Charles S. Dulcey

Covalent Binding of Pd Catalysts to Ligating Self‐Assembled Monolayer Films for Selective Electroless Metal Deposition

A new approach for the selective electroless (EL) metallization of surfaces is described. Surfaces are modified with a chemisorbed ligand‐bearing organosilane film, and then catalyzed with an aqueous Pd(II) catalyst solution. The catalyzed substrate is then immersed in an EL metal deposition bath to complete the metallization process. The ligating surfaces are produced by molecular self‐assembly of 2‐(trimethoxysilyl)ethyl‐2‐pyridine (PYR) on silicon or silica substrates. The catalyst consists of chloride‐containing aqueous Pd(II) solutions buffered at pH 5.0 to 6.4; oligomeric chloro and/or hydroxo‐bridged Pd(II) complexes act as the catalytic species at the surface. The activity of the catalyst has been characterized and modeled as a function of solution pH, [Cl−], and time from preparation. Adhesion of the Pd(II) EL catalyst to the substrate involves covalent bond formation with the surface ligand. An average minimum Pd(II) level on the surface of ~1015 Pd atom cm2 is shown to be necessary to initiate EL metallization of the substrate with an EL Co bath. This process involves fewer steps and displays improved selectivity compared to processes that involve a conventional Pd/Sn catalyst. Fabrication of high resolution metal patterns using the new metallization chemistry in conjunction with deep UV patterning of PYR films is demonstrated.

Channel‐Constrained Electroless Metal Deposition on Ligating Self‐Assembled Film Surfaces

Channel-constrained metallization is described as a novel process for fabrication of metal features useful as etchmasks and electrical interconnects in microelectronics applications. The method creates a requisite surface reactivity template through patterned exposure and development of photoresist films to open channels to an underlying ligand self-assembled film. Subsequent electroless metal deposition occurs selectively at exposed ligand sites in the channels, which constrain lateral metal growth detrimental to feature critical dimension (CD) control during plating. A characterization of the individual process steps is presented using a positive tone photoresist system as an example. Determination of the exposure and development conditions that promote clearance of photoresist residues from the channels while maintaining adequate feature CD control is identified as an important issue in successfully performing the process. The process has been successfully demonstrated using optical exposure sources and is compatible with a range of substrates relevant for electronics applications, including Si. The high plasma etching selectivity of a thin Ni metal masking layer was used in the fabrication of high aspect ratio structures (≤5:1) in Si.

Size‐Controlled Colloidal Pd(II) Catalysts for Electroless Ni Deposition in Nanolithography Applications

A new Pd(II) electroless metal deposition catalyst dispersion, PD2, prepared by quenching a PdCl 4 2 solution with HCl and excess NaCl following rapid hydrolysis at pH ∼ 7 and ∼0.8 mM NaCl is described. The precursors to the catalytic Pd(0) species are shown to be chloride-rich Pd(II) colloidal particles having negative surface charge by x-ray photoelectron spectroscopy, UV-visible spectroscopy, centrifugation, and chemical tests. The particles bind selectively and covalently at ligand-modified surfaces with complete surface coverage occurring for treatment times ≥2 min. Atomic force microscopy indicates that the average and maximum sizes of the bound particles are 9 ± 3 and 18 nm, respectively. A correspondingly narrow distribution (15 to 33 nm) of Ni particles of average size 21 ± 5 nm is obtained following metallization of catalyzed surfaces. The ability to control Ni particle morphology using PD2 is successfully exploited in the selective metallization of ∼15 nm features patterned by scanning tunneling microscopy. Metallization occurs with minimal distortion of feature geometries and no pattern degradation due to Ni overgrowth or bridging of adjacent features. Catalyst behavior is well described by a model in which domination of particle nucleation events and dispersion medium chemistry during colloid formation determine particle surface binding, stability, size, and dispersity

Deep ultraviolet patterning of monolayer films for high resolution lithography

A new process has been developed for high resolution photolithography that employs chemisorbed monolayer films as the surface imaging layers. Organosilane treated surfaces are exposed to patterned deep UV radiation, either from excimer laser or lamp sources. The photochemical process modifies the surface wettability and reactivity of the film. Organosilane films patterned by deep UV radiation are treated with a Pd/Sn catalyst and then metallized with electroless copper and nickel baths to yield metal films several 100 A thick. The metal is selectively deposited in the unexposed regions of the film to produce a positive tone image. The patterned metal film is then utilized as a plasma hard etch barrier in a reactive ion etch, allowing efficient pattern transfer into the underlying substrate and producing features with linewidths to 0.4 μm. Electrical testing of processed substrates demonstrates compatibility of the process with subsequent device performance, and working transistor test structures have been...

Surface chemistry of carbon removal from indium tin oxide by base and plasma treatment, with implications on hydroxyl termination

Abstract The surface chemistry of carbon removal from indium tin oxide (ITO) has been investigated with Auger electron spectroscopy (AES), high-resolution electron energy loss spectroscopy (HREELS), and high-resolution energy loss spectroscopy (HR-ELS). A vibrating Kelvin probe (KP) was used to monitor the work function ( Φ ) of ITO after cleaning, either by base-cleaning with alcoholic-KOH or by O 2 plasma-cleaning. Base-cleaning lowered Φ ITO as seen in the KP analysis, whereas plasma-cleaning slightly increased Φ ITO by an oxidative process. The degree of Φ ITO depression by base-cleaning was seen to depend on the initial surface, but the Φ depression itself was nonreductive to the ITO, as seen in the In-MNN AES lineshape. The nonreductive depression of Φ ITO by base-cleaning was further supported by a constant charge carrier density, as estimated from the HR-ELS. Base-cleaning was slightly more effective than the oxygen plasma in removing carbon from the ITO surface. However, base-cleaning preferentially removed graphitic carbon while leaving significant hydrocarbon contaminants, as determined by vibrational analysis with HREELS. All other ITO surfaces retained a significant carbon and hydrocarbon contamination as evidenced by AES and HREELS. There was little evidence of the formation of surface hydroxyl species, as expected for such an inherently contaminated surface as ITO.

Deep Ultraviolet Lithography of Monolayer Films with Selective Electroless Metallization

A top surface imaging approach for the fabrication of submicron features on solid substrates has been developed. A monolayer film is exposed to patterned deep ultraviolet radiation, then selectively metallized using electroless deposition such that a thin metal layer (200-400 A) is deposited only in the unexposed areas. The film/metal assembly is a highly effective mask for reactive ion etching which can subsequently be stripped from the substrate after feature definition. Features with 0.3 μm line width in polysilicon and working transistor test structures have been produced using this process

Projection x-ray lithography with ultrathin imaging layers and selective electroless metallization

Soft x-ray synchrotron radiation, of wavelength 14 nm, is used to pattern self-assembled monolayer films, which are then selectively metallized using electroless deposition. Organosilane precursors of the general type RSiX 3 (R=organic functional group; X = Cl, OCH 3 ) are used to form covalently bound ultrathin films by molecular self-assembly on Si wafers. These films are approximatively one monolayer (approximatively 1 nm) thick. X-ray exposure is used to remove or transform the R groups in selected areas of the film. The laterally patterned reactivity on the surface is then used as a template for the additive deposition of a thin layer of electroless nickel in the unexposed regions. The Ni metal layer can then be used as a plasma etch mask for pattern transfer. Metal features with linewidths <=0.25 μm are produced with exposure doses of 50 mJ/cm 2 .

Coplanar patterns of self-assembled monolayers for selective cell adhesion and outgrowth

Abstract A recently developed deep UV photolithographic method produces high resolution (1–200 μm feature size) patterns of coplanar self-assembled monolayers (SAMs) which spatially control the adhesion and outgrowth of biological cells. Characterization of these patterned SAMs, using wettability, X-ray photoelectron spectroscopy (XPS), and scanning Auger electron spectroscopy (AES), shows that high resolution adjacent regions of intact SAMs are formed in the same molecular plane. Selective adhesion and outgrowth of neuroblastoma cells, explanted rat hippocampal cells, and human umbilical vein endothelial cells are demonstrated on these SAM patterns. Patterned SAMs might provide new approaches to the study of intercellular communication and development, and allow arrangement of cells on surfaces of sensor devices, prosthetic implants, or tissue repair templates.

Photochemical studies of (aminoethylaminomethyl) phenethyltrimethoxysilane self-assembled monolayer films

Abstract The deep UV (193 nm) photochemistry of the self-assembled monolayer film PEDA, H 2 NCH 2 CH 2 NHCH 2 C 6 H 4 CH 2 CH 2 Si(OCH 3 ) 3 , has been studied on Si and SiO 2 surfaces using UV and X-ray photoelectron spectroscopies, contact angle goniometry, and laser-desorption Fourier transform mass spectrometry. Mechanistic studies show that Si-C cleavage is the ultimate photochemical pathway; however, interpretation of the photochemical data is complicated by formation of a surface-bound intermediate, as well as adsorption of photoproducts to the substrate surface. Treatment of the exposed film with high ionic strength aqueous solutions is found to remove the adsorbed material. Patterned 193 nm exposure of PEDA SAM films on SiO 2 produces a surface template of reactive amine groups at relatively low doses (~ 400 mJ cm −2 ), which can be used for selective, high-resolution attachment or deposition of materials on the unexposed regions of the film.

Patterned Metallization of Diamond and Alumina Substrates

High-density microelectronies increasingly requires advanced cooling strategies to ensure reliable, high performance. The use of substrates with high thermal conductivity, e.g., diamond, is an attractive approach to managing heat dissipation; however, the fabrication of metal circuitry on diamond films is hindered hy the chemical inertness of the surface. In this paper, we present an additive, channel constrained metallization process for the fabrication of metal circuitry on diamond surfaces. We address several issues specific to this application, including photoresist lithography and metal adhesion on substrates with significant surface roughness (peak-to-valley roughness --4 to 5 μm) and the fabrication of circuitry with sufficient electrical conductivity. Fabricated circuitry exhibits suitable resolution (∼10 μm), metal thickness (≥2 μm), effective electrical resistivity (∼10 μΩ-cm for composite Ni/Cu/Au traces), and adhesion (passes tape peel test) for operation at power levels of at least 22 W (i.e., I A, 22 V) without failure or delamination. Thermal modeling and IR images of operating circuitry show an ∼50% decrease in component junction temperature rise (from ambient) on diamond (k∼1200 W/m K) vs. alumina (k∼20 W/m K), consistent with thermal conductivity differences between these substrate materials.