OPC models with and without thick mask effect (3D-mask effect) are compared in their prediction capabilities of actual
2D patterns. We give some examples in which thin-mask models fail to compensate the 3D-mask effect. The models
without 3D-mask effect show good model residual error, but fail to predict some critical CD tendencies. Rigorous
simulation predicts the observed CD tendencies, which confirms that the discrepancy really comes from 3D-mask effect.
Design for Manufacturing (DFM) is being widely accepted as one of keywords in cutting edge lithography and OPC technologies. Although DFM seems to stem from designer's intensions to consider manufacturability and ultimately improve the yield, it must be well understood first by lithographers who have the responsibility of reliable printing for a given design on a wafer. Current lithographer's understanding of DFM can be thought of as a process worthy design, and the requirements set forth from this understanding needs to be well defined to a designer and fed forward as a necessary condition for a robust design. Provided that these rules are followed, a robust and process worthy design can be achieved as a result of such win-win feed-forward strategy. In this paper, we discuss a method on how to fully analyze a given design and determine whether it is process worthy, in other words DFM-worthy or not. Mask Error Enhancement Factor (MEEF), Through Focus MEEF (TF-MEEF) and Mean-To-Target (MTT) values for an initial tentative design provide good metrics to obtain a robust and process worthy design. Two remedies can be chosen as DFM solutions according to the aforementioned analysis results: modify the original design or manipulate the layout within a design tolerance during OPC. We will discuss on how to visualize the analyzed results for the robust and process worthy OPC with some relevant examples. In our discussions, however, we assumed that the robust model be being used for each design verification, and such a model derived with more physical parameters that correlates better to real exposure behavior. The DFM can be viewed as flattening the TF-MEEF across the design.
This research shows a 1mW Low Power and real-time imaging Tx/Rx communication system via RF-delay
smart Antenna using up to 10GHz UWB(Ultra WideBand) as a concept of Wireless Medical Telemetry Service
(WMTS). This UTCOMS (COMmunication System for Nano-scale USLI designed Endoscope using UWB technology)
results in less body loss(about 6~13dB) at high frequency, disposable and ingestible compact size of 5×10 mm2 and
multifunction, bidirectional communications, independent subsystem control multichannel, and high sensitivity smart
receiving antenna of three-dimensional image captured still and moving images.
While optical lithography is being pushed to its limits, there is a general concern as to which metrology tool is more suitable for inspection of new generation devices. Scatterometry is one of the few types of metrology that has true in-situ potential for deep submicron critical dimension and profile analysis. Physical metrology is the key element in maintaining adequate and affordable process latitude in lithography processing. Accurate metrology is needed for characterizing and monitoring the processing states, such as exposure, focus, post-exposure bake (PEB), critical dimension (CD) resolution, and uniformity. In addition, scatterometry is a good candidate tool to obtain data necessary to perform model-based optical proximity correction (OPC). However, it is unknown as to current scatterometry provides necessary sensitivity to yield results acceptable for OPC usage. In this paper, we have utilized scatterometry to measure test patterns used in a model-based OPC and performed OPC on DRAM bitline core and periphery adjoining region then, its results are compared to those model-based OPC performed using data obtained from CD-SEM and V-SEM. In doing so, we have attempted to obtain an ideal model which provides best performance in context of OPC. Furthermore, we have discussed 1-D and 2-D types of test patterns that are acceptable for OPC purpose and provided the verification results for each model using commercially available software.
The on-chip variation (OCV) should be critically controlled to obtain the high speed performance in logic devices. The variation from proximity dominantly contributes to OCV. This proximity effect can be compensated by applying well-treated optical proximity correction (OPC). Therefore, the accuracy of OPC is needed, and methods to enhance its result have to be devised. The optical proximity behaviors are severely varied according to the material and optical conditions. In point of material, the proximity property is affected by species of photo-resist (PR) and change of post exposure bake (PEB) conditions. 3σ values of proximity variation are changed from 9.3 nm to 15.2 nm according to PR species. Also, proximity variations change from 16.2 nm to 13.8 nm is observed according to PEB condition. Proximity variations changes of 11.6 nm and 15.2 nm are measured by changing the illumination condition. In order not to seriously deteriorate OPC, these factors should be fixed after the OPC rules are extracted. Proximity variations of 11.4 nm, 13.9 nm and 15.2 nm are observed for the mask mean-to-targets (MTT) of 0 nm, 2nm, and 4nm, respectively. The decrease the OPC grid size enhances the correction resolution and the OCV is reduced. The selective bias rule is generated by model using grid size of 1 nm and 0.5 nm. For the nominal CD of 87 nm, proximity variations are measured to be 14.6 nm and 11.4 nm for 1 nm and 0.5 nm grid sizes, respectively. The enhancement amount of proximity variations are 9.2 nm corresponding to 39% improvement. The CD uniformity improvement for adopting the small grid size is confirmed by measuring the CD uniformity on real SRAM pattern. CD uniformities are measured 11nm and 9.1nm for grid size of 1 nm and 0.5 nm, respectively. 22% improvement of the CD uniformity is achieved.
It is well known that flare, which increases the background intensity and loses the image contrast, degrades the pattern fidelity and CD uniformity. Usually there is little mid and long-range flare at the initial exposure tool introduction except the short-range flare, so called, aberration. However, flare effect is observed in used exposure tools. To estimate the influence of flare, both lens quality of the exposure tool and mask pattern layout with various open ratios are important parameters to be considered. So it is very crucial to make a standard mask layout to measure the flare value as a tool specification. So far, CD variation of the long-range flare has been measured and reported. The long-range flare includes the average influence of the short and mid-range flare and affects more than several hundred- micron distances. Recently it is observed that lens contamination is a dominant component among sources of flare and induced by the pattern layout with its different open ratio. Being contaminated, the lens malfunctions with various types of scattering sources. These scattering sources make the mid and long range flare. This type of flare source has time dependence. If there are proper monitoring methods for the flare measurement, it is possible to maintain the lens quality within the limit of mid range flare. In addition, matching the flare value to CD distribution is not easy because there is no standard measurement method to distinguish the short and mid-range flare from the long-range one. In this paper a LOcal Area Flare Evaluation Reticle (LOAFER) method is suggested. The LOAFER is designed to measure the local area flare of the lens, that is, the short and mid-range flare and the local flare distribution of the exposure tool lens can be characterized. Then matching the result to the real device pattern will be introduced.
The deprotection of chemically amplified resist is amplified by photogenerated acid during post exposure bake. The deprotection rate is mainly dependent on bake temperature and time. It has been assumed that the temperature of wafer surface and photoresist is to be raised instantaneously up to desired set temperature, but in real world it can not happen. We investigated the temperature change of wafer surface on a hot plate and obtained effective post exposure bake time. We applied the effective post exposure bake time to our simulation tool and the simulation results showed a better agreement with the experimental resist profile.
We investigated the thickness and optical constants, n and k, changes of the 193 nm chemically amplified resist for different thicknesses and soft bake conditions with in-situ measurements. During soft bake, the thickness, n and k change abruptly up to 90 s, then they settled down to certain values. It has been found that the optical properties of the resist after soft bake depend on the final resist thickness. The relationships between the optical constants and the resist thickness after soft bake were extracted from the experimental results and applied to our simulation. A series of simulations were carried out for various resist thicknesses. The simulation results showed considerable changes in line width when the changes of n and k after soft bake were considered. The results indicate that the changes of the optical constants by soft bake are not negligible and they can affect the lithography process significantly. Especially for the thin resist with a smaller critical dimension, the line width variation due to n and k change by soft bake becomes more significant and should be considered in simulation.
Some of the important areas to be improved for lithography simulation are getting correct exposure parameters and determining the change of refractive index. It is known that the real and imaginary refractive indices are changed during exposure. We obtained these refractive index changes during exposure for 193 nm chemically amplified resists. The variations of the transmittance as well as the resist thickness were measured during ArF excimer laser exposure. We found that the refractive index change is directly related to the concentration of the photo acid generator and de-protected resin. It is important to know the exact values of acid concentration from the exposure parameters since a small difference in acid concentration magnifies the variation in the amplified de-protection during post exposure bake. We developed and used a method to extract Dill ABC exposure parameters for 193 nm chemically amplified resist from the refractive index change upon exposure.