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 beam energy is a driving design parameter for electron beam lithography systems. To be able to compare the
differences of low kV (5 kV) and high kV (100 kV) for a high-throughput system the limitations of both types of systems
are evaluated. First the effect on the CD uniformity and throughput is analyzed. For any shot noise limited system the
dose that is needed to obtain a required CD uniformity can be calculated. This dose depends on the total spot size and the
efficiency of the electrons in the resist. For a smaller spot less dose is required than for a large spot. The current in a
single beam is also determined by the spot size. A larger spot has more current. With these parameters an optimization of
the required dose, spot size and single beam current can be made. It is found that although for high kV it is easier to
create a small spot with a high current the low resist-exposure efficiency of the high-energy electrons limits the
throughput, because the required dose is large. It is also found that for 10 wafers per hour multiple lenses or columns are
required. For practical reasons (a high kV lens cannot be made as small as a low kV lens) there is a clear preference for
the use of low energy in high-throughput systems. Another aspect that is crucial in the lithography process is the overlay.
One of the main differences between high and low energy systems is the power that is dissipated in the wafer and the
resulting error due to expansion. It is found that for both energies wafer heating is an issue, but for low kV there seem to
be solutions, while for high kV the problem is 30 times bigger.
The Multiple E-beam Direct Write (MEBDW) technology has been considered a promising solution for the next
generation lithography to delineate 32-nm half-pitch and beyond. A low-energy, say 5 keV, e-beam direct writing system
has advantages in lower exposure dosage, less heating effect on resist, and less damage to devices underneath, comparing
with a high energy one, such as 50 keV or 100 keV. However, the low-energy electron-beam is easily blurred due to
forward scattering in the substrate due to its shallow penetration and hence loses resolution. In this paper, variables
affecting patterning fidelity of a raster-scan MEBDW system are investigated.
In order to realize a MEBDW system with acceptable throughput, a relatively large beam size is chosen for sufficient
beam current to sustain throughput while maintaining enough resolution. The imaging resolution loss and the proximity
effect, due to beam blurring through the resist, have been observed. The in-house software MOSES, incorporating the
Monte Carlo simulation and the Double Gaussian model was used to evaluate 1-D and 2-D pattern fidelity with various
exposure conditions. The line width roughness, which represents 1-D fidelity, was evaluated on 32-nm dense lines.
Pattern fidelity of 2-D features such as the zigzag poly line and dense metal patterns was also examined. The impact to
LWR of using the edge dithering method, instead of dosage modulation, to control the line width accuracy beyond the
pixel size was studied.
In this paper, a quantitative evaluation of mask quality in the domain of 2D pattern fidelity and a method of assessing the OPC model effectiveness are investigated. The spirit of our algorithm is to characterize the wafer lithographic performances of both the real physical mask and the ideal OPCed layout mask that the physical mask is based on. To acquire these performances, we adopted a CD-SEM image process technique for transforming an actual SEM mask image into a simulation-friendly format like GDSII together with the methods to correctly handle the image transformation and interpret the simulation results. Finally, the images, such as the simulated aerial images, the simulated or observed resist top views, are superposed for comparison using logic operation.
The control of global critical dimension uniformity (GCDU) across the entire mask becomes an important factor for the high-end masks quality. Three major proceses induce GCDU error before after-developing inspection (ADI) including the E-Beam writing, baking, and developing processes. Due to the charging effect, the fogging effect, the vacuum effect and other not-well-known effects, the E-Beam writing process suffers from some consistent GCDU errors. Specifically, the chemical amplified resist (CAR) induces the GCDU error from improper baking. This phenomenon becomes worse with negative CARs. The developing process is also a source of the GCDU error usually appears radially. This paper reports the results of the study of the impact of the global CD uniformity on mask to wafer images. It also proposes solutions to achieve better masks.
Nowadays, the CD (Critical Dimension) control on masks manufacturing plays an important role in photolithography process for 90-nm node technology and below. The process performance of photolithography
will degrade severely even when the mask CD error is small. One of the most important process-induced mask CD errors comes from the dry etching process. With the loading effect due to environment pattern variations, isolated and dense patterns have different etching biases. Furthermore, the loading effect can induce an overall
CD variation called global loading effect contributed from the pattern density change in large areas and a CD variation on individual monitor pattern called micro-loading effect contributed from various feature dimensions in the near region. The micro-loading effect can also be classified as the “nearest spacing” effect which is dependent upon the space between the nearest neighbor pattern and the monitor pattern, and the “nearest
neighbor” effect which is dependent upon the size of the nearest neighbor feature around the monitor pattern. All of these effects enlarge the total range of mask CD linearity and proximity errors.
In this paper we report the result of the global loading effect and micro-loading effect by varying pattern densities and feature dimensions nearby. With the design of test pattern, the global loading effect and the micro-loading effect can be separated. The CD variation dominated by the micro-loading effect in the dry etching process is observed. This large etching bias change resulted from the micro-loading effect is consistent with the depletion of radical species in the narrow space during the etching process.