Growth Rate and Cross-Linking Kinetics of Poly(divinyl benzene) Thin Films Formed via Initiated Chemical Vapor Deposition.

Initiated chemical vapor deposition (iCVD) allows for the formation of highly cross-linked, polymer thin films on a variety of substrates. Here, we study the impact of substrate stage temperature and filament temperature on the deposition and cross-linking characteristics of iCVD from divinyl benzene. Maintaining a constant monomer surface concentration reveals that deposition rates upward of 15 nm/min can be achieved at substrate stage temperatures of 50 °C. The degree of cross-linking is limited by the rate of initiation of the pendant vinyl bonds. At a filament temperature of 200 °C, the pendant vinyl bond conversion is highly sensitive to the surface concentration of initiator radicals. A significant decrease of the pendant vinyl bond conversion is observed with increasing stage temperatures. At higher filament temperatures, the pendant vinyl bond conversion appears to plateau at approximately 50%. However, faster deposition rates yield lower conversion. This trade-off is mitigated by increasing the filament temperature to increase initiator radical production. A higher flux of initiator radicals toward the surface at a constant deposition rate increases the rate of initiation of pendant vinyl bonds and therefore their overall conversion. At a deposition rate of ∼7 nm/min, an increase in the filament temperature from 200 to 240 °C results in an 18% increase in the pendant vinyl bond conversion.

Ultrathin and Conformal Initiated Chemical-Vapor-Deposited Layers of Systematically Varied Surface Energy for Controlling the Directed Self-Assembly of Block CoPolymers.

Directed self-assembly (DSA) of block copolymer (BCP) thin films is a promising approach to enable next-generation patterning at increasingly smaller length scales. DSA utilizes interfacial wetting layers to force the BCP domains to self-assemble with the desired orientation with respect to the substrate. Here, we demonstrate that initiated chemical-vapor-deposited (iCVD) polydivinylbenzene (pDVB) ultrathin films can direct the self-assembly of poly(styrene- block-methylmethacrylate). We found that the methyl radicals formed at increased filament temperatures during the iCVD process result in the backbone methylation of pDVB. By tuning the degree of backbone methylation, we systematically changed the wetting properties of the iCVD pDVB from a slight poly(methylmethacrylate) preference to complete poly(styrene) preference. Additionally, we utilize the conformal nature of the iCVD to form a wetting layer over a topographical line and space pattern, which is subsequently used to produce self-assembled BCP films with both perpendicular orientation and long-range alignment.

Vapor deposition routes to conformal polymer thin films.

Vapor phase syntheses, including parylene chemical vapor deposition (CVD) and initiated CVD, enable the deposition of conformal polymer thin films to benefit a diverse array of applications. This short review for nanotechnologists, including those new to vapor deposition methods, covers the basic theory in designing a conformal polymer film vapor deposition, sample preparation and imaging techniques to assess film conformality, and several applications that have benefited from vapor deposited, conformal polymer thin films.

Sub-10-nm patterning via directed self-assembly of block copolymer films with a vapour-phase deposited topcoat.

Directed self-assembly (DSA) of the domain structure in block copolymer (BCP) thin films is a promising approach for sub-10-nm surface patterning. DSA requires the control of interfacial properties on both interfaces of a BCP film to induce the formation of domains that traverse the entire film with a perpendicular orientation. Here we show a methodology to control the interfacial properties of BCP films that uses a polymer topcoat deposited by initiated chemical vapour deposition (iCVD). The iCVD topcoat forms a crosslinked network that grafts to and immobilizes BCP chains to create an interface that is equally attractive to both blocks of the underlying copolymer. The topcoat, in conjunction with a chemically patterned substrate, directs the assembly of the grating structures in BCP films with a half-pitch dimension of 9.3 nm. As the iCVD topcoat can be as thin as 7 nm, it is amenable to pattern transfer without removal. The ease of vapour-phase deposition, applicability to high-resolution BCP systems and integration with pattern-transfer schemes are attractive properties of iCVD topcoats for industrial applications.

CVD Polymers for Devices and Device Fabrication.

Chemical vapor deposition (CVD) polymerization directly synthesizes organic thin films on a substrate from vapor phase reactants. Dielectric, semiconducting, electrically conducting, and ionically conducting CVD polymers have all been readily integrated into devices. The absence of solvent in the CVD process enables the growth of high-purity layers and avoids the potential of dewetting phenomena, which lead to pinhole defects. By limiting contaminants and defects, ultrathin (<10 nm) CVD polymeric device layers have been fabricated in multiple laboratories. The CVD method is particularly suitable for synthesizing insoluble conductive polymers, layers with high densities of organic functional groups, and robust crosslinked networks. Additionally, CVD polymers are prized for the ability to conformally cover rough surfaces, like those of paper and textile substrates, as well as the complex geometries of micro- and nanostructured devices. By employing low processing temperatures, CVD polymerization avoids damaging substrates and underlying device layers. This report discusses the mechanisms of the major CVD polymerization techniques and the recent progress of their applications in devices and device fabrication, with emphasis on initiated CVD (iCVD) and oxidative CVD (oCVD) polymerization.