| As the feature size decreases in ultra large-scale integrated circuits, the parasitic resistance and capacitance coupling (RC delay) becomes 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 recently. Besides low k value, the low-k dielectrics also demand good mechanical strength, thermal stability and low leakage current.In this paper, for the sake of lower k value, the porous SiCOH film was selected as the candidate of low-k materials due to low-k value of organic materials and good mechanical strength and thermal stability of inorganic materials. We also systematically and comparatively studied the performances of this film, such as chemical composition and structure, thermal stability, electrical and mechanical properties.Porous SiCOH films have been prepared using 1,2-bis(triethoxysily)ethane (BTEE), triethoxymethylsilane (MTES) and a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (P123) template by means of spin-coating. The Fourier transform infrared (FTIR) indicates that carbon is incorporated into Si-O-Si network. Small angle X-ray diffraction (XRD) patterns of the films show the porous matrix. Nanoindention test reveals that the reduced modulous (Er) and hardness (H) enhance as the increase of BTEE, which indicates that the BTEE precursor has the function of strengthening frameworks of the films. After the thermal treatment at 350℃for 2 hrs, films with molar ratio of BTEE: MTES= 6:4 exhibit a low k value of～2.0 and a leakage current density of 3×10-8 A/cm2 at 1MV/cm. In virture of the ultra-low k value, this kind of film was selected and analyzed deeply for the application of ultra-low-k films.After being annealed between 350 and 500℃for 30min, FTIR and TGA analyses show good thermal stability and fluctuant lvalues of 1.9～2.2. Er～4.05 GPa and H of～0.32 GPa are measured by nanoindenter. Compared to 350℃anneal, higher temperature anneal can improve the mechanical strength of the low-k films, i.e., Er-4.05 GPa,H～0.32 after 500℃anneal, however, which still can not withstand CMP process for planarizing interlayer dielectric films. Therefore, UV irradiation was used to improve mechanical properties of low-k films further. As the time prolong, Er and H of samples increase. When the irradiation time is increased to 6 hours, Er and H reach to about 7.4 and 1.0GPa respectively. FTIR and X-ray photoelectron spectroscopy (XPS) analyses indicate that the cross-link density and stiffness of films increase because UV irradiation cause the breakage and rebond in the bonding structure of SiCOH low-k films. However, UV treatment does not influence k value significantly. After 6-hour irradiation, the k is increased to 2.2 which shows 2.0 for non-irradiation film.The prorous SiCOH films were prepared successfully and show the ultra-low k value (～2.0). Also, in the rang 350-500℃, the chemical composition and dielectric constant keep stable. After UV irradiation, mechanical properties are improved significantly. Therefore, the resulting films indicate a promising candidate for future inter-level dielectrics. |
PDF Full Text Request