Numerical Investigation On AlN MOCVD Growth

AlN single crystal thin film is an important third generation semiconductor material,which has the characteristics of wide band gap,radiation resistance,high temperature resistance and is widely used in the preparation of semiconductor light-emitting devices and power devices.Metal organic chemical vapor deposition(MOCVD)is a key technology for the growth of AlN thin films.In MOCVD growth of AlN,the gas phase prereaction between Al(CH₃)₃(abbreviated as TMAl)and NH₃containing N precursor is easy to occur,resulting in low growth rate and poor film quality.The growth rate and mass of AlN films are directly related to the gas reaction path.This paper focuses on three main MOCVD reactors:CCS reactor,RDR reactor and planetary reactor.Numerical simulation study on the influence of the operating parameters and geometric parameters of the three reactors on the growth of AlN,and then optimization of the growth parameters of the reactor.The main contents of this paper are as follows:Firstly,according to previous studies,a chemical reaction path model for MOCVD growth of AlN was summarized,and a 2D model of the reactor was established.VR-Nitride software was used to conduct coupling simulation of transport process and chemical reaction for MOCVD growth of AlN thin film.Secondly,the effects of operating parameters on the growth rate and chemical reaction path of AlN were studied in CCS reactor.It was found that under the conditions of low V/III ratio,high H₂flow rate,high inlet temperature,high low pressure and low chamber height,the reaction path is the coexistence of addition path and pyrolysis path,and the film growth rate is high.On the contrary,the chemical reaction pathway is dominated by the additive pathway.When the V/III ratio is high,the concentration of Al particles is low,which may be due to the large NH₃flow rate which takes Al particles out of the growth area.The high H₂flow rate promotes the pyrolysis path because the precursor is diluted by H₂,which weakens the parasitic reaction.The effect of high inlet temperature on chemical reaction is due to the change of temperature gradient.However,the low pressure and low chamber height decrease the frequency of particle collisions,which weakens the parasitic response.Thirdly,the effects of operating parameters on the growth rate and chemical reaction path of AlN were studied in RDR reactor.It is found that high growth rate of AlN films can be obtained under high low pressure,low V/III ratio,1300 K substrate temperature,high substrate speed and high carrier gas H₂flow rate.Pyrolysis reaction intensity is weak,the contribution to the film growth can be ignored,the reaction path is mainly additive path.Under high pressure,the buoyancy convection is intensified in the reactor,and Al particles cannot reach the substrate surface smoothly.At high substrate rotation speed,a circular vortex is easily formed above the substrate,and the concentration range of the reaction precursor is compressed and close to the substrate surface,which improves the growth rate of AlN films.The high temperature substrate will cause the Al particles adsorbed on the substrate surface to break the chemical bonds and desorption migration.Under high V/III ratio,the NH₃flow rate is larger and the parasitic reaction is serious.High carrier gas H₂flow dilutes the source gas and inhibits parasitic reaction.Finally,the position of the substrate in planetary reactor was numerically simulated.The average growth rate of AlN is increased in the reactor with inverted and tilted substrates,and the film growth uniformity is good.The chemical reaction path in the conventional substrate reactor is dominated by the addition reaction,and the peak concentration of MMAl in the inverted substrate reactor is in the same order of magnitude(?10^-4)as the peak concentration of the amino compound DMAlNH₂and the adduct[DMAlNH₂]₂.The chemical reaction path is completed by the addition path and the pyrolysis path.The average growth rate of AlN films can be increased by adding and pyrolysis pathways.