KEYWORDS: Atomic force microscopy, Photoresist materials, 3D image processing, 3D metrology, 3D scanning, Image resolution, Laser scanners, Metrology, Line edge roughness, Scanners
As the feature size of the semiconductor device is becoming increasingly smaller and the transistor has
become three-dimensional (e.g. Fin-FET structure), a simple Line Edge Roughness (LER) is no longer
sufficient for characterizing these devices. Sidewall Roughness (SWR) is now the more proper metric for
these metrology applications. However, current metrology technologies, such as SEM and OCD, provide
limited information on the sidewall of such small structures. The subject of this study is the sidewall
roughness measurement with a three-dimensional Atomic Force Microscopy (AFM) using tilted Z scanner.
This 3D AFM is based on a decoupled XY and Z scanning configuration, in which the Z scanner can be
intentionally tilted to the side. A sharp conical tip is typically used for imaging, which provides high
resolution capability on both the flat surfaces (top and bottom) and the steep sidewalls.
KEYWORDS: Atomic force microscopy, Scanners, Photoresist materials, Critical dimension metrology, Line edge roughness, Line width roughness, Image resolution, Scanning electron microscopy, 3D metrology, Metrology
As the feature size in the lithography process continuously shrinks, accurate critical dimension (CD)
measurement becomes more important. A new 3-dimensional (3D) metrology atomic force microscope
(AFM) has been designed on a decoupled XY and Z scanner platform for CD and sidewall characterization.
In this decoupled scanner configuration, the sample XY scanner moves the sample and is independent from
the Z scanner which only moves the tip. The independent Z scanner allows the tip to be intentionally tilted
to easily access the sidewall. This technique has been used to measure photoresist line patterns. The tilted
scanner design allows CD measurement at the top, middle, and bottom of lines as well as roughness
measurement along the sidewall. The method builds upon the standard AFM tip design resulting in a
technique that a) maintains the same resolution as traditional AFM, b) can be used with sharpened tips for
increased image resolution, and c) does not suffer from corner inaccessibility from large radius of curvature
tips.
KEYWORDS: Atomic force microscopy, Scanners, 3D metrology, 3D image processing, Metrology, Atomic force microscope, Laser scanners, 3D scanning, Reflectivity, LCDs
The first generation AFM based on piezoelectric tube scanners has high spatial resolution and performs well
in qualitative measurements. However, it suffers from poor repeatability and accuracy due to the background
curvature and crosstalk between the x-y-z axes, making it inadequate for quantitative metrology. We
developed a new AFM platform with a x-y flexure scanner, decoupled from the z scanner, which has a highly
orthogonal and flat scan. The high speed z scanner with minimized drive mass provides a fast z servo
response, making true non-contact AFM practical. The new AFM can also be used in critical angle
measurements of microstructures such as reflective LCD display substrates. The design concept of the new
AFM was utilized to measure under-cut structures by intentionally changing the angle of the z scanner,
enabling the measurement and imaging of undercut structures as well as vertical sidewalls for the first time in
AFM history.
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.
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