Otsuka Yuji, Shimizu Yumiko, Tanaka Isao
Toray Research Center, Inc., Sonoyama 3-3-7, Otsu-shi, Shiga 520-8567, Japan.
J Electron Microsc (Tokyo). 2009 Apr;58(2):29-34. doi: 10.1093/jmicro/dfp009. Epub 2009 Feb 13.
Porous Si-O-C films with lower dielectric constant (kappa) relative to silicon dioxide have been widely studied as inter-layer dielectrics in new-generation microelectronic devices. On the analysis of the film by transmission electron microscopy (TEM), it is susceptible of beam damage during both sample preparation by a focused ion beam (FIB) technique and TEM observation. We use electron energy loss spectroscopy (EELS) to quantify the magnitude of the beam damage during these processes. The intensity of the 285-eV peak in C-K electron energy loss near edge structures (ELNES) is enhanced by the damage, which can be ascribed to the formation of the C=C double bonds as a result of the decomposition of the methyl groups by the beam. The use of cryo-holder for TEM at 100 K is found to be essential to reduce the damage of the low-kappa layers. The lowering of the acceleration voltage of FIB down to 5 keV does not change the spectra. Since the FIB damage is localized at the surface, the use of thick regions in the TEM foil such as 130 nm is preferred to reduce the superposition of EELS of the damaged region on those from the sample of interest.
相对于二氧化硅具有较低介电常数（κ）的多孔Si-O-C薄膜作为新一代微电子器件中的层间电介质已得到广泛研究。在用透射电子显微镜（TEM）对该薄膜进行分析时，在通过聚焦离子束（FIB）技术制备样品以及TEM观察过程中，它都容易受到束流损伤。我们使用电子能量损失谱（EELS）来量化这些过程中束流损伤的程度。损伤会使C-K电子能量损失近边结构（ELNES）中285 eV峰的强度增强，这可归因于束流使甲基分解从而形成C = C双键。发现使用100 K的低温样品杆对于减少低κ层的损伤至关重要。将FIB的加速电压降低至5 keV不会改变光谱。由于FIB损伤局限于表面，因此在TEM薄片中使用较厚区域（如130 nm）更有利于减少受损区域的EELS与感兴趣样品的EELS的叠加。
