The combinational or selective usage of the laser SQUID microscope, the non-bias laser terahertz emission microscope, and fault simulations in non-electrical-contact fault localization
Highlights
► In LSI chip failure analysis, fault isolation is one of the most important steps. ► We have developed L-SQ and NB-LTEM, as no electrical contact fault isolation tools. ► Laser SQUID microscope (L-SQ), no bias laser terahertz emission microscope (NB-LTEM). ► Combo use of L-SQ, NB-LTEM, and their simulators is useful in LSI fault isolation. ► Many cases of fault isolation using these tools have been demonstrated.
Introduction
The steps of LSI chip failure analysis are shown in Fig. 1.
The first step is the fault diagnosis. In the fault diagnosis step, we use only electrical test tools and software. The second step is the nondestructive (ND) fault localization. In the ND step, we use infrared optical beam induced resistance change (IR-OBIRCH), photo-emission microscope (PEM), etc. The third step is the Semi-D (destructive) fault localization. In the Semi-D step, we use nano-probing tools, resistive contrast imaging (RCI) method using electron beam absorbed current (EBAC), etc. The final step is destructive physical analysis. In the final step, we use focused ion beam (FIB), transmission electron microscope (TEM), etc.
The non-electrical-contact failure analysis tools such as the laser superconducting quantum interference device (SQUID) microscope (L-SQ) and the non-bias laser terahertz emission microscope (NB-LTEM) are categorized in the second (ND localization) step (Fig. 1). The L-SQ and the NB-LTEM do not require Vdd-bias and signal input. Also, they do not require signal output via electrodes. Therefore, they do not require electrical contact.
The main merits of using them, compared to using conventional ND tools, are as follows:
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We can use them before the end of wafer processing: fast feedback is possible.
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We can use them without troublesome pin handling and/or mechanical probing: efficient analysis is possible.
As a non-electrical-contact failure analysis tool, we have first developed the L-SQ [1], [2], [3], [4]. Using the L-SQ, we have succeeded to localize the open defects of common Vdd and GND lines. We could not, however, localize the open defects of individual Vdd/GND lines and signal lines. Also, we could not localize short defects of signal lines.
In order to overcome this issue, we have secondly developed the NB-LTEM system. Using the NB-LTEM, we have succeeded to localize these defects [5], [6], [7], [8], [9], [10].
In this paper, we would like to organize these our results from the viewpoint of failure mode and defect sites.
Section snippets
Basic concept of the L-SQ
Fig. 2 shows basic concept of the L-SQ. Continuous laser beam with wavelength of 1.06 μm is irradiated from the backside of the LSI chip. When the laser beam is irradiated at a p–n junction, a photocurrent is induced resulting magnetic flux generation. The magnetic flux is detected by the SQUID magnetometer, located above the LSI chip. The SQUID magnetometer is made from high Tc DC-SQUID.
System of the L-SQ
Fig. 3 shows schematic of the L-SQ system. Not only the sample stage but also the SQUID magnetometer can be
Basic concept of NB-LTEM
Fig. 9a and b shows the basic concept of conventional LTEM and the NB-LTEM, respectively. The conventional LTEM requires Vdd bias and, in some cases, input signal as shown in Fig. 9a [12], [13]. The NB-LTEM does not require Vdd bias and input signal. Both methods do not require signal output via electrodes.
In Fig. 9b showing the NB-LTEM, a femtosecond laser beam is focused near chip surface from the backside of an LSI chip. We use a 1.06 μm wavelength laser beam so that it transmit through Si
Combinational or selective usage of L-SQ, NB-LTEM and related simulations
Table 1 shows the review results organized from the viewpoint of failure modes and defect sites.
Using the L-SQ, we have localized the open defects of common Vdd and GND lines without simulation (Fig. 4, Ref. [3]). Using the L-SQ (+S-SQUID) with simulation, we have demonstrated to localize short defect between a signal line and an individual GND line (Fig. 7, Fig. 8).
Using the NB-LTEM, we have localized the open defects of individual GND lines and signal lines without simulation (Fig. 14, Fig. 15
Summary
We have developed the L-SQ, the NB-LTEM, and the related simulators. We have applied them to the simple test structures and the actual circuits.
The application results to simple test structures showed that the terahertz waveforms change with the metal line length and the open position.
Application results of the defect localization at the actual circuits are organized from the viewpoint of failure modes and defect sites. It showed that we could localize most of the defects in open and short
Acknowledgments
The authors would like to thank Hiroki Kitagawa, Yoshimitsu Aoki and Shouji Inoue for the sample preparation and measurement. The VLSI chip in this study has been fabricated in the chip fabrication program of VLSI Design and Education Center, the University of Tokyo. This work was supported by SENTAN, Japan Science and Technology Agency, Japan.
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2013, Microelectronics ReliabilityCitation Excerpt :These techniques require electrical contact with the semiconductor device to apply a bias voltage. Recently, laser terahertz emission microscopy (LTEM) [2–10] has been proposed as a new observation technique that does not require electrical contact. This technique is reportedly capable of detecting defects in wiring systems connected to the diffusion layer.
LSI failure analysis using laser terahertz emission microscope
2016, Seimitsu Kogaku Kaishi/Journal of the Japan Society for Precision Engineering