Electron Beam Lithography (EBL)
Electron beam lithography (EBL) has long been established as the premier technique for defining structures at the nanoscale. Since itís inception in 1979, the Cornell Nanoscale Science and Technology Facility (CNF) has remained at the forefront of nanofabrication research by providing state-of-the-art EBL tools to the academic and industrial user community. CNF has excelled in the application of EBL to research areas ranging from electronic devices and integrated optics to the emerging fields of nanoelectromechanical systems (NEMS), nanobiotechnology and nanomagnetics. Breakthroughs in these fields are a direct consequence of the unique lithographic processing capabilities developed at CNF over the past 37 years. These include:
CNF is currently meeting the demands of scientists working in the broad field of nanoscale science and engineering by providing two high resolution direct write EBL tools. These systems are available 24 hrs a day year round. Our qualified staff has a proven track record of guiding users through complex processing using EBL. Combined with a full suite of optical lithography, thin film deposition, thin film patterning and advanced metrology equipment, CNF is the right place to explore the world of nanoscale science.
- The ability to reproducibly achieve feature sizes below 20 nm
- Multilayer lithography with less than 20 nm overlay
- Mix and match EBL and photolithographic processing
- Nanoimprint template fabrication
- Patterning on thin silicon and silicon nitride membranes
- Substrate handling from small pieces to 300 mm wafers and 3" to 7" photomasks
:: ELECTRON-BEAM LITHOGRAPHY TOOLS ::
Optical lithography requires the fabrication of a mask. Generally, photomasks consist of a piece of glass of some type, coated with a film in which the pattern is formed. A layer of sputtered Cr about 100 nm thick coats the glass plate. Resist is then spun on the plate, and the exposure is made. After development, the Cr is removed from the unprotected areas with an acid etch, and an image of the pattern is left in the Cr. The exposure can be made with either an optical or an electron beam lithography tool. The lithography requirements at CNF usually allow you to make a mask faster, cheaper, and more easily with optical tools than with an electron beam lithography tool. The CNF currently operates two optical mask making tools: a Heidelberg Instruments DWL 66 and a Heidelberg Instruments DWL 2000.
:: MASK MAKING TOOLS ::
"Optical lithography has been used for over 30 years as the preferred method of image formation in the manufacture of silicon devices and other semiconductor components. Its demise as the premier imaging technology was predicted at about 1 micrometer feature size by proponents of alternative imaging technologies and others who underestimated the ability of optical tool manufacturers to improve optical and mechanical system performance to the degree necessary to support the production of increasingly complex devices with ever smaller features."
-C.W.T. Knight, The Future of Manufacturing with Optical Microlithography, Optics and Photonics News, Oct. 1990, p.11
CNF maintains a full compliment of optical lithography tools in order to support the needs of our user base. These tools include simple 1:1 contact lithography tools and complex projection step and repeat (stepper) systems. These tools have a variety of different features. Together they provide CNF user with a flexible tools set capable of performing exposures with feature sizes less than 200 nm on substrates ranging from 5 mm pieces to full 200 mm wafers.
:: PHOTOLITHOGRAPHY TOOLS ::
THIN FILM DEPOSITION, SYNTHESIS AND PROCESSING
Thin Film Deposition
Plasma-enhanced chemical vapor deposition (PECVD) is a process used to deposit thin films from a gas state (vapor) to a solid state on a substrate. Chemical reactions are involved in the process, which occur after creation of a plasma of the reacting gases. The plasma is generally created by RF (AC) frequency or DC discharge between two electrodes, the space between which is filled with the reacting gases. The CNF has five hot-process banks (20 tubes) for a diversity of process uses.
:: THIN FILM DEPOSITION TOOLS ::
Rapid Thermal Annealing (RTA)
The CNF has several locations for doing wet chemical etching of substrates. In addition to general chemistry hoods for using various acid and alkaline solutions we also have two tanks located in the furnace area for doing Nanostrip cleaning and Hot Phosphoric etching of silicon nitride. The CNF supplies various premixed solutions for etching of various metals. Below is information on the etch rates measured for the various materials as well as the recommended operating conditions.
:: ETCHING (RTA) TOOLS ::
Atomic Force Microscopy (AFM)
The operational principle of an atomic force microscope is described by considering a surface of interest being scanned with a sharp tip residing at the free end of a microfabricated cantilever beam. The apex of the tip either gently contacts the surface when imaging is performed in contact mode, or intermittently contacts the surface during tapping mode imaging. The ultrasmall repulsive or attractive forces existing between the tip and the sample cause the cantilever to move up and down in the direction vertical to the surface. This deflection is monitored using an optical deflection setup consisting of a laser beam focused at the free end of the oscillator reflecting into a quad cell photodetector. During this scanning process, bending deflection, oscillation and torsion of the cantilever can be simultaneously measured.
Scanning Electron Microscopy (SEM)
Scanning electron microscopy is critical for the analysis of nanoscale materials and structures. CNF operates two field emission scanning electron microscopes (SEMs): a Zeiss Supra 55 microscope capable of variable pressure (VP) operation and a Zeiss Ultra 55 microscope optimized for high resolution imaging. Like most modern SEMs, both systems are capable of operating at beam energies from 100 V to 30 kV. However, the unique electron optical design employed in the Zeiss systems enables unsurpassed performance at beam energies from 100 V to 8 kV. This is crucial for obtaining high resolution distortion free images of surface.
Focused Ion Beam (FIB)
Focused ion beam (FIB)-based systems provide a versatile tool for performing work at the nanoscale. They can be used to selectively remove material from substrates and to direct write insulator and metal patterns while providing a high resolution inspection system, comparable to that achieved in the scanning electron microscope. These features have made FIB instruments a staple in failure analysis labs and semiconductor foundries alike.
::CHARACTERIZATION TOOLS ::
CNF TECHNICAL BROCHURE
We have an "all in one" brochure describing all areas of the CNF research groups
MODELING AND SIMULATION
Computing Capabilities at the CNF
For many years, the Cornell NanoScale Facility (CNF) has offered CAD and simulation tools to assist in designing patterns, fracturing data, and analyzing results. Through generous donations by Intel Corporation, the CNF has also been able to provide high performance computing capabilities to users since early 2005. This effort is part of the greater computational initiative in the NNIN to provide nanoscale modeling resources that accelerate research and innovation. The Intel Computing Cluster consists of 152 Xeon processors (288 computing cores) linked with gigabit Ethernet connections. Users at the CNF have access to a platform for large scale computations that complements the various fabrication resources currently available.
The cluster hosts an ever-expanding and diverse suite of simulation tools for nanoscale systems including codes for first principles calculations, photonic devices, molecular dynamics and nanoscale transport. While numerous standard packages exist for well-known systems in different fields, cutting edge research often requires developing new algorithms or approaches to address unique problems. To this end, the CNF is dedicated to not only providing simulation tools, but also playing a role in their development. Since this is one of the few tools at the CNF that can be accessed from virtually anywhere, it can also have a dramatic impact on research from both local and remote users who can modify existing codes or if need requires, constructing new approaches. The cluster also serves as a crucial test-bed where codes developed in research groups can be tested by users in order to develop the robustness necessary for wide spread distribution. More information on the overall computational effort through the NNIN can be found at the NNIN/C website
:: COMPUTING TOOLS ::
The CNF has an Intel Computing Cluster that provides users of the CNF the opportunity to use a wide range of modeling software tailored for nanoscale systems. The cluster consists of 152 Xeon processors (288 computing cores). In addition, a subset of the nodes are linked with Inifiniband fabric. The cluster runs Red Hat Linux Enterprise. The CNF Cluster was made possible by donations from Intel Corporation in 2004, 2005, and 2007. In 2010, we also expanded the capability of the cluster with the additional of 20 new Xeon nodes with a large amount of RAM to handle memory intensive calculations.
:: MODELING TOOLS ::