TXRF TO MONITOR FOR HIGH K DIELECTRIC MATERIAL CONTAMINATION IN A SEMICONDUCTOR FAB, C. Sparks, M. Beebe, pp. 517-522

A silver tube anode was used for total reflection x-ray fluorescence (TXRF) spectroscopy to analyze for zirconium contamination on silicon wafers. There was good correlation between results obtained by TXRF and results from vapor phase decomposition inductively coupled plasma mass spectrometry (VPD-ICP-MS) until the detection limits of the TXRF were reached at ~1E10 atoms/cm. Calibration with either a nickel or a zirconium standard wafer was acceptable. The measurement precision using the silver anode was also acceptable (< 5% RSD). Introduction As new materials are introduced into semiconductor device manufacturing lines, analytical techniques must be developed or modified to insure the ability to measure any contamination that may arise. Recently, ZrO2 films were introduced as a high k gate dielectric (testing the feasibility of replacing SiOxNy) in the manufacturing line of International SEMATECH [1]. Prior to introduction of this new material, a majority of the process tools in the fab were baselined for elemental contamination with monitor wafers. The baseline covered zirconium as well as other metals that are potential candidates for a high k gate dielectric. Periodic process tool monitoring for contamination was also put in place. There are two primary pathways to wafer cross contamination. The first is mechanical transfer of contamination; that is, a wafer leaves behind contamination that is then transferred to the next wafer or set of wafers that come into contact with the contamination. An example would be contamination left on a handling robot or process equipment chuck. The second is a tool process environment type of contamination. In this case there is contamination in the wafer processing equipment that ends up contaminating a set of wafers as that particular process step occurs. Examples of this type could be particles moved around by gas flow in a chamber or a plasma sputtering contamination off the walls of a process chamber onto the wafer. We have found examples of both types of contamination while monitoring the process equipment toolset in our fab. Typical monitoring of tools involves analysis of two monitor wafers cycled after potential contaminating wafers. Figure 1 is an example of mechanical type of contamination. The zirconium values near 1E11 atoms/cm were determined to be Copyright (c)JCPDS-International Centre for Diffraction Data 2002, Advances in X-ray Analysis, Volume 45. 517