Method and device for detecting defective micro LED chips using photoluminescence

Abstract

The present invention relates to a method and a device for efficiently detecting defective chips having a leakage current component using photoluminescence (PL) imaging of a micro LED chip. The present invention can analyze defective chips caused by leakage current by comparing photoluminescence (PL) imaging of a micro LED chip acquired respectively under conditions of high and low excitation light intensity, thereby resolving the electrode probing problem, which has been a challenge in conventional electroluminescence (EL) inspection, while obtaining defective chip detection results with accuracy and precision close to those of electroluminescence inspection.

Description

Method and apparatus for detecting defective micro LED chips using photoluminescence

[0001] The present invention relates to a method and apparatus for detecting defective micro LED chips, and more specifically, to a method and apparatus for efficiently detecting defective chips by accurately predicting leakage current by measuring the output of a laser, which is an excitation light, using photoluminescence (PL) imaging of a micro LED chip and calculating the ratio of “high output PL light amount / low output PL light amount.”

[0002] Micro LEDs, which typically measure in micrometers, are gaining attention as a next-generation display technology due to their ability to achieve miniaturization and high resolution. However, compared to Macro LEDs, Micro LEDs present challenges in evaluating electrical characteristics during inspection processes. Macro LEDs measure in millimeters. In particular, due to the small chip size, there are technical limitations in probe contact with electrodes during Electro-Luminescence (EL) inspection using current injection. Consequently, when utilized in large displays such as TVs, there is a problem in that it is difficult to inspect tens of millions of chips at low cost and high efficiency.

[0003] Therefore, although photoluminescence (PL) inspection is being utilized as an alternative, it has limitations in completely replacing the accuracy and precision of field-luminescence (EL) inspection, so there is a need for technology to accurately detect leakage current in micro-LEDs under low current conditions.

[0004] Photoluminescence (PL) is a technology that analyzes the light emitted when excited electrons recombine after being irradiated with a light source onto a sample. It is essential for analyzing the electronic and optical properties of materials in a non-destructive manner and for evaluating optoelectronic devices such as semiconductors, nanomaterials, LEDs, and displays. The characteristics of photoluminescence (PL) technology include the ability to evaluate internal properties while minimizing damage to materials or devices through non-destructive inspection, the ability to detect very minute optical changes with high sensitivity, and wide applicability, which allows for the measurement of energy band gaps, detection of defects and impurities, and evaluation of material homogeneity.

[0005] Photoluminescence (PL) measurement follows a process that involves excitation irradiation, in which a light source of a specific wavelength is shone onto a sample to excite electrons; photoluminescence measurement, which analyzes the emission spectrum emitted as the excited electrons recombine; and finally, data interpretation, which evaluates the optical and electrical properties of the material through variations in emission intensity, wavelength, and time. Lasers or LEDs are primarily used as the excitation light for photoluminescence, and the wavelength, intensity, and irradiation angle of the excitation light are adjusted to suit the characteristics of the sample.

[0006] However, compared to field-luminescence (EL), photoluminescence (PL) technology has limitations in precisely detecting leakage current at low current levels, and there is a need to rapidly inspect a large number of devices in the display manufacturing process. High-magnification optical systems and high-resolution cameras are required to distinguish the light intensity of individual chips in small devices such as micro-LEDs.

[0007] Korean Registered Patent No. 10-1293493 relates to a [light-emitting element inspection device and a light-emitting element inspection method using the same], disclosing a light-emitting element inspection device and a light-emitting element inspection method using the same that can determine defects, such as the presence or absence of leakage current, without physical contact with the light-emitting element to be inspected. However, the above invention has a problem in that while it can be applied to various light-emitting elements by changing the ultraviolet light intensity of the light-emitting element and adjusting the color and intensity using an image processor, it is difficult to apply to micro LEDs.

[0008] [Prior Art Literature]

[0009] [Patent Literature]

[0010] (Patent Document 1) Korean Registered Patent No. 10-1293493

[0011] To solve these problems, the present invention aims to provide a method and apparatus for efficiently detecting defective micro LED chips with leakage current components by calculating the ratio of photoluminescence (PL) light intensity based on the control of the intensity of the excitation light.

[0012] The present invention relates to a method for detecting defective micro LED chips using photoluminescence, wherein the method comprises: a step of mounting a sample in which a plurality of micro LED chips are arranged on a stage of a micro LED defective chip detection device using photoluminescence; a step of assigning coordinates to each of the plurality of micro LED chips; a step of obtaining a first photoluminescence image from the sample in which the plurality of micro LED chips are arranged to which the coordinates are assigned by setting the excitation light power of the detection device to a first intensity value; a step of calculating a first light intensity for each of the plurality of micro LED chips in which the coordinates are assigned through image processing from the first photoluminescence image; a step of obtaining a second photoluminescence image from the sample in which the plurality of micro LED chips are arranged to which the coordinates are assigned by setting the excitation light power of the detection device to a second intensity value; and a step of calculating a second light intensity for each of the plurality of micro LED chips in which the coordinates are assigned through image processing from the second photoluminescence image. The present invention provides a method for detecting defective micro LED chips using photoluminescence, comprising: a step of calculating a chip-specific light intensity ratio, which is the ratio of a second light intensity to a first light intensity of each of a plurality of micro LED chips assigned to the above coordinates; a step of classifying a chip as defective if the chip-specific light intensity ratio deviates from a predetermined value; and a step of storing the coordinates of the defective chip and discharging a sample.

[0013] The present invention also provides a method for detecting defective micro LED chips using photoluminescence, wherein the excitation light power of the detection device is such that the first intensity is 50% of the second intensity, and preferably the first intensity is 25% of the second intensity.

[0014] The present invention also provides that the excitation light power value has a second intensity of 1 mW (318.3 W / cm²). 2A method for detecting defective micro LED chips using photoluminescence is provided.

[0015] The present invention also provides a micro LED defective chip detection device using photoluminescence, wherein the device comprises: a sample stage for fixing a sample; a micro photoluminescence (PL) image measurement unit for acquiring a micro photoluminescence (PL) image at high speed and high resolution, the sample stage comprising an excitation light source, a high-resolution optical system, and a camera for collecting image data; and a computer for processing and analyzing a micro image equipped with software for a coordinate matching algorithm, calculating light intensity from a photoluminescence (PL) image, and calculating a light intensity ratio for determining a defective chip.

[0016] The present invention also provides a micro LED defective chip detection device using photoluminescence, wherein the camera is a line scan camera or a high-resolution CCD camera.

[0017] The present invention also provides a micro LED defective chip detection device using photoluminescence, wherein the computer performs data mapping for defective chips and visualizes the results.

[0018] The present invention analyzes defective chips due to leakage current by comparing photoluminescence (PL) imaging of micro LED chips acquired under high and low excitation light intensity states, thereby solving the electrode probing problem that was a difficulty in conventional field luminescence (EL) inspection while obtaining defective chip detection results close to the accuracy and precision level of field luminescence inspection.

[0019] FIG. 1 is a conceptual diagram showing the sequence of a method for detecting defective micro LED chips using photoluminescence according to one embodiment of the present invention.

[0020] Figure 2 is a comparative diagram showing the difference in light luminescence amounts between good chips and defective chips as the power of the excitation light increases.

[0021] Figure 3 is a graph showing that when a micro LED chip is excited with low light power, there is a large difference in photoluminescence intensity between a good chip (normal chip) and a defective chip (NG chip) (light intensity difference of 4.5 times), but when excited with high light power, there is almost no difference in intensity (light intensity level similar).

[0022] Figure 4 shows the photoluminescence (PL) image of a micro LED chip under low light power excitation and the photoluminescence (PL) image of a micro LED chip under high light power excitation.

[0023] Figure 5 shows the light intensity ratio mapping of photoluminescence (PL) of a micro LED chip.

[0024] FIG. 6 is an enlarged image visualizing the light quantity ratio according to the excitation light power per micro LED chip for detecting defective chips according to one embodiment of the present invention.

[0025] Figure 7 is a comparison table of electric field luminescence (EL) and optical luminescence (PL) defective chip detection methods.

[0026] FIG. 8 is a conceptual diagram of a micro LED defective chip detection device using photoluminescence according to one embodiment of the present invention.

[0027] FIG. 9 is a conceptual diagram visualizing data mapping results using a micro LED defective chip detection device using photoluminescence according to one embodiment of the present invention.

[0028] In the description below, numerous specific details are disclosed for illustrative purposes to aid in a general understanding of one or more aspects. However, it should be recognized that these aspects may be practiced without each specific detail. The following description and the attached drawings describe specific exemplary aspects of one or more aspects in detail. However, these aspects are exemplary, and some of the various methods may be used in the principles of the various aspects, and the description is intended to include all such aspects and their equivalents.

[0029] Terms such as “Example,” “Example,” “Aspect,” “Example,” etc., as used herein shall not be interpreted as implying that any described aspect or design is superior or advantageous to other aspects or designs. Furthermore, the term “or” is intended to mean an implicit “or” rather than an exclusive “or.” That is, unless otherwise specified or clear from the context, “X uses A or B” is intended to mean one of the natural implicit substitutions. That is, if X uses A; if X uses B; or if X uses both A and B, “X uses A or B” may apply to either of these cases. Additionally, the term “and / or” as used herein shall be understood to refer to and include all possible combinations of one or more of the enumerated related items.

[0030] Additionally, the terms “comprising” and / or “comprising” should be understood to mean that the relevant feature, step, action, module, and / or component is present, but not to exclude the presence or addition of one or more other features, steps, actions, modules, components, and / or groups thereof. Furthermore, unless otherwise specified or clearly evident from the context to indicate a singular form, the singular in this specification and claims should generally be interpreted to mean “one or more.”

[0031] In this invention, photoluminescence (PL) technology is utilized to detect leakage current in micro LEDs, and accuracy and efficiency are significantly improved by comparing and analyzing photoluminescence images with controlled excitation light intensity. The invention will be described in detail below with reference to the drawings.

[0032] FIG. 1 is a conceptual diagram illustrating the sequence of a method for detecting defective micro LED chips using photoluminescence according to an embodiment of the present invention. The present invention provides a method for detecting defective micro LED chips using photoluminescence, comprising the steps of: mounting a sample in which a plurality of micro LED chips are arranged on a stage of a micro LED defective chip detection device using photoluminescence; assigning coordinates to each of the plurality of micro LED chips; setting the excitation light power of the detection device to a first intensity value to obtain a first photoluminescence image from the sample in which the plurality of micro LED chips are arranged to which the coordinates are assigned; calculating a first light amount for each of the plurality of micro LED chips in which the coordinates are assigned through image processing from the first photoluminescence image; and setting the excitation light power of the detection device to a second intensity value to obtain a second photoluminescence image from the sample in which the plurality of micro LED chips are arranged to which the coordinates are assigned. The method includes the steps of: calculating a second light intensity for each of a plurality of micro LED chips assigned to coordinates through image processing from the second light-luminescence image; calculating a chip-specific light intensity ratio, which is the ratio of the second light intensity to the first light intensity for each of the plurality of micro LED chips assigned to coordinates; classifying a chip as defective if the chip-specific light intensity ratio deviates from a predetermined value; and storing the coordinates of the defective chip and discharging the sample. The reason why defective chips can be classified by such a chip-specific light intensity ratio can be understood through Figures 2 to 6 below.

[0033] Figure 2 is a comparative diagram showing the difference in photoluminescence intensity between good chips and defective chips as the excitation light power increases, with optical power and intensity indicated. Optical power is a measured value of the power of the excitation laser reaching each chip. Although it is a value for comparing the photoluminescence intensity according to the excitation light power (absolute value), this figure is not practically suitable for comparison. This is because, in defect inspection of chips using micro PL, the light intensity of each individual chip is compared. Furthermore, to ensure fast inspection times, the shape of the excitation laser beam is converted to a linear (1-dimensional, within 10 mm) or 2-dimensional (minimum several mm) shape. Therefore, when referring to excitation light power in inspection using micro PL, it is reasonable to express it as excitation light power per unit area rather than the total power. In one embodiment of the present invention, the excitation light power of the detection device is such that the first intensity is 50% of the second intensity, and preferably, the first intensity is 25% of the second intensity. In one embodiment of the present invention, the excitation light power value is such that the second intensity is 1 mW (318.3 W / cm²). 2 )am.

[0034] This difference can be confirmed through Figure 3. Figure 3 is a graph showing that when a micro LED chip is excited with low light power, there is a large difference in photoluminescence intensity between a good chip (normal chip) and a defective chip (NG chip) (a difference of 4.5 times in light intensity), but when excited with high light power, there is almost no difference in intensity (similar light intensity levels).

[0035] Figure 4 shows the photoluminescence (PL) image of a micro LED chip when excited at low light power and the photoluminescence (PL) image of a micro LED chip when excited at high light power, and Figure 5 shows the light quantity ratio mapping of the photoluminescence (PL) of a micro LED chip, representing the ratio of the light quantity obtained from the photoluminescence image obtained with the first intensity of excitation light power and the light quantity obtained from the photoluminescence image obtained with the second intensity of excitation light power of a sample on which a micro LED is transferred. For clear distinction, the photoluminescence light quantities obtained at the two intensities were divided by the average to normalize the average light quantity at each intensity to 1. As can be seen in Figure 2, it can be seen that the light quantity ratio is close to 1 for a normal chip (light green), but for a defective chip, the light quantity ratio deviates significantly from 1 (1.3 or higher, red).

[0036] FIG. 6 is an enlarged image visualizing the ratio of light intensity according to the excitation light power for each micro LED chip for detecting defective chips according to an embodiment of the present invention. A chip that exhibits a ratio of light intensity at high excitation light power to light intensity at low excitation light power greater than or equal to a predetermined value can be marked as a defective chip. The predetermined value marked as a defective chip can be appropriately determined according to the amount of light emitted by the chip. Using such a photoluminescence image, it is possible to detect micro LED defective chips to a degree similar to electric field luminescence.

[0037] In one embodiment of the present invention, the excitation light power boundary value between the good chip and the defective chip is 500 W / cm² 2 100 - 125 W / cm² falling within the range of 1 / 4 to 1 / 5 of (Optical Power: 2 mW, Good Chip / Defective Chip Light Intensity Ratio: 1.22). 2 It can be set based on the following criteria: (Optical power: 0.3 - 0.4 mW, good / defective chip light intensity ratio: 2.66).

[0038] Figure 7 is a comparison table of the electric field luminescence (EL) and photoluminescence (PL) defective chip detection methods. While the electric field luminescence method analyzes based on electrical characteristics, the photoluminescence method can be judged solely by the amount of photoluminescence light. Therefore, unlike electric field luminescence, where the measurement time is proportional to the number of chips, the photoluminescence method has a low correlation with the number of chips, making it more advantageous as the number of chips increases. Additionally, while the electric field luminescence method can cause damage to the chips during the measurement process, the photoluminescence method has a low probability of chip damage.

[0039] The present invention provides technical details regarding both a method and an apparatus. FIG. 8 is a conceptual diagram of a micro LED defective chip detection device using photoluminescence according to an embodiment of the present invention. The present invention is a micro LED defective chip detection device using photoluminescence, comprising: a sample stage for fixing a sample; a micro photoluminescence (PL) image measurement unit for acquiring micro photoluminescence (PL) images at high speed and high resolution, comprising an excitation light source, a high-resolution optical system, and a camera for collecting image data; and a computer for processing and analyzing micro images equipped with a coordinate matching algorithm, software for calculating light intensity from photoluminescence (PL) images, and calculating a light intensity ratio for determining defective chips. In an embodiment of the present invention, the camera is a line scan camera or a high-resolution CCD camera.

[0040] FIG. 9 is a conceptual diagram visualizing the results of data mapping using a micro LED defective chip detection device using photoluminescence according to an embodiment of the present invention. In an embodiment of the present invention, the computer performs data mapping for defective chips and visualizes the results.

[0041] Although exemplary embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concepts of the present invention as defined in the following claims also fall within the scope of the present invention.

[0042] All technical terms used in this invention, unless otherwise defined, are used in the sense generally understood by those skilled in the art in the relevant field of this invention. The contents of all publications cited as references in this specification are incorporated into this invention.

Claims

1. A method for detecting defective micro LED chips using photoluminescence, wherein the method comprises: A step of mounting a sample having a plurality of micro LED chips arranged thereon onto a stage of a micro LED defective chip detection device using photoluminescence; A step of assigning coordinates to each of the plurality of micro LED chips; A step of acquiring a first photoluminescence image from a sample in which a plurality of micro LED chips are arranged to be assigned coordinates by setting the excitation light power of the detection device to a first intensity value; A step of calculating the first light intensity of each of the plurality of micro LED chips assigned to the coordinates through image processing from the first photoluminescence image; A step of acquiring a second photoluminescence image from a sample in which a plurality of micro LED chips are arranged to be assigned coordinates by setting the excitation light power of the detection device to a second intensity value; A step of calculating the second light intensity of each of the plurality of micro LED chips assigned to the coordinates through image processing from the second photoluminescence image; A step of calculating a chip-specific light quantity ratio, which is the ratio of a second light quantity to a first light quantity for each of a plurality of micro LED chips assigned the above coordinates; A step of classifying a chip as defective if the light intensity ratio of each chip deviates from a predetermined value; and A method comprising the step of storing the coordinates of the defective chip and discharging a sample. Method for detecting defective micro LED chips using photoluminescence.

2. In Paragraph 1, The excitation light power of the above detection device is such that the first intensity is 50% of the second intensity, and Preferably, the first intensity is 25% of the second intensity, Method for detecting defective micro LED chips using photoluminescence.

3. In Paragraph 2, The above excitation light power value is a second intensity of 1 mW (318.3 W / cm²) 2 )person, Method for detecting defective micro LED chips using photoluminescence.

4. A micro LED defective chip detection device using photoluminescence, wherein the device comprises: Sample stage for fixing the sample; Micro-optical luminescence (PL) image measuring unit for acquiring micro-optical luminescence (PL) images at high speed and high resolution, comprising an excitation light source, a high-resolution optical system, and a camera for collecting image data; and A computer for processing and analyzing micro-images equipped with a coordinate matching algorithm, software for calculating light intensity from photoluminescence (PL) images and calculating a light intensity ratio for determining defective chips, Micro LED defective chip detection device using photoluminescence.

5. In Paragraph 4, The above camera is a line scan camera or a high-resolution CCD camera, Micro LED defective chip detection device using photoluminescence.

6. In Paragraph 4, The above computer performs data mapping for defective chips and visualizes the results, Micro LED defective chip detection device using photoluminescence.

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