 2 is a graph of measuring contact resistance values of phase and bottom electrodes changed according to a heat treatment temperature in a conventional laser diode having phase and bottom electrodes including Cr.

At this time, the upper and lower electrodes are characterized in that the deposited to be sequentially stacked Cr, Ni, Au by E-Beam Evaporation (E-Beam Evaporation).

As shown in the graph, the upper electrode of the laser diode according to the conventional electrode forming method maintains a low contact resistance value well even at high temperature conditions such as during heat treatment, while the lower electrode has a large increase in contact resistance value at higher temperatures. There is a problem that the electrode characteristics deteriorate.

Accordingly, there is a need for a method of forming a lower electrode for realizing a laser diode having stable lower electrode characteristics without increasing or decreasing the contact resistance value of the lower electrode in a laser diode even at a high temperature condition such as during heat treatment.

In order to solve the above problems, the present invention forms a lower electrode of the laser diode by using a high energy deposition method, such as ion beam deposition, ion beam assisted deposition, ion beam sputtering RF / DC sputtering, thereby lowering the contact resistance of the lower electrode To provide a method for manufacturing a vertical electrode structure laser diode having a thermally stable electrode characteristics that can prevent the lower electrode contact resistance rises even when exposed to high temperature manufacturing environment, such as high temperature heat treatment process or soldering process. The purpose.

In the laser diode manufacturing method of the present invention, a lower cladding layer, a lower waveguide layer, an active layer, an electron blocking layer (EBL), an upper waveguide layer, an upper cladding layer, an ohmic layer, and an upper electrode are sequentially formed on a conductive substrate. Forming to; Lapping and polishing the conductive substrate underneath; Uniformly dry etching the lower portion of the conductive substrate; Ion Beam Deposition, Ion Beam Assisted Deposition, Ion Beam Sputtering, RF (Radio Frequency) Sputtering, DC (Direct Current) Sputtering And depositing a lower electrode through any one of the deposition methods.

Hereinafter, a preferred embodiment according to the laser diode manufacturing method of the present invention will be described in detail.

3A to 3C are cross-sectional views illustrating a preferred embodiment of the laser diode manufacturing method of the present invention.

3A illustrates a lower cladding layer 110a, a lower waveguide layer 120a, an active layer 130, an electron blocking layer (EBL) 140, and an upper waveguide layer 120b on the conductive substrate 100. After the upper clad layer 110b, the ohmic layer 160, and the upper electrode 170b are sequentially formed, the step of lapping and polishing the lower portion of the conductive substrate is shown.

Here, a gallium nitride (GaN) substrate doped with n-type impurities is used as the conductive substrate 100.

First, as shown, the lower clad layer 110a, the lower waveguide layer 120a, the active layer 130, the electron blocking layer 140, the upper waveguide layer 120b, on the conductive substrate 100, The upper clad layer 110b is grown sequentially.

In this case, the lower clad layer 110a and the lower waveguide layer 120a are formed by doping n-type impurities, and the upper cladding layer 110b and the upper waveguide layer 120b are doped with p-type impurities. It is formed.

In addition, the active layer 130 is preferably made of gallium nitride (GaN) -based material.

Meanwhile, the upper clad layer 110b is formed in a ridge structure in which a part of the center region is protruded through an etching method as shown, and the ohmic layer 160 is formed on the ridge structure. Let's do it.

Before forming the ohmic layer 160, it is preferable to form an insulating film 150 on the entire surface of the upper clad layer 110b including the ridge side surface.

In this case, it is preferable to form the insulating film 150 except for a region for forming the ohmic layer 160 on the ridge structure as shown.

An upper electrode 170b is formed on the ohmic layer 160 to electrically connect the laser diode to the outside.

After finishing this process and before forming the lower electrode under the conductive substrate, it is preferable to perform a lapping and polishing process in order to make the surface of the lower substrate uniform.

However, due to the lapping and polishing processes, mechanical damage regions may be formed on the lower surface of the substrate, and the surface needs to be more uniformly formed in order to further reduce the contact resistance of the electrode to be formed.

3B illustrates a step of dry etching the lower portion of the conductive substrate 100 uniformly.

In order to remove the non-uniformity and mechanical damage areas of the lower surface of the substrate as described above, it is desirable to etch the lower surface of the substrate using dry etching.

However, the etching residues 101 also suppress ohmic coupling of electrodes to be formed later, thereby increasing contact resistance, and then deteriorating ohmic characteristics even during heat treatment such as soldering. .

3C illustrates a step of forming a lower electrode 170a under the high energy deposition method under the conductive substrate 100 to complete a laser diode having a vertical electrode structure according to the present invention.

The high energy deposition method may include ion beam deposition, ion beam assisted deposition, ion beam sputtering, RF / direct current sputtering, and the like. have.

In addition, the lower electrode 170a may be formed of a metal material such as Cr, Ti, Al, or Pd, which may be in ohmic contact with a gallium nitride (GaN) substrate doped with n-type impurities.

At this time, unlike the conventional E-Beam Evaporation (E-Beam Evaporation), since the energy of the deposited particles can be adjusted from tens of eV to several hundred eV through the control of the deposition atmosphere, the effective ohmic coupling of the electrode There is an advantage to increase the density.

In addition, these high energy deposition methods remove the etch residues 101 generated as a by-product of the etching process, thereby providing a clean interface between the lower electrode 170b and the substrate 100. It can be ensured, and there is an effect of further reducing the contact resistance at the lower electrode.

On the other hand, the lower electrode deposition process is preferably carried out at the melting temperature of the solder (Solder), because the electrode properties deteriorate during the high temperature heat treatment process such as soldering (Soldering) during the device packaging process to be performed later This is to prevent it.

FIG. 4 is a graph measuring contact resistance values of the upper and lower electrodes changed according to a heat treatment temperature in the laser diode of the present invention having the upper and lower electrodes formed to include Ti.

As shown in the graph, the phase electrode and the lower electrode formed by sequentially stacking Ti, Pt and Au are all heat treated when compared with the phase electrode formed by sequentially stacking Cr, Ni and Au mentioned in FIG. It can be seen that the contact resistance is relatively low in the temperature range.

In particular, since the contact resistance of the lower electrode at a high temperature is relatively low and the difference in contact resistance between the upper electrode and the lower electrode is not large, an electrode forming method including Ti is much better for realizing thermally stable electrode characteristics. It can be seen that.

For reference, as shown in the drawing, the contact resistance value of the lower electrode is measured larger than the contact resistance value of the upper electrode, because of the difference in physical properties of the lower and upper conductive substrate.

As a representative gallium nitride (GaN) substrate of a conductive substrate, for example, the grown gallium nitride (GaN) substrate has a polarity in the direction perpendicular to the growth direction, and typically, a high quality substrate is a gallium (Ga) in the upper direction. ) It has a structure that forms polarity.

In addition, gallium nitride (GaN) substrates actually used in semiconductor devices such as laser diodes also have a gallium (Ga) polarity plane and a lower surface have a nitrogen (N) polarity plane. The characteristics of such a substrate also affect other factors such as upper and lower electrodes.

FIG. 5 is a graph measuring contact resistance values according to heat treatment temperatures during each surface treatment when various surface treatments are performed to ensure thermal stability during heat treatment of the lower electrode.

As shown, it has been shown that even after various wet etching or surface treatment of a gallium nitride (GaN) substrate, the thermal stability of the lower electrode of the substrate is not secured.

In the graph, group A shows the change of contact resistance value according to the temperature of the group which performed wet etching and the group B shows the contact resistance value according to the temperature of the group which performed wet cleaning. The change is shown.

Analyzing the graph, although the contact resistance with temperature was lower in group B than in group A, the contact resistance at high temperature is still high enough to degrade the electrical characteristics of the device.

These experimental results are due to two reasons or facts.

First, no matter what kind of surface treatment, there is no choice but to leave contaminants in the surface state, and the conventional electron beam deposition method does not secure an interface between a lower electrode having a clean interface and a gallium nitride (GaN) substrate.

Specifically, in the electron beam deposition method, since the energy of the deposited metal particles is so low that they do not collapse the contaminants remaining on the surface, and the metal particles are deposited thereon, eventually, the contaminants are included at the interface between the metal and the semiconductor. Done.

These contaminants are attributable to contamination by surface exposure after surface treatment, including cleaning residues after surface treatment.

These residues interfere with the formation of effective bonds between the metal and the semiconductor for the actual ohmic formation, for example Ti-N bonds, thereby degrading the ohmic contact properties.

In addition, these impurity bonds readily decompose at low temperatures, but as the temperature increases, they serve to further disrupt the surrounding effective ohmic bonds, thereby degrading electrode properties.

Second, the higher the energy of the material being deposited, the greater the probability of causing bond transitions on the substrate surface, which plays an important role for the n-omic formation of gallium nitride (GaN) substrates.

That is, for example, when Ti particles of high energy are irradiated onto a gallium nitride (GaN) substrate in order to form an ohmic electrode with Ti, the surface Ga-N bond of the substrate collapses and the Ti-N bond simultaneously. This is easily formed.

This bond produces a high density of N-Vacancy at the interface between the metal electrode and gallium nitride (GaN) substrate, which acts as an n donor on the gallium nitride (GaN) substrate. Thus, a high density n doping effect is induced at the interface.

Therefore, the width of the energy band between the electrode and the gallium nitride (GaN) substrate is reduced, and the probability of tunneling of electrons is greatly increased, thereby making it possible to produce an electrode having a low contact resistance value.

As already mentioned in the high-energy deposition method for making such an electrode, ion beam deposition, ion beam assisted deposition, ion beam sputtering, radio frequency (dc) / dc (direct) Current) sputtering and the like.

In addition, the ohmic bonds are suppressed by the energy of the irradiated particles, and the surface residual contaminants that degrade the ohmic properties during post-heat treatment are also removed, thereby securing a uniform interface property between the electrode and the gallium nitride (GaN) substrate. The contact resistance of the electrode is reduced.

FIG. 6 is a graph comparing contact resistance values according to heat treatment temperatures of lower electrodes formed by depositing Ti-based metals by E-Beam Evaporation and sputtering deposition according to the present invention. to be.

As shown, while the Ti-type back electrode formed by E-Beam Evaporation has a contact resistance value gradually increasing according to the temperature of various heat treatment processes, the sputtering method is one of the high energy deposition methods. The Ti-based back electrode formed by using does not increase the value of the contact resistance according to the temperature change during the heat treatment process.

As described above, in the case of the sputtered deposited Ti electrode, stable contact resistance values are exhibited at any temperature without being compared with the case of the Ti electrode by the conventional electron beam deposition method.

As a result, it is clearly shown that the electrode deposition method using the high energy deposition method of the present invention can realize a laser diode having thermally stable lower electrode characteristics.

While the configuration of the invention according to the embodiment of the present invention has been described in detail, the present invention is not necessarily limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention.

According to the laser diode manufacturing method of the present invention as described above, by forming a lower electrode using a high-energy deposition method, such as ion beam deposition, ion beam assisted deposition, sputtering, it is possible to implement a lower electrode having a thermal stability, In addition, by removing contaminants on the substrate surface, that is, etching residues, etc. that interfere with effective ohmic coupling during the high energy deposition process, there is an effect of implementing a laser diode having improved contact resistance, threshold voltage and driving voltage characteristics.

In addition, according to the method of manufacturing the laser diode of the present invention, the stability of contact resistance in an atmosphere such as high temperature exposure such as packaging or soldering of the nitride-based semiconductor laser diode is ensured, the threshold voltage and driving generated during packaging It effectively suppresses the voltage rise, improves the reliability of the device, and the rear electrode formed by the above method has the effect of showing a very excellent adhesion characteristics compared to the prior art.

Claims (3)

Sequentially forming a lower cladding layer, a lower waveguide layer, an active layer, an electron blocking layer, an upper waveguide layer, an upper cladding layer, an ohmic layer, and an upper electrode on the conductive substrate; Wrapping and polishing a lower portion of the conductive substrate; Dry etching a lower portion of the conductive substrate; And depositing a lower electrode on the conductive substrate by any one of ion beam deposition, ion beam assisted deposition, ion beam sputtering, and DC sputtering. The method of claim 1, The lower electrode, Laser diode manufacturing method consisting of any one of Cr, Ti, Al, Pd. The method of claim 1, wherein depositing the lower electrode comprises: A method of fabricating a laser diode that performs deposition at temperatures above the melting point of the solder.

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