Atmospheric-Pressure Synthesis of Atomically Smooth, Conformal, and Ultrathin Low-k Polymer Insulating Layers by Plasma-Initiated Chemical Vapor Deposition

Abstract

The straightforward synthesis of ultrathin low dielectric constant insulating polymer layers from four cyclic organosilicon monomers (i.e., two organo­cyclosiloxanes and two organo­cyclosilazanes) by atmospheric pressure plasma-initiated chemical vapor deposition (AP-PiCVD) is demonstrated. The combination of ultrashort plasma pulses (ca. 100 ns), as polymerization initiator, with long plasma off-times (10 ms), yields the formation of atomically smooth and conformal polymer layers with excellent insulating properties. Leakage current densities of 10–9 A cm– 2 are measured for film thicknesses as low as 12 nm. Low dielectric constants are obtained because of the retention of the cyclic structure of the monomers during the deposition. The polymer layers prepared from 1,3,5,7-tetramethyl-1,3,5,7-tetravinyl­cyclotrisiloxane display the lowest dielectric constant (k = 2.8). The present study demonstrates the ability to vary the dielectric constant of as-deposited polymer layers by varying the monomer bonds, i.e., siloxane and silazane, as well as their ring size.

Influence of double bonds and cyclic structure on the AP‐PECVD of low‐korganosilicon insulating layers

“…(a) The chemical structure, molecular weight (g·mol −1 ) and the vapour pressure ( P sat , mmHg; https://pubchem.ncbi.nlm.nih.gov) [ 12 ] of the studied organosiloxane monomers. (b) Growth rates per second according to the plasma pulse frequency (Hz) and (c) thickness increment per t ON + t OFF cycle for the thin films grown from 1,3,5,7‐tetramethyl‐1,3,5,7‐tetravinylcyclotetrasiloxane (V4D4), octamethylcyclotetrasiloxane (D4) and decamethyltetrasiloxane (DMTSO)…”

“…It is assumed that this behaviour is more pronounced for the monomer possessing a low vapour pressure ( P sat ) such as NVCL ( P sat, NVCL, 50°C = 0.355 mmHg), [ 35 ] GMA ( P sat, GMA, 20°C = 0.315 mmHg) [ 22 ] and V4D4 ( P sat, V4D4, 20°C = 0.040 mmHg). [ 12 ] Indeed, low P sat implies a lower concentration of the monomer in the gas phase, which induces a higher probability of interaction between the monomer and the active plasma species that is responsible for significant monomer depletion.…”

“…In particular, the PECVD of low‐ k dielectric thin films from constitutive porosities (e.g., cyclic precursor approach) is restricted by the disruption of the ring structure of cyclic precursors. [ 12 ] However, the low‐pressure initiated chemical vapour deposition (iCVD) of vinyl‐containing precursors allows the retention of the monomer structure and their polymerisation in a thin film form directly from the gas phase. The iCVD of 1,3,5‐trimethyl‐1,3,5‐trivinyl cyclotrisiloxane (V3D3) was notably reported to yield the formation of low‐ k polymer thin films (i.e., k = 2.2) that meet a wide range of requirements for the next generation of electronic devices.…”

“…[ 19 ] A recent approach called plasma‐initiated chemical vapour deposition (PiCVD) [ 20 ] combines ultrashort plasma pulses ( t ON < 100 ns) and plasma off‐times in the range of the free‐radical polymerisation lifetime ( t OFF from 1 to 100 ms) to yield the atmospheric‐pressure synthesis and deposition of atomically smooth, conformal ultrathin low‐ k polymer insulating layers. [ 12,21 ] This ultrashort square‐wave‐pulsed plasma process, displaying strong similarities with iCVD, has notably provided thin films with an unprecedented degree of polymerisation for plasma‐enhanced or atmospheric‐pressure CVD processes. [ 22 ] The significance of the ultrashort square‐wave pulses frequency [ 22‐24 ] and monomer saturation ratio, P M / P sat (with P M being the partial pressure of the monomer and P sat the saturation pressure of the monomer at the temperature of interest), has recently been demonstrated.…”

Insights into switchable thermoresponsive copolymer layers by atmospheric pressure plasma‐initiated chemical vapour deposition

“…Indeed, in the literature, plasma copolymerization involving unsaturated monomers, in particular monomers bearing two double carbon bonds such as N , N′ ‐methylenebisacrylamide [ 31,32 ] or ethylene glycol dimethacrylate, [ 33,34 ] is reported to improve film stability in water. On the basis of the excellent water‐resistance of the polymers produced by the PiCVD of 1,3,5‐trivinyl‐1,3,5‐trimethylcyclotrisiloxane (V3D3), [ 35 ] the copolymerisation of NVCL and V3D3 was firstly investigated. However, if the lowest investigated V3D3 flux (Table S1) yielded the formation of water stable and thermoresponsive p(NVCL‐co‐V3D3) films, the thermoresponsive effect remained limited.…”