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Evaluation of a low dielectric constant (Low-k) insulation thin film between layers using grazing incidence X-ray scattering


When X-rays enter a sample surface at a grazing angle, it is possible to determine the surface and thin-film structure of the sample. The most popular grazing-angle incident X-ray experiment is the X-ray reflectivity measurement. X-ray reflectivity can be used to calculate the density, thickness and roughness of thin films to a high precision, irrespective of composition, and is used for the thin-film structure analysis of multilayer films. Conventionally, it was considered to be difficult to measure particles and pores in a thin film; however, by means of the reflected X-ray small-angle scattering technique developed by Rigaku, it becomes possible to analyze the particle and pore size distribution in the thin film in a short time at high precision.

With the increasingly high integration of wiring technology, the parasitic capacitance of the insulating layer between wiring layers becomes problematic. To reduce the parasitic capacitance, technology to introduce pores in the insulating layer is actively studied. The pore rate corresponds to the density of the insulating layer, and it is possible to calculate the pore rate by the X-ray reflectivity measurement.


To calculate the parasitic capacitance between wiring layers, an accurate value for the film thickness is necessary. The X-ray reflectivity measurement excels here because it can extract precise information on density and thickness of the film. Figure 1 shows the results of X-ray reflectivity measurements taken with Rigaku's SmartLab multipurpose diffractometer for three kinds of insulating films between layers with a different relative permittivity.


Profiles of X-ray reflectivity
Figure 1: Profiles of X-ray reflectivity


When pores are introduced between layers in the insulating thin film, problems such as the degradation of the mechanical properties of the thin film itself and diffusion of the wiring material inside the pores occur. The more uniform and small the pore sizes become, the greater the insulation characteristics of the insulating film. For this reason, to evaluate the pore size distribution in the insulating film between layers becomes important. Figure 2 shows the pore size distribution obtained by the reflected X-ray small-angle scattering technique.

Pore size distributions
Figure 2: Pore size distributions