The infrared-optical beam induced resistance change (IR-OBIRCH) method is widely used to localize faults of semiconductor devices. Prior to the fault localization, the IR-OBIRCH generally requires a decapsulation of mold resin that covers the semiconductor devices. As an alternative, without the need for decapsulation, the authors propose the ultrasonic beam induced resistance change (SOBIRCH) method. This research examined a determination method of the optimal ultrasound frequency in order to improve the signal intensity of SOBIRCH even if the speed of sound and the thickness of mold resin are unknown. The resonant frequency estimated by using frequency component of signals of reflected wave agreed with the ultrasound frequency that maximized the intensity of SOBIRCH signal. The frequency dependence of SOBIRCH signal was also estimated. This research demonstrated that the proposed frequency determination method can estimate the resonant frequency on the fault observation of a practical device.

No abstract

In the process of the failure analysis for semiconductor devices, various optical methods are applied as techniques to localize faults of the semiconductor devices. Conventional optical techniques often require the decapsulation of the mold resin, since the mold resin is not optically transparent. As a new fault localization technique requiring no decapsulation, the authors are proposing the ultrasonic beam induced resistance change (SOBIRCH) method based on a heating by focused ultrasonic beam. In this report, the signal intensity of the SOBIRCH method for the capsulated samples was discussed through the experimental and the theoretical approaches. By comparing the experiment and the numerical analysis, it was suggested that a certain thickness of the thin mold resin can enhance the intensity of the SOBIRCH signal. Additionally, an expected effect of the standing wave in the thin mold resin was calculated, and a method to make use of the standing wave was proposed.

No abstract