As feature size shrinkage in semiconductor device progress, process fluctuation, especially focus strongly affects device performance. Because focus control is an ongoing challenge in optical lithography, various studies have sought for improving focus monitoring and control. Focus errors are due to wafers, exposure tools, reticles, QCs, and so on. Few studies are performed to minimize the measurement errors of auto focus (AF) sensors of exposure tool, especially when processed wafers are exposed. With current focus measurement techniques, the phase shift grating (PSG) focus monitor 1) has been already proposed and its basic principle is that the intensity of the diffraction light of the mask pattern is made asymmetric by arranging a π/2 phase shift area on a reticle. The resist pattern exposed at the defocus position is shifted on the wafer and shifted pattern can be easily measured using an overlay inspection tool. However, it is difficult to measure shifted pattern for the pattern on the processed wafer because of interruptions caused by other patterns in the underlayer. In this paper, we therefore propose "SEM-PSG" technique, where the shift of the PSG resist mark is measured by employing critical dimension-scanning electron microscope (CD-SEM) to measure the focus error on the processed wafer. First, we evaluate the accuracy of SEM-PSG technique. Second, by applying the SEM-PSG technique and feeding the results back to the exposure, we evaluate the focus accuracy on processed wafers. By applying SEM-PSG feedback, the focus accuracy on the processed wafer was improved from 40 to 29 nm in 3σ.
Operating Characteristic (OC) curves, which are probabilities of lot acceptance as a function of fraction defective p, are
powerful tools for visualizing risks of lot acceptance errors. The authors have used OC curves for the overlay sampling
optimization, and found that there are some differences in probability of acceptance between theoretical calculation and
empirical estimation. In this paper, we derive a theoretical formulation of the probability of acceptance for several simple
cases by decomposing overlay errors, and show that the origin of the differences is the use of stratified sampling in overlay inspection.
A new overlay control method called "Polar Correction" has been developed.
In the 3x nm half-pitch generation and beyond, even in the case of using a high-end optical exposure system such as
immersion lithography with NA 1.3 over, the overlay accuracy becomes the most critical issue, and the accuracy below
10nm is indispensable . In view of the severe overlay accuracy required, the shot-to-shot intra-field overlay control
cannot be disregarded in this generation. In particular, the shot-to-shot intra-field overlay error caused by the influence of
evaporation heat has been added in the immersion exposure system. However, it is impossible to correct the shot-to-shot
intra-field overlay error by the conventional overlay control method. Therefore, we have developed the new overlay
control method called Polar Correction for higher-order intra-field error dependent on the wafer coordinates.
In this paper, we explain our new overlay control method for higher-order intra-field error, and show the simulation data
and the experimental data. We believe that Polar Correction corresponds to the generation below 10nm overlay
Recently, the critical dimension (CD) abnormality due to lens aberrations of exposure tool has become one of the critical issues in production of semiconductor devices. The most remarkable feature of CD abnormality due to lens aberration is asymmetry of symmetric twin pattern. And the asymmetry is only caused by a particular aberration because the influence on CD abnormality of lens aberration depends on the device pattern shape. Therefore, it is important to know the interaction of the device pattern shape with lens aberrations, and to ensure that consideration of the interaction is reflected in the design of device. This paper introduces a pattern design methods robust to lens aberration is based on Zernike Sensitivity (ZS) method. We conclude that our method modifies a pattern sensitive to lens aberration so that it becomes a pattern robust to lens aberration without reduction of the depth of focus (DOF).
This paper discusses the compensation method and APC system to reduce errors in mix and matching overlay between scanners. We proposed the compensation model for intra-field errors in mix and matching. And we developed the advanced APC system also to improve dynamic scan distortion using the compensation model.