A Little Structural Organic Chemistry - 3. EE-527: MicroFabrication. A Little Structural Organic Chemistry - 1. Common Monomers and Their Polymers - 1

Size: px

Start display at page:

Download "A Little Structural Organic Chemistry - 3. EE-527: MicroFabrication. A Little Structural Organic Chemistry - 1. Common Monomers and Their Polymers - 1"

Isaac Wells
6 years ago
Views:

1 A Little Structural rgaic hemistry - 3 bezee pheol toluee 3 3 (ortho-) xylee EE-57: MicroFabricatio 3 3 (meta-) xylee 3 3 (para-) xylee Negative Photoresists 3 orthometapara- meas straight out meas beyod meas opposite ommo Moomers ad Their Polymers - MNMER PLYMER A Little Structural rgaic hemistry - ethylee 3 propylee polyethylee (PE) 3 polypropylee (PP) alkaes: (o double bods): 3 alkees: (at least double bod): 3 l viyl chloride l polyviyl chloride (PV) alkyes: (at least triple bod): 3 [alkees ad alkyes are usaturated hydrocarbos.] styree polystyree (PS) ommo Moomers ad Their Polymers - MNMER PLYMER 3 3 methyl acrylate polymethyl acrylate (PMA) A Little Structural rgaic hemistry - R alcohol R R' ether 3 methaol R aldehyde formaldehyde 3 3 R R' R ketoe acid formic acid 3 methyl methacrylate 3 polymethyl methacrylate (PMMA) R R' ester All rubbers are diee polymers 3 3 isopree polyisopree (PI) (-methyl-,3-butadiee) R R R' hydroperoxide peroxide

2 Molecular Weight of a Polymer M p = M m = umber of uits M m = molecular weight of moomer M p = molecular weight of polymer For use i a photoresist resi, eed a molecular weight of aroud 00,000-00,000 for proper viscosity, meltig poit, softeig poit, ad stiffess. Example: To get M p = 00,000 usig isopree (M m = 68. g/mole), eed to get chais of average legth of = 00,000/68. = 468 uits. This would lead to a molecule that is too log for proper photolithographic resolutio, so eed to coil the chais to make the legths shorter ad to icrease the mechaical stiffess. ommo Moomers ad Their Polymers - 3 D-glucose cellulose D-maose Polyisopree Rubber -methyl-,3-butadiee (isopree) spotaeously polymerizes ito atural latex rubber (polyisopree). Polyisopree becomes sticky ad looses its shape at warm temperatures. Natural latex rubber is the oly kow polymer which is simultaeously: elastic air-tight water-resistat log wearig adheres well to surfaces 3 polyisopree 5 8 Atomic Weights hydroge.0079 carbo.0 itroge oxyge silico sulfur 3.06 chlorie (distributio of isotopes gives rise to fractioal atomic weights) yclicized Poly(cis-isopree) - Poly(cis-isopree) is the substrate material for early all egative photoresists. cis- 3 groups are o the same side of the chai tras- 3 groups are o alteratigly opposite sides of the chai cis-isopree is eeded i order to curl the chais up ito rigs; (tras-isopree will ot work; 3 groups would hit each other). Two protos are added to cis-isopree to further saturate the polymer ad iduce curlig ito cyclicized versios. 3 3 moocyclic poly(cis-isopree) 0 6 Bicyclic ad tricyclic forms are also possible. (This is usually part of the proprietary part of photoresist maufacture. Molecular Weights ethylee 4 (.0) + 4(.0079) = 8.05 g/mole propylee 3 6 3(.0) + 6(.0079) = 4.08 g/mole viyl chloride 3 l (.0) + 3(.0079) = 6.50 g/mole styree 8 9 8(.0) + 9(.0079) = 05.6 g/mole methyl acrylate 4 6 4(.0) + 6(.0079) + (5.9994) = g/mole methyl methacrylate 5 8 5(.0) + 8(.0079) + (5.9994) = 00. g/mole isopree 5 8 5(.0) + 8(.0079) = 68. g/mole mole is Avogadro s umber of particles: N A = 6.03 x 0 3

3 AB Photosesitive ross-likig Aget + yclicized Poly(cis-isopree) - yclicized poly(cis-isopree) allows greater solids cotet i coatig solutios ad is less subject to thermal crosslikig. 3 4-methylcyclohexaoe N 3 4-azidobezaldehyde Property Ucyclicized yclicized Average Molecular Weight ~ 0 6 ~ 0 4 Desity 0.9 g/ml 0.99 g/ml 3 N N 3 Softeig Poit Itrisic Viscosity Usaturatio 4.7 mmole/g 4-8 mmole/g 3,6-bis(4-azidobezal)-4-methylcyclohexaoe "AB" Bis-Azide ross-likig Agets bis meas oppositely orieted---eeded to attach both eds of the cross liker to two differet substrate strads. It plays the same role as sulfur i vulcaizatio of rubber. The AB bis-azide compoud is photosesitive istead of beig thermally activated. Photosesitivity arises from explosophore groups o eds: N 3 azide group N itro group Lead azide Pb(N 3 ) is a primary explosive... Nitrees are photoioized azide groups with a triplet groud state ad a siglet excited state which is extremely reactive ad capable of bodig to hydrocarbo chais. Vulcaizatio (ross-likig) of Rubber Vulcaizatio of rubber uses sulfur atoms to form bridgig bods (cross-liks) betwee polymer chais. Sulfur is thermally activated; it is ot photosesitive S S S Bis-Azide ross-likig hemistry - hν R N 3 R N* + N photolysis of itree group: the oly photoreactio R N* + R N 3 R N + R N + 4 R N + 5 R N R N 6 R N + R N + ompoets of a Negative Photoresist. No-photosesitive substrate material About 80 % of solids cotet Usually cyclicized poly(cis-isopree). Photosesitive cross-likig aget About 0 % of solids cotet Usually a bis-azide AB compoud 3. oatig solvet Fractio varies Usually a mixture of -butyl acetate, -hexyl acetate, ad - butaol Example: Kodak KTFR thi film resist: work horse of the semicoductor idustry from 957 to 97.

4 The Gel urve Bis-Azide ross-likig hemistry Gel Fractio, W ~ 5 x 0 6 photos/cm, or ~ 8.3 x 0-8 Eisteis/cm percet of solids by weight i a gel Gel Poit iitial slope Exposure is measured i Eisteis/cm ( Eistei = mole of photos) Exposure, E (liear scale) Photolysis of itree group by ultraviolet light is the oly photoreactio. Reactio is the desired pathway which leads to oe ed of the AB compoud beig cross-liked to a isopree strad. Reactios, 3, ad 4 are a alterative pathway to the same result, ivolvig a itermediate groud state ad a radical state of the itree. The groud state itree ca combie with. (Reactio 5) This competes with cross-likig. This ca be used i a image reversal process. The radical state itree ca steal a additioal proto from a isopree strad ad termiate the AB compoud without formig a cross lik. (Reactio 6) This competes with cross-likig, also. The Sesitometric urve ross-likig Efficiecy Gel Fractio, W D G ~ 0-0 mj/cm percet of solids by weight i a gel iitial slope is the photographic cotrast, γ Gel Poit workig poit rage Exposure eergy dose i mj/cm Exposure Dose, D (logarithmic scale) χ is the efficiecy of thermal cross-likig of itree groups to isopree strads, set by the rates of reactios,,3,4 versus 5,6. φ is the quatum efficiecy of photolysis of the azide groups, set by the wavelegth ad absorptio of the resist. Φ = φχ is the quatum yield of cross-lik bod formatio. For a bis-azide resist, two bods are eeded (oe o each ed) to form a cross-lik betwee isopree strads; thus: Φ = φ χ This requires two photos per cross-lik, ad thus has very low photographic speed. This allows great variety i the substrate polymer chais. Exposure ad Dose alculatios N A = Avogadro s umber = 6.0 x 0 3 particles/mole h = Plack s costat = 6.66 x 0-34 J-s c = speed of light i vacuum =.998 x 0 8 m/s N A hc = 0.96 J-m/mole E = exposure i Eisteis/cm D = exposure eergy dose i mj/cm Assume early moochromatic exposure illumiatio of wavelegth λ hc λ N A hc λ Therefore: is the eergy per photo is the eergy i a mole of photos (oe Eistei) EN Ahc D = λ The Gel Poit All sites for cross-likig (chromophores) are equally likely; thus, larger polymer chais are more likely to bid together tha small oes. A may-brached supermolecule results from icreased exposure. This supermolecule permeates the irradiated area formig a lattice which solvet atoms ca peetrate, but ot disperse. The polymer chais have at this poit bee redered isoluble to the solvet, ad the exposure required to produce this is called the Gel Poit.

5 The Flory Fuctio - W = gel fractio (fractio of solids) = cross-lik fractio = degree of polymerizatio (a iteger) = M p /M m f() = distributio of polymerizatio, a log-ormal distributio β = dispersity, typically = average polymer chai legth The Flory fuctio relates the cross-lik fractio (proportioal to exposure) to the resultig gel fractio W (solids cotet) as a fuctio of the average chai legth ad dispersity of the polymer. sigle pass: A = R )( e ( ptical Absorptio by the Resist A = fractio of light that is absorbed by the photoresist layer d r = thickess of the photoresist layer α r = optical absorptio coefficiet of the photoresist layer ρ r = desity of the photoresist layer R = reflectivity of the air - photoresist boudary R = reflectivity of the photoresist - substrate boudary α r d r ) resist layer I(z) f ( ) (l l 0) exp β = W = = f ( ) [ W ] = f ( ) double pass: A rdr [ + R e ] αrdr α = ( R )( e ) I z) = I ( R ) e ( 0 α r z z The Flory Fuctio - ross-lik Fractio E = exposure i Eisteis/cm Gel Fractio, W A = absorbed fractio of light Φ = quatum efficiecy of cross-lik formatio.0 β = 0 β = β =.5 = cross-lik fractio EAΦ = umber of formed cross-liks i moles/cm d r ρ r = mass of resist i grams/cm 0.5 β = d r ρ r /M m = umber of possible cross-liks i moles/cm therefore, the fractio of possible cross-liks is proportioal to the exposure: Exposure, / gel EAΦM = d ρ r r m Dispersity ad otrast The slope of the sesitometric curve is the photographic cotrast of the resist: dw d(log E) dw de gel poit gel Desire a miimally dispersed polymer to optimize the sesitometric curve. Age icreases the dispersity of the polymer. This is a key factor i limitig the shelf life of photoresist. poit = e E = l(0) e gel β β = e β = γ Gel Poit Exposure The gel poit occurs whe each polymer strad, o average, has oe cross-lik. Thus, M m gel = = M The gel poit exposure is thus: dr ρ dr ρr Egel = = AΦM AΦM r m For Φ =, A =, d r = µm, M p = 0 5 g/mole, ad λ = 365 m, obtai that E gel = 0.5 x 0-9 Eisteis/cm ad D gel = 0. mj/cm. p p This is a bechmark for egative resist systems.

6 Negative Photoresist Strippers Most commoly used are: Methyl ethyl ketoe (MEK) Methyl isobutyl ketoe (MIBK) 3 3 methyl ethyl ketoe (MEK) methyl isobutyl ketoe (MIBK) Negative Photoresist Igrediets. No-photosesitive substrate material. Photosesitive cross-likig aget 3. oatig solvet 4. ther additives: (usually proprietary) atioxidats radical scavegers amies; to absorb durig exposure wettig agets adhesio promoters coatig aids dyes Sigle ompoet Negative Photoresists Electro beam irradiatio produces cross-likig. A aio A - is eeded to complete the reactio. 3 3 epoxide group glycidyl methacrylate ad ethyl acrylate copolymer A - + e-beam radiatio R A - R - A A - + R R R - e-beam radiatio R - Negative Photoresist Developmet - The uexposed (ucross-liked) areas of resist as well as polymer chais that have ot bee cross-liked to the overall etwork of the gel must be dissolved durig developmet. Negative photoresist developers are solvets which swell the resist, allowig ucross-liked polymer chais to utagle ad be washed away. A sequece of solvets is ofte used to keep the swellig reversible. The swellig of the resist durig developmet is the largest cotributor to loss of features ad liewidth limitatios. Negative Photoresist Developmet - volume expasio factor, V/V o 0 5 chloroform toluee bezee icreasig solubility parameter δ hexae 0 0% 50% 00% ethaol (base solvet) molecular percet of solvet i ethaol

POLYMERS

POLYMERS Short Aswer Questios: **1.What is PHBV? How is it useful to ma? As. PHBV is Poly β-hydroxy butyrate-co- β-hydroxy valerate.it is a biodegradable polymer. It is used i speciality packig, orthopaedic