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.
A comprehensive study of alternating phase shifting mask (Alt-PSM) including mask making, 3-dimensional aerial image simulation, and wafer printing is reported in this paper. For the mask making, we found that the micro-loading effect will be greatly improved using the etching recipe with high Reactive Ion Etching (RIE) power and low Inductively Coupled Plasma (ICP) power. However, this recipe has side effects of Cr film damage and rough quartz side wall. Due to the 3-dimensional mask complex effect, the optimal phase difference is not simply π calculated using optical path difference but is varied with mask features. The optimal phase difference is 165° other than 180° for hole patterns, while it is 176° for line-and-space patterns. The micro-loading effect with variant 2-dimensional complexities is also studied in this paper.
Resolving the very small feature size of contact holes for 65-nm technology node has placed enormous challenge on even the up-to-date optical lithography techniques. Resolution enhancement technique (RET) will be helpful and necessary to alleviate the strain posed by such a task. Here we report that a 193-nm alternating phase shift mask (Alt-PSM) with phase-shifted assist features is used to print the contact holes for 65-nm node. With a novel algorithm of phase assignment, the phases of the main features are assigned properly in the full chip with the assistant features added. The results show that DOF of 110-nm iso-contact hole can be enhanced up to 0.5 μm.
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