Nanoparticles have useful properties, but it is often important that they only start working after they are placed in a desired location. The encapsulation of nanoparticles allows their function to be preserved until they are released at a specific time or location, and this has been exploited in the development of self-healing materials and in applications such as drug delivery. Encapsulation has also been used to stabilize and control the release of substances, including flavours, fragrances and pesticides. We recently proposed a new technique for the repair of surfaces called 'repair-and-go'. In this approach, a flexible microcapsule filled with a solution of nanoparticles rolls across a surface that has been damaged, stopping to repair any defects it encounters by releasing nanoparticles into them, then moving on to the next defect. Here, we experimentally demonstrate the repair-and-go approach using droplets of oil that are stabilized with a polymer surfactant and contain CdSe nanoparticles. We show that these microcapsules can find the cracks on a surface and selectively deliver the nanoparticle contents into the crack, before moving on to find the next crack. Although the microcapsules are too large to enter the cracks, their flexible walls allow them to probe and adhere temporarily to the interior of the cracks. The release of nanoparticles is made possible by the thin microcapsule wall (comparable to the diameter of the nanoparticles) and by the favourable (hydrophobic-hydrophobic) interactions between the nanoparticle and the cracked surface.
Optimizing the photochemistry in extreme ultraviolet (EUV) photoresists due to EUV exposures may enable faster, more efficient resists, leading to a greater throughput in manufacturing. Since the fundamental reaction mechanisms in EUV resists are believed to be due to electron interactions after incident 92 eV photons (13.5 nm) generate photoelectrons during ionization events, understanding how these photoelectrons interact with resist components is critical for optimizing the performance of EUV resists and EUV lithography as a whole. The authors will present an experimental method to measure the cross section of incident electron induced decomposition of three different photoacid generators (PAGs). To study the photoelectrons generated by the EUV absorption and measure their effect within resists, photoresists were exposed to electron beams at electron energies between 80 and 250 eV. The reactions between PAG molecules and electrons were measured by using a mass spectrometer to monitor the levels of small molecules produced by PAG decomposition that outgassed from the photoresist. This methodology allowed us to determine the number of PAG molecules decomposed per incident electron. By combining this result with the average penetration depth of an electron at a given energy, the cross sections of PAG molecules were determined for energies ranging between 80 and 250 eV. Comparing the cross sections of PAG molecules can provide insight into the relationship between chemical structure, reactivity to the electrons, and trends in cross section versus electron energy. This research is a part of a larger SEMATECH research program to understand the fundamentals of resist exposures to help in the development of new, better performing EUV resists.
The lithography community has studied EUV photoresists for nearly thirty years. Yet, some of the most basic details of the interaction of EUV photons with photoresists remain poorly understood. In a typical photochemical reaction using long-wavelength light ( = 157-1000 nm), photons create excited states in photoactive compounds, thereby creating known quantities of intermediates and photoproducts at measurable rates.The photochemical reactions occurring during EUV exposure are much more complex and, as yet, not fully explored. The 92 eV EUV photons ionize molecules in the resist, creating holes and free electrons, however, the numbers of these electrons created, their reaction mechanisms, lifetimes and reaction cross-sections are not well known. Here, we will discuss experimental results and provide insight into these poorly understood aspects of EUV exposure mechanisms.
EUV photons expose photoresists by complex interactions starting with photoionization that create primary electrons (~80 eV), followed by ionization steps that create secondary electrons (10-60 eV).Ultimately, these lower energy electrons interact with specific molecules in the resist that cause the chemical reactions which are responsible for changes in solubility. The mechanisms by which these electrons interact with resist components are key to optimizing the performance of EUV resists. An electron exposure chamber was built to probe the behavior of electrons within photoresists. Upon exposure and development of a photoresist to an electron gun, ellipsometry was used to identify the dependence of electron penetration depth and number of reactions on dose and energy. Additionally, our group has updated a robust software that uses first-principles based Monte Carlo model called "LESiS", to track secondary electron production, penetration depth, and reaction mechanisms within materialsdefined environments. LESiS was used to model the thickness loss experiments to validate its performance with respect to simulated electron penetration depths to inform future modeling work.
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