Uses of photoconductlve, photoemissive, and electron-beam sampling in high-speed circuit characterization

Abstract

Recent advances in process technology and better understanding of design and scaling principles have led recently to the realization of very high-speed LSI and VLSI circuits. These circuits have gate delays well under the 50-ps mark and characteristic feature and wiring interconnect sizes smaller than 1 μm. Circuits built today are already beyond the testing capabilities of conventional equipment, both in terms of their capability to access internal nodes and in terms of their temporal resolution. On-chip wiring delays must also be accurately measured to ascertain the critical timing necessary to the operation of complex high-speed circuits. Characterization techniques are urgently needed to answer these challenges, both at the level of single device characterization and for contactless in situ probing of complex circuits. In addition, for digital devices which operate inherently in a nonlinear large-signal regime, it is most desirable to complement the frequency domain characterization as is now practiced with a direct time domain characterization, which reflects more closely the operation of the devices in their applications. The ultrafast laser technology provides attractive solutions to high-speed electrical characterization through several techniques which have been developed in the past years. This paper concentrates on reviewing three of these techniques: photoconductive sampling for single-device characterization, photoemissive sampling for probing voltage on interconnect lines on circuit or packages, and photoelectron electron-beam probing which brings the already well-developed electron-beam circuit probing technology into the picosecond regime and is particularly well suited to contactless probing of voltages in the LSI and VLSI environment with high-density circuits at minimal linewidth.