How to improve intra-field CDU of contact hole patterns in both X-Y directions with CDC technology

Abstract

In Dynamic Random Access Memory (DRAM) manufacturing process, contact hole (CH) patterns are critical and challenging array layers. Compared to line/space patterns, CH patterns generally tend to have a higher Mask Error Enhancement Factor (MEEF), therefore it will bring big challenges to wafer Global Critical Dimension Uniformity (GCDU) control, and it is also obvious to observe that the intra-field CDU error contributes mainly to the wafer GCDU variations compared with inter-field error. To improve CH patterns’ intra-field CDU, lithography process generally uses ASML scanner dose mapper (DOMA) solution. Here we introduce a new intra-field CDU improvement technology called CD Correction (CDC) by mask tuning, which is developed by Carl Zeiss and can obtain local illumination transmittance control with higher space resolution than DOMA. In our CDC application cases of contact hole (aka 2D pattern) layers, CDU in both X-Y directions is crucial for process, but different improvement results are found. When CDU in one direction is fully improved by CDC, improvement in the other direction is often insufficient or excessive and hard to achieve a win-win effect. By further experiments and analysis, the key factor we figure out is CDCR (CDC ratio), which is different in X-Y directions. In our work, first, we present a CDC implementation approach that trades off both X-Y directions of improvement. Second, the principle of different CDCR in X-Y directions is explored, it provides a theoretical interpretation for different CDCR and can predict CDCR in future applications.