Differential thermal measurements have been extended beyond simple fault isolation to quasi and fully dynamic test conditions. A new technique of Dynamic Digital Modulation has been developed that allows highly sensitive differential thermal measurements during active device operations. A quadrature version of the modulation also produces a thermal time constant map that allows for direct visualization of heat flow within a device structure. A wide range of potential applications in failure analysis, reliability and reverse engineering are opened up. Examples include in situ identification of resistive bonds, internal heat flow in packaged devices and die, dynamic heat loading, and localization of structural elements for reverse engineering.

Laser induced emission and photocurrents with exponential power scaling were discovered using a near IR Raman laser scanning microscope. The potential for utilizing these highly non-linear effects for sub-diffraction limited imaging has been explored both theoretically and experimentally. A three-fold improvement over the linear diffraction limit was predicted and experimentally validated.

Spatial resolution limitations of IR thermal microscopy also limit the temperature accuracy for small thermal sources. Use of Raman temperature measurements significantly improves spatial resolution and thereby temperature accuracy. Previous, visible-wavelength, Raman temperature measurements are limited to top side measurements in silicon. This paper describes the first ever IR Raman measurements in silicon and demonstrates its use for backside temperature measurements.

Thermal laser signal injection microscopy (T-LSIM) (aka TIVA and OBIRCH) has shown considerable promise in stateof- the-art digital integrated circuits. The technique has been utilized to locate shorts, leakage currents, problem vias, and timing issues in these devices. However, little has been published on the utility of this technique for analog and mixed signal devices. In this paper we demonstrate the application of T-LSIM on two different analog devices with defects that conventional FA technology and fault isolation techniques were unable to locate. Analog devices produce several unique challenges to the basic T-LSIM technique as typically utilized in the digital regime. Extensions of the basic T-LSIM technique were utilized to locate the failures, which produced unexpected results. The T-LSIM technique has proved essential in the quick identification and localization of failure sites. The T-LSIM technique provides the failure analyst with the analytical power not previously available on conventional fault isolation tools such as emission microscopy and liquid crystal.

Backside imaging through a silicon substrate introduces spherical aberration at high numerical apertures. For a typical 200 micron substrate thickness, these aberrations limit the resolution to less than 1 micron. A theoretical analysis of the aberrations describes the limiting factors. Means for correcting for these aberrations are described.

LIVA ( L ight I nduced V oltage A lterations) and TIVA ( T hermally I nduced V oltage A lterations) have demonstrated significant capability for fault isolation. A difficulty with both techniques is their use of a constant current source, whereas integrated circuits operate with a constant voltage source. A new technique that utilizes the constant current sensing of LIVA/TIVA, while allowing for use of constant voltage bias on the integrated circuit, has been developed. As a bonus, the technique is also significantly more sensitive (at least one order of magnitude) than the standard LIVA/TIVA approach.

Backside failure analysis techniques rely heavily on transmission of near infrared (IR) radiation through the silicon substrate. This statement applies both to emission techniques and active laser probing. Heavy doping of substrates causes them to become highly absorptive in the near IR due to band gap shifts, which effects phonon-assisted absorption, and to free-carrier absorption. Substrate thinning is often required to allow adequate optical transmission. This paper describes an empirical approach to determining the absorption coefficient in a heavily doped substrate and use of the coefficient in determining the amount of substrate thinning required.

The move towards flip-chip type packaging has produced significant obstacles for failure analysis. One such obstacle is the breakdown of traditional techniques for failure isolation via thermal mapping, typically used to isolate short circuits and leakage paths. This paper describes the application of near infrared (IR) phase-contrast techniques to allow highly sensitive, ~ 10mK, thermal mapping for backside failure analysis.