Porosity in plasma enhanced chemical vapor deposited SiCOH dielectrics: A comparative study

Abstract

The low dielectric constant (k) of plasma enhanced chemical vapor deposited SiCOH films has been attributed to porosity in the films. We have shown previously that the dielectric constant of such materials can be extended from the typical k values of 2.7–2.9 to ultralow-k values of k=2.0. The reduction in the dielectric constants has been achieved by enhancing the porosity in the films through the addition of an organic material to the SiCOH precursor and annealing the films to remove the thermally less-stable organic fractions. In order to confirm the relation between dielectric constant and film porosity the latter has been evaluated for SiCOH films with k values from 2.8 to 2.05 using positron annihilation spectroscopy, positron annihilation lifetime spectroscopy, small angle x-ray scattering, specular x-ray reflectivity, and ellipsometric porosimetry measurements. It has been found that the SiCOH films with k=2.8 had no detectable porosity, however the porosity increased with decreasing dielectric constant reaching values of 28%–39% for k values of 2.05. The degree of porosity and the pore size determined by the dissimilar techniques agreed within reasonable limits, especially when one takes into account the small pore size in these films and the different assumptions used by the different techniques. The pore size increases with decreasing k, however the diameter remains below 5 nm for k=2.05, most of the pores being smaller than 2.5 nm.

Low and Ultralow Dielectric Constant Films Prepared by Plasma‐enhanced Chemical Vapor Deposition

“…A comparison of the degrees of porosity and PSD values obtained by several methods for the same fi lms is presented in Table 1.3 [21]. The data show a scattering of the values obtained by the different techniques, however a calculation of fi lm densities and dielectric constants based on these porosity data showed reasonable agreement to the experimental data.…”

“…Typical PSDs of two pSiCOH fi lms of different k values, as obtained by ellipsometric spectroscopy are illustrated in Figure 1.24 [21]. A comparison of the degrees of porosity and PSD values obtained by several methods for the same fi lms is presented in Table 1.3 [21].…”

“…The techniques enable the determination of the degree of porosity in the fi lms and the pore size distribution (PSD). A description of the different techniques with further references to the details of the used methods can be found in references [21][22][23]. A detailed description is provided in Chapter 3 of this book.…”

X-ray metrology for advanced microelectronics

“…It can be specular when the X-ray beam is reflected at an angle identical to the incident angle, or diffuse when the X-ray radiation is scattered in all directions. Grazing incidence small angle X-ray scattering (GI-SAXS) is commonly used for the characterization of micro-and nano-structures such as porous layers [7], precipitates and quantum dots [8].…”

Synchrotron X-ray scattering and reflectivity studies of the structure of low dielectric constant SiOCH thin films prepared from bistrimethylsilylmethane by chemical vapor deposition

“…The resulting SiOCH dielectric films were extensively studied in terms of their chemical compositions and chemical, physical and dielectric properties (Grill & Patel, 1999;Jun et al, 2003;Kim et al, 2003;Loboda et al, 1998;Shirafuji et al, 1999). However, only a small number of studies on SiOCH dielectrics have examined the film structure, knowledge of which is critical to understanding the dielectric, physical and mechanical properties (Grill et al, 2003;Takahashi et al, 2003;Yu et al, 2003).…”