Physical Analysis of Semiconductor Wafers

Controlling process steps and analyzing physical structures of the semiconductor wafer employs various high resolution optical / electron / ion microscopes and specific spectrometers / diffractometers. Table 1 lists many of these technologies, while Table 2 illustrates their use in semiconductor fabrication.

Today’s wafer fabrication must deal with shrinking geometries, new materials, and novel architectures, critical device structures are simply too small to see or characterize with existing tools. As the device dimensions shrink, the requirements for image resolution and detector sensitivity become more stringent too: to visualize transistor structures in a < 10nm device, microscopes are required to have a resolution in the Angstrom range and, as the detectable signals coming from the extremely small probed volumes (< 0.001 um3) are very weak, signal detectors and read-out electronics are required to be highly sensitive and noise-free.

Thermo Fisher Scientific offers a wide range of electron and ion microscopes and other analytical instruments for wafer analysis at different stages of the industry cycles, i.e., during pathfinding and process development or during yield ramp and manufacturing.

During pathfinding and process development phases, technologists and designers push the boundaries of physics while engineering new devices at the atomic level. Thermo Fisher Scientific provides the most advanced toolsets that enable this advanced R&D to continue on the 10, 7 and even the sub-7nm technology nodes.

During the yield ramp phase it is crucial to accelerate yield learning as time to market is the key to commercial success of the new generation devices. Yield analysis at many of the steps in the manufacture of a semiconductor device used to be done with optical or SEM based tool sets, but is becoming increasingly dependent on TEM microscopy results. Thermo Fisher Scientific is enabling this transition from SEM to TEM with new high productivity tool workflows that combine highest performance with lowest cost per TEM sample.

Once the new technology has been developed and systematic process defects are eliminated during the yield ramp, high volume manufacturing requires a very precise and effective control of the critical and often marginal processes to maintain yield at economically sustainable levels. Thermo Fisher Scientific develops and proposes dedicated workflow solutions which enable high performance characterization of yield excursions in shortest time and in unprecedented volumes.

In addition to these analytical solutions for wafer analysis during the manufacturing process, Thermo Fisher Scientific product lines also include products that specifically serve Electrical Debug after Electrical wafer test or after packaged device test: Electrically failing devices need to be inspected and a root cause for the electrical failure needs to be found to be able to correct imperfections in the manufacturing process or in the electrical design. Electrical Failure Analysis consists of two vital steps, the first is to detect the physical location of the electrically defective nets in the device (fault isolation) and the second is to physically inspect that physical location on any physical or chemical device anomalies (fault identification). Fault Isolation methods are based on time modulated excitation of the device and measurement of the (also time modulated) signals emitted by the device. The device excitation can be physical (laser, heat) or electrical (electrical test vectors) and the device response can be physical or electrical as well. Lock In Thermography (LIT) is the technique where the device is uniformly heated by heat pulses of a given frequency and the local temperature response of the device is measured by a sensitive IR camera. OBIRCH (Optical Beam Induced Resistance Change) is a technique where an electrically powered device is locally heated by a pulsed laser and the response to this local heating is measured as a change in the electrical resistance of the device. In Emission Microscopy (EMMI) the device is electrically stimulated with dynamic signals by which transistors switch between on and off states and emit light. The emitted light is detected with ultrasensitive cameras with picosecond resolution. Nanoprobers, finally, can be used to contact and electrically test individual transistors in a pre-determined localized region. Nanoprobers are either SEM or AFM based.