Midterm Exam

# Midterm Exam - (30 points A boron predeposition diffusion...

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Unformatted text preview: (30 points) A boron predeposition diffusion is made into a wafer having an n-type background concentration Nae = lO'ch". A drive-in diffusion is performed at l 150 “C for 3 hours. After these dift‘usions, the junction depth is measured to be x,- = 3.16 pm. (a) What was the total number of boron atoms/cm"I at the end of the predep diffusion? (b) Suppose that instead of the above drive-in, the same predeposit had been followed by a drive- in of 17 hours at lOSO °C What WOuld the junction depth have been? (c) Ifthe drive—in had been 4 hours at 1150 0C plus 10 hours at 1050 “C what diﬁhsion coefﬁcient (in olfhr) would you have used to calculate the junction depth? ' (10 points) An epitaxial layer is grown by SiClt vapor phase itax on a p-type silicon substrate having a background concentration = 10I lcm . The epitaxial layer is grown will a SiCl. mole fraction V = 003 at 1270 °C Fm i minutes. During growth the layer is doped by using a gas-phase phosphorus/silicon ratio of 10". (a) What is the counce-mtration/cm3 of phosphorus in the grown layer? (b) How thick is the grown layer? (15 poims) If an X—ray Lithography system has a source diameter = 3m mask to wafer distance = 40pm, and a source to wafer distance =100cm. what is the maximum runout error when processing 300mm wafers? ‘25 points) A particular photoresist has the property that it will be completely removed in development if it is exposed to at least 85 mJt'cm’ of UV light. The minimum 2 amount of UV light required to begin exposure of the photoresist is 40 mJ/crn . (a) Is this a positive resist or a negative resist? (b) Calculate the resist contrast. (c) Calculate the resist Critical Modulation Transfer Function (d) If this resist is used in a stepper with a spatial coherence = 0.5 and a cutoff ﬁ-equency = 3.97 pm", what is the resolution in line pairs/pm? L/ 5. (5 points each) (a) In a few sentences, describe the basic features of the Czochralski process. (i.e. What is it used for? How does it work?) ,4"? . 7 t t- a; any" ( y"!r‘- -]uu -. ~ (b) In the table of diffusion coefﬁcients for bonﬁind phosphorus, why are there two values for each temperature for phosphorus while there is only one for boron? (c) Over the years, why have semiconductor manufacturers progressed ﬁ'om 7-6 using 3 inch wafers to using 12 inch wafers, and are now going to 18 inch N" wafers? Why have they also progressed to using shorter wavelength resist 9‘: . g‘r‘h I exposure sources? 1 It I. 111:};1. ’I’ (:1) Why are the common dopants that are used in vapor phase silicon epitaxial growth (arsenic, boron and phosphorus) not commonly used in silicon molecular beam epitaxial growth? Instead they are replaced by antimony, gallium and aluminum. 5;: Joe it?” n 7 (.1, f r‘ 1 l l _. l A r") f f '— K - I. - - f r um. . ’ ‘” WW? ‘9 / [rt-w HI! )1) (7 u” v” / "963"" I *7 ' . .. - , 1: Maw Ia. T.),r4£~w--ri? a fir/'56:?! L/ / ‘7 _ ~.'t;v”k¥/ ‘0 _ 1.. _ y ‘_ . ' / q ﬂiqdmer ‘ #156 15‘"be )9? I 9‘97 . [ .LI’H ' . f . u is“! 1/} ;f’! C? [by/H” ’1’? :1- r j/‘Cfé? w__ﬁ‘/”5 f' 1- n' A“ p...- a f if“... Byﬂfaﬂ [9 (§ﬁ C~€ﬁf~ nlﬁ’ﬁvy (fwd if" ,,' b J’ ‘_ . y; I. .‘ Lieﬂéﬁpiektv VV/(g/(P “3 1‘ /,/79f3/,/¢9/L(S- If, in Mprqxedcl'réul'v‘s f7 4’ @495 +4! ﬁ’kr’ l7“ 4””0» yard [4.» 7/0 - fl (fajn‘g'ltﬁkc, 347 MIL Gainer my ye Mfry‘" “25””? “WWW” 'ga‘frwé ‘ r r Ir. l rwr W3; #6/ rem {priawwﬁ m H” L931" aft/V CC? m1 I9de I“e1\$§/anciir? 95"? W? 43?”a .f ‘3 h ’ 3 _ r “a ‘1 I I i , 71W?” 6 11/ 3’ IV ‘3 .nj {1% iﬂéchge. 41,34? {2’96}, -" .3" {9533* d. H) i “5.. ...
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