= 0.5um Poly 1 Mask Poly 2 MaskContact 1 Mask Contact 2 Mask Homework 13 Spring 2006 Prof. Chenming Hu Due on the last day of class in the hw box in Cory hall at 5 pmProblem 1An NPN transistor is fabricated such that the collector has uniform doping of 51015cm-3.The emitter and base doping profiles are given by:NE = 1020 Exp(- x / 0.106[µm])cm-3 and NB = 4·1018 Exp(- x / 0.19[µm])cm-3 where x is in µm. (a) Find base width, WB.(b) Find base and emitter Gummel numbers. For simplicity, assume nie=nib=ni,uniform diffusion constant (make a rough estimate of Di ), and low level injectionsuch that. EBidxxNDGWWiii,,)(/121. (c)Find the current gain, beta, Problem 2For the following process steps, assume that you use a positive photo-resist and that etchselectivity is infinite. A composite plot of four photo-masks is given below.Assume that mask alignment is perfect. All contact sizes are 0.5m0.5m. Thepoly 1 and poly 2 areas are opaque, and the contact 1 and contact 2 areas are clearin the masks. Draw the cross-section at the end of each process step along the cut-line shown in the figure.(a) Grow 1m thermal oxide on <100> bare Si wafer.(b) Expose and develop photoresist with contact 1 mask. Assume that the resistthickness is 1m.(c) Etch the 1m thermal oxide anisotopically. Assume the final oxide profile isperfectly vertical.(d) Remove the photoresist with O2 plasma.(e) Implant phosphorous and anneal. Assume that the final junction depth is 0.3m.(f) Deposit 1m in-situ doped poly-silicon by LPCVD. The thickness on thesidewalls is the same as that on the flat surface.(g) Expose and develop the photoresist with poly 1 mask.(h) Etch the 1m poly-silicon anisotropically.(i) Remove the photoresist with O2 plasma.(j) Deposit 1um oxide with PECVD. Again, the thickness on the sidewalls is thesame as that on the flat surface.(k) Expose and develop photoresist with contact 2 mask(l) Etch 0.2m of the PECVD oxide with HF. Assume the profile is cylindrical asshown in Fig. 3-7a.(m)Etch the remaining 1.8m oxide anisotropically.(n) Remove the photoresist with O2 plasma.(o) Implant phosphorous and anneal. Assume the junction depth is 0.3m and thereis no additional dopant diffusion.(p) Deposit 1m in-situ doped poly-silicon by LPCVD. The thickness on thesidewalls is the same as that on the flat surface.(q) Expose and develop photo-resist with poly-2 mask.(r) Etch the 1.0m poly-silicon anisotropically.(s) Remove the photo-resist with O2 plasma.(This is just an exercise. The structure does not have any usefulness that we knowof.)Problems 3 and 4: Do not turn in these problems as part of your hw, however tryand work them out for your own benefit. Try working these problems out and thesolutions will be
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