ELEN_4944_-_midterm

ELEN_4944_-_midterm - 3) [15 pt] a) In a PVD system the...

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ELEN 4944 – Principle of device microfabrication Midterm – 31 st October 2011 Prof. Robert Laibowitz The exam is open books and open notes. 1) [20 pt] a) Given a concentration of As atoms of 3*10 17 cm -3 , calculate the resistivity of Si at 300K. Consider n i =1.45*10 10 cm -3 , μ n =1500 cm 2 /(V*s) and μ p =500 cm 2 /(V*s). b) Given a diffusivity of 5*10 -10 cm 2 /s how long would take to have an average diffusion length of 1μm? 2) [25 pt] a) Using the Grove’s kinetic model for CVD deposition, calculate the growth-rate of a silicon layer grown using the SiCl 4 precursor at 1100°C. The vapor-phase mass-transfer coefficient of the reactor is h g =5 cm/s, the surface reaction coefficient k s is given by k s =10 17 exp(- 1.9/k B T) cm/s, and the concentration of the SiCl 4 gas molecules is C g =3*10 16 cm -3 . b) How much would change the growth-rate if the reaction-temperature is increased to 1200°C? c) What is the structure of poly-Si films? Name an use for the poly-Si film.
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Unformatted text preview: 3) [15 pt] a) In a PVD system the mass lost from the source is measured to be 10-4 g/s and the source initial weight is 1 g. How long will be possible to deposit from the same source before the source is used up? b) When depositing on features with high aspect ratio the step coverage is very important. Which deposition technique would you choose to obtain the maximum edge coverage? c) Compare isotropic etching to anisotropic etching for features size less that 1 m. 4) [20 pt] a) For a simple cubic structure draw out the (1,1,1), (1,0,0) and (1,1,0) plane and find out the number of nearest atoms. b) Now, consider a face centered cubic (fcc) structure, compute the surface atoms density for the (1,0,0) plane. Consider a lattice constant of 3 Angstrom....
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