VARMA - Variability Modelling and Analysis Tool

Lead Research Organisation: Newcastle University
Department Name: Electrical, Electronic & Computer Eng


VARMA(Variability Modelling and Analysis) tool is under development as a user friendly tool which interfaces standard Process/Device simulators and Circuit simulators allowing the identification of process variations which will have most effect on device and circuit performance and their subsequent assimilation into circuit design stages. VARMA thus bridges the gap between design and technology. The rationale for its development is summarised below.To satisfy market demands, chip complexity is not only increasing from the aspect of the designer but also for fabrication. It is estimated that with current technologies the fabrication process requires in excess of 34 masks, 500 processing steps and over 600 hundred design rules, with an average, overall, design cost of $30M, with mask costs increasing by 50% with each advance to the next technology node. Furthermore, it is considered that for a new product the possibility for a re-spin is 50-80% introducing a 12-16 week delay in the product reaching the market place. Consequently first spin success is crucial in a market place where a product is considered to be old within a year and market profile over time looks more like an impulse function. However, it is considered that with sub 65nm technologies at least one design re-spin will be required before an acceptable manufacturing yield is obtained. In the past the main reasons for a design re-spin were functional design errors; although these have not been eliminated the major cause is now due to the effects of process variations. With the rapid changes in today's technologies, in order for products to compete in the market place, there are few opportunities to analyse the fabrication process to evolve a solution. Consequently, when there is a degree of uncertainty in the fabrication process the potential effects of fluctuations implicitly impact not only on the device manufacturability, yield and reliability but also on design 'aggressiveness' which affects device performance and subsequently the profitability of the product.As a result of both the complexity of present day design and the fabrication process, combating the effects of process variability can no longer be left to the semiconductor technologists to alleviate the problems by introducing a few 'tweaks' into the process as there are now too many variables to be considered. Consequently there is a need for a tool which bridges the gap between design and technology. The VARMA tool flow permits both the semiconductor technologist and designer to analyse the effects of process variations on device and circuit performance to improve the yield and also the optimisation of process parameters of manufactured devices so that their characteristics match the requirements of a given circuit application. Consequently, VARMA is being developed as a user friendly tool which interfaces standard Process/Device simulators and Circuit simulators.VARMA thus bridges the gap between design and technology with in-built user friendly tools for example, Process Wizard, technology library creator, cause and effect analyser etc., thus facilitating:a) The effects of process variability to be analysed.b) The optimisation of device and process parameters in order to achieve a given spread in circuit level performance characteristics.c) The automatic generation of technology libraries for Si, strained Si etc for a range of current and future processing nodes. VARMA differs form existing DFM tools in that it addresses variability issues related to their effects on the electrical behaviour of devices rather than on process steps which affect the design and physical implementation of the circuit.

Planned Impact

A major driver for the advances in semiconductor technology, to date, has been to satisfy market demands for systems with greater performance and functionality whilst having reduced power dissipation. Over the last three decades electronic systems have insidiously pervaded multi-various aspects of our daily lives. At present semiconductor manufacturing is a $150B business supporting an electronics industry which is approximately three times greater. Beneficiaries: The major direct beneficiary of this work is the semiconductor industry and indirectly, the electronics industry, which has a considerable societal impact . a) Semiconductor Industry: The major challenge to the industry, to date, is to achieve time to market targets with economical yield levels which can be maintained in volume production. Unfortunately this becoming more difficult to achieve due to the effects of process variability, which is creating significant parametric yield loss. To address some of the process variability issues a closer synergy is required between design and fabrication, this synergy can be realised through the use of the VARMA tool flow. Furthermore, it was identified at the House of Lords Select Committee Meeting on Science and Technology ( Chips with Everything ) that, as a result of the extremely high cost of capital investment, the UK was now excluded from entry into the semiconductor manufacturing industry. However, it was noted that there was ample scope, with the UK expertise in IC design and computer architecture, to set up fabless design houses. Within a fabless design house the VARMA tool can be used to good advantage in permitting the robustness of an initial design to be analysed without recourse to the fabrication of prototypes. The concept of the fabless design house also allows a new industry to emerge, namely, designing IP cores to be licensed to customers (cf success of ARM core). VARMA would also play a vital role regarding the design of IP cores as, in addition to the standard third party acceptance criteria for IP cores, customers are also interested in knowing the 'design for manufacturability' score for the core. It is estimated that by 2014 fables IC companies will command at least 27% of the IC market place. b) Electronics Industry: There is a very close synergy between the semiconductor and electronics industries and it is through this relationship that the work outlined in this proposal will, indirectly, have a large societal impact. Electronic systems have insidiously pervaded our daily lives and as the functionality and performance of ICs within them increases the diversity of application in health, wealth and culture will increase. For example electronic systems are widely used in health care, aerospace and automotive industries, environmental control of buildings, education, security and surveillance, consumer electronics. Communication/Engagement: This will be achieved through the following: a) Show casing the VARMA tool by linking it into the RelCel Project (Reliable cell design methods for variable processes), EP/G066361/1, 250,647. This three-year project is concerned with developing techniques to design robust cell circuits, as well as tools and techniques that will enable designers to achieve good performance in nanometre technologies with low supply voltage and large parametric variations. c) Interaction with companies and research institutes working on EDA tool development, for example, Synopsys, Mentor Graphics, Magma, IMEC; with the aim of integrating the tool into existing DFM suites under license. c) Demonstration of the capabilities of VARMA at company sites, for example X-Fab and Charter Semiconductor. It may also be possible to allow access to VARMA over the internet.


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