Routing is an essential step in the design of Very Large Scale Integrated (VLSI) circuits. It involves the process of connecting different electronic components in a circuit by creating a path for the electrical signals to travel from one component to another. Routing is a crucial step in the VLSI chip design process as it determines the functionality, performance, and reliability of the integrated circuit. A well-designed routing can significantly reduce the overall cost and time required for manufacturing the chip.
Detailed routing, on the other hand, involves the actual physical placement of the wires or interconnects on the chip. It is a more complex process that takes into account various factors such as signal timing, power consumption, and electromagnetic interference.
Routing in VLSI circuit design can be divided into two main categories: global routing and detailed routing. Global routing is the initial stage in which the basic routing structure of the chip is established. It involves defining the location of different functional blocks and their interconnections and determining the number of layers required to route the signals. Below are some more steps involved in how routing works in VLSI design:
Placement:
The placement step involves placing the electronic components of the circuit on the chip. During this step, the physical location of different functional blocks is determined, taking into account factors such as power consumption, signal timing, and electromagnetic interference.
Global Routing:
In this step, the basic routing structure of the chip is established. The routing tool determines the paths between different functional blocks and the number of metal layers required to route the signals.
Netlisting:
Once the placement and global routing are done, the design is not listed. This involves defining the connections between the different components in a file format that can be read by the routing tool.
Layer Assignment:
During the global routing phase, the routing tool determines the number of metal layers required to route the signals. Layer assignment involves assigning each net to a specific metal layer in the design.
Via Placement:
Vias are vertical interconnects that connect different metal layers. The routing tool places vias to connect the metal layers, taking into account various design rules and constraints.
Clock Tree Synthesis:
This is a specialized routing process that involves distributing the clock signal to all the flip-flops in the design, ensuring that the clock signal arrives at all the flip-flops at the same time. The routing tool generates a clock tree to ensure that the clock signal arrives at each flip-flop with minimal delay and skew.
Power Routing:
Power routing involves routing the power and ground signals throughout the chip, ensuring that all the components receive a clean and stable power supply. The routing tool generates power and ground grids and routes the power and ground signals to each functional block.
Detailed Routing:
This is the actual physical placement of wires or interconnects on the chip. The routing tool generates a detailed layout of the circuit, taking into account various factors such as signal timing, power consumption, and electromagnetic interference.
Design Rule Check:
The routing tool performs a design rule check (DRC) to ensure that the routing complies with the specified design rules and constraints. If any violations are found, the routing is modified accordingly.
Design Optimization:
The routing tool may perform design optimization to improve the performance and reliability of the design. This may involve adjusting the routing topology, changing the layer assignment, or modifying the clock tree.
Signal Integrity Analysis:
Once the routing is complete, the design is analyzed for signal integrity issues, such as reflections, crosstalk, and noise. The routing may need to be modified to mitigate these issues.
Post-Route Verification:
Once the routing is complete, the design is verified to ensure that it meets the specified performance and reliability criteria. This involves simulations to verify that the signal timing and power consumption meet the design requirements.
Design Closure:
Once the routing is complete, the design undergoes a design closure process, where the design is checked for compliance with the design rules, timing constraints, and power specifications. If any violations are found, the design is modified until it meets the specifications.
Tape-Out:
Once the post-route verification is complete and the design is closed, the design is taped out. This involves sending the final design data to the semiconductor foundry for manufacturing.
Design for Manufacturability (DFM) Checks:
Before tape-out, the design undergoes DFM checks to ensure that it can be manufactured with high yield and low cost. This involves checking for potential issues such as metal density, lithography, and process variations that could affect the manufacturing process.
Reticle Generation:
Once the design passes the DFM checks, the reticle is generated. The reticle is a patterned glass or quartz substrate used to project the circuit design onto the silicon wafer during the lithography process.
Lithography:
The lithography process involves using a reticle to project the circuit design onto the silicon wafer. This is a critical step in the manufacturing process as it determines the resolution and accuracy of the circuit.
Etching:
Once the circuit design is imprinted onto the silicon wafer, the etching process is used to remove the unwanted silicon material and create the actual circuit.
Metalization:
Metalization involves depositing a layer of metal on the circuit to create interconnects and wires. This is a critical step in the manufacturing process as it determines the performance and reliability of the circuit.
Dielectric Deposition:
Once the metalization is complete, the dielectric material is deposited on top of the metal layer to insulate the metal interconnects and wires.
In conclusion, routing is a critical step in the VLSI design process, where the physical interconnects between the electronic components are defined. A well-designed routing can significantly improve the performance and reliability of the integrated circuit, leading to a successful product. However, the routing process can be complex and time-consuming, requiring expertise. And experience to optimize the design for manufacturability and functionality.
Semiconductor testing companies play a crucial role in ensuring the quality and reliability of VLSI circuits. These companies provide services such as wafer sort, final test, and package test. Where the chips are tested to ensure that they meet the specified performance and reliability criteria. Testing is a critical step in the semiconductor manufacturing process, as it ensures that only functional and reliable chips are shipped to customers, reducing the cost of returns and warranty claims.
