Theoretical Test

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9. Photolithographic process (5 pts)Photolithography is a process used in semiconductor device fabrication totransfer a pattern from a photomask to the surface of a substrate. In a typicalphotolithography process, light is projected, through a mask that defines aparticular circuitry, onto a silicon wafer coated with a thin layer of photoresist.9-1. The earliest photoresists were based on the photochemistry thatgenerates a reactive intermediates from bis(aryl azide). Patterningbecomes possible through the cross-linking reaction of the nitrenesgenerated from the azides.SO 3- Na +N 3N 3+Na - O 3 Shνreactive intermediatecalled as nitrene+ 2 N 2Bis(aryl azide)9-1-1. Draw two possible Lewis structures of CH 3 -N 3 , the simplestcompound having the same active functional group of bis(aryl azide).Assign formal charges.9-1-2. Draw the Lewis structure of nitrene expected from CH 3 -N 3 .9-1-3. Draw the structures for two possible products, when this nitrene fromCH 3 -N 3 reacts with ethylene gas (CH 2 CH 2 ).9-2. Photoresists consisting of Novolak polymers, utilizes acid to changetheir solubility. The acid component can be produced photochemicallyfrom diazonaphthaquinone. In fact, “Novolaks” have been therepresentative “positive” photoresists of the modern microelectronicrevolution.OHCH 3nNovolak14
When irradiated, diazonaphthaquinone undergoes photochemicaldecomposition followed by rearrangement eventually producing acarboxylic acid.OSOROON 2Diazonahpthaquinonederivativehνcarbeneintermediate+ Nrearranged2intermediate+ H 2 OOSOROCO 2 H9-2-1. Draw three Lewis structures of diazoacetaldehyde (see below), thesimplest compound having the same active functional group ofdiazonaphthaquinone. Indicate formal charges.OH-C-CHN 2diazoacetaldehyde9-2-2. Draw a Lewis structure of the rearranged intermediate, A (see below),generated from diazoacetaldehyde after losing N 2 . A satisfies Lewis’octet rule and reacts with water to form acetic acid, CH 3 CO 2 H.OH CHN 2carbeneA CH 3 COOH_ intermediateN H 2 2 O9-3. Advanced photoresists were invented in 1982 based on chemicalamplification. The most popular chemical amplification for positive-toneinvolves the acid catalyzed deprotection of poly(p-hydroxystyrene) resinprotected by various acid-sensitive protecting groups such as t-butyloxycarbonyl (t-BOC).15
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Theoretical Test

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