Detection of thermal waves through optical reflectance

Abstract

We show that thermal wave detection and analysis can be performed, in a noncontact and highly sensitive manner, through the dependence of sample optical reflectance on temperature. Applications to the study of microelectronic materials are illustrated by an example of measuring the thickness of thin metal films.

Thickness-dependent thermal properties of amorphous insulating thin films measured by photoreflectance microscopy

“…It is based on the generation of thermal "waves" by intensity-modulated optical excitation. This technique was first proposed by A. Rosencwaig et al [20], and then widely used to determine the thermal properties of bulk materials [21,22], grains [23], coatings and thin films [24,25]. In this work, the frequency domain photoreflectance method is used to study the effect of thickness on the thermal properties of amorphous SiO 2 and Al 2 O 3 thin films.…”

Spatially localized measurement of thermal conductivity using a hybrid photothermal technique

“…8,9 In general, a thermal wave is a nonpropagating diffusion wave defined by a complex wavenumber. 18 In this section, models of thermal waves used for data analysis will be discussed.…”

“…6,7 In general, these methods use a pump laser for transient heating of the sample. This can be implemented in the frequency domain using an amplitude modulated continuous wave laser [8][9][10][11] or in the time domain using a pulsed laser. 12,13 Temperature sensing is accomplished by either recording black body radiation (laser flash) or using a probe laser to record small temperature induced changes in optical reflectivity (thermal reflectance).…”

Modulated Reflectance Measurement of Reactive-Ion and Plasma Etch Damage in Silicon Wafers

“…These waves are then detected by the HeNe "probe" laser through the pump-induced, 1 MHz modulation of the sample reflectivity at the wavelength of the probe laser. As described in [13][14][15][16], the effects of the thermal and plasma waves on the reflectivity of silicon result in a net modulated reflectivity signal that is very sensitive to the presence of disorder or defects in the surface region of the wafer. The measurement method is similar to that employed for ion implant monitoring [17,18] and polishing damage characterization [12] in which damage to the silicon is detected by the Therma-Probe system.…”