Application of Microscope in Strategic Emerging Industry LED
1. The specific application of Leica optical microscope and scanning electron microscope in LED upstream substrate material (sapphire material):
1. Introduction of sapphire substrate material
Because sapphire has good insulation, low dielectric loss, high temperature resistance and corrosion resistance. Good thermal conductivity, high enough in mechanical strength. And can be processed into a flat surface. The light transmission band is wide. Therefore, it is widely used in many fields of industry, national defense and scientific research. At the same time, it is also a good substrate material for light-emitting diodes with a wide range of uses. The resulting light-emitting diode is the most promising semiconductor light-emitting device substrate material for the sapphire substrate substrate in the high-brightness light-emitting diode family of the next-generation fluorescent light source. At present, these high-brightness light-emitting diodes have been widely used in advertising, traffic lights, instrument lights; and operating lights and other fields. With the increasing application of high-brightness light-emitting diodes.
Sapphire (Sapphire) is a single crystal of alumina, also known as corundum. Sapphire crystal has excellent optical properties, mechanical properties and chemical stability, high strength, high hardness, and erosion resistance, and can work under harsh conditions close to 2000°C. According to research, there are only four kinds of substrate materials that can be applied to LEDs at present (see Table 1 below). As an important technical crystal, sapphire has formed a relatively fashionable and mature application in the LED industry.
2. Application
The abnormal birefringence of sapphire crystals can be identified using Leica's polarizing microscope. Under certain circumstances, with the help of the conoscopic lens, the interferogram of the crystal can be observed to determine the axiality of the crystal, which is used to observe whether the direction of each wafer is uniform, so as to judge whether the substrate is good or bad.
2. Application of Leica microscope and scanning electron microscope in the production of LED epitaxial wafers and the preparation process of LED chips
1. Introduction of LED Epitaxial Wafer
The basic principle of LED epitaxial wafer growth is: on a substrate (mainly sapphire, SiC, Si) heated to an appropriate temperature, the gaseous substance InGaAlP is transported to the substrate surface in a controlled manner, and a specific single crystal film is grown. . At present, the LED epitaxial wafer growth technology mainly adopts metal organic chemical vapor deposition method (MOCVD)
2. LED chip introduction
LED chips, also known as LED light-emitting chips, are the core components of LED lights, which refers to the P-N junction. Its main function is to convert electrical energy into light energy, and the main material of the chip is monocrystalline silicon. Semiconductor wafer is made up of two parts, and a part is P-type semiconductor, and hole occupies an leading position in it, and the other end is N-type semiconductor, and here mainly is electron. But time these two kinds of semiconductors couple together, between them, just form a P-N junction. When electric current acts on this chip by wire time, electron will be pushed to P district, and in P district, electron is with hole recombination, then will send energy with the form of photon, the principle of LED luminescence that Here it is. And the wavelength of light i.e. the color of light, be determined by the material forming P-N junction.
3. Application:
a) Using a scanning electron microscope to detect the dislocation corrosion morphology information of the crystal plane after the growth of the epitaxial wafer;
The meaning provided by the dislocation corrosion morphology of the crystal plane: the dislocation corrosion of each sample has different shapes and is determined by the point group of the crystal and the structure of the crystal. The role of the chemical etchant is to destroy the interaction bonds between molecules and atoms inside the crystal. The ones with smaller bonds are destroyed first, thus forming corrosion spots of a specific shape. Therefore, good imaging and the perfect presentation of the details of corrosion spots can fully reflect the quality of crystal growth.
Improving the quality of the epitaxial lattice and reducing material defects are the prerequisites for producing high-performance and high-reliability LED devices, otherwise it is difficult to make up for it by other means. The influence of crystal quality of LED epitaxial materials on device reliability is clarified. Through the quality control of epitaxial materials, it is expected to reduce the defect density of materials, improve the crystal quality of epitaxial layers and effectively improve the reliability of LED devices.
b) Chip inspection before packaging: Check the surface of the material with an optical microscope to determine whether there is mechanical damage and pitting, whether the chip size and electrode size meet the process requirements, and whether the electrode pattern is complete.
c) LED chip oxidation thickness: detection techniques include color comparison, edge counting, interference, ellipsometer, engraved needle amplitude meter and scanning electron microscope;
d) Measurement of the junction depth of the chip wafer: the thickness detection of the PN junction depth of the LED chip wafer by the scanning electron microscope
e) The application of scanning electron microscopy in the research of surface roughening technology in the etching process of LED chips: the surface roughening technology solves the problem of total reflection of light with an incident angle greater than the critical angle because the refractive index of semiconductor materials (average 3.5) is greater than that of air. The loss caused by the exit. The emission of light on the roughened surface is very random, and a large number of experiments are needed to study the influence of roughness and roughness scale on the light emission rate. When light enters the air with a low refractive index from GaP, the material of the LED window layer with a high refractive index, total reflection will occur, and a large amount of outgoing light will be lost. The surface roughening method can suppress total reflection and improve light extraction efficiency. The scanning electron microscope can directly observe the surface structure of the sample after surface roughening, and compare the roughness of the surface before and after roughening. The scanning electron microscope has a large depth of field, and the image is full of three-dimensionality. It can observe the three-dimensional island structure on the roughened surface.
