Electro Optical Terahertz Pulse Reflectometry — an innovative fault isolation tool

Abstract

Electro Optical Terahertz Pulse Reflectometry (EOTPR), an innovative time domain reflectometry (TDR) system, has been successfully developed. This is the first system that applies terahertz technology to time domain reflectometry. The system has achieved 10 um resolution, 5.7ps rise time, 94dB signal/noise ratio and 150 mm testing range and it has been successfully integrated into fault isolation and failure analysis process flow. IntroductionTDR is an integral instrument for fault isolation (FI) and failure analysis (FA). It is a non-destructive fault isolation method that can locate the faults (open or short) in electrical circuit. The principle of TDR is to measure and display as a function of time, the reflections from the electrical signals being input into device under test (DUT). The reflected signals contain the information of the location and nature of discontinuities that have caused mismatch of characteristic impedance [1-2]. The method of applying TDR to fault isolation is waveform comparison -the waveform of failed unit is evaluated against the record of a known-good circuit to identify failure mode as well as the failing location within the circuit. A typical standard TDR system has the rise time of 35ps and the plug-in TDR module is ~20 GHz [1-2]. The resolution of this type of TDR had been evaluated to be around 500 m, which is the minimum distance between two known open failures that can result in appreciable difference in reflected signals when plotted side-by-side. With such resolution, one can determine if the failure is in the silicon die or in the package; nevertheless, substantial physical FA work including polishing and cross-section is still needed to pinpoint the fails, resulting in long FA through put time (TPT). In addition, there are many occasions when the current TDR cannot detect failure locations accurately or give misleading information, especially when the failures are in the vicinity of first level interconnect bumps in flip chip package technology.With decreasing metal trace line width and spacing for the next generation packages, simple, fast, and accurate nondestructive fault isolation instruments are necessary for the continuing success of failure analysis in future generations of microelectronic packages. Hence, there is an inherent development need for next generation TDR system with superior performance for the failure analysis community. Investigation had begun to identity other alternatives and more advanced time domain sampling technologies such as electrooptics (EO) and photoconductive switch (PCS). As depicted in Figure 1 [3], the best achievement of state-of-art conventional TDR is around 50GHz and 250 um resolution. But with PCS and EO technology, the bandwidth can reach as high as 2 THz

Failure Mode Characterization in Inkjet-Printed CPW Lines Utilizing a High-Frequency Network Analyzer and Post-Processed TDR Analysis

“…6(a)). A similar phenomenon is described in [18]. It can be seen in the optical photo as 15-µm-wide short conductor, presented in Fig.…”

Review of THz-based semiconductor assurance

“…Electro-optical terahertz pulse reflectometry (EOTPR) is an implementation of TDR technique at THz frequencies, which can be used to enhance fault isolation accuracy to better than 10 μm, since 2010. 146 As in conventional TDR, the fault detection accuracy of EOTPR is a function of the rise time of the incident pulse, the time-based jitter, and SNR. The EOTPR instrument generates a THz pulse using an ultrafast laser and a pair of photoconductive switches for signal generation and detection, resulting in a system with (i) high measurement bandwidth, (ii) low time-base jitter, and (iii) a high time-base resolution.…”

Terahertz Time-Domain Spectroscopy and Imaging

“…By sending a pulse of broadband THz radiation into a sample and recording the reflected/scattered THz radiation as a function of time, one can map the inner structures and compositions of the sample. A number of imaging applications have been reported in areas as diverse as medical diagnosis of human tissue, analysis of polymer samples, industry sensor for fault detection of integrated circuit packaging in semiconductors and online and offline tablet inspection in the pharmaceutical industry among others [12][13][14][15]. Other promising applications of THz technology include general nondestructive test, THz metamaterial devices and THz electronics for energy harvesting [1][2][3][4]16,17].…”