NONINVASIVE PROBING OF HIGH-FREQUENCY SIGNAL IN INTEGRATED-CIRCUITS USING ELECTROSTATIC FORCE MICROSCOPE

We report a noninvasive high speed voltage sampling technique by using atomic force microscope. This technique is based on the mixing of int eraction forces between a conductive probe-tip and a device interconne ct line. Mixing phenomena allow measurements of signals with frequenci es far above the mechanical resonance frequency of the cantilever. To increase the sensitivity and stability of the signal detection in ambi ent environment, we employed a delayed pulse sampling and lock-in ampl ifier detection of the small electrostatic force resulting from a high frequency signal on integrated circuits. Thp probing pulse is first m odulated by a low frequency sinusoidal voltage using a double-balanced diode mixer. The junction between probe-tip and integrated circuit in terconnection line works as the second mixer which mixes the probing v oltage with the high speed waveform in the interconnection Line. This technique can sense voltage signals even through a passivation layer o f a 0.5 mu m in thickness. We sampled an 8-bit vector signal repeating at 50 MHz through a passivation layer by using this technique. (C) 19 97 American Institute of Physics.