Logic product speed evaluation and forecasting during the early phases of process technology development using ring oscillator data

During the early stages of the development of a new technology, it is not possible to use product die to optimize parameters for a new technology. At this stage of technology development, integration engineers are forced to rely on test chips to make choices for the future technology. One of the vehicles for optimizing the speed of a technology which is typically available on test chips is ring oscillators. The frequency of oscillation of ring oscillators provides indications of likely product speed and can be measured in the early stages of the development of a new technology. Consequently, they provide us with an early indicator of the probable impact of process changes on circuit performance. However, traditionally, only nominal ring oscillators, with minimal interconnect loading, have been used to estimate the product speed impact of technology changes. As interconnect loading becomes more significant in determining product speed, technology choices based on nominal ring oscillator speed will not be optimal. In this paper, a methodology for using empirical data from ring oscillators, with different frontend and backend loading, to analyze tradeoffs between potential process changes, is presented