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

Lithography is a field in which advances proceed at a swift pace. This book was written to address several needs, and the revisions for the second edition were made with those original objectives in mind. Many new topics have been included in this text commensurate with the progress that has taken place during the past few years, and several subjects are discussed in more detail. This book is intended to serve as an introduction to the science of microlithography for people who are unfamiliar with the subject. Topics directly related to the tools used to manufacture integrated circuits are addressed in depth, including such topics as overlay, the stages of exposure, tools, and light sources. This text also contains numerous references for students who want to investigate particular topics in more detail, and they provide the experienced lithographer with lists of references by topic as well. It is expected that the reader of this book will have a foundation in basic physics and chemistry. No topics will require knowledge of mathematics beyond elementary calculus.

Principles of Lithography

The practicability and methodology of applying regularly placed contacts on layout design of standard cells are studied. The regular placement enables more effective use of resolution enhancement technologies, which in turn allows for a reduction of critical dimensions. Although placing contacts on a grid adds restrictions during cell layout, overall circuit area can be made smaller by a careful selection of the grid pitch, allowing slight contact offset, applying double exposure, and shrinking the minimum size and pitch. The contact level of 250 nm standard cells was shrunk by 10%, resulting in an area change ranging from -20% to +25% with an average decrease of 5% for the 84 cells studied. The areas of two circuits, a finite-impulse-response (FIR) filter and an add-compare-select (ACS) unit in the Viterbi decoder, decrease by 4% and 2%, respectively.

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Standard cell layout with regular contact placement

Integrating high electron mobility III–V materials on an existing Si based CMOS processing platform is considered as a main stepping stone to increase the CMOS performance and continue the scaling trend. Owing to the polar nature of III–V materials versus the nonpolar nature of Si, antiphase boundaries (APBs) arise in epitaxially grown III–V materials on Si. Here, we demonstrate an approach to restrict the generation of APBs by selectively depositing a III–V material in narrow Si-trenches as formed within the shallow trench isolation (STI) patterned Si(001) wafers. Based on the detailed crystal structures of Si and III–V materials, a concept has been developed comprising the deposition in “v-grooves” with {111} facets in the Si wafer. The grooves are formed by anisotropic wet etching of Si. When InP is deposited selectively into these “v-grooves”, the crystallographic alignment between the Si and InP restricts the APBs nucleation to the corners of the “v-grooved” trench. This approach offers a promising m...

Site Selective Integration of III–V Materials on Si for Nanoscale Logic and Photonic Devices

Lithography simulation is an increasingly important part of semiconductor manufacturing due to the decreasing k1 value. It is not only required in lithography process development, but also in RET design, RET verification, and process latitude analysis, from library cells to full-chip. As the design complexity grows exponentially, pure software based simulation tools running on general-purpose computer clusters are facing increasing challenges in meeting today’s requirements for cycle time, coverage, and modeling accuracy. We have developed a new lithography simulation platform (TachyonTM) which achieves orders of magnitude speedup as compared to traditional pure software simulation tools. The platform combines innovations in all levels of the system: algorithm, software architecture, cluster-level architecture, and proprietary acceleration hardware using application specific integrated circuits. The algorithm approach is based on image processing, fundamentally different from conventional edge-based analysis. The system achieves superior model accuracy than conventional full-chip simulation methods, owing to its ability to handle hundreds of TCC kernels, using either vector or scalar optical model, without impacting throughput. Thus first-principle aerial image simulation at the full-chip level can be carried out within minutes. We will describe the hardware, algorithms and models used in the system and demonstrate its applications of the full chip verification purposes.

Optimized hardware and software for fast full-chip simulation

A manufacturable shallow trench isolation (STI) technology using high density plasma (HDP) CVD oxide as trench filling material is reported for the first time, and compared to using sub-atmospheric CVD (SACVD) oxide as filling material. HDP filled STI has excellent immunity to double-hump, better gate oxide integrity and inverse narrow width effect, due to its lower deglaze rate and thus better corner protection compared to the SACVD case. The /spl Delta/Vt (between W=10 and 0.18 /spl mu/m) are 150 mV (NMOS). And 60 mV (PMOS) for the HDP case, and the transistor width reduction is /spl les/0.03 /spl mu/m for both cases. Trench wall passivation and a low sputtering component during deposition are necessary for HDP to achieve low diode edge leakage. 0.28 /spl mu/m intra-well isolation (or 0.46 /spl mu/m min. pitch), 0.6 /spl mu/m n/sup +/-to-p/sup +/ isolation, latch-up holding voltage of 2 V at 0.5 /spl mu/m n/sup +/-to-p/sup +/ spacing, together with outstanding CMOS transistor and inverter performance, have been achieved. These results are either comparable to or better than the best results reported to date. It is concluded that HDP trench filling oxide is a viable approach, while SACVD oxide is marginally acceptable, for the STI of 0.25/0.18 /spl mu/m CMOS.

A shallow trench isolation study for 0.25/0.18 /spl mu/m CMOS technologies and beyond

This article presents a study of the issues in integrating the pattern, fill, planarization, and surface cleanup processes to design a shallow trench isolation (STI) flow suitable for 0.25 μm complementary metal–oxide semiconductor technologies. Technological choices and their effects on the characteristics of the STI technology are discussed. Experimental data are presented to illustrate how process choices at various stages of the STI flow are made to optimize the STI structure.

Integration of unit processes in a shallow trench isolation module for a 0.25 μm complementary metal–oxide semiconductor technology

Among the valid gate pattern strategies for the 65nm technology node, att-PSM offers the advantage in cost and mask complexity over other contenders such as complimentary alt-PSM and chromeless phase lithography (CPL). A combination of Quasar illumination and sub-resolution assist features (SRAFs) provides a through pitch solution with a common depth of focus (DOF) better than 0.25um to support the aggressive scaling in both logic and high density SRAM. A global mask-source optimization scheme is adopted to explore the multi-dimensional space of process parameters and define the best overall solution that includes scanner optics such as NA and illumination, and SRAF placement rules for 1-dimensional line and space patterns through the full pitch range. Gate pattern capabilities in terms of DOF, exposure latitude, mask error enhancement factor (MEEF), optical proximity correction (OPC), CD control, and aberration sensitivity are reported in this paper. Conflict resolution and placement optimization are key to the success of implementation of SRAF to the complex 2-dimensional layouts of random logic. Reasonable CD control can be achieved based on the characterization and simulation of CD variations at different spatial and processing domains from local to across chip, across wafer, wafer-to-wafer, and lot-to-lot. Certain layout restrictions are needed for high performance devices which require a much tighter gate CD distribution. Scanner optimization and enhancement such as DoseMapper are key enablers for such aggressive CD control. The benefits, challenges, and possible extensions of this particular approach are discussed in comparison with other techniques.

65nm node gate pattern using attenuated phase shift mask with off-axis illumination and sub-resolution assist features

Design for Manufacturability through Design-Process Integration VII

Systems and methods are provided for refining a design cycle for an integrated circuit. An integrated circuit design is generated. A plurality of non-critical paths within the integrated circuit design are identified. A set of at least one of the plurality of non-critical paths is modified to produce a modified design in which the sensitivity of each of the set of non-critical paths to at least one parameter is enhanced. Each parameter is either a design parameter or a process parameter. An integrated circuit is fabricated according to the modified design. The fabricated integrated circuit is evaluated to measure a set of timing data representing each of the plurality of non-critical paths. The value of the parameter is determined from the measured set of timing data.

Mark E. Mason

Papers

A shallow trench isolation study for 0.25/0.18 /spl mu/m CMOS technologies and beyond

Integration of unit processes in a shallow trench isolation module for a 0.25 μm complementary metal–oxide semiconductor technology

65nm node gate pattern using attenuated phase shift mask with off-axis illumination and sub-resolution assist features

Design for Manufacturability through Design-Process Integration VII

Test Method and System for Characterizing and/or Refining an IC Design Cycle