How are LED chips manufactured?

What is an LED chip? So what are its characteristics? The main purpose of LED chip manufacturing is to manufacture effective and reliable low ohm contact electrodes, and to meet the relatively small voltage drop between contactable materials and provide pressure pads for soldering wires, while maximizing the amount of light output. The cross film process generally uses vacuum evaporation method. Under a high vacuum of 4Pa, the material is melted by resistance heating or electron beam bombardment heating method, and BZX79C18 is transformed into metal vapor and deposited on the surface of the semiconductor material under low pressure.
The commonly used P-type contact metals include alloys such as AuBe and AuZn, while the contact metal on the N-side is often made of AuGeNi alloy. The alloy layer formed after coating also needs to be exposed as much as possible in the luminescent area through photolithography process, so that the remaining alloy layer can meet the requirements of effective and reliable low ohm contact electrodes and solder wire pressure pads. After the photolithography process is completed, it also needs to go through the alloying process, which is usually carried out under the protection of H2 or N2. The time and temperature of alloying are usually determined by factors such as the characteristics of semiconductor materials and the form of the alloy furnace. Of course, if the blue-green and other chip electrode processes are more complex, it is necessary to add passivation film growth, plasma etching processes, etc.
In the manufacturing process of LED chips, which processes have a significant impact on their optoelectronic performance?
Generally speaking, after the completion of LED epitaxial production, its main electrical performance has been finalized, and chip manufacturing does not alter its core production nature. However, inappropriate conditions during the coating and alloying process can cause some electrical parameters to be poor. For example, low or high alloying temperatures can cause poor Ohmic contact, which is the main cause of high forward voltage drop VF in chip manufacturing. After cutting, some corrosion processes on the edges of the chip can be helpful in improving the reverse leakage of the chip. This is because after cutting with a diamond grinding wheel blade, there will be a lot of residual debris and powder at the edge of the chip. If these particles stick to the PN junction of the LED chip, they will cause electrical leakage and even breakdown. In addition, if the photoresist on the surface of the chip is not peeled off cleanly, it will cause difficulties in front soldering and virtual soldering. If it is on the back, it will also cause a high pressure drop. During the chip production process, surface roughening and trapezoidal structures can be used to increase light intensity.
Why do LED chips need to be divided into different sizes? What is the impact of size on LED optoelectronic performance?
LED chips can be divided into low-power chips, medium power chips, and high-power chips based on power. According to customer requirements, it can be divided into categories such as single tube level, digital level, dot matrix level, and decorative lighting. As for the specific size of the chip, it depends on the actual production level of different chip manufacturers and there are no specific requirements. As long as the process is passed, the chip can increase unit output and reduce costs, and the photoelectric performance will not undergo fundamental changes. The current used by a chip is actually related to the current density flowing through the chip. A small chip uses less current, while a large chip uses more current, and their unit current density is basically the same. Considering that heat dissipation is the main problem under high current, its luminous efficiency is lower than that under low current. On the other hand, as the area increases, the body resistance of the chip will decrease, resulting in a decrease in the forward conduction voltage.

What is the general area of LED high-power chips? Why?
LED high-power chips used for white light are generally seen in the market at around 40mil, and the power used for high-power chips generally refers to an electrical power of over 1W. Due to the quantum efficiency generally being less than 20%, most electrical energy is converted into thermal energy, so heat dissipation is important for high-power chips, requiring them to have a large area.
What are the different requirements for chip technology and processing equipment for manufacturing GaN epitaxial materials compared to GaP, GaAs, and InGaAlP? Why?
The substrates of ordinary LED red and yellow chips and high brightness quaternary red and yellow chips both use compound semiconductor materials such as GaP and GaAs, and can generally be made into N-type substrates. Using wet process for photolithography, and later cutting into chips using diamond grinding wheel blades. The blue-green chip made of GaN material uses a sapphire substrate. Due to the insulating nature of the sapphire substrate, it cannot be used as an LED electrode. Therefore, both P/N electrodes must be made on the epitaxial surface by dry etching and some passivation processes must be performed. Due to the hardness of sapphire, it is difficult to cut into chips with diamond grinding wheel blades. Its manufacturing process is generally more complex than that of GaP and GaAs materials for LED flood lights.

What is the structure and characteristics of a “transparent electrode” chip?
The so-called transparent electrode should be able to conduct electricity and be able to transmit light. This material is now widely used in liquid crystal production processes, and its name is indium tin oxide, abbreviated as ITO, but it cannot be used as a solder pad. When making, it is necessary to first prepare an ohmic electrode on the surface of the chip, then cover the surface with a layer of ITO, and then deposit a layer of solder pads on the ITO surface. In this way, the current coming down from the lead wire is evenly distributed across the ITO layer to each ohmic contact electrode. At the same time, due to the refractive index of ITO being between the air and the refractive index of the epitaxial material, the light angle can be increased, and the light flux can also be increased.

What is the mainstream development of chip technology for semiconductor lighting?
With the development of semiconductor LED technology, its application in the field of lighting is also increasing, especially the emergence of white LED, which has become a hot topic in semiconductor lighting. However, the key chips and packaging technologies still need to be improved, and the development of chips should focus on high power, high light efficiency, and reducing thermal resistance. Increasing power means increasing the usage current of the chip, and a more direct way is to increase the chip size. The commonly used high-power chips are around 1mm x 1mm, with a usage current of 350mA. Due to the increase in usage current, heat dissipation has become a prominent problem. Now, the method of chip inversion has basically solved this problem. With the development of LED technology, its application in the lighting field will face unprecedented opportunities and challenges.
What is an inverted chip? What is its structure and what are its advantages?
Blue light LEDs usually use Al2O3 substrates, which have high hardness, low thermal conductivity, and electrical conductivity. If a formal structure is used, on the one hand, it will bring anti-static problems, and on the other hand, heat dissipation will also become a major problem under high current conditions. At the same time, due to the positive electrode facing upwards, it will block some of the light and reduce the luminous efficiency. High power blue light LEDs can achieve more effective light output through chip flip technology than traditional packaging techniques.
The current mainstream inverted structure approach is to first prepare large-sized blue light LED chips with suitable eutectic welding electrodes, and at the same time, prepare a silicon substrate slightly larger than the blue light LED chip, and on top of it, make a gold conductive layer for eutectic welding and a lead out layer (ultrasonic gold wire ball solder joint). Then, high-power blue LED chips are soldered together with silicon substrates using eutectic welding equipment.
The characteristic of this structure is that the epitaxial layer directly contacts the silicon substrate, and the thermal resistance of the silicon substrate is much lower than that of the sapphire substrate, so the problem of heat dissipation is well solved. Due to the fact that the sapphire substrate faces upwards after inversion, becoming the emitting surface, the sapphire is transparent, thus solving the problem of emitting light. The above is the relevant knowledge of LED technology. I believe that with the development of science and technology, LED lights will become more and more efficient in the future, and their service life will be greatly improved, bringing us greater convenience.

Post time: May-06-2024