Preparation And Characterization Of Low-dielectric Constant SiCOH And SiCOF Films

As the feature size decreases in Ultra Large-scale integrated circuits, the parasitic resistance and capacitance coupling (RC delay) become the determining factor for the signal propagation. In order to decrease the RC delay, ultra low-dielectric-constant (low-k) materials (k<2.3) have been investigated widely in semiconductor and material industries. Besides low k value, the ideal low-k dielectrics should have good mechanical strength, thermal stability and low leakage current.In this thesis, the porous SiCOH film was selected as the low-k materials due to the incorporation of weak polar carbon groups and nano-pores for the sake of lower k value. The performances of this film are also studied, such as chemical composition and structure, electrical and mechanical properties. The main contents are as follows.Ultra-low-k porous SiCOH films are prepared, using 1,2-bis(triethoxysily)ethane (BTEE), triethoxymethylsilane (MTES) as the precursors, and Brij76 as the porogen. Through spin-coating method, ultralow-k:SiCOH films are successfully prepared. The Thermal Gravity Analysis results show that all samples lose about 35%-45% weight through the thermal treatment at 450℃ for 2 hours. The Fourier transform infrared (FTIR) results show that the porogen is effectively removed through annealing at 450℃. Nanoindention test shows that mechanical properties are significantly improved. After the thermal treatment at 450℃ for 2 hours, films with molar ratio of MTES:BTEE:Brij76=1:1:0.125 exhibit an ultralow-k of ～2.2 and a leakage current density of 9.3×10-10 A/cm2 at 0.8 MV/cm. In virture of such an ultralow-k value, The aforementioned film is further characterized. The result shows the excellent mechanical properties with Er of～8.5 GPa and H of～1.17 GPa.SiCOF films are prepared with triethoxymethylsilane (MTES), O2 and C2F6 by Plasma Enhanced Chemical Vapor Depostion (PECVD). With fixed 200℃ deposition temperature and the RF frequency of 13.56 MHz, the effect of different RF power and C2F6 flow rate on electrical performance is discussed.Consequently, it is hard to successfully deposit SiCOF films with RF power of 900W. As the RF power enhances, the deposition rate increases, and the k value decreases at first but increases above 500 W. Through changing C2F6 flow rate, lowest k value of 3.19 can be achieved.at the C2F6 flow rate of 500 sccm. X-ray Photoelectron Spectroscopy (XPS) results show that C and F elements have been successfully plugged into the films. The C 1s spectra shows that C exists as C-Si, C-C/C-H and C-CF. On the other hand, F is bonded as Si-F and C-F.Based on the experiments above, the promising condition to produce SiCOF low-κ films through PECVD is at 200 ℃ deposition temperature,13.56 MHz RF frequency,3 torr pressure,500 sccm flow rate of O2,500 sccm flow rate of C2F6,1 g/min liquid flow rate of MTES.In conclusion, ultralow-κ SiCOH films with excellent mechanical properties can be achieved, using BTEE and MTES as precursors, and Brij76 as porogen, by spin-coating method. In addition, SiCOF films with k value of 3.19 can be prepared through PECVD method. These materials are very promissing as interlevel dielectrics.