JP4501404B2 - Method for evaluating semiconductor light emitting device - Google Patents

Description

  The present invention relates to a method for evaluating a semiconductor light emitting element, in which individual evaluation is performed by a voltage application test (burn-in test) on a plurality of semiconductor light emitting elements formed on a wafer, particularly a surface emitting laser having an individual electrode on an upper surface.

  A surface-emitting laser is a vertical cavity laser that emits light in a direction perpendicular to the substrate surface, whereas an edge-emitting laser emits light in a direction parallel to the substrate surface. It is attracting attention as a light source for the system.

  Generally, a post-type mesa structure is used as a structure of a surface emitting laser (for example, Patent Document 1). This post-type mesa structure laser forms a multilayer structure including a current confinement layer and an active layer made of aluminum arsenic (AlAs) on a device wafer (substrate), and a circular post mesa having a mesa diameter of about 30 μmφ by a method such as dry etching. After processing into the structure, a current confinement portion for the active layer is formed by selective oxidation of the current confinement layer (AlAs). Furthermore, after selective oxidation, the structure is covered with an insulating film such as a dielectric, and a part of the mesa is selectively removed to form an electrode layer. Then, a ring electrode having a window for light output is provided. Is done. In such a surface emitting laser, a current is efficiently injected into the active layer by the current confinement portion, so that efficient laser oscillation is possible.

  Unlike edge-emitting lasers, this type of surface-emitting laser has the feature that each device can be individually driven in a juxtaposed state on the wafer surface. Individual assessments are possible. As an individual evaluation, in general, a so-called burn-in test is performed in which a current is driven in a high-temperature environment to stabilize the characteristics of a semiconductor device and to select and sort an initial degradation device. However, this is particularly effective in a surface emitting laser. (For example, Non-Patent Document 1 and Non-Patent Document 2).

  By the way, when such a burn-in test is performed on a surface emitting laser, there are the following problems. That is, as shown in FIG. 4, when a burn-in test is performed on the device wafer 100 using the probe card 102, the same relative position as that of a large number of individual electrodes 101 on the device wafer 100 in order to secure electrical contacts. It is necessary to provide the same number of probes 102A. In addition, for reliable contact on the entire surface, it is necessary to accurately control the card position and the crimping force. In addition, the probe card 102 must be produced with high accuracy, is very expensive, and is extremely difficult to manage.

As a method of evaluating a plurality of surface emitting lasers at once without using such a probe card, both n-type and p-type electrodes of each element are formed on one side of the wafer and connected in series for evaluation. There is something to do (Patent Document 2).
JP 2001-210908 A JP-A-63-306687 Bobby M. HAWINS and others Reliability of Various Size Oxide Aperture VCSELs Robert A. Hawthone III and others Reliability Study of 850 nm VCSELs for Data Communication (1996)

  However, in this evaluation method, when the element resistance is abnormal and there is even one high-resistance surface-emitting laser, the applied current at the time of evaluation does not flow, and therefore, all elements connected in series cannot be evaluated. There is a problem.

  The present invention has been made in view of such problems, and its purpose is to enable stable evaluation even when an element having an abnormal element resistance is included, and to reduce the number of probes of the probe card. Another object of the present invention is to provide a method for evaluating a semiconductor light-emitting element that improves operability and can reduce costs.

The method for evaluating a semiconductor light emitting device according to the present invention is for performing individual evaluation of a plurality of semiconductor light emitting devices in which one electrode is a common electrode and the other electrode is juxtaposed on the same surface of the same substrate as an individual electrode. A method of short-circuiting individual electrodes of at least two elements of a plurality of semiconductor light-emitting elements with one short-circuit pattern, and a predetermined voltage between the short-circuit pattern and a common electrode of the plurality of semiconductor light-emitting elements. a voltage applying step of applying is intended to include a step of removing the short-circuit pattern by a stripping solution after the voltage application process.

  In the evaluation method of the present invention, after the individual electrodes of at least two elements of the plurality of semiconductor light emitting elements are short-circuited by one short-circuit pattern in the short-circuit process, the short-circuit pattern and the common electrode are A predetermined voltage is applied between them, whereby individual evaluation of the semiconductor light emitting element is performed.

  In particular, the short-circuit pattern is composed of one bus line having a probe pad, a plurality of branch lines that electrically connect the bus line and the individual electrodes of the plurality of semiconductor light emitting elements, Even if a current concentration occurs in a semiconductor light emitting device having an abnormal element resistance, the branch line is formed of a so-called fuse by forming the line width so that it melts when a current exceeding a predetermined value (excessive current) flows. Therefore, there is no significant change in the current flowing through the other semiconductor light emitting elements, and a stable evaluation test is performed.

  According to the semiconductor light-emitting element evaluation method of the present invention, the individual electrodes of at least two of the plurality of semiconductor light-emitting elements are short-circuited by one short-circuit pattern, and voltage is applied through this short-circuit pattern. Even if semiconductor light-emitting elements with abnormal element resistance are included, highly reliable evaluation tests can be performed, and the number of probes on the probe card can be greatly reduced, improving operability and reducing costs. be able to.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a cross-sectional structure of a semiconductor light emitting element according to an embodiment of the present invention, for example, a surface emitting laser 1. The surface-emitting laser 1 has, for example, an n-type structure having a multilayer structure of, for example, n-type aluminum gallium arsenide (n-type AlGaAs) having a different composition on a device wafer (substrate) 10 made of n-type gallium arsenide (n-type GaAs). A DBR layer (Distributed Bragg Reflector) 11 is stacked, and an n-type cladding layer 12 made of, for example, i-type aluminum gallium arsenide (i-type AlGaAs), for example, gallium arsenide / An active layer (light emitting layer) 13 having a quantum well structure formed of aluminum gallium arsenide (GaAs / AlGaAs), for example, a p-type cladding layer 14 made of i-type aluminum gallium arsenide (i-type AlGaAs), and made of aluminum arsenic (AlAs). Current confinement layer 15, for example, p-type aluminum gallium arsenide (p After p-type DBR layer 16 made of p-type AlGaAs and p-type contact layer 17 made of p-type gallium arsenide (p-type GaAs) are stacked in this order, the surface of n-type DBR layer 11 is etched to form a cylindrical mesa structure. Is formed.

A ring-shaped p-type electrode (ring-shaped electrode) 18 is formed on the contact layer 17, and a light output window 19 is formed inside thereof. The inner diameter D ₀ of the light output window 19 is about 10 μm. The outer periphery of the current confinement layer 15 becomes an insulating region 15A by hydrogen oxidation, and the unoxidized central portion becomes a current passage region (current confinement portion 15B), which enables high-efficiency laser oscillation. The inner diameter D ₁ of the current confinement portion 15B is designed, for example, about 15 [mu] m. The diameter D ₂ of the cylindrical mesa structure is, for example, about 30 μm.

An n-type electrode 20 is provided on the back surface of the device wafer 10. The n-type electrode 20 is an electrode common to many surface emitting lasers formed on the same wafer. As will be described later, the p-type electrode 18 is provided with individual electrodes 22 (see FIG. 2) for each surface emitting laser. With this individual electrode 22, each surface emitting laser can be driven in a current state in a wafer state before element separation. The individual electrode 22 is made of, for example, gold (Au), and the surface emitting laser including the electrode is covered with an insulating layer that does not corrode with an alkaline solution or the like, for example, silicon dioxide (SiO ₂ ).

  In this surface emitting laser 1, when a predetermined voltage is applied between the p-type electrode 18 and the n-type electrode 20, carriers are injected into the active layer 13 through the current confinement portion 15B, and light is emitted from the active layer 13. At the same time, laser resonance occurs between the n-type DBR layer 11 and the p-type DBR layer 16, that is, in a direction perpendicular to the device wafer 10, and the laser beam thus generated is applied to the ring-shaped p-type electrode 18. The light output window 19 thus formed is taken out.

  For example, about 40,000 surface emitting lasers 1 as described above are arranged on the device wafer 10, and in this state, evaluation of good or defective of each surface emitting laser 1 is performed. Unlike the edge-emitting laser, the surface-emitting laser 1 has an individual electrode for each element and can be driven by a current in a wafer state. Therefore, the surface-emitting laser 1 is brought into contact with one probe using a short-circuit pattern as follows. Thus, a large number of surface emitting lasers can be simultaneously driven and evaluated.

  An evaluation method of the surface emitting laser 1 will be described with reference to FIG. In the present embodiment, when performing a burn-in test of a large number of surface emitting lasers 1 formed on the device wafer 10, after the individual electrodes 22 in the plurality of surface emitting lasers 1 are short-circuited by one short-circuit pattern 21, A voltage is applied between the short-circuit pattern 21 and the common electrode (n-type electrode 20) in the plurality of surface-emitting lasers 1.

  The short-circuit pattern 21 is electrically connected to, for example, one bus line 21A having a probe pad 21C, and the bus line 21A and each individual electrode 22 of a plurality of (for example, 100 to 1000) surface emitting lasers 1. And a plurality of branch lines 21B. The short-circuit pattern 21 is formed of, for example, a metal such as aluminum (Al), and the branch line 21B includes the defective surface-emitting laser 1 whose element resistance value is almost zero. Assuming the case where the above current flows, it plays the role of a so-called fuse, which is set to such a width that the branch line 21B corresponding to this laser is melted. This branch line prevents excessive current from concentrating on an abnormal laser. Further, an evaluation current injection probe 23 is brought into contact with the probe pad 21C so as to inject a current for evaluating the surface emitting laser 1.

  The surface emitting laser 1 can be manufactured as follows, for example.

First, using an MOCVD (Metal Organic Chemical Vapor Deposition) method or the like on the n-type GaAs substrate 1, the thickness is λ / 4 (λ: wavelength in the medium) and n-type Al. _{X Ga 1-X As (0} <x <1) consisting of comprising layers were, for example, 23-period stacking an n-type DBR layer 11, i-type aluminum gallium arsenide (i-type AlGaAs) n-type cladding layer 12, a gallium arsenide An active layer (light emitting layer) 13 made of / gallium arsenide (GaAs / AlGaAs) and having a quantum well structure, a p-type cladding layer 14 made of i-type aluminum gallium arsenide (i-type AlGaAs), and an AlAs layer the current confinement layer 15, n-type and the same thickness of p-type _{Al 1-X G X as (} 0 <x <1) formed by layers were, for example, 15-period stacking made of p-type DBR16, p-type gallium arsenide Sequentially stacking and p-type contact layer 17 made of p-type GaAs), obtain the device wafer 10.

  Next, lithography is performed on the device wafer 10 to form a cylindrical mesa structure (about 30 μmφ) as shown in FIG. At this time, in order to impart anisotropy by sharpening the side wall of the mesa structure, dry etching using a chlorine-based gas is used in the case of a GaAs material. Further, only the current confinement layer 15 made of AlAs is selectively oxidized from the outer periphery, and the central portion of the current confinement layer 15 is defined as a current confinement portion 15B. Next, a ring-shaped p-type electrode 18 is formed on the upper surface of the contact layer 17 and an n-type electrode 20 is formed on the back surface of the device wafer 10 by, for example, sputtering. At this time, a 100 μm square individual electrode 22 made of gold (Au) is provided so as to be connected to the ring-shaped p-type electrode 18 at the same time. Further, a short-circuit pattern 21 made of a metal such as aluminum (Al) is formed in a gap on the wafer using a sputtering method or the like for a group of about 100 to 1000 surface emitting lasers.

  As described above, a burn-in test for suppressing deterioration of initial characteristics is performed on the device wafer 10 provided with the short-circuit pattern 21. In this burn-in test, for example, while maintaining a constant light output operation state for several hours or more in an environment of about 80 ° C. or more and 200 ° C. or less for one element, the change in drive current value in this state over time is measured. The lifetime of the element is estimated by measurement. As a reference for the lifetime of the element, for example, the time until the drive current value increases by 20% compared to the drive current value at the start of the burn-in test is defined as the lifetime. If the lifetime thus estimated does not meet a certain time, this element is removed.

  After the evaluation is completed, the short-circuit pattern 21 is removed with an alkaline solution, and is individually divided, for example, like the strip-shaped device wafer 10A shown in FIG. 2, and only those that are determined to be non-defective by the result of the burn-in test are selected.

  In general, the element resistance of a surface emitting laser shows a distribution depending on the shape distribution of the current confinement portion, but is a distribution of about ± 20% at most, and the distribution of flowing current values is almost the same distribution. Become. From this, when each element is connected in parallel by the short-circuit pattern 21 as in the present embodiment, substantially the same current flows through each element, and each element can be evaluated equally. Even if there are some faults in this system and those elements are open, that is, no current flows through the faulty elements, the number of elements connected by the short-circuit pattern 21 is as many as 100 to 1,000. The influence of the current change on the element is small, and an evaluation can be performed without any problem with a failure of about 10% of the total number. On the other hand, when an element that is short-circuited due to a failure is included, that is, when there is an element whose element resistance can be regarded as zero, a current flows through the branch line 21B that connects the individual electrode 22 of the element and the bus line 21A. Since the current concentrates, the current does not flow evenly to the other elements, and the reliability of the evaluation is lacking. In the present embodiment, assuming such a case, the line width of the branch line 21B is set to a predetermined value so as to play a role of a so-called fuse that blows when an excess current of a certain value or more flows. It has become. Therefore, even when an excessive current flows, the device returns to the normal state after the branch line 21B is melted, so that the element evaluation can be continued.

  Thus, in this embodiment, since the short-circuit pattern 21 is provided for a plurality of surface emitting lasers, one probe may be brought into contact with one short-circuit pattern 21. Therefore, since it is sufficient to use a probe card having a number of probes corresponding to the number of short-circuit patterns 21, it is not necessary to use an expensive and highly accurate probe card, and the test can be performed at a low cost. It is possible to stabilize the initial characteristics and select good or bad. Further, since the short-circuit pattern 21 is formed of aluminum (Al), it can be completely removed with an alkaline solution when it becomes unnecessary after the evaluation. As a result, the subsequent element isolation step is not affected, and element destruction due to static electricity can be prevented.

  While the present invention has been described with reference to the embodiment, the present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above-described embodiment, the surface emitting laser is used as the semiconductor light emitting element, but it is also possible to use for evaluation of a light emitting diode (LED) other than the surface emitting laser.

  Further, in the above embodiment, the case where one electrode is a common electrode and the other is an individual electrode has been described, but the present invention can also be applied when both electrodes are individual electrodes. What is necessary is just to form a short circuit pattern with respect to each electrode.

  Furthermore, in the above-described embodiment, the short-circuit pattern has been described in which the branch line is only on one side of the bus line. However, the shape is arbitrary. For example, two branch lines are provided on both sides of the bus line. A pattern in which the element groups in the column are short-circuited at the same time may be used, or a pattern in which the bus lines meander.

It is sectional drawing showing the structure of the surface emitting laser which concerns on one embodiment of this invention. It is a figure for demonstrating the evaluation method of a surface emitting laser. It is a figure for demonstrating the separation process after evaluation. It is a figure for demonstrating the evaluation method of the conventional surface emitting laser.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor light emitting element (surface emitting laser), 10 ... Device wafer (substrate), 10A ... Strip-shaped device, 11 ... n-type DBR layer, 12 ... n-type clad layer, 13 ... Active layer (light emitting layer), 14 ... p-type cladding layer, 15 ... current confinement layer, 15A ... insulating region, 15B ... current confinement part, 16 ... p-type DBR layer, 17 ... p-type contact layer, 18 ... p-type electrode (ring electrode), 19 ... light Output window 20 ... n-type electrode (common electrode) 21 ... short circuit pattern, 21A ... bus line, 21B ... branch line, 21C ... probe pad, 22 ... individual electrode, 23 ... probe for evaluation current injection, 100 ... device wafer, 101 ... individual electrodes, 102 ... probe card, 102A ... probe, D ₀ ... light output window inside diameter, D ₁ ... current confinement inner diameter, D ₂ ... columnar mesa structure inside diameter, H ₀ ... output light

Claims (6)

A method for performing individual evaluation of a plurality of semiconductor light-emitting elements in which one electrode is a common electrode and the other electrode is juxtaposed on the same surface of the same substrate as an individual electrode,
A short-circuiting step of short-circuiting individual electrodes of at least two elements of the plurality of semiconductor light-emitting elements by one short-circuit pattern;
A voltage application step of applying a predetermined voltage between the short-circuit pattern and a common electrode of the plurality of semiconductor light-emitting elements ;
Evaluation method of the voltage application processing including semi-conductor light emitting device and removing the stripper the short pattern after. The short pattern that consists one and bus line having a probe pad, by a plurality of branch lines for electrically connecting the individual electrodes of the bus lines and the plurality of semiconductor light emitting devices
Evaluation method of a semiconductor light-emitting device of 請 Motomeko 1 wherein. The branch line, blown by a predetermined value or more of current flows
Evaluation method for a semiconductor light-emitting device 請 Motomeko 2 wherein. The short pattern, that is formed of aluminum (Al)
Evaluation method of a semiconductor light-emitting device of 請 Motomeko 1 wherein. The stripping solution, Ru alkaline solution der
Evaluation method of a semiconductor light-emitting device of 請 Motomeko 1 wherein. The semiconductor light-Ru Oh in the surface emitting laser
Evaluation method of a semiconductor light-emitting device of 請 Motomeko 1 wherein.

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