AVS 71 Session TF1-WeA: VSHOP V – Vapor Synthesis of Hybrid Materials and Their Properties

Molecular layer deposited (MLD) metal-organic photoresists have the potential to address the material challenges of extreme ultraviolet (EUV) lithography due to their advantages in thickness control and chemical homogeneity. Previous studies have utilized simple MLD schemes with a single precursor and counter-reactant pair to achieve patterning close to industrially relevant length scales. However, for further optimization, layer-by-layer deposition of multi-component films via a supercycle approach may be required to adjust properties such as sensitivity, contrast, etch resistance, mechanical strength, and others.

In this work, we explore the properties of multi-component MLD photoresists by depositing multi-metal alkoxide (‘metalcone’) films via both trimethylaluminum (TMA) and diethylzinc (DEZ), and ethylene glycol as the counter-reactant. Using a supercycle approach in which cycles of alucone growth (TMA and EG) are evenly distributed with cycles of zincone growth (DEZ and EG), we grow the multi-metalcone films with a range of Al/Zn ratios and characterize their properties. X-ray photoelectron spectroscopy (XPS) shows that significant transmetalation of Al and Zn occurs during deposition. However, the metal fraction can still be controlled between 40% and 95% Al (normalized against Al + Zn) by varying the fraction of alucone cycles within the supercycle between 0.25% and 50%. To assess the effect of the Al/Zn ratio on resist performance, line/space gratings with 24 nm half pitch are patterned on ~25 nm thick resist films via electron beam lithography as a proxy for EUV lithography and developed with hydrochloric acid at varying concentrations. The results show that compared to pure alucone or zincone films, the multi-metal resists have similar e-beam sensitivity (~70-100 mC/cm² depending on development conditions), but enhanced lithographic contrast (improving from a value of γ = 0.38 for alucone to a value of γ = 6.3 for the multi-metalcone) and pattern quality (reduced bridge defects and scumming). The improvements are observed even for minimal Zn incorporation in the multi-metalcone (~95% Al). From XPS studies of the resists after partial development, we attribute the improvement to the preferential dissolution of zincone from the unexposed multi-metal resist, which enhances solubility contrast. This work demonstrates the potential of supercycled MLD schemes to enable emergent interactions between components, vastly expanding the design space for this class of photoresists.

Micropatterning of 3-dimensional structures from arbitrary ceramic materials is complicated and often expensive. In this work, we explore a new platform technology for converting an easily patterned photopolymerizable resin into a 3D ceramic structure using vapor phase infiltration (VPI) and subsequent thermal combustion.VPI is a gas-phase technique in which inorganic vapors are sorbed into a polymer, creating an organic-inorganic hybrid material.Here we are interested in studying how the chemical design of this hybrid material can affect the thermal combustion process and its conversion to a final ceramic component, without significant cracking.Ethoxylated trimethylolpropane triacrylate (ETPTA) photo-polymerizable monomers are used because they are already known to create compliant networks that readily sorb high fractions of inorganic precursors during VPI.After VPI with trimethyl aluminum (TMA) and water, the hybrid films were thermally annealed to fully combust all organics.In this talk, we will discuss how process parameters including reactor temperature and precursor exposure duration affect cracking, shrinkage, and ceramic density.In general, increased precursor loading during VPI results in reduced cracking of the alumina film, and upwards of 60% of the original film thickness could be retained after organic burnout.To assess changes in the lateral dimension micro-patterned structures were also tested, and minimal change in lateral size were detected, likely due to substrate clamping.

Advanced interposers consist of alternate layers of copper and polymer dielectric materials. While copper has a low coefficient of thermal expansion (CTE) of 16 ppm/ ⁰C, ultra-low-k dielectric materials have CTEs in the range of 50-150 ppm/ ⁰C. This mismatch in CTE between copper and ultra-low-k dielectric materials results in lower thermomechanical reliability. Most methods available in literature involve the addition of oxide fillers to reduce the CTE of polymers. In this study, vapor phase infiltration (VPI) treatment is considered as a possible method to introduce AlO_x into dry films or spin-coated and cured films. Another challenge with respect to ultra-low-k dielectric films is the measurement of CTE. Conventional CTE measurement techniques such as thermomechanical analysis (TMA) require a sample thickness of the order of few millimeters. The films in the present study have thicknesses in the range of 0.5 to 5 μm matching closely with the typical dielectric layer thickness employed in advanced packaging substrates with very high-density interconnects. Therefore, TMA cannot be used for CTE measurement of these films. Instead, temperature dependent spectroscopic ellipsometry is used to track the thermal expansion of the films and determine their CTE.These measurements demonstrate the effectiveness of the VPI process to lower the CTE of low dielectric constant polymers by about 4 to 15 times depending on the dielectric polymer, placing them near the CTE of copper.The chemical mechanisms for this lowering of the CTE will be discussed in this talk.

This work was supported by the United States Department of Energy through competitively awarded contract number DE-SC0020609. This support does not constitute an express or implied endorsement on the part of the Government.