Sup4 - Polymers in Nanofabrication - UCSD NANO 134 - Darren Lipomi

The speaker introduces a three-part lecture series focusing on special topics in polymeric materials, beginning with nanofabrication techniques involving polymers. They mention that most of the content has already been commercialized and can be found in everyday devices. The lectures will cover topics from microfabrication, which is essentially nanofabrication, to polymer solar cells, and computational material science. The importance of nanoscale phenomena and their applications in various fields such as medicine, energy, and information technology is highlighted, with examples including semiconductor quantum dots, graphene, and gecko foot adhesion. The speaker also points out that while microprocessors and memory devices are nano in scale, they are not typically considered nanotechnology due to the suppression of quantum tunneling effects.

This paragraph delves into the technical aspects of nanofabrication, emphasizing the importance of mastering, which is the creation of nanoscale information. The process involves using electron beams to etch patterns in a resist material, which can then be replicated. The speaker explains the difference between positive and negative resists, using poly methyl methacrylate (PMMA) as an example of a positive resist. The replication process is then described, where photolithography is used to transfer the pattern onto a wafer at a much faster rate than e-beam lithography. The high cost and precision requirements of these processes are also discussed, along with the challenges of achieving nanoscale accuracy in a commercial setting.

The speaker discusses the significance of nanofabrication in the manufacturing of microprocessors, highlighting the precision and low error rates required in the industry. They mention Moore's Law and its prediction of the doubling of transistor counts on microprocessors every two years. The historical progression from early computers to modern devices with billions of transistors is outlined, emphasizing the remarkable engineering feats involved. The speaker also touches on the acceptable error rates in microfabrication, which are incredibly low, reflecting the high standards of the semiconductor industry.

The paragraph explores the challenges and innovations in photolithography, the primary technique used in microprocessor manufacturing. The limitations imposed by the diffraction of light are discussed, along with the strategies to overcome them, such as using high refractive index immersion fluids and phase-shifting masks. The speaker also explains the concept of resolution and how it is affected by factors such as wavelength, numerical aperture, and the system's sensitivity. The transition from using 157 nanometer light to 193 nanometer light is mentioned, along with the difficulties in moving to shorter wavelengths like extreme UV or x-ray light due to material absorption issues.

This section describes advanced techniques used to overcome the diffraction limitations in photolithography. The speaker introduces emergent optics, which involves projecting light through a medium with a higher refractive index than air, and phase-shifting masks that create interference patterns to produce sharper boundaries. The concept of double exposure patterning is also discussed as a way to increase resolution without increasing the number of masks used. The speaker highlights the need for new polymer chemistry to enable these techniques and the active research in this area.

The speaker presents a survey from 2008 that predicted the future of photolithography techniques by 2016. The predictions included a decline in 193-nanometer single exposure, an increase in 193-nanometer immersion double patterning lithography, and a rise in extreme UV lithography and maskless lithography. However, the actual outcomes have varied, with extreme UV and maskless lithography not living up to expectations. The speaker reflects on the accuracy of these predictions and the continued reliance on 193-nanometer double exposure patterning, despite its limitations.

The paragraph discusses alternative nanofabrication techniques that are more accessible and cost-effective than high-end photolithography. The speaker mentions the use of soft lithography, which employs a polymeric stamp to transfer patterns, allowing for the patterning of unconventional materials and form factors. The advantages of soft lithography, such as its compatibility with flexible and non-planar surfaces and its ability to pattern a variety of materials, are highlighted. The speaker also touches on the energy and cost efficiencies of these methods compared to traditional cleanroom processes.

This section provides an in-depth look at soft lithography, a technique that uses a silicone rubber stamp to replicate nanoscale patterns. The process involves creating a master with nanoscale features, which is then used to create a stamp that can be applied to various surfaces. The speaker describes different methods of soft lithography, including decal transfer printing, phase-shifting edge lithography, and nanoskiving. The ability to create high-resolution features, high aspect ratio structures, and interlocking patterns is emphasized, showcasing the versatility and potential of soft lithography for a wide range of applications.

The speaker explores innovative applications of soft lithography, such as particle replication for creating discrete particles with specific shapes that can be used in drug delivery, and the creation of 3D structures like photonic crystals. The use of phase-shifting edge lithography to produce tiny structures in resist films is also discussed. The paragraph highlights the potential for low-cost manufacturing using shrinky dink and inkjet printing to achieve nanoscale patterns, as well as the use of DNA polymers for self-assembly to create sub-50 nanometer features. The speaker concludes by emphasizing the importance of lithography in nanofabrication and its role in advancing various fields.