ASTM F1894-98(2011)

1.1 This test method covers the quantitative determination of tungsten and silicon concentrations in tungsten/silicon (WSi_x) semiconductor process films using Rutherford Backscattering Spectrometry (RBS). (1) This test method also covers the detection and quantification of impurities in the mass range from phosphorus ? (31 atomic mass units (amu) to antimony (122 amu).

1.2 This test method can be used for tungsten silicide films prepared by any deposition or annealing processes, or both. The film must be a uniform film with an areal coverage greater than the incident ion beam (∼2.5 mm).

1.3 This test method accurately measures the following film properties: silicon/tungsten ratio and variations with depth, tungsten depth profile throughout film, WSi_x film thickness, argon concentrations (if present), presence of oxide on surface of WSi_x films, and transition metal impurities to detection limits of 1×10¹⁴ atoms/cm².

1.4 This test method can detect absolute differences in silicon and tungsten concentrations of ±3 and ±1 atomic percent, respectively, measured from different samples in separate analyses. Relative variations in the tungsten concentration in depth can be detected to ±0.2 atomic percent with a depth resolution of ±70?.

1.5 This test method supports and assists in qualifying WSi_x films by electrical resistivity techniques.

1.6 This test method can be performed for WSi_x films deposited on conducting or insulating substrates.

1.7 This test method is useful for WSi_x films between 20 and 400 nm with an areal coverage of greater than 1 by 1 mm².

1.8 This test method is non-destructive to the film to the extent of sputtering.

1.9 A statistical process control (SPC) of WSi_x films has been monitored since 1993 with reproducibility to ±4 %.

1.10 This test method produces accurate film thicknesses by modeling the film density of the WSi_x film as WSi₂ (hexagonal) plus excess elemental Si². The measured film thickness is a lower limit to the actual film thickness with an accuracy less than 10 % compared to SEM cross-section measurements (see 13.4).

1.11 This test method can be used to analyze films on whole wafers up to 300 mm without breaking the wafers. The sites that can be analyzed may be restricted to concentric rings near the wafer edges for 200-mm and 300-mm wafers, depending on system capabilities.

1.12 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.13 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. The reader is referenced to Section 8 of this test method for references to some of the regulatory, radiation, and safety considerations involved with accelerator operation.