Abstract:

Critical feature sizes of modern semiconductor devices have surpassed the capabilities of traditional optical-based methods to measure particle concentrations in process chemicals and on wafers. Without adequate metrology for quantifying particle and particle precursor concentrations in process chemicals, device makers face challenges correlating component failures with fabrication steps. This is especially true for Marangoni drying, where Isopropyl Alcohol is the last chemical the wafer is exposed to during the cleaning process. In this work, we describe two state-of-the-art measurement methods that are capable of detecting particles in Isopropyl alcohol down to 3nm using Aerosolization and Threshold Particle Counting (TPC) and defects from IPA deposited on a wafer surface down to 8 nm using Surfaced Enhanced Particle Sizing (SEPS). This work also describes how the TPC measurement correlates with defects found on wafers.

Threshold particle counting utilizes a combination of Aerosolization and Condensation Particle Counting. Aerosolization is the dispersion of particles within a liquid into a gas phase. Condensation Particle Counting is the selective condensation of a secondary vapor onto aerosol particles larger than a threshold size. This condensation step increases the particle size by several orders of magnitude, allowing for detection using simple light scattering. This method has been shown to effectively mimics the deposition mechanism for particles and particle precursors via the evaporation of small droplets remaining on a wafer surface after exposure to the chemical .

SEPS utilizes a coating applied to the wafer surface that amplifies the amount of scattered light by many orders of magnitude. The coating also enhances Raman signals of individual particles, which can aid in identification of their composition. Wafers are prepared using Sequential Spin Coating of the process chemical, which mimics the processes used in wafer cleaning.

For this work, TPC and SERS are used to measure the particle and particle precursor contamination present in several semiconductor grade IPA between several manufacturers and correlate these contamination levels to particle defects on the wafer. In addition to the as received samples, the methods are also used to measure particle concentrations in samples spiked with colloidal silica, a dissolved particle precursor, and an organic acid; each at several different concentrations. These measurement data are then used to calculate a deposition factor that correlates liquid particle concentration and the concentration of defects added to a wafer.