Nanopatterning of polymer thin films is the basis for the vast majority of current microlithography processes used in integrated circuit manufacturing. Future scaling of such polymer patterning methods will require innovative solutions to overcome the prohibitively high tool and mask costs associated with current optical lithography methods, which will prevent their use in many applications. Scanning probe-based methods for surface modification are desirable in that they offer high resolution patterning while also offering the ability to perform in situ metrology. We report a new scanning probe lithography method that uses heated atomic force microscope cantilevers to achieve nanoscale patterning in thin polymer films via the local thermal decomposition of the polymer and in situ postdecomposition metrology. Specifically, cross-linked polycarbonate thin films are developed in this work and are shown to be excellent writing media for this process. This new method has the advantage that the tip can be heated and cooled on microsecond time scales and thus material can be removed and patterned without need for the disengagement of the tip from the polymer surface. This ability to write while the tip is constantly engaged to the surface offers significantly higher writing speeds for discontinuous patterns relative to other scanning probe techniques.
This paper reports a novel lithography method that utilizes local nanoscale thermal decomposition of polymer films using heated atomic force microscope cantilever probe tips. Cross-linkable polymers, for example based on poly(hydroxystyrene) (also referred to as PHOST), are used as the writing material in these methods. The experimental results show that the cross-linked polymer can prevent the thermal flowing induced by melting of the polymer, and very fine feature can be achieved. 100 nm lines have been successfully written using a heated cantilever probe in a cross-linked PHOST film. 60 &mgr;m/sec writing speeds have also been achieved using this technology. The amount of material decomposed by the heated tip can be very well controlled by modulating both the cantilever probe temperature and writing speed. This ability to modulate the removal rate of material from the film makes it possible to directly pattern 3-D structures into a polymer film using such heated AFM cantilever tips.
This paper reports a novel lithography method that utilizes local nanoscale thermal decomposition of polycarbonate
films using heated atomic force microscope cantilever probe tips. The effect of polycarbonate structure and
physiochemical properties on the lithographic performance of the thermal writing process have been explored. It is
observed that amorphous linear polycarbonates which possess glass transition temperatures lower than their
decomposition temperature generally exhibit substantial thermal deformation during thermal writing. In contrast,
thermal writing on crystalline regions of semi-crystalline linear polycarbonate films produced good pattern definition.
However, the semi-crystalline nature of the film results in substantial surface topography in the thin film which is
undesirable for high resolution patterning and the amorphous regions of the film still suffer from local thermal
deformation during writing. Amorphous cross-linkable polycarbonate sacrificial polymers have been synthesized and
are shown to be able to resist thermal deformation of features during writing and are shown capable of producing good
patterned images using the heated AFM probe writing technique.
Substantial recent interest in microelectronics manufacturing has motivated significant work on
non-traditional processes such as embossing-based lithography. This work has been generally
limited to manufacturing conventional microelectronics, producing two dimensional patterned
surfaces and structures. To date, little work has been done to produce microelectromechanical
systems (MEMS), which can require production of complex three-dimensional and possibly free
This paper reports a novel method for manufacturing three-dimensional microstructures that can
be freely standing and/or fully released. The method involves the use of thermally sacrificial
polymers, i.e. materials that can be cleanly decomposed to gaseous products upon heating at
elevated temperatures. Such sacrificial polymers can be directly embossed and subsequently
overcoated with a variety of materials including other polymers, dielectrics, semiconductors, and
metals. Following the deposition of the overcoat layer, further processing can be performed on
the overcoat layer (e.g. selective etching or deposition of additional materials). Finally, the entire
structure is heated to the decomposition temperature of the sacrificial polymer which results in
the “dry” removal of the sacrificial layer, thus releasing the desired structures. The various
sacrificial materials that have been investigated are polynorbornenes and polycarbonates, and the
overlayer materials include polyimides, silicon oxide, and metals. This paper discusses the
various properties of these sacrificial materials, the printing and processing conditions for these
materials, and the use of this method for the fabrication of a MEMS based microfluidic system
with free standing and suspended obstructions.
This novel manufacturing technique meets the needs of MEMS manufacturing in that it can
produce three dimensional and free standing microstructures. It permits the fabrication of devices
and systems in only a few process steps that would otherwise be either substantially more
complicated or impossible to achieve. This process of coating, embossing, and overcoating can
also be repeated to build-up complex multi-layered structures.