Until recently, power device manufacturers have been saddled with the task of sending power devices out for packaging prior to characterization and model extraction. This extra step adds cost, plus development schedules can often face delays of several weeks or months. By providing accurate, reliable and repeatable on-wafer power device characterization, our Tesla system eliminates this unfortunate detour by putting power device characterization on an ideal development path so power device manufacturers can swiftly and cost-effectively achieve critical time-to-market goals.
Here are 5 challenges we’ve addressed with Tesla that allow for accurate, wafer-level power device characterization:
1. Mounting thin wafers
PROBLEM: With an average thickness of 100 μm, today’s wafers introduce added complexity to device characterization. These thin wafers are difficult to hold down on a standard wafer chuck and are often prone to curling at the ends, much like a potato chip. This creates problems for wafer probing and, in particular, for securing low-contact resistance between the wafer and the chuck.
SOLUTION: Tesla features a state-of-the-art chuck for mounting thin wafers. With the uniform and dense distribution of fine vacuum holes (400 μm diameter), the innovative gold-plated chuck technology delicately provides the appropriate amount of vacuum to protect against wafer breakage or probe damage. For the most accurate backside connections, a highly polished gold-top surface ensures low-contact resistance between wafer and chuck.
2. Rds(on) measurements
PROBLEM: The pursuit for the ideal power device is leading engineers to drive the ON state resistance to increasingly lower and lower levels. With today’s power semiconductor devices requiring high-current pulses and VDMOS power devices having the drain on the backside, accurate Rds(on) measurements have proven to be more and more difficult and problematic to perform on-wafer.
SOLUTION: Tesla enables engineers to make Rds(on) measurements at values lower than ever before on a probe station. This extraordinary performance comes through the highly polished gold chuck surface and a superior vacuum pattern that provides contact resistance in the milliohm range. Measuring drain resistance at a very high current has never been easier with the HCP probes supporting up to 100 A pulses.
3. High-current probe burnout
PROBLEM: Accurate probing of power devices requires high-current measurement capabilities. Reliable wafer-level characterization of power devices has always been a challenge due to inconvenient device heating at the probe tip. Furthermore, smaller and smaller pad dimensions only increase the likelihood of problematic device heating at the probe tip.
SOLUTION: Tesla’s high-current probe reduces probe and/or device destruction at high currents. It supports 10 A DC and up to 100 A of pulsed current. By design, the probe tip minimizes contact resistance at the wafer-to-probe interface to prevent device heating at the tip. The probe distributes current over multiple contact points at the tip and is joined by a single heatsink that pulls pull heat from the probe tip.
4. Low-leakage measurement at high voltage
PROBLEM: Precision measurements of high-voltage devices present some formidable challenges for probe design. Higher voltage between the guard and shield elements of the probe drives higher leakage currents through the resistance of various isolating materials separating those elements. In order to prevent dielectric breakdown (arcing) and maintain a safe operation, the distance must increase between internal elements of the probe. Additionally, upgraded cables and connectors are required.
SOLUTION: To ensure precision measurements of today’s high-voltage devices, Tesla’s HVP probes provide increased isolation resistance and dielectric strength by incorporating advanced internal isolation materials, as well as custom cabling and connectors. The unique internal design of HVP probe layers and elements assures the distance achieved by isolating materials, as well as inter-layer creepage paths, will prevent any breakdowns at high voltage and still enable full triaxial capability.
5. Safety for device, operator and probing equipment
PROBLEM: With power devices requiring upwards of 200 V, the integrity of this high-performance electrical test environment starts with ensuring both hardware and humans are protected from damage and/or severe injury. The advent of home-spun device characterization systems can present several safety issues, as these in-house test systems often include several disparate components and may lack the know-how to include all required safety protocols.
SOLUTION: The entire Tesla system is deliberately designed to ensure operator safety while providing a high-performance electrical measurement path. Features like an integrated safety interlock light curtain ensure operator safety during measurements. Additionally, the probe, chuck, chuck environment, cables, connectors and interface panels all contribute to this ultra-safe test environment and high-performance electrical path.
We’d love to hear from you on what your wafer-level power device characterization challenges are. Please add your comments below.
