If you're planning a 40nm or 28nm design with TSMC, you have two options for meeting design for manufacturability (DFM) requirements -- either buy EDA tools and run DFM checks, or turn to a services provider to run them for you. On May 9, Cadence became the first EDA partner to be certified by TSMC for DFM services, including lithography process checks (LPC) and chemical mechanical polishing (CMP) checks. Here's some background on how that happened and what that means.
As I wrote in an Industry Insights blog post at the time, in 2009 TSMC mandated model-based DFM checks for LPC and CMP at 45/40nm. While TSMC had mandated rules-based checks at previous process nodes, this was their first mandate for model-based DFM, which relies on modeling and simulation rather than conformance to design rules. A TSMC executive said at the time that "rules are getting so complex that there is no way the customer can use a complete rule-based solution."
TSMC provided two options for meeting the model-based DFM mandates. First, customers could use commercial tools such as the Cadence Litho Physical Analyzer and Cadence CMP Predictor. Secondly, they could use TSMC's on-line DFM service. At the time TSMC expected that the services option would primarily appeal to smaller companies who didn't want to make a big investment in tools.
New Process Node, New Approaches
Fast forward to 2011, where design teams are targeting both 40nm and 28nm. CMP simulation is now recommended at 40nm and mandatory at 28nm, while LPC remains mandatory for both. Meanwhile, model-based DFM consumes far more resources at 28nm. For example, it takes significantly longer to run LPC checks at 28nm than it does at 40nm. Given the compute resource requirements, even some larger companies who have their own tools are now interested in DFM services for full chip signoff.
TSMC decided to rely on its partners to provide DFM services, and Cadence was more than ready. "We ramped up very fast," said Manoj Chacko, product marketing director at Cadence. He noted that Cadence has a large compute infrastructure in its secure VCAD (Virtual Integrated CAD) chambers, which basically provide a private cloud computing resource that is scalable to a large number of CPUs. Cadence also has DFM expertise available on a worldwide basis, and has tools such as the TSMC-qualified Litho Physical Analyzer and Cadence CMP Predictor.
In brief, Cadence provides two DFM services - model-based lithography process checks, and CMP hotspot analysis. The goal is to help design teams fix lithography or CMP "hot spots" (yield detractors) prior to tapeout. "If we can identify systematic problems in the layout, that is where DFM checks come in," Manoj said. "We want to run [checks] early on and fix them in the implementation flow."
Turnaround Time and Data Security
How do the DFM services work? The customer ships Cadence DFM Services a GDSII or OASIS file, and Cadence personnel run the DFM checks using the secure infrastructure. TSMC jointly reviews and validates the report. Then the report is provided to the customer, along with layout fixing guidelines. Manoj said the turnaround time will typically be about two days for small designs and varies depending on the size of the design. After the chip has been checked initially, Cadence DFM Services re-checks the design using smart hierarchical technology, and these incremental checks can run in a few hours.
Customers don't have to use Cadence layout tools to use the DFM services, but those who have Virtuoso 6.1.5 can take advantage of the automatic fixing capability available with that product release. Automatic fixing is also available with the Encounter Digital Implementation System.
Of course, data security is a big concern whenever data is shipped outside a company firewall. Cadence provides a kit that allows customers to encrypt their data, which is decrypted after it arrives at the Cadence VCAD chamber. Only a select number of people from Cadence and TSMC have physical access to the secure environment. CPUs used for DFM services are scalable based on need and are dedicated to DFM.
Into the Cloud?
The TSMC-certified Cadence DFM Services represents a careful step into a cloud computing environment, albeit a private cloud at present. As DFM compute resource needs become even more intense at 20nm and below, DFM services in public or private clouds may become a good alternative, or a complement, to using tools in one's own environment.
Further information is available at the new DFM Services site or by contacting email@example.com.