(Sub-) 100-nm gate patterning using 248-nm alternating PSM

For printing (sub-)100nm features with 248nm lithography strong optical enhancement techniques are required. In this paper we studied the use of alternating phase-shifting masks as one of the options to enhance the resolution, process windows and CD-control of these small features. Before converting the binary design into a phase-shift design, a detailed study is done towards the optimum process conditions. Illumination conditions and reticle chrome dimensions are varied in order to find the largest individual process window for the 100nm isolated lines. Mentor Graphics' Calibre RET tools suite is used for generating the phase-shifted regions based on the originally designed poly and active layers. For this study we focused on the dark-field double exposure approach. In this way the initial 0.15micrometers design was split up in a dark-field phase-shifting mask layout and a binary trim mask layout. On the phase-shifting mask the initial gate CDs were made 20nm (1X) smaller: 150nm lines become 130nm on the reticle. An extra 30nm shrink is applied by overexposing the phase-shifting mask. On the trim mask, the original design was not sized and contains only features that are 150nm or larger. We successfully patterned (sub-) 100nm poly gates using this technique and this with a very tight CD-control intra-field and across wafer. In this paper we will discuss the lithographic process optimization, phase-shift conversion and the final gate patterning in more detail.

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