Advanced characterization techniques for nanoscale photoresist structure
Miquel Salmeron, Slavomir Nemsak, and Patrick Naulleau
Lawrence Berkeley National Laboratory, University of California Berkeley
The spatial chemical structure of photoresists before and after processing is currently limited to a resolution of 10’s of nanometers, far above the desirable level of mono and sub-nm resolution that can enable the next generation of microelectronic circuits and devices. We will discuss in this presentation novel characterization techniques that will open the door for advanced spectroscopic characterization of polymer interfaces both in the latent image and the developed image. Among the new techniques being currently developed we will describe plasmonically enhanced infrared spectroscopy that provides FTIR spectra with nm x-y resolution along the interface between the photoresist and the substrate/underlayer. Additionally, we will present Standing Wave X-ray Photoelectron Spectroscopy in soft and tender X-ray regime, which provides elemental and chemical state composition in the z-direction across surfaces and buried interfaces. Currently these techniques have provided the first nanoscale characterization of the molecular structure of solid-liquid interfaces, revealing the chemical structure of the electrical double layer, of crucial importance in batteries, corrosion phenomena, and electrocatalysis. Applications to the polymer-substrate interface is currently underway.
In the usual surface forces apparatus arrangement, the determination of the distances between interacting surfaces, as well as their mutual forces, is based on the analysis of interference fringes originated between the surfaces. To enhances the contrast and sharpness of the fringes, a thin metallic coating is applied to the mica plates that form the interaction chamber. In this paper we try to improve the performance of the basic system just described by optimizing the metallic coating and also by computer processing the images of the visible fringes.
We have developed a general technique that combines the temporal resolution of ultrafast laser spectroscopy with the spatial resolution of scanned probe microscopy (SPM). Using this technique with scanning tunneling microscopy (STM), we have obtained simultaneous 2 ps time resolution and 50 angstrom spatial resolution. This improves the time resolution currently attainable with STM by nine orders of magnitude. The potential of this powerful technique for studying ultrafast dynamical phenomena on surfaces with atomic resolution is discussed.
Scanning Tunneling Microscopy (STM) image of adsorbed atoms and molecules on single crystal substrates provide important information on surface structure and order. In many cases images are interpreted qualitatively based on other information on the system. To obtain quantitative information a theoretical analysis of the STM image is required. A new method of calculating STM images is presented that includes a full description of the STM tip and surface structure. This method is applied to experimental STM images of sulfur adsorbed on Re(0001). The effects of adsorption site, adsorbate geometry, tip composition and tunnel gap resistance on STM image contrast are analyzed. The chemical identity of the tip apex atom and the substrate subsurface structure are both shown to significantly affect STM image contrast.
The application of the STM and AFM techniques to imaging of biomolecules is reviewed. It is shown that in order to image poorly conductive molecules of nanometer dimensions, the STM has to be operated at high gap resistances in the 1012 ohm range. The correlation between forces and currents between tip and surface is investigated in model organic films of alkylsiloxanes on SiO2/Si(100) surfaces. The application of the AFM in the attractive and repulsive modes is also reviewed.