Backside probing of flip-chip circuits using electrostatic force sampling

A non-contact scanning probe microscopy technique for measuring high-freque ncy voltage waveforms from the backside of a nip-chip mounted integrated ci rcuit is presented. The signals on interconnects on the frontside of the di e are accessed by mechanical thinning and focused ion beam milling through the backside of the die. A scanning force microscopy micromachined probe is placed inside the focused ion beam hole so that it is in close proximity t o the circuit measurement point, Internal circuit voltage waveforms are mea sured by using the scanning probe in a non-contact mode and sensing the loc al electrostatic force on the tip of the probe. The instrument currently ha s a 3 GHz bandwidth and a capacitive loading on the test point of less than 1 fF. The output waveforms from ring oscillator Aip-chip test circuits are measured. (C) 2000 Elsevier Science Ltd. All rights reserved.