(1) Domestic MOCVD equipment is still in the stage of technical tracking, and the level of equipment industrialization cannot meet the production needs. At present, the maximum capacity of MOCVD equipment developed in China is 6 pieces (48 GaN-MOCVD). However, as of June 5438+February, 2007, among the latest MOCVD equipment imported from abroad, Ai Siqiang has imported 42 planetary reactors (AIX2800G4 HT) and 30 CCS reactors (CRIUS).
Due to the gap in production capacity, the production cost of small batch MOCVD equipment epitaxial wafers is high, which greatly reduces the cost performance of the equipment, making the domestic equipment lag behind just after development. The minimum requirement of batch production enterprises for single batch capacity is more than 30 pieces.
(2) High equipment cost and high application risk. Most manufacturers tend to buy imported equipment with mature technology. MOCVD equipment is expensive, and the price of producing MOCVD equipment is as high as1000 ~ 20 million yuan. Manufacturers are very cautious about purchasing this kind of equipment, and are more willing to purchase imported equipment with mature technology and perfect after-sales service, which makes the promotion of domestic MOCVD equipment in an embarrassing situation.
(3) Independent innovation needs to be strengthened, and domestic MOCVD equipment faces patent barriers.
At present, the research and development of MOCVD equipment in China is still in the stage of "digestion and absorption", while the mainstream foreign commercial models have established strict patent protection. For example, AstraZeneca's planetary reactor, Thomas Sow's CCS (Tightly Coupled spray head Reactor), VEECO's turbo-disk reactor and Japanese SANSO's dual/multi-beam airflow (TF) reactor are all unique patented technologies, and the industrialization of domestic MOCVD equipment is facing the test of patent barriers.
Third, the development trend and production efficiency
1, production efficiency and cost overview
MOCVD technology is quite mature in the world. The mainstream equipment has increased from 6-8 pieces in 2003, 12 pieces in 2004, 15 pieces in 2005 and 2 1-24 pieces in 2006 to 42, 45 and 49 pieces (49 pieces of 2-inch substrates can be installed at a time). With the continuous expansion of epitaxial furnace capacity, the unit production cost of LED epitaxial wafer production enterprises has dropped rapidly and greatly. At present, the minimum requirement of mass production enterprises for single batch capacity is more than 30 pieces.
2, 4 inch MOCVD equipment will become the mainstream.
At present, the epitaxial manufacturers in Taiwan Province Province have the technical ability to produce 4-inch and 6-inch, but for cost reasons, most manufacturers in Taiwan Province Province still take 2-inch MOVCD equipment as the main production line; Most European, American and Korean manufacturers are already using 4-inch MOVCD equipment.
The market predicts that once the material cost of 4-inch epitaxial wafer collapses sharply (the current cost price of 4-inch epitaxial wafer is about 4 times that of 2-inch epitaxial wafer), 2-inch MOCVD equipment will be gradually replaced by 4-inch epitaxial wafer.
Ai Siqiang and SemiLEDs jointly developed a 6-inch blue LED chip in May 2009. On the structure of 6x6-inch AIX 2800G4 HT MOCVD reactor, the output is increased by about 30% (compared with the traditional 42x2-inch structure), which not only has good uniformity, but also reduces the edge effect. But at present, most of the difficulties still lie in the high price of 6-inch substrate and the challenge of epitaxial wafer cutting technology.
In fact, for MOCVD and MBE technology, there is not much difference in epitaxial structure and device performance. The most attractive part of MOCVD technology lies in its universality. As long as the appropriate metal-organic source can be selected, epitaxial growth can be carried out. Moreover, as long as the uniform distribution of air flow and temperature is ensured, a large area of uniform materials can be obtained, which is suitable for large-scale industrial production.
The main disadvantages of MOCVD technology are mostly related to the reaction sources used. First of all, the used organometallic compounds and hydride sources are expensive. Secondly, some sources are flammable, explosive or toxic, so they are dangerous. Moreover, the products after the reaction need to be treated harmlessly to avoid environmental pollution. In addition, because the source used contains other elements (such as C, H, etc. ), the reaction process needs to be carefully controlled to avoid introducing unintentionally doped impurities.
Generally speaking, the process of MOCVD growth can be described as: introducing a reaction source material with precisely controlled flow rate into a reaction chamber of timely or stainless steel under the action of a carrier gas (usually H2 or N2 in some systems), and growing an epitaxial layer after the upper surface of a substrate placed on a heating pedestal reacts. After the reaction, the residual tail gas is blown out of the reaction chamber, and the particles and toxicity are removed by the tail gas treatment device and then discharged from the system. The working principle of MOCVD is shown in the figure.
MOCVD growth equipment can be simply divided into the following four parts.
(1) gas operating system:
The gas operation system includes all valves, pumps, various equipment and pipelines used to control the gas flow, as well as the mixture of group III metal organic sources and group V hydride sources. Among them, the most important part is to precisely control the amount of raw materials introduced into the reaction chamber for reaction. It mainly includes a mass flow controller (MFC) to control the flow, a pressure controller (PC) to control the pressure and thor malbath to control the temperature of the metal-organic source.
(2) reaction chamber:
The reaction chamber is the core component of MOCVD growth system, and the design of the reaction chamber has a vital influence on the growth effect. Different MOCVD equipment manufacturers have different designs for the reaction chamber. But the ultimate goal is the same, that is, to avoid off-wall jet and turbulence in the reaction chamber and ensure only laminar flow, so as to realize the uniform distribution of air flow and temperature in the reaction chamber, which is conducive to uniform growth in a large area.
3) heating system:
There are three main heating methods for substrates in MOCVD system: radio frequency heating, infrared radiation heating and resistance heating. In RF heating mode, graphite matrix is heated by RF coil through inductive coupling. This heating form is often used in large reaction chambers, but the system is usually too complicated. In order to avoid the complexity of the system, infrared radiation heating is usually used in a slightly smaller reaction chamber. The thermal energy generated by tungsten halogen lamp is converted into infrared radiation energy, and the graphite base absorbs this radiation energy and then converts it back into thermal energy. In the resistance heating mode, the heat energy is provided by the current flowing through the metal base.
(4) Tail gas treatment system:
Because most of the sources used in MOCVD system are flammable and explosive, and the hydride source in rain is highly toxic, it is necessary to treat the tail gas after the reaction. The usual treatment method is to remove particles (such as p, etc. ) is separated from the tail gas by a particle filter, and then introduced into a gas scrubber for detoxification with a detoxification solution. Another way to detoxify is to use a combustion chamber. The combustion chamber is equipped with a high-temperature furnace, which can pyrolyze and oxidize the substances in the tail gas at 900 ~ 1 000℃ to achieve harmlessness. The products produced by the reaction are deposited on the inner wall of the quartz tube and can be easily removed.