JP4851066B2 - Method for stabilizing semiconductor device - Google Patents

Description

  The present invention relates to a stabilization processing method performed for stabilizing the characteristics of a semiconductor element.

  There is an increasing need for surface-emitting lasers as signal light sources for high-speed optical transmission at medium distances called metro access systems and short distances such as LANs. Such high-speed optical transmission requires a gigahertz order modulation band. Further, particularly in transmission over a medium distance, a surface emitting laser that oscillates in a single mode or a state close to a single mode is necessary to avoid signal degradation due to wavelength dispersion in the optical fiber.

  By the way, in general, in the manufacturing process of a semiconductor element such as a semiconductor laser element, the element is kept at a high temperature for a certain period of time for the purpose of absorbing and stabilizing initial selection of element characteristics such as element selection and light output. A process called burn-in is often performed.

  This burn-in is often performed based on the description of the optical semiconductor device reliability assurance specification of Telcordia, USA. In the specification of Telcordia, the constant current control by flowing a constant current of 150 mA at 100 ° C. is described in section 4.2.3 of Non-Patent Document 1 as a condition for conducting screening of semiconductor laser elements (sorting of defective elements). The condition that constant light output control at the maximum rated light output is performed for 96 hours at 70 ° C. after the time has been performed is described.

In addition, as an example of performing burn-in on a surface emitting laser, as shown in Non-Patent Document 2, conditions such as a current of 15 mA flowing at 100 ° C. for 20 hours are described.
Telcordia GR-468-CORE, "Generic reliability assurance requirements for optoelectronic devices used in telecommunications equipment", Issue 1, USA, Dec. 1998 Robert A. Hawthorne III, James K. Guenter, David N. Granville, Mary K. Hibbs-Brenner and Robert A. Morgan, `` Reliability study of 850 nm VCSELs for data communications '', Reliability Physics Symposium, 34th Annual Proceedings, IEEE International, 1996, p.203 -210

  By the way, as described above, in the surface emitting laser element as a light source for high-speed optical transmission, it is necessary to obtain a sufficient modulation band, but the modulation band is determined by the product of the element capacitance and the element resistance value. In particular, even in the case of a single mode element or a multimode element, the element having a large current resistance has become a bottleneck in an element having a current injection region close to a single mode diameter (hereinafter referred to as a pseudo single mode element).

  In this regard, the present inventors pay attention to the fact that burn-in, which is usually performed for the purpose of element selection and light output stabilization, is also effective as a process for reducing the element resistance value of a surface emitting laser. did.

  However, conventional burn-in conditions have not been sufficient for surface emitting lasers. One reason is that conventional burn-in conditions are not optimized from the viewpoint of reducing the element resistance value. Another reason is that the burn-in condition disclosed in Patent Document 1 assumes a general semiconductor laser such as a Fabry-Perot type. The burn-in condition shown in Non-Patent Document 2 is intended for a multimode surface emitting laser in which a current is injected into a relatively large area among surface emitting lasers, and is a single mode type or a pseudo single type. It was not the optimum condition for the mode type surface emitting laser.

  For this reason, when the temperature and current values used in conventional burn-in are adopted, it takes much time to reduce the element resistance value of the surface emitting laser, or equipment with extremely high temperatures is required. There was a problem.

  In view of the above, an object of the present invention is to provide a surface emitting laser element having a wide modulation band by reducing the element resistance value of the surface emitting laser element by performing burn-in under appropriate conditions.

In order to achieve the above object, the present inventors set the current density to 20 KA / cm 2 or more and 50 KA / cm 2 or less as burn-in conditions that can effectively reduce the element resistance value, particularly in a surface emitting laser. Was found to be effective.
The method for stabilizing a surface-emitting laser according to the first aspect of the present invention includes an active region (current) of a single-mode or pseudo- single-mode surface-emitting laser having a current confinement structure at a constant processing temperature. A stabilization processing method for reducing the element resistance value of the surface emitting laser and performing a stabilization process by supplying a current to the injection region) at a predetermined current density for a predetermined time , the area of the current injection region Is 30 μm ² or less, the surface emitting laser has an average thermal resistance of 2000 K / W or more, the processing temperature is 70 ° C. to 100 ° C. , and the predetermined current density is 30 kA / cm ² or more, 50 kA. / cm ² or less, as the surface-emitting laser wherein the predetermined time to reduce the element resistance value is the time required to stabilize the becomes 10 hours or less than 100 hours, the temperature before Wherein the predetermined current density is determined.
Thus, by performing burn-in at a higher current density than in the past, the element resistance value can be reduced in a short time of 100 hours or less at a relatively low temperature of 100 ° C. or less.

  In particular, since the surface emitting laser has a thick multilayer mirror, the thermal resistance is larger than that of other general lasers such as a Fabry-Perot type, and the value is 2000 K / W or more. Since the heat resistance is large in this way, the amount of heat generated with current injection is large, so even if the ambient temperature is not high, the temperature rise of the element is large, and the burn-in effect can be sufficiently obtained.

The burn-in condition described above is particularly effective for devices having a current injection area that is quasi-single mode of 50 μm ² or less, and particularly remarkable for devices having a size of 30 μm ² or less.

  According to the present invention, burn-in of a surface emitting laser element can be performed in a short time at a relatively low temperature, and the cost for inspection before element shipment can be greatly reduced. Moreover, since the element resistance value of the surface emitting laser can be reduced and stabilized by burn-in, a surface emitting laser element having a wide modulation band suitable for high-speed optical transmission can be provided.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.

The surface emitting laser element to be used is a pseudo single mode element or a single mode element having an oxidation type current confinement structure and a small current injection area of 50 μm ² or less.

  The apparatus used for burn-in may be a commonly used apparatus. In other words, a thermostatic chamber and a current-carrying device in which the ambient temperature is kept constant by the temperature control device are used, and an element for performing burn-in is installed in the thermostatic chamber using an appropriate holder according to the element shape and the like And The temperature of the thermostatic chamber is defined as the burn-in temperature.

  Since the element resistance value varies depending on the applied voltage based on non-ohmicity, it is defined as the differential resistance value when the differential resistance value is minimized by changing the applied voltage to the surface emitting laser element.

As the time in burn-in elapses, the element resistance value decreases and eventually stabilizes. The state where the element resistance value is stabilized is defined as follows. FIG. 1 is a schematic diagram showing a change in element resistance value due to burn-in as a curve C. FIG. The horizontal axis represents time, and the vertical axis represents the element resistance value. The element resistance value gradually decreases from the initial value R _int with time during burn-in, and reaches a saturation value R _sat when a sufficient time elapses. Here, when two points P and Q separated by Δt with respect to time are taken along the curve C, the difference in element resistance value corresponding to the points P and Q is less than a measurement error, for example, 1% or less of R _int , etc. Then, it is considered that the element resistance is stabilized at the point Q, and the time corresponding to the point Q is defined as the element resistance stabilization time.

  FIG. 2 shows the burn-in current density and the element resistance stabilization time for the above-described surface-emitting laser element, using the temperature of the thermostatic chamber as a parameter. This finding was obtained as a result of many experiments conducted by the inventors. The current density is a value obtained by dividing the supplied current value by the current injection area of the surface emitting laser element. The current injection area will be described later.

Here, when the current value conventionally adopted as the burn-in condition is converted into the current density in the quasi-single mode type surface emitting laser element, it is about 10 to ²⁰ kA / cm ² . In such a low current density region, it is impossible to stabilize the element resistance value unless the burn-in temperature is set to a high temperature of, for example, 100 ° C. or more and long-time burn-in of 100 hours or more is not performed. It is clear from 2.

On the other hand, when the current density is 20 kA / cm ² or more, the element resistance can be stabilized at a lower burn-in temperature or a shorter burn-in time. In particular, when the current density is 30 kA / cm ² or more, the element resistance can be stabilized by burn-in at 100 ° C. or less and 100 hours or less, which is advantageous in reducing the cost required for burn-in.

In addition, it is not preferable to perform burn-in under a condition where the current density is too large because the surface emitting laser element is deteriorated. As a result of many experiments, the present inventors have found that the current density is desirably 50 KA / cm ² or less regardless of the burn-in temperature.

  Thus, the reason why burn-in can be performed at a low temperature is considered to be due to the fact that the thermal resistance of the element is large because the surface emitting laser has a multilayer reflector. That is, since the contribution of heat generation by current injection is large, the effect can be obtained even when the ambient temperature is low. In general, the thermal resistance of a surface emitting laser using AlGaAs as a multilayer mirror is 2000 to 10000 K / W. Accordingly, the burn-in method of the present invention can be applied to semiconductor lasers and semiconductor elements other than surface emitting lasers as long as they have the same or higher thermal resistance.

  Next, a specific example is shown in Examples 1-3 about said best embodiment.

[Example 1]
First, as a structure of a surface emitting laser that performs burn-in, a longitudinal sectional view in the vicinity of a current injection region is shown in FIG. The surface emitting laser element includes a lower multilayer reflector 2 made of p-type Al _0.2 Ga _0.8 As / Al _0.9 Ga _0.1 As and a GaAs / AlGaAs active layer on a p-type GaAs substrate 1. A resonator 3 and an upper multilayer mirror 4 made of n-type Al _0.2 Ga _0.8 As / Al _0.9 Ga _0.1 As are laminated. Also, a mesa post 5 including at least the upper multilayer film reflecting mirror 4 is formed. A part of the lower multilayer reflector 2 near the resonator 3 is made of AlAs instead of Al _0.9 Ga _0.1 As, and this AlAs layer is a region near the center of the mesa post 5 by oxidation treatment. Is oxidized into an annular AlO _x layer 6 surrounding the substrate. That is, the cross-sectional shape in the direction parallel to the substrate of the non-oxidized AlAs region at the center of the mesa post 5 is substantially circular, and the non-oxidized AlAs region is referred to herein as an oxidized aperture, and the cross-sectional shape in the direction parallel to the substrate is Let the diameter be d _ox . In order to obtain single mode oscillation, in this embodiment, d _ox = 5 to 6 μm. Therefore, the oxidized aperture area is 20 to 30 μm ² . This oxidized aperture area becomes the current injection area.

  An upper electrode 7 for injecting current is provided in a ring shape above the mesa post 5, and a light emitting portion 8 is formed inside the upper electrode 7. A pad electrode 9 connected to the upper electrode 7 is formed on the upper surface of the surface emitting laser element with an insulating film 10 interposed therebetween. A lower electrode 11 is formed on the back surface of the p-type GaAs substrate 1.

After the surface emitting laser structure as described above is fabricated on-wafer, it is cut out into individual chips, mounted on a commonly used can package, and burn-in is performed. The burn-in temperature is 70 ° C. here. Then, in order to achieve the purpose of stabilizing the element resistance by burn-in within 40 hours, the current density is set to 40 kA / cm ² based on FIG. The oxidation aperture area of the surface emitting laser element may be obtained by means such as an infrared microscope, and the current value may be set so that the above current density is obtained.

The present invention can be applied regardless of the structure of the surface emitting laser. That is, a surface emitting laser element having a current injection area of 50 μm ² or more may be used, and the cross-sectional shape in the direction parallel to the substrate of the non-oxidized AlAs region is not limited to a substantially circular shape, but may be a rhombus, for example. Good. Further, it may be a surface emitting laser element having a current confinement structure other than an oxidation type, such as an ion implantation type. It goes without saying that the present invention can be applied regardless of the material constituting the active layer and the conductivity type of the semiconductor substrate.

[Example 2] In Example 1, an example was shown in which burn-in of a surface emitting laser element was performed at 70 ° C. However, according to the present invention, stabilization of element resistance can be achieved without such a high-temperature equipment. It is possible to realize. For example, if a current density of 50 kA / cm ² is applied at a room temperature of 25 ° C., it is derived from FIG. 2 that the element resistance can be stabilized by energization for 100 hours.

  [Embodiment 3] In Embodiment 1, the example in which the surface emitting laser element is burned in while mounted on the can package has been shown. However, as described in Embodiment 3, the burn-in is performed with a bar-shaped chip. May be.

The third embodiment is characterized in that, when the surface emitting laser element as shown in FIG. 3 is fabricated on-wafer, inter-element connection electrodes for connecting pad electrodes of the respective elements to each other are provided on the upper surface of the wafer. is there. Examples of patterns of pad electrodes and inter-element connection electrodes are shown in FIGS. These drawings are top views of the wafer, and the same components as those in FIG. 1 are denoted by the same reference numerals. Each surface-emitting laser element on the wafer has a light emitting portion 8 surrounded by a ring-shaped upper electrode 7, and a pad electrode 9 connected to the upper electrode 7 and the pad electrode 9 are mutually connected. The inter-element connection electrode 12 is connected.

  The material constituting the inter-element connection electrode 12 is not limited as long as it is a material having sufficient conductivity. However, the reliability of the surface emitting laser element, the reliability of the inter-element connection electrode itself, the convenience in manufacturing, etc. Therefore, it is preferable to use the same material as that of the pad electrode 9. The inter-device connection electrode 12 may be prepared by a commonly used method such as vapor deposition or plating.

  By preparing an element holder for energization provided with an electrode for energization at a position corresponding to the arrangement of the inter-element connection electrodes 12, energization can be performed in units of a plurality of elements. For example, in the pattern of FIG. 4, since four elements are connected by one inter-element connection electrode, current can be supplied in units of four elements. As a result, the operation cost associated with the burn-in operation is reduced as compared with the case of the can package.

  Burn-in can be performed on a wafer-by-wafer basis, or can be performed on a single or multiple chips. For example, a rectangular region surrounded by a dotted line d in FIG. 4 may be cut out and burned in as a chip bar composed of 2 × 5 elements. The number of elements included in the chip bar may be selected as appropriate. By performing burn-in in the chip bar state in this way, even when manufacturing a one-dimensional array or a two-dimensional array using a surface emitting laser that is becoming important in the field of parallel interconnection technology using light, This is advantageous in that burn-in can be performed in units of arrays, and it can also serve as a sorting process for defective array elements.

In the third embodiment, as already described, the burn-in condition and the burn-in temperature and time are determined in the range of 30 kA / cm ^{2 to} 50 kA / cm ² per element as described above.

It is a schematic diagram explaining the change of the element resistance value during the burn-in of the surface emitting laser element. It is the graph which showed the burn-in condition which concerns on embodiment of this invention. It is a longitudinal cross-sectional view which shows the structure of the surface emitting laser element which concerns on Example 1 of this invention. It is a top view which shows the surface emitting laser element which concerns on Example 3 of this invention. It is a top view which shows the surface emitting laser element which concerns on Example 3 of this invention. It is a top view which shows the surface emitting laser element which concerns on Example 3 of this invention.

Explanation of symbols

1 p-type GaAs substrate 2 lower multilayer reflector 3 resonator 4 upper multilayer reflector 5 mesa post 6 AlO _x layer 7 upper electrode 8 light emitting portion 9 pad electrode 10 insulating film 11 lower electrode 12 inter-element connection electrode

Claims (4)

By supplying a current at a predetermined current density for a predetermined time to an active region (current injection region) of a single mode type or pseudo single mode type surface emitting laser having a current confinement structure at a constant processing temperature. A stabilization processing method for reducing the element resistance value of the surface emitting laser and performing a stabilization process,
The area of the current injection region is 30 μm ² or less,
The surface emitting laser has an element having an average thermal resistance of 2000 K / W or more,
Wherein the processing temperature is 100 ° C. from 70 ° C.,
Wherein the predetermined current density 30 kA / cm ² or more and 50 kA / cm ² or less,
The temperature and the predetermined current density are determined so that the predetermined time, which is a time required for reducing and stabilizing the element resistance value of the surface emitting laser, is not more than 100 hours and not less than 10 hours. A method for stabilizing a surface emitting laser characterized by the above. 2. The method of stabilizing a surface emitting laser according to claim 1, wherein the current confinement structure is formed of an oxidized portion and a non-oxidized portion. 3. The method of stabilizing a surface emitting laser according to claim 1, wherein the stabilization processing is performed in a chip state including one or a plurality of the surface emitting lasers. The stabilization treatment, the surface stabilization treatment method of the surface emitting laser according to any one of claims 1 to 3, characterized in that the emitting laser one or more inclusive wafer state.

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