IEEE transactions on computer-aided design of integrated circuits and systems : a publication of the IEEE Circuits and Systems Society

The phase-shifting mask consists of a normal transmission mask that has been coated with a transparent layer patterned to ensure that the optical phases of nearest apertures are opposite. Destructive interference between waves from adjacent apertures cancels some diffraction effects and increases the spatial resolution with which such patterns can be projected. A simple theory predicts a near doubling of resolution for illumination with partial incoherence σ < 0.3, and substantial improvements in resolution for σ < 0.7. Initial results obtained with a phase-shifting mask patterned with typical device structures by electron-beam lithography and exposed using a Mann 4800 10× tool reveals a 40-percent increase in usuable resolution with some structures printed at a resolution of 1000 lines/mm. Phase-shifting mask structures can be used to facilitate proximity printing with larger gaps between mask and wafer. Theory indicates that the increase in resolution is accompanied by a minimal decrease in depth of focus. Thus the phase-shifting mask may be the most desirable device for enhancing optical lithography resolution in the VLSI/VHSIC era.

Improving resolution in photolithography with a phase-shifting mask

IEEE transactions on very large scale integration (VLSI) systems

This book provides broad and comprehensive coverage of the entire EDA flow. EDA/VLSI practitioners and researchers in need of fluency in an "adjacent" field will find this an invaluable reference to the basic EDA concepts, principles, data structures, algorithms, and architectures for the design, verification, and test of VLSI circuits. Anyone who needs to learn the concepts, principles, data structures, algorithms, and architectures of the EDA flow will benefit from this book.


Covers complete spectrum of the EDA flow, from ESL design modeling to logic/test synthesis, verification, physical design, and test - helps EDA newcomers to get "up-and-running" quickly 
Includes comprehensive coverage of EDA concepts, principles, data structures, algorithms, and architectures - helps all readers improve their VLSI design competence 
Contains latest advancements not yet available in other books, including Test compression, ESL design modeling, large-scale floorplanning, placement, routing, synthesis of clock and power/ground networks - helps readers to design/develop testable chips or products 
Includes industry best-practices wherever appropriate in most chapters - helps readers avoid costly mistakes



Table of Contents


Chapter 1: Introduction Chapter 2: Fundamentals of CMOS Design Chapter 3: Design for Testability Chapter 4: Fundamentals of Algorithms Chapter 5: Electronic System-Level Design and High-Level Synthesis Chapter 6: Logic Synthesis in a Nutshell Chapter 7: Test Synthesis Chapter 8: Logic and Circuit Simulation Chapter 9:?Functional Verification Chapter 10: Floorplanning Chapter 11: Placement Chapter 12: Global and Detailed Routing Chapter 13: Synthesis of Clock and Power/Ground Networks Chapter 14: Fault Simulation and Test Generation.

Electronic Design Automation: Synthesis, Verification, and Test

International Symposium on Quality Electronic Design

Increasingly significant variational effects present a great challenge for delivering desired clock skew reliably. Non-tree clock network has been recognized as a promising approach to overcome the variation problem. Existing non-tree clock routing methods are restricted to a few simple or regular structures, and often consume excessive amount of wire-length. In this paper, we suggest to construct a low cost non-tree clock network by inserting cross links in a given clock tree. The effects of the link insertion on clock skew variability are analyzed. Based on the analysis, we propose two link insertion schemes that can quickly convert a clock tree to a non-tree with significantly lower skew variability and very limited wirelength increase. In these schemes, the complicated non-tree delay computation is circumvented. Further, they can be applied to the recently popular non-zero skew routing easily. Experimental results on benchmark circuits show that this approach can achieve significant skew variability reduction with less than 2 increase of wirelength.

Reducing clock skew variability via cross links

Clock skew is becoming increasingly difficult to control due to variations. Link based non-tree clock distribution is a cost-effective technique for reducing clock skew variations. However, previous works based on this technique were limited to unbuffered clock networks and neglected spatial correlations in the experimental validation. In this work, we overcome these shortcomings and make the link based non-tree approach feasible for realistic designs. The short circuit risk and multi-driver delay issues in buffered non-tree clock networks are investigated. Our approach is validated with SPICE based Monte Carlo simulations, considering spatial correlations among variations. The experimental results show that our approach can reduce the maximal skew by 47%, improve the skew yield from 15% to 73% on average with a decrease on the total wire and buffer capacitance.

Practical techniques to reduce skew and its variations in buffered clock networks

A leaf-level clock mesh is known to be very tolerant to variations (Restle et al., 2001). However, its use is limited to a few high-end designs because of the high power/resource requirements and lack of automatic mesh synthesis tools. Most existing works on clock mesh (Restle et al., 2001) either deal with semi-custom design or perform optimizations on a given clock mesh. However, the problem of obtaining a good initial clock mesh has not been addressed. Similarly, the problem of achieving a smooth tradeoff between skew and power/resources has not been addressed adequately. In this work, we present MeshWorks, the first comprehensive automated framework for planning, synthesis and optimization of clock mesh networks with the objective of addressing the above issues. Experimental results suggest that our algorithms can achieve an additional reduction of 26% in buffer area, 19% in wirelength and 18% in power, compared to the recent work of Venkataraman et al., (2006) with similar worst case maximum frequency under variation.

/pdf/meshworks-an-efficient-framework-for-planning-synthesis-and-2cr4kmx3ab.pdf

MeshWorks: an efficient framework for planning, synthesis and optimization of clock mesh networks

Clock network synthesis is a key step in the ultra deep sub-micron (UDSM) VLSI Designs Most existing clock network synthesis algorithms are designed for nominal operating condition, which are insufficient to address the growing problem of process, voltage and temperature (PVT) fluctuations Link based clock networks have been suggested as a possible way of reducing skew variability [1-3] However, [1,2] deal with only unbuffered clock networks, making them impractical In [3], the problem of constructing a link based buffered clock network has been addressed  But [3] requires special kind of tunable buffers, which might consume more area/power and might not be available for all designs Also, [3] uses SPICE for tuning the locations of internal nodes and buffer delays, thereby making it slow even for clock networks with a few hundred sinks In this paper, we propose a unified algorithm for synthesizing a variation tolerant, balanced buffered clock network with cross links Our approach can make use of ordinary buffers and does not require SPICE for clock network synthesis SPICE based Monte Carlo simulations show that our methodology results in a buffered clock network with 50% reduction in skew variability with minimal increase in wire-length, buffer area and CPU time

/pdf/variation-tolerant-buffered-clock-network-synthesis-with-2rdplosqfe.pdf

Variation tolerant buffered clock network synthesis with cross links

In the nanometer VLSI technology, the variation effects like manufacturing variation, power supply noise, temperature etc. become very significant. As one of the most vital nets in any synchronous VLSI chip, the Clock Distribution Network (CDN) is especially sensitive to these variations. Recently proposed link-based non-tree [1] addresses this problem by constructing a non-tree that is significantly more tolerant to variations when compared to a clock tree. Although the two algorithms proposed in [1] are effective in reducing the skew variability, they have a few drawbacks including high complexity, lengthy links and uneven link distribution across the clock network. In this paper, we propose two new algorithms that can overcome these disadvantages. The effectiveness of the proposed algorithms has been validated using HSPICE based Monte Carlo simulations. Experimental results show that the new algorithms are able to achieve the same or better skew reduction with an average of 5% wire length increase when compared to the 15% wire length increase of the existing algorithms in [1]. Moreover, the new algorithms scale extremely well to big clock networks, i.e., the bigger the clock network, the less overall link cost (less than 2% for the biggest benchmark we have).

Anand Rajaram

Papers

Reducing clock skew variability via cross links

Practical techniques to reduce skew and its variations in buffered clock networks

MeshWorks: an efficient framework for planning, synthesis and optimization of clock mesh networks

Variation tolerant buffered clock network synthesis with cross links

Improved algorithms for link-based non-tree clock networks for skew variability reduction