Manufacturing process of LED chips
The main purpose of LED chip manufacturing is to manufacture effective and reliable low-ohmic contact electrodes that can meet the minimum voltage drop between contactable materials and provide pressure pads for bonding wires, and at the same time meet as much light output as possible. The main process is shown in Figure 27-1
Epitaxy material inspection
cleaning
Coating
photolithography
alloy
warehousing
Package
detect
cut
The coating process generally uses the vacuum evaporation method, which mainly uses resistance heating or electron beam bombardment heating method under the high vacuum of 1.33*10-4pa to melt the material under low pressure into metal vapor and deposit on the surface of the semiconductor material. Generally, P type is used. The most common contact metals include AuBe, AuZn, etc. The contact metals on the N side often use AuGeNi alloys. The most common problem in the coating process is the cleaning of the semiconductor surface before the coating. The coating is not strong, and the alloy layer formed after coating needs to expose as much of the light-emitting area as possible through the photolithography process, so that the remaining alloy layer can meet the requirements of effective and reliable low-ohm contact electrodes and wire bonding pads. The most commonly used shape is a circle. For the back, if the material is transparent, a circle should also be engraved.
After the photolithography process is completed, an alloying process is required. Alloying is usually carried out under H2 or N2 protection. The time and temperature of alloying is usually based on the properties of the semiconductor material. Factors such as the form of the alloy furnace determine, usually the alloying temperature in the red-yellow LED material is between 350 degrees and 550 degrees. After successful alloying, the I-V curve between the two adjacent electrodes on the semiconductor surface is usually in a linear relationship. Of course, if the semi-green chip is more complicated in the electrode process, the growth of the passivation film and the plasma etching process must be increased.
The red and yellow LED die cutting method is similar to the silicon wafer die cutting process. Commonly used are diamond wheel blades. The blade thickness is generally 25um. For the blue-green chip process, since the substrate material is Al2O3, it must be scratched with a diamond knife and then broken.
The detection basis of the light-emitting diode chip generally includes testing its forward conduction voltage, wavelength, light intensity, and reverse characteristics.
Chip finished packaging generally includes white film packaging and blue film packaging. The white film package is generally attached to the film with the surface of the pad, and the chip spacing is also large and suitable for manual operation. The blue film packaging is generally glued to the film on the back. Smaller chip pitches are suitable for automata.
