We present a novel diffractive optical element, the quantum dot array diffraction grating (QDADG), used in soft x-ray spectroscopy. Because of its sinusoidal transmission it effectively suppress higher order diffractions, which can improve the precision and SNR of soft x-ray spectroscopy in laser plasma diagnosis. There are, however, many difficulties in the fabrication of a soft x-ray spectroscopy QDADG because of its small dimensions and complex pattern. We propose a hybrid lithography to fabricate a QDADG, including electron-beam lithography and x-ray lithography. The diffraction property of the QDADG is also proved to be consistent with a theoretical prediction using experiments.
X-ray transmission gratings (TG) have attracted much interest because of its wide use in x-ray
telescope, synchrotron radiation facilities, and target diagnostic in inertial confinement fusion, etc. In
this work, a 200 nm period master TG to diffract x-ray in the energy range 0.1-8keV has been
successfully fabricated by electron beam lithography followed by gold electroplating. In fabrication
processes, 500 nm resist was exposed by focused electron beam on polyimide free-standing-membrane
coated with a Cr/Au plating base. According to numerical simulation, the proximity effect due to
electron back-scattering from the substrate can be sharply reduced because of the thin polyimide
free-standing membrane substrates. PMMA resist was chosen due to its high resolution and good
performance in subsequent processes. After delicate dose test and shape modification of the proximity
effect caused by electron front-scattering, resist grating bars with 95 nm width and 200 nm period were
achieved. Subsequently, resist patterns were transferred to gold layer by electroplating. In future work,
with this master mask of TG, thousands of TG to diffract x-ray can be sufficiently replicated using
x-ray lithography.
A novel diffractive optical element (DOE), quantu-dot-array diffraction grating(QDADG), used in soft X-ray
spectroscopy has been fabricated for the first time. The QDADG, which consists of a large number of quantum dots
distributed on a substrate as sinusoidal function, has many advantages in theory over conventional transmission grating
(TG) in soft X-ray spectroscopy, such as doubtless diffraction efficiency, no higher-order diffraction and no
subordination diffraction maximum, and so on. So, it can be predicted theoretically to improve the precision and Signal
Noise Ratio of soft X-ray spectroscopy in laser plasma diagnosis. But, there are many difficulties in the fabrication of
soft X-ray spectroscopy QDADG because of its much small dimension and complex pattern. In this paper, a combined
lithography was proposed to fabricate QDADG including electron beam lithograph (EBL) and proximity X-ray
lithograph(XRL). The diffraction property of QDADG has also been proved to be consistent with theoretical prediction
from test experiment. In the process of fabrication, because of the thin film substrate of soft X-ray QDADG, the
backscattering of incidence electrons can be effectively restrained in the electron beam lithograph, which can cause
much higher resolution. Without proximity effect correction, QDADG with 250nm minimal unit has been successfully
fabricated. In order to further increase the spectroscopy resolution and dispersion power of QDADG, it is necessary to
carry out proximity effect correction in electron beam lithograph.
Hydrogen silsesquioxane (HSQ) is a kind of inorganic negative-tone resist for electron beam lithography with high pattern resolution of about 5 nm. It is a kind of promising resist used in fabrication of nanostructures such as transmission grating (TG), dots array, and chiral structures. But the poor sensitivity limits the extensive application of HSQ. And the property of HSQ in electron beam lithography is also studied little before. In this paper, from the viewpoint of chemical structure the property of HSQ in electron beam lithography has been proposed and experiments have also been presented with the variety of the exposure dose and development conditions. It is proved by experiments not only the sensitivity and contrast of HSQ but also the influence of proximity effect can be modulated by changing the baking temperature and concentration of developer with the same exposure conditions. 100 nm lines at 200 nm pitch grating patterns with excellent vertical side-wall and line-edge roughness have been achieved in more than 450 nm thickness HSQ layer by increasing the concentration of developer and reducing the baking temperature in combination with optimization of exposure conditions.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.