Low pressure CVD and PlasmaEnhanced CVD Ronald Curley Thomas McCormack and Matthew Phipps CVD overview Chemical Vapor Deposition Thin films on substrate Chemical oven insert gas deposited film CVD overview Four steps 1 1 2 3 4 Transport gas species to surface Gas species absorption into surface Reaction deposits products Remove unwanted products and leftover reactant CVD overview Velocity ratio molecules s not meters s Mass transport velocity Depends on pressure Surface reaction velocity Does not depend on pressure Low ratio pure well controlled thickness High ratio contaminants poorly controlled thickness CVD overview Atmospheric pressure CVD APCVD velocity ratio too high 1 1 Mass transport velocity proportional to 1 pressure 2 1 atm 100 kPa LPCVD LPCVD typical pressure 10 1000 Pa Ratio 1 100 1 10 000 Reduced film variation Increased purity LPCVD Substrate inserted Tube evacuated to 0 1 Pa Process gas working gas added at 10 1000 Pa Reaction performed Substrate removed Source 3 LPCVD Best for polysilicon using SiH4 Oxides PSG as well Nitride encapsulation Source 4 LPCVD Advantages Disadvantages Excellent uniformity of thickness purity Simple Reliable reproducible Homogenous layer Slows down deposition rate Requires high temperatures 600 C PECVD Plasma added with reactive gases RF voltage excites plasma Only electrons are hot not ions low temperatures possible PECVD Picture http timedomaincvd com CVD Fundamentals plasmas capacitive plasma html Film Reactive Gas Silicon Nitride Silicon dioxide SIH4 or S1H2C12 NH3 SiH4 O2 Amorphous silicon SiH441 Thermal Deposition CVD Celsius 750 Plasma Enhanced CVD Celsius 200 500 350 550 200 400 550 650 200 400 Table http www eng auburn edu tzengy ELEC7730 ELEC 207730 20Fall 202003 Fall 202003 20Presentation 201 Park 20 20PECVD ppt PECVD Conformal step coverage of PECVD SixNy http www hitech projects com dts docs pecvd htm PECVD Advantages Disadvantages Equipment is expensive Plasma bombardment is stressful Small batch sizes 1 4 wafers one side Compare to LPCVD at least 25 wafers both sides 5 Low temperature Higher film density Higher dielectric constant Good step coverage Chamber easy to clean Questions References 1 A Stoffel A Kov cs W Kronast and B M ller LPCVD against PECVD for micromechanical applications J Micromech Microeng Vol 6 No 1 pp 20 33 Mar 1996 2 Ivanda Mile Implementation and Development of the LPCVD Process Online Available http www irb hr en str zfm labs lmf Previous projects LPCVD Accessed 24 Nov 2011 3 Dow Corning Chemical Vapor Deposition Online Available http www dowcorning com content etronics etronicschem etronics newcvd tutorial3 asp DCWS El ectronics DCWSS Chemical 20Vapor 20Deposition Accessed 25 Nov 2011 4 Doolittle Alan Thin Film Deposition and Epitaxy Online Available FTP http users ece gatech edu alan ECE6450 Lectures ECE6450L13and14 CVD 20and 20Epitaxy pdf Accessed 23 Nov 2011 5 MEMSnet MEMS Thin Film Deposition Processes Online Available http www memsnet org mems processes deposition html Accessed 23 Nov 2011 6 Plasma Enhanced CVD Hitech Projects 2011 28 Nov 2011 http www hitechprojects com dts docs pecvd htm 7 Mahalik Nitaigour Introduction to Microelectromechanical Systems MEMS New Delhi India Tata McGraw Hill 2007 8 Plasma Physics Wikipedia 29 Nov 2011 29 Nov 2011 http en wikipedia org wiki Plasma 28physics 29 9 Fundamentals of Chemical Vapor Deposition Plasmas for CVD TimeDomain CVD Inc 2002 29 Nov 2011 http timedomaincvd com CVD Fundamentals plasmas plasma deposition html
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