JP5103818B2 - Semiconductor laser element - Google Patents

Description

  The present invention relates to a semiconductor laser element.

Patent Document 1 listed below discloses a method for mounting an optical semiconductor element by vacuum-sucking the optical semiconductor element to an end face of a collet (holding member), transporting it to a predetermined position on a table, and bonding.
In recent years, with the increase in the speed and capacity of optical fiber communication, the speed of a semiconductor laser used as a signal light source has been increased. For example, as shown in FIG. 3, a semiconductor laser for optical communication has a semiconductor buried layer for current confinement around a mesa structure including an active layer processed into a stripe shape, and further this semiconductor buried layer In order to reduce the capacitance caused by the above, trench grooves are provided on both sides of the mesa structure. As described above, when the surface of the semiconductor laser is uneven, if the semiconductor laser element is transported using the method described in the cited document 1, there is a problem that inconvenience such as deformation or breakage of the semiconductor laser element occurs during the transport. is there.

Japanese Patent Laid-Open No. 5-21820

  When the semiconductor laser chip is mounted on a package or a submount, the semiconductor laser chip is held and transported to the collet by vacuum suction. At this time, when the semiconductor laser chip is brought into contact with the collet and vacuum-adsorbed, it is necessary to apply a predetermined load to the collet in order to securely hold the semiconductor laser chip. At this time, due to the unevenness of the surface of the semiconductor laser chip, the surface of the semiconductor laser chip and the contact surface of the collet do not come into uniform contact, and a large stress is applied to the semiconductor laser chip, which may cause cracks. This crack may reach the active layer of the semiconductor laser and may destroy the semiconductor laser element.

  In particular, an embedded semiconductor laser used as a light source for optical fiber transmission has a trench groove in an embedded region with a mesa structure including an active layer processed in a stripe shape, but obtains higher operating characteristics. For this reason, there is a tendency to further narrow the distance between the active layer region and the trench groove. For example, in a semiconductor laser element operating at a modulation frequency of about 2 GHz, the interval between the trench grooves is about 7 to 20 μm. However, in a semiconductor laser operating at a modulation frequency of 10 GHz, the interval between the trench grooves is as narrow as about 6 μm. It is formed. In this case, in the mounting of a buried type semiconductor laser chip having a trench groove, the semiconductor laser chip having a narrower distance between the active layer region and the trench groove is more prone to cracks and causes a problem of element destruction. Became clear. This is because the contact area between the bottom surface of the collet and the semiconductor laser chip becomes smaller due to the narrowing of the gap between the active layer region and the trench groove, or the unevenness of the surface becomes remarkable, so that the bottom surface of the collet is the semiconductor laser chip. The collet may incline when contacting the surface of the semiconductor, and may contact linearly. As a result, it is considered that the pressure on the semiconductor laser chip due to the load of the collet becomes larger. On the other hand, if the collet load is reduced in order to reduce damage, reliable vacuum suction becomes difficult and productivity is lowered.

  Accordingly, an object of the present invention is to provide a semiconductor optical device having excellent characteristics and reliability without causing cracks or destruction of the device when mounting the semiconductor laser device.

A semiconductor laser device according to the present invention includes a semiconductor substrate of a first conductivity type, an active layer formed on the semiconductor substrate, a striped mesa portion including the active layer, and a periphery of the mesa portion embedded with a semiconductor. and the buried layer, and a second conductivity type contact layer and the electrode formed on the active layer, a buried semiconductor laser device trenches are formed on the buried layer, wherein The semiconductor laser device has a collet holding resin pad thicker than the electrode on the surface of the semiconductor laser element .

  According to the semiconductor laser device having the above configuration, when mounting the semiconductor laser chip using the collet, the bottom surface of the collet contacts the resin pad before contacting the electrode formed on the surface of the semiconductor laser device, Even if a load due to the collet is applied to the semiconductor element and a stress is generated, the semiconductor laser element can be prevented from being cracked or broken by being absorbed and relaxed by the resin pad.

  In particular, when mounting a semiconductor laser element capable of high-speed modulation in which the distance between the stripe-shaped mesa portion and the trench groove is narrow, the generation of cracks can be prevented and a highly reliable semiconductor laser element can be provided. it can.

In the semiconductor laser device according to the present invention, the resin pad is formed in a region other than the electrode formed on the surface of the semiconductor laser device and the trench groove , and the electrode formed on the stripe mesa portion; It is arranged to be isolated from the trench groove . By forming the resin pad separately from the electrode formed on the active layer or the trench groove, it is possible to reduce the influence of the stress generated when the semiconductor laser element is held by the collet on the active layer.

Further, in the semiconductor laser device according to the present invention, two or more resin pads may be formed so as to be substantially symmetrical with respect to the striped mesa portion. Since the bottom surface of the collet can be in uniform contact with the surface of the resin pad over a wide area, the stress when the collet comes into contact can be reduced. The resin pad may be made of a photosensitive resin.

  According to the present invention, since the semiconductor optical device has the resin pad for holding the collet formed on the surface thereof, a highly reliable semiconductor optical device can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

First Embodiment FIGS. 1A and 1B are schematic views showing a semiconductor optical device 30 according to a first embodiment of the present invention. Examples of the semiconductor optical device include a semiconductor laser device (laser diode) and an optical modulator.

  The embodiment shown in FIG. 1 has an embedded semiconductor laser structure in which a semiconductor layer is embedded around a stripe mesa portion 6 processed into a stripe shape. In the striped mesa portion 6 of this semiconductor laser element, an n-type InP cladding layer 2, an InGaAsP quantum well structure active layer 3, and a first p-type InP cladding layer 4 are sequentially stacked on the upper surface of a substrate 1 made of an n-type InP semiconductor. Have Around the striped mesa portion 6, there is a buried layer 5 made of an InP semiconductor, and a trench groove 10 is formed in the buried layer. The buried semiconductor layer has a function of confining current in the active layer 3 of the striped mesa portion 6 in addition to the function of forming a refractive index waveguide for controlling the transverse mode of the semiconductor laser, and is a p-type. The InP semiconductor layer 5a, the n-type InP semiconductor layer 5b, and the p-type InP semiconductor layer 5c are sequentially stacked. A second p-type InP clad layer 7 and a p-type InGaAs contact layer 8 are stacked on the top surfaces of the striped mesa portion 6 and the buried layer 5. A stripe-shaped p-side electrode 15 is provided on the p-type InGaAs contact layer of the stripe-shaped mesa portion, and an electrode pad 17 for wire bonding for electrical connection to the outside is provided. . An n-side electrode 20 is formed on the lower surface of the n-type InP semiconductor substrate 1. The p-side electrode 15 is an ohmic electrode made of, for example, Ti / Pt / Au, and the n-side electrode 20 is an ohmic electrode made of an AuGeNi alloy. By injecting a current into the active layer through the p-side electrode 15 and the n-side electrode 20, laser oscillation can be obtained from the semiconductor laser element.

When the semiconductor laser is in an operating state, the pn junction of the buried layer 5 is reverse-biased, so that the current flowing through the buried layer 5 is blocked. On the other hand, the pn junction is depleted and has a large capacitance. Have. In order to reduce this capacitance, trench grooves 10 reaching the substrate are formed on both sides of the striped mesa portion 6 in the semiconductor buried layer region. As the distance between the trench grooves formed on both sides of the striped mesa portion is reduced, the capacitance of the buried layer can be reduced and high speed operation can be expected. For example, in a semiconductor laser capable of high-speed operation with a modulation frequency of 10 GHz, the interval between the trench grooves on both sides of the striped mesa portion 6 is 6 μm.

  A resin pad 25 for holding a collet is formed on the surface of the semiconductor laser element. For example, a photosensitive polyimide resin or a photosensitive BCB resin (benzocyclobutene resin) can be used as the resin material. By using a photosensitive resin, the resin pad 25 having a predetermined pattern can be easily formed by a normal photolithography process. The thickness of the p-side electrode 15 and the electrode pad 17 is usually about 2 to 3 μm. On the other hand, by making the thickness of the resin pad 25 larger than the thickness of the p-side electrode 15, it is possible to directly contact the electrode of the semiconductor laser chip and the like even during vacuum suction by the collet when mounting the semiconductor laser chip. Can be prevented. Moreover, since the resin functions as a buffer material, even if the collet contacts the resin, it is possible to reduce the influence of the stress on the semiconductor laser chip. The thickness of the resin is, for example, about 4 to 5 μm, and is formed to be about 2 to 3 μm thicker than the thickness of the p-side electrode.

  The resin pad 25 is disposed separately from the striped mesa portion 6 and the trench groove 10. This is to prevent the stress due to the collet load from being transmitted to the active layer even when the semiconductor laser chip is held by the collet. In FIG. 1, the resin pads 25 are arranged substantially symmetrically on both sides of the striped mesa portion 6. When the collet holds the semiconductor laser chip, the bottom surface of the collet and the resin pad can be in uniform contact with each other over a relatively wide area by disposing them on both sides of the striped mesa portion 6. As a result, the stress at the time of contact can be dispersed. It is possible to prevent the semiconductor laser chip from being cracked or broken due to an excessive stress applied to the semiconductor laser chip due to the collet being inclined and contacting linearly or a part of the collet contacting. Two resin pads are not necessarily required as long as both sides of the striped mesa portion 6 are provided, and a plurality of resin pads may be arranged. Even in this case, it is more preferable that the stripe-shaped mesa portions 6 are arranged substantially symmetrically.

Second Embodiment FIG. 2 is a cross-sectional view showing a method of manufacturing a semiconductor optical device according to a second embodiment of the present invention. Examples of the semiconductor optical device include a semiconductor laser device (laser diode) and an optical modulator.

  In FIG. 2, a resin pad region 25 for holding the collet is provided apart from the striped mesa portion 6 and the trench groove 10. In the case where the semiconductor laser chip is held by the collet, in the first embodiment, the collet contacts the resin pads 25 disposed on both sides of the striped mesa unit 6 across the striped mesa unit 6 or the trench groove 10. In this embodiment, since the resin pad is provided in a region away from the striped mesa portion 6 and the trench groove 10, the influence of stress on the active layer can be further reduced and cracks can be generated. It is possible to prevent the element from being damaged due to the above. The resin pad may be divided into a plurality of parts as long as the resin pads are arranged so as to come into uniform contact with the bottom surface of the collet.

Next, main steps for manufacturing the semiconductor laser chip in the first embodiment as shown in FIG. 1 will be described. On an n-type InP substrate 1, an n-type InP cladding layer 2, a lower InGaAsP optical confinement layer (not shown), an InGaAsP / InGaAsP multiple quantum well structure active layer 3, an upper InGaAsP optical confinement layer (not shown), a first p The type InP cladding layer 4 is successively grown by MOCVD. Next, a SiN insulating film mask is formed in a region where the striped mesa portion is formed by a photolithography process, and a region where the striped mesa portion other than the insulating film mask is not formed is removed by wet etching, and a stripe including the active layer is formed. The mesa portion 6 is formed. Subsequently, the p-type InP buried layer 5a, the n-type InP buried layer 5b, and the p-type InP buried layer 5c are successively grown by MOCVD. After the growth, the SiO ₂ insulating film mask is removed. Thereafter, the second p-type InP cladding layer 7 and the p-type InGaAs contact layer 8 are grown over the striped mesa portion 6 and the buried layer 5 (5a, 5b, 5c).

Next, a SiN insulating film mask is formed in a region other than the region for forming the trench groove, and etching is performed by wet etching until the n-type InP cladding layer is reached, thereby forming the trench groove 10. At this time, the pattern of the insulating film mask is formed so that the distance between the trench groove 10 and the striped mesa portion 6 is 2.5 μm, and the distance between the trench groove and the trench groove is 6 μm. After forming the trench groove 10, an insulating film 19 made of SiN is formed, and a photoresist for forming an opening for the p-side electrode to contact the InGaAs contact layer 8 on the striped mesa portion is formed. Using this photoresist mask, the insulating film is removed to form an opening for electrode contact, and Ti / Pt / Au is formed by vapor deposition. Further, a gold film having a thickness of about 1.5 μm is formed on the electrode by plating. The total thickness of the electrode at this time is about 2 μm.
Thereafter, the lift-off method is used to remove together with the resist the electrode metal formed outside the stripe-shaped mesa region and the electrode pad region.

  Next, in order to form a resin pad for holding a collet, a photosensitive resin is uniformly formed. For example, a photosensitive polyimide resin or a photosensitive BCB resin can be used as the photosensitive resin. The photosensitive resin is formed by spin coating, and then heat treatment at 280 ° C. for 6 minutes. The thickness of the formed photosensitive resin is, for example, 5 μm. Thereafter, the photosensitive resin is removed by photolithography, leaving only the resin pad region 25 for holding the collet.

  Next, the InP substrate 1 is ground to 100 μm by lapping, and an AuGeNi alloy is formed on the back surface of the InP substrate 1 as an n-side electrode by vapor deposition. Thereafter, the substrate is divided by cleavage so as to have a desired resonator length (here, 300 μm), whereby the semiconductor laser device 30 according to the first embodiment of the present invention shown in FIG. 1 is completed.

  Since the resin height of the resin pad 25 for holding the collet is formed higher than the height of the p-side electrode metal 15, when the semiconductor laser chip is held by the collet, the bottom surface of the collet is the p-side electrode 15. The resin pad 25 having a certain degree of elasticity is contacted without contact with the resin. Therefore, the stress due to the collet load generated when the semiconductor laser chip is held by the collet is not cracked or broken. In particular, even in a high-frequency semiconductor laser device in which the interval between trench grooves is narrowed for the purpose of reducing the capacitance of the device, it is possible to prevent the introduction or destruction of cracks due to vacuum adsorption by a collet during mounting.

  The process for manufacturing the semiconductor laser chip in the second embodiment also differs from the semiconductor laser chip in the first embodiment in the region where the resin pad for holding the semiconductor laser chip is formed. It can manufacture using the process similar to the manufacturing process in.

  The present invention has been described in detail based on the embodiments. However, the present invention is not limited to the above embodiment. The present invention can be variously modified without departing from the gist thereof.

(A) is a perspective view of the semiconductor laser device according to the first embodiment of the present invention, and (b) is a cross-sectional view of the semiconductor laser device according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view of a semiconductor laser device according to the second embodiment of the present invention. FIG. 3 is a diagram showing a conventional semiconductor laser element and a state held by a collet during mounting.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... n-type InP substrate, 2 ... n-type InP clad layer, 3 ... InGaAsP quantum well structure active layer, 4 ... 1st p-type InP clad layer, 5, 5a, 5b, 5c ... buried layer, 6 ... striped mesa , 7 ... second p-type InP cladding layer, 8 ... p-type InGaAs contact layer, 10 ... trench groove, 15 ... p-side electrode, 17 ... electrode pad, 19 ... insulating film, 20 ... n-side electrode, 25 ... resin pad , 30 ... Semiconductor laser chip, 103 ... Active layer, 105, 105a, 105b ... Embedded layer, 115 ... Electrode, 117 ... Electrode pad, 119 ... Insulating film, 150 ... Collet

Claims (3)

A first conductivity type semiconductor substrate;
An active layer formed on the semiconductor substrate;
A striped mesa portion including the active layer;
A buried layer embedded with a semiconductor around the striped mesa portion;
A second conductivity type contact layer and an electrode formed on the active layer;
An embedded semiconductor laser element in which a trench groove is formed in the embedded layer,
Have a thick collet retaining resin pad than the thickness of the electrode on the semiconductor laser element surface,
The resin pad is formed in a region other than the electrode and the trench groove, and is disposed separately from the electrode formed on the striped mesa portion and the trench groove. .   2. The semiconductor laser device according to claim 1, wherein two or more of the resin pads are arranged substantially symmetrically with respect to the striped mesa portion. The semiconductor laser device according to claim 1, wherein the resin pad is made of a photosensitive resin.

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