Research

The following are some brief overviews of current research project topics in the Henderson Research Group. If you clink on the hyperlink title of one of the research areas, it will take you to a page with additional information on the topic.

1. Design, Synthesis, and Characterization of Block Copolymers for Directed Self Assembly (DSA) - As

feature sizes have continued to shrink in integrated circuit manufacturing, current 193 nm optical lithography

methods have reached the limits of their capabilities in terms of single layer resist patterning at a pattern pitch

of ~80nm. To achieve smaller pitches, various multiple patterning schemes are being employed. To progress

below 40 nm pitch features, alternative methods are needed. Directed self assembly (DSA) of block

copolymers is one promising alternative for patterning pitches smaller than 40 nm. In such DSA techniques,

one takes advantage of the general fact that most polymers are phase immiscible with one another, and thus

block copolymers have a natural tendency to microphase separate on a length scale that is commensurate with

the polymer block dimensions. Thus, pattern pitch in features made by DSA can be controlled by controlling

the size of the block copolymers (i.e. by controlling the polymers degree of polymerization). Our work in this

area is directed at developing high chi block copolymers that can achieve very small pattern pitches and

developing the materials and processes needed to achieve directed assembly of such block copolymers into

useful nanostructures.

2. Modeling and Simulation of Block Copolymer Phase Separation and Directed Self Assembly - In support

of our DSA work mentioned above, we are also developing techniques and models to simulate the phase

separation process in block copolymer systems, with a particular emphasis on studying the directed assembly

process in thin block copolymer films. Our group, in collaboration with Professor Pete Ludovice (GT ChBE), are

developing new techniques for performing fast annealing of copolymers in molecular dynamics simulations in

order to access the large time and length scales needed in the simulations to probe questions of interest in

DSA. For example, for a given block copolymer system, what is the expected defect level in such a process?

What is the ideal guiding layer material for a given block copolymer? What is the scaling of phase separated

pattern pitch with block copolymer characteristics (e.g. degree of polymerization and chi)? We are utilizing

our custom GPU computing cluster to perform simulations with effectively millions to tens of millions of atoms

on fast time scales (e.g. 7 million effective atom block copolymer phase separation simulation completed in <12

hours).

3. Pattern Collapse in Polymeric and Photoresist Nanostructures - The semiconductor industry has continued

its drive for smaller feature sizes, as typically described by Moore's Law, in integrated circuits devices now for

roughly 50 years using essentially the same type of lithographic process which involves ultraviolet exposure of

a polymeric resist followed by a wet "development" of the resist image in either an organic solvent or aqueous

alkaline solution. same types of basic photoresist technology. As feature sizes have now reached below the 50

nm size scale, the collapse of those resist features as a result of the capillary forces experience by the features

during drying following wet development has become a major problem and possible limiter for future reductions

in feature size. Our work in this area has focused on three main issues: (1) characterizing and understanding

the mechanical behavior of polymeric nanostructures such as those formed during high resolution lithography,

(2) developing methods and models to perform such physical property measurements on nanoscale structures,

and (3) developing materials and methods to help prevent such pattern collapse via methods that are

compatible with standard integrated circuit manufacturing processes.

4. Synthesis and Characterization of Graphene and Graphene-based Electronic Devices - Graphene is an

exciting material which is nominally a single sheet of carbon atoms arranged into an sp² hybridized graphite

lattice. Graphene has a variety of unique properties including extremely large very high carrier mobility (i.e. up

to possibly 200,000 cm²/Vs) and large mechanical strength. Graphene is of particular interest as a possible

replacement for current transparent conductors such as ITO (indium tin oxide) and as a replacement

semiconductor for silicon in high speed electronic circuits. Our work in this area is focused on several issues

including: (1) developing low temperature routes to the synthesis of graphene films and nanostructures based

on directed synthesis techniques, (2) developing methods for opening a bandgap in graphene and controllably

doping the material, and (3) developing silicon compatible processing schemes whereby graphene devices can

be integrated with current CMOS technology.

5. Fundamental Studies of the Physicochemical Behavior of Polymer Ultra-thin Films - The observed

physical properties of polymers changes dramatically when they are confined into ultra-thin film form. For

example, a decrease in the diffusion coefficient of molecules within the polymer film of several orders of

magnitude as compared to bulk properties can be observed in sub-100 nm thick films. Our work in this area is

focused on characterizing the physical properties of such ultra-thin polymer films, developing an understanding

of the origins of such proprty changes, and exploiting these properties in a variety of applications ranging from

semiconductor manufacturing to fuel cells.

6. Development of Methods and Materials for 3-D Stereolithography - Stereolithography refers to processes

in which 3-D objects are made directly from electronic CAD design data. One common method for achieving

this is through the build-up of such objects via the layer-by-layer photopolymerization of reactive monomers to

form solid cross-linked polymer objects. Our work in this area focuses on both developing new

stereolithographic methods and tools based on projection imaging systems and the development of new

materials for use in stereolithography to build functional objects for applications such as tissue engineering.

7. Modeling of Polymerization and Photopolymerization Kinetics - In order to control such processes and

design improved materials and methods, a better understanding of and modeling capability for the

photopolymerization processes involved is needed. Our work in this area focuses on characterizing the kinetics

and behavior of such photopolymerization processes and developing predictive models of such processes

based on this characterization data. We utilize a combination of experimental measurements (e.g. real-time

FTIR kinetics measurements, photo-DSC, etc.) and molecular and monte carlo modeling techniques to

accomplish these goals.