Inspection method of laser diode with modulator and contact method of inspection probe

Abstract

To provide an inspection method of a laser diode with a modulator capable of preventing contact failure of a probe, and a contact method of an inspection probe.SOLUTION: Electric charges are accumulated in a modulator electrode 5 of an electric field absorption modulator 2 of a laser diode 100 with a modulator. The position of a modulator electrode 5 is recognized by moving a charge investigation probe 19 along the surface of an electric field absorption modulator 2 in which charges are accumulated in the modulator electrode 5 and investigating the charge distribution on the surface of the electric field absorption modulator 2. An inspection probe 22 is brought into contact with the modulator electrode 5 whose position is recognized to inspect the electric characteristics of the electric field absorption modulator 2.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present disclosure relates to a method for testing a laser diode with a modulator and a method for contacting a test probe. [Background technology]

[0002] Modulator-equipped laser diodes in which dynamic chirp is reduced by serially integrating a laser diode and an electroabsorption optical modulator are widely used (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-246343 Summary of the Invention [Problem to be solved by the invention]

[0004] When inspecting the electroabsorption optical modulator of a modulator-equipped laser diode, a needle-shaped probe is applied to the modulator electrode of the electroabsorption optical modulator. However, to ensure high-frequency response characteristics, the modulator electrode is made small. This makes it difficult to apply the probe to the modulator electrode. It is also difficult to recognize the presence or absence of contact from an image, and variations in probe positioning lead to contact failures.

[0005] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to provide an inspection method for a laser diode with a modulator and an inspection probe contact method that can prevent probe contact failure. [Means for solving the problem]

[0006] The method for inspecting a laser diode with a modulator according to the present disclosure is characterized by comprising the steps of: storing charges in the modulator electrodes of the electroabsorption modulator of the laser diode with a modulator; identifying the position of the modulator electrodes by moving a charge inspection probe along the surface of the electroabsorption modulator in which the charges have been stored in the modulator electrodes to examine the charge distribution on the surface of the electroabsorption modulator; and inspecting the electrical characteristics of the electroabsorption modulator by contacting an inspection probe with the modulator electrodes whose positions have been identified. [Effects of the Invention]

[0007] In this disclosure, charges are accumulated in the modulator electrodes of the electroabsorption modulator, and the position of the modulator electrodes is recognized by examining the charge distribution on the surface of the electroabsorption modulator. This allows the position of the probe to be controlled with high precision to ensure reliable contact with the modulator electrodes. As a result, poor probe contact can be prevented. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing a laser diode with a modulator. [Figure 2] FIG. 1 is a cross-sectional view of a laser diode with a modulator taken along the resonator direction. [Figure 3] FIG. 1 is a cross-sectional view showing a laser diode. [Figure 4] FIG. 1 is a cross-sectional view showing an electroabsorption modulator. [Figure 5] FIG. 1 is a top view showing a laser diode with a modulator. [Figure 6] 1A to 1C are diagrams illustrating a method for inspecting a laser diode with a modulator according to an embodiment. [Figure 7] 1A to 1C are diagrams illustrating a method for inspecting a laser diode with a modulator according to an embodiment. [Figure 8] 1A to 1C are diagrams illustrating a method for inspecting a laser diode with a modulator according to an embodiment. [Figure 9] 1A to 1C are diagrams illustrating a method for inspecting a laser diode with a modulator according to an embodiment. [Figure 10] 1A to 1C are diagrams illustrating a method for inspecting a laser diode with a modulator according to an embodiment. [Figure 11] 10 is a flowchart of a method for inspecting a laser diode with a modulator according to an embodiment. [Figure 12] 10A and 10B are diagrams illustrating the movement of an inspection probe when pressed against a bonding pad. [Figure 13] 10A and 10B are diagrams illustrating the movement of an inspection probe when pressed against a bonding pad. DETAILED DESCRIPTION OF THE INVENTION

[0009] First, the configuration of a modulator-equipped laser diode to be inspected by the inspection method according to this embodiment will be described. FIG. 1 is a perspective view showing a modulator-equipped laser diode. In a modulator-equipped laser diode 100, a laser diode 1 and an electroabsorption modulator 2 are integrated on a single chip and connected in series. The laser diode 1 and the electroabsorption modulator 2 each have a mesa structure formed by a groove 3. A laser electrode 4 is formed on the top surface of the laser diode 1. A modulator electrode 5 is formed on the top surface of the electroabsorption modulator 2. The laser diode 1 generates laser light 6. The electroabsorption modulator 2 modulates the laser light 6. The modulated laser light 6 is emitted from the front end face of the chip into an optical fiber or the like.

[0010] Figure 2 is a cross-sectional view of a modulator-equipped laser diode along the cavity direction. A laser diode 1 and an electroabsorption modulator 2 are formed on a semiconductor substrate 7. The laser diode 1 has an n-type cladding layer 8, an active layer 9, a p-type cladding layer 10, and a p-type contact layer 11, which are formed in this order on the semiconductor substrate 7. A laser electrode 4 is formed on the p-type contact layer 11. The electroabsorption modulator 2 has an n-type cladding layer 8, a light absorption layer 12, a p-type cladding layer 10, and a p-type contact layer 11, which are formed in this order on the semiconductor substrate 7. A modulator electrode 5 is formed on the p-type contact layer 11. A bottom electrode 13 is formed on the entire bottom surface of the semiconductor substrate 7. The active layer 9 and the light absorption layer 12 are butt-jointed.

[0011] The semiconductor substrate 7 is made of, for example, n-type InP. The active layer 9 is made of, for example, undoped InGaAsP. The light absorption layer 12 is made of, for example, undoped InGaAsP. The n-type cladding layer 8 and the p-type cladding layer 10 are made of InP. The p-type contact layer 11 is made of, for example, InGaAs, InGaAsP, etc.

[0012] 3 is a cross-sectional view of a laser diode. The laser diode 1 has a buried structure in which the sides of a ridge structure including an active layer 9 are buried with a current blocking layer 14. The current blocking layer 14 is made of a semi-insulating semiconductor such as Fe-InP. This buried structure is formed into a mesa structure by a groove 3. The sides of the mesa structure are covered with an insulating film 15. The insulating film 15 is made of, for example, SiN, SiO, or the like.

[0013] FIG. 4 is a cross-sectional view of an electroabsorption modulator. FIG. 5 is a top view of a modulator-equipped laser diode. The electroabsorption modulator 2 has a high mesa structure including an optical absorption layer 12. The sides of the high mesa structure are covered with an insulating film 15. The modulator electrode 5 includes a top electrode 5a formed on the mesa structure of the electroabsorption modulator 2, a bonding pad 5b for bonding a wire, and a wiring 5c ​​connecting the top electrode 5a and the bonding pad 5b. The bonding pad 5b is formed on the top surface of one of the terraces outside the high mesa structure. The bonding pad 5b is circular in plan view, and its diameter is 50 μm or less. Note that the widths of the top electrode 5a and the wiring 5c ​​are smaller than the diameter of the bonding pad 5b, so the test probe described below contacts the bonding pad 5b rather than the top electrode 5a and the wiring 5c.

[0014] 6 to 10 are diagrams illustrating a method for inspecting a modulator-equipped laser diode according to an embodiment. FIG. 11 is a flowchart illustrating the method for inspecting a modulator-equipped laser diode according to an embodiment. The inspection apparatus 200 includes a stage 16 on which an object to be inspected is placed and fixed, a moving device 17 that moves a probe up, down, left, and right relative to the stage 16, and a control unit 18 that controls the moving device 17 and performs the inspection. The moving device 17 allows the control unit 18 to acquire the position of the probe tip. Examples of such a moving device 17 include a motor with a built-in encoder, such as a servo motor, that can detect the rotation angle, or a motor, such as a stepping motor, that can adjust the rotation angle according to commands from the control unit 18. The control unit 18 is realized by a processing circuit, such as a CPU or system LSI, that executes a program stored in memory. Alternatively, multiple processing circuits may cooperate to perform the above functions. As shown in FIGS. 8 and 10, a charge inspection probe 19 or an inspection probe 22 is attached to the moving device 17 as the probe to be moved. The control unit 18 has an amplifier 20 and a voltmeter 21 electrically connected in series with the charge investigation probe 19 , and an inspection unit electrically connected with the inspection probe 22 .

[0015] First, as shown in FIG. 6, the laser diode 100 with a modulator is placed on the stage 16 and fixed by vacuum suction or the like. The control unit 18 applies a bias to the laser electrode 4 and the bottom electrode 13 to cause the laser diode 1 to emit light (step S1). After step S1, the laser light 6 emitted from the laser diode 1 is absorbed by the electroabsorption modulator 2, generating electric charge, which is then accumulated in the modulator electrode 5 (step S2). At this time, the bottom electrode 13 is grounded, and the modulator electrode 5 is not in contact with any part of the inspection device 200, such as a probe, and is therefore floating. As shown in FIG. 7, when the laser light 6 passes through the light absorption layer 12 of the electroabsorption modulator 2, carriers in the valence band of the semiconductor are excited into a conductor, causing polarization. This generates a potential difference, and a negative charge accumulates in the modulator electrode 5.

[0016] After step S2, as shown in FIG. 8, the charge investigation probe 19 is moved by the moving device 17 to bring the charge investigation probe 19 close to the surface of the modulator electrode 5 so that the distance between the tip of the charge investigation probe 19 and the surface is several micrometers (step S3). In other words, after being moved in step S3, the surface of the modulator electrode 5 and the tip of the charge investigation probe 19 are not in contact with each other. After step S3, the charge investigation probe 19 is moved along the surface of the electroabsorption modulator 2 by the moving device 17 to examine the charge distribution on the surface of the electroabsorption modulator 2 (step S4). In step S4, the distance between the surface of the modulator electrode 5 and the tip of the charge investigation probe 19 is maintained at several micrometers, as set in step S3. In other words, in step 4, the charge investigation probe 19 moves along the surface of the electroabsorption modulator 2 while the surface of the modulator electrode 5 and the tip of the charge investigation probe 19 are not in contact with each other. Here, when the charge investigation probe 19 is brought close to the negatively charged modulator electrode 5, the charge investigation probe 19 becomes positively charged, which is the opposite polarity to that of the modulator electrode 5. The positive charge stored on the charge investigation probe 19 is amplified by the amplifier 20, and the voltage is detected by the voltmeter 21. Therefore, when the modulator electrode 5 is located directly below the charge investigation probe 19, a higher voltage value is detected by the voltmeter 21 compared to when the modulator electrode 5 is not located directly below the charge investigation probe 19. Therefore, it is possible to determine whether the modulator electrode 5 is located directly below the charge investigation probe 19 based on the voltage detected by the voltmeter 21. The control unit 18 acquires the movement position of the charge investigation probe 19 and the voltage detected by the voltmeter 21, and stores the movement position of the charge investigation probe 19 and the voltage detected by the voltmeter 21 in association with each other. In the inspection method according to this embodiment, the charge investigation probe 19 is moved in a zigzag pattern along the surface of the electroabsorption modulator 2, as shown in FIG. 9, to investigate the charge distribution on the surface of the electroabsorption modulator 2. Thereafter, the operation of the laser diode 1 is turned off.

[0017] The control unit 18 creates a two-dimensional mapping showing the positions of the bonding pads 5b on the surface of the electroabsorption modulator 2 based on the movement positions of the charge investigation probe 19 and the voltage detected by the voltmeter 21, which are stored in association with each other. This two-dimensional mapping shows that there is an area with a higher voltage value than the surrounding area, and that the bonding pads 5b of the modulator electrodes 5 are located in this area. In this way, the positions of the bonding pads of the modulator electrodes 5 can be recognized by the two-dimensional mapping.

[0018] After step S4, the control unit 18 determines, based on the two-dimensional mapping, the position at which the test probe 22 is pressed down so that the tip of the test probe 22 comes into contact with the vicinity of the center of the bonding pad 5b (step S5).

[0019] 10, while the modulator-equipped laser diode 100 is fixed on the stage 16, the control unit 18 moves the inspection probe 22 by the moving device 17 to the position of the bonding pad 5b and presses it down to contact the bonding pad 5b (step S6). The control unit 18 then passes a current between the modulator electrode 5 and the lower electrode 13 via the contacted inspection probe 22 to inspect the electrical characteristics of the electroabsorption modulator 2 (step S7). The electrical characteristics inspected here include, for example, measurement of leakage current of the electroabsorption modulator 2 when the operation of the laser diode 100 is in the off state.

[0020] 12 and 13 are diagrams showing the movement of the test probe when pressed against a bonding pad. The modulator-equipped laser diode 100 is manufactured by cutting the laser diode 100 from a wafer along a cut surface perpendicular to the thickness direction of the modulator-equipped laser diode 100. Therefore, there is variation in the chip thickness of the cut modulator-equipped laser diode 100. When the test probe 22 is pressed against the bonding pad 5b, the test probe 22 bends to absorb the variation in chip thickness. At this time, the tip of the pressed test probe 22 slides on the surface of the bonding pad 5b. As shown in FIG. 12, if the tip of the sliding test probe 22 protrudes from the bonding pad 5b, a contact failure occurs.

[0021] In this embodiment, the position of the bonding pad 5b of the modulator electrode 5 is recognized by examining the charge distribution on the surface of the electroabsorption modulator 2. This allows the position of the inspection probe 22 to be controlled with high precision relative to the bonding pad 5b, ensuring reliable contact. As a result, contact failure of the inspection probe 22 can be prevented.

[0022] For example, if the tip of the test probe 22 is bent to the left, pressing the test probe 22 against the bonding pad 5b will cause the tip of the test probe 22 to slide to the left. Therefore, as shown in Figure 13, the position at which the test probe 22 is pressed is offset to the right from the center of the bonding pad 5b by the average value of the sliding distance. This prevents the tip of the pressed test probe 22 from protruding from the bonding pad 5b.

[0023] Furthermore, a two-dimensional mapping is created from the charge distribution to indicate the positions of the bonding pads 5b on the surface of the electroabsorption modulator 2, and the position to press down the inspection probe 22 is determined based on this two-dimensional mapping. In this way, by feeding back the map data to the probe position control, high-precision positioning with small error is possible.

[0024] An inspection probe 22 may be used as the charge investigation probe 19. In this case, it is possible to switch between a state in which the inspection probe 22 is electrically connected in series to the amplifier 20 and voltmeter 21 and a state in which the inspection probe 22 is electrically connected to the inspection unit. This eliminates the need to switch probes between scanning to examine the charge distribution on the surface of the electroabsorption modulator 2 and inspecting the electrical characteristics of the electroabsorption modulator 2. This simplifies the inspection process.

[0025] Alternatively, an electron beam may be irradiated onto the modulator electrode 5 to accumulate charge in the modulator electrode 5. However, this requires the provision of an electron irradiation device and the irradiation of the electron beam in a vacuum state. On the other hand, by having the electroabsorption modulator 2 absorb the laser light 6 emitted from the laser diode 1 and accumulate charge in the modulator electrode 5 as in this embodiment, a large-scale electron beam irradiation device and vacuuming are not required, thereby reducing costs.

[0026] Furthermore, in step S3, the movement of the charge investigation probe 19 is not limited to a zigzag movement, as long as it is possible to investigate the charge distribution on the surface of the electroabsorption modulator 2. For example, the charge investigation probe 19 may be moved in a spiral pattern from the outer periphery of the electroabsorption modulator 2 toward the center along the surface of the electroabsorption modulator 2.

[0027] Alternatively, in step S2, the tip of the charge investigation probe 19 may be brought into contact with the surface of the modulator electrode 5, and in step S3, the charge investigation probe 19 may be moved along the surface of the electroabsorption modulator 2 while the tip of the charge investigation probe 19 is in contact with the surface of the modulator electrode 5. However, by moving the charge investigation probe 19 along the surface of the electroabsorption modulator 2 while the tip of the charge investigation probe 19 is not in contact with the surface of the modulator electrode 5, as in this embodiment, it is possible to prevent the charge investigation probe 19 from scratching the surface of the electroabsorption modulator 2.

[0028] Although the preferred embodiments have been described above in detail, the present disclosure is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims. Various aspects of the present disclosure are collectively described below as appendices. (Appendix 1) storing charges on a modulator electrode of an electroabsorption modulator of the modulated laser diode; a step of identifying the position of the modulator electrode by moving a charge investigation probe along the surface of the electroabsorption modulator where the charge has accumulated on the modulator electrode and examining the charge distribution on the surface of the electroabsorption modulator; and a step of contacting an inspection probe with the modulator electrode whose position has been recognized to inspect the electrical characteristics of the electroabsorption modulator. (Appendix 2) the laser diode with the modulator is placed and fixed on a stage, and the charge investigation probe is moved along the surface of the electroabsorption modulator by a moving device to investigate the charge distribution; A method for inspecting a laser diode with a modulator as described in Appendix 1, characterized in that while the laser diode with a modulator is fixed on the stage, the inspection probe is moved to the position of the modulator electrode by the moving device and pressed down to contact the modulator electrode. (Appendix 3) generating a two-dimensional mapping from the charge distribution that indicates the position of the modulator electrode on the surface of the electroabsorption modulator; 3. The method for inspecting a laser diode with a modulator according to claim 2, wherein the position at which the inspection probe is pressed down is determined based on the two-dimensional mapping. (Appendix 4) 4. The method for inspecting a laser diode with a modulator according to any one of claims 1 to 3, wherein the inspection probe is used as the charge investigation probe. (Appendix 5) A method for inspecting a laser diode with a modulator according to any one of appendices 1 to 4, characterized in that the laser diode of the laser diode with a modulator is caused to emit light, and the laser light emitted from the laser diode is absorbed by the electroabsorption modulator to generate the electric charge, and the electric charge is accumulated in the modulator electrode. (Appendix 6) the modulator electrode has an upper surface electrode formed on a mesa structure of the electroabsorption modulator, a bonding pad, and a wiring connecting the upper surface electrode and the bonding pad; A method for inspecting a laser diode with a modulator according to any one of claims 1 to 5, characterized in that the position of the bonding pad is recognized from the charge distribution, and the inspection probe is brought into contact with the bonding pad to inspect the electrical characteristics of the electroabsorption modulator. (Appendix 7) 7. The method for inspecting a laser diode with a modulator according to claim 6, wherein the diameter of the bonding pad is 50 μm or less. (Appendix 8) 8. A method for inspecting a laser diode with a modulator according to claim 1, wherein when the charge distribution is examined, the charge examination probe moves without contacting the surface of the electroabsorption modulator. (Appendix 9) storing electric charges on electrodes on the surface of the chip; a step of scanning the surface of the chip with the charges accumulated on the electrodes in a non-contact manner with a charge investigation probe to examine the charge distribution on the surface of the chip and thereby recognize the positions of the electrodes; and contacting the electrode whose position has been recognized with the inspection probe. (Appendix 10) The chip is placed and fixed on a stage, and the charge investigation probe is moved by a moving device to scan the surface of the chip in a non-contact manner to investigate the charge distribution; The inspection probe contact method described in Appendix 9, characterized in that while the chip is fixed on the stage, the inspection probe is moved to the position of the electrode by the moving device and pressed down to contact the electrode. [Explanation of symbols]

[0029] 1 laser diode, 2 electroabsorption modulator, 5 modulator electrode, 5a upper electrode, 5b bonding pad, 5c wiring, 6 laser light, 17 moving device, 19 charge inspection probe, 22 inspection probe, 100 laser diode with modulator

Claims

1. storing charges on a modulator electrode of an electroabsorption modulator of the modulated laser diode; a step of identifying the position of the modulator electrodes by moving a charge investigation probe along the surface of the electroabsorption modulator with the charges stored on the modulator electrodes to investigate the charge distribution on the surface of the electroabsorption modulator; and a step of contacting an inspection probe with the modulator electrode whose position has been recognized to inspect the electrical characteristics of the electroabsorption modulator.

2. the laser diode with the modulator is placed and fixed on a stage, and the charge investigation probe is moved along the surface of the electroabsorption modulator by a moving device to investigate the charge distribution; 2. A method for inspecting a laser diode with a modulator according to claim 1, wherein the laser diode with a modulator is fixed on the stage, and the inspection probe is moved to the position of the modulator electrode by the moving device and pressed down to contact the modulator electrode.

3. generating a two-dimensional mapping from the charge distribution that indicates the position of the modulator electrode on the surface of the electroabsorption modulator; 3. The method for testing a laser diode with a modulator according to claim 2, wherein the position at which the test probe is pressed down is determined based on the two-dimensional mapping.

4. 4. The method for inspecting a laser diode with a modulator according to claim 1, wherein the inspection probe is used as the charge investigation probe.

5. A method for inspecting a laser diode with a modulator according to any one of claims 1 to 3, characterized in that the laser diode of the laser diode with a modulator is caused to emit light, and the laser light emitted from the laser diode is absorbed by the electroabsorption modulator to generate the electric charge, and the electric charge is accumulated in the modulator electrode.

6. the modulator electrode has an upper surface electrode formed on a mesa structure of the electroabsorption modulator, a bonding pad, and a wiring connecting the upper surface electrode and the bonding pad; A method for inspecting a laser diode with a modulator according to any one of claims 1 to 3, characterized in that the position of the bonding pad is recognized from the charge distribution, and the inspection probe is brought into contact with the bonding pad to inspect the electrical characteristics of the electroabsorption modulator.

7. 7. The method for testing a laser diode with a modulator according to claim 6, wherein the diameter of said bonding pad is 50 [mu]m or less.

8. A method for inspecting a laser diode with a modulator as described in any one of claims 1 to 3, characterized in that when examining the charge distribution, the charge investigation probe moves without contacting the surface of the electroabsorption modulator.

9. storing electric charges on electrodes on the surface of the chip; a step of identifying the position of the electrode by moving a charge investigation probe along the surface of the chip on which the charge has been accumulated and examining the charge distribution on the surface of the chip; and contacting the electrode whose position has been recognized with the inspection probe.

10. The chip is placed and fixed on a stage, and the charge investigation probe is moved by a moving device to examine the charge distribution on the surface of the chip; 10. The method for contacting an inspection probe according to claim 9, wherein the chip is fixed on the stage, and the inspection probe is moved to the position of the electrode by the moving device and pressed down to contact the electrode.

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