Defect testing method for laser

Abstract

The invention provides a defect testing method of a laser, which comprises the following steps of: carrying out light emissivity testing of positive current on the laser to obtain a positive test defect position, carrying out light emissivity testing of reverse bias on the laser to obtain a reverse test defect position, and combining and comparing failure analysis data under different scenes to facilitate accurate positioning of defects; besides, when the first light emissivity image and the light-emitting microscopic image are obtained, the applied positive current is far smaller than the threshold current, large-area bright spots and dark areas generated in a near field in the laser emission process are effectively avoided, and therefore defect positioning is more accurate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of laser defect testing, and relates to a laser defect testing method. BACKGROUND

[0002] Vertical Cavity Surface Emitting Laser (VCSEL) is widely used in short-distance data communication field. In the production of VCSEL, defect testing is particularly important. Through defect detection to identify the source of defects, it can guide process improvement and has important significance to ensure product quality and yield.

[0003] At present, there are two important defect positioning methods in VCSEL failure analysis. The first is electroluminescent technology (EL), which can determine whether the defect exists and the active region is intact by applying a small current to the VCSEL and taking an infrared micrograph, and then judging the micrograph. However, this test method can only determine whether the overall light emission is intact, and cannot accurately determine the defect position. The other is InGaAs emission microscope (EMMI), which can determine the defect position by applying a reverse bias to the VCSEL and judging the light emission image of the VCSEL under reverse bias. However, this test method cannot directly reflect the defect condition of the VCSEL under forward current.

[0004] The above two test methods cannot completely and accurately test the defects of VSCEL alone, so a more perfect defect testing scheme is needed. SUMMARY

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a laser defect testing method, which can solve the problem that the single test method in the prior art cannot accurately position the defect point.

[0006] To achieve the above-mentioned purposes and other related purposes, the present application provides a laser defect testing method, comprising the following steps:

[0007] providing a laser to be tested, and placing the laser in a test device;

[0008] obtaining a surface micrograph of the laser in a non-powered state, the surface micrograph serving as a reference image for subsequent data;

[0009] applying a forward current to the laser, obtaining a first light emission rate image of the laser, and obtaining a forward test defect position of the laser based on the first light emission rate image and the reference image;

[0010] A reverse bias voltage is applied to the laser to obtain a second optical emissivity image of the laser. Based on the second optical emissivity image and the reference image, the location of the reverse test defect of the laser is obtained.

[0011] By comparing the forward test defect location and the reverse test defect location, the defect location of the laser can be accurately located.

[0012] Optionally, during the acquisition of the first light emissivity image, a positive current not exceeding one-thousandth of the threshold current is applied to the laser, and the light intensity of the laser is integrated over a first preset time.

[0013] During the acquisition of the second light emissivity image, a reverse bias voltage of -10 to -1V is applied to the laser, and the light intensity of the laser is integrated over a second preset time.

[0014] Optionally, the first preset time is 10 to 100 seconds, and the second preset time is 10 to 100 seconds.

[0015] Optionally, before obtaining the first light emissivity image, the method further includes the following steps:

[0016] A positive current not exceeding one percent of the threshold current is applied to the laser to obtain a emission microscopic image of the laser. Based on the emission microscopic image, the emission morphology of the laser is obtained. The positive current applied when obtaining the emission microscopic image is greater than the positive current applied when obtaining the first light emissivity image.

[0017] Optionally, the method further includes a step of obtaining the surface emissivity of the laser when the laser is not powered on, wherein the surface emissivity obtained when the laser is not powered on is used as background noise; wherein,

[0018] In the process of acquiring the first light emissivity image, the light emissivity obtained by applying a positive current to the laser is reduced by the background noise to obtain the first light emissivity image;

[0019] In the process of acquiring the second light emissivity image, the background noise is subtracted from the light emissivity obtained by applying a reverse bias voltage to the laser to obtain the second light emissivity image.

[0020] Optionally, the laser is a vertical cavity surface-emitting laser.

[0021] Optionally, the laser is a bare chip, and power is applied to the laser by piercing it with a probe station.

[0022] Optionally, the laser is a packaged structure, and the laser is clamped and powered by a test fixture, or the laser is powered by a probe station.

[0023] As described above, in the laser defect testing method of the present invention, the laser is subjected to a positive current light emissivity test to obtain the forward test defect location, and the laser is subjected to a reverse bias light emissivity test to obtain the reverse test defect location. By combining and comparing failure analysis data under different scenarios, it helps to accurately locate the defect. In addition, when acquiring the first light emissivity image and the emission microscopic image, the applied positive current is much smaller than the threshold current, which effectively avoids large bright spots and dark areas generated in the near field during laser emission, thereby making the defect location more accurate. Attached Figure Description

[0024] Figure 1 The diagram shown is a flowchart of a defect testing method for a laser in an embodiment of the present invention.

[0025] Figure 2 The image shown is a schematic diagram of a surface micrograph in an embodiment of the present invention.

[0026] Figure 3 The image shown is a schematic diagram of a light-emitting micrograph in an embodiment of the present invention.

[0027] Figure 4 The diagram shown is a schematic representation of a light-emitting microscopic image superimposed onto a surface microscopic image in an embodiment of the present invention.

[0028] Figure 5 This is a schematic diagram showing the overlay of a first light emissivity image onto a surface micrograph in an embodiment of the present invention.

[0029] Figure 6 The image shown is a schematic diagram of the second light emissivity image in an embodiment of the present invention.

[0030] Figure 7 This is a schematic diagram showing the second light emissivity image overlay onto a surface micrograph in an embodiment of the present invention. Detailed Implementation

[0031] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0032] Please see Figures 1 to 7It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0033] This embodiment provides a method for testing defects in a laser. Please refer to [link / reference]. Figure 1 The flowchart shown is a defect testing method for a laser in an embodiment of the present invention, including the following steps:

[0034] S1: Provide the laser to be tested and place the laser in the test apparatus;

[0035] S2: In the unpowered state, acquire a surface microscopic image of the laser, which serves as a reference image for subsequent data.

[0036] S3: Apply a positive current to the laser, acquire a first light emissivity image of the laser, and obtain the location of the positive test defect of the laser based on the first light emissivity image and the reference image;

[0037] S4: Apply a reverse bias voltage to the laser, acquire a second optical emissivity image of the laser, and obtain the reverse test defect location of the laser based on the second optical emissivity image and the reference image;

[0038] S5: Compare the forward test defect location and the reverse test defect location to accurately locate the defect location of the laser.

[0039] The defect testing method for the laser in this embodiment will be described in detail below with reference to the specific accompanying drawings.

[0040] First, perform step S1: provide the laser to be tested and place the laser in the test apparatus.

[0041] As an example, in this embodiment, the laser to be tested is a vertical cavity surface-emitting laser.

[0042] As an example, the testing device is a microscope that can apply extremely small currents, has a spectral response range that includes the emission wavelength of the laser (VCSEL emission wavelength is generally between 850nm and 1550nm), and can detect extremely weak light intensity.

[0043] As an example, the laser is placed in the chuck of the test apparatus. If the laser is a bare chip, the laser is powered by the probe of the test apparatus through a DC probe station. If the laser is a packaged structure, the laser is powered by clamping it with a test fixture, or by the probe of the laser through the probe station, depending on the requirements.

[0044] Next, step S2 is performed: in the unpowered state, a surface microscopic image of the laser is acquired, and the surface microscopic image is used as a reference image for subsequent data.

[0045] As an example, the surface of the laser is scanned through a lens in a power-off state to obtain a microscopic image of the surface. The overlay function is selected to place the microscopic image at the bottom. In subsequent tests, the microscopic image will be below the test data image, serving as the background image for the subsequent test data images. Specifically, in this embodiment, the microscopic image is an infrared microscopic image.

[0046] For example, please refer to Figure 2 The image shown is a schematic diagram of a surface micrograph in an embodiment of the present invention. In actual device fabrication, the surface micrograph obtained after lens scanning will vary depending on the design shape of the laser, and is not limited to this embodiment.

[0047] Next, step S3 is executed: a positive current is applied to the laser to obtain a first light emissivity image of the laser, and the location of the positive test defect of the laser is obtained based on the first light emissivity image and the reference image.

[0048] As an example, before acquiring the first light emissivity image, the method further includes applying a positive current to the laser to acquire a light emission microscopic image of the laser. Based on the light emission microscopic image, the light emission appearance of the laser is obtained. In this embodiment, the light emission microscopic image is an infrared microscopic image. The light emission microscopic image can visually display the laser's emission status, determine whether the laser's emission is uniform, and identify any defects. When it is determined that the laser has a positive light emission defect, subsequent acquisition of the first and second light emissivity images is performed. When it is determined that the laser does not have a positive light emission defect, subsequent acquisition of the first and second light emissivity images is not performed. In some examples, for high-precision testing requirements, even when it is determined that the laser does not have a positive light emission defect, subsequent acquisition of the first and / or second light emissivity images can still be performed to analyze and confirm whether there are any minute potential defects.

[0049] As an example, this invention mainly focuses on the location analysis of laser failure points, such as... Figure 3The image shown is a schematic diagram of a light-emitting micrograph in an embodiment of the present invention. Figure 3 It can be seen that in the active region at the very center, there is a relatively dark "I"-shaped region, and the openings on the left and right sides of the "I"-shaped region are relatively bright regions. From this, we can obtain the existence of light-emitting defects and their approximate locations (the darker "I"-shaped region).

[0050] As an example, during the acquisition of the luminescent microscopic image, the positive current applied to the laser does not exceed one percent of the threshold current, that is, the luminescent microscopic image is acquired under a relatively small positive current.

[0051] Specifically, in this embodiment, the threshold current of the laser is 0.6mA-0.9mA, and the positive current applied to the laser during the acquisition of the luminescent microscopic image is 0.1μA, which is on the order of one ten-thousandth of the threshold current.

[0052] As an example, the luminescence micrograph is acquired in a dark chamber. Since the positive current applied when acquiring the luminescence micrograph is very small, the emitted light is weak. Acquiring the luminescence micrograph under dark conditions avoids the adverse effects of external light on the test.

[0053] For example, please refer to Figure 4 The diagram shows a stacked image of a light-emitting micrograph overlaid on a surface micrograph in an embodiment of the present invention. By adjusting the contrast of the light-emitting micrograph, the underlying surface micrograph (background image) is revealed, thus visually displaying the light emission of the laser at different locations.

[0054] For example, please refer to Figure 5 The image shown is a schematic diagram of a first light emissivity image superimposed onto a surface micrograph in an embodiment of the present invention. By adjusting the contrast of the first light emissivity image, the surface micrograph, which serves as a background image, is revealed, thus visually showing the location of the forward test defect in the laser.

[0055] As an example, in this embodiment, during the acquisition of the first light emissivity image, the positive current applied to the laser does not exceed one-thousandth of the threshold current. That is, the first light emissivity image is acquired under an extremely small positive current, effectively avoiding large bright spots and dark areas generated in the near field during laser emission. Specifically, the positive current applied when acquiring the first light emissivity image is less than the positive current applied when acquiring the light emission microscopic image. In this embodiment, the positive current applied to the laser during the acquisition of the first light emissivity image is 1 nA, which is on the order of one hundred-thousandth of the threshold current.

[0056] As an example, this embodiment only schematically illustrates that the positive current applied when acquiring the first light emissivity image is 1nA, and is not limited to this embodiment. In some examples, if overexposure occurs when acquiring the first light emissivity image, the positive current applied to the laser can be appropriately reduced. Overexposure refers to the laser emitting light intensity being too strong, and some areas in the image have reached the maximum value that the image display can achieve, resulting in a loss of detail. In severe cases, "highlight overflow" will occur, causing dark areas to be blocked. If the light intensity is too low, it is difficult to detect and distinguish, and the positive current applied to the laser can be appropriately increased.

[0057] As an example, the steps for obtaining the first light emissivity image include:

[0058] (i) Obtaining the surface light emissivity of the laser when the laser is not powered on, wherein the surface light emissivity obtained when the laser is not powered on is used as background noise;

[0059] (ii) Apply a positive current of 1nA to the laser, subtract the background noise from the obtained light emissivity, and obtain the first light emissivity image.

[0060] Specifically, subtracting background noise when acquiring the first light emissivity image can prevent the first light emissivity image from being affected by background noise, thereby improving the accuracy of defect testing.

[0061] As an example, during the acquisition of the first light emissivity image, since the applied positive current is extremely small and the light emission is weak, a lens with a long integration time is used in conjunction with a photomultiplier tube to integrate the light field and calculate the average value, so that the obtained first light emissivity image is more stable and reliable.

[0062] As an example, during the process of acquiring the first light emissivity image, the time for integrating the light field is 10 to 100 seconds, for example, it can be 10 seconds, 20 seconds, 30 seconds, 40 seconds, 50 seconds, 60 seconds, 70 seconds, 80 seconds, 90 seconds, 100 seconds, etc., and can be selected according to the requirements.

[0063] Next, step S4 is executed: a reverse bias voltage is applied to the laser to obtain a second light emissivity image of the laser, and the location of the reverse test defect of the laser is obtained based on the second light emissivity image and the reference image.

[0064] As an example, during the acquisition of the second light emissivity image, the reverse bias voltage applied to the laser is -10V to -1V, for example, it can be -10V, -9V, -8V, -7V, -6V, -5V, -4V, -3V, -2V, -1V, etc., and can be selected according to the requirements.

[0065] Similarly, when obtaining the second light emissivity image, if overexposure occurs, the reverse bias voltage applied to the laser can be appropriately reduced; if the light intensity is too low and difficult to detect and distinguish, the reverse bias voltage applied to the laser can be appropriately increased.

[0066] As an example, the step of obtaining the second light emissivity image includes: applying a reverse bias voltage to the laser, subtracting the background noise from the obtained light emissivity, and obtaining the second light emissivity image.

[0067] Specifically, subtracting background noise when acquiring the second light emissivity image can prevent the second light emissivity image from being affected by background noise, thereby improving the accuracy of defect testing.

[0068] As an example, in the process of acquiring the second light emissivity image, since the light emission at the emission point is extremely weak, a lens with a long integration time is used in conjunction with a photomultiplier tube to integrate the light field and calculate the average value, so that the obtained second light emissivity image is more stable and reliable.

[0069] As an example, during the process of acquiring the second light emissivity image, the duration of integrating the light field is 10 to 100 seconds, for example, it can be 10 seconds, 20 seconds, 30 seconds, 40 seconds, 50 seconds, 60 seconds, 70 seconds, 80 seconds, 90 seconds, 100 seconds, etc., and can be selected according to the requirements.

[0070] For example, please refer to Figure 6 The image shown is a schematic diagram of the second light emissivity image in an embodiment of the present invention. Please refer to [link / reference]. Figure 7 The contrast of the second light emissivity image is adjusted to reveal the surface micrograph as a background image, so as to visually show the location of the reverse test defect in the laser.

[0071] As an example, in this embodiment, the first light emissivity image is acquired first, and then the second light emissivity image is acquired. In another example, the second light emissivity image can be acquired first, and then the first light emissivity image can be acquired. That is, the positions of steps S3 and S4 can be adjusted during the test and selected according to the requirements.

[0072] Next, step S5 is performed: the forward test defect position and the reverse test defect position are compared to accurately locate the defect position of the laser.

[0073] As an example, such as Figure 5As shown, during the forward test, in the central active region, the left and right regions have higher luminescence (red), the area between the left and right regions has relatively lower luminescence (orange), and the upper and lower regions have the lowest luminescence (green and blue). This indicates that defects exist in the upper and lower regions and the central region, with defects in the upper and lower regions having a more severe impact. Figure 7 As shown, during reverse testing, the central active region has a linear light-emitting area. The upper and lower regions of the light-emitting area have relatively high luminous efficiency, while the central region has relatively low luminous efficiency, indicating defects in both the upper and lower regions and the central region, with the upper and lower regions exhibiting more severe defects. In this embodiment, the defect locations in both forward and reverse testing are essentially generated by the same laser defect point. The forward test defect location can show the approximate area where the laser defect point is located, while the reverse test defect point can accurately pinpoint the location of the laser defect point. Figure 5 and Figure 7 This is to accurately display the location of the laser defect.

[0074] As an example, after accurately detecting the defect location, the defect location of the laser can be sliced ​​to analyze the specific defect type at the defect location.

[0075] In summary, the laser defect testing method of this invention involves performing a positive current photoemissivity test on the laser to obtain the location of the defect in the forward direction, and performing a reverse bias photoemissivity test on the laser to obtain the location of the defect in the reverse direction. By combining and comparing failure analysis data under different scenarios, it helps to accurately locate the defect. Furthermore, when acquiring the first photoemissivity image and the emission microscopic image, the applied positive current is much smaller than the threshold current, effectively avoiding large bright spots and dark areas generated in the near field during laser emission, thus making the defect location more accurate. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0076] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for testing defects in a laser, characterized in that, Includes the following steps: Provide a laser to be tested and place the laser in the test apparatus; In the unpowered state, a surface microscopic image of the laser is acquired, and the surface microscopic image is used as a reference image for subsequent data. A positive current is applied to the laser, and a first optical emissivity image of the laser is obtained. Based on the first optical emissivity image and the reference image, the location of the positive test defect of the laser is obtained. A reverse bias voltage is applied to the laser to obtain a second optical emissivity image of the laser. Based on the second optical emissivity image and the reference image, the location of the reverse test defect of the laser is obtained. By comparing the forward test defect location and the reverse test defect location, the defect location of the laser can be accurately located.

2. The defect testing method for lasers according to claim 1, characterized in that: During the acquisition of the first light emissivity image, a positive current not exceeding one-thousandth of the threshold current is applied to the laser, and the light intensity of the laser is integrated over a first preset time. During the acquisition of the second light emissivity image, a reverse bias voltage of -10 to -1V is applied to the laser, and the light intensity of the laser is integrated over a second preset time.

3. The defect testing method for lasers according to claim 2, characterized in that: The first preset time is 10 to 100 seconds, and the second preset time is 10 to 100 seconds.

4. The defect testing method for a laser according to claim 2, characterized in that, Before obtaining the first light emissivity image, the following steps are also included: A positive current not exceeding one percent of the threshold current is applied to the laser to obtain a emission microscopic image of the laser. Based on the emission microscopic image, the emission morphology of the laser is obtained. The positive current applied when obtaining the emission microscopic image is greater than the positive current applied when obtaining the first light emissivity image.

5. The defect testing method for a laser according to claim 1, characterized in that: The method also includes a step of obtaining the surface light emissivity of the laser when the laser is not powered on, wherein the surface light emissivity obtained in the state of laser de-powered is used as background noise; wherein... In the process of acquiring the first light emissivity image, the light emissivity obtained by applying a positive current to the laser is reduced by the background noise to obtain the first light emissivity image; In the process of acquiring the second light emissivity image, the background noise is subtracted from the light emissivity obtained by applying a reverse bias voltage to the laser to obtain the second light emissivity image.

6. The defect testing method for a laser according to claim 1, characterized in that: The laser is a vertical cavity surface-emitting laser.

7. The defect testing method for a laser according to claim 1, characterized in that: The laser is a bare chip, and power is applied to the laser by piercing it with a probe station.

8. The defect testing method for a laser according to claim 1, characterized in that: The laser is a packaged structure. The laser is clamped and powered by a test fixture, or the laser is powered by a probe station.

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