Kiyoshi Nikawa

New capabilities of OBIRCH method for fault localization and defect detection

We have improved the optical beam induced resistance change (OBIRCH) method so as to detect (1) a current path as small as 10-50 /spl mu/A from the rear side of a chip, (2) current paths in silicide lines as narrow as 0.2 /spl mu/m. (3) high-resistivity Ti-depleted polysilicon regions in 0.2 /spl mu/m wide silicide lines, and (4) high-resistivity amorphous thin layers as thin as a few nanometers at the bottoms of vias. All detections were possible even in observation areas as wide as 5 mm/spl times/5 mm. The physical causes of these detections were characterized by focused ion beam and transmission electron microscopy.

Laser terahertz emission microscope for inspecting electrical failures in integrated circuits

The inspection and fault analysis of semiconductor devices has become a critical issue with increasing demands for quality and reliability in circuits as stated in L. A. Krauss et al. (2001), K. Nikawa (2002) and K. Nikawa et al. (2003). Recently, we have developed a laser-terahertz (THz) emission microscope (LTEM) that can be applied for the noncontact and nondestructive inspection of the electrical faults in circuits presented in K. Nikawa et al. (2003). The LTEM can image the amplitude profile of the THz wave emitted by scanning the sample with femtosecond (fs) laser pulses. The amplitude of the THz emission generated by the transient photocurrent is proportional to the local electric field at the laser-irradiated area according to T. Kowa et al. (2003). Therefore, the LTEM image of the semiconductor device while it operates reflects the electric field distribution in the chip. By comparing the LTEM image of a damaged chip with that of a normal one, we can localize the electrical faults. In this work, we report experimental results on a biased 8-bit microprocessor, as well as unbiased MOSFETs embedded in a test element group (TEG).

Failure analysis case studies using the IR-OBIRCH (infrared optical beam induced resistance change) method

The IR-OBIRCH (infrared optical beam induced resistance change) method was proposed and developed by Nikawa and Tozaki in 1993 and this method has been shown to be applicable for detecting defects and current paths by using test structures and/or artificial failures. Here we present the results of the actual failure analysis from real failures of DRAMs, ASICs, power MOSFETs and microcomputers, which failed during mass production, development, user tests, and ESD simulation. In the analysis of a microcomputers we applied test vectors from an ATE docked to the IR-OBIRCH system, in order to reproduce the failure state during IR-OBIRCH imaging. The results showed that the IR-OBIRCH is suitable not only for improving reliability but also for increasing yield.

Noncontact inspection technique for electrical failures in semiconductor devices using a laser terahertz emission microscope

We have proposed and demonstrated a novel technique for the noncontact inspection of electrical failures in semiconductor devices using a laser terahertz emission microscope. It was found that the waveforms of the terahertz pulses, emitted by exciting p-n junctions in semiconductor circuits with focused ultrafast laser pulses, depend on the interconnection structures of the circuits. We successfully distinguished damaged silicon metal-oxide-semiconductor field effect transistor circuits with disconnected wires from normal ones by comparing the images of terahertz emission amplitudes between a normal chip and a defective one.

New applications of focused ion beam technique to failure analysis and process monitoring of VLSI

The applications presented are: (1) microscopic selective cross-sectioning and in situ observation of the cross section; and (2) the observation of aluminum microstructure. These applications make failure analysis techniques simpler and less time-consuming. >

Monte Carlo Calculations Based on the Generalized Electromigration Failure Model

The dependence of electromigration failure-time on line width and current density was studied using Monte Carlo calculations. In constructing the model used here, A total of three factors were considered: the metallurgical properties of the film, the thermal process during failure propagation, and the stress induced mass flow. In the study on line width dependence, median time to failure (t50) was revealed to decrease as line width decreased to about median grain size, and to increase steeply as the line width decreased further, in good agreement with previous experiments. A wide variety of values assigned to an exponential factor (n) in current density dependence of t50 (t50¿ J-n) was successfully explained by introducing the effective length where a stress gradient has built up.

Novel Method for Defect Detection in Al Stripes by Means of Laser Beam Heating and Detection of Changes in Electrical Resistance

We have successfully detected defects (voids and Si nodules) in Al stripes using an optical beam induced current (OBIC) system in which defects, even those beneath a metal surface, were detectable as the difference in changes in resistance, produced by laser beam heating, between defective and defect-free areas. Our method, which we refer to as optical beam induced resistance change (OBIRCH), is nondestructive since the temperature increase caused by laser irradiation is on the order of 1° C and the density of the base current applied to the stripes is on the order of 106 A/cm2 or less. The results of scanning ion microscopy (SIM) (conducted after areas identified by OBIRCH as being defective had been successively cross-sectioned with a focused ion beam [FIB]) indicated that the minimum void size detectable by OBIRCH was on the order of 10-3 µ m3, and we are able to show that OBIRCH has many advantages over conventional void detection methods.

LSI failure analysis using focused laser beam heating

Three new applications of a focused laser beam to VLSI interconnect diagnosis have been reported, in which interconnect heating by a laser beam and current change measurement are used. One is a void and Si nodule detection method that monitors current changes caused by resistance changes induced by the laser beam heating, through temperature dependence of resistance. Another is a current measurement method that monitors current changes caused by resistance changes induced by the laser beam heating, through temperature dependence of resistance. The last is a void and other types of anomalies detection method that monitors current changes caused by the laser beam heating through the thermoelectric effect. In this paper, we present new results on these three methods, and discuss the advantages and disadvantages of these methods over other methods.

Backside observation of large-scale integrated circuits with multilayered interconnections using laser terahertz emission microscope

We have developed a laser terahertz emission microscope utilizing excitation laser pulses at 1.06 μm wavelength for the inspection and localization of electrical failures in large-scale integrated circuits with multilayered interconnection structures. The system enables to measure terahertz emission images from the backside of a large-scale integrated circuits chip with a multilayered interconnection structure that prevents the observation from the front side. By comparing the terahertz emission images, we successfully distinguish a normal circuit from damaged ones with different positions of the interconnection defects without any electrical probing.

Imaging of current paths and defects in Al and TiSi interconnects on very-large-scale integrated-circuit chips using near-field optical-probe stimulation and resulting resistance change

The optical-beam-induced resistance-change-detection (OBIRCH) method has been improved by using a near-field optical probe as the heat source instead of a laser beam. The near-field OBIRCH method has two advantages over the conventional one: (1) its spatial resolution is higher (50 vs 400 nm) and (2) the optical-probe-induced resistance change caused by heating can be observed using a metallized probe without interference from a photocurrent created by electron–hole-pair generation. In the conventional-OBIRCH method, the laser beam creates not only a resistance change, but also a photocurrent that can mask the resistance change signals.