17 June 2022
CompoundTek and STAr co-develop silicon photonics wafer testers
Singapore-based silicon photonic (SiPh) foundry services provider CompoundTek Pte Ltd and reliability test system and probe-card supplier STAr Technologies Inc of Hsinchu, Taiwan have developed a silicon photonics (SiPh) wafer test solution with automatic fiber array block edge coupling.
This should help to address the demand from SiPh product companies and manufacturers to be able to test the wafer according to how the light is coupled into the SiPh product in the end application, thus expanding the test coverage capability of the wafer test. This is possibly the only SiPh tester with the capability for edge coupling fiber arrays automatically to SiPh ICs with trench widths smaller than 100µm, with high repeatability and efficiency.
“Testing the die using vertical grating coupler will compromise the test coverage of the wafer testing, as the test condition is not the same as per what it is going to be used in the field,” notes CompoundTek’s CEO Raj Kumar. “Furthermore, designers will have to allocate space in the prime die for this vertical grating coupler and their test structure, increasing the die size as a result, while lowering gross die per wafer,” he adds.
“Skipping the wafer test totally will drive up the overall cost of products, as companies cannot identify SiPh known good dies (KGD) before assembling with other dies, resulting in overall high costs and material wastage if a defective SiPh is assembled,” Kumar continues.
SiPh is now a technology that is not only used to displace traditional electrical interconnects but also used in a broad range of applications, including light detection & ranging (LiDAR), quantum computing, and biosensing. However, the integration of optical components on a chip creates a host of new engineering and high-volume manufacturing challenges in wafer-level testing of SiPh devices as most of the products use an edge coupler to couple the light in and out of the chip. To get around the challenges of the edge coupler, most product companies either use a vertical grating coupler during wafer test or they choose to skip wafer test and only test after the SiPh test is assembled and packaged. CompoundTek and STAr enable this technology with very precise positioning of a fiber array block with accuracy and repeatability down to 0.1µm, in a narrow trench typically less than 100µm wide. The test fibers can deflect the light at about 90 degrees into the edge coupler with low optical power insertion loss and extremely low light reflection. This is enabled through patent-pending fiber alignment test kits and pattern recognition software that applies to all SiPh devices for both optical-optical and electro-optical tests.
“The jointly developed tester managed to address the technical challenges required for wafer-level efficient edge coupling testing with up to 50% reduction in setup and alignment test time while keeping test system cost as low as 40% lower than that of others available in the market,” says STAr’s CEO & founder Dr Choon Leong. “This partnership marks a new milestone for SiPh testing that successfully meets the market’s present and future needs for a reliable and cost-efficient test system for both vertical and edge coupling, especially for high-volume testing. We believe that our test solution has hit the sweet spot in terms of meeting performance and cost requirements.”
The technology shift in the form of SiPh demonstrates the potential for measurable gains in speed, power efficiency and density, says CompoundTek. The first wave of the SiPh revolution is poised to roll over data centers around the world with optical interconnects that break the barriers set by copper wire. In parallel, the development of SiPh transceivers has resulted in increased demand for cost-effective wafer test solutions, enabling the industry to improve its quality control coverage at the wafer level, potentially driving down product costs due to failures after packaging. CompoundTek has a line-up of over 20 global commercial customers alongside collaborations with more than 20 research institutes and universities in various applications such as telecommunications, automotive radar, data communications, biosensing, artificial intelligence (AI), quantum computing and smart sensors.