Deposition of Fluorinated Amorphous Carbon Thin Films with Low Dielectric Constant and Thermal Stability
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Deposition of Fluorinated Amorphous Carbon Thin Films with Low Dielectric Constant and Thermal Stability Sang-Soo Han and Byeong-Soo Bae Laboratory of Optical Materials and Coating(LOMC), Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology(KAIST), 373-1,Kusongdong, Yusonggu,Taejon, 305-701, Korea ABSTRACT Fluorinated amorphous carbon (a-C:F) thin films were deposited by inductively coupled plasma enhanced chemical vapor deposition (ICP-CVD) with increasing CF4:CH4 gas flow rate ratio, and then annealed with increasing annealing temperature (100, 200, 300, and 400℃). We have found the reduction mechanism of the dielectric constant and the thermally stable condition for the a-C:F films. On the basis of the results, the optimal condition to satisfy both the low dielectric constant and the thermal stability is followed as ; the a-C:F films have to have the compatible F content to make a compromise between the two properties ; the C-Fx bonding configuration has to exist as a form of C-F2 & C-F3 instead of C-F ; The films should be somewhat cross-linked structure. INTRODUCTION Decrease of the feature size in integrated circuits makes interconnect lengths long and contributes to propagation delays due to the increase in RC time constant. Because highly conductive metals and low dielectric materials can reduce propagation delays, the low dielectric interlayer materials are required to improve the circuit performance. Promising candidate materials are fluoropolymers such as polytetrafluoroethylene (PTFE) since their dielectric constants are low (k~1.9) and mechanical strength is reasonably high [1-3]. However, polymer thin films have a difficulty to satisfy desired characteristics such as thermal stability, adhesion, and gap-filling property during integration processing in microelectronics. Thus, the fluorinated amorphous carbon thin films deposited using HDP-CVD (High Density Plasma Chemical Vapor Deposition) have been investigated as new interlayer dielectric materials since they may have similar composition to PTFE with cross-linked structures.[4-8] However, it has been reported that the low dielectric constant and the thermal stability are incompatible properties. Thus, the compromise between the two properties is required and the optimal condition to satisfy the two properties is more favorable to use the a-C:F films as an interlevel dielectrics. In this study, we investigated the reduction mechanism of dielectric constant in the a-C:F thin films and the thermally stable condition. From the results, we will present the optimal conditions to satisfy both the low dielectric constant and the thermal stability. EXPERIMENTAL a-C:F thin films were deposited on (100) p-type Si substrate by inductively coupled plasma enhanced chemical vapor deposition (ICP-CVD) with increasing CF4 gas flow rate (4, 8, 20, and 40 sccm) at constant flow rate of CH4 gas (4sccm), deposition temperature (25℃) and RF power
D5.6.1
(400W). More detailed experimental was described in the previous report
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