VLSI design: Fab your semiconductor chip virtually

Date: 24/06/2015
In semiconductor chip fabrication, up to 90 nm node, the challenge was more of printing smallest patterns on photoresist material to carry out successful lithography of a planar silicon wafer/disk. In this era of 14 nm and lesser node chip fabrication, it was more of a material and structural changes including three-dimensional transistors. As the structural and material complexity enters down the 14nm node, semiconductor and nanotechnology researchers while developing new ideas, they don't really need to fabricate a real device, instead they can use virtual fabrication tool/software, basically computer simulated structural/behavioral simulation of their new ideas/development. VLSI design is already driven by heavy use of software tools from concept to production, but they are dependent on chip-fabs to make the real sample chip, now that can be done virtually in your computer.

From three-dimensional finFETs, silicon photonics, mems to three-dimensional memory stacking, Virtual fabrication environment saves semiconductor designers time and money in fabricating the real device. Virtual fabrication is extremely relevant for more than Moore technology such as system on module (SOM), system in package (SIP), 3D IC kind of single device non-monolithic assembly of subsystems. Same technology can also be used for designing highly compact printed circuit board such as smart phones.

The nanotechnology simulation tools take into consideration the atomic level properties of the material used. Fujitsu Laboratories has successfully simulated the electrical properties of a 3,000-atom nano device, which Fujitsu claims a threefold increase over previous efforts using a supercomputer.

The two popular electronic design automation software companies in this domain are Silvaco and Coventor.
The product called SEMulator3D from Coventor provides features such as model calibration and verification, Predictive modeling of source/drain embedded epitaxy.
Coventor explains "SEMulator3D is predictive tool for process integration that can replace costly and time-consuming cycles of silicon learning during the integration and yield-ramp phases of FinFET FEoL technology development".

Coventor has published multiple number of white papers with titles "3D NAND Flash Processing", "MEMS Devices Virtual Metrology & DRIE", "BEOL Metallization", " Front end of line (FEOL) Process Integration", "back end of line (BEOL) Virtual Patterning" which can be downloaded from its web page at URL:

The other interesting company Silvaco has started in year 1984 with basically a product to do parameter extraction, device characterization and modeling. It is now the leading supplier of Technology Computer Aided Design (TCAD) for nanotechnology fabrication design along with its range of other VLSI design EDA software packages.

Silvaco offers products both for process simulation and device simulation and also a virtual wafer fab product. Silvaco's "Victory 3D" device simulator performs DC, AC, and transient analysis for silicon, binary, ternary, and quaternary material-based devices. Athena, the process simulator product from Silvaco helps in virtually conduct experiments in semiconductor fabs at a cost and speed better than the real semiconductor fabs.

Another product named "Device 3D" can be used to analyse DC, AC and time domain characteristics of a wide variety of silicon, complex compound semiconductor devices such as SiGe, GaAs, AlGaAs, InP, SiC, GaN, AlGaN and InGaN and characterizes physics-based devices for electrical, optical, and thermal performance without costly split-lot experiments.

Virtual Wafer Fab (VWF) does advanced analysis tasks like Design of Experiments (DOE) or Optimization, using any of the Silvaco simulators. The value addition is in solving semiconductor fab yield and process variation problems.

All this points to, VLSI design is becoming more of graphics driven supercomputing enabled complex image processing from the simple HDL coding.

This concept is not specific to electronics, it is also used in mechanical engineering to design complex mechanical systems such as aircrafts, automobiles, precision manufacturing including semiconductor equipments. When the computer models of each mechanical components are used to simulate assembly process of the subsystem such as engine. The computer models of each component can feature a set of specifications and it can tell the assembly line engineer, how the one component specs connect to other component specs when both are assembled together and also can generate a new set of specifications of the combined unit.

Fujitsu's Virtual Product Simulator for 3D modeling performs design analysis (manufacturability) using 3D data on full-assembly models to ensure there is no component interference in the assembly process, and VPS GP4 (Global Protocol for Manufacturing), which enables production-line simulations.

A more or less similar concept is used in case of virtual semiconductor fabrication environment where the various specifications parameters of each nano device is created. When such nano devices are integrated together the Virtual fabrication tool can tell the engineer the issues which may crop up when they're really integrated.

The process of a complete chip fabrication can be simulated with the availability of various soft models of some components such as finFETs. 3D data associated with each component need to cover design analysis, production-line layout, and process simulations, and volume manufacturing needs.

But to handle virtual fabrication software, you may need supercomputer kind of systems with high MIPS rating to handle a rich graphics and three-dimensional data.

Author: Srinivasa Reddy N
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