JP2004349595A - Nitride semiconductor laser device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor laser device of a long life and its manufacturing method. <P>SOLUTION: The nitride semiconductor laser device has a chip of a nitride semiconductor laser diode, a p-type electrode 101 formed in one surface of the chip, an n-type electrode 120 formed in the other surface of the chip and a sub-mount 105 jointed to the p-type electrode 101 surface via at least the metallic film 102 and a solder 103. A metallic layer formed of the p-type electrode 101 and the metallic film 102 has at least a first layer, a second layer, a third layer and a fourth layer one by one from the layer in contact with the chip, the solder is a fifth layer, the first layer contains at least one kind of Pd, Ru, Rh, Os and Ir, the second layer is Mo, the third layer contains at least one kind of Pt, Pd, Ru, Rh, Os and Ir, the fourth layer is Au, and the fifth layer comprises at least one kind of Sn, Ag, In, and Pb. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nitride semiconductor laser device in which a chip of a nitride semiconductor laser diode is mounted on a mount member, and a method for manufacturing the same.
[0002]
[Prior art]
At present, a laser device using a nitride semiconductor as a light emitting material in the blue to ultraviolet region is being developed and put into practical use. However, the life and high output characteristics of the laser device at high temperatures are not sufficient. In the nitride semiconductor laser device, as a method of suppressing input power, reducing heat generation, improving high-temperature life, and improving high-output characteristics, it is necessary to secure good current-voltage characteristics of a p-type electrode. No.
[0003]
For example, in Patent Document 1, a Ni layer and an Au layer (from the contact layer side) are formed as a p-type electrode, and then O and one or more of Cu, Ag, Pd, Pt, and Rh are formed. A method is shown in which a metal layer is formed, a metal layer of at least one of Pt, Ru, W, and Mo is formed, and an Au layer is formed on the metal layer. Non-patent Document 1 discloses a method of forming Pd / Pt / Au (from the contact layer side).
[0004]
In a semiconductor laser device, heat dissipation is also an important factor, and heat generated by a laser diode (hereinafter, referred to as LD) chip (hereinafter, referred to as an LD chip) during operation thereof is efficiently radiated to a support base. In order to suppress the characteristic deterioration due to the temperature rise of the light emitting unit, the semiconductor LD chip is die-bonded (or mounted) to a mount member using a conductive bonding agent (solder).
[0005]
Among the above-described methods for mounting a semiconductor LD chip, the junction-down structure has a short distance from the periphery of the active layer, which generates a large amount of heat, and the periphery of the p-type electrode to the submount, and has excellent heat dissipation. It is considered promising as a structure that achieves higher output, longer life, and high-temperature stability.
[0006]
FIG. 13 is a schematic sectional view of a conventional semiconductor laser device having a junction-down structure. 101 is a p-type electrode, 120 is an n-type electrode, 1601 is a conductive substrate, 1602 is a semiconductor growth layer, 1603 is a nitride semiconductor LD chip composed of the conductive substrate 1601 and the semiconductor growth layer 1602, and 1604 is a metal film (semiconductor LD). 1605 is a solder, 1606 is a metal film (submount side), 1607 is an active layer, and 1608 is a submount.
[0007]
In the junction down structure, usually, a conductive material is used for the substrate, the p-type electrode 101 is formed on the semiconductor growth layer 1602 side, the n-type electrode 120 is formed on the conductive substrate 1601 side, and the submount 1608 is formed on the semiconductor growth layer 1602 side. The semiconductor LD chip 1603 is mounted so as to oppose.
[0008]
A method of mounting the semiconductor LD chip 1603 on a mounting member will be described. The solder 1605 is melted by heating the mount member (here, the submount 1608) and the solder 1605 to about 100 to 400 ° C. (at this time, the semiconductor LD chip 1603 may or may not be heated). Then, pressure is applied to the semiconductor LD chip 1603 on the submount 1608 (or moved to the submount 1608 after soldering) via the solder 1605 to join the semiconductor LD chip 1603 and the submount 1608. .
[0009]
As shown in FIG. 13, in the junction-down structure, the metal layer on the p-type electrode 101 side (the p-type electrode 101 and the metal film 1604 below the p-type electrode) comes into contact with the solder 1605. At this time, unless the material type, the laminating method, the combination of the types, and the thicknesses of the metal layers on the p-type electrode 101 side are optimized, mutual diffusion between the metal layers or between the metal layer and the solder 1605 is not controlled. (There are places where mutual diffusion is desirable and places where mutual diffusion is not desirable), current-voltage characteristics (IV characteristics) are deteriorated on the p-type electrode 101 side, and the bonding strength between the semiconductor LD chip 1603 and the submount 1608 is weakened. Such a problem occurs.
[0010]
[Patent Document 1]
Japanese Patent No. 3255224
[Non-patent document 1]
Japan Journal of Applied Physics
Vol. 40 (2001) pp. 3206-3210
[0011]
[Problems to be solved by the invention]
However, conventionally, the metal layers around the p-type electrode or the interdiffusion between the metal layer and the solder during the die bonding in the junction down structure of the nitride semiconductor LD chip has not been sufficiently considered. Therefore, unnecessary metal diffuses to the contact layer during die bonding, and the IV characteristics after die bonding are degraded, and the bonding strength between the semiconductor LD chip and the mount member is reduced due to the reactivity between the metal layers. Such a phenomenon occurs.
[0012]
When the IV characteristics are deteriorated, the drive voltage increases, and heat is easily generated, which is not desirable from the viewpoint of life. According to our study, the bonding strength and the heat radiation from the semiconductor LD chip to the mounting member are closely related. When the bonding strength decreases, the heat radiation from the semiconductor LD chip to the mounting member also decreases. The life is shortened, which is not preferable.
[0013]
An object of the present invention is to provide a long-life nitride semiconductor laser device and a method of manufacturing the same in view of the above problems.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a nitride semiconductor laser diode chip, a p-type electrode formed on one surface of the chip, and an n-type electrode formed on the other surface of the chip. A nitride semiconductor laser device comprising at least a metal film and a mount member joined to a surface of the p-type electrode via solder, wherein a metal layer including the p-type electrode and the metal film is in contact with the chip In order from the layer, it has at least a first layer, a second layer, a third layer, and a fourth layer, and the solder is a fifth layer, and the first layer is one of Pd, Ru, Rh, Os, and Ir. The second layer is at least one of Mo, the third layer is at least one of Pt, Pd, Ru, Rh, Os, and Ir, and the fourth layer is Au. , The fifth layer is composed of a small amount of Sn, Ag, In, and Pb. Both those characterized by comprising one or more.
[0015]
According to this configuration, it is possible to prevent the deterioration of the IV characteristics and the deterioration of the bonding strength between the semiconductor LD chip and the mount member due to the reactivity between the metal layers, thereby providing a long-life nitride semiconductor laser device. can do.
[0016]
Note that the first layer preferably has a thickness of 5 nm or more and 300 nm or less. If the thickness of the first layer is less than 5 nm, the second layer may partially contact the p-type contact layer after die bonding, and sufficient ohmic characteristics may not be obtained. On the other hand, when the first layer is thicker than 400 nm, it is difficult to form the second layer with a uniform thickness, and the electrode characteristics may be degraded by the die bonding process.
[0017]
The thickness of the second layer is preferably 5 nm or more and 400 nm or less. When the thickness of the second layer is less than 5 nm, the first layer cannot be sufficiently protected, and atoms from other layers diffuse to the first layer and the surface of the p-type contact layer through the die bonding process. As a result, the IV characteristics may be deteriorated. On the other hand, when the second layer is thicker than 400 nm, the absolute amount of impurities such as oxides in the layer increases, and these move and concentrate on the interface between the Mo layer and the other layers due to heating during die bonding, and the IV The characteristics may be degraded. As described above, when the IV characteristics are deteriorated, it is considered that the drive voltage increases, heat is easily generated, and the life is shortened.
[0018]
The thickness of the third layer is preferably 50 nm or more and 5000 nm or less. If the thickness of the third layer is less than 50 nm, the bonding strength of the p-type electrode after die bonding may not be ensured in some cases. On the other hand, when the third layer is unnecessarily thick (when the thickness exceeds about 5000 nm), the heat radiation may be rather deteriorated.
[0019]
In the present invention, the mounting member means a component for directly mounting a semiconductor LD chip, for example, a submount for a semiconductor light emitting element chip, or a holder (stem, stem) directly without using a submount. In the case of mounting on a frame or a package, the term refers to the support base of the stem, the frame or the package itself.
[0020]
In the present invention, die bonding (or mounting) refers to bonding a semiconductor LD chip to a mounting member using solder or the like. In the present invention, the solder is a material for joining the semiconductor LD chip and the mounting member. In the present invention, the mounting surface refers to a surface of the semiconductor LD chip that faces the holding member with the solder therebetween when mounting the semiconductor LD chip on the holding member.
[0021]
In the present invention, the LD wafer includes a growth substrate and a semiconductor layer grown on the substrate. The semiconductor LD chip includes a substrate and a semiconductor growth layer, and includes an electrode and / or a metal multilayer film when an electrode or a metal multilayer film is formed on the substrate or the semiconductor growth layer. In some cases.
[0022]
In FIG. 13, the p-type electrode and the solder are distinguished, but the p-type electrode indicates a metal layer in contact with the p-type contact layer of the nitride semiconductor and a part of the outer layer of the metal layer, After that, since it reacts with solder, it cannot be strictly classified.
[0023]
In this specification, the metal layer on the p-type electrode side refers to a combination of both the p-type electrode and the solder (metal film) under the p-type electrode.
[0024]
Further, the nitride semiconductor described in this specification means at least Al _x Ga _y In _z The semiconductor includes N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1). Further, in the nitride semiconductor, about 20% or less of the nitrogen element which is a component thereof may be replaced with at least one of the elements of As, P, and Sb. Further, impurities such as Si, O, Cl, S, C, Ge, Zn, Cd, Mg, and Be may be doped in the nitride semiconductor.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
<Embodiment 1>
In this embodiment, the metal layer on the p-type electrode side is Pd / Mo / Pt / Au / Au-30Sn solder from the p-type contact layer side, and a double-sided electrode LD chip using a GaN substrate as a substrate is connected to a junction-down. A description will be given of a nitride semiconductor laser device manufactured by being directly mounted on a stem by the method.
[0026]
FIG. 1 is a schematic cross-sectional view around a chip of the nitride semiconductor laser device according to the present embodiment. In this embodiment, a metal organic chemical vapor deposition (MOCVD) method is used for growing the semiconductor layer.
[0027]
In FIG. 1, reference numeral 121 denotes a metal multilayer film on an n-type electrode, 120 denotes an n-type electrode, 119 denotes an n-type GaN substrate, and an n-type GaN layer 118 having a thickness of 3 μm and 1.0 μm in order from the substrate 119 side. N-type cladding layer 117 (n-type Al _0.1 Ga _0.9 N), 0.1 μm n-type guide layer 116 (n-type GaN), active layer 115 (InGaN multiple quantum well structure), 0.03 μm p-type evaporation prevention layer 114 (p-type Al _0.2 Ga _0.8 N), 0.1 μm p-type guide layer 113 (p-type GaN), 0.6 μm p-type cladding layer 112 (p-type Al _0.1 Ga _0.9 N), a 0.1 μm p-type contact layer 111 (p-type GaN) is laminated, and a metal layer on the p-type electrode side (p-type electrode 101 and metal film 102 below the p-type electrode) is formed. ing.
[0028]
Also, 107 is the ridge width (2.0 μm), 108 is the ridge height (0.6 μm), and 109 is the thickness of the buried region (0.6 μm). In the present embodiment, the ridge height 108 and the thickness 109 of the buried region are the same, but the effects of the present invention can be obtained even if they are not the same. 103 is an Au-30Sn solder, 105 is a SiC submount, 106 is a surface of the SiC submount 105, and 104 is a metal film on the SiC submount 105.
[0029]
Here, the active layer 115 has a configuration of n-type GaN guide layer / barrier layer / well layer / barrier layer / well layer / barrier layer / well layer / barrier layer in order from the layer in contact with the n-type guide layer 116. The p-type cladding layer 112 and the p-type contact layer 111 are provided with a stripe-shaped ridge having a width of 2 μm extending in the resonator direction by photolithography technology. Except for the ridge portion, a buried region (undoped AlN) 110 having a thickness of 0.6 μm is provided between the contact layers 111 by MOCVD.
[0030]
Here, the p-type electrode 101 is composed of Pd as the first layer (0.05 μm before die bonding) and Mo as the second layer (0.15 μm before die bonding) from the side close to the p-type contact layer 111. is there. Under the metal layer 102 under the p-type electrode (Pt as a third layer from the p-type electrode 101 side (0.10 μm before die bonding), Au as a fourth layer (0.15 μm before die bonding) ) Is provided. Further below that, there is Au-30Sn solder (2.0 μm before die bonding) as a fifth layer.
[0031]
As shown in FIG. 1, the p-type electrode 101, the metal film 102 below the p-type electrode, and the solder 103 are sandwiched between the nitride semiconductor LD chip and the submount 105.
[0032]
The first Pd layer is a layer for taking ohmic contact with the p-type contact layer 111, the second Mo layer functions as a block layer for suppressing mutual diffusion, and the third Pt layer is a Mo layer. And the Au layer of the fourth layer intervening between them and increase the bonding strength between the Mo layer and the Au layer (Pt diffuses to some extent into the Au layer and the Mo layer).
[0033]
The layer configuration of the n-type electrode 120 is Hf (0.05 μm) and Al (0.15 μm) from the substrate 119 side. The metal multilayer film 121 on the n-type electrode 120 was formed in the order of Mo (0.01 μm), Pt (0.10 μm), and Au (0.15 μm) from the substrate 119 side. The Hf / Al layer is a layer for achieving ohmic contact with the n-type GaN substrate 119, the Mo layer thereon is a block layer for suppressing mutual diffusion, and the Pt layer is interposed between the Mo layer and the Au layer. Au is a layer for increasing the bonding strength between the Mo layer and the Au layer, and Au is a layer for hitting a wire.
[0034]
In order to form such a metal thin film with good controllability of the film thickness, a vacuum evaporation method is suitable, and this method is also used in this embodiment, but other methods such as an ion plating method and a sputtering method are used. May be used.
[0035]
After forming the electrodes and the metal multilayer film as described above, 5 × 10 ^-4 Under pressure of Pa or less, or N ₂ , Ar or other inert gas, O ₂ The heat treatment may be performed at a temperature of 200 ° C. or more and 700 ° C. or less for a certain period of time in an atmosphere gas using at least one of the above.
[0036]
In this embodiment, the semiconductor LD chip is manufactured using the above-described material. However, the material is not limited to the above-described material. For the substrate 119, a nitride semiconductor material other than GaN may be used. Not limited to Si, SiC, ZrB ₂ , GaAs and the like can be changed.
[0037]
Further, a nitride semiconductor (for example, p-type AlGaInN for the p-type cladding layer 112 and GaInNAs, GaInNP, or the like for the active layer 115) may be used for the growth layer. Further, a multiple quantum well may be used for the cladding layer, and an InGaN crack preventing layer may be inserted between the n-type GaN layer 118 and the n-type cladding layer 117. As described above, the semiconductor LD chip used in the present embodiment has a so-called ridge stripe structure.
[0038]
Hereinafter, a method for manufacturing the nitride semiconductor laser device of the present embodiment will be described. FIG. 2 is a schematic view of a nitride semiconductor LD wafer on which a large number of individual semiconductor laser structures are formed. 201 is an end face of the laser cavity, 202 is the surface of the metal film below the p-type electrode, 210 is a dividing line (A) for dividing into bars, and 211 is a metal layer (p-type electrode 101 and A metal layer 102 under the p-type electrode) and 212 are metal layers on the n-type electrode side (the n-type electrode 120 and the metal film 121 on the n-type electrode).
[0039]
First, an LD semiconductor growth layer is formed on a semiconductor LD wafer by appropriately applying a process used for manufacturing a semiconductor device. As described above, in this embodiment, the MOCVD method is used for growing the semiconductor layer.
[0040]
Next, the thickness of the wafer is adjusted to a thickness of usually about 40 to 200 μm by polishing or etching from the back side of the n-type GaN substrate. This is a step for facilitating division of the wafer into individual LD chips in a later step. In particular, when the laser cavity end face 201 is formed by division, it is desirable to adjust the thickness to a small value of 25 to 150 μm. In this embodiment, the thickness of the wafer was adjusted to about 150 μm using a grinder, and then adjusted to about 100 μm using a polishing machine. The back surface of the wafer is flat because it is polished by a polishing machine.
[0041]
Next, as shown in FIG. 2, the wafer in this state is cleaved or etched in a direction perpendicular to the stripe direction to form a bar. FIG. 3 is a schematic diagram of an LD bar obtained by dividing the nitride semiconductor LD wafer of FIG. 2 at a dividing line (A) 210. In FIG. 3, reference numeral 310 denotes a dividing line (B) for dividing into chips.
[0042]
Next, in the state of the LD bar in FIG. 3, a coating of an optical thin film is formed on the laser resonator end face 201 by vapor deposition to form SiO.sub. ₂ Layer and TiO ₂ The layers are coated to form a multilayer film. At this time, the coating dielectric film is not applied to the metal layer 211 on the p-type electrode side which is the mounting surface.
[0043]
Thereafter, as shown in FIG. 3, the LD bar is divided into individual semiconductor LD chips by cutting along a dividing line (B) 310, and as shown in FIGS. 4 (a) and 4 (b) described later. Obtain a nitride semiconductor LD chip.
[0044]
This step was performed as follows. An LD bar was placed on a stage with the metal layer 212 side on the n-type electrode side facing up, the scratching position was aligned using an optical microscope, and a scribe line was formed on the wafer at a diamond point. Then, a proper force was applied to the wafer to divide the wafer along the scribe line, thereby producing a nitride semiconductor LD chip having a width of 400 μm and a resonator length of 600 μm.
[0045]
Here, the chip dividing process by the scribing method has been described, but as other methods, a dicing method of making a cut or cut using a wire saw or a thin blade, irradiation of a laser beam such as an excimer laser and heating followed by rapid cooling are used. A laser scribing method in which a crack is generated in a portion and a scribe line is used as the scribe line, or a laser ablation method in which a high energy density laser beam is applied to evaporate the portion to perform grooving may be used.
[0046]
FIG. 4A is a schematic view of the nitride semiconductor LD chip before die bonding of the present embodiment obtained by the above method from the back surface (GaN substrate side), and FIG. FIG. 3 is a schematic view from the surface of the chip (the growth layer side). In the figure, 401 is the surface of the metal film on the n-type electrode, 110 is the buried region (basically an insulating material is desirable, but the insulation on the semiconductor growth layer side is ensured so that the current is confined in the ridge portion. If possible, a portion may be conductive), 402 denotes an LD chip width, 403 denotes an LD chip resonator length, and 410 denotes a semiconductor LD chip including all of the above.
[0047]
In the case of junction down, the surface 202 side (growth layer side, p-type electrode side) of the metal film under the p-type electrode of the LD chip 410 becomes a mounting surface. In this embodiment, the LD chip width 402 is 400 μm, and the LD chip resonator length 403 is 600 μm.
[0048]
Next, the LD chip 410 is mounted on the submount 105 by a die bonding method, and the submount on which the LD chip is mounted is mounted on the stem.
[0049]
FIG. 5 is a schematic cross-sectional view of the semiconductor laser device, and FIG. 6 is a perspective view of the semiconductor laser device. 5 and 6, reference numeral 501 denotes a supporting base of the stem, 502 denotes PbSn solder for bonding the SiC submount 105 and the supporting base 501 of the stem, and 503 denotes a supporting base 501 side for increasing the bonding strength of the PbSn solder 502. A metal film on the SiC submount 505, 504 is a semiconductor growth layer of a nitride semiconductor LD chip, 505 is a wire for a p-type electrode, 506 is a wire for an n-type electrode, 507 is a stem pin, and 601 is the entire stem. Point. The wire 505 for the p-type electrode is necessary when using the non-conductive SiC submount 105 as in the present embodiment, but is particularly necessary when there is conductivity such as the Cu submount. do not do.
[0050]
This step was performed as follows. The semiconductor LD chip 410 obtained above is prepared, and the sheet-shaped Au-30Sn solder 103 and the semiconductor LD chip 410 are placed on the SiC submount 105 with the p-type electrode 101 side down and heated to about 300 ° C. Then, when the Au-30Sn solder 103 is melted, pressure is applied to the semiconductor LD chip 410 to join the semiconductor LD chip 410.
[0051]
Next, a sheet-like PbSn solder 502 is placed on the supporting base 501 of the stem 601, and the stem 601 is heated to 180 ° C. slightly higher than the melting point of the PbSn solder 502. The SiC submount 105 with 410 is mounted on the PbSn solder 502 / support base 501. After the PbSn solder 502 was solidified, an n-type electrode wire 506 was connected to the stem pin 507 from the surface of the metal film 121 on the n-type electrode 120. Thus, the nitride semiconductor laser device shown in FIG. 6 was obtained. The supporting base 501 is made of a metal mainly composed of Cu, and has a Pd film / Au film formed on the surface thereof by plating.
[0052]
The element characteristics of the nitride semiconductor laser device manufactured by the above method will be described below. The IV characteristic used as an index a voltage value when a current of 50 mA was passed, and was 4.85 V in the device of the present embodiment (average of 105 devices).
[0053]
The bonding strength was determined by applying a force in the horizontal direction from the side surface of the chip and using a value when the chip was peeled off from the mounting member (arbit unit: hereinafter referred to as au) as an index. In the device of the present embodiment (average of 30 devices), the bonding strength was 52.6 (au).
[0054]
The heat dissipation is indicated by the thermal resistance (° C./W) as an index (indicating a temperature rise when 1 W of power is applied), and the smaller the value is, the better the heat dissipation is. In the device of this embodiment (average of 35 devices), the thermal resistance was 9.6 ° C./W.
[0055]
The lifetime is determined by using an index based on the auto power control (APC) “light output = 30 mW, 30 ° C., DC” and the time at which the current value becomes 1.2 times the initial current value. , And life (mean time to failure (MTTF)) was 2115 hours.
[0056]
A comparative example will be described below, and a comparison with the semiconductor laser device of the first embodiment will be described. Comparative Example 1 is a nitride semiconductor laser in which the metal layer on the p-type electrode side is Pd (0.05 μm) / Mo (0.15 μm) / Au (0.15 μm) / Au-30Sn solder from the p-type contact layer side. Device. That is, compared to the device of the first embodiment, the third layer, Pt, is omitted.
[0057]
FIG. 7 is a schematic cross-sectional view around the metal layer on the p-type electrode side in Comparative Example 1. 701 indicates a Pd layer, 702 indicates a Mo layer, and 703 indicates an Au layer. Except when forming the metal layer on the p-type electrode side, it was manufactured in the same manner as in Embodiment 1. The element characteristics (average value) of this nitride semiconductor laser device will be described below.
[0058]
When a current of 50 mA flows, the operating voltage is 4.93 V, the bonding strength is 8.2 (au), the thermal resistance is 67.3 ° C./W, and the life is 46.3 hours (MTTF: light). Output = 30 mW, 30 ° C., DC, APC).
[0059]
As described above, Comparative Example 1 and Embodiment 1 had the same IV characteristics, but the bonding strength of Comparative Example 1 was reduced. It is considered that the reason why the bonding strength of Comparative Example 1 is lower than that of Embodiment 1 is that the Au layer 703 and the Mo layer 702 are in contact with each other. At the interface between the Au layer 703 and the Mo layer 702, the amount of interdiffusion is very small, and the interface does not adhere even by the die bonding step. Conversely, impurities such as oxides in the Au layer 703 and the Mo layer 702 influence the heating at the time of die bonding, and the bonding strength at the interface between the Au layer 703 and the Mo layer 702 is reduced. It is presumed.
[0060]
FIG. 8 is a schematic cross-sectional view around the metal layer on the p-type electrode side according to the first embodiment in comparison with Comparative Example 1. Reference numeral 801 denotes a Pt layer. Conversely, the reason why the bonding strength is high in the first embodiment is that the Au layer 703 and the Mo layer 702 are not in contact with each other, the Au layer 703 is in contact with the Pt layer 801, and the interface between the Au layer 703 and the Pt layer 801 has some extent. It is considered that the interdiffusion occurs, and that the interdiffusion occurs to some extent between the Mo layer 702 and the Pt layer 801 and also between the Mo layer 702 and the Pd layer 701, and that the bonding strength is secured as a whole. . It is not clear why the bonding strength is good when mutual diffusion is above a certain level, but when mutual diffusion is difficult to occur, that is, when impurities are segregated at the interface, each layer is easily peeled off from the segregated portion. It can be inferred.
[0061]
FIG. 9 is a schematic cross-sectional view of the periphery of the metal layer on the p-type electrode side of the nitride semiconductor LD in which the p-type electrode exists only immediately above the ridge. As described above, even when the p-type electrode (Pd layer 701 / Mo layer 702) exists only immediately above the ridge, the Pt layer 801 between the Au layer 703 and the Mo layer 702 has a similar good effect. The effect is obtained. Similarly, it has been confirmed that a good effect can be obtained by the function of the Pt layer 801 between the Au layer 703 and the Mo layer 702 regardless of the size of the p-type electrode.
[0062]
As in the present invention, when the Au layer 703 and the Pt layer 801 are in contact with each other and the Au layer 703 and the Pd layer are in contact with each other, it is confirmed that the IV characteristics are secured and the bonding strength is further improved, thereby extending the life. . Specifically, in the case of (Pd (0.05 μm) / Mo (0.15 μm) / Pd (0.10 μm) / Au (0.15 μm)), the lifetime is 2550 hours (MTTF: optical output = 30 mW, 30 ° C, DC, APC).
[0063]
Examples of the present invention other than the above include a relationship between a layer containing at least one of Pd, Ru, Rh, Os, and Ir as a first layer and a Mo layer as a second layer. A relationship between a Mo layer as two layers and a layer including at least one of Pt, Pd, Ru, Rh, Os, and Ir as a third layer, and an Au layer as a fourth layer, Regarding the relationship with the layer containing at least one of Pt, Pd, Ru, Rh, Os, and Ir as the third layer, similar to the above, appropriate diffusion occurs and the IV characteristics are secured. In addition, the bonding strength is further improved, so that the life is considered to be extended.
[0064]
When a metal layer other than Ni or Mo is inserted between the Au layer and the third layer, for example, at least one of Pt, Pd, Ru, Rh, Os, and Ir having a different composition from the third layer is used. When a layer containing more than one type is inserted, Hf, Ti, Co, Cu, Ag, Sc, Au, Cr, La, W, Al, Tl, Y, La, Ce, Pr, Nd, Sm, Eu, It is considered that the same effects as those of the present invention can be obtained even when Tb, Zr, Hf, V, Nb, Ta and their compounds are used.
[0065]
Conversely, in a structure where the Au layer 703 is not in contact with the Pd layer or the Pt layer 801, such as when the Au layer 703 and the Ni layer are in contact with each other, such as when the Au layer 703 is in contact with the Mo layer 702, the diffusion amount is reduced. However, it is not preferable because the bonding strength and the life are reduced.
[0066]
In Comparative Example 2, the metal layer on the p-type electrode side is Pd (0.05 μm) / Ni (0.15 μm) / Pt (0.15 μm) / Au (0.15 μm) from the p-type contact layer side. This is a nitride semiconductor laser device.
[0067]
FIG. 10 is a schematic cross-sectional view around the metal layer on the p-type electrode side in Comparative Example 2, and 1001 denotes a Ni layer. Except when the metal layer on the p-type electrode side was formed, it was manufactured in the same manner as in the first embodiment. The element characteristics (average value of 120) of this nitride semiconductor laser device will be described below.
[0068]
When a current of 50 mA flows, the operating voltage is 5.81 V, the bonding strength is 48.9 (au), the thermal resistance is 27.6 (° C./W), and the life is 51.3 hours (MTTF). : Light output = 30 mW, 30 ° C., DC, APC).
[0069]
As described above, although the comparative example 2 and the first embodiment were similar in the bonding strength, the comparative example 2 had lower IV characteristics. It is considered that the cause of the deterioration of the IV characteristics in Comparative Example 2 is that Ni, impurities such as metal oxides, Pt, and the like diffuse relatively much into the Pd layer as the first layer. It is considered that the heat generation amount required for laser oscillation increases due to the deterioration of the IV characteristics, which adversely affects the life characteristics.
[0070]
The tendency of the above IV characteristics to deteriorate is that (from the p-type contact layer side) Ni / Au / CuO / Pt / Au, Ni / Au, γ-GaN alloy / Pt / Au, Ni / Pt / Au, Pt The same applies to the case of / Au, Pd / Pt / Au, which is a phenomenon seen when Mo is not in contact with a metal that can contact the p-type contact layer and can secure ohmic characteristics.
[0071]
Conversely, the reason why the IV characteristics are good in the first embodiment is considered that the Mo layer 702 protects the Pd layer 701 in contact with the p-type contact layer and suppresses diffusion from other layers (Mo itself). Also relatively low diffusion).
[0072]
(Appropriate layer thickness of the second layer)
Next, the layer thickness at which the effect of the second Mo layer 702 is observed will be described. In the first embodiment, when the thickness of the Mo layer is 5 nm or more and 400 nm or less, the operating voltage (at a current of 50 mA) is reduced and the life is improved. When the Mo layer was thinner than 5 nm and thicker than 400 nm, the bonding strength at the interface was lowered.
[0073]
The cause can be inferred as follows. When the thickness of the second Mo layer is less than 5 nm, the first Pd layer cannot be sufficiently protected, and atoms and impurities from other layers are not protected by the first Pd layer and the p-type contact layer. It is considered that they diffused to the 111 surface and deteriorated the IV characteristics. At this time, the bonding strength has also decreased.
[0074]
Further, when the second Mo layer is thicker than 400 nm, the absolute amount of impurities such as oxides in the layer increases, and these move and concentrate at the interface between the Mo layer and another layer due to heating during die bonding. It is considered that the IV characteristics are deteriorated. As described above, when the IV characteristics are deteriorated, the driving voltage is increased, heat is easily generated, and the life is considered to be reduced.
[0075]
(Appropriate layer thickness of the first layer)
Next, the layer thickness at which the effect of the first layer is observed will be described. In the first embodiment, the effect was observed when the thickness of the first layer was 5 nm or more and 300 nm or less.
[0076]
If the first Pd layer is less than 5 nm, the Mo layer may come into contact with the p-type contact layer 111 during die bonding, so that sufficient ohmic characteristics may not be obtained. When the first Pd layer is thicker than 300 nm, the absolute amount of impurities such as oxides in the third Pt layer increases, and these impurities move to the interface with other layers due to heating during die bonding. It is considered that the bonding strength at the interface was lowered, and the characteristics of the device were lowered.
[0077]
(Appropriate thickness of the third layer)
Next, the layer thickness at which the effect of the third layer is observed will be described. In the first embodiment, the effect was observed when the thickness of the third layer was 50 nm or more and 5000 nm or less.
[0078]
If the thickness of the third Pt layer is less than 50 nm, the bonding strength with the fourth Au layer cannot be ensured during die bonding. Further, when the third Pt layer is thicker than 5000 nm, the absolute amount of impurities such as oxides in the third Pt layer increases, and these are heated by die bonding to form the third Pt layer and other layers. It is considered that the bond has moved to the interface with, and the bonding strength at the interface has been lowered.
[0079]
Here, the relationship between the bonding strength, the thermal resistance, and the life will be described. The low bonding strength means that impurities that hinder the thermal conductivity at the metal layer interface are likely to be segregated, which results in poor heat dissipation from the semiconductor LD chip, lowering thermal resistance, and further reducing nitriding. It is considered that the life of the semiconductor laser device is reduced.
[0080]
In the present invention, the solder for joining the nitride semiconductor LD chip and the mounting member is not only Au-30Sn but also AuSn (Au-90Sn, etc.), In, InPb, InSn, InAg, InAgPb, Sn, SnPb, SnSb, SnAg. , SnSb, SnAgPb, SnAgCu, SnPbSb, PbSb, PbAg, or PbZn, the bonding strength can be secured, diffusion of solder or the like into the first Pd layer can be suppressed, and the heat of the nitride semiconductor laser device can be reduced. It has been confirmed that resistance and life are improved.
[0081]
<Embodiment 2>
FIG. 11 is a schematic cross-sectional view around the active layer of the nitride semiconductor LD chip when the p-type electrode 101 does not cover the entire surface of the mount. In FIG. 11, reference numeral 1401 denotes a metal layer below the buried region 110, and reference numeral 1410 denotes a region immediately above the ridge. Other configurations are the same as those of the first embodiment.
[0082]
<Embodiment 3>
FIG. 12 is a schematic cross-sectional view around the active layer of the nitride semiconductor LD chip when the metal layers (p-type electrode 101, metal layer 102 under the p-type electrode, metal layer 1401 under the buried region) do not cover the entire surface of the mount. FIG. Other configurations are the same as those of the first embodiment.
[0083]
As described above, the present invention can take the forms of Embodiments 1 to 3. At this time, the metal layer structure on the surface of the mount member joined to the nitride semiconductor LD chip is Mo, Ni, Au, or Mo, Pt, Au, or Ti, Au, or Ti, Pt, Au, Alternatively, even when Mo, Ti, or Au is used, the same effect is obtained. In the first embodiment, TiO is used as the dielectric film. ₂ , And SiO ₂ But AlN, TiN, SiN, ZrO ₂ , Ta ₂ O ₅ , Al ₂ O ₃ , TiON, MgF ₂ Alternatively, the same effect is obtained even when another oxide, fluoride, or nitride is used.
[0084]
In the first embodiment, only one end face coating is performed. However, in the case where both face end coatings are performed, the effects of improving the thermal characteristics and the life can be obtained by applying the present invention. In the first embodiment, Cu is used for the submount, but similar effects can be obtained with other submounts. Other materials having a higher coefficient of thermal expansion than nitride semiconductors, such as Ag, Fe, CuW, BeO, Al ₂ O ₃ , GaAs or the like can give a compressive strain to the nitride semiconductor light emitting element chip, thereby improving the characteristics of the light emitting device. Further, those having high thermal conductivity are preferable because of excellent heat dissipation.
[0085]
In the first embodiment, the semiconductor LD chip is mounted on the SiC submount. However, the semiconductor LD chip may be mounted directly on the support base of the stem without using the submount. In this case, the mounting member becomes a support base for the stem.
[0086]
Further, in the first embodiment, PbSn solder is used as the solder for bonding the submount and the supporting base of the stem. However, other solder having a low melting point, for example, In-based solder such as InPb, InSn, InAg, and InAgPb. Alternatively, a solder containing Sn such as Sn, SnPb, SnSb, SnAg, SnSb, SnAgPb, SnPbSb, SnAgCu, or a solder containing Pb such as PbSb, PbAg, PbZn, or a powder of Ag, Au, Cu, etc. The same effect can be obtained by using epoxy resin, polyimide, or the like.
[0087]
The solder may be formed by a coating method, a sputtering method, a printing method, a plating method, etc. other than the vapor deposition method, and a sheet-shaped solder may be placed on the supporting base of the stem. If possible, it is desirable that the melting point be lower than that of the solder, in order to avoid the adverse effect on the existing solder. In addition, in addition to the above, the solder may be formed by a vapor deposition method, a coating method, a sputtering method, a printing method, a plating method, or the like.
[0088]
In the first embodiment, Hf / Al is used for the n-type electrode. However, other than Hf, Ti, Co, Cu, Ag, Ir, Sc, Au, Cr, Mo, La, W, Al, Tl, Y, and La are used. , Ce, Pr, Nd, Sm, Eu, Tb, Zr, Hf, V, Nb, Ta, Pt, Ni, Pd and their compounds may be used. In addition to Al, Au, Ni, Ag, Ga, In, Sn, Pb, Sb, Zn, Si, Ge and their compounds may be used, and the film thickness is not limited to the above thickness.
[0089]
Further, the semiconductor LD chip of the first embodiment is not limited to a specific example, and may be made of Si, SiC, ZrB ₂ , GaAs or other nitride semiconductor materials can be used, and the material system of the semiconductor growth layer is, for example, GaNαX _1- α (0.51 ≦ α ≦ 1) (X is an element containing at least one of P, As, Sb, Bi and the like), BNβX _1- β (0.51 ≦ β ≦ 1), AlγN _1- γ (0.51 ≦ γ ≦ 1), AlδGa _1- δNεX _1- ε (0 <δ <1, 0.51 ≦ ε ≦ 1), InNζX _1- ζ (0.51 ≦ ζ ≦ 1), InηGa _1- ηNμX _1- μ (0 <η <1, 0.51 ≦ μ ≦ 1), InνGaξAl _1- ν ₋ ξNτX _1- τ (0 <ν <1, 0 <ξ <1, 0.51 ≦ τ ≦ 1) may be used.
[0090]
The filling material on the p-type electrode side of the semiconductor LD chip of the first embodiment is SiO, SiO ₂ , TiO ₂ , SiN, GaAs, GaP, GaN, InN and other nitride semiconductors may be used.
[0091]
Further, a pad portion for wire bonding can be further provided on the submount mounting surface, and a mark for positioning at the time of die bonding can be provided. The present invention can be applied to a semiconductor laser device on which a semiconductor LD chip having three or more electrodes is mounted, such as a so-called multi-beam laser, based on the above principle.
[0092]
Further, as is well known, various films can be interposed between the solder and the submount, for example, a film for improving the adhesion between the submount and the solder, and a film between the submount and the solder. A film for preventing the reaction described above, and a film for improving the adhesion between these films or preventing oxidation may be appropriately laminated. It is assumed that various films are interposed between the solder, the bonding pad, and the submount for the same purpose.
[0093]
【The invention's effect】
According to the present invention, it is possible to prevent the deterioration of the IV characteristics and the deterioration of the bonding strength between the semiconductor LD chip and the mount member due to the reactivity between the metal layers, thereby providing a long-life nitride semiconductor laser device. can do.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view around a chip of a nitride semiconductor laser device according to a first embodiment.
FIG. 2 is a schematic view of a nitride semiconductor LD wafer on which a large number of individual semiconductor laser structures according to the present invention are formed.
FIG. 3 is a schematic view of an LD bar obtained by dividing the nitride semiconductor LD wafer of FIG. 2 at a dividing line (A) 210.
FIG. 4 (a) is a schematic view from the back surface (GaN substrate side) of a nitride semiconductor LD chip before die bonding according to the first embodiment.
FIG. 4B is a schematic view from the surface (growth layer side) of the semiconductor LD chip.
FIG. 5 is a schematic sectional view of a semiconductor laser device of the present invention.
FIG. 6 is a perspective view of a semiconductor laser device of the present invention.
FIG. 7 is a schematic cross-sectional view around a metal layer on a p-type electrode side in Comparative Example 1.
FIG. 8 is a schematic cross-sectional view around a metal layer on a p-type electrode side according to the first embodiment.
FIG. 9 is a schematic cross-sectional view of the vicinity of a metal layer on a p-type electrode side of a nitride semiconductor LD in which a p-type electrode exists only immediately above a ridge according to the present invention.
FIG. 10 is a schematic cross-sectional view around a metal layer on a p-type electrode side in Comparative Example 2.
FIG. 11 is a schematic cross-sectional view around the active layer of the nitride semiconductor LD chip when the p-type electrode of the present invention does not cover the entire surface of the mount.
FIG. 12 is a schematic cross-sectional view around the active layer of a nitride semiconductor LD chip when the metal layer of the present invention does not cover the entire surface of the mount.
FIG. 13 is a schematic cross-sectional view of a conventional semiconductor laser device having a junction-down structure.
[Explanation of symbols]
101 p-type electrode
102 metal film
103 Solder
105 Submount (mounting member)
120 n-type electrode
211 metal layer
410 Chip of nitride semiconductor laser diode

Claims (6)

A chip of a nitride semiconductor laser diode, a p-type electrode formed on one surface of the chip, an n-type electrode formed on the other surface of the chip, and at least a metal film and solder on the p-type electrode surface. And a mounting member joined through the nitride semiconductor laser device,
The metal layer composed of the p-type electrode and the metal film has at least a first layer, a second layer, a third layer, and a fourth layer in order from a layer in contact with the chip, and the solder is a fifth layer. ,
The first layer includes at least one of Pd, Ru, Rh, Os, and Ir,
The second layer is Mo,
The third layer includes at least one of Pt, Pd, Ru, Rh, Os, and Ir,
The fourth layer is Au,
The nitride semiconductor laser device, wherein the fifth layer contains at least one of Sn, Ag, In, and Pb. 2. The solder according to claim 1, wherein the solder is AuSn, In, InPb, InSn, InAg, InAgPb, Sn, SnPb, SnSb, SnAg, SnSb, SnAgPb, SnAgCu, SnPbSb, PbSb, PbAg, or PbZn. Nitride semiconductor laser device. A method for manufacturing a nitride semiconductor laser device comprising a step of mounting a chip of a nitride semiconductor laser diode on a mount member,
Forming a metal layer composed of a p-type electrode and a metal film on one surface of the chip, and forming an n-type electrode on the other surface of the chip;
The metal layer has at least a first layer, a second layer, a third layer, and a fourth layer in order from a layer in contact with the chip,
The first layer includes at least one of Pd, Ru, Rh, Os, and Ir,
The second layer is Mo,
The third layer includes at least one of Pt, Pd, Ru, Rh, Os, and Ir,
The fourth layer is Au,
A method for manufacturing a nitride semiconductor laser device, wherein a mount member is joined to a surface of the metal layer via a solder containing at least one of Sn, Ag, In, and Pb. 4. The method according to claim 3, wherein the thickness of the first layer of the chip before being bonded to the mount member is 5 nm or more and 300 nm or less. 5. 4. The method according to claim 3, wherein the thickness of the second layer of the chip before being bonded to the mount member is 5 nm or more and 400 nm or less. 5. 4. The method according to claim 3, wherein the thickness of the third layer of the chip before being bonded to the mount member is 50 nm or more and 5000 nm or less. 5.

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