2 pages. MASSACHUSETTS TECHNOLOGY Closed book 3.155J/6.152J Microelectronics Processing Technology Spring term, 2003 Quiz 90 min/90 points total March 19 2003 Note: Be brief and relevant in your answers, and use sketches. Show your work kB=1.3810JK=86210°eV/K 40 1. Film deposition, cvd a)Discuss briefly what factors affect the microstructure of a film grown on a substrate [15] b)A CVd process is used to deposit P-doped silica at 1200 K. The reactions are SiH4 -- Si(s)+ 2H2(g) k=0. 1 exp(-E/kBT)cm/s where E=1.0ev Silane=10- cm2/s Silane=102 cm-3 PH(g)-->P(s)+3/2H2(g) k=2 exp (-E/kBT)cm/ where e= 1.2ev =106cm2/s In the reactor, the average boundary layer thickness is 2 mm. N=5x10" for the film Calculate the films growth rate and composition. [15] c) Suppose the flow velocity of the gases is doubled What happens to the answer to part(b)? [5 d)Cvd processes such as the one in part b) are often run at fairly high pressures, e.g. several Torr. Speculate briefly on what might be different if the process is instead run at a very low pressure, e.g. in the mTorr range. [5] 25 2. Diffusion a) a thin layer of As is deposited onto the surface of a Si wafer containing a uniform concentration of 10cmof B The As layer is only 10 nm thick If the sample is annealed for I hour at 1000 k, calculate the profile of the As (Assume Si and As atoms are the same size. I cm' of si contains 5x10 cm)[15] b)Write down the assumptions you used in reaching this answer, and discuss how valid they are.[10] For as:D°=0066cm2s;E°=34eV D=12 cm/s: E=4.0eV ForB:D°。=0.037cm2sE°=34eV Dt。=04cm2/s,E+=34eV 25 3. Lithography and etch a) Define in one or two sentences the differences between the following: [10] i. Depth of focus, Resolution of imaging system and Resolution of resist ii. Positive and negative resist iii. Proximity and projection printing2 pages. M A S S A C H U S E T T S I N S T I T U T E O F T E C H N O L O G Y Closed book 3.155J/6.152J Microelectronics Processing Technology Spring Term, 2003 Quiz 1 90 min/ 90 points total March 19 2003 Note: Be brief and relevant in your answers, and use sketches. Show your work. kB = 1.38 10-23 J/K = 8.62 10-5 eV/K 40 1. Film deposition, CVD a) Discuss briefly what factors affect the microstructure of a film grown on a substrate [15] b) A CVD process is used to deposit P-doped silica at 1200 K. The reactions are: SiH4 --> Si (s) + 2H2 (g) k = 0.1 exp (-E/ kBT) cm/s where E = 1.0eV -3 Dsilane = 10-5 cm2 /s csilane = 1021 cm PH3(g) ---> P (s) + 3/2 H2 (g) k = 2 exp (-E/ kBT) cm/s where E = 1.2eV -3 Dphosphine = 10-6 cm 2 /s cphosphine = 1020 cm In the reactor, the average boundary layer thickness is 2 mm. N = 5x1022 cm-3 for the film. Calculate the film’s growth rate and composition. [15] c) Suppose the flow velocity of the gases is doubled. What happens to the answer to part (b)? [5] d) CVD processes such as the one in part b) are often run at fairly high pressures, e.g. several Torr. Speculate briefly on what might be different if the process is instead run at a very low pressure, e.g. in the mTorr range. [5] 25 2. Diffusion a) A thin layer of As is deposited onto the surface of a Si wafer containing a uniform concentration of 1018 cm-3 of B. The As layer is only 10 nm thick. If the sample is annealed for 1 hour at 1000 K, calculate the profile of the As. (Assume Si and As atoms are the same size. 1 cm3 of Si contains 5x1022 cm-3) [15] b) Write down the assumptions you used in reaching this answer, and discuuss how valid they are. [10] For As: Do o = 0.066 cm2 /s; Eo = 3.4 eV D￾o = 12 cm2 /s; E- = 4.0 eV For B: Do o = 0.037 cm2 /s; Eo = 3.4 eV D+ o = 0.4 cm2 /s; E+ = 3.4 eV 25 3. Lithography and Etch a) Define in one or two sentences the differences between the following: [10] i. Depth of focus, Resolution of imaging system and Resolution of resist ii. Positive and negative resist iii. Proximity and projection printing