ASTM F1894
Scope
1.1 This test method covers the quantitative determination of tungsten and silicon concentrations in tungsten/silicon (WSix) 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 Ã… (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, WSix film thickness,
argon concentrations (if present), presence of oxide on surface of WSix 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 ±70Å.
1.5 This test method supports and assists in qualifying WSix films by electrical resistivity techniques.
1.6 This test method can be performed for WSix films deposited on conducting or insulating substrates.
1.7 This test method is useful for WSix 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 WSix 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 WSix 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.
Keywords
analysis of tungsten silicide; backscattering analysis; composition; metallization films; quantitative analysis; RBS; WSix; Backscattering analysis; Composition analysis--semiconductor
applications; Density--electronic applications; Metal electronic components/devices; Quantitative analysis/measurement; Rutherford backscattering spectrometry; Tungsten silicide (WSix)
ICS Code
ICS Number Code 29.045 (Semiconducting materials)
DOI: 10.1520/F1894-98R11