Gavin Fisher, Customer Applications and Product Solutions, FormFactor, Inc.

Gavin Fisher is a member of the Customer Application and Product Solutions (CAPS) Group at FormFactor, providing application support and technical services to FormFactor’s customers. With more than a decade of experience working with Cascade probe systems, and with his deep technical knowledge in a broad spectrum of applications such as high-frequency measurement, calibration and power device measurement, he educates and trains customers on best practices to achieve accurate measurement results. He has made several presentations at European Microwave Week, MOS-AK workshops, and Agilent/Keysight seminars. Prior to joining FormFactor, he served as a Mechanical Engineer at Alenia Marconi Systems. He holds an upper-second degree from Brunel University in Mechanical Engineering with electronic systems.

Autonomous RF Measurement and Calibration

RF device overtemperature characteristics are generally a core requirement for all accurate semiconductor device models. On-wafer over temperature test is highly advantageous in terms of time and cost reduction, but can be a time consuming and frustrating business. During temperature transitions the RF characteristics of the probes and cables vary, necessitating recalibration at different temperatures. In addition, the wafer probe, positioning hardware, prober and the wafer itself all vary in geometry, sometimes very slowly which can cause mechanical misalignments during a test sequence. Calibration is done typically with ambient temperature substrates and the time taken to calibrate means the probes can cool during calibration affecting accuracy, so very fast work is required. Until now this all involved highly skilled users that can operate wafer probers quickly, efficiently and in many cases frequently attending to the prober during a test sequence. We felt this had to stop so we developed our Autonomous RF measurement assistant. The Autonomous RF measurement assistant is a complete system that fully automates the process of over temperature RF testing with the very minimum of additional code for test executive. Once a 10-minute training process is completed by the user the system is capable of :

  • Transitioning to new temperatures keeping the probes at a constant separation distance from the wafer and maintaining probe XY spacing
  • Wafer and die soaks that are done with probes only just above the wafer at align height to get the probes quickly to consistent operating temperature
  • Automatically calibrating without user input, as fast as is possible with dynamically adjusted probe placement to get accurate probe-to-probe X separation and scrub
  • Automatically carrying out wafer and die thermal soaking and then positioning probes to suit the DUT
  • Adjusting to multiple probe to named probe spacings for different device geometries
  • Monitoring calibration drift and recalibrating on the fly when required

In this presentation, we will talk in detail about the entire system and show the methodologies used to qualify operation. Videos of actual operation and some scripting will be shown to highlight how simple the tool is to use. We will also touch on the approaches that are taken for RF test cells in general to minimize the issues associated with over temperature testing.