Model-based retarget for 45nm node and beyond

Abstract

In the past several years, DFM (design for manufacturability) is widely used in semiconductor process. DFM is to make layout design optimized for manufacturability's sake. Lithography friendly design (LFD) is one branch of DFM. To enhance process margin of photolithography, layout designers typically modify their layout design with the application of DFM or LFD tools. Despites those application, it is still not enough to realize enough process window as technology node goes to beyond 45nm. For these reasons, OPC (Optical proximity correction) engineers apply additional layout treatment prior to applying OPC. That is called as table-driven retarget, which is typically conducted by rule-based table. Similar to rule-based OPC, table-driven retarget also has limitations in its application.In this paper, we presented a model-based retargeting method to overcome the limitation of table-driven retarget. Once the criteria of process window has been set, we let OPC tool simulate the process window of each layout of design firstly. Then, if the output value of the simulated result cannot meet the preset criteria, OPC tool resizes the layout dimension automatically. OPC tool will do retarget-OPC-retarget iterations until process windows of all of designs become within the criteria. After all, the model-based retarget can guarantee accurate retarget and avoid over or under retarget in order to improve process window of full chip design.

Integrated model-based retargeting and optical proximity correction

“…However, this overhead is relatively small compared to process variation aware resolution enhancement methods such as PWOPC, which usually require multiple image simulations during OPC iterations. The run-time is also significantly smaller than any brute-force model-based method for retargeting or hot-spot fixing that performs full OPC and process window verification to identify lithographic hot-spots and iteratively fix these through retargeting 8,9 . In Section 2, we describe the algorithm behind integrated retargeting and OPC.…”

“…The advantage of using NILS as a metric for optimization lies in the low computational overhead of NILS computation compared to finding full process window information. The use of full process-window information for retargeting has also been previously proposed 8 . Calculating process window involves multiple aerial image simulations at different dose and focus corners, after which the contours are compiled into process variability bands.…”

Design-aware lithography

“…Further, we observe that in electrically non-critical shapes like local wires, the exact target shape is not a fixed value, but can be modified, which increases the feasibility region for the OPC tool, allowing it to reach a more optimal solution. The process of modifying the target layout during dataprep is called retargeting [7,8,9]. We propose to utilize the notion of tolerances to drive retargeting, to enable us to reach a more robust patterning solution without perturbing electrical properties.…”

AIR (Aerial Image Retargeting): A novel technique for in-fab automatic model-based retargeting-for-yield

“…However, this is on the expense of adding the systematic deviation discussed in the previous section. There are several re-targeting approaches in PWOPC [8], [9] , but unfortunately, all of them require preforming full PWOPC in order to extract the on-wafer design, which is very computationally intensive and cannot fit efficiently into the parameter extraction flow. One good thing is that PWOPC deviations are in the order of few nanometers in the 32nm and smaller nodes compared to the rule based CATOPC which can deviate more than 10 nm.…”