Metal–organic materials such as [NH2(CH2–CHCH2)2][Cr7NiF8(Pivalate)16] can act as negative
tone resists
for electron beam lithography (EBL) with high-resolution patterning
of sub-40 nanometer pitch while exhibiting ultrahigh dry etch selectivities
>100:1 and giving line dose exposures >11,000 pC/cm. It is clear
that
the resist sensitivity is too low to be used to manufacture the latest
nanoscale photomasks that are suitable for extreme ultraviolet lithography.
Therefore, the focus of this work here is to improve the sensitivity
of this resist while maintaining its resolution and dry etch selectivity.
Using our latest Monte Carlo simulation called Excalibur, we predict
that the sensitivity would increase by a factor of 1.4 when the nickel
atom is substituted by a cadmium atom. EBL studies showed an excellent
agreement with the simulation, and plasma etching studies demonstrated
that this did not affect the dry etch performance of the resist which
remains very good with a selectively of ca. 99:1 for the etching of
silicon at these resolutions with a low sensitivity of 7995 pC/cm.
In this paper, we report on a novel metal organic photoresist based on heterometallic rings that was designed for electron beam and extreme ultraviolet lithography. From initial electron beam lithography studies, the resist performance demonstrated excellent resolution of 15 nm half-pitch (HP) and a silicon dry etch selectivity of 100:1 but at the expense of sensitivity. To improve sensitivity, a 3D Monte Carlo simulation was employed that utilizes a secondary electron generation model. The simulation suggested that the sensitivity could be dramatically improved while maintaining high resolution by incorporating HgCl2 species into the resist molecular design. This considerably improved the resist sensitivity without losing the high resolution, where it was determined that the resist sensitivity was increased by a factor of 1.6 and 1.94 while demonstrating a resolution of 15 nm and 16 nm HP when exposed with electrons and EUV radiation respectively. Using x-ray photoelectron spectroscopy measurements, we show that after exposure to the electron beam the resist materials are transformed into a metal oxyfluoride and this is why the resist demonstrates high resistance to silicon dry etch conditions achieving a selectivity of 60:1 at a resolution of 15 nm HP.
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