Spatially resolved analysis of plasma etch discharges using a novel optical emission spectroscopy sensor.

Abstract

One of the major issues in integrated circuit manufacturing is the macroscopic uniformity of a process over an entire wafer. As wafer sizes increase from the 100 mm diameter sizes of the 1980's and early 1990's to 150, 200, and 300 mm sizes, uniformity has become even more of a critical issue due to the increased overall value of the wafer. In addition, these larger sizes pose a challenge to tool manufacturers to produce larger discharges with comparable uniformity to the smaller discharges previously needed. Diagnostics which can measure the uniformity of these discharges and provide not only process discharge uniformity information, but wafer state uniformity information, are needed for tool development, process setpoint design, and process control sensing. Optical emission spectroscopy is a very well established, non-invasive plasma diagnostic. However, until recently, the spatial resolution of this diagnostic has been limited by the optical access of the plasma tools. A novel method for mapping the radial emissivity profiles of azimuthally symmetric plasma discharges in these confining geometries has been designed, and a sensor which uses this method was built and tested at the University of Michigan. This method uses the intensity of light emitted from a single wavelength from a well defined, wedge-shaped field of view as a function of that wedge's location within the discharge. The integral relationship between the radial emissivity profile and measured emission intensity is then used to solve for the radial emissivity profile. To address the noise amplification of this ill-posed problem, a first derivative constraint is placed on the final emissivity profile through a Tikonov regularizer. This emissivity profile mapping system has been used to study processing discharges. Spatially resolved emissivity profiles of the 750.39 nm Ar I transition have been correlated with physical sputtering of silicon dioxide using a pure argon discharge in a GEC reference cell. In addition, spatially resolved emissivity profiles have also been obtained for the first time in an unmodified commercial plasma processing tool, a Lam TCP 9400 SE and compared to silicon etch depths. These emissivity profiles have provided the first spatially resolved fluorine actinometry results in an SF6/Ar discharge. Spatially resolved emissivity profiles have been correlated to argon metastable density profiles at various process setpoints in a GEC reference cell to compare the relationship between argon emission and metastable production rates. This thesis provides a detailed discussion of the concepts behind this sensor's operability, the sensor's design, the emissivity profile reconstruction process, and experimental verification of the sensors capabilities as a factory floor process state uniformity sensor.