Slight change of OPC pattern shape may influence transistor characteristics. So inputting the result of Litho-
Simulation, Contour, to SPICE-simulator, we investigated the change of the transistor characteristic. First of all, we
investigated the sensitivity of the transistor characteristics to OPC pattern change. We found that the difference of shape
with Isolated, Dense pattern, and a different OPC tool caused difference after SPICE-simulation. In this investigation, we
report focusing on the transient and DC analysis of transistor characteristics. Contour data was measured and averaged
before input to SPICE and a change of transistor characteristic was able to be detected. We came to the conclusion that
this investigation method is effective to check the influence of the transistor characteristics due to OPC pattern change.
And we can adopt this method as one technique for deciding the applicability of the OPC tool and its upgrade, which
were issues for MASK data processing.
This paper reports a technique of reticle inspection incorporating the use of an image filter. In this technique, optical intensity distribution is calculated by optical simulation of electron beam lithography (EB) data or an image file obtained from a SEM photograph to evaluate the printability of defects on a reticle. When an image file is compared with the EB data, the image file has differences at the rounded corners as well as at the areas with defects because the image file is obtained from the reticle pattern. To reduce the differences, an image filter (or reticle filter), which simulates the pattern creation process on a reticle, was applied to the EB data. The simulated EB data is defined as the non-defect reference pattern. The optical intensity and critical dimension (CD) were then obtained. Image files of defects were obtained from the SEM photographs of reticle patterns having various sizes of defects. By applying optical simulation to patterns obtained from the image files, the optical intensity and CD were calculated and compared with those of the reference pattern, and the differences are evaluated. The evaluation results showed that optical intensity and CD changes fluctuate regardless of the size or type of defect. Correlation was confirmed between the differences in optical intensity and the CD changes in the defect area. It was thus concluded that defect printability can be evaluated by the differences in optical intensity obtained from image files.
We conducted an experiment to determine if the use of image filter method for simulation that calculates the distribution of light intensity on a wafer can reduce processing time in comparison to the use of the Fourier transform. The image filter table value is set by changing the value of Gaussian distribution. The image filter method was approximated with the light intensity of optical simulation that keeps accuracy within the range of the allowance. In this experiment, we examined the differences between the distributions calculated using the Fourier transform and the calculation time by varying the sizes of the image filter tables. For the experiment, we used pattern data having a line width that used in the most advanced technology. When the area of pattern data was wide, the experiment revealed that use of the image filter method reduced calculation time by approximately 50 percent or more in comparison to a simulation that used the Fourier transform. As we decreased the size of the image filter tables, the calculation time became shorter, but the differences from the distribution calculated using the Fourier transform became larger. We intend to study the possibility of simulation by expanding the area of pattern data and using the image filter method for simulation-based OPC.