Ik-Tae Im

Improvement of TiN Flow Modulation Chemical Vapor Deposition from TiCl4 and NH3 by Introducing Ar Purge Time

TiN films were deposited by using TiCl4/NH3 flow modulation chemical vapor deposition (FMCVD). FMCVD consists of repetitive TiN deposition periods by TiCl4/NH3, each of which is followed by Cl reduction period. TiN deposition periods are typically 3 s and Cl reduction periods are 1 s. The effect of the number of deposition/reduction cycles and the effect of the partial pressure of TiCl4 and NH3 on film uniformity and resistivity were investigated. For a total reduction period of 100 s, increasing the number of reduction periods from 100×1-s periods to 300×0.33-s periods decreased the step coverage. This decrease in coverage was due to residual TiCl4 during the Cl reduction period by NH3 that cleared out TiCl4 at a constant rate, independent of the length of the period of reduction cycle. An Ar purge cycle was used between the deposition and reduction cycles to allow the residual TiCl4 to clear out before the NH3 was used for the film reduction cycle. This significantly improved the film step coverage from 50% to over 90%. The minimum film resistivity occurred when the NH3 partial pressure was 0.25 Torr. NH3 partial pressure less than 0.25 Torr inhibited film reduction, and NH3 partial pressure higher than 0.25 Torr enhanced the deposition rate, which also inhibited film reduction. By using the optimum conditions determined in this study, we could obtain TiN films that had film resistivity of about 240 µΩcm and step coverage of about 98% at 410°C.

Effects of thermal contact resistance on film growth rate in a horizontal MOCVD reactor

Effects of thermal contact resistance between heater and susceptor, susceptor and graphite board in a MOCVD reactor on temperature distribution and film growth rate were analyzed. One-dimensional thermal resistance model considering thermal contact resistance and heat transfer area was made up at first to find the temperature drop at the surface of graphite board. This one-dimensional model predicted the temperature drop of 18K at the board surface. Temperature distribution of a reactor wall from the three-dimensional computational fluid dynamics analysis including the gap at the wafer position showed the temperature drop of 20K. Film growth rates of InP and GaAs were predicted using computational fluid dynamics technique with chemical reaction model. Temperature distribution from the three-dimensional heat transfer calculation was used as a thermal boundary condition to the film growth rate simulations. Temperature drop due to the thermal contact resistance affected to the GaAs film growth a little but not to the InP film growth.

Multiscale Model of the GaAs MOVPE Process for the Fast Numerical Simulation

As a successive work to clarify the film growth kinetics of GaAs, a new lumped model for computer simulation of film growth during MOCVD process is proposed. The film growth process in a horizontal reactor using trimethylgallium (TMGa) and tertiarybutylarsine (TBAs) is considered. Analyzing methodologies at two different scales have been used to revise our previous simulation model. One is the micro-scale analysis using a selective-area growth method and the other is the reactor-scale macro analysis using numerical simulation. Species concentration profiles are obtained from the macro-scale computational fluid dynamics study incorporated with chemical reactions. Surface reaction rate constants are extracted from the selective-area growth experiments. From the multi-scale analysis that combined the two-scale analyses, surface formation from the source gas, TMGa, is included to the previous model. The kinetic data for the surface reaction of TMGa are deduced from the quantitative analysis for the species concentrations from both of the analyses. Simulation results using the new model show that monomethylgallium is the major source of film deposition, but deposition from TMGa is important in the upstream region of the reactor.

Study on the surface reaction kinetics of InGaAs related materials MOCVD through analyses of growth rate distribution in the selective area growth

Wide stripe selective area growth was proposed as a tool for getting information on surface kinetics in the metalorganic chemical vapor deposition (MOCVD). GaAs and InP were grown over patterned substrates using SiO/sub 2/ mask. The characterized growth-rate enhancement profiles were successfully fitted with 2-dimensional simulation taking only gas phase diffusion into account except for the profiles in the vicinity of mask edge, which seemed to reflect surface diffusion. Considering that gas phase diffusion coefficient can be estimated by observing a reactor-scale growth-rate profile, the only parameter determining growth-rate enhancement profile was sticking probability of a film precursor on the surface of GaAs. The estimated sticking probability was 0.05 - 0.4 for GaAs and 0.26 - 0.5 for InP. The information on the surface reaction was gathered in various conditions, such as temperature, group V partial pressure. The study on polycrystalline growth over mask was also carried out using the information of SAG analysis. It is shown that polycrystals was generated when the concentration of a film precursor just above the mask exceeded a critical value. This information is important not only for the design of selective area growth process but also for constructing more realistic reaction model of MOCVD.