Physical verification

Last updated February 25, 2024

Physical verification is a process whereby an integrated circuit layout (IC layout) design is verified via EDA software tools to ensure correct electrical and logical functionality and manufacturability. Verification involves design rule check (DRC), layout versus schematic (LVS), XOR (exclusive OR), antenna checks and electrical rule check (ERC).^[1]

Design Rule Check (DRC)

DRC verifies that the layout meets all technology-imposed constraints. DRC also verifies layer density for chemical-mechanical polishing (CMP).^[1]

Layout Versus Schematic (LVS)

LVS verifies the functionality of the design. From the layout, a netlist is derived and compared with the original netlist produced from logic synthesis or circuit design.^[1]

XOR check

This check is typically run after a metal spin, where the original and modified database are compared. This is done to confirm that the desired modifications have been made and no undesired modifications have been made by accident. This step involves comparing the two layout databases/GDS by XOR operation of the layout geometries. This check results a database which has all the mismatching geometries in both the layouts.

Antenna check

The antenna basically is a metal interconnect, i.e., a conductor like polysilicon or metal, that is not electrically connected to silicon or grounded, during the processing steps of the wafer.^[1] During the manufacturing process charge accumulation can occur on the antenna during certain fabrication steps like Plasma etching, which uses highly ionized matter to etch. If the connection to silicon does not exist, charges may build up on the interconnect to the point at which rapid discharge does take place and permanent physical damage results to thin transistor gate oxide. This rapid and destructive phenomenon is known as the antenna effect. Antenna errors can be cured by adding a small antenna diode to safely discharge the node or splitting the antenna by routing up to another metal layer and then down again.^[1]

The antenna ratio is defined as the ratio between the physical area of the conductors making up the antenna to the total gate oxide area to which the antenna is electrically connected.

Electrical Rule Check (ERC)

ERC verifies the correctness of power and ground connections, and that signal transition times (slew), capacitive loads and fanouts are appropriately bounded.^[1] This might include checking for

Well and substrate areas for proper contacts and spacings thereby ensuring correct power and ground connections
Unconnected inputs or shorted outputs.

Gates should not connect directly to supplies; connection should be through TIE high/low cells only. ERC checks are based upon assumptions about the normal operating conditions of the ASIC, so they may give many false warning on ASICs with multiple or negative supplies. They can also check for structures susceptible to electrostatic discharge (ESD) damage.

Related Research Articles

An integrated circuit, also known as a microchip or IC, is a small electronic device made up of multiple interconnected electronic components such as transistors, resistors, and capacitors. These components are etched onto a small piece of semiconductor material, usually silicon. Integrated circuits are used in a wide range of electronic devices, including computers, smartphones, and televisions, to perform various functions such as processing and storing information. They have greatly impacted the field of electronics by enabling device miniaturization and enhanced functionality.

<span class="mw-page-title-main">Very Large Scale Integration</span> Creating an integrated circuit by combining many transistors into a single chip

Very-large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining millions or billions of MOS transistors onto a single chip. VLSI began in the 1970s when MOS integrated circuit chips were developed and then widely adopted, enabling complex semiconductor and telecommunication technologies. The microprocessor and memory chips are VLSI devices.

An application-specific integrated circuit is an integrated circuit (IC) chip customized for a particular use, rather than intended for general-purpose use, such as a chip designed to run in a digital voice recorder or a high-efficiency video codec. Application-specific standard product chips are intermediate between ASICs and industry standard integrated circuits like the 7400 series or the 4000 series. ASIC chips are typically fabricated using metal–oxide–semiconductor (MOS) technology, as MOS integrated circuit chips.

Electronic design automation (EDA), also referred to as electronic computer-aided design (ECAD), is a category of software tools for designing electronic systems such as integrated circuits and printed circuit boards. The tools work together in a design flow that chip designers use to design and analyze entire semiconductor chips. Since a modern semiconductor chip can have billions of components, EDA tools are essential for their design; this article in particular describes EDA specifically with respect to integrated circuits (ICs).

<span class="mw-page-title-main">Integrated circuit layout</span> Representation of an integrated circuits components as planar shapes

In integrated circuit design, integrated circuit (IC) layout, also known IC mask layout or mask design, is the representation of an integrated circuit in terms of planar geometric shapes which correspond to the patterns of metal, oxide, or semiconductor layers that make up the components of the integrated circuit. Originally the overall process was called tapeout, as historically early ICs used graphical black crepe tape on mylar media for photo imaging.

Place and route is a stage in the design of printed circuit boards, integrated circuits, and field-programmable gate arrays. As implied by the name, it is composed of two steps, placement and routing. The first step, placement, involves deciding where to place all electronic components, circuitry, and logic elements in a generally limited amount of space. This is followed by routing, which decides the exact design of all the wires needed to connect the placed components. This step must implement all the desired connections while following the rules and limitations of the manufacturing process.

In electronic design automation, a design rule is a geometric constraint imposed on circuit board, semiconductor device, and integrated circuit (IC) designers to ensure their designs function properly, reliably, and can be produced with acceptable yield. Design rules for production are developed by process engineers based on the capability of their processes to realize design intent. Electronic design automation is used extensively to ensure that designers do not violate design rules; a process called design rule checking (DRC). DRC is a major step during physical verification signoff on the design, which also involves LVS checks, XOR checks, ERC, and antenna checks. The importance of design rules and DRC is greatest for ICs, which have micro- or nano-scale geometries; for advanced processes, some fabs also insist upon the use of more restricted rules to improve yield.

VLSI Technology, Inc., was an American company that designed and manufactured custom and semi-custom integrated circuits (ICs). The company was based in Silicon Valley, with headquarters at 1109 McKay Drive in San Jose. Along with LSI Logic, VLSI Technology defined the leading edge of the application-specific integrated circuit (ASIC) business, which accelerated the push of powerful embedded systems into affordable products.

In electronic design, a semiconductor intellectual property core, IP core or IP block is a reusable unit of logic, cell, or integrated circuit layout design that is the intellectual property of one party. IP cores can be licensed to another party or owned and used by a single party. The term comes from the licensing of the patent or source code copyright that exists in the design. Designers of system on chip (SoC), application-specific integrated circuits (ASIC) and systems of field-programmable gate array (FPGA) logic can use IP cores as building blocks.

In semiconductor design, standard-cell methodology is a method of designing application-specific integrated circuits (ASICs) with mostly digital-logic features. Standard-cell methodology is an example of design abstraction, whereby a low-level very-large-scale integration (VLSI) layout is encapsulated into an abstract logic representation.

While the term front end of line (FEOL) refers to the first portion of any IC fabrication where the individual devices are patterned in the semiconductor, back end of line (BEOL) comprises the subsequent deposition of metal interconnect layers. Thus, BEOL is the second portion of IC fabrication process where the individual devices get interconnected with wiring by deposited metalization layers.

<span class="mw-page-title-main">Integrated circuit design</span> Engineering process for electronic hardware

Integrated circuit design, or IC design, is a sub-field of electronics engineering, encompassing the particular logic and circuit design techniques required to design integrated circuits, or ICs. ICs consist of miniaturized electronic components built into an electrical network on a monolithic semiconductor substrate by photolithography.

Placement is an essential step in electronic design automation — the portion of the physical design flow that assigns exact locations for various circuit components within the chip's core area. An inferior placement assignment will not only affect the chip's performance but might also make it non-manufacturable by producing excessive wire-length, which is beyond available routing resources. Consequently, a placer must perform the assignment while optimizing a number of objectives to ensure that a circuit meets its performance demands. Together, the placement and routing steps of IC design are known as place and route.

Design Closure is a part of the digital electronic design automation workflow by which an integrated circuit design is modified from its initial description to meet a growing list of design constraints and objectives.

The Layout Versus Schematic (LVS) is the class of electronic design automation (EDA) verification software that determines whether a particular integrated circuit layout corresponds to the original schematic or circuit diagram of the design.

An Integrated circuit layout editor or IC layout editor is an electronic design automation software tool that allows a user to digitize the shapes and patterns that form an integrated circuit. Typically the view will include the components, metal routing tracks, vias and electrical pins. Software of this type is similar to computer aided drafting software, but is specialized for the task of integrated circuit layout. The typical flow for the layout of analog circuits might be :

<span class="mw-page-title-main">Physical design (electronics)</span>

In integrated circuit design, physical design is a step in the standard design cycle which follows after the circuit design. At this step, circuit representations of the components of the design are converted into geometric representations of shapes which, when manufactured in the corresponding layers of materials, will ensure the required functioning of the components. This geometric representation is called integrated circuit layout. This step is usually split into several sub-steps, which include both design and verification and validation of the layout.

<span class="mw-page-title-main">Floorplan (microelectronics)</span> Layout of major electronic circuit blocks

In electronic design automation, a floorplan of an integrated circuit is a schematic representation of tentative placement of its major functional blocks.

In the automated design of integrated circuits, signoff checks is the collective name given to a series of verification steps that the design must pass before it can be taped out. This implies an iterative process involving incremental fixes across the board using one or more check types, and then retesting the design. There are two types of sign-off's: front-end sign-off and back-end sign-off. After back-end sign-off, the chip goes to fabrication. After listing out all the features in the specification, the verification engineer will write coverage for those features to identify bugs, and send back the RTL design to the designer. Bugs, or defects, can include issues like missing features, errors in design, etc. When the coverage reaches a maximum percentage then the verification team will sign it off. By using a methodology like UVM, OVM, or VMM, the verification team develops a reusable environment. Nowadays, UVM is more popular than others.

In integrated circuits (ICs), interconnects are structures that connect two or more circuit elements together electrically. The design and layout of interconnects on an IC is vital to its proper function, performance, power efficiency, reliability, and fabrication yield. The material interconnects are made from depends on many factors. Chemical and mechanical compatibility with the semiconductor substrate and the dielectric between the levels of interconnect is necessary, otherwise barrier layers are needed. Suitability for fabrication is also required; some chemistries and processes prevent the integration of materials and unit processes into a larger technology (recipe) for IC fabrication. In fabrication, interconnects are formed during the back-end-of-line after the fabrication of the transistors on the substrate.

References

1 2 3 4 5 6 A. Kahng, et al.: VLSI Physical Design: From Graph Partitioning to Timing Closure, ISBN 978-3-030-96414-6, doi : 10.1007/978-3-030-96415-3, p. 9.