FormFactor
Devices in the consumer, infrastructure and defense markets, are going higher and higher in frequency. This includes devices such as 5G (28-40 GHz), automotive radar (77 GHz) and Vehicle to Everything, as well as next generation Wi-Fi (60 GHz). These higher frequencies make it more challenging to design, fabricate and test these new RF devices. IC designers use PDKs (process design kits), which, to reduce design cycles, must be modeled and characterized very precisely – not only at the operating frequency of the circuit, but way beyond and over a very broad band. Typically, 40 GHz 5G devices would use transistors characterized up to 120 GHz with no room for error in a transistor model. Considering the latest generation processors contain billions of transistors, small errors accumulate, meaning the IC will not perform as intended, and a new design iteration is required. Ultimately the more accurate the PDKs, the higher the success rate of IC designs and faster time to market.
Accurate measurements in the engineering lab start with the best instrumentation, RF wafer probes, proven and traceable calibration standards and a repeatable calibration algorithm. However, over time and process variations and under different conditions such as bias and temperature, large volumes of measurements need to be taken from many thousands of devices. This characterization process is extremely time consuming and requires skilled engineers to operate.
One new productivity technology recently introduced allows engineers to measure more devices, and ensures known accuracy of the measurements, leading to better quality PDK’s and faster time to market. This new technology is the Autonomous RF Measurement Assistant (AutoRF, see Figure 4).
Figure 4. Autonomous RF Measurement Assistant prober.
With AutoRF operators can make measurements 24 hours a day, seven days a week, even when measuring thousands of transistors, on up to 50 wafers at a time and over multiple temperatures. The test cell can be left running with confidence unattended overnight and weekends. AutoRF will constantly monitor calibration accuracy, and automatically re-calibrate when the error exceeds a defined limit. It also re-calibrates when changing test temperature, corrects for any thermal errors introduced, and automatically aligns the probe to the pads during each touch down. This ensures confidence that measurement accuracy is always within a known limit and removes measurement uncertainty. This new technology is fully autonomous and can controlled and monitored remotely, something that is important to all of us during these challenging times of social distancing.
In production RF wafer test, the development and rollout of 5G is driving most of the growth in RF test in semiconductor with high volume manufacturing requirements for fast, and cost effective, throughput. The carrier aggregation, as well as higher density MIMO and the addition of 20+ GHz bands, are the primary drivers leading to a five times increase in the number of RF analog semiconductor devices (handset and base station).
FormFactor has a few wafer probing technologies for production test. This includes our flagship Pyramid Probe (see Figure 5) that has been used in wafer test for many years in both RF Front End Devices (< 5 GHz filters, switches, power amplifiers), high speed devices including high speed digital components for infrastructure, and coming to automotive radar devices that operate up to 81 GHz. Pyramid Probe has been shown in test to be fully capable of volume production support to the largest semiconductor manufacturers, with capability to multi-site probing with full RF calibration for the most accurate measurements for wafer sort.
In addition, FormFactor has been developing the Pyrana technology for even higher multi-site capability with RF performance for 5G devices (see Figure 6). It is using vertical MEMS contactors that provide mechanical robustness and repairability that customers require, as well as good signal integrity out to 10 GHz. FormFactor has also been working to release a new implementation of Pyrana, called ePyrana, that will be able to support test up to 45 GHz bandwidth for 5G device. This new product will be released in the second half of 2020..
Keysight Technologies
mmWave semiconductor testing is a key part of the Keysight offering since the 1997 with the launch of the 8510XF Network Analyzer. This system has been designed to make fully calibrated, single-sweep measurements of broadband devices to 110 GHz, in 1.0 mm coax. The 1.0 mm connector was used to carry the signal to the DUT without the limitation of the waveguide transmission lines, previously used at this very high frequency. Cascade Microtech (now FormFactor) designed a wafer probe station and probes for the first time enabling the possibility to perform fully calibrated on wafer measurement with a single touchdown. This solution marks the start of a successful collaboration between the two companies that, during the last three decades, jointly launched several solutions, always with the objective to collaborate and maximize knowledge and competence. Today, the wafer level measurement solution is a clear example of this synergy. With guaranteed system configuration, integration and support, a wafer level measurement solution from Keysight Technologies and FormFactor provides accurate and repeatable testing, minimizing the time to first measurement, while enabling data correlation between multiple locations.
A typical configuration will include instruments from Keysight such as a PNA or PNA-X network analyzer, a B1500A Semiconductor Device Parameter Analyzer, and a N6705C DC power analyzer together with Keysight’s WaferPro Express (WaferPro-XP) measurement software platform. This is integrated with a FormFactor semi-automated wafer probe station, WinCal XE calibration software and Impedance Standard Substrates for calibration. The N5291A 900 Hz to 120 GHz PNA system is the instrument of choice for this solution (see Figure 7). This powerful single-sweep solution with compact frequency extenders deliver very accurate and stable measurements fully traceable at the probe tips, making this solution unique in the market. Two and four ports configuration are available to test the most challenging devices.
Figure 7. Keysight N5291A Broadband Network Analyzer.
Integrated Photonic Test is another important area where Keysight and FormFactor are joining forces. Integrated Photonics, often called Silicon Photonics, promises additional benefits for industrial segments such as intra data center communication and data center interconnects (DCI), Telecom, 5G and automotive connectivity, high-performance computing, LIDAR, sensing and medical. The joint solution includes: Keysight's N4372E 110 GHz Lightwave Component Analyzer, shown in Figure 8, that delivers unprecedented bandwidth for both optical receiver testing and optical transmitter testing with guaranteed specifications for electro-optical S-parameter measurements for device traceability.
Figure 8. Keysight N4372E 110 GHz Lightwave Component Analyzer.
The FormFactor CM300xi-SiPh, with automated wafer level photonics positioning combined with Keysight's industry standard IL/PDL engines and N7700C Photonics Application Suite (PAS), to support wavelength repeatability of ±1.5 pm at two-way sweeps up to 200 nm/s within 1,240 to 1650 nm to ensure accuracy and repeatability from O- to L-band.
The KS8400A Keysight Test Automation Platform (TAP) allows fast execution, test flow visualization, analysis and insights. Keysight Test Automation on PathWave (TAP) is a modern Microsoft .NET-based application that can be used standalone or in combination with higher level test executive software environments. Instrument plugins provide test steps that can be added to work-flow sequences without needing to use instrument level programming commands. The N4370P01A LCA TAP Plug-In steps further simplify the Electrical/Optical (E/O) and Optical/Electrical (O/E) measurements by handling the interface to both the PNA instrument and the LCA optical hardware and software. The PNA settings needed for LCA measurements are provided in the test steps for easy configuration. To ensure ease of use, the FormFactor's SiPh software enables automated calibrations and alignments and simplifies integration with Keysight's PathWave software platform, as well as optical instrumentation.
