Investigation of fundamental mechanisms of pore and network formation in mesoporous low-k dielectrics by combining spectroscopic techniques

• Applicants: Professor Dr.-Ing. Stefan E. Schulz; Dr. Andreas Wagner
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Synthesis and Properties of Functional Materials
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 398216953

• Final Report Year: 2023

Final Report Abstract

In a collaborative effort the TU Chemnitz and the Institute for Radiation Physics at the Helmholtz- Zentrum Dresden-Rossendorf studied fundamental mechanisms for the formation of porous network structures of ultra low-k dielectrics. The investigations included the comparison between the two production processes of chemical vapor deposition (CVD) and the spin-on process (SP), followed in both processes by the temperature-induced curing process. Micropores could be found in both materials while those produced by SP also contain larger mesopores. The number of micropores generated inside the network matrix has shown no dependence on the curing time. Moreover, a larger restructuring of the network material occurs in spinon materials. The pore size distribution and the number of pores are also higher for spin-on materials but they show the same dielectric constant. Surprisingly, the spin-on dielectrics studied were found to be unsuitable for use in highly-integrated circuits due high porosities with significantly larger pore diameters and the onset of pore-crosslinking. Specifically, the pore-crosslinking can lead to a high degree of damage by process steps such as structuring by plasma etching. This crosslinking of the pores was observed at higher curing temperatures (T > 400 °C). The reason for this is the breaking of the Si-CH3 bonds, which can cause the transition from isolated pores to interconnected pores for already existing high pore volumes. CVD-dielectrics, on the other hand, are therefore much more suitable for use in the leading edge region, whereas a purely thermal curing process does not cause pore crosslinking but it can result in defective network bonds, which in turn favors water absorption. This effect increases with increasing porosity and it also occurs after the Si-CH3 bonds are broken. UV-assisted curing can prevent the formation of such defective bonds in CVD materials. However, the additional radiation leads to the formation of carbon-rich residues in the material, which, just like the absorption of water, can lead to a degradation of electrical properties. Based on these studies, it can be concluded that the use of porous ultra-low-k materials should be carried out by CVD processes, since neither mesopores are expected, nor does crosslinking of the pores occur, thus ensuring the functionality of the circuit.

Publications

• Ultra lowk organosilica films with benzene bridge and small pore size," Advanced Metallization Conference 2019 (ADMETA 2019), Oktober 2019
  C. Liu, C. Lv, N. Koehler, X. Wang, H. Lin, Z. He, S. Wei, J. Zhang und M. R. Baklanov
  
• A detailed ellipsometric porosimetry and positron annihilation spectroscopy study of porous organosilicate-glass films with various ratios of methyl terminal and ethylene bridging groups. Microporous and Mesoporous Materials, 306 (2020, 10), 110434.
  Rasadujjaman, M.; Wang, Y.; Zhang, L.; Naumov, S.; Attallah, A.G.; Liedke, M.O.; Koehler, N.; Redzheb, M.; Vishnevskiy, A.S.; Seregin, D.S.; Wu, Y.; Zhang, J.; Leu, J.; Wagner, A.; Vorotilov, K.A.; Schulz, S.E. & Baklanov, M.R.
  
• Fundamental studies on the curing behavoir of porous CVD and spin-on dielectrics. 2020 IEEE International Interconnect Technology Conference (IITC) (2020, 10, 5), 112-114. American Geophysical Union (AGU).
  Koehler, Nicole; Attallah, Ahmed G.; Liedke, Maciej O.; Butterling, Maik; Hirschmann, Eric; Ecke, Ramona; Wagner, Andreas & Schulz, Stefan E.
  
• Positron annihilation analysis of nanopores and growth mechanism of oblique angle evaporated TiO2 and SiO2 thin films and multilayers. Microporous and Mesoporous Materials, 295, 109968.
  García-Valenzuela, Aurelio; Butterling, Maik; Liedke, Maciej Oskar; Hirschmann, Eric; Trinh, Thu Trang; Attallah, Ahmed G.; Wagner, Andreas; Alvarez, Rafael; Gil-Rostra, Jorge; Rico, Victor; Palmero, Alberto & González-Elipe, Agustín R.
  
• Properties of organosilicate low-k films with 1,3- and 1,3,5-benzene bridges between Si atoms. Japanese Journal of Applied Physics, 59(SL), SLLG01.
  Liu, Chunhui; Lv, Chunguang; Kohler, Nicole; Wang, Xuesong; Lin, Hongxiao; He, Zhiwei; Wu, Yu-Hsuan; Leu, Jihperng; Wei, Shuhua; Zhang, Jing; Yan, Jiang; Palov, Alexander P. & Baklanov, Mikhail R.
  
• Thermal kinetics of free volume in porous spin-on dielectrics: Exploring the network- and pore-properties. Microporous and Mesoporous Materials, 308 (2020, 12), 110457.
  Attallah, A.G.; Koehler, N.; Liedke, M.O.; Butterling, M.; Hirschmann, E.; Ecke, R.; Schulz, S.E. & Wagner, A.