Novel Approach for the Improvement of Post Exposure Delay Stability in ArF Resist Composed of Alicyclic Polymer

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1 Journal of Photopolymer Science and Technology Volumel2,Number3(1999) TAPJ Novel Approach for the Improvement of Post Exposure Delay Stability in ArF Resist Composed of Alicyclic Polymer Jae-Chang Jung, Hyeong-Soo Kim, and Ki-Ho Baik Semiconductor Advanced Research Division, Hyundai Electronics Industries Co., San 136-1, Ami-ri, Bubal-eub, Ichon-si, Kyoungki-do, , Korea, Tel : , Fax : Gci_u_ngna r. hei. co. kr Ltd. To overcome post exposure delay (PED) effect caused by airborne contamination, novel concept of rheological approach was introduced. By changing the polymer structures in resist solution, shear thinning resists were made. The method to make shear thinning resist includes, using of shear thinning solvent, modification of polymer structure, and temperature control of resist solution. Shear thinning resists exhibit good PED stability. Keywords: shear thinning resist, post exposure delay, ArF resist, alicyclic polymer Introduction After a lot of research and development efforts, KrF DUV (X=248nm) lithography has been successfully introduced into high volume semiconductor manufacturing for 180nm applications and is being pushed to its limit down to sub-150nm regime. ArF DUV (? =193nm) lithography is rapidly emerging after the 248nm lithography because of the demand for further resolution improvement and wider DOF (Depth Of Focus). However, the 193nm lithography requires innovative development in various areas, such as laser sources, resist chemistry, and optics materials. A considerable progress has been made for the 193nm lithography recently. ArF excimer laser sources with high power and ArF resist with the high resolution, large DOF, good adhesion, and good etch resistance have been demonstrated. ArF optics with a new material (CaF2) and new multicoating lenses to reduce lenses damage have been demonstrated. Chemically amplified resist system was introduced as a best solution for DUV resist in order to cope with lower illumination power with maintaining high throughput and the only used resist system for application in DUV resist. [ 1 '4] However, in spite of its wide acceptance as production worthy materials, there was a obstacle to be solved, so-called "Post Exposure Delay(PED) effect". This PED effect deteriorated latent image of photoresist and formation of T-top profile which could make line width variations. [5~ l 0] By 14C labeling technique, it was found that the contamination by airborne was the main cause of PED effectj5,6,11] To overcome PED effect, a lot of research efforts have been performed. The annealing concept was introduced to solve PED effect problem. [ 12'- 16] Other methods for solving PED effect are addition of organic base[17, 18, 19], over coating method[20, 21], and using of acetal type polymer[22]. As the transition of wavelength from 248nm to 193nm, the chemistry related treatment methods for PED stability can not applied into 193nm resist materials. Because of the 193nm absorption of aromatic resin, the base resin of 193nm resist had to be an aliphatic resin.[23'32] In order to have etch resistance, the aliphatic resin had to contain cyclic moieties in its resin. However, these alicyclic moieties increased Tg of resin. To anneal these high Tg resin, annealing temperature, soft bake temperature (SB), also had to be high and post exposure bake(peb) also high for acid diffusion. But high PEB made poor profile by high diffusion of acid. In case of organic base additives, especially amine additive, the amine reacted with maleic anhydride and made amide linkage. Amide linkage highly absorbed 193nm radiation and made slope profile. In this Received Accepted April 20, 1999 June 1,

2 I. Photopolym. Sci. Technol., Vol.12, No.3, 1999 paper, we will scrutinize old method for PED effect and propose a new approach, "rheological approach" for PED stability study. Using this rheological method, we can apply to synthesis of highly PED stable photoresist for 193 nm. Experimental Preparation of polymer and photoresist solution As shown in 1, polymer was synthesized and supplied by Dong Jin Chem. Ind. Co., Ltd. as the same formula in early publications.[29, 30, 33] The triphenylsulfonium triflate (TPST) was used as a photo acid generator (PAG). To make a resist solution, polymer and TPST were dissolved in various solvents. The resist solutions were filtered through 0.2 µm membrane filter. held at this temperature for 3 min and they cooled at rate 20t/min. The exposures carried out on an ISI ArF stepper (X193nm, =NA=0.6) with Off-Axis Illumination. Results and Discussion Resist solvent dependency on PED effect The resist consists of the Poly[HNC/NC/ BNC/MA] (see 1), TPST as a PAG and PGMEA as a solvent. Under the severe amine contaminated environment ('35 ppb), when the SB and PEB conditions are 110 C for 90 s, we could not obtain any pattern up to 80 mj/cm2. 2 SEM micrographs for 0.13,um 1:1 VS patterns obtained with top coating 1 Synthetic scheme of Poly[HNC/NC/BNC/MA] Characterization The molecular weight of polymer was determined by gel permeation chromatography (GPC) in tetrahydrofuran using a TOSOH HLC The molecular weight of this synthesized polymer is between 5,700 and 1,000 and its poly dispersity is between 1.30 and The shear viscosities of resist solution were measured by an Advanced Rheometric Expansion System (ARES) (Rheometrics, Inc.). In the rheological measurements, a couette fixture (cup diameter=50mm; bob diameter=48mm; bob length=25mm) was employed and the shear rate sweep test carried out from 0.01 s' to 500 s' at 25 C. The thermal characterization studies were carried out on a Perkin-Elmer, DSC-7. The heating rate was 20 C /min and calibration of the instrument was carried out on a high purity indium and zinc. Before the dynamic scanning measurement, the samples were heated to 170 C, At the same bake condition with over coating materials, we obtained 0.13 tm 1:1 L/S pattern as shown in 2. This main difference was caused by amine contamination. However, with KrF exposure tool (NA=0.6) where chemical filter was installed to keep low amine contamination (< 1 ppb), as shown in 3 there is no big difference between resist and over coated resist. We thought that poor environmental stability was caused from large free volume of resist film, so airborne materials easily penetrated resist film through this free volume. To minimize this free volume, we tested several resist solvents that could make the polymer rigid rod or ellipsoidal structure. The basic concept is that if polymer has rigid rod or ellipsoidal structure at highly shear condition, it orients parallel to the share direction and is coated more tightly and small free volume will be formed. Of course, high shear condition means high rpm coating method of resist. 4 is the viscosity change to the share rate depending on the resist solvents. The resist solutions of Isobutyl methyl ketone (IBMK), 2-Heptanone (2-H), and (2- Methoxy)ethyl acetate (MEA) are shear thinning fluid but that of PGMEA is Newtonian fluid. From 4, we can guess the resist polymer shapes in 470

3 4 3 SEM micrographs for 0.16,um 1:1 L/S pattern obtained (a) with top coating, (b) without top coating using chemical filter established KrF exposure tool(2=248nm, 0.6 NA, OAI) Shear viscosity of various resist solution of Poly [HNC/NC/BNC/MA] solvents. In the case of IBMK solvent which is the most shear thinning resist, the polymers exist in the highly ellipsoidal structure and they are more tightly coated than any other solvent and small free volume will be formed during coating. From the order of shear thinning degree we can guess that the order of PED stability is IBMK, 2-H, MEA, and PGMEA. 5 is the real experimental data of optimum energy to obtain 0.24 tm L/S pattern for various PED times. When SB and PEB 5 Optimum exposure energy to obtain 0.24 pm 1:1 LIS under 35 ppb amine contaminated condition with resist solutions for various FED times. of IBMK is the most stable solvents for PED but there is no major difference among the other shear thinning resists. In the case of PGMEA (Newtonian fluid), it demonstrates poor PED stability. With 130 C/90 s SB and PEB condition, sub-0.20 tm patterns could not be obtained. When the SB condition is 150 C/90 s and PED condition is 140 C/90 s resist pattern up to 0.13µm L/S obtained pm 1:1 L/S patterns of 6 show PED stability of resist for various solvents. When we used PGMEA, vertical fine pattern could be obtained with 8 mj/cm2 exposure energy at 5 min PED delay. But in the case of 15 min delay, we could observe delay effect at the top of the patterns as shown in 6. After 30 min delay, there is serious delay effect and spade shape patterns were obtained. The exposure energy is 15 mj/cm2 that is about two times to compare with the case of 5 min delay. In the case of MEA solvent, the tendency of delay effect is similar to that of PGMEA but the exposure does is lower than PGMEA. In the case of 2-H solvent which is more shear thinning resist than MEA, though the pattern was collapsed in 6, better PED stability observed in profile than PGMEA. In addition to, the exposure energy is IOmJ/cm2 that is only 2mJ/cm2 bigger energy than 5 min delay case. When we used IBMK as a resist solvent it shows the highest shear thinning resist. As expectation, we can observe high PED stability of IBMK resist as shown in 6. Any serious change cannot be observed between 5 min and 15 min delay case in profile and exposure energy. In the case of 30 min delay, slight T- top profile 471

4 b 0.15 /tm 1:1 L/S patterns obtained under 35ppb amine contaminated condition for time with Poly[HNC/NC/BNC/MA]. various PED 472

5 J. Photopolym. Sci. Technol., Vo1.12, No.3, um 1:1 L/S patterns obtained under 35ppb amine contaminated condition for various PED time with polymer (A) tm 1:1 L/S patterns obtained PED time with polymer (B). under 35ppb amine contaminated condition for various tm 1:1 L/S patterns obtained under 35ppb amine contaminated condition for S min PED with Poly [HNC/NC/BNC/MA]. 473

6 ,um 1:1 L/S patterns obtained under 35ppb amine contaminated condition for 25 min PED with polymer(a). 11 Depth of focus of 0.13 pm 1:1 L/S patterns obtained under 35ppb amine contaminated condition for 35 min FED with polymer(a). Exposure energy is 30mJ/cm and 0.15pm 1:1 LJS patterns obtained under 35ppb amine contaminated condition for various FED time with Poly[HNC/NC/BNC/MA]. Resist solution temperatures are 40 and 50 ~: 474

7 observed and exposure energy is 3mJ/cm2 higher energy than 5 min delay case. However, the low boiling point of IBMK makes it difficult to use as a resist solvent due to the thickness variation. Therefore, we selected 2-H solvent as a standard resist solvent in the following evaluation. Resin structure dependency on PED effect From the solvent dependency of PED effect, we observed that when resist polymer existed in rigid rod or ellipsoidal structure in solvent, it showed good PED stability. Therefore, we have focused on the development of new resin that has pseudo shear thinning fluid in solvent. Two kinds of resists were developed with very tiny modification of Poly[HNC/NC/ BNC/MA]. 7 is the 0.15 µm L/S patterns that obtained by using type (A) polymer for various delay times. The polymer (A) is shear-thinning fluid in both PGMEA and 2-H. From the profile of delayed patterns of 7, resists that formulated with polymer (A) show strong PED stability in both PGMEA and 2-H solvent. The vertical profiles of 7 give strong evidence that the resist structure in solvent affects the PED stability. The resists of 2-H require 26 mj/cm2 exposure energy for 35 min delay and 20 mj/cm2 min for 10 min delay case. But the resist of PGMEA requires 35 mjlcm2 exposure energy for 35 min delay and 25 mjlcm2 min for 10 min delay case. 2-H resist requires 30% more energy in 35 min delay case than 10 min delay case and PGMEA resist requires 40% more energy, which can be explained as solvent dependency of PED effect as explained previous section. 8 shows SEM micrographs of Polymer (B) resist for PED variation. Of course, Polymer (B) is also shear thinning fluid in both PGMEA and 2-H solvent. Because of stronger PED stability of 2-H solvent, PED effect was tested for 2-H solvent case only. Polymer (B) shows high PED stability as Polymer (A) resist. After 5 min delay, the resolution limit of poly[hnc/nc/bnc.ma] with various solvent is 0.13 µm as shown in and 11 indicate the resolution limit of polymer (A) resist with various delay times µm L/S pattern can be obtained after 25 and 35 min PED under severe amine contaminated condition (35ppb). If we assume that the only mechanism of PED effect is amine contamination and transfer of amine into the wafer is controlled by effusion, 35 min delay corresponds to 6 hours delay in 1 ppb amine contaminated condition. 12 is the DSC curves of Poly[HNC/NC/BNC/MA], polymer (A), and polymer (B). No major change was detected in DSC curves. As we made tiny modification for making shear-thinning polymer, detectable change would not happen. To compare with PB condition and thermal history of DSC, we conclude that the PED stability of Polymer (A) and (B) is not caused by annealing effect but by shear thinning effect of polymer in solution. Solution temperature dependency of resist on PED effect As structure of polymer in solution is strongly dependent upon temperature, perturbation of polymer structure by controlling of temperature of resist solution can be a solution for PED effect. As shown in 13, when the coating temperature of resist solution is 40 and 50 C, PED stability enhanced. The resolution limit of high temperature coated resist after 10 and 20 min delay was shown in Fig 13. This solution temperature effect also can be evidence that polymer structure in resist solution can increase PED stability of resist. 12. DSC curves of three type of polymer Conclusions To overcome PED effect caused by airborne contamination, we have focused on changing the polymer structures in resist solution and found that shear thinning resists made by changing solvent, modification of polymer structure, and resist solution temperature exhibit good PED stability. Using these methods, 0.13 tm L/S patterns can be obtained in severe amine contaminated environment (35ppb) after 35 min PED. Acknowledgements The authors would like to express our thanks to 475

8 Dr. I1-Hyun Choi and Dr. Dae-Noon Lee for their supports and interests for this project and to Chi- Hyeong Roh and Keun-Kyu Kong for the assistance of new resin synthesis and resist evaluation. We thank to Seok-Ho Hwang of KITECH for the shear viscosity study and Dr. Joo- Hyun Park and Dr. Sung-Joo Kim of Kumho Petrochemical Co. for supplying TSPT. We also thank Se-Jin Choi, Hyun-Jin Kim, Seung-Il Hyun, Deog-Bae Kim of Dong Jin Chem. Ind. Co., for the supplying of Poly[HNC/NCIBNC/MA]. References 1. H. Ito C. G. Willson, Technical Papers of SPE Regional Conference on Photopolymers, (1982) H. Ito, C. G. Willson, and J. Frechet, Digest of Technical Papers of 1982 Symposium on VLSI Technology, (1982) H. Ito, C. G. Willson, and J. Frechet, US Patent No. 4,491,628, (Jan. 1, 1985) 4. H. Ito, in "New Aspects of Radiation Curing in Polymer Science and Technology ", J. P. Fouassier and J. F. Rabek, eda., Elsevier, London, 4, (1993) Chapter S. A. MacDonald, N. J. Clecak, H. R. Wendt, C. G. Willson, C. D. Snyder, C. J. Knors, N. B. Deyoe, J. G. Maltabes, J. R. Morrow, A. E. McGuire, and S. J. Holmes, Proc. SPIE, 2, (1990) S. A. MacDonald, W. D. Hinsberg, H. R. Wendt, N. J. Clecak, C. G. Willson, and C. D. Snyder, Chem. Mater., 5, (1993) Nalamasu, E. Reichmanis, M. Cheng, V. Pot, J. M. Kometani, F. M. Houlihan, T. X. Neenan, M. P. Bohrer, D. A. Mixon, L. F. Thompson, and C. Takemoto, Proc. SPIE, 1466, (1991) G. Schwartzkopf, N. N. Niazy, S. Das, G. Surendran, and J. B. Covington, Proc. SPIE, 1466, (1991) L. Schlegel, T. Ueno, N. Hayashi, and T. Iwayanagi, J. Vac. Sci. Technol., B9(2), (1991) H. Ban. J. Nakamura, K. Deguchi, and A. Tanaka, J. Vac. Sci. Technol., B9(6), (1991) W. D. Hinsberg, S. A. MacDonald, N. J. Clecak, and C. D. Snyder, J. Photopolymer Sci. Technol., 6, (1993) W. D. Hinsberg, S.A. MacDonald, N. J. Clecak, C. D. Snyder, and H. Ito, Proc. SPIE, 1925, (1993) H. Ito, W. P. England, R. Sooriyakumaran, N. J. Clecak, G. Breyta, W. D. Hinsberg, H. Lee, and D. Y. Yoon, J. Photopolymer Sci. and Technol., 6, (1993) G. Breyta, D. C. Hofer, H. Ito, D. Seeger, K. Petrillo, H. Moritz, and T. Fischer, J. Photopolymer Sci. and Technol, 7, (1994) H. Ito, G. Breyta, D. Hofer, R. Sooriyakumaran, K. Petrillo, and D. Seeger, J. Photopolymer Sci. and Technol, 7, (1994) H. Ito, G. Breyta, R. Sooriyakumaran, and D. Hofer, J. Photopolymer Sci. and Technol, 8, (1995) Y. Kawai, A. Otaka, J. Nakamura, A. Tanaka, and T. Matsuda, J. Photopolymer Sci. and Technol., 8, (1995) S. Saito, N. Kihara, T. Naito, M. Nakase, T. Nakasugi, and Y. Kato, J. Photopolymer Sci. and Technol., 9, (1996) S. Funato, Y. Kinoshita, T. Kuto, S. Masuda, H. Okazaki, M. Padmanaban, K. J. Przybilla, N. Suehiro, and G. Pawlowski, J. Photopolymer Sci. and Technol., 8, (1995) J. Nakamura, H. Ban, Y. Kawai, and A. Tanaka, J. Photopolymer Sci. and Technol., 8, (1995) A. Oikawa, Y. Hatakenaka, Y. Ikeda, Y. Kokubo, S. Miyata, N. Santoh, and N. Abe, J. Photopolymer Sci. and Technol., 8, (1995) T. Hattori, A. Imai, R. Yamanaka, T. Ueno, and H. Shiraishi, J. Photopolymer Sci. and Technol., 9, (1996) R. D. Allen et al., J. Photopolymer Sci. and Technol., 11, (1998) R. D. Allen et al., Proc. SPIE, 2724, (1996) R. D. Allen et al., J. Photopolymer Sci. and Technol., 9, (1996) K. Nozaki and E. Yano, J. Photopolymer Sci. and Technol., 10, (1997) K. Nakano, K. Maeda, S. Iwasa, and E. Hasegawa, J.Photopolymer Sci. and Technol., 10, (1997) Thomas I. Wallow, Francis M. Houlihan, Omkaram Nalamasu, Edwin A. Chandross, Thomas X. Neenan, and Elsa Reichmanis, Proc. SPIE, 2724, (1996) J. C. Jung, C. K. Bok, and K. H. Baik, Proc. SPIE, 3333, (1998) J. C. Jung, M. H. Jung, and K. H. Baik, J. Photopolymer Sci. and Technol, 11, (1998) U. Okoroanyanwu, J. Byers, T. Shimokawa, and C. G. Wilson, Chem. Mater. 10, (1998) J. Byers, K. Patterson, S. Cho., M. McCallum, C. G. Willson, J. Photopolymer Sci. and Technol., 11, (1998) J. C. Jung, C. K. Bok, and K. H. Baik, J. Photopolymer Sci. and Technol, 10, (1997)