Abstract
Reducing the cell size of DRAMs in 0.35 micron and follow-on technologies requires failure analysis techniques that can analyze single storage node trench capacitors on both test sites and actual product. A combination of electrical microprobing, probeless voltage contrast and physical delayering procedures, all based on focused- ion-beam (FIB) techniques, are described. Because of precise fail localization, high resolution scanning electron microscope (SEM) imaging enables the distinction between process defects and intrinsic breakdowns of node dielectric defects. Isolated storage cells can be electrically characterized by depositing small probe pads, using FIB for contact hole milling and probe-pad deposition. To localize trench capacitors with a leakage path to the surrounding substrate, the trenches are isolated by mechanical polishing and probeless voltage contrast in the FIB tool. Failing trench capacitors can be marked in the FIB tool. Physical isolation of leaking trench capacitors can be achieved by recessing the adjacent trench capacitors, with the FIB used for milling and a subsequent wet chemical removal added for the remaining substrate material. Alternatively, trench capacitors can be inspected from the backside when stabilized by a quartz deposition on top, followed by mechanical polishing from the side and a wet chemical etching of the remaining substrate material. In both cases, the dielectric of the node trench capacitors can be inspected by high resolution SEMs and the defect areas precisely analyzed.
Failure Analysis of a Half-Micron CMOS IC Technology