E. Schaub

Optical method for the measurement of the thermomechanical behaviour of electronic devices

Abstract We present in this paper a laser probing method for the study of the surface deformation and thermomechanical behaviour of electronic components. The method has been applied to running power devices and creep analysis of solder joints in after-fabrication processes. The set-up allows following the whole surface deformation as a function of time even in the long-term range. The method is based upon electronic speckle pattern interferometry (ESPI) and allows measuring surface normal deformation with a 10nm resolution.

Thermomechanical deformation imaging of power devices by Electronic Speckle Pattern Interferometry (ESPI)

We present an original imaging method to measure the three components of the surface displacement of working power devices with a nanometric resolution. The method takes advantage of the speckle structure of the analysed object recorded on a CCD camera. This method is complementary of IR thermography and provides interesting information concerning stress and reliability in power devices

Laser diode COFD analysis by thermoreflectance microscopy

We present thermoreflectance measurements upon a 980 nm wavelength laser diode. Using the energy conservation law, we are able to determine the temperature increase near the active region due to surface absorption. In this paper, we have studied the influence of this surface source contribution for three different configurations of the input current: below the threshold current ITh, for a moderate current above ITh and finally for a current far above ITh. We can analyse frome these reliability issues for the diode in terms of carastrophic optical facet damage (COFD)

Localisation of heat sources in electronic circuits by microthermal laser probing

Abstract In this work we present an original method for detection and localisation of heat sources at microscopic scale upon integrated circuits. The methodology is based upon thermoreflectance and interferometry, which allows us the measurement of surface temperature and dilatation with resolution better than micrometer. The heat sources are transistors electrically activated. The optical probes we have build act as a thermal antenna sensitive to the presence of thermal wave emitted by the heat source. By a set of three measurements of the phase of the thermal wave we are able to localise the heat source which generates the wave. This methodology is applied to microelectronics to detect and localise faults in CMOS integrated circuits.

High-resolution interferometry and electronic speckle pattern interferometry applied to the thermomechanical study of a MOS power transistor

We present an original optical approach for the thermomechanical study of electronic devices. We have applied it to image the deformation undergone by a MOS power transistor due to its operation. This imaging method allows the derivation of the three components of the displacement vector of each point of the surface of the component while heated by Joule effect while running. The method has a nanometric resolution for the displacement measurement and is based on the analysis of the speckle structure of the device while illuminated by coherent light. A high-resolution interferometer is also used to record the transient behavior of the normal surface displacement of a point of the surface. These optical approaches provide interesting quantitative information about strain and stress in electronic power devices and allow testing of finite element simulations. These techniques can be compared to Moire thermomechanical studies but with better resolution and sensitivity.

Laser diode light efficiency determination by thermoreflectance microscopy

In this paper, we present the thermoreflectance measurements done on 980 nm wavelength laser diodes. We determine the light output power for a given electric power input by using the energy conservation law.

Fault localisation in ICs by goniometric laser probing of thermal induced surface waves

Abstract New methods for fault detection in ICs are needed due to new technological trends. The detection of heat generated by faults offers interesting perspectives in this respect. Periodic heat released at the surface or inside ICs generates a surface thermal wave that can be detected by appropriate laser probing at distances up to 500 μm from the source. We propose in this paper a goniometric laser probing method allowing the determination of the direction and distance of a fault with respect to the probing point.

Differential Thermal Testing: An Approach to its Feasibility

Testing techniques based on the functional behaviour, the propagation delay and the levels of quiescent current have been used with great success for the last two decade technologies. However, the efficiency of such techniques is dubious for future technologies, characterised by huge mixed-mode complex circuits and very low supply voltage levels. In this paper the feasibility of using internal thermal sensors to detect heat sources provoked by structural defects are considered and evaluated.

Sondes laser et méthodologies pour l'analyse thermique à l'échelle micrométrique. Application à la microélectronique

Abstract We have developed optical techniques for thermal characterisation at micrometric scale based upon the detection and the analysis of the modifications of a reflected laser beam. The modifications are induced by a well controlled thermal excitation originating from electric heating. According to this principle we have developed a very compact, high sensitivity and high resolution optical bench. It includes a homodyne stabilised Michelson interferometer, a reflectometer and a differential interferometer. It is capable of detecting a temperature variation as small as 10−3 K and a thermal dilatation as small as 10−15 m. It has a large bandwidth ranging from DC to 125 MHz. The optical bench also includes a microscope and a visualisation system allowing analysis at micrometric scale. In the field of thermal studies in microelectronics, we have been able to determine the temperature of running microelectronic components in order to estimate their quality and reliability, to study the temperature distribution and to detect hot spots in integrated circuits and to study thermooptical and thermophysical properties of materials used in microelectronics.

Thermomechanical effects in metal lines on integrated circuits analysed with a differential polarimetric interferometer

Abstract We present a new laser probe, a differential polarimetric interferometer, which is dedicated to the study of common failure mechanisms in microelectronic interconnects. Our investigation is mainly concentrated on the study of thermomechanical stress build-up and electromigration in metal lines. In the differential interferometer, two laser beams, separated by a few microns, are reflected from the surface of the device under test. Reflectance, phase and polarization changes between the two beams can be observed, this allows surface temperature and surface bending measurements together with the observation of stress induced in the silicon dioxide layer by Joule thermal expansion. The laser probe provides unique and useful information about local thermal effects due to electromigration. It also shows, for the first time to our knowledge, induced local stress effects due to the mismatch of thermal expansion coefficients of the metal, Si and SiO 2 involved in running interconnect lines.