EXAM_I_Problems_and_solns - 5360 Exam I Problems and...

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5360 Exam I Problems and Solutions 1. (15pts) MOS devices have been scaled from minium dimensions of .5-1 micron down to dimensions of 450 angstroms. Discuss the major technology issues that needed and it many ways have been addressed in the unit processes of a. Lithography b. Etching c. Oxidation d. Diffusion/Ion Implantation 2. A resistor for an analog integrated circuit is made using a layer of deposited polysilicon 0.5 µm thick, as shown below. (a) (5pts) The doping of the polysilicon is 1 × 10 16 cm 3 . The carrier mobility µ = 100 cm 2 V 1 sec 1 is low because of scattering at grain boundaries. If the lateral resistor has L=100µm, W=10µm, what is its resistance in Ohms? (b) (10pts) A thermal oxidation is performed on the polysilicon for 2 hours at 900 ˚C in H 2 O . Assuming B/A for polysilicon is 2/3 that of <111> silicon, what is the polysilicon thickness that remains. (c) (10pts) Assuming that all of the dopant remains in the polysilicon (i.e. does not segregate to oxide), what is the new value of the resistor in (a). Assume the mobility does not change. Si SiO 2 Polysilicon
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Answer: (a) ρ = 1 nq µ = 1 1 × 10 16 ( ) 1.6 × 10 19 ( ) 100 ( ) = 6.25 cm ρ S = ρ x j = 6.25 0.5 × 10 4 = 125k R = 100 10 ρ S = 1.25M (10 squares) (b) The linear rate coefficient at 900 ˚C is B A poly = 2
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EXAM_I_Problems_and_solns - 5360 Exam I Problems and...

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