EE143_Midterm1_Solns_Sp08

EE143_Midterm1_Solns_Sp08 - UNIVERSITY OF CALIFORNIA...

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Unformatted text preview: UNIVERSITY OF CALIFORNIA College of Engineering Department of Electrical Engineering and Computer Sciences EECS 143 Professor Ali J avey Spring 2008 Exam 1 Name: Answer SID: Closed book. One sheet of notes is allowed. There are a total of 12 pages on this exam, including the cover page. _ - _ — _ H O Kl] Oxide thickness (1.1.. m) 10 1.0 0.1 <100>Silicon 1.0 Oxidation time (hr) 10 100 “0/90 1) True/False I20 ptsl Circle either (T)rue or (F)alse (2 pt each) a. For negative photoresist processing, the developer removes the photoresist that is exposed to UV light. T / 63 b. One monitors the completion of poly silicon etch by the changes in color of the film. @ / F c. RIE (Reactive Ion Etching) is generally less selective than wet etch' . 7 / F d. We can use pyrex glassware to perform HF etching of substrates. (Q T / , e. You wear a gown in the clean room mainly to protect yourself from hazardous and corrosive chemicals. T / 6) f. An HF etch has high selectivity for silicon dioxide over silicon. ( i / F g. The gate oxide is grown in steam, because generally wet oxidation has better quality. T / (9 h. Intrinsic Si has zero free holes and electrons at room temperature. T / G) i. The density of states in Silicon is nearly independent of temperature. EIE‘HNGF‘ CF (10(3prqu DOS. (Th9fi%€$ \mu‘y 5h? kHy due +0 . “fwd ES 1') dependent".6 ~ j. The band gap of Sllicon increases as the temperature 1s reduced. : T/F; / F 2) Photolithography |20 ptsl 90 nm ——>|l<— Patterned PR Thickness t Substrate The profile above was created using a projection photolithographic method. The light source was an ArF excimer laser at 193nm. (a) If the projection system is 5:1, what is the actual width of the mask feature shown in the above figure? [4 pts] fiOnvniFtS : L150nm 5" ?(o;geol'im (b) Calculate the numerical aperture, NA, necessary to produce this patterned feature size. (assume k1=0.6) [4 pts] ;\ fl” 1 k‘ 7;; hf. 0.9 X: \‘Bvim I QM : ‘iOnm NA; k\ %\ :V‘Lc‘ (c) If the half-angle of the maximum cone of light that can enter or exit the objective lens is 70°, what is the index of refraction between the lens and the photoresist? [4 pts] NW fl $3M) Wm Y\—> mime/2) (aha.ch (d) Experimentally, how do you achieve the index of refraction of part (c). (l sentence max) [3 pts] Tmmwsi'o“ (livid (X 50W 6W5 n21 (e) Give one major advantage and one disadvantage of having a large NA. Briefly explain (3 sentences max). [Spts] Advekaa. c,“ (\sefihr g:er 332,6 fist)de (Smaller «Each/Le 413,24) . DiSquekaaficz SMCF ‘66?“4. gm 3) Spacer Lithography [20 ptsl Spacer lithography is a patterning technique used in research to define very short feature lengths by using sacrificial layer and conformal thin film growth. Spacer lithography produces features smaller than photolithographic limits (and it’s used here in the Microlab at Berkeley!). The process involves the following. A patterned sacrificial layer of height ‘4h’ is first made. A conformal thin film is then deposited on the substrate and the sacrificial layer with thickness ‘h’ (schematic). This conformal film covers all exposed surfaces with the same thickness, as pictured below. A purely anisotropic etch of the conformal film (degree of anisotropy A f: l) is then performed using RIE with the following parameters: 0 The RIE process etches the conformal film at h nm/min o The RIE process etches the sacrificial layer at 2 * h nm/min o The RIE process does not etch the subStrate Note: ‘h’ has nm unit. Conformal Film h -> ‘- Sacrificial Layer / V/////////¢ 7 W. (a) Starting from the above schematic, draw the cross section after 3 minutes of RIE etching. Be sure to include relevant dimensions in terms of ‘h’. [5 pts] \« \A a a / 2k %‘ A (b) What is the etch selectivity for this process between the conformal film and the sacrificial layer? [5 pts] 3— “W ~ A t ‘1 (Miami 2‘“ ‘(c) What is the etch selectivity for this process between the conformal film and the substrate? [5 pts] S $ (Cmth __ L _ 00 r ’ 0 $213.54?“ (d) Draw the cross section using the same etch rates only now the etching is isotropic. [5pts] 15} Mao) eve/fling mm W SubSVlTa/("L «215M 3m. 4) Etching —— KOH |20 ptsl (a) What is the main difference between an amorphous and crystalline material (2 sentences max). [5 pts] AM‘DY‘PhGU‘S ' Ruhtibm arrangemen‘l‘ o; Q‘l‘oms ($51346) CWSMH'Y‘Q — Regular Qweangemen‘l’ o§ Q‘loms CkSp‘iS) (b) Can Si and SiOz materials be either amorphous or crystalline, depending on their deposition/growth/synthesis? Briefly explain (2 sentences max). [5 pts] Si .' Typrcotl \y Crystal \ Pine m process i‘ng (apt?) Fauna as amorphous r‘n nature. (if: it) . Com also be pal ycrys‘l‘ctl l \‘h e g' 0'2; Ty Pica“), amoepkc us I‘m proceSslns~+bermcxl 5? CV D ($153+ 3) A Lso Fauna gs crys‘inWhe Quqf‘l'z i‘n names A particular wet etch chemistry, involving KOH, can be used to etch crystalline silicon. When etching a [100] wafer, like the ones used in lab, the etch forms side walls that are at 54.7 degree angles. The selectivity of the etch for silicon over silicon dioxide is 120, and the etch rate is given by x nm/min, where x = 2400. Patterned PR 54.7 degrees Si Substrate (c) Given what you know about crystalline Silicon, speculate why you may get the above profile for this particular wet etch. [5 pts] Etch seiechm‘ly is higher 570p [too] Prune arth D. r] Mama (9115,53) Speculation on anctker‘ Pessible. meqhgm‘sm g: 5,333) DfsctASSicrh on ifsoir‘opy 0.;- 0h ef¢h_ (3‘05: 5P+S> (d) The side profile of your wafer appears below. Draw a side profile of the wafer and label its dimensions after a two minute long etch with this etch chemistry. Label the relevant thicknesses in terms of “x”. [5 pts] xnm _§ ‘— Patterned PR l» 53m» +m+ Hm bulk substrate "5 etch“ Petm‘W‘ (‘ F” ‘1. Label l‘ka‘l‘ "Hue Subs—taking. has x ’rw‘ckhess remainlhg .099 3 . Show ’l'l‘d'l “~l—rgnck" \‘s shallower ’Hnmh “Hue, bulk elm} Comes (1 POD/Vi. (l 33+) u 4‘ Some ether ad'th c’r \‘eCehCH‘\“S 94”“ mlHfifiW‘xhdcm' (OrgPtS) '1. Label “Hne cl€pHn 05""le fiendish 019*) 5. Show fixes? flue si‘ée walls owe oh<3\ecl. 5) Oxidation |20 pts| Nitride Region A A bare Si wafer is oxidized for 5 hour at 1100°C in dry oxygen. It has then the oxide removed on Regions B&C and a nitride film is deposited on Region C. The cross- sectional View at this point is shown above. The whole wafer is then wet-oxidized at 1100°C for 30 minutes. (a) What is the oxide thickness in each region (far from the edge boundaries) after the wet oxidation step? Hint: use the chart that you are given and show your strategy/work for partial credit. When reading the chart, just approximate the numbers if between the ticks.[7 pts] WWI/r "p97 oxiae-ufimn : .v p. 3%,” 0.3/14.» 7< LZMIVJM’fb Azybm op 'wo‘f 0x7 0». 0.5‘vars “Mfimafi wort ox. -—> Noe/.4... : h2,a/rrV\A neg/:6,“ B ; M Mint-7i ox, 031% a ND.%/Am pea/7m C x M we? (b) Please draw an accurate cross-sectional sketch of the above structure after the wet I oxidation step. [5 pts] 10 (Pf. 11 (c) For each of the following, state how the oxidation rate will change (i.e, increase, decreases, or no change), and briefly (2 sentences max) explain why. [8 pts] (i) Introducing HCl in Crau‘i firm 5 H219 M M‘— J.. 3 21,13 (ii) Increasing e P doping concentration of the substrate \ m Magus _ WI, 11f: 12 BONUS Question [5 pts] (a) Briefly (3 sentences max) state what determines the resolution of electron beam lithography. [3 pts] Versi- luck $4~HM"5.(su$s(—mt‘o) l v67 nut/(4431‘ . (b) Is electron beam lithography a viable method for future large-scale manufacturing? Briefly explain (1 sentence) [2 pts] 13 ...
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This note was uploaded on 10/14/2008 for the course EE 143 taught by Professor Alijavay during the Spring '08 term at University of California, Berkeley.

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EE143_Midterm1_Solns_Sp08 - UNIVERSITY OF CALIFORNIA...

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