In-situ Thickness Measurements by Laser Reflectance for Improved MOCVD Process Development Pratheep Balendra Justin Daniel Meyer April 14, 1997 Senior Design Project Stevens Institute of Technology

Plan l Chemical Vapor Deposition: basic problem l Thickness measurement by Laser Reflectance –Principle –Model –Equipment design l Growth of Yttrium Oxide (Y 2 O 3 ) –Laser Reflectance attenuation –Effect of ambient pressure –Argon (carrier) flow rate

Development of New CVD Materials Heater & SiC Precursor, Carrier, and Oxygen Exhaust l CVD process –Heat substrate –Introduce reactants –Cool substrate –Determine growth l Inability to determine growth without substrate removal l Time intensive

Development of New CVD Materials Heater & SiC Exhaust FT IR: Reaction Products IR Spectroscopy (C. Dubourdieu) Chemical Analysis Gas Phase Surface

Development of New CVD Materials Heater & SiC Exhaust Laser Reflectance Real-time Thickness Measurement

In Situ Laser Reflectance Principle l Problems –Electrical noise –Vibration –Windows –Absorption l Solutions –Smooth substrate –Signal processing –Model To PC S Beam Splitting Cube HeNe Laser BE-7 Windows 95% Transmission Film Substrate P  Brewster's angle

System Refinements l Reduction of electrical noise through filtering cicuit and electronic shielding l Virtual elimination of mechanical vibration through component isolation l Design and fabrication of optical window cup –Evenly distributed stresses –Allows use of optically flat windows

Physical Model l Signal attenuation l Temperature dependence of n l Film growth changes the Brewster angle Thickness Reflectance

Experiment Control MOCVD Reactor Signal Amplifier Detector D/A A/D Process Controls HeNe Laser Heater Substrate Senior Design Rocks!

Shortened Development Time of MOCVD Materials l Variation of process parameters on new material l 1/2 hour runs under each scenario l Compilation of growth data over a week –Over 192 combinations –Presently 10 per week l Analysis of growth trends and refinement of parameters (repeat process)

Summary l Successful execution of Laser Reflectance to measure film thickness in real-time l Yttrium oxide growth- increase ambient pressure and powder density l Through process parameter variation, a growth database will be created in a short time l Trend evaluation will result in an “Operating Window” for CVD of the investigated material