Toshiki Kanamoto

Dummy filling methods for reducing interconnect capacitance and number of fills

In recent system-on-chip (SoC) designs, floating dummy metals inserted for planarization have created serious problems because of increased interconnect capacitance and the enormous amount of fill required. We present new methods to reduce the interconnect capacitance and the amount of dummy metals needed. These techniques include three ways of filling: (1) improved floating square fills, (2) floating parallel lines, and (3) floating perpendicular lines (with spacing between dummy metals above and below signal lines). We also present efficient simple formulas for estimating the appropriate spacing and number of fills. In our experiments, the capacitance increase using the traditional regular square method was 13.1%, while that using the methods of improved square fills, extended parallel lines, and perpendicular lines was 2.5%, 2.4%, and 1.1%, respectively. Moreover, the number of necessary dummy metals can be reduced by two orders of magnitude through use of the parallel line method.

Efficient capacitance extraction method for interconnects with dummy fills

The accuracy of parasitic extraction has become increasingly important for system-on-chip (SoC) designs. In this paper, we present a practical method of dealing with the influences of floating dummy metal fills, which are inserted to assist planarization by the chemical-mechanical polishing (CMP) process, in extracting interconnect capacitances. The method is based on reducing the thicknesses of dummy metal layers according to electrical field theory. We also clarify the influences of dummy metal fills on the parasitic capacitance, signal delay, and crosstalk noise. Moreover, we address that the existence of the interlayer dummy metal fills has more significant influences than the intralayer dummies in terms of the impact on coupling capacitances. When dummy metal fills are ignored, the error of capacitance extraction can be more than 30%, whereas the error of the proposed method is less than about 10% for many practical geometries. We also demonstrate, by comparison with capacitance results measured for a 90-nm test chip, that the error of the proposed method is less than 8%.

Test structure measuring inter- and intralayer coupling capacitance of interconnection with subfemtofarad resolution

We present a new test structure measuring inter- and intralayer coupling capacitance parasitic to the same target interconnection with subfemtofarad resolution. The coupling capacitance as well as fringing capacitance measured by the test structure are demonstrated for two-level copper interconnections used in 90-nm technology node. In addition, we demonstrate that the accuracy of layout parameters extraction is improved by nondestructive inverse modeling of a copper interconnect cross-sectional structure, which reproduces the pitch dependence of the measured inter- and intralayer coupling capacitance within about a 1% error.

Measurement of supply noise suppression by substrate and deep N-well in 90nm process

This paper measures and compares power supply and ground noises in a triple-well structure and a twin-well stricture. The measurement results of power supply and ground waveforms in a 90 nm CMOS process reveal that the power noise reduction thanks to the increased junction capacitance associated with the triple-well structure overwhelms the ground noise suppression due to the resistive network of p-substrate in the twin-well structure. These noise suppression effects are well correlated with the simulation that uses on-chip RC power distribution model with package inductance, chip-level p-substrate resistive mesh and distributed well junction capacitances.

The D30V/MPEG multimedia processor

MPEG-2 decoding and encoding are important applications for multimedia systems. Real-time capability and low-cost implementation are the main design considerations for these systems. Due to the high computational requirements of real-time applications, multimedia systems typically use special-purpose processors to handle data. However, due to the inherent inflexibility of their designs, these dedicated processors are of little use in various application environments-digital videocassette recorders, for example. This article introduces Mitsubishis D30V/MPEG multimedia processor, which integrates a dual-issue RISC with minimal hardware support for a real-time MPEG-2 decoder. This approach is advantageous because of the small chip area it requires and the flexibility of the easy-to-program RISC processor for multimedia applications.

Supply Noise Suppression by Triple-Well Structure

This brief discusses the impact of twin- and triple-well structures on power supply noise, and a substrate model for simulating the power supply noise. We observed Vss noise reduction by the resistive network of the p-substrate and Vdd noise reduction by the junction capacitance of a triple-well structure on a 90-nm test chip. Measurement results also showed that the total noise reduction of a triple-well structure is superior to that of a twin-well structure. The measurement results correlate well with the results obtained from the power supply noise simulation using a hierarchical resistive mesh model. Our simulation-based verification indicates that in common CMOS design, a triple-well structure can reduce the power supply drop by 10%-40% or the decoupling capacitance area by 5%-10%. We also verified that supply drop sensitivity to variation of the well junction capacitance is sufficiently small and that supply noise reduction using a triple-well structure is robust to process variation.

A Method of Precise Estimation of Physical Parameters in LSI Interconnect Structures

This paper proposes a new non-destructive methodology to estimate physical parameters for LSIs. In order to resolve the estimation accuracy degradation issue for low-k dielectric films, we employ a parallel-plate capacitance measurement and a wire resistance measurement in our non-destructive method. Due to (1) the response surface functions corresponding to the parallel-plate capacitance measurement and the wire resistance measurement and (2) the searching of the physical parameter values using our cost function and simulated annealing, the proposed method attains higher precision than that of the existing method. We demonstrate the effectiveness of our method by application to our 90 nm SoC process using low-k materials.

Impact of well edge proximity effect on timing

This paper studies impact of the well edge proximity effect on digital circuit delay, based on model parameters extracted from test structures in an industrial 65 nm wafer process. The experimental results show that up to 10% of delay increase arises by the well edge proximity effect in the 65 nm technology, and it depends on interconnect length. Furthermore, due to asymmetric increase in pMOS and nMOS threshold voltages, delay may decrease in spite of the threshold voltage increase. From these results, we conclude that considering WPE is indispensable to cell characterization in the 65 nm technology.

Impact of Well Edge Proximity Effect on Timing

This paper studies impact of the well edge proximity effect on digital circuit delay, based on model parameters extracted from test structures in an industrial 65 nm wafer process. The experimental results show that up to 10% of delay increase arises by the well edge proximity effect in the 65 nm technology, and it depends on interconnect length. Furthermore, due to asymmetric increase in pMOS and nMOS threshold voltages, delay may decrease in spite of the threshold voltage increase. From these results, we conclude that considering WPE is indispensable to cell characterization in the 65 nm technology.

Si-substrate Modeling toward Substrate-aware Interconnect Resistance and Inductance Extraction in SoC Design

This paper proposes a simple yet sufficient Si-substrate modeling for interconnect resistance and inductance extraction. The proposed modeling expresses Si-substrate as four filaments in a filament-based extractor. Although the number of filaments is small, extracted loop inductances and resistances show accurate frequency dependence resulting from the proximity effect. We experimentally prove the accuracy using FEM (Finite Element Method) based simulations of electromagnetic fields. We also show a method to determine optimal size of the four filaments. The proposed model realizes substrate-aware extraction in SoC design flow.