Although extreme ultraviolet (EUV) lithography is being considered as one of the most promising next-generation lithography techniques for patterning sub-20 nm features, the development of suitable EUV resists remains one of the main challenges confronting the semiconductor industry. The goal is to achieve sub-20 nm line patterns having low line edge roughness (LER) of <1.8 nm and a sensitivity of 5 to 20 mJ/cm2. The present work demonstrates the lithographic performance of two nonchemically amplified (n-CARs) negative photoresists, MAPDST homopolymer and MAPDST-MMA copolymer, prepared from suitable monomers containing the radiation sensitive sulfonium functionality. Investigations into the effect of several process parameters are reported. These include spinning conditions to obtain film thicknesses <50 nm, baking regimes, exposure conditions, and the resulting surface topographies. The effect of these protocols on sensitivity, contrast, and resolution has been assessed for the optimization of 20 nm features and the corresponding LER/line width roughness. These n-CARs have also been found to possess high etch resistance. The etch durability of MAPDST homopolymer and MAPDST-MMA copolymer (under SF6 plasma chemistry) with respect to the silicon substrate are 7.2∶1 and 8.3∶1, respectively. This methodical investigation will provide guidance in designing new resist materials with improved efficiency for EUVL through polymer microstructure engineering.
It is expected that EUV resists must simultaneously pattern 20-nm half-pitch and below, with an LWR of <1.8 nm, and a sensitivity of 5–20 mJ/cm2. In order to make a resist perform optimally, new resist chemistry is required. One such approach being investigated by us is the development of polymeric non-CAR negative photo resists for sub 16 nm technology which is directly sensitive to radiation without utilizing the concept of chemical amplification (CARs). These resist designs are accomplished by homopolymers which are prepared from monomers containing sulfonium groups. We have achieved 20 nm patterns by e-beam lithography using this system. Here we will discuss in detail process parameters such as: spinning conditions for film thicknesses <50 nm and resulting surface topographies, baking regimes, exposure conditions and protocols on sensitivity, contrast, resolution and LER/LWR. Etch resistance data on these thin films will also be provided. Our results are aimed to provide a clear understanding of how these critical steps in the lithographic imaging process will affect extendibility of the non-CAR resist concept to sub 20 nanoscale features. Photodynamics and EUV exposure data will be covered.
The design, synthesis and characterization of non-chemically amplified negative tone electron-beam and EUV resists
based on the inclusion of a radiation sensitive sulfonium functional group are outlined.. MAPDST (4-(methacryloyloxy phenyldimethylsulfoniumtriflate) and MANTMS (1-(4-(methacryloyloxy)naphthalen-1-yl)tetrahydro-1H thiopheniumtrifluoromethane sulfonate) monomers each containing the sulfonium group underwent homo- and copolymerizations using free radical polymerization with 2,2'-azobisisobutyronitrile (AIBN) initiator. These resist materials were evaluated by EB lithography using 20 keV electron beam and EUV lithography to obtain sub-20 nm line patterns. These features were optimized ranging from resist coating, pre-exposure bake, exposure to e-beam, postexposure bake, development and imaging. Our investigation showed that these newly synthesized resists are potential viable candidates for EUV lithography based on their ability to form flaw free thin films < 50nm, sensitivity, resolution and LER control.
We report the lithography performance of novel non chemical amplified (n-CARS) negative photoresist materials which are accomplished by homopolymers and copolymers that are prepared from monomers
containing sulfonium groups. The latter have long been found to be sensitive to UV radiation and undergo polarity change on exposure. For this reason, these groups were chosen as radiation sensitive groups in non-
CARs that are discussed herein. Novel n-CAR negative resists were synthesized and characterized for EUVL applications, as they are directly sensitive to radiation without utilizing the concept of chemical amplification. The n-CARs achieved 20 and 16 nm L/2S, L/S patterns to meet the ITRS requirements. We will also discuss the
sensitivity and LER of these negative n-CARS to e-beam irradiation which will provide a basis for EUVL down
to the 16 nm node and below. These new negative tone resist provide a viable path forward for designing non-
chemically amplified resists that can obtain higher resolutions than current chemically amplified resists at competitive sensitivities.
Herein, we describe preliminary results on organic-inorganic hybrid photoresists, capable of showing line
patterns up to 16 nm under e-beam exposure studies, prepared by incorporating polyoxometalates (POMs)
clusters into organic photoresist materials. Various Mo and W based clusters such as (TBA)2[Mo6O19],
(TBA)5(H)[P2V3W15O62] and (TBA)4[P2Mo18O61] (where TBA = tetrabutyl ammonium counter ion) have been
incorporated into PMMA matrix by mixing POM solutions and standard PMMA polymer in anisole (MW ~
95000, MicroChem) in 1:33 w/v ratio. E-beam exposure followed by development with MIBK solutions showed
that these new organic-inorganic hybrid photoresists show good line patterns upto 16 nm, which were not
observed in the case of control experiments done on pure PMMA polymer resist. The observed enhancement of
resist properties in the case of hybrid resists could possibly be due to a combination of features imparted to the
resist by the POM clusters such as increased sensitivity, etch resistance and thermal stability.