Feasibility study on 3-D shape analysis of high-aspect-ratio features using through-focus scanning optical microscopy
Ravikiran Attota, Peter Weck, John A. Kramar, Bunday Benjamin, Victor H. Vartanian
In-line metrologies currently used in the semiconductor industry are being challenged by the aggressive pace of device scaling and the adoption of novel device architectures. Metrology and process control of three-dimensional (3D) high-aspect-ratio (HAR) features are becoming increasingly important and also challenging. In this paper we present application of the through-focus scanning optical microscopy (TSOM) method for bottom critical dimension, sidewall angle and depth (3D shape) process monitoring of HAR features. The TSOM method makes use of 3D optical data collected using a conventional optical microscope for 3D shape analysis. Simulation results of trenches and holes down to the 11 nm node are presented. The ability of the TSOM method to analyze an array of HAR features or a single isolated HAR feature is also presented. This allows for the use of targets with area 300 times smaller than that of conventional gratings, saving valuable real estate on the wafers. Indications are that the sensitivity of TSOM may match or exceed the ITRS measurement requirements for the next several years. Both simulations and experimental results are presented. The simplicity, low cost, high throughput, and nanometer scale 3D shape sensitivity of the TSOM method make it an attractive inspection and process monitoring solution for nanomanufacturing.