A design flow to quantify and limit multiple patterning effects

Abstract

Despite the slight progress in Next Generation Lithography (NGL), including Extreme Ultra Violet (EUV) lithography, Multiple Patterning Technology (MPT) is still the solution used in sub-20nm technology nodes. The impact of using such technology is not well understood by circuit designers who face difficulties to predict the impact of MPT on their circuit's figures of merit. One of the impacts is the change in the coupling capacitance, since one physical layer should be patterned using 2 or more masks in MPT. The overlay error between the masks will change the intra-layer spaces between patterns, resulting in coupling capacitance deviation from designer's expectation. The uncertainty in the capacitance value at one node produces uncertainty at the node's waveform. This is crucial in circuits that are dependent on capacitance as a foundation of their working theory, like ring oscillators. In this paper, we are going to study how MPT can affect the output frequency of a ring oscillator. Moreover, we are going to provide a flow to capture that impact, which can be applied on other circuits. A feedback mechanism is implemented to provide the designer with sensitivity information of electrical node pairs. This mechanism can help designer to decide the appropriate layout modifications that can make his design less prone to MPT effects.