LED chip manufacturing process and inspection project analysis

The chip is the most important raw material of LED , and its quality directly determines the performance of the LED. Especially for high-end LEDs used in automotive or solid-state lighting , defects are never allowed, which means that the reliability of such devices must be very high. However, LED packaging factory due to lack of experience and equipment incoming inspection of the chip, the chip is not normally perform incoming inspection, after a failed chip available, often only eat Yaba Kui. Based on the accumulation of a large number of LED failure analysis cases, Jinjian Testing introduced the LED chip incoming inspection business and identified the advantages and disadvantages of the chip by using high-end analytical instruments. This testing service can be used as a supplement to the incoming inspection of the LED packaging factory/chip agent to prevent defective chips from being placed in the warehouse and avoid the overall loss of the lamp beads due to chip quality problems.

Test items:

First, the chip performance parameter test

Photoelectric performance test of Wd (primary wavelength), Iv (brightness), Vf (forward voltage), Ir (leakage), ESD (antistatic capability), etc. Jinjian as a third-party testing agency can identify suppliers' products Whether the data is up to standard.

Second, chip defect search

Test content:

1. Chip size measurement, chip size and electrode size meet the requirements, and the electrode pattern is complete.

2. Whether the chip has defects such as solder joint contamination, solder joint damage, crystal grain damage, grain cutting size, and grain cutting inclination.

Damage to the LED chip directly leads to LED failure, so it is important to improve the reliability of the LED chip. In the evaporation process, it is sometimes necessary to fix the chip with a spring clip, so that a pinch is generated. If the development of the yellow light is incomplete and the mask has holes, there will be residual metal in the light-emitting area. In the pre-stage process, various processes such as cleaning, evaporation, yellow light, chemical etching, fusion, grinding, etc. must use tweezers and flower baskets, carriers, etc., so there will be scratches of the die electrodes.

Effects of electrode pads of the chip: the chip is not deposited solid electrode itself, resulting in damage or falling off after the wire electrode; chip electrodes themselves poor solderability, solder balls can lead Weld; cause improper storage electrode chip surface oxidation, surface contamination Etc., slight contamination of the bonding surface can affect the diffusion of metal atoms between the two, causing failure or solder joints.

3. Defect search in the epitaxial region of the chip

LED epitaxial wafer in a high Wen Zhangjing process, the substrate, the remaining deposition MOCVD reaction chamber, the peripheral gas introduction and Mo sources are impurities that penetrate the epitaxial layer can prevent gallium nitride crystal nucleation to form various Various epitaxial defects eventually form tiny pits on the surface of the epitaxial layer, which also seriously affect the crystal quality and performance of the epitaxial film material. Jinjian developed detection method for detecting rapid identification chip epitaxial defect region, at low cost, quickly detected 80% of the epitaxial layer, the epitaxial defective chip, to help customers choose a high quality LED wafer, chip.

4. Chip process and cleanliness observation

Electrode processing is the key process for making LED chips, including cleaning, evaporation, yellowing, chemical etching, fusion, and grinding. It will come into contact with many chemical cleaning agents. If the chip cleaning is not clean enough, it will cause harmful chemicals to remain. These harmful chemicals react electrochemically with the electrodes when the LEDs are energized, resulting in dead lights, light decay, darkness, and blackening. Therefore, identifying chip chemical residues is critical to LED packaging plants.

Case Study (1):

A customer's red light bead found a dark problem, but has been unable to find a reason, commissioned Jin Jian analysis of the reasons for failure. After a series of instrumental analysis to eliminate the packaging reasons, Jinjian tested the bare crystals supplied by the supplier and found that the light-emitting areas of each chip have different areas of pollutants. The energy spectrum analysis results show that the pollutants contain C and O. Two elements indicate that the contaminant is organic. We recommend that customers pay attention to the chip manufacturer's production process specifications and workshop environment assessment, and strengthen the incoming inspection of the chip.

Case Study (2):

A batch of lamp beads produced by a customer has a leakage problem, and the gold medal is entrusted to find the cause. Jin Jian used scanning electron microscopy to identify the cause of leakage of the lamp bead due to electrostatic breakdown and the bare crystal provided by the supplier. It was found that there were a lot of black voids on the surface of the epitaxial layer. These defects indicate that the epitaxial layer crystal quality is poor, PN junction. There are defects inside. The discovery of the void helps the client to identify the responsible party responsible for the incident and recover the loss for the customer.

Note: LED chip manufacturing process

LED chip manufacturing process flow chart

Epitaxial waferâ†’cleaningâ†’plating transparent electrode layerâ†’transparent electrode pattern lithographyâ†’corrosionâ†’debondingâ†’platform pattern lithographyâ†’dry etchingâ†’degractionâ†’annealingâ†’SiO2 depositionâ†’window pattern lithographyâ†’SiO2 corrosionâ†’degglomerateâ†’ N-pole pattern lithography â†’ pre-cleaning â†’ coating â†’ stripping â†’ annealing â†’ P-pole pattern lithography â†’ coating â†’ stripping â†’ grinding â†’ cutting â†’ chip â†’ finished product testing.

After growing into an epitaxial wafer, the next step is to make an electrode (P pole, N pole) on the LED epitaxial wafer, and then start cutting the LED epitaxial wafer with a laser or diamond knife, after manufacturing the chip, and then on the wafer. Nine points are extracted from different locations for parameter testing. This is mainly to test the voltage, wavelength, and brightness. The wafer that meets the normal shipping standard parameters continues to operate in the next step. If it does not meet the requirements, it will be disposed of separately. After the wafer is diced into chips, 100% visual inspection (VI/VC) is required, and the operator should perform visual inspection under a microscope magnified 30 times. The chip is then fully automated, selected, tested, and classified using a fully automated sorter based on different voltage, wavelength, and brightness prediction parameters. Finally, the LED chip is inspected (VC) and labeled. Chip type, lot number, quantity, and photometric statistics are recorded on the label and attached to the back of the glossy paper. The chip on the blue film will be the final inspection test. The visual inspection standard is the same as the first time, ensuring that the chips are neatly arranged and qualified. This is the manufacturing process of the LED chip.

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