Christine Boué

Back side thermal imaging of integrated circuits at high spatial resolution

In integrated circuits, most of the heating is produced in the active layers below the surface, making thermal measurements extremely difficult. The authors demonstrate that near infrared thermoreflectance can provide thermal imaging inside the circuit, through its silicon substrate. The use of an InGaAs camera with a noncoherent illumination in the 1.1–1.7μm band allows fast thermal imaging with a diffraction-limited resolution of 1.7μm. A silicon solid immersion lens was then used to further improve the resolution to 440nm, corresponding to an effective numerical aperture of 2.36.

Heat transfer modeling for surface crack depth evaluation

This paper presents a theoretical approach for the quantitative depth evaluation of linear opened surface cracks by using lock-in infrared thermography. In order to simulate heat flow near a crack, a three-dimensional simulation model has been developed by using finite element simulation. We show that, under a periodic local thermal excitation in the vicinity of the crack, the second spatial derivative of the amplitude image can provide information on this depth. The influence of the simulation parameters are discussed for the optimal characterization of defects.

Micron scale photothermal imaging

Abstract In this paper, we present various experimental results which demonstrate the ability of photothermal methods to perform heat diffusion imaging at the micron scale. Photoreflectance microscopy measurements have been performed on a composite sample presenting a strong anisotropy of thermal properties and on microelectronic devices. We will then introduce the CCD array photothermal microscopy which permits the acquisition of a complete image in a single shot, without moving the sample. A stroboscopic technique must be used in order to adjust to the relatively low frame rate of the CCD camera. We will discuss two cases: homodyne and heterodyne detection.

High resolution thermal imaging inside integrated circuits

Purpose – Heating is a major cause of failure in integrated circuits. The authors have designed thermoreflectance‐based systems operating at various wavelengths in order to obtain temperature images. This paper aims to explore the possibilities of each wavelength range and detail the charge coupled device (CCD)‐based thermal imaging tools dedicated to the high‐resolution inspection of integrated circuits.Design/methodology/approach – Thermoreflectance is a non‐contact optical method using the local reflectivity variations induced by heating to infer temperature mappings, and can be conducted at virtually any wavelength, giving access to different types of information. In the visible, the technique is now well established. It can probe temperatures through several micrometers of transparent encapsulation layers, with sub‐μm spatial resolution and 100 mK thermal resolution.Findings – In the ultraviolet range, dielectric encapsulation layers are opaque and thermoreflectance gives access to the surface temper...

Lock-in thermography, penetrant inspection, and scanning electron microscopy for quantitative evaluation of open micro-cracks at the tooth–restoration interface

The evaluation of a dental restoration in a non-invasive way is of paramount importance in clinical practice. The aim of this study was to assess the minimum detectable open crack at the cavity–restorative material interface by the lock-in thermography technique, at laser intensities which are safe for living teeth. For the analysis of the interface, 18 box-type class V standardized cavities were prepared on the facial and oral surfaces of each tooth, with coronal margins in enamel and apical margins in dentine. The preparations were restored with the Giomer Beautifil (Shofu) in combination with three different adhesive systems. Three specimens were randomly selected from each experimental group and each slice has been analysed by visible, infrared (IR), and scanning electron microscopy (SEM). Lock-in thermography showed the most promising results in detecting both marginal and internal defects. The proposed procedure leads to a diagnosis of micro-leakages having openings of 1 µm, which is close to the diffraction limit of the IR camera. Clinical use of a thermographic camera in assessing the marginal integrity of a restoration becomes possible. The method overcomes some drawbacks of standard SEM or dye penetration testing. The results support the use of an IR camera in dentistry, for the diagnosis of micro-gaps at bio-interfaces.

Experimental and numerical investigation of ultrasonic transmission through the skull bone and associated temperature rise

The feasibility of transcranial high‐intensity focused‐ultrasound (HIFU) therapy within the brain relies on the ability to transmit ultrasound through the skull bone at relatively high ultrasound power. Absorption of ultrasound through the skull bone may cause important temperature rises, and is therefore an important parameter to control. Ultrasonic measurements have shown that the ultrasound beam undergoes a significant attenuation when propagating through the skull, with values on the order of 10 to 20 dB/cm/MHz. To predict temperature rise from such values, it is fundamental to weigh the relative role of absorption to the total ultrasonic attenuation (scattering + absorption + specular reflection). In this work, two types of numerical simulations and experiments are performed to investigate this relative role. Through‐transmission of 1 MHz ultrasound was performed numerically using a 3D Finite‐Difference Time‐Domain (FDTD) algorithm coupled to a 3D bone model obtained from high‐resolution synchrotron ...