Surface patterning of polychloromethylstyrene films

Divalent-anion salt effects in polyelectrolyte multilayer depositions

We systematically investigate the effects of divalent anions on the assembly of polyelectrolyte multilayers by fabricating polystyrene sulfonate (PSS)/polyallylamine hydrochloride (PAH) multilayer films from aqueous solutions containing SO(4)(2-), HPO(4)(2-), or organic dicarboxylate dianions. The chosen concentrations of these anions (i.e., ≤0.05 M) allow us to isolate their effects on the assembly process from those of the polyelectrolyte solubility or solution ionic strength (maintained constant at μ = 1.00 M by added NaCl). Compared to a control film prepared from solutions containing only Cl(-) anions, stratified multilayers deposited in the presence of dianions exhibit increased UV absorbance, thickness, and roughness. From the dependence of film properties on the solution concentration of SO(4)(2-) and number of polyelectrolyte layers deposited, we derive a generic model for the PSS/PAH multilayer formation that involves adsorption of PAH aggregates formed in solution via electrostatic interactions of PAH with bridging dianions. Experiments using HPO(4)(2-) and organic dicarboxylate species of varying structure indicate that the separation, rigidity, and angle between the discrete negatively charged sites in the dianion govern the formation of the PAH aggregates, and therefore also the properties of the multilayer film. A universal linear relationship between film UV absorbance and thickness is observed among all dianion types or concentrations, consistent with the model.

Statistical analysis of plating variable effects on the electrical conductivity of electroless copper patterns on paper

We describe a process for selective metallization of paper substrates bearing inkjet printed patterns of a commercial Pd/Sn colloidal catalyst ink plated using a commercial electroless Cu bath. The electrical conductivity of the Cu films is analyzed as a function of feature geometry (line dimensions (L) and spacing (S)), type of paper (P), age of the Pd/Sn patterns (A), plating time (T), and plating temperature (H) using a two-level factorial design. Conductivity is influenced predominantly by the P, T, and H factors, with lesser contributions attributed to pair-wise interactions among several of the variables studied. Increases in T and/or H enhance conductivity of the Cu films, whereas increases in P, corresponding to the use of rougher, more porous, paper substrates, yield Cu films exhibiting decreased conductivity. Our analysis leads to a model that predicts Cu film conductivity well over the ranges of variables examined, provides guidelines for identification of optimum conditions for plating highly conductive Cu films, and identifies areas for further process improvement.

Selective electroless metallization of patterned polymeric films for lithography applications

The fabrication of electrical interconnects to provide power for and communication with computers as their component complementary metal oxide semiconductor (CMOS) devices continue to shrink in size presents significant materials and processing compatibility challenges. We describe here our efforts to address these challenges using top-surface imaging and hybrid photoresist/self-assembled monolayer patterning approaches, in conjunction with selective electroless metal deposition, to develop processes capable of fabricating appropriate submicron and nanoscale metal features useful as electrical interconnects, as well as plasma-etch-resistant masks and metal diffusion barriers. Our efforts focus on the development of cost-effective methods compatible with a manufacturing environment that satisfy materials and process constraints associated with CMOS device production. We demonstrate the fabrication of approximately 50-nm-width features in metal with high fidelity and sufficient control of edge acuity to satisfy current industry design rules using our processes and discuss the challenges and opportunities for fabrication of analogous sub-10-nm metal features.

Formation of aromatic siloxane self-assembled monolayers

We describe reproducible protocols for the chemisorption of self-assembled monolayers (SAMs), useful as imaging layers for nanolithography applications, from p-chloromethylphenyltrichlorosilane (CMPS) and 1-(dimethylchlorosilyl)-2-(p,m-chloromethylphenyl)ethane on native oxide Si wafers. Film chemisorption was monitored and characterized using water contact angle, X-ray photoelectron spectroscopy, and ellipsometry measurements. Atomic force microscopy was used to monitor the onset of multilayer deposition for CMPS films, ultimately allowing film macroscopic properties to be correlated with their surface coverage and nanoscale morphologies. Although our results indicate the deposition of moderate coverage, disordered SAMs under our conditions, their quality is sufficient for the fabrication of sub-100-nm-resolution metal features. The significance of our observations on the design of future imaging layers capable of molecular scale resolution in nanolithography applications is briefly discussed.

Fabrication of biological nanostructures by scanning near-field photolithography of chloromethylphenylsiloxane monolayers

We demonstrate the fabrication of sub-100-nm DNA surface patterns by scanning near-field optical lithography using a near-field scanning optical microscope coupled to a UV laser and a chloromethylphenylsiloxane (CMPS) self-assembled monolayer (SAM). The process involves 244-nm exposure of the CMPS SAM to create nanoscale patterns of surface carboxylic acid functional groups, followed by their conversion to the N-hydroxysuccinimidyl ester and reaction of the active ester with DNA to spatially control DNA grafting with high selectivity.

Protein micropatterns using a pH-responsive polymer and light

Protein and peptide microarrays are popular candidates for medical diagnostics because of the possibility for high sensitivity and simultaneous marker screening. To realize the potential of these arrays, new strategies for ligand patterning are needed. We report a method for patterning proteins that utilizes a pH-responsive polymer, deep ultraviolet (DUV) light, and a photoacid generator (PAG). Poly(3,3'-diethoxypropyl methacrylate) (PDEPMA) contains reactive acetal side chains which are converted to aldehydes following treatment with acid. PDEPMA was spin-coated onto Si-SiO(2) substrates and was either chemically deprotected with 1 M HCl or photochemically deprotected by exposure to DUV in the presence of triphenylsulfonium triflate. Conversion to aldehyde groups was confirmed with Purpald and by reaction with a green fluorescent hydroxylamine. Protein microarrays were demonstrated by incubating photochemically patterned surfaces with an aldehyde-reactive biotin followed by red fluorescent streptavidin. This methodology provides a new substrate for the precise patterning of both peptides and proteins for various biological applications including medical sensors.

Preparation and photoinduced patterning of azidoformate-terminated self-assembled monolayers

This paper presents a new method for the patterning of self-assembled monolayers (SAMs) using UV light. Azidoformate-terminated SAMs starting from 18-acetoxy-octadecyltrichlorosilane SAMs on silicon, prepared for the first time, are electrophilic and photosensitive, and can be patterned by UV irradiation through a mask. The resulting structured surfaces are still electrophilic and can be reacted with nucleophilic functions, for example, primary amines.