Search

Significant efforts have been dedicated to the development of inorganic-organic hybrid materials for next-generation EUV resists. Among the various synthesis, vapor-phase infiltration of metal source into existing e-beam photoresists using ALD process has drawn great attention. In this work, we have demonstrated the vapor-phase infiltration of both Hf and Al precursors into PMMA and HSQ resists, respectively. For example, under the electron exposure with 100 eV, both hybrid resists show relatively higher EUV absorption, increasing positive and negative tone. The detailed photochemical reactions of on electron exposure were investigated using an in-situ FTIR equipped with electron gun capability.

We have developed an organic-inorganic hybrid resist platform featuring versatile ex-situ control of its performance by incorporating inorganic elements using vapor-phase infiltration (VPI) into standard organic resists. With poly(methyl methacrylate) (PMMA)-AlOx hybrid as a model composition we unveiled controllability of the critical exposure dose, contrast (as high as ~30), and etch resistance; estimated Si etch selectivity over ~300, demonstrating high aspect ratio ~17 with ~30 nm resolution Si fin-structures. Building upon the demonstration of PMMA-AlOx hybrid resist, we expanded our material portfolio to a high sensitivity resist and other inorganic moieties. We present preliminary results obtained from the extreme ultraviolet (EUV) lithography dose tests conducted on corresponding infiltrated hybrids and optimization of infiltration with the help of transmission electron microscopy (TEM).

We demonstrate a simple ex-situ inorganic infiltration route for transforming standard organic resists into high-performance positive tone hybrid resist platform. A model thin film PMMA-AlOx hybrid resist system has been synthesized by hybridization of PMMA with AlOx and investigated for electron beam lithography. The approach possesses full controllability of the resist performance in terms of critical does, patterning contrast reaching up to 30 and etch resistance for plasma-based pattern transfer processes. The high selectivity Si etching capability demonstrated using a low-temperature cryo-Si etch process, based on the controlled infiltration outperforms commercial resists and typical hard mask material thermal SiO2, with estimated achievable selectivity in excess of ~300. Si nanostructures down to ~30 nm with aspect ratio up to ~17 are also transferred into the Si substrate. Easy implementation and adaptability for different inorganic infiltrations, this platform is well capable of potentially delivering the resist performance and throughput necessary for EUV lithography.

Atomically thin two-dimensional (2D) semiconductors boast numerous intriguing enhanced material properties for various potential electronic device applications. For optoelectronic devices, such as photodetectors and photovoltaics, an efficient light harvesting is highly demanded, and the relatively low absolute optical absorption of 2D semiconductors can, therefore, limit associated device performances, including photodetector responsivity and solar cell power conversion efficiency. Recently, the sensitization by quantum dots (QDs) has shown promises for improving the optical absorption in 2D semiconductors. In this talk, I will highlight our recent efforts towards utilizing QD sensitization for improving the photo-response of 2D semiconductor field-effect transistor (FET) photodetectors. The first example demonstrates a 500% enhancement in photocurrent response by the application of energy transfer from CdSe/ZnS core/shell QDs in 2D SnS2, a model 2D system with indirect band gap nature. Also detailed is the case of 2D MoS2, where we show that the light-intensity-dependent photo-response characterized by scanning photocurrent microscopy (SPCM) can distinguish two fundamental modes of interfacial interaction between QDs and 2D materials, namely energy and charge transfers, which are extremely difficult to distinguish under typically optical interrogation methods. I will try to discuss the potential implication of these two modes towards the optoelectronic application of QD-2D hybrid materials.

Gallium nitride (GaN) nanowires (NW) and various nanostructures were grown by thermal reaction of gallium oxide and ammonia. The interplay between Ga/N reactant ratio and characteristic lengths of polar surfaces explained morphology variation. Field effect transistors were patterned on 40~185 nm diameter NWs by Ga + focused ion beam (FIB) direct Pt deposition. The devices exhibited no gate responses with liner I-V for "small" diameter NWs. Linear I-V was unexpected since Pt forms Schottky barriers on n-GaN. I-V-T characteristics of the FIB-Pt contacts evolved from ohmic to rectifying with increasing NW diameter with strongly nonmetallic T-dependence. For small diameters, two-dimensional variable range hopping explained the contact conduction, the disorder being associated with ion-beam-induced sputtering and amorphization in the GaN under the FIB-Pt, as corroborated by transmission electron microscopy (TEM). For large diameters, back-to-back Schottky barriers explained the nonlinear I-V. High carrier concentration was confirmed explaining the absence of gate responses. Finally, Young's modulus E and quality factor Q of GaN NW were measured using in-situ TEM electromechanical resonance analysis. For large diameters, E was ~300 GPa but decreased for smaller diameters. Q was greater than was obtained from micromachined Si resonators with comparable surface-to-volume ratio, implying significant advantages of GaN NW for nanoelectromechanical applications.