Inorganic Hardmask Research Articles

Conversion of a Patterned Organic Resist into a High Performance Inorganic Hard Mask for High Resolution Pattern Transfer.

Polyphthalaldehyde is a self-developing resist material for electron beam and thermal scanning probe lithography (t-SPL). Removing the resist in situ (during the lithography process itself) simplifies processing and enables direct pattern inspection, however, at the price of a low etch resistance of the resist. To convert the material into a etch resistant hard mask, we study the selective cyclic infiltration of trimethyl-aluminum (TMA)/water into polyphthalaldehyde. It is found that TMA diffuses homogeneously through the resist, leading to material expansion and formation of aluminum oxide concurrent to the exposure to water and the degradation of the polyphthalaldehyde polymer. The plasma etch resistance of the infiltrated resist is significantly improved, as well as its stability. Using a silicon substrate coated with 13 nm silicon nitride and 7 nm cross-linked polystyrene, high resolution polyphthalaldehyde patterning is performed using t-SPL. After TMA/H2O infiltration, it is demonstrated that pattern transfer into silicon can be achieved with good fidelity for structures as small as 10 nm, enabling >10× amplification and low surface roughness. The presented results demonstrate a simplified use of polyphthalaldehyde resist, targeting feature scales at nanometer range, and suggest that trimethyl-aluminum infiltration can be applied to other resist-based lithography techniques.

Inorganic hardmask development for extreme ultraviolet patterning

Extreme ultraviolet (EUV) patterning offers an opportunity to explore hardmask materials and patterning approaches. Traditional patterning stacks for deep ultraviolet patterning have been based on optimizing multilayer schemes for reflectivity control and pattern transfer. At the EUV wavelength, the patterning challenges are dominated by stochastics and aspect ratio control. This offers an opportunity to think differently about underlayer design for sub-36-nm pitch patterning. The choice of hardmask can be used to modulate postlitho defectivity to mitigate the stochastics effects and enable more efficient pattern transfer. Through different case studies this paper will explore a range of silicon-based inorganic hardmasks for sub-36-nm EUV patterning. How film properties dominate patterning performance will be studied systematically. The relative merits of patterning a chemically amplified organic resist directly on an inorganic hardmask or having different types of organic adhesion promoters as an intermediate layer will also be presented.

Photopatternable inorganic hardmask

The authors present a directly photopatternable inorganic hardmask for 193 nm lithography based on the solution-deposited dielectric metal oxide sulfate (MSOx) system. To demonstrate pattern fidelity, 18 nm half-pitch features were written at a dose near 240 μC/cm2 (30 keV) with line width roughness values between 1.6 and 1.8 nm. Well-resolved and uniform 30 nm contact holes were fabricated via a litho-freeze-litho-etch process employing electron beam exposure and a simple thermal freeze. ZircSOx has a high index of refraction approaching 1.9 at 193 nm, and the extinction coefficient, k, can be varied by an order of magnitude by substituting Zr with Hf. Optical interference lithography at 193 nm was used to realize 60 nm half-pitch lines in MSOx at a dose of 25 mJ/cm2.

A Novel Approach for the Patterning and High-Volume Production of Sub-40-nm Gates

A novel approach for the patterning and manufacturing of sub-40-nm gate structures is presented. Rather than using resist or an inorganic hardmask as the patterning layer, this gate patterning scheme uses an amorphous carbon (a:C) and cap hardmask to pattern small gates. Healthy and manufacturable gate lengths have been achieved below 35 nm with this scheme, and the potential exists for further extendibility.