Novel negative resists for ArF excimer laser lithography based on the crosslinking reaction between acetal and hydroxyl groups were evaluated with copolymers of Cholic acid methacrylate and 1,3 Dioxolane-2-yl-ethyl methacrylate. The work of adhesion increases as the amount of 1,3 Dioxolane-2-yl-ethyl methacrylate in the copolymer increases, which means cyclic ethers enhance adhesion. The polymers have a good transmittance at 193nm and possess good thermal stability up to 230 ℃. But due to low hydrophile-lipophile balance, they were not developed by TMAH solution. To promote developability in TMAH solution, we introduced itaconic anhydride into the copolymer and the resist formulated with this material shows the resolution of 5μm pattern at a dose of 45 mJ $cm^{-2}$ using a mercury-xenon lamp in a contact printing mode and TMAH as a developer.
Two kinds of homopolymers derived from cholic and lithocholic acids containing cyclic acetal as a pendant crosslinker, poly(1,3dioxolane-2-yl-ethyl cholate methacrylate) and poly(1,3dioxolane-2-yl-ethyl lithocholate), were synthesized for negative photoresists. Cyclic acetals were confirmed to crosslink with hydroxyl groups of bile acids. From the high values of work of adhesion of homopolymers with pendant cyclic acetals, cyclic ethers are proved to be a good adhesion enhancer. Negative photoresist using poly(dioxolane cholate methacrylate) showed a resolution of 5 ㎛.
Alicyclic polymers have the necessary transparency and etch resistance, but their incorporation gives rise to poor adhesion to a silicon substrate. Therefore, hydrophilic moiety such as a hydroxyl group should be incorporated in the matrix polymer. However, the matrix polymer containing hydroxyl groups showed foot profiles due to cross-linking during a lithographic process. Poly (norbornene-2-carboxylic acid tert-butyl lithocholate ester-co-succinic acid 2-(5-norbornene-2-carbonyloxy)-ethyl ester ethyl ester-co-maleic anhydride) was synthesized. The succinic acid ester group was introduced into the matrix polymer in order to improve adhesion on a silicon wafer without causing cross-linking during post-exposure bake. The work of adhesion of the resist increased as the content of succinic acid 2-(5-norbornene-2-carbonyloxy)-ethyl ester ethyl ester group increased. The dry-etch resistances of Poly (norbornene-2-carboxylic acid tert-butyl lithocholate ester-co-succinic acid 2-(5-norbornene-2-carbonyloxy)-ethyl ester ethyl ester-co-maleic anhydride) are much better than that of poly(tert-butyl methacrylate) and comparable to that of poly(4-hydroxystyrene). The resist formulated with Poly (norbornene-2-carboxylic acid tert-butyl lithocholate ester-co-succinic acid 2-(5-norbornene-2-carbonyloxy)-ethyl ester ethyl ester-co-maleic anhydride) gave 0.15 ㎛ line and space patterns without foot profiles.
We have synthesized a new type of matrix polymer, poly(tert-butyl cholate methacrylate-co- γ-butyrolactone-2-yl methacrylate), which has alicyclic groups and cyclic esters in side chains. A 0.15 ㎛ line and space patterns were obtained at a dose of 11 $mJ/cm^{-2}$ using an ArF excimer laser stepper and 2.38 wt.-% TMAH aqueous solution as a developer. The dry-etching resistance of this resist was better than that of the poly(4-hydroxystyrene) for $CF_4$ -based gas.
We proposed a new type of matrix polymer, Methyl 4-(14-methacryloyloxy-18-hydroxy-6,11-dimethyl-7-oxa-8-oxotetracyclo$[8.8.0.0^{2,6}.0^{11,16}]$ octadec-5-yl) pentanoate which contains 7,7-dimethyloxepan-2-one group as acid labile groups. $^{13}C$ NMR spectroscopy investigation confirmed the acid-catalyzed ring opening reaction of 7,7- dimethyloxepan-2-one group into the carboxylic acid. The matrix polymer does not release the gaseous byproducts due to the ring-opening reaction during and after exposure.
Cholic acid methacrylate와 1,3 Dioxolane-2-yl-ethyl methacrylate을 공중합 하여 이들의 아세탈과 하이드록실기의 가교반응에 의한 네가티브 포토레지스트의 특성을 검토하였다. 1,3 Dioxolane-2-yl-ethyl methacrylate 의 공중합 비율이 클수록 접착일이 증가하는 것에서 사이클릭 에텔이접착력을 증가하는 역할을 하는 것이 확인되었다. Poly(CAM-co-DEM)은 193nm에서 투과도가 양호하였으며 230oC까지 내열성을 갖고 있다. 그러나 본 고분자의 HLB값이 낮아서 TMAH에 현상이 안 되었으나 itaconic anhydride와의 삼원공중합체는 TMAH에 현상성이 좋았으며 본 삼원공중합체를 이용한 포토레지스트는 수은크세논 램프로 $45 mJ cm^{-2}$ 로 노광, TMAH에 현상시 해상도 5μm의 패턴을 얻었다.
가교제로서 사이클릭 아세탈을 각각 공유결합한 콜린산과 리소콜린산의 메타아크릴레이트를 이용한 호모폴리머인 Poly(1,3dioxolane-2-yl-ethyl cholate methacrylate)와 Poly(1,3dioxolane-2-yl-ethyl lithocholate)을 네가티브 포토레지스트용으로서 중합하였다. 사이클릭 아세탈은 알리사이클릭 하이드록실기와 가교반응하는 것이 NMR로 확인되었다. 하이드록실기가 없는 Poly(1,3dioxolane-2-yl-ethyl lithocholate)에서도 접착일의 수치가 높은 것에서 사이클릭 아세탈은 접착력을 증진하는 기능이 있음을 확인하였다. poly(dioxolane cholate methacrylate)을 이용한 네가티브 포토레지스트는 해상도 ㎛ 의 패턴을 나타내었다.
알리사이클릭 폴리머는 자외선에 대한 투명성과 에칭저항성이 좋으나 실리콘 기재에 대한 접착력이 나쁘다. 따라서 하이드록실기와 같은 친수성기가 도입된다. 그러나 하이드록실기가 도입된 포지티브 레지스트는 리소그라피 공정에서 가교에 의한 footing현상이 일어난다. Poly (norbornene-2-carboxylic acid tert-butyl lithocholate ester-co-succinic acid 2-(5-norbornene-2-carbonyloxy)-ethyl ester ethyl ester-co-maleic anhydride)를 합성하였다.. succinic acid ester group이 고분자에 도입됨으로서 실리콘 웨이퍼에 대한 접착력이 개선되었으며 본 고분자를 이용한 포지티브 레지스트는PEB과정에서 footing현상이 없었다. 본 공중합수지에서 succinic acid 2-(5-norbornene-2-carbonyloxy)-ethyl ester ethyl ester group 이 증가함에 따라 접착일이 증가하였다. Poly (norbornene-2-carboxylic acid tert-butyl lithocholate ester-co-succinic acid 2-(5-norbornene-2-carbonyloxy)-ethyl ester ethyl ester-co-maleic anhydride)의 에칭 저항성은 poly(tert-butyl methacrylate)보다 월등히 우수하였으며poly(4-hydroxystyrene)에 필적하는 정도였다. Poly (norbornene-2-carboxylic acid tert-butyl lithocholate ester-co-succinic acid 2-(5-norbornene-2-carbonyloxy)-ethyl ester ethyl ester-co-maleic anhydride)를 이용한 포지티브 포토레지스트는 footing현상이 없었으며 0.15 ㎛의 line and space patterns을 보였다.
알리사이클릭 구조와 사이클릭 에스텔 구조가 있는 고분자Poly(tert-butyl cholate methacrylate-co- γ-butyrolactone-2-yl methacrylate)을 합성하였다. 본 고분자를 이용한 포지티브 포토레지스트는 ArF excimer laser stepper 에 의한 $11 mJ/cm^{-2}$ 의 노광 및 2.38 wt.-% TMAH에 의한 현상에서 0.15 ㎛의 해상도를 나타내었다. $CF_4$ 에 대한 본 레지스트의 에칭저항성은 Poly(4-hydroxystyrene)보다 우수하였다.
모노머에 acid labile group인7,7-dimethyloxepan-2-one group을 함유하는 매트릭스 폴리머, Methyl 4-(14-methacryloyloxy-18-hydroxy-6,11-dimethyl-7-oxa-8-oxotetracyclo$[8.8.0.0^{2,6}.0^{11,16}]$ octadec-5-yl) pentanoate acid 를 합성하였다. $^{13}C$ NMR spectroscopy로 조사한 결과, 7,7- dimethyloxepan-2-one group이 산 촉매에 의하여 carboxylic acid로 변한 것을 확인하였다. 본 매트릭스 폴리머는 노광 중 및 노광 후 개환에 의한 기체상 부산물을 발생하지 않는다.
