Semiconductor design rules are a set of guidelines that dictate how a semiconductor circuit is designed. They are used to ensure that the semiconductor is manufactured correctly and that the electrical characteristics of the circuit are as intended.
In this blog post, we’ll take a closer look at what semiconductor design rules are, and some of the most important ones to know. We’ll also discuss some tips for following them correctly. So, let’s get started!
What Are Semiconductor Design Rules (DRs)?
Design rules implemented inside a semiconductor foundry or semiconductor fabrication plant are called semiconductor design rules. Design rules for semiconductors are set parameters of geometric and connectivity restrictions to allow for significant discrepancies that could occur in the semiconductor manufacturing process. These rules ensure the designs of the relevant developers are reliable, effective, and capable of producing the desired outcome within acceptable discrepancies that don’t affect the functionality of the product.
The semiconductor process engineers who fabricate, design, analyze, and package semiconductor devices must follow these defined semiconductor manufacturing process parameters set within the design rules. This is used to create mask sets with sufficient margins for error to ensure the final product’s parts can work together effectively. These products are most semiconductor chips inside integrated circuits which can be used in many applications ranging from low-power to high-performance mobile applications and many more.
Ensuring that these design rules are being followed is done through a process called design rule checking, which we explored below.
What Is Design Rule Checking (DRC)?
Design rule checking is the process of making sure that designers do not violate the dedicated rules of design specified by the semiconductor manufacturer, to preserve the geometry and topology of the design.
Together with DRC, electronic design automation which is the semiconductor manufacturing process technology in the form of software tools, ensures sufficient margins are maintained by designers when building various components for the product. It is to be noted that design rule checking differs according to the chosen manufacturing process for the semiconductor. Below are various different DRs used in semiconductor manufacturing processes.
The Different Design Rules In A Semiconductor Manufacturing Process
Design rules for semiconductors vary extensively, ranging from layout rules for different layers to design rules for analog modules, and much more. There could be many errors that arrive out of manually fabricating semiconductor devices without a layout, where wires could be too close, and related utilities may be too far causing a final product that is not functional, especially in the long term.
The design rules can be symbolic with schematic drawings or color convention coding denoting each layer, or use stick diagrams that are both scalable or absolute since technology keeps transforming with time.
Layout Design Rules
The layout DRs are criteria that establish a step-by-step manner that must be followed to build the various masks required to fabricate integrated circuits starting from the bottommost semiconductor layer laying the foundation for the insulator and conductor layers that follow it.
Below are some of the basic layout rules needed to check and ensure the development of a working semiconductor device that will not result in chip failure unlike the lower-quality versions built without following design rules, which ultimately causes a complete waste of resources. There are more advanced rules that can support advanced planarization processes, different mobility enhancement techniques, and more.
The Three Basic Design Rule Checks
These are the first and foremost rules for single and two-layer semiconductors, followed in wafer foundries by design engineers. However, there are many more ranging from minimum area rules to antenna rules, minimum channel length rules, rules for spacing between metal lines, and much more. With layout-aware modeling, you can fabricate effective semiconductor chips for your integrated circuits and other devices built through them.
There are different types of design rule checks, but below are three basic and most common ones that designers from various industries look out for.
Width Rule
This rule refers to the minimum width for any shape used in the design. This applies to all single layers and every semiconductor manufacturing process’s layer has these rules.
Spacing Rule
This refers to the space between two objects next to each other. This design rule check, along with the width rule applies to all layers. As of 2007, the lowest layers have the smallest rule of typically 100 nm, and the highest metal layer has a larger rule ranging from 400nm.
Enclosure Rule
There are also two-layer rules. An enclosure rule is applied for different layers, where an object of one type, such as a contact or via, must be covered, by a metal layer with some additional margin. As of 2007, average enclosure rule values were around 10nm.
Topological Design Rules
These design rules ensure sufficient margins are maintained in front-end-of-line (FOEL) and back-end-of-line (BOEL) topologies in design. What this means is that the first stage of fabrication which is FOEL interconnects through transistors, capacitors, and other components to the metal conductive layer.
Topological design rules are clear instructions on how to layer and interconnect the semiconductors to the wireless transistors and then further to the contacts, interconnected wires, etc. in the BOEL fabrication phase. Designers must follow these topology design rules to ensure the final product works without faulty processes due to inconsistent fabrication.
Coverage Rules and Insertion Utilities
The demand for increased density and improved performance for planarity procedures has presented a surplus in coverage and insertion requirements. As a result, the foundry developed and provided new definitions of the layout coverage rules to designers. To support high-k/metal gate patterning and process integration, technological improvements consider both the worldwide and regional coverage of the front-end-of-line (FEOL) dielectric layers, to the back-end-of-line (BEOL) Cu layers and Al layers.
In order to meet coverage limits for automation and related modeling, integrated circuit (IC) manufacturers developed a new set of rules for dummy feature insertion, along with fill insertion, cell insertion, and other techniques. Together coverage rules and insertion utilities support the chemical mechanical polishing (CMP) process which has a high coverage dependency.
Following these design rules are essential in the development of semiconductor devices for ICs, and other applications while keeping up with the highly-demanding technological requirements.
More Design Rules
There are many other design rules ranging from analog modules to memory modules, reliability-driven rules, stress-related layout design rules, and many more. There are many different processes used to design, analyze and fabricate semiconductor devices, and each process has its own set of design rules and diverse design rule-checking methods too,
Resources To Learn More About Design Rules For Semiconductors
If you’re interested in learning more about this in detail, a highly recommended purchase would be the book, Design Rules in a Semiconductor Foundry which offers a foundry-integrated perspective. It comprises chapters carefully selected to cover topics relevant to every aspect of design rules inside a semiconductor foundry and its applications. It also lists specified regulations for static random-access memory (SRAM), embedded poly fuse (ePF), and more in relation to layout DRs.
Driving Quality Production With Semiconductor Design Rules
Semiconductor design rules are a set of guidelines that need to be followed in order to produce a quality semiconductor that can work in collaboration with the other interconnected layers and components. By driving adherence to these rules, manufacturers can ensure that their products are free from errors and meet customer demands.
These design rules guide the pathway for checking manufacturing processes to check for rule compliance and correct any issues before they become irreparable problems. In addition, understanding the different types of design rules will help you create better-quality products with fewer defects to ensure engineers, the foundries, and customers are investing in profitable resources.
FAQs
DRC means design rule checking, which is the process of ensuring that semiconductor fabrication is done within set parameters. This ensures that no damage or circuit failure takes place later on.
Automotive qualification is ensuring semiconductor devices in the automotive industry are up to standard to be used. Semiconductor fabrication should have followed the relevant industry-specific design rules for automobiles.
