Irradiation of Polymers - American Chemical Society

Chapter 28

Advanced Materials and Forms: Photosensitive Metathesis Polymers Downloaded by NORTH CAROLINA STATE UNIV on October 14, 2012 | http://pubs.acs.org Publication Date: May 5, 1996 | doi: 10.1021/bk-1996-0620.ch028

A. Mühlebach and U. Schaedeli Materials Research, Ciba-Geigy Ltd., CH-1723 Marly 1, Switzerland

The synthesis and ring opening metathesis homo- and copolymerization (ROMP) of the exo-7-oxa-norbornene- and exo-norbornene-carboximid esters, 1-3 and 1'-3' respectively, have been investigated. Molecular weights were controlled with 2-butene-l,4-diol as chain transfer agent. These homo- and copolymers were used to formulate very sensitive positive tone high resolution resists. They are the first positive working photoresists based on a metathesis polymer backbone. Cycloolefins with strained rings can be polymerized by the so called ROMP-reaction (= ring-opening-metathesis-polymerization) yielding linear chains with one double bond per repeat unit: Scheme 1. Whereas classical catalysts like WC1 /A1Et C1 (1) have a very limited tolerance towards functional groups such as ketones, esters, amides and imides, and the recently discovered Schrock-type catalysts (Mo- and W-carbenes) (2) have a somewhat broader tolerance, certain ruthenium(II)-complexes allow the polymerization of almost any functionalized monomers even in aqueous or ethanolic solution. 6

2

Scheme 1: Principle of the ring opening metathesis polymerization (ROMP). Therefore, polymers bearing almost any functional groups useful for specific applications can be designed. There is a fast increasing demand for speciality polymers for applications in many high technology fields. For example, homo- and copolymers containing specific acid cleavable side groups are used in today's chemically amplified positive tone photoresists (3). The excellent physical properties like high Tg-values and good thermostabilities of ROMP polymers derived from exo-7-oxabicyclo[2.2.1]hept-5-ene-2,3dicarboximides (4) attracted our attention. Therefore we decided to synthesize specific exo-(7-oxa-)norbomene-carboximids with photochemically or thermally cleavable

0097-6156/96/0620-0364$12.00/0 © 1996 American Chemical Society In Irradiation of Polymers; Clough, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1996.

Downloaded by NORTH CAROLINA STATE UNIV on October 14, 2012 | http://pubs.acs.org Publication Date: May 5, 1996 | doi: 10.1021/bk-1996-0620.ch028

28. MUHLEBACH & SCHAEDELI

Advanced Materials and Forms

365

protecting groups. [Ru(H20)6]tos2 (tos=p-toluenesulfonate) (5) was used as ROMP catalyst because it turned out to be one of the most active catalysts known so far for aqueous ROMP (6), although photochemically activated Ru(H)-sandwich or Ru(II)acetonitrile complexes allow also a photoinduced ring opening metathesis polymerization (PROMP) as we discovered recently (7). An easy and straightforward synthesis of the hitherto unknown monomers exo-(7-oxa-) norbornene-carboximid esters 1-3* (Scheme 2) will be reported in this paper. Homo- as well as copolymerizations with the other (oxa-)norbornene type monomers 4-8 using [Ru(H20)6]tos2 as catalyst will be described. In the last chapter, these homo- and copolymers with controlled molecular weights will be used, inter alia, to formulate sensitive positive tone high resolution microresists. To the best of our knowledge, metathesis polymers have not yet been described as backbones for such high performance positive resists.

4

5

6

7

Scheme 2: Monomers used in this study.

In Irradiation of Polymers; Clough, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1996.

8

366

IRRADIATION OF POLYMERS

Experimental Materials. Laboratory grade reagents and solvents were used as received (Fluka, Aldrich, Merck). cis-5-Norbornene-exo-2,3-dicarboxylic anhydride was synthesized by thermal isomerization (lh, 200°C) of the endo derivative (Merck) and subsequent recrystallization from toluene; m.p.: 109°C. [Ru(H20)6]tos2 was synthesized according to the literature

Physical measurements. H - and C - N M R spectra were recorded in CDCI3 on a Bruker A C 300 instrument; chemical shifts (S) are given in ppm relative to internal TMS. IR-spectra were measured on a Nicolet 20 SX with 2 cm~l resolution. Differential scanning calorimetric measurements (DSC) and thermogravimetric analyses (TGA) were performed on a Mettler T A 3000 system, heating rate: 10°C/mia Melting points were measured either by D S C or on a Reichert Thermovar microscope with hot stage. Gel permeation chromatographic measurements (GPC) were performed in THF on a Waters 600E apparatus from Millipore Corp. (Milford, M A , USA) with Maxima 820 software. The M - and M^values (g/mol) refer to polystyrene-standards, which were used to calibrate the system. The scanning electron microscopy analysis (SEM) was executed on a Cambridge S120 stereoscan instrument.


1

1 3

n

2

Monomers. The monomers exo-3-(3,5-dioxo-10-om-4-aza-tricyclof5.2J.0 ^Jdec-8-en-

4-yl)-benzoic acid 1-phenyl-ethyl ester (1), exo-4-(3 5-dioxo-10-oxa-4-azatricyclo[5.2.1.0 >6]dec-8-en-4-yl)-benzoic acid 1-phenyl-ethyl ester (2) exo-3-(3 5dioxo-10-om-4-aza-tncyclof5.2JM ^Jdec-8-en-4-yl)-bem acid benzyl ester (3) and exo, exo-7-oxa-bicyclo[2.2.1]hept-5-ene-2 3-dicarboxylic acid dibenzyl ester (4) were synthesized as described before (8). 2 3-Bistrifluoromethyl-7-oxa-bicyclo[2.2.1]hepta2,5-diene (5) (9) 4-methyI-10-oxa-4-aza-tricyclo[5.2.1.0 * ]dec-8-ene-3,5-dione (6) (4) and exo-dicyclopentadiene (7) (10) were synthesized according to literature procedures, bicyclo[2.2.1]hept-2-ene (2-norbomene) (8) was used as receivedfromFluka. exo-3-(3,5-Dioxo-4-aza-tricycIo[5.2.1.0 > 6]dec-8-en-4-yl)-benzoic acid 1-phenyl-ethy t

2

t

t

2

t

t

2

6

2

ester (V): 2.8 g (0.017 mol) cis-5-norbornene-exo-2,3-dicarboxylic anhydride were dissolved in 50 ml DMSO. 2.34 g (0.017 mol) 3-Aminobenzoic acid were added and the homogeneous red solution was stirred for 24h under nitrogen. 10.39 g (0.068 mol) 1,8Diazabicyclo-[5,4,0]undec-7-ene (DBU) was than added dropwise followed by 12.63 g (0.068 mol) 1-phenylethyl bromide (PEB). Stirring was continued for another 24 h and the solution poured into 100 ml water. Filtration, washings with water and cold EtOH and drying at 50°C in vacuo gave the product in 89% yield (6.61 g). It was further purified by recrystallization from toluene. M.p.: 148°C; Elemental analysis: calc. (found): C: 74.40 (73.69), H : 5.46 (5.62), N : 3.62 (3.65); *H-NMR: 8 1.50, 1.63 (2xd, J=9.9Hz, 2H: CH (10), 1.68 (d, J=6.6Hz, 3H: C H ) , 2.88 (s, 2H, CH(1), CH(7)), 3.42 (s, 2H, CH(2), CH(6)), 6.13 (q, J=6.6 Hz, 1H, C H (phenylethyl ester)), 6.36 (s, 2H, CH(8), CH(9)), 7.30-7.58 (m, 7H), 7.97 (s, 1H), 8.11 (d, J=7.6Hz, 1H), totally 9 aromat.H). 2

3

2

exo-4-(3,5-Dioxo-4-aza-tricyclo[5.2.1.0 > 6]dec-8-en-4-yl)-benzoic acid 1-phenyl-ethy f

ester (2 ): Synthesis similar to / ' , using 4-aminobenzoic acid instead of 3-aminobenzoic acid. The pure product was obtained by recrystallization from EtOH in 74% yield. M.p.: 1320Q Elemental analysis: calc. (found): C: 74.40 (73.54), H: 5.46 (5.33), N: 3.62 (3.45); ^H-NMR: 8 1.47, 1.61 (2xd, J=9.9Hz, 2H: CH (10), 1.68 (d, J=6.6Hz, 3H. C H ) , 2.88 (s, 2H, CH(1), CH(7)), 3.42 (s, 2H, CH(2), CH(6)), 6.13 (q, J=6.6 Hz, 1H, C H (phenylethyl ester)), 6.36 (s, 2H, CH(8), CH(9)), 7.30-7.44 (m, 7H), 8.17 (d, J=7.6Hz, 2H), totally 9 aromat.H); IR (KBr): 1775 cm" , 1708 cm" (C=0 imide and ester). 2

1

3

1


28.

M U H L E B A C H & SCHAEDELI


367 f

exo-3-(3,5-Diaco^-azchtricycb[5.2J.()2^

acid benzyl ester (3 ):

Synthesis similar to V, using benzylbromide instead of 1-phenylethyl bromide. The product was recrystallized from toluene. Yield: 77%; m.p.: 180°C; Elemental analysis: calc. (found): C: 73.98 (73.27), H : 5.13 (5.28), N : 3.75 (3.81); *H-NMR: 8 1.50, 1.64 (2xd, J=9.9Hz, 2H. CH (10), 2.88 (s, 2H, CH(1), CH(7)), 3.42 (s, 2H, CH(2), CH(6)), 5.37 (s, 2H, C H (benzyl)), 6.36 (s, 2H, CH(8), CH(9)), 7.32-7.57 (m, 7H), 7.98 (s, 1H), 8.11 (d, J=7.6Hz, 1H), totally 9 aromat.H); 2

2


Homo- and Copolymers. In a typical example,

1-2 g of the monomer mixture and 100 mg 2-butene-l,4-diol were dissolved in ca. 10 ml Ar saturated dioxane/EtOH (1:1) and 15 mg [Ru(H20)6]tos2 (tos=p-toluenesulfonate) were added. The solution was kept under Ar at 60°C for 48 h. The polymer was precipitated in 100 ml MeOH. Washing with water and M e O H and drying 24 h at 50°C in vacuo gave the pure product. Further details are gjven elsewhere (6, 8).

Lithography. Resist

films were obtained by spin casting of the resist formulation on 3 inch silicon wafers (lithography) or 1 inch quarz disks (UV measurements). Resist film thickness was measured using a Zeiss Axiospeed FT instrument. Visible absorption spectra were recorded on a Varian Cary I E UV/visible spectrometer. Exposures were performed on an Oriel contact printing tool through a 254 nm narrow band pass filter.

Results and Discussion Monomer Synthesis.

The synthesis of polyimides with pendent 1-phenylethyl ester groups, using a direct one-pot polyaddition/imidizatiori/esterification reaction of an aro matic tetracarboxylic acid dianhydride with 3,5-diamino-benzoic acid and a DBU/PEB mixture in D M S O was recently described (77). Surprisingly, this reaction sequence worked also with aliphatic anhydrides as starting materials, e.g. exo-3,6-epoxy-A^tetrahydro-phthalic anhydride (the Diels-Alder adduct offiiraneand maleic anhydride) (72) or the exo-Dicyclo[2.2.1]hept-5-ene-2,3-dicarboxyUc anhydride and therefore gave an easy and straightforward access to the desired monomers l-3 : Scheme 3. f

x

X:C^,0;

R:H,C^

Scheme 3: Monomer synthesis. Homo- and Copolymer Synthesis.

Homo- and copolymerizations were performed with 1-2% [Ru(H20)6]tos in monomer saturated EtOH/dioxane solution (the monomers 1-3' are not sufficientiy soluble in pure EtOH): Scheme 4. Fig. 1 shows the *H-NMR of poly-1 (b) compared with the monomer 1 (a). 2




368

e

1 o

1

I

I o




369

X

RutHgO^2+

*

0

Dioxane/EtOH


X: CHj, O;

R: H, CHj O

R

Scheme 4: Polymerization reaction of Monomers 1-3*.

Control of molecular weights. The control of molecular weights in polymers is crucial for most applications. For example, in microresist technology a l p thick film is generated on a silicon wafer by solvent casting. Polymers with high molecular weights usually observed in ROMP with Ru-catalysts (6) - show very high solution viscosities which make their application difficult if the spincoating technology is used: films tend to be much thinner than the specified thickness. Furthermore, studies on resist polymers with different molecular weights show clearly, that the microresist properties have their optimum in a distinct molecular weight range, usually M =10-30,000 g/mol. We used the ring-opening-metathesis-polymerization of exo,exo-5,6-bis(methoxycarbonyl)-7-oxabicyclo[2.2.1]hept-2-ene as a test system for different chain transfer agents (CTA), having investigated its polymerization in great detail (d): Scheme 5. The following olefins were tested as CTA's for their influence on molecular weights, polydispersities and yields in the polymerization reaction: 2-Butene-l,4-diol, cyclohexane, endo-dicyclopentadiene, 2,3-dimethyl-2-butene, 3-butene-l-ol (allyl alcohol) and 1-hexene. n

O

MeOOC

COOMe

Scheme 5: ROMP of exo, exo-56-bis(methoxycarbonyl)-7-oxabicyclo[2.2.1]hept-2ene. 9

Only 3-butene-l-ol and especially 2-butene-l,4-diol showed good results. The molecular weight was considerably lowered without significant changes in the polymerization yield and the polymer structure (% trans double bonds). However, the molecular weight distribution tends to become broader: Tab. 1. These results are in good agreement with literature data on a similar monomer/CTA-system (13).



370

Table 1: Control of molecular weights in oxa-norbornene derivatives: Influence of 2-butene-l,4-diol on the ROMP of exo,exo-5,6-bis(methoxycarbonyl)-7-oxa-bicyclo[2.2.1]hept-2-ene with [Ru(H 0)6]tos . Experimental conditions: 2 mmol monomer and 0.008 mmol catalyst in 25 ml EtOH, 24h at 60°C under Ar.


2

Weight % 2butene-l,4-diol (rel. to monomer) 0 0.1 2.0 20.0

2

Polym. Yield

M (g/mol)

Mw/M

(g/mol)

(%) 90-98 91 97 83

236000 112000 13800 7700

340000 306000 63400 44400

1.4 2.7 4.6 5.7

w

Mol% trans double bonds ca. 50 48 47 47

n

10% 2-Butene-l,4-diol was added as C T A in the homo- and copolymerization of the ester-imides 1-3* which led to M =20-50000 g/mol and molecular weight distributions (Mw/Mn) of 1.5 to 2.7, see Figure 2 and Tables 2 and 3. Without this regulator, the mo lecular weights tend to be about one order of magnitude higher, as can be seen in the homopolymerization of 1 or in the copolymerization of 1 and 8 (Tab. 2 and 3). On the other hand, polymerization yields dropped in the presence of 2-butene-l,4-diol, especially for the 2-norbornene derivatives without the oxygen bridge (1\ 3'). This could be due to some kind of blocking of the catalyst precursor by the C T A , as was suggested in a previous paper (d). This blocking would be considerably influenced by the monomer/catalyst/solvent system. Polymerization yields also depend strongly on the monomer concentration (d) and therefore the low yield of poly-2 is sternrning from the lower monomer concentration in the reaction mixture (because of the low solubility of 2 in EtOH/dioxan 50/50). Table 2 lists yields, molecular weights and glass transition tempera tures (Tg) of the homopolymers and Tab. 3 those of the copolymers of 1 with 4-8. n

Table 2: Homopolymerizations Polymer a

poly-l poly-1 poly-2 poly-3 poly-l poly-3' f

a

Yield (%) 95 52 33 57 45 49

M (g/mol) 100000 24000 10600 7900 20000 9700 n

M (g/mol) 240000 36000 18600 15400 42000 23000 w

Mw/Mn 2.4 1.5 1.8 1.9 2.1 2.4

(°C) 115 112 110 140 130 129

without 2-butene-l,4-diol.





log Molecular Height Figure 2.

GPC of poly-1 (M =24'000, M =36'000, M / M = l .5). n

w

w

n


371


372

Table 3: Copolymerizations of 1 with different comonomers Comonomer

4 5


6 7 8 8b

Yield (%) 52 27 76 a 1 9

31 66

Mol % of Mol % of 1 1 in feed in copolymer 52 65 51 54 44 48 38 41 14 20 61 62

M M (g/mol) (g/mol) 41000 22000 52000 19000 64000 36000 160000 55000 160000 60000 230000 520000 n

w

MJ M 1.9 2.7 1.8 1.9 2.7 2.3 n

(°C) 60 114 135 108 70 117

plus variable amounts of insoluble polymer, copolymerization was done without 2-butene-l,4-diol.

Although the yields lie far below 100%, the copolymer composition corresponds well to the feed ratio of the monomers. Therefore we assume that the copolymerization of 1 leads to a mainly random distribution of the different monomer units along the polymer chain. The following observations further support this hypothesis: • Molecular weight distributions of the copolymers are monomodal and quite narrow. • Only one Tg-value in the range of60 - 135°C is observed. • The presence of A B sequences (beside A A - and BB-sequences) is clearly visible in the N M R spectra of the copolymers, see e.g. Fig. 3a displaying the *H-NMR spectrum of the copolymer between 1 and 8 (second last entry in Tab. 3). This spectrum is not a simple superposition of the respective homopolymer spectra (as expected for a completely blocky copolymer) as revealed by a comparison with the ijI-NMR spectra of pure poly-1 (Fig. lb) and pure poly(norbornene) (Fig. 3b). Instead, the peaks belonging to the olefinic protons of the 1-unit are slightly shifted and additional peaks, such us a multiplett at 5.6 ppm and broad signals at 4.9 and 4.5 ppm, are visible, indicating the formation of A B sequences.

Lithographic Applications In the semiconductor industry there has been an ever increasing demand for new type, photostructurable materials having improved physical properties, as compared to the established systems. Especially for printed circuit board applications, where improved electrical and water resorbing properties would be desired, as well as for microlithography, where the potential of polymeric backbones different from novolaks / poly(4-hydroxy styrene)'s would be of interest to explore. The newly introduced ring-opening-metathesis-polymers represent a new class of potentially photostructurable materials. These polymers cover a broad range of different physical properties: pure hydrocarbon polymers as well as polymers having a wide variety of functional side groups have been successfully synthesized to date. In other words, the design of new materials, tailormade for well defined specific applications, seems feasible. There are several ways of introducing photosensitivity to formulations based on metathesis polymers:





373

i 1 oo

Irradiation of Polymers - American Chemical Society

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