Smaller device dimensions and tighter process control windows have created a need for metrology tools that measure more than just one-dimensional critical dimension (CD)features. The need to easily detect, identify, and measure changes in feature profiles is becoming critical to controlling current and future semiconductor lithography and etch processes. Measuring changes in sidewall angle and resist height, as well as detecting subtle phenomena such as line-rounding, t-topping, and resist footing, is now as important as the traditional CD line-width measurement. This additional profile information can be used to enhance process-control mechanisms and can also be used to evaluate and characterize the performance of a stepper/track module. Traditional CD metrology techniques give no indication of a measured feature's sidewall angle or height.
Spectroscopic CD (SCD) is an optical metrology technique that can address these needs. SCD is based on parallel data acquisition zero-order diffraction by spectroscopic ellipsometry (SE) over the spectral range 200-900 nm, a widely used optical technique for measuring film thickness and film properties. This talk presents the SCD measurement technique, which is an inverse electromagnetic wave scattering method to estimate the parameters describing the shape of a grating unit cell. SCD results are compared to results from a CD SEM and a cross-section SEM. Repeatability, long-term stability, and matching data from a gate-level nominal process are also presented. These repeatability and stability tests verify that SCD meets the roadmap requirements for current and future semiconductor processes.
I will describe the mathematical framework for both the "rigorous" forward solve, and the optimization techniques of the inverse method, as well as the computer resources required to achieve acceptable turn-around times on the production fab floor. Directions for research to accelerate the computational throughput will be assessed.