Numerical Investigation On AlN MOCVD Growth

Aluminum nitride?AlN?is an important?-?compound semiconductor thin film material,which is widely used in high-brightness LED,ultraviolet detector and high-frequency high-power devices.Metal organic vapor chemical deposition?MOCVD?is the main method to grow AlN.In the MOCVD growth of AlN,the strongest chemical bond energy between Al-N leads to strong parasitic reactions in the gas phase,resulting in a large number of nanoparticles,which not only wastes the reaction source,but also affects the crystal quality.Therefore,it is very important to study the transport process and gas phase reaction of AlN growth in order to improve the film growth efficiency and quality.For planetary and high-speed rotating disk reactors,the growth of AlN under different geometric structures and operating parameters of the reactor was numerically simulated,and the geometric structure and inlet design of the reactor were optimized to obtain better AlN film quality and higher growth rate.The main contents of this paper are as follows:1.Around the growth of AlN-MOCVD,the principle,reactor types,transport process,chemical reactions,research status and development trend of MOCVD are summarized in detail.According to previous experience,the main chemical reaction kinetics model of AlN-MOCVD was determined.The gas transport and chemical reactions of AlN-MOCVD growth were numerically simulated by VR-Nitride software.2.Aiming at the influence of the geometric structure of the planetary reactor on the gas phase reaction path and AlN growth rate,numerical simulation research is carried out from the aspects of reactor inlet mode,inlet quantity,outlet position and size.The results show that:?1?The reaction tends to pyrolyze in an inverted two-inlet planetary reactor,and the growth rate of AlN film is higher but the uniformity is poor.On this basis,optimizing the position of the separator can improve the uniformity of the film.?2?In both triple and five-inlet planetary reactors,the reactions tend to be additive paths.The growth rate of AlN thin films is increased with the increase of the number of inlets,while the uniformity of the thin films is also ensured.?3?Changing the outlet position to the vertical outlet?outlet direction downward?,the reaction path is more inclined to the pyrolysis path than the horizontal outlet,the growth rate is higher,and the nanoparticles are easier to be discharged from the reaction.3.In view of the influence of the operating parameters in the planetary reactor on the gas phase reaction path and growth rate of AlN growth,numerical simulation research is carried out from three aspects of pressure,carrier gas flow rate and V/III ratio.The research shows that:?1?the increase of pressure enhances the addition reaction and weakens the pyrolysis path.?2?When the carrier gas flow is small,the reaction tends to the addition path;However,at high carrier gas flow rate,TMAl is more prone to pyrolysis reaction,and the concentration distribution of growth precursor presents an elongated shape,which makes the film more uniformly and AlN grows at a higher rate.?3?During the increase of TMAl flow rate,the trend of reaction path is similar to that of addition path.At low TMAl flow rate,the growth rate of AlN increases linearly with TMAl flow rate.Low NH₃ flow and high TMAl flow can reduce parasitic reaction and obtain higher AlN growth rate.4.According to the optimization of the geometry structure and inlet design of the high-speed rotating disk reactor,the simulation is carried out from the three aspects of the height of the reaction chamber,the number of inlets and the length of the inlet separator respectively.It is found that reducing the height of the reaction chamber can make Al-containing particles closer to the substrate and increase the growth rate of AlN.On this basis,the reactor is designed as a10-ring concentric ring inlet with the length of separator is 5 mm.At this time,Al-containing particles are closer to the substrate,so the growth rate is significantly increased.When the length of the separator is further increased to 10 mm,the growth rate of AlN increases slightly,but the uniformity of the film becomes worse.Therefore,the geometry structure and inlet design are optimized:the height of the reaction chamber is reduced to 20 mm,10 rings of concentric ring inlets are added,and the length of the partition plate is designed to be 5 mm.After optimization,the pyrolysis path in the reactor is enhanced,but the reaction is still dominated by the addition path.