Fast, Accurate, Automated Via Insertion During Design Implementation Requires Foundry Rule Compliance

As the scaling of silicon technology proceeds, via resistance is becoming a dominant factor in integrated circuit (IC) yield, performance, and reliability. At advanced nodes, interconnects and via dimensions decrease, while the number of metallization layers increases. To moderate the impact of via resistance on yield and reliability and reduce electromigration (EM) and voltage drop (IR) effects, designers typically insert additional vias during design optimization, which helps reduce the total resistance of a circuit. A part of the Calibre DesignEnhancer tool recently introduced by Siemens EDA to provide automated layout optimization during design implementation, the Calibre DesignEnhancer Via use model provides an automated via insertion process to optimize and speed up this via insertion, while ensuring that all inserted vias are compliant with design rule checking (DRC) constraints.

The Calibre DesignEnhancer Via kit guides this automated via insertion process based on foundry design rule decks, resulting in correct-by-construction solutions that guarantee inserted vias are DRC-clean. To ensure the accuracy and effectiveness of a Via kit, it must comply with the corresponding foundry rule deck being used. When a rule deck changes, the corresponding Via kit must be updated to ensure continuing compliance. An innovative automated migration methodology speeds Via kit conversions while maintaining the accurate and correct-by-construction via insertion process.

Via kit development and migration

While the Calibre DesignEnhancer Via kit separates technology rules (DRC rule deck) from the technology-independent layout modification, it must still obtain the requirements and constraints detail from the rule deck. If a design rule deck is revised, a customized rule deck is developed, or a company shifts to a different process node and corresponding rule deck, foundry and independent device manufacturer (IDM) engineers must update the Via kit to match the new requirements. However, updating a Via kit would require manually checking every via-related parameter in the Via use model against the rule deck, and modifying each one as needed, a tedious and time-consuming process. To improve ease of use, ensure consistency with all rule decks, and provide accurate and more timely updates, the Calibre DesignEnhancer Via kit incorporates an automated migration utility.

Via kit migration utility

The popularity of the Calibre DesignEnhancer Via kit has increased significantly since its introduction. However, Siemens EDA recognized that requiring design companies and foundries to manual update and maintain Via kits for an ever-increasing number of rule decks would not be a viable long-term option. Not only does it require the expenditure of time and resources that could be better utilized elsewhere, but the time needed to deliver an updated Via kit would introduce external roadblocks and delays in a design company’s tapeout schedule.

Efficiently migrating a Via kit from one technology node to another, or quickly updating the Calibre DesignEnhancer Via use model to incorporate a rule deck revision or custom rule deck, is critical for design companies. The availability of an updated Via use model enables designers to continue performing automated via insertion on a timely basis, even as they shift from one process node or one IC design to another.

The Via kit migration utility performs comparison and categorization of differences in the applicable design rules, enabling the automatic update of parameters for rules that satisfy certain criteria. The Via kit migration utility also highlights any new, missing, or unsupported rules in the rule deck comparison. This notice ensures that Via kit developers do not overlook rules that may need to be manually incorporated when updating a Via kit. While there will usually be some rules that require manual updating, the amount of manual effort and time required is significantly reduced with the Via kit migration utility.

Summary update flow

The Via kit migration process flow (figure 1) performs the following steps:

1. Extract the Via-related rules from both the base rule deck and the revised rule deck.
2. Compare corresponding rules and identify differences between the two rules:
   • Mark the difference
   • Categorize affected rules in each rule deck by metal layer and rule type
   • Save results in HTML format
3. Using the comparison results, update each changed parameter in technology files:
   • via_variable
   • enc_template
   • tcl
4. Generate the new Via use model for the revised/custom rule deck.

Fig. 1: Calibre DesignEnhancer Via kit automated migration flow.

Rule categorization

The migration utility categorizes rule comparison differences into five types, with each type receiving different handling.

1. Identical rules context with values changes
2. Subset or redundant rules
3. Rule context changes
4. Unsupported rules
5. New rule or missing rule

Results viewing

At the end of the migration utility rule comparison process, the migration developers receive a final report file in HTML format, and an updated Via kit. They must check the report file to determine if any manual rule analysis is required to complete the Via kit migration process. For example, they may need to add any new rules to the technology files, or remove rules no longer included in the revised rule deck.

Productivity improvement

Figure 2 demonstrates the results of a Via automated migration performed on a 3nm rule deck. The comparison is between a foundry rule deck and a customized version of that rule deck. Typically, this type of migration does not result in significant changes to the Via use model.

After the migration analysis of 2000+ via-related rules, 26 via-related rules were identified as having differences between the two rule decks. Developers can ignore categories 1 and 2, as the migration engine handles those changes automatically. There were no category 3 rule context changes in this conversion. Category 4 results are processed in the post-filter DRC run, as previously described. Category 5 identifies 13 new or missing rules between the two rule decks. After the automated migration analysis, kit developers only need to manually evaluate the impact of these 13 new/missing rules. In this update, the automated migration utility reduced the time spent manually comparing rule differences by at least 80%.

Fig. 2: Results from actual Via kit migration based on a 3nm rule deck.

Summary

The Calibre DesignEnhancer Via use model helps designers moderate the impact of via resistance on reliability and reduce electromigration (EM) and voltage (IR) drop effects by automatically inserting additional vias during design optimization, which helps reduce the total resistance of a circuit and improves power management earlier in the design flow. To ensure correct by construction results, the Via use model relies on a Via kit that implements foundry rule requirements for via insertions. This Via kit must be updated whenever foundry rules change.

The Calibre DesignEnhancer Via kit automated migration utility enables a significant time savings in the creation of updated Via kits, while ensuring accurate updates that maintain DRC-clean compliance for via insertions. Automated analysis of rule differences and categorization of comparison results greatly reduces the amount of manual rule analysis required, enabling faster support of new nodes and customized rule decks. A real-world conversion project resulted in an 80% decrease in the time spent by developers in manual rule comparisons and updating. With the Calibre DesignEnhancer Via kit automated migration utility, design companies and foundries can receive updated Via kits more quickly, and confidently use the updated Via use model automated via insertion on their designs.

For more information about the Calibre DesignEnhancer tool and its fill capabilities, read or download our technical paper, Calibre DesignEnhancer design-stage layout modification improves power management faster and earlier. A more detailed description of the Calibre DesignEnhancer Via kit migration utility is available in this technical paper: Calibre DesignEnhancer Via kit migration utility ensures accurate, timely updates.