26. Januar 2021, 15:30 Uhr | Ralf Higgelke
Agnes Jahnke is Product Marketing Manager SiC and GaN at X-Fab Semiconductor Foundries.
For gallium nitride, there is already a properly working foundry business, but not for silicon carbide. Agnes Jahnke, Product Marketing Manager SiC and GaN at X-Fab Semiconductor Foundries, disclosed to DESIGN&ELEKTRONIK which challenges and opportunities exist when processing SiC in a foundry.
DESIGN&ELEKTRONIK: Mrs. Jahnke, how did X-Fab actually get into the foundry business for silicon carbide?
Agnes Jahnke: X-Fab is a foundry group for analog and mixed-signal semiconductor technologies. We offer CMOS and SOI-on-silicon based technologies from 1.0 micron down to 0.13 micron. Our offering is complemented by MEMS and wide bandgap processes. Silicon carbide is currently processed only in Lubbock, Texas, at our 6-inch facility, which we purchased from Texas Instruments in 1999, originally to run normal CMOS processes.
In 2013, we started with the idea of processing SiC wafers on the same production line as silicon wafers. However, we soon realized that simply retooling the equipment was not enough. Therefore, over time, we have continued to add new dedicated SiC machinery to the production line. Most of these are capable to process 8-inch wafers. Today, X-Fab has the world's largest pure-play foundry for silicon carbide. We are constantly increasing our volumes in this sector and could actually use the entire fab capacity in Lubbock for silicon carbide. We have added all the necessary equipment to manufacture high quality diodes, JFETs and MOSFETs. Recently, we started up our own epi reactor for high quality SiC wafers.
Does the foundry business model work the same way for SiC as it does for silicon?
Agnes Jahnke: There are several differences indeed. Usually, silicon foundries develop open technology platforms for wafer processing. Customers can create their IC design using a so-called process development kit and well-known software tools such as those from Cadence or Mentor. The foundry is responsible for developing the semiconductor manufacturing process and fabricating the wafer. In the end, this is an extremely scalable business model.
However, some partners want to implement not only their own design but also their own process IP and use the foundry solely as a manufacturing site – the so-called "copy exact" approach. We used this business model in the early years with silicon carbide as well, but with each customer and our own R&D learning cycles, we started to see similar best practice processes for the same devices. Therefore, we decided to develop standard processes for common manufacturing steps, called Standard Process Blocks. As a result, less experienced customers can now start a process development with silicon carbide by bringing their process architecture, design and specific implantation plan. Alternatively, customers can purchase SiC design or process IP from our partners.
Please tell us more about the standard process blocks.
Agnes Jahnke: A standard process block is a set of process steps for a specific part of the overall process, which summarizes all necessary steps for a layer within the process flow. Examples are the formation of the gate connection or the ohmic contacts. A standard process block includes three elements. First, it includes block routing specifications and routing spec values. This is a description of the necessary process steps and the sequence - called routing- that define the corresponding process step, such as a gate formation. Second, a standard process block includes specifications for building blocks that prescribe the outcome of the process. And third, test structures and methods are needed for quality control within and outside the manufacturing line, which are part of the test plan.
So, the customer comes to X-Fab and asks for a process with a characteristic flow. We have put together a so-called onboarding team that reviews the requirements and aligns them with the standard process blocks that we have already developed. We provide the customer with a Process Installation Kit that contains all the necessary information so that a tape-out can take place. The onboarding team then proposes a process flow to the customer based on our standard process blocks. In some cases, a new block needs to be developed or some blocks need to be modified. Especially the implantation plan is very critical for the device properties and belongs to the customer therefore. The onboarding team then helps to implement the customer's own process as a copy exactly into the process flow. In a few cases, it may also be necessary to insert a new machine.
Standard process blocks thus help the customer to set up a process more quickly that best fits the capabilities of the manufacturing equipment in the foundry.