Parasitic Resistor Extraction with HIPEX-R

Introduction

Layout parasitic extraction (LPE) plays an important role in post-layout verification process. Verification of the full chip layout is increasingly becoming a problem because sizes of IC layouts continue to grow due to new IC technologies. The complexity of IC design is demanding to consider the effects caused by parasitic capacitors and resistors. Parasitic devices are responsible for effects such as time delay, voltage drop, and signal integrity violation, that lead to low chip performance.

HIPEX-R is part of HIPEX software package for physical verification of multimillion transistor designs. It is a hierarchical full chip parasitic resistance extraction tool.

HIPEX-R flow is depicted on Figure 1.

 

Figure 1. Hipex-R flow.

 

HIPEX-R can read either a GDSII or SLF input design.

The rules according to which HIPEX-R will extract the parasitic resistors are set in the technology file. Note that HIPEX-R also extracts the active device defined in HIPEX-NET technology file (which is also used by HIPEX-R).

A set of options customizing the extraction is defined in the option file.

Once the extraction is done, HIPEX-R generates a hierarchical and/or flat SPICE netlist, as well as a GWL/WLDS proprietary format hierarchical netlist (used by DistRC utility for RC distribution). All the information related to the extraction is output into a summary file.

HIPEX-R also optionally generates a “stripe” database (SDB) and a resistance database (RDB), containing geometrical and electrical parasitic informations.

The SDB can be used by HIPEX-C to extract parasitic capacitors, while the RDB will be used by DistRC utility (together with the CDB produced by HIPEX-C) for RC distribution.

 

Features

HIPEX-R can extract two types of parasitic resistors: horizontal resistors and vertical (contact) resistors. It does extract these resistors on the layers specified by the user in the technology file.

The parasitic extraction is mainly based on a fragmentation algorithm that guarantees a decomposition of the parasitic layer into resistors (body and terminals) along an estimated current direction.

During the fragmentation, terminals may be created wherever there are bends (L-shapes, T-shapes, Cross-shapes) or wherever the layer to be extracted touches or overlaps another layer.

Figure 2 represents the main configurations handled by HIPEX-R fragmentation.

 

Figure 2. Hipex-R layer fragmentation configurations

 

Once the fragmentation is done, the resistor values are calculated according to user specified sheet and/or area resistivities, and the connectivity between the different resistors and the active device is then established or updated.

Finally, parasitic subnode names are assigned to the resistor terminals, and the active device terminal names are updated based on the connectivity information.

The extraction of parasitic resistors is done hierarchically, starting from the deepest substructure of the design. The hierarchical connectivity between instances of substructures in the design is updated throughout the extraction.

HIPEX-R enables you to control the output of the extraction with multiple options.

The main option are described below.

 

Fragmentation options

  • HIPEX-R enables you to specify the maximum length of a fragmented resistor body. If a resistor body is greater than this value, it will be cut into smaller pieces of length less than or equal to this value, see Figure 3
     
  • Contact oversizing and contact clustering are two other options that can be very useful to reduce the number of extracted body resistors and simplify the fragmentation, see Figure 4

 

Figure 3. Long resistor fragmentation

 

Figure 4. Contact oversizing and clustering

 

Extraction options

  • HIPEX-R enables you to specify a resistance threshold value. All parasitic resistors found with a resistance less than this threshold will be ignored while connectivity is preserved
     
  • HIPEX-R extraction can be performed either on the whole design or on a specified cell
     
  • HIPEX-R extraction can be performed on a set of selected nets. It is also possible to ignore a set of specified nets as well as dangle nets
    Output options
     
  • HIPEX-R generates the parasitic netlist in hierarchical and/or flat SPICE format, as well as in hierarchical GWL/WLDS format. Geometrical and physical information can also be outputed to the netlist, such as the coordinates of the parasitic resistors, their size and their layer
     
  • HIPEX-R can output a layout of all parasitic resistors’ geometries (body and terminals) and parasitic nodes as text elements
     
  • Finally, HIPEX-R can be used to generate the stripe database needed by capacitor extractor HIPEX-C, and the resistance database needed by DistRC utility for RC distribution

 

Conclusion

An introduction to HIPEX-R features and benefits was presented in this article. Thanks to its hierarchical architecture, this full chip parasitic resistance extraction tool provides quick and efficient algorithms able to handle large IC designs. HIPEX-R can be used as a stand-alone product or as part of the HIPEX flow.

Download pdf version of this article