# A Short Review of Through-Silicon via (TSV) Interconnects: Metrology and Analysis
## 2 TSV Metrology
### Profile  
In the world of 3D semiconductor packaging, TSVs or through-silicon vias play a crucial role in enabling the electrical connection of vertically stacked wafers. As a result, it is essential to monitor and control the profile of the TSVs to ensure that they are defect-free, as any issues in these holes can lead to electrical disconnections between stacked wafers. In recent years, TSV technology has made significant progress, allowing for the creation of holes smaller than 10 \(\upmu\)m and length-to-diameter ratios greater than 10. However, accurately measuring the profile of these TSV holes using traditional optical metrology methods has become increasingly difficult. To overcome this challenge, destructive methods, such as scanning electron microscopy (SEM) and tunneling electron microscopy (TEM), are commonly used to measure the profile of TSV holes for process development and quality control. However, these methods cannot be used for non-destructive TSV metrology, as they are time-consuming and the samples are destroyed in the process. Therefore, there is a need for new measurement methods that can provide non-destructive and in-line TSV metrology to enable the development of better TSV processes. Researchers are exploring various techniques, such as X-ray computed tomography (XCT), infrared microscopy, and terahertz spectroscopy [27], which could potentially offer a faster, non-destructive, and more accurate way of measuring TSV profiles. Non-destructive fault isolation (FI) techniques play a crucial role in detecting multiple faults within complex 3D packages, leading to reduced production time and improved success rates. In the case of open circuit and high resistance faults, time domain reflectometry (TDR) and electro-optical terahertz pulse reflectometry (EOTPR) have demonstrated effectiveness in system-in-package (SIP) configurations with package-on-package (POP) arrangements. TDR, a cost-effective and conventional non-destructive FI technique, is employed for identifying electrical faults in flip chip packages. It involves injecting step electrical pulses with a rise time of 35-40 ps into the package interconnect and analyzing the changes in impedance along the circuit by interpreting the reflected signals acquired from the package. By comparing the reflected waves from the faulty cell with those from a known reference cell and the bare substrate, the location of the fault can be pinpointed within the chip or package substrate. The resolution of TDR depends on the rise time, bandwidth of the TDR system, and material properties present within the package. The time domain resolution of TDR can be estimated as approximately 1/10 th to 1/5 th of the TDR rise time. The key to pinpointing short-circuit faults in 3D microelectronic packages is to obtain \(z\)-dimensional information about the defect in addition to x and y position data. Locked-in thermography (LIT) is a very promising technique designed to locate hot spots caused by short-term faults using a real-time graphical locking method designed to detect small signals hidden in higher intensity random noise. Scanning superconducting quantum interference device (SQUID) microscopy (SSM) has been applied as a non-destructive FI technique for short failures in conventional packages [27]. By developing more precise and reliable TSV metrology methods, manufacturers can enhance the quality and performance of 3D semiconductor packaging, paving the way for further advancements in the field. The geometrical shape of the TSV hole is defined by the following three parameters: top CD (diameter of the TSV hole on the surface, which can be measured using visible light), bottom CD (diameter of the TSV hole at the bottom, which is difficult to be measured using the visible light directly), and the depth of the TSV hole. [PERSON] et al. [28] pointed out that the diameter, aspect ratio, and defects of the TSV hole all have an effect on the thermal behavior and stress field of the TSV structure.