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What is Design for Manufacturability and Yield (DFM/DFY)?
Design and manufacturing have operated essentially as separate worlds for more than four decades. The DFM/DFY-concept represents a paradigm shift in the operation of semiconductor business. What exactly is Design for Manufacturability DFM and Design for Yield DFY? Design for Manufacturability DFM is the management of technology constraints (sizing rules) applied to the circuit design. DFM allows to precisely replicate on the chip, that which is designed and laid out by the design team. A manufacturable design however is not necessarily a high-robust or high-yielding design. The concept of Design for Yield DFY, as part of Design for Manufacturability DFM, concentrates on the development and quality of the circuit design in the pre- and post-layout phase. DFY is the management of design sensitivities to the manufacturing process and helps to guarantee high-yielding devices.
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Analog, mixed-signal and digital Technology
Analog components are an important part of integrated systems: either in terms of elements and areas in mixed-signal systems (e.g. in telecommunication or automotive mixed-signal systems) or as vital system functions in digital systems (e.g. power-on reset, pad driving, clock generation). Despite their importance, design automation of analog circuits still trails behind that of digital circuits. As a consequence, analog components are often a bottleneck in the design flow of both digital and mixed-signal circuits. So long the lack of designers and also design-supporting software was a limiting factor in circuit development. Today´s predominantly manually done analog design is increasingly unable to overview the complex coherence between circuit characteristics and adjustable design-parameters. Software based analysis and optimization tools will show the designer new possibilities to improve the performance of his/her circuits.
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Analog Sizing and Design Centering
Analog Sizing and Design Centering is complicated because it does not only consist of topology and layout analysis but also of component sizing. Additionally, it has to incorporate physical effects like process variations, variations in operating conditions and matching constraints or noise. It becomes even more complicated, as more and more mixed-signal systems and systems-on-chip (SoC) are designed with customized analog and especially RF components. From the 70's to 90's, analog topology synthesis, nominal design optimization, and sizing with respect to tolerances (design centering, yield optimization) were the focus of research interest. Recent research has revealed that sizing tasks have a key potential for providing automation support to the designer, especially when considering process and operating tolerances and mismatch.
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Operating Range Influence
The specification of an analog circuit can be written as a set of inequalities that the performances of a fault-free circuit must fulfill. Performances may be any scalar values that can be calculated by simulation, like slew rate or gain bandwidth. Without loss of generality, bounds are considered as lower bounds here. An important part of the specification is the operating range e.g. temperature. The parameters defining the operating range are called the operating parameters. In the operating range, all specifications must be fulfilled for a sample circuit to be fault-free. The set of operating parameters values that lead to the lowest performance is called the range parameter worst-case corner set. Experience shows, that the performance depends on the operating parameters usually in a monotonic behavior. In this case, a single sensitivity analysis is sufficient to calculate the operating parameters.
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Process Variations
Although all sample circuits of the same design are manufactured in the same way, they differ due to process fluctuations. Those fluctuations are described by statistical parameters, e.g. oxide thickness or threshold voltage. The percentage of produced circuits that fulfill the specification is called the parametric yield. The circuit designer aims to maximize the yield by sizing the circuit, i.e. by selecting optimal values for tuning parameters like width and length of transistors. The strong separation of tuning and statistical parameters may not seem obvious at a first glance, but it provides a more flexible way to consider process variations during circuit sizing, and to distinguish local effects from global ones. Each performance is a function of the parameter vectors of tuning, statistical and operating parameters. Some tuning parameters influence the variances of statistical parameters. For example, transistor width and length determine the variance of local threshold voltage variations.
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Performance and Yield Improvement
MunEDA solves the above problems and challenges by offering software based circuit design analysis and optimization tools for the following reasons. Software based design tools give the circuit designer a repertory of analysis methods. This enables one to check already completed design steps. Faulty developments can be identified earlier and eliminated faster. Design supporting software with its complex physical models is able to reduce the influence of the manufacturing process on the designed circuit with much higher security than manual design, which can only go back to rough formulas, experience values and rough calculation. By tool-supported analysis and optimization, uncertainties of design decisions and probabilities of fault emerging can be reduced by ranges. In this way, the design methodologies of analog components are distinguished from that of digital design. Analog design automation is still not as advanced, and in practice, is often limited to a final verification of a completely manuall undertaking. MunEDA offers with our software solutions several powerful methods for automated analyzing and optimization of analog, mixed-signal and digital circuit design.
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Benefit from DFM/DFY!
The approach of Design for Manufacturability and Yield provides several benefits to the circuit developer and semiconductor manufacturer. First, there are enormous cost savings by faster time to market and higher yield designs. Secondly, the lifetime of very expensive photolithographic equipment can be extended. Design for Manufacturability and Yield methodologies are absolutely essential at sub-100 nm feature sizes, in order to guarantee manufacturability and quality of the underlying integrated circuits. Click on picture for an overview of benefits when using DFM-DFY technologies.
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Supporting your DFM/DFY-Project!
MunEDA has longterm experience in delivering DFM and DFY know-how and technology to our customers. Within a MunEDA-supported DFM/DFY-project we can help you to increase the robustness and yield of your designs and circuits. Setting up a DFM-project within your company enables you to venture into new technology structures in the sub-deep micron space. Please contact us, to receive your individual DFM/DFY project proposal.
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