edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 28 NO. 3 6 at the second probe. This setup enables simultaneous input voltage and current measurement across the failure. Typical EBIRCH operating currents ranged from 100 nA to several µA, and the electron beam penetration depth was controlled by adjusting the accelerating voltage (1-5 kV) according to the approximate rule of thumb of 100 nm per kV in silicon. All reported currents account for the series resistance of the measurement setup (~5-6 kΩ), which reduces the measured current relative to the simple V/R device estimate. For clarity, this measured current will be referred to as the “EBIRCH current” throughout the remainder of the text. LOW-OHMIC DEFECT LOCALIZATION A localized low-ohmic resistance variation was iden- tified in a metal line of a 3 nm technology node device having an overall resistance of 150 Ohms (Fig. 2a). Electrical characterization indicated a globally low resistance with a subtle localized increase attributed to a geometric narrowing of the interconnect, rather than an open or diode-like behavior. EBIRCH imaging was performed by applying a 20 mV external bias, resulting in an EBIRCH current of approximately 1.4 µA through the line using 500 V and 9 nA electron beam voltage and current, respectively (Fig. 2b). The EBIRCH image revealed a confined region of resistance modulation, appearing as a localized peak, precisely aligned with the narrowed metal segment (Fig. 2c). This contrast is consistent with localized beaminduced heating in a low-resistance structure. Complementary EBIV imaging of the same region showed a distinct voltage contrast transition across the narrowed segment (Fig. 2e), directly reflecting the localized voltage drop caused by the resistance increase. While EBIV provided a clear mapping of the voltage gradient, EBIRCH enabled precise defect localization through sensitivity to subtle resistance variations. INTERMEDIATE-OHMIC DEFECT LOCALIZATION A low-ohmic short (13 kΩ) was found between the gate and source terminals of a SRAM n-MOS transistor in a 22 nm technology node device (Fig. 3a). I–V characterization with the LCT revealed a nearly linear response consistent with a resistive short (Fig. 4b), unlike the diode-like curve of intact devices (Fig. 4a). EBIRCH imaging (Fig. 3b) was performed by applying a 0.02 V bias, resulting in an EBIRCH current flow of 770 nA through the defect, and an electron beam voltage of 1 kV at 75 pA beam current. The EBIRCH image revealed a localized region of resistance modulation corresponding precisely to the shorted contact pair (Fig. 3c). Fig. 2 Metal line in a 3 nm technology-node device. (a) SEM image showing the two-probe configuration with a 5 µm probeto-probe spacing. (b) Raw EBIRCH image. (c) Overlay image showing the EBIRCH red spot coinciding with the metal line narrowing (cyan arrow). (d) SEM image corresponding to the EBIV image shown in (e); note the contrast change (circled) located at the metal line narrowing in the EBIV image. The scale bar represents 500 nm. (a) (b) (c) (d) (e)
RkJQdWJsaXNoZXIy MTYyMzk3NQ==