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Author: Admin | 2025-04-28
Unexposed resist. This serves to enhance the resolution of the lithography technique and minimizes the formation of standing wave patterns which may form from exposure to phase shifted light reflected from beneath the resist layer, demonstrated in Fig. 1.35.Fig. 1.35(a) An example of reflected light created by exposure of photoresist without an antireflective coating (ARC) used. The ARC layer serves to absorb the light after it penetrates the resist and prevent or minimize the formation of reflected waves. (b) An example profile of a standing wave profile formed into the sidewall of an exposed resist featureFull size image1.7.6 Multiple Patterning ApproachesSingle patterning 193 nm immersion lithography enables the formation of features to roughly 40 nm half-pitch. In order to enable continued scaling of device features in the absence of a viable EUV lithography solution for sub-30 nm process nodes, alternative means of forming sub-resolution features have been devised. Common techniques to accomplish this are pitch division, spacer-based approaches, and implant-based pitch division methods.1.7.6.1 Pitch Division MethodsThe most basic form of pitch division is to divide a desired pattern to be imaged, which contains sub-resolution features, into individual masks such that there are no features on any individual mask which are closer than the resolution limit of the lithography tool as shown in Fig. 1.36. This approach was the first one taken to image sub-resolution features for CMOS processing. Two similar approaches have been developed based upon this idea: litho-etch-litho-etch (LELE) and litho-freeze-litho-etch (LFLE) [5]. Both of these approaches add additional operations to achieve sub-resolution features. In particular, the lithography patterning is repeated in both processes and presents a challenge in terms of alignment or registration of these operations. These alignment challenges and increased count of processing operations are significant limiters to adoption of these techniques.Fig. 1.36Example of mask decomposition for a double patterning approach. The features of the pattern (a) are located closer than can be resolved with the lithography tool and the mask is decomposed into two separate masks (b)Full size image1.7.6.2 Litho-Etch-Litho-Etch (LELE) Pitch DivisionLELE processes entail two litho operations and two etch operations to image a single
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