Gratings for metrology and process control 2: Thin film thickness measurement

Abstract

A method of measuring thin film thickness is described, based on a previous paper where the authors analyzed a graphical means for grating modulation calculation. Metallic or dielectric films on any substrate may be measured, and precision was shown to be comparable with that achieved ellipsometrically at least in the 300-1500-A thickness range. The method is non-contact and destructive: the grating is recorded on the film. Measurements are simple, requiring a low-power He-Ne laser and a photodetector, and may be carried out at a distance from the sample. Experimental results are presented for three types of sample, including measurements by reflection and transmission. II. Theory The thickness of a thin film is measured by recording a lamellar grating in its full depth. The problem of film thickness measurement is then converted into one of grating modulation. In Part 1 we showed that the latter may be easily done with a nomogram. 1 The latter provides the grating modulation h (which actually represents the film thickness), its bar-to-period width ratio aid (not relevant for our present purpose), and a criterion for checking whether the grating on the sample fulfils the required theoretical conditions. 1 Figure 1 is a schematic description of a rectangular grating re-The authors are with

Continuous Optical Measurement of the Dry Etching of Silicon Using the Diffraction of a Lamellar Grating

“…The optical modulation of a lamellar grating recorded in the full depth of a layer may be used to monitor the etch rate of the layer by measuring the first-to-zero diffraction intensity orders ratio IJIo (4,5). If a substrate is etched through a lamellar grating masking layer, the etched depth h may also be determined by measuring the I,/Io ratio, of the grating being formed in the process, as shown in Fig.…”

“…In our experiment, we shall choose a/d = 0.5 for which value the IJIo ratio is less sensitive to a/d variations (4 If we assume the plasma etching to be infinitely selective (which means that the film thickness T remains constant throughout the process), the I,/Io ratio should be periodic in h with a spatial period H --M(2n0). It means that two successive extrema appearing in the I,/Io measured ratio represent a variation in the substrate etched depth (h) of M(4n0).…”

“…The approach here is similar, except that, in this case, the film thickness T is constant and the substrate etched depth h is the variable in Eq. [4].…”

“…Mendes et al (3)(4)(5)(6) further developed a method using lamellar gratings for thickness measurement and etching monitoring which permits one to measure the point-bypoint evolution of the depth of the layer being etched. In this paper, we shall profit from the previous developments, extending the method to monitor the etching of the substrate, and accounting for the selectivity of the process with respect to the mask layer.…”

Resonant and scatterometric grating-based nanophotonic structures for biosensing

“…This happens at a specific wavelength and incidence angle of the incident beam [14] at which the resonance condition is satisfied, whereby the re-diffracted beam destructively interferes with the transmitted beam, so that the incident light beam is completely reflected [15,16]. Scattering from non-resonant grating structures have also been shown to be highly sensitive to the grating parameters and to the layers surrounding the grating structure [17][18][19][20][21][22][23][24]. This property is being used to optically monitor layers thickness, critical dimension and overlay mis-registration, which are crucial parameters to control the fabrication process in the nanoelectronic industry.…”