Integrated Magnetic Probe and Application for Device Diagnosis

The spatial resolution of coil-based magnetic probe is determined by the coil size. A smaller coil has a higher spatial resolution but a weaker level of output signal, which results in a worse signal-to-noise (S/N) ratio. A solution of this trade-off problem is integration of a small coil with a low-noise amplifier on a semiconductor chip. In this presentation, firstly, structures and fabrication procedure of our integrated magnetic probes will be introduced along with their characteristics. Next, an estimation method of current distribution from measurement data of the magnetic probe is introduced, as a theoretical basis of the integrated magnetic probe application. It is a reverse modeling from magnetic field data to current distribution in circuit. Though it is a straightforward procedure to calculate magnetic field based on a known current distribution in general, a practical problem is the existence of noise. Here a method to estimate most-likely current distribution from magnetic field with random noise will be introduced under the constraint of KCL. Finally, two examples of application will be shown. The first example is measurement results of gate leak current in power devices (IGBT), where the location of the leakage has been successfully detected based on “valley detection method” with a good agreement of a microscopic device diagnosis. The second example is an analysis of power network integrity of LSI. By comparing a normal chip with an abnormal chip with missing VIAs in power network, the magnetic probe has successfully detected subtle differences in magnetic fields, which has been translated to an abnormal power current map analytically. Both the above examples show that the integrated magnetic probe has a potential to be utilized for improving device reliability and fabrication technologies.