KR102465334B1 - VCSEL with Improved Yield and Operating Efficiency - Google Patents

Abstract

Disclosed is a vertical cavity surface emitting laser device with improved yield and operation efficiency. According to an aspect of the present embodiment, the vertical cavity surface emitting laser (VCSEL) device comprises: a first reflector comprising a plurality of distributed bragg reflector (DBR) pairs; a second reflector comprising the relatively smaller number of DBR pairs than that of the first reflector; a cavity layer disposed between the first reflector and the second reflector to emit light while a hole generated from one of the first reflector and the second reflector and an electron generated from the other are coupled to each other; a first metal layer brought into contact with the second reflector to supply power to the second reflector; a second metal layer which supplies power to the first reflector; and a metal pad layer brought into contact with the first metal layer to supply power supplied from the outside to the first metal layer, wherein the first metal layer comprises a titanium (Ti) layer, a titanium nitride (TiN) layer, and a gold (Au) layer.

Description

Vertical resonance surface emitting laser device with improved yield and operating efficiency {VCSEL with Improved Yield and Operating Efficiency}

The present invention relates to a vertical resonance surface emitting laser (VCSEL) device capable of improving yield and operating efficiency.

The content described in this section merely provides background information for the present embodiment and does not constitute the prior art.

In general, semiconductor laser diodes are a side-emitting laser diode (EEL, Edge Emitting Laser Diode, hereinafter abbreviated as 'EEL') and a vertical resonance type surface emitting laser diode (VCSEL: Vertical Cavity Surface Emitting Laser, hereinafter abbreviated as 'VCSEL'). ) is included. Since the EEL has a resonance structure that is parallel to the stacking surface of the device, it oscillates a laser beam in a direction parallel to the stacked surface, and the VCSEL has a resonance structure that is perpendicular to the stacked surface of the device, so that the laser beam is converted into an element. oscillate in a direction perpendicular to the lamination plane of

VCSEL has a shorter optical gain length than EEL, so it can realize low power, and since high-density integration is possible, it is advantageous for mass production. In addition, the VCSEL can oscillate a laser beam in a single-ended mode (Single Longitudinal Mode) and can be tested on a wafer. VCSELs have been mainly used as light sources in optical devices in optical communication, optical interconnection, optical pickup, and the like.

In recent years, the VCSEL is being used as a light source in an image forming apparatus, such as LiDAR, facial recognition, motion recognition, AR (Augmented Reality) or VR (Virtual Reality) device, the range of its use has been expanded.

The profile of the laser beam output from the VCSEL is shown in FIG. 13 .

13 is a diagram illustrating a profile of a laser beam output from a VCSEL.

Referring to FIG. 13 , when a relatively low current is applied to each electrode of the VCSEL, a laser beam having a uniform beam profile is output from the VCSEL as shown in FIG. 13( a ). Since this is a low current density, the output laser beam has a circular uniform beam profile. However, when the intensity of the current applied to increase the intensity of the output laser beam increases, the laser beam profile becomes non-uniform and separated as shown in FIGS. 13(b) to 13(d). When the strength of the applied current increases and the current density increases, the current is concentrated around the electrode and the laser beams are separated. When the intensity of the laser beam to be output is determined, the conventional VCSEL has difficulty in responding to the change in the profile of the laser beam as described above because the intensity of the current to be applied to output the intensity is determined.

In manufacturing a conventional VCSEL, it is necessary to form a positive electrode to which a current is to be applied on the emitter. To this end, a photo-resist (PR) patterning process is generally performed to form an electrode shape, and then electrode metal is deposited by an E-beam evaporator or sputter method, and then lift-off ( Lift-off) process was performed to remove the metal deposited on the area outside the electrode, and then the electrode was formed. However, during the lift-off process, PR or metal floating matter may remain in the laser output area due to the structure or shape of the designed electrode. In the VCSEL, it was difficult to output a laser beam having an intact profile due to the residue, which caused a problem of lowering the yield in the VCSEL manufacturing process.

An embodiment of the present invention has an object to provide a VCSEL with improved yield and increased operating efficiency.

According to an aspect of the present invention, a first reflector including a plurality of DBR (Distributed Bragg Reflector) pairs, a second reflector including a DBR pair relatively smaller than the first reflector, and the first reflector; a cavity layer positioned between the second reflecting unit and oscillating light by combining a hole (hole) generated in any one of the first reflecting unit and the second reflecting unit and electrons generated in the other one; 2 In contact with the reflective part, the first metal layer for supplying power to the second reflective part and the second metal layer and the first metal layer for supplying power to the first reflective part, and a metal pad layer for transferring power supplied from the outside to the first metal layer, wherein the first metal layer includes a titanium layer (Ti), a titanium nitride layer (TiN), and a gold layer (Au). VCSEL is provided.

According to one aspect of the present invention, the VCSEL further comprises an oxide layer formed in the cavity layer or adjacent to the cavity layer

The first metal layer may further include a platinum layer between the titanium nitride layer and the gold layer.

According to one aspect of the present invention, the first metal layer is characterized in that it includes one or more notches (notch).

According to an aspect of the present invention, the notch is formed to penetrate inside and outside the first metal layer.

According to one aspect of the present invention, when the notch is implemented in plurality, it is characterized in that it is formed at predetermined intervals.

According to one aspect of the present invention, the notch is characterized in that it has a predetermined thickness.

As described above, according to one aspect of the present invention, there are advantages in that the yield is improved and the operation efficiency can be increased.

1 is a cross-sectional view of a VCSEL according to an embodiment of the present invention.
2 to 6 are diagrams illustrating a manufacturing process of a VCSEL according to an embodiment of the present invention.
7 is a view illustrating a cross-section of a first metal layer according to an embodiment of the present invention.
8 is a graph illustrating a change in the contact resistance of an alloy that varies according to the type and amount of an element added to gold.
9 is a graph illustrating a result of Auger electric spectroscopy of the first metal layer according to an embodiment of the present invention.
10 is a view showing the structure of the first metal layer according to the first embodiment of the present invention.
11 and 12 are views showing the structure of the first metal layer according to the second embodiment of the present invention.
13 is a diagram illustrating a profile of a laser beam output from a VCSEL.

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to a specific embodiment, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing each figure, like reference numerals have been used for like elements.

Terms such as first, second, A, and B may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component. and/or includes a combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being “connected” or “connected” to another component, it may be directly connected or connected to the other component, but it is understood that other components may exist in between. it should be On the other hand, when it is said that a certain element is "directly connected" or "directly connected" to another element, it should be understood that no other element is present in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. It should be understood that terms such as “comprise” or “have” in the present application do not preclude the possibility of addition or existence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification in advance. .

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

In addition, each configuration, process, process or method included in each embodiment of the present invention may be shared within a range that does not technically contradict each other.

1 is a cross-sectional view of a VCSEL according to an embodiment of the present invention.

Referring to FIG. 1 , a VCSEL 100 according to an embodiment of the present invention includes a substrate 110 , a first reflector 120 , a cavity layer 130 , a second reflector 140 , and a cap layer 150 . ), passivation layers 160 , 164 , 168 , a first metal layer 170 , a second metal layer 175 , and a metal pad layer 180 .

The substrate 110 allows each layer in the VCSEL 100 to be grown or deposited.

The first reflector 120 may be made of a semiconductor material doped with a p-type dopant, and may be made of AlGaAs, which is a semiconductor material including Al. The first reflector 120 includes a plurality of DBR (Distributed Bragg Reflector, or 'Distributed Bragg Reflector') pairs. The DBR pair consists of a High Al Composition Layer comprising a high Al ratio of 85 to 100% and a High Al Composition Layer comprising a low Al ratio of 0 to 20%. A plurality of them are implemented as one pair. The first reflector 120 includes a larger number of DBR pairs than the second reflector 140 , and has relatively higher reflectivity. Accordingly, the light or laser oscillated from the cavity layer 130 is oscillated in the direction of the second reflector 140 having a low reflectivity due to a relatively small number of pairs.

The cavity layer 130 is a layer in which holes generated by the first reflecting unit 120 and electrons generated by the second reflecting unit 140 meet and recombine, and light is generated by recombination of electrons and holes. The cavity layer 130 may include a single quantum well (SQW) structure or a multiple quantum well (MQW) structure having a plurality of quantum well layers. When a multi-quantum well structure is included, the cavity layer 130 has a structure in which well layers (not shown) and barrier layers (not shown) having different energy bands are alternately stacked once or more. The well layer (not shown)/barrier layer (not shown) of the cavity layer 230 may be formed of InGaAs/AlGaAs, InGaAs/GaAs, or GaAs/AlGaAs.

The cavity layer 130 further includes an oxide layer. The oxide layer is an oxidized portion of a certain length through an oxidation process, and determines the characteristics of the laser output and the diameter of the opening according to the length of the oxidized portion. The oxide layer is made of aluminum (Al) having a higher concentration than that of the first and second reflectors 120 and 140 . The higher the aluminum concentration, the higher the rate of oxidation. As the oxide layer is implemented with a relatively higher aluminum concentration than both of the reflection units 210 and 240 , oxidation can be selectively performed during subsequent oxidation. For example, the oxide layer may be implemented with AlGaAs having an Al ratio of 98% or more, and each of the reflection units 120 and 140 may be implemented with AlGaAs having an Al ratio of 0% to 100%.

The second reflector 140 may be implemented as an n-type semiconductor layer doped with an n-type dopant, and may be formed of AlGaAs, which is a semiconductor material including Al. The second reflector 140 is also configured of a plurality of DBR pairs. However, as described above, since the first reflector 120 includes a relatively smaller number of DBR pairs, the reflectivity is relatively low. Accordingly, the light or laser oscillated from the cavity 130 layer is oscillated in the direction of the second reflector 140 having a low reflectivity due to a relatively small number of pairs.

The cap layer 150 is stacked on the second reflection unit 140 .

The passivation layer 160 is applied on the cap layer 150 to protect the cap layer 150 from the outside.

The passivation layer 164 is applied on the side surfaces of the first reflective layer 120 , the cavity layer 130 , and the second reflective layer 140 , and on the passivation layer 160 , to protect each component from the outside.

The passivation layer 168 is applied to the outermost portion of the VCSEL 100 to protect each component from the outside. The passivation layer 168 has a structure such that a part of the metal pad layer 180 is exposed to the outside, so that power can be easily supplied to the first metal layer 170 through the metal pad layer 180 from the outside. .

The first metal layer 170 is in contact with the second reflection unit 140 so that power can be supplied to the second reflection unit 140 . The first metal layer 170 is implemented as p-metal including a titanium layer (Ti), a titanium nitride layer (TiN), a platinum layer (Pt), and a gold layer (Au). As the first metal layer 170 is formed on the upper end of the second reflection unit 140 (with reference to FIG. 1 ), power applied through the metal pad layer 180 is transmitted to the second reflection unit 140 . do.

The second metal layer 175 allows power to be supplied to the first reflector 120 from the lower end of the substrate 110 . The second metal layer 175 transmits power applied from the outside to the first reflector 120 . As opposed to the first metal layer 170 , the second metal layer 175 may be n-metal.

The metal pad layer 180 is in contact with the first metal layer 170 , and transmits power supplied from the outside to the first metal layer 170 .

VCSELs having such a structure are manufactured through the processes of FIGS. 2 to 6 .

2 to 6 are diagrams illustrating a manufacturing process of a VCSEL according to an embodiment of the present invention.

Referring to FIG. 2 , a first reflective layer 120 , a cavity layer 130 , a second reflective layer 140 , and a cap layer 150 are grown on a substrate 110 , and a first metal layer is formed on the cap layer 150 . 170 is deposited.

Referring to FIG. 3 , each layer grown on the substrate 110 is etched into a mesa structure, and a passivation layer 160 is applied on the cap layer 150 and the first metal layer 170 .

Referring to FIG. 4 , an oxidation process is performed to form an oxide layer in the cavity layer 130 or adjacent to the cavity layer 130 . A passivation layer 164 is applied on each layer etched in the mesa structure and on the passivation layer 160 . The passivation layers 160 and 164 on the first metal layer 170 are etched so that the first metal layer 170 is exposed to the outside.

Referring to FIG. 5 , a metal pad layer 180 is deposited on the passivation layer 164 .

Referring to FIG. 6 , a passivation layer 168 is deposited on the metal pad layer 180 , and a portion of the passivation layer 168 is etched to expose a portion of the metal pad layer 168 . On the other hand, the second metal layer 175 is deposited on the opposite surface of the one surface of the substrate 110 on which the first reflective layer 120 is grown. In this case, when the second metal layer 175 is deposited, etching may be performed on the opposite surface of the substrate on which the second metal layer 175 is to be deposited.

After the second metal layer 175 is deposited, an annealing process is performed.

Through the above-described process, the VCSEL may be manufactured. However, as pointed out in the technical part that is the background of the invention, as mentioned in FIGS. 2, 4 and 6, etc., when leaving only a part or etching a part, etching using PR (Photo Resist) is usually performed. However, in a conventional VCSEL, in particular, in a lift-off process of PR patterning the structure or shape of the first metal layer and removing metal other than the PR and electrode region after the electrode deposition process, the laser output region It happens that PR and metal floats remain on the layer. As such, when the PR and metal floats remain on the layer, it causes a problem that has a fatal effect on the quality of the laser beam to be output.

The annealing process is usually performed at a temperature of about 250 °C. At this time, the conventional first metal layer is implemented with a titanium layer (Ti) and a gold layer (Au). At a high temperature such as an annealing process, the titanium element diffuses to gold and reacts with gold, TiAu, TiAu ₂ , Ti ₃ Au, etc. made from an alloy of The alloy thus produced increases the contact resistance (Specific Resistance) as shown in FIG. 8, which will be described later. An increase in the contact resistance causes an increase in the current to be applied, which causes a decrease in the profile of a laser beam to be output and causes a problem of generating a lot of heat.

In addition, the conventional structure of the first metal layer has a problem in that it is difficult to adjust the laser beam profile to be output.

To solve this problem, the first metal layer has the structure shown in FIGS. 7 to 12 .

7 is a view illustrating a cross-section of a first metal layer according to an embodiment of the present invention.

Referring to FIG. 7 , the first metal layer 170 according to an embodiment of the present invention includes a titanium layer 710 , a titanium nitride layer 720 , and a gold layer 740 . Furthermore, the first metal layer 170 may further include a platinum layer 730 .

The titanium layer (Ti) 710 serves as an adhesive layer between another layer component such as a semiconductor substrate or another metal component and the gold layer 740 .

The platinum layer 730 is positioned between the titanium layer 710 and the gold layer 740 to prevent the formation of an intermetallic between titanium and gold. However, in a high temperature environment such as an annealing process, the titanium 710 particles may be diffused into the platinum layer 730 through grain boundaries. When diffusion proceeds to the platinum layer 730 , the titanium 710 particles may pass through the platinum layer 730 to form an alloy with the gold 740 . Accordingly, the platinum layer 730 alone was insufficient to sufficiently prevent the diffusion of the titanium 710 particles into the gold layer 740 .

Accordingly, a titanium nitride layer (TiN) 720 is additionally disposed between the titanium layer 710 and the platinum layer 730 . The titanium nitride layer 720 has a predetermined thickness or more at the corresponding position, thereby preventing a reaction between the titanium layer 710 and the gold layer 740 . Here, the preset thickness may be about 350 Å. When the titanium nitride layer 720 has a predetermined thickness, the contact resistance of the first metal layer 170 is reduced several times to ten times compared to the case where it is not. Changes in the first metal layer 170 due to the presence of the titanium nitride layer 720 are illustrated in FIGS. 8 and 9 .

8 is a graph showing a change in the contact resistance of an alloy that changes according to the type and amount of element added to gold, and FIG. It is a graph showing electron spectroscopy).

Referring to FIG. 8 , in the case of the same amount of addition (eg, 2% shown in FIG. 8 ), it can be seen that the diffusion rate of titanium (Ti) particles is significantly faster than that of other particles. It can be seen that the size of the contact resistance due to diffusion of titanium particles into gold at a certain amount of addition is significantly larger than that of other particles. As described above, since the increase in contact resistance is proportional to the formation of an alloy due to bonding of gold and other particles, it can be seen that the diffusion rate of titanium particles is significantly faster than that of other particles.

Referring to FIG. 9 , referring to the results of Auger electro-spectroscopy of the first metal layer, when the sputtering time is about 0 to 8 minutes, it can be confirmed that most of the particles detected are gold.

On the other hand, looking at about 13 to 18 minutes, it can be seen that titanium nitride and titanium particles are overlapped.

That is, referring to the graph shown in FIG. 9 , it can be confirmed that the titanium particles diffuse only to titanium nitride due to the presence of titanium nitride, but not to gold. It can be seen that the titanium particles hardly diffuse even to platinum by the titanium nitride layer.

As such, since the titanium nitride layer significantly prevents the diffusion of titanium, even when titanium is exposed to high temperatures through an annealing process, etc., it is possible to prevent an increase in contact resistance by minimizing the bonding between the titanium layer and the gold layer.

10 is a view showing the structure of the first metal layer according to the first embodiment of the present invention, Figures 11 and 12 are views showing the structure of the first metal layer according to the second embodiment of the present invention.

Referring to FIG. 10 , the first metal layer 170 includes one or more notches 1010 .

The notch 1010 is formed in the first metal layer 170 to penetrate inside and outside the first metal layer 170 . One or more than one notch 1010 may be formed.

When two or more notches 1010 are formed, they may be formed at preset intervals.

As such, when the notch 1010 is formed in the first metal layer 170 , the current density caused by the first metal layer 170 may be relatively lowered. When the current density is lowered, the beam profile of the laser beam to be output can be made more uniform.

One or more notch 1010 in the first metal layer 170 may be formed in consideration of the intensity of the laser beam to be output and the intensity of the current to be applied accordingly.

As shown in FIG. 10 , the notch 1010 may have a shape in which the opening located inside the first metal layer 170 and the opening located outside the first metal layer 170 are located on the same line, but as shown in FIG. 1 The opening 1010b located inside the metal layer 170 and the opening 1010a located outside the metal layer 170 may have a shape located on different lines. A predetermined depth is etched between the openings 1010a and 1010b in directions facing each other at different positions, and a connection part 1110 connecting both openings is additionally formed as in a stepped shape.

When the notch 1010 is formed in the shape shown in FIG. 10 , a portion where the first metal layer 170 does not exist exists in the circumferential direction of the first metal layer 170 . Accordingly, the density of the current may be relatively lower. On the other hand, when the notch 1010 is formed in the shape shown in FIG. 11 , there may be a portion where the first metal layer 170 is relatively less in the circumferential direction of the first metal layer 170 , but the first The metal layer 170 does not exist. Accordingly, a current density generated in the first metal layer 170 may be relatively increased.

Accordingly, the current density of the first metal layer 170 may be more finely adjusted (so that the laser beam profile to be output has a uniform circular shape) according to the number of the notches 1010 and the shape of the notches 1010 .

However, the present invention is not necessarily limited thereto, and since the notch 1010 is implemented in a diagonal shape in the first metal layer 170 , an effect similar to the notch 1010 of the form shown in FIG. 11 may be brought about.

In addition, since the notch 1010 is formed to penetrate the inside and the outside of the first metal layer 170 in any shape as described above, the PR used in the etching process does not easily remain in the first metal layer 170 , etc. allow it to be removed. Accordingly, it is possible to prevent deterioration of the profile of the output laser beam due to the residual PR in the manufacturing process.

The above description is merely illustrative of the technical idea of this embodiment, and various modifications and variations will be possible without departing from the essential characteristics of the present embodiment by those of ordinary skill in the art to which this embodiment belongs. Accordingly, the present embodiments are intended to explain rather than limit the technical spirit of the present embodiment, and the scope of the technical spirit of the present embodiment is not limited by these embodiments. The protection scope of this embodiment should be interpreted by the claims below, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present embodiment.

100: VCSEL
110: substrate
120: first reflective layer
130: cavity layer
140: second reflector
150: cap layer
160, 164, 168: passivation layer
170, 175: metal layer
180: metal pad layer
710: titanium layer
720: titanium nitride layer
730: platinum layer
740: gold layer
1010: notch
1110: connection
1120: opening

Claims (7)

A first reflector including a plurality of DBR (Distributed Bragg Reflector) pairs;
a second reflector including a DBR pair that is relatively smaller than that of the first reflector;
It is located between the first reflector and the second reflector, and a hole (hole) generated in any one of the first reflecting part and the second reflecting part and electrons generated in the other one are combined to oscillate light. a cavity layer;
a first metal layer in contact with the second reflective part so that power can be supplied to the second reflective part;
a second metal layer for supplying power to the first reflecting unit; and
and a metal pad layer in contact with the first metal layer and transmitting power supplied from the outside to the first metal layer,
The first metal layer includes a titanium layer (Ti), a gold layer (Au), a platinum layer (Pt) positioned between the titanium and the gold layer, and a titanium nitride layer (TiN) positioned between the titanium layer and the platinum layer including,
The titanium nitride layer has a thickness as much as a preset error range based on 350 Å,
The first metal layer includes one or more notches,
The notch is etched by a predetermined depth in a direction in which the opening located inside the first metal layer and the opening located outside the first metal layer are facing each other at different positions, and both openings are connected in a stepped or diagonal shape. VCSEL, characterized in that it is formed in a form in which a connecting portion is formed. According to claim 1,
The VCSEL of claim 1, further comprising an oxide layer formed in the cavity layer or adjacent to the cavity layer. delete delete delete According to claim 1,
The notch is
VCSEL, characterized in that formed at predetermined intervals when implemented in plurality. According to claim 1,
The notch is
VCSEL, characterized in that it has a preset thickness.

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