As semiconductor features shrink in dimension and pitch, the excessive control of critical-dimension uniformity (CDU) and pattern fidelity is essential for mask manufacturing using electron-beam lithography. Requirements of the electronbeam shot quality affected by shot unsteadiness become more important than before for the advanced mask patterning. Imperfect electron optical system, an inaccurate beam deflector, and imprecise mask stage control are mainly related to the shot unsteadiness including positioning and dose perturbations. This work extensively investigates impacts of variable shaped beam dose and positioning perturbations on local CDU using Monte Carlo simulation for various mask contrast enhancement approaches. In addition, the relationship between the mask lithographic performance and the shot count number correlated with mask writing time is intensively studied.
The inverse polarizing effect of Sub-Wavelength Metallic Gratings (SWMGs) is employed to improve the lithography performance by controlling the polarization. The SWMGs are intentionally created on the top surface of mask. Its polarization selectivity is deliberately designed according to the bottom mask patterns. A series of simulations and optimizations on SWMG structures were done in order to achieve better image quality. We demonstrate that the contrast of aerial image can be improved by designing the inverse polarizer on mask (iPOM) for some specific layout patterns. We also reveal that the double diffraction inevitably occurring in-between the iPOM and layout pattern may damage the image quality in most situations. This leads to narrow usage of iPOM. An alternative to overcome the double diffraction is proposed by optimizing the refractive index and thickness of layout absorber to make the polarization selection feasible without iPOM.
This paper discusses the CD Bossung tilt phenomena in low-k1 lithography using interference harmonics and rigorous
EM spectrum analysis. Interference harmonics analysis is introduced to explain the interaction of diffraction orders in the
focal region leading to this abnormal CD behavior. This method decomposes the vector image formula into a
superposition of cosine components to describe the interference of diffraction orders. The symmetry properties of
components of an optical projection system were investigated to find out three potential sources for the asymmetric
Bossung behavior, namely mask 3D (M3D) effect, lens aberration, and wafer reflectivity. Under good lens aberration
and substrate reflectivity controls, the M3D effect accounts for most of the CD Bossung tilt. A rigorous EM mask
spectral analysis was performed to reveal the impact of mask topography on the near-field intensity of mask transmission
and the far-field image formation. From the analysis, the asymmetric phase distribution in the mask spectrum is the root
cause for CD Bossung tilt. Using both the interference harmonics and the rigorous EM spectrum analysis, the effect of
various resolution enhancement techniques (RET) to the Bossung tilt is also studied to find the best RET combination for
M3D immunity. In addition, a pupil optimization algorithm based on these two analyses is proposed to generate the
phase compensation map for M3D effect counteraction.
This paper presented an integrated simulation framework linking our in-house mask writer simulator and the optical lithography simulation engines to include the mask corner rounding effect in lithographic performance evaluations. In the writer simulator, a modified two-dimensional Gaussian function is used as the functional form of the convolution kernel (point spread function). Parameters of the kernel function for different writing machines are automatically extracted from scanning electron microscope (SEM) photographs of simple mask pattern geometries. The convolution results of the kernel and the mask layout form the intensity distribution for pattern definition. The isocontour of the resulting image at the desired level of bias can be regarded as a good approximation of the mask shape obtained from a real mask writer. The writer simulator then saves the contour data as the user-specified format of mask file for subsequent lithography simulations. With the aid of this simulation tool, the impacts of mask corner rounding effects on two-dimensional OPCed pattern for 90-nm and 65-nm node lithography processes are quantitatively evaluated. The results show the line end shortening (LES) is greatly influenced by mask corner rounding effects. The LESs in the 65-nm node process are over twice of those in the 90-nm node process. The resolution capability of a 2-stage 16X mask manufacturing process was also studied in this paper. Simulation results indicate the ArF lithography might be required to make this innovative mask-making technology suitable for 90-nm generation and beyond.
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.