Polymers in Microlithography - American Chemical Society

Chapter 18

Pyrimidine Derivatives as Lithographic Materials Yoshiaki Inaki, Minoo Jalili Moghaddam, and Kiichi Takemoto

Downloaded by PEPPERDINE UNIV on August 24, 2017 | http://pubs.acs.org Publication Date: October 31, 1989 | doi: 10.1021/bk-1989-0412.ch018

Department of Applied Fine Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565, Japan

Pyrimidine derivatives were found to be applicable to both negative and positive type deep-UV photoresists. Intermolecular photodimerization of pyrimidine bases in the side chain of various polymeric and dimeric compounds upon irradiation of UV light (270 nm) led to the photocrosslinking of the polymer chains or photopolymerization of the dimeric compounds. This in turn allows the use of these materials as deep-UV negative type photoresists. Photolithographic evaluation of a typical polymer showed very high sensitivity with good resolution. On the other hand, the polymers containing a thymine photodimer in the main chain underwent dissociation of the thymine photodimers upon irradiation to UV light (250 nm), leading to breakage of the polymer chains. These polymers could be used as positive type photoresists and high resolution (0.3µm)was demonstrated. It is well known that pyrimidine bases convert to photodimers upon irradiation to UV light near the λ max( > 270 nm). This photochemical reaction has a lethal effect in biological systems due to the photochemical transformation of pyrimidine bases of nucleic acids. However the photodimerization is a reversible reaction and the photodimers split to afford the original monomers very efficiently upon irradiation at a shorter wavelengths as shown in Scheme 1(1).

Scheme 1 This knowledge regarding the efficient photochemical dimerization of the pyrimidine bases, led us to study, in detail, both the intramolecular 0097-6156/89/0412-0303$06.00/0 © 1989 American Chemical Society

Reichmanis et al.; Polymers in Microlithography ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


304

POLYMERS IN MICROLITHOGRAPHY

photodimerization of pyrimidine bases grafted onto the side chain of a polymer and dimeric model compounds (2-13), as well as the intermolecular photodimerization. The latter reaction leads to photocrosslinking of the oligomers and polymers thus allowing them to be applied as negative type photoresists. On the other hand, due to the efficient photoreversal reaction of the pyrimidine photodimers at shorter wavelength, the design of a new type of polymers containing thymine photodimers in the main chain seemed to be of interest. Photolysis of these polymers causes cleavage of the photodimers in the polymer chain and reduces the molecular weight of the polymer. This decrease in molecular weight would be expected to increase the solubility of the polymers in the irradiated regions allowing their use as positive photoresists. These polymers might be obtained by photopolymerization of the corresponding dimeric models containing pyrimidine bases at the ends of their molecules. The object of this study is to develop new photoresists for deep-UV lithography, by using the reversible photoreaction of pyrimidine bases (17-19). Applicability of pyrimidine containing polymers to both negative and positive type photoresists is due to this photoreversible reaction in which cyclobutane dimers are either formed or cleaved depending on the exposure wavelength (Scheme 2).

* : 0 0

R

Ν

R

' 2

xx R

2

^

0

Ch^CH^—~X — C H 2 C H 2 λ 2 7 0 nm

λ < 2 7 0 nm

CH CH W

2

2

CH2CH2

2

λ > 2 7 0 nm

CH2CH2—~x

Scheme 2 EXPERIMENTAL Material Negative Type photoresists: Polymet acrylates and copolymers of butadiene and methacrylate having /arious pyrimidine derivatives (Figures 1, and 2) were prepared by free radical polymerization of the methacrylate monomers (14-16). In the case of the poly(MAOT -alt-MAOT Me ), the polymer was obtained by the reaction of the polymethacrylic anhydride with the hydroxyethyl v

1

3

1


18. INAKIETAK

Pyrimidine Derivatives as Lithographic Materials

Thymine Amax.= 272nm φ =0.0074

Uracil λ max.= 266nm φ = 0.038

DF


η ρ

5-Cyanouracil Amax.= 282nm φ = 0.00037 D F

Ο ^ Ν Γ CN

5-Bromouracil Amax.= 282nm

6-Methyluracil λ max.= 267nm φ = 0.0094 D

Figure 1.

0

Polymethacrylates containing pyrimidine bases.

polyiMAOT ) (7)

poly(MA0T Me ) (8)

1

]

polyiMAOT-co-MAOrMe ) (lOa-e) 1

Figure 2.

F

6-Cyanouracil Amax.= 292nm φ ρ = 0.0Α1

3

poly (MAOTW ) (8)

polyiMAOT -alt-MAOT Me ) (11)

Polymethacrylates containing thymine derivatives.


305

POLYMERS IN MICROLITHOGRAPHY

306

derivatives of thymine followed by the reaction of another cyclic type of thymine derivatives (18). Bis-pyrimidine derivatives were prepared by the reaction of the hydroxyethyl derivatives of pyrimidine with various bifunctional compounds such as dichloro-siloxane derivatives (Figure 3) (20).


Positive Type Photoresists: Polyamides containing thymine photodimer units in the main chain (17a,b) were prepared by polycondensation of thymine photodimer derivatives (15a,b), which were obtained by the photochemical reaction of the monomeric compound, and various diamines by the activated ester method (Figures 4 and 5) (17, 19). Instrumentation The photosensitivity spectra were recorded on a Nihon spectrophotograph, CT-40 and a 500 W Xe-short arc lamp was chosen as the deep-UV source. A Canon mask aligner (PLA-521F) with cold mirror (CM250, in the case of resolution evaluation of the positive photoresist, and CM290 in the case of negative type photoresist) was used as the UV irradiation instrument in which a Xe-Hg lamp was chosen as the light source, and irradiation of the silicon wafers were carried out with contact printing through a mask. Ultraviolet spectra were measured with a Nihon-Bunko (UVIDEC-660) spectrophotometer. Glass transition temperature (Tg) of the polymers were measured with a Seiko differential scanning calorimeter(DSC-20). The molecular weight distribution of the polymers were determined by GPC method using Toyo Soda HLC-CP8000 with a thermostated column TSK gel G4000HT, and a UV detector operating at 270 nm with dimethylformamide as the eluent.

RESULTS AND DISCUSSION Photodimerization of the Pyrimidines Photochemical reactions of the pyrimidine polymers in solution were studied to determine the quantum yields of the intramolecular photodimerization of the pyrimidine units along the polymer chains. Photoreactions of the polymers were carried out in very dilute solutions to avoid an intermolecular(interchain) photodimerization. Quantum yields determined at 280 nm for the polymers (1-6 in Figure 1) are listed in Table I. The quantum yield of the 5-bromouracil polymer [poly(MA0U-5Br)] could not be determined because of side reactions of the base during the irradiation. Among the examples shown in Table I, the 5-cyanouracil derivative [poly(MA0U-5CN)] had the lowest photochemical reactivity, while the 6-cyanouracil analog [poly(MA0U-6CN)] had the highest reactivity. The highest photodimerization reactivity of the 6-cyanouracil derivative might be caused by the capto-dative substituent effect; the electron donating group is the N - l group, and the electron acceptor group is the cyano group (12).


18. INAKI ET AL.

CN

CN

^ N - S

0

f^N'

O^NÔ

O^NÔ

Ç 2

Ç 2

H

2

0

" l \

C H 3

H C^ ^CH

H

Â

3

N

O^N^CN NC^NÔ CH

H

CH -0-X-0-CH

CH

2

CH -0-X-0-CH

2

2

(18) Downloaded by PEPPERDINE UNIV on August 24, 2017 | http://pubs.acs.org Publication Date: October 31, 1989 | doi: 10.1021/bk-1989-0412.ch018

307

Pynmidine Derivatives as Lithographic Materiah

H C^ .CH3

3

3

O^NÔ CH

2

2

N

O^NÔ CH

2

CH "0- X~0*CH

2

2

2

(19)

(20)

-Χ α : -Si(CH ) -0-Si(CH3) -0-Si(CH )23

b :

2

2

3

-Si(CH )^-0-Si(CH ) 3

3

-SiPh

Figure 3.

9

2

2

0-SiPh 2

Bis-pyrimidine derivatives.

î CH-» CH-» u

9 CH* M ÇH,CHC00H 2

HOOCCHCH 2

(15a)

î Oh Η S ^ C O O ^ ' 0

C

2

CHCHCOO-@>

2

2

2

E (mJ/cm ) 0

2

— 34.6 95.0 76.9 19.5 19.8

a) Quantum yields of photodimerization in dimethyl sulfoxide solution. b) Photosensitive wavelength range. c) Maximal photosensitive wavelength. d) Minimum required energy for photocrosslinking at the maximal wave length. The quantum yields for the polymeric thymine derivatives, 7-11 in Figure 2, determined at 280 nm in dimethyl sulfoxide solution are plotted against the molar composition of the polymers as shown in Figure 6a. Poly(MAOT -co-MAOT Me )s have lower quantum yields for intramo lecular photodimerization than polyiMAOT )and poly(MAOT Me ). Among the copolymers, polyiMAOT -alt- M A 0 T M e ) , in which the T and T M e base units are strictly alternating, has a slightly lower quantum yield than random copolymer, poly(MAOT -co-MAOT Me ) of the the same composition. These provided that the photodimerization reaction of the adjacent T and T M e bases imparts more strain to the polymer chain than the equivalent reaction of T units or T M e units. 1

3

1

1

1

3

3

1

1

1

3

1

1

3

3

1

1

1

1

3

a

Photopolymerization: Photopolymerizations of the bis-pyrimidine derivatives were carried out in solid film by irradiation with UV light from a s pec troir radiator. The rate of the photopolymerization was found to depend on the wavelength of light. The highest reactivity was observed at ~ 300 nm (Figure 7a), while the highest reactivity for photoreversal of the photodimer was obtained by irradiation at ~ 240 nm (Figure 7b). The polymers obtained the photopolymerization were not soluble in ethyl acetate. Therefore, sensitivity curves for insolubilization of the bis-pyrimidine derivatives via photopolymerization were obtained by development with ethyl acetate/toluene (Figure 8). The photopolymerization using an eximer laser (XeCl: 308 nm) source gave essentially the same result. Photoreversal of the Pyrimidine Photodimers Photodissociation of the polyamides (Figures 4 and 5) was carried out in the solid films. Polymer films (1-2 μ. m) were cast onto quartz substrates and were exposed to monochromatic 250 nm light from a spec troir radiator. The dissociation of the thymine photodimers was followed by monitoring the absorbance at 270 nm. The results obtained for the polyamide prepared from the reaction of propane diamine and the isomers of the thymine photodimer (cis-syn(17a), cis-anti(17b), and


18.

Pyrimidine Derivatives as Lithographic Materials

INAKIETAL.

0

t v « A H

ΗΝ

N

0 ^

CH I CH -C II

2


â:

L-N-40 F*2

-ICKCH > CNt

-

Polymers in Microlithography - American Chemical Society

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