Chemical Structure Effects of Ring-Type Siloxane Precursors on Properties of Plasma-Polymerized Porous SiOCH Films

Abstract

Physical and chemical properties of plasma-polymerized SiOCH films were investigated using ring-type siloxane monomers with several kinds of side-chain chemicals, and a design principle of the material and plasma-process was derived to obtain a porous SiOCH film of k Ͻ 2.5 with sub-nanometer-scaled porous structure framed by the original ring siloxane backbone. Here, the backbone siloxane structure is fixed as a six-membered Si-O ring of the 0.35 nm, and no progen gas and no post-cure-process were utilized. It was found that unsaturated hydrocarbon side chains such as vinyl increase the deposition rate, and the original monomer structure tends to be kept, reducing the dielectric constant with the porous structure. Large alkyl groups increase the hydrocarbon content in the film as well as the deposition rate. The low radio-frequency power plasma with high precursor concentration also helps the original chemical structure to be preserved. The best solution is to use the ring-type siloxane with both of the vinyl ͑unsaturated hydrocarbon͒ and the large alkyl ͑saturated hydrocarbon͒ under the low-power plasma condition with the high partial pressure of the precursor. The plasma-polymerized porous SiOCH film is a strong candidate for the low-k film in scale-down 45/32 nm node ultralarge-scaled integrated interconnects featured by the simple and low-cost fabrication processes.The scaling of complementary metal oxide semiconductors ͑CMOS͒ device dimensions has contributed to the high-speed operation and extensive integrity of ultralarge scale integrated ͑ULSI͒ devices. 1 These features are achieved by scaling of not only metal oxide semiconductor field-effect transistors ͑MOSFETs͒ but also interconnects. The interconnect performances such as the resistancecapacitance ͑RC͒ time constant, cross-talk, and power consumption, however, have been degraded by the square of the scaling factor due to the parasitic capacitance increment. 2 One approach to reduce the capacitance is introduction of low-k materials into the intermetal dielectrics ͑IMDs͒. Low-k films such as LO-x ͑k = 3.0͒, 3 rigidSiOCH ͑k = 2.9͒, 4 and porous-SiOCH ͑k = 2.6͒, 5,6 have been introduced as IMD for 130, 90, and 65 nm node devices, respectively.Carbon-doped silicon oxides ͑CDOs͒ are one of the well-known low-k materials comprised of Si, O, C, and H. 7-12 The Si-C bonds in CDOs are more covalent than the Si-O ionic ones, because Si and O have large difference in their electronegativity, increasing the ionic polarization, or essentially the dielectric constant. Recently, CDOs have been shown to have pseudo-porosity in the dense cross-linked SiO 2 lattice by chemical decoration of the Si atoms with sterichindered alkyl groups, reducing the film density or eventually the k value. Plasma-enhanced chemical vapor deposition ͑PECVD͒ and spin-on deposition ͑SOD͒ are used for the CDO deposition. The PECVD utilizes gas-phase chemicals in a vacuumed reactor to produce high-quality films in a controllable system. For the PECVD CDO films, SiH 4 /hydrocarbon gas mixture,...

Low-k SiCxNyFilms Prepared by Plasma-Enhanced Chemical Vapor Deposition Using 1,3,5-trimethyl-1,3,5-trivinylcyclotrisilazane Precursor

“…Simultaneously, the absorption intensity of the Si-H bond increased, as deposition temperature was increased. 23 In addition to infrared analysis, the compositions of SiC x N y films deposited at various deposition temperatures and their relative ratios to Si were quantified by XPS. These are summarized in Table II.…”

“…The N/Si ratio of the SiC x N y films decreased from 0.46 at 25 • C to 0.25-0.23 for deposition temperature between 100 • C and 400 • C. In contrast, their respective C/Si ratio decreased from 0.86 at 25 • C to 0.7-0.81 at T ∼100-300 • C and then there was a more radical decrease to 0.29 at a deposition temperature of 400 • C. This implied that during the deposition of SiC x N y film at 400 • C by PECVD, the desorption of CH x bonds may occur simultaneously, due to a pyrolysis process, which resulted in the rearrangement of the films' structure and the subsequent formation of dense SiC x N y films. 23 In addition to the XPS results, Figure 4 shows the position of the absorption band of N-Si-N in SiC x N y films deposited by PECVD at various temperatures, as measured by FT-IR analysis. At temperatures ≤200 • C, the Si-N absorption band was centered at 1047-1048 cm −1 and still displayed the characteristics of cyclic N-Si-N. As the deposition temperature was raised to 300 and then 400 • C, the Si-N absorption band was downshifted to 1043 and 1038 cm −1 , respectively.…”

Pore morphology of low-k SiCxNy films prepared with a cyclic silazane precursor using plasma-enhanced chemical vapor deposition

“…Since there is little work on porous SiC x N y films, the pore sizes of asdeposited SiC x N y films in this study were compared to PECVD porous SiCOH films prepared using single precursor [12,13] and/or conventional approach using a precursor and an oxidant [26] The pore sizes in our study were found to be larger than SiCOH films prepared using single precursor [12,13]. Tada et al [12] reported PECVD porous SiOCH films with pore sizes ranging from 0.39 to 0.66 nm using a ring-type siloxane precursor with both of the vinyl and the alkyl side-groups at 350°C and under high pressure and low-power plasma condition to preserve the original ring-type chemical structure. C. H. Lo et al [13] reported SiCOH film prepared by using octamethylcyclotetrasiloxane (OMCTS) and pore diameter 0.74-0.76 nm for the matrix structure and 0.6-0.7 nm for big cages.…”

“…To further reduce the dielectric constant of silicon carbonitride materials, the primary approach is to reduce the film density, in addition to the continued increase of C/Si ratio. A similar approach has been demonstrated for low-k SiC x O y interlayer dielectric films by using single precursors with volumic cyclic structures, such as a 6, 8, or 10-membered Si-O ring [12,13] to introduce intrinsic and induced porosity for lowering the film's density.…”

Ultra Low Dielectric Constant Materials for 22 nm Technology Node and Beyond

“…Meanwhile detection of such groups in pristine low-k materials is extremely important because sp 2 carbon based residues (conjugated carbon polymers and amorphous carbon) are conductive and therefore they can be the reasons of high leakage current and low breakdown voltage in the integrated materials. Generally such residues can be detected by Raman spectroscopy [16] but application of these measurements for thin low-k films is quite challenging. Eslava and Marsik developed a method for detection of porogen residue from UV absorption spectra.…”