Testing VCSEL Devices On-Wafer

Vertical-Cavity Surface-Emitting Lasers, or VCSELs, are seeing unparalleled demand, thanks to new uses for them in smartphone and automotive applications. 3D sensing for facial recognition is the key application in smartphones, with up to three VCSEL dies being integrated into a single phone. Emerging automotive applications such as driver monitoring, infotainment control and LiDAR will provide an additional boost to the VCSEL market and sustain its continued growth. As 3D sensing, enabled by VCSELs, continues to find new applications, the technology we use on a regular basis will become securer, safer, and smarter.

When it comes to testing VCSEL devices on wafer, however, there are multiple challenges. A major requirement is single and dual-sided testing – probing from the front or backside of the wafer. The probe system must support thin, warped wafer handling (GaAs, InP, and others, 4” and 6”). As there is no thermal chuck possible when probing both sides of the wafer, the measurement setup requires a localized cooling/heating source for accurate cool-to-hot dual sided testing. A complex test suite of measurements such as far-field, near-field and light-I-V (LIV) require multiple optics and detectors that also need multiple test setups and passes to complete the measurements. In addition, multi-side testing complicates both the probe card design and the DUT temperature control.

To manage these challenges, we’ve developed a high precision double-sided and thermally controlled probe system mainly for the VCSEL market. Triple optics, including LIV, near field and far field, can be mounted on top of the prober while probing is done from the bottom side of the wafer. The double-sided chuck design allows free access to both sides of the wafer. The wafer itself can be fixed by vacuum or mechanically clamped to allow testing up to the substrate edge.

The patented design of the thermally controlled probe unit (FireProbe) enables the test for both high and low temperature with very stable and accurate conditions. Both probe card and probe positioner types can be chosen for this new technology. Our extensive portfolio of high-performance probes suits most requirements.

We offer choices of probe systems, including:

• PA200DSP – a semi-automated double-sided probe system for R&D usage
• PA200DS BlueRay – a semi/fully automated double-sided probe system for production

Testing optical devices directly on wafer requires sophisticated automated probing solutions. FormFactor addresses these challenges with a range of dedicated manual, semi- and fully automated probe stations for high-precision single and dual sided optical on wafer measurements.