PULSED LASER MICRO LED INSPECTION

The system includes a laser generator, an antenna, and a processor. The laser generator is configured to emit a pulsed laser beam toward an LED. The LED generates a photovoltaic radio frequency signal when radiated by the pulsed laser beam. The antenna is configured to receive the photovoltaic radio frequency signal generated by the LED. The processor is in electronic communication with the antenna and is configured to read the photovoltaic radio frequency signal and determine whether the LED is a defective LED or a functioning LED based on the photovoltaic radio frequency signal.

FIELD OF THE DISCLOSURE

This disclosure relates to micro LED manufacturing and, more particularly, to inspection processes for micro LEDs and manufacturing micro LED displays.

BACKGROUND OF THE DISCLOSURE

In the manufacturing of micro LEDs, thousands of LEDs (less than 100 μm in size) are fabricated on a single semiconductor wafer. Each micro LED must be separated from the wafer (and the other LEDs) to be assembled into a micro LED display panel. In this process, inspection and testing is used to ensure that each LED is functional before it is placed in the display panel assembly to avoid defective LEDs in the display panel. Given the massive amount of micro LEDs on a small wafer, testing each LED can be a very difficult and time consuming process.

Typical LED testing includes photoluminescence (PL) and electroluminescence (EL) tests. PL tests can test LED chips without contact, but have a lower detection efficiency compared to EL test. EL tests are able to identify more defects, but they test LED chips by setting up electric currents which requires contacting the LED chips that might lead to chip damages. For micro LED inspection, applying EL tests can be very difficult and slow as the chip size is too small for conventional testing equipment, and using PL tests might miss some defects, resulting in lower efficiency.

Therefore, what is needed is a method of micro LED inspection that is contactless and has high detection efficiency.

BRIEF SUMMARY OF THE DISCLOSURE

An embodiment of the present disclosure provides a system. The system may comprise a laser generator configured to emit a pulsed laser beam toward an LED. The LED may generate a photovoltaic radio frequency signal when radiated by the pulsed laser beam. The system may further comprise an antenna configured to receive the photovoltaic radio frequency signal generated by the LED. The system may further comprise a processor in electronic communication with the antenna that is configured to read the photovoltaic radio frequency signal and determine whether the LED is a defective LED or a functioning LED based on the photovoltaic radio frequency signal.

In some embodiments, the pulsed laser beam may have a frequency of 5 to 10 MHz.

In some embodiments, the LED may comprise an array of LEDs disposed on a substrate.

In some embodiments, the laser generator may be configured to radiate a single LED of the array of LEDs.

In some embodiments, the system may further comprise a stage configured to move in a plane perpendicular to the pulsed laser beam. The substrate may be disposed on the stage. The laser generator may be further configured to scan the pulsed laser beam across the array of LEDs by moving the stage relative to the laser generator, such that each LED generates a photovoltaic radio frequency signal when radiated by the pulsed laser beam.

In some embodiments, the LED may have a lateral chip structure.

In some embodiments, the antenna may be annular and may define an aperture. The laser generator may be configured to emit the pulsed laser beam toward the LED through the aperture of the antenna.

In some embodiments, the processor may comprises a receiving circuit configured to receive the photovoltaic radio frequency signal from the antenna, an amplifying circuit configured to amplify the photovoltaic radio frequency signal received by the receiving circuit, and a determining circuit configured to determine whether the LED is a defective LED or a functioning LED based on the photovoltaic radio frequency signal amplified by the amplifying circuit.

In some embodiments the processor may be configured to determine whether the LED is a defective LED or a functioning LED by comparing the photovoltaic radio frequency signal to a model waveform. The LED may be determined to be a defective LED or a functioning LED based on a similarity of the photovoltaic radio frequency signal to the model waveform.

In some embodiments, the system may further comprise an oscilloscope. The oscilloscope may be in electronic communication with the processor and may be configured to display the photovoltaic radio frequency signal.

Another embodiment of the present disclosure provides a method. The method may comprise: generating a pulsed laser beam using a laser generator; directing the pulsed laser beam toward an LED; generating a photovoltaic radio frequency signal based on interaction between the pulsed laser beam and the LED; receiving the photovoltaic radio frequency signal using an antenna; reading the photovoltaic radio frequency signal with a processor in electronic communication with the antenna; and determining, using the processor, whether the LED is a defective LED or a functioning LED based on the photovoltaic radio frequency signal.

In some embodiments, the LED may comprise an array of LEDs disposed on a substrate, and directing the pulsed laser beam toward the LED may comprise directing the pulsed laser beam toward the array of LEDs to radiate a single LED of the array of LEDs.

In some embodiments, the LED may comprise an array of LEDs disposed on a substrate, and directing the pulsed laser beam toward the LED may comprise scanning the pulsed laser beam across the array of LEDs, such that each LED generates a photovoltaic radio frequency signal when radiated by the pulsed laser beam.

In some embodiments, the substrate may be disposed on a stage that is movable in a plane perpendicular to the pulsed laser beam, and scanning the pulsed laser beam across the array of LEDs may comprise scanning the pulsed laser beam across the array of LEDs by moving the stage relative to the laser generator.

In some embodiments, before directing the pulsed laser beam toward the LED, the method may further comprise dicing the substrate to electrically separate each LED of the array of LEDs.

In some embodiments, the method may further comprise singulating the substrate to physically separate each LED of the array of LEDs; and transferring each functioning LED of the array of LEDs to a display assembly.

In some embodiments, the antenna may be annular and may define an aperture, and directing the pulsed laser beam toward the LED may comprise directing the pulsed laser beam toward the LED through the aperture of the antenna.

In some embodiments, determining, using the processor, whether the LED is a defective LED or a functioning LED may comprise comparing, using the processor, the photovoltaic radio frequency signal to a model waveform. The LED may be determined to be a defective LED or a functioning LED based on a similarity of the photovoltaic radio frequency signal and the model waveform.

DETAILED DESCRIPTION OF THE DISCLOSURE

An embodiment of the present disclosure provides a system100. The system100may be part of a semiconductor manufacturing system, for example, in the fabrication of micro LEDs for micro LED display panels. As shown inFIG.1, the system100may comprise a substrate110(e.g., a semiconductor wafer) having at least one LED115disposed thereon. In some embodiments, there may be an array of LEDs115disposed on the substrate110. The substrate110may be comprised of GaAs, GaN, or other semiconductor wafer materials. The substrate110may be rectangular, square, circular, or other shapes. In some instances, the substrate110may have a width/diameter of 2-8 inches (e.g., 2, 3, 4, 6, or 8 inches, and any size therebetween). During the fabrication process of the LEDs115, each LED may be electrically connected together. A dicing process may be used to electrically separate (i.e., sever the electrical connections) the LEDs115, and then a singulation process may be used to physically separate each LED115from each other and from the substrate110for placement in a display panel assembly. The singulation process may comprise elastomer stamping, electrostatic transfer, electromagnetic transfer, laser-assisted, transfer, fluid self-assembly, or any other mass transfer process used to transfer each LED115from the substrate110to a target substrate. Perforations111(shown inFIGS.5A-5C) may represent the lines on which the dicing and singulation processes may be performed on the substrate110. Additional perforations may be present to undercut portions of the LED115connected to the substrate110, according to the structure of the LEDs115and the singulation process. The LEDs115may be micro LEDs (e.g., less than 100 μm in length and width and less than 8 μm in height) or other sizes. For example, each LED115may be 10 μm by 10 μm. Based on the size of the substrate110and the size of each LED115, there may be over 1,000,000 LEDs115disposed on the substrate110. Each LED115shown inFIG.1andFIGS.5A-5Cmay represent a single LED or an array of LEDs. Accordingly, additional perforations111may be present to separate each LED of the array of LEDs within each illustrated LED115.

The LEDs115may have various structure, such as lateral chip (shown inFIG.2A), flip-chip (shown inFIG.2B), vertical chip (shown inFIG.2C), or other structures. In general, each LED115may comprise an N-doped layer10, a P-doped layer20, and a multiple quantum well layer30disposed between N-doped layer10and the P-doped layer20. Connecting a negative electrode to the N-doped layer10and connecting a positive electrode to the P-doped layer20causes a forward bias between the N-doped layer10and the P-doped layer20, via the multiple quantum well layer30, which generates photons to emit light. In the lateral chip structure shown inFIG.2A, a metal post40is disposed on the N-doped layer10. The negative electrode is connected to the metal post40, and the positive electrode is connected to the P-doped layer20. In the flip-chip structure shown inFIG.2B, a metal post40is disposed on the P-doped layer20, and a bonding layer50is disposed on the N-doped layer10and the metal post40. The negative electrode is connected to the bonding layer50on the N-doped layer10, and the positive electrode is connected to the bonding layer50on the metal post40. In the vertical chip structure shown inFIG.2C, a bonding layer50is disposed on the N-doped layer10. The negative electrode is connected to the bonding layer50, and the positive electrode is connected to the P-doped layer20.

The system100may further comprise a laser generator120. The laser generator120may be configured to emit a pulsed laser beam121toward the LED115. The pulsed laser beam121may be directed at the LED115perpendicular to the substrate110, or at one or more oblique angles relative to the substrate110. The laser generator120may be movable or rotatable to adjust the angle of incidence of the pulsed laser beam121. The pulsed laser beam121may have a frequency of 5 to 10 MHz. The wavelength of the pulsed laser beam121may be less than or equal to the emission wavelength of the LED115. For example, a pulsed laser beam121having a wavelength in the ultra-violet spectrum may be used to inspect red, green, and blue LEDs115. Based on the size of the pulsed laser beam121, the laser generator120may be configured to simultaneously radiate at least some of the array of LEDs115with the pulsed laser beam121. In some embodiments, the pulsed laser beam121may be sized such that the laser generator120radiates a single LED115. Accordingly, the pulsed laser beam121may have a diameter of corresponding to the size of a single LED115. For example, the diameter of the pulsed laser beam121may be 100 μm or smaller, depending on the size of the LED115. Upon interaction with the pulsed laser beam121, the LED115may generate a photovoltaic radio frequency signal122. For example, the pulsed laser beam121may cause a forward bias between the N-doped layer10and the P-doped layer20of the LED115, which may emit near-field radio waves, forming the photovoltaic radio frequency signal122. The photovoltaic radio frequency signal122generated by the LED115may vary, depending on whether the LED115is a defective LED or a functioning LED. For example, a defective LED may emit no radio frequency signal122or may emit a radio frequency signal122having a different frequency, amplitude, or phase shift compared to that of a functioning LED. The LED115may emit the photovoltaic radio frequency signal122in a direction away from the substrate110. The LED115may have a slow decay and may continue to emit the photovoltaic radio frequency signal122after interaction with the pulsed laser beam121. Additional laser pulses may increase the intensity and the duration of the photovoltaic radio frequency signal122emitted by the LED115. Accordingly, few laser pulses may be used to activate the LED115under test, and the number of laser pulses may be optimized to improve throughput.

The system100may further comprise an antenna130. The antenna130may be disposed between the laser generator120and the substrate110. The antenna130may be configured to receive the photovoltaic radio frequency signal122generated by the LED115. The sensitivity of the antenna130may be small enough to distinguish the photovoltaic radio frequency signals122emitted by defective LEDs and functioning LEDs. For example, the sensitivity of the antenna130may be configured such that the signals of defective LEDs and functioning LEDs are 5 standard deviations apart. In some embodiments, the antenna130may be annular. For example, as shown inFIG.3, the antenna130may define an aperture131, which may be circular or other shapes. The laser generator120may be configured to emit the pulsed laser beam121toward the LED115through the aperture131of the antenna130. The diameter of the aperture131may be slightly larger than the diameter of the pulsed laser beam121, to maximize the area of the bottom surface132of the antenna, which receives the photovoltaic radio frequency signal122. The size of the antenna130may vary, depending on the size of the substrate110, the distance between the antenna130and the substrate110, and geometric constraints within the system100. In some embodiments, the antenna130may be about ⅓ of the size of the substrate110. When the antenna130is positioned closer to the substrate110, the size of the antenna130may be smaller compared to the antenna130being positioned farther from the substrate110.

The system100may further comprise a processor140. The processor140may include a microprocessor, a microcontroller, or other devices.

The processor140may be coupled to the components of the system100in any suitable manner (e.g., via one or more transmission media, which may include wired and/or wireless transmission media) such that the processor140can receive output. The processor140may be configured to perform a number of functions using the output. A wafer inspection tool can receive instructions or other information from the processor140. The processor140optionally may be in electronic communication with another wafer inspection tool, a wafer metrology tool, or a wafer review tool (not illustrated) to receive additional information or send instructions.

The processor140may be part of various systems, including a personal computer system, image computer, mainframe computer system, workstation, network appliance, internet appliance, or other device. The subsystem(s) or system(s) may also include any suitable processor known in the art, such as a parallel processor. In addition, the subsystem(s) or system(s) may include a platform with high-speed processing and software, either as a standalone or a networked tool.

The processor140may be disposed in or otherwise part of the system100or another device. In an example, the processor140and may be part of a standalone control unit or in a centralized quality control unit. Multiple processors140may be used, defining multiple subsystems of the system100.

The processor140may be implemented in practice by any combination of hardware, software, and firmware. Also, its functions as described herein may be performed by one unit, or divided up among different components, each of which may be implemented in turn by any combination of hardware, software and firmware. Program code or instructions for the processor140to implement various methods and functions may be stored in readable storage media, such as a memory.

If the system100includes more than one subsystem, then the different processors140may be coupled to each other such that images, data, information, instructions, etc. can be sent between the subsystems. For example, one subsystem may be coupled to additional subsystem(s) by any suitable transmission media, which may include any suitable wired and/or wireless transmission media known in the art. Two or more of such subsystems may also be effectively coupled by a shared computer-readable storage medium (not shown).

The processor140may be configured to perform a number of functions using the output of the system100or other output. For instance, the processor140may be configured to send the output to an electronic data storage unit or another storage medium. The processor140may be further configured as described herein.

The processor140may be configured according to any of the embodiments described herein. The processor140also may be configured to perform other functions or additional steps using the output of the system100or using images or data from other sources.

The processor140may be communicatively coupled to any of the various components or sub-systems of system100in any manner known in the art. Moreover, the processor140may be configured to receive and/or acquire data or information from other systems (e.g., inspection results from an inspection system such as a review tool, a remote database including design data and the like) by a transmission medium that may include wired and/or wireless portions. In this manner, the transmission medium may serve as a data link between the processor140and other subsystems of the system100or systems external to system100. Various steps, functions, and/or operations of system100and the methods disclosed herein are carried out by one or more of the following: electronic circuits, logic gates, multiplexers, programmable logic devices, ASICs, analog or digital controls/switches, microcontrollers, or computing systems. Program instructions implementing methods such as those described herein may be transmitted over or stored on carrier medium. The carrier medium may include a storage medium such as a read-only memory, a random access memory, a magnetic or optical disk, a non-volatile memory, a solid state memory, a magnetic tape, and the like. A carrier medium may include a transmission medium such as a wire, cable, or wireless transmission link. For instance, the various steps described throughout the present disclosure may be carried out by a single processor140(or computer subsystem) or, alternatively, multiple processors140(or multiple computer subsystems). Moreover, different sub-systems of the system100may include one or more computing or logic systems. Therefore, the above description should not be interpreted as a limitation on the present disclosure but merely an illustration.

The processor140may be in electronic communication with the antenna130. The processor140may be configured to read the photovoltaic radio frequency signal122received by the antenna130. The processor140may be further configured to determine whether the LED115is a defective LED or a functioning LED based on the photovoltaic radio frequency signal122.

In some embodiments, the processor140may comprise a receiving circuit141, an amplifying circuit142, and a determining circuit143, as shown inFIG.4. The receiving circuit141may be configured to receive the photovoltaic radio frequency signal122from the antenna130. The amplifying circuit142may be configured to amplify the photovoltaic radio frequency signal122received by the receiving circuit141, which may reduce noise in the signal and help differentiate the signals of defective LEDs and functioning LEDs. The determining circuit143may be configured to determine whether the LED115is a defective LED or a functioning LED based on the photovoltaic radio frequency signal122amplified by the amplifying circuit142. The determining circuit143may be further configured to compare the photovoltaic radio frequency signal122to a model waveform. The LED115may be determined to be a defective LED or a functioning LED based on waveform fitting. For example, the waveform of the photovoltaic radio frequency signal122may be compared to a model waveform, and the LED115may be determined to be a defective LED or a functioning LED based on the waveform of the photovoltaic radio frequency signal122being similar to the model waveform. In an instance, for a pulsed laser beam121modelled as the function sin2x, a model waveform of a photovoltaic radio frequency signal122of a functioning LED may be 10·(1−e−0.1x)+sin2x·(e−0.01x). The model waveform may be defined based on previous test data, e.g., by fitting a function to the received photovoltaic radio frequency signal122of a functioning LED. Other methods of analyzing the photovoltaic radio frequency signal122to determine whether the LED115is a defective LED or a functioning LED are possible (e.g., threshold comparison), and is not limited herein.

The system100may further comprise a stage150. The substrate110may be disposed on the stage150. The stage150may be configured to move relative to the pulsed laser beam121. For example, the stage150may be configured to move in a plane perpendicular to the pulsed laser beam121, as shown inFIG.5A. The stage150may be movable by one or more actuators or other means and is not limited herein. Alternatively, the laser generator120may be configured to move relative to the stage150. When the stage150moves relative to the laser generator120, the pulsed laser beam121may scan across the array of LEDs115, so as to radiate each LED115with the pulsed laser beam121. The pulsed laser beam121may radiate a single LED115or multiple LEDs115. For example, the pulsed laser beam121may be configured to radiate a first set of LEDs116of the array of LEDs115(shown inFIG.5B), based on the diameter of the pulsed laser beam121, and by moving the stage150, the pulsed laser beam121may be configured to radiate a second set of LEDs117of the array of LEDs115(shown inFIG.5C). The LEDs115within the first set of LEDs116and the second set of LEDs117may be mutually exclusive or may overlap. By radiating the first set of LEDs116, the second set of LEDs117, and any number of additional sets of LEDs (or each single LED115), all LEDs of the array of LEDs115may be radiated by the pulsed laser beam121, and each LED generates a photovoltaic radio frequency signal122. The stage150may move such that one or more pulses of the pulsed laser beam121radiate each LED115. As each pulse may increase the intensity of the photovoltaic radio frequency signal122generated by each LED115, the number of pulses may be optimized for sufficient signal reception and increased throughput. It should be understood that while a single LED115may be radiated by the pulsed laser beam121, adjacent LEDs115may also be partially radiated by the pulsed laser beam121. To avoid these partially-radiated LEDs115from affecting measurements, the stage150may move such that a non-continuous sequence of LEDs115on the substrate110are radiated by the pulsed laser beam121.

The processor140may be in electronic communication with the actuators or other means configured to move the stage150. In particular, the processor140may control the one or more actuators to move the stage150in a particular sequence in order to radiate each LED115on the substrate110. The processor140may also track the position of the stage150and the position of each LED115under test. Accordingly, the processor140may map the position of each LED115to the decision whether the LED115is a defective LED or a functioning LED. This mapping may be used to identify the functioning LEDs that can be used, and the defective LEDs that can be discarded.

The system100may further comprise an oscilloscope160. The oscilloscope160may be in electronic communication with the processor140. The oscilloscope160may be configured to display the photovoltaic radio frequency signal122received by the antenna130. The oscilloscope160may also display threshold lines and/or exemplary waveforms corresponding to defective and functioning LEDs. Accordingly, a user may read the photovoltaic radio frequency signal122on the oscilloscope160to determine whether the LED115is a defective LED or a functioning LED by comparing the measured value to the displayed threshold and/or exemplary waveforms.

With the system100, the pulsed laser beam121may be used to inspect the LEDs115in a contactless manner, and the photovoltaic radio frequency signal122generated by the LEDs115may be received by the antenna130to determine whether each LED115is a defective LED or a functioning LED. The system100may therefore allow efficient testing of large amounts of micro LEDs manufactured on a substrate110, so that defective LEDs are identified and not transferred to a display assembly.

Another embodiment of the present disclosure provides a method200. With reference toFIG.6, the method200may comprise the following steps.

At step210, a pulsed laser beam is generated using a laser generator. The pulsed laser beam may have a frequency of 5 to 10 MHz. The wavelength of the pulsed laser beam may be selected based on the LED under test. For example, the wavelength of the pulsed laser beam may be less than or equal to the emission wavelength of the LED. In an instance, the pulsed laser beam may have a wavelength in the ultra-violet spectrum to inspect red, green, and blue LEDs. The pulsed laser beam may also be sized based on the LED under test. For example, the pulsed laser beam may have a diameter corresponding to a single LED. In some embodiments, the pulsed laser beam may have a diameter of 100 μm or smaller.

At step220, the pulsed laser beam is directed toward an LED. The LED may be disposed on a substrate comprising an array of LEDs. The substrate may be comprised of GaAs, GaN, or other semiconductor wafer materials. The substrate may be rectangular, square, circular, or other shapes. In some instances, the substrate may have a width/diameter of 2-8 inches (e.g., 2, 3, 4, 6, or 8 inches, and any size therebetween). The LEDs may have various structure, such as lateral chip (shown inFIG.2A), flip-chip (shown inFIG.2B), vertical chip (shown inFIG.2C), or other structures. The LEDs may be micro LEDs (e.g., less than 100 μm in in length and width and less than 8 μm in height) or other sizes. For example, each LED may be 10 μm by 10 μm. Based on the size of the substrate and the size of each LED, there may be over 1,000,000 LEDs disposed on the substrate. The pulsed laser beam may be directed toward the LED perpendicular to the substrate, or at one or more oblique angles relative to the substrate. The laser generator may be movable or rotatable to adjust the angle of incidence of the pulsed laser beam.

In some embodiments, the pulsed laser beam may be directed toward the array of LEDs to simultaneously radiate at least some of the array of LEDs. For example, based on the diameter of the pulsed laser beam, the pulsed laser beam may simultaneously radiate one or more LEDs of the array of LEDs.

In some embodiments, the pulsed laser beam may be scanned across the array of LEDs, such that each LED is radiated by the pulsed laser beam. For example, the substrate may be disposed on a stage that is movable in a plane perpendicular to the pulsed laser beam. By moving the stage relative to the laser generator, the pulsed laser beam may scan across the array of LEDs to radiate each LED.

At step230, a photovoltaic radio frequency signal is generated based on interaction between the pulsed laser beam and the LED. When radiated by the pulsed laser beam, the LED may generate a photovoltaic radio frequency signal that is emitted in a direction away from the substrate. For example, the pulsed laser beam may cause a forward bias between the N-doped layer and the P-doped layer of the LED, which may emit near-field radio waves, forming the photovoltaic radio frequency signal. The photovoltaic radio frequency signal generated by the LED may vary, depending on whether the LED is a defective LED or a functioning LED.

At step240, the photovoltaic radio frequency signal is received using an antenna. The sensitivity of the antenna may be small enough to distinguish the photovoltaic radio frequency signals emitted by defective LEDs and functioning LEDs. For example, the sensitivity of the antenna may be configured such that the signals of defective LEDs and functioning LEDs are 5 standard deviations apart. The antenna may be annular. For example, the antenna may define an aperture, which may be circular or other shapes. The laser generator may be configured to emit the pulsed laser beam toward the LED through the aperture of the antenna. The diameter of the aperture may be slightly larger than the diameter of the pulsed laser beam, so as to maximize the area of the bottom surface of the antenna, which receives the photovoltaic radio frequency signal. The size of the antenna may vary, depending on the size of the substrate, the distance between the antenna and the substrate, and geometric constraints within the system. In some embodiments, the antenna may be about ⅓ of the size of the substrate. When the antenna is positioned closer to the substrate, the size of the antenna may be smaller compared to the antenna being positioned farther from the substrate.

At step250, the photovoltaic radio frequency signal is read with a processor in electronic communication with the antenna. For example, the antenna may be connected to the processor to send the photovoltaic radio frequency signal by wired and/or wireless transmission.

At step260, the processor determines whether the LED is a defective LED or a functioning LED based on the photovoltaic radio frequency signal. For example, the processor may compare the photovoltaic radio frequency signal to a model waveform to determine whether the LED is a defective LED or a functioning LED. The LED may be determined to be a defective LED or a functioning LED based on waveform fitting. For example, the waveform of the photovoltaic radio frequency signal may be compared to the model waveform, and the LED may be determined to be a defective LED or a functioning LED based on the waveform of the photovoltaic radio frequency signal being similar to the model waveform. The model waveform may be defined based on previous test data, e.g., by fitting a function to the received photovoltaic radio frequency signal122of a functioning LED. Other methods of analyzing the photovoltaic radio frequency signal to determine whether the LED is a defective LED or a functioning LED are possible (e.g., threshold comparison), and is not limited herein.

The processor may be in electronic communication with the actuators or other means configured to move the stage. In particular, the processor may control the one or more actuators to move the stage in a particular sequence in order to radiate each LED on the substrate. The processor may also track the position of the stage and the position of each LED under test. Accordingly, the processor may map the position of each LED to the decision whether the LED is a defective LED or a functioning LED. This mapping may be used to identify the functioning LEDs that can be used, and the defective LEDs that can be discarded.

In some embodiments, before directing the pulsed laser beam toward the LED at step210, the method200may further comprise step205. At step205, the substrate is diced to electrically separate each LED of the array of LEDs. During the fabrication process of the LEDs, each LED may be electrically connected together. By dicing the substrate, the electrical connections between each LED may be severed, in order to test each of the LEDs with the pulsed laser beam.

In some embodiments, the method200may further comprise the following steps.

At step265, the substrate is singulated to physically separate each LED of the array of LEDs. By singulating the substrate, each LED can be physically separated from each other. For example, the functioning LEDs can be separated from the defective LEDs, as determined by the processor. The singulation process may comprise elastomer stamping, electrostatic transfer, electromagnetic transfer, laser-assisted, transfer, fluid self-assembly, or any other mass transfer process used to transfer each LED from the substrate to a target substrate.

At step270, each functioning LED of the array of LEDs may be transferred to a display assembly. The functioning LEDs may be transferred manually or by a pick and place robot. The method of transfer may depend on the type of singulation process used, and is not limited herein. When there are a group of functioning LEDs in proximity to each other, the group of functioning LEDs may be transferred to the display assembly together. Each defective LED may not be transferred to the display assembly. For example, each defective LED may remain on the substrate or may be discarded.

With the method200, the pulsed laser beam may be used to inspect the LEDs in a contactless manner, and the photovoltaic radio frequency signal generated by the LEDs may be received by the antenna to determine whether each LED is a defective LED or a functioning LED. The method200may therefore allow efficient testing of large amounts of micro LEDs manufactured on a substrate, so that defective LEDs are identified and not transferred to a display assembly.