JP4065723B2 - Manufacturing method of surface emitting laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser used for optical communication, and more particularly to a method for manufacturing a surface emitting laser.
[0002]
[Prior art]
As a semiconductor laser used for optical communication, a so-called edge emitting laser that emits in the direction of the edge of a substrate has been used so far.
[0003]
However, according to such an edge-emitting laser, the operation inspection can be performed only after the fabrication due to structural problems, and there is a disadvantage that the productivity is inferior.
[0004]
In other words, the substrate is divided to form an end surface, and light is irradiated from that surface. However, since the substrate is divided, it is necessary to handle each chip individually, so that it is compared with what is inspected in the wafer state. Thus, a considerable time is required for the inspection process.
[0005]
In order to solve such problems, in recent years, so-called surface emitting lasers that emit light in a direction perpendicular to the substrate surface have been actively developed.
[0006]
The surface emitting laser is that it allows inspection in web wafer state, it is possible to significantly reduce the testing costs.
[0007]
In other words, by setting the wafer on the prober stage and performing the electro-optic measurement while applying the probe needle to the electrode of the element, the alignment is performed once, and then all samples are automatically inspected. Can be performed, and several samples can be evaluated simultaneously, resulting in a significant reduction in required time.
[0008]
In addition, the fluctuation of the characteristic with respect to the temperature change is small, so that it is not necessary to keep the temperature of the element constant, and as a result, the power consumption is greatly reduced. Furthermore, it is a promising element in terms of increasing the capacity of optical communication because it can perform high-speed switching.
[0009]
In order to manufacture such a surface emitting laser, particularly a surface emitting laser used in the field of optical communication, it is necessary to obtain a structure in which different kinds of semiconductors are integrated. For this purpose, a separate semiconductor substrate is prepared. A manufacturing technique has been proposed in which a reflective layer and an active layer are crystal-grown on each substrate, and then both substrates are bonded together so as to bond the reflective layer and the active layer.
[0010]
[Problems to be solved by the invention]
When different types of substrates are to be bonded to each other, the linear expansion coefficients of the respective substrates are different, so that there is a problem that the substrates are warped after high-temperature processing and damage the crystal. In particular, the damage occurred in an InGaAsP-based active layer in which a thin film crystal was grown on an InP substrate.
[0011]
According to the InGaAsP-based active layer, the crystal itself has a low mechanical strength, and stress is applied to the crystal, thereby causing damage to the active layer. As a result, the luminous efficiency, which is the most important required characteristic of the light-emitting device, is obtained. Had fallen.
[0012]
In addition, there is a problem that the adhesion strength is deteriorated and the film is peeled off.
[0013]
In addition, according to the surface emitting laser, the area of the light emitting portion is usually about φ2 to 6 μm, so that the mesa structure suitable for the surface has a diameter of about 30 μm. On the other hand, the surface emitting laser chip usually has a size of about 300 μm square so as to be suitable for handling after being divided for each element.
[0014]
In other words, the crystal can be grown on the entire surface of the substrate, but the portion of the crystal growth film that is actually used is less than 1%, so the number of chips per wafer is reduced, resulting in a lower manufacturing cost. It was high.
[0015]
This problem is not only because the Inp substrate itself is expensive, but also in the InGaAsP-based active layer grown on it, the quaternary composition control and the control of the film thickness of the quantum well structure included in the active layer. Therefore, the use efficiency of the active layer on which the crystal is grown greatly depends on the price of the device.
[0016]
Furthermore, in order to obtain a single transverse mode, the AlGaAs layer is selectively oxidized from the lateral direction of the mesa shape to confine the current, but in such an oxidation method, the oxidation rate varies depending on the fluctuation of the composition and the film thickness, As a result, there is a problem that it is difficult to produce the film uniformly in a plane and with good reproducibility.
[0017]
[Means for Solving the Problems]
In the method of manufacturing a surface emitting laser according to the present invention, a first InGaAs layer, an active layer composed of a multilayer film of InGaAsP semiconductor, and a second InGaAs layer are sequentially formed on one main surface of an InP substrate by a crystal growth method. Next, this active layer is processed into a mesa shape, a plurality of disk-like active layer chips are arranged on the InP substrate, and the active layer chips removed from the InP substrate are successively used in the following (1) A method for producing a surface-emitting laser, which is subjected to steps (7) to (7).
(1) reflected by sequentially forming a layer of _{GaAs / Al z Ga 1-z} As semiconductor first reflective layer made of (0 <Z) and the recess forming by crystal growth method on a substrate made of GaAs or Si A member is produced.
(2) A hollow disk-shaped recess is formed in the recess-forming layer of the reflecting member.
(3) inclusive solution the active layer chip, placed in the reflective member, the solution was stirred was fitted to the active layer chip to the recess, pulling out of solution the reflecting member.
(4) on the surface of the active layer chips distribution in the _{recess, GaAs / Al z Ga 1-} z As semiconductor (0 <Z) Tona Ri by the crystal growth method on a substrate made of GaAs or Si, wherein Another reflecting member formed by forming a second reflecting layer having a reflectance lower than that of the first reflecting layer is disposed , and heated and pressed to be bonded.
(5) The substrate of the other reflecting member is removed.
(6) to mesa processing the second reflective layer of other reflective member so as to leave the second reflective layer on the active layer chip.
(7) Electrodes are formed on the second reflective layer on the active layer chip and on the other main surface of the substrate of the reflective member.
[0018]
According to the surface emitting laser manufacturing method of the present invention, even when two types of substrates having greatly different linear expansion coefficients as in the above configuration are used, one is processed by a substrate and the other is processed into a chip shape. By disposing the chip on the substrate, the amount of distortion is greatly reduced, thereby eliminating damage to the active layer and obtaining good photoelectric characteristics.
[0019]
In addition, since the amount of strain is reduced, the current confinement layer can be formed before the substrates are bonded together, whereby an excellent single transverse mode can be stably obtained.
[0020]
In addition, both in terms of material and fabrication, the active layer on the expensive InP substrate can be processed into blocks to increase the number of wafers taken per wafer by about two orders of magnitude, resulting in reduced manufacturing costs. Thus, a low-cost surface emitting laser can be obtained.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a method for manufacturing a surface emitting laser according to the present invention will be described with reference to the drawings.
[0022]
(Production of active layer chip)
First, a method for producing an active layer chip will be described.
[0023]
FIG. 1 is a manufacturing process diagram (flow chart) of an active layer chip, and sequentially goes through the respective steps (a) to (c).
[0024]
Process (I):
An InGaAs layer 2 is formed as an etching stopper layer on the single crystal InP semiconductor substrate 1 by crystal growth, and then an active layer 3 composed of a multilayer film of InGaAsP semiconductor is crystal-grown. In addition, an InGaAs layer 2 as an etching stopper layer is formed by crystal growth.
[0025]
The active layer 3 has a superlattice structure composed of a thin InGaAsP layer and another InGaAsP layer, and one layer becomes a quantum well layer having a smaller band gap than the other layer. The other is the barrier layer.
[0026]
The or falling edge of quenching the stopper layer, the etching rate for a etching solution, a layer structure so as to be smaller by orders of magnitude as compared with the etching rate for InP substrate.
[0027]
Process (b):
The active layer 3 is mesa-etched. At this time, the etching stopper layer 2 was also etched into the same shape.
[0028]
The etchant used for such etching is hydrochloric acid (HCl + H ₂ O) for etching the active layer, and sulfuric acid (H ₂ SO ₄ + H ₂ O ₂ + for etching the etching stopper layer. H ₂ O) may be used.
[0029]
Process (c):
Next, the back surface of the InP semiconductor substrate is polished to a thickness of several tens of μm, and the substrate is completely removed chemically by wet etching, whereby many active layer chips are obtained. Each chip is, for example, about 30μm in diameter and has a thickness of 0.5μm order of discoid (shaped disks). Hereinafter, such an active layer chip is referred to as a disk 4.
[0030]
The polishing described above may be physically etched using a solution containing slurry. For the chemical wet etching, hydrochloric acid (HCl + H ₂ O) may be used as the etching solution.
[0031]
(Method for manufacturing surface emitting laser)
As shown in FIGS. 2 and 3, the following steps (1) to (7) are sequentially performed using each disk 4.
[0032]
Step (1):
_{GaAs / Al z Ga 1-z} As semiconductor are sequentially formed a reflecting layer 6 and the layer 7 of the recess formed consisting of (0 <Z) to produce the reflecting member by a crystal growth method on a substrate 5 made of Si.
[0033]
The reflection layer 6 is a multilayer reflection mirror structure composed of periodic GaAs layers / AlGaAs layers formed by crystal growth, and a combination of GaAs layers / AlGaAs layers was grown in 30 cycles. In this example, a GaAs layer is grown as a recess forming layer 7 on such a multilayer reflective mirror structure.
[0034]
Step (2):
A recess 8 is formed by subjecting the layer 7 for forming the recess of the reflecting member to a recess. The recess 8 has a hollow disk shape, and has a diameter of about 32 μm and a depth of about 0.3 μm.
[0035]
In such recess processing, a resist is patterned by a photolithography process, and then etching is performed.
[0036]
Step (3):
By this step, the disk 4 is disposed in the recess 8.
This step will be described in more detail. The reflecting member subjected to the recess processing obtained in the previous step is put into the solution containing the disk 4, and such a solution is stirred. For this stirring, it is preferable to use a stirrer or an ultrasonic wave. For example, when the stirrer has a structure in which a magnetic bar is rotated by a motor, the metal bar thrown into the solution may be rotated.
[0037]
Through such agitation, the disk 4 is fitted into the recess (recess 8) after a while.
[0038]
If the diameter of the recess 8 is about 1 to 10 μm larger than that of the disk 4, the disk 4 is easy to fit in, and further, the stuck thing is difficult to come out.
[0039]
Also, in the subsequent process, another reflecting member is bonded to the disk 4 so that the depth of the recess 8 is made smaller than the thickness (0.6 to 3 μm) of the disk 4.
[0040]
Step (4):
On the surface of the disk 4 that is distribution to the recesses 8, the other reflective members, arranged so as to face the reflective layer 6.
[0041]
The other reflecting member has the following configuration.
That is, making the reflective layer 10 made of _{GaAs / Al z Ga 1-z} As semiconductor (0 <Z) by crystal growth method on a substrate 9 made of Si, the reflective layer 10 is periodic GaAs layer / A multilayer reflecting mirror structure composed of an AlGaAs layer was formed by crystal growth, and a combination of GaAs layer / AlGaAs layer was grown in 20 cycles.
[0042]
The mirror structure used in step (1) is a 30-cycle GaAs layer / AlGaAs layer (high reflection mirror), but according to this step, a 20-cycle GaAs layer / AlGaAs layer (low reflection mirror). Grew. With such a laminated structure, one mirror reflectivity is higher than the other mirror reflectivity, so that the laser beam generated inside is emitted from the low reflectivity side (low reflection mirror).
[0043]
As described above, the disk 4 is arranged in the recess 8 in the step (3), and then pulled up from the solution in that state. For this purpose, for example, a substrate fixed to a jig or the like may be taken out from the solution together with the jig. Then, in the next step (4), a structure in which another reflecting member is stacked on the disk 4 is obtained. By using an oven or the like, a bonded structure is obtained.
[0044]
The pressing strength at this time is, for example, 300 to 900 g / cm ² per contact area, and the heating temperature may be, for example, 450 to 650 ° C., which maximizes the mechanical strength at the joint, and Good electrical connection is obtained.
[0045]
Step (5):
The substrate 9 of the other reflecting member is removed.
For this, for example, it is polished or chemically removed by wet etching.
[0046]
Step (6):
The reflective layer 10 of another reflective member is mesa processed. According to this processing, the resist is patterned by a photolithography process and then etched.
[0047]
Step (7):
Ring electrodes 11 are formed on the reflective layer 10 on the reflective layer 10 of the other reflective member and on the other principal surface of the substrate 5, respectively. 4 is formed. These electrodes 11 and 12 are formed by vacuum deposition.
[0048]
The electrodes 11 and 12 are preferably made of a two-layer structure of Zn / Au in the case of having an ohmic junction with a p-type GaAs semiconductor. In addition, Cr / Au, Mn / Au, and Cr / AuGe / Cr / Au may be used. In the case of an n-type GaAs structure, AuGe / Ni / Au may be used.
[0049]
Thus, according to the method for manufacturing a surface emitting laser of the present invention, the disk 4 is manufactured by the steps (A) to (C), and further, the steps (1) to (7) are sequentially performed, whereby the distortion amount of the substrate. By significantly reducing the active layer, eliminating damage to the active layer, obtaining good photoelectric characteristics, and processing the active layer on the expensive InP substrate into a block shape, both in terms of material and production, increasing the number taken per wafer, manufacturing costs I'm thereto is reduced, low-cost surface emitting laser can be obtained.
[0050]
In addition, according to the surface emitting laser obtained by the manufacturing method of the present invention, the current constriction layer can be formed before the substrates are bonded because the amount of distortion of the substrate is reduced. The transverse mode can be obtained stably.
[0051]
FIG. 4 is a schematic cross-sectional view of a surface emitting laser having a current confinement layer 13 formed thereon.
[0052]
Further, as shown in FIG. 5, when the current confinement structure opening is formed at the bottom of the depression, if the current confinement layer has a thickness of 20 nm or more, it becomes difficult to make contact with the emission wavelength. It is preferable that a contact is made after forming a transparent material that can be further electrically connected, such as Si or Ge, and filling the hole in the opening of the current confinement structure.
[0053]
It should be noted that the present invention is not limited to the above embodiment, and various modifications and improvements can be made without departing from the scope of the present invention.
[0054]
For example, was produced a reflective layer of _{GaAs / Al z Ga 1-z} As semiconductor (0 <Z) by crystal growth method on a substrate made of Si as a reflecting member, crystal on a substrate made of GaAs Alternatively or a reflective member manufactured a reflective layer of _{GaAs / Al z Ga 1-z} As semiconductor (0 <Z) by deposition.
[0055]
Further, an Al _α Ga _{1- α} As layer (0.8 <α) may be provided between the reflective layer 6 and the substrate 1 or between the reflective layer 10 and the substrate 9. That is, when separating the substrate and the reflective layer, it is preferable in that the Al _α Ga _{1- α} As layer is oxidized and thus selective etching is performed to facilitate separation from the substrate.
[0056]
Furthermore, as shown in FIG. 6, before forming the ring electrode 11 on the surface side, an insulating film 14 made of a synthetic resin or the like may be applied, whereby the periphery of the mesa is insulated to form the electrode. This is preferable in that it is easy to prevent oxidation and the like from around the mesa.
[0057]
【The invention's effect】
As described above, according to the surface emitting laser manufacturing method of the present invention, even though two types of substrates having greatly different linear expansion coefficients are used, one is processed by a substrate and the other is processed into a chip shape. Is placed on the substrate, the amount of distortion is greatly reduced, thereby eliminating the damage to the active layer, obtaining good photoelectric characteristics, and reducing the amount of distortion, thereby reducing the current confinement layer. As a result, a high-quality and high-reliability surface emitting laser capable of stably obtaining a high-quality and high-reliability single transverse mode can be obtained.
[0058]
Moreover, in the manufacturing method of the present invention, the manufacturing cost is reduced by increasing the number of wafers taken per wafer, thereby providing a low-cost surface emitting laser.
[Brief description of the drawings]
FIGS. 1A to 1C are flowcharts showing a manufacturing process of an active layer chip.
FIGS. 2 (1) to (4) are flowcharts showing a manufacturing process of a surface emitting laser.
FIGS. 3A to 3G are flowcharts showing a manufacturing process of a surface emitting laser. FIGS.
FIG. 4 is an explanatory view showing a schematic cross section of a surface emitting laser according to the present invention.
FIG. 5 is an explanatory view showing a schematic cross section of another surface emitting laser according to the present invention.
FIG. 6 is an explanatory view showing a schematic cross section of still another surface emitting laser according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... InP semiconductor substrate 2 ... InGaAs layer 3 ... Active layer 4 ... Disk 5, 9 ... Substrate 6 made of Si, 10 ... Reflective layer 7 ... For forming recesses Layer 8 ... recesses 11, 12 ... electrodes

Claims (1)

A first InGaAs layer, an active layer composed of a multilayer film of InGaAsP-based semiconductor, and a second InGaAs layer are sequentially formed on one main surface of the InP substrate by a crystal growth method, and then this active layer is processed into a mesa shape. A plurality of disk-shaped active layer chips are arranged on the InP substrate, and the following steps (1) to (7) are sequentially performed using each active layer chip removed from the InP substrate. A method of manufacturing a surface-emitting laser, which is characterized.
(1) reflected by sequentially forming a layer of _{GaAs / Al z Ga 1-z} As semiconductor first reflective layer made of (0 <Z) and the recess forming by crystal growth method on a substrate made of GaAs or Si A member is produced.
(2) A hollow disk-shaped recess is formed in the recess-forming layer of the reflecting member.
(3) inclusive solution the active layer chip, placed in the reflective member, the solution was stirred was fitted to the active layer chip to the recess, pulling out of solution the reflecting member.
(4) on the surface of the active layer chips distribution in the _{recess, GaAs / Al z Ga 1-} z As semiconductor (0 <Z) Tona Ri by the crystal growth method on a substrate made of GaAs or Si, wherein Another reflecting member formed by forming a second reflecting layer having a reflectance lower than that of the first reflecting layer is disposed , and heated and pressed to be bonded.
(5) The substrate of the other reflecting member is removed.
(6) to mesa processing the second reflective layer of other reflective member so as to leave the second reflective layer on the active layer chip.
(7) Electrodes are formed on the second reflective layer on the active layer chip and on the other main surface of the substrate of the reflective member.

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