Practical Electron Microscopy and Database

Figure 1602a shows an example of the setups of the electron beam probing (eBP) systems. [1] The electron beam probing system utilized an IDS 10K+ E-beam Prober (EBPr) to capture both repeating (clocks) and non-repeating signals from a test chip fabricated using TSMC's 180 nm CMOS technology. The sample preparation involved global mechanical thinning of the die to a remaining silicon thickness of 40 µm, using an Allied Hi-Tech polishing wheel, followed by a fine polish with 0.25 µm grit paper. Local thinning was performed with a focused ion beam (FIB) system (Credence OptiFIB), which thinned a 50 x 200 µm area down to 7 µm of remaining silicon. The process was carefully controlled to maintain planarity during thinning, crucial for subsequent operations.

Once prepared, the device under test (DUT) was mounted on a custom PCB load board connected to power and signal sources via vacuum-compatible adapter plates. To minimize electromagnetic interference, the load board was wrapped in insulation and conductive foil, forming a Faraday cage. A Tektronix HFS9003 was used to feed clock and random data streams into the DUT, simulating real-world debug conditions. Signals were acquired at various loop lengths, with short loops of 1 µs and longer loops of 1000 µs.

The eBP system was able to acquire voltage contrast images, differentiating between n-FET and p-FET transistors by detecting variations in secondary electron energy caused by voltage-driven charge accumulation. Clock signals at 100 Mb/s and 200 Mb/s were measured, and the system demonstrated a high sensitivity to voltage changes. A linear dependency was observed between clock waveforms and the input voltage, with device failure detected at lower operating voltages. This setup proved effective for probing the backside of transistors and measuring voltage contrast and signal behavior, providing valuable insights into failure mechanisms in flip-chip packaged devices.

Figure 1602b illustrates a vacuum-compatible thermal control solution designed for the eBP system. This system allows for the flow of super-cooled nitrogen, which helps dissipate localized heat during the probing process. The cooling solution is necessary because, in backside electron beam probing, thinning the silicon reduces the natural heat sink effect that would normally help manage heat dissipation in high-performance devices. By integrating this thermal control solution, the system can maintain stable device operation and prevent overheating during measurements. This is especially important for ensuring accurate data collection in vacuum conditions.

[1] R.K. Jain; T. Malik; T. Lundquist; R. Schlangen; R. Leihkauf; U. Kerst; C. Boit, Novel Flip-Chip Probing Methodology Using Electron Beam Probing, 2007 14th International Symposium on the Physical and Failure Analysis of Integrated Circuits, DOI: 10.1109/IPFA.2007.4378054, 2007.