Blake Davis

Liquid immersion lithography: evaluation of resist issues

We address in this report a set of key questions tied to the implementation of liquid immersion lithography, from the perspective of the resist materials. We discuss the broad question of whether chemically amplified resists are capable of achieving the spatial resolution that ultimately will be required for the most advanced immersion scenario. Initial studies undertaken using model 193 nm resist materials provide some insight into how an aqueous liquid immersion process can affect the resist material.

High-throughput directed self-assembly of core-shell ferrimagnetic nanoparticle arrays.

Magnetic nanoparticles (MNPs) provide a set of building blocks for constructing stimuli-responsive nanoscale materials with properties that are unique to this scale. The size and the composition of MNPs are tunable to meet the requirements for a range of applications including biosensors and data storage. Although many of these technologies would significantly benefit from the organization of nanoparticles into higher-order architectures, the precise placement and arrangement of nanoparticles over large areas of a surface remain a challenge. Herein, we demonstrate the viability of magnetic nanoparticles for patterned recording media utilizing a template-directed self-assembly process to afford well-defined nanostructures of magnetic nanoparticles and access these assemblies using magnetic force microscopy and a magnetic recording head. Photolithographically defined holes were utilized as templates to form assemblies of ferrimagnetic nanoparticle rings or pillars selectively over a large area (>1 cm(2)) in just 30 s. This approach is applicable to other nanoparticle systems as well and enables their high-throughput self-assembly for future advanced device fabrication.

Characterization and acid diffusion measurements of new strong acid photoacid generators

As resist feature sizes have decreased and the performance demands on chemically amplified photoresists have increased the role of the photoacid generator (PAG) in determining overall resist performance has become increasingly apparent. Over the past 20 years a variety of different types of PAGs have been introduced as researchers have sought to optimize properties such as acid strength, acid volatility, diffusion length, wavelength response, solubility etc. PAGs that produce very strong organic acids are widely used, in part because of requirements for high photospeed resists. Most of these acid generators are based on perfluoroalkyl sulfonic acid based onium salts. In an effort to identify and characterize alternative PAGs we have investigated the performance of a variety of photoacid generators that are not based on sulfonic acids. In this report we will describe the relative reactivities of these PAGs under a variety of exposure wavelengths and processing conditions including acid diffusion proprieties and photospeed measurements.

Facile chemical rearrangement for photopatterning of POSS derivatives

We report a useful acid-catalyzed crosslinking reaction which enables the direct photopatterning of POSS derivatives to form robust nanoporous matrices. Octakis(dimethylacetoxyethyl siloxy) POSS and octakis(dimethylacetoxypropyl siloxy) POSS were synthesized from commercially available octahydrido-POSS. Both the acetoxyethyl- and acetoxypropyl functionalities were observed to undergo thermal rearrangement at temperatures above 300 °C to form Si–O–Si bonds, thus forming a crosslinked POSS network. Interestingly, the same functionalities were also acid sensitive, and the chemical rearrangement occurred at much lower temperatures. Thus, patterned nanoporous features were lithographically generated when a photoacid generator (PAG) was used as a photosensitive agent to initiate the crosslinking of the POSS derivatives. The dielectric properties were evaluated for the crosslinked POSS films, which had a dielectric constant ∼2.3 and an elastic modulus of ∼2.0 GPa. These materials hold great promise for developing a photopatternable low-k material which eliminates the need for sacrificial layers when patterning low-k dielectric films.

Topographically directed self-assembly of goldnanoparticles

We present a simple and facile strategy for the formation and placement of two-dimensional nanoparticle arrays by spin-coating of polystyrene-modified gold nanoparticles onto lithographically patterned substrates.

Evaluation of functional properties of imaging materials for water immersion lithography

The introduction of an immersion fluid in contact with the resist-coated substrate is, from the perspective of the resist material, a significant departure from the conventional lithographic process. The impact of this modification on the lithographic imaging materials is as yet only poorly characterized. We report the results of studies aimed at an improved understanding of how immersion in water during exposure influences the functional properties of films of lithographic materials. We have evaluated the water permeability of candidate immersion topcoat materials; the role of immersion topcoat materials in reducing airborne contamination and water-resist interactions; the impact of water immersion on image blur in chemically amplified resists; and high-resolution imaging of candidate immersion resist materials under conditions of poor aerial image contrast. Analytical techniques such as QCM and reflectance analysis of thin films, DUV interferometric immersion lithography, and trace organic analysis are applied in this work.

Studies of acid diffusion in low Ea chemically amplified photoresists

Critical lithographic dimensions will soon place particularly severe demands on the performance of chemically amplified (CA) resists. Although Extreme Ultraviolet (EUV) and 193 nm (immersion interferometric) lithographic results have demonstrated half pitch imaging down to 35 nm there is nonetheless a concern that image blur due to acid diffusion will begin to seriously impact the utility of CA photoresists. Previously we demonstrated that low activation energy resists and E-Beam lithography can be used to print line/space arrays with resolution approaching 20 nm. We described the factors impacting the reactivity of ketal/pHOST based resists and compared the attainable resolution under different processing conditions. In this report we describe studies on acid diffusion emphasizing the role of water in low Ea systems. We also discuss methods for the control of water absorption in low Ea resists.

Two complementary methods to characterize long range proximity effects due to develop loading

Variations in critical dimension (CD) as a function of the proximity of an individual feature to other exposed areas are a continuing problem both in mask fabrication and in optical lithography. For example, the CD uniformity (CDU) may degrade significantly depending on the proximity to densely or sparsely exposed areas. These pattern density effects will continue to worsen as feature sizes decrease to 22 nm and below. Pattern density effects in electron beam lithography using chemically amplified resists are believed to arise from several sources. One such source, fogging, refers to the backscattering of secondary electrons onto the resist to cause deviations from the nominal pattern size. A second contributor is acid volatility, where photogenerated acid is presumed to redeposit on the wafer or mask during exposure or bake; here we refer to this effect as chemical flare. A third source of pattern density effects is develop loading, which results in local depletion of developer in highly exposed regions. All three of these may simultaneously contribute to a net observed CD variation. In this report we describe the application of two different techniques for evaluating these proximity effects. The first is based on electron-beam lithography patterning, and compares CD values of test patterns which are exposed under brightfield and dark-field conditions. The second uses a series of different test patterns formed by DUV (248nm) exposure and a custom liquid flow cell to separately characterize resist related density effects.

Multilevel integration of patternable low-κ material into advanced Cu BEOL

In this paper, we wish to report, for the first time, on a simple, low-cost, novel way to form dual-damascene copper (Cu) on-chip interconnect or Back-End-Of-the-Line (BEOL) structures using a patternable low dielectric constant (low-κ) dielectric material concept. A patternable low-κ dielectric material combines the functions of a traditional resist and a dielectric material into one single material. It acts as a traditional resist during patterning and is subsequently converted to a low-κ dielectric material during a post-patterning curing process. No sacrificial materials (separate resists or hardmasks) and their related deposition, pattern transfer (etch) and removal (strip) are required to form dual-damascene BEOL patterns. We have successfully demonstrated multi-level dual-damascene integration of a novel patternable low-κ dielectric material into advanced Cu BEOL. This κ=2.7 patternable low-κ material is based on the industry standard SiCOH-based (silsesquioxane polymer) material platform and is compatible with 248 nm optical lithography. Multilevel integration of this patternable low-κ material at 45 nm node Cu BEOL fatwire levels has been demonstrated with very high electrical yields using the current manufacturing infrastructure.

Integration of Photo-Patternable Low-κ Material into Advanced Cu Back-End-Of-The-Line

We report herein the demonstration of a simple, low-cost Cu back-end-of-the-line (BEOL) dual-damascene integration using a novel photo-patternable low-κ dielectric material concept that dramatically reduces Cu BEOL integration complexity. This κ=2.7 photo-patternable low-κ material is based on the SiCOH-based material platform and has sub-200 nm resolution capability with 248 nm optical lithography. Cu/photo-patternable low-κ dual-damascene integration at 45 nm node BEOL fatwire levels has been demonstrated with very high electrical yields using the current manufacturing infrastructure. The photo-patternable low-κ concept is, therefore, a promising technology for highly efficient semiconductor Cu BEOL manufacturing.