Silicon substrate LED chip manufacturing process

Since 1993, the world's first GaN based blue LED came out, the development of LED manufacturing technology. At present, the commercialization of GaN based LED is made on sapphire substrate or SiC substrate. But sapphire due to the high hardness, conductivity and poor thermal conductivity and other reasons, bring a lot of inconvenience to the post processing and application of SiC devices, the same inadequacies of high hardness and high cost, and relatively inexpensive Si substrate with excellent thermal conductivity properties and mature technics and other advantages, so Si substrate GaN based LED manufacturing technology is widely concerned by the industry.

Japan Nichia monopoly on sapphire based GaN LED patented technology, the United States CREE company a monopoly on SiC substrate GaN based LED technology patent. Therefore, the research and development of GaN based LED production on other substrates has become a hot topic in the world. Nanchang University in cooperation with the Xiamen Hualian Electronics Co., bear the National 863 project "power GaN based LED Si substrate manufacturing technology based on the development, after nearly three years of development, has been adopted by the Ministry of science and technology project approval.

1 Si substrate, LED chip manufacturing

1.1 technical route

The growth of GaN on Si substrate, making LED blue chip.

Process: grown on Si substrate with AlN buffer layer, N type, GaN growth growth of InGaN/GaN multiple quantum well light emitting layer, p layer, AIGaN growth and growth of P type GaN layer, bonding with Ag reflecting layer and the formation of P type ohmic contact electrode, substrate and buffer layer, remove the peel n type Si doped layer ohmic contact electrode, and the passivation, dicing, alloy testing and packaging.

1.2 main manufacturing process

Adopts ThomasSwanCCS low voltage MOCVD system in 50mmsi (111) growth of GaN based MQW structure on a substrate. Using Trimethylgallium (TMGa) for the Ga source, three methyl aluminum (TMAI) as Al source, trimethyl indium (TMIn) as In source, ammonia (NH3) as N source, silane (SiH4) and two (CP2Mg) were used as Mao mg n type and P type dopant. At first, Si (111) AlN buffer layer on the substrate epitaxial growth, followed by growth of N type GaN layer, InGaN/GaN multiple quantum well light emitting layer, P AlGaN layer, P GaN layer, and then in the P surface production of Ag mirror and the formation of P type ohmic contact, then the epitaxial layer transfer onto a conductive substrate by hot pressure welding method, and then the Si corrosion corrosion of Si substrate removal and exposure of N type GaN layer, using the coarsening of N type surface alkali corrosive liquid after the formation of N type ohmic contact, thus completing the production of the vertical structure of the LED chip. Figure 1

From structure diagram shows that the Si substrate for flip chip thin film structure, from the bottom to the top is the back of the Au electrode, Si substrate, bonding metal, metal mirror, GaN (P ohmic electrode) epitaxial layer, rough surface and Au electrode. The structure chip has the advantages of vertical distribution of electric current, high thermal conductivity of the substrate and high reliability; the back surface of the light-emitting layer is a metal reflector, and the surface of the light-emitting layer is provided with a coarse structure.

1.3 key technology and innovation

Si GaN light emitting diode substrate, although the manufacturing cost of LED is greatly reduced, but also solve the problem of patent monopoly, but compared with sapphire and SiC, grown on Si substrate GaN is more difficult, because between the lattice mismatch and thermal mismatch is greater, Si and GaN the thermal expansion coefficient difference will also lead to GaN membrane cracking, the lattice constant difference will cause a high density of dislocations in GaN epitaxial layer; another Si substrate LED may also be due to the heterojunction barrier 0.5V between Si and GaN and the turn-on voltage increased and the crystal integrity caused by poor P type doping leads to low efficiency and series resistance increased, and Si absorption of visible light will reduce the external quantum efficiency of LED. Therefore, in view of the above problems, in-depth study and the light emitting layer dislocation density control technology, chemical stripping substrate transfer technology and high reliability high reflection characteristics of P type GaN ohmic electrode preparation technology and bonding technology, high technology design vertical structure optimization chip epitaxial material surface roughening technology, graphics technology, the substrate the efficiency of light, in a large number of experiments and exploration, to solve many technical problems, the ultimate success of the preparation of size 1mm * 1mm, blue light output power is greater than 380mW, the wavelength of the light 451nm, working voltage of 3.2V under 350mA light emitting chip, finish the project standard. The key technology and technical innovation are the following aspects.

(1) using a variety of online control technology, reduces the epitaxial material in edge and screw dislocations, improved between Si and GaN of the lattice mismatch and thermal mismatch, solve the cracking problem of GaN single crystal film, the crack free GaN epitaxial film thickness greater than 4 mu m.

(2) by introducing AIN, AlGaN multilayer buffer layer, greatly ease the Si substrate GaN epitaxial material stress, and improve the quality of the crystals, so as to improve the luminous efficiency.

(3) between the concentration of structure and optimization design of n-GaN layer in Si quantum well / barrier interface growth conditions, and reduces the chip reverse leakage current and improve the antistatic property of chip.

(4) by adjusting the P type layer of magnesium concentration structure, reduce the working voltage of the device; through the optimization of P GaN thickness, improve the efficiency of the chip.

(5) by optimizing the structure and distribution of doped epitaxial layer, reduce series resistance, reduce working voltage, reduce heat generation rate, enhance the reliability and improve the working efficiency of LED devices.

(6) multilayer metal structure, and at the same time, ohmic contact, reflection properties, bonding properties and reliability, optimization of welding technology, solves the silver