Measurement Capabilities of X-ray Fluorescence for Bpsg Films

Deposition of borophosphosilicate glass (BPSG) films as dielectrics is one of the many steps involved in semiconductor device manufacturing. Accurate control of boron and phosphorus concentrations in these films, is essential in maintaining desired film properties. The narrowing process specification limits with the industry trend towards shrinking device sizes, is putting an increasing demand on the precision and accuracy of metrology tools used for film characterization. This paper evaluates the ability of x-ray fluorescence (XRF) technique in measuring boron and phosphorus concentrations in BPSG films deposited by chemical vapor deposition. Repeatability and reproducibility studies were conducted to evaluate precision of the x-ray fluorescence measurement technique. The spread and shift of the normal probability distribution curves from this data is quantified in terms of the statistical indices for capability potential (C,), and for process control and centering (Crk). These indices are used as an indication of the precision and accuracy of dopant concentration measurements provided by the XRF technique. The 6-sigma capability of this technique has also been evaluated. Introduction Deposition of dielectric films by chemical vapor deposition (CVD) is one of the various steps involved in IC device fabrication. The dielectric films deposited by CVD techniques, often need to be doped with boron and phosphorus to modify film properties. Boron is typically added to lower the glass transition temperature while phosphorus acts as a gettering agent for mobile metal ions. Accurate control of these dopant levels in the deposited film is essential for maintaining high yield of the IC devices that constitute the end product. A highly capable metrology tool in terms of its accuracy, precision, and stability becomes necessary to keep these dopant concentrations within the process specification limits. The degree of uncertainty in the measurement must be low in comparison to the uncertainties characteristic of the CVD process. Wet chemical analyses (WCA), Fourier Transform Infrared Spectrometry (FTIR), X-ray fluorescence (XRF), are some of the common dopant measurement techniques used by the semiconductor industry. Copyright 0 JCPDS-International Centre for Diffraction Data 1997 Copyright (C) JCPDS-International Centre for Diffraction Data 1997